Radio communication system

Abstract

To provide a radio communication system for allowing a mobile reception station to make switching to an appropriate demodulation system on the basis of a determination result by determining an area at which radio waves arrive from a plurality of transmission base stations.SOLUTION: In a radio communication system including a plurality of transmission base stations installed at optional positions, for example, an A station and a B station, and a mobile reception station movable to an optional position to communicate disaster prevention information about a natural disaster or the like by using a same wave multi-station transmission technology, a mobile station 3 calculates propagation path power between each base station and the mobile station on the basis of a synchronous word of a data frame transmitted from each base station in a synthetic data frame, compares respective propagation path power, determines to use a demodulation system in a first demodulation part in the case of determining that the mobile station is located at an area where radio waves from the A station and the B station approximately equally arrive, and determines to use a demodulation system in a second demodulation part in the case of determining that it is located at an area where one of the radio waves from the A station and the B station dominantly arrives.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a wireless communication system using a same-wave multi-station transmission technique. [Background technology]

[0002] In wireless communication systems that cover a wide area with narrowband signals (e.g., metropolitan disaster prevention radio systems, prefectural disaster prevention radio systems, etc.), it is known that frequency utilization efficiency can be improved by using a same-wave, multi-station transmission technique in which multiple transmitting base stations transmit the same signal at the same frequency to mobile receiving stations. For example, the wireless communication system shown in Figure 32 (A) is composed of multiple transmitting base stations BS1, BS2, etc., arranged so that their communication areas partially overlap, and a mobile receiving station MS1 ​​mounted on a moving object such as an automobile, and multiple mobile receiving stations MS2-MS4 carried by pedestrians, etc. The multiple transmitting base stations BS1 and BS2 are arranged so that the communication areas reached by their transmission waves partially overlap each other, and transmit transmission waves Tx1 and Tx2 of the same data in a broadcast manner using the same frequency. This allows the mobile receiving stations MS1-MS4 to receive the transmission wave Tx1 or Tx2 at the same carrier frequency regardless of their location within the communication areas of the transmitting base stations BS1 and BS2.

[0003] In such a wireless communication system, as shown in FIG. 32(B), in areas where the transmitted wave Tx2 is out of phase with the transmitted wave Tx1 and the signal level ratio of Tx1 / Tx2 is 0 dB, identical wave interference (hereinafter also referred to as beat interference) occurs in the composite wave Tx1+Tx2 of the transmitted waves Tx1 and Tx2. Such beat interference occurs in multiple stripes, as depicted by vertical lines in FIGS. 32(A) and 32(B). Mobile receiving stations MS2 and MS3, located away from the beat interference occurrence point, can communicate with transmitting base station BS1 or BS2. In contrast, mobile receiving station MS4, located at the beat interference occurrence point, cannot communicate with transmitting base station BS1 or BS2. Furthermore, as the moving speed of mobile receiving station MS1 ​​increases, the effect of Doppler shift becomes more pronounced, and Rayleigh fading and Rician fading occur due to temporal fluctuations in the propagation path. In addition, since the waves arriving from multiple transmitting base stations each undergo independent Rayleigh fading or Rician fading, the demodulation performance deteriorates due to the influence of independent propagation path fluctuations of each arriving wave.

[0004] On the other hand, it is known that using an adaptive equalizer (Decision Feedback Equalization; DFE) such as a decision feedback equalizer is effective for tracking the propagation path when the mobile receiving station MS1 ​​moves at high speed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-070348 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, when the mobile receiving stations MS1 to MS4 move, there will be a mixture of areas where transmission waves Tx1 and Tx2 from two transmitting base stations BS1 and BS2 arrive and areas where transmission waves Tx1 or Tx2 from a single transmitting base station BS1 or BS2 predominantly arrive. In areas where multiple transmission waves Tx1 and Tx2 arrive, demodulation processing for same-wave multi-station transmission (e.g., processing using an adaptive equalizer) is appropriate, while in areas where transmission waves Tx1 or Tx2 from a single transmitting base station predominantly arrive, demodulation processing using a conventional system (e.g., digital simplex radio system) is appropriate.

[0007] Therefore, if the mobile receiving stations MS1 to MS4 can identify the situation in such areas, they can demodulate while switching to an appropriate demodulation method, and can prevent degradation of the bit error rate (BER) characteristics. However, the situation in such areas is not simply determined by the distance from each transmitting base station BS1, BS2, but is thought to be more complex and mixed due to the occurrence of shielding and other factors caused by the environment (topography and buildings) around the mobile receiving stations MS1 to MS4.

[0008] Therefore, an object of the present invention is to provide a wireless communication system that can determine whether a mobile receiving station is located in an area where radio waves from multiple transmitting base stations arrive at approximately equal rates, or in an area where radio waves from a single transmitting base station arrive predominantly, and can switch to an appropriate demodulation method based on the determination result. [Means for solving the problem]

[0009] In order to solve the above problem, the invention of claim 1 provides a wireless communication system comprising a plurality of transmitting base stations each equipped with a wireless transmitting device that transmits the same modulated data frame at the same frequency, and a mobile receiving station each equipped with a wireless receiving device that receives and demodulates the data frame, wherein the plurality of wireless transmitting devices respectively transmit the data frame, each comprising known header data, a plurality of block data each having the same number of symbols as the header data, and a no-data section arranged between the header data and the first block data, with a time difference corresponding to a predetermined offset number of symbols, and the wireless receiving device comprises receiving means that receives a combined data frame formed by combining the plurality of data frames in space and outputs a received signal of each symbol, first demodulation means that inputs the received signal to a decision feedback adaptive equalizer and performs a demodulation process on the received signal after equalization, second demodulation means that demodulates the received signal output from the receiving means, and and determining means for calculating a propagation path power between the one adjacent transmitting base station and the mobile receiving station as a first propagation path power based on header data of the data frame transmitted from the one adjacent transmitting base station, and for calculating a propagation path power between the other adjacent transmitting base station and the mobile receiving station as a second propagation path power based on header data of the data frame transmitted from the other adjacent transmitting base station among the composite data frame, and for comparing the first propagation path power with the second propagation path power, and determining to use a demodulation method in the first demodulation means when it is determined that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station and the other adjacent transmitting base station arrive approximately equally, and determining to use a demodulation method in the second demodulation means when it is determined that the mobile receiving station is located in an area where radio waves from either the one adjacent transmitting base station or the other adjacent transmitting base station arrive predominantly.

[0010] The invention of claim 2 is characterized in that, in the wireless communication system of claim 1, the decision feedback adaptive equalizer performs a first equalization process to adjust tap coefficients used in the equalization process based on received signals of the plurality of header data included in the combined data frame and a pre-stored reference signal; a second equalization process to use received signals of combined block data constituting the combined data frame as an equalizer input, perform equalization process based on the equalizer input and current tap coefficients, and obtain approximation values ​​of the symbols of the block data included in the combined block data as an equalizer output; and a third equalization process to calculate an error between a hard decision value of the equalizer output and the equalizer output, and update the tap coefficients to latest values ​​using the calculated error, the current tap coefficients, and a new equalizer input, and repeats the second equalization process and the third equalization process until all approximation values ​​of the symbols of the block data are output from the combined data frame.

[0011] The invention of claim 3 relates to the wireless communication system of claim 1, wherein the wireless receiving device further comprises third demodulation means for performing demodulation processing on the received signal output from the receiving means, and the third demodulation means performs a first demodulation process of demodulating one of the plurality of data frames as a data frame to be demodulated and data frames other than the data frame to be demodulated as cancel data frames, demodulating block data of the data frame to be demodulated, the reception time of which does not overlap with other data, to generate demodulated data; a replica data generation process of re-modulating the demodulated data based on the header data, and generating replica data corresponding to the block data of the cancel data frame; and a replica data generation process of generating the replica data from composite block data obtained by combining the block data of different data frames. a block data separation process for subtracting replica data from the data frame to be demodulated and separating the block data of the data frame to be demodulated; a second demodulation process for demodulating the block data of the data frame to be demodulated separated by the block data separation process to generate demodulated data; and the replica data generation process and the block data separation process based on the demodulated data generated by the second demodulation process are repeated until demodulation of all the block data of the data frame to be demodulated is completed; and when the determination means determines that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station and the other adjacent transmitting base station arrive at approximately equal intensities, it decides to use the demodulation method of the first demodulation means or the demodulation method of the third demodulation means.

[0012] The invention described in claim 4 is characterized in that, in the wireless communication system described in claim 3, the third demodulation means determines the first transmitted data frame among the multiple data frames transmitted with a time difference from the multiple wireless transmitting devices as the data frame to be demodulated, and determines data frames other than the data frame to be demodulated as cancellation data frames.

[0013] The invention described in claim 5 is characterized in that, in the wireless communication system described in claim 3, the third demodulation means compares the signal level of the first transmitted data frame with the signal level of the last transmitted data frame among the multiple data frames transmitted from the multiple wireless transmitting devices with a time difference, and if the signal level of the first transmitted data frame is higher than the signal level of the last transmitted data frame by a predetermined value or more, demodulates only the first transmitted data frame without performing the first demodulation process, the replica data generation process, the block data separation process, and the second demodulation process.

[0014] The invention of claim 6 is characterized in that, in the wireless communication system of claim 3, the wireless receiving device comprises a storage means for storing the combined data frame obtained by combining one frame of the plurality of data frames transmitted from the plurality of wireless transmitting devices with a time difference and the header data of a next frame, and the third demodulation means compares a signal level of the first transmitted data frame with a signal level of the last transmitted data frame among the plurality of data frames transmitted from the plurality of wireless transmitting devices with a time difference, and when the signal level of the first transmitted data frame is higher than the signal level of the last transmitted data frame, the first transmitted data frame is the data frame to be demodulated and the header data of the next frame is used for the replica data generation process, and when the signal level of the last transmitted data frame is higher than the signal level of the first transmitted data frame, the last transmitted data frame is the data frame to be demodulated and the header data of the first transmitted data frame is used for the replica data generation process.

[0015] The invention described in claim 7 is characterized in that, in the wireless communication system described in claim 6, the third demodulation means demodulates only the data frame with a higher signal level, without performing the first demodulation process, the replica data generation process, the block data separation process, and the second demodulation process, when the difference between the signal level of the data frame transmitted first and the signal level of the data frame transmitted last is equal to or greater than a predetermined value.

[0016] The invention of claim 8 is the wireless communication system of claim 3, wherein the third demodulation means executes a frame set generation process for generating a plurality of frame sets in which one of the plurality of data frames is a data frame to be demodulated and data frames other than the data frame to be demodulated are data frames to be cancelled, and for each of the plurality of frame sets, a first demodulation process for demodulating block data of the data frame to be demodulated, the reception time of which does not overlap with other data, to generate demodulated data; a replica data generation process for re-modulating the demodulated data based on the header data, to generate replica data corresponding to the block data of the cancel data frame; a block data separation process for subtracting the replica data from composite block data obtained by combining block data to separate the block data of the data frame to be demodulated; a second demodulation process for demodulating the block data of the data frame to be demodulated separated by the block data separation process to generate demodulated data; and a third demodulation process for repeating the replica data generation process and the block data separation process based on the demodulated data generated by the second demodulation process until all the block data of the data frame to be demodulated has been separated, combining the block data of the data frame to be demodulated obtained for each of the plurality of frame sets, and demodulating the combined data.

[0017] The invention of claim 9 is characterized in that, in the wireless communication system of claim 1, the determination means calculates average first propagation path power and second propagation path power in a plurality of the composite data frames, compares the calculated average first propagation path power and the calculated average second propagation path power, and determines to use the demodulation method of the first demodulation means if it determines that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station and the other adjacent transmitting base station arrive approximately equally, and determines to use the demodulation method of the second demodulation means if it determines that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station or the other adjacent transmitting base station arrive predominantly. [Effects of the Invention]

[0018] According to the invention described in claim 1, a no-data section is provided between the header data and the first block data, and each data frame is transmitted with a time difference corresponding to a predetermined offset symbol number. Therefore, at least a portion of the header data of the data frames from two adjacent transmitting base stations does not overlap with other symbols, making it possible to properly calculate the first propagation path power between one adjacent transmitting base station and the mobile receiving station and the second propagation path power between the other adjacent transmitting base station and the mobile receiving station. Then, by comparing the first propagation path power and the second propagation path power, i.e., based on which transmitting base station has the larger propagation path power, it is determined which area the mobile receiving station is located in. This makes it possible to properly determine whether the mobile receiving station is located in an area where radio waves from multiple transmitting base stations arrive approximately equally or in an area where radio waves from a single transmitting base station arrive predominantly. Furthermore, based on the determination result, a demodulation method appropriate for each area is switched for demodulation, thereby preventing degradation of bit error rate (BER) characteristics and improving demodulation performance.

[0019] According to the invention of claim 2, when it is determined that the mobile receiving station is located in an area where radio waves from a plurality of transmitting base stations arrive at approximately the same frequency, the demodulation method is switched to a demodulation method using decision feedback adaptive equalization, and beat interference is avoided by combining signals transmitted offset from the plurality of transmitting base stations, while the tap coefficients are updated for each symbol from the combined wave. Therefore, even in a simultaneous transmission environment from a plurality of base stations, even if the mobile receiving station moves at high speed and the propagation path changes, it is possible to follow the changes and perform stable fading compensation.

[0020] According to the invention of claim 3, when it is determined that the mobile receiving station is located in an area where radio waves from a plurality of transmitting base stations arrive at approximately the same frequency, the options for switchable demodulation methods are expanded, making it possible to demodulate using a more appropriate demodulation method. Also, when switching to a demodulation method using replica data in the third demodulation unit, replica data corresponding to the block data of the cancellation data frame is generated based on the block data of the data frame to be demodulated, and this replica data is used to separate the block data of the data frame to be demodulated from the composite block data, making it possible to separate and demodulate only the data frame to be demodulated from the composite data frame.

[0021] According to the invention described in claim 4, when switching to a demodulation method using replica data in the third demodulation unit, the first data frame transmitted among multiple data frames transmitted from multiple base stations with a time difference is adopted as the data frame to be demodulated, so that subsequent processing can be started more quickly and the efficiency of the demodulation processing can be improved.

[0022] According to the invention described in claim 5, when switching to a demodulation method using replica data in the third demodulation unit, the signal level of the first transmitted data frame is compared with the signal level of the last transmitted data frame, and if the signal level of the first transmitted data frame is higher than the signal level of the last transmitted data frame by a predetermined value or more, only the first transmitted data frame is demodulated without performing the first decoding process, etc., thereby reducing the load on the demodulation process and shortening the processing time.

[0023] According to the invention of claim 6, when switching to a demodulation method using replica data in the third demodulation unit, one frame of multiple data frames and header data of the next frame are stored, and the signal level of the first transmitted data frame is compared with the signal level of the last transmitted data frame. If the signal level of the first transmitted data frame is higher than that of the last transmitted data frame, the first transmitted data frame is selected as the data frame to be demodulated. Conversely, if the signal level of the last transmitted data frame is higher than that of the first transmitted data frame, the last transmitted data frame is selected as the data frame to be demodulated. This makes it possible to demodulate data frames with higher signal levels, thereby improving the accuracy of the demodulation process. Furthermore, when the last transmitted data frame is selected as the data frame to be demodulated, header data of the next frame, which has a signal level closer to that of the last transmitted data frame, is used in the replica data generation process, thereby further improving the accuracy of the demodulation process.

[0024] According to the invention described in claim 7, when switching to a demodulation method using replica data in the third demodulation unit, if the difference between the signal level of the first transmitted data frame and the signal level of the last transmitted data frame is equal to or greater than a predetermined value, only the data frame with the higher signal level is demodulated without performing the first decoding process, etc., thereby improving the accuracy of the demodulation process, reducing the load on the demodulation process, and shortening the processing time.

[0025] According to the invention of claim 8, when it is determined that the mobile receiving station is located in an area where radio waves from a plurality of transmitting base stations arrive at approximately the same frequency, the options for switchable demodulation methods are expanded, making it possible to demodulate using a more appropriate demodulation method. Also, when switching to a demodulation method using replica data in the third demodulation unit, multiple frame sets each consisting of a data frame to be demodulated and a cancellation data frame are generated, and block data of the data frame to be demodulated is generated from composite block data using the replica data for each frame set, and the block data of the data frame to be demodulated obtained for each frame set is composited and demodulated, thereby making it possible to further improve the accuracy of the demodulation process.

[0026] According to the invention described in claim 9, the area in which the mobile receiving station is located is determined by comparing the average first propagation path power and the average second propagation path power in multiple composite data frames, so it becomes possible to more accurately determine whether the mobile receiving station is located in an area where radio waves from multiple transmitting base stations arrive at approximately the same rate, or whether it is located in an area where radio waves from a single transmitting base station arrive predominantly. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram showing a schematic configuration of a wireless communication system in accordance with Embodiment 1 of the present invention. [Figure 2] 1A shows the configuration of a data frame transmitted from a base station, and FIG. 1B shows a composite data frame received by a mobile station. [Figure 3] 2 is a functional block diagram showing a schematic configuration of a radio communication device of the mobile station shown in FIG. [Figure 4] 4 is a functional block diagram showing a schematic configuration of a demodulation method switching unit shown in FIG. 3. FIG. [Figure 5] 4 is a flowchart showing a determination procedure in the first embodiment. [Figure 6] FIG. 6 is a diagram showing area types in the determination of FIG. 5. [Figure 7] 4 is a graph showing a bit error rate of the wireless communication system according to the first embodiment. [Figure 8] FIG. 5 is a block diagram showing a schematic configuration of the decision feedback adaptive equalizer shown in FIG. [Figure 9] FIG. 9 is a block diagram showing the configuration of a delay device shown in FIG. 8. [Figure 10] FIG. 10 is a block diagram showing a schematic configuration of a decision feedback adaptive equalizer when there are two base stations. [Figure 11] FIG. 10 is an explanatory diagram showing a process of outputting approximate values ​​of symbols of block data from a combined data frame by a decision feedback adaptive equalizer. [Figure 12] FIG. 10 is an explanatory diagram showing a process of outputting an approximate value of a symbol of block data from a specific composite block data by a decision feedback adaptive equalizer. [Figure 13] 10(A) shows the configuration of data frames transmitted from three base stations in the second embodiment, and FIG. 10(B) shows a combined data frame received by a mobile station. [Figure 14] 10 is a flowchart showing the procedure for area determination in the second embodiment. [Figure 15] FIG. 15 is a diagram showing area types in the area determination of FIG. [Figure 16] FIG. 10 is a block diagram showing a schematic configuration of a decision feedback adaptive equalizer when there are three base stations. [Figure 17] FIG. 10 is an explanatory diagram showing a process of outputting an approximate value of a symbol of block data from a combined data frame of three stations by a decision feedback adaptive equalizer. [Figure 18] 11 is a flowchart showing the procedure of area determination in the third embodiment. [Figure 19] FIG. 11 is a functional block diagram showing a schematic configuration of a radio communication device of a mobile station in a fourth embodiment. [Figure 20] 20 is a functional block diagram showing a schematic configuration of a demodulation method switching unit shown in FIG. 19. FIG. [Figure 21]It is a flowchart showing the procedure of the demodulation process in the third demodulation means in Embodiment 4. [Figure 22] It is a processing block diagram showing the demodulation process in the third demodulation means in Embodiment 4. [Figure 23] It is a processing block diagram showing the demodulation process in the third demodulation means in Embodiment 5. [Figure 24] It is a flowchart showing the procedure of the demodulation process in the third demodulation means in Embodiment 6. [Figure 25] It is a functional block diagram showing the schematic configuration of the wireless communication device of the mobile station in Embodiment 7. [Figure 26] It is a diagram showing the range of the data frame buffered in the demodulation process by the third demodulation means in Embodiment 7. [Figure 27] It is a flowchart showing the procedure of the demodulation process in the third demodulation means in Embodiment 7. [Figure 28] It is a processing block diagram showing the demodulation process when DF_B is set as the demodulation target in the demodulation process in the third demodulation means in Embodiment 7. [Figure 29] It is a processing block diagram showing the demodulation process in the third demodulation means in Embodiment 8. [Figure 30] It is a diagram showing the data frame and composite data frame configurations with the number of offset symbols M and the number of symbols N of the block data being M≠N. [Figure 31] It is a diagram showing the data frame and composite data frame configurations with the number of offset symbols M (M = N) in the synchronization word section and the number of offset symbols M (M < N) in the data section. [Figure 32] It is a schematic diagram showing the occurrence state of beat interference in a conventional wireless communication system.

Embodiments for Carrying Out the Invention

[0028] The present invention will be described below based on the illustrated embodiments. Note that the following description focuses on the characteristic configuration of the present invention, and omits a description of the conventional mechanism for wireless communication.

[0029] (Embodiment 1) Fig. 1 is a diagram showing a schematic configuration of a wireless communication system 1 according to an embodiment of the present invention. The wireless communication system 1 is for communicating disaster prevention information relating to, for example, natural disasters, and includes a plurality of transmitting base stations installed at arbitrary locations, such as base station A and base station B (hereinafter also referred to as station A and station B), and a mobile receiving station that can move to any location, such as mobile station D. Base station A and base station B each include a wireless communication device (wireless transmitting device) 2, and mobile station D includes a wireless communication device (wireless receiving device) 3. These wireless communication devices 2 and 3 are connected to each other by a wireless line 4 via antennas 2a and 3a.

[0030] In the wireless communication system 1 according to this embodiment, when a mobile station D receives and demodulates the same data frame at the same frequency modulated and transmitted from a plurality of base stations A and B, the system determines whether the mobile station D is located in an area where radio waves from base station A and base station B arrive approximately equally, or whether the mobile station D is located in an area where radio waves from base station A or base station B arrive predominantly, and switches to an appropriate demodulation method based on the determination result.

[0031] In order to suppress the above-mentioned beat interference, the wireless communication devices 2 of base stations A and B according to this embodiment each transmit a data frame comprising a known synchronization word (header data), multiple block data having the same number of symbols (data length) as the synchronization word, and a no-data section arranged between the synchronization word and the first block data, with a time difference corresponding to a predetermined number of offset symbols.

[0032] 2(A) shows an example of a data frame transmitted from base station A and base station B. The data frame DF_A from base station A is, for example, PSK modulated and comprises, from the beginning on the left, a synchronization word SW_A (SW: Sync Word), a no-data section ND_A, and multiple, for example, seven, blocks of data BD_A. The blocks of data BD_A are assigned block numbers A1, A2, A3, A4, A5, A6, and A7, respectively.

[0033] The synchronization word SW_A is known data having a predetermined number of symbols N (for example, 32 symbols in this embodiment) and indicates the beginning of the data frame DF_A. The no-data section ND_A is provided so that when mobile station D simultaneously receives data frame DF_A from station A and data frame DF_B from station B, the synchronization word SW_B of data frame DF_B can be received independently without overlapping with other data (in other words, without being combined). The number of symbols in the no-data section ND_A in this embodiment is the same as the number of symbols N of the synchronization word SW_A.

[0034] Modulated transmission data is stored in A1, A2, A3, A4, A5, A6, and A7 of block data BD_A, respectively. The number of symbols in A1, A2, A3, A4, A5, A6, and A7 of block data BD_A is the same as the number of symbols N of synchronization word SW_A.

[0035] The data frame DF_B transmitted from base station B comprises, from the beginning on the left, a synchronization word SW_B, a no-data interval ND_B, and multiple, for example, seven, blocks of data BD_B. The data frame DF_B is identical to the data frame DF_A of base station A, and the synchronization word SW_B, no-data interval ND_B, and blocks of data BD_B correspond to the synchronization word SW_A, no-data interval ND_A, and blocks of data BD_A, respectively.

[0036] Block numbers B1, B2, B3, B4, B5, B6, and B7 are assigned to the block data BD_B, respectively. The transmission data stored in B1, B2, B3, B4, B5, B6, and B7 of the block data BD_B is the same as the transmission data stored in A1, A2, A3, A4, A5, A6, and A7 of the block data BD_A in the data frame DF_A.

[0037] The no-data section ND_B is provided so that when mobile station D simultaneously receives data frame DF_A from station A and data frame DF_B from station B, the first block data BD_A1 of data frame DF_A can be received alone without overlapping with other data (in other words, without being combined).

[0038] Base station A and base station B are connected to, for example, a central control device (not shown) of a disaster prevention radio system. The wireless communication devices 2 of base station A and base station B modulate and convert transmission data received from this central control device into data frames DF_A and DF_B, and transmit the data frames DF_A and DF_B in accordance with instructions from the central control device. At this time, base station B transmits the data frame DF_B with a time difference equivalent to a predetermined offset number of symbols M (shown as Msym in the figure) relative to the transmission of the data frame DF_A, in order to avoid beat interference at the time of reception. In this embodiment, the offset number of symbols M is a time difference equivalent to the number of symbols N (32 symbols) of the synchronization word SW_A. In other words, base station B transmits the data frame DF_B with a delay of the number of symbols M relative to the data frame DF_A. By delaying the transmission of data frame DF_B relative to data frame DF_A, when wireless equipment 3 of mobile station D simultaneously receives data frame DF_A and data frame DF_B, it can use the no-data intervals ND_A and ND_B to receive synchronization word SW_A, synchronization word SW_B, and A1 of the first block data BD_A of data frame DF_A individually without overlapping (combining) with other data.

[0039] Data frames DF_A and DF_B transmitted as radio waves from antennas 2a of wireless communication devices 2 of base stations A and B are combined as they propagate through space, generating a combined data frame DF_A+DF_B as shown in Figure 2(B).

[0040] The combined data frame DF_A+DF_B is formed by transmitting the data frame DF_B of base station B with an offset of the number of symbols M relative to the data frame DF_A of base station A, so that the synchronization word SW_A of the data frame DF_A, the synchronization word SW_B of the data frame DF_B, the block data BD_A of the data frame DF_A, and the block data BD_B of the data frame DF_B are arranged in transmission order. As shown in Fig. 2(A), the data frames DF_A and DF_B each have a no-data interval ND_A and a no-data interval ND_B, and therefore the synchronization word SW_B is placed at the position of the no-data interval ND_A, and A1 of the block data BD_A is placed at the position of the no-data interval ND_B.

[0041] Furthermore, among the plurality of block data A1 to A7 of BD_A and B1 to B7 of BD_B, block data transmitted at the same time are combined to generate combined block data.

[0042] Specifically, A1 of block data BD_A and no-data section ND_B of block data BD_B are combined to generate combined block data A1. Similarly, A2 of block data BD_A and B1 of block data BD_B are combined to generate combined block data A2+B1. A3 of block data BD_A and B2 of block data BD_B are combined to generate combined block data A3+B2. A4 of block data BD_A and B3 of block data BD_B are combined to generate combined block data A4+B3. A5 of block data BD_A and B4 of block data BD_B are combined to generate combined block data A5+B4. A6 of block data BD_A and B5 of block data BD_B are combined to generate combined block data A6+B5. A7 of block data BD_A and B6 of block data BD_B are combined to generate combined block data A7+B6. It should be noted that B7 of the block data BD_B does not overlap with other data in terms of reception time, and is therefore placed after the combined block data A7+B6.

[0043] The data frames DF_A and DF_B transmitted as radio waves from the wireless communication devices 2 of the base stations A and B are received as a composite wave of the composite data frame DF_A+DF_B by the wireless communication device 3 of the mobile station D. The received signal r of this composite wave at time k is k can be expressed by the following equation (1).

[0044] Here, L in equation (1) A is the number of effective paths between base station A and mobile station D (multipath if 2 or more), L B is the number of effective paths between base station B and mobile station D (multipath if 2 or more), h A,i is the impulse response value between base station A and mobile station D, h B,i is the impulse response value between base station B and mobile station D, x k is the primary modulation symbol transmitted from base station A at time k, n kis the noise (e.g., additive white Gaussian noise: AWGN) added by mobile station D at time k. As can be seen from equation (1), signal loss due to beat interference can be avoided by offsetting the transmission of data frames by M symbols between base station A and base station B.

[0045]

number

[0046] 3 is a functional block diagram showing a schematic configuration of the wireless communication device 3 of the mobile station D. Note that the wireless communication devices 2 of the base station A and base station B have the same configuration as the wireless communication device 3, and therefore detailed explanations thereof will be omitted.

[0047] The wireless communication device 3 includes a modulation unit 31 and a transmission unit 32 used to transmit data frames, as well as a reception unit (reception means) 33 used to receive data frames, a first demodulation unit (first demodulation means) 35, a judgment unit (judgment means) 36, and a second demodulation unit (second demodulation means) 37, and further includes an interface unit 38.

[0048] The interface unit 38 mainly includes a data circuit-terminating device 381 (including equipment called data communication equipment and data circuit equipment). The interface unit 38 receives input of transmission data to be communicated, and outputs the transmission data to the modulation unit 31 via the data circuit-terminating device 381.

[0049] The modulation unit 31 receives transmission data output from the interface unit 38, inserts a synchronization word into the transmission data to generate a data frame, and then superimposes a carrier signal of a predetermined frequency onto the data frame to digitally modulate and output the data. Note that the modulation method used in the wireless communication system 1 is not limited to PSK, and QAM, etc. may also be used.

[0050] The transmitter 32 receives the digitally modulated data frame output from the modulator 31, performs digital-to-analog conversion on the data frame using a D / A converter, and then converts the data frame into a high-frequency signal using a local oscillator and mixer. The transmitter 32 also passes the frequency-converted data frame through a transmission filter that passes only signals in a predetermined frequency band, amplifies it using a power amplifier, and then outputs it.

[0051] The data frame that has been digitally modulated in the modulation unit 31 and frequency converted in the transmission unit 32 is then guided from the transmission unit 32 to the antenna 3a via the splitter 39, and is then transmitted as radio waves from the antenna 3a via the wireless line 4 to the antenna 2a of the wireless communication device 2 of base station A and base station B.

[0052] Furthermore, when data frames DF_A and DF_B are transmitted as radio waves from antennas 2a of wireless communication devices 2 of base stations A and B, the data frames DF_A and DF_B are combined as they propagate through space to generate a combined data frame DF_A+DF_B. When the combined data frame DF_A+DF_B is received by antenna 3a of wireless communication device 3 of mobile station D, antenna 3a converts the received combined data frame DF_A+DF_B into an electrical signal (received signal) and outputs it.

[0053] The combined data frame DF_A+DF_B converted into an electrical signal and output from the antenna 3 a is guided to the receiving unit 33 via the branching filter 39 .

[0054] The receiving unit 33 receives the combined data frame DF_A+DF_B as input, passes the combined data frame DF_A+DF_B through a receiving filter that only passes signals in a specified frequency band, amplifies the combined data frame DF_A+DF_B using a preamplifier, and then converts it into a low-frequency signal using a local oscillator and mixer.

[0055] The receiving unit 33 further amplifies the frequency-converted signal with a power amplifier and performs analog-to-digital conversion with an A / D converter, and outputs a combined data frame DF_A+DF_B consisting of a digital signal.

[0056] The first demodulation unit 35 is a demodulation unit that performs demodulation processing using an appropriate demodulation method when the mobile station D is located in an area where radio waves from base station A and base station B arrive at approximately equal rates, and as shown in Figure 4, performs demodulation processing using a decision feedback adaptive equalizer (hereinafter also referred to as equalizer or DFE) 34.

[0057] The DFE 34 is an adaptive equalizer that shapes the received signal waveform distorted by the transmission path characteristics by feeding back and weighting the combined data frame DF_A+DF_B output from the receiving unit 33 using signals determined by a hard decision device, thereby eliminating the influence of inter-symbol interference caused by previously determined symbols. The DFE 34 also has a function of outputting an approximation of the symbol of the block data BD_A from the combined data frame DF_A+DF_B.

[0058] The transmission data extracted by demodulating the block data BD_A output from the DFE 34 is output to the decision unit 36 ​​.

[0059] The demodulation process by the DFE 34 in the first demodulator 35 is a demodulation method that is particularly effective when the mobile station D moves at high speed.

[0060] The second demodulation unit 37 is a demodulation unit that performs demodulation processing using a demodulation method that is appropriate when the mobile station D is located in an area where radio waves from base station A or base station B are dominant, and is appropriate for transmission from a single base station, and performs demodulation processing using primary demodulation as shown in Figure 4.

[0061] The second demodulation unit 37 performs primary demodulation on the combined data frame DF_A+DF_B output from the receiving unit 33 to extract the transmission data, and outputs the extracted transmission data to the determination unit 36. Here, primary demodulation refers to a method of directly demodulating data without performing equalization processing, such as converting PSK symbols to binary data. Primary demodulation also includes so-called digital simple radio systems.

[0062] The determination unit 36 ​​determines the area in which the mobile station D is located based on the composite data frame DF_A+DF_B output from the receiving unit 33, and based on the result, determines an appropriate demodulation method.From the transmission data (demodulation results) extracted from the first demodulation unit 35 and the second demodulation unit 37, the determination unit 36 ​​selects the transmission data demodulated by the appropriate demodulation method and outputs it to the interface unit 38.

[0063] In this embodiment, the first demodulation unit 35 (including the DFE 34), the second demodulation unit 37, and the judgment unit 36 ​​constitute a demodulation method switching unit 40A, and in the demodulation method switching unit 40A, demodulation processing by the DFE 34 in the first demodulation unit 35, demodulation processing by primary demodulation in the second demodulation unit 37, and area judgment processing and demodulation method determination processing in the judgment unit 36 ​​are performed to perform demodulation method switching processing.

[0064] Next, the process executed by the determination unit 36 ​​in the demodulation method switching process in the demodulation method switching unit 40A will be described with reference to the flowchart shown in FIG. 5, the diagram showing area types in FIG. 6, and the bit error rate graph in FIG.

[0065] As shown in FIG. 5, the determination unit 36 ​​executes a first propagation path power calculation process S1a, a second propagation path power calculation process S2a, a propagation path power comparison process S3a, an area determination process S4a, and a demodulation method determination process S5a.

[0066] As shown in Fig. 2, the combined data frame DF_A+DF_B is formed by combining the synchronization words SW_A, SW_B, block data BD_A, and block data BD_B contained in the data frames DF_A and DF_B transmitted with a time difference from base station A and base station B in the order of transmission. Note that base station A and base station B are adjacent transmitting base stations, as shown in Fig. 6.

[0067] Here, base station B delays transmission of data frame DF_B by a predetermined offset number M of symbols relative to data frame DF_A, so that when radio equipment 3 of mobile station D simultaneously receives data frames DF_A and DF_B, it can receive synchronization word SW_A independently without overlapping with other data (without being combined). Furthermore, because a no-data interval ND_A is provided in data frame DF_A, when radio equipment 3 of mobile station D simultaneously receives data frames DF_A and DF_B, it can receive synchronization word SW_B independently without overlapping with other data (without being combined). In this way, the independently received synchronization words SW_A and SW_B are used to calculate the propagation path power between each base station and mobile station D.

[0068] In the first propagation path power calculation process S1a, the decision unit 36 ​​calculates the first propagation path power P between the base station A and the mobile station D using the received synchronization word SW_A. A,K Calculate.

[0069] In the second propagation path power calculation process S2a, the decision unit 36 ​​calculates the second propagation path power P between the base station B and the mobile station D using the received synchronization word SW_B. B,K Calculate.

[0070] In the propagation path power comparison process S3a, the decision unit 36 ​​compares the first propagation path power P A,K and the second propagation path power P B,K and the power ratio R AB,K Calculate.

[0071] [Number 2] R AB,K = P A,K / P B,K ···(2)

[0072] In the area determination process S4a, the determination unit 36 ​​determines the power ratio R AB,K Based on the value of the power ratio R AB,K is the power ratio R AB,K If the threshold value for the upper limit of the power ratio (called the "power ratio upper limit threshold") is larger than Rut [dB], as shown in Figure 6 (1), the mobile station D is in area E where radio waves from base station A are dominant. A In addition, the power ratio R AB,K is the power ratio R AB,K If the power ratio is smaller than the threshold value for the lower limit (called the "power ratio lower limit threshold") Rlt [dB], as shown in Figure 6 (3), the mobile station D is in area E where radio waves from base station B are dominant. B It is determined that the point is located at R AB,K When the power ratio is equal to or greater than the power ratio lower threshold Rlt [dB] and equal to or less than the power ratio upper threshold Rut [dB], as shown in FIG. 6(2), the mobile station D is in an area E where the radio waves from base station A and base station B arrive almost equally. AB It is determined to be located at

[0073] The power ratio upper threshold Rut [dB] and the power ratio lower threshold Rlt [dB] are not limited to specific values, and for example, as shown in Fig. 7, the bit error rate when demodulation processing is performed using the demodulation method (DFE 34) in the first demodulator 35 and the bit error rate when demodulation processing is performed using the demodulation method (primary demodulation) in the second demodulator 37 may be measured, and the power ratio values ​​at two points where the bit error rates of the two demodulation processings match may be set as the upper and lower limits. Furthermore, the power ratio upper threshold Rut and the power ratio lower threshold Rlt may be set to have the same absolute value, or may be set to have different absolute values.

[0074] In the demodulation method determination process S5a, the determination unit 36 ​​determines an appropriate demodulation method when the mobile station D is located in each area. A or Area E B When it is determined that the power ratio is R AB,K is greater than the power ratio upper threshold Rut [dB], and the power ratio R AB,K is smaller than the power ratio lower limit threshold Rlt [dB], it is decided to use the demodulation method (primary demodulation) in the second demodulation unit 37, and the transmission data (demodulation result) extracted and buffered from the second demodulation unit 37 is adopted and output to the interface unit 38.

[0075] Meanwhile, mobile station D is in area E. AB If it is determined that the location is R AB,K is greater than or equal to the power ratio lower threshold Rlt [dB] and less than or equal to the power ratio upper threshold Rut [dB], it is decided to use the demodulation method (DFE 34) in the first demodulation unit 35, and adopts the transmission data (demodulation result) extracted from the first demodulation unit 35 and buffered, and outputs it to the interface unit 38.

[0076] In the demodulation method switching unit 40A, the determination unit 36 ​​may be provided before the first demodulation unit 35 and the second demodulation unit 37. In that case, the determination unit 36 ​​determines the area in which the mobile station D is located based on the combined data frame DF_A+DF_B output from the receiving unit 33. If the determination unit 36 ​​determines that the mobile station D is located in an area where radio waves from the base station A and the base station B arrive at approximately equal intensity, it decides to use the demodulation method (DFE 34) in the first demodulation unit 35, demodulates the combined data frame DF_A+DF_B output from the receiving unit 33 in the first demodulation unit using the DFE 34, and outputs the extracted transmission data (demodulation result) to the interface unit 38. On the other hand, the judgment unit 36 ​​judges the area in which the mobile station D is located based on the combined data frame DF_A+DF_B output from the receiving unit 33, and if it judges that the mobile station D is located in an area where radio waves from base station A or base station B are predominantly received, it decides to use the demodulation method (primary demodulation) in the second demodulation unit 37, primarily demodulates the combined data frame DF_A+DF_B output from the receiving unit 33 in the second demodulation unit 37, and outputs the extracted transmission data (demodulation result) to the interface unit 38.

[0077] Next, the demodulation process by the DFE 34 in the first demodulation unit 35 will be described in detail.

[0078] 8 is a block diagram showing a schematic configuration of the DFE 34. The DFE 34 includes an equalization filter unit 341, a hard decision unit 342 connected to the output of the equalization filter unit 341, an error calculation unit 343 connected to the hard decision unit 342 and the equalization filter unit 341, and a tap update unit 344 connected to the error calculation unit 343 and the equalization filter unit 341.

[0079] The equalization filter unit 341 includes a feed-forward filter (hereinafter referred to as an FF filter) 3411, a feedback filter (hereinafter referred to as an FB filter) 3412, and an adder 3413 that adds the output of the FF filter 3411 and the output of the FB filter 3412. The equalization filter unit 341 reduces propagation path distortion and inter-symbol interference (ISI) by feeding back the output from the FB filter 3412 via the hard decision unit 342.

[0080] The FF filter 3411 is a filter for the received signal r k N with input FF The FB filter 3412 includes taps 3411a and a plurality of delay elements 3411b. k The hard decision value y d , k Or training signal x k-(Tref-1) Enter k Let N FB The delay circuit 3411b includes taps 3412a and multiple delay elements 3412b. Delay elements 3411b and 3412b provide a delay for M symbols, and as shown in FIG. 9, there are M delay elements provided, each providing a delay for one symbol.

[0081] In such a DFE 34, the equalizer input at time k is N FF Received signals r k ,r k-M ,…r k-M(NFF-1) and the filter output y k is obtained by the following formula (3): i (i=1,…,N FF ) is the FF filter tap coefficient, b i (i=1,…,N FB ) is the FB filter tap coefficient, signal d k is the filter output y at time k k The hard decision value y d , k Or training signal x k-(Tref-1) Signal d kWhen the equalizer input is the sync word section (SW_A, SW_B) of the combined data frame DF_A+DF_B, the known signal x k-(Tref-1) When the data interval is (A1, A2 + B1 ... A7 + B6, B7), the filter output y k The hard decision value y d , k That is, at time k, the equalizer output y d , k can be obtained.

[0082]

number

[0083] The error calculation unit 343 calculates the signal d k and the filter output y k The error signal e k The tap update unit 344 uses an adaptive algorithm such as LS (Least Squares), LMS (Least Mean Squares), or RLS (Recursive Least Squares) to calculate the error signal e k Based on this, the tap coefficient a i , b i Update.

[0084] To explain the configuration of the DFE34 more simply, A =L B Let us consider the case of =1 (when mobile station D is moving, even if there is only one wave arriving from base stations A and B, the propagation path impulse response value fluctuates over time, and the propagation paths of base stations A and B fluctuate independently). We also consider that there is no AWGN. In this case, the received signal r k can be expressed by the following formula (4).

[0085]

number

[0086] Here, at time k, the desired symbol x is extracted from the received signal sequence.k-1 Consider the case where the DFE 34 demodulates the known signal x k-(Tref-1) In this case, T ref =M+1. In this case, the configuration of the DFE 34 is as shown in FIG. 10. Specifically, when the received signal r k and a delay unit 3411b. k The hard decision value y d , k Or training signal x k-(Tref-1) Enter k The FB filter 3412 includes one tap 3412a for setting the delay time to M and one delay element 3412b, and the delay elements 3411b and 3412b provide a delay for M symbols.

[0087] According to the characteristics of a general DFE described in the following reference (1), the number of taps of the FF filter is set to the number of delayed symbols included in the delayed wave (in this embodiment, the wave arriving from base station B) plus 1 or more, thereby obtaining a diversity effect. In this embodiment, an M-symbol delay unit is used, so "N FF ≧(M / M)+1=2”. Also, according to the following reference (1), the number of taps of the FB filter should be the number of delayed symbols included in the delayed wave (in this embodiment, the wave arriving from base station B). In this embodiment, an M-symbol delayer is used, so “N FB ≧(M / M)=1”. References (1): Masakazu Sanpei, Decision Feedback Adaptive Equalizer for Land Mobile Communications, Communications Research Laboratory Quarterly Report, 1991, https: / / www.nict.go.jp / publication / shuppan / kihou-journal / kihou-vol37no1 / 0501.pdf

[0088] Next, a process of outputting an approximate value of the symbol of the block data BD_A from the combined data frame DF_A+DF_B by the DFE 34 will be described.

[0089] 11 represents the received signal sequence input to the DFE 34 as a frame, and the received signal for N symbol time is expressed as a unit called a block. The blocks on the left side of the figure represent older signals (signals received earlier).

[0090] DFE_m (m=1, 2, ... 8) represents the same DFE 34 itself in which the tap coefficient values ​​of the FF filter 3411 and FB filter 3412 in each block m have been updated by the tap update unit 344. DFE_1 represents a DFE in which the tap coefficients at the frame start time are calculated using SW_A, SW_B, and a reference signal. The reference signal is stored in advance in the wireless communication device 3 of the mobile station D.

[0091] The processing procedure for outputting approximate values ​​of the symbols of the block data BD_A from the combined data frame DF_A+DF_B is as follows [1] to [6].

[0092] [1] SW_A, SW_B section: FF filter tap coefficients and FB filter tap coefficients are calculated based on SW_A, SW_B, and the reference signal. More specifically, the tap updater 344 generates FF filter tap coefficients from SW_A and the reference signal using an adaptive algorithm such as LS, LMS, or RLS, and generates FB filter tap coefficients using the generated FF filter tap coefficients, SW_A, SW_B, and the reference signal.

[0093] [2] Section A1: The input received signal is delayed by delay devices 3411b and 3412b.

[0094] [3] A2+B1 section: The received signal in the composite block data A2+B1 and the received signal in the A1 section held by the delay devices 3411b and 3412b are input to the equalizer, and equalization processing is performed using the tap coefficients of DFE_1, obtaining an approximation of the transmitted symbol in the block data A1 as the equalizer output.

[0095] [4] The error between the hard decision value of the approximation of the transmitted symbol in the block data A1 obtained as the equalizer output and the equalizer output is calculated, and the FF filter tap coefficients and FB filter tap coefficients are updated to the latest values ​​using this error, the current filter tap coefficients, and the equalizer input to obtain DFE_2.

[0096] [5] A3+B2 section: The received signal in the A2+B1 section is delayed by delay devices 3411b and 3412b. The received signal in the A3+B2 section of the combined block data and the received signal in the A2+B1 section held by delay devices 3411b and 3412b are input to the equalizer, which performs equalization processing using the tap coefficient of DFE_2 and obtains an approximation of the transmitted symbol in block data A2 as the equalizer output.

[0097] [6] Calculate the error between the hard decision value of the approximation of the transmitted symbol in block data A2 obtained as the equalizer output and the equalizer output, and use this error, the current filter tap coefficients, and the equalizer input to update the FF filter tap coefficients and FB filter tap coefficients to the latest values ​​to obtain DFE_3. After that, repeat the same processes as shown in [5] and [6].

[0098] To explain the equalization process in more detail, the procedure of the equalization process in a certain block data section will be explained. Fig. 12 shows the processing procedure of the DFE 34 in the m-th combined block data section of the combined data frame DF_A+DF_B. In this processing procedure, the received signal at time k is k The DFE 34 at this time is represented as DFE_m,k. The FF filter tap coefficients in DFE_m,k are respectively a 1,m,k ,a 2,m,k ,…a NFF,m,k In addition, the FB filter tap coefficients in DFE_m,k are respectively 1,m,k ,b 2,m,k ,…b NFB,m,k Let's say.

[0099] The DFE 34 performs the following processes [1] to [5] in order at time k. [1] Received signal rk is input into DFE34. [2] In the FF filter, the received signal r k ,r k-M ,r k-2M ,…r k-NFFM and FF filter tap coefficient a 1,m,k ,a 2,m,k ,…a NFF,m,k In addition, the FB filter calculates the convolution value of the hard decision value d k-M ,d k-2M ,…d k-NFBM and FB filter tap coefficient b 1,m,k ,b 2,m,k ,…b NFB,m,k Then, the convolution value of the filter output y k get.

[0100]

number

[0101] [3] Filter output y k The equalizer output y d,k At this time, if the tap coefficients are pulled in as desired, "y d,k =x k-(Tref-1) =x k-M (T ref =M+1) can be obtained.

[0102] Next, the tap coefficients are updated. Here, an update method based on the LMS algorithm is described, but an algorithm such as RLS may also be used. For convenience, the filter tap coefficients in DFE_m,k are expressed as a column vector w k =[a 1,m,k a 2,m,k …a NFF,m,k b 1,m,k b 2,m,k …b NFB,m,k ] T , The received signal retained in the FF filter is expressed as a column vector r k =[r k r k-M…r k-NFFM ] T It is defined as:

[0103] At time k, after the above demodulation process, the following tap coefficient update processes are performed in order. [4] Error signal “e k =d k -y k =y d,k -y k " is calculated. [5] Filter tap coefficients w used at the next time (k+1) k+1 is updated using the following equation (6), where μ is the step size and is set to a value smaller than 1. The superscript * represents a complex conjugate.

[0104] [Number 6] w k+1 = w k +μr k e k * ···(6)

[0105] Next, at time k+1, the DFE 34 performs the following processes [1] to [5] in order. [1] Received signal r k+1 is input into DFE34. [2] In the FF filter, the received signal r k+1 ,r k-M+1 ,r k-2M+1 ,…r k-NFFM+1 and FF filter tap coefficient a 1,m,k+1 ,a 2,m,k+1 ,…a NFF,m,k+1 In addition, the FB filter calculates the convolution value of the hard decision value d k-M+1 ,d k-2M+1 ,…d k-NFBM+1 and FB filter tap coefficient b 1,m,k+1 ,b 2,m,k+1 ,…b NFB,m,k+1 Then, the convolution value of the filter output y k+1 get.

[0106]

number

[0107] [3] Filter output y k+1 The equalizer output y d,k+1 At this time, if the tap coefficients are pulled in as desired, "y d,k+1 =x k-M+1 " can be obtained. [4] Error signal “e k+1 =d k+1 -y k+1 =y d,k+1 -y k+1 " is calculated. [5] Filter tap coefficients w used at the next time (k+2) k+2 is updated using the following equation (8).

[0108] [Number 8] w k+2 = w k+1 +μr k+1 e k+1 * ···(8)

[0109] Thereafter, the same process is repeated to obtain block data BD_A. The obtained block data BD_A is output from the DFE to the first demodulation unit .

[0110] As described above, according to the first embodiment, a no-data section is provided between the synchronization word and the first block data, and each data frame is transmitted with a time difference corresponding to a predetermined offset symbol number. Therefore, at least a part of the synchronization words SW_A and SW_B of the data frames from the two adjacent base stations A and B does not overlap with other symbols, and the first propagation path power P A,K and the second propagation path power P between base station B and mobile station D. B,K This makes it possible to properly calculate the first propagation path power P A,K and the second propagation path power P B,KIn other words, based on which transmitting base station has the largest propagation path power, the area in which the mobile station D is located is determined. Therefore, the mobile station D is located in an area E where radio waves from base station A and base station B arrive at approximately the same frequency. AB Area E is located in the area where radio waves from base station A or base station B are dominant. A or E B Furthermore, based on the results of this determination, the system switches to a demodulation method appropriate for each area, preventing degradation of bit error rate (BER) characteristics and improving demodulation performance.

[0111] Furthermore, according to this embodiment, when it is determined that the mobile station D is located in an area where radio waves from base station A and base station B arrive at approximately the same frequency, the demodulation method is switched to one using the DFE 34, and beat interference is avoided by combining signals transmitted with an offset from base station A and base station B. The tap coefficients are updated for each symbol from the combined wave. Therefore, even in a simultaneous transmission environment from multiple base stations, even if the mobile station D moves at high speed and the propagation path changes, it is possible to follow the changes and perform stable fading compensation.

[0112] (Embodiment 2) Next, a second embodiment of the present invention will be described. In the first embodiment above, the case where there are two transmitting base stations, base station A and base station B, has been described, but the present invention can also be applied to an environment where three or more base stations transmit simultaneously. Therefore, in this embodiment, a case where the same data frame is transmitted from three transmitting base stations, base station A, base station B, and base station C, will be described. Note that detailed description of the same configuration as in the first embodiment will be omitted.

[0113] 13(A) shows an example of a data frame transmitted from base station A, base station B, and base station C. The data frame DF_A from base station A is, for example, PSK modulated and comprises, from the beginning on the left, a synchronization word SW_A, no-data intervals ND_A1 and ND_A2, and a plurality of, for example, seven, blocks of data BD_A. The block data BD_A are assigned block numbers A1, A2, A3, A4, A5, A6, and A7, respectively.

[0114] The synchronization word SW_A is known data comprising a predetermined number of symbols N (for example, 32 symbols in this embodiment) and indicates the beginning of the data frame DF_A. The no-data sections ND_A1 and ND_A2 are provided so that when a mobile station D simultaneously receives a data frame DF_A from base station A, a data frame DF_B from base station B, and a data frame DF_C from base station C, the synchronization word SW_B of the data frame DF_B and the synchronization word SW_C of the data frame DF_C can be received independently without overlapping with other data (in other words, without being combined). The number of symbols in the no-data section ND_A in this embodiment is the same as the number of symbols N of the synchronization word SW_A.

[0115] Modulated transmission data is stored in A1, A2, A3, A4, A5, A6, and A7 of block data BD_A, respectively. The number of symbols in A1, A2, A3, A4, A5, A6, and A7 of block data BD_A is the same as the number of symbols N of synchronization word SW_A.

[0116] The data frame DF_B transmitted from base station B comprises, from the beginning on the left, a synchronization word SW_B, no-data intervals ND_B1 and ND_B2, and multiple, for example, seven, blocks of data BD_B. The data frame DF_B is identical to the data frame DF_A of base station A, and the synchronization word SW_B, no-data intervals ND_B1 and ND_B2, and blocks of data BD_B correspond to the synchronization word SW_A, no-data intervals ND_A1 and ND_A2, and blocks of data BD_A, respectively.

[0117] Block numbers B1, B2, B3, B4, B5, B6, and B7 are assigned to the block data BD_B, respectively. The transmission data stored in B1, B2, B3, B4, B5, B6, and B7 of the block data BD_B is the same as the transmission data stored in A1, A2, A3, A4, A5, A6, and A7 of the block data BD_A in the data frame DF_A.

[0118] The no-data sections ND_B1 and ND_B2 are provided so that when mobile station D simultaneously receives data frame DF_A from station A, data frame DF_B from station B, and data frame DF_C from station C, the first block data BD_A1 of data frame DF_A can be received alone without overlapping with other data (in other words, without being combined).

[0119] The data frame DF_C transmitted from base station C comprises, from the beginning on the left, a synchronization word SW_C, no-data intervals ND_C1 and ND_C2, and multiple, for example, seven, blocks of data BD_C. The data frame DF_C is identical to the data frame DF_A of base station A, and the synchronization word SW_C, no-data intervals ND_C1 and ND_C2, and block data BD_C correspond to the synchronization word SW_A, no-data intervals ND_A1 and ND_A2, and block data BD_A, respectively.

[0120] Block numbers C1, C2, C3, C4, C5, C6, and C7 are assigned to the block data BD_C, respectively. The transmission data stored in C1, C2, C3, C4, C5, C6, and C7 of the block data BD_C is the same as the transmission data stored in A1, A2, A3, A4, A5, A6, and A7 of the block data BD_A in the data frame DF_A.

[0121] The no-data sections ND_C1 and ND_C2 are provided so that when mobile station D simultaneously receives data frame DF_A from station A, data frame DF_B from station B, and data frame DF_C from station C, the first block data BD_A1 of data frame DF_A can be received alone without overlapping with other data (in other words, without being combined).

[0122] As in the first embodiment, base station A, base station B, and base station C are connected to a central control unit (not shown) of the disaster prevention radio system. The wireless communication devices 2 of base station A, base station B, and base station C modulate and convert transmission data received from this central control unit into data frames DF_A, DF_B, and DF_C, and transmit the data frames DF_A, DF_B, and DF_C in accordance with instructions from the central control unit. At this time, base station B transmits data frame DF_B with a time difference equivalent to a predetermined offset number of symbols M (shown as Msym in the figure) relative to the transmission of data frame DF_A, in order to avoid beat interference at the time of reception. Similarly, base station C transmits data frame DF_C with a time difference equivalent to a predetermined offset number of symbols 2M relative to the transmission of data frame DF_A, in order to avoid beat interference at the time of reception. In this embodiment, a time difference equivalent to the number of symbols N (32 symbols) of the synchronization word SW_A is used as the number of offset symbols M. That is, N BS When transmitting data frames from base stations, M is used as the offset time base, and M,2M,···,N BS Each station transmits M symbols with an offset in time.

[0123] Data frames DF_A, DF_B, and DF_C transmitted as radio waves from antennas 2a of wireless communication devices 2 of base stations A, B, and C are combined as they propagate through space, and a combined data frame DF_A+DF_B+DF_C is generated, as shown in Figure 13(B).

[0124] The combined data frame DF_A+DF_B+DF_C is formed by offsetting data frame DF_B by the number of symbols M relative to data frame DF_A and offsetting data frame DF_C by the number of symbols 2M relative to data frame DF_A, so that synchronization word SW_A, synchronization word SW_B, synchronization word SW_C, and block data BD_A, block data BD_B, and block data BD_C are combined in transmission order. As shown in Fig. 13(A), data frames DF_A, DF_B, and DF_C have no-data intervals ND_A1, ND_A2, no-data intervals ND_B1, ND_B2, and no-data intervals ND_C1, ND_C2, so that synchronization word SW_B is placed at the position of no-data interval ND_A1, synchronization word SW_C is placed at the positions of no-data intervals ND_A2 and ND_B1, and block data BD_A1 is placed at the positions of no-data intervals ND_B2 and ND_C1.

[0125] Furthermore, among the multiple block data BD_A A1 to A7, block data BD_B B1 to B7, and block data BD_C C1 to C7, block data transmitted at the same time are combined to generate composite block data, specifically, composite block data A1, composite block data A2+B1, composite block data A3+B2+C1, composite block data A4+B3+C2, composite block data A5+B4+C3, composite block data A6+B5+C4, composite block data A7+B6+C5, composite block data B7+C6, and composite block data C7.

[0126] The data frames DF_A, DF_B, and DF_C transmitted as radio waves from the wireless communication devices 2 of base stations A, B, and C are received as a composite wave of the composite data frame DF_A+DF_B+DF_C by the wireless communication device 3 of mobile station D. The received signal r of this composite wave at time k is k can be expressed by the following equation (9).

[0127] Here, L in equation (9) A is the number of effective paths between base station A and mobile station D (multipath if 2 or more), L B is the number of effective paths between base station B and mobile station D (multipath if 2 or more), L C is the number of effective paths between base station C and mobile station D (multipath if 2 or more), h A,i is the impulse response value between base station A and mobile station D, h B,i is the impulse response value between base station B and mobile station D, h C,i is the impulse response value between base station C and mobile station D, x k is the primary modulation symbol transmitted from base station A at time k, n k is the noise (AWGN) added at time k by mobile station D. As can be seen from equation (9), offset transmission of data frames at base stations A, B, and C can avoid signal loss due to beat interference.

[0128]

number

[0129] Next, the processing executed by the determination unit 36 ​​of the wireless communication device 3 of the mobile station D when the same data frame is transmitted from the three transmitting base stations, base station A, base station B, and base station C, will be described with reference to the flowchart shown in FIG. 14 and the diagram showing area types in FIG. 15.

[0130] As shown in FIG. 14, the determination unit 36 ​​executes a first propagation path power calculation process S1b, a second propagation path power calculation process S2b, a third propagation path power calculation process S3b, a propagation path power comparison process S4b, an area determination process S5b, and a demodulation method determination process S6b.

[0131] As shown in Fig. 13, the combined data frame DF_A+DF_B+DF_C is formed by offsetting data frame DF_B by M symbols from data frame DF_A and offsetting data frame DF_C by 2M symbols from data frame DF_A, thereby combining synchronization words SW_A, SW_B, and SW_C with block data BD_A, block data BD_B, and block data BD_C in transmission order. As shown in Fig. 15, base station A and base station B are adjacent, base station B and base station C are adjacent, and base station A and base station C are adjacent.

[0132] Here, base station B delays transmission of data frame DF_B by a predetermined offset number M of symbols relative to data frame DF_A. Therefore, when radio equipment 3 of mobile station D simultaneously receives data frame DF_A from base station A, data frame DF_B from base station B, and data frame DF_C from base station C, it can receive synchronization word SW_A independently without overlapping with other data (without being combined). Furthermore, because no-data intervals ND_A1 and ND_A2 are provided in data frame DF_A, when radio equipment 3 of mobile station D simultaneously receives data frame DF_A from base station A, data frame DF_B from base station B, and data frame DF_C from base station C, it can receive synchronization word SW_B of data frame DF_B and synchronization word SW_C of data frame DF_C independently without overlapping with other data (without being combined). In this way, the propagation path power between each base station and mobile station D is calculated using the independently received synchronization words SW_A, SW_B, and SW_C.

[0133] In the first propagation path power calculation process S1b, the decision unit 36 ​​uses the received synchronization word SW_A to calculate the first propagation path power P A,K Calculate.

[0134] In the second propagation path power calculation process S2b, the decision unit 36 ​​uses the received synchronization word SW_B to calculate the second propagation path power P B,K Calculate.

[0135] In the third propagation path power calculation process S3b, the decision unit 36 ​​calculates the third propagation path power P between the base station C and the mobile station D using the received synchronization word SW_C. C,K Calculate.

[0136] In the propagation path power comparison process S4b, the decision unit 36 ​​compares two of the first to third propagation path powers. Specifically, the first propagation path power P A,K and the second propagation path power P B,K and the power ratio R AB,K Also, the second propagation path power P B,K and the third propagation path power P C,K and the power ratio R BC,K Furthermore, the first propagation path power P A,K and the third propagation path power P C,K and the power ratio R AC,K Calculate.

[0137] [Number 10] R AB,K = P A,K / P B,K ···(10)

[0138] [Number 11] R BC,K = P B,K / P C,K ···(11)

[0139] [Number 12] R AC,K = P A,K / P C,K ···(12)

[0140] In the area determination process S5b, the determination unit 36 ​​determines the power ratio R AB,K , R BC,K and RAC,K Based on the value of R, the area in which the mobile station D is located is determined. AB,K When the power ratio upper limit threshold Rut [dB] is larger than the power ratio upper limit threshold Rut [dB], as shown in FIG. 15(1), the mobile station D is in an area E where radio waves from the base station A are dominant. A It is determined that the point is located at R AB,K When the power ratio is equal to or greater than the power ratio lower threshold Rlt [dB] and equal to or less than the power ratio upper threshold Rut [dB], as shown in FIG. 15(2), the mobile station D is in an area E where radio waves from base station A and base station B arrive approximately equally. AB It is determined that the point is located at R AB,K is smaller than the power ratio lower threshold Rlt [dB], or R BC,K When the power ratio upper limit threshold Rut [dB] is larger than the power ratio upper limit threshold Rut [dB], as shown in FIG. 15(3), the mobile station D is in an area E where radio waves from the base station B are dominant. B It is determined that the point is located at R BC,K When the power ratio is equal to or greater than the power ratio lower threshold Rlt [dB] and equal to or less than the power ratio upper threshold Rut [dB], as shown in FIG. 15(4), the mobile station D is in an area E where radio waves from base station B and base station C arrive at approximately the same frequency. BC It is determined that the point is located at R BC,K is smaller than the power ratio lower threshold Rlt [dB], or R AC,K If the power ratio is smaller than the lower threshold Rlt [dB], as shown in FIG. 15(5), the mobile station D is in an area E where radio waves from the base station C are dominant. C It is determined that the point is located at R AC,K When the power ratio is equal to or greater than the power ratio lower threshold Rlt [dB] and equal to or less than the power ratio upper threshold Rut [dB], as shown in FIG. 15(6), the mobile station D is in an area E where radio waves from base station A and base station C arrive at approximately the same frequency. AC It is determined to be located at

[0141] In the demodulation method determination process S6b, the determination unit 36 ​​determines an appropriate demodulation method when the mobile station D is located in each area. A , Area E B or Area E C When it is determined that the power ratio is R AB,K , RBC,K , R AC,K is greater than the power ratio upper threshold Rut [dB], and the power ratio R AB,K , R BC,K , R AC,K is smaller than the power ratio lower limit threshold Rlt [dB], it is decided to use the demodulation method (primary demodulation) in the second demodulation unit 37, and the transmission data (demodulation result) extracted and buffered from the second demodulation unit 37 is adopted and output to the interface unit 38.

[0142] On the other hand, mobile station D is in area E. AB , Area E BC or Area E AC When it is determined that the power ratio is R AB,K , R BC,K , R AC,K is greater than or equal to the power ratio lower threshold Rlt [dB] and less than or equal to the power ratio upper threshold Rut [dB], it is decided to use the demodulation method (DFE 34) in the first demodulation unit 35, and adopts the transmission data (demodulation result) extracted from the first demodulation unit 35 and buffered, and outputs it to the interface unit 38.

[0143] Next, the demodulation process by the DFE 34 in the first demodulator 35 when the same data frame is transmitted from three transmitting base stations, base station A, base station B, and base station C, will be described in detail.

[0144] Here, in order to more simply explain the configuration of the DFE 34, in the above formula (9), L A =L B =L C Let us consider the case of =1 (when mobile station D is moving, even if there is only one wave arriving from base stations A, B and C, the propagation path impulse response value fluctuates over time, and the propagation paths of base stations A, B and C fluctuate independently). We also consider that there is no AWGN. In this case, the received signal r k can be expressed by the following equation (13).

[0145]

number

[0146] Here, at time k, the desired symbol x is extracted from the received signal sequence. k-2M Consider the case where the DFE 34 demodulates the known signal x k-(Tref-1) In this case, T ref = 2M + 1. In this case, the configuration of the DFE 34 is as shown in FIG. 16. Specifically, when the received signal r k and a FF filter 3411 having three taps 3411a and two delay devices 3411b, each of which receives a filter output value y k The hard decision value y d , k Or training signal x k-(Tref-1) Enter k The delay circuit 3411b and 3412b provide a delay for M symbols.

[0147] According to the characteristics of a general DFE described in the above reference (1), a diversity effect can be obtained by setting the number of taps of the FF filter to be equal to or greater than the number of delayed symbols included in the delayed waves (in this embodiment, the waves arriving from base stations B and C) plus 1. In this embodiment, an M-symbol delay device is used, so "N FF ≧(N BS -1)+1=3". Also, according to reference (1), the number of taps of the FB filter may be set to the number of delayed symbols contained in the delayed waves (in this embodiment, the waves arriving from base stations B and C). In this embodiment, an M-symbol delayer is used, so "N FB ≧N BS -1=2".

[0148] In such a DFE 34, the equalizer input at time k is N FF = 3 received signals r k ,r k-M ,r k-2M and the filter output y kis obtained by the following equation (14): where a1, a2, and a3 are FF filter tap coefficients, b1 and b2 are FB filter tap coefficients, and the signal d k is the filter output y at time k k The hard decision value y d , k Or training signal x k-(Tref-1) Signal d k When the equalizer input is the sync word section (SW_A, SW_B, SW_C) of the synthesized data frame DF_A+DF_B+DF_C, the known signal x k-(Tref-1) When the data section is (A1, A2 + B1 ... B7 + C6, C7), the filter output y k The hard decision value y d , k That is, at time k, the equalizer output y d , k can be obtained.

[0149]

number

[0150] 17 illustrates the process of outputting an approximate value of the symbol of block data BD_A from the combined data frame DF_A+DF_B+DF_C by the DFE 34 shown in FIG. 16. The process by the DFE 34 is the same as that in the first embodiment except that the number of taps is increased, so a detailed description will be omitted. However, the input signal of the FF filter is as shown in the following equations (15) to (17). In addition, d k =x k-2M The filter output obtained when the above equations are satisfied is as shown in the following equation (18). Here, the tap coefficients a1, a2, a3 and b1, b2, and the impulse response values ​​h between the base stations A, B, C and the mobile station D are A,0 ,h B,0 ,h C,0 If the relationship between these is expressed as the following equation (19), then the following equation (20) becomes y k =x k-2MThese approximate values ​​can be obtained by using an adaptive algorithm such as LMS or RLS.

[0151]

number

[0152]

number

[0153]

number

[0154]

number

[0155]

number

[0156]

number

[0157] As described above, according to this embodiment, as in the first embodiment, a no-data section is provided between the synchronization word and the first block data, and each data frame is transmitted with a time difference corresponding to a predetermined offset symbol number. Therefore, at least a part of the synchronization words SW_A, SW_B, and SW_C of the data frames from the three adjacent base stations A, B, and C do not overlap with other symbols, and the first propagation path power P A,K and the second propagation path power P between base station B and mobile station D. B,K and the third propagation path power P between base station C and mobile station D. C,KThis makes it possible to properly calculate the first propagation path power P A,K and the second propagation path power P B,K , the second propagation path power P B,K and the third propagation path power P C,K , and the first propagation path power P A,K and the third propagation path power P C,K In other words, based on which transmitting base station has the largest propagation path power, the area in which mobile station D is located is determined. Therefore, mobile station D is located in area E where radio waves from base station A and base station B arrive at approximately the same frequency. AB or mobile station D is located in area E where radio waves from base station B and base station C arrive at approximately the same frequency. BC or mobile station D is located in area E where radio waves from base station A and base station C arrive at approximately the same frequency. AC or area E where radio waves from base station A, base station B, or base station C arrive predominantly. A or E B or E C Furthermore, based on the results of this determination, the system switches to a demodulation method appropriate for each area, preventing degradation of bit error rate (BER) characteristics and improving demodulation performance.

[0158] Furthermore, according to this embodiment, as in the first embodiment, when it is determined that the mobile station D is located in an area where radio waves from base station A and base station B arrive at approximately equal intensities, when it is determined that the mobile station D is located in an area where radio waves from base station B and base station C arrive at approximately equal intensities, or when it is determined that the mobile station D is located in an area where radio waves from base station A and base station C arrive at approximately equal intensities, the demodulation method is switched to one using the DFE 34, and beat interference is avoided by combining signals transmitted with offsets from base station A, base station B, and base station C, while the tap coefficients are updated for each symbol from the combined wave. Therefore, even if the mobile station D moves at high speed and the propagation path changes in an environment where multiple base stations are simultaneously transmitting, it is possible to follow the changes and perform stable fading compensation.

[0159] (Embodiment 3) Next, a third embodiment of the present invention will be described. In the first embodiment above, a case has been described in which the determination unit 36 ​​calculates the first propagation path power and the second propagation path power in a single combined data frame and compares the first propagation path power and the second propagation path power to perform area determination. However, in this embodiment, a case will be described in which the determination unit 36 ​​calculates the average first propagation path power and the average second propagation path power in a plurality of combined data frames and compares the calculated average first propagation path power and the second propagation path power to perform determination. Note that detailed description of the same configuration as in the first and second embodiments will be omitted.

[0160] The processing executed by the determination unit 36 ​​in this embodiment will be described with reference to the flowchart shown in Fig. 18. The determination unit 36 ​​executes a first propagation path power calculation process S1c, a second propagation path power calculation process S2c, an average value calculation process S3c, a propagation path power comparison process S4c, an area determination process S5c, and a demodulation method determination process S6c. The combined data frame DF_A+DF_B used in the propagation path power calculation is the same as that in the first embodiment.

[0161] In the first propagation path power calculation process S1c, the decision unit 36 ​​uses the received synchronization word SW_A to calculate the first propagation path power P A,K Calculate.

[0162] In the second propagation path power calculation process S2c, the decision unit 36 ​​uses the received synchronization word SW_B to calculate the second propagation path power P B,K Calculate.

[0163] In the average value calculation process S3c, the decision unit 36 ​​calculates the first propagation path power P A,K The average power of the first propagation path P A,ave,K Similarly, the second propagation path power P B,K The average power of the second propagation path PB,ave,K Calculate.

[0164] In the propagation path power comparison process S4c, the decision unit 36 ​​compares the average first propagation path power P A,ave,K and the average second path power P B,ave,K and the power ratio R AB,K Calculate.

[0165] [Number 21] R AB,K = P A,ave,K / P B,ave,K ···(twenty one)

[0166] In the area determination process S5c, the determination unit 36 ​​determines the power ratio R AB,K Based on the value of , the area in which the mobile station D is located is determined, and in the demodulation method determination process S6c, the determination unit 36 ​​determines the appropriate demodulation method when the mobile station D is located in each area based on the result of the area determination. The specific processing method is the same as in the first embodiment, so a detailed description will be omitted.

[0167] The above processing executed by the determination unit 36 ​​in this embodiment is also applicable to a wireless communication system having three or more base stations as in Embodiment 2. A detailed description of the specific processing method will be omitted.

[0168] As described above, according to this embodiment, the average first propagation path power P A,ave,K and the average second path power P B,ave,K In order to determine the area in which the mobile station D is located, the mobile station D is located in an area E where radio waves from base station A and base station B arrive at approximately the same frequency. AB Area E is located in the area where radio waves from base station A or base station B are dominant. A or E B It is possible to more accurately determine whether the object is located in the

[0169] (Fourth embodiment) Next, a fourth embodiment of the present invention will be described. In the first embodiment, the demodulation method switching unit 40A is described as having the first demodulation unit 35 and the second demodulation unit 37. In this embodiment, however, a case will be described in which the demodulation method switching unit 40B further includes a third demodulation unit (third demodulation means) 41, as shown in Figures 19 and 20. Note that detailed descriptions of the same configurations as those in the first to third embodiments will be omitted.

[0170] The third demodulation unit 41 is a demodulation unit that performs demodulation processing using an appropriate demodulation method when the mobile station D is located in an area where radio waves from base station A and base station B arrive approximately equally, and performs demodulation processing using replica data, as described below.

[0171] In this embodiment, as shown in Figures 19 and 20, the first demodulation unit 35 (including DFE 34), the second demodulation unit 37, the third demodulation unit 41, and the judgment unit 36 ​​constitute a demodulation method switching unit 40B, and in the demodulation method switching unit 40B, demodulation processing by DFE 34 in the first demodulation unit 35, demodulation processing by primary demodulation in the second demodulation unit 37, demodulation processing using replica data in the third demodulation unit 42, and area judgment processing and demodulation method determination processing in the judgment unit 36 ​​are performed.

[0172] In this embodiment, when the determination unit 36 ​​determines in the area determination process S4a shown in Fig. 5 that the mobile station D is located in an area where radio waves from base station A and base station B arrive at approximately equal rates, the determination unit 36 ​​can select in the demodulation method determination process S5a whether to use the demodulation method in the first demodulation unit 35 or the demodulation method in the third demodulation unit 41. The demodulation process by the first demodulation unit 35 can be preferably used when the mobile station D moves at high speed, for example, and the demodulation process by the third demodulation unit can be preferably used when the mobile station D moves at low speed, for example.

[0173] Next, the demodulation process executed by the third demodulator 41 in the demodulation method switching process in the demodulation method switching unit 40B will be described with reference to the flowchart shown in Fig. 21 and the processing block diagram shown in Fig. 22. The third demodulator 41 executes a comparison process S1d, a first demodulation process S2d, a replica data generation process S3d, a block data separation process S4d, and a second demodulation process S5d.

[0174] In comparison process S1d, the received synchronization words SW_A and SW_B are compared. Specifically, a correlator is used to find the correlation between the received multiple synchronization words SW_A and SW_B and synchronization words (hereinafter referred to as reference signals) that are stored in advance as reference data in wireless communication device 3 of mobile station D, and the signal level of data frame DF_A is compared with the signal level of data frame DF_B (for example, B / A level ratio), and a phase difference Δθ between data frame DF_A and data frame DF_B is calculated.

[0175] In the first demodulation process S2d, one of the multiple data frames included in the received composite data frame DF_A+DF_B is selected as the data frame to be demodulated, and data frames other than the data frame to be demodulated are selected as cancellation data frames, and block data included in the data frame to be demodulated that does not overlap with other data in reception time is demodulated to generate demodulated data.

[0176] Specifically, of the multiple data frames DF_A and DF_B transmitted with a time difference from multiple base stations A and B, the first transmitted data frame DF_A is set as the data frame to be demodulated, and the data frames DF_B other than the data frame to be demodulated are set as cancellation data frames.

[0177] Furthermore, in the first demodulation process S2d, among the block data included in the data frame DF_A, which is the data frame to be demodulated, block data whose reception time does not overlap with other data, i.e., A1 of the block data BD_A, is demodulated to generate demodulated data. This demodulated data becomes transmission data TD_A1 extracted from A1 of the block data BD_A.

[0178] In the replica data generation process S3d, the demodulated data generated in the first demodulation process S2d is re-modulated based on the comparison result of the comparison process S1d to generate replica data corresponding to the block data of the cancellation data frame. Specifically, the demodulated data generated in the first demodulation process S2d is re-modulated based on the B / A level ratio and AB phase difference, which are the comparison results of the comparison process S1d, and the amplitude and phase are adjusted to generate replica data (replica B1) of B1 of the block data BD_B.

[0179] In the block data separation process S4d, replica data is subtracted from the composite block data to generate block data of the data frame to be demodulated. Specifically, the replica B1 generated in the replica data generation process S3d is subtracted from the composite block data A2+B1 by a subtractor to separate A2 of the block data BD_A of the data frame DF_A, which is the data frame to be demodulated.

[0180] In the second demodulation process S5d, the block data separated in the block data separation process S4d is demodulated to generate demodulated data of the data frame to be demodulated. Specifically, A2 of the block data BD_A separated in the block data separation process S4d is demodulated to generate demodulated data of the data frame DF_A, which is the data frame to be demodulated. This demodulated data becomes transmission data TD_A2 extracted from A2 of the block data BD_A.

[0181] In the next step S6d, it is determined whether or not demodulation of all block data of the data frame DF_A, which is the data frame to be demodulated, has been completed. As described above, in the first round of the second demodulation process S5d, only up to A2 of the block data BD_A of the data frame DF_A has been demodulated, so the process returns to the replica data generation process S3d.

[0182] In the second round of replica data generation processing S3d, the demodulated data TD_A2 generated in the second demodulation processing S5d is re-modulated based on the comparison results of the comparison processing S1d, and the amplitude and phase are adjusted to generate replica data (replica B2) of B2 of the block data BD_B.

[0183] In the second round of block data separation processing S4d, replica B2 generated in replica data generation processing S3d is subtracted from composite block data A3+B2 using a subtractor to generate block data A3 of block data BD_A of data frame DF_A, which is the data frame to be demodulated.

[0184] In the second demodulation process S5d of the second round, A3 of the block data BD_A separated in the block data separation process S4d is demodulated to generate demodulated data of the data frame DF_A, which is the data frame to be demodulated. This demodulated data becomes transmission data TD_A3 extracted from A3 of the block data BD_A.

[0185] In step S5d of the second cycle, it is determined whether or not demodulation of all block data of the data frame DF_A, which is the data frame to be demodulated, has been completed. As described above, in the second demodulation process S5d of the second cycle, only up to A3 of block data BD_A of the data frame DF_A has been demodulated, so the process returns to the replica data generation process S3d.

[0186] As described above, the third demodulation unit 41 repeats steps S3d to S6d until demodulation of all block data of the data frame DF_A is completed. This allows the transmission data TD_A1, TD_A2, TD_A3, TD_A4, TD_A5, TD_A6, and TD_A7, which are the demodulated data of the data frame DF_A, which is the data frame to be demodulated, to be obtained. The obtained transmission data TD_A1, TD_A2, TD_A3, TD_A4, TD_A5, TD_A6, and TD_A7 are output from the third demodulation unit 41 to the determination unit 36.

[0187] As described above, according to the fourth embodiment, when it is determined that the mobile receiving station is located in an area where radio waves from a plurality of transmitting base stations arrive at approximately the same frequency, the options for switchable demodulation methods are expanded, making it possible to demodulate using a more appropriate demodulation method. Furthermore, when switching to a demodulation method using replica data in the third demodulation unit, replica data (e.g., replica B1) corresponding to the block data of the cancellation data frame is generated based on the block data of the data frame to be demodulated (e.g., A1 of block data BD_A), and this replica data is used to separate the block data of the data frame to be demodulated (e.g., A2 of data frame DF_A) from the composite block data, making it possible to separate and demodulate only the data frame to be demodulated from the composite data frame DF_A+DF_B.

[0188] Furthermore, according to this embodiment, of the multiple data frames DF_A and DF_B transmitted with a time difference from multiple base stations A and B, the first transmitted data frame DF_A is adopted as the data frame to be demodulated, so that subsequent processing can be started more quickly, thereby making it possible to improve the efficiency of the demodulation processing.

[0189] (Embodiment 5) Next, a fifth embodiment of the present invention will be described. In the fourth embodiment above, the case where there are two transmitting base stations, base station A and base station B, has been described, but the present invention can also be applied to an environment where three or more base stations transmit simultaneously. Therefore, in this embodiment, the demodulation process using replica data performed in the third demodulation unit when the same data frame is transmitted from three transmitting base stations, base station A, base station B, and base station C, will be described using the processing block diagram shown in Fig. 23. Note that detailed description of the same configuration as in the first to fourth embodiments will be omitted.

[0190] In comparison processing S1d by the third demodulation unit 41, the received multiple synchronization words SW_A, SW_B, and SW_C are compared. Specifically, a correlator is used to find the correlation between the received multiple synchronization words SW_A, SW_B, and SW_C and a reference signal pre-stored in the wireless communication device 3 of the mobile station D, and the signal levels of the data frames DF_A, DF_B, and DF_C are compared (for example, B / A level ratio and C / A level ratio) to calculate a phase difference ΔθAB between the data frames DF_A and DF_B and a phase difference ΔθAC between the data frames DF_A and DF_C.

[0191] Furthermore, in the first demodulation process S2d, among the block data included in the data frame DF_A, which is the data frame to be demodulated, block data whose reception time does not overlap with other data, i.e., A1 of the block data BD_A, is demodulated to generate demodulated data. This demodulated data becomes transmission data TD_A1 extracted from A1 of the block data BD_A.

[0192] In the replica data generation process S3d, the demodulated data of A1 of the block data BD_A generated in the first demodulation process S2d is re-modulated based on the comparison result of the comparison process S1d, and the amplitude and phase are adjusted to generate replica data (replica B1) of B1 of the block data BD_B.

[0193] In the block data separation process S4d, the replica B1 generated in the replica data generation process S3d is subtracted from the composite block data A2+B1 by a subtractor to separate A2 from the block data BD_A of the data frame DF_A, which is the data frame to be demodulated.

[0194] In the second demodulation process S5d, A2 of the block data BD_A separated in the block data separation process S4d is demodulated to generate demodulated data of the data frame DF_A, which is the data frame to be demodulated. This demodulated data becomes transmission data TD_A2 extracted from A2 of the block data BD_A.

[0195] In the next step S6d, it is determined whether or not demodulation of all block data of the data frame DF_A, which is the data frame to be demodulated, has been completed. As described above, in the first round of the second demodulation process S5d, only up to A2 of the block data BD_A of the data frame DF_A has been demodulated, so the process returns to the replica data generation process S3d.

[0196] In the second-round replica data generation process S3d, the demodulated data TD_A2 generated in the second demodulation process S5d is re-modulated based on the comparison result of the comparison process S1d, and the amplitude and phase are adjusted to generate replica data (replica B2) of B2 of the block data BD_B. Also, in the second-round replica data generation process S3d, the phase and amplitude of the replica B1 generated in the first-round replica data generation process S3d are adjusted by an adjuster based on the comparison result of the comparison process S1d to generate replica data (replica C1) of C1 of the block data BD_C.

[0197] In the second round of block data separation processing S4d, replica B2 and replica C1 generated in the second round of replica data generation processing S3d are added using an adder to generate replica B2+C1, and replica B2+C1 is subtracted using a subtractor from the composite block data A3+B2+C1 to generate block data A3 of block data BD_A of data frame DF_A, which is the data frame to be demodulated.

[0198] In the second demodulation process S5d of the second cycle, A3 of the block data BD_A generated in the second cycle of the block data separation process S4d is demodulated to generate demodulated data of the data frame DF_A, which is the data frame to be demodulated. This demodulated data becomes transmission data TD_A3 extracted from A3 of the block data BD_A.

[0199] In step S6d of the second cycle, it is determined whether or not demodulation of all block data of the data frame DF_A, which is the data frame to be demodulated, has been completed. As described above, in the second demodulation process S5d of the second cycle, only up to A3 of block data BD_A of the data frame DF_A has been demodulated, so the process returns to the replica data generation process S3d.

[0200] As described above, the third demodulation unit 41 repeats steps S3d to S6d until demodulation of all block data of the data frame DF_A is completed. This allows the transmission data TD_A1, TD_A2, TD_A3, TD_A4, TD_A5, TD_A6, and TD_A7, which are the demodulated data of the data frame DF_A, which is the data frame to be demodulated, to be obtained. The obtained transmission data TD_A1, TD_A2, TD_A3, TD_A4, TD_A5, TD_A6, and TD_A7 are output from the third demodulation unit 41 to the determination unit 36.

[0201] As described above, according to the fifth embodiment, when switching to a demodulation method using replica data in the third demodulation unit, even when the communication areas of three or more base stations overlap, the data frame can be demodulated while suppressing the influence of beat interference, so there are no restrictions on the placement of base stations.

[0202] (Embodiment 6) Next, a sixth embodiment of the present invention will be described. This embodiment differs from the fourth embodiment in that, among a plurality of data frames transmitted from a plurality of base stations with a time difference, the signal level of the first transmitted data frame is compared with the signal level of the last transmitted data frame, and if the signal level of the first transmitted data frame is higher than the signal level of the last transmitted data frame by a predetermined value or more, only the first transmitted data frame is demodulated without performing the first demodulation process, etc. Note that detailed description of the same configurations as those of the first to fifth embodiments will be omitted.

[0203] As shown in the flowchart of Figure 24, in this embodiment, in the first comparison process S1d, the signal level of the first transmitted data frame DF_A is compared with the signal level of the last transmitted data frame DF_B, and in the next step S8d, if the signal level of the data frame DF_A is higher than the signal level of the data frame DF_B by a predetermined value or more, the first demodulation process S2d, the replica data generation process S3d, the block data separation process S4d, and the second demodulation process S5d are not performed, and only the data frame DF_A is demodulated (step S9d).

[0204] Note that the case where the signal level of the data frame DF_A is higher than the signal level of the data frame DF_B by a predetermined value or more may be, for example, when the signal level ratio of the data frame DF_A to the signal level of the data frame DF_B (DF_A / DF_B) is a predetermined dB or more (for example, 5 dB or more). Note that this predetermined value is merely an example and can be set appropriately depending on the communication environment, the performance of the wireless communication device, etc.

[0205] As described above, according to the sixth embodiment, when switching to a demodulation method using replica data in the third demodulation unit, if the signal level of the first transmitted data frame DF_A is higher than the signal level of the last transmitted data frame DF_B by a predetermined value or more, only the data frame DF_A is demodulated without performing the first demodulation process S2d, etc., thereby reducing the load on the demodulation process and shortening the processing time.

[0206] (Embodiment 7) Next, a seventh embodiment of the present invention will be described. This embodiment differs from the fourth embodiment in that a data frame to be demodulated is set according to the signal level of a received data frame. Note that detailed description of the same configuration as in the first to sixth embodiments will be omitted.

[0207] 25, the demodulation method switching unit 40C includes a storage unit (storage means) 42 in front of the third demodulation unit 41. That is, in the present embodiment, the demodulation method switching unit 40C is configured with the first demodulation unit 35 (including the DFE 34), the second demodulation unit 37, the third demodulation unit 41, the storage unit 42, and the determination unit 36, and the demodulation method switching unit 40C performs demodulation processing by the DFE 34 in the first demodulation unit 35, demodulation processing by primary demodulation in the second demodulation unit 37, demodulation processing using replica data in the third demodulation unit 42, storage processing in the storage unit 42, and area determination processing and demodulation method determination processing in the determination unit 36.

[0208] As shown in FIG. 26, the memory unit 42 temporarily stores (buffers) one frame (the nth frame) of multiple data frames DF_A and DF_B transmitted by base station A and base station B with a time difference, and the synchronization words SW_A and SW_B of the next frame (the n+1th frame).

[0209] As shown in the flowchart of FIG. 27, in a comparison process S1d by the third demodulation unit 41 of the mobile station D, the signal levels of the received multiple synchronization words SW_A and SW_B are compared. If the signal level of the synchronization word SW_A is higher than that of the synchronization word SW_B (YES in step S10d), the data frame DF_A is set as the data frame to be demodulated, and the data frame DF_B is set as the cancellation data frame (step S11d). In this case, as shown in the processing block diagram of FIG. 22, the combined data frame DF_A+DF_B of the nth frame is processed in ascending order (in ascending order of the data number of the block data) based on the synchronization word SW_A and synchronization word SW_B of the nth frame. Note that the process of ascending order is the same as in the fourth embodiment, and therefore will not be described here.

[0210] If the signal level of the synchronization word SW_B is higher than that of the synchronization word SW_A (NO in step S10d), the data frame DF_B is set as the data frame to be demodulated, and the data frame DF_A is set as the cancel data frame (step S12d).

[0211] When the data frame DF_B is set as the data frame to be demodulated, as shown in Figure 28, the composite data frame DF_A+DF_B from A1 of the block data BD_A of the data frame DF_A of the nth frame to the synchronization word SW_A and synchronization word SW_B of the next frame (n+1 frame) is processed in descending order (in descending order of the data number of the block data) based on the synchronization word SW_A and synchronization word SW_B of the next frame (n+1 frame).

[0212] In the descending order process, a comparison process S1d compares the synchronization words SW_A and SW_B of the next frame (n+1 frame). Specifically, a correlator is used to find the correlation between the synchronization words SW_A and SW_B of the next frame (n+1 frame) and the reference signal, and the signal level of the data frame DF_A is compared with the signal level of the data frame DF_B (for example, the B / A level ratio), and the phase difference Δθ between the data frame DF_A and the data frame DF_B is calculated.

[0213] In the first demodulation process S2d, among the block data included in the data frame DF_B, which is the data frame to be demodulated, block data whose reception time does not overlap with other data, i.e., B7 of block data BD_B, is demodulated to generate demodulated data. This demodulated data becomes transmission data TD_B7 extracted from B7 of block data BD_B.

[0214] In the replica data generation process S3d, the demodulated data generated in the first demodulation process S2d is re-modulated based on the comparison result of the comparison process S1d to generate replica data corresponding to the block data of the cancellation data frame. Specifically, the demodulated data generated in the first demodulation process S2d is re-modulated based on the comparison result of the comparison process S1d, and the amplitude and phase are adjusted to generate replica data (replica A7) of A7 of the block data BD_A.

[0215] In the block data separation process S4d, the replica A7 generated in the replica data generation process S3d is subtracted from the composite block data A7+B6 by a subtractor to generate B6 of the block data BD_B of the data frame DF_B, which is the data frame to be demodulated.

[0216] In the second demodulation process S5d, B6 of the block data BD_B generated in the block data separation process S4d is demodulated to generate demodulated data of the data frame DF_B, which is the data frame to be demodulated. This demodulated data becomes transmission data TD_B6 extracted from B6 of the block data BD_B.

[0217] In the next step S6d, it is determined whether or not demodulation of all block data of the data frame DF_B, which is the data frame to be demodulated, has been completed. As described above, in the first round of the second demodulation process S5d, only up to B6 of the block data BD_B of the data frame DF_B has been demodulated, so the process returns to the replica data generation process S3d.

[0218] In the second round of replica data generation processing S3d, the demodulated data TD_B6 generated in the second demodulation processing S5d is re-modulated based on the comparison results of the comparison processing S1d, and the amplitude and phase are adjusted to generate replica data (replica A6) of A6 of the block data BD_A.

[0219] In the second round of block data separation processing S4d, the replica A6 generated in the second round of replica data generation processing S2d is subtracted from the composite block data A6+B5 using a subtractor to generate B5 of block data BD_B of data frame DF_B, which is the data frame to be demodulated.

[0220] In the second demodulation process S5d of the second cycle, B5 of the block data BD_B generated in the second cycle of the block data separation process S4d is demodulated to generate demodulated data of the data frame DF_B, which is the data frame to be demodulated. This demodulated data becomes transmission data TD_B5 extracted from B5 of the block data BD_B.

[0221] In step S6d of the second cycle, it is determined whether or not demodulation of all block data of the data frame DF_B, which is the data frame to be demodulated, has been completed. As described above, in the second demodulation process S5d of the second cycle, only up to B5 of block data BD_B of the data frame DF_B has been demodulated, so the process returns to the replica data generation process S3d.

[0222] As described above, the third demodulation unit 41 repeats steps S3d to S6d until demodulation of all block data of the data frame DF_B is completed. This allows the transmission data TD_B1, TD_B2, TD_B3, TD_B4, TD_B5, TD_B6, and TD_B7, which are the demodulated data of the data frame DF_B, which is the data frame to be demodulated, to be obtained. The obtained transmission data TD_B1, TD_B2, TD_B3, TD_B4, TD_B5, TD_B6, and TD_B7 are output from the third demodulation unit 41 to the determination unit 36.

[0223] As described above, according to the seventh embodiment, when switching to a demodulation method using replica data in the third demodulation unit, one frame of the transmitted data frames DF_A and DF_B and the synchronization word SW_A and synchronization word SW_B of the next frame are stored, and the signal level of the first transmitted data frame DF_A is compared with the signal level of the last transmitted data frame DF_B. If the signal level of the first transmitted data frame DF_A is higher than the signal level of the last transmitted data frame DF_B, the first transmitted data frame DF_A is selected as the data frame to be demodulated. Conversely, if the signal level of the last transmitted data frame DF_B is higher than the signal level of the first transmitted data frame DF_A, the last transmitted data frame DF_B is selected as the data frame to be demodulated. This allows data frames with higher signal levels to be demodulated, thereby improving the accuracy of the demodulation process. Furthermore, when the last transmitted data frame DF_B is the data frame to be demodulated, the synchronization words SW_A and SW_B of the next frame, which are closer to the signal level of that data frame DF_B, are used in the replica data generation process S3d, thereby further improving the accuracy of the demodulation process.

[0224] In this embodiment, the demodulation process is performed on either the data frame DF_A or the data frame DF_B as the data frame to be demodulated, but if, for example, the difference in signal level between the first transmitted data frame DF_A and the last transmitted data frame DF_B is equal to or greater than a predetermined value, it is also possible to demodulate only the data frame with the higher signal level without performing processes such as the first demodulation process S2d. This improves the accuracy of the demodulation process, reduces the load on the demodulation process, and shortens the processing time.

[0225] (Embodiment 8) Next, an eighth embodiment of the present invention will be described. This embodiment differs from the fourth embodiment in that the ascending order processing and the descending order processing described in the seventh embodiment are performed together, and the block data obtained by the ascending order processing and the block data obtained by the descending order processing are combined and demodulated. Note that detailed description of the same configuration as the first to seventh embodiments will be omitted.

[0226] 29, after receiving the combined data frame DF_A+DF_B, the third demodulation unit 41 according to the present embodiment performs an ascending order process to separate A1, A2, A3, A4, A5, A6, and A7 of the block data BD_A of the data frame DF_A from the combined block data A2+B1, A3+B2, A4+B3, A5+B4, A6+B5, and A7+B6, with the data frame DF_A as the data frame to be demodulated. Simultaneously with this ascending order process, the third demodulation unit 41 performs a descending order process to separate B1, B2, B3, B4, B5, B6, and B7 of the block data BD_B of the data frame DF_B from the combined block data A2+B1, A3+B2, A4+B3, A5+B4, A6+B5, and A7+B6, with the data frame DF_B as the data frame to be demodulated.

[0227] That is, the third demodulation unit 41 generates multiple frame sets by changing the demodulation target data frame, each frame set having one of the received multiple data frames DF_A and DF_B as the demodulation target data frame and the other data frames as the cancellation data frames. Next, for each frame set, the third demodulation unit 41 executes a first demodulation process S2d that demodulates block data whose reception time does not overlap with other data to generate demodulated data, a replica data generation process S3d that re-modulates the demodulated data based on the comparison result of the comparison process S1d to generate replica data corresponding to the block data of the cancellation data frame, and a block data separation process S4d that subtracts the replica data from the composite block data to separate the block data of the demodulation target data frame. Next, a second demodulation process S5d is performed to demodulate the block data generated by the block data separation process S4d to generate demodulated data for the data frame to be demodulated, and a replica data generation process S3d and a block data separation process S4d based on the demodulated data generated by the second demodulation process S5d are repeated until all block data for the data frame to be demodulated are generated.

[0228] The third demodulation unit 41 then combines A1, A2, A3, A4, A5, A6, and A7 of the block data BD_A obtained by the process in ascending order with B1, B2, B3, B4, B5, B6, and B7 of the block data BD_B obtained by the process in descending order using an adder, and demodulates the combined data (corresponding to the third demodulation process). As a result, the third demodulation unit 41 demodulates the combined result of the multiple data frames DF_A and DF_B to obtain transmission data TD_1, TD_2, TD_3, TD_4, TD_5, TD_6, and TD_7.

[0229] As described above, according to Embodiment 8, when switching to the demodulation method using replica data in the third demodulation unit, a time difference is provided to transmit a plurality of data frames DF_A and data frames DF_B. Therefore, the block data received at the same time has different frequencies when viewed microscopically, and it is possible to suppress the occurrence of beat interference. In addition, a plurality of frame sets each composed of a demodulation target data frame and a cancellation data frame (an ascending frame set and a descending frame set) are generated. For each frame set, the block data of the demodulation target data frame is separated from the combined block data using replica data, and the block data of the demodulation target data frame obtained for each frame set is combined and demodulated. Therefore, it is possible to further improve the accuracy of the demodulation process. Furthermore, since it is possible to receive and process a combined data frame in which a plurality of data frames are combined, there is no restriction on the arrangement of the base stations.

[0230] The embodiments of this invention have been described above. However, the specific configuration is not limited to the above embodiments, and even if there are design changes and the like within the scope not departing from the gist of this invention, they are included in this invention.

[0231] For example, in the above embodiment, when offsetting and transmitting the data frame DF_B with respect to the data frame DF_A, the number of offset symbols M was set to the number of symbols N (M = N) of the data block. However, M≠N may also be used. For example, as shown in FIG. 30, when M < N, in the combined data frame DF_A + DF_B, an interval SW_A + SW_B in which the synchronization words SW_A and SW_B of each base station A and B are multiplexed occurs. In this case, the multiplexed interval may be truncated, and the propagation path power may be calculated using the intervals SW_A and SW_B received independently. In this way, by devising the processing, M≠N can be achieved. In particular, by setting M < N, the length of one frame from the head of the data frame DF_A to the end of the data frame DF_B can be shortened, and it is possible to improve the data transmission efficiency.

[0232] Also, when shortening the data frame length after receiving the synchronization words SW_A and SW_B individually, the same frame transmission between base stations is no longer performed. However, as shown in FIG. 31, the synchronization word SW section may be transmitted with an N-symbol offset, and the data section may be transmitted with an M (M < N) - symbol offset. Note that the process of setting M ≠ N (M < N) is also applicable to a wireless communication system including three or more base stations as in the second embodiment.

Explanation of Signs

[0233] 1 Wireless communication system 2 Wireless communication device (wireless transmission device) 3 Wireless communication device (wireless reception device) 33 Receiver (reception means) 34 Decision feedback equalizer 341 Equalization filter section 342 Hard decision device 343 Error calculation section 344 Tap update section 3411 Feedforward filter 3412 Feedback filter 3413 Adder 35 First demodulation section (first demodulation means) 36 Decision section (decision means) 37 Second demodulation section (second demodulation means) 40A, 40B, 40C Demodulation method switching section 41 Third demodulation section (third demodulation means) 42 Memory section (memory means) A, B, C Base stations D Mobile station DF_A, DF_B, DF_C Data frames DF_A + DF_B Composite data frame DF_A + DF_B + DF_C Composite data frame[[ID=5X]] SW_A, SW_B Synchronization words BD_A, BD_B, BD_C Block data

Claims

1. A wireless communication system comprising a plurality of transmitting base stations each having a wireless transmitting device for transmitting the same modulated data frame at the same frequency, and a mobile receiving station each having a wireless receiving device for receiving and demodulating the data frame, the plurality of wireless transmission devices transmit the data frame, each of the data frames including known header data, a plurality of block data each having the same number of symbols as the header data, and a no-data section disposed between the header data and a first block data, at a time difference corresponding to a predetermined offset number of symbols; The wireless receiving device a receiving means for receiving a composite data frame obtained by spatially combining a plurality of the data frames and outputting a received signal for each symbol; a first demodulation means for inputting the received signal to a decision feedback adaptive equalizer and performing demodulation processing on the equalized received signal; a second demodulation means for performing demodulation processing on the received signal output from the receiving means; determination means for calculating a propagation path power between the one adjacent transmitting base station and the mobile receiving station as a first propagation path power based on header data of the data frame transmitted from the one adjacent transmitting base station among the composite data frames, and for calculating a propagation path power between the other adjacent transmitting base station and the mobile receiving station as a second propagation path power based on header data of the data frame transmitted from the other adjacent transmitting base station among the composite data frames, and for comparing the first propagation path power with the second propagation path power, and for determining that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station and the other adjacent transmitting base station arrive approximately equally, and for determining that the mobile receiving station is located in an area where radio waves from either the one adjacent transmitting base station or the other adjacent transmitting base station arrive predominantly, and for determining that the demodulation method of the second demodulation means is used; A wireless communication system comprising:

2. The decision feedback adaptive equalizer comprises: a first equalization process for performing tap coefficients used in the equalization process based on a received signal of the plurality of header data included in the combined data frame and a pre-stored reference signal; a second equalization process in which a received signal of composite block data constituting the composite data frame is input to an equalizer, and equalization is performed based on the equalizer input and current tap coefficients to obtain an approximation value of a symbol of the block data included in the composite block data as an equalizer output; a third equalization process for calculating an error between the hard decision value of the equalizer output and the equalizer output, and updating the tap coefficients to the latest values ​​using the calculated error, the current tap coefficients, and a new equalizer input; repeating the second equalization process and the third equalization process until all approximations of the symbols of the block data are output from the combined data frame; 2. The wireless communication system according to claim 1.

3. the radio receiving device further comprises a third demodulation means for performing a demodulation process on the received signal output from the receiving means; The third demodulation means a first demodulation process for generating demodulated data by demodulating block data of the demodulation target data frame whose reception time does not overlap with other data, the first demodulation process being a demodulation target data frame, and the data frames other than the demodulation target data frame being cancel data frames; a replica data generation process of re-modulating the demodulated data based on the header data and generating replica data corresponding to the block data of the cancellation data frame; a block data separation process for separating the block data of the data frame to be demodulated by subtracting the replica data from composite block data obtained by combining the block data of the different data frames; repeating a second demodulation process of demodulating the block data of the demodulation target data frame separated by the block data separation process to generate demodulated data, and the replica data generation process and the block data separation process based on the demodulated data generated by the second demodulation process until demodulation of all the block data of the demodulation target data frame is completed; when the determination means determines that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station and the other adjacent transmitting base station arrive at approximately equal intensities, the determination means determines to use the demodulation method of the first demodulation means or the demodulation method of the third demodulation means.

2. The wireless communication system according to claim 1.

4. The third demodulation means Among the plurality of data frames transmitted from the plurality of wireless transmission devices with a time difference, the first transmitted data frame is set as the demodulation target data frame, and data frames other than the demodulation target data frame are set as cancellation data frames.

4. The wireless communication system according to claim 3.

5. The third demodulation means comparing a signal level of the first transmitted data frame with a signal level of the last transmitted data frame among the plurality of data frames transmitted from the plurality of wireless transmission devices with a time difference; When the signal level of the first transmitted data frame is higher than the signal level of the last transmitted data frame by a predetermined value or more, the first demodulation process, the replica data generation process, the block data separation process, and the second demodulation process are not performed, and only the first transmitted data frame is demodulated.

4. The wireless communication system according to claim 3.

6. The wireless receiving device a storage means for storing the composite data frame obtained by combining one frame of the plurality of data frames transmitted from the plurality of wireless transmission devices with a time difference and the header data of the next frame; The third demodulation means comparing a signal level of the first transmitted data frame with a signal level of the last transmitted data frame among the plurality of data frames transmitted from the plurality of wireless transmission devices with a time difference; When the signal level of the first transmitted data frame is higher than the signal level of the last transmitted data frame, the first transmitted data frame is set as the data frame to be demodulated, and the header data of the next frame is used in the replica data generation process; When the signal level of the last transmitted data frame is higher than the signal level of the first transmitted data frame, the last transmitted data frame is set as the data frame to be demodulated, and the header data of the first transmitted data frame is used in the replica data generation process.

4. The wireless communication system according to claim 3.

7. The third demodulation means when a difference between the signal level of the first transmitted data frame and the signal level of the last transmitted data frame is equal to or greater than a predetermined value, the first demodulation process, the replica data generation process, the block data separation process, and the second demodulation process are not performed, and only the data frame with the higher signal level is demodulated.

7. The wireless communication system according to claim 6.

8. The third demodulation means a frame set generation process for generating a plurality of frame sets, each of which is configured to set one of the plurality of data frames as a demodulation target data frame and set the other data frames as cancellation data frames; For each of the plurality of frame sets, a first demodulation process for demodulating block data of the demodulation target data frame, the reception time of which does not overlap with other data, to generate demodulated data; a replica data generation process of re-modulating the demodulated data based on the header data and generating replica data corresponding to the block data of the cancellation data frame; a block data separation process for separating the block data of the data frame to be demodulated by subtracting the replica data from composite block data obtained by combining the block data of the different data frames; a second demodulation process for demodulating the block data of the demodulation target data frame separated by the block data separation process to generate demodulated data, and the replica data generation process and the block data separation process based on the demodulated data generated by the second demodulation process are repeated until all the block data of the demodulation target data frame are separated; performing a third demodulation process of combining and demodulating the block data of the demodulation target data frames obtained for each of the plurality of frame sets; 4. The wireless communication system according to claim 3.

9. the determination means calculates an average of the first propagation path power and the second propagation path power in a plurality of the composite data frames, compares the calculated average of the first propagation path power and the second propagation path power, and when it is determined that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station and the other adjacent transmitting base station arrive in approximately equal amounts, determines to use the demodulation method in the first demodulation means, and when it is determined that the mobile receiving station is located in an area where radio waves from the one adjacent transmitting base station or the other adjacent transmitting base station arrive predominantly, determines to use the demodulation method in the second demodulation means.

2. The wireless communication system according to claim 1.

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