Infrared wireless communications

Abstract

The performance of an infrared wireless spread spectrum system using biorthogonal codes under the effect of multipath dispersion is evaluated through theoretical analysis and computer simulations. The performance of the system with (i) biorthogonal Walsh codes and (ii) biorthogonal random codes are investigated in a simulated non-directed line-of-sight infrared channel. An approximation to the bit error probability is derived by using a Gaussian approximation for the intersymbol interference due to multipath propagation. The average probability of error as a function of signal-to-noise ratio is used as the performance criteria. Results show that a biorthogonal spread spectrum system is able to combat the effect of multipath dispersion since only small power penalties are incurred while increasing the system spectral efficiency. It is also observed that biorthogonal Walsh codes have a slightly worse performance than random biorthogonal codes in a less dispersive channel. However, the former has superior performance than the later in a more dispersive channel. Comparison of the analytical and simulation results show that the Gaussian approximation becomes more accurate in less dispersive channels and when the length of the code sequence increases.