Hi there, I am trying to synchronize the transmitted signal with the receiver by energy detection. The transmitted signal is a sine wave and I plan to autocorrelate it to obtain the peak and then transmitting the data. Could you please help me in implementing the autocorrelation using Stratix II. Thanks a lot.... -S

--- Quote Start --- I am trying to synchronize the transmitted signal with the receiver by energy detection. The transmitted signal is a sine wave and I plan to autocorrelate it to obtain the peak and then transmitting the data. Could you please help me in implementing the autocorrelation using Stratix II. --- Quote End --- If the transmitted signal is a sinusoid, then the autocorrelation is a cosine. Auto-correlation not help you synchronize, cross-correlation does; you correlate a reference signal to the incoming signal and try to 'find' the start of the transmitted signal. Since the peaks of the cross-correlation of two sinusoids repeat every period, the synchronization is ambiguous, so it won't work very well. Synchronization based on autocorrelation typically uses pseudo-random binary sequences (PRBS), since the auto-correlation, or really the cross-correlation of a PRBS at the receiver, with the incoming PRBS has a peak. When you move the peak to the zeroth lag, you are synchronized to the transmitter. Radar and sonar systems use FM chirp pulses (linear FM), Barker codes, and other signals with sharp autocorrelation peaks. There is no peak in your scheme, so it won't work. Why don't you explain what you are trying to do. Can you change the transmit signal? Cheers, Dave

thanks for the reply Dave.I really appreciate your interest. I am basically using OFDM kinda thing for Spatial Modulation. I am transmitting a sinusoid of say freq f1 for synchronization and subsequently of freq f2 for data and will be performing correlation with sinusoid of freq f1 on the receiver side. I expect to get a peak of approx 1 for auto-correlation which will trigger my receiver to collect data. The problem I have is that I am using 128 data length for each symbol and I am using altera blockset (simulink) and I am totally confused about what blocks to use for performing the correlation thing. thanks...

--- Quote Start --- I am basically using OFDM kinda thing for Spatial Modulation. I am transmitting a sinusoid of say freq f1 for synchronization and subsequently of freq f2 for data and will be performing correlation with sinusoid of freq f1 on the receiver side. I expect to get a peak of approx 1 for auto-correlation which will trigger my receiver to collect data. The problem I have is that I am using 128 data length for each symbol and I am using altera blockset (simulink) and I am totally confused about what blocks to use for performing the correlation thing. --- Quote End --- In direct spread spectrum (DSS) systems like CDMA, base stations transmit PRBS codes for synchronization. I have not looked into OFDM, so I am not familiar with their technique. However, your description does not sound correct, perhaps you really mean different 'carriers' for modulated data. Can you please provide a reference for OFDM where they discuss synchronization. Altera has some application notes on OFDM, so how do they synchronize? Cheers, Dave

I might have confused you by all that description. For now, lets just forget the other things(OFDM,SM and all). I will mention my exact problem. I am generating a sine wave using a LUT with 128 sample points x1=round(((2^10)-1)*(1+sin(linspace(0,2*pi,128)))); now I need to perform w=xcorr(x1,x1,'coeff'); through the blocks in altera DSP Builder Blockset.

--- Quote Start --- I might have confused you by all that description. For now, lets just forget the other things(OFDM,SM and all). I will mention my exact problem. I am generating a sine wave using a LUT with 128 sample points x1=round(((2^10)-1)*(1+sin(linspace(0,2*pi,128)))); now I need to perform w=xcorr(x1,x1,'coeff'); through the blocks in altera DSP Builder Blockset. --- Quote End --- I'm not sure how to do this using specific blockset components, however, the two mathematical techniques are autocorrelation in the lag domain, and multiplication in the frequency domain. For autocorrelation in the lag domain, you multiply samples delayed by registers, eg., see this document (p11 has a hardware implementation) http://www.ovro.caltech.edu/~dwh/wbsddc/correlator_efficiency.pdf (http://www.ovro.caltech.edu/%7edwh/wbsddc/correlator_efficiency.pdf) For autocorrelation in the frequency domain, you can use an FFT, and take the magnitude squared of the output frequency channels. Cheers, Dave

Problem in Implementing Autocorrelation on Stratix II EP2S60 DSP Development Board

23 Replies

Altera_Forum
Honored Contributor
14 years ago
--- Quote Start ---
I am working with frequencies of 3MHz(transmitted signal) and trying to make a model of visible light communication.
--- Quote End ---
That's a little vague.

What are you trying to do "in detail".

You have a DSP board, what are you sending to the DAC, what are you sending to the ADC? Do you have two boards that are supposed to communicate, or are you just looping things back on the same board? How are the TX and RX connected, eg. just a wire, or are you using the 'visible light communications' interface? What is that interface, and IR source? Are the source and destination using the same clock, or are they asynchronous?

What kind of direction have you been given for this project?

Cheers,
Dave
Altera_Forum
Honored Contributor
14 years ago
I am having a hard time with my ADC. Its AC coupled and changes the signal I send. Could you please send me something about handling the ADC.

Thanks bro,
Saket
Altera_Forum
Honored Contributor
14 years ago
--- Quote Start ---
I am having a hard time with my ADC. Its AC coupled and changes the signal I send. Could you please send me something about handling the ADC.

--- Quote End ---

If the ADC is AC coupled, then it will have a low-frequency limit. You need to check the bandwidth of the AC coupling circuit. Is it just some capacitors or is it a balun? Are you using an Altera board, or custom board?

There are some spectra in here from the Stratix II DSP Kit:

http://www.ovro.caltech.edu/~dwh/correlator/pdf/lfsr_tutorial.pdf

The spectrum looks fine at 3MHz (if this is the board you are using).

Cheers,
Dave

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Problem in Implementing Autocorrelation on Stratix II EP2S60 DSP Development Board

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