channel estimation is to detect the channel impulse response {h}.

Detection ? what do you meant "symbol detection or what in general "

I agree with Walid about channel estimation. It is used to estimate the symbol distortion, when transmitting in that RF channel. You might use this to estimate the settings to be used in an adaptive equalizer, for instance, to restore symbols more or less to their ideal shape (after reception by a receiver, or even before transmission by a transmitter, perhaps). This paper explains different types of equalizers:

http://thesai.org/Downloads/Volume2No3/Paper%2011-%20Adaptive%20Equalization%20Algorithms%20An%20Overview.pdf

I think detection probably refers to sensing whether there is some other device using an RF channel, before your device can begin transmissions. For example, when using "TV white spaces," the "white space device" needs to sense whether there's a TV station already on that channel, before attempting to transmit.

So in this case, all you want is a very sensitive receiver, to make sure that the channel is truly unoccupied. For example, sensitive enough that it can detect a TV station, even when your white space device is in a poor reception location, for a TV station on that channel. You don't really care about multipath distortion or any such details, just whether the channel is okay to use, by your unlicensed device.

That's what came to mind. Or, it could refer to detecting whether there's any signal transmissions on a channel, unrelated to any white space device. As you might have in a police channel scanner.

Decoding at the receiver is what I meant by Decision making.

Dear Abdelwahab,

I agree with the colleges and add, the channel estimation is to measure the channel transmission properties in time domain it is h(t) and in the frequency domain it is H(f). Modern communication relay on the estimation of the channel characteristics to remove the distortion in the received signal in a process called equalization.

Detection; is the identification of a specific signal in the received signal. Extraction of the modulating signals form the carrier is called detection or demodulation.

Signal detection in the presence of interference and noise is one of the most demanding task in the communication systems. In fact, one receives the symbols, detect them which means determine there magnitude and phase. and then decode them in a bi nary form in a process called demapping.

Correlators and matched filters are two devices used to detect the symbols from the received signals.

In the logic symbols one has to classify the logic symbols either logic one or zero.

Every logic symbol is represented by a range of values. If the values are greater than certain threshold the logic value will be one other wise it will be zero. Decision is always required when we have to classify the symbols as they have discrete values.

Best wishes

The estimation of the channel is known for the TX or RX. For TX to do resource allocation and for the receiver for coherent detection.

Hi Abdelwahab Fawzy,

Channel estimation is meant to obtain an estimate of channel impulse response h(t). In general, detection is the action of accessing information without specific cooperation from or synchronization with the transmitter. Decision means, we extract bits from the received symbols. In simple words, it is symbol to bit conversion. There are two types of decision, one is soft decision and other is hard decision. Soft decision offers better performance since we take the Euclidean distance (or calculated log-likelihood ratios) in account while Hard decision is based on Hamming distance.

If Channel estimation is bad, then it messes up completely with decision making. Hope, I have clarified your doubt. Dont hesitate to ask more if you need better explanation.

Regards,

Dr. KC

channel estimation is the process of finding channel impulse response with goal for receiver equalization this done in many statistical operation such as MSE with pilot or not, detection is the process of finding the channel is busy or ideal i.e find the presence or absences of signal in specific channel with goal to serve Cognitive Radio application and Multiple access terminology, decision making is the report or the action that will be taken depending on the detected parameters in channel detection phase.

Best Wishes

In general, estimation deals with finding out a vector (or scalar) of real values from data. There are an infinitude of possibilities for the estimate. In channel estimation, you try to estimate either the channel impulse response, or the frequency response of the communication channel. The channel values can be any complex number and a member of CM where C is the set of complex numbers and M is the dimension of the estimate.

Regarding detection, we have an "easier" problem. We receive something and we are trying to classify what we receive into some known possibilities. For example, at any instant we may be transmitting one of four symbols a, b, c or d. Due to channel imperfections, we may receive some scaled and noise added (perturbed) version of these symbols. Now, we try to classify each of the received symbols into the set (constellation) a, b, c or d.

Note that in detection, we will know in advance the (finite) set of possibilities of what is being transmitted. That is, the transmitter has a finite number of states and the receiver is trying to classify the received signal into one of these states. But in estimation, no such prior knowledge exists since there are an infinity of possibilities.

Channel estimation is an estimation problem and signal detection is a detection problem.