JPH0373623A - Multiplex reception maximum likelihood decoding circuit - Google Patents

Abstract

PURPOSE:To attain maximum likelihood decoding to plural reception signals simultaneously with a simple circuit and to obtain the same effect as that of an ideal synthesis diversity by using one maximum likelihood decoding circuit to decode a demodulation signal demodulated by plural reception demodulation devices. CONSTITUTION:A signal 3 sent to a decoding circuit 106 is received and demodulated by 2 reception demodulation devices 115, 117 and latched by a demodulation signal likelihood holding circuit 108. Then a survival path is selected in ACS circuits 107 in existing by a status number depending on the combination of information bits included in a restriction length in the coding. In the case of deciding a maximum likelihood path in the ACS circuit, it is different from the decision of a conventional maximum likelihood decoding circuit, the likelihood of two demodulation signals by two reception demodulators is added respectively to the likelihood of paths to be selected (in this embodiment, 2 paths) and in total 4 new likelihood paths are calculated. Then the 4 new likelihood paths are compared by a likelihood comparison circuit 111 and a path offering the maximum likelihood is selected and the selected maximum likelihood is given to the likelihood of the path. The succeeding processing is similar to that of a conventional maximum likelihood decoding circuit.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a transmission system that receives error-correction coded signals in a diversity manner. This relates to a maximum likelihood decoding circuit.

[Prior Art] Since a circuit for maximum likelihood decoding using a plurality of received demodulated signals has not been proposed in the past, let us consider level combining diversity, which is a similar method for detecting information from a plurality of received demodulated signals. This type of circuit is configured as shown in Figure 3, where 1 is transmission information, 2 is a transmitter, 3 is a transmission signal,
4 is a receiver, 5 is a received signal, 6 is an S/N estimation circuit, 7 is a received signal level adjustment circuit, 8 is a level-adjusted signal,
9 is a level synthesis circuit, 10 is a demodulation circuit, and 11 is received information. The operation of this type of circuit is as follows. The transmission signal 3 transmitted from the transmission circuit 2 is received by a plurality of receivers 4, and the SlN of each received signal is estimated. Next, the received signal level adjustment circuit 7 adjusts the level of each received signal in S/N proportion, and the level-adjusted signal 8
Level synthesis is performed by the level synthesis circuit 9, and the received signal SlN is improved. The problem with a circuit that performs such an operation is that in order to perform ideal level combining diversity, each received signal level is set as Sl+S2*...S, and SlN is set as P1+P2+...p, , the level synthesis that ideally improves SlN is Sl
op, +S2 ・P2+ . . . 10S, ・P, it was necessary to adjust and combine each received signal level at a ratio proportional to its SlN. Therefore, it is necessary to estimate the SlN for each received signal, and there is a drawback that an SlN estimation circuit must be added. Furthermore, the level synthesis circuit used analog synthesis, which made it difficult to make the circuit non-adjustable, and there were problems with reliability.

In addition, the configuration of a conventional general maximum likelihood decoding circuit has a transmission efficiency of 1.
FIG. 4 shows an example of a decoding circuit for a convolutional encoded signal having a length of 3.2 and a constraint length of 3. 101 is transmission data, 102 is a convolutional encoding circuit, 103 is an encoded signal, 2 is a transmitter, 3
is a transmission signal, 104 is a receiving demodulator, 105 is a demodulated signal of the receiving demodulator, 106 is a maximum likelihood decoding circuit, 107 is an AC8 circuit, 108 is a demodulated signal likelihood holding circuit, and 109 is holding the likelihood of a path. circuit, 110 is a likelihood calculation circuit, 111
is a likelihood comparison circuit, 112 is a new likelihood holding circuit, 113
is a path memory, and 114 is a decoded signal. Note that the wiring within the decoding circuit focuses on one AC8 circuit, and one AC3 circuit.
Only the connections related to the circuit are shown.

The operation of this circuit is as follows. Transmission data 101 is encoded by convolutional encoding circuit 102 and transmitted by transmitter 2 . The transmitted signal 3 is sent to the receiver demodulator 104
It is received and demodulated by

The signal level of the demodulated signal takes an intermediate value between "1" and "Oo" due to noise in the transmission path, and is supplied to the decoding circuit as a soft detection signal obtained by quantizing the signal level.Here, the signal level is the demodulated signal. The demodulated signal with this likelihood information is once held in the demodulated signal likelihood holding circuit 108E.Next, it is determined by the combination of information bits included within the constraint length in encoding. A surviving path is selected within the AC8 circuit 107 that exists in the number of states (2 (3-1) states in the case of the example).The maximum likelihood path determination in the AC8 circuit : The likelihood of the demodulated signal is added to the likelihood of the two paths) to calculate a total of two new likelihood values.Next, these two new likelihood values are compared by the likelihood comparison circuit 111. Then, the path that gives the highest likelihood is selected, and the selected high likelihood value is given as the likelihood of that path.The new likelihood is determined by a circuit that maintains the likelihood of the path for each state. The selected path information is then transmitted to the path memory 113 in which the past history of each path is recorded.

In the path memory, as a result of this path selection, the memory values of the unselected paths are erased, the memory values of the selected paths are left as they are, and the path history resulting from the path selection is recorded at the latest time position. The last memory value of the path memory is output as the final decoded signal, and the decoding ends.

Such an intra-film maximum likelihood decoding circuit has a drawback that it cannot perform maximum likelihood decoding of a plurality of demodulated signals at the same time by maximum likelihood decoding of a demodulated signal by one receiver.

[Problem 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 that are performed when performing maximum likelihood decoding, and without adding almost any additional circuit to the conventional maximum likelihood decoding circuit. To provide a multiplex reception maximum likelihood decoding circuit which can simultaneously perform maximum likelihood decoding of a plurality of received signals with a simple circuit and, as a result, can obtain the same effect as ideal combining diversity.

[Means and operations for solving the problem] In order to achieve the above object, the present invention receives and demodulates an encoded transmission signal by a plurality of receivers, and receives and demodulates the demodulated a plurality of received demodulated signals. In a maximum likelihood decoding circuit that performs maximum likelihood decoding using
The decoding circuit is configured to select one surviving path from among the paths, and as an operation of the decoding circuit, a demodulated signal demodulated by a receivers is processed in the decoding circuit to perform a likelihood calculation for maximum likelihood determination. A CS (Add Compar
e 5elect) into the circuit, then the number of states determined by the constraint length and the transmission efficiency n/m (2”-1)
In order to select one surviving path from m paths in each AC5 circuit with +''), add the likelihood of the demodulated signal of a to the likelihood of m paths, and calculate the new likelihood value of the total amount Xn. The path with the highest likelihood value among the new likelihood values obtained is selected as the surviving path, and the likelihood value corresponding to the selected path is stored as the likelihood value of the surviving path. It is characterized by decoding by extracting the past information of each path selected from a path memory in which the history of each path is recorded as a decoded signal, and demodulated by multiple receiving demodulators. By decoding the demodulated signal with one maximum likelihood decoding circuit, a gain equivalent to that of composite diversity can be obtained.This improves the reliability of the circuit because it can be realized entirely with digital circuits without using analog circuits. .

[Embodiment] FIG. 1 shows an embodiment of the present invention, and a case will be described in which convolutional encoding 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 encoding circuit, 1
03 is a coded signal, 2 is a transmitter, 3 is a transmission signal, 115
116 is the demodulated signal of the second receiving demodulator, 117 is the second receiving demodulator, 118 is the demodulated signal of the second receiving demodulator, 106 is the maximum likelihood decoding circuit, 107 is the AC3 circuit, 108 109 is a demodulated signal likelihood holding circuit, 109 is a circuit that holds 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 a path memory, and 114 is a This is the decoded signal.

The operation of this circuit is as follows. Transmission data 101 is encoded by a convolutional encoding circuit 102 and sent to the transmitter 2.
Sent by. The transmitted signal 3 is received and demodulated by two receiving 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 within the constraint length in encoding (in the case of the example, 2+3-1+
A surviving path is selected in the ACS circuit 107 that exists only in the state of . Maximum likelihood path determination in the AC8 circuit differs from conventional maximum likelihood decoding circuits in that the likelihood of the path to be selected (in the example: two paths) is determined by the likelihood of the two demodulated signals by the two receiving demodulators. are added respectively,
A total of four new likelihood values are calculated. Next, these four new likelihood values are compared by the likelihood comparison circuit 111, the path giving the highest likelihood is selected, and the selected high likelihood value is given as the likelihood of that path. In the following, the new likelihood is held in a circuit 109 that holds the likelihood of a path for each state, similar to the conventional maximum likelihood decoding circuit. Next, information on the selected path is transmitted to the path memory 113 in which the past history of each path is recorded. In the path memory, as a result of this path selection, the memory values of the unselected paths are erased, the memory values of the selected paths are left as they are, and the path history resulting from the path selection is recorded at the latest time position. The last memory value of the path memory is output as the final decoded signal, and the decoding ends.

Here, the likelihood of the received demodulated signal indicates the S/N of the received signal, and is expressed by information representing the uncertainty of the signal, such as the received signal level and the phase error of the signal phase.

FIG. 2 shows the characteristics of this embodiment. It shows the relationship between E b /N- of two demodulated signals when the error rate of the decoded signal is 10-3 (when PSK absolute synchronous detection is used). For comparison, we also show a case where selection diversity is used to select a channel with good quality and demodulate reception. As can be seen from Fig. 2, the S/
It can be seen that when N is equal, there is an improvement effect of 2 dB, which is comparable to the 3 dB improvement effect obtained with ideal composite diversity.

The present invention can be implemented in a similar manner even when a signal convolutionally encoded with a transmission efficiency n/m s constraint length is received at station a. 2(k-1)++ AC8 per state
A demodulated signal of a and a demodulated signal of m are provided in one ACS circuit.
Maximum likelihood decoding becomes possible by calculating the likelihood from the paths and finding the path with the highest likelihood.

[Effects of the Invention] As explained above, by decoding demodulated signals demodulated by a plurality of reception demodulators with one maximum likelihood decoding circuit,
Gain equivalent to composite diversity can be obtained. This allows the reliability of the circuit to be improved without using analog circuits.
This is improved because everything can be realized using digital circuits. In addition, the circuit scale is exactly the same as the conventional maximum likelihood decoding circuit in that the configuration of the path memory, which occupies more than half of the maximum likelihood decoding circuit, is very small. It can be realized with almost the same configuration as the maximum likelihood decoding circuit.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing improved characteristics of the embodiment of FIG. 1, FIG. 3 is a configuration explanatory diagram showing conventional level synthesis diversity, and FIG. FIG. 4 is a configuration explanatory diagram showing a conventional maximum likelihood decoding circuit. 2... Transmitter, 102... Convolutional encoding circuit, 1
15...-th receiving demodulator, 117... second receiving demodulator, 106... maximum likelihood decoding circuit, 107... AC8 circuit, 108... demodulated signal likelihood holding circuit, 109...・
Likelihood holding circuit of the path, 110... likelihood calculation circuit,
111... Likelihood comparison circuit, 112... New likelihood holding circuit, 113... Path memory.

Claims (1)

[Claims] In a maximum likelihood decoding circuit that receives and demodulates an encoded transmission signal by a plurality of receivers and performs maximum likelihood decoding using the demodulated a plurality of reception demodulated signals, the encoded signal is The configuration is such that the maximum likelihood judgment at the time of decoding selects one surviving path from m paths, and the operation of the decoding circuit is to select the demodulated signal a demodulated by the a receivers from the maximum likelihood judgment in the decoding circuit. ACS (AddC) that performs likelihood calculation for likelihood determination
ompareSelect) circuit, and then one out of m paths in each ACS circuit with the number of states (2^(^K^-^1^)^a) determined by the constraint length k and transmission efficiency n/m. In order to select a surviving path, the likelihood of the demodulated signal of a is added to the likelihood of the path of m, a total of m×n new likelihood values are obtained and compared, and the most likely of the new likelihood values obtained is A path with a high degree value is selected as a surviving path, the likelihood value corresponding to the selected path is stored as the likelihood value of the surviving path, and the history of each path is recorded as a decoded signal. A multiple reception maximum likelihood decoding circuit characterized in that decoding is performed by extracting the most recent information of a selected path from memory.