7,876 research outputs found
Learning Based Relay and Antenna Selection in Cooperative Networks
We investigate a cross-layer relay selection scheme based on Q-learning algorithm. For the study, we consider multi-relay adaptive decode and forward (DF) cooperative diversity networks over multipath time-varying Rayleigh fading channels. The proposed scheme selects relay subsets that maximizes the link layer transmission efficiency without having knowledge of channel state information (CSI). Results show that the proposed scheme outperforms the capacity based cooperative transmission with the same number of reliable relays in terms of transmission efficiency gain. Furthermore, a Q-learning based cross-layer antenna selection for the multiple antenna relay networks is proposed, where multiple antennas allow more links from the relays to the destination under time varying Rayleigh fading channel. We studied the performance of multi-antenna relay networks and compared with single antenna case. Both schemes are shown to offer high bandwidth efficiency from low to high signal-to-noise ratios (SNRs). Finally, we conclude that cooperative diversity with learning offers improved performance enhancement and bandwidth efficiency for the communication network
Recovering Multiplexing Loss Through Successive Relaying Using Repetition Coding
In this paper, a transmission protocol is studied for a two relay wireless
network in which simple repetition coding is applied at the relays.
Information-theoretic achievable rates for this transmission scheme are given,
and a space-time V-BLAST signalling and detection method that can approach them
is developed. It is shown through the diversity multiplexing tradeoff analysis
that this transmission scheme can recover the multiplexing loss of the
half-duplex relay network, while retaining some diversity gain. This scheme is
also compared with conventional transmission protocols that exploit only the
diversity of the network at the cost of a multiplexing loss. It is shown that
the new transmission protocol offers significant performance advantages over
conventional protocols, especially when the interference between the two relays
is sufficiently strong.Comment: To appear in the IEEE Transactions on Wireless Communication
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
Optimal Relay Selection for Physical-Layer Security in Cooperative Wireless Networks
In this paper, we explore the physical-layer security in cooperative wireless
networks with multiple relays where both amplify-and-forward (AF) and
decode-and-forward (DF) protocols are considered. We propose the AF and DF
based optimal relay selection (i.e., AFbORS and DFbORS) schemes to improve the
wireless security against eavesdropping attack. For the purpose of comparison,
we examine the traditional AFbORS and DFbORS schemes, denoted by T-AFbORS and
TDFbORS, respectively. We also investigate a so-called multiple relay combining
(MRC) framework and present the traditional AF and DF based MRC schemes, called
T-AFbMRC and TDFbMRC, where multiple relays participate in forwarding the
source signal to destination which then combines its received signals from the
multiple relays. We derive closed-form intercept probability expressions of the
proposed AFbORS and DFbORS (i.e., P-AFbORS and P-DFbORS) as well as the
T-AFbORS, TDFbORS, T-AFbMRC and T-DFbMRC schemes in the presence of
eavesdropping attack. We further conduct an asymptotic intercept probability
analysis to evaluate the diversity order performance of relay selection schemes
and show that no matter which relaying protocol is considered (i.e., AF and
DF), the traditional and proposed optimal relay selection approaches both
achieve the diversity order M where M represents the number of relays. In
addition, numerical results show that for both AF and DF protocols, the
intercept probability performance of proposed optimal relay selection is
strictly better than that of the traditional relay selection and multiple relay
combining methods.Comment: 13 page
Joint Adaptive Modulation-Coding and Cooperative ARQ for Wireless Relay Networks
This paper presents a cross-layer approach to jointly design adaptive
modulation and coding (AMC) at the physical layer and cooperative truncated
automatic repeat request (ARQ) protocol at the data link layer. We first derive
an exact closed form expression for the spectral efficiency of the proposed
joint AMC-cooperative ARQ scheme. Aiming at maximizing this system performance
measure, we then optimize an AMC scheme which directly satisfies a prescribed
packet loss rate constraint at the data-link layer. The results indicate that
utilizing cooperative ARQ as a retransmission strategy, noticeably enhances the
spectral efficiency compared with the system that employs AMC alone at the
physical layer. Moreover, the proposed adaptive rate cooperative ARQ scheme
outperforms the fixed rate counterpart when the transmission modes at the
source and relay are chosen based on the channel statistics. This in turn
quantifies the possible gain achieved by joint design of AMC and ARQ in
wireless relay networks.Comment: 5 pages, 4 figures, To appear in the Proceedings of the 2008 IEEE
International Symposium on Wireless Communication Systems (ISWCS), Rykevick,
Island, Oct 200
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