3. TDMA(Time division multiple access)
Time-division multiplexing (TDM) is a method of transmitting and receiving
independent signals over a common signal path by means of synchronized
switches at each end of the transmission line so that each signal appears on the
line only a fraction of time in an alternating pattern.
Each frame consists of a set of time slots
Usually used with digital signal or analog signal carrying digital data
Each source is assigned one or more time slots per frame
4. ADVANTAGES of TDMA
In addition to increasing the efficiency of transmission, TDMA offers a number of other
advantages over standard cellular technologies. First and foremost, it can be easily adapted
to the transmission of data as well as voice communication. TDMA offers the ability to
carry data rates of 64 kbps to 120 Mbps (expandable in multiples of 64 kbps).
It is the most cost effective technology for upgrading analog to digital.
It provides the user with extended battery life and talk time.
It is the only technology that offers an efficient utilization of hierarchal cell structures like
Pico, micro and macro cells.
Dual band 800/1900 MHz
5. The Disadvantages of TDMA
One of the disadvantages of TDMA is that each user has a predefined time slot. However,
users roaming from one cell to another are not allotted a time slot.
Another problem with TDMA is that it is subjected to multipath distortion. A signal coming
from a tower to a handset might come from any one of several directions. It might have
bounced off several different buildings before arriving
6. FDMA(Frequency division multiple access)
Number of signals are carried simultaneously on the same medium
Each signal is modulated to a different carrier frequency
Useful bandwidth of medium should exceed required bandwidth of channels
Carrier frequency separated so signal do not overlap
Eg: FM radio, CATV
7. ADVANTAGES Of FDMA
It does not need synchronization between its transmitter and receiver.
Frequency division multiplexing (FDM) is simpler and easy demodulation.
Due to slow narrow band fading only one channel gets affected.
It is used for analog signals.
A large number of signals (channels) can be transmitted simultaneously.
8. Disadvantages of FDMA
• It does not differ significantly from analog systems; improving the capacity
depends on the signal-to-interference reduction, or a signal-to-noise ratio (SNR).
• The maximum flow rate per channel is fixed and small.
• Guard bands lead to a waste of capacity.
• Hardware implies narrowband filters, which cannot be realized in VLSI and
therefore increases the cost.
15. ylabel('amplitude');
title('modulated Signal from user');
subplot(3,1,3)
plot(z(i,:),'color',C{i}); % demodulated signal
xlabel('time index');
ylabel('amplitude');
title('demodulated Signal from
user at the base station');
end
figure
plot(ch_op) %
xlabel('time index’);
ylabel('amplitude');
title('Signal after passing
through the channel')
19. OSTBC(orthogonal space time block code)
The OSTBC Encoder block encodes an input symbol sequence using orthogonal
space-time block code (OSTBC). The block maps the input symbols block-wise
and concatenates the output codeword matrices in the time domain.
20.
21. SNR
The SNR is a ratio of the signal power to the total noise power. To get total noise
power, we assume that the shot noise is approximately Gaussian with of course
mean equal to the average photo-current. Then since shot and thermal
processes are independent Gaussian random processes, the variance of the
total noise is equal to the sum of the variances of the two noises.
SNR is the difference between the . Also, in terms of definition, the noise floor is
the specious background transmissions that are produced by other devices or by
devices that are unintentionally generating interference on a similar frequency.
Therefore, to ascertain the signal to noise ratio, one must find the quantifiable
difference between the desired signal strength and the unwanted noise by
subtracting the noise value from the signal strength value
22. BER
In digital transmission, the number of bit errors is the number of received bits of a
data stream over a communication channel that have been altered due to noise,
interference, distortion or bit synchronization errors. The bit error rate (BER) is
the number of bit errors per unit time.
BER=Errors / Total Number of Bits
The main reasons for the degradation of a data channel and the corresponding
bit error rate, BER is noise and changes to the propagation path
28. ABOUT THE PROJECT
It is based on the performance and comparsion analysis of the orthogonal
frequency division multiplexing(OFDM) and multiple input and multiple
output(MIMO)
By using BPSK modulation at the transmitting end via multiple Txs we get a
medium propagation signal in many-many layout
It improve the reliability of the network with multi-path potential.
29. MIMO
MIMO systems use a combination of multiple antennas and multiple signal paths
to gain knowledge of the communications channel. By using the spatial dimension
of a communications links.
Increased data rates
Multiplexing increases capacity and spectral efficiency with no additional power or
bandwidth expenditure
30. OFDM
Stands for orthogonal Frequency division multiplexing
It has improved the quality of long-distance communication by eliminating Inter
Symbol Interference (ISI) and improving Signal-to-Noise ratio (SNR).
It reduce multi-path fading
It ability for high –data rate transmission over multipath fading channel
High spectral efficiency , low receiver complexity
31. BEAMFORMING
Beamforming is a technique that focuses a wireless signal towards a specific
receiving device, rather than having the signal spread in all directions from a
broadcast antenna.
improves the spectral efficiency by providing a better signal-to-noise ratio (SNR).
Spatial randomness of the signal is optimized
42. Introduction
The purpose of error control coding is to enable the
receiver to detect or even correct the errors by
introducing some redundancies in to the data to be
transmitted. There are basically two mechanisms for
adding redundancy:
1. Block coding
2. Convolutional coding
43. Linear Block Codes
The encoder generates a block of n coded bits from k
information bits and we call this as (n, k) block codes. The
coded bits are also called as code word symbols.
Why linear??? A code is linear if the modulo-2 sum of two
code words is also a code word.
n code word symbols can take 2^𝑛 possible values. From that
we select 2^𝑘 code words to form the code. A block code is
said to be useful when there is one to one mapping between
message m and its code word c
44. Generation Matrix
All code words can be obtained as linear combination of basis vectors.
• The basis vectors can be designated as {𝑔1, 𝑔2, 𝑔3,….., 𝑔𝑘}
• For a linear code, there exists a k by n generator matrix such that 𝑐1∗𝑛 = 𝑚1∗𝑘 . 𝐺𝑘
∗𝑛 where c={𝑐1, 𝑐2, ….., 𝑐𝑛} and m={𝑚1, 𝑚2, ……., 𝑚𝑘}
• In this form, the code word consists of (n-k) parity check bits followed by k bits of
the message.
• The rate or efficiency for this code R= k/n
• G = [ 𝐼𝑘 P] , C = m.G = [m mP] Message part Parity part
45. PARITY CHECK MATRIX (H)
When G is systematic, it is easy to determine the parity check
matrix H as: H = [𝐼𝑛−𝑘 𝑃 𝑇 ]
The parity check matrix H of a generator matrix is an (n-k)-by-
n matrix satisfying: 𝐻(𝑛−𝑘)∗𝑛𝐺𝑛∗𝑘 = 0
Then the code words should satisfy (n-k) parity check
equations 𝑐1∗𝑛𝐻𝑛∗(𝑛−𝑘) = 𝑚1∗𝑘𝐺𝑘∗𝑛𝐻𝑛∗(𝑛−𝑘) = 0
46. SYNDROME AND ERROR DETECTION
For a code word c, transmitted over a noisy channel, let r be the received vector at the output
of the channel with error
Syndrome of received vector r is given by: s = r.H =(𝑠1, 𝑠2, 𝑠3, … … . . , 𝑠𝑛−𝑘)
Properties of syndrome:
The syndrome depends only on the error pattern and not on the transmitted word. s = (c+e).H
= c.H + e.H = e.H
All the error pattern differ by atleast a code word have the same syndrome s.
47. MINIMUM DISTANCE OF A BLOCK CODE
Hamming weight w(c ) : It is defined as the number of non-zero components of c. For
ex: The hamming weight of c=(11000110) is 4
Hamming distance d( c, x): It is defined as the number of places where they differ . The
hamming distance between c=(11000110) and x=(00100100) is 4
The hamming distance satisfies the triangle inequality d(c, x)+d(x, y) ≥ d(c, y)
The hamming distance between two n-tuple c and x is equal to the hamming weight of
the sum of c and x d(c, x) = w( c+ x) For ex: The hamming distance between
c=(11000110) and is 4 and the weight of c + x = (11100010) is 4. x=(00100100)
The Hamming distance between two code vectors in C is equal to the Hamming weight
of a third code vector in C. d = min{w( c+x):c, x €C, c≠x} = min{w(y):y €C, y≠ 0} = w min
≠
48. Minimum min hamming distance d : It is defined as the smallest distance between
any pair of code vectors in the code.
For a given block code C, d min is defined as: d min =min{ d(c, x): c, min x€C, c x}
The Hamming distance between two code vectors in C is equal to the Hamming
weight of a third code vector in C.
d min= min{w( c+x):c, x €C, c≠x}
= min{w(y): y €C, y≠ 0}
= w min
49. Applications
Communications:
Satellite and deep space communications.
Digital audio and video transmissions.
Storage:
Computer memory (RAM).
Single error correcting and double error detecting code.
50. ADVANTAGES
It is the easiest and simplest
technique to detect and correct
errors.
Error probability is reduced.
DISADVANTAGES
Transmission bandwidth
requirement is more.
Extra bits reduces bit rate of
transmitter and also reduces its
power
51. Code:
%Given H Matrix
H = [1 0 1 1 1 0 0;
1 1 0 1 0 1 0;
0 1 1 1 0 0 1]
k = 4;
n = 7;
% Generating G Matrix
% Taking the H Matrix Transpose
P = H';
% Making a copy of H Transpose Matrix
L = P;
% Taking the last 4 rows of L and storing
52. L((5:7), : ) = [];
% Creating a Identity matrix of size K x K
I = eye(k);
% Making a 4 x 7 Matrix
G = [I L]
% Generate U data vector, denoting all information sequences
no = 2 ^ k
% Iterate through an Unit-Spaced Vector
for i = 1 : 2^k
53. if rem(i - 1, 2 ^ (-j + k + 1)) >= 2 ^ (-j + k)
u(i, j) = 1;
else
u(i, j) = 0;
end
% To avoid displaying each iteration/loop value
echo off;
end
end
54. echo on;
u
% Generate CodeWords
c = rem(u * G, 2)
% Find the min distance
w_min = min(sum((c(2 : 2^k, :))'))
% Given Received codeword
r = [0 0 0 1 0 0 0];
r
55. %Find Syndrome
ht = transpose(H)
s = rem(r * ht, 2)
for i = 1 : 1 : size(ht)
if(ht(i,1:3)==s)
r(i) = 1-r(i);
break;
end
end
56. disp('The Error is in bit:')
disp(i)
disp('The Corrected Codeword is :')
disp(r)
62. TABLE OF CONTENT
Introduction to the phenomena of diversity
Classification of diversity
Types of diversity on the basis of resource
Diversity techniques
Maximal ratio technique
Equal gain technique
Matlab code
Output
63. INTRODUCTION TO THE PHENOMENA OF
DIVERSITY
Used for wireless communication systems
Applied to improve the performance over a Fading radio channel
Rx.is catered with multiple intel signal transmitted over multiple channels
It is based on the fact that individual channels experience different levels of fading
and interference
64. Types of diversity on the basis of resource
Time diversity: Multiple versions of the same signal are transmitted at different time
instants.
Frequency diversity : The signal is transmitted using several frequency channels or
spread over a wide spectrum that is affected by frequency-selective fading
Space diversity : The signal is transmitted over several different propagation paths.
In the case of wired transmission, this can be achieved by transmitting via multiple
wires. In the case of wireless transmission, it can be achieved by using multiple
transmitter antennas and multiple receiving antennas.
Multiuser diversity : it is a diversity technique using user scheduling
in multiuser wireless channels where user scheduling allows the base station to
select high quality channel users so as to transmit information through a relatively
high quality channel in time, frequency and space domains based on the channel
quality
65. CLASSIFICATION OF DIVERSITY
Macro diversity: It is a form of antenna combining, and requires an infrastructure
that mediates the signals from the local antennas or receivers to a central receiver
or decoder. Transmitter may be a form of simulcasting, where the same signal is
sent from several nodes.
Micro diversity: Provides a method to mitigate the effects of multipath fading as in
case of small scale fading
66. DIVERSITY TECHNIQUE
• Time diversity:
Transmission in which signals representing the same information are sent over the
same channel at different times. The delay between replicas > coherence time
uncorrelated channels
Space diversity: Two antennas separated by several wavelengths will not generally
experience fades at the same time
Space Diversity can be obtained by using two receiving antennas and switching instant-
by- instant to whichever is best
Frequency diversity: Using frequency channel separated in frequency more than the
channel coherence bandwidth
Polarization diversity: using antenna with different polarizations
67. Maximal Ratio Technique
In maximal-ratio combining, the signals from all of the M branches are weighted
according to their individual SNRs and then summed. The individual signals must
be cophased before being summed.
the signals from each channel are added together
The Gain of each channel is made Proportional to the rms signal level and
inversely proportional to the mean square noise level in that channel.
68. Equal gain technique
It combining is similar to maximal-ratio combining except that the weights are all
set to unity. The possibility of achieving an acceptable output SNR from a number
of unacceptable inputs is still retained. The performance is marginally inferior to
maximal ratio combining.
