Fundamental limits of the two-user gaussian x channel with limited receiver cooperation

Abstract

Modern wireless communications via the X channel where each transmitter has an independent message for the corresponding receiver have become an active topic of research since they can support various services transmitted from sources to users or obtain different types of data transmitted from users to sources. However, interference is the important phenomenon that occurs unavoidably in these wireless communications and affects directly on the performance of the system. Cooperation is one of several methods that can mitigate the effect of interference and is considered in several communication scenarios. Unfortunately, the basic comprehension of the X channel with cooperation is somewhat less. In this dissertation, we study the two-user Gaussian X channel with limited receiver cooperation where both receivers exchange messages over the orthogonal receiver-cooperative links through the perspective of information theory that can be divided into 3 parts as follows: In the first part, we investigate the fundamental limits of the two-user Gaussian X channel with limited receiver cooperation using the Fano’s inequality, the data processing inequality, and the genie-aided techniques. The obtained result is called an outer bound. In the second part, we characterize the generalized degrees-of-freedom under the channel symmetric setting by using our proposed outer bound. The results in this part imply that the performance of our system can be improved when the amount of exchanged information between both receivers increases. However, the system reaches the saturation point of the receiver cooperation when the normalized capacity of the receiver-cooperative link \\kappa >= 1/2, 1, 3/2 and 2 and 2 for the normalized interference level \\alpha \\in [0, 3/2], (3/2, 2], (2,5/2], and (5/2, 3] respectively. In the final part, we propose the strategies consisting of transmission scheme based on Han-Kobayashi strategy and cooperative protocol based on quantize-map-and-forward scheme and then give achievable rate regions based on the proposed strategies for both the general case and the strong Gaussian X channel type I case where SNR1 > INR2 and SNR2 > INR1. The obtained results show that our proposed strategy in the strong Gaussian X channel type I case achieves the capacity region to within 2 bits/s/Hz per message when \\beta and \\gamma in the common rate constraints at the transmitter are set such that most of the bounds in the achievable rate region reach theirs maximum value. This constant is independent of the channel parameters.