Radio communications system

Abstract

To provide a radio communications system capable of determining whether a mobile receiving station is located in an area where radio waves from a plurality of transmitting base stations arrive substantially equally or in an area where radio waves from a single transmitting base station arrive dominantly.SOLUTION: In a composite data frame DF_A+DF_B, propagation path power between a base station A and a mobile station D is calculated as first propagation path power on the basis of a synchronization word SW_A of a data frame DF_A transmitted from the adjacent one base station A, and propagation path power between a base station B and the mobile station D is calculated as second propagation path power on the basis of a synchronization word SW_B of a data frame DF_B transmitted from the other adjacent base station B. The first propagation path power and the second propagation path power are compared, and it is determined whether the mobile station D is located in an area where radio waves from the base station A and the base station B arrive substantially equally or in an area where radio waves from the base station A or the base station B arrive dominantly.SELECTED DRAWING: Figure 4

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 12 (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. 12(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. 12(A) and 12(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 status of such areas, they can demodulate while switching to an appropriate demodulation process, and can prevent degradation of the bit error rate (BER) characteristics. However, the status of 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 approximately equally, or in an area where radio waves from a single transmitting base station arrive predominantly. [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 transmit the data frame each equipped with a 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 for receiving a combined data frame in which the plurality of data frames are combined in space, and receiving means for receiving the data frame transmitted from one of the adjacent transmitting base stations from the combined data frame. and area 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 a data frame transmitted from the other adjacent transmitting base station among the composite data frame, 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 to determine whether 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, or whether 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 described in claim 2 is characterized in that, in the wireless communication system described in claim 1, the area determination means calculates the average first propagation path power and the average second propagation path power in a plurality of the composite data frames, and compares the calculated average first propagation path power and the average second propagation path power to determine whether 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 proportions, or whether 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]

[0011] According to the invention of 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 part of the header data of the data frames from two adjacent transmitting base stations does not overlap with other symbols, and it becomes 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 in what area the mobile receiving station is located. Therefore, it is possible to determine whether the mobile receiving station is located in an area where radio waves from multiple transmitting base stations arrive at approximately the same frequency, It is possible to properly determine whether the mobile station is located in an area where radio waves from a single transmitting base station are dominant.

[0012] According to the invention described in claim 2, 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 in an area where radio waves from a single transmitting base station arrive predominantly. [Brief explanation of the drawings]

[0013] [Figure 1] This is a diagram showing the schematic configuration of a wireless communication system according to Embodiment 1 of the present invention. [Figure 2] (A) shows the configuration of a data frame transmitted from a base station, and (B) is a diagram showing a combined data frame received by a mobile station. [Figure 3] This is a functional block diagram showing the schematic configuration of the wireless communication device of the mobile station shown in FIG. 1. [Figure 4] This is a flowchart showing the procedure for area determination in Embodiment 1. [Figure 5] This is a diagram showing the area types in the area determination of FIG. 4. [Figure 6] (A) shows the configuration of a data frame transmitted from three base stations in Embodiment 2, and (B) is a diagram showing a combined data frame received by a mobile station. [Figure 7] This is a flowchart showing the procedure for area determination in Embodiment 2. [Figure 8] This is a diagram showing the area types in the area determination of FIG. 7. [Figure 9] This is a flowchart showing the procedure for area determination in Embodiment 3. [Figure 10] This is a diagram showing the configurations of a data frame and a combined data frame in which the number of offset symbols M and the number of symbols N of block data are set such that M≠N. [Figure 11] This is a diagram showing the configurations of a data frame and a combined data frame in which the number of offset symbols in the synchronization word section is set to M (M = N), and the number of offset symbols in the data section is set to M (M < N). [Figure 12] This is a schematic diagram showing the occurrence state of beat interference in a conventional wireless communication system.

Embodiments for Carrying Out the Invention

[0014] 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.

[0015] (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.

[0016] 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, it is possible to determine whether the mobile station D is located in an area where radio waves from base station A and base station B arrive in approximately equal proportions, or in an area where radio waves from base station A or base station B arrive predominantly.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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).

[0024] 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 that time, base station B adds a predetermined offset number of symbols M (Msy in the figure) to the transmission of data frame DF_A in order to avoid beat interference at the time of reception. In this embodiment, the base station B transmits the data frame DF_B with a time difference corresponding to the number of symbols N (32 symbols) of the synchronization word SW_A as the number of offset symbols M. In other words, the base station B delays the transmission of the data frame DF_B by the number of symbols M relative to the data frame DF_A. By delaying the transmission of the data frame DF_B relative to the data frame DF_A, when the radio equipment 3 of the mobile station D simultaneously receives the data frames DF_A and DF_B, it can use the no-data intervals ND_A and ND_B to independently receive the synchronization word SW_A, the synchronization word SW_B, and A1 of the block data BD_A at the beginning of the data frame DF_A without overlapping with (being combined with) other data.

[0025] 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).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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).

[0030] 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.

[0031]

number

[0032] 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.

[0033] 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, a demodulation unit 34, and an area determination unit (area determination means) 35 used to receive data frames, and further includes an interface unit 36.

[0034] The interface unit 36 ​​mainly includes a data circuit-terminating device 361 (including equipment called data communication equipment and data circuit equipment). The interface unit 36 ​​receives input of transmission data to be communicated, and outputs the transmission data to the modulation unit 31 via the data circuit-terminating device 361.

[0035] The modulation unit 31 receives transmission data output from the interface unit 36, 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.

[0036] 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.

[0037] 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 37, 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.

[0038] 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.

[0039] 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 37 .

[0040] 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.

[0041] 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.

[0042] The demodulation unit 34 receives the combined data frame DF_A+DF_B output from the receiving unit 33, demodulates the combined data frame DF_A+DF_B using a plurality of demodulation methods to extract the transmission data, and outputs the extracted transmission data to the area determination unit 35. In this embodiment, demodulation processing is performed using a conventional system suitable for transmission from a single base station (for example, a method of directly performing primary demodulation, a digital simplex radio method), and demodulation processing for same-wave multi-station transmission (for example, processing using an adaptive equalizer, a replica cancellation method).

[0043] The area determination unit 35 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, selects transmission data demodulated by an appropriate demodulation method from the transmission data extracted from the demodulation unit 34 and outputs it to the interface unit 36.

[0044] The area determination unit 35 may be provided before the demodulation unit 34. In this case, the area determination unit 35 determines the area in which the mobile station D is located based on the combined data frame DF_A+DF_B output from the reception unit 33. Based on the result of the determination, the demodulation unit 34 demodulates the combined data frame DF_A+DF_B output from the reception unit 33 using an appropriate demodulation method to extract the transmission data, and outputs the extracted transmission data to the interface unit 36.

[0045] Next, the processing executed by the area determination unit 35 will be described with reference to the flowchart shown in FIG. 4 and the diagram showing area types in FIG.

[0046] The area determination unit 35 executes a first propagation path power calculation process S1a, a second propagation path power calculation process S2a, a propagation path power comparison process S3a, and an area determination process S4a.

[0047] 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. 5.

[0048] 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.

[0049] In the first propagation path power calculation process S1a, the received synchronization word SW_A is used to calculate the first propagation path power P A,K Calculate.

[0050] In the second propagation path power calculation process S2a, the received synchronization word SW_B is used to calculate the second propagation path power P B,K Calculate.

[0051] In the propagation path power comparison process S3a, the first propagation path power P A,Kand the second propagation path power P B,K and the power ratio R AB,K Calculate.

[0052] [Number 2] R AB,K = P A,K / P B,K ···(2)

[0053] In the area determination process S4a, the power ratio R AB,K Based on the value of R, the area in which the mobile station D is located is determined. AB,K When the signal strength is greater than 0 dB, as shown in FIG. 5(1), the mobile station D is in area E where the radio waves from base station A are dominant. A It is determined that the point is located at R AB,K When the signal strength is approximately 0 dB, as shown in FIG. 5(2), the mobile station D is in area E where the radio waves from base station A and base station B arrive almost equally. AB It is determined that the point is located at R AB,K When is smaller than 0 dB, as shown in FIG. 5(3), the mobile station D is in the area E where the radio waves from the base station B are dominant. B It is determined to be located at

[0054] In the area determination process S4a, the mobile station D is in area E. A or Area E B If it is determined that the area is located in the area where the area is located, demodulation processing by a conventional system (for example, a method of directly performing primary demodulation, a digital simplex radio method) that is suitable for transmission from a single base station becomes appropriate. Therefore, the area determination unit 35 selects transmission data demodulated by the conventional system from the transmission data extracted from the demodulation unit 34, and outputs the selected transmission data to the interface unit 36 ​​(if the area determination unit 35 is located before the demodulation unit 34, the demodulation unit 34 performs demodulation processing by the conventional system to extract the transmission data, and outputs the extracted transmission data to the interface unit 36).

[0055] On the other hand, in the area determination process S4a, mobile station D is in area E ABIf it is determined that the area is located in the area, demodulation processing for same-wave multi-station transmission (for example, processing using an adaptive equalizer or replica cancellation method) becomes appropriate. Therefore, the area determination unit 35 selects transmission data demodulated by demodulation processing for same-wave multi-station transmission from the transmission data extracted from the demodulation unit 34, and outputs the selected transmission data to the interface unit 36 ​​(if the area determination unit 35 is located before the demodulation unit 34, the demodulation processing for same-wave multi-station transmission is performed in the demodulation unit 34 to extract the transmission data, and the extracted transmission data is output to the interface unit 36).

[0056] As described above, according to this 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,K In 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 It is possible to properly determine whether the object is located at the position indicated by the arrow.

[0057] (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 the second embodiment, an area determination will be described for a case where the same data frame is transmitted from three transmitting base stations, base station A, base station B, and base station C. Note that detailed description of the same configuration as in the first embodiment will be omitted.

[0058] 6(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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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).

[0064] The data frame DF_C transmitted from base station C consists of, in order from the left end, a synchronization word SW_C, no-data sections ND_C1 and ND_C2, and a plurality of, for example, seven block data. 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.

[0065] 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.

[0066] 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).

[0067] 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.

[0068] 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 6(B).

[0069] 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. 6(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 located at the position of no-data interval ND_A1, synchronization word SW_C is located at the positions of no-data intervals ND_A2 and ND_B1, and block data BD_A1 is located at the positions of no-data intervals ND_B2 and ND_C1.

[0070] In addition, among the plurality of block data BD_A's A1 to A7, block data BD_B's B1 to B7, and block data BD_C's C1 to C7, block data BD_C's C1 to C7 are the block data that are transmitted at the same time. The data 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 are generated.

[0071] 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 (3).

[0072] Here, L in equation (3) 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 (3), offset transmission of data frames at base stations A, B, and C can avoid signal loss due to beat interference.

[0073]

number

[0074] Next, the processing executed by the area determination unit 35 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. 7 and the diagram showing area types in FIG. 8.

[0075] The area determination unit 35 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, and an area determination process S5b.

[0076] As shown in Fig. 6, the combined data frame DF_A+DF_B+DF_C is formed by transmitting data frame DF_B offset by the number of symbols M from data frame DF_A, and transmitting data frame DF_C offset by the number of symbols 2M from data frame DF_A, so that synchronization words SW_A, SW_B, and SW_C and block data BD_A, block data BD_B, and block data BD_C are combined in transmission order. Note that, as shown in Fig. 8, 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.

[0077] Here, base station B delays transmission of data frame DF_B by a predetermined offset number M of symbols with respect to data frame DF_A, so that 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). Also, since no-data intervals ND_A1 and ND_A2 are provided in data frame DF_A, radio equipment 3 of mobile station D can simultaneously receive 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. When the mobile station D simultaneously receives a data frame DF_A from base station B, a data frame DF_B from base station C, 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 (combining) with other data. In this way, the independently received synchronization words SW_A, SW_B, and SW_C are used to calculate the propagation path power between each base station and the mobile station D.

[0078] In the first propagation path power calculation process S1b, the received synchronization word SW_A is used to calculate the first propagation path power P A,K Calculate.

[0079] In the second propagation path power calculation process S2b, the received synchronization word SW_B is used to calculate the second propagation path power P B,K Calculate.

[0080] In the third propagation path power calculation process S3b, the received synchronization word SW_C is used to calculate the third propagation path power P C,K Calculate.

[0081] In the propagation path power comparison process S4b, two of the first to third propagation path powers are compared. 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.

[0082] [Number 4] R AB,K = P A,K / P B,K ···(4)

[0083] [Number 5] R BC,K = P B,K / P C,K ···(5)

[0084] [Number 6] R AC,K = P A,K / P C,K ···(6)

[0085] In the area determination process S4b, the power ratio R AB,K , R BC,K and R AC,K Based on the value of R, the area in which the mobile station D is located is determined. AB,K is greater than 0 dB, or R AC,K When the reception frequency is greater than 0 dB, as shown in FIG. 8(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 signal strength is about 0 dB, as shown in FIG. 8(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 that the point is located at R AB,K is less than 0 dB, or R BC,K When the signal strength is greater than 0 dB, as shown in FIG. 8(3), the mobile station D is in an area E where the radio waves from the base station B are dominant. B It is determined that the point is located at R BC,K When the signal strength is about 0 dB, as shown in FIG. 8(4), the mobile station D is in an area E where the radio waves from base station B and base station C arrive almost equally. BC It is determined that the point is located at R BC,K is less than 0 dB, or R AC,K When the signal strength is smaller than 0 dB, as shown in FIG. 8(5), the mobile station D is in an area E where the radio waves from the base station C are dominant. C It is determined that the point is located at R AC,K When the signal strength is about 0 dB, as shown in FIG. 8(6), the mobile station D is in an area E where the radio waves from base station A and base station C arrive almost equally. AC It is determined to be located at

[0086] In the area determination process S4b, the mobile station D is in area E. A , Area E B or Area E C If it is determined that the signal is located in the vicinity of the station, demodulation processing using a conventional system suitable for transmission from a single base station (for example, a method of directly performing primary demodulation, a digital simple radio system) is appropriate. The area determination unit 35 selects transmission data demodulated by the conventional system from the transmission data extracted from the demodulation unit 34, and outputs the selected transmission data to the interface unit 36 ​​(if the area determination unit 35 is located before the demodulation unit 34, the demodulation unit 34 performs demodulation processing using the conventional system to extract the transmission data, and outputs the extracted transmission data to the interface unit 36).

[0087] On the other hand, in the area determination process S4b, mobile station D is in area E AB , Area E BC or Area E AC If it is determined that the area is located in the area, demodulation processing for same-wave multi-station transmission (for example, processing using an adaptive equalizer or replica cancellation method) becomes appropriate. Therefore, the area determination unit 35 selects transmission data demodulated by demodulation processing for same-wave multi-station transmission from the transmission data extracted from the demodulation unit 34, and outputs the selected transmission data to the interface unit 36 ​​(if the area determination unit 35 is located before the demodulation unit 34, the demodulation processing for same-wave multi-station transmission is performed in the demodulation unit 34 to extract the transmission data, and the extracted transmission data is output to the interface unit 36).

[0088] As explained above, according to the second 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,K This 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,Kand 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 It is possible to properly determine whether the object is located at the position indicated by the arrow.

[0089] (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 area determination unit 35 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 the third embodiment, a case will be described in which the area determination unit 35 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 area determination. Note that detailed description of the same configuration as in the first embodiment will be omitted.

[0090] The processing executed by the area determination unit 35 in this embodiment will be described with reference to the flowchart shown in Fig. 9. The area determination unit 35 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, and an area determination process S5c. The combined data frame DF_A+DF_B used in the propagation path power calculation is the same as that in the first embodiment.

[0091] In the first propagation path power calculation process S1c, the first propagation path power P between the base station A and the mobile station D is calculated using the received synchronization word SW_A. A,K Calculate.

[0092] In the second propagation path power calculation process S2c, the received synchronization word SW_B is used to calculate the second propagation path power P B,K Calculate.

[0093] In the average value calculation process S3c, the first propagation path power P calculated for the most recent multiple combined data frames DF_A+DF_B is 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 P B,ave,K Calculate.

[0094] In the propagation path power comparison process S4c, 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.

[0095] [Number 7] R AB,K = P A,ave,K / P B,ave,K ···(7)

[0096] In the area determination process S5c, the power ratio R AB,K Based on the value of , the area in which the mobile station D is located is determined. The specific processing method is the same as in the first embodiment, so a detailed description will be omitted.

[0097] The above processing executed by the area determination unit 35 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.

[0098] As described above, according to the third embodiment, the average first propagation path power P in a plurality of combined data frames DF_A + DF_B A,ave,K and the average second propagation path power P B,ave,K are compared to determine in which area the mobile station D is located. Thus, it is possible to more appropriately determine whether the mobile station D is located in the area E AB where radio waves from the base stations A and B arrive substantially equally, or in the area E A or E B where radio waves from the base station A or the base station B predominantly arrive.

[0099] The embodiments of this invention have been described above. However, the specific configuration is not limited to the above embodiments, and design changes and the like within the scope not departing from the gist of this invention are also included in this invention.

[0100] For example, in the above embodiment, when offset-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 in the data block (M = N). However, M≠N may also be used. For example, as shown in FIG. 10, when M < N, in the combined data frame DF_A + DF_B, an interval SW_A + SW_B where the synchronization words SW_A and SW_B of each base station A and B overlap occurs. In this case, the overlapping interval can be truncated, and the propagation path power can be calculated using the intervals SW_A and SW_B received independently. Thus, by devising the processing, M≠N can be achieved. In particular, by setting M < N, the length of one frame from the start of the data frame DF_A to the end of the data frame DF_B can be shortened, and the data transmission efficiency can be improved.

[0101] Also, when shortening the data frame length after receiving the synchronization words SW_A and SW_B individually, although the same frame transmission is not used between base stations, as shown in FIG. 11, 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 Embodiment 2.

Explanation of Signs

[0102] 1 Wireless communication system 2 Wireless communication device (wireless transmission device) 3 Wireless communication device (wireless reception device) 33 Receiver (reception means) 34 Demodulation section 35 Area determination section (area determination 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 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; an area 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 to determine whether 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, or whether it 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; A wireless communication system comprising:

2. the area determination means calculates average first propagation path power and second propagation path power in a plurality of the composite data frames, and compares the calculated average first propagation path power with the calculated average second propagation path power to determine whether 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, or whether 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.

2. The wireless communication system according to claim 1.

Images