221 research outputs found
Cooperative Multiplexing in the Multiple Antenna Half Duplex Relay Channel
Cooperation between terminals has been proposed to improve the reliability
and throughput of wireless communication. While recent work has shown that
relay cooperation provides increased diversity, increased multiplexing gain
over that offered by direct link has largely been unexplored. In this work we
show that cooperative multiplexing gain can be achieved by using a half duplex
relay. We capture relative distances between terminals in the high SNR
diversity multiplexing tradeoff (DMT) framework. The DMT performance is then
characterized for a network having a single antenna half-duplex relay between a
single-antenna source and two-antenna destination. Our results show that the
achievable multiplexing gain using cooperation can be greater than that of the
direct link and is a function of the relative distance between source and relay
compared to the destination. Moreover, for multiplexing gains less than 1, a
simple scheme of the relay listening 1/3 of the time and transmitting 2/3 of
the time can achieve the 2 by 2 MIMO DMT.Comment: 5 pages, 5 figures submitted to ISIT 200
Product Multicommodity Flow in Wireless Networks
We provide a tight approximate characterization of the -dimensional
product multicommodity flow (PMF) region for a wireless network of nodes.
Separate characterizations in terms of the spectral properties of appropriate
network graphs are obtained in both an information theoretic sense and for a
combinatorial interference model (e.g., Protocol model). These provide an inner
approximation to the dimensional capacity region. These results answer
the following questions which arise naturally from previous work: (a) What is
the significance of in the scaling laws for the Protocol
interference model obtained by Gupta and Kumar (2000)? (b) Can we obtain a
tight approximation to the "maximum supportable flow" for node distributions
more general than the geometric random distribution, traffic models other than
randomly chosen source-destination pairs, and under very general assumptions on
the channel fading model?
We first establish that the random source-destination model is essentially a
one-dimensional approximation to the capacity region, and a special case of
product multi-commodity flow. Building on previous results, for a combinatorial
interference model given by a network and a conflict graph, we relate the
product multicommodity flow to the spectral properties of the underlying graphs
resulting in computational upper and lower bounds. For the more interesting
random fading model with additive white Gaussian noise (AWGN), we show that the
scaling laws for PMF can again be tightly characterized by the spectral
properties of appropriately defined graphs. As an implication, we obtain
computationally efficient upper and lower bounds on the PMF for any wireless
network with a guaranteed approximation factor.Comment: Revised version of "Capacity-Delay Scaling in Arbitrary Wireless
Networks" submitted to the IEEE Transactions on Information Theory. Part of
this work appeared in the Allerton Conference on Communication, Control, and
Computing, Monticello, IL, 2005, and the Internation Symposium on Information
Theory (ISIT), 200
Exploiting quantization uncertainty for enhancing capacity of limited-feedback MISO ad hoc networks
In this paper we investigate the capacity of random wireless networks in which transmitters are equipped with multiantennas. A quantized version of channel direction information (CDI) is also available, provided by the associated single antenna receivers. We adopt tools of stochastic geometry and random vector quantization to incorporate the impacts of interference and quantization errors, respectively. We first study the capacity of Aloha, and channel quality information (CQI)-based scheduling, whereby the transmissions decision in each transceiver pair depends on the strength of the CQI against a prescribed threshold. We then propose a new scheduling scheme, namely modified CQI (MCQI), by which the quantization error is effectively incorporated in the scheduling. Further we obtain the capacity of MCQI-based scheduling. Simulation results confirm our analysis and show that the proposed MCQI-based scheduling improves the capacity compared to the CQI-based scheduling and Aloha. It is also seen that the performance boost is more significant where the feedback capacity is low and the network is dense. In comparison with the case of high feedback capacity, the network capacity is not reduced by low feedback capacity in the MCQI-based scheduling. This is of practical importance since the network designer can save the feedback resources by employing MCQI-based scheduling without compromising the capacity and increasing the receivers’ complexity
Opportunistic Scheduling and Beamforming for MIMO-SDMA Downlink Systems with Linear Combining
Opportunistic scheduling and beamforming schemes are proposed for multiuser
MIMO-SDMA downlink systems with linear combining in this work. Signals received
from all antennas of each mobile terminal (MT) are linearly combined to improve
the {\em effective} signal-to-noise-interference ratios (SINRs). By exploiting
limited feedback on the effective SINRs, the base station (BS) schedules
simultaneous data transmission on multiple beams to the MTs with the largest
effective SINRs. Utilizing the extreme value theory, we derive the asymptotic
system throughputs and scaling laws for the proposed scheduling and beamforming
schemes with different linear combining techniques. Computer simulations
confirm that the proposed schemes can substantially improve the system
throughput.Comment: To appear in the Proceedings of the 18th Annual IEEE International
Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC),
Athens, Greece, September 3 - 7, 200
Robust Power Allocation and Outage Analysis for Secrecy in Independent Parallel Gaussian Channels
This letter studies parallel independent Gaussian channels with uncertain
eavesdropper channel state information (CSI). Firstly, we evaluate the
probability of zero secrecy rate in this system for (i) given instantaneous
channel conditions and (ii) a Rayleigh fading scenario. Secondly, when non-zero
secrecy is achievable in the low SNR regime, we aim to solve a robust power
allocation problem which minimizes the outage probability at a target secrecy
rate. We bound the outage probability and obtain a linear fractional program
that takes into account the uncertainty in eavesdropper CSI while allocating
power on the parallel channels. Problem structure is exploited to solve this
optimization problem efficiently. We find the proposed scheme effective for
uncertain eavesdropper CSI in comparison with conventional power allocation
schemes.Comment: 4 pages, 2 figures. Author version of the paper published in IEEE
Wireless Communications Letters. Published version is accessible at
http://dx.doi.org/10.1109/LWC.2015.249734
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