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In this paper, collaborative use of relays to form a beamforming system with the aid of perfect channel state information (CSI) and to provide physical-layer security is investigated. In particular, a decode-and-forward-based relay beamforming design subject to total and individual relay power constraints is studied with the goal of maximizing the secrecy rate. The total power constraint leads to...
A novel linear precoding technique for the two user broadcast channel is presented. The performance measure used is the cross rate, defined as the difference between the sum throughputs of the system and its transpose. We show that the cross rate optimization problem can be reformulated as an alternating optimization of the steering matrix and power allocation. We solve the power allocation problem...
This paper presents a novel fair scheme for resource sharing between nodes in OFDMA mesh networks. The problem is to maximize the overall system rate, under each user's maximal power and minimum rate constraints. To solve the underlying problem, we propose an approach that combines the merits of the well known Lagrange dual framework and the Lambert-W function. By using the Lambert-W function, resource...
A variable bit rate coding scheme designed for new generation SAR satellites is presented. This coding is based on previous schemes of Block Adaptive Quantizer (BAQ) and is intended as a possible improvement over Sentinel-1 FDBAQ. In this project, the number of quantizers is considered a design choice and the optimization is carried out looking for a set of reflectivity classes in which partition...
This paper considers the DFE transceiver optimization for time-varying memoryless MIMO channels under zero-forcing (ZF) constraint. For time-varying channels, the uncoded average BER of the conventional geometric mean decomposition (GMD) based systems is not minimized because of the diverse arithmetic MSEs at different block times. To minimize the BER, a new GMD transceiver is proposed, in which the...
This paper studies the structure of the channel quantization codebook for multiuser MISO systems with limited channel state information at the base-station. The problem is cast in the form of minimizing the sum power subject to the worst-case SINR constraints over spherical channel uncertainty regions. This paper adopts a zero-forcing approach for beamforming vectors design, and uses a robust optimization...
Adaptive modulation has been widely adopted in broadband wireless communication systems to improve spectrum efficiency. On the other hand, user cooperative diversity has been investigated to improve system coverage and efficiency. How to take the advantage of adaptive modulation for user cooperative transmissions to maximize network throughput under the constraint of the bit error rate (BER) requirement...
In this paper we present system level simulation results of a self-optimizing load balancing algorithm in a long-term-evolution (LTE) mobile communication system. Based on previous work, we evaluate the network performance of this algorithm that requires the load of a cell as input and controls the handover parameters. We compare the results for different simulation setups: for a basic, regular network...
Much work has been done aiming at minimization of energy consumption for transmission of information in energy constrained wireless networks. However, most of them assume uncoded system, not considering the effect of channel coding. In this paper, using the relation between channel capacity or cutoff rate of MQAM modulation in AWGN channel and signal to noise ratio (SNR), we formulate the problem...
Most of previous researches in Multiple-Input- Multiple-Output (MIMO) downlink beamforming based on uplink-downlink duality assume sum power constraints. However, the powers of antennas are limited individually in realistic implementations. Per-antenna power constrains are considered in this paper. In the uplink-downlink duality, it is shown the noise power at uplink receive antennas are dual to the...
In this paper we propose a call admission protocol that adapts the transmit power and data rate of interfering links in WLANs in order to maximize the aggregate and per-node throughput of the network. Power and data rate are adapted in a distributed way by discovering the statistical parameters of the channel and communicating those parameters to neighboring nodes. To ensure accurate results, we consider...
An innovative approach to jointly estimate and compensate the radial velocity and acceleration of non-cooperative targets in HRR (High Range Resolution) processing for a frequency stepped radar has been proposed in. The estimation is performed using different approaches mainly based on the maximization or the minimization of a proper functional (contrast, correlation-like or entropy) of the reconstructed...
Ultra wideband communication is a promising technology with attractive features of low power, low complexity transceiver and rich multipath diversity that can be used for transmitting both high and low data rates. Exploiting the inherent capabilities of UWB communication is up to perfect synchronization between transmitter and the receiver which is a serious bottleneck of these systems. Using very...
Cooperative communication is an emerging and effective technology which can overcome the limitation and improve overall system performance of wireless networks. As important design parameters, relay selection, power and bandwidth allocation have been investigated respectively in previous literature. However, most of the existing schemes mainly consider single-relay selection, which may result in imbalance...
Imaging protocols must obtain maximum information under tight time constraints, to minimize patient discomfort or attrition, and motion artifacts. As part of a pilot study optimizing DTI sequences for the Alzheimer's Disease Neuroimaging Initiative, we scanned 8 subjects with 3 DTI protocols of equal duration at two time-points (48 scans). If scan duration is fixed, collecting more diffusion-sensitized...
This paper develops cross-layer adaptive modulation and coding as an efficient method for bit interleaved coded OFDM packet transmission. As objective function, we adopt the goodput, or the number of data bits delivered without error per unit of time. After the formalization of the optimization problem through an accurate modeling on the link performance, an iterative solution is derived based on...
The eigenspace-based (ESB) beamformer demonstrates much more robust capabilities than the minimum variance distortionless (MVDR) beamformer. However, when the pointing error falls in some certain positions near the mainlobe edge or the integer times of half of the mainlobe width, its performance will suffer from severely degradation. To avoid the certain positions, the paper proposed a modified algorithm...
We consider a wireless relay network with one source, one relay and one destination, where communications between nodes are preformed over N orthogonal channels. This, for example, is the case when orthogonal frequency division multiplexing is employed for data communications. Since the power available at the source and relay is limited, we study optimal power allocation strategies at the source and...
In this paper, we investigate the optimization problem of resource allocation in downlink of multiuser MISO-OFDM system. Multiple users with different BER and minimum transmission rate requirements are considered. We propose a novel heuristic allocation algorithm (HAA) of radio resource, which minimizes the total transmit power of the base station while meeting individual users'QoS requirements. The...
In wireless cooperative networks, the asynchronism between the relays can be a source of diversity which is similar in its essence to the multipath diversity of frequency selective channels. In this context, an asynchronous two-relay cooperative wireless network using the Decode-and-Forward protocol is studied. Two strategies for relay coding are studied: independent coding and repetition coding....
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