JPS6367376B2 - - Google Patents

Description

Detailed Description of the Invention The present invention transmits the same data at two or more frequencies or at different times, and demodulates the most reliable data signal from the received signals on the receiving side. This relates to a diversity method that outputs data.

Conventional methods of this type include frequency diversity, which modulates the same data using two or more frequencies, time diversity, which modulates the same data at different times, and spatial diversity, which modulates the same data at different times. Diversity, etc. is a method that compares signal levels modulated with the same data and outputs the signal with the highest level as the received signal to the demodulator, so if there is interference etc., the apparent There was a problem in that when the upper level became high, even a signal with poor quality was determined to be "good" and was output to the demodulator.

In view of the above-mentioned circumstances, the present invention adopts the maximum likelihood decoding method on the data receiving side, and uses the likelihood function or likelihood function difference calculated at the time of decoding, so that the data can be decoded independently of the apparent reception level. The purpose of this invention is to provide a diversity method that can perform correct comparison and determination of data signals.

The maximum likelihood decoding method adopted in the present invention is a type of so-called error correction method.To explain its basic principle, first, input data is encoded using a convolutional code etc. on the data transmitting side, and then this is encoded on the data receiving side. Send to. On the data receiving side, a likelihood function LF expressed by the following equation is calculated.

LF=P(〓｜〓)=〓 _i (y _i ｜a ^l _i ) (1) Here, 〓 is the received data sequence vector〓=
(y ₁ , y ₂ , ... y _i , ...), 〓 is the l-th input data sequence vector determined by the encoder installed on the data transmitting side, and 〓 = (a ^l ₁ , a ^l ₂ … _{al i} ^… ).

In other words, on the data receiving side, the likelihood function of equation (1) above is calculated for all received data sequences determined by the encoder provided on the transmitting side, and the calculated likelihood function LF and its corresponding Memorize all received data series. After calculation of a certain length, the received data sequence corresponding to the largest likelihood function LF among the stored likelihood functions LF is sequentially output as demodulated data. In other words, the maximum likelihood decoding method is a method in which the data receiving side selects the data sequence that is considered to be closest to the transmitted data sequence, and as is clear from equation (1) above, even if there is an error in the received data sequence, In this case, the calculated likelihood function LF becomes smaller. From this, it can be seen that the likelihood function represents the decoding quality of received data and has a property that is independent of the reception level. By applying the properties of such a likelihood function, it is possible to always make a correct diversity judgment. The present invention is characterized in that it applies the properties of such a likelihood function.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, a frequency diversity system using two frequencies will be described below in detail with reference to the drawings.

An encoder 1 is provided on the data transmitting side, the encoder 1 encodes the input data, and the encoded signal is sent to one of the transmitters 2 at the next stage at a frequency F ₀
At the same time, the other transmitter 3 modulates the signal at the frequency _F1 , and the synthesizer 4 combines the two and transmits the result. On the data receiving side, the received signal received via the antenna is demultiplexed by the demultiplexer 5, the receivers 6 and 7 receive frequencies F ₀ and F ₁ , and the maximum likelihood decoders 8 and 9 receive the maximum likelihood decoders, respectively. Decrypt. Then, the data and likelihood function decoded by one maximum likelihood decoder 8 and the data and likelihood function decoded by the other maximum likelihood decoder 9 are input to the comparator 10, and the likelihood of these two is input to the comparator 10. A data signal corresponding to a large likelihood function is output from the comparator 10 as demodulated data. If diversity judgment is performed using a likelihood function that is unrelated to the reception level in this way, interference, etc.
Even if the apparent reception level increases, diversity judgment can always be made correctly.

Furthermore, the likelihood function sequence calculated using equation (1) above is as follows:
The difference between the largest likelihood function and the second largest likelihood function also has the property that the more errors there are, the smaller the difference becomes. It can be used to determine diversity. In this case, the maximum likelihood decoder 8
and 9 output the data corresponding to the largest likelihood function and the difference (likelihood function difference) between the largest likelihood function and the second largest likelihood function to the comparator 10, respectively. It's fine if you do.

As described in detail above, the present invention uses a likelihood function or a likelihood function difference that is unrelated to the apparent reception level to determine diversity, so it is suitable for data demodulation in data transmission where there is a lot of interference. This is particularly effective and greatly contributes to improving the decoding quality.

[Brief explanation of drawings]

The drawing is a block diagram showing an embodiment of the diversity system according to the present invention. 1... Encoder, 2, 3... Transmitter, 4... Combiner, 5... Demultiplexer, 6, 7... Receiver, 8, 9
... Maximum likelihood decoder, 10... Comparator.

Claims (1)

[Claims] 1 An encoder is provided on the data transmitting side and a maximum likelihood decoder is provided on the data receiving side, and data signals are compared and judged based on the likelihood function or likelihood function difference calculated by the maximum likelihood decoder. A diversity method that is characterized by: