DESIGN AND
IMPLEMENTATION OF MULTILAYER
QOS MODEL FOR M-ARY SYSTEM
4.1.
Introduction
From results of last
chapter, it observed that for spectral efficient modulation techniques such as
M-PSK, BER performance degrades as value of a modulation order M (≥4) increase
as shown in Fig. 4.1. This is because the distance between symbols on
constellation decreases as number of symbol increases with modulation order.
Fig. 4.1 BER performance of BPSK, QPSK, 8-PSK, 16-PSK
Fig. 4.2 Constellation Diagram of BPSK
Fig. 4.3 Constellation Diagram of 4-PSK
Fig. 4.4 Constellation Diagram of 8-PSK
Fig. 4.5 Constellation Diagram of 32-PSK
Also from constellations
diagrams of BPSK, 4-PSK, 8-PSK and 32-PSK (shown in Figures 4.2-4.5), it is
observed that constellations of symbols are upward compatible i.e.
constellation of symbols of BPSK can be derived from constellation of symbols
of 4-PSK, 8-PSK and so on. Similarly, constellation of symbols of 4-PSK can be
derived from constellation of symbols of 8-PSK, 16-PSK and so on.
The idea behind this part of
thesis is that the user easily switches from one level of BER performance to
another actively (on demand) without changing the actual MODEM. This is
possible by using computerized encoding and decoding at transmitter and
receiver respectively.
Fig. 4.6 Logical decision boundary of QoS level 4
Fig. 4.7 Logical decision boundary of QoS level 3
Fig. 4.8 Logical decision boundary of QoS level 2
Method: The comprising of encoding and decoding techniques
with 32-PSK MODEM circuitry. For level-1, this technique work normally as
32-PSK transceiver. For level-2, the input bits are grouped into 3-bits symbol
and a zero is added in 4th bit place. Appending a zero in end in
digital signal is equivalent by multiplication by 2. The resultant signal is
mapped to 32 bit PSK such as block coded modulation. It also behaves like
repetitive constellation points. At receiver side, the decision boundary is
extended logically such that any phase difference between 0o to 45o is resemble symbol “0” (=000) and between 45o
to 90o resemble symbol “1” (=001) and so on. similarly level 2
and 3 signals are encoded, mapped and decoded.
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Fig. 4.9 Simulated SER performance of 4-Level QOS system.
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1.1.
Simulation Results and Analysis
Fig. 4.9 Simulated SER performance of 4-Level QOS system.
Fig. 4.10 Simulated BER performance of 4-Level QOS
system.
1.2.
Conclusion
In this chapter, it is
concluded that constellation signals of lower modulation order can be encoded
to constellation signal of higher modulation order and can be demodulated by
same higher order demodulator. Fig. 4.10 shows the comparison of BER performance
of different levels of QoS system. Different level of QoS is assigned to these
BER performances such as QoS level 1 is assigned to 32-PSK constellation
signal, QoS level 2 is assigned to 8-PSK constellation signal, QoS level 3 is
assigned to 4-PSK constellation signal and QoS level 4 is assigned to BPSK
constellation signal and BER performance is getting better as lower constellation
signal is mapped to higher constellation signal. Same conclusion is derived
from Fig. 4.9 on the basis of SER
