4,618 research outputs found
Pulse Shaping Diversity to Enhance Throughput in Ultra-Dense Small Cell Networks
Spatial multiplexing (SM) gains in multiple input multiple output (MIMO)
cellular networks are limited when used in combination with ultra-dense small
cell networks. This limitation is due to large spatial correlation among
channel pairs. More specifically, it is due to i) line-of-sight (LOS)
communication between user equipment (UE) and base station (BS) and ii)
in-sufficient spacing between antenna elements. We propose to shape transmit
signals at adjacent antennas with distinct interpolating filters which
introduces pulse shaping diversity eventually leading to improved SINR and
throughput at the UEs. In this technique, each antenna transmits its own data
stream with a relative offset with respect to adjacent antenna. The delay which
must be a fraction of symbol period is interpolated with the pulse shaped
signal and generates a virtual MIMO channel that leads to improved diversity
and SINR at the receiver. Note that non-integral sampling periods with
inter-symbol interference (ISI) should be mitigated at the receiver. For this,
we propose to use a fractionally spaced equalizer (FSE) designed based on the
minimum mean squared error (MMSE) criterion. Simulation results show that for a
2x2 MIMO and with inter-site-distance (ISD) of 50 m, the median received SINR
and throughput at the UE improves by a factor of 11 dB and 2x, respectively,
which verifies that pulse shaping can overcome poor SM gains in ultra-dense
small cell networks.Comment: Accepted to 17th IEEE International Workshop on Signal Processing
Advances in Wireless Communication
Spatial Multiplexing of QPSK Signals with a Single Radio: Antenna Design and Over-the-Air Experiments
The paper describes the implementation and performance analysis of the first
fully-operational beam-space MIMO antenna for the spatial multiplexing of two
QPSK streams. The antenna is composed of a planar three-port radiator with two
varactor diodes terminating the passive ports. Pattern reconfiguration is used
to encode the MIMO information onto orthogonal virtual basis patterns in the
far-field. A measurement campaign was conducted to compare the performance of
the beam-space MIMO system with a conventional 2-by-?2 MIMO system under
realistic propagation conditions. Propagation measurements were conducted for
both systems and the mutual information and symbol error rates were estimated
from Monte-Carlo simulations over the measured channel matrices. The results
show the beam-space MIMO system and the conventional MIMO system exhibit
similar finite-constellation capacity and error performance in NLOS scenarios
when there is sufficient scattering in the channel. In comparison, in LOS
channels, the capacity performance is observed to depend on the relative
polarization of the receiving antennas.Comment: 31 pages, 23 figure
Delay Constrained Throughput Analysis of a Correlated MIMO Wireless Channel
The maximum traffic arrival rate at the network for a given delay guarantee
(delay constrained throughput) has been well studied for wired channels.
However, few results are available for wireless channels, especially when
multiple antennas are employed at the transmitter and receiver. In this work,
we analyze the network delay constrained throughput of a multiple input
multiple output (MIMO) wireless channel with time-varying spatial correlation.
The MIMO channel is modeled via its virtual representation, where the
individual spatial paths between the antenna pairs are Gilbert-Elliot channels.
The whole system is then described by a K-State Markov chain, where K depends
upon the degree of freedom (DOF) of the channel. We prove that the DOF based
modeling is indeed accurate. Furthermore, we study the impact of the delay
requirements at the network layer, violation probability and the number of
antennas on the throughput under different fading speeds and signal strength.Comment: Submitted to ICCCN 2011, 8 pages, 5 figure
Fundamental Limits in Correlated Fading MIMO Broadcast Channels: Benefits of Transmit Correlation Diversity
We investigate asymptotic capacity limits of the Gaussian MIMO broadcast
channel (BC) with spatially correlated fading to understand when and how much
transmit correlation helps the capacity. By imposing a structure on channel
covariances (equivalently, transmit correlations at the transmitter side) of
users, also referred to as \emph{transmit correlation diversity}, the impact of
transmit correlation on the power gain of MIMO BCs is characterized in several
regimes of system parameters, with a particular interest in the large-scale
array (or massive MIMO) regime. Taking the cost for downlink training into
account, we provide asymptotic capacity bounds of multiuser MIMO downlink
systems to see how transmit correlation diversity affects the system
multiplexing gain. We make use of the notion of joint spatial division and
multiplexing (JSDM) to derive the capacity bounds. It is advocated in this
paper that transmit correlation diversity may be of use to significantly
increase multiplexing gain as well as power gain in multiuser MIMO systems. In
particular, the new type of diversity in wireless communications is shown to
improve the system multiplexing gain up to by a factor of the number of degrees
of such diversity. Finally, performance limits of conventional large-scale MIMO
systems not exploiting transmit correlation are also characterized.Comment: 29 pages, 8 figure
A universal space-time architecture for multiple-antenna aided systems
In this tutorial, we first review the family of conventional multiple-antenna techniques, and then we provide a general overview of the recent concept of the powerful Multiple-Input Multiple-Output (MIMO) family based on a universal Space-Time Shift Keying (STSK) philosophy. When appropriately configured, the proposed STSK scheme has the potential of outperforming conventional MIMO arrangements
Cooperative Symbol-Based Signaling for Networks with Multiple Relays
Wireless channels suffer from severe inherent impairments and hence
reliable and high data rate wireless transmission is particularly challenging to
achieve. Fortunately, using multiple antennae improves performance in wireless
transmission by providing space diversity, spatial multiplexing, and power gains.
However, in wireless ad-hoc networks multiple antennae may not be acceptable
due to limitations in size, cost, and hardware complexity. As a result, cooperative
relaying strategies have attracted considerable attention because of their abilities
to take advantage of multi-antenna by using multiple single-antenna relays.
This study is to explore cooperative signaling for different relay networks,
such as multi-hop relay networks formed by multiple single-antenna relays and
multi-stage relay networks formed by multiple relaying stages with each stage
holding several single-antenna relays. The main contribution of this study is the
development of a new relaying scheme for networks using symbol-level
modulation, such as binary phase shift keying (BPSK) and quadrature phase shift
keying (QPSK). We also analyze effects of this newly developed scheme when it
is used with space-time coding in a multi-stage relay network. Simulation results
demonstrate that the new scheme outperforms previously proposed schemes:
amplify-and-forward (AF) scheme and decode-and-forward (DF) scheme
Asymptotic Performance of Linear Receivers in MIMO Fading Channels
Linear receivers are an attractive low-complexity alternative to optimal
processing for multi-antenna MIMO communications. In this paper we characterize
the information-theoretic performance of MIMO linear receivers in two different
asymptotic regimes. For fixed number of antennas, we investigate the limit of
error probability in the high-SNR regime in terms of the Diversity-Multiplexing
Tradeoff (DMT). Following this, we characterize the error probability for fixed
SNR in the regime of large (but finite) number of antennas.
As far as the DMT is concerned, we report a negative result: we show that
both linear Zero-Forcing (ZF) and linear Minimum Mean-Square Error (MMSE)
receivers achieve the same DMT, which is largely suboptimal even in the case
where outer coding and decoding is performed across the antennas. We also
provide an approximate quantitative analysis of the markedly different behavior
of the MMSE and ZF receivers at finite rate and non-asymptotic SNR, and show
that while the ZF receiver achieves poor diversity at any finite rate, the MMSE
receiver error curve slope flattens out progressively, as the coding rate
increases.
When SNR is fixed and the number of antennas becomes large, we show that the
mutual information at the output of a MMSE or ZF linear receiver has
fluctuations that converge in distribution to a Gaussian random variable, whose
mean and variance can be characterized in closed form. This analysis extends to
the linear receiver case a well-known result previously obtained for the
optimal receiver. Simulations reveal that the asymptotic analysis captures
accurately the outage behavior of systems even with a moderate number of
antennas.Comment: 48 pages, Submitted to IEEE Transactions on Information Theor
Multifunctional MIMO systems: A combined diversity and multiplexing design perspective
In this treatise we investigate the design alternatives of different multiple-input multiple-output schemes while considering the attainable diversity gains, multiplexing gains, and beamforming gains. Following a brief classification of different MIMO schemes, where the different MIMO schemes are categorized as diversity techniques, multiplexing schemes, multiple access arrangements, and beamforming techniques, we introduce the family of multifunctional MIMOs. These multifunctional MIMOs are capable of combining the benefits of several MIMO schemes and hence attaining improved performance in terms of both their bit error rate as well as throughput. The family of multifunctional MIMOs combines the benefits of both space-time coding and the Bell Labs layered space-time scheme as well as those of beamforming. We also introduce the idea of layered steered space-time spreading, which combines the benefits of space-time spreading, V-BLAST, and beamforming with those of the generalized multicarrier direct sequence code-division multiple access concept. Additionally, we compare the attainable diversity, multiplexing, and beamforming gains of the different MIMO schemes in order to document the advantages of multifunctional MIMOs over conventional MIMO schemes
Reduced-Complexity Maximum-Likelihood Detection in Downlink SDMA Systems
The literature of up-link SDMA systems is rich, but at the time of writing there is a paucity of information on the employment of SDMA techniques in the down-link. Hence, in this paper a Space Division Multiple Access (SDMA) down-link (DL) multi-user communication system invoking a novel low-complexity Maximum Likelihood (ML) space-time detection technique is proposed, which can be regarded as an advanced extension of the Complex Sphere Decoder (CSD). We demonstrate that as opposed to the previously published variants of the CSD, the proposed technique may be employed for obtaining a high effective throughput in the so-called “over-loaded” scenario, where the number of transmit antennas exceeds that of the receive antennas. The proposed method achieves the optimum performance of the ML detector even in heavily over-loaded scenarios, while the associated computational complexity is only moderately increased. As an illustrative example, the required Eb/N0 increased from 2 dB to 9 dB, when increasing the normalized system load from unity, representing the fully loaded system, to a normalized load of 1.556
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