WO2007000745A1

WO2007000745A1 - A method and apparatus for spatial channel decoding

Info

Publication number: WO2007000745A1
Application number: PCT/IB2006/052145
Authority: WO
Inventors: Gang Wu
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-06-29
Filing date: 2006-06-28
Publication date: 2007-01-04

Abstract

In the present invention, a spatial channel decoding method and apparatus thereof are proposed. This method comprises the steps of: (a) performing inverse spatial channel code (SCC) encoding process on a received SCC signal to obtain an inverse SCC encoded signal; (b) performing SCC encoding process on the inverse SCC encoded signal to obtain a SCC re-encoded signal; (c) calculating error between the received SCC signal and the SCC re-encoded signal; and (d) obtaining corresponding decoded signal based on the inverse SCC encoded signal and the error, according to the measured channel quality. By using this method and apparatus, the complexity of the spatial channel decoding can be reduced while a better system performance is kept.

Description

A METHOD AND APPARATUS FOR SPATIAL CHANNEL DECODING

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for decoding in wireless communication system, and more particularly, to a method and apparatus for spatial channel decoding.

BACKGROUND OF THE INVENTION

As the mobile communication is becoming popular, voice centric mobile communication cannot meet the use's demanding for information. However, mobile data communication has a promising future for it could provide various kinds of contents for office and entrainment conveniently. Therefore, High Speed Downlink Packet Access (HSDPA), which can support high speed data transmission, especially provide the downlink from a base-station to a user equipment, has become one of the main goals for future wireless communication system.

However, as the development of wireless communication, resources, such as spectra, time slot and spreading code, are becoming limited for the traditional communication system. In order to increase the data rate further more, one method is to utilize spatial resource reasonably. Recently, Multiple Input Multiple Output (MIMO) technology is introduced. MIMO utilizes multiple transmit and receive antennas to construct multiple parallel wireless channels in space so as to increase the system's data transmission rate by utilizing the spatial resource sufficiently. In existing MIMO technologies, Bell Lab Layered Space Time (BLAST) technology, which comes from Bell Lab, is one of the typical MEVIO technologies and it can increase the data rate greatly. Recently, besides BLAST technology, other MIMO technologies using in 3GPP system are introduced, such as Per Antenna Rate Control (PARC), Rate Control Multipath Diversity (RC MPD) and Double Space Time Transmit Diversity - Sub-Group Rate Control (DSTTD-SGRC), etc.

A MIMO scheme is described in the patent application Serial No. 200410056552.0, entitled "Method and Apparatus for Spatial Channel Encoding/Decoding in Multi-channel

Parallel Transmission" filed by KONINKLIJKE PHILIPS ELECTRONICS N. V. on Aug. 9, 2004, which is incorporated here by reference. According to the Spatial Channel Coding (SCC) method provided by this patent application, the channel coding is combined with multi-channel parallel architecture, by adding some redundant information into multi-channel parallel signals, so that there is spatial correlation between multi-channel parallel signals, which helps the UE at the receiving side to demodulate the multi-channel parallel signals. By using such a method, the UE can realize high speed data transmission even with single or limited receive antennas.

Fig.l shows the block diagram of the architecture for the transmitter (such as base station) and the receiver (such as UE) adopting the spatial channel coding method proposed in accordance with above patent application. In transmitter 500, the data to be transmitted is first fed into SCC architecture 510 for SCC encoding and transferred into multi-channel parallel coded signals. Then, the coded signal from each parallel channel is interleaved in interleaving unit 102, spread by orthogonal variable spreading frequency (OVSF) code in OVSF spreading unit 103, scrambled in scrambling unit 104, added with signals from multiple code channels in multiplexer unit 105, then the overlapped signals are pulse shaped in pulse shaping unit 106 and modulated into multi-channel RF signals in radio frequency (RF) unit 107. Finally the signals are transmitted into the space through multiple transmit antennas.

Multi-channel parallel RF signals arrive at the receiver 600 of UE via wireless channel. Fig.l illustrates the case that receiver 600 has only one receive antenna. The signals received by this receive antenna are the superimposition of all paths of signals transmitted via multiple parallel spatial channels. The multi-channel RF signals received from this receive antenna are transformed into baseband signals in RF unit 208 and send into RRC filter and over- sampling unit 206, so that the analog signals are converted into discrete signals. Then, the discrete signals are sent into SCC decoding architecture 610, after being de-spread in de-spreading and detecting unit 204 and de-interleaved in de-interleaving unit 202. While, the channel characteristics of multiple parallel spatial channels are estimated according to the received pilot signal in channel estimation unit 220. Next, SCC decoding architecture 610 utilizes the channel characteristics of multiple channels estimated by channel estimation unit 220 to perform Soft Decision Space-Time Viterbi Decode on the de-interleaved superimposed signals according to the SCC encode architecture 510 adopted by transmitter 500. In this way, the added multi-channel parallel signals are decoded and transformed into single-channel serial data, which are the user data.

When only a single receive antenna is used, the performance of SCC technology is better than that of other MIMO technologies. But the complexity of space-time Viterbi soft decoding, which is implemented in the SCC decoding architecture 610 at the receiver, exponentially increases as the number of transmit antennas increases. This will bring very heavy burden for the baseband signal processing at the receiver and block the further application of SCC technology in UE.

Therefore, it is necessary to introduce a better SCC decoding solution in SCC communication system, so as to decrease the decoding complexity at UE side and keep better decoding performance at the same time.

OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatus for SCC decoding, with which the decoding complexity at UE side can be reduced.

A spatial channel decoding method according to the present invention comprises the steps of: (a) performing inverse spatial channel code (SCC) encoding process on received SCC signal to obtain inverse SCC encoded signal;

(b) performing SCC re-encoding process on the inverse SCC encoded signal to obtain SCC re-encoded signal;

(c) calculating error between the received SCC signal and SCC re-encoded signal; and (d) obtaining corresponding decoded signal based on the inverse SCC encoded signal and the error, according to the measured channel quality.

A spatial channel decoder according to the present invention comprises: a inverse encoding apparatus for performing inverse spatial channel code (SCC) encoding on received SCC signal to obtain inverse SCC encoded signal; a re-encoding apparatus for performing SCC re-encoding process on the inverse SCC encoded signal output from the inverse encoding apparatus to obtain SCC re-encoded signal; an error calculating apparatus for calculating error between the received SCC signal and the SCC re-encoded signal; and an output apparatus for outputting corresponding decoded signal based on the inverse SCC encoded signal and the error, according to the measured channel quality. Especially when the system channel quality is good, the structure of SCC decoding solution provided by the present invention is simpler than that of the pure space-time Viterbi decode solution, and the decoding complexity can be reduced greatly under the condition of keeping the system performance,. Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:

Fig. l is a block diagram of the structure of the transmitter and receiver adopting SCC encoding/decoding technology, in which the transmitter has multiple transmit antenna and the receiver has only one receive antenna;

Fig.2 is the flow chart for the SCC decoding method of the present invention; Fig. 3 is a block diagram of the SCC architecture according to the SCC decoding method of the present invention;

Fig.4 is a block diagram of the SCC re-encoding architecture according to an embodiment of present invention in Fig.3;

Fig.5 a block diagram of the SCC inverse encoding architecture according to an embodiment of present invention in Fig.3;

Fig.6 is a graph of FER (Frame Error Rate) varying with SNR (Signal to Noise Ratio) of received signal measured in simulation; and Fig.7 is a graph of saved decoding complexity varying with SNR in the case of adopting the SCC decoding method of the present invention.

Through all drawings, the same reference numbers indicates similar or corresponding characteristics or function.

DETAILED DESCRIPTION OF THE INVENTION

Different from for the soft decision space-time Viterbi decoding method adopted in SCC decoding architecture 610 in No. 200410056552.0 Chinese patent application, the SCC decoding method according to the present invention utilizes Inverse Spatial Channel Code (Inverse SCC) technology to encode the received signal when channel quality is good. This method is also called Pre-Processing SCC Decode (PPSD), and the details are shown in Fig.2.

Fig.2 is the flow chart of PPSD method provided by the present invention. First, the serial/parallel conversion is performed on the signal r received by the receiver, which is to be decoded, so that the received signal is converted into multi-channel parallel signals (Step SlO);

Next, the inverse SCC encoding is performed on the multi-channel parallel signals (Step SIl). The detailed description for this inverse SCC encoding method will be given later in conjunction with Fig.4 and Fig.5;

After being inverse SCC encoded, the multi-channel parallel signals are added in modulus 2 so as to obtain signal s (Step S 12), wherein signal s includes the original data signal I and the system noise n at the transmitter side, i.e. s = I + n.

Serial/parallel conversion is implemented for signal s (Step S 13) so that the corresponding multi-channel parallel signals are obtained;

The multi-channel parallel signals obtained in Step S 13 are SCC re-encoded to obtain signal r ' (Step S 14);

The difference between the signal r, which is serial/parallel converted and to be encoded, and signal r ' is calculated. And the calculated result is parallel/serial converted to obtain an error signal e (Step S 16).

A variation of the error signal e (i.e. the difference between each error signal e) is calculated to obtain the variation ev_ar of e (Step S 17);

The variation eva_r of e is compared with a pre-defined threshold T_g (Step S 18);

If ev_ar>T_g» it indicates that system noise exceeds an acceptable range of the receiver at that time. Then space-time Viterbi decoding method is used to decode the error signal e.

The result of decoding is added with signal s in modulus 2 so as to obtain final decoded signal (Step S 19);

If eva_r ≤ T_g, it indicates that system noise is within an acceptable range of the receiver, in other word, the SNR (signal to noise ratio) meets certain requirement at that time. Then signal s is output directly as the final decoded signal (Step S20).

Fig. 3 is a block diagram of a PPSD decoding structure of present invention designed according to the PPSD method shown in Fig.2. The received signal r to be decoded is serial/parallel converted into multi-channel parallel signals in the first serial/parallel conversion unit 601. Then, in inverse SCC encoding unit 602, the inverse SCC encoding process is performed on the multi-channel parallel signals output from the first serial/parallel conversion unit 601.

Afterwards, the multi-channel parallel signals output from the inverse SCC encoding unit 602, which is inverse SCC encoded, are added in modulus 2 in first summing unit 604, so as to obtain signal s.

The signal s is serial/parallel converted again in second serial/parallel conversion unit 605, so as to obtain the corresponding multi-channel parallel signals. The multi-channel parallel signals output from the second serial/parallel conversion unit 605 are SCC re-encoded in SCC re-encoding unit 606, so as to obtain signal r '.

The output signal r of first serial/parallel conversion unit 601, which has been serial/parallel converted and to be decoded, is delayed by D register 603 and fed into error signal calculating unit 607. Then the difference between the signal r and the signal r' from SCC re-encoding unit 606 is calculated in the error signal calculating unit 607.

The output result of the error signal calculating unit 607 is parallel/serial converted in the parallel/serial conversion unit 608, so as to obtain error signal e.

Error signal e is sent into evar calculation control unit 609 to calculated the variation of the error signal e, so that the variation e_Var of the error signal e is calculated. The e_Var calculation control unit 609 can also be used to compare the variation e_Var with a predefined threshold T_g.

If eva_r calculation control unit 609 judges eva_r>T_g, eva_r calculation control unit 609 makes the control switch 611 to connect with space-time Viterbi decoder 612, so that error signal e is processed by using the space -time Viterbi decoding method in the space-time Viterbi decoder 612. The decoded result and the signal s are added in modulus 2 in the second summation unit 613, so as to output the final decoded signal.

If evar calculation control unit 609 judges evar≤ T_g, evar calculation control unit 609 makes space-time Viterbi decoder 612 not work anymore. The second summation unit 613 outputs signal s as the final decoded signal.

In conjunction with Fig.4 and Fig.5, one simple example is given to describe the encode structure and encode method of above inverse SCC encoding unit 602 and SCC re-encoding unit 606 in detail.

Assumed that the transmitter adopted SCC has two transmit antennas, BPSK modulation scheme and the number of input bits for SCC encoding is 1. According to above settings, a SCC structure, under the condition that two transmit antenna and one receive antenna are used, is formed as shown in Fig.4. As shown in Fig.4, serial data bit bl is shifted into the registers of four parallel encoding branches, each of which has nine D registers. Each processing branch implements the encoding process according to the predefined encoding rules. For example, the generated code Go of the first channel encoding branch is 111110111 and the generated code Gi of the second channel encoding branch is 100100010, wherein each bit of the generated code is corresponding to one D register. The detailed encoding process is that: in each branch, the bit status stored in each register, of which the corresponding bit of the generated code is 1, is extracted and added in modulus 2, so that the encoded bit signal is obtained; then, the encoded bits of the first and second branches are combined and processed by BPSK mapping unit 621, so that the symbol CiC₂ to be transmitted via the first antenna is obtained. In a similar way, the encoded bits of the third and fourth branches are processed by BPSK mapping unit 622, so that the symbol C3C₄ to be transmitted via the second antenna is obtained. Thus, according to the structure shown in Fig.4, a single-channel serial data are coded and mapped into two-channel parallel signals being channel encoded and the obtained two-channel parallel signals are spatially correlated with each other.

The code generation matrix G of SCC encoding structure in Fig.4 is shown as equation (1):

The code generation matrix G^" of the inverse SCC encoding structure corresponding to the above code generation matrix G is:

Similar with the SCC code structure designed in Fig.4, the inverse SCC encoding structure is designed according to the code generation matrix G^"1, as shown in Fig.5. The received signal is processed by BPSK de-mapping unit 620 and sent into the D registers of each encoding branch respectively, wherein each bit of the code generation matrix G^" is corresponding to one D register. The bit status stored in each D register, of which the corresponding bit is 1, is extracted and added in modulus 2, so that the encoded bit signal is obtained. Fig.5 is corresponding to one embodied structure for the dashed part of Fig.3 (including SCC encoding unit 602, the first serial/parallel conversion unit 601 and the first summation unit 604).

The structure of SCC re-encoding unit 606 in Fig.3 is same as the SCC encoding structure in transmitter. Therefore, Fig.4 can be treated as one embodied structure corresponding to SCC re-encoding unit 606.

Above, it is only described the case that transmitter has two transmit antennas and receiver has one receive antenna. Certainly, the present patent is not limited to this. It can also be used in the case where more transmit antennas can be used, or the receiver has more receive antennas.

Since inverse SCC encoding structure and SCC re-encoding structure, which are adopted in PPSD technology solution provided by present patent, are more simpler than the conventional space-time Viterbi decoding structure, the decoding complexity is decreased greatly under the condition that system performance is kept unchanged, when the SCC decoding structure of present invention is compared with the one adopted conventional space-time Viterbi decoding structure, especially when system's SNR is higher (i.e. eva_r≤T_g). This will be approved in the following simulation experiment.

This experiment is based on the assumption that transmission channel is quasi-static flat fading channel, the number of bits is 130 in each data frame during data transmission and setting T_g=0.1. Other parameters of the simulation experiment is set according to 3GPP

UMTS FDD standard.

The simulation experiment is implemented under above condition to test the performance of FER (frame error rate) varying with SNR, and the simulation result is shown in Fig.6 Fig.6 is the graphs for the FER of received signal varying with SNR, in the case that

PPSD decoding solution of present invention and the SCC decoding solution with space-time Viterbi decoding are adopted respectively. In the figure, the abscissa is SNR of the received signal and ordinate is FER. From fig.6, it can be seen easily that the performance is nearly same for the two decoding solutions. In order to show the advantages of PPSD decoding solution of present invention further more, following equation (3) is used to measure the saved complexity of PPSD decode solution:

Saved complexity = Time of PPSD/Time of SCC ( 3 ) According to equation (3), the graph of saved decode complexity varying with SNR is shown in Fig.7. It can be seen that the higher the system's SNR is, the more the saved decode complexity of PPSD decoding solution is.

It should be understood for those skilled in the art that the method and apparatus of spatial channel code disclosed in above invention can be modified or improved without departing from the content of present invention. Therefore, the scope of the present invention should be determined by the appended claims.

Claims

CLAIMS:

1. A spatial channel decoding method, comprising the steps of:

(a) performing inverse spatial channel code (SCC)encoding process on a received SCC signal to obtain an inverse SCC encoded signal;

(b) performing SCC re-encoding process on the inverse SCC encoded signal to obtain a SCC re-encoded signal;

(c) calculating an error between the received SCC signal and the SCC re-encoded signal; and (d) obtaining a corresponding decoded signal based on the inverse SCC encoded signal and the error, according to the measured channel quality.

2. The method of claim 1, wherein the step (c) comprises a step of: (cl) calculating a variation of the error.

3. The method of claim 2, wherein the step (d) comprises a step of:

(dl) outputting the inverse SCC encoded signal as a decoded signal, when the variation of the error is less than a predefined threshold.

4. The method of claim 2, wherein the step (d) comprises the steps of:

(d2) performing space-time Viterbi decoding process on the error to obtain error decoded signal, when the variation of the error is greater than the predefined threshold,; and

(d3) adding the error decoded signal and the inverse SCC encoded signal in modulus 2 to obtain a decoded signal.

5. The method of claim 3 or 4, wherein, in step (a), the SCC signal is transmitted through a plurality of transmit antennas and received by at least one receive antenna.

6. The method of claim 3 or 4, comprising a step of:

performing delay process on the received SCC signal, so as to calculate the error and the variation of the error between the received SCC signal and the SCC re-encoded signal in step (c).

7. A spatial channel decoder, comprising: an inverse encoding means for performing inverse spatial channel code (SCC) encoding on a received SCC signal to obtain an inverse SCC encoded signal; a re-encoding means for performing SCC re-encoding process on the inverse SCC encoded signal output from the inverse encoding means to obtain a SCC re-encoded signal; an error calculating means for calculating error between the received SCC signal and the SCC re-encoded signal; and an output means for outputting a corresponding decoded signal based on the inverse

SCC encoded signal and the error, according to the measured channel quality.

8. The spatial channel decoder of claim 7, comprising: a control means for calculating a variation of the error.

9. The spatial channel decoder of claim 8, wherein the output means outputs the inverse SCC encoded signal as the decoded signal when the variation of the error is not greater than a predefined threshold.

10. The spatial channel decoder of claim 8, further comprising: a Viterbi decoding means for performing space-time Viterbi decoding process on the error to obtain an error decoded signal when the variation of the error is greater than the predefined threshold; and the output means is further used for adding the error decoded signal and the inverse SCC encoded signal in modulus 2, so as to output the decoded signal.

11. The spatial channel decoder of claim 10, further comprising a delay means for performing delay process on the received SCC signal and inputting the delayed signal to the error calculating means.

12. A wireless terminal, comprising: at least one receive antenna for receiving spatial channel code (SCC) signal; at least a channel estimation unit for performing channel estimation on a plurality of wireless channels which transmitting the SCC signal, according to received pilot signal; and a spatial channel decoder for decoding the received signal by using the channel estimation result, wherein the spatial channel decoder comprises: an inverse encoding means for performing inverse spatial channel code (SCC) encoding on the received SCC signal to obtain an inverse SCC encoded signal; a re-encoding means for performing SCC re-encoding process on the inverse SCC encoded signal output from the inverse encoding means to obtain a SCC re-encoded signal; an error calculating means for calculating an error between the received SCC signal and the SCC re-encoded signal; and an output means for outputting corresponding decoded signal based on the inverse SCC encoded signal and the error, according to the measured channel quality.

13. The spatial channel decoder of claim 12, comprising: a control means for calculating a variation of the error.

14. The spatial channel decoder of claim 13, wherein the output means outputs the inverse SCC encoded signal as the decoded signal if the variation of the error is not greater than a predefined threshold.

15. The spatial channel decoder of claim 13, further comprising: a Viterbi decoding means for performing space-time Viterbi decoding process on the error to obtain error decoded signal if the variation of the error is greater than the predefined threshold; and the output means is further used for adding the error decoded signal and the inverse SCC encoded signal in modulus 2, so as to output the decoded signal.