Zhengdao Wang — Page 2

arXiv2011

Interference Alignment and Degrees of Freedom Region of Cellular Sigma Channel

We investigate the Degrees of Freedom (DoF) Region of a cellular network, where the cells can have overlapping areas. Within an overlapping area, the mobile users can access multiple base stations. We consider a case where there are two base stations both equipped with multiple antennas. The mobile stations are all equipped with single antenna and each mobile station can belong to either a single cell or both cells. We completely characterize the DoF region for the uplink channel assuming that global channel state information is available at the transmitters. The achievability scheme is based on interference alignment at the base stations.

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arXiv2011

Superposition Noisy Network Coding

We present a superposition coding scheme for communication over a network, which combines partial decode and forward and noisy network coding. This hybrid scheme is termed as superposition noisy network coding. The scheme is designed and analyzed for single relay channel, single source multicast network and multiple source multicast network. The achievable rate region is determined for each case. The special cases of Gaussian single relay channel and two way relay channel are analyzed for superposition noisy network coding. The achievable rate of the proposed scheme is higher than the existing schemes of noisy network coding and compress-forward.

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arXiv2010

Degrees of Freedom Regions of Two-User MIMO Z and Full Interference Channels: The Benefit of Reconfigurable Antennas

We study the degrees of freedom (DoF) regions of two-user multiple-input multiple-output (MIMO) Z and full interference channels in this paper. We assume that the receivers always have perfect channel state information. We first derive the DoF region of Z interference channel with channel state information at transmitter (CSIT). For full interference channel without CSIT, the DoF region has been fully characterized recently and it is shown that the previously known outer bound is not achievable. In this work, we investigate the no-CSIT case further by assuming that the transmitter has the ability of antenna mode switching. We obtain the DoF region as a function of the number of available antenna modes and reveal the incremental gain in DoF that each extra antenna mode can bring. It is shown that in certain cases the reconfigurable antennas can bring extra DoF gains. In these cases, the DoF region is maximized when the number of modes is at least equal to the number of receive antennas at the corresponding receiver, in which case the previously outer bound is achieved. In all cases, we propose systematic constructions of the beamforming and nulling matrices for achieving the DoF region. The constructions bear an interesting space-frequency interpretation.

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arXiv2010

On the Rate Achievable for Gaussian Relay Channels Using Superposition Forwarding

We analyze the achievable rate of the superposition of block Markov encoding (decode-and-forward) and side information encoding (compress-and-forward) for the three-node Gaussian relay channel. It is generally believed that the superposition can out perform decode-and-forward or compress-and-forward due to its generality. We prove that within the class of Gaussian distributions, this is not the case: the superposition scheme only achieves a rate that is equal to the maximum of the rates achieved by decode-and-forward or compress-and-forward individually. We also present a superposition scheme that combines broadcast with decode-and-forward, which even though does not achieve a higher rate than decode-and-forward, provides us the insight to the main result mentioned above.

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arXiv2010

Wireless Network Code Design and Performance Analysis using Diversity-Multiplexing Tradeoff

Network coding and cooperative communication have received considerable attention from the research community recently in order to mitigate the adverse effects of fading in wireless transmissions and at the same time to achieve high throughput and better spectral efficiency. In this work, we design and analyze deterministic and random network coding schemes for a cooperative communication setup with multiple sources and destinations. We show that our schemes outperform conventional cooperation in terms of the diversity-multiplexing tradeoff (DMT). Specifically, it achieves the full-diversity order at the expense of a slightly reduced multiplexing rate. We establish the link between the parity-check matrix for a $(N+M,M,N+1)$ systematic MDS code and the network coding coefficients in a cooperative communication system of $N$ source-destination pairs and $M$ relays. We present two ways to generate the network coding matrix: using the Cauchy matrices and the Vandermonde matrices, and establish that they both offer the maximum diversity order.

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arXiv2010

Diversity-Multiplexing Tradeoff of Cooperative Communication with Linear Network Coded Relays

Network coding and cooperative communication have received considerable attention from the research community recently in order to mitigate the adverse effects of fading in wireless transmissions and at the same time to achieve high throughput and better spectral efficiency. In this work, we analyze a network coding scheme for a cooperative communication setup with multiple sources and destinations. The proposed protocol achieves the full diversity order at the expense of a slightly reduced multiplexing rate compared to existing schemes in the literature. We show that our scheme outperforms conventional cooperation in terms of the diversity-multiplexing tradeoff.

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arXiv2010

On the Degrees of Freedom Regions of Two-User MIMO Z and Full Interference Channels with Reconfigurable Antennas

We study the degrees of freedom (DoF) regions of two-user multiple-input multiple-output (MIMO) Z and full interference channels in this paper. We assume that the receivers always have perfect channel state information. We derive the DoF region of Z interference channel with channel state information at transmitter (CSIT). For full interference channel without CSIT, the DoF region has been obtained in previous work except for a special case M1< N1<min(M2,N2), where M_i and N_i are the number of transmit and receive antennas of user i, respectively. We show that for this case the DoF regions of the Z and full interference channels are the same. We establish the achievability based on the assumption of transmitter antenna mode switching. A systematic way of constructing the DoF-achieving nulling and beamforming matrices is presented in this paper.

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