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See detailJoint and competitive caching designs in large-scale multi-tier wireless multicasting networks
Cui, Ying; Wang, Zitian; Yang, Yang UL et al

in IEEE Transactions on Communications (2018), 66(6), 3108-3121

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See detailTransceiver design of optimum wirelessly powered full-duplex MIMO IoT devices
Xue, Jiang; Biswas, Sudip; Cirik, Ali Cagatay et al

in IEEE Transactions on Communications (2018), 66(5), 1955-1969

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See detailCache-Aided Millimeter Wave Ad-Hoc Networks with Contention-Based Content Delivery
Vuppala, Satyanarayana UL; Vu, Thang Xuan UL; Gautam, Sumit UL et al

in IEEE Transactions on Communications (2018)

The narrow-beam operation in millimeter wave (mmWave) networks minimizes the network interference leading to a noise-limited networks in contrast with interference-limited ones. The medium access control ... [more ▼]

The narrow-beam operation in millimeter wave (mmWave) networks minimizes the network interference leading to a noise-limited networks in contrast with interference-limited ones. The medium access control (MAC) layer throughput, and interference management strategies heavily depend on the noise-limited or interference-limited regime. Yet, these regimes are not considered in recent mmWave MAC layer designs, which can potentially have disastrous consequences on the communication performance. In this paper, we investigate the performance of cache-enabled MAC based mmWave ad-hoc networks, where randomly distributed nodes are supported by a cache. The adhoc nodes are modeled as homogenous Poisson Point Processes (PPP). Specifically, we study the optimal content placement (or caching placement) at desirable mmWave nodes using a network model that accounts for uncertainties both in node locations and blockages. We propose a contention-based multimedia delivery protocol to avoid collisions among the concurrent transmissions. Subsequently, only the node with smallest back-off timer amongst its contenders is allowed to transmit. We then characterize the average success probability of content delivery. We also characterize the cache hit ratio probability, and transmission probability of this system under essential factors, such as blockages, node density, path loss and caching parameters. [less ▲]

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See detailImpact of Residual Additive Transceiver Hardware Impairments on Rayleigh-Product MIMO Channels with Linear Receivers: Exact and Asymptotic Analyses
Papazafeiropoulos, Anastasios; Sharma, Shree Krishna UL; Ratnarajah, Tharmalingam et al

in IEEE Transactions on Communications (2017)

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See detailMulti-gateway Data Predistortion for Non-linear Satellite Channels
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in IEEE Transactions on Communications (2015), 63(10), 3789-3802

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See detailAdaptive Compression and Joint Detection for Fronthaul Uplinks in Cloud Radio Access Networks
Vu, Thang Xuan UL; Nguyen, Hieu Duy; Quek, Tony Q.S.

in IEEE Transactions on Communications (2015), 63(11), 4565-4575

Cloud radio access network (C-RAN) has recently attracted much attention as a promising architecture for future mobile networks to sustain the exponential growth of data rate. In C-RAN, one data ... [more ▼]

Cloud radio access network (C-RAN) has recently attracted much attention as a promising architecture for future mobile networks to sustain the exponential growth of data rate. In C-RAN, one data processing center or baseband unit (BBU) communicates with users via distributed remote radio heads (RRHs), which are connected to the BBU via high capacity, low latency fronthaul links. In this paper, we study the compression on fron- thaul uplinks and propose a joint decompression algorithm at the BBU. The central premise behind the proposed algorithm is to ex- ploit the correlation between RRHs. Our contribution is threefold. First, we propose a joint decompression and detection (JDD) algorithm which jointly performs decompressing and detecting. The JDD algorithm takes into consideration both the fading and compression effect in a single decoding step. Second, block error rate (BLER) of the proposed algorithm is analyzed in closed-form by using pair-wise error probability analysis. Third, based on the analyzed BLER, we propose adaptive compression schemes subject to quality of service (QoS) constraints to minimize the fronthaul transmission rate while satisfying the pre-defined target QoS. As a dual problem, we also propose a scheme to minimize the signal distortion subject to fronthaul rate constraint. Numerical re- sults demonstrate that the proposed adaptive compression schemes can achieve a compression ratio of 300% in experimental setups. [less ▲]

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See detailMultiple Gateway Transmit Diversity in Q/V Band Feeder Links
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel et al

in IEEE Transactions on Communications (2015)

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q ... [more ▼]

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q/V band and an exploitation of multiple gateways (GW) as a transmit diversity measure for overcoming severe propagation effects are being considered. In this context, this contribution deals with the design of a feeder link comprising N + P GWs (N active and P redundant GWs). Towards provisioning the desired availability, a novel switching scheme is analysed and practical aspects such as prediction based switching and switching rate are discussed. Unlike most relevant works, a dynamic rain attenuation model is used to derive analytically average outage probability in the fundamental 1 + 1 gateway case. Building on this result, an analysis for the N +P scenario leading to a quantification of the end􀀀to􀀀end performance is provided. This analysis aids system sizing by illustrating the interplay between the number of active and redundant gateways on the chosen metrics : average outage and average switching rate. [less ▲]

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See detailEnergy Efficient Coordinated Beamforming for Multicell System: Duality-Based Algorithm Design and Massive MIMO Transition
He, Shiwen; Huang, Yongming; Yang, Luxi et al

in IEEE TRANSACTIONS ON COMMUNICATIONS (2015), 63(12), 4920-4935

In this paper, we investigate joint beamforming and power allocation in multicell multiple-input single-output (MISO) downlink networks. Our goal is to maximize the utility function defined as the ratio ... [more ▼]

In this paper, we investigate joint beamforming and power allocation in multicell multiple-input single-output (MISO) downlink networks. Our goal is to maximize the utility function defined as the ratio between the system weighted sum rate and the total power consumption subject to the users' quality of service requirements and per-base-station (BS) power constraints. The considered problem is nonconvex and its objective is in a fractional form. To circumvent this problem, we first resort to an virtual uplink formulations of the the primal problem by introducing an auxiliary variable and applying the uplink-downlink duality theory. By exploiting the analytic structure of the optimal beamformers in the dual uplink problem, an efficient algorithm is then developed to solve the considered problem. Furthermore, to reduce further the exchange overhead between coordinated BSs in a large-scale antenna system, an effective coordinated power allocation solution only based on statistical channel state information is reached by deriving the asymptotic optimization problem, which is used to obtain the power allocation in a long-term timescale. Numerical results validate the effectiveness of our proposed schemes and show that both the spectral efficiency and the energy efficiency can be simultaneously improved over traditional downlink coordinated schemes, especially in the middle-high transmit power region. [less ▲]

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See detailOptimal training sequences for joint timing synchronization and channel estimation in distributed communication networks
Nasir, Ali A.; Mehrpouyan, Hani; Durrani, Salman et al

in IEEE Transactions on Communications (2013), 7(61), 3002-3015

For distributed multi-user and multi-relay cooperative networks, the received signal may be affected by multiple timing offsets (MTOs) and multiple channels that need to be jointly estimated for ... [more ▼]

For distributed multi-user and multi-relay cooperative networks, the received signal may be affected by multiple timing offsets (MTOs) and multiple channels that need to be jointly estimated for successful decoding at the receiver. This paper addresses the design of optimal training sequences for efficient estimation of MTOs and multiple channel parameters. A new hybrid Cramer-Rao lower bound (HCRB) for joint estimation of MTOs and channels is derived. Subsequently, by minimizing the derived HCRB as a function of training sequences, three training sequence design guidelines are derived and according to these guidelines, two training sequences are proposed. In order to show that the proposed design guidelines also improve estimation accuracy, the conditional Cramer-Rao lower bound (ECRB), which is a tighter lower bound on the estimation accuracy compared to the HCRB, is also derived. Numerical results show that the proposed training sequence design guidelines not only lower the HCRB, but they also lower the ECRB and the mean-square error of the proposed maximum a posteriori estimator. Moreover, extensive simulations demonstrate that application of the proposed training sequences significantly lowers the bit-error rate performance of multi-relay cooperative networks when compared to training sequences that violate these design guidelines. [less ▲]

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See detailTree expectation propagation for ml decoding of LDPC codes over the BEC
Salamanca Mino, Luis UL; Olmos, P. M.; Murillo-Fuentes, J. J. et al

in IEEE Transactions on Communications (2013), 61(2), 465-473

We propose a decoding algorithm for LDPC codes that achieves the maximum likelihood (ML) solution over the bi- nary erasure channel (BEC). In this channel, the tree-structured expectation propagation (TEP ... [more ▼]

We propose a decoding algorithm for LDPC codes that achieves the maximum likelihood (ML) solution over the bi- nary erasure channel (BEC). In this channel, the tree-structured expectation propagation (TEP) decoder improves the peeling decoder (PD) by processing check nodes of degree one and two. However, it does not achieve the ML solution, as the tree structure of the TEP allows only for approximate inference. In this paper, we provide the procedure to construct the structure needed for exact inference. This algorithm, denoted as generalized tree-structured expectation propagation (GTEP), modifies the code graph by recursively eliminating any check node and merging this information in the remaining graph. The GTEP decoder upon completion either provides the unique ML solution or a tree graph in which the number of parent nodes indicates the multiplicity of the ML solution. We also explain the algorithm as a Gaussian elimination method, relating the GTEP to other ML solutions. Compared to previous approaches, it presents an equivalent complexity, it exhibits a simpler graphical message-passing procedure and, most interesting, the algorithm can be generalized to other channels. [less ▲]

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See detailWeighted sum rate maximization for MIMO broadcast channels using dirty paper coding and zero-forcing methods
Le-Nam, Tran; Juntti, M.; Bengtsson, M. et al

in IEEE Transactions on Communications (2013), 6(61), 2362-2373

We consider precoder design for maximizing the weighted sum rate (WSR) of successive zero-forcing dirty paper coding (SZF-DPC). For this problem, the existing precoder designs often assume a sum power ... [more ▼]

We consider precoder design for maximizing the weighted sum rate (WSR) of successive zero-forcing dirty paper coding (SZF-DPC). For this problem, the existing precoder designs often assume a sum power constraint (SPC) and rely on the singular value decomposition (SVD). The SVD-based designs are known to be optimal but require high complexity. We first propose a low-complexity optimal precoder design for SZF-DPC under SPC, using the QR decomposition. Then, we propose an efficient numerical algorithm to find the optimal precoders subject to per-antenna power constraints (PAPCs). To this end, the precoder design for PAPCs is formulated as an optimization problem with a rank constraint on the covariance matrices. A well-known approach to solve this problem is to relax the rank constraints and solve the relaxed problem. Interestingly, for SZF-DPC, we are able to prove that the rank relaxation is tight. Consequently, the optimal precoder design for PAPCs is computed by solving the relaxed problem, for which we propose a customized interior-point method that exhibits a superlinear convergence rate. Two suboptimal precoder designs are also presented and compared to the optimal ones. We also show that the proposed numerical method is applicable for finding the optimal precoders for block diagonalization scheme. [less ▲]

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See detailOn the Variations in Mutual Information of MIMO Communication Systems Due to Perturbed Channel State Information at Transmitter
Shankar, Bhavani UL; Hari, K. V. S.

in IEEE Transactions on Communications (2006), 54(9), 1593-1603

In this paper, we address the issue of perturbed information at the transmitter in a multiple-input multiple-output (MIMO) system. Two schemes, correlation matrix feedback and channel information feedback ... [more ▼]

In this paper, we address the issue of perturbed information at the transmitter in a multiple-input multiple-output (MIMO) system. Two schemes, correlation matrix feedback and channel information feedback, are proposed to convey information necessary for achieving capacity to the transmitter. This information is perturbed due to various impairments. A perturbation analysis is carried out to study the variations in mutual information for each of the proposed schemes. For ergodic channels, this analysis is used to design a MIMO system with a limited rate feedback. Using a codebook-based approach, vector quantizers are designed to minimize the loss in ergodic capacity for each of the proposed schemes, and their performance is studied. A non-codebook method, parameter-based feedback, is also presented, and the underlying rate-performance tradeoff is highlighted [less ▲]

Detailed reference viewed: 68 (6 UL)