CN1138370C - Interference Suppression Processing Method for Forward Link - Google Patents

Abstract

An interference suppression processing method for a forward link, wherein a correspondence table between pilot codes and spreading codes is established, and a mobile station consults the correspondence table according to received pilot codes of other users to obtain the spreading codes of the user. Frequency code; and the mobile station obtains the channel characteristics of all users in the same cell/sector through channel estimation, compares the power of other users with a threshold, and only performs interference suppression on other users whose power exceeds the threshold and this user.

Description

Interference Suppression Processing Method for Forward Link

The present invention relates to a wireless spread spectrum communication system, in particular to an interference suppression processing method used in the forward link of the wireless spread spectrum communication system.

In the wireless spread spectrum multi-user system, due to the incomplete orthogonality of the spread spectrum codes, even if the spread spectrum codes used are completely orthogonal, the influence of the multipath channel (inter-code crosstalk) will lead to the inconsistency of the spread spectrum codes. Orthogonal, thus causing serious multiple access interference, affecting the performance of the system. In order to overcome multiple access interference or reduce the impact of multiple access interference, joint detection, interference suppression technology, or smart antenna technology and other signal processing methods are often used to improve system performance, but these technologies are generally relatively It is complex, and it is still difficult to apply it to the base station of the mobile communication system. For mobile stations, it is conceivable that the difficulty of using the above technologies will be even greater.

For example, for smart antenna technology, due to the relatively small space occupied by the mobile station, and the spatial characteristics of the signal received by the mobile station, and to reduce costs and power consumption, it is unlikely to use smart antenna technology for general portable terminals. From the point of view of space only, for the smart antenna generally used, the distance between the antenna elements is half of the wavelength, plus factors such as the height of the antenna element itself, it is relatively large for mobile stations, and it is impossible to apply it at this stage .

For joint detection and interference suppression technology, because most of the interference suppression and joint detection algorithms require the mobile station to know the channel information and spreading code information of other users in the cell before processing, but for general communication systems , for a certain user cannot know the information of other users, even if each mobile station in the cell can get the information of other users, the processing complexity will limit the application of this kind of algorithm in the mobile station.

However, with the development of communication systems and data communication services, as well as the development of digital signal processing technology and chip technology, the importance of transmitting high-speed data from base stations to mobile stations (ie forward link) is becoming more and more obvious. The performance of mobile stations must be improved.

The purpose of the present invention is to propose a forward link interference suppression processing method, which can obviously improve the performance of the mobile station without increasing the complexity of the mobile station.

The purpose of the present invention is achieved in this way: a forward link interference suppression processing method is characterized in that: the correspondence table between the pilot code and the spreading code is established, and the mobile station is based on the received pilot code of other users. The frequency code consults the corresponding relationship table to obtain the spreading code of the user; and the mobile station obtains the channel characteristics of all users in the same cell/sector through channel estimation, compares the power of other users with a threshold, and only uses the power exceeding the threshold Other users and this user perform interference suppression.

Preferably, the pilot codes of all users in the same cell/sector are obtained from the same basic code through different shifts, and the corresponding relationship table is specifically expressed as the shift of the basic code and the spreading code Correspondence table between.

Preferably, the correspondence table is broadcast by the base station to the mobile stations in the cell/sector, and can also be fixed in the mobile stations.

Preferably, the threshold is set for different multipath powers of other users, and when the power of one path of other users exceeds the threshold, it is considered that the power of the user exceeds the threshold.

Preferably, the threshold is set for the power sum of each multipath signal of other users, and when the power sum of each multipath signal of other users exceeds the threshold, it is considered that the power of the user exceeds the threshold.

Preferably, the threshold can be adjusted by the mobile station or by the base station during the operation of the mobile station.

Preferably, the wireless transceiver of the base station adopts an array antenna.

Preferably, parallel interference suppression or serial interference suppression may be used when performing interference suppression on other users whose power exceeds a threshold and the current user.

Preferably, when the mobile station compares the power of other users with the threshold, the power of each other user is multiplied by a weight, and the weight reflects the degree of influence of the other user on the user.

The interference suppression processing method of the forward link of the present invention can simply implement interference suppression in the forward link, and can obviously improve the performance of the mobile station under the condition that the complexity of the mobile station is not greatly increased. It is especially applicable when the number of users working at the same time is relatively small. Even when the number of users working at the same time is relatively large, the calculation amount of the mobile station can be flexibly reduced by adjusting the threshold.

In order to make the object, technical solution and advantages of the present invention clearer, the following examples are given in conjunction with the accompanying drawings to further describe the present invention in detail. It should be understood that it is only used for illustration and not limitation of the present invention. in

Fig. 1 shows a schematic diagram of reception of a mobile station according to a preferred embodiment of the present invention.

The interference suppression technology in the reverse link is a relatively mature technology. Since the equipment using the interference suppression technology in the reverse link is mainly the base station, which itself is the distributor of the spreading code, it is easy to know the frequency of the cell. /The spreading codes of all users in the sector, and the software and hardware equipment of the base station allow to perform large amount of calculation and complex processing, so interference suppression is easier to implement. However, the situation in the forward link is completely different from that in the reverse link. The equipment using interference suppression technology in the forward link is mainly a mobile station, and the mobile station generally cannot know all the users in the cell/sector Spread spectrum codes, and the mobile station is small in size, and generally cannot perform large-scale calculations and complex processing, so it is impossible to mechanically introduce the interference suppression technology in the reverse link to the forward link.

The present invention proposes an interference suppression method for the forward link on the basis of discovering the above problems. The invention provides the spreading codes of all users of the mobile station by establishing a corresponding relationship between the pilot code and the spreading code and transmitting the corresponding relationship to the mobile station. In addition, the present invention only performs interference suppression on certain users with large interference and the user by introducing a threshold, thereby reducing the workload of the mobile station. Especially in the third-generation mobile communication system, due to the use of time division-code division multiple access, in fact, the number of users working simultaneously in each time burst (time slot) of the cell is relatively small, such as 16 or 32 user (code channel), and thus is more suitable for the present invention.

The burst structure of pilot can be midamble, preamble, pilot etc., in a preferred embodiment of the present invention, the pilot code of each user is formed by a basic code shift a (i), each user's shift The number of bits a(i) is different, and the difference W=a(i)-a(i-1) of the number of shifts of each user is determined according to the characteristics of the channel (multipath delay). For this, please refer to reference [1], namely, Bernd Steiner, Peter Jung, Optimum and Suboptimum Channel Estimation for the Uplink of CDMA Mobile RadioSystems with Joint Detection, 1994, Vol.5, No.1, 39-50.

A table corresponding to the basic code shift a and the spreading code is set in the system, and this table is sent to the mobile station through signaling or when the mobile station accesses it using a common channel or other time, and can also be fixed in the mobile station.

When the mobile station receives the signal, it first performs channel estimation. Because of the shifting characteristics of the pilot, it is easy to obtain the channel estimation value h _ij of each user, where i represents different users, and j represents different paths in multipath (different delay ). That is, the mobile station obtains information of all users affecting the mobile station in the system through channel estimation, and can obtain spreading codes and channel characteristics of other users.

The channel estimation of other users obtains the power of different delays of other users, and a threshold is set when receiving. When the power of different delays of other users exceeds the threshold, it will be further processed, and the components that do not exceed the threshold are ignored. This step may also be to set a judgment threshold for the power sum of all delayed signals of a certain user, and process signals exceeding the threshold.

Interference suppression is performed on other user signals exceeding the threshold and this user signal, such as parallel interference suppression, serial interference suppression, and so on. For example, the steps of parallel interference suppression can be mainly as follows:

Parallel interference suppression operates the same for all users. (1), use the output of each matched filter as the first estimated signal of each user; (2), then use the first estimated signal to go through judgment, amplitude estimation and respreading to reconstruct the received signal; (3), to A certain user k subtracts the interference signals of all interfering users from the total received signal, and obtains a new estimate of the user signal; (4), then sends it to the second-stage matched filter, and after judgment A new estimated value of each user information bit is obtained.

Then repeat steps (2), (3), (4) until the bit error rate meets the requirements, or all paths of all users have been processed. Compliance with the bit error rate can be obtained by estimating the variance (eye diagram) of the received user signal or by other methods.

The selection of the power threshold will be selected according to the implementation complexity of the mobile station, performance requirements and performance of the actual system. The selection of the threshold has a great impact on the performance and complexity of the system. The smaller the threshold is selected, the greater the complexity of the implementation and the better the performance.

The selection of the threshold can also be set in such a way that when the threshold exceeds a certain threshold, several of the largest multipath components are selected. In this way, it can be ensured that the total calculation amount of interference suppression is within a certain range.

If the system uses an array antenna at the sending end, in general, the number of other users that cause multiple access interference to a certain user will be greatly reduced. Threshold, in this case, the complexity of the mobile station is easier to control within an acceptable range.

In another preferred embodiment of the present invention, reference is made to the TD-SCDMA system of CWTS (China Wireless Communications Standards Organization) or the TDD scheme of 3GPP high code rate option for the system module of the base station. The specific method can be as follows: the system adopts TDD mode and adopts burst (burst) time slot structure; the burst structure includes the pilot structure in reference [1]; assigns pilot codes with different shift positions to each user; The spreading code of each user is obtained according to the shifted position of the pilot code of the user; after spreading, all users are sent out through the array antenna, and each user is sent out through different beamforming.

On the mobile station side, all user signals are received at a specific mobile station after passing through the radiation channel. Due to the beamforming of the transmitted signal through the array antenna, not all users have the same power. The following is divided into five steps A, B, C, D, and E to describe the receiving structure and process of the mobile station in detail, and please refer to Figure 1:

A. After the signal is received by the antenna, the baseband signal R is obtained after radio frequency processing and other processing.

B. Perform channel estimation on the received signal according to the pilot frequency. The channel estimation method is to use the pilot code to estimate, for example, the calculation formula can be used as h = Me , where M = ( G ^★T G ) ^-1 G ^★T , the matrix _ is a Toeplitz matrix, and its elements are composed of the pilot frequency of each user The specific method and parameter setting of channel estimation can be found in reference [1]. The specific implementation method can adopt the technology of fast Fourier transform to simplify and reduce the amount of calculation. In this way, the channel characteristics of all users relative to a specific mobile station are obtained at one time.

The channel characteristics (channel impulse response) of each user, i indicates the i-th user, and j indicates that the relative delay is the j-th chip.

C. Estimate the power of the multipath components of other users' signals according to the channel estimation. The power estimation can directly take the square of the channel estimation amplitude, which can be obtained by $P(i\&Center\; Dot;j)=h_{(i\·.j)}\&Center\; Dot;h_{(i\&Center\; Dot;i)}$ As a result, a threshold is set for P(i, j), and only the multipath components with P(i, j)>Pm are further processed. The threshold is set by the amount of calculation that can be provided by the mobile station. In the TD-SCDMA system, since the base station uses array antennas, the multipath components of other users that need to be processed will be greatly reduced.

D. Obtain the multipath components of other users and the multipath components of this user according to the third step, and perform further processing. The spreading code corresponding to the user to be processed is obtained according to the shifted position of the pilot of each multipath component to be processed.

E. Perform interference suppression processing according to the users to be processed and their multipath components. In this example, the processing method of serial interference suppression is adopted. Assuming that the received baseband signal is R, (1) demodulate (despread) the strongest path of each user to obtain the symbol data S(i, 0) of each user, (2) then perform spread spectrum reconstruction by S(i, 0) Signal R(i, 0) before despreading. (3) Remove the reconstructed signal R=Rh _(i,0) ·R(i,0) from the received signal. (4) Despread the sub-intensive path of each user to obtain S'(i, k). S(i, k)=S(i, k-1)+S'(i, k) and then repeat steps 2, 3, and 4 until the demodulated data bit error rate of the mobile station meets the requirements, or all users’ paths have been processed. Wherein, meeting the requirements of the bit error rate can be obtained by estimating the variance (eye diagram) of the received user signal or by other methods.

The above embodiments are only used to illustrate the present invention without limiting it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that various embodiments of the present invention can be carried out according to the principle and spirit of the present invention. Any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the claims of the present invention.

Claims (9)

1, a kind of interference inhibiting treatment method of forward link is characterized in that: set up the mapping table between pilot code and the spreading code, travelling carriage is consulted the spreading code that this mapping table obtains this user according to other users' that receive pilot code; And travelling carriage obtains the channel characteristics of all users in the same cell/section by channel estimating, with other users' power and a threshold ratio, only other users and this user that power is surpassed threshold value disturbs inhibition, and described threshold value is determined according to the hardware condition and the design requirement of travelling carriage.

2, the interference inhibiting treatment method of forward link as claimed in claim 1, it is characterized in that: all users' pilot code obtains by the difference displacement by same basic code in the same cell/section, and described mapping table is embodied in described to the displacement of basic code and the mapping table between the spreading code.

3, the interference inhibiting treatment method of forward link as claimed in claim 1 is characterized in that: described mapping table also can be solidificated in the travelling carriage by the travelling carriage of base station broadcast to this cell/section.

4, the interference inhibiting treatment method of forward link as claimed in claim 1, it is characterized in that: described threshold value is at the power setting of other users' different multipaths, when the power in other user's a footpath surpasses this threshold value, think that then this user's power surpasses threshold value.

5, the interference inhibiting treatment method of forward link as claimed in claim 1, it is characterized in that: described threshold value is provided with at the power sum of each multipath signal of other users, when the power sum of each multipath signal of other users surpasses this threshold value, think that then this user's power surpasses threshold value.

6, the interference inhibiting treatment method of forward link as claimed in claim 1 is characterized in that: described threshold value can be adjusted by travelling carriage or by the base station in the operating mobile station process.

7, the interference inhibiting treatment method of forward link as claimed in claim 1 is characterized in that: the radio receiving-transmitting unit of base station adopts array antenna.

8, the interference inhibiting treatment method of forward link as claimed in claim 1 is characterized in that: disturb when suppressing other users that power surpassed threshold value and this user, can adopt parallel interference to suppress or serial interference suppresses.

9, the interference inhibiting treatment method of forward link as claimed in claim 1, it is characterized in that: travelling carriage is when comparing other users' power and described threshold value, each other user's power all is multiplied by a weight, and this weight reflects the influence degree of these other users to this user.