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Fundamental Limits of Wireless Two-Way Full-Duplex Communication Networks

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posted on 28.10.2014, 00:00 by Zhiyu Cheng
Most wireless communication networks are two-way, where nodes act as both sources and destinations of messages. This allows for ``adaptation'' at or ``interaction'' between the nodes -- a node's channel inputs may be functions of its message(s) and previously received signals allowing for potentially larger rates than those achievable in feedback-free one-way channels where inputs are functions of messages only. However, examples exist of channels where adaptation is not beneficial from a capacity perspective; we ask whether analogous results hold for several multi-user two-way networks. We first consider deterministic two-way channel models: the binary modulo-2 addition channel and a generalization of this, and the linear deterministic channel which models Gaussian channels at high SNR. For these deterministic models we obtain the capacity region for the two-way multiple access/broadcast channel, the two-way Z channel and the two-way interference channel (under certain ``partial'' adaptation constraints in some regimes). We permit all nodes to adapt their channel inputs to past outputs (except for portions of the linear high-SNR two-way interference channel where we only permit 2 of the 4 nodes to fully adapt). However, we show that the two-way fully or partially adaptive capacity region consists of two parallel ``one-way'' regions operating simultaneously in opposite directions, i.e. adaptation is useless. We next consider two noisy channel models: first, the Gaussian two-way MAC/BC, where we show that adaptation can at most increase the sum-rate by 1/2 bit in each direction. Next, for the two-way interference channel, partial adaptation is shown to be useless when the interference is very strong. In the strong and weak interference regimes, we show that the non-adaptive Han and Kobayashi scheme utilized in parallel in both directions achieves to within a constant gap for the symmetric rate of the fully (for some regimes) or partially (for the remaining regimes) adaptive models. Then we generalize the two-way interference channel to the K-pair-user two-way interference channel (TWIC) and show that for symmetric scenarios and certain interference regimes, non-interactive schemes again achieve to within a constant gap for the fully adaptive Gaussian model. Furthermore, we investigate the degrees of freedom (DoF, also known as the multiplexing gain) of the K-pair-user TWIC with and without a MIMO relay, where we emphasize all nodes operate in full-duplex mode. We first derive a new outer bound (allows interaction) to demonstrate that the optimal DoF of the K-pair-user TWIC is K: full-duplex operation doubles the DoF, but interaction does not further increase the DoF. We next employ a MIMO relay in the K-pair-user TWIC. If the relay is non-causal/instantaneous (at time k forwards a function of its received signals up to time k) and has 2K antennas, we demonstrate a one-shot scheme where the relay mitigates all interference to achieve the interference-free 2K DoF. In contrast, if the relay is causal (at time k forwards a function of its received signals up to time k-1), we show that a full-duplex MIMO relay cannot increase the DoF of the K-pair-user TWIC beyond K, as if no relay or interaction is present. We comment on reducing the number of antennas at the instantaneous relay.



Devroye, Natasha


Electrical and Computer Engineering

Degree Grantor

University of Illinois at Chicago

Degree Level


Committee Member

Tuninetti, Daniela Ansari, Rashid Zefran, Milos Soljanin, Emina

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