| Cognitive radios have been studied recently as a means to utilize spec-trum in a more efficient manner.This paper focuses on the fundamental limits of opera-tion of a MIMO cognitive radio network with a single licensed user and a single cogni-tive user. The channel setting is equivalent to an interference channel with degraded message sets(with the cognitive user having access to the licensed user's message).An achievable region and an outer bound is derived for such a network setting.It is shown that the achievable region is optimal for a portion of the capacity region that includes sum capacity. In this paper, a cognitive MIMO system with space-frequency coding is proposed, in which the cognitive link communicates using two transmission antennas and one receiving antenna. Cognitive MIMO systems allow the licensed spectrum to be opportunistically exploited by the cognitive user, so they enable public access to the underutilized spectral bands and therefore the overall spectral efficiency can be eco-nomically increased. While in some situations, such as high-mobility environment or channel fading rapidly, it may be difficult and costly to estimate the channel accurately for cognitive MIMO systems. To solve the problem, space-frequency coding scheme has been proposed for cognitive MIMO systems. The construction of the transmitter and receiver for the cognitive MIMO system is provided. |
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