## Digital FM Demodulation - Filtering

Started by in comp.dsp17 years ago 15 replies

Hi, I have no experience of 'software radio', however I am now trying to model a digital FM radio. I am using a simple arctan of the I and Q...

Hi, I have no experience of 'software radio', however I am now trying to model a digital FM radio. I am using a simple arctan of the I and Q to generate the instantaneous phase and then differentiating by subtracting successive phases and dividing by the sample interval to give the FM output. My questions are: What if any low pass filtering should I put on the output of my FM demodula...

## Phase and sampling relationship in digital demodulation

Started by in comp.dsp6 years ago 3 replies

Hi I tried to demodulate FSK (8 bit uart data caller id) according to the theory but was not successful unless i did bit processing at proper...

Hi I tried to demodulate FSK (8 bit uart data caller id) according to the theory but was not successful unless i did bit processing at proper phase by looking at already implemented FSK demodulator source code by some one. rxbit=demodulate(); // getting result by matched filters for 0 and 1 if ( (prevbit != 0) && (rxbit == 0) && (FSKstatus == 10) ) //not my code { status = 9;...

## magnitude response of IdQ-QdI

Started by in comp.dsp10 years ago 9 replies

I am trying to find the mathmatical magnitude response of the following FM demodulation...

I am trying to find the mathmatical magnitude response of the following FM demodulation equation: I[n-1]*(Q[n]-Q[n-2])-Q[n-1]*(I[n]-I[n-2]) ----------------------------------------- I[n-1]^2+Q[n-1]^2 How do I represent I and Q in terms of some x[n] to find the z transform of the equation? I know I[n]=x[n]*cos(phi) and Q[n]=x[n]*-sin(phi). But phi is also a function of 'n'. No...

Started by in comp.dsp16 years ago 4 replies

Hi! I have to demodulate a signal (detect the envelope) for which the bandwidth is not known in advance. By filtering out the "noise" with a...

Hi! I have to demodulate a signal (detect the envelope) for which the bandwidth is not known in advance. By filtering out the "noise" with a bandpass filter, I can get a substantial improvement in signal to noise ratio of the demodulated signal. I was thinking about using an adaptive filter of some kind, but maybe somebody already has some expirience or ideas on this. I think that ju...

## Instantaneous Frequency with I-Q demodulation

Started by in comp.dsp12 years ago 10 replies

Hello everybody, I have a few questions, maybe you can help me. I have 2 signal I,Q @ 40khz and the task is to obtain the instantaneous...

Hello everybody, I have a few questions, maybe you can help me. I have 2 signal I,Q @ 40khz and the task is to obtain the instantaneous frequency. What i did in matlab is this: first of all i found the phase with atan2, i unwrapped the phase and I derivated in order to have the frequency (with command diff). A first issue is here: I had to average the phase to see somenthings in frequency 'c...

## BER vs SNR under BPSK bandlimited channel

Started by in comp.dsp5 years ago 1 reply

Hi I have done some work with BPSK modulation such modulating and demodulating the waveform and plotting the BER vs SNR under BPSK for...

Hi I have done some work with BPSK modulation such modulating and demodulating the waveform and plotting the BER vs SNR under BPSK for AWGN channel. However I wonder how would I perform the simulation if the channel is bandlimited meaining that assume frequency response of channel is w/(w^3+w^2+w+1) then how to do demodulation and eventually finding the bit-error ? Thanks. ----------------...

## FM demodulation

Started by in comp.dsp14 years ago 4 replies

Hi, I modulate a 10.7 MHz center frequency with 20 kHz deviation. When I send a 1 kHz sinus signal to modulate the 10.7MHz, I demodulate this...

Hi, I modulate a 10.7 MHz center frequency with 20 kHz deviation. When I send a 1 kHz sinus signal to modulate the 10.7MHz, I demodulate this FM signal with IdQ-QdI. So this result is a goos sinusoide signal at 1 kHz But when I calculate I=B2+Q=B2, there's a 20 kHz sinus on this signal and so when I do (IdQ-QdI)/(I=B2+Q=B2) I have this 20 kHz signal modulated on my 1 kHz sinus wanted.. ...

## about MRC techniques for OFDM

Started by in comp.dsp11 years ago 8 replies

Hello all, Please, I wanna know more about maximal ratio combining post DFT techniques. I'm studing this receving method, also i found a...

Hello all, Please, I wanna know more about maximal ratio combining post DFT techniques. I'm studing this receving method, also i found a chipset improving this technique: http://www.teamcast.com/en/maj-e/c2a2i15040/products/dibcom-products/dvb-t-diversity-demodulatio n-chipset.htm but i do not understand the theory. The combining is frequency domain ? Someone can help me ? Best regar

## Robust FSK demodulator ?

Started by in comp.dsp9 years ago 2 replies

Dear all, We are looking for a robust FSK demodulator and framer solution for an SDR application (decoding of simultaneous narrow channels at...

Dear all, We are looking for a robust FSK demodulator and framer solution for an SDR application (decoding of simultaneous narrow channels at some kbps each from a wider baseband stream) : channel filtering, center frequency tracking, demodulation, bit-level timing recovery, synchronisation frame detection, etc. Could be either DSP or FPGA based. Any "off the shelf" industrial-level I...

## Receiving symbols using non-coherent M-FSK

Started by in comp.dsp13 years ago 3 replies

Hi There, How does the demodulator of a non-coherent M-FSK system correctly time the "reading" of the symbols? In the book on Digital Comms...

Hi There, How does the demodulator of a non-coherent M-FSK system correctly time the "reading" of the symbols? In the book on Digital Comms by Proakis, it is mentioned that a bank of 2M correlators can be used. In the book there is also a model for non-coherent M-FSK in an AWGN environment. I have used the model to create a matrix of metrics and done the decoding/demodulation from there....

## Tracking a moving FM carrier

Started by in comp.dsp11 years ago 4 replies

Hello, I'm looking into a demodulation application for an FM signal. The message signal is fixed bandwidth (~30kHz), but due to the measurement...

Hello, I'm looking into a demodulation application for an FM signal. The message signal is fixed bandwidth (~30kHz), but due to the measurement environment, the carrier (nominally around 500kHz) moves above and below the nominal frequency within about a 100kHz range. To demodulate, I'd like to mix to baseband, so I need to find the carrier of the incoming FM signal. The carrier moves about t...

## some help please on more efficient way to detect tones?

Started by in comp.dsp11 years ago 27 replies

I could use some help, since I am very new to DSP. Here is my situation: I am recieving I/Q data at 250kHz rate, demodulating it with...

I could use some help, since I am very new to DSP. Here is my situation: I am recieving I/Q data at 250kHz rate, demodulating it with demodulation algorithm: IdQ+QdI/I^2+Q^2. Then storing 800 samples and using the Goertzel algorithm to detect 4 different tones. Currently the DSP cannot calculate all of this and I am getting data overrun, I have a flag which tells me that the Goertzel is not...

## 16-PAM Demodulation and Viterbi

Started by in comp.dsp15 years ago 1 reply

Hi, If I have a 16-QAM demodulator I know I can use the I and Q values to access a lookup table and output soft codes for a Viterbi uisng...

Hi, If I have a 16-QAM demodulator I know I can use the I and Q values to access a lookup table and output soft codes for a Viterbi uisng LLR What do I do if I'm using 16-PAM? If my information is right its just amplitude modulation. So out of the demodulator I will get 1 of 16 values. How do I then create the soft codes indicating how strong, or weak the '1's and '0's are? Thanks Mike ...

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

Started by in comp.dsp15 years ago 5 replies

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...

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

## O-QPSK Demodulation

Started by in comp.dsp15 years ago 6 replies

Hi all, I have to demodulate an O-QPSK signal. As usual in this kind of modulation, symbols (chips) have an half-sine shape, and the Q...

Hi all, I have to demodulate an O-QPSK signal. As usual in this kind of modulation, symbols (chips) have an half-sine shape, and the Q channel has a 90 degree (half simbol) offset with respect to the I channel. The first thing I have to do (and perhaps the most difficult) is removing the frequency offset from the received I and Q signals. I cannot use a simple Costas loop since it doesn't wo...

## coherent sampling and I/Q demod

Started by in comp.dsp15 years ago 1 reply

(how) does coherent sampling (used primarily in A/D testing?) differ from I/Q demodulation? Say for instance I'm using I/Q to close a PLL. In...

(how) does coherent sampling (used primarily in A/D testing?) differ from I/Q demodulation? Say for instance I'm using I/Q to close a PLL. In this case the 'sine wave' I'm locked to is being sampled at x4 the sine frequency. This would seem to satisfy the coherent sampling requirement that regarding the digitizer clock. next question - coherent sampling removes the need for windowing in FFT ap...

## DSP Algorithm for LVDT Synchronous AM Demodulation

Started by in comp.dsp9 years ago 9 replies

Hello, I am wondering if anyone can provide some insight into how one may go about doing the following: To obtain magnitude and phase of a...

Hello, I am wondering if anyone can provide some insight into how one may go about doing the following: To obtain magnitude and phase of a sinusoidal output of an LVDT transducer that can be implemented on a TI C2000 series of DSPs. The magnitude of the sinusoid varies linearly with the distance of the plunger from the center and the phase changes depending on which side of the LVDT's center...

## GMSK demodulation question

Started by in comp.dsp17 years ago 1 reply

A common way of demodulating a 2-FSK signal involves shifting the complex baseband up and down by the deviation, convolving each shifted result...

A common way of demodulating a 2-FSK signal involves shifting the complex baseband up and down by the deviation, convolving each shifted result with a rectangular filter, and differencing the magnitudes at the filter outputs. This essentially places a sinx/x response at each tone frequency, and works well considering its low complexity. Now, suppose the signal is GMSK. The deviation is one ...

## Alamouti MIMO simulation works with PSK but not QAM?

Started by in comp.dsp12 years ago 3 replies

Dear All, I'm currently simulating a Alamouti MIMO system to find out the BER for the different number of antennas and different modulation...

Dear All, I'm currently simulating a Alamouti MIMO system to find out the BER for the different number of antennas and different modulation schemes over the Rayleigh fading channel with AWGN for the selected SNR range. I've been using the predefined "modem.pskmod" and "modem.qammod" in matlab for my modulation, demodulation and maximum likelihood decoding. All is working well for the PSK m...

## Re: AM digital demodulation using the absolute value

Started by in comp.dsp10 years ago

I don't think you are grasping the idea of the low pass filter. It is to r= eject the carrier, not just the aliasing. You want the modulated...

I don't think you are grasping the idea of the low pass filter. It is to r= eject the carrier, not just the aliasing. You want the modulated signal wi= thout the carrier. So the cutoff frequency of the filter would be above yo= ur modulating signal frequency and below the carrier frequency. Everything= else you decide will depend on the details of your problem. =20 BTW, you can do bett...