Wireless communication system

Abstract

To provide a wireless communication system that performs tap coefficient pulling-in processing of a decision feedback adaptive equalizer at a high speed.SOLUTION: A wireless communication system performs: a first process in which a data frame DF_B is transmitted from a station B at timing delayed by an offset symbol number M of a symbol number B the same as a synchronization word SW_A in response to a data frame DF_A transmitted from a station A, and a tap coefficient is pulled in for a combined data frame DF_A+DF_B obtained by combining the data frames DF_A and DF_B; a second process of performing an equalization process based on equalizer input and the tap coefficient to obtain an approximation value of a symbol of block data contained in combined block data as equalizer output; and a third process of calculating an error between a hard decision value of the equalizer output and the equalizer output, and updating the tap coefficient to the latest value using the calculated error, the tap coefficient, and new equalizer input. The wireless communication system repeats the second process and the third process until all approximations of the symbol of the block data are output.SELECTED DRAWING: Figure 7

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] In order to suppress the effects of beat interference, a technique is known in which different mappings are used for modulating communication data between adjacent base stations, thereby constantly shifting the location where striped beats occur and suppressing beat interference (see, for example, Patent Document 1).Furthermore, techniques for compensating for fading that utilize decision feedback equalization (DFE) and maximum likelihood sequence estimation (MLSE) are known (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-166293 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-070348 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology described in Patent Document 1 requires that the communication areas of transmitting base stations using the same mapping do not overlap, which imposes restrictions on the placement of transmitting base stations. Furthermore, the MLSE described in Patent Document 2 achieves a low bit error rate, but the amount of calculation required increases depending on the number of states. On the other hand, the DFE described in Patent Document 2 requires less calculation than MLSE, but in the case of same-wave multi-station transmission, the tap coefficients of the forward filter and feedback filter are trained using a synchronization word (SW) multiplexed with transmission waves from multiple base stations. When a receiving station moves at high speed, the propagation paths between each base station and the receiving station become independent Rayleigh fading environments, making it impossible to adequately perform tap acquisition using the multiplexed synchronization word.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a wireless communication system that is capable of performing high-speed tap coefficient acquisition processing in a decision feedback adaptive equalizer. [Means for solving the problem]

[0008] 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 having a wireless transmitting device that transmits the same modulated data frame at the same frequency, and a mobile receiving station each having a wireless receiving device that receives and demodulates the data frame, wherein the plurality of wireless transmitting devices respectively transmit the data frame, each data frame comprising known header data, a plurality of block data each having the same number of symbols as the header data, and a no-data interval which is placed between the header data and the first block data and has the same number of symbols as the header data, with a time difference corresponding to the number of symbols of the header data as an offset symbol number, and the wireless receiving device comprises receiving means for receiving a combined data frame formed by combining the plurality of data frames in space and outputting a received signal of each symbol, and a decision feedback adaptive equalizer to which the received signal is input, the decision feedback adaptive equalizer performs a first process of deriving tap coefficients used for equalization processing based on received signals of the plurality of header data included in the combined data frame and a pre-stored reference signal; a second process of using received signals of combined block data constituting the combined data frame as an equalizer input, performing equalization processing based on the equalizer input and current tap coefficients, and obtaining approximation values ​​of symbols of the block data included in the combined block data as an equalizer output; and a third process of calculating an error between a hard decision value of the equalizer output and the equalizer output, and updating the tap coefficients to latest values ​​using the calculated error, the current tap coefficients, and a new equalizer input, and repeating the second process and the third process until approximation values ​​of symbols of the block data are all output from the combined data frame. [Effects of the Invention]

[0009] According to the invention recited in claim 1, when the same data frame is transmitted from a plurality of transmitting base stations, data frames each having a no-data section with the same number of symbols as the header data are transmitted with a time difference equivalent to the number of symbols of the header data, where the number of offset symbols is an offset symbol number. This allows the header data used for the tap coefficient pull-in process in the decision feedback adaptive equalizer to be received independently without overlapping with other data (in other words, without being combined), eliminating the need for a means for identifying which of the plurality of transmitting base stations the header data belongs to (for example, coding of the transmission signal from each station), and enabling high-speed pull-in of the tap coefficients. [Brief explanation of the drawings]

[0010] [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] FIG. 4 is a block diagram showing a schematic configuration of the decision feedback adaptive equalizer shown in FIG. [Figure 5] FIG. 5 is a block diagram showing the configuration of a delay device shown in FIG. [Figure 6] FIG. 10 is a block diagram showing a schematic configuration of a decision feedback adaptive equalizer when there are two base stations. [Figure 7] 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 8] 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 9] 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 10] FIG. 10 is a block diagram showing a schematic configuration of a decision feedback adaptive equalizer when there are three base stations. [Figure 11] 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 12] FIG. 1 is a schematic diagram showing a state in which beat interference occurs in a conventional wireless communication system. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] (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.

[0013] In the wireless communication system 1 according to this embodiment, when a mobile station D receives and demodulates the same data frame of the same frequency modulated and transmitted from a plurality of base stations A and B, the system performs high-speed tap coefficient acquisition processing in a decision feedback adaptive equalizer.

[0014] In order to suppress the above-mentioned beat interference, the wireless communication devices 2 of base stations A and B according to this embodiment transmit data frames each including 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 and having the same number of symbols as the synchronization word, with a time difference equivalent to the number of symbols of the synchronization word as the offset symbol number.

[0015] 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.

[0016] 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 is the same as the number of symbols N of the synchronization word SW_A.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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).

[0021] 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, in order to avoid beat interference at the time of reception, base station B transmits data frame DF_B with a time difference equivalent to the number of symbols N (32 symbols) of synchronization word SW_A, as an offset symbol number M (shown as Msym in the figure), relative to the transmission of data frame DF_A. In other words, base station B transmits data frame DF_B with a delay of the number of symbols M relative to 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.

[0022] 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).

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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).

[0027] 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 k is 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.

[0028]

number

[0029] 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.

[0030] The wireless communication device 3 includes a modulation unit 31 and a transmission unit 32 used to transmit data frames, a reception unit (reception means) 33 used to receive data frames, a decision feedback adaptive equalizer 34, and a demodulation unit 35, and further includes an interface unit 36.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 .

[0037] 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.

[0038] 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.

[0039] The decision feedback adaptive equalizer (hereinafter also referred to as equalizer or DFE) 34 is an adaptive equalizer that shapes the received signal waveform distorted by the transmission path characteristics by feeding back and weighting the signals determined by a hard decision device from the combined data frame DF_A+DF_B output from the receiving unit 33, thereby eliminating the influence of inter-symbol interference due to 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.

[0040] The demodulation unit 35 receives the block data BD_A output from the DFE 34, demodulates the block data BD_A, extracts the transmission data, and outputs the extracted transmission data to the interface unit 36.

[0041] 4 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.

[0042] 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.

[0043] 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. 5, there are M delay elements provided, each providing a delay for one symbol.

[0044] In such a DFE 34, the equalizer input at time k is NFF Received signals r k ,r k-M ,…r k-M(NFF-1) and the filter output y k is obtained by the following formula (2): 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 k When 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.

[0045]

number

[0046] The error calculation unit 343 calculates the signal d k and the filter output y k The error signal e is the difference between 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.

[0047] 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 (3).

[0048]

number

[0049] 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. 6. 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.

[0050] 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

[0051] 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.

[0052] 7 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).

[0053] 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.

[0054] 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].

[0055] [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.

[0056] [2] Section A1: The input received signal is delayed by delay devices 3411b and 3412b.

[0057] [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.

[0058] [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.

[0059] [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 an equalizer, which performs equalization processing using the tap coefficients of DFE_2 and obtains an approximation of the transmitted symbol in block data A2 as the equalizer output.

[0060] [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].

[0061] To explain the equalization process in more detail, the procedure of the equalization process in a certain block data section will be explained. Figure 8 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.

[0062] The DFE 34 performs the following processes [1] to [5] in order at time k. [1] Received signal r k 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.

[0063]

number

[0064] [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.

[0065] 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:

[0066] 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 (5), where μ is the step size and is set to a value smaller than 1. The superscript * represents a complex conjugate.

[0067] [Number 5] w k+1 = w k +μr k e k * ···(5)

[0068] 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.

[0069]

number

[0070] [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 (7).

[0071] [Number 7] w k+2 = w k+1 +μr k+1 e k+1 * ···(7)

[0072] Thereafter, the same process is repeated to obtain block data BD_A. The obtained block data BD_A is output from the DFE 34 to the demodulation unit 35.

[0073] As described above, according to this embodiment, when the same data frame is transmitted from a plurality of transmitting base stations, data frames each having a no-data section with the same number of symbols as the synchronization word are transmitted with an offset symbol number M, with a time difference corresponding to the number of symbols N of the synchronization word. Therefore, the synchronization word used in the tap coefficient pull-in process in the DFE can be received independently without overlapping with other data (in other words, without being combined), and there is no need for means for identifying which of the plurality of transmitting base stations the synchronization word belongs to (for example, coding of the transmission signal from each station), making it possible to quickly pull in the tap coefficients.

[0074] (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, 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.

[0075] 9(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 multiple, 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.

[0076] 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 is the same as the number of symbols N of the synchronization word SW_A.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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).

[0081] 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.

[0082] 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.

[0083] 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).

[0084] As in the first embodiment, base station A, base station B, and base station C are connected to a central control device (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 device 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 device. At this time, base station B, in order to avoid beat interference at the time of reception, transmits data frame DF_B with a time difference equivalent to the number of symbols N (32 symbols) of synchronization word SW_A as an offset symbol number M (indicated as Msym in the figure) relative to the transmission of data frame DF_A. Similarly, in order to avoid beat interference at the time of reception, base station C, in order to avoid beat interference at the time of reception, transmits data frame DF_C with a time difference equivalent to the total number of symbols 2N (64 symbols) of synchronization word SW_A and synchronization word SW_B as an offset symbol number 2M relative to the transmission of data frame DF_A. That is, 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.

[0085] 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 9(B).

[0086] 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. 9(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.

[0087] 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.

[0088] 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 (8).

[0089] Here, L in equation (8) 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 (8), by offsetting the transmission of data frames at base stations A, B, and C, signal loss due to beat interference can be avoided.

[0090]

number

[0091] To explain the configuration of the DFE34 more simply, 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 (9).

[0092]

number

[0093] Here, at time k, the desired symbol x is extracted from the received signal sequence. k-2MConsider 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. 10. 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.

[0094] 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".

[0095] 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 k is obtained by the following equation (10): 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 kk 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.

[0096]

number

[0097] 11 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. 10. 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 (11) to (13). In addition, d k =x k-2M The filter output obtained when the above equations are satisfied is as shown in the following equation (14). 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 (15), then the following equation (16) becomes y k =x k-2M These approximate values can be obtained by using an adaptive algorithm such as LMS or RLS.

[0098]

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[0099]

number

[0100]

number

[0101]

number

[0102]

number

[0103]

number

[0104] As explained above, according to the second embodiment, as in the first embodiment, when the same data frame is transmitted from a plurality of transmitting base stations, data frames each having a no-data section with the same number of symbols as the synchronization word are transmitted with an offset symbol number M, with a time difference corresponding to the number of symbols N of the synchronization word. Therefore, the synchronization word used in the tap coefficient pull-in process in the DFE can be received independently without overlapping with other data (in other words, without being combined), and there is no need for means for identifying which of the plurality of transmitting base stations the synchronization word belongs to (for example, coding of the transmission signal from each station), making it possible to pull-in the tap coefficients at high speed.

[0105] The above describes an embodiment of the present invention, but the specific configuration is not limited to the above embodiment, and even if there are design changes or the like within the scope of the gist of the present invention, they are included in the present invention. [Explanation of symbols]

[0106] 1. Wireless communication systems 2. Wireless communication equipment (wireless transmitter) 3. Wireless communication equipment (wireless receiving equipment) 33 Receiving unit (receiving means) 34 Decision Feedback Equalizer 341 Equalization filter section 342 Hard judger 343 Error calculation section 344 Tap Update Unit 3411 Feedforward Filter 3412 Feedback Filter 3413 Adder A,B,C base station 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 Sync Word BD_A,BD_B,BD_C block data

Claims

[Claim 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 respectively transmit the data frame, the data frame 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 and having the same number of symbols as the header data, with a time difference corresponding to the number of symbols of the header data as an offset symbol number; the wireless receiving device comprises: receiving means for receiving a combined data frame obtained by spatially combining a plurality of the data frames and outputting a received signal of each symbol; and a decision feedback adaptive equalizer to which the received signal is input; The decision feedback adaptive equalizer comprises: a first process of performing tap coefficients used in equalization processing 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 process of performing equalization processing based on the equalizer input and current tap coefficients as an equalizer output, the second process being an equalizer input for receiving a composite block data constituting the composite data frame, and obtaining an approximation value of the symbol of the block data included in the composite block data; a third process of 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 process and the third process until all approximate values of the symbols of the block data are output from the composite data frame; A wireless communication system comprising:

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