## Forums Search for: Viterbi

## Interleaving with soft-decision

inHi, I have a problem with interleaving and soft-decision. First, i explain what i have realized. I have done a 16FSK receiver with FEC...

Hi, I have a problem with interleaving and soft-decision. First, i explain what i have realized. I have done a 16FSK receiver with FEC decoded Viterbi 1/2 and k=7. Then, a symbol are 4 bits and i have 16 tones for 16 symbols: For example: 1001 is the symbol 9 and the tone number 9. 0010 is the symbol 2 and the tone number 2. (Actually, i also use Gray Code, but that's is not im...

## 180 phase ambiguity

inHey, I get why diffrential encoder in the transmitter and then a differential decoder at the receiver help overcome the possible 180 phase...

Hey, I get why diffrential encoder in the transmitter and then a differential decoder at the receiver help overcome the possible 180 phase ambiguity. what I don't get is how the viterbi decoder can handle that if we use a convolutional coding in our communication system (assume a gray-coded QPSK, means 180-phase causes "00" "11","01" "10"). In the receiver, the 180-phased codeword will t

## Optics and Channel Coding

inHave been looking at some reports on optical transmission. Looks like channel coding concepts used in wireless, wired comms can be applied to...

Have been looking at some reports on optical transmission. Looks like channel coding concepts used in wireless, wired comms can be applied to optics as well. It appears to have convolutional encoding. viterbi decoding etc etc. How prevelant is this channel coding in optics ? What are the major differences in channel coding between wireless and optics ?

## relation of equalizer and channel coding

inHello, Well known that decision-feedback equalizer is generally superior than linear equalizer, I was surprised to read the statement in a...

Hello, Well known that decision-feedback equalizer is generally superior than linear equalizer, I was surprised to read the statement in a paper: "Finally it is to mention that a combination of channel coding (Viterbi Decoding) and DFE did not lead to a performance gain compared to channel coding and linear equalization. It is well known that this combination represents a critical one..." ...

## Voice Activity Detection (VAD)

inFor a couple of reasons my attention has been drawn to voice activity detection (speech/non-speech detection). The speechies (and I count...

For a couple of reasons my attention has been drawn to voice activity detection (speech/non-speech detection). The speechies (and I count myself in that camp) tend to use tools that speechies know, and do something like train up a two state HMM with mixture Gaussian densities for each state and do a Viterbi decode to decide what is speech and what is not. However, that assumes that the n...

## GMSK/MSK constellation derotation and Channel impulse response estimation

inI am trying to implement a GMSK receiver I have a block diagram of the receiver which is like this Received IQ Samples - > constellation...

I am trying to implement a GMSK receiver I have a block diagram of the receiver which is like this Received IQ Samples - > constellation derotation -> CIR estimation from training sequence -> MLSE (viterbi) equalizer The constellation derotation is supposed to collapse the four end points of GMSK constellations (+1, +j,-1,-j) to a two point (+1,-1) constellation. My question is how

## difference between Log Likelihood Ratio (LLR) and soft demodulated output

inhi all, i am back again with questions :-). as i am into viterbi decoder, i am stuck with understanding of LLR and soft...

hi all, i am back again with questions :-). as i am into viterbi decoder, i am stuck with understanding of LLR and soft demodulated output. the other day, my post on comp.dsp has filled with code.this time (according to Tim wescott's advice) i am putting just question the other day, the posted code is 1. I could see many papers proposing soft demodulated outputs. lets say a value...

## problem with matlab function

inHello, I am using a matlab function "vitdec" to simulate viterbi decoding in awgn channel. I noticed a rather weird problem with it. When I...

Hello, I am using a matlab function "vitdec" to simulate viterbi decoding in awgn channel. I noticed a rather weird problem with it. When I increase the msglength the BER improves(eventually plateaus down), my understanding is that BEr improves with the traceback length. Attached is the matlab code and the BERs I observed, traceback length was fixed to 15 for a constraint length of 3. Is the...

## Soft Output MIMO detection

Hello, I simulated a soft output MIMO detection scheme in which a mimo detector produces LLRs which are fed to a soft input viterbi...

Hello, I simulated a soft output MIMO detection scheme in which a mimo detector produces LLRs which are fed to a soft input viterbi decoder(using vitdec matlab function). LLRs (using max-log approx.) are computed based on the euclidean distances of the received point wrt to the lattice points. I noticed that the LLRs have large magnitudes ( 40-50 or even more) at higher SNR. I observed that t...

## Puzzled about (171 133) convolutional encoder

inHi, I am implementing a Viterbi decoder. When I prepare for the test vector with its encoder. I am puzzled about the encoder output is not what I...

Hi, I am implementing a Viterbi decoder. When I prepare for the test vector with its encoder. I am puzzled about the encoder output is not what I expect. I use Matlab script: trellis=poly2trellis(7,[171 133],171); raw_data = [1; zeros(256*4,1)]; % 1 0 0 0 0 0 0 0 0 ... code0 = convenc(raw_data, trellis); % Encode a string of ones. I supposed that code0 will converge to state 0 af...

## Changing the FEC to LDPC, help me convincing the RF Guy

inDear All, We have a Solar Power operated X Band qpsk transmitter in a remote region. The FEC used is 1/2 rate viterbi, the output bitrate is...

Dear All, We have a Solar Power operated X Band qpsk transmitter in a remote region. The FEC used is 1/2 rate viterbi, the output bitrate is 100 Mbps. I want to increase the effective bitrate and improve BER by switching to 7/8 LDPC, but wasn't successfull to persuade the RF Guy (he is also the Project Manager). Since the device is Solar powered, the power consumption of the X Band trans...

## Soft demmaper - LLRs calculations

inHi all, Few questions: I developed soft demmaper(exact LLR Algorithm) and test with my own Soft Input Viterbi decoder. and results I get, are...

Hi all, Few questions: I developed soft demmaper(exact LLR Algorithm) and test with my own Soft Input Viterbi decoder. and results I get, are very close to teoretical(almost identical). But after while, I ask my self is my LLR algorithm good. Why I say that?-Exact LLR Algorithm on mathworks site(just type in google: Mathworks exact LLR algorithm), you will see : L(b)=log(Pr(b=0|r=(x,y)) / Pr(b=1|...

## TCM decoder (Viterbi). Prevent overflow in metric path

inHi, I'm writing TCM decoder on VHDL. My question is: how I can prevent overflow in metric path. I've found one way - subtraction minimum...

Hi, I'm writing TCM decoder on VHDL. My question is: how I can prevent overflow in metric path. I've found one way - subtraction minimum metric, but it's so difficult operation (find minimum and subtraction it), any body know another way? Thanks.

## Minimum ADC Sampling Rate / Symbol Rate for a PSK Modem with Time and Carrier Recovery.

inDear DSP Gurus, I have to demodulate a 50 MHz wide (3 dB bandwidth) OQPSK modulates Signal. The Signal properties are: OQPSK Modulated AWGN...

Dear DSP Gurus, I have to demodulate a 50 MHz wide (3 dB bandwidth) OQPSK modulates Signal. The Signal properties are: OQPSK Modulated AWGN channel Has Doppler Shift (5 KHz/sec max) Pulse shaping filtered (0.35) Viterbi+RS The HW I am using is: Zero IF Receiver ADC on I&Q channels (12 bit output) Has a signal processor (Output is IQ corrected,DC Removed,AGC) The Output is: I ...

## Transition States for K = 7 viterbi decoder

Hi I need to know output of convolutional encoder for K = 7 means (6 memory elements), output with corresponding (transition) states. I could...

Hi I need to know output of convolutional encoder for K = 7 means (6 memory elements), output with corresponding (transition) states. I could found this for K = 3 (means 2 memory elements) with 4 states and 4 different outputs and in other way 8 possible outputs which are written on arrows leading from one stage of trellis to another trellis stage. Its dimension should be 64 x 2 which means 64...

## explicit duration HMM

inhi, I'm looking for a methodology to find the optimal state sequence given an observation sequence (using viterbi or otherwise) in an explicit...

hi, I'm looking for a methodology to find the optimal state sequence given an observation sequence (using viterbi or otherwise) in an explicit duration HMM. All the papers on explicit duration HMM give an optimal state at time step t, gvien an observation sequence. They give is as q(t) = argmax(gamma(i)), where gamma is combination of the forward-backward variables alpha and beta. The...

## Decoding

inDear all Can any one help me to understand LDPC code 1) If LDPC code decode using viterbi algorithm and sum product algorithm , which...

Dear all Can any one help me to understand LDPC code 1) If LDPC code decode using viterbi algorithm and sum product algorithm , which one will be performance better ? 2) What are the different decoding algorithms for LDPC ? 3) What is the advantage of itterative decoding over non itterative ? 4) Why the sum product algorithm is the best decoding algorithm for LDPC ? than...