3,597 research outputs found
Opportunistic Spectrum Sharing using Dumb Basis Patterns: The Line-of-Sight Interference Scenario
We investigate a spectrum-sharing system with non-severely faded mutual
interference links, where both the secondary-to-primary and
primary-to-secondary channels have a Line-of-Sight (LoS) component. Based on a
Rician model for the LoS channels, we show, analytically and numerically, that
LoS interference hinders the achievable secondary user capacity. This is caused
by the poor dynamic range of the interference channels fluctuations when a
dominant LoS component exists. In order to improve the capacity of such system,
we propose the usage of an Electronically Steerable Parasitic Array Radiator
(ESPAR) antenna at the secondary terminals. An ESPAR antenna requires a single
RF chain and has a reconfigurable radiation pattern that is controlled by
assigning arbitrary weights to M orthonormal basis radiation patterns. By
viewing these orthonormal patterns as multiple virtual dumb antennas, we
randomly vary their weights over time creating artificial channel fluctuations
that can perfectly eliminate the undesired impact of LoS interference. Because
the proposed scheme uses a single RF chain, it is well suited for compact and
low cost mobile terminals
Asymptotic Mutual Information Statistics of Separately-Correlated Rician Fading MIMO Channels
Precise characterization of the mutual information of MIMO systems is
required to assess the throughput of wireless communication channels in the
presence of Rician fading and spatial correlation. Here, we present an
asymptotic approach allowing to approximate the distribution of the mutual
information as a Gaussian distribution in order to provide both the average
achievable rate and the outage probability. More precisely, the mean and
variance of the mutual information of the separatelycorrelated Rician fading
MIMO channel are derived when the number of transmit and receive antennas grows
asymptotically large and their ratio approaches a finite constant. The
derivation is based on the replica method, an asymptotic technique widely used
in theoretical physics and, more recently, in the performance analysis of
communication (CDMA and MIMO) systems. The replica method allows to analyze
very difficult system cases in a comparatively simple way though some authors
pointed out that its assumptions are not always rigorous. Being aware of this,
we underline the key assumptions made in this setting, quite similar to the
assumptions made in the technical literature using the replica method in their
asymptotic analyses. As far as concerns the convergence of the mutual
information to the Gaussian distribution, it is shown that it holds under some
mild technical conditions, which are tantamount to assuming that the spatial
correlation structure has no asymptotically dominant eigenmodes. The accuracy
of the asymptotic approach is assessed by providing a sizeable number of
numerical results. It is shown that the approximation is very accurate in a
wide variety of system settings even when the number of transmit and receive
antennas is as small as a few units.Comment: - submitted to the IEEE Transactions on Information Theory on Nov.
19, 2006 - revised and submitted to the IEEE Transactions on Information
Theory on Dec. 19, 200
Achievable Rate of Rician Large-Scale MIMO Channels with Transceiver Hardware Impairments
Transceiver hardware impairments (e.g., phase noise,
in-phase/quadrature-phase (I/Q) imbalance, amplifier non-linearities, and
quantization errors) have obvious degradation effects on the performance of
wireless communications. While prior works have improved our knowledge on the
influence of hardware impairments of single-user multiple-input multiple-output
(MIMO) systems over Rayleigh fading channels, an analysis encompassing the
Rician fading channel is not yet available. In this paper, we pursue a detailed
analysis of regular and large-scale (LS) MIMO systems over Rician fading
channels by deriving new, closed-form expressions for the achievable rate to
provide several important insights for practical system design. More
specifically, for regular MIMO systems with hardware impairments, there is
always a finite achievable rate ceiling, which is irrespective of the transmit
power and fading conditions. For LS-MIMO systems, it is interesting to find
that the achievable rate loss depends on the Rician -factor, which reveals
that the favorable propagation in LS-MIMO systems can remove the influence of
hardware impairments. However, we show that the non-ideal LS-MIMO system can
still achieve high spectral efficiency due to its huge degrees of freedom.Comment: 7 pages, 1 table, 3 figures, accepted to appear in IEEE Transactions
on Vehicular Technolog
Exact ZF Analysis and Computer-Algebra-Aided Evaluation in Rank-1 LoS Rician Fading
We study zero-forcing detection (ZF) for multiple-input/multiple-output
(MIMO) spatial multiplexing under transmit-correlated Rician fading for an N_R
X N_T channel matrix with rank-1 line-of-sight (LoS) component. By using matrix
transformations and multivariate statistics, our exact analysis yields the
signal-to-noise ratio moment generating function (m.g.f.) as an infinite series
of gamma distribution m.g.f.'s and analogous series for ZF performance
measures, e.g., outage probability and ergodic capacity. However, their
numerical convergence is inherently problematic with increasing Rician
K-factor, N_R , and N_T. We circumvent this limitation as follows. First, we
derive differential equations satisfied by the performance measures with a
novel automated approach employing a computer-algebra tool which implements
Groebner basis computation and creative telescoping. These differential
equations are then solved with the holonomic gradient method (HGM) from initial
conditions computed with the infinite series. We demonstrate that HGM yields
more reliable performance evaluation than by infinite series alone and more
expeditious than by simulation, for realistic values of K , and even for N_R
and N_T relevant to large MIMO systems. We envision extending the proposed
approaches for exact analysis and reliable evaluation to more general Rician
fading and other transceiver methods.Comment: Accepted for publication by the IEEE Transactions on Wireless
Communications, on April 7th, 2016; this is the final revision before
publicatio
- …