Hieu T. Do

Achievable Rates for Embedded Bidirectional Relaying in a Cellular Downlink

In this work we provide an achievable rate region for the cellular downlink with three users where two users want to communicate with each other. Due to the side information from the prior uplink, gains are achievable by combining bidirectional and classical broadcast channel coding strategies. A coding theorem for the bidirectional broadcast channel with random state non-causally known at the encoder is generalized to continuous alphabets and applied to Gaussian channels with an average power constraint. The single-user capacities are achievable if one decoder additionally knows the channel state. Accordingly, we see that a more comprehensive view on the information flow in a multi-user network can lead to a larger achievable rate region.

An achievable rate region for the Gaussian Z-interference channel with conferencing

This paper presents an achievable rate region for a 2-user Gaussian Z-interference channel with a noiseless and bidirectional digital communication link between the receivers. The region is achieved by utilizing the rate-splitting encoding technique, and the decode-and-forward and compress-and-forward strategies. In the very strong interference regime, the capacity region is achieved. In the weak interference regime, the asymptotic sum rate is characterized and shown to be possibly unbounded, which is in contrast to a recent result by Yu and Zhou for a similar scenario, however, with a unidirectional communication link between the receivers.

Noisy network coding approach to the interference channel with receiver cooperation

This work proposes a new coding scheme for the discrete memoryless two-user interference channel whose receivers can cooperate to decode their desired messages. The coding scheme is built upon Han-Kobayashi rate splitting and superposition coding at the transmitters, noisy network coding, and non-unique joint decoding at the receivers. As a case study the general achievable region leads to an inner bound for the Gaussian interference channel whose receivers cooperate through rate-limited orthogonal channels. It is shown that this inner bound is equivalent to the one-round quantize-bin-and-forward inner bound established by Wang and Tse, thereby showing that noisy network coding achieves within 1 bit/s/Hz to the capacity region when the interference is strong, and achieves within 1 bit/s/Hz to the capacity region of the Gaussian compound multiple access channel with conferencing decoders regardless of channel parameters.

A new inner bound for the interference relay channel

This paper proposes a new coding scheme for the discrete memoryless interference channel with a dedicated relay. The scheme is built upon rate-splitting encoding, layered noisy network coding, and joint decoding. The result is extended to two Gaussian channels. For the Gaussian channel whose relay is connected to the destinations via orthogonal links we indirectly show that the proposed scheme achieves a bounded gap to the capacity region under certain channel conditions. For the Gaussian channel wherein the relay receives and transmits in the same spectral resource with the transmitters the numerical results show that the proposed scheme achieves higher sum rate than other compress-forward-based schemes. This work, together with our previous work [1], shows that noisy network coding can be extended by the well-known rate-splitting technique of the interference channel to achieve a bounded gap to the capacity region of some multi-unicast networks.

Capacity bounds for the Z channel

We present a new achievable rate region for the discrete memoryless Z channel (DM-ZC) using Marton coding with rate splitting. The region is shown to include previously known achievable rate regions. Secondly we study a class of degraded Z channels, the bijective degraded Z channel (BDZC). An outer bound for the BDZC is proved, which is shown to meet the inner bound for the deterministic settings. For the Gaussian Z channel with weak crossover link, we show that if Gaussian inputs are optimal then a coding scheme based on Marton coding without rate splitting achieves to within half a bit per real dimension from the boundary of the capacity region.

The Gaussian Z-Interference Channel with Rate-Constrained Conferencing Decoders

We derive achievable rate regions for a 2-user Gaussian Z-interference channel with conferencing decoders. We identify different cases where the rate-limitedness of the conference link from the interference-free receiver to the interfered receiver affects the conferencing strategy as well as the achievable rate region. Furthermore, an outer bound to the capacity region based on cut-set and genie-aided bounds is presented.

Layered Coding for the Interference Channel With a Relay

This paper studies and derives new results for the interference channel with a relay (ICR). Three inner bounds for the discrete memoryless ICR are proposed, based on three coding strategies that employ layered code at the relay. The first scheme is inspired by layered noisy network coding, proposed by Lim et al. for the two-way relay channel, the second and the third schemes rely on simpler encoding and decoding processes, dubbed layered quantize-forward. Performance of the proposed schemes is investigated for two classes of channels with Gaussian noise: the interference channel with in-band relay reception/out-of-band relay transmission and the interference with in-band relay reception/in-band relay transmission. For the former class of channels, it is shown that the first proposed scheme achieves the same inner bound as the generalized hash-forward scheme with incremental binning. In addition, the inner bound is within 0.5 bit of the capacity region under certain conditions on the channel parameters. For the latter class of channels, new upper bounds on sum-rate are established by extending known upper bounds for symmetric channels. The first inner bound is shown to be within 0.5 bit of the capacity region if the relays power exceeds a certain threshold, which depends on channel parameters. Numerical examples show that the proposed schemes can achieve significantly higher sum-rates when compared with other compress-forward schemes. Analysis also reveals a tradeoff between achievable rates, coding delay, and complexity of the proposed schemes. Results in this paper provide a better understanding of coding for the ICR, in particular, they show that layered coding is a beneficial element in multiuser networks with relays.

Layered quantize-forward for the two-way relay channel

This paper proposes two new coding schemes for the discrete memoryless two-way relay channel. The main target is to show the benefits of compress-forward without Wyner-Ziv binning and of layered relaying in networks wherein a relay is to help multiple destinations, that may have unequal channel quality and/or have access to different side information. Numerical results for a Gaussian channel show that the new coding schemes outperform variants of compress-forward relaying and offer a good trade-off between achievable rates and complexity and decoding delay. The idea can also be applied to other relay networks.

Coding for the Z channel with a digital relay link

This paper considers a discrete memoryless four-node network where two nodes want to send three independent messages to the other two nodes. The two receiving nodes are allowed to cooperate by means of a unidirectional noiseless link with finite capacity. A coding scheme is proposed which combines rate splitting, block Markov multi-level superposition coding with binning and joint decoding. The general achievable rates are then specialized to degraded channel and Gaussian channel, where it is shown that the sum capacity for the Gaussian channel is achieved under certain conditions. Results in this paper recover and unify previously known results for the discrete memoryless Z channel without cooperation, and results for the Gaussian Z-interference channel with a digital relay link.

Capacity region of a class of interfering relay channels

This paper studies a new model for cooperative communication, the interfering relay channels. We show that the hash-forward scheme introduced by Kim for the primitive relay channel is capacity achieving for a class of semideterministic interfering relay channels. The obtained capacity result generalizes and unifies earlier capacity results for a class of primitive relay channels and a class of deterministic interference channels.