224 research outputs found
Optimal power control in Cognitive MIMO systems with limited feedback
In this paper, the problem of optimal power allocation in Cognitive Radio
(CR) Multiple Input Multiple Output (MIMO) systems is treated. The focus is on
providing limited feedback solutions aiming at maximizing the secondary system
rate subject to a constraint on the average interference caused to primary
communication. The limited feedback solutions are obtained by reducing the
information available at secondary transmitter (STx) for the link between STx
and the secondary receiver (SRx) as well as by limiting the level of available
information at STx that corresponds to the link between the STx and the primary
receiver PRx. Monte Carlo simulation results are given that allow to quanitfy
the performance achieved by the proposed algorithms
TDMA is Optimal for All-unicast DoF Region of TIM if and only if Topology is Chordal Bipartite
The main result of this work is that an orthogonal access scheme such as TDMA
achieves the all-unicast degrees of freedom (DoF) region of the topological
interference management (TIM) problem if and only if the network topology graph
is chordal bipartite, i.e., every cycle that can contain a chord, does contain
a chord. The all-unicast DoF region includes the DoF region for any arbitrary
choice of a unicast message set, so e.g., the results of Maleki and Jafar on
the optimality of orthogonal access for the sum-DoF of one-dimensional convex
networks are recovered as a special case. The result is also established for
the corresponding topological representation of the index coding problem
Coordinated Shared Spectrum Precoding with Distributed CSIT
In this paper, the operation of a Licensed Shared Access (LSA) system is
investigated, considering downlink communication. The system comprises of a
Multiple-Input-Single-Output (MISO) incumbent transmitter (TX) - receiver (RX)
pair, which offers a spectrum sharing opportunity to a MISO licensee TX-RX
pair. Our main contribution is the design of a coordinated transmission scheme,
inspired by the underlay Cognitive Radio (CR) approach, with the aim of
maximizing the average rate of the licensee, subject to an average rate
constraint for the incumbent. In contrast to most prior works on underlay CR,
the coordination of the two TXs takes place under a realistic Channel State
Information (CSI) scenario, where each TX has sole access to the instantaneous
direct channel of its served terminal. Such a CSI knowledge setting brings
about a formulation based on the theory of Team Decisions, whereby the TXs aim
at optimizing a common objective given the same constraint set, on the basis of
individual channel information. Consequently, a novel set of applicable
precoding schemes is proposed. Relying on statistical coordination criteria,
the two TXs cooperate in the lack of any instantaneous CSI exchange. We verify
by simulations that our novel coordinated precoding scheme outperforms the
standard underlay CR approach
Efficient FPGA implementation of high-throughput mixed radix multipath delay commutator FFT processor for MIMO-OFDM
This article presents and evaluates pipelined architecture designs for an improved high-frequency Fast Fourier
Transform (FFT) processor implemented on Field Programmable Gate Arrays (FPGA) for Multiple Input Multiple Output
Orthogonal Frequency Division Multiplexing (MIMO-OFDM). The architecture presented is a Mixed-Radix Multipath Delay
Commutator. The presented parallel architecture utilizes fewer hardware resources compared to Radix-2 architecture,
while maintaining simple control and butterfly structures inherent to Radix-2 implementations. The high-frequency
design presented allows enhancing system throughput without requiring additional parallel data paths common in
other current approaches, the presented design can process two and four independent data streams in parallel
and is suitable for scaling to any power of two FFT size N. FPGA implementation of the architecture demonstrated
significant resource efficiency and high-throughput in comparison to relevant current approaches within
literature. The proposed architecture designs were realized with Xilinx System Generator (XSG) and evaluated
on both Virtex-5 and Virtex-7 FPGA devices. Post place and route results demonstrated maximum frequency
values over 400 MHz and 470 MHz for Virtex-5 and Virtex-7 FPGA devices respectively
Generation of correlated Rayleigh fading channels for accurate simulationof promising wireless communication systems
In this paper, a generalized method is proposed for the accurate simulation of equal/ unequal power correlated Rayleigh fading channels to overcome the shortcomings of existing methods. Spatial and spectral correlations are also considered in this technique for different transmission conditions. It employs successive coloring for the inphase and quadrature components of successive signals using real correlation vector of successive signal envelopes rather than complex covariance matrix of the Gaussian signals which is utilized in conventional methods. Any number of fading signals with any desired correlations
of successive envelope pairs in the interval [0, 1] can be generated with high accuracy. Moreover, factorization of the desired covariance matrix is avoided to overcome the shortcomings and high computational complexity of conventional methods. Extensive simulations of different representative scenarios demonstrate the effectiveness of the proposedtechnique. The simplicity and accuracy of this method will help the researchers to study and simulate the impact of fading correlation on the performance evaluation of various multi-antenna and multicarrier communication systems. Moreover, it enables the engineers for efficient design and deployment of new schemes for feasible wireless
application
Joint Sensing and Reception Design of SIMO Hybrid Cognitive Radio Systems
In this paper, the problem of joint design of Spectrum Sensing (SS) and
receive beamforming (BF), with reference to a Cognitive Radio (CR) system, is
considered. The aim of the proposed design is the maximization of the
achievable average uplink rate of a Secondary User (SU), subject to an
outage-based Quality-of-Service (QoS) constraint for primary communication. A
hybrid CR system approach is studied, according to which, the system either
operates as an interweave (i.e., opportunistic) or as an underlay (i.e.,
spectrum sharing) CR system, based on SS results. A realistic Channel State
Information (CSI) framework is assumed, according to which, the direct channel
links are known by the multiple antenna receivers (RXs), while, merely
statistical (covariance) information is available for the interference links. A
new, closed form approximation is derived for the outage probability of primary
communication, and the problem of rate-optimal selection of SS parameters and
receive beamformers is addressed for hybrid, interweave and underlay CR
systems. It is proven that our proposed system design outperforms both underlay
and interweave CR systems for a range of system scenarios
Robust leakage-based distributed precoder for cooperative multicell systems
Coordinated multipoint (CoMP) from long term evolution (LTE)-advanced is a promising technique to enhance the system spectral efficiency. Among the CoMP techniques, joint transmission has high communication requirements, because of the data sharing phase through the backhaul network, and coordinated scheduling and beamforming reduces the backhaul requirements, since no data sharing is necessary. Most of the available CoMP techniques consider perfect channel knowledge at the transmitters. Nevertheless for practical systems this is unrealistic. Therefore in this study the authors address this limitation by proposing a robust precoder for a multicell-based systems, where each base station (BS) has only access to an imperfect local channel estimate. They consider both the case with and without data sharing. The proposed precoder is designed in a distributed manner at each BS by maximising the signal-to-leakage-and-noise ratio of all jointly processed users. By considering the channel estimation error in the design of the precoder, they are able to reduce considerably the impact of these errors in the system's performance. The results show that the proposed scheme has improved performance especially for the high signal-to-noise ratio regime, where the impact of the channel estimation error may be more pronounced
Interference Alignment and Cancellation
The throughput of existing MIMO LANs is limited by the number of antennas on the AP. This paper shows how to overcome this limit. It presents interference alignment and cancellation (IAC), a new approach for decoding concurrent sender-receiver pairs in MIMO networks. IAC synthesizes two signal processing techniques, interference alignment and interference cancellation, showing that the combination applies to scenarios where neither interference alignment nor cancellation applies alone. We show analytically that IAC almost doubles the throughput of MIMO LANs. We also implement IAC in GNU-Radio, and experimentally demonstrate that for 2x2 MIMO LANs, IAC increases the average throughput by 1.5x on the downlink and 2x on the uplink.United States. Defense Advanced Research Projects Agency. Information Theory for Mobile Ad-Hoc Networks Progra
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