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Wireless Communications, IEEE Transactions on

Issue 4 • Date April 2013

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Displaying Results 1 - 25 of 52
  • Table of contents

    Page(s): c1 - c4
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  • Staff list

    Page(s): c2
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  • Performance Analysis of Packet Aggregation for IEEE 802.11 PCF MAC-Based Wireless Networks

    Page(s): 1441 - 1447
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (345 KB) |  | HTML iconHTML  

    In this paper, we investigate the effect of packet aggregation on the delay performance of the IEEE 802.11 Point Coordination Function (PCF) MAC. We intend to use packet aggregation to reduce polling overhead of 802.11 PCF and improve the delay performance. We consider two different polling schemes for assembling variable-length packets for transmission: poll once and multiple poll. An analytical model is developed for evaluating the queueing delay of packets at nodes using 802.11 PCF MAC for medium access. Based on this model, we derive several closed-form expressions for computing average delay and queue length. To verify the correctness of our analytical model, we also develop a simulator for the 802.11 PCF MAC. The simulation results well match the analytical results. Several quantitative examples are given for illustrating the reduced average delays under various load conditions and limits of aggregated frames. We find that the average delay decreases with the limit of aggregated frames. We also find that, between the two polling schemes, the multiple-poll scheme achieves a smaller average delay and queue length. View full abstract»

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  • Dynamic Multilevel Priority Packet Scheduling Scheme for Wireless Sensor Network

    Page(s): 1448 - 1459
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (543 KB) |  | HTML iconHTML  

    Scheduling different types of packets, such as realtime and non-real-time data packets, at sensor nodes with resource constraints in Wireless Sensor Networks (WSN) is of vital importance to reduce sensors' energy consumptions and end-to-end data transmission delays. Most of the existing packet-scheduling mechanisms of WSN use First Come First Served (FCFS), non-preemptive priority and preemptive priority scheduling algorithms. These algorithms incur a high processing overhead and long end-to-end data transmission delay due to the FCFS concept, starvation of high priority real-time data packets due to the transmission of a large data packet in nonpreemptive priority scheduling, starvation of non-real-time data packets due to the probable continuous arrival of real-time data in preemptive priority scheduling, and improper allocation of data packets to queues in multilevel queue scheduling algorithms. Moreover, these algorithms are not dynamic to the changing requirements of WSN applications since their scheduling policies are predetermined. In this paper, we propose a Dynamic Multilevel Priority (DMP) packet scheduling scheme. In the proposed scheme, each node, except those at the last level of the virtual hierarchy in the zone-based topology of WSN, has three levels of priority queues. Real-time packets are placed into the highest-priority queue and can preempt data packets in other queues. Non-real-time packets are placed into two other queues based on a certain threshold of their estimated processing time. Leaf nodes have two queues for real-time and non-real-time data packets since they do not receive data from other nodes and thus, reduce end-to-end delay. We evaluate the performance of the proposed DMP packet scheduling scheme through simulations for real-time and non-real-time data. Simulation results illustrate that the DMP packet scheduling scheme outperforms conventional schemes in terms of average data waiting time and end-to-end delay. View full abstract»

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  • SINR and Throughput Analysis for Random Beamforming Systems with Adaptive Modulation

    Page(s): 1460 - 1471
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    In this paper, we derive the exact probability distribution of post-scheduling signal-to-interference-plus-noise ratio (SINR) considering both user feedback and scheduling. We also develop an optimized adaptive modulation scheme in orthogonal random beamforming systems with M transmit antennas and K single-antenna users. The exact probability distributions of each user's feedback SINR and the exact postscheduling SINR are derived rigorously by direct integration and multinomial distribution. It is also shown that the derived cumulative distribution function (CDF) of the post-scheduling SINR happens to be identical to the the existing approximate CDF for SINR higher than 0 dB. The closed form expressions of system performance, such as average spectral efficiency (ASE) and average bit error ratio (A-BER), are derived using the CDF of the post-scheduling SINR. The optimal SINR thresholds that maximize the ASE with a target A-BER constraint are solved using the derived closed form CDF and a Lagrange multiplier. Key contributions of this paper include the derivation of the exact CDF of post-scheduling SINR by direct integration, and its application to an optimized adaptive modulation based on a Lagrange multiplier. Simulations show the correspondence between theoretical and empirical CDF's, and the performance improvement of the proposed adaptive modulation method in terms of ASE. View full abstract»

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  • Achievable Degrees of Freedom on MIMO Two-way Relay Interference Channels

    Page(s): 1472 - 1480
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (474 KB) |  | HTML iconHTML  

    In this paper, we study new network information flow called multiple-input multiple-output (MIMO) two-way relay interference channels where two links of relay systems are interfering with each other. In this system, we characterize the achievable total degrees of freedom (DOF) when all user nodes and relays have M and N antennas, respectively. We provide three different methods, namely, time-division multiple access, signal space alignment for network coding (SSANC), and a new interference neutralization (IN) scheme. In the SSA-NC scheme, one relay is selected to fully exploit the dimension of the chosen relay for network coding. For the IN, we propose a new relay transmission scheme where two relays cooperatively design the beamforming vectors so that the interference signals are neutralized at each receiver. By adopting three different relaying strategies, we show that the DOF of max {min(4N, 2M), min(2N, 2⌊4/3M⌋), min(2N - 1, 4M)} is achieved for MIMO two-way relay interference channels. View full abstract»

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  • A Practical Cooperative Multicell MIMO-OFDMA Network Based on Rank Coordination

    Page(s): 1481 - 1491
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (447 KB) |  | HTML iconHTML  

    An important challenge of wireless networks is to boost the cell edge performance and enable multi-stream transmissions to cell edge users. Interference mitigation techniques relying on multiple antennas and coordination among cells are nowadays heavily studied in the literature. Typical strategies in OFDMA networks include coordinated scheduling, beamforming and power control. In this paper, we propose a novel and practical type of coordination for OFDMA downlink networks relying on multiple antennas at the transmitter and the receiver. The transmission ranks, i.e. the number of transmitted streams, and the user scheduling in all cells are jointly optimized in order to maximize a network utility function accounting for fairness among users. A distributed coordinated scheduler motivated by an interference pricing mechanism and relying on a masterslave architecture is introduced. The proposed scheme is operated based on the user report of a recommended rank for the interfering cells accounting for the receiver interference suppression capability. It incurs a very low feedback and backhaul overhead and enables efficient link adaptation. It is moreover robust to channel measurement errors and applicable to both open-loop and closed-loop MIMO operations. A 20% cell edge performance gain over uncoordinated LTE-A system is shown through system level simulations. View full abstract»

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  • Minimum Energy Channel Codes for Nanoscale Wireless Communications

    Page(s): 1492 - 1500
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB) |  | HTML iconHTML  

    It is essential to develop energy-efficient communication techniques for nanoscale wireless communications. In this paper, a new modulation and a novel minimum energy coding scheme (MEC) are proposed to achieve energy efficiency in wireless nanosensor networks (WNSNs). Unlike existing studies, MEC maintains the desired code distance to provide reliability, while minimizing energy. It is analytically shown that, with MEC, codewords can be decoded perfectly for large code distances, if the source set cardinality is less than the inverse of the symbol error probability. Performance evaluations show that MEC outperforms popular codes such as Hamming, Reed-Solomon and Golay in the average codeword energy sense. View full abstract»

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  • Second-Order Cyclostationarity of BT-SCLD Signals: Theoretical Developments and Applications to Signal Classification and Blind Parameter Estimation

    Page(s): 1501 - 1511
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1029 KB) |  | HTML iconHTML  

    This paper investigates the second-order cyclostationarity of block transmitted-single carrier linearly digitally modulated (BT-SCLD) signals, and its applications to signal classification and blind (non-data aided) parameter estimation. Analytical closed-form expressions are derived for the cyclic autocorrelation function (CAF), cyclic spectrum (CS), complementary CAF (CCAF), complementary CS (CCS), and corresponding cycle frequencies (CFs). Furthermore, the conditions for avoiding aliasing in the cycle and spectral frequency domains are obtained. Based on these findings, we propose algorithms for classifying BTSCLD, orthogonal frequency division multiplexing (OFDM), and SCLD signals, and for the blind estimation of the BT-SCLD block transmission parameters. Simulation and laboratory experiments demonstrate the effectiveness of the proposed algorithms under low signal-to-noise ratios (SNRs), short sensing times, and various channel conditions. Furthermore, these algorithms have the advantage of not requiring the recovery of carrier, waveform, and symbol timing information, or the estimation of signal and noise powers. View full abstract»

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  • Critical Density for Connectivity in 2D and 3D Wireless Multi-Hop Networks

    Page(s): 1512 - 1523
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1603 KB) |  | HTML iconHTML  

    In this paper we investigate the critical node density required to ensure that an arbitrary node in a large-scale wireless multi-hop network is connected (via multi-hop path) to infinitely many other nodes with a positive probability. Specifically we consider a wireless multi-hop network where nodes are distributed in ℝ2 (d = 2, 3) following a homogeneous Poisson point process. The establishment of a direct connection between any two nodes is independent of connections between other pairs of nodes and its probability satisfies some intuitively reasonable conditions, viz. rotational and translational invariance, nonincreasing monotonicity, and integral boundedness. Under the above random connection model we first obtain analytically the upper and lower bounds for the critical density. Then we compare the new bounds with other existing bounds in the literature under the unit disk model and the log-normal model which are special cases of the random connection model. The comparison shows that our bounds are either close to or tighter than the known ones. To the best of our knowledge, this is the first result for the random connection model in both 2D and 3D networks. The result is of practical use for designing large-scale wireless multihop networks such as wireless sensor networks. View full abstract»

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  • ProHet: A Probabilistic Routing Protocol with Assured Delivery Rate in Wireless Heterogeneous Sensor Networks

    Page(s): 1524 - 1531
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (764 KB) |  | HTML iconHTML  

    Due to different requirements in applications, sensors with different capacities are deployed. How to design efficient, reliable and scalable routing protocols in such wireless heterogeneous sensor networks (WHSNs) with intermittent asymmetric links is a challenging task. In this paper, we propose ProHet: a distributed probabilistic routing protocol for WHSNs that utilizes asymmetric links to reach assured delivery rate with low overhead. The ProHet protocol first produces a bidirectional routing abstraction by finding a reverse path for every asymmetric link. Then, it uses a probabilistic strategy to choose forwarding nodes based on historical statistics using local information. Analysis shows that ProHet can achieve assured delivery rate ρ if ρ is set within its upper-bound. Extensive simulations are conducted to verify its efficiency. View full abstract»

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  • Binary Inference for Primary User Separation in Cognitive Radio Networks

    Page(s): 1532 - 1542
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (603 KB) |  | HTML iconHTML  

    Spectrum sensing problem, which focuses on detecting the presence of primary users (PUs) in the cognitive radio (CR) network receives much attention recently. In this paper, we introduce the PU separation problem, which concerns with the issue of distinguishing and characterizing the activities of PUs in the context of collaborative spectrum sensing and monitor selection. Observations of secondary users (SUs) are modeled as boolean OR mixtures of underlying binary PU sources. We devise a binary inference algorithm for PU separation. With binary inference, not only PU-SU relationship are revealed, but PUs' transmission statistics and activities at each time slot can also be inferred. Simulation results show that without any prior knowledge regarding PUs' activities, the algorithm achieves high inference accuracy even in the presence of noisy measurements. View full abstract»

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  • Hierarchical Competition for Downlink Power Allocation in OFDMA Femtocell Networks

    Page(s): 1543 - 1553
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (503 KB) |  | HTML iconHTML  

    This paper considers the problem of downlink power allocation in an orthogonal frequency-division multiple access (OFDMA) cellular network with macrocells underlaid with femtocells. The femto-access points (FAPs) and the macro-base stations (MBSs) in the network are assumed to compete with each other to maximize their capacity under power constraints. This competition is captured in the framework of a Stackelberg game with the MBSs as the leaders and the FAPs as the followers. The leaders are assumed to have foresight enough to consider the responses of the followers while formulating their own strategies. The Stackelberg equilibrium is introduced as the solution of the Stackelberg game, and it is shown to exist under some mild assumptions. The game is expressed as a mathematical program with equilibrium constraints (MPEC), and the best response for a one leader-multiple follower game is derived. The best response is also obtained when a quality-of-service constraint is placed on the leader. Orthogonal power allocation between leader and followers is obtained as a special case of this solution under high interference. These results are used to build algorithms to iteratively calculate the Stackelberg equilibrium, and a sufficient condition is given for its convergence. The performance of the system at a Stackelberg equilibrium is found to be much better than that at a Nash equilibrium. View full abstract»

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  • Enhanced Limited Feedback Schemes for DL MU-MIMO ZF Precoding

    Page(s): 1554 - 1561
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    This paper proposes new limited-feedback Channel State Information (CSI) calculation schemes for Zero Forcing (ZF)-precoded downlink Multi-User Multiple-Input Multiple-Output (MU-MIMO) systems. It is a common understanding that the feedback quantized by the codebook limits the performance of MU-MIMO. In this paper, through a quasi-ZF or a quasi-Minimum Mean-Squared Error (MMSE) weight, the channel matrix is transferred to one of the codebook vectors, based on which, the CSI is calculated. Thus, the quantization error is minimized. Meanwhile, the selection for the codebook vector guarantees the maximizing of the estimated Signal to Interference plus Noise Ratio (SINR). We verify that the proposed scheme obtains accurate feedback information, and the predicted weight can be the same as the optimal linear decoder as if the receiver knew all the precoder information that is fed-forward from the BS, as long as the number of antennas for each receiver equals that for the transmitter, and equals that for the total transmit data streams. Compared to the commonly used Precoding Matrix Index (PMI) based method, which uses rank-one single user (SU)-MIMO feedback, simulation results show that the proposed schemes achieve higher sum capacities in different scenarios. Moreover, since the weight can be directly used as the decoder, the feed-forward overhead is reduced. View full abstract»

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  • Co-Optimization of Communication and Motion Planning of a Robotic Operation under Resource Constraints and in Fading Environments

    Page(s): 1562 - 1572
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (614 KB) |  | HTML iconHTML  

    We consider the scenario where a robot is tasked with sending a fixed number of given bits of information to a remote station, in a limited operation time, as it travels along a pre-defined trajectory, and while minimizing its motion and communication energy costs. We propose a co-optimization framework that allows the robot to plan its motion speed, transmission rate and stop time, based on its probabilistic prediction of the channel quality along the trajectory. We show that in order to save energy, the robot should move faster (slower) and send less (more) bits at the locations that have worse (better) predicted channel qualities. We furthermore prove that if the robot must stop, it should then stop only once and at the location with the best predicted channel quality. We also prove some properties for two special scenarios: the heavy-task load and the light-task load cases. We also propose an additional stop-time online adaptation strategy to further fine tune the stop location as the robot moves along its trajectory and measures the true value of the channel. Finally, our simulation results show that our proposed framework results in a considerable performance improvement. View full abstract»

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  • A Game-Theoretic Approach to Stimulate Cooperation for Probabilistic Routing in Opportunistic Networks

    Page(s): 1573 - 1583
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB) |  | HTML iconHTML  

    Opportunistic networking is an important technique to enable users to communicate in an environment where contemporaneous end-to-end paths are unavailable or unstable. To support end-to-end messaging in opportunistic networks, a number of probabilistic routing protocols have been proposed. However, when nodes are selfish, they may not have incentives to participate in probabilistic routing, and the system performance will degrade significantly. In this paper, we present novel incentive schemes for probabilistic routing that stimulates selfish nodes to participate. We not only rigorously prove the properties of our schemes, but also extensively evaluate our schemes using GloMoSim. Evaluation results show that there is an up to 75.8% gain in delivery ratio compared with a probabilistic routing protocol providing no incentive. View full abstract»

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  • Proportional Fair Scheduling in Hierarchical Modulation Aided Wireless Networks

    Page(s): 1584 - 1593
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    Theoretically, superposition coding (SPC) can achieve the capacity of a degraded Gaussian broadcast channel. A practical implementation of SPC, hierarchical modulation (HM), has recently been adopted in industry. Using HM, how to explore the multi-user diversity gain in a time-varying wireless environment to maximize throughput and maintain fairness is an open issue. Using greedy opportunistic scheduling algorithms will lead to a severe starvation problem. In this paper, we study the proportional fair scheduling (PFS) problem in an HM aided wireless network, jointly considering the user selection and utility maximization problems. Shannon capacity based and practical HM based optimal scheduling problems are formulated. An optimal algorithm and a low complexity suboptimal algorithm are proposed to solve the practical scheduling problem combining the opportunistic PFS and HM. Simulation results demonstrate that the proposed algorithms can achieve 50% to 100% throughput gain compared to the single-user opportunistic PFS solution depending on the number of users and have better fairness performance than the existing single-user and HM-based solutions. View full abstract»

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  • On the Optimal Switching Probability for a Hybrid Cognitive Radio System

    Page(s): 1594 - 1605
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    Cognitive radio (CR) systems are typically classified into two types. In overlay CR, a secondary user opportunistically accesses primary user's spectrum when it is unused, while a secondary user in underlay CR accesses the spectrum at any time as long as the interference power received at a primary user is below a certain level. This paper investigates a hybrid CR system where a secondary user probabilistically changes its spectrum access mode for secondary user's throughput maximization while guaranteeing primary user's target throughput. Basically, the hybrid CR works like overlay CR. The secondary user constantly monitors activity of the primary user and transmits data with maximum transmit power if transmission of the primary user is not detected. However, the only difference from overlay CR is that even when transmission of the primary user is detected, the secondary users are able to access the spectrum with regulated low transmit power with switching rate c. We show that there is a trade-off of increasing c due to recursive interactions between primary and secondary users, and optimizing c is crucial to balance the gain and loss of secondary user's underlay spectrum access. The proposed hybrid CR is shown to achieve higher throughput and be more robust to detection errors than conventional CR systems. View full abstract»

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  • Ultra-Wideband TOA Estimation in the Presence of Clock Frequency Offset

    Page(s): 1606 - 1616
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (881 KB) |  | HTML iconHTML  

    The paper is concerned with the impact of clock frequency offsets on the accuracy of ranging systems based on time of arrival (TOA) measurements. It is shown that large TOA errors are incurred if the transmitter and receiver clocks are mistuned by more than just one part per million (ppm). This represents a serious obstacle to the use of commercial low-cost quartz oscillators, as they exhibit frequency drifts in the range of ±10 ppm and more. A solution is to estimate first the transmitter clock frequency relative to the receiver's and then compensate for the difference by acting on the receiver clock tuning. An algorithm is proposed that estimates the transmitter clock frequency with an accuracy better than 0.1 ppm. Computer simulations indicate that its use in ranging systems makes TOA measurements as good as those obtained with perfectly synchronous clocks. View full abstract»

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  • Iterative D.C. Optimization of Precoding in Wireless MIMO Relaying

    Page(s): 1617 - 1627
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (615 KB) |  | HTML iconHTML  

    Optimizations of precoding matrices in precode-and-forward (PF) MIMO relaying are nonconvex programs in precoding matrix variables. The semidefinite relaxation (SDR) technique, which relaxes the concerned nonconvex quadratic constraints by (convex) semi-definite ones, can locate the optimal solutions, provided that the numbers of relaying antennas and users are very small. The computational complexity of the SDR grows explosively even with a very moderate increase in the numbers of relaying antennas and/or users, making the existing semidefinite programming (SDP) solvers incapable. In this paper, much more efficient problem formulations of precoding matrix design that exploit the spectral matrix optimization are developed. Such formulations have a low dimensionality and are computationally-tractable nonconvex matrix programs. Furthermore, by exploiting their partial convex structures in the d.c. (difference of two convex functions) framework, new effective iterative solutions are obtained. Extensive simulation results are presented to support the computational advantage of the proposed approach and show that the proposed approach can effectively handle all three considered optimization problems of precoding matrices in MIMO PF relaying, while the SDR approach either is computationally impractical or fails. View full abstract»

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  • Delay-Constrained Random Access Transport Capacity

    Page(s): 1628 - 1639
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (650 KB) |  | HTML iconHTML  

    In this paper, we consider delay-constrained wireless multi-hop ad hoc networks where a packet should be delivered to the destination within the maximum allowed delay while satisfying the target outage probability. The proposed performance metric for analyzing networks is the delay-constrained random access transport capacity (D-RATC), which quantifies the maximum end-to-end (e2e) link achievable rate per unit area of a delay-constrained network using a random access protocol. The scaling of the D-RATC is obtained for various slotted ALOHA (SA) protocols and it is shown that the SA protocol is order-optimal for delay-constrained random networks when interference control is used with an additional feature such as rate control or admission control. If interference control is not used, the SA protocol suffers from the negatively infinite scaling exponent except the case of using rate control where a finite but suboptimal scaling exponent may be achieved. Also, it is shown that multi-hop control does not affect the scaling exponent but just improves the D-RATC pre-constant. View full abstract»

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  • EMBA: An Efficient Multihop Broadcast Protocol for Asynchronous Duty-Cycled Wireless Sensor Networks

    Page(s): 1640 - 1650
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (551 KB) |  | HTML iconHTML  

    In this paper, we propose an efficient multihop broadcast protocol for asynchronous duty-cycled wireless sensor networks (EMBA) where each node independently wakes up according to its own schedule. EMBA adopts two techniques of the forwarder's guidance and the overhearing of broadcast messages and ACKs. A node transmits broadcast messages with guidance to neighbor nodes. The guidance presents how the node forwards the broadcast message to neighbor nodes by using unicast transmissions. This technique significantly reduces redundant transmissions and collisions. The overhearing of broadcast messages and ACKs helps to reduce the number of transmissions, thus it minimizes the active time of nodes. We implement EMBA and conventional protocols of ADB and RIMAC broadcast in ns-2 simulator to compare their performance. The simulation results show that EMBA outperforms ADB and RI-MAC broadcast in both sparse and dense networks. EMBA achieves lower message cost than the conventional protocols and significantly improves the energy efficiency in terms of both duty cycle and energy consumption. View full abstract»

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  • Joint Base Station Association and Power Control via Benders' Decomposition

    Page(s): 1651 - 1665
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (489 KB) |  | HTML iconHTML  

    Heterogeneous cellular network (Hetnets), where various classes of low power base stations (BS) are underlaid in a macro-cellular network, is a promising technique for future green communications. These new types of BSs can achieve substantial improvement in spectrum-efficiency and energy-efficiency via cell splitting. However, mobile stations perceive different channel gains to different base stations. Therefore, it is important to associate a mobile station with the right BS so as to achieve a good communication quality. Oftentimes, the already-challenging BS association problem is further complicated by the need of transmission power control, which is an essential component to manage co-channel interference in many wireless communications systems. Despite its importance, the joint BS association and power control (JBAPC) problem has remained largely unsolved, mainly due to its non-convex and combinatorial nature that makes the global optimal solution difficult to obtain. This paper aims to circumvent this difficulty by proposing a novel algorithm based on Benders' Decomposition to solve the non-convex JBAPC problem efficiently and optimally. In particular, we endeavor to maximize the system revenue and meanwhile associate every served mobile station with the right BS with the minimum total transmission power. We first propose a single-stage formulation that captures the two objectives simultaneously. The problem is then transformed in a way that can be efficiently solved using the proposed joint BS Association and poweR coNtrol algorithm (referred to as BARN) that is derived from classical Benders' Decomposition. Finally, we derive a closed-form analytical formula to characterize the effect of the termination criterion of the algorithm on the gap between the obtained solution and the optimal one. For practical implementation, we further propose an Accelerated BARN (A-BARN) algorithm that can significantly reduce the computational time. By carefully choosing th- termination criterion, both BARN and A-BARN are guaranteed to converge to the global optimal solution. View full abstract»

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  • Load-Aware Modeling and Analysis of Heterogeneous Cellular Networks

    Page(s): 1666 - 1677
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1242 KB) |  | HTML iconHTML  

    Random spatial models are attractive for modeling heterogeneous cellular networks (HCNs) due to their realism, tractability, and scalability. A major limitation of such models to date in the context of HCNs is the neglect of network traffic and load: all base stations (BSs) have typically been assumed to always be transmitting. Small cells in particular will have a lighter load than macrocells, and so their contribution to the network interference may be significantly overstated in a fully loaded model. This paper incorporates a flexible notion of BS load by introducing a new idea of conditionally thinning the interference field. For a K-tier HCN where BSs across tiers differ in terms of transmit power, supported data rate, deployment density, and now load, we derive the coverage probability for a typical mobile, which connects to the strongest BS signal. Conditioned on this connection, the interfering BSs of the ith tier are assumed to transmit independently with probability p%, which models the load. Assuming - reasonably - that smaller cells are more lightly loaded than macrocells, the analysis shows that adding such access points to the network always increases the coverage probability. We also observe that fully loaded models are quite pessimistic in terms of coverage. View full abstract»

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  • Unified SER Performance Analysis and Improvement for Multiuser MIMO Downlink with Correlation Rotation Linear Precoding

    Page(s): 1678 - 1685
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1877 KB) |  | HTML iconHTML  

    In multiuser multiple-input multiple-output (MIMO) downlink communications, system performance suffers from multiuser interference (MUI). Contrary to common practice where MUI is suppressed, correlation rotation (CR) linear precoding makes MUI constructive via rotating the angle of correlation between transmitted symbols. With the derived closed-form instantaneous SINR expression, we analyze the unified SER performance for CR precoding, and identify the channel condition under which the MUI exploitation via CR precoding will fail and consequently lead to the unified SER performance degradation. To solve the problem, two power allocation schemes that are subject to power constraint are proposed: one is iterative scheme that directly minimizes the unified SER, and the other has a closed-form solution that maximizes the minimum user SINR. The asymptotic behavior and computational complexity of the proposed schemes are analyzed. Numerical and simulation results show that both schemes can avoid the degradation of unified SER performance and furthermore offer performance gains. Moreover, the closed-form solution with much lower complexity can provide a comparable performance to that of the iterative scheme. View full abstract»

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The IEEE Transactions on Wireless Communications publishes high-quality manuscripts on advances in the state-of-the-art of wireless communications.

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Editor-in-Chief
Jeff Andrews
Cullen Trust for Higher Education Endowed Professor of Engineering