WO2009119057A1

WO2009119057A1 - Wireless communication device and error correction encoding method

Info

Publication number: WO2009119057A1
Application number: PCT/JP2009/001262
Authority: WO
Inventors: 謙一栗; 憲一三好; 昭彦西尾; 元彦井坂
Original assignee: パナソニック株式会社
Priority date: 2008-03-24
Filing date: 2009-03-23
Publication date: 2009-10-01

Abstract

In a wireless communication system in which parallel processing of turbo decoding is performed, provided is a wireless communication device capable of improving the decoding accuracy of the turbo decoding while suppressing the degradation of the ratio Eb/No. In the wireless communication device, an encoding unit (102) divides data according to the information bit sequence length inputted from a control unit (110) and the number of parallel decodes and periodically inserts a termination control bit at the tailing end of each of the divided data sections. Moreover, depending on whether an input to an encoder comprising delay elements is the information bit or the termination control bit, the encoding unit (102) changes input data to the encoder and performs an encoding process. In this case, the encoding unit (102) partially performs termination processing before the time point of starting parallel decoding and limits the number of states at the time point of starting the parallel decoding.

Description

Wireless communication apparatus and error correction encoding method

The present invention relates to a wireless communication apparatus and an error correction coding method.

The 3rd generation mobile communication service has started, and multimedia communication such as data communication and video communication has become popular. In the future, it is predicted that the data size will further increase and the demand for higher data rates will increase.

Therefore, the use of a turbo code as an error correction coding for realizing a high-speed transmission of 100 Mbps is being studied.

Also, in order to improve the decoding throughput of turbo codes, parallel processing of turbo decoding has been studied (see Non-Patent Documents 1 and 2).

Furthermore, in order to improve the decoding characteristics of turbo codes, it has been studied to perform termination processing (see Non-Patent Document 3). By applying the termination process to the codeword, it is possible to perform both decoding from the beginning of the codeword and decoding from the end of the codeword when performing turbo decoding.
OY Takeshita, "On maximum contention-free interleaversand permutation polynomials over integer rings", IEEE Trans. Inform. Theory, vol. 52, no. 3, pp. 1249-1253, Mar. 2006 R1-063137, Ericsson, "Quadratic Permutation Polynomial Interleavers for LTE Turbo Coding", 3GPP TSG RAN WG1 # 47, Riga, Latvia, November. 6-10, 2006 3GPP TS 36.212 v8.1.0 (2007-11) "Multiplexing and Channel Coding"

Fig. 1 shows a trellis diagram for a codeword with information bit string length K = 16. In the turbo decoding process, the forward probability α, the backward probability β, and the log likelihood ratio LLR are calculated. When 4-parallel turbo decoding is applied to this codeword, forward probabilities α are calculated from the four time points T0, T1, T2, and T3, respectively, and backward from the four time points T4, T3, T2, and T1, respectively. A probability β and a log likelihood ratio LLR are calculated.

However, as shown in FIG. 2, since the state is not specified at each start time of the parallel decoding at the time points T1, T2, T3, and T4, the decoding accuracy of turbo decoding becomes low. If the state cannot be specified, an equal probability (= 1/8) is usually given to all states.

On the other hand, as shown in FIG. 3, when termination processing is applied to all states in order to specify the states at the start of parallel decoding at time points T1, T2, T3, and T4, extra parity bits increase. As a result, Eb / No deteriorates.

An object of the present invention is to provide a radio communication apparatus and an error correction coding method capable of improving the decoding accuracy of turbo decoding while suppressing deterioration of Eb / No in a radio communication system in which parallel processing of turbo decoding is performed. That is.

A radio communication apparatus according to the present invention is a radio communication apparatus used in a radio communication system in which parallel processing of turbo decoding is performed, and a plurality of decodings constituting the parallel processing are performed in an information bit string constituting one codeword. Insertion means for performing a termination process for periodically inserting a number of termination bits smaller than the number of delay elements used for generating an encoded bit string to a position corresponding to immediately before each end point of processing, and using the delay elements And encoding means for generating the encoded bit string by performing error correction encoding on the information bit string.

The error correction coding method of the present invention is an error correction coding method used in a wireless communication system in which parallel processing of turbo decoding is performed, and the parallel processing is configured in an information bit string constituting one codeword. An insertion step of performing a termination process for periodically inserting a number of termination bits smaller than the number of delay elements used to generate an encoded bit string at a position corresponding to immediately before each end point of a plurality of decoding processes, And an encoding step for generating the encoded bit string by performing error correction encoding on the information bit string using a delay element.

According to the present invention, the decoding accuracy of turbo decoding can be improved while suppressing the deterioration of Eb / No.

Trellis diagram for code word with information bit string length K = 16 (conventional) Trellis diagram for code word with information bit string length K = 16 (conventional) Diagram showing conventional termination process The figure which shows the structure of the radio | wireless communication apparatus (data transmission side) which concerns on Embodiment 1 of this invention. The figure which shows the structure of the encoding part which concerns on Embodiment 1 of this invention. The figure which shows operation | movement of the switching part in Embodiment 1 of this invention. The figure which shows operation | movement of the switching part in Embodiment 1 of this invention. The figure which shows the encoding bit sequence which concerns on Embodiment 1 of this invention. The figure which shows a response | compatibility with the encoding process which concerns on Embodiment 1 of this invention, and a trellis diagram The figure which shows the structure of the radio | wireless communication apparatus (data receiving side) which concerns on Embodiment 1 of this invention. The figure which shows a response | compatibility with the coefficient k which shows the input bit index of the trellis diagram based on Embodiment 1 of this invention, and the demodulated likelihood information The figure which shows the calculation condition of the forward probability (alpha) which concerns on Embodiment 1 of this invention. The figure which shows the calculation condition of the backward probability (beta) which concerns on Embodiment 1 of this invention. The figure which shows the structure of the encoding part which concerns on Embodiment 2 of this invention. The figure which shows the encoding bit sequence which concerns on Embodiment 2 of this invention. The figure which shows a response | compatibility with the encoding process which concerns on Embodiment 3 of this invention, and a trellis diagram (when channel quality is bad) The figure which shows a response | compatibility with the encoding process which concerns on Embodiment 3 of this invention, and a trellis diagram (when channel quality is good)

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

(Embodiment 1)
In the present embodiment, partial termination processing is performed for one turbo codeword in turbo coding, the number of times being smaller than the number of delay elements in the convolutional encoder immediately before each start time of parallel decoding. The normal termination process is a process of transitioning to a specific one state by a feedback input of the number of times equal to the number of delay elements in the convolutional encoder, whereas the partial termination process is a state by a single feedback input. This is a limited process.

FIG. 4 shows the configuration of radio communication apparatus 100 on the data transmission side according to the present embodiment.

In the wireless communication apparatus 100, a CRC (Cyclic Redundancy Check) unit 101 performs error detection coding on the information bit string and outputs data to which the CRC parity bit is added to the coding unit 102.

The encoding unit 102 divides data based on the information bit string length (K) and the parallel decoding number (P) input from the control unit 110, and periodically adds a termination control bit to the end of each divided data. insert. In addition, encoding section 102 performs turbo encoding on the information bit string at the mother encoding rate, and outputs a codeword matching the encoding rate input from control section 110 to modulating section 103. Furthermore, the encoding unit 102 determines the input content to the convolutional encoder depending on whether the input to the convolutional encoder composed of the delay element D and the adder is an information bit or a termination control bit. Switch to perform encoding processing. Details of the encoding unit 102 will be described later.

Modulation section 103 modulates the code word data input from encoding section 102 according to the modulation level input from control section 110 to generate data symbols, and outputs the data symbols to multiplexing section 104.

The multiplexing unit 104 arranges the data symbol input from the modulation unit 103 in the allocated frequency resource input from the control unit 110. In addition, multiplexing section 104 multiplexes the data symbol, pilot signal, and control information input from control section 110 to generate a baseband signal.

The transmission RF unit 105 converts the frequency of the baseband signal into an RF signal, and transmits the frequency-converted signal from the antenna 106.

The reception RF unit 107 receives a control signal via the antenna 106 and converts the frequency of the control signal into a baseband signal. This control signal includes a CQI (Channel Quality Indicator) and an ACK / NACK signal.

The demodulator 108 demodulates the control signal and outputs it to the decoder 109.

The decoding unit 109 decodes the demodulated control signal and outputs it to the control unit 110.

The control unit 110 controls the information bit string length (K), the parallel decoding number (P), the coding rate, the modulation level, the allocated frequency resource, and the retransmission based on the control signal input from the decoding unit 109. In addition, control section 110 outputs the parallel decoding number and coding rate to coding section 102, outputs the modulation level to modulation section 103, and outputs control information such as allocated frequency resources to multiplexing section 104.

The CQI included in the control signal may be an average SINR, average SIR, or MCS (Modulation and Coding Scheme) parameter.

Next, details of the encoding unit 102 will be described. FIG. 5 shows the configuration of encoding section 102 according to the present embodiment.

As shown in FIG. 5, the encoding unit 102 includes two termination bit insertion units, two element encoding units, and an internal interleaver. Each termination bit insertion unit includes an insertion unit and a switching unit.

Hereinafter, a case where the information bit string length K = 16 and the parallel decoding number P = 4 will be described as an example.

In accordance with the information bit string length K = 16 and the parallel decoding number P = 4, the insertion unit 111 has one termination control bit (Termination Control Bit) at an interval of 4 (= K / P = 16/4) bit intervals in the information bit string C _k . : Insert TCB). Therefore, [C ₀ , C ₁ , C ₂ , C ₃ , TCB, C ₄ , C ₅ , C ₆ , C ₇ , TCB, C ₈ , C ₉ , C ₁₀ , C ₁₁ , TCB, C ₁₂ , C ₁₃ , C ₁₄ , C ₁₅ , TCB] is output from the insertion unit 111.

On the other hand, the insertion unit 121 inserts termination control bits one by one at intervals of 4 bits in the information bit string C ′ _k interleaved by the internal interleaver 15. _{Therefore, [C '0, C'} 1, C '2, C' 3, TCB, C '4, C' 5, C '6, C' 7, TCB, C '8, C' 9, C '10 , C ′ ₁₁ , TCB, C ′ ₁₂ , C ′ ₁₃ , C ′ ₁₄ , C ′ ₁₅ , TCB] are output from the insertion unit 121.

The switching

units

112 and 122 switch switches according to the input content from the

insertion units

111 and 121. That is, when the input from the

insertion units

111 and 121 is an information bit ('0' or '1'), the switching

units

112 and 122 switch the switches C _k and C ′ _k as shown in FIG. 6A. To output the information bits to the

element encoding units

13 and 14. On the other hand, when the input from the

insertion units

111 and 121 is a termination control bit, the switching

units

112 and 122 connect the switch to the feedback input and set the feedback bit (= termination bit) as shown in FIG. 6B. The data is output to the

element encoding units

13 and 14.

The

element encoding units

13 and 14 are convolutional encoders including a delay element D and an adder, and perform convolutional encoding on inputs from the switching

units

112 and 122. FIG. 7 shows an encoded bit string for the coefficient k indicating the input bit index. FIG. 8 shows the correspondence between the encoding process and the trellis diagram. In FIG. 7, “ _{P1_n} ” and “ _{TP1_n} ” indicate parity bits obtained by the element encoding unit 13. Also, 'P2 _{_n'} and 'TP2 _{_n'} indicates the parity bits obtained by the element encoding unit 14. Also, 'TP1 _{_n'} and 'TP2 _{_n'} denotes the parity bit obtained from the termination bits.

As shown in FIG. 7, the total number of encoded bits of the turbo codeword generated by the turbo encoding according to the present embodiment is 72 (= 22 * 3 + 6). Further, according to this embodiment, as shown in FIGS. 7 and 8, the start time t = 5 for parallel decoding, 10, 15, a state which can be taken by 20, all states S _000, S _100, S _{_{_{010, S 110, S 001,}}} S 101, S 011, a portion from the S ₁₁₁ state S _000, S _010, it is possible to limit to S _001, S _011.

Thus, according to the present embodiment, since the termination process is partially performed before each start time of parallel decoding, it is possible to limit the number of states at each start time of parallel decoding and One long codeword can be made without terminating the codeword at the start.

FIG. 9 shows the configuration of the wireless communication device 200 on the data receiving side according to the present embodiment.

In the wireless communication device 200, the reception RF unit 202 receives the signal transmitted from the wireless communication device 100 (FIG. 4) via the antenna 201, and converts the frequency of the received signal into a baseband signal.

The demultiplexing unit 203 demultiplexes the received signal into data symbols, pilot signals, and control information (allocated frequency resource, information bit string length, number of parallel decoding, coding rate, and modulation level). Separation section 203 then outputs data symbols corresponding to the allocated frequency resource to demodulation section 204, outputs a pilot signal to channel quality estimation section 207, and outputs control information to demodulation section 204 and decoding section 205.

The demodulator 204 demodulates the data symbol input from the separator 203 according to the modulation level included in the control information.

Based on the information bit string length (K) and the number of parallel decoding (P) included in the control information, the decoding unit 205 specifies the start time of parallel decoding and also displays likelihood information for each demodulated bit as a trellis diagram. Corresponding to, error correction decoding is performed to obtain a decoded bit string. In addition, when the ACK signal is input from the error detection unit 206, the decoding unit 205 discards the reception data stored in the memory in the decoding unit 205. Details of the decoding process in the decoding unit 205 will be described later.

The error detection unit 206 performs error detection (CRC) on the decoded bit string input from the decoding unit 205. Then, as a result of error detection, the error detection unit 206 generates a NACK signal as a response signal when there is an error in the decoded bit string, and generates an ACK signal as a response signal when there is no error in the decoded bit string. Alternatively, the ACK signal is output to decoding section 205 and control signal generation section 208. Further, the error detection unit 206 outputs the decoded bit string as a received bit string when there is no error in the decoded bit string.

Channel quality estimation section 207 estimates channel quality (SINR) from the pilot signal and outputs the SINR estimated value to control signal generation section 208.

Control signal generation section 208 generates a feedback information frame from the ACK / NACK signal input from error detection section 206 and the SINR estimation value input from channel quality estimation section 207, and outputs the frame to encoding section 209. .

The encoding unit 209 and the modulation unit 210 encode and modulate the feedback information input from the control signal generation unit 208 and output the feedback information to the transmission RF unit 211.

The transmission RF unit 211 converts the frequency of the encoded and modulated feedback information signal into an RF signal, and transmits the frequency-converted signal from the antenna 201 to the wireless communication apparatus 100 (FIG. 4).

Next, details of the decoding process in the decoding unit 205 will be described.

Hereinafter, a decoding process corresponding to the above encoding process in the encoding unit 102 will be described.

The decoding unit 205 includes two element decoding units respectively corresponding to the element encoding units 13 and 14 (FIG. 5), and performs parallel processing of turbo decoding.

FIG. 10 shows the correspondence between the coefficient k indicating the input bit index of the trellis diagram and the demodulated likelihood information. Each element decoding unit in the decoding unit 205 performs turbo decoding parallel processing as follows.

That is, in one element decoding unit, 4 (= 16/4) time points based on the information bit string length (K = 16) and the number of parallel decoding (P = 4) included in the control information input from the separation unit 203 Specify that partial termination processing was performed once at intervals (k = 4, 9, 14). Further, according to the information identified, k = to 4, 9, 14 parts of the likelihood information of the parity bits obtained from termination bits _{_{(TP1 _0, TP1 _1, TP1}} _2) associates. Further, likelihood information (16 pieces: C ₀ -C ₁₅ ) of systematic bits (C _k ) is associated in order from the head of k, avoiding the position where termination is performed. Also, the likelihood information of the parity bits (P1 _{_n)} (22 pieces: P1 _{_0} - P1 _{_21)} and associates from the head of the k sequentially. Note that the same identification and association are performed in the other element decoding unit.

Further, in the process of turbo decoding in each element decoding unit, a forward probability α and a backward probability β are calculated. Since parallel decoding is applied to turbo decoding, the probability α of transitioning forward from four time points of

time points

0, 5, 10, and 15 in FIG. 10 is calculated in parallel. FIG. 11 shows the calculation status of the forward probability α from time = 5 to time = 10. As described above, in the present embodiment, at the time of initial decoding, the initial value = 1/4 is given to the four states (S ₀₀₀ , S ₀₁₀ , S ₀₀₁ , S ₀₁₁ ) at the time point = 5, and the forward probability α for each time point. Perform the calculation. Further, the backward probability β is calculated in parallel backward from the four time points of time point = 20, 15, 10, 5 in FIG. FIG. 12 shows the calculation status of the backward probability β from time = 5 to time = 0. As described above, in the present embodiment, at the time of initial decoding, the initial value = 1/4 is given to the four states (S ₀₀₀ , S ₀₁₀ , S ₀₀₁ , S ₀₁₁ ) at the time point = 5, and the backward probability β for each time point. Perform the calculation. In the second and subsequent iterations, the probabilities derived from the decoding results up to the previous time are given to the four states at the start of each parallel decoding.

As described above, conventionally, the termination process is applied only to the end of the turbo codeword to identify one state among the eight states, whereas in the present embodiment, the partial termination process is applied once. By doing so, it is specified as 4 out of 8 states. In parallel decoding, intermediate decoding results can be shared between adjacent decoding processes, so that four states can be narrowed down to one state during the decoding process. Therefore, according to the present embodiment, it is possible to improve decoding accuracy by limiting the number of states at each start time of parallel decoding, and one long code without terminating a codeword at each start time of parallel decoding A large coding gain can be obtained by using words. That is, according to the present embodiment, it is possible to improve the decoding accuracy of turbo decoding while suppressing the deterioration of Eb / No.

In addition, the number of states can be halved by one partial termination process. In other words, the number of states can be reduced by four from 8 states to 4 states in the first partial termination process, whereas only two states can be reduced from 4 states to 2 states in the second partial termination process. Therefore, in the present embodiment, the number of partial termination processes is set to one that is more effective. However, in the present invention, the number of partial termination processes may be smaller than the number of delay elements constituting the element encoding unit.

(Embodiment 2)
In the present embodiment, only one of the two element coding units constituting coding unit 102 (FIG. 4) performs the termination process shown in the first embodiment.

FIG. 13 shows the configuration of encoding section 102 according to the present embodiment. That is, the encoding unit 102 shown in FIG. 13 is obtained by removing one insertion unit 121 from FIG. 5 (Embodiment 1).

Therefore, in the present embodiment, the encoded bit string for the coefficient k indicating the input bit index is as shown in FIG. While the total number of encoded bits of the turbo codeword generated by the turbo encoding in Embodiment 1 is 72 (= 22 * 3 + 6), it is generated by the turbo encoding of the present embodiment. The total number of encoded bits of a turbo codeword is 66 (= 22 * 2 + 19 + 3) as shown in FIG. Thus, according to the present embodiment, it is possible to reduce 6 parity bits as compared with the first embodiment.

On the other hand, the decoding unit 205 (FIG. 9) may transfer the parallel decoding improvement effect by partial termination in one element decoding unit to the other element decoding unit as prior information. Thereby, the parallel decoding improvement effect by partial termination can be indirectly obtained also in the other element decoding part.

Thus, according to the present embodiment, the number of extra parity bits due to partial termination processing can be suppressed, and termination processing is performed by external information from the element decoding unit to which partial termination processing is applied. Even in an element decoding unit that is not applied, it is possible to indirectly obtain an error rate characteristic improvement effect by limiting the number of states.

(Embodiment 3)
Control unit 110 (FIG. 4) according to the present embodiment determines the number of partial termination processes according to the line quality.

When the channel quality (SINR) is less than the threshold value (when the channel quality is poor), the control unit 110 determines the number of partial termination processes to be two, and the channel quality (SINR) is equal to or greater than the threshold value. When the line quality is good, the number of partial termination processes is determined as one. The number of partial termination processes determined in this way is reported to the wireless communication apparatus 200 (FIG. 9) as control information, in the same way as the parallel decoding number (P). Further, the line quality information is reported from the wireless communication apparatus 200 (FIG. 9).

Therefore, when the line quality is poor, the correspondence between the encoding process and the trellis diagram is as shown in FIG. 15 (the number of partial termination processes: 2). When the line quality is good, the encoding process and the trellis are shown. The correspondence with the diagram is as shown in FIG. 16 (the number of partial termination processes: once).

The decoding unit 205 (FIG. 9) identifies the position where the partial termination processing is applied based on the number of partial terminations input from the separation unit 203, the information bit string length, and the number of parallel decodings.

Thus, in this embodiment, when the line quality is poor, the number of partial termination processes is increased, so when the line quality is bad, the number of states at each start time of parallel decoding is further limited, and The parity bit can be increased. Therefore, according to the present embodiment, it is possible to enhance error tolerance when the line quality is poor.

In this embodiment, the example in which the number of partial termination processes is determined according to the line quality has been described. However, in the present invention, the number of partial termination processes is determined according to the modulation scheme used at the time of transmission. Also good.

The embodiment of the present invention has been described above.

In the mobile communication system, the wireless communication device is a wireless communication base station device or a wireless communication mobile station device. When the wireless communication device 100 (FIG. 4) is a wireless communication base station device, the wireless communication device 200 (FIG. 9) is a wireless communication mobile station device. Further, when the wireless communication device 100 (FIG. 4) is a wireless communication mobile station device, the wireless communication device 200 (FIG. 9) is a wireless communication base station device.

Also, the number of parallel decoding (P) that is unique to the information bit string length (K) may be determined in advance.

Further, although cases have been described with the above embodiment as examples where the present invention is configured by hardware, the present invention can also be realized by software.

Further, each functional block used in the description of the above embodiment is typically realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

Further, the method of circuit integration is not limited to LSI, and implementation with a dedicated circuit or a general-purpose processor is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

Furthermore, if integrated circuit technology that replaces LSI emerges as a result of advances in semiconductor technology or other derived technology, it is naturally also possible to integrate functional blocks using this technology. Biotechnology can be applied.

The disclosure of the description, drawings and abstract contained in the Japanese application of Japanese Patent Application No. 2008-076287 filed on Mar. 24, 2008 is incorporated herein by reference.

The present invention can be applied to a mobile communication system or the like.

Claims

A wireless communication device used in a wireless communication system in which parallel processing of turbo decoding is performed,
Termination of a number smaller than the number of delay elements used to generate a coded bit string to a position corresponding to immediately before each end point of the plurality of decoding processes constituting the parallel processing in an information bit string constituting one code word Insertion means for performing termination processing for periodically inserting bits;
Encoding means for generating the encoded bit string by error correction encoding the information bit string using the delay element;
A wireless communication apparatus comprising:
Comprising the two encoding means,
The insertion means performs the termination process only in an information bit string that is error-correction encoded by either one of the two encoding means.
The wireless communication apparatus according to claim 1.
The inserting means determines the number of termination bits to be inserted according to the line quality;
The wireless communication apparatus according to claim 1.
An error correction coding method used in a wireless communication system in which parallel processing of turbo decoding is performed,
Termination of a number smaller than the number of delay elements used to generate a coded bit string to a position corresponding to immediately before each end point of the plurality of decoding processes constituting the parallel processing in an information bit string constituting one code word An insertion step for performing a termination process for periodically inserting bits;
An encoding step for generating the encoded bit string by error correction encoding the information bit string using the delay element;
An error correction coding method comprising: