Dear Mr. Tarek Mohamed Salem,

Carrier phase information is needed for Coherent systems.Receiver use matched filters (or correlation receiver) to detect and decide the transmitted data. Non-coherent systems do not need carrier phase information and use methods like square law (push detection or energy detection) to recover the transmitted data at receiver end.

please declare me this statement:

the energy detector requires O ( 1/SNR)2 samples for a given detection probability

So if SNR = -10 to -40 db energy detector suffers from long detection.

Dear Mr. Tarek Mohamed Salem, You want to say that it has no solution or incomplete.

Coherency in signal processing is similar to correlation in statistics. In statistics two random variables are correlated if there exists a linear relationship between the two. Perfectly coherent signals are signals such that one is the response of a linear system to the other applied signal. Hence there exists a linear system such that one signal is the input and the other signal is its output. Coherence is between 0 and 1. The higher the coherency is, the better one can explain the spectral content of the first signal by analyzing the spectral content of the other signal since a linear system is completely characterized by the system's associated Frequency Reponse Function (FRF). As a result the formal definition is the cross spectrum of both signals devided by the square root of the auto spectra. Note that for the FRF we obtain that the FRF is given by the cross spectra of the input and output signal divided by the autospectrum of the input.

In simple meaning, Coherent signals are signals having same phase and frequency.

Regards,

Nitish

They do not need to have the same phase but the difference in phase is required to be constant over time. Linear systems change the phase of the input and coherency measures the linearity between both signals.

Coherent systems need carrier phase information at the receiver and they use matched filters to detect and decide what data was sent , while noncoherent systems do not need carrier phase information and use methods like square law to recover the data.

Coherent systems means that the receiver need the phase information of the transmitter (the carrier phase) to recover the transmitted data at receiver side. The phase information comes from either a reference from the transmitter or could be from a local oscillator (at the receiver side). The oscillators used at both the transmitter and receiver are not phase locked; therefore there is a phase difference between the reference signal transmitted and the reference signal used in the demodulator. This phase difference must be estimated and corrected. The receiver is more complicated and expensive. Better bit error rate of detection.

In non coherent systems, the receiver do not need the phase information of the transmitter carrier to recover the signal. Do not require expensive and complex carrier recovery circuit. Lower bit error rate of detection.

In coherent detection of symbol, the decision on which data bits has been sent carried out by design of matched filter that consequently relates to requirements of transmitted signal phase at Rx. side. The optimum design of matched filter leads to accurate detection of data bits, further reduce BER.

In very simple term, the coherence image meaning is the image which is formed from two signal with the different wave length equal to 0 or any whole number of this wave length.

With my regard

This is related with the definition of the conditions of COHERENCE waves.

Raad

regards

For coherence, you need to know the phase shift when the RX receives the transmitted signal.

For non-coherence, you don't need to know anything about phase shift. We can use any method to analyze the transmitted data at the RX.

In coherent system we need the carrier phase i, but in non-coherent system we don't need carrier phase and we use other ways in getting data.

It is simply about the knowledge of the phase at the receiver

In non_ coherent system the receiver detect transition waves with out needed to information about the carrier phase

In many radar and communications applications, received signals have very low SNR due to the weakening of the signal from the propagation loss in the presence of various noise sources. Engineers often try finding new ways to overcome this by having multiple received copies of the same information. The idea is to add as many copies of received signals as possible; the objective is to have a large 'integration gain'. This 'integration ' approach provides amplification by adding copies of the signal. This is called the integration gain. However, integration requires that those received copies of information are ideally equal and noise is uncorrelated. While signal amplifies as N, noise is expected to attenuate as sqrt(N), ideally. If the addition of signal copies provides an integration gain, they are called to be 'coherent'. It is like adding two sine waveforms; they will only be coherent if their frequencies are the same. Their relative phase values determine the integration gain. Often incoherence is also hard to get. Partial coherence is what we observe and we try to focus on and work in this gray area. You can imagine where you can place those 'signal copies' in series or in parallel. You can think of the repetitive pulses of a pulse-doppler signal, TDMA signals and etc. are examples of series transmission. FDMA and antenna array beamforming is the other for communications and radar, respectively. Keep up the good work!

In coherent detection we use the signal of same frequency as that of the signal used in the transmitter. At coherent mostly uses a LPF or BPF to obtain the original signal so the same frequency used for both modulation and demodulation

non coherent or incoherent we use signals of two different frequencies in transmitter and receiver side. at the receiver we use an Envelope Detector for detecting the information signal.

Yes as mentioned sbove answers

In coherent detection the local carrier generated at the receiver is phase locked with. the carrier at the transmitter. Hence it is also called synchronous detection. In non coherent detection the local carrier generated at the receiver not be phase. Locked with the carrier at the transmitter.

Coherent and Non-coherent Receivers : https://www.southampton.ac.uk/~sqc/EL334/Coh-non.pdf

Dear Tarek Mohamed Salem ,

Hope you are well!

Coherency means complete phase agreement or phase coincide such as

A sin (wt +phi) and B sin (wt +phi)

Noncoherent means that

different static phase phi in the two waveforms.

or two different frequencies

Or different frequency and phase.

Signals having same frequency and different static phases called synchronous

If two synchronous signals have the same static phase they will be coherent.

Best wishes