Mimo Design
We began the work on our project by studying the concept of Fading and Diversity in transmission channels. For our particular case, we shall be considering a Rayleigh-fading model, in which the complex gain is actually a random variable with circularly-symmetrical zero-mean Gaussian distribution, so that the amplitude has a Rayleigh distribution whereas its phase has a uniform distribution.
We also understood the basic concept behind diversity which is that transmission ought to be done simultaneously across multiple channels, because it is highly unlikely that all the channels in consideration will fade simultaneously. The diversity can be achieved through three ways: in time, in frequency or in space.
Receiver Diversity
Consider the case of a SIMO model (Single Input Multiple Output). The model follows the following equation
r = ah + n (i)
where a the transmitted symbol,
h = [h1, h2, h3
hn]T the channel gain vector,
n the noise matrix.
For the current case of study of receiver diversity, we consider n=1, i.e. single transmitter and m receivers.
There can be multiple ways in which we can combine the outputs from various antennae 1. Switched combining.
2. Selection combining.
3. Equal-gain combining.
4. Maximal-ratio combining.
Assuming that the transmitted code was modulated by 4-QAM, i.e. the transmitted symbol a' can be equal to either of the four complex values {±1± j}(Eb)1/2. Also, the alphabet has been scaled so that the energy per symbol is 2Eb .Since 4-QAM transmits 2 bits of information, the energy per bit is Eb. Furthermore, AWGN is assumed with zero mean and variance equaling No/2.
Maximal-ratio combining:-
The analysis in [1] conveys that...
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