Abstract:
The industry of wireless digital communications has matured since the 1970s with the introduction
of cellular technology, to the present rollout of fourth generation infrastructure. The discovery and
refining of technology such as orthogonal frequency division multiplexing (OFDM), code division
multiple access (CDMA) and later multiple-input multiple-output (MIMO) techniques has set the
stage for the current and future high capacity broadband wireless cellular networks. A number of
organisations have developed standards for wireless communication technologies, most notably the
Third Generation Partnership Project with the Long Term Evolution series of standards and the Institute
of Electrical and Electronics Engineers (IEEE) with its IEEE 802 series of standards.
This work aims to contribute to the afore mentioned field of research by amalgamating three key
technologies into a wireless communication system. The methodology adopted has centred on orthogonality
with the utilisation of OFDM, CDMA employing completely orthogonal complementary
codes and MIMO techniques. OFDM provides a reduced complexity means for managing multipath
environments by taking advantage of the fast Fourier transform (FFT) algorithm for modulation and
demodulation. Furthermore the cyclic rotation scheme applied to the orthogonal complete complementary
codes allows the use of spread spectrum technology without the inherent rate loss while providing multiple access. The recent advances in multiple antenna communication technology have led to the development of
two branches in the field. The first of these was the introduction of the spatial multiplexing concept
which increases the system capacity and the second was the development of many diversity achieving
spatial coding techniques. Of the diversity achieving techniques orthogonal space-time block codes
(OSTBC) are most notable due to their linear detectability.
The performance of two communication systems has been evaluated through simulation. Both employ
the multi carrier CDMA based on the cyclically rotated complete complementary codes however the
fundamental difference between them is the spatial coding. Spatial multiplexing and OSTBCs have
been utilised with a matrix algebraic framework description unifying both. The spatial multiplexed
signals are detected with a non-linear sphere decoder and the OSTBC data is detected linearly.
The results have shown that the systems achieve the expected diversity orders in flat fading conditions.
The OSTBC system achieves added gains in multipath conditions due to the spread spectrum coding.
The codes provide multiple access as well as extract added multipath diversity that would otherwise
be unavailable. Interestingly, both systems were unaffected by Doppler since perfect channel state
information was assumed and the spreading was performed in frequency domain.
