CN1555211A - Coding Method of Hybrid Recursive Trellis Space-Time Codes - Google Patents

Abstract

The invention relates to a hybrid recursive grid space-time code encoding method, which is used in a serial cascaded space-time code system. It can be based on different modulation methods, such as four-phase phase-shift keying modulation, eight-phase phase-shift keying modulation, hexadecimal quadrature amplitude modulation and other 2 ⁿ -order modulation methods. Coding includes selecting the component code and determining the mapping method, that is, determining the modulation method according to the required transmission rate, and at the same time determining the number of states of the code, and then determining the state number, code rate and coding method of the component code. The component code adopts a code rate of 1/2 The two-state system recursive convolutional code, the number of codes is equal to the required transmission rate value, the encoding method is a class of systematic codes, and the mapping method includes different transmission symbol mapping and different position mapping, that is, the information output by each component code Bits and parity bits are respectively mapped to different positions of different symbols. This method greatly improves its anti-fading performance while keeping the complexity of the serial cascaded system unchanged.

Description

Coding Method of Hybrid Recursive Trellis Space-Time Codes

Technical field:

The invention relates to a space-time coding technique, in particular to a coding method of a hybrid recursive lattice space-time code, which can be used to improve the performance of a serial cascade system.

Background technique:

In the increasingly popular third-generation mobile communication system research, there is a very important research content, which is how to achieve the highest possible transmission rate under limited bandwidth, and how to use efficient coding methods to effectively resolve the gap between bandwidth and transmission rate. contradictions between. Space-time coding has attracted much attention due to the use of multi-antenna array transmission and reception technology, which can effectively improve the system frequency band utilization.

In the current research, space-time codes are often used in cascade with other error-correcting codes, that is, a serial cascade system is used to complete the space-time coding process. The serial cascade system includes two parts: a transmitting unit 70 and a receiving unit 71 . Wherein, the transmitting unit 70 includes an outer code encoder 700, an interleaver 701, a space-time encoder 702, and a transmitting antenna; the receiving unit 71 includes an outer code decoder 710, a deinterleaver 711, a space-time decoder 712, and a receiving antenna, As shown in Figure 6. In this system, taking the interleaver as a reference point, the codeword before the interleaver is called the outer code, and the codeword after the interleaver is called the inner code, and it is space-time coded. The above-mentioned outer code encoding and decoding can adopt convolutional codes, parallel concatenated convolutional (Turbo) codes or low density check codes (LDPC), when using convolutional codes or parallel concatenated convolutional (Turbo) codes, interleaving The interleaver 701 adopts a random interleaver or a parity interleaver, and the interleaver 701 may not be used when a low density check (LDPC) code is used. The basic working principle of the system is: at the sending end, the information sequence t is encoded and interleaved to form a bit sequence u, and then the bit sequence u is space-time coded to obtain a symbol sequence, and the symbol sequence is passed through the transmitting antenna at the same time Send out; at the receiving end, the receiving antenna will process the received symbol sequence through the corresponding space-time decoding process to form an external information sequence about each bit, and the external information sequence will be processed by the external code to form the corresponding external information. At this time, an iterative decoding is completed, and the external information generated by the external code decoder is sent to the space-time decoder, and the above process is repeated together with the channel received signal to complete multiple iterative decoding until the information sequence t is correctly detected or reaches a certain value The number of iterations is judged and output, and the information sequence t is restored.

The current serial concatenated space-time coding system (SCSTC) is divided into two categories: one is using block space-time code as inner code, and the other is using recursive trellis space-time code (R-STTC) as inner code . The advantage of using packet space-time codes as inner codes is that the system complexity is relatively low, but the performance is poor. Using the recursive trellis space-time code (R-STTC) as the inner code can obtain additional interleaving gain, and the performance is relatively good, so it has a promising future at present. When designing a recursive lattice space-time code, it can be split into two modules, namely the component code module and the mapper module. In this case, the design of the recursive trellis space-time coding is transformed into the following two problems, that is, how to choose each component code and how to choose the mapping method, so as to be more conducive to improving the performance of the serial cascaded system.

The currently known recursive trellis space-time code (R-STTC) can adopt quadrature phase shift keying (QPSK) modulation or octal phase shift keying (8PSK) modulation, all of which are given on the basis of delay diversity . If quadrature phase-shift keying (QPSK) modulation is adopted, the encoding state is four states, and the generation of the code is shown in Figure 7a, including two parts of the component code 80 and the mapper 81, and "" in the figure represents the modulus 2 Add operation. The component code unit includes two repetition delay codes, the code rate of each repetition delay code is 1/2, the number of states is 2, and each includes a shift register D ₀ or a shift register D ₁ ; the mapper unit includes two symbol mapper. In this encoding, the information sequence is sent to the recursive trellis space-time code (R-STTC) encoder according to a group of two bits a _i b _i . The encoding process is as follows: first, the two component codes of the encoder, that is, the repetition delay code, respectively encode the two input bits a _i b _i to obtain the output of 4 bits; then, use the mapper to map the data of these 4 bits into two quadrature phase shift keying (QPSK) symbols, The two transmitted symbols are denoted by S ₁ and S ₂ respectively, wherein one symbol S ₁ is transmitted through antenna 1, and the other symbol S ₂ is transmitted through antenna 2.

If eight-phase phase-shift keying (8PSK) modulation is used, the encoding state is eight states, and the generation of the code is shown in Figure 7b, including two parts of the component code 90 and the mapper 91, and "" in the figure represents the modulus 2 Add operation. The component code unit 90 includes three repeated time-delay codes, the code rate of each repeated time-delay code is 1/2, the number of states is 2, and each includes a shift register, that is, a shift register D ₀ and a shift register D ₁ and shift register D ₂ ; mapper unit 91 includes two symbol mappers. In this encoding, the bit sequence is sent to the encoder in groups of three bits. First, the three component codes of the encoder, that is, the repetition delay code, encode the three bits respectively to obtain an output of 6 bits; then , use the mapper to map the 6-bit data into two eight-phase phase-shift keying (8PSK) symbols S ₃ and S ₄ , where one symbol S ₃ is transmitted through antenna 1, and the other symbol S ₄ is transmitted through antenna 2 send it out. For example, the article "Concatenated Codes for Fading Channels Based on Recursive Space-Time Trellis Codes" published by Gulati and KRNarayanan in the first issue of IEEE Trans.On Wireless Communication in 2003 mentioned. This article studies the cascaded system based on recursive lattice space-time codes under fading channels. The system performance of the space-time code (R-STTC) has been improved to some extent, but there is still a large gap between the performance and the system capacity, and it cannot fully meet the system requirements, and this recursive grid space-time code There are still two deficiencies: one is that the minimum Hamming distance of the repetitive delay code is only 2, which is not conducive to improving the overall distance of the code; the other is that the mapping method is not ideal, and the output bits of each component code are mapped to different symbols. In the same position, the diversity cannot be fully utilized.

What was invented:

The purpose of the present invention is to overcome the defective of existing method, provide a kind of hybrid recursive trellis space-time code coding method applicable to serial cascaded system, when guaranteeing that serial cascaded space-time coding system (SCSTC) complexity is constant In the case of , the anti-fading performance of the system can be further improved.

The basic train of thought that realizes the object of the present invention is to adopt the component code and the component code output mapping mode that are different from existing recursive grid space-time code to optimize the distance structure of grid space-time code, namely at first utilize the change of component code to increase the Hamming distance, the repeated delay code is replaced by a systematic recursive convolutional code; and then the hybrid mapping method is used to ensure that the output bits of a single component code are mapped to different positions of different symbols. The encoding process is as follows:

The first step is to determine the modulation method according to the required transmission rate, and thus determine the number of coding states of the hybrid recursive trellis space-time code (HSR-STTC). When the transmission rate is n bits/slot, use 2 ⁿ - order modulation, the number of coding states is 2 ⁿ ;

The second step is to select the component code, including determining the number of states, code rate and encoding method of the component code. The component code adopts a two-state system recursive convolutional code with a code rate of 1/2, and the number of convolutional codes is equal to the required The transmission rate value, that is, when the transmission rate is n bits/slot, the number of convolutional codes is n, and its encoding method is a type of systematic code, which refers to the encoded output of each recursive convolutional code Among the bits, there must be one input information bit, and the rest are parity bits;

The third step is to use a mixed mapping method to map the information bits and check bits output by each component code to different positions of different transmitted symbols, that is, to include different transmitted symbol mappings and different position mappings. The different transmitted symbol mappings are Refers to selecting one bit from the 2 output bits of all component codes to be mapped to a transmission symbol, and all the remaining bits are mapped to another symbol; the different position mapping means that the 2 output bits of any component code are respectively Mapped to different positions of two symbols, if one of the bits is mapped to a certain position (L) of a transmitted symbol, when the other output bit is mapped to another transmitted symbol, the above position (L) can be selected any other position.

The above hybrid recursive lattice space-time code encoding method, wherein the determination of the modulation method is based on quadrature phase shift keying (QPSK) modulation, octal phase shift keying (8PSK) modulation, hexadecimal quadrature amplitude (16QAM) Modulation and other 2 ⁿ -order different modulation methods, the n value is equal to the required transmission rate value; for the hybrid recursive lattice space-time code coding method using different modulation methods, the selection and mapping methods of the component codes are different.

In the hybrid recursive trellis space-time coding method described above, when the modulation mode of quadrature phase-shift keying (QPSK) is adopted, two two-state system recursive convolutional codes with a code rate of 1/2 are selected as the component codes.

Above-mentioned hybrid recursive trellis space-time code coding method, wherein when adopting the modulation mode of quadrature phase-shift keying (QPSK), the different transmission symbol mappings and different position mappings that its hybrid mapping includes are respectively:

The different transmission symbol mapping refers to first selecting an information bit and a parity bit from the output bits of the two component codes respectively, and mapping these two bits into a quadrature phase shift keying (QPSK) symbol S ₁ , the remaining two bits are mapped to another quadrature phase-shift keying (QPSK) symbol S ₂ , and the two transmission symbols S ₁ and S ₂ are sent out from two antennas respectively;

The mapping of the different positions means that h ₀ and h ₁ represent two different bit positions of each quadrature phase shift keying (QPSK) symbol, if an output bit of the same component code is mapped to a quadrature phase shift keying (QPSK) symbol phase keying (QPSK) symbol S ₁ h ₀ position, then another output bit should be mapped to h ₁ position of another quadrature phase shift keying (QPSK) symbol S ₂ .

In the above hybrid recursive lattice space-time code encoding method, when the eight-phase phase-shift keying (8PSK) modulation method is adopted, the component codes use three 1/2 code rate two-state system recursive convolutional codes.

Above-mentioned hybrid recursive trellis space-time code coding method, wherein when adopting the modulation mode of eight-phase phase-shift keying (8PSK), the different transmission symbol mappings and different position mappings that its hybrid mapping includes are respectively:

The different transmission symbol mapping refers to first selecting two information bits and one check bit from the output bits of the three component codes, and mapping these three bits into an eight-phase phase-shift keying (8PSK) symbol S ₃ , the remaining three bits are mapped to another eight-phase phase-shift keying (8PSK) symbol S ₄ , and the two transmission symbols S ₃ and S ₄ are sent out from two antennas respectively;

The mapping of the different positions refers to the three different bit positions of each eight-phase phase-shift keying (8PSK) symbol represented by h ₂ , h ₃ , h ₅ , if one of its output bits is mapped to an eight-phase shift keying (8PSK) symbol phase keying (8PSK) symbol _S3 at _h2 position, then another output bit can be mapped to any position except _h2 of another eight-phase phase shift keying (8PSK) symbol _S4 .

In the above hybrid recursive lattice space-time code encoding method, when the hexadecimal quadrature amplitude (16QAM) modulation method is used, the component codes use four 1/2 code rate two-state system recursive convolutional codes.

The above-mentioned hybrid recursive grid space-time code encoding method, wherein when the modulation mode of hexadecimal quadrature amplitude (16QAM) is adopted, the different transmission symbol mappings and different position mappings included in the hybrid mapping are respectively:

The different transmission symbol mapping refers to selecting two information bits and two parity bits from the output bits of the four component codes, or selecting three information bits and one parity bit, and then mapping the four bits to is a hexadecimal quadrature amplitude (16QAM) symbol S ₅ , and the remaining four bits are mapped to another hexadecimal quadrature amplitude (16QAM) symbol S ₆ , and the two transmitted symbols S ₅ and S ₆ are respectively sent out from two antennas;

The mapping of the different positions refers to the four different bit positions of each hexadecimal quadrature amplitude (16QAM) symbol represented by h ₅ , h ₆ , h ₇ , h ₈ , for each component code, if it One output bit of is mapped to the h ₅ position of a hexadecimal quadrature amplitude (16QAM) symbol S ₅ , then the other output bit can be mapped to another hexadecimal quadrature amplitude (16QAM) symbol S ₆ Any position except h ₅ .

For the hybrid recursive trellis space-time code (HSR-STTC) based on other ²ⁿ -order modulation methods, the component codes and mapping methods can be selected in a similar way.

Compared with the prior art, the present invention has the following advantages:

1. The overall product distance of the serial concatenated space-time coding system has been improved, because in the present invention, the small weight input information bit is corresponding to the small weight product distance, and the minimum Hamming distance of any error correction code has a certain In this way, when the present invention is used in cascade with other error-correcting codes, the output codeword of the outer code does not actually contain these small-weight codewords, thereby ensuring that the overall performance of the serial concatenated space-time coding system is improved. Product distance.

2. The coding gain and anti-fading performance of the serial cascaded space-time coding system are improved. It can be seen from Fig. 5a and Fig. 5b that for the hybrid recursive trellis space-time coding (HSR-STTC) based on quadrature phase shift keying (QPSK) modulation and octal phase shift keying (8PSK) modulation respectively, in quasi-static fading Both channel and fast fading channel can obtain system diversity gain higher than that of the prior art without increasing the complexity of the system.

Description of drawings

Fig. 1 is a schematic diagram of the system structure of the present invention

Figure 2a is a schematic diagram of encoding based on the quadrature phase-shift keying modulation method of the present invention

Figure 2b is a state transition diagram based on the quadrature phase-shift keying modulation method of the present invention

Figure 3a is a schematic diagram of encoding based on eight-phase phase-shift keying modulation in the present invention

Figure 3b is a state transition diagram based on the eight-phase phase-shift keying modulation method of the present invention

Figure 4a is a schematic diagram of the present invention based on the hexadecimal quadrature amplitude modulation method, and each symbol mapped to antenna 1 has two information bits and two check bits

Fig. 4b is a schematic diagram of encoding of three information bits and one parity bit for each symbol mapped to antenna 1 based on the hexadecimal quadrature amplitude modulation method in the present invention

Fig. 5 is the simulation performance curve figure of the present invention under quasi-static and fast fading channels

Figure 6 is a schematic diagram of the composition and structure of the existing serial cascaded space-time coding system

Figure 7a is a schematic diagram of the existing recursive trellis space-time code encoding based on the quadrature phase-shift keying modulation method

Figure 7b is a schematic diagram of the existing recursive trellis space-time code encoding based on the eight-phase phase-shift keying modulation method

Detailed ways

Referring to FIG. 1 , the serial cascaded lattice space-time coding system of the present invention includes: a transmitting unit 10 and a receiving unit 11 . Wherein, the transmitting unit 10 includes an outer code encoder 100 and an inner code encoder 102 ; the receiving unit 11 includes an outer code decoder 112 and an inner code decoder 110 . The inner code encoder 102 uses the hybrid recursive trellis space-time code (HSR-STTC) as the inner code to perform space-time encoding, and correspondingly, the inner code decoder 110 also uses the hybrid recursive trellis space-time code as the inner code to perform space-time encoding. decoding. Furthermore, the outer code encoder 100 is a low density check code (LDPC) encoder, and the outer code decoder 112 is a low density check code (LDPC) decoder. The working process of the system is as follows: at the sending end, through the sending unit, the information sequence t is subjected to outer code encoding and interleaving processing to form a bit sequence, and then the bit sequence is encoded with an inner code, that is, the hybrid recursive lattice space-time encoding is performed to obtain the symbol Sequence, the symbol sequence is sent out through the transmitting antenna; at the receiving end, the receiving antenna will process the received symbol sequence through hybrid recursive lattice space-time decoding processing to form an outer information sequence about each bit, and the outer information sequence is then passed through the outer code After the decoding process, the corresponding external information is formed, and an iteration is completed at this time; the external information generated by the external code decoder is sent to the space-time decoder, and the above process is repeated together with the channel received signal to complete multiple iterations of decoding until the correct Detect the information sequence t or reach a certain number of iterations to judge the output, and get the restored information sequence t. The hybrid recursive grid space-time coding method is as follows:

The first step: according to the required transmission rate, determine the different modulation methods of four-phase phase-shift keying or eight-phase phase-shift keying or hexadecimal quadrature amplitude modulation, and thus determine the hybrid recursive lattice space-time code (HSR-STTC) coding state number, if the required transmission rate is n bits/time slot, then the corresponding modulation method is 2 ⁿ phase shift keying (2 ⁿ -PSK) or 2 ⁿ order quadrature amplitude modulation ( 2 ⁿ -QAM), and the number of encoding states is 2 ⁿ .

The second step is to select component codes, including determining the number of states, code rates and encoding methods of component codes, that is, to use systematic codes or non-systematic codes. The component code adopts a plurality of recursive convolutional codes, and its encoding method is that the coded output bits of each recursive convolutional code must contain one input information bit, and the rest are check bits. The number of states and the code rate of each component code are determined by the required transmission rate and the number of coding states of the hybrid recursive lattice space-time code. If the required transmission rate is n bits/time slot, the component codes used are n two-state system recursive convolutional codes with a code rate of 1/2. For example, if the transmission rate is 2 bits/slot, that is, 2 bits are transmitted in each time slot, a four-state hybrid recursive lattice space-time code modulated by four-phase phase-shift keying can be used, and its component code can be composed of two A two-state systematic recursive convolutional code with a code rate of 1/2 is formed; and an eight-state hybrid recursive trellis space-time code using quadrature phase-shift keying modulation can be formed by two systematic recursive convolutional codes, one of which is four state, the other is two states, the code rate is 1/2 and so on. For a hybrid recursive trellis space-time code with octal phase-shift keying and hexadecimal quadrature amplitude modulation, the number of states for each component code can be assigned similarly.

Step 3: Determine the mapping method, which is a hybrid mapping method, that is, the information bits and check bits output by each component code are mapped to different positions of different symbols. For the hybrid recursive lattice space-time coding method with different modulation methods, the mapping methods of the component codes are different.

Let the transmitted symbols on the two antennas be x ₁ , x ₂ , all n component codes are m ₀ , m ₁ ,..., m _n-1 respectively, and the two output bits of the i-th component code m _i are respectively a _i ⁰ , a _i ¹ , 2 ⁿ -order modulation symbols are labeled b ₀ b ₁ ...b _b-1 , then:

The method of mapping to different symbols is as follows: one bit is selected from all n component codes and mapped to a transmitted symbol x ₁ , and the remaining n bits are mapped to another transmitted symbol x ₂ .

The method of mapping to different positions is: if the output bit a _i ⁰ of the i-th component code m _i is mapped to the j-th position of the symbol x ₁ , then its other output symbol a _i ¹ must be mapped to the symbol x ₂ on the remaining n-1 positions.

With reference to Fig. 2 a, if the present invention determines to adopt quadrature phase-shift keying (QPSK) modulation mode, then the coding state number of this hybrid recursive trellis space-time code (HSR-STTC) is four states, and its coding structure includes component code unit 20 and mapper unit 21. "" in the figure indicates modulo 2 addition operation. The component code unit 20 includes two recursive convolutional codes, the code rate of each convolutional code is 1/2, and each convolutional code includes a shift register, i.e. shift register D ₀ and shift register D ₁ , the state numbers of the two shift registers are both 2; the mapper unit 21 includes two symbol mappers. Since there are two antennas at the sending end, two different sending symbols will be generated at the same time during encoding, denoted by S ₁ and S ₂ respectively. The encoding process is as follows: let the encoded input bit sequence u include a ₀ , b ₀ , a ₁ , b ₁ , ..., a _i , b _i in turn, divide the bit sequence into groups of two bits, and then This hybrid recursive trellis space-time coding is performed on two bits in each group. Let (a _i , b _i ) be the input information of the encoder at the i-th moment, then (a _i , b _i ) should have four possible combinations, namely 00, 01, 10, 11, in the figure a _{i- 1} ′ and b _i-1 ′ are the values in shift register D ₀ and shift register D ₁ respectively, a _i-1 ′ and b _i-1 ′ also have four possible combinations, namely 00, 01, 10, 11. In this way, after encoding the two bits (a _i , b _i ) by two component codes, the output of 4 bits is obtained, that is, a _i , b _i , a _i-1 ′ and b _i-1 '; then the mapper maps the data of these 4 bits into two quadrature phase-shift keying (QPSK) symbols S ₁ and S ₂ , and the different sending symbol mappings and different position mappings included in the mapping process are respectively:

The different transmission symbol mapping is to select an information bit from the output bit of one of the component codes, and select a check bit from the output bit of the other component code at the same time, and map these two bits into a four-phase shift The keying symbol S ₁ , the remaining two output bits, that is, the check bits of the previous component code and the information bits of the next component code, are mapped to another four-phase shift keying symbol S ₂ , and the two transmission symbols S ₁ and S ₂ are sent out from two antennas respectively;

The mapping of different positions requires two bits output by the same component code to be mapped to different positions of two quadrature phase shift keying (QPSK) symbols S ₁ and S ₂ respectively. A quadrature phase-shift keying (QPSK) symbol consists of two bits, and these two positions are represented by h ₀ and h _1. If the information bit of one of the component codes corresponds to a quadrature phase-shift keying (QPSK) symbol At the h ₀ position of S ₁ , the check bit of the component code corresponds to the h ₁ position of another quadrature phase shift keying (QPSK) symbol S ₂ , and the check bit of another component code will correspond to In the position _h1 of the quadrature phase shift keying (QPSK) symbol _S1 , the information bit corresponds to the position _h0 of another quadrature phase shift keying (QPSK) symbol _S2 .

As shown in FIG. 2 b , according to the above-mentioned encoding method of the hybrid recursive trellis space-time code for quadrature phase-shift keying (QPSK), the corresponding state transition rules are obtained. Let (a _i , b _i ) be the input information of the encoder at the i-th moment, a _i-1 ′ and b _i-1 ′ are the values in the shift register D ₀ and shift register D ₁ respectively, then mix The value in the shift register D ₀ in the recursive lattice space-time code will change from a _i-1 ′ to a _i ′=a _i a _i-1 ′, and the value in the shift register D ₁ in the mixed recursive lattice space-time code The value of will change from b _{i-1 ′} to b _i ′=b _i b _i-1 ′, where “” represents the modulo 2 addition operation. Furthermore, at the i-th moment, the hybrid recursive grid space-time The state encoded by the code (HSR-STTC) will change from a _i-1 ′+2b _i-1 ′ to a _i ′+2b _i ′. For example, when (a _i-1 ′, b _i-1 ′)=(0,1), (a _i , b _i )=(0,1), a _i ′=a _i  can be obtained according to the above coding rules a _i-1 ′=00=0, b _i ′=b _i b _i-1 ′=11=0, further get a _i-1 ′+2b _i-1 ′=2, a _i ′ +2b _i ′=0, a _i +2b _i ＝2, correspondingly, the current state of encoding is a _i-1 ′+2b _i-1 ′=2, and the state at the next moment is a _i ′+2b _i ′ =0, the input symbol is a _i + _2bi =2, and the output symbols corresponding to the two antennas are obtained according to the above mapping rules as S ₁ =1 and S ₂ =2, which are represented by "12/2" in Fig. 2b. In this way, every time a set of values of a _i-1 ′ and b _i-1 ′ is determined, a value of a _i-1 ′+2b _i-1 ′ is correspondingly determined. At this time, four possible inputs (a _i , b _i ) determines four possible values of a _i ′+2b _i ′, that is, one encoding state a _i-1 ′+2b _i-1 ′ can be transferred to four possible states.

The specific state transition rules are as follows. 0 to 3 in Figure 2b respectively represent the points in the signal constellation diagram. In the first line of data on the left side of the figure, the "00/0" on the left side of the slash in "00/0" " are the two corresponding output symbols when the hybrid recursive trellis space-time code (HSR-STTC) encoder transitions from state 0 to state 0, and the "0" on the right side of the slash indicates that the input information symbol at this time is 0 ; "20" on the left side of the slash in "20/1" is the two corresponding output symbols when the hybrid recursive trellis space-time code (HSR-STTC) encoder is transferred from state 0 to state 1, the slash The "1" on the right indicates that the input information symbol at this time is 1; the "02" on the left side of the slash in "02/2" means that the hybrid recursive trellis space-time code (HSR-STTC) encoder starts from 0 state When transitioning to state 2, the corresponding two output symbols, the "2" on the right side of the slash indicates that the input information symbol at this time is 2; the "22" on the left side of the slash in "22/3" is the mixed recursion When the trellis space-time code (HSR-STTC) encoder transitions from state 0 to state 3, the corresponding two output symbols, the "3" on the right side of the slash indicates that the input information symbol at this time is 3.

In the second row of data in Figure 2b, the "21" on the left side of the slash in "21/1" is the corresponding Two output symbols, "1" on the right side of the slash indicates that the input information symbol at this time is 1; "01" on the left side of the slash in "01/0" is the hybrid recursive grid space-time code (HSR- When the STTC) encoder transitions from state 1 to state 1, the corresponding two output symbols, the "0" on the right side of the slash indicates that the input information symbol at this time is 0; the "23/3" on the left side of the slash "23" is the two corresponding output symbols when the hybrid recursive trellis space-time code (HSR-STTC) encoder transitions from state 1 to state 2, and "3" on the right side of the slash represents the input information symbol at this time is 3; "03" on the left side of the slash in "03/2" is the corresponding two output symbols when the hybrid recursive lattice space-time code (HSR-STTC) encoder is transferred from state 1 to state 3, The "2" on the right side of the slash indicates that the symbol of the input information at this time is 2.

In the data in the third row of Figure 2b, the "12" on the left side of the slash in "12/2" is when the HSR-STTC encoder transitions from state 2 to state 0, corresponding The two output symbols of the slash, the "2" on the right side of the slash indicates that the input information symbol at this time is 2; the "32" on the left side of the slash in "32/3" is the hybrid recursive grid space-time code (HSR -STTC) When the encoder transfers from state 2 to state 1, the corresponding two output symbols, the "3" on the right side of the slash indicates that the input information symbol at this time is 3; the left side of the slash in "10/0" The "10" in the figure is the two corresponding output symbols when the hybrid recursive trellis space-time code (HSR-STTC) encoder transitions from 2 states to 2 states, and the "0" on the right side of the slash represents the input information at this time The symbol is 0; the "30" on the left side of the slash in "30/1" is the corresponding two output symbols when the hybrid recursive lattice space-time code (HSR-STTC) encoder is transferred from state 2 to state 3 , the "1" on the right side of the slash indicates that the symbol of the input information at this time is 1.

In the data in the fourth row of Figure 2b, the "33" on the left side of the slash in "33/3" is when the HSR-STTC encoder transitions from state 3 to state 0, corresponding The two output symbols of the slash, the "3" on the right side of the slash indicates that the input information symbol at this time is 3; the "13" on the left side of the slash in "13/2" is the hybrid recursive lattice space-time code (HSR -STTC) When the encoder transfers from state 3 to state 1, the corresponding two output symbols, the "2" on the right side of the slash indicates that the input information symbol at this time is 2; the left side of the slash in "31/1" "31" is the two corresponding output symbols when the hybrid recursive trellis space-time code (HSR-STTC) encoder transitions from state 3 to state 2, and "1" on the right side of the slash represents the input information at this time The symbol is 1; the "11" on the left side of the slash in "11/0" is the corresponding two output symbols when the hybrid recursive lattice space-time code (HSR-STTC) encoder is transferred from 3 states to 3 states , the "0" on the right side of the slash indicates that the symbol of the input information at this time is 0.

With reference to Fig. 3 a, if the present invention determines to adopt eight-phase phase-shift keying (8PSK) modulation mode, then the encoding state of this hybrid recursive trellis space-time code (HSR-STTC) is eight states, and its encoding structure comprises component code unit 30 and mapper unit 31 . "" in the figure indicates modulo 2 addition operation. The component code unit 30 includes three recursive convolutional codes, the code rate of each convolutional code is 1/2, and each convolutional code includes a shift register, i.e. shift register D ₀ , shift register D _i and shift register D ₂ , the state numbers of these three shift registers are all 2; the mapper unit 31 includes three symbol mappers. Since there are two antennas at the sending end, two different sending symbols will be generated at the same time during encoding, denoted by s ₃ and s ₄ respectively. Let the input sequence u of the encoder include a ₀ , b ₀ , c ₀ , a ₁ , b ₁ , c ₁ ,,..., a _L , b _L , c _L in sequence, then the input information at the i-th moment (a _i , _bi , c _i ) should have eight possible combinations, namely 000, 001, 010, 011, 100, 101, 110, 111, in the figure a _i-1 ′, bi _-1 ′ and c _{i- 1} ′ are the values in shift register D ₀ , shift register D ₁ and shift register D ₂ respectively, then a _i ′=a _i a _i-1 ′ determines the hybrid recursive lattice space-time code (HSR-STTC ) the value of the shift register D ₀ in the encoder at time i, b _i ′=b _i  _{b i-1} ′ determines the shift register D ₁ in the hybrid recursive trellis space-time code (HSR-STTC) encoder at i The value at time, c _i ′=ci _ c _i-1 ′ determines the value of shift register D ₂ in the hybrid recursive trellis space-time code (HSR-STTC) encoder at time i. Therefore, at time i, the encoding state will shift from a _i-1 ′+2b _i-1 ′+4c _i-1 ′ to a _i ′+2b _i ′+4c _i ′, as shown in Figure 3b. After encoding the input information (a _i , b _i , c _i ) by component codes, an output of 6 bits is obtained, and then the mapper maps the 6-bit data into two eight-phase phase-shift keying ( 8PSK) symbols S ₃ and S ₄ , the different sending symbol mappings and different position mappings included in the mapping process are:

The different transmission symbol mapping is to select one information bit from the output bits of the two component codes, and select one check bit from the output bits of the third component code. These three bits are mapped to an eight-phase shift Phase keying (8PSK) symbol S ₃ , the remaining three bits, that is, the check bits of the first two component codes and the information bits of the third component code, are mapped to another eight-phase phase shift keying (8PSK) symbol S ₄ , the two transmitted symbols S ₃ and S ₄ are respectively sent from two antennas;

The mapping of different positions requires two bits output by the same component code to be mapped to different positions of two eight-phase phase-shift keying (8PSK) symbols S ₃ and S ₄ . An eight-phase phase-shift keying (8PSK) symbol consists of three bits, and the positions of the three bits are represented by h ₂ , h ₃ , h ₄ , if the information bit of a component code corresponds to one of the eight-phase phase-shift keying (8PSK) symbol S ₃ h ₂ position, then when the parity bit of the component code corresponds to another eight-phase phase shift keying (8PSK) symbol S ₄ , other arbitrary two positions other than h ₂ can be selected , when the two output bits of the other two component codes are mapped to two eight-phase phase-shift keying (8PSK) symbols S ₃ and S ₄ , they also have a similar positional relationship.

Referring to Fig. 3b, if the present invention determines to adopt the 8-phase phase-shift keying (8PSK) modulation mode, the code state transition rule is similar to the case of adopting the 4-phase phase-shift keying (QPSK) modulation mode. 0 to 7 in the figure represent the points in the signal constellation diagram respectively, and the meanings of the numbers on the left side are similar to those in Figure 2b, except that they are based on the transition between eight states.

With reference to Fig. 4, if the present invention determines to adopt the hexadecimal quadrature amplitude (16QAM) modulation mode, then the encoding state of this hybrid recursive trellis space-time code (HSR-STTC) is sixteen states, and its encoding structure includes component codes unit 40 and mapper unit 41. "" in the figure indicates modulo 2 addition operation. The component code unit 40 includes four recursive convolutional codes, the code rate of each convolutional code is 1/2, and each convolutional code includes a shift register, i.e. shift register D ₀ , shift register D ₁ , shift register D ₂ and shift register D ₃ , the state numbers of these four shift registers are 2; the mapper unit 41 includes four symbol mappers. Since there are two antennas at the sending end, two different sending symbols will be generated at the same time during encoding, denoted by S ₅ and S ₆ respectively. Let the input sequence of the encoder be u, including a ₀ , b ₀ , c ₀ , d ₀ , a 1 , b ₁ , c ₁ , _{d 1} ,..., a _i , b _i , c _i , d _i , then the input information (a _i , bi _, c _i , d _i ) at the i-th moment should have sixteen possible combinations 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001 , 1010, 1011, 1100, 1101, 1110, 1111. In the figure, a _i-1 ′, b _i-1 ′, c _i-1 ′ and d _i-1 ′ are respectively shift register D ₀ , shift register D ₁ , shift register D ₂ and shift register D ₃ , then a _i ′=a _i  _{a i-1} ′ determines the value of the shift register D ₀ in the hybrid recursive trellis space-time code (HSR-STTC) encoder at time i, b _i ′= _bi b _i-1 ′determines the value of the shift register D ₁ in the hybrid recursive trellis space-time code (HSR-STTC) encoder at time i, c _i ′=ci _{c i-1} ′determines the hybrid recursive trellis The value of the shift register D ₂ in the space-time code (HSR-STTC) encoder at time i, d _i ′=d _i d _i-1 ′ determines the The value of shift register D ₃ at time i, therefore, at time i, the encoded state will be transferred from a _i-1 ′+2b _i-1 ′+4c _i-1 ′+8d _i-1 ′ to a _i ′+2b _i ′+4c _i ′+8d _i ′. After encoding the input information (a _i , b _i , ci _, d _i ) by the component code, an 8-bit output is obtained, and then the mapper maps the 8-bit data into two hexadecimal positive Cross-amplitude (16QAM) symbols S ₅ and S ₆ , the mapping process includes different transmission symbol mappings and different position mappings:

There are two ways to map the different transmitted symbols. One is to select one information bit from the output bits of the two component codes, and then select one check bit from the output bits of the other two component codes. Four bits are mapped to one hexadecimal quadrature amplitude (16QAM) symbol S ₅ , and the remaining four bits are mapped to another hexadecimal quadrature amplitude (16QAM) symbol S ₆ , the two symbols S ₅ and S ₆ are sent out from two antennas respectively; the second is to select an information bit from the output bits of the three component codes, and then select a check bit from the output bits of the other component code, and combine the four Bits are mapped to one hexadecimal quadrature amplitude (16QAM) symbol S ₅ , and the remaining four bits are mapped to another hexadecimal quadrature amplitude (16QAM) symbol S ₆ , the two symbols S ₅ and S ₆ are sent out from the two antennas respectively;

The mapping of different positions requires the two output bits of each component code to be mapped to different positions of two hexadecimal quadrature amplitude (16QAM) symbols S ₅ and S ₆ . A hexadecimal quadrature amplitude modulation (16QAM) symbol consists of four bits, and these four positions are represented by h ₅ , h ₆ , h ₇ , h ₈ , if the information bit of a component code corresponds to one of the sixteen In the h ₅ position of the hexadecimal quadrature amplitude modulation (16QAM) symbol S ₅ , the parity bit of the component code corresponds to another hexadecimal quadrature amplitude modulation (16QAM) symbol S ₆ , except h Any other three positions other than position ₅ , when the two output bits of the remaining three component codes are mapped to two hexadecimal quadrature amplitude modulation (16QAM) symbols, they also have a similar positional relationship.

The difference between Fig. 4a and Fig. 4b lies in the slight difference in the combined mapping forms of the output bits of the component codes.

Referring to Fig. 5, through the comparison of several sets of simulation curves, it can be seen that the present invention greatly improves the performance of the serial cascaded system under quasi-static fading channels and fast fading channels. In the simulation test, select the simulation parameters as follows (see Table 1):

1) Outer code: the outer code adopts a 1/2 code rate regular low-density check code, and the degree distribution sequence is (3, 6), as shown in Table 1;

2) The length of the information bit is 504 bits;

3) inner code: respectively adopt prior art, i.e. recursive grid space-time code (R-STTC) and the present invention, i.e. the encoding method of hybrid recursive grid space-time code (HSR-STTC), as shown in table 1;

4) Channel: Two different channels are used, namely quasi-static fading channel and fast fading channel. The quasi-static fading channel refers to a channel whose channel fading factor remains unchanged in one frame and changes independently at the beginning of the next frame, while A fast fading channel refers to a channel in which the channel fading factor changes independently every other symbol period;

5) Antennas: two transmitting antennas and two receiving antennas.

Table 1 Modulation Quadrature Phase Shift Keying (QPSK) Eight phase phase shift keying (8PSK) outer code (3,6) LDPC Internal Code R-STTC (Fig. 7a) HSR-STTC (Fig. 2a) R-STTC (Fig. 7b) HSR-STTC (Fig. 3a) Interleaver none serial cascade system SCST1 SCST2 SCST3 SCST4

Figure 5a is the performance curve of the serial concatenated space-time coding system (SCSTC) using quadrature phase-shift keying (QPSK) modulation under quasi-static and fast fading channels, and the abscissa in the figure is the signal-to-noise of each receiving antenna Ratio (SNR), the unit is decibel (dB), and the vertical axis is the frame error rate. The solid line in the figure represents the performance curve under the quasi-static fading channel, and the dotted line represents the performance curve under the fast fading channel. The curves in the figure represent from right to left: the circled curve on the rightmost solid line represents the recursive trellis space-time code (R-STTC) that adopts quadrature phase-shift keying modulation, that is, the prior art as serial The internal code of the cascaded system, and the performance curve of the serial cascaded system with 2 transmit and 2 receive terminals in the quasi-static channel, the system is represented by SCST1; the curve with a box on the second solid line from the right Represents the hybrid recursive trellis space-time code (HSR-STTC) that adopts four-phase phase-shift keying modulation, that is, the present invention is the inner code of the serial cascade system, and the transceiver end is a serial cascade system with 2 sending and 2 receiving The performance curve under the quasi-static channel, the system is represented by SCST2; the circled curve on the dotted line represents the recursive trellis space-time code (R-STTC) using quadrature phase-shift keying modulation, that is, the prior art as serial The internal code of the cascaded system, and the performance curve of the serial cascaded system SCST1 with 2 transmitters and 2 receivers in the fast fading channel; the curve with a box on the dotted line represents the mixed recursive modulation using quadrature phase shift keying Grid space-time code (HSR-STTC), that is, the performance curve of the serial cascade system SCST2 in the fast fading channel, which is used as the inner code of the serial cascade system in the present invention, and the transceiver end is 2 transmit 2 receive serial cascade system SCST2.

From the slope of the curve in Figure 5a, it can be seen that the serial concatenated system using the Hybrid Recursive Trellis Space-Time Code (HSR-STTC) as the inner code can obtain the full diversity gain provided by the system under the quasi-static fading channel, and the anti-fading performance is better than The serial concatenated space-time coding system with recursive trellis space-time code (R-STTC) as the inner code has been greatly improved. When the frame error rate is 10-2 and the number of receiving antennas is 2, the serial cascaded system SCST2 has a gain of about 2.5 decibels (dB) compared with the serial cascaded system SCST1 under the fast fading channel; in the quasi-static fading channel Next, the serial cascade system SCST2 has a gain of nearly 2 decibels (dB) over the serial cascade system SCST1. Obviously, no matter in the quasi-static fading channel or in the fast fading channel, if the serial concatenated space-time coding system adopts the hybrid recursive trellis space-time code (HSR-STTC) modulated by quadrature phase shift keying (QPSK) ) as an inner code, the anti-fading performance is greatly improved without increasing the complexity of the system.

Figure 5b is the performance curve of the serial concatenated space-time coding system (SCSTC) using 8-phase phase-shift keying (8PSK) modulation under quasi-static and fast fading channels, and the abscissa in the figure is the signal-to-noise of each receiving antenna Ratio (SNR), the vertical axis is the frame error rate. The curves in the figure represent in turn from right to left: the crossed curve on the rightmost solid line represents the recursive trellis space-time code (R-STTC) using eight-phase phase-shift keying modulation, that is, the prior art as serial The internal code of the serial cascading system, and the performance curve of the serial cascading system with 2 sending and 2 receiving at the transceiver end under the quasi-static channel, the system is represented by SCST3; the second solid line from the right is a curve with a triangle Represents the hybrid recursive trellis space-time code (HSR-STTC) that adopts eight-phase phase-shift keying modulation, that is, the present invention is used as the inner code of the serial cascade system, and the transceiver end is a serial cascade system with 2 sending and 2 receiving The performance curve under the quasi-static channel, the system is represented by SCST4; the crossed curve on the dotted line represents the recursive trellis space-time code (R-STTC) using eight-phase phase-shift keying modulation, that is, the prior art as serial The internal code of the cascaded system, and the performance curve of the serial cascaded system SCST3 with 2 transmitters and 2 receivers at the fast fading channel; the curve with a triangle on the dotted line represents the hybrid recursive network using eight-phase phase-shift keying modulation HSR-STTC, which is the inner code of the serial cascade system in the present invention, and the performance curve of the serial cascade system SCST4 with 2 transmission and 2 reception at the fast fading channel. It can be seen from Fig. 5b that when the signal-to-noise ratio is greater than a certain given value, the serial cascaded system SCST3 and the serial cascaded system SCST4 can obtain approximately the same diversity gain. When the frame error rate is 10 ^-2 and the number of receiving antennas is 2, the serial cascaded system SCST4 has a gain of about 3 decibels (dB) compared with the serial cascaded system SCST3 in the fast fading channel; in the quasi-static fading channel Next, the serial cascade system SCST4 has a gain of nearly 1 decibel (dB) over the serial cascade system SCST3.

The above simulation results can prove that, compared with the serial concatenated space-time coding system using recursive trellis space-time code (R-STTC), the serial concatenated space-time coding system using hybrid recursive trellis space-time code (HSR-STTC) as inner code The cascaded system can obtain higher diversity gain than the former in both the quasi-static fading channel and the fast fading channel, and the coding gain is also greatly improved, which can achieve better results without increasing the complexity of the system.

The above-described embodiment is a four-state hybrid recursive trellis space-time code (HSR-STTC) based on quadrature phase-shift keying (QPSK) modulation and an eight-state hybrid recursive trellis space-time code based on eight-phase phase-shift keying (8PSK) modulation. The embodiment of time code (HSR-STTC), in actual application, can choose different hybrid recursive trellis space-time code (HSR-STTC) arbitrarily according to the needs of the system or users, such as: based on four-phase phase-shift keying (QPSK) modulated eight-state hybrid recursive trellis space-time code (HSR-STTC), sixteen-state hybrid recursive trellis space-time code (HSR-STTC), etc., only need to select the system component code and the corresponding The mapping method is fine. In a word, the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention.

Claims (8)

1. one kind is mixed recurrence grid space-time coding method, and its cataloged procedure is as follows:

The first step, transmission rate is as requested determined modulation system, and determines that thus this mixes the encoding state number of the empty time-code of recurrence grid (HSR-STTC), when transmission rate is n bit/time slot, adopts 2 ⁿThe modulation system on-rank, encoding state number are 2 ⁿ

Second step, select component code, comprise status number, code check and the coded system of determining component code, this component code adopts the two condition systematic recursive convolutional sign indicating number of 1/2 code check, and the number of convolution code equals the transmission rate value of requirement, promptly when transmission rate is n bit/time slot, the number of convolution code is n, and its coded system is a type systematic sign indicating number, and this type systematic sign indicating number is meant in the coding output bit of each recursive convolution sign indicating number, must comprise an input information bits, all the other are check bit;

The 3rd step, adopt and mix mapping mode, the information bit of each component code output is mapped to respectively on the diverse location of different transmission symbols with check bit, promptly comprise different send sign map and diverse location mappings, this difference sends sign map and is meant that respectively choosing a bit correspondence mappings from two output bits of all component codes is a transmission symbol, and remaining all bit is mapped as another symbol; This diverse location mapping is meant, two output bits of arbitrary component code are mapped to respectively on the diverse location of two symbols, if one of them bit is mapped on certain position (L) of a transmission symbol, when then another output bit being mapped to another transmission symbol, can select all the other optional positions except that above-mentioned position (L).

2. mixing recurrence grid space-time coding method according to claim 1 is characterized in that modulation system comprises quaternary PSK (QPSK) modulation, eight phase phase-shift keyings (8PSK) modulation, hexadecimal quadrature amplitude (16QAM) modulation and other 2 ⁿThe modulation system on-rank, the n value equals the transmission rate value of requirement; For the mixing recurrence grid space-time coding method that adopts the different modulating mode, the selection of its component code is different with mapping mode.

3. mixing recurrence grid space-time coding method according to claim 1 and 2 is characterized in that component code is selected the two condition systematic recursive convolutional sign indicating number of two 1/2 code checks for use when adopting the modulation system of quaternary PSK (QPSK).

4. mixing recurrence grid space-time coding method according to claim 1 and 2 is characterized in that when adopting the modulation system of quaternary PSK (QPSK), and the difference that the mixing mapping comprises sends sign map and the diverse location mapping is respectively:

This difference sends sign map and is meant, selects an information bit and check bit at first respectively from the output bit of two component codes, and these two bits are mapped as a quaternary PSK (QPSK) symbol S ₁, will remain two bits then and be mapped as another quaternary PSK (QPSK) symbol S ₂, these two send symbol S ₁And S ₂Go out from two antenna transmission respectively;

The mapping of this diverse location is meant, uses h ₀, h ₁Two different bit positions representing each quaternary PSK (QPSK) symbol are if an output bit of same component code is mapped to a quaternary PSK (QPSK) symbol S ₁H ₀On the position, then another output bit should be mapped to another quaternary PSK (QPSK) symbol S ₂H ₁The position.

5. mixing recurrence grid space-time coding method according to claim 1 and 2, when it is characterized in that adopting the modulation system of eight phase phase-shift keyings (8PSK), component code is selected the two condition systematic recursive convolutional sign indicating number of three 1/2 code checks for use.

6. mixing recurrence grid space-time coding method according to claim 1 and 2, when it is characterized in that adopting the modulation system of eight phase phase-shift keyings (8PSK), the difference that the mixing mapping comprises sends sign map and the diverse location mapping is respectively:

This difference sends sign map and is meant, selects two information bits and a bit check bit at first respectively from the output bit of three component codes, and these three bits are mapped as one eight phase phase-shift keying (8PSK) symbol S ₃, then remaining three bits are mapped as another eight phases phase-shift keying (8PSK) symbol S ₄, these two send symbol S ₃And S ₄Go out from two antenna transmission respectively;

The mapping of this diverse location is meant, uses h ₂, h ₃, h ₄Three different bit positions representing each eight phase phase-shift keying (8PSK) symbol are to each component code, if its an output bit is mapped to one eight phase phase-shift keying (8PSK) symbol S ₃H ₂On the position, then another output bit can be mapped to another eight phases phase-shift keying (8PSK) symbol S ₄Remove h ₂On outer any position.

7, mixing recurrence grid space-time coding method according to claim 1 and 2, when it is characterized in that adopting the modulation system of hexadecimal quadrature amplitude (16QAM), component code is selected the two condition systematic recursive convolutional sign indicating number of four 1/2 code checks for use.

8. mixing recurrence grid space-time coding method according to claim 1 and 2, when it is characterized in that adopting the modulation system of hexadecimal quadrature amplitude (16QAM), the difference that the mixing mapping comprises sends sign map and the diverse location mapping is respectively:

This difference sends sign map and is meant, from the output bit of four component codes, select two information bits and two bit check bits at first respectively, perhaps select three information bits and a bit check bit, then these four bits are mapped as a hexadecimal quadrature amplitude (16QAM) symbol S ₅, remaining four bits then are mapped as another hexadecimal quadrature amplitude (16QAM) symbol S ₆, these two send symbol S ₅And S ₆Go out from two antenna transmission respectively.

The mapping of this diverse location is meant, uses h ₅, h ₆, h ₇, h ₈Four different bit positions representing each hexadecimal quadrature amplitude (16QAM) symbol are to each component code, if its an output bit is mapped to a hexadecimal quadrature amplitude (16QAM) symbol S ₅H ₅On the position, then another output bit is mapped to another hexadecimal quadrature amplitude (16QAM) symbol S ₆Remove h ₅On outer any position.

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