• KSII Transactions on Internet and Information Systems
    Monthly Online Journal (eISSN: 1976-7277)

Degrees of Freedom of Y Channel with Single-Antenna Users: Transmission Scheme and Beamforming Optimization

Vol. 8, No.12, December 31, 2014
10.3837/tiis.2014.12.004, Download Paper (Free):

Abstract

In this paper, we investigate the degrees of freedom (DOF) of the Y channel consisting of three single-antenna users and a two-antenna common access relay, where each user intends to exchange independent messages with the other two users with the assistance of the relay. We show that the DOF of this particular scenario is 1.5. In order to prove this result, we firstly derive a DOF upper bound based on cut-set bound by allowing cooperation among users, which shows that the total DOF is upper bounded by 1.5. Then we propose a novel transmission scheme based on asymmetric signal space alignment (ASSA) to demonstrate the achievability of the upper bound. Theoretical evaluation and numerical results confirm that the upper bound can be achieved by utilizing ASSA, which also proves the optimality of the ASSA-based scheme in terms of DOF. Combining the upper bound and achievability, we conclude that the exact DOF is 1.5. Moreover, we present a novel iterative joint beamforming optimization (I-JBO) algorithm to further improve the sum rate. Numerical simulations have been provided to demonstrate the convergence speed and performance advantage of the I-JBO algorithm.


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Cite this article

[IEEE Style]
Wei Long, Hui Gao, Tiejun Lv and Chau Yuen, "Degrees of Freedom of Y Channel with Single-Antenna Users: Transmission Scheme and Beamforming Optimization," KSII Transactions on Internet and Information Systems, vol. 8, no. 12, pp. 4305-4323, 2014. DOI: 10.3837/tiis.2014.12.004

[ACM Style]
Long, W., Gao, H., Lv, T., and Yuen, C. 2014. Degrees of Freedom of Y Channel with Single-Antenna Users: Transmission Scheme and Beamforming Optimization. KSII Transactions on Internet and Information Systems, 8, 12, (2014), 4305-4323. DOI: 10.3837/tiis.2014.12.004