1,301 research outputs found
Relaying systems with reciprocity mismatch : impact analysis and calibration
Cooperative beamforming can provide significant performance improvement for relaying systems with the help of the channel state information (CSI). In time-division duplexing (TDD) mode, the estimated CSI will deteriorate due to the reciprocity mismatch. In this work, we examine the impact and the calibration of the reciprocity mismatch in relaying systems. To evaluate the impact of the reciprocity mismatch for all devices, the closed-form expression of the achievable rate is first derived. Then, we analyze the performance loss caused by the reciprocity mismatch at sources, relays, and destinations respectively to show that the mismatch at relays dominates the impact. To compensate the performance loss, a two-stage calibration scheme is proposed for relays. Specifically, relays perform the intra-calibration based on circuits independently. Further, the inter-calibration based on the discrete Fourier transform (DFT) codebook is operated to improve the calibration performance by cooperation transmission, which has never been considered in previous work. Finally, we derive the achievable rate after relays perform the proposed reciprocity calibration scheme and investigate the impact of estimation errors on the system performance. Simulation results are presented to verify the analytical results and to show the performance of the proposed calibration approach
Massive MIMO for Next Generation Wireless Systems
Multi-user Multiple-Input Multiple-Output (MIMO) offers big advantages over
conventional point-to-point MIMO: it works with cheap single-antenna terminals,
a rich scattering environment is not required, and resource allocation is
simplified because every active terminal utilizes all of the time-frequency
bins. However, multi-user MIMO, as originally envisioned with roughly equal
numbers of service-antennas and terminals and frequency division duplex
operation, is not a scalable technology. Massive MIMO (also known as
"Large-Scale Antenna Systems", "Very Large MIMO", "Hyper MIMO", "Full-Dimension
MIMO" & "ARGOS") makes a clean break with current practice through the use of a
large excess of service-antennas over active terminals and time division duplex
operation. Extra antennas help by focusing energy into ever-smaller regions of
space to bring huge improvements in throughput and radiated energy efficiency.
Other benefits of massive MIMO include the extensive use of inexpensive
low-power components, reduced latency, simplification of the media access
control (MAC) layer, and robustness to intentional jamming. The anticipated
throughput depend on the propagation environment providing asymptotically
orthogonal channels to the terminals, but so far experiments have not disclosed
any limitations in this regard. While massive MIMO renders many traditional
research problems irrelevant, it uncovers entirely new problems that urgently
need attention: the challenge of making many low-cost low-precision components
that work effectively together, acquisition and synchronization for
newly-joined terminals, the exploitation of extra degrees of freedom provided
by the excess of service-antennas, reducing internal power consumption to
achieve total energy efficiency reductions, and finding new deployment
scenarios. This paper presents an overview of the massive MIMO concept and
contemporary research.Comment: Final manuscript, to appear in IEEE Communications Magazin
Impact of RF mismatches on the performance of massive MIMO systems with ZF precoding
Thanks to the channel reciprocity, the time division duplex (TDD) operation is more preferred in massive multiple-input multiple-output (MIMO) systems. Avoiding the heavy feedback of downlink channel state information (CSI) from the user equipment (UE) to the base station (BS), the uplink CSI can be exploited for the downlink precoding. However, due to the mismatches of the radio frequency (RF) circuits at both sides of the link, the whole communication channels are usually not symmetric in practical systems. This paper is focused on the RF mismatches at the UEs and the BS for the multi-user massive MIMO systems with zero forcing (ZF) precoding. The closed-form expressions of the ergodic sum-rates are derived for evaluating the impact of RF mismatches on the system performance. Theoretical analysis and simulation results show that the RF mismatches at the UEs only lead to a negligible performance loss. However, it is imperative to perform reciprocity calibration at the BS, because the RF mismatches at the BS contribute to the inter-user interference (IUI) and result in a severe system performance degradation
Analyzing the Reduced Required BS Density due to CoMP in Cellular Networks
In this paper we investigate the benefit of base station (BS) cooperation in
the uplink of coordinated multi-point (CoMP) networks. Our figure of merit is
the required BS density required to meet a chosen rate coverage. Our model
assumes a 2-D network of BSs on a regular hexagonal lattice in which path loss,
lognormal shadowing and Rayleigh fading affect the signal received from users.
Accurate closed-form expressions are first presented for the sum-rate coverage
probability and ergodic sum-rate at each point of the cooperation region. Then,
for a chosen quality of user rate, the required density of BS is derived based
on the minimum value of rate coverage probability in the cooperation region.
The approach guarantees that the achievable rate in the entire coverage region
is above a target rate with chosen probability. The formulation allows
comparison between different orders of BS cooperation, quantifying the reduced
required BS density from higher orders of cooperation.Comment: Accepted for presentation in IEEE Globecom Conf., to be held in
Atlanta, USA, Dec. 2013. arXiv admin note: text overlap with arXiv:1302.159
Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks
Conventional cellular wireless networks were designed with the purpose of
providing high throughput for the user and high capacity for the service
provider, without any provisions of energy efficiency. As a result, these
networks have an enormous Carbon footprint. In this paper, we describe the
sources of the inefficiencies in such networks. First we present results of the
studies on how much Carbon footprint such networks generate. We also discuss
how much more mobile traffic is expected to increase so that this Carbon
footprint will even increase tremendously more. We then discuss specific
sources of inefficiency and potential sources of improvement at the physical
layer as well as at higher layers of the communication protocol hierarchy. In
particular, considering that most of the energy inefficiency in cellular
wireless networks is at the base stations, we discuss multi-tier networks and
point to the potential of exploiting mobility patterns in order to use base
station energy judiciously. We then investigate potential methods to reduce
this inefficiency and quantify their individual contributions. By a
consideration of the combination of all potential gains, we conclude that an
improvement in energy consumption in cellular wireless networks by two orders
of magnitude, or even more, is possible.Comment: arXiv admin note: text overlap with arXiv:1210.843
Preliminary Results on 3D Channel Modeling: From Theory to Standardization
Three dimensional beamforming (3D) (also elevation beamforming) is now
gaining a growing interest among researchers in wireless communication. The
reason can be attributed to its potential to enable a variety of strategies
like sector or user specific elevation beamforming and cell-splitting. Since
these techniques cannot be directly supported by current LTE releases, the 3GPP
is now working on defining the required technical specifications. In
particular, a large effort is currently made to get accurate 3D channel models
that support the elevation dimension. This step is necessary as it will
evaluate the potential of 3D and FD(Full Dimensional) beamforming techniques to
benefit from the richness of real channels. This work aims at presenting the
on-going 3GPP study item "Study on 3D-channel model for Elevation Beamforming
and FD-MIMO studies for LTE", and positioning it with respect to previous
standardization works
Automated tracking of the Florida manatee (Trichechus manatus)
The electronic, physical, biological and environmental factors involved in the automated remote tracking of the Florida manatee (Trichechus manatus) are identified. The current status of the manatee as an endangered species is provided. Brief descriptions of existing tracking and position locating systems are presented to identify the state of the art in these fields. An analysis of energy media is conducted to identify those with the highest probability of success for this application. Logistic questions such as the means of attachment and position of any equipment to be placed on the manatee are also investigated. Power sources and manateeborne electronics encapsulation techniques are studied and the results of a compter generated DF network analysis are summarized
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