On Ergodic Sum Capacity of Fading Cognitive Multiple-Access and Broadcast Channels

TL;DR

This paper investigates the maximum achievable data rates in fading cognitive radio networks, deriving optimal power allocation strategies and demonstrating the optimality of D-TDMA schemes for both multiple-access and broadcast channels under various power constraints.

Contribution

It provides the first comprehensive analysis of ergodic sum capacity in fading cognitive MAC and BC channels, including optimal power allocation and conditions for D-TDMA optimality.

Findings

Optimal power allocation schemes derived for various constraints.

D-TDMA is optimal for ergodic sum capacity in both channels.

Conditions identified under which D-TDMA achieves capacity.

Abstract

This paper studies the information-theoretic limits of a secondary or cognitive radio (CR) network under spectrum sharing with an existing primary radio network. In particular, the fading cognitive multiple-access channel (C-MAC) is first studied, where multiple secondary users transmit to the secondary base station (BS) under both individual transmit-power constraints and a set of interference-power constraints each applied at one of the primary receivers. This paper considers the long-term (LT) or the short-term (ST) transmit-power constraint over the fading states at each secondary transmitter, combined with the LT or ST interference-power constraint at each primary receiver. In each case, the optimal power allocation scheme is derived for the secondary users to achieve the ergodic sum capacity of the fading C-MAC, as well as the conditions for the optimality of the dynamic time-division-multiple-access (D-TDMA) scheme in the secondary network. The fading cognitive broadcast channel (C-BC) that models the downlink transmission in the secondary network is then studied under the LT/ST transmit-power constraint at the secondary BS jointly with the LT/ST interference-power constraint at each of the primary receivers. It is shown that D-TDMA is indeed optimal for achieving the ergodic sum capacity of the fading C-BC for all combinations of transmit-power and interference-power constraints.