Effect of imperfect CSI on interference alignment in multiple-High Altitude Platforms based communication

Interference Alignment (IA) offers maximum sum-rate in a wireless X channel. Though IA was proposed for maximizing sum-rate, its application for exploiting high data rate in air-to-ground communication has not been explored much. In this paper, the application of IA in a High Altitude Platform (HAP) to Ground Station (GS) communication is considered. Recent studies suggest that IA provides maximum sum-rate for a 2 × 2 transmitter-receiver system. However, independent channels are required to achieve IA conditions. The application of IA is proposed here for a generalized channel in an HAP-to-GS communication link that takes into account angle-of-departure and angle-of-arrival at the transmitter and at the receiver, respectively. We verify the minimum distance criteria in receiving nodes to achieve independent channels. Receivers are placed at optimal distance for best error performance. Furthermore, in view of an actual scenario, we investigate the effect of imperfect CSI, resulting from changes in imperfection in HAP's stabilization, in the performance of our model. The performance, in terms of Bit Error Rate (BER), is presented for IA and non-IA based communication. For this purpose, an analytical expression is developed for the probability of error. A perfect match is shown between the error rate measured with Monte Carlo simulations and the error probability found using the derived analytical expressions.