JP2945686B2 - Multiple reception maximum likelihood decoding circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a transmission system that diversity-receives an error-correction-coded signal, in which a plurality of received signals are input to a single decoding circuit and multiplexed reception is performed simultaneously. It relates to the maximum likelihood decoding method.

[Prior Art] Conventionally, a circuit for performing maximum likelihood decoding using a plurality of received demodulated signals has not been proposed, so consider level combining diversity, which is a similar method in detecting information from a plurality of received demodulated signals. This type of circuit is configured as shown in FIG. 3, where 1 is transmission information, 2 is a transmitter, 3 is a transmission signal, 4 is a receiver, 5 is a reception signal, 6 is an S / N estimation circuit, 7
Is a reception signal level adjustment circuit, 8 is a level-adjusted signal, 9 is a level synthesis circuit, 10 is a demodulation circuit, and 11 is reception information. The operation of this type of circuit is as follows. The transmission signal 3 transmitted from the transmission circuit 2 is received by the plurality of receivers 4, and the S / N of the received signal is estimated. Next, the received signal level adjusting circuit 7 adjusts the level of each received signal so as to be in S / N proportion. The level adjusted signal 8 is subjected to level synthesis by the level synthesizing circuit 9, and the received signal S / N is adjusted.
N is improved. As a problem of the circuit performing such an operation, in order to perform ideal level combining diversity,
The received signal levels are S ₁ , S ₂ ,..., S _a , and the S / N is P ₁ , P ₂ ,.
_{When a} is set, the level synthesis that ideally improves the S / N is S ₁
Each received signal level As _{P 1 + P 2 · P 2} + ... + S a · P a
It was necessary to adjust and synthesize the ratio in proportion to the S / N. For this reason, it is necessary to estimate the S / N for each received signal, and the S / N
However, there is a drawback in that an estimation circuit must be added. Furthermore, analog synthesis is used for the level synthesis circuit, and it is difficult to adjust the circuit without adjustment, and there is a problem in reliability.

In addition, the configuration of the conventional general maximum likelihood decoding circuit is
FIG. 4 shows an example of a decoding circuit for a convolutional coded signal having a constraint length of 1/2 and a constraint length of 3. 101 is transmission data, 102 is a convolutional coding circuit, 103 is a coded signal, 2 is a transmitter, 3 is a transmission signal, 104 is a reception demodulator, 105 is a demodulation signal of the reception demodulator, 10
6 is a maximum likelihood decoding circuit, 107 is an ACS circuit, 108 is a demodulated signal likelihood holding circuit, 109 is a circuit holding the likelihood of a path, 110 is a likelihood calculation circuit, 111 is a likelihood comparison circuit, and 112 is a new Is a likelihood holding circuit, 113 is a path memory, and 114 is a decoded signal. In addition,
The connection in the decoding circuit focuses on one ACS circuit and one ACS circuit.
Only connections related to the circuit are shown.

The operation of this circuit is as follows. The transmission data 101 is encoded by the convolution encoding circuit 102 and transmitted by the transmitter 2. The transmitted signal 3 is received and demodulated by the reception demodulator 104. The demodulated signal takes an intermediate value between "1" and "0" due to noise in the transmission line, and is supplied to the decoding circuit as a soft detection signal obtained by quantizing the signal level. Here, the signal level is a likelihood indicating the ambiguity of the demodulated signal. The demodulated signal having this likelihood information is once held in the demodulated signal likelihood holding circuit 108. Next, a surviving path is selected in the ACS circuit 107 in which there are only the number of states (in the example: 2 ^(3-1) states) determined by the combination of information bits included in the constraint length in encoding.
In the determination of the maximum likelihood path in the ACS circuit, the likelihood of the demodulated signal is added to the likelihood of a path to be selected (in the example, two paths), and a total of two new likelihood values are calculated.
Next, these two new likelihood values are compared by the likelihood comparison circuit 111, and the path giving the highest likelihood is selected, and the selected high likelihood value is given as the likelihood of the path. The new likelihood is held in the circuit 109 for holding the likelihood of the path for each state. Next, the information of the selected path is stored in the path memory where the past history of each path is recorded.
It is conveyed to 113. In the path memory, by this path selection, the memory value of the path not selected is erased, the memory value of the selected path is kept as it is, and the history of the path by the path selection is recorded at the latest time position. As the final decoded signal, the oldest memory value of the path memory is output, and the decoding ends.

Such a general maximum likelihood decoding circuit has a drawback that a plurality of demodulated signals cannot be simultaneously subjected to the maximum likelihood decoding by performing the maximum likelihood decoding of the demodulated signal by one receiver.

[Problems to be Solved by the Invention] In order to eliminate these drawbacks, the present invention makes effective use of the maximum likelihood path selection and likelihood calculation process performed in the case of maximum likelihood decoding. Multiplex reception maximum likelihood decoding method that enables maximum likelihood decoding of a plurality of received signals simultaneously with a simple circuit without adding any additional circuits to the result, thereby achieving the same effect as ideal combining diversity. The purpose is to provide.

[Means and Actions for Solving the Problems] In order to achieve the above object, the present invention provides a transmission efficiency n / m,
In a multiplex reception maximum likelihood decoding method for receiving and demodulating a convolutionally encoded transmission signal having a constraint length k by a plurality of receivers and performing maximum likelihood decoding using the demodulated a plurality of received demodulated signals, a constraint length k And the number of states determined by the transmission efficiency n / m (2
Perform likelihood calculation for ^{(k-1) n} ) maximum likelihood determination
The demodulated signal of a demodulated by a receivers is taken into each ACS circuit of an ACS (Add Compare Select) circuit,
In order to select one surviving path from m paths in the S circuit, the likelihood of the demodulated signal of a is added to the likelihood having m paths, and a total likelihood value of m × a is calculated and compared. The path having the highest likelihood value among the new likelihood values is selected as the surviving path, the likelihood value corresponding to the selected path is stored as the surviving path likelihood value, and each decoded signal is It decodes by extracting the oldest information of the selected path from the path memory where the path history is recorded, and decodes the demodulated signal demodulated by a plurality of receiving demodulators into one By decoding with a likelihood decoding circuit, a gain equivalent to that of combining diversity can be obtained. As a result, the reliability of the circuit is improved since it can be realized entirely by a digital circuit without using an analog circuit.

[Embodiment] Fig. 1 shows an embodiment of the present invention, in which convolutional coding with a transmission efficiency of 1/2 and a constraint length of 3 is performed, and reception is performed by two receiving stations. 101 is transmission data, 102 is a convolutional coding circuit, 103 is a coded signal, 2 is a transmitter,
3 is a transmission signal, 115 is a first reception demodulator, 116 is a demodulation signal of the first reception demodulator, 117 is a second reception demodulator, 118 is a second reception sub-long-term demodulation signal, 106 is a maximum likelihood decoding circuit, 107 is an ACS circuit, 108 is a demodulation signal likelihood holding circuit, 109 is a circuit for holding the likelihood of a path, 110 is a likelihood calculation circuit, 111 is a likelihood comparison circuit, 112 is a new likelihood holding circuit, 113 Is the path memory, 114
Is a decoded signal. The operation of this circuit is as follows.
The transmission data 101 is encoded by the convolution encoding circuit 102 and transmitted by the transmitter 2. The transmitted signal 3 is 2
Reception and demodulation are performed by two reception demodulators 115 and 117. The demodulated signal is once held in the demodulated signal likelihood holding circuit 108. Next, the number of states determined by the combination of information bits included in the constraint length in encoding (in the example: 2 ^(3-1)
), The surviving path is selected in the ACS circuit 107 which exists only in the state (1). The maximum likelihood path determination in the ACS circuit differs from the conventional maximum likelihood decoding circuit in that the likelihood of a path to be selected (in the example: two paths) is the likelihood of two demodulated signals by two receiving demodulators. Are added, and a total of four new likelihood values are calculated. Next, these four new likelihood values are compared by the likelihood comparison circuit 111, a path giving the highest likelihood is selected, and the selected high likelihood value is given as the likelihood of the path. Hereinafter, like the conventional maximum likelihood decoding circuit, the new likelihood is held in the circuit 109 for holding the likelihood of the path for each state. Next, the information of the selected path is transmitted to the path memory 113 in which the past history of each path is recorded. In the path memory, by this path selection, the memory value of the path not selected is erased, the memory value of the selected path is kept as it is, and the history of the path by the path selection is recorded at the latest time position. As the final decoded signal, the oldest memory value of the path memory is output and decoding is completed. Here, the likelihood of the received demodulated signal indicates the S / N of the received signal, and the received signal level and signal phase Is represented by information representing the uncertainty of the signal such as the position error of the signal.

FIG. 2 shows characteristics in this embodiment.
When the error rate of the decoded signal is 10 ^-3 ,
Shows the relationship between E _b / N _o (when using a PSK absolute coherent detection). For comparison, a case where selection diversity for selecting a high-quality line and receiving and demodulating is used is also shown. As can be seen from FIG. 2, when the S / N of the two demodulated signals is equal, an improvement effect of 2 dB is obtained, and an improvement effect equivalent to the improvement effect of 3 dB obtained in ideal combining diversity can be obtained.

The present invention can be realized in a similar manner when a convolutionally coded signal having a transmission efficiency of n / m and a constraint length of k is received at the station a. 2 An ACS circuit is provided for each ^{(k-1) n} state, and one
In the ACS circuit, the likelihood from the demodulated signal a and the path m is calculated, and the path having the highest likelihood is obtained, so that the maximum likelihood decoding becomes possible.

[Effects of the Invention] As described above, by decoding a demodulated signal demodulated by a plurality of receiving demodulators with one maximum likelihood decoding circuit, a gain equivalent to that of combining diversity can be obtained. As a result, the reliability of the line is improved because the circuit can be entirely realized by a digital circuit without using an analog circuit.
Further, the circuit scale is exactly the same as the conventional maximum likelihood decoding circuit, and the configuration of the path memory occupying more than half of the maximum likelihood decoding circuit is
There are very few extensions to implement the invention,
It can be realized with almost the same configuration as the conventional maximum likelihood decoding circuit.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing improved characteristics of the embodiment of FIG. 1, FIG. 3 is an explanatory diagram of a configuration showing a conventional level combining diversity, FIG. FIG. 4 is an explanatory diagram showing a configuration of a conventional maximum likelihood decoding circuit. 2 Transmitter 102 Convolutional coding circuit 115 First reception demodulator 117 Second reception demodulator 106 Maximum likelihood decoding circuit 107 ACS circuit 108 Demodulation Signal likelihood holding circuit, 109: Likelihood holding circuit with path, 110: Likelihood calculating circuit, 111: Likelihood comparing circuit, 112: New likelihood holding circuit, 113: Path memory.

──────────────────────────────────────────────────続 き Continuation of the front page Examiner Masaaki Suzuki (56) References JP-A-2-149023 (JP, A) JP-A-1-311642 (JP, A) JP-A-60-41831 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) H03M 13/00-13/22 H04B 7/00 H04B 7/02-7/12 H04L 1/02-1/06

Claims (1)

(57) [Claims] 1. A convolutionally encoded transmission signal having a transmission efficiency of n / m and a constraint length of k is received and demodulated by a plurality of receivers.
In a multiplex reception maximum likelihood decoding method for performing maximum likelihood decoding using a plurality of demodulated demodulated signals of a, a constraint length k and a transmission efficiency n /
ACS (Add Compare Selec) that executes the likelihood calculation for the maximum likelihood determination for the number of states (2 ^{(k-1) n} ) determined by m
t) A demodulated signal of a demodulated by a receivers is taken into each ACS circuit of the circuit, and one surviving path is selected from m paths in each ACS circuit. The likelihood of the demodulated signal of a is added, a total m × a new likelihood value is obtained and compared, and a path having the highest likelihood value among the obtained new likelihood values is selected as a surviving path, and selected. The likelihood value corresponding to the selected path is stored as the likelihood value of the surviving path, and as the decoded signal, the oldest information of the selected path is extracted from the path memory in which the history of each path is recorded. Multiplex reception maximum likelihood decoding method, characterized in that decoding is performed by the following method.