: General description of inter-software functionalities for WiMAX transceivers
Optical and Wireless PHY Integration
stored in the target environment (i.e. MATLAB) via galaxy ports (e.g. CoSimInputOpt) and
on is executed. The expected output data are then collected and fed back
interoperable model and evaluate its preliminary performance, a IEEE802.16d
WiMAX OFDM transceiver model was built in MATLAB and applied at the VPI CoSim
transmitter and receiver, demonstrating
modelling platforms. The performance of
WiMAX channels was modelled with no channel coding applied in order to present a worst case
software functionalities for WiMAX transceivers
Chapter 3 Optical and Wireless PHY Integration
58
At the transmitter, following the symbol formation and serial to parallel conversion in
MATLAB, the subcarrier mapping block could be used to insert guard carriers for a brick-wall
spectrum shape [35].
The resulting frequency domain signal was subsequently transformed to the time domain using
the 256 point IFFT prior to parallel to serial conversion and cyclic prefix addition. The
quantisation process and signal shaping are performed in VPI.
At the other end, the WiMAX receiver performs the inverse functions to those of the
transmitter. The 14 bits digital to analog (D/A) and analog to digital (A/D) converters at the
transmitter and receiver respectively were used to minimise quantisation noise [35]. The cyclic
prefix removal, FFT and wireless channel equalisation at the receiver are performed in
MATLAB while VPI is used for estimating the symbol error rate (SER) and EVMs.
Critically, estimating the SER of the electrical mQAM signal in RoF systems raises additional
issues compared to classical systems where only additive white Gaussian noise (AWGN)
influences signal quality [37]. The probability density function (PDF) of the received I and Q
signals does not always follow a Gaussian distribution. It was shown that this PDF is Gaussian
when electrical or optical noise (ASE) is the main impairment [37]. On the other side, when
composite triple beat (CTB) also called third-order inter-modulation distortions (IMD3) occurs,
this PDF tends to an Exponential distribution. More generally, the PDF lies between a Gaussian
and an Exponential distribution, making the SER more complicated to estimate. In addition to
the above, nonlinear distortions can be amplitude-dependent so that the distribution statistics
(e.g. the variance) may be different for each symbol [37].
To account for these characteristics, the SER estimation is based on an independent
approximation of the left and right tails of the signal’s PDF, corresponding to each mQAM
symbol [38].
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