809 research outputs found
Spectral Efficiency Scaling Laws in Dense Random Wireless Networks with Multiple Receive Antennas
This paper considers large random wireless networks where
transmit-and-receive node pairs communicate within a certain range while
sharing a common spectrum. By modeling the spatial locations of nodes based on
stochastic geometry, analytical expressions for the ergodic spectral efficiency
of a typical node pair are derived as a function of the channel state
information available at a receiver (CSIR) in terms of relevant system
parameters: the density of communication links, the number of receive antennas,
the path loss exponent, and the operating signal-to-noise ratio. One key
finding is that when the receiver only exploits CSIR for the direct link, the
sum of spectral efficiencies linearly improves as the density increases, when
the number of receive antennas increases as a certain super-linear function of
the density. When each receiver exploits CSIR for a set of dominant interfering
links in addition to the direct link, the sum of spectral efficiencies linearly
increases with both the density and the path loss exponent if the number of
antennas is a linear function of the density. This observation demonstrates
that having CSIR for dominant interfering links provides a multiplicative gain
in the scaling law. It is also shown that this linear scaling holds for direct
CSIR when incorporating the effect of the receive antenna correlation, provided
that the rank of the spatial correlation matrix scales super-linearly with the
density. Simulation results back scaling laws derived from stochastic geometry.Comment: Submitte
TD-SCDMA Relay Networks
PhDWhen this research was started, TD-SCDMA (Time Division Synchronous Code
Division Multiple Access) was still in the research/ development phase, but
now, at the time of writing this thesis, it is in commercial use in 10 large cities in
China including Beijing and Shang Hai. In all of these cities HSDPA is enabled.
The roll-out of the commercial deployment is progressing fast with installations
in another 28 cities being underway now.
However, during the pre-commercial TD-SCDM trail in China, which started
from year 2006, some interference problems have been noticed especially in the
network planning and initialization phases. Interference is always an issue in
any network and the goal of the work reported in this thesis is to improve
network coverage and capacity in the presence of interference.
Based on an analysis of TD-SCDMA issues and how network interference arises,
this thesis proposes two enhancements to the network in addition to the
standard N-frequency technique. These are (i) the introduction of the concentric
circle cell concept and (ii) the addition of a relay network that makes use of
other users at the cell boundary. This overall approach not only optimizes the
resilience to interference but increases the network coverage without adding
more Node Bs.
Based on the cell planning parameters from the research, TD-SCDMA HSDPA
services in dense urban area and non-HSDPA services in rural areas were
simulated to investigate the network performance impact after introducing the
relay network into a TD-SCDMA network.
The results for HSDPA applications show significant improvement in the TDSCDMA
relay network both for network capacity and network interference
aspects compared to standard TD-SCDMA networks. The results for non-
HSDPA service show that although the network capacity has not changed after
adding in the relay network (due to the code limitation in TD-SCDMA), the
TD-SCDMA relay network has better interference performance and greater
coverage
Maximizing Energy Efficiency for Consumption Circuit Power in Downlink Massive MIMO Wireless Networks
Massive multi-input–multi-output (MIMO) systems are crucial to maximizing energy efficiency (EE) and battery-saving technology. Achieving EE without sacrificing the quality of service (QoS) is increasingly important for mobile devices. We first derive the data rate through zero forcing (ZF) and three linear precodings: maximum ratio transmission (MRT), zero forcing (ZF), and minimum mean square error (MMSE). Performance EE can be achieved when all available antennas are used and when taking account of the consumption circuit power ignored because of high transmit power. The aim of this work is to demonstrate how to obtain maximum EE while minimizing power consumed, which achieves a high data rate by deriving the optimal number of antennas in the downlink massive MIMO system. This system includes not only the transmitted power but also the fundamental operation circuit power at the transmitter signal. Maximized EE depends on the optimal number of antennas and determines the number of active users that should be scheduled in each cell. We conclude that the linear precoding technique MMSE achieves the maximum EE more than ZF and MRTbecause the MMSE is able to make the massive MIMO system less sensitive to SNR at an increased number of antennas
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