How can you calculate, or how can you measure?
SNR in any kind of channel is independent of transmitted power. But perhaps you're asking how you can measure SNR, by varying transmitted power?
It's a summation problem. The most basic equation being,
transmitted power - channel loss >= receiver sensitivity, to achieve reception. (Power and sensitivity expressed as dBm.)
Channel loss would ideally be channel loss through free space, of course. Otherwise, you're introducing more variables, such as antenna heights above terrain.
So, if you're interested in measuring SNR, and you know the receiver sensitivity, you would see how much power above this theoretical minimum is needed to just barely achieve reception. That total power, over the minimum theoretical, expressed in dB, would be the SNR in the channel.
The other complicating factor here is that in fading channels, different receivers would behave differently. A receiver with lots of echo tolerance would use some of the interference power as "signal," and you might measure good SNR. A receiver with poorer echo tolerance would instead treat that interference power as pure noise, resulting in lower SNR measurement.
Thank you. i mean how can express SNR as function of transmitted power.
In AWGN SNR=Prx / (N0*BW) and Prx=(PTX /cosnt *d)
But in fadding channel SNR depend on average fading power. such as SNR= Ω*Prx / (N0*BW)
so what is the value or expression of the average fading power Ω
In electrical engineering, computer science and information theory, channel capacity is the tight upper bound on the rate at which information can be reliably transmitted over a communications channel. By the noisy-channel coding theorem, the channel capacity of a given channel is the limiting information rate (in units of information per unit time) that can be achieved with arbitrarily small error probability.
Information theory, developed by Claude E. Shannon during World War II, defines the notion of channel capacity and provides a mathematical model by which one can compute it. The key result states that the capacity of the channel, as defined above, is given by the maximum of the mutual information between the input and output of the channel, where the maximization is with respect to the input distribution.
AWGN channel capacity with the power-limited regime and bandwidth-limited regime indicated. Here, \frac{\bar{P}}{N_o}=10^6.
more details you can consult :
Saleem Bhatti. "Channel capacity". Lecture notes for M.Sc. Data Communication Networks and Distributed Systems D51 -- Basic Communications and Networks.
or in general: http://en.wikipedia.org/wiki/Channel_capacity
Why wouldn't that depend entirely on the type of fading?
Atmospheric fading, like signal bouncing variably off the ionosphere, might change that Prx to some time function, such as
Prx = Ptx / (A*f(d, t))
which you can then average over time. If its a sinusoid modulating the free space propagation loss, for instance, you can calculate the RMS value of that sinusoid, to reduce the SNR by some average amount.
What if it's Rayleigh fading experienced by a vehicle moving through an urban environment? The answer might be very different, right? Assuming the noise power doesn't change, if you're using OFDM with adequately wide guard interval, or if you're using CDMA with an adequate rake filter, you might end up with an equation which looks much like your AWGN example.
So I guess "it depends," is the best answer.
You should supply more information. Are you talking of slow fading or fast fading? Is there any diversity technique you are using? Are there multiple antennas or there is single antenna? Actually the answer will be different for all these scenarios. I am attaching a simple article, that may answer if you are assuming slow fading.
I have a question can we change channel coding scheme packet by packet in mimo.I mean if we transmit one packet with turbo coding after channel instantaneous SNR we sent other packet with LDPC .is it possible .can someone refer best paper or books for this topic.
Dear Abdelhay,
My answer came late but it may be useful for other researchers. The colleagues gave answers bt i want to elaborate on the answers.
Assume the transmitted power is Pt , assume that the channel gain factor is h, then the power gain factor will be h^2. Then the received power will be Pr= h^2 Pt,
h can be any channel, line of sight , falt feeding, selective fading where h the channel gain factor changes with time .
To get the average received power overtime we have only to get the effective or the average of h^2 Pt= E(h^2 Pt)= (Integral h^2 Pt dt from 0 to T)/T where T is the integration time. As Pt is constant during the integration one can average only the power gain of the channel across the time.
Best wishes
i am calculating the SNR for a SISO channel matrix H as below:
snr_linear = (tx_power .*(abs(h0).^2));
how do i change it for MIMO scenario? now that my H matrix is 2x2 MIMO channel?
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