38 research outputs found
Multihop Diversity in Wideband OFDM Systems: The Impact of Spatial Reuse and Frequency Selectivity
The goal of this paper is to establish which practical routing schemes for
wireless networks are most suitable for wideband systems in the power-limited
regime, which is, for example, a practically relevant mode of operation for the
analysis of ultrawideband (UWB) mesh networks. For this purpose, we study the
tradeoff between energy efficiency and spectral efficiency (known as the
power-bandwidth tradeoff) in a wideband linear multihop network in which
transmissions employ orthogonal frequency-division multiplexing (OFDM)
modulation and are affected by quasi-static, frequency-selective fading.
Considering open-loop (fixed-rate) and closed-loop (rate-adaptive) multihop
relaying techniques, we characterize the impact of routing with spatial reuse
on the statistical properties of the end-to-end conditional mutual information
(conditioned on the specific values of the channel fading parameters and
therefore treated as a random variable) and on the energy and spectral
efficiency measures of the wideband regime. Our analysis particularly deals
with the convergence of these end-to-end performance measures in the case of
large number of hops, i.e., the phenomenon first observed in \cite{Oyman06b}
and named as ``multihop diversity''. Our results demonstrate the realizability
of the multihop diversity advantages in the case of routing with spatial reuse
for wideband OFDM systems under wireless channel effects such as path-loss and
quasi-static frequency-selective multipath fading.Comment: 6 pages, to be published in Proc. 2008 IEEE International Symposium
on Spread Spectrum Techniques and Applications (IEEE ISSSTA'08), Bologna,
Ital
Interference Analysis for Spatial Reused Cooperative Multihop Wireless Networks
International audienceWe consider a decode-and-forward based wireless multihop network with a single source node, a single destination node, and N intermediate nodes. To increase the spectral efficiency and energy efficiency of the system, we propose a cooperative multihop communication with spatial reuse, in which interference is treated as noise. The performance of spatial-reused space-time coded cooperative multihop network is analyzed over Rayleigh fading channels. More specifically, the exact closedform expression for the outage probability at the nth receiving node is derived when there are multiple interferences over noni. i.d. Rayleigh fading channels. Moreover, in high SNR scenario, closed-form asymptotic formulas for the outage probability are derived, from which, we show that the full-spatial diversity is still achievable given interferences from the transmission of concurrent packets. In addition, we propose a simple power control scheme which is only dependent on the statistical knowledge of channels. Finally, the analytic results were confirmed by simulations. It is shown by simulations that the spatialreused multihop transmission outperforms the interference-free multihop transmission in terms of energy efficiency in low and medium SNR scenarios
Random Access Transport Capacity
We develop a new metric for quantifying end-to-end throughput in multihop
wireless networks, which we term random access transport capacity, since the
interference model presumes uncoordinated transmissions. The metric quantifies
the average maximum rate of successful end-to-end transmissions, multiplied by
the communication distance, and normalized by the network area. We show that a
simple upper bound on this quantity is computable in closed-form in terms of
key network parameters when the number of retransmissions is not restricted and
the hops are assumed to be equally spaced on a line between the source and
destination. We also derive the optimum number of hops and optimal per hop
success probability and show that our result follows the well-known square root
scaling law while providing exact expressions for the preconstants as well.
Numerical results demonstrate that the upper bound is accurate for the purpose
of determining the optimal hop count and success (or outage) probability.Comment: Submitted to IEEE Trans. on Wireless Communications, Sept. 200