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The shared computational resources provided by the mobile cloud computing paradigm offer the opportunity for mobile devices to reduce the energy expended, or the latency incurred, in performing significant computational tasks. To maximize their impact, cloud computing systems must jointly optimize the allocation of the computational and radio resources. We consider a scenario in which two mobile users...
A low-complexity version of the offset maximization technique for robust precoding is developed for massive MISO downlink systems. Offset maximization precoding provides sub-stantial robustness under different channel uncertainty models, and can be modified to handle per-antenna power constraints. We also provide an improved power loading technique for any set of beamforming directions. This technique...
The design of a set of beamformers for the multiple-input single-output (MISO) downlink that provides the scheduled users with the quality-of-service (QoS) level that they requested can be quite sensitive to the accuracy of the channel state information (CSI) that is available at the base station. To mitigate that sensitivity, models for the uncertainty in the CSI can be incorporated in the design...
Ordered successive interference cancellation (OSIC) is a well-established detection strategy for multiple-input multiple-output (MIMO) systems. It offers good performance and has an efficient hardware implementation. Typically, the order in which the symbols are detected is based on the channel matrix and the noise statistics. In this paper, a modified ordering scheme that makes use of the information...
Mobile cloud computing provides shared computational resources to which mobile devices can offload computational tasks in order to reduce energy consumption or reduce the latency of the task execution. The decision of whether or not to offload a task can be formulated as a joint optimization problem over the available computational and radio resources. When multiple users seek to offload tasks through...
In this paper, we consider the problem of optimal opportunistic spectrum access using full-duplex (FD) radios in presence of uncertain primary user (PU) channel statistics and propose a Sensing-and-Selectively-Transmit protocol (SaST). To optimize its throughput, the SU sensing period has to be carefully tuned. However, in absence of the exact knowledge of PU activity statistics, under SaST, the PU's...
This paper develops low-complexity design techniques for robust linear precoders suitable for various multi-cell multiple-input single-output (MISO) downlink systems. The goal is to satisfy pre-specified SINR requirements for users in multiple cells under some base station power constraints, in the absence of perfect channel state information (CSI). First, we consider the case of full cooperation...
A low-complexity robust power loading technique is developed for multiple-input single-output (MISO) downlink systems. The technique uses straightforward probability insights from the second-order statistics of the channel estimation errors to develop a low-complexity iterative algorithm that provides control over the outage probability of each user. In the case of "massive MIMO" channels...
We consider the design of a linear precoder for a multiple-input single-output (MISO) downlink system that seeks to mitigate the impact of the imperfections in the channel state information (CSI) that is available at the base station (BS). The goal of the design is to minimize the outage probability of signal-to-interference-and-noise ratio (SINR) targets specified by the receivers, while satisfying...
A linear precoding scheme is developed for unbounded MIMO downlink networks with quasi-static channels that have a hexagonal cell architecture. In the scheme developed herein, the equivalent channel model is structured to be decomposable, and the linear precoders at the base stations are designed to be decomposable as well. The proposed scheme is based the principles of fractional spatial reuse precoding...
We consider the design of the linear precoder for a multiple-input single-output (MISO) downlink in a system that employs limited feedback using Grassmannian quantization. The goal is to minimize the outage probability of a target signal-to-interference-andnoise ratio (SINR) under a transmitted power constraint. By approximating the outage constraint by a zero-outage region, employing a semidefinite...
The design of a pulse shaping filter which provides maximal robustness to an unknown frequency-selective channel is formulated as a convex optimization problem from which an optimal filter can be efficiently obtained. Robustness is measured by the worst-case mean square error of the data estimate over a class of deterministically bounded channels, and the optimization is subject to a constraint on...
In this paper, we propose a structured linear interference alignment scheme that can achieve 2 degrees of freedom in the 3-cell downlink network with arbitrary time-invariant channels using only local feedback. The scheme employs a finite number of channel extensions and results in an equivalent channel matrix that is 2-level decomposable. The linear precoders at the transmitters are constructed from...
In wireless networks, the availability of multiple transmitting antennas can be exploited in several ways. One way is to reduce the interference to unintended receivers by placing beamforming nulls in those directions, as is done in zero-forcing beamforming. Another is to boost the received signal strength at the desired receiver using “matched” transmit beamforming. This work studies a partial zero-forcing...
Interference Alignment is an intriguing approach to the development of interference management schemes for wireless networks. Even for networks of single antenna nodes with time-invariant channels, several approaches to interference alignment have been proposed. Those schemes construct transmitted signals that are not circularly symmetric by using symbols from real-valued constellations. In this paper...
For MIMO systems with binary or QPSK signalling, soft demodulation techniques based on semidefinite relaxation (SDR) offer a desirable balance between performance and computational cost. In this paper we expand on an extension of that approach to systems with higher-order QAM signalling. In particular, we develop a customized dual-scaling algorithm to solve the semidefinite program that constitutes...
Mutual interference is the main bottleneck on the throughput of large random spectrum sharing networks. This work examines the extent to which the performance of such networks can be improved by employing multiple transmitting antennas, without degrading the average performance of individual users. By extending partial zero-forcing beamforming to spectrum sharing networks, the aggregate interference...
We consider the three-cell MIMO interfering broadcast channel (IBC) with K users assigned to each base station. Each base station has M = 2K + 1 antennas and each user has N antennas. We propose two different linear precoding schemes to achieve the optimal degrees of freedom (DoF) for the case in which each user receives only one data stream. The first scheme finds the transmit precoders and receive...
We consider the two-cell MIMO interfering broadcast channel (IBC) with K users assigned to each base station, and we develop two closely-related Interference Alignment schemes that are well suited to a limited feedback implementation. The schemes are developed for BSs with K + 1 antennas and receivers with K or K + 1 antennas, respectively. The schemes achieve the maximum degrees of freedom (DoF),...
In this paper we propose a structured low-latency interference alignment scheme for the two-user single-input single-output (SISO) time-invariant X channel. The scheme is based on asymmetric (non-circular) complex signals generated by linear precoders and linear zero-forcing receivers. In addition to achieving the optimal (sum) degrees of freedom (DoF) of 4/3, the precoders are balanced in the sense...
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