8-PSK TCM Encoder

423

02:53:17

Rate 2/3 8-PSK Trellis Coded Modulation encoder.
Modulation: 8-Phase Shift Keying.
Encoding: Rate 1/2 feedback convolutional encoder, 2-bit memory depth.
Constellation mapper implemented using standard combinational logic elements, as multiplexers are unavailable. Therefore the set-partitioning is rather arbitrary, with the coset selector and signal selector implemented as an integrated unit. 
The signal set is implemented using a bank of 8 oscillators with 45 degrees of phase spacing between adjacent symbols.
Grey mapping is used, except between symbol 1 and 8.
Data bit-stream generator implemented using 2-bit ADC output with sinusoidal input (which should give a fairly normal distribution of output symbols).

published 6 years ago

fatcat2

6 years ago

Are you using 16-QAM?

calvin21

6 years ago

No, 8-PSK. The bit generator isn't great, so play around with different ADC inputs to see how the TCM encoded output changes. The signal set is basically (from top left): s1 = sin(wt+0), s2 = sin(wt + 45), s3 = sin(wt + 90), s4 = sin(wt + 135). Then from bottom left: s5 = sin(wt + 180), s6 = sin(wt + 225), s7 = sin(wt +270), s8 = sin(wt + 315). Where w = 2*pi*1000.

calvin21

6 years ago

There is a flaw in the constellation mapper. The input stream 10 doesn't map to any signal vector. The rest seems to work fine though.

fatcat2

6 years ago

The real thing is that idk trellis error correction code; my book on communications says that tells encoding is beyond the reach of the book. However, I notice 2 different amplitude levels..

calvin21

6 years ago

Yes, that's an error in the combinational logic of the signal constellation mapper. Signal vectors s4 and s5 are erroneously transmitted at the same time. Here's a great resource on ECC: Lin and Costello - Error Control Coding 2nd edition.

fatcat2

6 years ago

Thank you very much for suggesting a book!

Darklord122

6 years ago

You're pretty good buuuuut it's too complicated to learn from. I hope u post easier circuits next time so I can learn from u.

fatcat2

6 years ago

A wee bit, Fortune!

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