Solutions
The solutions provided here mainly discuss how to decrease the processing time. It also addresses some of the issues listed in the previous section.
Reentrant VIs
LabVIEW is a data flow programming tool. It can execute data independent codes in parallel if programmed in such a way. In the simulation there are several instances where a same chunk of code is repeated a number of times. This code is defined as a VI and is called every time the main code wants to utilize it. However by def... Continue reading ...
The simulation model aims in finding the BER value for
various SNR values and plots them on a chart. The processes involving in
finding a BER value for a single SNR value are random generation of a large
number of symbols, modulation of these symbols using one of the modulation
schemes such as PSK, MIMO- STC scheme encoding, generating and applying a
Rayleigh flat fading profile to it, generating and adding AWGN to it, decoding,
demodulation and BER calculation. Each of... Continue reading ...
Posted by Ujjval Shah on Wednesday, April 22, 2009,
In :
Simulation
Posted by Ujjval Shah on Wednesday, April 22, 2009,
In :
Simulation
Posted by Ujjval Shah on Wednesday, April 22, 2009,
In :
Simulation
Posted by Ujjval Shah on Wednesday, April 22, 2009,
In :
Simulation
Posted by Ujjval Shah on Wednesday, April 22, 2009,
In :
Simulation
Posted by Ujjval Shah on Wednesday, April 22, 2009,
In :
Simulation
Posted by Ujjval Shah on Tuesday, April 14, 2009,
In :
Theory
Some important results:
- Rate one generalized complex orthogonal designs do not exist for more than two transmit antennas
- The rate of a generalized complex orthogonal design cannot exceed R = 3/4 for more than two antennas
- Rate half, R = 0.5, generalized complex orthogonal designs exist for any number of transmit antennas
- For a generator matrix for a given rate and number of antennas, a generator matrix of same rate for number of tranmist antennas less by one can be obtained by simply removin...
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Selection combining involves the process of selecting one of the multiple receiver antennas and thus the communication channel which is least affected by noise.
The question: Is it possible to use this technique if there are more than two transmitter antennas?
My instinct says no, however i need to find out the answer and the reason for it as well. ------------------ edited on 22nd April well the answer is yes as well as know. for STBC you need to lock into one receiver antenna only during the tran... Continue reading ...
Posted by Ujjval Shah on Friday, April 3, 2009,
In :
Theory
Till now most of the concentration was on diversity gains achieved by using both transmit and receive antennas in a multiple-input multiple-output (MIMO) channel. However, multiple transmit antennas can be utilized to achieve other goals as well. A higher capacity and as a result a higher transmission rate is possible by increasing the number of transmit antennas. Assume a MIMO channel with equal number of transmit and receive antennas. Then in a rich scattering environment the capacity incre... Continue reading ...
Posted by Ujjval Shah on Saturday, March 28, 2009,
In :
Simulation
The following result is for Alamouti Encoding with RX diversity using Maximal Ratio Combining technique at the Recevier
Following curves are the expected theoretical curves for various different TX and RX antennas. The dotted curve for Na=4 is the curve to be compared with the above simulated curve.
Following is a quick comparison of all the three curves simulated till now:
Continue reading ...
Posted by Ujjval Shah on Saturday, March 28, 2009,
In :
Theory
RX Diversity means to have multiple antennas at the receiver.
There are basically three types of method to obtain RX Diversity:
- Selection Combining (SC): Here the receiver selects the best branch of all the receiver antennas and decodes the signal coming from that antenna. It is suboptimal and doesnt utilizes the energy of the signals from the other antennas.
- Maximal Ratio Combining (MRC): Here, the limitation of the SC technique is removed. In MRC, signals from all the antennas are weighted app...
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Posted by Ujjval Shah on Tuesday, March 24, 2009,
In :
Simulation
How does the inclusion of upconversion and downconversion affect the simulation results and upto what extent do they affect?
As of now it is observed that for a set of same given symbol rate, samples per symbol, no of message symbols and other parameters the BER curves for the simulation using upconversion and downconversion and the one without using them are almost the same.
Continue reading ...
Posted by Ujjval Shah on Tuesday, March 24, 2009,
In :
Simulation
As mentioned in previous posts, those curves were plotted at a symbol rate varying from 2-10Hz.
The published ones are plotted at 2bits/sec ie 1symbol/sec for QPSK.
In all the curves shown till now, none of them match exactly to the published ones.
However it is observed that as the symbol rate is gradually increased, the simulated curve tends to become more and more similar to the published ones.
Consider following values: symbol rate =500 no of samples per symbol =8 no of symbols =5k doppler ... Continue reading ...
Posted by Ujjval Shah on Wednesday, March 18, 2009,
In :
Simulation
The BER curves in the previous posts were plotted with the Fading and AWGN profile varying with each iteration and Eb/No value. Hence the graph had abrupt changes when the channel used to suddenly dive deep blotting out the signal, thus making the comparison for various Eb/No value difficult. Moreover a number of iterations had to be taken and mean was required to find out to get the most suitable reading; this resulted into lot of compuatational time.
Hence to avoid this a constant fading pro... Continue reading ...
Posted by Ujjval Shah on Monday, March 16, 2009,
In :
Simulation
The BER curves donot follow exactly as per the ones published in the book i am referring to, however they do resemble them. moreover the performance after using alamouti scheme does increases but not significantly as per the book. i have attached the pics of simulated curves. they were taken with 3.5K no of symbols, 10Hz symbol rate, 1 Hz doppler spread, 8 samples per symbol and mean of 20 iterations per SNR value. These values gives a very good result but the time taken for it outrageously l... Continue reading ...
Posted by Ujjval Shah on Sunday, March 8, 2009,
In :
Simulation
The simulation is complete. As discussed in previous post, the entire simulation of a siso and mimo (with alamouti scheme) has been done.
Entire simulation is done for QAM Modulation. But the same can be realised for other modulation schemes too as only the values of the complex symbols (values I and Q) are going to change with modulation scheme and the Alamouti encoding remaining constant.
Two major impairments are included in the simulation- The Additive White Guassian Noise (AWGN) and Rayleig... Continue reading ...
Previously, i had already developed a code to encode complex constellation symbols into alamouti codes for two transmit antennas.
For the decoding process at the receiver (only one antenna currently) i am using the maximum likelihood receiver (mlr) algorithm for finding the original transmitted symbols. To find the advantage of using alamouti code i am comparing it with a siso transmission system. in this case i am using the QAM transreceiver example provided by NI. however besides the given A... Continue reading ...
Today I had
an hour long meeting with Prof. A. S. Ranade. It was the first official meeting
where we discussed the project. I started off from point 0 – explaining what
MIMO is. Then we moved on to ‘Diversity’- i.e. in a nutshell- sending replicas
of signal to achiever better performance, which is the main idea behind mimo.
Space Diversity being the area of interest in this project, we discussed what physical
ways of achieving it are. Following that we discussed the two techniques of
Ma... Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
In :
Theory
The received signals at a receiver antenna in two time slots can be written as: For
more than two antennas, the max lik rec function will be
... Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
In :
Theory
The goal of
space-time coding is to achieve the maximum diversity of NM, the maximum
coding gain, and the highest possible throughput. In addition, the
decoding complexity is very important.
Alamouti code
N = 2
M = 1
To transmit b bits/cycle,
we use a modulation scheme that maps every b bits to one symbol from
a constellation with 2bsymbols
First, the
transmitter picks two symbols from the constellation using a block of 2b bits.
If s1 and s2 are the selected symbols for a block... Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
In :
Theory
M receiver antennas receive M signals each represented as:
r_{m} = α_{m}s + η_{m},
where η_{m} is a white Gaussian noise
sample added to the mth copy of the signal. A maximum-likelihood (ML) decoder combines
these M received signals to find
the most likely transmitted signal.We consider a coherent detection scheme
where the receiver knows the channel path gains, α_{m. }
Owing to its array gain, MRC typically achieves a few dB better
SNR than does SC.
... Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
In :
Theory
The source of diversity does not affect the method of combination
with the exception of transmit antenna diversity. For example, receiving two
versions of the transmitted signal through polarization diversity is the same
as receiving two signals from two receive antennas for the purpose of combining
There are two main combining methods that are utilized
at the receiver: - Maximum Ratio Combining (MRC)
- Selection Combining
... Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
In :
Theory
__Probability
Error for Diversity__
P= c_{1}e^{-c2 γ}
γ –snr
in fading
without diversity
In fading with diversity of N_{t}xN_{r}=N_{d}
__Probability Error for Array Gain__
... Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
In :
Theory
The replica of the transmitted signal can be sent through
different means [99]. For example, it can be transmitted in a different time
slot, a different frequency, a different polarization, or a different antenna.
The goal is to send two or more copies of the signal through independent fades.
Then, since it is less likely to have all the independent paths in deep fades,
using appropriate combining methods, the probability of error will be lower.
- Time slot – repetition
- Frequency – fdd
- Pol...
Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
In :
Theory
The main idea
behind “diversity” is to provide different replicas of the transmitted signal
to the receiver. If these different replicas fade independently, it is less
probable to have all copies of the transmitted signal in deep fade
simultaneously. Therefore, the receiver can reliably decode the transmitted
signal using these received signals. This can be done, for example, by picking
the signal with the highest SNR or by combining the multiple received signals.
As a result, the probabi... Continue reading ...
Posted by Ujjval Shah on Friday, February 27, 2009,
Brief Summary of the
project
__Definition:__
Simulation of a
Multiple Input Multiple Output (MIMO) system using various Space Time Coding
(STC) techniques in LabVIEW
MIMO-STC
technique is one of the salient features of the WiMAX Mobile standarad, which
along with Multiple Access scheme for multiple users, also marks it different
from the WiMAX Fixed standard. The above simulation will be done specifically
keeping in mind the WiMAX standard.
The success of
the simulation will be done after com... Continue reading ...
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