## Forums Search for: Viterbi

## BER estimation for a modem

inHi everybody, Someone explains to me that to estimate the SNR of the channel (and then the BER of a modem), i have to use the output bits of...

Hi everybody, Someone explains to me that to estimate the SNR of the channel (and then the BER of a modem), i have to use the output bits of the viterbi decoder. These bits are convolutionnally encoded and the output is compared with the signal received. Someone can tell me about the precision of this method ? I've tried to search informations with google but i didn't find anything. ...

## Help : Super Orthogonal Space Trellis Code

inHi all, I am trying to reproduce the result of the Super-Orgonal Spce Trellis Code of Jafarhani using his recently introduced generator...

Hi all, I am trying to reproduce the result of the Super-Orgonal Spce Trellis Code of Jafarhani using his recently introduced generator matrix notation. I am presently stranded in the decoding part. The decoding is through viterbi decoder. What i have is not decoding rightly. Please i should appreciate it if someone one know this can be of help.

## Oversampling and receiver

inHi all, I would like to know if the folling would be possible. Lets say that my tx use a raised cosine filter to limit the bandwidth of my...

Hi all, I would like to know if the folling would be possible. Lets say that my tx use a raised cosine filter to limit the bandwidth of my transmitted signal. At the receiver I would oversample the received signal by a factor of x and by using a Viterbi algorithm I would be able to approximate every symbol affected by ISI caused by the memory of my raised cosine filter. By doing this would i...

## Shortening Typical Viterbi Decoding Depth

inTypically the decoding depth is set at 5 * K, where K is the constraint length. It is also known that the shorter the decoding depth, the...

Typically the decoding depth is set at 5 * K, where K is the constraint length. It is also known that the shorter the decoding depth, the higher the probability of bit errors Pe becomes. Have there been any studies or is there a rule of thumb on how the Pe changes as D decreases from 5 * K? -- Randy Yates DSP/Firmware Engineer 919-577-9882 (H) 919-720-2916 (C)

## fast simulations of convolutional codes in C

inI'm involved in simulating space-time trellis codes, and would like to parallelize my C code ( e.g. the part that does the Viterbi...

I'm involved in simulating space-time trellis codes, and would like to parallelize my C code ( e.g. the part that does the Viterbi decoding). Would anyone know of places to look for C or Fortran programs that simulate convolutional codes using parallelized code ( in other words, several processors are used to do say, the decoding part) ? thanks, David Bernier

## Decoder for Tail-Biting Convolutional Code

inCould someone please tell me how to implement a decoder for a tail-biting convolutional code? I've been working on it all day and can't figure...

Could someone please tell me how to implement a decoder for a tail-biting convolutional code? I've been working on it all day and can't figure it out. My basic approach bas been to take a Viterbi decoder and modify it such that it does not assume the initial state is 0. This works about 50% of the time. When it fails, it only gets 1 or 2 bits wrong and they're toward the very beginning ...

## Coding Gain Definition

inI have a doubt. Gain code is defined as the reduction, usually expresed in decibels, in the required Eb/No to achieve a especified error...

I have a doubt. Gain code is defined as the reduction, usually expresed in decibels, in the required Eb/No to achieve a especified error probability of the coded system over an uncoded system with the same modulation and channel characteristics. But, what about Bit rate? The definition considers the same Bit Rate in both cases?????. For example: I have implemented a Viterbi Receptor(r=1/2 ...

## GMSK demodulator

inHello, everybody. Who knows how to demodulate baseband GSM signal? I know that it can be realized by 1)typical complex FM discriminator,timing...

Hello, everybody. Who knows how to demodulate baseband GSM signal? I know that it can be realized by 1)typical complex FM discriminator,timing recovery and slicer or by 2)Viterbi algorithm I have filtered baseband GSM signal with 1 sample per symbol. Should i interpolate or not to get 2x or 4x sample rate? I must provide error free bitstream recovery with 10dB SNR at the input. Thank you. Pa...

## Where is the matched filtering operation in this?

inHi... I am struggling to understand the following: If r(t) = sum_i{s(t)*h_i(t-tau_i)} + n(t) is the received signal where h_i(t) is the...

Hi... I am struggling to understand the following: If r(t) = sum_i{s(t)*h_i(t-tau_i)} + n(t) is the received signal where h_i(t) is the overall channel impulse response, the MLSE Viterbi algorithm is simply done by calculating branch metrics of the form |r(t)-noiseless_r(t)|, where noiseless_r(t) is a reconstructed version of r(t) using the estimated channel impulse response taps h_est_i(t). ...

## VITERBI DECODING

inHI, I want to know about error correcting capability of a convolution code i.e. how many errors can be corrected in a continuous input data...

HI, I want to know about error correcting capability of a convolution code i.e. how many errors can be corrected in a continuous input data pattern (e.g. a 1/2 rate code with constraint length of 7 has free distance of 10 and is said to correct 4 errors, whether these errors cab be burst type also and what will be the relation of this error correction to input data)? Thanks

## Help Required for "vitdec" built-in command of of MATLAB

Hi All I want to know how one can initialize a particular state (not necessarily zero state) for "vitdec" built-in command of MATLAB? I want...

Hi All I want to know how one can initialize a particular state (not necessarily zero state) for "vitdec" built-in command of MATLAB? I want to use this functionality for Tail-Biting Viterbi Decoding in which decoder saves state while trellis construction as well as traceback. Any reply, would be appreciable. Thank you. Hope to hear from you soon. Best Regards Ahmed SALIM

## BER for convolutional encoder

inHi, I was looking at the upper bound on BER for convolutional encoder. "High Rate Punctured Convolution Coded for Viterbi and...

Hi, I was looking at the upper bound on BER for convolutional encoder. "High Rate Punctured Convolution Coded for Viterbi and Sequential Decoding" by David Haccoun and Guy Begin talks about the BER plots for BPSK and QPSK with and without puncturing. I am not able to find anything which talks about BEr calculation for QAM. Can someone suggest reference? thanks in advance!

## OFDM + Convolutional code

inI have finished a basic OFDM simulation with BPSK modulation on it. Now I want to use the convolutional code in transmitter and a...

I have finished a basic OFDM simulation with BPSK modulation on it. Now I want to use the convolutional code in transmitter and a multipath channel with AWGN. At receiver , a viterbi decoder would be used. But I have some question in it.First,when the data have done FFT at the receiver.There would be still imaginary part in signal,should I discard the imaginary part or not? Second,because ...

## DVB-H FEC decoder question ...

inHello, I was looking at the DVB-H standard which has a serially concatenated encoding with Reed Solomon code (RS(204,188, t=8) from...

Hello, I was looking at the DVB-H standard which has a serially concatenated encoding with Reed Solomon code (RS(204,188, t=8) from RS(255,239, t=8) ) as the outer code and Convolution code (K=7) as the inner code. At the receiver, I can think of at least four decoding options, 1. Viterbi followed by RS decoder. 2. MAP (BCJR) followed by RS decoder. 3. MAP followed by soft input RS decode...

## soft bit metric

inhello everyone... my questions are related to k=7 rate=1/2 decoder and i am thinking of implementing it on FPGA using VHDL.....a general...

hello everyone... my questions are related to k=7 rate=1/2 decoder and i am thinking of implementing it on FPGA using VHDL.....a general solution will also be appreciated. first question..for 3 bit soft-decision coding is it the encoder that encodes 1 input to 2 3-bit encoded outputs or is it the reciever before viterbi decoder that quantizes the recieved encoded value to 2 3-bit encoded v...

## Constellation symbol to bit's soft-probability?

inHi all, I am new to demodulation and FEC. How can I get each bit's soft-probability from the constellation? For example, the modulation...

Hi all, I am new to demodulation and FEC. How can I get each bit's soft-probability from the constellation? For example, the modulation method is 16QAM, How can I get P(bit1=0),P(bit2=0),P(bit3=0),P(bit4=0) from a symbol? Is it belong to the subject of detection and need viterbi algorithm? Or can you recommend some key words of this subject? Best regards, Davy

## Problems in Segmental K-means algorithm

Dear Friends; I have implemented Segmental K-means algorithm for better HMM parameter initialization (Rabiner: A tutorial on Hidden Markov...

Dear Friends; I have implemented Segmental K-means algorithm for better HMM parameter initialization (Rabiner: A tutorial on Hidden Markov models and selected applications in speech recognition 1989). But I have some problems: 1- After some iteration of running Viterbi algorithm for each training sample of the word and segmenting it according to the optimal path, observation vectors of some...

## Punctured Viterbi decoding

inHello Is it a generally accepted fact that the best punctured convolutional code performance approaches the performance of the...

Hello Is it a generally accepted fact that the best punctured convolutional code performance approaches the performance of the equivalent non-punctured code at the same rate. Is there any figure of merit as to what the traceback depth should be given a certain puncturing scheme. For example, I notice that: with a rate 1/2, constraint length K=7 unpunctured code, tracebach depth D=5*K...

## Iterative decoding with viterbi decoder

inHi , i'm trying to do iterative decoding using vitdec from matlab, i would like to know how can i get the metrics of the bits to intruce them in...

Hi , i'm trying to do iterative decoding using vitdec from matlab, i would like to know how can i get the metrics of the bits to intruce them in the demodulator again, using the function vitdec. The output of this function is the final sequence , but i just want the metrics of the bits. Thank you TA

## Viterbi Metric for a BFSK

inIn the hard decsion case, if I receive [0,1] say, then the metric compared to [0,0] is 1. Suppose I received [0.9,1.1] in the soft decision...

In the hard decsion case, if I receive [0,1] say, then the metric compared to [0,0] is 1. Suppose I received [0.9,1.1] in the soft decision case. Is the metric compared to [0,1]... (0.9)^2 + (1.1)^2 ??? or 0.9 + 1.1 ????? Note: 0.9 is the correlation for a symbol 0 Note: 1.1 is the correlation for a symbol 1 Both correlations have been calculated by Quadrature Receiver (nocoheren...