902 research outputs found
On the Non-Coherent Wideband Multipath Fading Relay Channel
We investigate the multipath fading relay channel in the limit of a large
bandwidth, and in the non-coherent setting, where the channel state is unknown
to all terminals, including the relay and the destination. We propose a
hypergraph model of the wideband multipath fading relay channel, and show that
its min-cut is achieved by a non-coherent peaky frequency binning scheme. The
so-obtained lower bound on the capacity of the wideband multipath fading relay
channel turns out to coincide with the block-Markov lower bound on the capacity
of the wideband frequency-division Gaussian (FD-AWGN) relay channel. In certain
cases, this achievable rate also meets the cut-set upper-bound, and thus
reaches the capacity of the non-coherent wideband multipath fading relay
channel.Comment: 8 pages, 4 figures, longer version (including proof) of the paper in
Proc. of IEEE ISIT 201
Optimal relay location and power allocation for low SNR broadcast relay channels
We consider the broadcast relay channel (BRC), where a single source
transmits to multiple destinations with the help of a relay, in the limit of a
large bandwidth. We address the problem of optimal relay positioning and power
allocations at source and relay, to maximize the multicast rate from source to
all destinations. To solve such a network planning problem, we develop a
three-faceted approach based on an underlying information theoretic model,
computational geometric aspects, and network optimization tools. Firstly,
assuming superposition coding and frequency division between the source and the
relay, the information theoretic framework yields a hypergraph model of the
wideband BRC, which captures the dependency of achievable rate-tuples on the
network topology. As the relay position varies, so does the set of hyperarcs
constituting the hypergraph, rendering the combinatorial nature of optimization
problem. We show that the convex hull C of all nodes in the 2-D plane can be
divided into disjoint regions corresponding to distinct hyperarcs sets. These
sets are obtained by superimposing all k-th order Voronoi tessellation of C. We
propose an easy and efficient algorithm to compute all hyperarc sets, and prove
they are polynomially bounded. Using the switched hypergraph approach, we model
the original problem as a continuous yet non-convex network optimization
program. Ultimately, availing on the techniques of geometric programming and
-norm surrogate approximation, we derive a good convex approximation. We
provide a detailed characterization of the problem for collinearly located
destinations, and then give a generalization for arbitrarily located
destinations. Finally, we show strong gains for the optimal relay positioning
compared to seemingly interesting positions.Comment: In Proceedings of INFOCOM 201
A review of modulation techniques for use in a satellite multipath environment
Modulation techniques for use in satellite multipath environmen
Initial synchronisation of wideband and UWB direct sequence systems: single- and multiple-antenna aided solutions
This survey guides the reader through the open literature on the principle of initial synchronisation in single-antenna-assisted single- and multi-carrier Code Division Multiple Access (CDMA) as well as Direct Sequence-Ultra WideBand (DS-UWB) systems, with special emphasis on the DownLink (DL). There is a paucity of up-to-date surveys and review articles on initial synchronization solutions for MIMO-aided and cooperative systems - even though there is a plethora of papers on both MIMOs and on cooperative systems, which assume perfect synchronization. Hence this paper aims to ?ll the related gap in the literature
Quasi-orthogonal space-frequency coding in non-coherent cooperative broadband networks
© 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.So far, complex valued orthogonal codes have been used differentially in cooperative broadband networks. These codes however achieve less than unitary code rate when utilized in cooperative networks with more than two relays. Therefore, the main challenge is how to construct unitary rate codes for non-coherent cooperative broadband networks with more than two relays while exploiting the achievable spatial and frequency diversity. In this paper, we extend full rate quasi-orthogonal codes to differential cooperative broadband networks where channel information is unavailable. From this, we propose a generalized differential distributed quasi-orthogonal space-frequency coding (DQSFC) protocol for cooperative broadband networks. Our proposed scheme is able to achieve full rate, and full spatial and frequency diversity in cooperative networks with any number of relays. Through pairwise error probability analysis we show that the diversity gain of our scheme can be improved by appropriate code construction and sub-carrier allocation. Based on this, we derive sufficient conditions for the proposed code structure at the source node and relay nodes to achieve full spatial and frequency diversity.Peer reviewe
Performance of MIMO Relay DCSK-CD Systems over Nakagami Fading Channels
A multi-access multiple-input multiple-output (MIMO) relay differential chaos
shift keying cooperative diversity (DCSK-CD) system is proposed in this paper
as a comprehensive cooperation scheme, in which the relay and destination both
employ multiple antennas to strengthen the robustness against signal fading in
a wireless network. It is shown that, with spatial diversity gains, the bit
error rate (BER) performance of the proposed system is remarkably better than
the conventional DCSK non-cooperation (DCSK-NC) and DCSK cooperative
communication (DCSK-CC) systems. Moreover, the exact BER and close-form
expressions of the proposed system are derived over Nakagami fading channels
through the moment generating function (MGF), which is shown to be highly
consistent with the simulation results. Meanwhile, this paper illustrates a
trade-off between the performance and the complexity, and provides a threshold
for the number of relay antennas keeping the user consumed energy constant. Due
to the above-mentioned advantages, the proposed system stands out as a good
candidate or alternative for energy-constrained wireless communications based
on chaotic modulation, especially for low-power and low-cost wireless personal
area networks (WPANs).Comment: 11 pages, 15 figures. IEEE Transactions on Circuits and System-
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