Results 1 
7 of
7
A Converse for the Wideband Relay Channel with Physically Degraded Broadcast
 IEEE INFORMATION THEORY WORKSHOP
, 2011
"... We investigate the multipath fading relay channel in the limit of a large bandwidth, and in the noncoherent setting, where the channel state is unknown to all terminals, including the relay and the destination. We derive a lower bound on the capacity by proposing and analyzing a peaky frequency bin ..."
Abstract

Cited by 6 (1 self)
 Add to MetaCart
We investigate the multipath fading relay channel in the limit of a large bandwidth, and in the noncoherent setting, where the channel state is unknown to all terminals, including the relay and the destination. We derive a lower bound on the capacity by proposing and analyzing a peaky frequency binning scheme. The achievable rate obtained coincides with the blockMarkov lower bound on the capacity of the wideband frequencydivision Gaussian relay channel. When the broadcast channel is physically degraded, this achievable rate meets the cutset upperbound, and thus reaches the capacity of the noncoherent wideband multipath fading relay channel. In this case, a hypergraph model of the multipath fading relay channel is proposed, and the relaying scheme of concern is shown to reach its mincut. Even if the source treats the broadcast channel as physically degraded when it is stochastically degraded, the achievable hypergraph bound is the mincut.
On the geometry of wireless network multicast in 2D
, 1106
"... Abstract—We provide a geometric solution to the problem of optimal relay positioning to maximize the multicast rate for lowSNR networks. The network we consider consists of a single source, multiple receivers and the only intermediate and locatable node as the relay. We construct network the hyperg ..."
Abstract

Cited by 1 (0 self)
 Add to MetaCart
Abstract—We provide a geometric solution to the problem of optimal relay positioning to maximize the multicast rate for lowSNR networks. The network we consider consists of a single source, multiple receivers and the only intermediate and locatable node as the relay. We construct network the hypergraph of the system nodes from the underlying information theoretic model of lowSNR regime that operates using superposition coding and FDMA in conjunction (which we call the “achievable hypergraph model”). We make the following contributions. 1) We show that the problem of optimal relay positioning maximizing the multicast rate can be completely decoupled from the flow optimization by noticing and exploiting geometric properties of multicast flow. 2) All the flow maximizing the multicast rate is sent over at most two paths, in succession. The relay position depends on only one path (out of the two), irrespective of the number of receiver nodes in the system. Subsequently, we propose simple and efficient geometric algorithms to compute the optimal relay position. 3) Finally, we show that in our model at the optimal relay position, the difference between the maximized multicast rate and the cutset bound is minimum. We solve the problem for all (Ps,Pr) pairs of source and relay transmit powers and the path loss exponent α ≥ 2. Index Terms—LowSNR, broadcast relay channel, geometry. I.
1Asymptotic Capacity and Optimal Precoding in MIMO MultiHop Relay Networks
"... Abstract—A multihop relaying system is analyzed where data sent by a multiantenna source is relayed by successive multiantenna relays until it reaches a multiantenna destination. Assuming correlated fading at each hop, each relay receives a faded version of the signal from the previous level, pe ..."
Abstract
 Add to MetaCart
(Show Context)
Abstract—A multihop relaying system is analyzed where data sent by a multiantenna source is relayed by successive multiantenna relays until it reaches a multiantenna destination. Assuming correlated fading at each hop, each relay receives a faded version of the signal from the previous level, performs linear precoding and retransmits it to the next level. Using free probability theory and assuming that the noise power at relays— but not at destination — is negligible, the closedform expression of the asymptotic instantaneous endtoend mutual information is derived as the number of antennas at all levels grows large. The soobtained deterministic expression is independent from the channel realizations while depending only on channel statistics. This expression is also shown to be equal to the asymptotic average endtoend mutual information. The singular vectors of the optimal precoding matrices, maximizing the average mutual information with finite number of antennas at all levels, are also obtained. It turns out that these vectors are aligned to the eigenvectors of the channel correlation matrices. Thus they can be determined using only the channel statistics. As the structure of the singular vectors of the optimal precoders is independent from the system size, it is also optimal in the asymptotic regime. Index Terms—asymptotic capacity, correlated channel, free probability theory, multihop relay network, precoding. I.
Low SNR – When Only Decoding Will Do
"... Abstract—We investigate the issue of distributed receiver cooperation in a multiplerelay network with memoryless independent fading channels, where the channel state information can’t be obtained. The received signals at distributed receiving nodes are first compressed or quantized before being se ..."
Abstract
 Add to MetaCart
(Show Context)
Abstract—We investigate the issue of distributed receiver cooperation in a multiplerelay network with memoryless independent fading channels, where the channel state information can’t be obtained. The received signals at distributed receiving nodes are first compressed or quantized before being sent to the decoder via ratelimited cooperation channels for joint processing. We focus on the low SNR regime and analyze the capacity bounds using network equivalence theory and a multiplelayer binning peaky frequency shift keying (FSK). When the received signals at the relaying nodes are in low SNR regime and the cooperation rates are not sufficiently high, compressed/quantized observations at relaying nodes become useless and only decoding can help. Index Terms—Low SNR, distributed receivers, network equivalence, peaky FSK, MMSE I.