8,433 research outputs found
Analyse Eines Mehrbenutzer-Mehrfachzugriffskanals Mit Mimo
The increasing number of connected users as well as the availability of new services and mobile applications drive the need for higher data rates. In order to fulfill such expectations different strategies such as spatial multiplexing have been introduced. This thesis is centered on the Multi-User Uplink Channel where different users transmit to a single base station with multiple antennas. The purpose of this thesis is to design the transmitter and the receiver architectures so that the maximum sum rate of a Multi-User Uplink Channel reaches the capacity for single and multi-antenna users. In the literature there is a lack of practical implementations and not many studies exploit the multi-antenna user scenario. It is important to properly characterize the capacity region and define practical implementation schemes on the uplink direction to design the architecture for the Multi-User Downlink Channel also referred as the Broadcast Channel, which is a more complex problem based on the uplink solution. The design of the optimal transmitter is motivated by the analysis of capacity first for the single user scenario with Multi Input Multi Output Peer-to-Peer (MIMO P2P) communica- tions followed by the Multi-User scenario for single and multi-antenna users. At the receiver three types of beamformers are analyzed and compared: Zero Forcing, QR and Minimum Mean Squared Error beamformer. Results for the Bit Error Rate performance and maximum sum rate for the different receivers are provided. The thesis results show that the optimal architecture for the Multi-User Uplink with multi- antenna users that achieves capacity is the combination of the optimal MIMO P2P design, based on the Singular Value Decomposition of the channel matrix and the Water Filling power allocation. For the receiver part the Minimum Mean Squared Error beamformer is proven to achieve capacity. Channel State Information is needed at the transmitter and receiver, therefore a channel estimation algorithm is provided based on orthogonal sequences and is proven to deliver good Bit Error Rate results
Hardware Impairments in Large-scale MISO Systems: Energy Efficiency, Estimation, and Capacity Limits
The use of large-scale antenna arrays has the potential to bring substantial
improvements in energy efficiency and/or spectral efficiency to future wireless
systems, due to the greatly improved spatial beamforming resolution. Recent
asymptotic results show that by increasing the number of antennas one can
achieve a large array gain and at the same time naturally decorrelate the user
channels; thus, the available energy can be focused very accurately at the
intended destinations without causing much inter-user interference. Since these
results rely on asymptotics, it is important to investigate whether the
conventional system models are still reasonable in the asymptotic regimes. This
paper analyzes the fundamental limits of large-scale multiple-input
single-output (MISO) communication systems using a generalized system model
that accounts for transceiver hardware impairments. As opposed to the case of
ideal hardware, we show that these practical impairments create finite ceilings
on the estimation accuracy and capacity of large-scale MISO systems.
Surprisingly, the performance is only limited by the hardware at the
single-antenna user terminal, while the impact of impairments at the
large-scale array vanishes asymptotically. Furthermore, we show that an
arbitrarily high energy efficiency can be achieved by reducing the power while
increasing the number of antennas.Comment: Published at International Conference on Digital Signal Processing
(DSP 2013), 6 pages, 5 figure
Power Scaling of Uplink Massive MIMO Systems with Arbitrary-Rank Channel Means
This paper investigates the uplink achievable rates of massive multiple-input
multiple-output (MIMO) antenna systems in Ricean fading channels, using
maximal-ratio combining (MRC) and zero-forcing (ZF) receivers, assuming perfect
and imperfect channel state information (CSI). In contrast to previous relevant
works, the fast fading MIMO channel matrix is assumed to have an arbitrary-rank
deterministic component as well as a Rayleigh-distributed random component. We
derive tractable expressions for the achievable uplink rate in the
large-antenna limit, along with approximating results that hold for any finite
number of antennas. Based on these analytical results, we obtain the scaling
law that the users' transmit power should satisfy, while maintaining a
desirable quality of service. In particular, it is found that regardless of the
Ricean -factor, in the case of perfect CSI, the approximations converge to
the same constant value as the exact results, as the number of base station
antennas, , grows large, while the transmit power of each user can be scaled
down proportionally to . If CSI is estimated with uncertainty, the same
result holds true but only when the Ricean -factor is non-zero. Otherwise,
if the channel experiences Rayleigh fading, we can only cut the transmit power
of each user proportionally to . In addition, we show that with an
increasing Ricean -factor, the uplink rates will converge to fixed values
for both MRC and ZF receivers
Uplink Performance of Time-Reversal MRC in Massive MIMO Systems Subject to Phase Noise
Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an
excess of base station (BS) antennas (Massive MIMO) offer unprecedented
multiplexing gains and radiated energy efficiency. Oscillator phase noise is
introduced in the transmitter and receiver radio frequency chains and severely
degrades the performance of communication systems. We study the effect of
oscillator phase noise in frequency-selective Massive MIMO systems with
imperfect channel state information (CSI). In particular, we consider two
distinct operation modes, namely when the phase noise processes at the BS
antennas are identical (synchronous operation) and when they are independent
(non-synchronous operation). We analyze a linear and low-complexity
time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both
operation modes we derive a lower bound on the sum-capacity and we compare
their performance. Based on the derived achievable sum-rates, we show that with
the proposed receive processing an array gain is achievable. Due
to the phase noise drift the estimated effective channel becomes progressively
outdated. Therefore, phase noise effectively limits the length of the interval
used for data transmission and the number of scheduled users. The derived
achievable rates provide insights into the optimum choice of the data interval
length and the number of scheduled users.Comment: 13 pages, 6 figures, 2 tables, IEEE Transactions on Wireless
Communications (accepted
Energy-Efficient Resource Allocation in Multiuser MIMO Systems: A Game-Theoretic Framework
This paper focuses on the cross-layer issue of resource allocation for energy
efficiency in the uplink of a multiuser MIMO wireless communication system.
Assuming that all of the transmitters and the uplink receiver are equipped with
multiple antennas, the situation considered is that in which each terminal is
allowed to vary its transmit power, beamforming vector, and uplink receiver in
order to maximize its own utility, which is defined as the ratio of data
throughput to transmit power; the case in which non-linear interference
cancellation is used at the receiver is also investigated. Applying a
game-theoretic formulation, several non-cooperative games for utility
maximization are thus formulated, and their performance is compared in terms of
achieved average utility, achieved average SINR and average transmit power at
the Nash equilibrium. Numerical results show that the use of the proposed
cross-layer resource allocation policies brings remarkable advantages to the
network performance.Comment: Proceedings of the 16th European Signal Processing Conference,
Lausanne, Switzerland, August 25-29, 200
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