Besides maximizing multiplexing gain, improving diversity is important for reliable communications in the presence of interference. In this context, on-off switched interference alignment (IA) is investigated, where IA is intermittently utilized by switching IA on/off in order to improve diversity gain in an interference channel and hence to maximize diversity multiplexing tradeoff (DMT). This paper adopts Alamouti coding based IA for the on-off switched IA, which requires only local channel state information at the transmitter. Optimizing the portion of IA utilization of the proposed scheme in closed form, we derive the achievable DMT and show that the intermittent utilization of IA with simultaneous non-unique decoding can improve DMT in the 2-user X-channel with two antennas. The proposed scheme, to the best of our knowledge, surpasses any other existing schemes for the 2-user X-channel with two antennas and is closed to the ideal DMT.

To improve diversity gain in an interference channel and hence to maximize diversity multiplexing tradeoff (DMT), we propose an on-off switched interference alignment (IA) where IA is intermittently utilized by switching IA on/off. For onoff switching, either IA with symbol extension or IA with Alamouti coding is adopted in this paper. Deriving and analyzing DMT of the proposed schemes, we reveal that the intermittent utilization of IA with simultaneous non-unique decoding can improve DMT in the 2-user X-channel with two antennas. Both proposed schemes are shown to achieve a diversity gain of 4 and DoF per user of 3. In particular, the on-off switched IA with Alamouti coding, to the best of our knowledge, surpasses any other existing schemes for the 2-user X-channel with two antennas and nearly approaches the ideal DMT.

This paper studies a two-user single-input single- output (SISO) interference channel with a cognitive relay (ICCR) under delayed feedback. We consider three types of feedback: delayed channel state information at transmitter (CSIT), delayed output feedback, and no feedback. For each feedback information, we derive the optimal degrees of freedom (DoF) region of the two-user ICCR where delayed feedback information is available at all transmitters. We show that while a cognitive relay with no feedback cannot improve the sum DoF beyond 1 in the two-user interference channel, delayed feedback can increase the sum DoF to 4/3.

This paper studies the interference channel with a cognitive relay under delayed feedback. Three types of delayed feedback are studied: delayed channel state information at the transmitter, delayed output feedback, and delayed Shannon feedback. Outer bounds are derived for the degrees of freedom (DoF) region of the two-user multiple-input multiple-output interference channel with a cognitive relay with delayed feedback as well as without feedback. For the single-input single-output scenario, optimal schemes are proposed based on retrospective interference alignment. It is shown that while a cognitive relay without feedback cannot improve the sum-DoF in the two-user single-input single-output interference channel, delayed feedback in the same scenario can increase the sum-DoF to 4/3. For the multiple-input multiple-output case, achievable schemes are obtained via extensions of retrospective interference alignment, leading to the DoF regions that meet the respective upper bounds.

We propose new ergodic interference alignment techniques forK-user interference channels with delayed feedback. Two delayed feedback scenarios are considered - delayed channel information at transmitter (CIT) and delayed output feedback. It is proved that the proposed techniques achieve total 2K/(K+2) DoF which is higher than that by the retrospective interference alignment for the delayed feedback scenarios.

This paper proposes a new strategy combining interference alignment (IA) and rate splitting for a three user interference channel with a cognitive transmitter. Although a half of available dimensions are sacrificed to align interference signals from other users in conventional IA, the proposed scheme recycles the sacrificed dimensions with the help of a cognitive transmitter. The achievable rate region and generalized degrees of freedom are derived. Compared with conventional IA, the proposed scheme improves achievable rate and generalized degrees of freedom.

This paper analyzes the capacity of a three-user interference channel with a cognitive transmitter which non-causally knows the messages of the other two transmitters. Especially, We derive the capacity region when all interference channel gains are strong and show that the capacity is achieved by superposition coding. From the capacity results for the specific channel conditions, we also analyze the capacity region for three-user Gaussian interference channel with a cognitive transmitter.