2,235 research outputs found
Spectrum Sharing in Wireless Networks via QoS-Aware Secondary Multicast Beamforming
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 ldquocohabitationrdquo 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
Symbol Based Precoding in The Downlink of Cognitive MISO Channels
This paper proposes symbol level precoding in the downlink of a MISO
cognitive system. The new scheme tries to jointly utilize the data and channel
information to design a precoding that minimizes the transmit power at a
cognitive base station (CBS); without violating the interference temperature
constraint imposed by the primary system. In this framework, the data
information is handled at symbol level which enables the characterization the
intra-user interference among the cognitive users as an additional source of
useful energy that should be exploited. A relation between the constructive
multiuser transmissions and physical-layer multicast system is established.
Extensive simulations are performed to validate the proposed technique and
compare it with conventional techniques.Comment: CROWNCOM 201
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