Abstract
This paper proposes a low complexity spatial modulation (SM) scheme
that combines spatial shift keying (SSK) with pulse position modulation (PPM)
for optical wireless communication systems. SM is a multi-transmitter technique
for achieving increased data rate over the traditional on-off keying (OOK)
and PPM signalling methods. Analysis of the error performance of the system
in the presence of noise is presented and validated via simulations. There
is a perfect agreement between the simulation and the theoretical analysis
for the case of <i>M</i> = 2 bits/symbol and other values of <i>M</i> at symbol error rate (SER) of less
than 10<sup>-2</sup>.
At higher SER values the analytical prediction is about 1.2 dB
more than that of the simulation. We also show the energy efficiency/bandwidth
requirement trade-off involved when determining the system parameters such
as the number of transmitters and the number of bits per symbol <i>M</i>. Using fewer transmitters improves
the energy efficiency but requires more bandwidth. Moreover, the error performance
of SPPM is dictated by both the individual channel gains of the multiple transmitters
and the difference between these channel gains or path losses. Hence, distinct
channel gains are a prerequisite in spatial modulation. An experimental set
up to measure and show the dependence of the channel gains on the relative
position of the transmitter to the receiver is also presented. These measured
channel parameters are then used to evaluate the system error performance.
The performance of the SPPM is also compared, in terms of energy and spectral
efficiencies, with the classical SSK and repetition coded (RC) schemes in
which the multiple transmitters are used to transmit the same data simultaneously.
The results show the SPPM as a multi-transmitter signalling scheme that combines
the energy efficiency of the PPM with the high spectral efficiency of the
SSK.
© 2012 IEEE
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