1,313 research outputs found
Wireless Cellular Networks
When aiming for achieving high spectral efficiency in wireless cellular networks, cochannel interference (CCI) becomes the dominant performancelimiting factor. This article provides a survey of CCI mitigation techniques, where both active and passive approaches are discussed in the context of both open- and closed-loop designs.More explicitly, we considered both the family of flexible frequency-reuse (FFR)-aided and dynamic channel allocation (DCA)-aided interference avoidance techniques as well as smart antenna-aided interference mitigation techniques, which may be classified as active approach
AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing
The enormous success of advanced wireless devices is pushing the demand for
higher wireless data rates. Denser spectrum reuse through the deployment of
more access points per square mile has the potential to successfully meet the
increasing demand for more bandwidth. In theory, the best approach to density
increase is via distributed multiuser MIMO, where several access points are
connected to a central server and operate as a large distributed multi-antenna
access point, ensuring that all transmitted signal power serves the purpose of
data transmission, rather than creating "interference." In practice, while
enterprise networks offer a natural setup in which distributed MIMO might be
possible, there are serious implementation difficulties, the primary one being
the need to eliminate phase and timing offsets between the jointly coordinated
access points.
In this paper we propose AirSync, a novel scheme which provides not only time
but also phase synchronization, thus enabling distributed MIMO with full
spatial multiplexing gains. AirSync locks the phase of all access points using
a common reference broadcasted over the air in conjunction with a Kalman filter
which closely tracks the phase drift. We have implemented AirSync as a digital
circuit in the FPGA of the WARP radio platform. Our experimental testbed,
comprised of two access points and two clients, shows that AirSync is able to
achieve phase synchronization within a few degrees, and allows the system to
nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC
and higher layer aspects of a practical deployment. To the best of our
knowledge, AirSync offers the first ever realization of the full multiuser MIMO
gain, namely the ability to increase the number of wireless clients linearly
with the number of jointly coordinated access points, without reducing the per
client rate.Comment: Submitted to Transactions on Networkin
Iterative Multiuser Detection and Decoding with Spatially Coupled Interleaving
Spatially coupled (SC) interleaving is proposed to improve the performance of
iterative multiuser detection and decoding (MUDD) for quasi-static fading
multiple-input multiple-output systems. The linear minimum mean-squared error
(LMMSE) demodulator is used to reduce the complexity and to avoid error
propagation. Furthermore, sliding window MUDD is proposed to circumvent an
increase of the decoding latency due to SC interleaving. Theoretical and
numerical analyses show that SC interleaving can improve the performance of the
iterative LMMSE MUDD for regular low-density parity-check codes.Comment: Long version of a paper submitted to IEEE Wireless Commun. Let
Fundamental Limits in MIMO Broadcast Channels
This paper studies the fundamental limits of MIMO broadcast channels from a high level, determining the sum-rate capacity of the system as a function of system paramaters, such as the number of transmit antennas, the number of users, the number of receive antennas, and the total transmit power. The crucial role of channel state information at the transmitter is emphasized, as well as the emergence of opportunistic transmission schemes. The effects of channel estimation errors, training, and spatial correlation are studied, as well as issues related to fairness, delay and differentiated rate scheduling
A Hierarchical Rate Splitting Strategy for FDD Massive MIMO under Imperfect CSIT
In a multiuser MIMO broadcast channel, the rate performance is affected by
the multiuser interference when the Channel State Information at the
Transmitter (CSIT) is imperfect. To tackle the interference problem, a
Rate-Splitting (RS) approach has been proposed recently, which splits one
user's message into a common and a private part, and superimposes the common
message on top of the private messages. The common message is drawn from a
public codebook and should be decoded by all users. In this paper, we propose a
novel and general framework, denoted as Hierarchical Rate Splitting (HRS), that
is particularly suited to FDD massive MIMO systems. HRS simultaneously
transmits private messages intended to each user and two kinds of common
messages that can be decoded by all users and by a subset of users,
respectively. We analyse the asymptotic sum rate of HRS under imperfect CSIT. A
closed-form power allocation is derived which provides insights into the
effects of system parameters. Finally, simulation results validate the
significant sum rate gain of HRS over various baselines.Comment: Accepted paper at IEEE CAMAD 201
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