WO2004107623A1 - 無線通信システム及び無線通信方法 - Google Patents
無線通信システム及び無線通信方法 Download PDFInfo
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- WO2004107623A1 WO2004107623A1 PCT/JP2004/007898 JP2004007898W WO2004107623A1 WO 2004107623 A1 WO2004107623 A1 WO 2004107623A1 JP 2004007898 W JP2004007898 W JP 2004007898W WO 2004107623 A1 WO2004107623 A1 WO 2004107623A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/02—Channels characterised by the type of signal
- H04L5/023—Multiplexing of multicarrier modulation signals
- H04L5/026—Multiplexing of multicarrier modulation signals using code division
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7073—Synchronisation aspects
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7097—Interference-related aspects
- H04B1/711—Interference-related aspects the interference being multi-path interference
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
Definitions
- the present invention relates to a wireless communication system and a wireless communication method.
- the present invention relates to a technique for increasing uplink communication capacity in a wireless communication system that transmits uplink signals from a plurality of communication terminals to a base station using different spreading codes.
- TDMA Time Division Multiple Access
- OFDM Orthogonal Frequency Division Multiplexing
- CDMA Code Division Multiple Access
- a number of subcarriers forming an OFDM signal are transmitted to a communication terminal, each of which is defined as a so-called frequency hobbing. Must be assigned to prevent interference between communication terminals.
- a non-orthogonal code such as an m-sequence is used as a spreading code (for example, see Japanese Patent Application Laid-Open No. 11-088293).
- a code division multiplexed signal transmitted from a base station and addressed to multiple communication terminals reaches each communication terminal without causing a shift between codes, but in uplink transmission, it is transmitted from each communication terminal.
- the spread signal inevitably arrives at the base station with a time lag corresponding to the difference between the distance between each communication terminal and the base station.
- multipath caused by reflection of terrestrial objects is generated. This is because it differs depending on the terminal. In other words, in uplink transmission, even if the spreading codes are orthogonal, the effect cannot be obtained due to time lag or non-identity of multipath. It is necessary to use a spreading code such as an m-sequence that can be obtained.
- orthogonal spreading codes are used as in downlink transmission, so that a spreading code such as an m-sequence must be used.
- the spreading code of the m-sequence is not completely orthogonal to the orthogonal spreading code, so that the error rate characteristics after despreading deteriorate in proportion to the increase in the number of codes used. Therefore, there is a disadvantage that the number of communication terminals that can transmit at the same time decreases and the communication capacity decreases.
- the conventional uplink transmission using the CDMA technique has a drawback that the communication capacity is significantly reduced as compared with the downlink transmission because orthogonality of the spreading code cannot be secured. Disclosure of the invention
- An object of the present invention is to provide a radio communication system and a radio communication method that can apply an orthogonal spreading code by ensuring orthogonality of a spreading code in uplink transmission and can significantly increase uplink communication capacity. To provide.
- each communication terminal spreads transmission data using its own orthogonal spreading code and OFDM modulates the spread signal, so that even in uplink transmission, a multi-core using orthogonal codes in space is used.
- the base station receives the OFC DM signal from each communication terminal, performs OFDM demodulation on the received signal, and performs orthogonal modulation unique to each communication terminal on the OFDM demodulated signal. This is achieved by performing despreading processing using a spreading code to obtain transmission data from each communication terminal.
- FIG. 1 is a diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention.
- FIG. 2 is a block diagram illustrating a configuration of an OFDM modulator. 7898
- FIG. 3 is a diagram for explaining a guard interval in OFDM
- FIG. 4 is a diagram for explaining a guard interval in OFDM
- FIG. 5 is a block diagram showing a configuration of an OFDM demodulator
- Figure 6 is a waveform diagram of each spreading code when quadruple spreading is performed
- Figure 7 is a waveform diagram of each spreading code subjected to multipath distortion
- Figure 8 is a diagram for explaining the transmission time lag between communication terminals
- FIG. 9 is a flowchart showing a procedure for setting a guard interpolator length in the second embodiment
- Figure 10 is a diagram for explaining the transmission / reception timing adjustment by time advance
- Fig. 11 is a block diagram of communication terminals and base stations for explaining functions for realizing time advance
- FIG. 12 is a flowchart showing a procedure for setting a guard interval length when performing time advance
- Figure 13 is a diagram showing the state of fluctuation in the time and frequency directions
- FIG. 14 is a block diagram showing the configuration of the communication terminal according to the third embodiment.
- Figure 15 shows the case where the pilot signal is time-multiplexed and the case where code-multiplexing is performed
- FIG. 16 is a block diagram showing the configuration of the communication terminal according to the fourth embodiment.
- Figure 17 is a diagram used to explain the case where the pilot signal is longer than the transmission data and is spread with an orthogonal spreading code
- FIG. 18 is a block diagram showing a configuration of a communication terminal according to the fifth embodiment.
- FIG. 19 is a block diagram showing a configuration of a communication terminal according to the sixth embodiment.
- Figure 20 shows the concept of differential coding
- FIG. 21 is a diagram for explaining random access according to the seventh embodiment
- FIG. 22 is a flowchart illustrating a random access procedure according to the seventh embodiment
- FIG. 23 is a diagram illustrating a communication terminal according to the eighth embodiment. Block diagram showing the configuration; as well as
- FIG. 24 is a block diagram showing the configuration of the communication terminal according to the ninth embodiment. BEST MODE FOR CARRYING OUT THE INVENTION
- FIG. 1 shows the overall configuration of the wireless communication system of the present invention.
- the wireless communication system 100 includes a plurality of communication terminals MS # 1 to MS #N and a base station BS, and the base station BS receives and receives uplink signals transmitted from each of the communication terminals MS # 1 to MS #N. I am getting data.
- FIG. 1 shows only a part related to uplink communication.
- the communication terminals MS # 1 to MS #N have a transmission signal processing system for transmitting downlink signals to MS # 1 to MS #N, and the communication terminals MS # 1 to MS #N receive and demodulate downlink signals from the base station BS.
- the downlink signal includes a synchronization signal for each communication terminal MS # 1 to MS #N to synchronize with the base station BS, and each communication terminal MS # 1 to MS #N synchronizes with the base station BS. Then, an OFCDM signal is transmitted.
- Each of the communication terminals 1 ⁇ 3 # 1 to ⁇ [3 # spreads transmission data by the spreading units 101-1-1 to 101-1N.
- the spreading sections 101-1 to 101-N of the communication terminals MS # 1 to MS #N are spreading sections 101-1 to 1 of the other communication terminals MS # 1 to MS #N; Spreading is performed using a spreading code that is orthogonal to. That is, the spreading code used in spreading section 101-1 of communication terminal MS # 1 is orthogonal to all the spreading codes used in spreading sections 101-2 to 101-N of other communication terminals MS # 2 to MS #N.
- the spreading codes used in spreading section 101-2 of communication terminal MS # 2 are spreading sections 101-1 and 101-3-3 of other communication terminals MS # 1 MS # 3 to MS #N: L 01—all extensions used in N It is orthogonal to the scatter code.
- Each of the communication terminals MS # 1 to MS #N has an OFDM modulator l 02-1 to 102 -N, and performs OFDM modulation on the spread signal.
- OFDM modulators 102-1 to 102-N of communication terminals MS # 1 to MS # N have the same configuration.
- Each of the communication terminals MS # 1 to MS #N converts an OFCDM signal obtained by OFDM modulation into a radio signal by a radio processing unit (not shown), and transmits the radio signal via an antenna.
- the base station BS receives a signal in which all OFCDM signals from the communication terminals MS # 1 to MS #N are combined by an antenna, and converts the radio signal to a baseband signal by a radio processing unit (not shown). After the conversion, it is input to OFDM demodulation section 110.
- OFDM demodulation section 110 performs OFDM demodulation processing on the received baseband signal.
- the base station BS has a plurality of despreading sections 1 1 1-1 to 1 1 1 1 N.
- Each of the despreading units 1 1 1 1 1 1 to 1 1 1 -N performs despreading processing using the same orthogonal spreading code as the orthogonal spreading code used in each of the communication terminals MS # 1 to MS #N.
- the despreading unit 1 1 1 1 1 1 performs despreading processing using the same orthogonal spreading code as the spreading unit 101-1 of the communication terminal MS # 1
- the despreading unit 1 1 1-2 performs communication terminal MS # 1
- the despreading process is performed by using the same orthogonal spreading code as that of the spreading unit 101-2 of FIG.
- the despreading unit 1 1 1—N uses the same orthogonal spreading code as the spreading unit 101—N of the communication terminal MS # N. To perform despreading. Thereby, reception data corresponding to the transmission data transmitted from each of communication terminals MS # 1 to MS # N can be obtained from despreading sections 1111-11 to 1111N.
- the 0 ⁇ 1 modulation sections 102-1 to 102-N of each of the communication terminals MS # 1 to MS #N are configured as shown in FIG.
- the OFDM modulator 102-1 (102-2 to 102-N) performs SZP conversion processing on the spread signal obtained by the spreader 101-1 in an S // P (serial Z-parallel) processing unit 121, and performs S / P conversion.
- the signal after the P conversion processing is sent to IFFT (Inverse Fast Fourie Transform) processing section 122. I?
- the processing unit 122 performs IFFT processing on the signal subjected to the S / P conversion processing, and sends each signal after the IFFT to the PZS (parallel Z serial) processing unit 123. ?
- the / 3 processing unit 123 performs a PZS conversion process on the signal after the IFFT process, and sends the signal after the PZS conversion process to the guard addition unit 124.
- the guard adding unit 124 inserts a guard interval into the signal after the P / S conversion processing. Thereby, an OFCDM signal is formed.
- guard adding section 124 forms a guard interval by copying the waveform after the OFDM symbol to the beginning of the OFDM symbol. As a result, a signal arrival time difference having a length corresponding to the time for copying as a guard interval can be allowed.
- the discontinuous portion P does not enter the FFT section.
- the sum of the sine waves of the preceding wave A and the delayed wave B is obtained.
- Adding sine waves changes the phase and amplitude, but keeps the sine wave, so there is no signal distortion.
- a signal arrival time difference corresponding to the guard interval is allowed. Since the phase and amplitude can be easily estimated by preparing a pilot signal passing through the same line, any phase rotation or amplitude fluctuation can be compensated.
- this guard interval is used to allow multipath, but in the present invention, a guard interval is added to multipath, and signal arrival of OFCDM signals from communication terminals MS # 1 to MS #N is performed. It is used to allow for time differences.
- OFDM demodulation section 110 is configured as shown in FIG. OFDM demodulation section 110 inputs the OFC DM signal to guard removal section 131.
- Guard remover 1 31 removes the guard interval portion from the OFCDM signal, and sends the signal after the guard interval removal to the SZP processing section 132.
- the S / P processing unit 132 performs SZP conversion processing on the signal after the guardinterpal removal, and sends the signal after SZP conversion processing to the FFT (Fast Fourie Transform) processing unit 133.
- FFT Fast Fourie Transform
- the processing unit 133 obtains a signal superimposed on each subcarrier by performing FFT processing on the signal subjected to the S / P conversion processing. ?
- the three processing unit 134 performs a PZS conversion process on the signal after the FFT process. As a result, the OFDM demodulation section 110 outputs a signal to which the spread signals spread by the communication terminals MS # 1 to MS # N are added.
- the OF CDM signal obtained by being spread by each communication terminal MS # 1 to MS #N using the orthogonal spreading code unique to each station and OFDM modulated is the same at the same timing from each communication terminal MS # 1 to MS #N. Is transmitted in the frequency band.
- the OFCDM signals from the communication terminals MS # 1 to MS # N are all added and received by the base station BS.
- the guard removing section 131 of the OFDM demodulating section 110 removes the guard interval of the OF CDM signal.
- an inter-code interference portion that is, a portion where orthogonality is lost
- orthogonality of the spreading code in the effective symbol portion is ensured.
- Figure 7 shows the appearance of each code when there is multipath distortion.
- a spreading code is used for uplink transmission as in the radio communication system 100 of this embodiment, the line conditions between the communication terminals MS # 1 to MS #N and the base station BS are different from each other. Then, each of the spreading codes 1 to 4 is received with a different amplitude and phase change.
- the OFDM modulation process is performed after spreading by the spreading code
- the length of the delayed wave is longer than the length of the guard interval (GI) as shown in FIG. If it is short, the part that performs FFT processing (that is, the effective symbol part) does not need to affect other codes. Also, the orthogonality is maintained regardless of the phase of each code. As a result, it is possible to secure orthogonality of the spreading code in uplink transmission, which cannot be realized by conventional CDMA.
- the amount of interference when CDMA is simply applied to uplink transmission is calculated.
- the base station receives A signal (spreading code) on each path from a certain communication terminal receives a total of 7 interferences, 6 from the other communication terminal (spreading code) (3 codes x 2 paths) and 1 from the own code.
- the spreading factor is 4, the interference can be suppressed to 1 Z4, resulting in interference of magnitude 7 Z4.
- the interference can be halved, and as a result, interference of magnitude 7-7 can be suppressed.
- the interference with the magnitude of 7Z8 is 0.6 dB in SNR (Signal-to-Noise Ratio), and the receiving performance is significantly deteriorated.
- SNR Signal-to-Noise Ratio
- BER Bit Error Rate
- the interference amount is 5-8, but the SNR is still about 2 dB. Only when the number of spreading codes is 2, the SNR becomes 4.3 dB. The required 5 dB cannot be reached. Therefore, the number of spreading codes that can be actually used is less than half of the spreading factor.
- the use of multi-level modulation such as 16 QAM (Quadrature Amplitude Modulation) further increases the required SNR, so that the number of usable spreading codes is further reduced.
- the wireless communication system 100 of the present embodiment basically, orthogonality between the spreading codes can be ensured, so that spreading codes corresponding to the spreading factor can be used, and when QPSK modulation is performed. Can achieve more than twice the uplink communication capacity of simply using CDMA for uplink transmission, and can achieve even higher communication capacity when 16 QAM is performed.
- CDMA Code Division Multiple Access
- uplink transmission may not be able to use M-ary modulation even with one code when multipath interference is severe, but in the present embodiment, even the original spreading code is used. If they are orthogonal, no inter-code interference will occur even if transmission is performed simultaneously using the same frequency band from the communication terminals for the number of spreading codes. The original data can be restored.
- a multicarrier CDMA (or OFCDM) technology combining CDMA and OFDM modulation has already been proposed.
- the base station spreads data addressed to each communication terminal with a spreading code unique to each communication terminal to obtain a code division multiplexed signal, and superimposes this signal on one OFDM signal to at once. Is to be sent to Then, each communication terminal demodulates the received signal by OFDM, and then performs despreading processing on the code division multiplexed spread signal using a spreading code unique to the own station. 4 007898
- the OFC DM signal from each communication terminal is received by the base station via a different multipath transmission path, so that each of the signals that did not occur in the reception during the downlink transmission Inter-code interference occurs due to a shift in code reception timing.
- the inventor of the present invention has proposed that, in OFDM modulation, a guard interval is generally added, and if this guard interval is used effectively, inter-code interference (orthogonality of orthogonality) due to a shift in reception timing at the time of uplink transmission is considered. (Collapse) can be avoided. If the orthogonality can be prevented, the use of orthogonal spreading codes for uplink transmission can increase the number of communication terminals capable of simultaneous transmission, compared to using non-orthogonal spreading codes such as m-sequences. In addition, they have found that the error rate characteristics at the base station can be improved, and have reached the present invention.
- orthogonality of spread signals transmitted from a plurality of communication terminals at the same timing is ensured by effectively using guardinterval in OFDM.
- guard guard suitable for further increasing the uplink communication capacity.
- the longer the guard interval the lower the communication capacity.
- this embodiment proposes a method of setting an optimal guardinterval capable of securing orthogonality of spread codes while suppressing a decrease in communication capacity.
- FIG. 8 illustrates a transmission time shift between the communication terminals MS # 1 and MS # 2.
- Fig. 8 shows the transmission time lag between communication terminals MS # 1 and MS # 2 when there is no multipath, where T1 is the one-way transmission time between base station BS and communication terminal MS # 1, and T2 is This is a one-way transmission time between the base station BS and the communication terminal MS # 2.
- the communication terminals M S # 1 and MS # 2 synchronize with the downstream signal and transmit it at a fixed interval d, so that there is a time difference of 2 (T2-T1) in round trip.
- the guard interval only needs to be long enough to absorb the time difference 2 (T2-T1) and the maximum delay difference ⁇ max between the multipath paths.
- the length of the guard interval GIL is By setting as follows, it is possible to set an optimal guard interval that can ensure orthogonality between signals from the communication terminals MS # 1 to MS #N.
- GIL max + 2 Tmax (1 Actually, by determining the length of the guard interval by the procedure shown in Fig. 9, the frame format of the OFCDM signal transmitted by each communication terminal MS # 1 to MS #N can be changed. First, input the maximum cell radius R accommodated by the base station BS.This maximum cell radius R is a value determined by the circuit design.Next, the maximum cell radius R is determined by the speed of light 3e + 8. By dividing by [m / s], the maximum arrival time difference Tmax between each of the communication terminals MS # 1 to MS #N and the base station BS is obtained. The maximum arrival time difference Tmax is the maximum one-way propagation time between transmission and reception, and is uniquely determined by the cell radius R and the speed of light.
- the maximum arrival time difference ⁇ max is the time difference between the longest delayed wave and the path that arrives directly between the transmission and reception, and is related to the cell radius but also to buildings, mountains, rivers, and other terrestrial features. It is specified by design and radio wave propagation experiments.
- input the sampling period Tsamp determined by the system.
- the number of samples required in the guard interpal GI that is, the guard interval GI length is obtained by the following equation.
- GI length I NT ⁇ max + 2 Tmax) / Tsainp + 1 ⁇ (2)
- this embodiment proposes a method of further reducing the guard interval length by adjusting the transmission timing in each of communication terminals MS # 1 to MS #N.
- the base station receives signals from communication terminals MS # 1 and MS # 2 at almost the same timing as shown in Fig. 10.
- FIG. 10 proposes a method of further reducing the guard interval length by adjusting the transmission timing in each of communication terminals MS # 1 to MS #N.
- the communication terminal MS # 1 receives the downlink signal from the base station BS after a time T1 from the transmission, and the communication terminal MS # 2 receives the downlink signal transmitted at the same time after the time T2. .
- This method is a method established as time advance.
- Fig. 11 shows an example of the configuration of a communication terminal and a base station for realizing time-advance.
- Base station Transmission is performed according to the quasi-timing, and the communication terminal synchronizes with the signal and transmits based on the timing.
- the base station compares the received signal with the reference timing, calculates a time difference as to how soon the communication terminal should transmit, and transmits the calculation result as a time-advance signal on the transmission signal.
- the communication terminal receives the time advance signal, it adjusts the synchronization timing based on the time advance signal and transmits the signal. By repeating this, the corresponding transmission signal from each communication terminal can reach the base station almost simultaneously.
- the communication terminals MS # 1 to MS #N and the base station BS shown in FIG. 1 are provided with a time advance processing function as shown in FIG. 11, a plurality of communication terminals MS # 1 to MS # Between N and the base station BS, corresponding signals from the communication terminals MS # 1 to MS #N can reach the base station BS at substantially the same time.
- this embodiment proposes a method of setting an optimal guard interpal when time advance is performed between communication terminals MS # 1 to MS # N and base station BS.
- Figure 12 shows the method of setting the guard interval length when performing the time advance processing. First, find the maximum time difference Tadv that remains even after performing the time advance.
- the maximum time difference Tadv is a value determined by the accuracy of the time-dance as described above.
- GI length I NT ⁇ max + Tadv) ZTsamp + 1 ⁇ (3)
- the guard addition section 124 of N provides the guard interval length (GI length By adding the guard interval of (2), it is possible to add an optimal guard interval that can ensure the orthogonality of the spreading code while suppressing a decrease in communication capacity.
- the guard interval length in Equation (3) can be shorter than the guard interval length in Equation (2) because of the time advance. it can.
- the maximum delay difference between multipaths, max, and the distance between each of the communication terminals MS # 1 to MS #N and the base station BS is suppressed. Since an interval can be added, it is possible to realize a wireless communication system capable of further increasing the communication capacity in addition to the effects of the first embodiment.
- each of communication terminals MS # 1 to MS #N performs spreading only in the time direction.
- the spread signal is superimposed on a plurality of subcarriers constituting an OFDM signal
- the spread in the frequency direction is performed over different subcarriers at the same time, the spread in the time direction of the same subcarrier in the time direction, and the spread in the frequency direction.
- each of the communication terminals MS # 1 to MS #N performs only the time-direction spreading. .
- the orthogonality between the spreading code and the spreading code can be increased.
- Figure 13 shows fluctuations in the time and frequency directions.
- the square 1 Each square represents one OFDM symbol.
- the guardinterpal length In order to allow multipath, the guardinterpal length must be taken to some extent (in the present invention, it must be taken more to allow the difference in signal arrival time from each communication terminal). Inevitably, a certain length is required (at least several s).
- time fluctuation is more gradual than frequency fluctuation.
- the inventor of the present invention pays attention to this point, and arranges spread signals in a time direction in which fluctuations are gradual to form OFC DM signals, so that spread codes from communication terminals MS # 1 to MS #N can be obtained. It is thought that the base station BS is able to further secure the orthogonality of the spread code when the base station BS receives signals from each of the communication terminals MS # 1 to MS #N, since the base station BS is less susceptible to variation for each code.
- FIG. 14 shows a configuration example of each of communication terminals MS # 1 to MS #N of this embodiment.
- Communication terminal MS # 1 (MS # 2 to MS #N) is roughly divided into a time direction mapping section 201 for transmitting data and a time direction spreading section 202 for spreading transmission data mapped in the time direction in the time direction.
- an OFDM modulator 203 that arranges transmission data spread in the time direction in the time direction of each subcarrier.
- the time direction mapping unit 201 first performs a serial / parallel conversion process on the transmission data X by the serial / parallel conversion unit (SZP) 204 into the number of subcarriers.
- SZP serial / parallel conversion unit
- the symbol rate of transmission data X is X [symbol Zs]
- N 4 in Fig. 14
- the symbol rate is X / N [symbol / s].
- the transmission data X 1, X 2, X 3, and X 4 output from the SZP 204 and arranged on each subcarrier are transmitted to the time direction copy unit 205.
- the time spreading unit 202 converts the copied transmission data XI, ⁇ 2, ⁇ 3, ⁇ 4 Each is multiplied by its own unique spreading code and transmitted to IF FT section 206 of OFDM modulation section 203.
- IFFT section 206 forms a subcarrier in which the chips after spreading for transmission data X1, X2, X3, and X4 are arranged in the time axis direction.
- the chip after spreading the transmission data XI is arranged in the time axis direction of the first subcarrier
- the chip after spreading the transmission data X2 is arranged in the time axis direction of the second subcarrier
- the chip after spreading of transmission data X3 is arranged in the time axis direction of the third subcarrier
- the chip after spreading of transmission data X4 is arranged in the time axis direction of the fourth subcarrier.
- the chip rate on each subcarrier becomes XY / N [chip Zs] by copying in the time direction, and the reciprocal of this chip rate directly becomes the effective symbol length of one symbol of OFDM.
- each of the communication terminals MS # 1 to MS #N arranges the spread chip only in the time direction of the subcarrier.
- the receiving side base station BS side
- demodulation is simplified because each subcarrier can be demodulated independently.
- each of communication terminals MS # 1 to MS #N code-multiplex a data signal with a data signal and transmit the data signal in wireless communication system 100 described in the first embodiment. I do.
- the accuracy of the estimation by the receiver on the receiving side using the pilot signal is improved, so that the demodulation processing can be performed with higher accuracy, and the error rate characteristics of the demodulated data can be improved. be able to.
- the pilot signal is used to compensate for phase fluctuation and amplitude fluctuation of the received signal.
- the base station of the wireless communication system shown in FIG. 1 has a demodulation unit (not shown) after the despreading unit, and the demodulation unit propagates the despread signal based on the pilot signal. Path compensation is performed, and then error correction decoding processing is performed. others Therefore, the detection result of the pilot signal greatly affects the error rate characteristics of the received data.
- Figure 15 (a) shows the time direction signal arrangement when the pilot signal and the data signal are time-multiplexed.
- P in the figure indicates a pilot signal
- D indicates a data signal.
- pilot signals are arranged at a certain interval with respect to the data signal.
- FIG. 15 (b) shows a signal arrangement in the time direction according to the present embodiment in which a pilot signal and a data signal are code-multiplexed. That is, in the present embodiment, the pilot signal is spread with a spreading code (code 1) different from the spreading code (code 2) used for the data signal, and these are multiplexed. As a result, the pilot signal is always arranged at the same time as the data signal, so that even if the line fluctuation is fast, it is possible to follow the propagation path compensation and to correct the error of the received data. The rate characteristics can be improved.
- FIG. 16 shows the configuration of the communication terminal of this embodiment.
- the communication terminal MS #l (MS # 2 to MS #N) of this embodiment includes a time-direction mapping unit 201 that maps transmission data X in the time direction, a time-direction spreading unit 202, and an OFDM modulation unit.
- the time direction mapping unit 301 that maps the pilot data P in the time direction, the time spreading unit 302, and the multiplexing of the transmission data and the pilot data spread in the time direction It has a part 303.
- the time direction mapping unit 301 has the same configuration as the time direction mapping unit 201.
- the time direction spreading section 302 and the time direction spreading section 202 have the same configuration except that the orthogonal spreading codes (spreading code A and spreading code B) used are different.
- the chip after spreading is An OFCDM signal arranged in the time direction of the subcarrier and multiplexed with transmission data and pilot data is output.
- a pilot signal is code-multiplexed into transmission data, so that the error rate characteristic of received data is reduced even in a propagation environment where line fluctuations are severe. Can be prevented.
- one symbol of OFDM has a long symbol length and thus is susceptible to line fluctuations.
- the effects of line fluctuations are well compensated based on pilot signals code-multiplexed on the receiving side. become able to.
- the length of the orthogonal spreading code used to spread the pilot data is made equal to the length of the orthogonal spreading code used to spread the transmission data.
- the length of the orthogonal spreading code used to spread the data be an integer (2 or more) times the length of the orthogonal spreading code used to spread the transmission data.
- the code resources of the spreading code used for pilot data can be reduced, and the efficiency of using the spreading code in the system is improved. For example, if the transmission data and pilot data are both spread four times, only two communication terminals can be multiplexed because two spreading codes are used per communication terminal.
- signals for three communication terminals can be code-multiplexed.
- the orthogonal code tree one of the quadruple spreading codes is assigned to pilot P, and furthermore, the triplex spreading code in the layer below the orthogonal code tree is assigned to pilot P, and pilot P is assigned. It can be realized by spreading 12 times.
- FIG. 17 shows an example in which the transmission data D is spread four times and the pilot data P is spread 12 times, but the three communication terminals MS # 1, MS # 2, and MS # 3 Is the power to use different orthogonal spreading codes 2, 3 and 4 for transmission data D mutually.
- Use code code 1).
- the orthogonal spreading code for pilot data P is used as a 12-fold spreading code using the triple spreading code of the lower layer, and this triple spreading code is used for communication terminals MS # 1 and MS # 2. Pick a different one for each MS # 3.
- the orthogonal spreading code for the pilot P of each communication terminal MS # 1, MS # 2, and MS # 3 is the same in upper layer and different code 1-1 in lower layer in orthogonal code stream. 1-2, codes 1-3 are used.
- the codes 111, 112, and 113 are orthogonal to each other, and the codes 2, 3, and 4 for data are also orthogonal.
- the despreading of the pilot data can be maintained at the optimal position for the receiving symbol because the orthogonality is maintained regardless of the division as shown in the figure. Further, a larger spreading factor is more convenient because it can suppress interference with other cells and suppress noise, and can also reduce transmission power.
- FIG. 18 in which parts corresponding to those in FIG. 16 are assigned the same reference numerals, shows the configuration of the communication terminal of this embodiment.
- the communication terminal of this embodiment has the same configuration as the communication terminal of FIG. 16 except that the configurations of pilot data time direction mapping section 401 and time direction spreading section 402 are different.
- Multiplexing section 403 adds pilot data that has been spread 12 times and transmission data that has been spread 4 times.
- the code length of the pilot data and the code length of the transmission data are different. 2004/007898
- the number of chips per unit time is the same since the original pilot data rate is the transmission data rate (1 Z 3 in this example).
- the length of the orthogonal spreading code used for spreading the pilot signal is set to an integer (2 or more) times the length of the orthogonal spreading code used for spreading the transmission data.
- the optimum position for the received data symbol is selected.
- the result of despreading of the pilot signal can be obtained.
- each of the communication terminals MS # 1 to MS #N is provided with a differential encoding unit that performs differential encoding between symbols.
- a delay detection unit for delay-detecting the differentially encoded symbols in the base station BS.
- code multiplexing of a pilot signal certainly improves the propagation path compensation accuracy on the receiving side. Transmitting only the amount of code multiplexing of the pilot signal There is also a disadvantage that the number of spreading codes available for data is reduced. Therefore, in this embodiment, it is not necessary to send a pilot signal by performing differential encoding on transmission data. Also, the combination of differential coding and differential detection has a feature that easily follows line fluctuations, and is particularly effective for the transmission method of the present invention that transmits a ⁇ FDM symbol having a long one symbol length.
- the communication terminal MS # 1 (MS # 2 to MS # N) of this embodiment includes a serial / parallel conversion unit (SZP) 204 and a time direction copy unit 205. JP2004 / 007898
- the configuration is the same as that of the communication terminal shown in FIG. 14 except that a differential encoding processing unit 500 is provided between the communication terminal and the communication terminal of FIG.
- the differential encoding processing section 500 performs differential encoding for each of the transmission data X1, X2, X3, and X4 arranged in each subcarrier.
- BPSK Binary Phase Shift Keying
- EXOR exclusive OR
- differential encoding processing may be performed by, for example, MOD (modulo) operation.
- FIG. 20 shows the concept of differential coding.
- B indicates a block in which OFDM symbols are spread (after spreading)
- P indicates a reference block (over head) required for differential coding.
- differential coding is performed, as shown in FIG. 20, adjacent OFDM symbols are associated with each other, so that even if a line fluctuation occurs, it is possible to compensate for the line fluctuation with good tracking by delay detection. become. Since the delay detection is a known technique, its description is omitted here.
- differential coding processing is performed at each of communication terminals MS # 1 to MS #N, and differential detection processing is performed at base station BS.
- error resilience particularly resistance to frequency shift
- differential detection processing is performed at base station BS.
- the inventor of the present invention pays attention to the fact that the wireless communication system 100 described in the first embodiment is very compatible with random access, and that if random access is applied to the wireless communication system 100, the system will be improved. We thought that the configuration could be simplified. In other words, this embodiment takes advantage of the advantage of the present invention that the orthogonality of the spreading code at the base station can be ensured, and considers that a plurality of communication terminals randomly access the base station. 7898
- FIG. 21 shows an example of random access.
- orthogonal spreading code 1 is assigned to communication terminals MS # 1 and MS # 4
- orthogonal spreading code 2 is assigned to communication terminals MS # 2 and MS # 5
- communication terminals MS # 3 and MS # 6 are assigned.
- Orthogonal spreading code 3 is assigned.
- the communication terminals using different orthogonal spreading codes are accessing at the same time, so the base station converts the OFC DM signals from all communication terminals from the orthogonal spreading codes of other communication terminals.
- the demodulation can be performed well without receiving the inter-code interference.
- a collision occurs because the communication terminals MS # 1 and MS # 4 using the same orthogonal spreading code 1 are simultaneously accessing, and the transmission data of the communication terminals MS # 1 and MS # 4 are transmitted. One or both of them cannot be demodulated. Even if a collision occurs in this way, the transmission data of the communication terminals MS # 2 and MS # 3 using a spreading code different from the collision orthogonal spreading code 1 are completely affected by the collision. Can be demodulated without using This is because the orthogonality of the orthogonal spreading code is ensured.
- the wireless communication system 100 of the present invention even if a collision occurs at the time of random access, orthogonality between the spreading codes is ensured, so that other spreading codes are not affected, and The signal from the terminal can be demodulated correctly.
- FIG. 22 shows an example of a random access operation when random access is applied to the wireless communication system 100.
- Communication terminals MS # 1 to MS #N are steps 8
- step SP1 If there is a call from the base station BS in SP0, random access processing is started, and the process proceeds to step SP1.
- the communication terminals MS # 1 to MS #N wait in the step SPI until a good time slot for transmitting the uplink signal is reached, and when the time slot is good for transmitting the uplink signal, move to step SP2. Then, an OFC DM signal is transmitted using a predetermined orthogonal spreading code.
- Steps SP3 and SP4 when an ACK signal is returned from the base station BS, and an ACK signal is returned from the base station BS, that is, when a positive result is obtained in Step SP3, this is This means that the signal of the own station has been correctly demodulated without any collision by the base station BS, so the process goes to step 4 and an ACK signal is returned from the base station BS even after waiting for a predetermined time. If not, that is, if a positive result is obtained in step SP5, the process proceeds to step 6 and waits for a random time, and then returns to step SP1. That is, the communication terminals MS # 1 to MS #N wait for a random time in step SP6 and then perform retransmission. This makes it possible to avoid re-collision when colliding with another user transmitted in the same time slot with the same orthogonal spreading code.
- the present embodiment by performing random access in wireless communication system 100 of the first embodiment, it is possible to reduce the uplink communication capacity as compared with the first embodiment. Therefore, the access from the communication terminals MS # 1 to MS #N to the base station BS can be simplified, and the system configuration can be simplified.
- FIG. 23 in which parts corresponding to FIG. 14 are assigned the same reference numerals, shows the configuration of the communication terminal of this embodiment.
- the communication terminal MS #l (MS # 2 to MS #N) of this embodiment performs error correction coding on the transmission data by the error correction coding unit 611, and then performs an interleaving unit 60 After performing the interleaving process by 2, it is supplied to the time direction mapping unit 201.
- the signal subjected to the error correction code is arranged over all the subcarriers, so that it is possible to give a frequency diversity effect to the error correction coded data.
- the possibility of correcting an error increases, and the error rate characteristics can be improved.
- the signal of the own station and the signal of the other station have independent lines, not only noise but also some interference from the signal of the other station (the spreading code is orthogonal). However, the interference may slightly occur due to distortion, etc.). Therefore, a quality difference easily occurs for each subcarrier, and a frequency diversity effect is more easily obtained.
- error correction coded data is arranged over a plurality of subcarriers.
- the ratio of the desired signal to the interference signal becomes more prominent, and the quality among the subcarriers further varies.
- interleaving is performed in such an environment, so that even if the same code interferes with each other, the entire transmitted signal can be transmitted due to the quality of the subcarrier signal. Expect to be saved.
- each of communication terminals MS # 1 to MS #N performs an interleave process on transmission data after error correction coding, and then forms an OFC DM signal.
- the error correction capability can be enhanced by the frequency diversity effect, and the error rate characteristic of the received data can be further improved.
- an intra-carrier scrambling unit 701 is provided before the OFDM modulation unit 203.
- the intra-carrier scrambler unit 701 scrambles the spread signal by using a scramble code unique to its own unit.
- the intra-carrier scrambling section 701 scrambles spread signals in the same subcarrier. This makes it possible to form an OFCDM signal that is resistant to other-cell interference without breaking the orthogonality of the spreading code.
- a spread signal is subjected to scramble processing using a scramble code unique to its own cell, and thus Embodiments 1 to In addition to the effect of 8, the effect can be obtained when it becomes stronger against other cell interference.
- the orthogonal spreading code is used for the up link, the symbol timing with other cells can be easily aligned because the short spreading code can be assigned to a relatively large number of communication terminals. Becomes effective.
- One aspect of the wireless communication system is a wireless communication system having a plurality of communication terminals and a base station for receiving signals from the plurality of communication terminals, wherein each communication terminal transmits transmission data by itself.
- the base station includes: a spreading unit that spreads using a station-specific spreading code; and an OFDM modulation unit that performs OFDM modulation on the spread signal.
- the base station since the propagation path difference between each communication terminal and the base station differs for each communication terminal, the base station receives the OFC DM signal from each communication terminal at a different timing. Since a guard interval is added to the power OFC DM signal by OFDM modulation, the guard interval absorbs the reception timing deviation of the OFC DM signal, and the base station secures orthogonality of the spreading code. Furthermore, by using OFDM, distortion does not occur in each subcarrier as long as the maximum delay time difference is absorbed by the guard interval, even if the way of multipath generation differs depending on the communication terminal. Even when multipath exists, orthogonality of the spreading code is maintained. As a result, the transmission data is correctly restored by the despreading process of the base station.
- the OFDM modulating means of each communication terminal uses a maximum signal arrival time difference between each communication terminal and a base station and a maximum multipath maximum delay difference.
- the configuration to select the guardinter pal length is adopted.
- One aspect of the wireless communication system according to the present invention performs time-advance processing, and the OFDM modulating means of each communication terminal retains a signal from each communication terminal to the base station even after performing time-advance processing.
- a configuration is adopted in which the guard interval length is selected based on the arrival time difference and the multipath maximum delay difference.
- the signal arrival time difference from each communication terminal to the base station is reduced by the time-advance processing, so that the guard interval length can be shortened by that amount and the substantial communication capacity can be increased. become able to.
- the guard interval length was selected based on the signal arrival time difference remaining even after time advance and the maximum multipath delay difference, the orthogonality of the spreading code was reduced when time advance processing was performed. An optimal guard interval that can be secured can be added.
- One aspect of the wireless communication system of the present invention employs a configuration in which each communication terminal arranges spread chips in a time direction of a subcarrier.
- the spread chips are arranged in the time direction where the line fluctuation is smaller than in the frequency direction, so that it is possible to further suppress the collapse of orthogonality between spread codes.
- each communication terminal includes a first spreading unit that spreads transmission data using an orthogonal spreading code, and an orthogonal orthogonal orthogonal to the orthogonal spreading code for a pilot signal.
- the base station since the pilot signal is transmitted by code-multiplexing the transmission data, the base station performs channel compensation on the transmission data based on the pilot signal subjected to the same channel fluctuation as the transmission data. As a result, it becomes possible to improve the error rate characteristics of received data in a propagation environment in which line fluctuations are severe. Especially OFD PT / JP2004 / 007898
- the error rate characteristics can be significantly improved in a propagation environment where the line fluctuation is severe compared to the case where a pilot signal is inserted every other symbol. it can.
- the second spreading means uses a spreading code whose code length is an integer (two or more) times that of the spreading code used in the first spreading means. Take.
- each communication terminal includes differential encoding processing means for performing differential encoding processing between symbols
- the base station includes a differentially encoded symbol.
- a delay detection means for delay detection.
- One aspect of the wireless communication system of the present invention employs a configuration in which each communication terminal performs random access to a base station.
- each communication terminal randomly transmits the OFC DM signal (random access) without determining the transmission order of each communication terminal by the base station.
- Access can be simplified and system design can be simplified.
- the power that a signal using the same spreading code may collide at the base station is orthogonal to the spreading code at the time of receiving the base station in the present invention. Therefore, transmission data between communication terminals using the same spreading code may not be able to be restored, but transmission data from communication terminals using other spreading codes does not cause inter-code interference. 2004/007898
- each communication terminal includes error correction coding means for performing error correction coding processing on transmission data, and interleaving means for interleaving data after error correction coding. Then, the interleaved data is spread and the spread chips are arranged in the time direction of the subcarrier.
- the data after the error correction coding is interleaved and then spread in the time direction.
- the error correction coding data is arranged over a plurality of subcarriers, and the error correction coding is performed. Frequency diversity effect on the coded data. As a result, even if there is a difference in quality between subcarriers, it is more likely that an error can be corrected, and the error rate characteristics can be improved.
- Each communication terminal includes scramble means for scrambling transmission data or a spread signal using a cell-specific scrambling code.
- One aspect of the communication terminal of the present invention employs a configuration including spreading means for spreading transmission data using an orthogonal spreading code unique to the own station, and OFDM modulation means for OFDM modulating the spread signal.
- One aspect of the radio base station according to the present invention is an OFDM demodulation unit that performs OFDM demodulation on a received signal, and performs despreading processing on the signal after OFDM demodulation using an orthogonal spreading code unique to each communication terminal
- a configuration having despreading means for obtaining transmission data from each communication terminal is adopted.
- each communication terminal transmits transmission data to its own station.
- An OFCDM signal is formed by spreading the spread signal using an orthogonal spreading code, and the spread signal is subjected to OFDM modulation.
- the OFCDM signal is transmitted, and the base station transmits the OFCDM signal from each communication terminal.
- Receives the DM signal performs OFDM demodulation on the received signal, and performs inverse spreading processing using the orthogonal spreading code unique to each communication terminal on the signal after OFDM demodulation, thereby transmitting the signal from each communication terminal. Get data.
- the present invention is not limited to the above-described embodiment, but can be implemented with various modifications.
- each communication terminal spreads transmission data using its own unique orthogonal spreading code, and forms an OFCDM signal by OFDM modulating the spread signal.
- the base station receives the OFC DM signal from each communication terminal, performs OFDM demodulation on the received signal, and performs despreading processing on the signal after OFDM demodulation using an orthogonal spreading code specific to each communication terminal.
- transmission data from each communication terminal is obtained so that orthogonality can be ensured in uplink transmission even when an orthogonal spreading code is applied.
- a wireless communication system and a wireless communication method that can significantly increase the uplink communication capacity can be realized.
- the present specification is based on Japanese Patent Application No. 2003-157103, filed on June 2, 2003. All its contents are included here. Industrial applicability
- the present invention relates to a wireless communication system and a wireless communication method, and is suitably applied to, for example, a mobile communication system ⁇ ⁇ wireless LAN system.
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US10/558,678 US20070053280A1 (en) | 2003-06-02 | 2004-06-01 | Wireless communication system and wireless communication method |
EP20040735665 EP1638229A1 (en) | 2003-06-02 | 2004-06-01 | Radio communication system and radio communication method |
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JP2003157103A JP2004363721A (ja) | 2003-06-02 | 2003-06-02 | 無線通信システム及び無線通信方法 |
JP2003-157103 | 2003-06-02 |
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CN (1) | CN1795632A (ja) |
WO (1) | WO2004107623A1 (ja) |
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2004
- 2004-06-01 KR KR20057023147A patent/KR20060022674A/ko not_active Application Discontinuation
- 2004-06-01 EP EP20040735665 patent/EP1638229A1/en not_active Withdrawn
- 2004-06-01 US US10/558,678 patent/US20070053280A1/en not_active Abandoned
- 2004-06-01 WO PCT/JP2004/007898 patent/WO2004107623A1/ja not_active Application Discontinuation
- 2004-06-01 CN CNA2004800142651A patent/CN1795632A/zh active Pending
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CN101433038A (zh) * | 2006-05-01 | 2009-05-13 | 卢森特技术有限公司 | 上行链路参考信号的分配 |
WO2007137489A1 (fr) * | 2006-05-15 | 2007-12-06 | Huawei Technologies Co., Ltd. | Procédé de réception et d'émission de signaux dans le système de multiplexage par répartition orthogonale de la fréquence et appareil correspondant |
Also Published As
Publication number | Publication date |
---|---|
EP1638229A1 (en) | 2006-03-22 |
CN1795632A (zh) | 2006-06-28 |
JP2004363721A (ja) | 2004-12-24 |
US20070053280A1 (en) | 2007-03-08 |
KR20060022674A (ko) | 2006-03-10 |
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