WO2003023999A1

WO2003023999A1 - A method of error-correcting encoding source data elements and corresponding iterative decoder

Info

Publication number: WO2003023999A1
Application number: PCT/CN2001/001296
Authority: WO
Inventors: Yonghui Li; Yongsheng Zhang
Original assignee: Linkair Communications, Inc.
Priority date: 2001-08-31
Filing date: 2001-08-31
Publication date: 2003-03-20
Also published as: CN1471766A; CN1210888C

Abstract

A constructing error-correcting codes based on 'expanded' encoding the product codes, is characterized that: after the input information is N-dimension product codes encoded, 'expanded' encoding operations are carried out on M-dimensional (1?=M?=N) directions therein. The 'expanded' encoding contains 'assembling' and 'shuffling' operations. Every group of 'expanded' encoding operations obtain a set of check symbols, new error-correcting codes are constructed by assembling the obtained M groups of check symbol and original N-dimension product codes. Also, the present invention discloses the corresponding iterative decoding method, wherein the iterative decoder is made up of a plurality of component decoders, every component decoder contain a soft-input-soft-output decoding unit and possible 'deassembling' and 'deshuffling' unit, which corresponds to the component code of the original product codes or 'expanded' encoding. At the same time, the interconnection between the respective component decoders can adopt a serial, parallel or combined form, wherein each stage of component decoder utilizes the outputs of all or part of component decoders which are added as a priori information to participant in this stage of decoding. Analysis and emulation all indicate that the error-correcting codes and decoding method of the present invention are capable of satisfy the design demand of a series of code rates, code lengths and performance requirements, simultaneously can employ varied embodiments according to actual situations, such as paralleling level, computation amount, decoding delay requirements, etc.

Description

Transmission diversity method and transmission diversity device TECHNICAL FIELD

The present invention relates to a diversity method and a diversity device for a wireless communication system, and particularly to a transmission diversity method and a transmission diversity device suitable for a time division duplex (TDD) communication system. Background technique

In a mobile environment, the quality of the connection between different transceivers in a wireless communication system is constantly changing. For example, in densely populated areas, buildings and other obstacles scatter signals, and due to the interaction of n input waveforms, the antenna The received signal will suffer fast fading and deep fading, and channel fading is one of the main factors that degrade system performance. The main method used to overcome the effects of fading is diversity technology, which is used to reduce the effects of fading. Without increasing the transmitter power or channel bandwidth, the reliability of the system is improved. Diversity technologies common in existing systems mainly include transmit diversity and receive diversity. This article will focus on transmit diversity techniques.

In the prior art, commonly used transmit diversity technologies mainly include STTD (Space Time Transmitter Diversity), OTD (Orthogonal Transmitter Diversity), T switched TD (Time Switched Transmitter Diversity), STD (Selective Transmitter Diversity), and so on. In the 3GPP TDD system, STTD, OTD, and T switched TD are all open-loop modes. STD uses a half-open-loop mode, that is, the transmit diversity of the base station needs to select the downlink antenna according to the uplink data sent by the mobile station. Furthermore, since the continuous pilot signal is used for channel estimation and demodulation, the base station also needs to provide a downlink instruction to notify the mobile station which pilot channel should be used for demodulation.

The above-mentioned existing transmit diversity methods have the following disadvantages: For example, when an open-loop transmit diversity method is used, the improvement of the system's receiving performance is not ideal, the accuracy is not high enough, and it is very sensitive to the environment. Open-loop transmit diversity method, the implementation is more complicated, because it needs to rely on The pilot signal is connected to perform channel estimation and demodulation, and then a downlink instruction is provided according to this, which is more complicated to implement and has a limited application range. un content

In order to solve the defects and shortcomings of the prior art, the present invention proposes a transmit diversity method and a transmit diversity device that can improve the transmit performance.

To this end, a transmit diversity method for a time division duplex communication system is provided according to the present invention, including the following steps: S1. The base station of the time division duplex communication system measures a fading factor on a common channel;

S2. Initially select the antenna for downlink transmission according to the measurement results, and use the selected antenna for the first downlink data transmission; S3. The mobile station that has received the downlink data sent by the base station uploads the quality information of the used channel and feeds it back to The base station; S4. The base station performs channel estimation according to the received uplink data and calculates the fading factor of the uplink; S5. The base station> predicts the downlink according to the uplink channel estimation result The fading factor of the channel; the base station in S6 chooses to send downlink data on the corresponding antenna according to the prediction result; and repeats steps S3 to S6 until all the downlink data is sent.

According to another aspect of the present invention, a transmission diversity device for a time division silent communication system is further provided, including: a base station receiver, configured to receive uplink data, and despread and demodulate the received data, And perform channel estimation; at least two antennas; a downlink signal generator configured to complete the transmission of a service signal and a pilot signal; a fading factor predictor, configured to estimate an uplink fading factor, and predict each A downlink fading factor corresponding to the antenna; an antenna selector, according to the downlink fading factor predicted by the fading factor predictor, selecting an antenna with a larger fading factor among the above antennas will occur from the downlink signal The data to be sent received by the router is sent out.

By adopting the transmit diversity method and the transmit diversity device of the present invention, the downlink fading factor can be correctly estimated due to the use of prediction technology, while the traditional STD simply uses the reverse fading factor to select the forward transmission, and No predictions were made, so the method of the invention Antennas can be selected more accurately than STD. Because the dedicated pilot channel is used for demodulation, the present invention no longer needs forward and reverse instruction instructions, saves the transmission of control instructions, and can achieve the performance that can be achieved by using a closed-loop STD system.

The transmit diversity method and the transmit diversity device according to the present invention can be applied to any wireless system in which transceivers communicate with each other through a wireless link. One such wireless system may be a cellular wireless system, which generally includes multiple cells, and each cell includes a base station that communicates with user terminals in its area. At each base station, at least two or more antennas are used to send signals. . The present invention is described below by taking a cellular wireless communication system, more specifically, a base station device of the system as an example, but the present invention is not limited thereto.

In the existing mobile communication system, the base station uses multiple antennas, so the performance of the base station can be optimized by using the base station receiving diversity technology, and the performance of the mobile station can be optimized by using the base station transmitting diversity. Although only one antenna is used for receiving at the mobile station, by using transmit diversity technology at the base station, the receiver can achieve diversity effect by using time-space diversity receiver, and overcome the influence of fading to effectively improve the system performance.

Based on the traditional STD, this solution presents a new type of transmit diversity technology suitable for TDD systems, namely STSTD (Smart Time Seized Transmitt Diversity), which uses advanced prediction technology for adaptive transmission antenna selection. This technique uses an open-loop model, but can achieve the performance of a closed-loop system. Compared with the traditional STD technology, STSTD has the following main advantages.

1. According to the symmetry and continuity of the forward channel of the TDD system, the fading factor of the forward channel is used to estimate the fading factor of the forward channel, so that the transmitting antenna can be adaptively selected at the transmitting end according to these estimated fading factors. (This is where the STSTD name comes from).

2. The downlink uses dedicated pilot channels for channel estimation and demodulation.

3. Neither forward nor reverse instructions are required.

The first advantage is that STSTD can use the advanced prediction technology, so it can correctly The downlink fading factor is estimated, and the traditional STD simply uses the reverse fading factor to select the forward transmission without any prediction. Therefore, STSTD selects the antenna more accurately than STD. '

The second advantage is that STSTD does not need a forward indication command because it uses dedicated pilot demodulation. For a mobile station, it does not need to care which antenna the base station uses to transmit, so compared to STD, it can save the transmission of control instructions.

The third advantage is that STSTD uses an open-loop mode, but achieves the performance that can be achieved with a closed-loop STD system. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below with reference to the accompanying drawings and the preferred embodiments of the present invention. In the drawings: FIG. 1 shows the channel usage of the method of the present invention.

Fig. 2 shows a schematic diagram of a transmit diversity device according to the present invention.

Fig. 3 shows a working flowchart for implementing the method of the present invention.

Figure 4 shows the structure of an LMS predictor used to implement the method of the present invention.

Figure 5 shows the algorithm principle of the LMS adaptive filter implementing the method of the present invention.

FIG. 6 shows a flowchart of the implementation of the LMS prediction algorithm in the method of the present invention. detailed description

Referring to FIG. 1, FIG. 1 shows a channel situation used by the method of the present invention.

The downlink signal sent by the base transceiver station 101 is transmitted in the downlink via at least two antennas (two antennas in this embodiment, that is, antenna 102 or antenna 103). At the receiving end, the mobile station transceiver 1 05 is received via antenna 1 04. Among them, a number of dedicated pilot channels are designed in the logical channel between the base station transceiver 1 01 and the mobile station transceiver 1 05, which are divided into uplink and downlink dedicated pilot channels, and pilot signals transmitted through the dedicated pilot channels. Channel estimation and demodulation; and several The uplink and downlink traffic channels are used for uplink and downlink data transmission.

FIG. 2 shows a schematic diagram of an STSTD transmission diversity device according to the present invention, which mainly shows a simplified base station transceiver 101, including a base station receiver 204, a fading factor predictor 203, an antenna selector 202, at least Two antennas 102 and 103 and a downlink signal generator 201. After receiving the uplink data, the base station receiver 204 first performs despreading, demodulation, and then performs channel estimation. The fading factor of the uplink channel is estimated in the fading factor predictor 203, and then the fading factor predictor 203 uses the estimated uplink The channel fading factor (as the training sequence of the predictor) is used to predict the fading factor of the downlink channel corresponding to each antenna. This prediction can be implemented by LMS, RLS prediction, or other prediction techniques. The fading factor predictor 203 sends the prediction result to the antenna selector 202, and in the downlink signal generator 201, the data to be sent is also sent to the antenna selector 202 via the uplink dedicated pilot channel and the uplink traffic channel. The selector 202 will select the antenna with a larger fading factor value to send the data in the downlink signal generator 201 according to the prediction results of the at least two antenna fading factors.

FIG. 3 shows a working flowchart for implementing the method STSTD of the present invention.

When the base station wants to send data, first measure the fading factor on the common channel, that is, the quality of the channel (step S1); initially select the antenna for downlink transmission according to the measurement result, and use the selected antenna for the first downlink data transmission ( Step S2); the mobile station that has received the downlink data sent by the base station uploads the quality information of the used channel to the base station (step S3); the base station performs channel estimation based on the received uplink data, and calculates the channel The uplink fading factor (step S4); the base station predicts the downlink fading factor according to the uplink channel estimation result (step S5); the base station selects to send the downlink on the corresponding antenna according to the prediction result Data (step S6); repeating the steps S3 to S6 until all the downlink data has been sent (step S7).

Wherein, a dedicated pilot channel is used for channel estimation and demodulation on the downlink channel.

The following is a detailed description of the prediction algorithm used in the transmit diversity method of the present invention, the LMS (Leas t Mean Square) prediction algorithm. FIG. 4 shows the structure of a fading factor predictor 203 according to the present invention. As shown in FIG. 4, the fading factor predictor 203 mainly includes a device (not shown) for estimating an uplink fading factor, and an input filter 402, which is used to average the input signals, thereby improving the signal-to-noise ratio; the source filtering A device 403 is configured to predict an input source signal; and an LMS prediction and filtering device 404 is configured to perform LMS filtering on a result of the source prediction.

The fading factor predictor 203 first sends the estimated fading factor of the uplink channel into the input filter 402 as a training sequence, and the data output from the filter 402 is sent to the source predictor 403 for signal processing. The linear prediction of the source is then output to the LMS prediction and filtering device 404 to complete the prediction.

Referring to Figure 5, assuming fading factor predictor 203 on the right foot of the estimated channel fading factor X _t, Y _t to give the fading factor of the downlink channel predicted by LMS prediction and filtering means 404, and Y _t Approximation To the desired signal D _t .

In the embodiment of the present invention, a first-order LMS linear prediction algorithm is adopted, which is mainly implemented by using the following formula.

, ( 1 )

e '= ^D' - ^Y '(2)

iy, ₊₁ = ω _ι + 2με, Χ _ι (3)

Among them, X _t is the estimated fading factor in the uplink channel, Y _t is the predicted fading factor in the downlink channel, D _t is the desired value of the fading factor Y _t in the downlink channel, (^ is the 1 ^ 3 prediction and filtering means coefficients, [mu] is a gain factor, is the difference between the desired value of the fading factor Y _t D _t of the downlink channel fading factor of the downlink channel Y _t, X _t _i source is the output of predictor 403 ; P represents the order of the LMS prediction and filtering device, which consists of P shift registers, and therefore has P tap coefficients; t represents the time index of the signal sequence, and i represents the i-th tap coefficient.

In the above formula, if let "'be the inverse of the fading factor Y _t in the downlink channel. The fading factor Y _{t in} the downlink channel can be solved by iterating the above formulas (1), (2), and (3) . In addition, the present invention also proposes an improved method for the LMS algorithm, that is, an adaptive gain normalization and sequential regression algorithm (AGMSR).

The convergence speed of the LMS algorithm largely depends on the gain factor ^^. In order to adaptively adjust the gain factor ^ according to the speed of the channel fading, the inventor introduced the AGMSR algorithm. This method uses gain normalization to overcome non-stationarity in fast-fading channels.

The easiest way to normalize the variance is to normalize the gain factor using the variance of the input signal of the received LMS filter.

at this time

ω _{ι +} = ω, + 2μ (σ _χ ) e, X _t

Among them, a is the coefficient of the exponentially weighted filter. It depends on the application conditions. If the channel correlation is strong and the channel changes slowly, the value of a should be larger, otherwise it should be smaller. _T is the normalized gain factor. , 1 represents the time index of the input sequence, and ^2, represents the estimated variance value (Λ represents the estimated value, and the subscript t represents the variance is time-varying, that is, its value changes with time), σ _χ ² represents the stationary condition (That is, σ _χ ² does not change with time) ideal variance value, σ _χ , _t ² represents the ideal variance value under non-stationary conditions (that is, σ _χ ² changes with time).

In practice, take ,, + μ ₂ ·

Among them, μ ₂ is a constant.

FIG. 6 shows a flowchart of implementing an LMS prediction algorithm in the STSTD transmit diversity method of the present invention. In FIG. 6, steps S51 to S56 are detailed descriptions of step 5 in FIG. 3. Wherein, the uplink fading factor is calculated in step S4; then, the estimated fading factor of the uplink channel is first sent to the input filter 402 of the LMS fading factor predictor as a training sequence (step S5 1); from the input The data output from the filter 402 is sent to the source predictor 403 of the LMS (step S52); according to the output signal of the source predictor 403, the LMS predictor sets the initial values X ₀ , ω required for the iteration of the LMS prediction algorithm. , Μο (step 53); in step S54, iterative operation is performed according to the above formulas (1), (2), (3); in step S55, gain normalization is used to overcome the non-fading in the fast fading channel Stationarity; then, all prediction values in one subframe are accumulated as a basis for selecting a base station antenna (step S56).

Although the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to this. According to the method of the present invention, those skilled in the art can easily implement the present invention or improve it by other means. It should be known that Any improvement without departing from the idea of the invention is within the scope of the claims of the invention.

Claims

Claim

1. A transmit diversity method for a time division duplex communication system, comprising the following steps:

(S1) the base station of the time division duplex communication system measures a fading factor on a common channel; (S2) initially selects an antenna for downlink transmission according to the measurement result, and uses the selected antenna for the first downlink data transmission;

(S3) the mobile station that has received the downlink data sent by the base station uploads the quality information of the used channel and feeds it back to the base station;

(54) The base station performs channel estimation according to the received uplink data, and calculates a fade factor of the uplink;

It is characterized in that the transmission diversity method further includes the following steps:

(55) The base station predicts a downlink fading factor according to an uplink channel estimation result;

(56) The base station selects to send downlink data on a corresponding antenna according to the prediction result; and repeats the steps (S3) to (S6) until all downlink data is completely sent.

2. The transmit diversity method for a time division worker communication system according to claim 1, characterized in that a dedicated pilot channel is used for channel estimation and demodulation on its downlink channel.

3. The transmit diversity method for a time division silent communication system according to claim 1, wherein the step (S5) is implemented by the following first-order LMS linear prediction method:

Y, = ∑ ^ X

,. = ο, —,, (1)

( 2 )

Among them, Xt is the estimated fading factor in the uplink channel, Yt is the predicted fading factor in the downlink channel, Dt is the desired value of the fading factor Yt in the downlink channel, ot is the coefficient of the LMS prediction and filtering device, μ is Gain factor, ^e 'is the desired value Dt of the fading factor Yt in the downlink channel And the fading factor Yt in the downlink channel, Xt-i is the output of the source predictor (403), P is the order of the LMS predictor, t is the time index of the signal sequence, i is the first i tap coefficients. '

Let ^ '= 1, then "' is the reciprocal of the fading factor Yt in the downlink channel. The fading factor Yt in the downlink channel is solved by iterating the above formulas (1), (2), and (3).

4. The transmit diversity method for a time-division duplex communication system according to claim 1, characterized in that the gain factor ^ is normalized by using the following formula,

at this time

take

Where a is the coefficient of the exponentially weighted filter, μ 2 is a constant, indicating the normalized gain due to, 1 is the time index of the input sequence, and ' ² is the estimated variance value (Λ represents the estimated value, the The standard t indicates that the variance is time-varying, that is, its value changes with time), σ χ2 represents the ideal variance value under stationary conditions (that is, σ χ2 does not change with time), and σ χ, t2 represents non-stationary conditions (that is, σ χ2 Variance over time) Ideal variance value.

5. The transmit diversity method for a time division duplex communication system according to any one of claims 1-4, wherein the logical channel between the base station and the mobile station is divided into the uplink dedicated guide Frequency channel, uplink dedicated data channel, downlink dedicated pilot channel, and downlink dedicated data channel.

6. The transmit diversity method for a time division duplex communication system according to any one of claims 1-4, wherein the step (S5) further comprises fading within the length of the next 3 sub-frames. Factors to make predictions.

7. The transmit diversity method for a time division duplex communication system according to any one of claims 1-4, wherein in the step (S6), selecting an antenna having a larger fading factor value The data is sent out.

8. A transmission diversity device for a time division Chinese laborer communication system, comprising:

A base station receiver (204), configured to receive uplink data, despread, demodulate, and perform channel estimation on the received data;

At least two antennas (102; 103);

A downlink signal generator (201), configured to complete transmission of a service signal and a pilot signal;

It is characterized in that the transmission diversity device further includes:

A fading factor predictor (203), configured to estimate a fading factor of an uplink and predict a fading factor of a downlink corresponding to each of the antennas;

An antenna selector (202) selects an antenna with a larger fading factor from the downlink signal generator (201) according to a downlink fading factor predicted by the fading factor predictor (203). The received data to be sent is sent out.

9. The transmission diversity device for a time division duplex communication system according to claim 8, characterized in that a dedicated pilot channel is used for channel estimation and demodulation in a downlink channel thereof.

The transmission diversity device for a time division duplex communication system according to claim 8 or 9, wherein the fading factor predictor (203) predicts a fading factor of a downlink by using the following equation:

D ' ^-Y ' (2)

_{ω, + ι = ω, +} 2μβ ι Χ ί (3)

Among them, Xt is the estimated fading factor in the uplink channel, Yt is the predicted fading factor in the downlink channel, Dt is the desired value of the fading factor Yt in the downlink channel, and co t is the coefficient of the LMS prediction and filtering device, μ Is the gain factor, ^e <is the desired value of the fading factor Yt in the downlink channel Dt And the fading factor Yt in the downlink channel, Xt-i is the output of the source predictor (403), P represents the order of the LMS predictor, t represents the time index of the signal sequence, and i represents I-th tap coefficient.

Let "" be the reciprocal of the fading factor Yt in the downlink channel. The fading factor Yt in the downlink channel is solved by iterating the above formulas (1), (2), and (3).

11. The transmit diversity device for a time division duplex communication system according to claim 8 or 9, wherein the fading factor predictor (203) normalizes the gain factor ^ by the following formula, σ _χ

at this time

. 2 1- α

σ ,, =

la, = ^μ , where a is the coefficient of the exponentially weighted filter, μ2 is a constant, which represents the normalized gain factor, 1 is the time index of the input sequence, and ^. ' ² is the estimated variance value, σχ2 Represents the ideal variance value under stationary conditions, and σχ, t2 represents the ideal variance value under non-stationary Naiware.

12. The transmit diversity device for a time division duplex communication system according to claim 8 or 9, wherein the fading factor predictor (203) comprises an input filter (402) for inputting signals Performing averaging to improve the signal-to-noise ratio; a source filter (403) for predicting an input source signal; and an LMS prediction and filtering device (404) for performing LMS filtering on a result of the source prediction.