19,461 research outputs found
Performance Gains of Optimal Antenna Deployment for Massive MIMO Systems
We consider the uplink of a single-cell multi-user multiple-input
multiple-output (MIMO) system with several single antenna transmitters/users
and one base station with antennas in the regime. The
base station antennas are evenly distributed to admissable locations
throughout the cell.
First, we show that a reliable (per-user) rate of is achievable
through optimal locational optimization of base station antennas. We also prove
that an rate is the best possible. Therefore, in contrast to a
centralized or circular deployment, where the achievable rate is at most a
constant, the rate with a general deployment can grow logarithmically with ,
resulting in a certain form of "macromultiplexing gain."
Second, using tools from high-resolution quantization theory, we derive an
accurate formula for the best achievable rate given any and any user
density function. According to our formula, the dependence of the optimal rate
on the user density function is curiously only through the differential
entropy of . In fact, the optimal rate decreases linearly with the
differential entropy, and the worst-case scenario is a uniform user density.
Numerical simulations confirm our analytical findings.Comment: GLOBECOM 201
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Performance Limits and Geometric Properties of Array Localization
Location-aware networks are of great importance and interest in both civil
and military applications. This paper determines the localization accuracy of
an agent, which is equipped with an antenna array and localizes itself using
wireless measurements with anchor nodes, in a far-field environment. In view of
the Cram\'er-Rao bound, we first derive the localization information for static
scenarios and demonstrate that such information is a weighed sum of Fisher
information matrices from each anchor-antenna measurement pair. Each matrix can
be further decomposed into two parts: a distance part with intensity
proportional to the squared baseband effective bandwidth of the transmitted
signal and a direction part with intensity associated with the normalized
anchor-antenna visual angle. Moreover, in dynamic scenarios, we show that the
Doppler shift contributes additional direction information, with intensity
determined by the agent velocity and the root mean squared time duration of the
transmitted signal. In addition, two measures are proposed to evaluate the
localization performance of wireless networks with different anchor-agent and
array-antenna geometries, and both formulae and simulations are provided for
typical anchor deployments and antenna arrays.Comment: to appear in IEEE Transactions on Information Theor
Dealing with Interference in Distributed Large-scale MIMO Systems: A Statistical Approach
This paper considers the problem of interference control through the use of
second-order statistics in massive MIMO multi-cell networks. We consider both
the cases of co-located massive arrays and large-scale distributed antenna
settings. We are interested in characterizing the low-rankness of users'
channel covariance matrices, as such a property can be exploited towards
improved channel estimation (so-called pilot decontamination) as well as
interference rejection via spatial filtering. In previous work, it was shown
that massive MIMO channel covariance matrices exhibit a useful finite rank
property that can be modeled via the angular spread of multipath at a MIMO
uniform linear array. This paper extends this result to more general settings
including certain non-uniform arrays, and more surprisingly, to two dimensional
distributed large scale arrays. In particular our model exhibits the dependence
of the signal subspace's richness on the scattering radius around the user
terminal, through a closed form expression. The applications of the
low-rankness covariance property to channel estimation's denoising and
low-complexity interference filtering are highlighted.Comment: 12 pages, 11 figures, to appear in IEEE Journal of Selected Topics in
Signal Processin
Collaborative Beamforming for Distributed Wireless Ad Hoc Sensor Networks
The performance of collaborative beamforming is analyzed using the theory of
random arrays. The statistical average and distribution of the beampattern of
randomly generated phased arrays is derived in the framework of wireless ad hoc
sensor networks. Each sensor node is assumed to have a single isotropic antenna
and nodes in the cluster collaboratively transmit the signal such that the
signal in the target direction is coherently added in the far- eld region. It
is shown that with N sensor nodes uniformly distributed over a disk, the
directivity can approach N, provided that the nodes are located sparsely
enough. The distribution of the maximum sidelobe peak is also studied. With the
application to ad hoc networks in mind, two scenarios, closed-loop and
open-loop, are considered. Associated with these scenarios, the effects of
phase jitter and location estimation errors on the average beampattern are also
analyzed.Comment: To appear in the IEEE Transactions on Signal Processin
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