JP2007049617A - Communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology by which a sub carrier quality can be estimated without adding a new symbol for estimating the same. <P>SOLUTION: A time-varying waveform of a preamble received is subjected to FFT to be stored in a reception memory as a received signal. A replica coming from a base station other than a station whose transmission channel is searched is subtracted from the received signal to obtain a signal Rk. Subsequently, a complex conjugate of a code Ck of the corresponding base station and the signal Rk are multiplied together to determine a frequency response of a transmission channel from BS-k. A signal present in a sample in a domain other than a time domain is judged as a noise to be eliminated where an impulse response obtained by converting the frequency response into a time-varying waveform is concentrated. A reapplication of the FFT allows the frequency response of the transmission channel to be obtained. Based on the output, the transmission channel from a transmission side to a reception side in a wireless communication can be estimated. At the same time, a sub channel quality estimating unit estimates the corresponding sub channel quality, based on a difference obtained by doing a subtraction between an output from the replica memory and an output from the reception memory. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for performing wireless communication by a multicarrier transmission system typified by OFDM (Orthogonal Frequency Division Multiplexing), and more particularly to a reception technique that considers not only a desired wave but also an interference wave.

  In recent years, an increasing number of users are demanding further speedup of wireless communication systems. As one of the wireless communication systems that can realize high speed and large capacity, a multicarrier transmission system represented by OFDM attracts attention.

  The OFDM system is a system in which tens to thousands of carriers are arranged at a minimum frequency interval where theoretically no interference occurs and information signals are transmitted in parallel by frequency division multiplexing. This OFDM scheme has the advantage that if the number of subcarriers used is increased, the symbol time becomes longer than that of a single carrier scheme of the same transmission rate, so that it is less susceptible to multipath interference.

  As a system in which this OFDM technology is applied to a one-cell repetitive cellular system, there is a DPC-OF / TDMA (Dynamic Parameter Controlled Orthogonal Frequency and Time Division Multiple Access) system disclosed in Non-Patent Document 1. This system uses OFDM as a transmission method and performs communication using the same frequency in all cells of the cellular system. A frame configuration example of the DPC-OF / TDMA system is shown in FIG. As shown in FIG. 14, the access method of the DPC-OF / TDMA system is a method in which several blocks are formed in the frequency direction and the time direction, and one user is multiplexed as a basic access unit (one block is a slot). Called). In FIG. 14, there are 12 divisions in the frequency direction and 9 divisions in the time direction. Of the unit time channels divided in the time direction, the time channel at the head of the frame is used for transmission of control information, and the subsequent eight time channels are used for data transmission.

  When the same frequency is used in all cells as in this DPC-OF / TDMA system, the reception characteristics may be significantly degraded due to the influence of interference waves coming from neighboring cells. By using techniques such as adaptive slot allocation and adaptive modulation that selects the data symbol modulation method and coding rate according to the channel conditions, it is possible to maintain good reception characteristics and realize 1-cell repetition. can do. However, when the above-described techniques (dynamic slot allocation, adaptive modulation) are used in the downlink, not only the power of the desired signal but also the power of the interference signal arriving from the base station of the adjacent cell (or desired signal power versus interference signal). It is necessary for the receiving (terminal) side to grasp a power ratio DUR (Desired signal to Undesired signal power Ratio), and Non-Patent Document 1 discloses a technique using a DUR estimation symbol.

  FIG. 15 is a diagram illustrating a slot configuration example in Non-Patent Document 1. In FIG. 15, reference numeral 1000 is a propagation path estimation symbol, reference numeral 1001 is a DUR estimation symbol, reference numeral 1002 is a modulation scheme notification symbol for notifying the receiving side of the modulation scheme when adaptive modulation is performed, and reference symbol 1003 is a data symbol. is there. As shown in FIG. 15, in the technique shown in Non-Patent Document 1, a DUR estimation method using a DUR symbol provided with a DUR estimation symbol after a propagation path estimation symbol and using a different code for each cell is used. It is shown.

  The transmitter configuration on the base station side in Non-Patent Document 1 is shown in FIG. 16, reference numeral 1100 is a multiplex part, reference numerals 1101-a to l are error correction code parts, reference numerals 1102-a to l are serial / parallel conversion parts (S / P conversion parts), reference numeral 1103 is a mapping part, reference numeral 1104 Is a symbol estimation unit for channel estimation, reference numeral 1105 is a symbol generation unit for DUR estimation, reference numeral 1106 is a preamble insertion unit, reference numeral 1107 is an IFFT unit, reference numeral 1108 is a parallel / serial conversion unit (P / S conversion unit), reference numeral 1109 Is a guard interval insertion unit (GI insertion unit), 1110 is a digital / analog conversion unit (D / A conversion unit), 1111 is a wireless transmission unit, and 1112 is an antenna unit. However, in FIG. 16, the number of subcarriers per slot is 64, and the number of FFT points is 1024.

  The multiplex unit 1100 in FIG. 16 receives the information data of each slot and the modulation scheme information for each slot (information for notifying the receiving side of the modulation scheme used when performing adaptive modulation), and is prepared for each slot. Sent to the error correction code units 1101-a to l. Information encoded in error correction coding sections 1101-a to l is modulated in mapping section 1103 via S / P conversion sections 1102-a to l. Then, in preamble insertion section 1106, a known propagation path estimation symbol generated by propagation path estimation symbol generation section 1104 and a DUR estimation symbol generated by DUR estimation symbol generation section 1105 using a base station specific code Are time-multiplexed to form slots as shown in FIG. The signal formed in this way is converted into a time-domain signal for each symbol in IFFT section 1107, and after passing through P / S conversion section 1108, a guard interval is added in GI insertion section 1109. Then, the signal is converted into an analog signal by the D / A converter 1110, frequency-converted to a frequency that can be wirelessly transmitted by the wireless transmission unit 1111, and then transmitted from the antenna unit 1112.

  FIG. 17 is a diagram illustrating a configuration example of a receiver on the terminal side in Non-Patent Document 1. In FIG. 17, reference numeral 1200 denotes an antenna unit, reference numeral 1201 denotes a radio reception unit, reference numeral 1202 denotes an analog / digital conversion unit (A / D conversion unit), reference numeral 1203 denotes a synchronization unit, reference numeral 1204 denotes a GI removal unit, and reference numeral 1205 denotes an S / S. P conversion section, reference numeral 1206 is an FFT section, reference numeral 1207 is a preamble extraction section, reference numeral 1208 is a propagation path estimation section, reference numeral 1209 is a code generation section, reference numeral 1210 is a correlation calculation section, reference numeral 1211 is a DUR calculation section, and reference numeral 1212 is propagation. A path compensation / demapping unit, reference numerals 1213-a to l are P / S conversion units, reference numerals 1214-a to l are error correction decoding units, and reference numeral 1215 is a demultiplexing unit.

  A signal transmitted from the base station of each cell is first received by the antenna unit 1200 of FIG. A signal received by the antenna unit 1200 is frequency-converted to a frequency that can be A / D converted by the wireless reception unit 1201, and converted to a digital signal by the A / D conversion unit 1202. The signal converted into the digital signal by the A / D converter 1202 is OFDM symbol-synchronized by the synchronizer 1203, and the guard interval is removed by the GI remover 1204. Thereafter, the signal is separated into signals for each subcarrier in the FFT unit 1206 via the S / P conversion unit 1205. The preamble extraction unit 1207 separates the propagation path estimation signal, the DUR estimation signal, and the information signal, the propagation path estimation signal to the propagation path estimation unit 1208, the DUR estimation signal to the correlation operation unit 1210, and the information signal to propagate. It is sent to the road compensation / demapping unit 1212, respectively. The propagation path estimation unit 1208 performs propagation path estimation using a known propagation path estimation symbol. Correlation calculation section 1210 performs correlation calculation between the received DUR estimation signal and the base station-specific code used in the desired base station and the interference base station.

  Here, the code used in the desired base station and the interference base station is generated in the code generation unit 1209. As a result of the calculation in the correlation calculation unit 1210, the desired signal power and the interference signal power of each frequency channel are obtained, and the DUR calculation unit 1211 calculates the DUR by taking the ratio between the desired signal power and the interference signal power. The information signal sent to the propagation path compensation / demapping section 1212 is subjected to propagation path compensation and demapping based on the propagation path estimation value sent from the propagation path estimation section 1208, and the P / S conversion section 1213-1313. After being decoded by error correction decoding units 1214-a to l prepared for each frequency channel via a to l, they are output from the demultiplexing unit 1215.

  16 and 17, the base station side transmitting device and the terminal side receiving device transmit and receive DUR estimation symbols using base station-specific codes, and are used by the received DUR estimation symbols and each base station. The power of the signal arriving from each base station is calculated by performing the correlation calculation with the code in the terminal side receiving apparatus. Further, in Non-Patent Document 1, an orthogonal code is used as a base station specific code used for DUR estimation. This is to reduce the influence of errors generated in the correlation calculation in the correlation calculation unit 1210 by making the respective codes orthogonal. An example of the orthogonal code shown in Non-Patent Document 1 will be described with reference to FIG. FIG. 18 shows a reception spectrum when three base stations transmit known signals every two subcarriers and other subcarriers do not transmit. At this time, the code of the base station A is (100100100100100100100100 ...), the code of the base station B is (010010010010010010010010 ...), and the code of the base station C is (001001001001001001001001 ...). Each power can be measured without any problem. Non-Patent Document 1 shows that DUR can be obtained with high accuracy by such a method.

Koshimizu et al., IEICE Technical Report RCS2004-85 (2004-06)

  However, in the configuration shown in Non-Patent Document 1, in addition to the propagation path estimation symbol, a DUR estimation symbol that is used only for subcarrier quality (DUR) estimation is required. In Non-Patent Document 1, two symbols for DUR estimation are provided in a slot for the purpose of improving DUR estimation accuracy. With such a configuration, there is a problem that data transmission efficiency deteriorates.

  An object of the present invention is to provide a technique capable of estimating quality without adding a new symbol for subcarrier quality estimation.

According to an aspect of the present invention, a unique code is assigned to each of a plurality of transmission sources, and the unique code assigned to the transmission source is assigned to each transmission source by each transmission source. Used in an OFDM communication system for receiving OFDM symbols transmitted from the first time frequency converting means for converting the received signal into a signal on the frequency axis, and storing the received signal converted on the frequency axis Receiving memory, replica creating means for creating one or more replicas of each interference wave from the received signal based on a code used in a transmission source transmitting an interference wave other than the desired wave, and creation Means for subtracting the one or more replica signals from the received signal in the receiving memory;
There is provided an OFDM receiver having means for estimating a propagation path of a desired wave based on the subtracted signal and a code used in a desired wave transmission source. Thereby, it is possible to achieve high accuracy in propagation path estimation.

  The replica creation means multiplies the received signal stored in the reception memory by a complex conjugate of a unique code used in the transmission source to be created, and uses the frequency time conversion means to generate a signal on the frequency axis. Is converted into a signal on the time axis, and an unnecessary signal on the time axis is removed by the noise removing unit, and then converted into a signal on the frequency axis using the second time frequency conversion means. A means for multiplying by a code is preferable. The influence of noise can be removed by multiplying the signal after removing the noise by a unique code.

  It is possible to provide as many replica creation means as the number of replica memories. Thereby, the load of arithmetic processing can be reduced.

  According to another aspect of the present invention, a unique code is assigned to each of a plurality of transmission sources, and a unique code assigned to the transmission source is assigned to each subcarrier at each transmission source and transmitted. First time-frequency conversion means used in an OFDM communication system for receiving OFDM symbols transmitted from each transmission source and converting received received signals into signals on the frequency axis, and the reception converted on the frequency axis A reception memory for storing the signal, a plurality of replica generation means for simultaneously generating a replica of the interference wave from the reception signal based on a code used in each transmission source, and a replica signal of the interference wave in the reception memory Means for subtracting from the received signal; and means for estimating the propagation path of the desired wave based on the code used in the desired wave transmission source for the subtracted signal. Apparatus is provided.

  One of the plurality of replica creation means multiplies the reception signal stored in the reception memory by a complex conjugate of a unique code used in the transmission source to be created by the replica, and uses frequency time conversion means to A signal on the axis is converted into a signal on the time axis, and an unnecessary signal on the time axis is removed by the noise removing unit, and then the signal is converted into a signal on the frequency axis using the second time frequency conversion means. The unit is preferably a means for multiplying the unique code. By providing a plurality of replica creation means, processing can be performed at high speed.

  According to still another aspect of the present invention, the same predetermined code is assigned to each of a plurality of transmission sources, the code is assigned to each subcarrier, and the phase between adjacent subcarriers is assigned to the transmission source. The received signal is used in an OFDM communication system that receives an OFDM symbol transmitted from each transmission source by adjusting the frequency so that the received signal is time-frequency converted and converted onto the frequency axis. And multiplying by the complex conjugate of the predetermined code, adjusting the phase between subcarriers on the transmission side with a value opposite to the value adjusted by a specific value, and further performing frequency-time conversion to remove noise. The unit removes unnecessary signals, performs time-frequency conversion, and multiplies the code to create a replica of the desired wave, and determines the quality of the received signal from the accumulated received signal and the replica of the desired wave. OFDM reception apparatus is provided, characterized by a constant. According to the receiving apparatus, it is possible to accurately estimate the quality of the received signal.

  According to another aspect of the present invention, a unique code is assigned to each of a plurality of transmission sources, and a unique code assigned to the transmission source is assigned to each subcarrier in each transmission source and transmitted. A reception method in an OFDM communication system that receives OFDM symbols transmitted from each transmission source, the step of converting a received signal received into a signal on a frequency axis, and the received signal converted on a frequency axis. And a step of creating one or a plurality of replicas of each interference wave from the received signal based on a code used in a transmission source transmitting an interference wave other than a desired wave. An OFDM receiving method is provided.

  The propagation path of the desired wave can be accurately estimated by subtracting the created replica of one or a plurality of interference waves from the reception wave stored in the reception memory. Further, the propagation path information and the reception wave or interference wave From the replica, the reception quality for each subcarrier or the reception quality for each subchannel can be estimated.

  According to the present invention, it is possible to estimate the propagation path with high accuracy and to estimate the reception quality for each subchannel with high accuracy. In addition, since OFDM symbols for channel estimation are used for subchannel quality estimation, there is an effect that it is not necessary to increase new OFDM symbols for estimation.

  Hereinafter, embodiments of the present invention will be described in more detail and specifically.

  In this embodiment, it is assumed that the desired wave and the interference wave are synchronized at a certain level. Here, a certain level means that when an OFDM symbol synchronization is performed on a desired wave at the receiver and an FFT window is applied, each OFDM wave does not change within the window. However, there is no problem even if the delay wave exists at a low level and the delay wave changes within the window.

  An example will be described in which the downlink access method in which the terminal station receives data from the base station is OFDMA (Orthogonal Frequency Division Multiple Access). The OFDMA scheme is a scheme that uses OFDM and accesses by TDMA (Time Division Multiple Access) and FDMA (Frequency Division Multiple Access). The number of OFDM subcarriers used here is a, and the number of FDMA basic subchannels is S. For simplicity, the number of subcarriers per subchannel is made uniform and a / S.

  In order to improve communication efficiency in this OFDMA system, it is necessary for each terminal to access through a subchannel with good reception. When the terminal can communicate with two base stations, communication with a base station having a higher quality subchannel increases the efficiency of the entire cell and enhances the user diversity effect. In particular, in a system having a frequency reuse factor of 1 (a system in which all cells use the same frequency), it is highly necessary to use this user diversity effect.

The base station uses a known OFDM symbol for channel estimation (hereinafter referred to as “CE: Channel Estimate”).
Signals ". ) To some extent synchronized. The complex phase point of the subcarrier in CE is represented by cn (n = 1 to a), and the code C in the CE of the base station BS-k is represented by CK = {c1, c2,. Let C be a unique value at the base station.

  The radio communication technique according to the present embodiment estimates the quality of the subchannel from the propagation path estimation result using this CE. In this embodiment, propagation path estimation means that the amount of fluctuation of the amplitude and phase of each subcarrier is estimated by a receiving apparatus in communication using OFDM, and channel quality estimation is an OFDMA access unit. This means that the quality of a certain frequency channel (consisting of several to several tens of subcarriers) is estimated.

  FIG. 1 is a block diagram for estimating a propagation path and quality for each subchannel using CE in a receiver of a terminal in a wireless communication system according to the present embodiment. In the figure, reference numeral 1 is an FFT (Fast Fourier Transform) part, reference numeral 2 is a reception memory, reference numeral 3 is a subtraction part, reference numeral 4 is a code multiplication part, reference numeral 5 is an IFFT part, reference numeral 6 is a time window part, and reference numeral 7 is power. Limiting unit, reference numeral 8 is an FFT unit, reference numeral 9 is a code multiplication unit, reference numeral 10 is a CE code generation unit, reference numeral 11 is a complex conjugate unit, reference numerals 12-1 to 12-K are replica memory units, and reference numeral 14 is all An adder that adds a replica obtained by removing one replica. Reference numeral 50 denotes a subchannel quality estimation unit.

  FIG. 2 is a block diagram illustrating a configuration example of the subchannel quality estimation unit 50. Reference numeral 51 denotes a subtraction unit, reference numeral 52 denotes a sub-channel division unit, and reference numerals 53-1 to 53-S denote quality estimation units.

FIG. 3 is a flowchart showing an example of the processing flow in this embodiment.
Hereinafter, a method for estimating subchannel quality will be described with reference to FIGS. 1, 2, and 3. Here, the code used by the desired base station as CE is CK, and the base station is BS-K.

  First, when reception processing of signals transmitted from the transmission source almost simultaneously is started (start), the replica memory is cleared and k = 1 and N = 0 are set (step S1). Here, k (1 ≦ k ≦ K−1) is a subscript indicating an interference base station, and k = K is a subscript indicating a desired base station. N is the number of repetitions of an interference cancellation operation described later. The total number of interfering base stations is K, and the maximum number of cancel operations is M.

  The received time waveform of the preamble is subjected to FFT in the FFT unit 1 and converted to a frequency axis waveform (step S2). The waveform converted to the frequency axis is stored in the reception memory 2 as a reception signal (step S3). The adder 13 is a block for adding replicas from base stations other than the base station that is seeking the propagation path. When k = 1, the replica of CE from the base station other than k = 1 is added. (Step S4). The added replica is subtracted from the received signal (step S5). The signal obtained here is defined as Rk.

  Subsequently, the process of (Step S6) and the process of estimating the propagation path from the impulse response are performed. Details of these processes are shown in the flowchart of FIG.

  A code Ck of a base station corresponding to k of Rk is generated by the CE generation unit 10, a complex conjugate is obtained by the complex conjugate unit 11, and the obtained value and Rk are multiplied by the code multiplication unit 4 (step S61). The signal thus obtained is the frequency response of the propagation path from BS-k. When this frequency response is converted into a time waveform by the IFFT unit 5, an impulse response is obtained (step S62). Usually, since this impulse response is concentrated in a certain time region, in the time window 6, a signal clearly present in a sample other than that time is determined as noise and deleted (step S63). In addition, even within that time, a component with low power is also determined as noise and deleted by the power limiting unit 7 (step S64). Then, the frequency response of the propagation path can be obtained by performing the FFT again in the FFT unit 8 (step S65). In the above description, the output of the code multiplier 4 and the output of the FFT unit 8 both show the same frequency response of the propagation path, but noise is removed by the time window and the power limiting block. The latter shows superior properties under many conditions. Usually, only the time window is used among the power limit block and the time window block. In this embodiment, if there is at least one time window, the same effect can be obtained. Based on the output of the FFT 8, it is possible to estimate the propagation path in the wireless communication from the transmission side to the reception side.

  On the other hand, the subchannel quality estimation unit 50 may estimate the quality of the corresponding subchannel based on the difference obtained by subtracting the output from any of the replica memories 12-1 to 12-k and the output from the reception memory. it can.

  In (step S8), it is determined whether or not k = K. If k = K is not satisfied, k = k + 1 is set, and the process returns to (step S4). The same operation is repeated until k = K. By this work, replicas are sequentially created for CEs from interfering base stations, and replicas from all interfering base stations are created at k = K−1. These replicas are temporarily stored in the replica memories C1 (12-1) to Ck (12-k), respectively. Then, at k = K, replicas from all interfering base stations are subtracted by the subtraction operation in step S5, and a propagation path of k = K can be obtained with high accuracy. This series of operations is an interference wave canceling operation.

By repeating this canceling operation, the performance is improved. In (Step S10) and (Step S11), the number of cancellations is determined, and when the number of cancellations reaches a predetermined number M, the operation is terminated, and the replica obtained from the frequency response of the CK propagation path is subjected to channel quality estimation. It outputs to the block 50 (step S12). Further, the frequency response waveform of the received signal stored in the reception memory is also input to the subchannel estimation block 50.
(Step S14) is a step of estimating the quality of each subchannel from the propagation path information, and details thereof will be described with reference to FIG. As shown in FIG. 5, in the subchannel quality estimation block, the subtraction unit 51 vector subtracts the replica frequency response (Ck replica) from the received signal Rk for each subcarrier (step S141). This subtracted signal is considered to be the sum of noise and interference signals for the radio waves from BS-K. Both subcarrier-unit data are input to the subchannel quality estimation units 53-1 to 53-S in the subchannel division unit 52 (step S142). Each quality estimation unit 53-1 to 53 -S takes the ratio of signal power and noise power and outputs it as the SINR (Signal power to Interference power and Noise power Ratio) of the corresponding subchannel (step S 143). ). Through the above operation, the estimation accuracy is improved by repeatedly estimating the propagation path while removing the interference, and further, the quality estimation accuracy for each channel is improved.

  The system of the first embodiment operates accurately when the number of interfering base stations and the CE code Ck used by the base station are known in advance. However, it is necessary to obtain such information in advance.

  In the second embodiment of the present invention, it is assumed that there is no such information. FIG. 6 is a diagram illustrating a configuration example of blocks necessary for estimating the quality of each subchannel in the receiver in order to realize the present embodiment. The blocks having the same functions as those in FIG. The difference between FIG. 6 and FIG. 1 is that the impulse power determination unit 15 is inserted and the power limiting unit 7 is removed. The presence or absence of the power limiting unit may be any (arbitrary). The impulse power determination unit 15 is a block that calculates the total power of the impulse obtained from the time window 6 and determines the presence or absence of CE for the code Ck used at that time. If a predetermined threshold value is set and there is power greater than the threshold value, a replica is created as in the case of the first embodiment. If the threshold value is not exceeded, the following circuit is not operated or all 0s are output. Then, it works like this.

  FIG. 7 is a flowchart showing the flow of processing according to this embodiment. The flowchart shown in FIG. 7 corresponds to the flowchart of FIG. 4 in the first embodiment, and the processing corresponding to the processing of the flowchart shown in FIG. 4 may be the same. That is, up to (Step S63), the same processing as in the first embodiment may be performed. If the output waveform in (Step S63) is IMP, the total power of IMP is calculated in (Step S66), and this is set as Pp. In (Step S67), Pp is compared with Pthr that is a preset threshold value. If the condition that Pp is equal to or greater than Pthr (Step S67) is satisfied, IMP is output to the FFT processing unit 8, and Pp If the condition that is equal to or greater than Pthr is not satisfied, all signals are set to 0 and output to the FFT processing unit 8. The propagation path can be estimated from this output. Thereafter, the same processing as in the first embodiment is performed.

  By performing these processes for all Ck that may cause interference, it is possible to accurately perform the interference removal operation even when there is no interference base station information. In the above description, the description has been made on the assumption that there is no information on the interfering base station. However, the method according to the present embodiment is applied even when there is information on the interfering base station, that is, in the case of the first embodiment. Even in this case, when the radio wave from the interfering base station is low, there is no need to perform processing, and the performance can be improved.

  Next, a third embodiment of the present invention will be described. In the first and second embodiments, the method of removing interference at random (without giving priority to processing) on the assumption that the propagation path state with the interference base station is unknown is shown. However, a communication system currently used for wireless communication generally constitutes a predetermined frame, and generally exchanges data based on a repeated frame format. Therefore, it is reasonable to consider that there is information on the propagation path in advance. In this embodiment, a method for improving characteristics when the propagation path state from the interference base station is known in the previous frame or the like will be described. The difference from the second embodiment is that the impulse power memory unit 17 stores the probability of the signal and determines the replica creation order based on this.

  FIG. 8 is a functional block diagram of the communication apparatus according to the present embodiment. As shown in FIG. 8, the impulse power memory unit 17 is added to the functional block diagram of the second embodiment, but the propagation path and quality can be estimated.

  FIG. 9 is a flowchart showing the flow of processing according to the present embodiment. In the flowchart of the first embodiment, a process (step S30) for rearranging the priority order of interference waves due to power is inserted between (step S1) and (step S2). The process related to k is converted to k ′.

  The impulse power memory unit 17 stores the power of the interference wave in the previous frame. By performing interference cancellation similar to that in the first or second embodiment in the order of the impulse power, it is possible to cancel the interference wave with higher accuracy. That is, since it is considered that the interference wave having the higher impulse power has a higher signal reliability, it can be subtracted from the more probable signal replica by performing the calculation in the order of the higher impulse power.

  In this embodiment, the case where the order of performing the cancel operation is determined from the information from the previous frame has been described. However, when the cancel operation is repeatedly performed, the order in which the cancel operation is performed is based on the information at the time of the previous cancel operation. It can also be updated or changed.

  As described above, in Examples 1 to 3, the radio wave from the desired base station, that is, BS-K is treated as special, and the cancel operation is performed so that the processing is the last. However, it is not necessary to perform such special handling, and the same effect can be obtained even if all radio waves are handled equally. In particular, in Example 3, since the power from the desired base station is often the highest, the accuracy is higher when all the base stations are processed equally.

  In the first to third embodiments, the processing is assumed to be serial processing, and the canceling processing is sequentially performed to cancel the interference wave and then the sub-channel quality is estimated. However, in this embodiment, the parallel processing is performed. Indicates when to do. That is, it differs from Example 1 in having a plurality of propagation path estimation units.

  FIG. 10 is a diagram illustrating a configuration example of the receiving apparatus according to the present embodiment, which is the same configuration as FIG. 1 used in the first embodiment. However, it is different in that some blocks are surrounded by a thick square and are numbered from 100-1 to 100-k. This means that there are k blocks in the square, and each performs the same operation. The different processing in each block is that k is assigned a different value in each block.

  In this process, in the first process, propagation paths for all base stations are obtained without subtraction by replicas. In the second and subsequent processes, since the propagation path for each base station is obtained, the characteristics are improved by subtracting the sum of replicas of waveforms other than the self. That is, in the first to third embodiments, the method of subtracting the interference wave one by one is used, whereas in this embodiment, the subtraction process is performed by obtaining the sum of replicas. Compared to the above, the time required for the cancel operation can be shortened.

  Table 1 shows characteristics of the degree of estimation when the number of cancel operations M = 0 and M = 4.

  The example shown in Table 1 is an example in which 16 subchannels are set for 1024 OFDM signals, the interference wave is 1 wave, and the power ratio between the interference wave and the desired wave is 0 dB. It is apparent that the estimation accuracy is improved when M = 4 regardless of the SNR, and the improvement degree is about 2 dB. According to the present embodiment, it is possible to improve the processing speed related to quality estimation.

  In the first to fourth embodiments, the case where the codes for CE allocated between the base stations are unique codes is shown as an example. In the present embodiment, although a code is unique, a description will be given of a configuration and a method of measuring the C / I ratio of each subchannel when a special relationship is satisfied.

  In the first to fourth embodiments, the complex phase point of the subcarrier in CE is cn (n = 1 to a), the code C in the CE of the base station BS-k is Ck = {c1, c2,. The example used is shown. Therefore, Ck was completely independent between base stations.

  On the other hand, the code used in the present embodiment first makes the amplitude and phase of each subcarrier the same and gives a constant phase rotation. That is, Ck = {e0, ejθk, ejθk × 2,... Ejθk × a}. Further, a basic code Cb = {C1-b, C2-b,..., Ca-b} is multiplied to generate a code. Accordingly, θk, which is first given as the phase rotation amount in each base station, is a unique value in each base station.

FIG. 11 is a block diagram for generating a CE based on this embodiment. In FIG. 11, reference numeral 101 denotes a phase rotation unit, and reference numeral 102 denotes a code multiplication unit. At reference numeral 101, the above-described phase rotation specific to the base station is given, and at reference numeral 102, the same reference sign is multiplied by all the base stations. The order of these two blocks is variable.

  FIG. 12 is a diagram illustrating a configuration example of a receiver in the present embodiment. The blocks having the same functions as those in FIG. The main difference between FIG. 12 and FIG. 1 is that the function of creating a replica does not exist in FIG. 12, which means that no cancellation is performed. This is because each base station uses a CE generated based on the same code, so that the impulse response obtained after IFFT in block 5 can be separated by the same code. FIG. 13 is a diagram showing the concept of the impulse response (upper diagram) which is the output of the IIFFT block 4 in the first to fourth embodiments and the impulse response (lower diagram) output in the present embodiment. In the first to fourth embodiments, since codes different from one base station to another are used, only a signal with a matching code is observed as an impulse response near 0 of the IFFT sample. On the other hand, when the code as shown in the present embodiment is used, the basics are the same code, so that the signal component with the completely matched code is observed as an impulse response near 0 of the IFFT sample. For the other signal components, the signals are concentrated and observed near different IFFT samples according to the phase rotation amount θk. Therefore, it is possible to extract only the desired wave in the time window, and the cancel operation as shown in the first to fourth embodiments is not necessary.

  Therefore, if θk is appropriately selected for the number of necessary base stations to be separated, the propagation path can be separated, and the propagation path and quality for each subchannel are estimated in the same manner as in the first to fourth embodiments. It becomes possible. Here, assuming that the number of FFT points is F, the impulse response is shifted by G points if θk × F = 2πG is satisfied.

In the first to fifth embodiments, the method for estimating the quality for each subchannel has been described. However, by setting the number of subcarriers constituting a subchannel to 1, the propagation path and quality for each subcarrier can be reduced. It is also possible to estimate. Also,
In the first to fifth embodiments, the SINR is measured as a quality evaluation method for the received signal, but it is obvious that the power of the interference wave can be estimated in all configurations. Therefore, SIR (Signal power to Interference power Ratio) can be easily used as an evaluation method.

  Further, in the first to fifth embodiments, the interference wave has been handled as another base station. However, the present invention can be applied to a case where one base station forms a sector, and MIMO (Multi-Input Multi-Output) Even if the system is treated as a radio wave from the same base station, the same processing can be performed and the estimation accuracy of the propagation path and quality for each subchannel can be improved.

  The present invention can be used as a wireless communication device.

It is a block diagram for estimating the quality for every subchannel using CE in the receiver of the terminal in the radio | wireless communications system by Example 1 of this invention. 3 is a block diagram showing a configuration example of a subchannel quality estimation unit 50. FIG. FIG. 6 is a flowchart illustrating an example of a process flow in the first embodiment. It is a flowchart figure which shows the detail of the process of step S6, and the process which estimates a propagation path from an impulse response. It is a figure which shows the structural example of a subchannel quality estimation block. It is a figure which shows the structural example of a block required in order to implement | achieve Example 2, in order to estimate the quality for every subchannel in a receiver. FIG. 10 is a flowchart illustrating a process flow according to the second embodiment. 6 is a functional block diagram of a communication device according to Embodiment 3. FIG. FIG. 10 is a flowchart illustrating a process flow according to the third embodiment. FIG. 10 is a diagram illustrating a configuration example of a receiving device according to a fourth embodiment. FIG. 10 is a block diagram for generating a CE based on the fifth embodiment. 10 is a diagram illustrating a configuration example of a receiver in Embodiment 5. FIG. It is a figure which shows the concept of the impulse response (upper figure) which is the output of IFFT block 4 in the case of Example 1 to 4 and the impulse response (lower figure) output in the case of this Example 5. FIG. It is a figure which shows the example of a frame structure of a DPC-OF / TDMA system. FIG. 3 is a diagram showing an example of a slot configuration in Non-Patent Document 1. 2 is a diagram illustrating a configuration example of a transmitter on the base station side in Non-Patent Document 1. FIG. 7 is a diagram illustrating a configuration example of a terminal-side receiver in Non-Patent Document 1. FIG. 6 is a diagram illustrating an example of orthogonal codes shown in Non-Patent Document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... FFT part, 2 ... Reception memory, 3 ... Subtraction part, 4 ... Code multiplication part, 5 ... IFFT part, 6 ... Time window part, 7 ... Power restriction part, 8 ... FFT part, 9 ... Code multiplication part, 10 ... CE code generator, 11 ... complex conjugate part, 12-1 to 12-K ... replica memory part, 14 ... adder, 50 ... subchannel quality estimator.

Claims (22)

A unique code is assigned to each of a plurality of transmission sources, the unique code assigned to the transmission source is assigned to each subcarrier at each transmission source, and OFDM symbols transmitted from each transmission source are received. Used in OFDM communication systems,
First time frequency conversion means for converting a received signal received into a signal on a frequency axis;
A reception memory for storing the received signal converted on the frequency axis;
Replica creating means for creating one or more replicas of each interference wave from the received signal based on a code used in a transmission source transmitting an interference wave other than the desired wave;
Means for subtracting the created replica signal or signals from the received signal in the receiving memory;
An OFDM receiving apparatus comprising: means for estimating a propagation path of a desired wave based on the subtracted signal and a code used in a desired wave transmission source. The replica creation means includes
Multiply the reception signal stored in the reception memory by the complex conjugate of the unique code used in the transmission source to be created as a replica, and use the frequency time conversion means to convert the signal on the frequency axis to the signal on the time axis. The signal after the unnecessary signal on the time axis is removed by the noise removing unit is converted into a signal on the frequency axis using the second time frequency conversion means, and multiplied by the unique code. The OFDM receiver according to claim 1. The signal obtained by subtracting the replica is multiplied by the complex conjugate of the code used by the transmission source transmitting the desired wave,
By converting to a signal on the time axis using the frequency time conversion means, removing unnecessary signals by the noise removal means, and then converting to a signal on the frequency axis using the second time frequency conversion means. The OFDM receiver according to claim 2, wherein a propagation path is estimated. Furthermore, based on the propagation path information of the desired wave, a signal replica generated by a unique code of the desired wave is created by multiplying the code used by the transmission source transmitting the desired wave,
When the replica of the interference wave and the replica of the desired wave are used to re-create one or more replicas of the interference wave and the replica of the desired wave, a part or all of the replica other than the replica to be re-created Subtract from the received signal stored in the reception memory,
The received signal obtained by subtracting the replica is converted into a signal on the frequency axis by using the time frequency conversion means,
Multiply by the complex conjugate of the unique code used by the source you are replicating,
Furthermore, using the frequency time conversion means, it converts to a signal on the time axis,
4. The OFDM receiver according to claim 3, wherein after the unnecessary signal is removed by the noise removing unit, the signal is converted into a signal on a frequency axis by using the second time frequency converting unit.   5. The replica according to claim 1, wherein the replica is created or the replica is re-created in order from a transmission source having a large reception power by using propagation path information from each transmission source. The OFDM receiver according to item.   6. The OFDM receiving apparatus according to claim 4, wherein the replicas are recreated in descending order of the power of the replicas created in advance.   The impulse power determination unit further comprising: an impulse power determination unit that calculates the total power of the time-axis signal obtained from the noise removal unit and determines the presence or absence of an OFDM symbol for the code used at that time based on the power. The OFDM receiver according to any one of 2 to 6.   The OFDM receiving apparatus according to any one of claims 1 to 7, further comprising an impulse power memory unit that stores the probability of the signal and determines a replica creation order based on the storage.   The OFDM receiving apparatus according to any one of claims 1 to 8, wherein the number of replica creation units is equal to the number of replica memories. A unique code is assigned to each of a plurality of transmission sources, and each transmission source assigns a unique code assigned to the transmission source to each subcarrier, and transmits an OFDM symbol transmitted from each transmission source. Used in receiving OFDM communication systems,
First time frequency conversion means for converting a received signal received into a signal on a frequency axis;
A reception memory for storing the received signal converted on the frequency axis;
A plurality of replica creating means for simultaneously creating a replica of an interference wave from the received signal based on a code used in each transmission source;
Means for subtracting the replica signal of the interference wave from the reception signal in the reception memory;
An OFDM receiving apparatus comprising: means for estimating a propagation path of a desired wave based on a code used in a desired wave transmission source for the subtracted signal. One of the plurality of replica creation means is:
Multiply the reception signal stored in the reception memory by the complex conjugate of the unique code used in the transmission source to be created as a replica, and use the frequency time conversion means to convert the signal on the frequency axis into a signal on the time axis. The signal after converting and removing the unnecessary signal on the time axis by the noise removing unit is converted into a signal on the frequency axis by using the second time frequency conversion means, and multiplied by the unique code. The OFDM receiver according to claim 10. Furthermore, it has means for simultaneously creating a replica of the desired wave,
When recreating a replica using the replica of the interference wave and the replica of the desired wave, a process of creating a replica by subtracting a part or all of the replica other than the replica to be recreated from the received signal stored in the reception memory 12. The OFDM receiver according to claim 11, wherein the OFDM receiver repeats a predetermined number of times.   13. The OFDM receiver according to claim 1, wherein the quality of the signal is estimated from all or any one of the received signal, the interference wave replica, and the desired wave replica. The same predetermined code is assigned to each of a plurality of transmission sources, the code is assigned to each subcarrier, and the phase between adjacent subcarriers is adjusted to be a value specific to the transmission source for transmission. Used in an OFDM communication system that receives OFDM symbols transmitted from each transmission source, time-frequency-converts the received signal received, stores the received signal converted on the frequency axis, and stores the predetermined code Multiply by the complex conjugate, adjust the phase between subcarriers on the transmission side with the inverse of the value adjusted by a specific value, further perform frequency time conversion, remove unnecessary signals by the noise removal unit, time frequency Create a replica of the desired wave by converting and multiplying by the sign,
An OFDM receiver characterized in that the quality of a received signal is estimated from the stored received signal and a replica of a desired wave.   15. The OFDM receiver according to claim 13, wherein either SINR or SIR for each OFDM subcarrier is used as the quality of a received signal to be measured.   15. The OFDM receiver according to claim 13, wherein SINR or SNR for each OFDMA subchannel is used as the quality of a received signal to be measured. The time frequency transforming means is a discrete Fourier transform (DFT) or fast Fourier transform (FFT) means,
The OFDM receiver according to any one of claims 1 to 16, wherein the frequency time conversion means is an inverse discrete Fourier transform (IDFT) or an inverse fast Fourier transform (IFFT).   The OFDM receiver according to any one of claims 2 to 17, wherein the noise removal is performed using a time window.   The OFDM receiver according to any one of claims 2 to 17, wherein the noise removal is to delete a waveform having a predetermined power or less. OFDM in which a plurality of transmission sources use unique codes, each transmission source assigns a unique code assigned to the transmission source to each subcarrier, and receives OFDM symbols transmitted from each transmission source A reception method in a communication system, comprising:
Converting the received signal into a signal on the frequency axis;
Accumulating the received signal converted on the frequency axis;
Creating one or a plurality of replicas of each interference wave from the received signal based on a code used in a transmission source transmitting an interference wave other than the desired wave Reception method. The step of creating a replica of the interference wave includes:
Multiply the accumulated received signal by the complex conjugate of the unique code used by the transmission source that is the object of replica creation, and convert the signal on the frequency axis to a signal on the time axis, and an unnecessary signal on the time axis 21. The OFDM receiving method according to claim 20, wherein a propagation path of the received signal is estimated by converting the signal after removing the noise into a signal on a frequency axis. The step of creating a replica of the interference wave includes:
Multiply the accumulated received signal by the complex conjugate of the unique code used by the transmission source that is the object of replica creation, and convert the signal on the frequency axis to a signal on the time axis, and an unnecessary signal on the time axis The signal after removing the noise is converted into a signal on the frequency axis and multiplied by the code used in the target transmission source, and the created one or more interference wave replicas are 21. The OFDM receiving method according to claim 20, further comprising the step of estimating the quality of the received signal by subtracting from the accumulated received wave.

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