Spreading-sequence design for partially connected multirelay networks under multipath fading

Abstract

Multipath fading can degrade the performance of a wireless communication system significantly when the data rate is as high as those systems beyond Long-Term Evolution Advanced (LTE-A). To combat the multipath-fading effects, orthogonal frequency-division multiplexing (OFDM) techniques have been extensively studied and used in existing systems. However, another effective method to combat multipath fading is a code-division multiple access (CDMA) scheme, which has not been extensively investigated for relay network communication systems. This paper considers uplink CDMA relay networks (consisting of multiple sources, multiple relays, and a single destination) and downlinks (consisting of a combined source, multiple relays, and multiple destinations) under multipath fading. The objective of this paper is to propose a unique, simple, and effective method of finding optimum nonbinary pseudo noise (PN) spreading and despreading sequences employing a maximum signal-to-interference-plus-noise ratio (SINR) criterion and channel state information (CSI). This paper also examines the sensitivity of the proposed schemes to 1-bit quantization, mistiming alignment, wideband jamming, and imperfect CSI. Simulation results verify that the proposed method shows much faster convergence in finding optimum PN sequences and better performance than existing schemes under the same environment.