Spectrum Sharing in Wireless Networks via QoS-Aware Secondary Multicast Beamforming

Abstract

Abstract-Secondary spectrum usage has the potential to considerably increase spectrum utilization. In this paper, quality-of-service (QoS)-aware spectrum underlay of a secondary multicast network is considered. A multiantenna secondary access point (AP) is used for multicast (common information) transmission to a number of secondary single-antenna receivers. The idea is that beamforming can be used to steer power towards the secondary receivers while limiting sidelobes that cause interference to primary receivers. Various optimal formulations of beamforming are proposed, motivated by different "cohabitation" scenarios, including robust designs that are applicable with inaccurate or limited channel state information at the secondary AP. These formulations are NP-hard computational problems; yet it is shown how convex approximation-based multicast beamforming tools (originally developed without regard to primary interference constraints) can be adapted to work in a spectrum underlay context. Extensive simulation results demonstrate the effectiveness of the proposed approaches and provide insights on the tradeoffs between different design criteria.

Optimal Spectrum Sharing in MIMO Cognitive Radio Networks via Semidefinite Programming

“…Robust optimization techniques are employed in these papers to deal with the worst-case channel realization. The case where only channel statistics is known to the SU transmitter is also studied in [10]. This is similar to a special case of the third scenario considered in our paper, when the receivers have only one antenna.…”

“…Insightful solution methods are proposed to provide better intuition that may not be obtainable from a numerical optimization perspective. The issue of imperfect CSI estimation is considered in [8]- [10] for multiple-input single-output (MISO) CR networks. Therein, robust optimization problems are formulated to ensure the service qualities for both SUs and PUs are satisfactory in the worst case.…”

“…That is, there is no need to solve the QCQP problem in this case. We should emphasize that the incomplete CSI here is not to be confused with that in [8]- [10], where it is assumed that the SU knows the CSI on all links, except that there may be uncertainty in the channel estimation. Robust optimization techniques are employed in these papers to deal with the worst-case channel realization.…”

MSE-Based Transceiver Designs for Full-Duplex MIMO Cognitive Radios

“…Channel estimation between SUs can be accomplished using standard signal processing techniques via training through the pilots and feedback [38]. Channel estimation between SUs and PUs is more challenging, because PUs are unlikely to cooperate with SUs.…”

“…Channel estimation between SUs and PUs is more challenging, because PUs are unlikely to cooperate with SUs. But, if the primary system adopts the TDD scheme, by exploiting the channel reciprocity, channel between SUs and PUs can be acquired at the SUs by overhearing the transmissions between PU transmitter and receiver pair [38]- [42]. If TDD scheme is not feasible, blind beamforming techniques can be employed [38].…”