CORE-4: Cognition oriented relaying exploiting 4-D spectrum holes

In cognitive relay systems, spectrum holes exist in 4 dimensions (4-D), namely, time, frequency, location, and direction. How to efficiently utilize these different kinds of spectrum holes to provide quality-of-service (QoS) guarantees for secondary users (SU) is a challenging task. In this paper, we first identify the benefits of separately applying cooperative beamforming and rateless coding aided relaying technologies. Specifically, cooperative beamforming has the particular advantage of exploiting spatial or directional spectrum holes without causing interference to PUs. On the other hand, rateless coding is capable of utilizing different kinds of spectrum opportunities in an aggregate way with low complexity. Both cooperative beamforming and rateless coding aided cognitive relaying schemes have been proposed to support either elastic or real-time traffics for SUs. Furthermore, we combine cooperative beamforming and rateless coding together in order to provide an efficient and robust way to utilize 4-D spectrum holes in cognitive relay systems, where spectrum sensing and channel estimation may be imperfect. A substantial performance gain can be obtained by the combination, compared to using these two techniques separately.