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In this paper, we derive the maximum likelihood (ML) channel estimate in the presence of phase noise (PHN) and I/Q imbalance for OFDM systems. Since it is estimated jointly with I/Q and PHN, the channel estimate is more robust to these RF impairments compared to the conventional schemes. The complexity of the joint estimator is reduced using an approximate cost functions for both PHN and I/Q imbalance...
High peak-to-average power ratio (PAPR) of the transmitted signals is a major drawback of orthogonal frequency division multiple access (OFDMA) systems. The selected mapping (SLM) method is one of the major schemes employed for PAPR reduction. Unfortunately, the computational complexity of traditional SLM scheme is relatively high since a number of inverse fast Fourier transforms (IFFTs) are required...
The problem of resource allocation (RA) in a downlink OFDMA system with minimum user rate requests is examined under the realistic scenario of partial (imperfect) channel state information (CSI) at the base station. The challenge in this setting is the non-zero probability of outage events which may lead to significant performance degradation if algorithms assuming perfect CSI are utilized. In this...
In this work we consider the optimization of the power assigned to the user streams, in a coordinated base station downlink environment, when zero-forcing is employed to remove interference among users. Two schemes based on the waterfilling technique are proposed and compared to the optimal solution, which can be obtained numerically, by using convex optimization. We show that the proposed schemes...
In this paper, a practical solution to implement the distributed interference alignment (IA) algorithm of [1] in a cellular communication system is proposed. In the training period of the proposed strategy, the User Equipment (UE) and the Base Station (BS), without knowing a priori the interference covariance matrix, update directly the preceding and interference suppression matrices based on the...
We develop an efficient hard-detector for multiple-input multiple-output (MIMO) channels, which adaptively combines maximum-likelihood detection (MLD) and minimum-mean-square-error (MMSE) with a successive interference canceler (SIC) together. Unlike the conventional joint combination scheme which may suffer from considerable degradation in bit-error-rate (BER) performance over correlated channels...
In this paper, we consider a precoder selection criterion for the maximum-likelihood (ML) detector in limited feedback spatial multiplexing systems. When the ML detector is employed, the exhaustive search for the optimal precoder selection requires very high computational complexity. As a good compromise, we propose a simple precoder selection scheme for the ML detector. It reduces the computational...
Maximum distance separable (MDS) array codes are XOR-based optimal erasure codes that are particularly suitable for use in disk arrays. This paper develops an innovative method to build MDS array codes from an elegant class of nested graphs, termed complete-graph-of-rings (CGR). We discuss a systematic and concrete way to transfer these graphs to array codes, unveil an interesting relation between...
We study the scaling laws for wireless ad hoc network in which the distribution of nodes in the network is homogeneous but the traffic is heterogeneous. More specifically, we consider the case in which a node is the sink to k sources sending different information, while the rest of the nodes are part of unicast communications with a uniform assignment of source-destination pairs. We prove that the...
The emerging biometric cryptography has gained significant interests for key management and privacy protection, but the previously proposed schemes using set metrics for fingerprints may either be too weak to offer enough security or suffer from the performance limitations. In this paper, a new fuzzy cryptographic technique without use of chaff data, Randomized Dissolvent Template (RDT), is proposed...
Fingerprinting localization techniques provide reliable location estimates and enable the development of location aware applications especially for indoor environments, where satellite based positioning is infeasible. In our approach we utilize received signal strength (RSS) fingerprints collected in known locations and employ a radial basis function (RBF) neural network to approximate the function...
Video streaming over wireless links is a challenging problem due to both the unreliable, time-varying nature of the wireless channel and the stringent delivery requirements of media traffic. Layered encoded video can be used to improve the system performance by adapting the sending rate for different video frame layers to the varying network and playout situations. In this paper, we study the adaptive...
Based on the variational Bayes expectation-maximization (VBEM) algorithm, a low complexity semi-blind Bayesian iterative receiver with joint signal detection and channel tracking is proposed in this paper for MIMO-OFDM systems over time-varying multi-path channels. Since the VBEM algorithm provides distribution estimation of all parameters, the detection performance can be improved by taking the channel...
In orthogonal frequency-division multiplexing (OFDM) systems operating over rapidly time-varying channels, the orthogonality between subcarriers is destroyed leading to inter-carrier interference (ICI) and resulting in an irreducible error floor. In this paper, a new and low-complexity maximum a posteriori probability (MAP) detection algorithm is proposed for OFDM systems operating over rapidly time-varying...
Initialization is an indispensable process for wireless sensor networks since newly deployed sensors lack a reliable infrastructure for communication. Many efforts have been made to address the problem on initialization. However, most of them fall into the category of energy efficiency. In mission-critical scenarios, it is vital to reduce the initialization time in order to gather information as early...
In this work we design efficient soft output demodulators (also referred to as fast soft demodulators) for the 2 ?? 2 Golden code, which is a promising candidate space time block code in the evolving IEEE and 3GPP cellular standards. For this code, the naive approach for maximum likelihood (ML) hard decision as well as soft-output demodulation entails a complexity of O(M4), where M denotes the cardinality...
Transmitter Leakage has a significant impact on the system performance in mobile devices using zero-IF receivers and thus requires a suitable compensation. In contrast to analog approaches, digital Tx Leakage compensation approaches can easily be reconfigured and therefore are highly attractive for future mobile devices, using software defined radios. In this contribution we present a digital Tx Leakage...
We propose a new limited feedback scheme for the downlink of multiuser MIMO OFDM systems based on fixed linear beamforming, i.e. the linear beamforming vectors are chosen from a fixed transmit codebook. The proposed feedback method allows the base station to uniformly approximate all multiuser rates for any selection of users and any combination of beamforming vectors defined by the transmit codebook;...
This paper presents a VLSI implementation of a high-throughput and area-efficient MIMO detector. We propose a modified Dijkstra's algorithm and a pre-calculation technique to improve the throughput by allowing overlapped processing. In addition, we propose a simple approximation of L2-norm to reduce the computational complexity without degrading the error performance noticeably. A MIMO detector based...
In this paper, we consider joint end-to-end congestion control and multiuser scheduling in multi-hop wireless networks, where orthogonal frequency-division multiple access (OFDMA) is the air interface. Compared to its single-channel counterpart, this problem is significantly more challenging because subchannel assignment and power allocation for all nodes and network traffic need to be jointly optimized...
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