KR20010095459A - Apparatus for multichannel interference cancellation - Google Patents

Abstract

PURPOSE: A multipath interference canceller is provided to simplify hardware by reducing the complication of a system, due to a generic multiuser detection interference canceller, using a rake receiver interference cancellation system that carries out only interference cancellation for a desired user's multipath signal generated from an existing rake receiver. CONSTITUTION: In a CDMA system that consists of an RF(Radio Frequency) part(1), an A/D(Analog to Digital) converter(2), a rake receiver(4) comprised of a plurality of fingers, a combiner(5) and a discriminator(6), a multipath interference canceller(9) is composed of an interference canceller(8) and a buffer(7). The interference canceller(8) receives signals obtained from the fingers of the rake receiver(4), removes interference signals from the received signals, and outputs them. The buffer(7) stores the received signals outputted from the fingers of the rake receiver(4).

Description

Multipath interference cancellation

The present invention relates to a multipath interference canceller. More specifically, the present invention relates to a Rake receiver which is applied to improve the performance and reduce the influence on the multipath signal of the desired user signal in the CDMA system, by using the output signal from the finger by each path The present invention relates to a multipath interference canceller for improving the performance by removing the influence of the generated multipath signal.

Most commercial code division multiple access (CDMA) systems currently employ a single user signal detection method using a rake receiver composed of a finger or the like to reduce the multipath as shown in FIG. Signals in and other paths are treated as interference noise. Therefore, as the number of other users sharing the same frequency increases, the interference caused by the multiple access interference noise and the multipath signals increases, thereby increasing the bit error rate of the received signal, thereby degrading the performance of the system. Therefore, the current CDMA system has maintained the performance of the system by a certain level by limiting the number of users belonging to the base station.

In addition, since future IMT-2000 (International Mobile Telecommunications-2000) needs to provide multimedia services such as video services, the bit error rate of the received signal should be further reduced, and in order to satisfy this, the number of users serviced by one base station is further increased. It is expected to be limited.

Recently, researches on interference cancellers are actively conducted to improve the performance of a system by reducing multiple access interference by other users. Among them, NTT, DoCoMo, OkI, Interdigital, GBT, etc., propose a multi-user signal detection interference canceller as the standard of IMT-2000 system. The multi-user signal detection method improves the capacity and performance of the system by reducing the multiple access interference by estimating and reproducing a signal by another user who has been treated as interference noise in a single-user signal detector and removing it from the received signal. The multi-user signal detector has a method through an optimal multiuser detection technique based on the maximum likelihood sequence estimation (MLSE) technique, and may have higher gain in a complete power control situation. However, the optimal receiver method has a lot of difficulties in actual implementation because its complexity increases exponentially with the number of multiple users. In order to reduce the complexity of such an implementation, a recent suboptimum multiuser detection technique has been proposed. The quasi-optimal multi-user reception method includes a serial interference cancellation (SIC) method that sequentially removes signals from other users, and a parallel interference cancellation (PIC) method that simultaneously removes signals from other users. The method which mixed these is mentioned. However, we do not consider interference cancellation by multipath.

Conventional interference cancellation schemes that require the code of another user Note that the multi-user interference cancellation scheme, which is a multi-user interference cancellation scheme, removes signals that act as a large interference noise to other users among the received signals, thereby increasing the accuracy of signal estimation. . However, the processing time is long because it repeats sequentially until the signal of the weakest user belonging to the same cell is detected. Therefore, since this removal process must be performed before the next signal is received, the number of users may be limited by the processing time. In addition, since the parallel interference cancellation method removes signals of other users at the same time, processing delay time can be shortened. However, in an incomplete power control environment, signals having different signals are received. In addition, a weak user signal, which can be incorrectly determined to simultaneously remove all other user's signals from the received signals, is also used to estimate the desired user signal, thereby degrading the performance of the system. As the number of other users belonging to one base station increases, the multi-access interference noise increases, which increases the bit error rate of the estimated signal, increases the system complexity, increases the price, and is difficult to apply because the terminal cannot have another user's code. There is this

Accordingly, the present inventors have conducted numerous studies and experiments to solve the above problems. As a result, the present inventors only remove interference for a desired multipath signal generated from a conventional rake receiver without removing signals for other users. The present invention has been made by reducing the complexity of the system by a general multi-user detection interference canceller as an interference cancellation system of a rake receiver and reducing the hardware increase and advantageously applying to a terminal.

1 is a block diagram of a conventional CDMA system.

2 is a block diagram of a CDMA system according to the present invention;

3 is a block diagram of a terminal side of a CDMA system according to the present invention;

4 is a block diagram of a base station side of a CDMA system according to the present invention;

5 is a detailed block diagram of the present invention.

Figure 6 is a block diagram illustrating the operation of the signal regeneration unit of the present invention.

<Explanation of symbols for main parts of the drawings>

1: RF section, 2: A / D converter,

3: finger, 4: rake receiver,

5: combiner, 6: discriminator,

7: buffer, 8: interference canceller,

9: multipath interference canceller, 31: correlator,

32: channel estimator, 33: time estimator,

81: signal regeneration unit, 82: removal unit,

83: correlation unit, 84: determination unit,

85: diffusion

The present invention provides a CDMA system comprising an RF unit, an A / D converter, a rake receiver and a combiner composed of a plurality of fingers, and an interference canceller and a receiver for receiving a signal obtained from a finger and removing the interference signal from the rake receiver. A multipath interference canceller characterized in that it consists of a buffer for storing a signal.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a conventional CDMA system.

2 is a block diagram of a CDMA system according to the present invention, FIG. 3 is a block diagram of a terminal side of a CDMA system according to the present invention, and FIG. 4 is a block diagram of a base station side of a CDMA system according to the present invention.

Figure 5 is a detailed block diagram of the present invention, Figure 6 is a block diagram illustrating the operation of the signal regenerator of the present invention.

The present invention provides a CDMA system comprising an RF unit 1, an A / D converter 2, a rake receiver 4 composed of a plurality of fingers 3, a combiner 5, a discriminator 6, and the like. A multipath consisting of an interference canceller 8 for receiving a signal obtained from the finger 3 to a plurality of fingers 3 of the rake receiver 4 to remove and output an interference signal, and a buffer 7 for storing the received signal. The interference canceller 9 is configured.

In addition, the interference canceller 8 may select and use one of a series interference canceller, a parallel interference canceller, a series-parallel mixed interference canceller, and a linear interference canceller.

As shown in Figs. 2, 3 and 4, the signal from the antenna assumes a signal for a reception direction to the base station and the terminal. In this case, the received signal receives a multipath signal received from various directions instead of a single path signal. Therefore, the received signal is a signal passed through the RF unit 1 and the A / D converter (2) is input to the plurality of fingers (3) constituting the rake receiver (4) is output and the signal output from the finger (3) The received signal is input to the buffer 7 and stored, and the multipath signal is input to the interference canceller 8.

The interference canceller 8 removes and outputs the signal of each unwanted path by the received signal stored in the buffer 7.

This will be described in more detail with reference to FIG. 5 as follows.

The signal passing through the A / D converter 2 is input to the finger 3 composed of a correlator 31, a channel estimator 32, and a time estimator 33. The signal output from the correlator 31 of the finger 3 is a signal of the interference canceller 8 composed of a signal regenerator 81 (regenerator), a canceller 82, and a correlator 83 (correlator). It is input to the regeneration unit 81.

The signal regenerating unit 81 includes a discriminating unit 84 and a spreading unit 85, and as illustrated in FIG. 6, a signal received from the correlating unit 31 of the finger 3 through the discriminating unit 84. Determine the signal for the desired user's path and apply the channel parameter obtained from the channel estimator 32 to the signal spread through the spreader 85 in consideration of the desired user's code set by the path delay. Generates a path signal.

The path signal of the desired user generated by the signal regeneration unit 81 is input to the removal unit 82 to remove signals of the desired user received through other paths from the signals passed through the A / D converter 2 and the desired user. A path signal is output, and a signal from which another path signal has been removed is output through the correlator 83 of the interference canceller 8.

Each signal output from the correlator 83 of the interference canceler 8 is combined by obtaining a desired user signal by the combiner 5 to determine data from the discriminator 6.

In this case, when the serial interference canceller is applied as the interference canceller 8, signals are sequentially reproduced and removed from the signal of another path having the largest received power. The reason is that a signal with a large reception power acts as the biggest interference to a signal in another path, and a signal with a large reception power is likely to be reproduced correctly.

The operation in the case of applying such a serial interference canceller is as follows.

The received baseband signal is stored in the buffer 7 and then despreaded by the finger 3 to output channel parameters and decision variables. The series interference canceller selects the decision variable having the largest received power, and the selected decision variable is output after being judged by the determiner 6 and reproduced using the channel parameter output from the finger 3. The reproduced signal is removed by the baseband signal stored in the buffer 7. These operations are repeated until the path signal with the weakest reception power is determined.

In addition, even when the interference canceller 8 is applied as a parallel interference canceller, the determinants output by being despread from the finger 3 are reproduced by using the determined channel parameters. The reproduced signal can reduce the multiple access interference components caused by other path signals by removing signals of all other paths except the signal of the desired path from the signal stored in the buffer 7.

It is considered that if the method of operating only the path having a certain level of output value as well as the signal of all paths in the serial interference canceller and the parallel interference canceller, it is possible to reduce the processing delay time and reduce the hardware recovery.

Therefore, the reverse spreading is performed using the signal from which the other path signal is removed, and the desired path signal is determined and output.

In addition to the serial interference canceller or the parallel interference canceller, other existing interference cancellation techniques can be used to perform interference cancellation for the multipath as in the present invention rather than interference cancellation by other users.

The present invention as described above can reduce the bit error rate of the received signal, improve the performance of the signal received from the terminal, etc. can extend the life of the battery of the terminal and can receive a better quality call or video, service providers Etc. can increase the efficiency of the limited frequency resources to generate more benefits.

Claims (4)

In a CDMA system including an RF unit, an A / D converter, a rake receiver composed of a plurality of fingers, and a combiner, an interference canceller and a receiver which receives a signal obtained from a finger and removes and outputs a multipath interference signal to the rake receiver. Multipath interference canceller, characterized in that consisting of a buffer for storing the signal. The method of claim 1, A multipath interference canceller comprising an interference canceller comprising a signal regenerator, a canceller and a correlator. The method of claim 2, A multipath interference canceller comprising: a signal regeneration section comprising a discriminating section and a spreading section. The method of claim 1, A multipath interference canceller, characterized in that it is selected from a series interference canceller, a parallel interference canceller, a serial-to-parallel mixed interference canceller, and several existing interference cancellers.