arXiv subjects

Hamid Behroozi

Publications and source records attributed to Hamid Behroozi.

22 records · Page 2Linked to original sources

arXiv2014

On the Ice-Wine Problem: Recovering Linear Combination of Codewords over the Gaussian Multiple Access Channel

In this paper, we consider the Ice-Wine problem: Two transmitters send their messages over the Gaussian Multiple-Access Channel (MAC) and a receiver aims to recover a linear combination of codewords. The best known achievable rate-region for this problem is due to [1],[2] as $R_{i}\leq\frac{1}{2}\log\left(\frac{1}{2}+{\rm SNR}\right)$ $(i=1,2)$. In this paper, we design a novel scheme using lattice codes and show that the rate region of this problem can be improved. The main difference between our proposed scheme with known schemes in [1],[2] is that instead of recovering the sum of codewords at the decoder, a non-integer linear combination of codewords is recovered. Comparing the achievable rate-region with the outer bound, $R_{i}\leq\frac{1}{2}\log\left(1+{\rm SNR}\right)\,\,(i=1,2)$, we observe that the achievable rate for each user is partially tight. Finally, by applying our proposed scheme to the Gaussian Two Way Relay Channel (GTWRC), we show that the best rate region for this problem can be improved.

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arXiv2013

Nested Lattice Codes for Gaussian Two-Way Relay Channels

In this paper, we consider a Gaussian two-way relay channel (GTRC), where two sources exchange messages with each other through a relay. We assume that there is no direct link between sources, and all nodes operate in full-duplex mode. By utilizing nested lattice codes for the uplink (i.e., MAC phase), and structured binning for the downlink (i.e., broadcast phase), we propose two achievable schemes. Scheme 1 is based on compute and forward scheme of [1] while scheme 2 utilizes two different lattices for source nodes based on a three-stage lattice partition chain. We show that scheme 2 can achieve capacity region at the high signal-to-noise ratio (SNR). Regardless all channel parameters, the achievable rate of scheme 2 is within 0.2654 bit from the cut-set outer bound for user 1. For user 2, the proposed scheme achieves within 0.167 bit from the outer bound if channel coefficient is larger than one, and achieves within 0.2658 bit from the outer bound if channel coefficient is smaller than one. Moreover, sum rate of the proposed scheme is within 0.334 bits from the sum capacity. These gaps for GTRC are the best gap-to-capacity results to date.

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arXiv2013

On the Achievable Rate-Regions for State-Dependent Gaussian Interference Channel

In this paper, we study a general additive state-dependent Gaussian interference channel (ASD-GIC) where we consider two-user interference channel with two independent states known non-causally at both transmitters, but unknown to either of the receivers. An special case, where the additive states over the two links are the same is studied in [1], [2], in which it is shown that the gap between the achievable symmetric rate and the upper bound is less than 1/4 bit for the strong interference case. Here, we also consider the case where each channel state has unbounded variance [3], which is referred to as the strong interferences. We first obtain an outer bound on the capacity region. By utilizing lattice-based coding schemes, we obtain four achievable rate regions. Depend on noise variance and channel power constraint, achievable rate regions can coincide with the channel capacity region. For the symmetric model, the achievable sum-rate reaches to within 0.661 bit of the channel capacity for signal to noise ratio (SNR) greater than one.

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arXiv2008

On the Capacity of Pairwise Collaborative Networks

We derive expressions for the achievable rate region of a collaborative coding scheme in a two-transmitter, two-receiver Pairwise Collaborative Network (PCN) where one transmitter and receiver pair, namely relay pair, assists the other pair, namely the source pair, by partially decoding and forwarding the transmitted message to the intended receiver. The relay pair provides such assistance while handling a private message. We assume that users can use the past channel outputs and can transmit and receive at the same time and in the same frequency band. In this collaborative scheme, the transmitter of the source pair splits its information into two independent parts. Ironically, the relay pair employs the decode and forward coding to assist the source pair in delivering a part of its message and re-encodes the decoded message along with private message, which is intended to the receiver of the relay pair, and broadcasts the results. The receiver of the relay pair decodes both messages, retrieves the private message, re-encodes and transmits the decoded massage to the intended destination. We also characterize the achievable rate region for Gaussian PCN. Finally, we provide numerical results to study the rate trade off for the involved pairs. Numerical result shows that the collaboration offers gain when the channel gain between the users of the relay pair are strong. It also shows that if the channel conditions between transmitters or between the receivers of the relay and source pairs are poor, such a collaboration is not beneficial.

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