Orthogonal receive symbols at the receiver for fast-fading Rayleigh channels

Abstract

In this article we consider uncoded single user spread spectrum systems for transmissions over frequency-flat, strongly time-variant (timely correlated) Rayleigh fading channels. The article extends the idea of [1] that designs transmit symbols such that they are orthogonal at the output of such a channel. Knowledge of the channel coefficient's auto-correlation function is assumed at the transmitter and at the receiver. We show a concrete and numerically stable algorithmic implementation that designs higher order modulations, while being able to handle larger time variances. A new algorithm is proposed that designs signals under a given bandwidth constraint. Algorithm initialization and convergence speed are improved. Bit error rate simulations show superior performance to classical incoherent orthogonal FSK transmission, and that the new transmission scheme is relatively robust against design or estimation errors regarding the channel's maximum Doppler frequency.