Abstract
Interference alignment (IA) is an effective technique to eliminate the interference among wireless nodes. In a multiinput multi-output (MIMO) cognitive radio system, multiple secondary users can coexist with the primary user without generating any interference by using the IA technology. However, few works have considered the fairness of secondary users. In this paper, not only is the interference eliminated by IA, but also the fairness of secondary users is considered by two kinds of algorithms. Without losing generality, one primary user andKsecondary users are considered in the network. Assuming perfect channel knowledge at the primary user, the interference from secondary users to the primary user is aligned into the unused spatial dimension which is obtained by water-filling among primary user. Also, the interference between secondary users can be eliminated by a modified maximum signal-to-interference-plus-noise algorithm using channel reciprocity. In addition, two kinds of fairness algorithms, max-min fairness and proportional fairness, among secondary users are proposed. Simulation results show the effectiveness of the proposed algorithms in terms of suppressed interference and fairness of secondary nodes. What is more, the performances of the two fairness algorithms are compared.
Highlights
With the rapid deployment of various wireless systems, the limited radio spectrum is becoming increasingly crowded
We propose a modified version of the iterative maximum signalto-interference-plus-noise (MSINR) algorithm in [7] for Interference alignment (IA) of the secondary users in the presence of the primary user whose interference is aligned with such a similar algorithm
We have presented a cognitive IA scheme, allowing multiple secondary users to access the free spatial dimensions of a primary user, which protects the transmission of the primary user while providing interference-free communication for the secondary users
Summary
With the rapid deployment of various wireless systems, the limited radio spectrum is becoming increasingly crowded. The key feature of the cognitive radio is to allow a class of radio devices, called secondary users, to opportunistically access a licensed spectrum that is left unused by the primary user as long as the secondary users will not affect the operation of the primary user adversely. This improves the spectral efficiency greatly for allowing more users to coexist in the same frequency band. It is quite natural to combine the MIMO and the cognitive radio techniques to achieve higher spectral efficiency. This technological combination results in the so-called cognitive MIMO radio [2]
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