Page 29 - 2019

Ph.D.
(Engineering & Technology)
PERFORMANCE ENHANCEMENT OF WIRELESS LINK

Ph.D. Scholar : Patel Himanshu Amritlal
Research Supervisor : Dr. D. J. Shah

Regi. No.: 11146051011
Abstract :
Orthogonal Frequency Division Multiplexing (OFDM) is the transmission technique which
employs multiple overlapped and orthogonal subcarriers which gives efficient bandwidth
utilization and combat with ISI and noise in the channel. OFDM based systems are used
in various technologies like Digital Subscriber loop (DSL) modem, Digital Television,
Digital Radio, Wi-Fi, Wi-MAX, Wireless Local Area Network (LAN), Wireless Metropolitan
Area Network (MAN), Wireless Personal Area Network (PAN), Long Term Evolution (LTE)
and even in some complex military operations. The possible expansion date of Fifth
Generation (5G) is around 2020 and people are inclined towards technologies like OFDM
and massive Multiple Input and Multiple Output (MIMO). In OFDM, post IFFT process at
transmitter side, the frequency domain signal is converted into time domain signal. Due
to this process, the amplitudes in time domain are added up giving rise to an increase in
peak values of amplitude levels. If such peaks are not reduced, then they can go to
nonlinear region of High Power Amplifier (HPA) in transmitter and can cause in-band and
out-band radiation. This high PAPR (Peak to Average Power Ratio) problem leads to work
towards the method to reduce it. Many techniques are developed to reduce the PAPR
problem such as, Clipping method, SLM technique, PTS technique, Tone Injection
technique, Tone Rejection technique etc. The companding is one of the methods to help
reducing PAPR. Proposed work is done for piecewise companding technique in which one
function is used to expand the lower amplitude levels while other function(s) take care of
contraction of higher amplitude levels. The beauty of such transform is that the average
signal power, before and after companding, remains the same in the method used.
Optimized method for Two Piecewise Companding (2PWC) is proposed here and
compared with the existing work of 2PWC where approximation has been taken into
consideration. Three Piecewise Companding (3PWC) technique is also proposed with its
optimization. The optimized 3PWC method reduces more PAPR compared to optimized
exact 2PWC one. The comparison is based on optimization for the BER of 10-5 at the
Eb/No of 19.5 dB in both cases considering PAPR at CCDF of 10-5. The PAPR reduction
causes the reduction in peak in HPA of transmitter. The main advantage of reducing the
PAPR problem is that the backup time of Mobile Equipment (ME) increases. Reducing the
PAPR in OFDM system lowers the complexity and the cost of HPA. It is universally
acknowledged that battery and HPA are very costly elements of terminal equipment. After
the reduction of PAPR in 3PWC, if we increase its peak power to the earlier peak power
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