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.
Bibliographical noteFunding Information:
Manuscript received May 12, 2008; accepted February 04, 2009. First published February 24, 2009; current version published May 15, 2009. The associate editor coordinating the review of this paper and approving it for publication was Dr. Qing Zhao. This work was supported in part by the Natural Sciences and Engineering Research Council (NSERC) of Canada and in part by the Alberta Ingenuity Foundation, Alberta, Canada. The work of N.D. Sidiropoulos was supported by the European Commission FP6 FET project COOPCOM. This work was presented in part at the IEEE Sensor Array and Multi-Channel Signal Processing Workshop (SAM), Darmstadt, Germany, July 2008.
- Secondary spectrum usage
- Semidefinite programming (SDP)