JPH07264111A - Code division multiple address receiver - Google Patents

Abstract

PURPOSE:To eliminate interference between multi-paths among other stations by generating a reception signal replica of each mobile station including the multi-path and excluding the replica from the reception signal. CONSTITUTION:Correlation values S1-S3 are obtained by taking correlation between a reception signal R and spread codes (PN codes) of each station to make spread again thereby obtaining re-spread signals S1A1-S3A3. A replica RP is generated by suming the signals of all stations and a difference between the replica RP and the reception signal R is obtained. The correlation between the error signal E and PN codes A1-A3 of each station is taken to correct values S1-S3 to be Si=Si-epsiloni (i=1-3) corresponding to correlation values epsilon1-epsilon3. The replica RP is generated by using the corrected values S1-S3, the operation above is repeated to correct the correlation values so that the error is made zero. Finally when data of the 1st station are obtained, the interference with respect to the signal of the 1st station is excluded by subtracting re-spread signals S2A2, S3A3 of the 2nd and 3rd stations from the reception signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to code division multiple access (Co
The present invention relates to a receiver of a mobile communication system base station based on a de-division multiple access (CDMA) communication system, and more particularly to a code division multiple access receiver having an interference cancellation function.

[0002]

2. Description of the Related Art In the CDMA communication system, all mobile stations communicate using the same frequency band. Therefore, in one mobile station, the signals of other stations all interfere. In the reverse link (connection from the mobile station to the base station), the mobile station controls the transmission power so that the signal strengths when received by the base station are all equal. As a result, the speech quality of each mobile station at the base station is approximately 1 when the number of mobile stations is N.
/ (1-N) (see the following Document 1). Reference 1: Klein S. Gilhousen et al. "On the Capacit
y of a Cellular CDMA System "IEEE Trans. on Vehicul
ar Tec. Vol.40, No.2, May 1991. That is, as the number of mobile stations connected to the base station increases, the interference increases, the call quality deteriorates, and accommodation of more mobile stations is hindered. Further, in a multipath environment, if the delay between the paths of the received signal is 1 chip or more, the PN code shifts, which causes interference with the own station, which deteriorates the call quality and reduces the number of accommodated mobile stations. . A method of removing these other station interference waves and multipath interference waves is disclosed in, for example, the following Document 2. Reference 2: Young C. Yoon et al. "A Spread-Spectrum Mul
ti-Access System with a Cascade of Co-Channel Inte
rference Cancellers for Multipath Fading Channels "
ISSSTA'92, 1992 However, in such a system, since the tap coefficient in the filter is updated by the least square method for each chip, for example, the calculation amount increases and the delay in demodulation increases.

[0003]

SUMMARY OF THE INVENTION As described above, CDMA
In the reverse link of the system, the number of mobile stations that the base station can accommodate is roughly determined by the number of mobile stations and the number of multipaths. In order to increase the number of accommodating stations, it is necessary to suppress the interference that causes poor quality. Further, in removing interference, the amount of calculation of the removing circuit must be suppressed so that the demodulation delay does not increase. An object of the present invention is to propose a method of removing interference between other stations and between multipaths by creating a received signal replica of each mobile station including multipath and removing it from the received signal.

[0004]

The present invention relates to a code division multiple access receiver having an interference canceling function used in a mobile communication system, which comprises a first stage means, one or more intermediate stage means, and a final stage means. I have. The first stage is created by the correlation / spreading unit that correlates the baseband received signal with the spreading code of each mobile station and multiplies the result by the spreading code of each station as the correlation coefficient of each station to respread, and the correlation / spreading unit. The re-spread signal is added to all the stations to create a replica of the received signal, and an error calculation unit that obtains an error signal from the difference between the received signal and the replica is included. The intermediate stage is a correlation / spreading unit that correlates the error signal obtained in the previous stage with the spread code of each station, corrects and updates the correlation coefficient obtained in the previous stage according to the result, and then applies the spread code of each station and re-spreads. When,
The re-spread signal generated by the correlation / spreading unit is added to all the stations to create a replica of the received signal, and an error calculation unit that obtains an error signal from the difference between the received signal and the replica is included. The final stage correlates and spreads the error signal obtained in the previous stage with the spreading code of each station, corrects and updates the correlation coefficient obtained in the previous stage according to the result, and then applies the spreading code to each station to perform re-spreading. And a interference removal unit that removes signals other than the own station or signals other than the own wave from the received signal as interference.

[0005]

In the present invention, the number of mobile stations accommodated in the base station is increased by removing the interference between other stations and the interference between multipaths. The outline of the present invention is shown in FIG. In FIG. 1, the number of mobile stations connected to the base station is assumed to be 3, and multipath is not considered. Referring to FIG. 1, in the first stage, correlation values (correlation coefficients) S1 and S are obtained by taking a correlation between a received signal R and a spreading code of each station, for example, a PN code.
2, get S3. Re-diffusion is performed using this. If each station PN code is A1, A2, A3, S1A1, S2A2, S3A3
Is the respread signal for each station. This is added to all stations to create a replica RP, and the difference between this replica RP and the received signal R is calculated. This difference is an error between the replica and the received signal due to the correlation detection. In the middle stage and thereafter, this error signal E
And the PN codes A1, A2, A3 of each station are taken, and the above correlation coefficients S1, S2, S3 are Si = Si-εi according to the correlation values (error correlation coefficients) ε1, ε2, ε3. (However, i = 1 to 1
Correct as in 3). Furthermore, the corrected correlation coefficient S1,
A replica RP is created using S2 and S3, and the above operation is repeated. As a result, the correlation value is corrected so that the error becomes zero. That is, the replica is created so as to be the same as the actual received signal. When the error becomes zero or becomes small to some extent, or after repeating a specified number of times that can be expected to become small, the correlation value S at that time
It is assumed that 1, S2 and S3 are the estimated propagation paths of each station. In the final stage, if you want to get the data of the first station,
Respread signals S2A2, S of the second and third stations from the received signal
By subtracting 3A3, the interference with the signal of the first station is removed. Similar measures are taken for the second and third stations. The above is also applicable to multipath.

[0006]

FIG. 2 is a block diagram of the essential parts of a code division multiple access receiver showing an embodiment of the present invention.
3 shows an example of a three-stage configuration including a second stage circuit 3 and a final stage circuit 4, 5 to 7 being 2-bit delay units, 8, 10 and
And 12 are correlation / re-diffusion units, 9 and 11 are error calculation units,
Reference numeral 13 is an interference removal (IC) unit, and 14 is a correlation / determination unit. 3 is a block diagram showing the detailed configuration of the first stage circuit 2 in FIG. 2, FIG. 4 is a block diagram showing the detailed configuration of the second stage circuit 3 in FIG. 2, and FIG. 5 is a detail of the final stage circuit 4 in FIG. It is a block diagram showing a configuration, and one embodiment of the present invention will be described with reference to these figures. The signal received by the base station is first stripped of the carrier component and dropped into the baseband band. Hereinafter, the received signal is in the baseband. Further, when the received signal is dropped into the baseband band, it is separated into two I and Q orthogonal phase components. In FIG. 2, the I and Q components are collectively denoted by R. 3 to 5, only the configuration corresponding to one Q component is shown, but the configuration for the other I component is similar. The number of mobile stations connected to the base station is 3 (mobile station number i = 1 to 3).

In the first-stage circuit 2 in FIG. 2, as shown in FIG. 3, the correlation / re-spreading unit 8 in FIG. 2 has matched filters (MF) 21 to 23 and a PN code generator (PNi) 24.
-26 and multipliers 27-29, the error calculator 9 of FIG. 2 is composed of an adder 30 and a subtractor 32.
In FIG. 3, first, the matched filters 21 to 23 correlate the received signal Q (t), which is one component of the baseband received signal, with each station. Correlation is the received signal Q
(t) is multiplied by the PN code of each station and accumulated for 1 bit. The reason why the matched filter is used as the means for obtaining the correlation is that the synchronization positions of the respective stations are different because of asynchronous communication, and the synchronized position is searched while the correlation is obtained by the matched filter. The matched filters 21 to 23 perform correlation while shifting the correlation position by one chip or a fraction of a chip, and the correlation position (that is, delay time) and the correlation result are obtained. The correlation result (correlation coefficient) Si1 (S11 to S31) of each station is obtained for each bit, and the 1-bit interval is Tb.

Re-spreading is performed using this correlation coefficient Si1.
The respread signals are PN code generators (PNi) 24-26.
It can be obtained by multiplying the PN code Ai (t-τi1) of each station generated in 1) by the correlation coefficient Si1 of each station. τ represents the delay time of each station, and is adjusted so that the respread signal of each station is delayed by 2 Tb. That is, if the synchronization position of the first station is delayed by τ1 from a certain reference time, then τ11 = τ1 +
It becomes 2Tb. The respread signals are added for all stations by the adder 30 to form a replica RP (t-2Tb) of the received signal Q (t). This replica RP (t-2Tb) is S1A1 + S2A in FIG.
Corresponds to the Q component of 2 + S3A3. Next, in the subtractor 32, the error between the replica RP (t-2Tb) and the actual received signal Q (t-2Tb) delayed by 2Tb is obtained to obtain the error signal E (t-2Tb). The received signal Q (t-2Tb) is delayed by 2Tb by the delay device 5 in FIG. This considers the maximum delay difference Tb between the stations in the received signal and the time Tb required for the correlation in the correlation / respreading unit. The error signal E (t-2Tb) is sent to the second stage circuit 3 of FIG.

In the second stage circuit 3 of FIG. 2, as shown in FIG. 4, the correlation / re-spreading unit 10 of FIG. 2 has matched filters (MF) 41 to 43, correlation coefficient updating units 44 to 46, P.
N code generator (PNi) 47 to 49, and multiplier 50
2 to 52, the error calculation unit 11 of FIG.
3 and a subtractor 55. Error signal E (t-2Tb)
Are correlated by the matched filters (MF) 41 to 43 of each station. The correlation result (error correlation coefficient) εi1 is input to the correlation coefficient update units (CR) 44 to 46. The correlation coefficient updating units (CR) 44 to 46 update the correlation coefficient Si1 obtained in the preceding circuit according to the error correlation coefficient εi1 as shown in the following equation. Si2 = Si1−α · εi1 α in this expression is a constant smaller than 1 for preventing the error correlation coefficient εi1 itself from further containing an error and causing divergence of the iterative update operation. In the example, it is 0.2.

Re-spreading is performed using the updated correlation coefficient Si2. The re-spreading is performed by the PN code generator (P
Ni) PN code Ai (t-τi2) generated in 47-49
Is multiplied by the correlation coefficient Si2 in the multipliers 50 to 52. Next, the re-spread signals are added to all stations by the adder 53 to form a replica RP (t-4Tb). Next, the replica signal RP (t-4Tb) is subtracted from the received signal Q (t-4Tb) delayed by 4Tb using the subtractor 55 to generate the error signal E (t-4Tb). The error signal E (t-4Tb) is sent to the final stage circuit 4 of FIG.

In the final stage circuit 4 in FIG. 2, as shown in FIG. 5, the correlation / re-spreading unit 12 in FIG. 2 has matched filters (MF) 61 to 63, correlation coefficient updating units 64 to 66, P.
N code generators (PNi) 67 to 69, and multiplier 70
2 to 72, the interference removing unit (IC) 13 of FIG.
It is composed of adders 73 to 75 and subtractors 77 to 79.
The error signal E (t-4Tb) is output from the matched filter (MF) 61.
Correlations are taken at ~ 63. Using the error correlation coefficient εi2, the correlation coefficient updating units (CR) 64 to 66 are used as in the preceding circuit.
Then, the correlation coefficient Si3 is updated. Furthermore, PN code A
PN code generator (PNi) 67 for generating (t-τi3)
69 and multipliers 70 to 72 are used to perform re-spreading as in the preceding circuit.

The respread signal is subjected to interference removal for each station by adders 73 to 75 and subtractors 77 to 79, and the signal from which the interference wave is removed obtains Ui. For the first station, the respread signals of the second station and the third station are added using the adder 73, and this is used as the interference wave of the first station. By subtracting this interference wave from the received signal Q (t-6Tb) using the subtractor 77, the signal from which the interference wave is removed obtains U1. The received signal Q (t-6Tb) is delayed by a total of 6Tb by the delay device 7 in FIG. For the second station, the first station signal and the third station signal are removed using the adder 74 and the subtractor 78, and for the third station, the adder 75 and the subtractor 79 are used. , The first station signal and the second station signal are removed.

The signal Ui of each station from which interference is removed is shown in FIG.
In the correlation / determination unit 14 of, the correlation is obtained for each station,
Data determination is performed for both I and Q. In this example,
Although the example in which the number of mobile stations is 3 is shown, the same operation is performed even if the number of stations increases. In addition, this embodiment shows an example of a three-stage circuit configuration. However, in the case of a one-stage circuit configuration, only the final-stage circuit is used, and in the case of a two-stage circuit configuration, a first-stage circuit and a final-stage circuit, When the number of circuits is four or more, a circuit having the same configuration as the second circuit is added.

FIG. 6 is a block diagram showing another configuration example of the first-stage circuit 2 in FIG. 2. Similar to FIG. 3, matched filters (MF) 81, 82, PN code generators 84 to 84 are provided.
87, multipliers 88 to 91, adder 92, and subtractor 93
Consists of. In a multipath environment, if the delay time of the signal of the local station is 1 chip or more, the PN code shifts to cause interference. Therefore, it is desirable to similarly perform channel estimation and interference cancellation. FIG. 6 shows an example of the configuration of the first-stage circuit in this case. In this example, the number of mobile stations is 2 and the delay wave is 1.
In FIG. 6, matched filters 81 and 82 are used to obtain correlation with each station. Since the matched filter performs correlation while shifting the correlation position, the correlation result and delay time of the first wave and second wave of each station can be obtained. That is, the first station obtains the first wave correlation result S1a1, the delay time τ1a1, the second wave correlation result S1b1, and the delay time τ1b1.
The first wave correlation result S2a1, the delay time τ2a1, the second wave correlation result S2b1, and the delay time τ2b1 are obtained. By multiplying each of these correlation results by the PN code Ai (t-ia1), Ai (t-ib1),
A respread signal of each wave of each station is obtained. Interference cancellation is performed using these respread signals. In addition, in the determination after the interference is removed, only the first wave or the first wave of the highest intensity is detected.
There are methods such as making a decision using only waves or making a decision by combining several waves. In this example, the delay wave 1 (the number of paths is 2) and the delay is 1 chip are shown, but in reality, the number of paths and the delay time vary depending on the place / time. For this reason, it is desirable to set the number of paths that are considered to be necessary for interference removal, select only the set number of paths of the incoming waves with strong intensity, and remove them.

The present invention is generally used on the base station side in consideration of the fact that it is applied to asynchronous communication in which the synchronization timing of each station is inconsistent and the circuit size, but it can also be used on the mobile station side. Is.

[0016]

As described above, according to the present invention, it is possible to remove an interference wave other than the own station or the own wave,
It is possible to increase the number of mobile stations accommodated in the base station.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the present invention.

FIG. 2 is a block diagram of a main part of a code division multiple access receiver according to the present invention.

FIG. 3 is a block diagram showing a configuration of a first-stage circuit in FIG.

FIG. 4 is a block diagram showing a configuration of a second stage circuit in FIG.

5 is a block diagram showing a configuration of a final stage circuit in FIG.

FIG. 6 is a block diagram showing another configuration of the first-stage circuit in FIG.

[Explanation of symbols]

 2 First-stage circuit 3 Second-stage circuit 4 Final-stage circuit 5-7 Delay device 8 Correlation / re-spreading unit 9 Error calculation unit 10 Correlation / re-spreading unit 11 Error calculation unit 12 Correlation / re-spreading unit 13 Interference removal (IC) unit 14 Correlation / Determination Unit 21-23 Matched Filter 24-26 PN Code Generator 27-29 Multiplier 30 Adder 32 Subtractor 41-43 Matched Filter 44-46 Correlation Coefficient Updater (CR) 47-49 PN Code Generation 50-52 Multiplier 53 Adder 55 Subtractor 61-63 Matched filter 64-66 Correlation coefficient updating unit (CR) 67-69 PN code generator 70-72 Multiplier 73-75 Adder 77-79 Subtractor E error signal Q baseband Q-phase reception signal R baseband reception signal RP reception signal replica S correlation coefficient ε error correlation coefficient

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display H04B 1/707

Claims (1)

[Claims] 1. A correlation / spreading unit for performing re-spreading by correlating a baseband received signal with a spreading code of each mobile station, and multiplying the resulting correlation coefficient of each station by the spreading code of each station. , An error calculation unit that adds all the re-spread signals created by the correlation / spreading unit to create a replica of the received signal, and then obtains an error signal by taking the difference between the received signal and the replica, Means, and the error signal obtained in the previous stage and the spread code of each station are correlated, and the correlation coefficient of each station obtained in the previous stage is corrected and updated according to the error correlation coefficient of each station obtained as a result, correction update A correlation / spreading unit that performs respreading by multiplying the correlation coefficient of each station by the spreading code of each station, and all the stations of the respreading signals created by the correlation / spreading unit are added to create a replica of the received signal, and then The received signal And an error calculation unit that obtains an error signal from the difference between the replicas, and the error signal obtained in the previous stage is correlated with the spread code of each station, and the error correlation coefficient of each station obtained as a result is used. Then, the correlation coefficient of each station obtained in the previous stage is corrected and updated, the correlation coefficient of each station that is corrected and updated is multiplied by the spreading code of each station, and re-spreading is performed. A code division multiple access receiving apparatus in a base station, comprising: a final stage unit having an interference removing unit that removes a signal or a signal other than its own wave as interference.