# Coherent and non-coherent detection

Let's say I am simulating something as simple as BFSK. It has two symbols, one entirely on the real plane, and one entirely on the complex plane for representing let's say zero. That is how the constellation of BFSK looks like. Now let's say we added AWGN (N) and Rayleigh fading (h) as well. Rx= h*x + N;

Now when I tried to detect it on the receiving side I will have to divide this entire Rx by an h, makes sense. Now my entire graphs for BER matches non-coherent detection for FSK. It exactly matches with theory. Now how to do the same for non-coherent detection? If I didn't divide ****Rx/h**** I get very bad results and that doesn't match anything. Theory tells us that in non-coherent detection, prior knowledge of the channel impulse response is not known at the receiver.

1. In coherent systems, the receiver needs phase information of the transmitter (the carrier phase) to recover the transmitted data at the receiver side. Is there any phase information in FSK? I haven't use any such thing but still simulation results for BER matches theory for Coherent FSK, may be dividing by channel response did some magic?
2. Some books tell us that NON COHERENT In this technique we use signals of two different frequencies for encoding and decoding, Should we do same? how?
3. While some say non-coherent systems do not need carrier phase information and use methods like square law to recover the data. Well I am simply simulating it, I don't think so they are going to make a difference.

Can someone here help me with this?

• Yes, with non-coherent detection, you don't know h. What is your non-coherent detection algorithm? Are you attempting to estimate something about the channel at all? May 18 '20 at 10:34
• So what I have done is not correct? I divided it by h and it gave a non-coherent BET curve. Like for BPSK we generate random bits and then data= round(rand(1,num_bit)); %Generate binary data source bpskModulated = 2*data-1 % mapping to -1 and +1 can we do same for BFSK like s=data+j*(~data); %Baseband BFSK modulation as constellation of BFSK is on 1+0*j [1,0,0] and other on entirely on imganary plane [0,1,0] May 18 '20 at 12:20
• I was asking about on the receiving side, how you do your non-coherent detection. Not about how you generate random bits, etc., on the transmitting side. May 18 '20 at 15:36

## 1 Answer

Minimum Shift Keying as used in GSM phones is phase-continuous, to greatly reduce the leakage into adjacent channels.

• Yes but My question is about coherent and Non coherent simulation. Should I divide it by h ? May 17 '20 at 14:13