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A Comparative Performance Analysis of Interweaved and Underlay Multi-Antenna Cognitive Radio Networks

An analytical performance study is realized in this paper, focusing on multiple-input-single-output (MISO) cognitive radio (CR) systems with the aim of comparing the two most popular CR approaches, namely, the interweaved and underlay setups. The throughput-based comparison is accomplished on a fair basis, by measuring the achievable ergodic capacity of secondary communication, given an average rate-based, quality of service (QoS) constraint on primary communication. We derive closed form expressions for the outage probability at the primary user (PU), along with expressions for the ergodic capacity of the secondary user (SU). These expressions are derived as a function of key design parameters, under a rate-optimal sensing protocol for the interweaved approach, and a standard precoding and power allocation scheme for the underlay approach. By conducting this comparative study, we reveal the existence of specific regimes (in terms of primary activity, number of transmit antennas, quality of spectrum sensing), where the interweaved approach outperforms the underlay one and vice versa.