WO2004062132A1

WO2004062132A1 - A method and system for adaptive space-time closed-loop transmit diversity

Info

Publication number: WO2004062132A1
Application number: PCT/CN2004/000002
Authority: WO
Inventors: Aijun Cao; Branislav M. Popovic; Mattias WENNSTRÖM
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2003-01-03
Filing date: 2004-01-02
Publication date: 2004-07-22
Also published as: CN1516370A; CN100454795C

Abstract

The present invention discloses a method and system for adaptive space-time closed-loop transmit diversity. In each time slot, the symbols to be transmitted make space-time coding and output two signals; sending to two groups of antennas after amplifying the signals, respectively, and sending the two signals to a mobile terminal, then the mobile terminal estimates the each-path signals from each antenna, and computing the power of the first group antenna and the second group antenna and comparing them so as to obtain FBI bits, and transmitting them to the base station over uplink channel, then the base station will storage the FBI bits In the delay line; retrieving power ratio from the FBI bits. In the delay line; computing the weighting of transmit power of the first group antenna and the second group antenna according to the power ratio, and adjusting the transmit power of the two antennas. The disclose of the present Invention may adjust the transmit power of the two groups of transmit antennas adaptively, and having more diversity gain comparing with open-loop way.

Description

Method and system for adaptive space-time closed-loop transmit diversity

The present invention relates to space-time transmission diversity technology, and in particular, to a space-time transmission diversity method and device for adjusting signal transmission power in an adaptive manner in real time. Background of the invention

In the third generation (3G, Third Generation) mobile communication system based on the code division multiple access (CDMA) method, a wideband CDMA (WCDMA, Wideband CDMA) system, because different users in the same cell and neighboring cells Different users share the same frequency band at the same time, so users have interference with each other, and these interferences limit system capacity and information transmission rate. In order to increase the system capacity, multiple diversity methods can be used, such as multipath diversity, space diversity, and antenna diversity. In a system using diversity technology, there are multiple independent copies of the same information content. After these independent copies are received by the receiver, according to the Maximum Likelihood (ML) principle, the redundant characteristics of the information are fully utilized. By adding certain special processing, the bit error rate of transmitted information can be greatly reduced, and the energy required for wireless data transmission is reduced, thereby reducing mutual interference between users. It can be seen that diversity technology can effectively increase system capacity.

The development of semiconductor technology has made it possible to integrate more than two antennas with transmit diversity; as the number of transmit antennas increases, the obtained diversity gain is greater. In the existing CDMA standard, four-antenna transmit diversity mainly includes an open-loop space-time transmit diversity method (Open-loop STTD). In this transmit diversity method, due to the lack of information on the current wireless channel, two sets of transmit antennas are always The transmission is performed in the same power manner, and the time-varying wireless channel cannot be adaptively adjusted, so there is a certain performance loss. Summary of the Invention

In order to solve the above problem, the present invention aims to propose an adaptive space-time closed-loop transmit diversity method, which can adaptively adjust the transmit power of two sets of transmit antennas and improve the diversity gain. Another object of the present invention is to provide a system for implementing the above-mentioned adaptive space-time closed-loop transmit diversity method.

To achieve the above objective, the technical solution of the present invention is as follows:

An adaptive space-time closed-loop transmit diversity method. In each time slot, the method includes the following steps: a. The base station performs space-time coding on symbols to be transmitted and outputs two signals;

b. The two signals are amplified and sent to two groups of antennas. Each group of antennas consists of two antennas. The two antennas in the first group and the second group of antennas send the two signals to the mobile with a fixed phase difference. Terminal, and the two groups of antennas keep the same time difference;

c. The mobile terminal estimates the signals from each antenna and obtains the composite channel responses corresponding to the two antennas;

d. Calculate and compare the power of the first group of antennas and the second group of antennas based on the composite channel response, and determine whether the power of the first group of antennas is greater than the power of the second group of antennas. If so, the feedback signal (FBI) bit is 1 Otherwise, the FBI bit is 0;

e. The FBI bits are transmitted to the base station through the uplink channel, and the base station stores at least one FBI bit recently received in the delay line;

f. According to the predetermined mapping relationship between the FBI bits and the power ratio, the FBI bits stored in the delay line in step e are restored to the success ratio ratio;

g. Calculate the weights of the transmit power of the first group of antennas and the second set of antennas according to the power ratio recovered in step f, and adjust the transmit powers of the two antennas.

In the above solution, step a further includes: coding the symbols to be transmitted according to every two symbols as a unit block, outputting two signals, one of which is the same as the input symbol, and the other of which is the reverse order of the conjugate of the input symbol and the first symbol is inverted .

In step b, the amplification factors used for the two sets of signal amplification are both 1; the difference between the fixed phases is large. The following formula is used to obtain the composite channel response corresponding to two groups of antennas as described in step c:

Where is the composite channel response corresponding to the first group of antennas, β is the composite channel response corresponding to the second group of antennas,: is the number of paths transmitted by the wireless channel, / ¾ ₁ and / _k are the wireless channel responses of each path of the first group of antennas, A _3k and / z _4k are the wireless channel responses of each diameter of the second group of antennas, φ and ψ are fixed phase differences, and j is the symbol of the imaginary part.

The calculation of the power of the first group of antennas and the second group of antennas described in step d uses the following formula:, where is the power of the first group of antennas, and P ₂ is the power of the second group of antennas.

The weights for calculating the transmit power of the first and second antennas in step g are as follows:

Wherein the weight _Wl transmission power of a first group of antenna weight, transmit weight w ₂ of the second power of the antenna weight group, R is the power ratio.

An adaptive space-time closed-loop transmit diversity system includes: a space-time coding module located at a base station, two antenna groups consisting of two antennas, an FBI decoder, a channel estimation module located at a mobile terminal, and an FBI encoder; The time encoding module encodes the symbols to be transmitted, the output signal is sent to the mobile terminal through the antenna group, the channel estimation module estimates the signals of each path, the encoder calculates the power of the two groups of antennas and compares them, and outputs FBI bits Sending to the decoder through an uplink channel, and the decoder obtains weights of the transmit powers of the two groups of antennas, and adjusts the transmit powers of the two groups of antennas.

The decoder further includes a delay line module, a power ratio generator, and a weight calculator, and FBI bits are stored in the delay line module. The power ratio generator obtains FBI bits from the delay line module, and recovers the address. The power ratio is sent to the weight calculator, and the weight calculator outputs an antenna transmission power weight. The delay line module includes no less than 1 storage unit, and is configured to store the latest transmission unit. Coming FBI bits.

By adopting the present invention, since no less than one FBI bit can be obtained in real time, without increasing the processing delay, the quantization accuracy can be improved, and the transmit power of the antenna group can be adaptively adjusted, thereby improving the adaptive space-time transmit diversity system. Performance. Brief description of the drawings

FIG. 1 is a schematic structural diagram of an adaptive space-time transmit diversity system according to the present invention;

FIG. 2 is a schematic diagram showing a phase difference between two antennas of the present invention;

3 is a flowchart of generating FBI bits according to the present invention;

4 is a schematic structural diagram of an FBI decoding device according to the present invention;

FIG. 5 is a schematic diagram of the diversity performance comparison between the present invention and an open-loop STTD. Mode of Carrying Out the Invention

The present invention will be described in further detail below with reference to the drawings and specific embodiments.

Figure 1 shows the adaptive space-time closed-loop transmit diversity scheme of the present invention.

First, the symbols to be transmitted are space-time encoded by the space-time encoding module 101 according to the following rules. The input symbols are encoded every 2 symbols (, for the unit block, and two signals are output: one remains the same as the input block (, S ₂ ), The other is the reverse order of the input conjugate, and the first output sign is inverted, that is, output (-S ;, s;). The two outputs are amplified and sent to two sets of antennas, where antennas Aa and Ab constitute The first group of antennas, antennas Ac and Ad constitute the second group of antennas. Amplification factors; and 1 according to existing standards; In the first group of antennas, the phase difference p between the antennas Aa and Ab is determined by the existing standards as π, and each phase difference value maintains at least two symbols; also in the second group of antennas, the phase difference between the antennas Ac and Ad ^ is also determined by existing standards as π, and each phase difference holding time is the same as the first The group antennas are the same. As shown in FIG. 2, FIG. 2 is a correspondence relationship between the phase difference ρ of the first group of antennas and the phase difference ^ of the second group of antennas.

Then, in the receiver of the mobile terminal, the corresponding feedback signal is generated according to the following method: The channel estimation module 102 estimates each multipath signal k _lk , h _2k , h _2k and A _4k from each antenna, and And calculate the two "composite" channel responses according to the following formula:

The two-path composite response is input into the FBI encoder 103, and the encoding process shown in FIG. 3 is performed: the received power of, then the output

The FBI bit is 1, otherwise the output FBI bit is 0. This process is performed every time slot. After the FBI bits are transmitted on the uplink channel, they are sent to the base station, which is collected and processed by the base station, and the transmit power weight of each antenna is determined accordingly.

Then, the FBI bits received by the base station are processed by the FBI decoder 104. Figure 4 shows the FBI bit decoding process: After receiving the FBI bits, the base station stores the most recent FBI bits into the delay line 105. L in Figure 4 Represents the length of a delay line, and the delay line module 201 includes at least one storage unit for storing a recently received FBI bit.

After that, the power ratio generator 202 obtains the FBI bits from the delay line module 201, and according to the latest FBI bits of the L bits and the predetermined mapping relationship, the power ratio generator 106 recovers the power ratio R, Table 1, Table 2, Table 3 gives the mapping relationship between the FBI bits and the power ratio R at L = 1, 2, and 3. The mapping relationship between each FBI bit combination shown in the table and the transmit power ratio of the antenna is preset. Among them, Table 1 is a mapping table of the delay line length L = 1, Table 2 is a mapping table of the delay line length L = 2, and Table 3 is a mapping table of the delay line length L = 3;

FBI (k) FBI (k-1) Radio (dB) 1 0 0

0 1 0

0 0 -6

Table III

Finally, the power ratio generator 202 sends the recovered power ratio R to the weight calculator 107. After receiving the power ratio R, the weight calculator 107 calculates and outputs the weight wl of the transmission power of the two transmitting antennas according to formula (1). And w2:

After calculating the weights wl and w2, the transmit powers of the two sets of transmitting antennas are adjusted according to the currently obtained wl and w2.

By adopting the present invention, on the premise of maintaining compatibility with the existing protocol, the transmission power of two sets of transmitting antennas is adaptively adjusted according to the information about the current wireless channel fed back. Compared with the open loop method, Set gain is greater. Fig. 5 shows the comparison between the performance of the present invention and the four-antenna open-loop STTD transmit diversity after computer simulation, where the abscissa is the speed, the unit is km / h, and the ordinate is the decibel of the signal-to-noise ratio (Eb / No) ( dB) number; taking abscissa = 20 as a reference, the first curve from top to bottom is the performance curve of transmit diversity in the case of 2ANT-STTD PC1, DS1, ER4; the second curve is in the case of 4ANT-STTDPC1, DS1, ER4 The performance curve of the transmit diversity under the third; the third curve is the performance curve of the transmit diversity under 2ANT-ASTTDPC1, DS1, ER4; the fourth curve is the performance curve of the transmit diversity under 4ANT-ASTTDPC1, DS1, ER4. It can be seen that the performance of the ASTTD after applying the present invention is better than the existing open-loop STTD transmit diversity performance at different speeds.

The above description is only the preferred embodiments of the present invention, and is not intended to limit the protection scope of the present invention.

Claims

Claim

1. An adaptive space-time closed-loop transmit diversity method, characterized in that, in each time slot, the method includes the following steps:

a. The base station performs space-time coding on the symbols to be transmitted and outputs two signals;

b. The two signals are amplified and sent to two groups of antennas. Each group of antennas consists of two antennas. The two antennas in the first group and the second group of antennas send the two signals to the mobile with a fixed phase difference Terminal, and the two groups of antennas keep the same time difference;

d. Calculate and compare the power of the first group of antennas and the second group of antennas according to the composite channel response, and determine whether the power of the first group of antennas is greater than the power of the second group of antennas. If so, the feedback signal (FBI) bit is 1, Otherwise the FBI bit is 0;

f. According to the predetermined mapping relationship between the FBI bits and the power ratio, restore the success ratio ratio of the FBI bits stored in the delay line in step e;

2. The adaptive space-time closed-loop transmit diversity method according to claim 1, wherein step a further comprises: encoding the symbols to be transmitted according to every two symbols as a unit block, outputting two signals, one input and The symbols are the same, the other is the reverse order of the conjugate of the input symbols and the first symbol is inverted.

3. The adaptive space-time closed-loop transmit diversity method according to claim 1, characterized in that: the amplification factor used for the two sets of signal amplification in step b is 1.

4. The adaptive space-time closed-loop transmit diversity method according to claim 1, wherein the fixed phase difference in step b is π.

5. The adaptive space-time closed-loop transmit diversity method according to claim 1, wherein: In C, the composite channel responses corresponding to the two groups of antennas are obtained according to the following formula:

Where α is the composite channel response corresponding to the first group of antennas, β is the composite channel response corresponding to the second group of antennas, is the number of paths transmitted by the wireless channel, and / and / _i2k are the wireless channel responses of each path of the first group of antennas, A _3k And ^ are the responses of the wireless channels of the second group of antenna diameters, φ and ψ are fixed phase differences, and j is the symbol of the imaginary part.

6. The adaptive space-time closed-loop transmit diversity method according to claim 1, wherein the calculation of the power of the first group antenna and the second group antenna in step d is based on the following formula: Pf l ^ f, p ₂ = ∑ |?, | ² , where? !! Is the power of the first group of antennas, and ρ ₂ is the power of the second group of antennas,

7. The adaptive space-time closed-loop transmit diversity method according to claim 1, characterized in that: in step _g , the weights for calculating the transmit power of the first group of antennas and the second group of antennas adopt the following formula:

8. An adaptive space-time closed-loop transmit diversity system, comprising: a space-time coding module located at a base station, two antenna groups consisting of two antennas, an FBI decoder, a channel estimation module located at a mobile terminal, and an FBI An encoder; the space-time encoding module encodes a symbol to be transmitted, an output signal is sent to a mobile terminal through the antenna group, the channel estimation module estimates signals of each path, and the encoder calculates the power of two groups of antennas and In comparison, the FBI bit is output, and the decoder is obtained by using an uplink channel to send the weight to the decoder, and the decoder obtains a weight of the transmit power of the two groups of antennas, and adjusts the transmit power of the two groups of antennas.

9. The adaptive space-time closed-loop transmit diversity system according to claim 8, wherein the decoder further comprises a delay line module, a power ratio generator, a weight calculator, and FBI bits are stored in the delay line module. The power ratio generator obtains FBI bits from the delay line module, recovers the power ratio and sends the weight ratio calculator to the weight calculator, and the weight calculator outputs an antenna transmission power weight.

10. The adaptive space-time closed-loop transmit diversity system according to claim 8, wherein the delay line module includes no less than one storage unit for storing recently sent FBI bits.