International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 3 – Jul 2014
Improvement in Signal Quality with the use of
Maximal Gain Combining Diversity Technique
Mr. Prashant Singh
India
Abstract- Diversity is a technique of combining two or
more signals in such a manner that the effects of fading
in the communication channel can be overcome. This
technique improves the signal to noise ratio of the
received signal and diminishes the undesirable effects of
interference. The diversity has three major kinds of
techniques: Selection combining, maximal ratio
combining and Equal Gain Combining. Out of these
three techniques the best technique is Maximal Ratio
combining technique.
Keywords: Signal to noise ratio, Rayleigh fading,
Additive White Gaussian Noise channel, Binary Phase
Shift Keying,
Signal to noise ratio.
I. INTRODUCTION
In this paper, I have discussed the maximal ratio combining
diversity technique that is used to improve the signal to
noise ratio. The mathematical model of the multihop
wireless communication channels with diversity technique
applied has been discussed and the types of relaying
multihop diversity channels has been discussed.
The system[8] model for multihop wireless communication
channels with diversity is composed of a source terminal, a
receiving terminal and intermediate terminal[8]s.T1 is the
source terminal,T2 through T(n) are the intermediate
terminals and T(n+1) is the destination terminal.n is the
number of hops along the transmission path.In this model
there is signal connectivity between non adjacent
terminals.[8]
Amplified relaying multihop diversity channel is the
channel in which each intermediate [8]terminal combines
and amplifies the received signals from all preceding
terminals before retransmission. Noise is propagated along
the multihop channel. The decoding error is introduced at
the destination terminal.[8]
Decoded relaying multihop diversity channel is the channel
in which each intermediate terminal combines, decodes and
reencodes[8] the received signals from all preceding
terminals before retransmission. This channel does not
propagate noise along the multihop channel. The
possibility of decoding error is introduced at each
intermediate terminal.[8]
II. FADING
Fading is defined as the decrease in the signal to noise ratio
due to the information signal travelling along different
paths and encountering various propagation phenomenon
such as diffraction, scattering and reflection[1].Large scale
fading is called attenuation or path loss[2].It is the
logarithmic decrease in the average power of the received
signal with the distance between the transmitter and the
receiver.[2]Small scale fading is the signal loss due to the
interference between the signals that travel along multiple
paths.[1]
III. MATHEMATICAL MODEL
Fig 1 Multihop wireless communication channel with diversity
ISSN: 2231-5381
Fig 2 Multihop wireless communication channels without diversity
The model for multihop[8] wireless communication
channels without diversity consists of a source terminal, a
destination terminal and intermediate number of potential
intermediate relaying terminals[8].T1 is the source terminal,
T(n+1) is the destination terminal,T2 through T(n) are
intermediate terminals., is the total number of hops. s (i) is
the sent signal amplitude and r(i,j) is the received signal
amplitude.[8]
The decoded relaying multihop channel is the channel in
which each terminal digitally decodes and reencodes the
received signal from[8] the immediately preceding terminal
before retransmission. The amplified relaying multihop
channel is the channel in which each terminal amplifies the
received signal from the immediately preceding terminal
before retransmission.[8]
In this model there is no connectivity between the non
adjacent terminals[8].
While implementing the diversity combining techniques
the parameters that are taken care of are feedback and feed
forward interference, propagation and processing delay,
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 3 – Jul 2014
interference between signals and power control. Feedback
interference is the interference between a signal that is before
the considered terminal and the signal at the terminal itself.
Feedforward interference is the interference between the
signal that is after the considered terminal and the signal at
the considered terminal. Propagation delay is the delay caused
by the propagation of a signal from one terminal to another.
Relaying channels face the problem of propagation delay
more than single hop channels due to the multihop route that
they follow. The decoded relaying channel also initiates the
problem of processing delay due to the tme it takes to decode
and re-encode the signal. The power control has to be
distributed between the terminals .It involves the use of
tedious power control algorithms.[5]
IV. MAXIMAL RATIO COMBINING
DIVERSITY TECHNIQUE
In the maximal ratio combining technique, the signal branches
are used simultaneously. Each of the signal branch is assigned
a weight in proportion to its signal to noise ratio[5].The signal
brnches are then all added up after bringing them to a
common phase. The major challenge in this technique is the
cop hasing of the individual signal branches after assigning a
particular weight to them.[4]
Fig 5 Bit error rate vs signal to noise ratio for maximal ratio combining
technique and that of system without diversity.
nRx=1 represents the Rayleigh fading channel while nRx=2
represents the Maximal ratio combining technique.
VI. CONCLUSION
Here I have analysed how the error can be reduced and the
signal quality can be improved by using the Maximal ratio
combining diversity technique. This diversity technique is
generally the best when signal to noise ratio has to be
improved. The fading concept in the multihop wireless
communication channels has been discussed briefly with the
definitions of large scale fading and small scale fading being
discussed. Binary phase shift keying technique and Rayleigh
fading statistics have been used while implementing the
results.
VII. REFERENCES
Fig 3 Maximal Ratio Combining Technique
V.
IMPLEMENTATION AND RESULT
[1] Simon Haykin,”Communication Systems”,Wiley Publisher
[2] T Rappaport,”Wireless Communication:Principles and practice”,Prentice
Hall,Inc New Jersey,1996
[3] William Jakes,”Microwave Mobile Communications,IEEE Press 1974
[4] J D Parsons,”The Mobile Radio Propagation Channel”,John Wiley and
Sons Limited,2000
[5] J Proakis,”Digital Communications”,McGraw Hill,Inc New York,Third
edition ,1995
[6] J Proakis and M Salehi,”Contemporary Communication Systems using
MATLAB”,Brooks/Cole,2000
[7] J Preyton Z Peebles,”Probability,random variables and random signal
principles”,McGraw Hill,Inc 1993
[8] Thesis on multihop wirelesss communication channels by J Boyer,2001
Fig 4 System model
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