8,415 research outputs found
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
Partner selection in indoor-to-outdoor cooperative networks: an experimental study
In this paper, we develop a partner selection protocol for enhancing the
network lifetime in cooperative wireless networks. The case-study is the
cooperative relayed transmission from fixed indoor nodes to a common outdoor
access point. A stochastic bivariate model for the spatial distribution of the
fading parameters that govern the link performance, namely the Rician K-factor
and the path-loss, is proposed and validated by means of real channel
measurements. The partner selection protocol is based on the real-time
estimation of a function of these fading parameters, i.e., the coding gain. To
reduce the complexity of the link quality assessment, a Bayesian approach is
proposed that uses the site-specific bivariate model as a-priori information
for the coding gain estimation. This link quality estimator allows network
lifetime gains almost as if all K-factor values were known. Furthermore, it
suits IEEE 802.15.4 compliant networks as it efficiently exploits the
information acquired from the receiver signal strength indicator. Extensive
numerical results highlight the trade-off between complexity, robustness to
model mismatches and network lifetime performance. We show for instance that
infrequent updates of the site-specific model through K-factor estimation over
a subset of links are sufficient to at least double the network lifetime with
respect to existing algorithms based on path loss information only.Comment: This work has been submitted to IEEE Journal on Selected Areas in
Communications in August 201
Selective Combining for Hybrid Cooperative Networks
In this study, we consider the selective combining in hybrid cooperative
networks (SCHCNs scheme) with one source node, one destination node and
relay nodes. In the SCHCN scheme, each relay first adaptively chooses between
amplify-and-forward protocol and decode-and-forward protocol on a per frame
basis by examining the error-detecting code result, and () relays will be selected to forward their received signals to the
destination. We first develop a signal-to-noise ratio (SNR) threshold-based
frame error rate (FER) approximation model. Then, the theoretical FER
expressions for the SCHCN scheme are derived by utilizing the proposed SNR
threshold-based FER approximation model. The analytical FER expressions are
validated through simulation results.Comment: 27 pages, 8 figures, IET Communications, 201
Wireless Powered Cooperative Relaying using NOMA with Imperfect CSI
The impact of imperfect channel state (CSI) information in an energy
harvesting (EH) cooperative non-orthogonal multiple access (NOMA) network,
consisting of a source, two users, and an EH relay is investigated in this
paper. The relay is not equipped with a fixed power source and acts as a
wireless powered node to help signal transmission to the users. Closed-form
expressions for the outage probability of both users are derived under
imperfect CSI for two different power allocation strategies namely fixed and
dynamic power allocation. Monte Carlo simulations are used to numerically
evaluate the effect of imperfect CSI. These results confirm the theoretical
outage analysis and show that NOMA can outperform orthogonal multiple access
even with imperfect CSI.Comment: 6 pages, 6 figures, accepted in IEEE GLOBECOM 2018 NOMA Worksho
A Simple Cooperative Diversity Method Based on Network Path Selection
Cooperative diversity has been recently proposed as a way to form virtual
antenna arrays that provide dramatic gains in slow fading wireless
environments. However most of the proposed solutions require distributed
space-time coding algorithms, the careful design of which is left for future
investigation if there is more than one cooperative relay. We propose a novel
scheme, that alleviates these problems and provides diversity gains on the
order of the number of relays in the network. Our scheme first selects the best
relay from a set of M available relays and then uses this best relay for
cooperation between the source and the destination. We develop and analyze a
distributed method to select the best relay that requires no topology
information and is based on local measurements of the instantaneous channel
conditions. This method also requires no explicit communication among the
relays. The success (or failure) to select the best available path depends on
the statistics of the wireless channel, and a methodology to evaluate
performance for any kind of wireless channel statistics, is provided.
Information theoretic analysis of outage probability shows that our scheme
achieves the same diversity-multiplexing tradeoff as achieved by more complex
protocols, where coordination and distributed space-time coding for M nodes is
required, such as those proposed in [7]. The simplicity of the technique,
allows for immediate implementation in existing radio hardware and its adoption
could provide for improved flexibility, reliability and efficiency in future 4G
wireless systems.Comment: To appear, IEEE JSAC, special issue on 4
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