Multi - antenna multi - carrier space – time - frequency precoded code division multiple access employing complete complementary codes

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.