Effective Capacity of Statistical Delay QoS Guarantees with Imperfect Channel Information in Spectrum-Sharing Networks

This paper considers a spectrum-sharing cognitive network in which a secondary user shares spectrum with an existing primary user as long as the interference caused by the secondary user to the primary user is below permissible levels. We investigate the delay quality-of-service (QoS) guaranteed capacity gains with imperfect channel state information (CSI) between the secondary transmitter and the primary receiver in Rayleigh fading environments. In particular, we quantify the relation between the secondary link effective capacity and the interference inflicted on the primary user. The impacts of channel estimation error on the performance of the secondary link are studied. We further evaluate and compare the capacity gains using proposed power allocation policies and truncated channel inversion with fixed rate (TIFR) transmission policies under different constraint conditions. Our results indicate channel estimation errors, especially in the smaller value range, lead to considerably degradation of capacity gains for the looser delay QoS requirements. Numerical simulations are conducted to corroborate our theoretical analysis. 