This paper studies the cooperation between a primary system and a cognitive system in a cellular network where the cognitive base station (CBS) relays the primary signal using amplify-and-forward or decode-and-forward protocols, and in return it can transmit its own cognitive signal. While the commonly used half-duplex (HD) assumption may render the cooperation less efficient due to the two orthogonal channel phases employed, we propose that the CBS can work in a full-duplex (FD) mode to improve the system rate region. The problem of interest is to find the achievable primary-cognitive rate region by studying the cognitive rate maximization problem. For both modes, we explicitly consider the CBS transmit imperfections, which lead to the residual self-interference associated with the FD operation mode. We propose closed-form solutions or efficient algorithms to solve the problem when the related residual interference power is non-scalable or scalable with the transmit power. Furthermore, we propose a simple hybrid scheme to select the HD or FD mode based on zero-forcing criterion, and provide insights on the impact of system parameters. Numerical results illustrate significant performance improvement by using the FD mode and the hybrid scheme.
For improvement of achievable rate region in cognitive radio channels, a transmission method for secondary users is proposed. At first, the rate region of the sensing based cognitive radio scheme in which secondary users access the channel based on their channel sensing results with sensing error is analyzed. In the multiuser information theory, it is well-known that interference channel cases where both users transmit their own signal simultaneously achieve better rate region than the time-sharing method based on sensing outcomes. Based on this theoretical result, we propose the new transmission scheme in which a secondary transmitter relays primary userpsilas signal with a full-duplex amplify and forward (AF) manner while transmitting its own data at the same time. In the proposed method, we take account of practical implementation issues which are ignored in the theoretical method guaranteeing an upper bound of a rate region. With different geometric locations and power ratios between the relaying signal and the secondary userpsilas one, we evaluate the achievable rate region of the proposed method and compare with those of the conventional ones. Cognitive radios are promising solutions to the problem of overcrowded and inefficient licensed spectrum. In this work we explore the throughput potential of cognitive communication. We summarize different cognitive radio techniques that underlay, overlay and interweave the transmissions of the cognitive user with those of the licensed users. Recently proposed models for cognitive radios based on the overlay technique are described. For the interweave technique, we present a two switch' cognitive radio model and develop inner and outer bounds on the secondary radio capacity. Using the two switch model, we investigate the inherent tradeoff between the sensitivity of primary detection and the cognitive link capacity. With numerical results, we compare the throughputs achieved by the secondary user in the different models. Cognitive radio promises a low-cost, highly flexible alternative to the classic single-frequency band, single-protocol wireless device. By sensing and adapting to its environment, such a device is able to fill voids in the wireless spectrum and can dramatically increase spectral efficiency. In this paper, the cognitive radio channel is defined as a two-sender, two-receiver interference channel in which sender 2 obtains the encoded message sender 1 plans to transmit. We consider two cases: in the genie-aided cognitive radio channel, sender 2 is noncausally presented the data to be transmitted by sender 1 while in the causal cognitive radio channel, the data is obtained causally. The cognitive radio at sender 2 may then choose to transmit simultaneously over the same channel, as opposed to waiting for an idle channel as is traditional for a cognitive radio. Our main result is the development of an achievable region which combines Gel'fand-Pinkser coding with an achievable region construction for the interference channel. In the additive Gaussian noise case, this resembles dirty-paper coding, a technique used in the computation of the capacity of the Gaussian multiple-input multiple-output (MIMO) broadcast channel. Numerical evaluation of the region in the Gaussian noise case is performed, and compared to an inner bound, the interference channel, and an outer bound, a modified Gaussian MIMO broadcast channel. Results are also extended to the case in which the message is causally obtained. In this paper, we consider a communication scenario in which the primary and the cognitive radios wish to communicate to different receivers, subject to mutual interference. In the model that we use, the cognitive radio has noncausal knowledge of the primary radio's codeword. We characterize the largest rate at which the cognitive radio can reliably communicate under the constraint that 1) no rate degradation is created for the primary user, and 2) the primary receiver uses a single-user decoder just as it would in the absence of the cognitive radio. The result holds in a ldquolow-interferencerdquo regime in which the cognitive radio is closer to its receiver than to the primary receiver. In this regime, our results are subsumed by the results derived in a concurrent and independent work (Wu , 2007). We also demonstrate that, in a ldquohigh-interferencerdquo regime, multiuser decoding at the primary receiver is optimal from the standpoint of maximal jointly achievable rates for the primary and cognitive users.