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Communications Letters, IEEE

Issue 4 • Date April 2008

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Displaying Results 1 - 25 of 39
  • Table of contents

    Publication Year: 2008
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    Freely Available from IEEE
  • Information-guided channel-hopping for high data rate wireless communication

    Publication Year: 2008 , Page(s): 225 - 227
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB) |  | HTML iconHTML  

    In this letter, we introduce information-guided channel-hopping, a new scheme for high data rate communication over Rayleigh fading channel using multiple transmit antennas. This scheme is proposed based on the fact that the independence character of multi-channel can be used as an additional information transmitting channel, and the maximum likelihood decoding can be achieved in a simple way by decoupling of the signals conveyed by different methods. The analysis results prove that the capacity behavior of this scheme is better than that of the space-time block coding for more than two transmit antennas. View full abstract»

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  • Adaptive path selective fuzzy decorrelating detector under impulsive noise for multipath fading CDMA systems

    Publication Year: 2008 , Page(s): 228 - 230
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    This letter proposes a novel adaptive path selective fuzzy decorrelating (APSFD) detector for direct-sequence code- division multiple-access (DS-CDMA), systems with time-varying multipath fading channels under impulsive noise. The proposed detector combines adaptive path selective decorrelating (APSD) detector with a fuzzy median filter which is based on fuzzy rank ordering of samples to eliminate the effect of impulsive noise. Simulation results clearly show that the proposed detector eliminates the effect of impulsive noise and improves the performance of APSD detector under high impulsive noise. View full abstract»

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  • Corrections to, and comments on, "an improved approximation for the Gaussian Q-Function"

    Publication Year: 2008 , Page(s): 231
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (102 KB) |  | HTML iconHTML  

    In a recent letter, Karagiannidis and Lioumpas (see ibid., vol.11, no.8, p.644-6, Aug. 2007) proposed a new approximation for the Gaussian Q-function. We provide corrections to two equations, corrected entries to a table, and an alternative to a figure in the letter, as well as a few comments. View full abstract»

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  • On determining cluster size of randomly deployed heterogeneous WSNs

    Publication Year: 2008 , Page(s): 232 - 234
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (149 KB) |  | HTML iconHTML  

    Clustering is an efficient method to solve scalability problems and energy consumption challenges. For this reason it is widely exploited in Wireless Sensor Network (WSN) applications. It is very critical to determine the number of required clusterheads and thus the overall cost of WSNs while satisfying the desired level of coverage. Our objective is to study cluster size, i.e., how much a clusterhead together with sensors can cover a region when all the devices in a WSN are deployed randomly. Therefore, it is possible to compute the required number of nodes of each type for given network parameters. View full abstract»

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  • Amplify-and-forward with partial relay selection

    Publication Year: 2008 , Page(s): 235 - 237
    Cited by:  Papers (110)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    This letter offers a statistical analysis of the basic two-hop Amplify-and-Forward link, where the relay node is selected based on instantaneous and partial knowledge of the channel. In contrast with previously reported work, where relay selection requires global knowledge (2 hops) of the relaying link, the problem considered is interesting in practical ad-hoc systems, where only neighboring (1 hop) channel information is available to the nodes. The probability density function of the received signal-to-noise ratio for the considered relaying link is approximated in closed form, and an asymptotic exponential expression is proposed to simplify performance estimation. View full abstract»

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  • Performance analysis of IEEE 802.15.4 non-beacon mode with the unslotted CSMA/CA

    Publication Year: 2008 , Page(s): 238 - 240
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    We provide a simple mathematical model of IEEE 802.15.4 unslotted CSMA/CA by busy cycle of M/G/l queueing system to obtain several performance measures. Our performance measures can be used for determining the optimal number of devices while supporting the required QoS constraints on the average packet delay and the packet loss probability, and also for calculating battery lifetime. View full abstract»

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  • Adaptive delay threshold-based priority queuing scheme with opportunistic packet scheduling for integrated service in mobile broadband wireless access systems

    Publication Year: 2008 , Page(s): 241 - 243
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    In this letter, we propose a novel method of implementing an opportunistic priority queuing scheme that supports both latency-sensitive real-time (RT) and best-effort non-realtime (NRT) service classes in mobile broadband wireless (MBWA) systems. It employs an adaptive delay threshold as a dynamic reference of prioritizing the urgent RT service users over others, which allows for fully leveraging the multiuser diversity gain of NRT service users under the varying system conditions. It is shown that the overall system capacity can be further increased by the proposed adaptation rule, as compared with the existing opportunistic priority queuing scheme with the fixed delay threshold. View full abstract»

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  • Ricean parameter estimation using phase information in low SNR environments

    Publication Year: 2008 , Page(s): 244 - 246
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (133 KB) |  | HTML iconHTML  

    A new Ricean parameter estimator is considered in the context of wireless communications. In comparison to existing methods, the proposed estimator is especially useful in low signal-to-noise environments. It is less reliant on knowledge of the transmitted signal frequency than existing methods, and it performs well in communications environments where the frequency is varying in time. View full abstract»

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  • An enhanced packet scheduling algorithm combined with HARQ for HSDPA system

    Publication Year: 2008 , Page(s): 247 - 249
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (149 KB) |  | HTML iconHTML  

    High speed downlink packet access (HSDPA) is a packet-based data service that supports downlink data rates of up to 14 Mbps in the WCDMA (wideband code division multiple access) system. In HSDPA, the packet scheduler is a key element for high-speed and efficient transmissions. In addition, hybrid automatic request (HARQ) plays a significant role in improving system performance. We propose an enhanced scheduling algorithm combined with HARQ to reduce transfer delay without the degradation of system throughput. View full abstract»

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  • Distributed resource allocation for rate-constrained users in multi-cell OFDMA networks

    Publication Year: 2008 , Page(s): 250 - 252
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (142 KB) |  | HTML iconHTML  

    This letter addresses resource allocation in multi-cell OFDMA networks. It describes a heuristic for distributed sum power minimization under target data rate requirements. The proposed method establishes a set of target SINR per user and subcarrier, determined to reach the target data rate of each user, while avoiding power divergence situations. Power control can then be performed independently over each subcarrier. Compared to iterative water-filling, this method proves to be very efficient at any load in terms of resource consumption and users' rejection. View full abstract»

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  • Fixed power allocation with nulling for TDD-based cellular uplink

    Publication Year: 2008 , Page(s): 253 - 255
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (119 KB) |  | HTML iconHTML  

    We propose two fixed power allocation schemes with nulling (FPA-N1 and FPA-N2) for time division duplex (TDD) based cellular uplink according to the location of mobile stations (MSs). In the FPA-N1 scheme, MSs located near a base station (BS) do not transmit data when the wireless channels between the MSs and their home cell BS experience deep fading. In the FPA-N2 scheme, MSs located near cell boundaries do not transmit data when the wireless channels between the MSs and neighboring cell BSs cause high interference channel gain because, in this case, their data transmission may induce large interference to neighboring cells. Numerical results show that the proposed power allocation scheme improves the uplink capacity in cellular networks. View full abstract»

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  • Optimizing uplink TCP-ACK transmission in WiMAZ OFDMA systems

    Publication Year: 2008 , Page(s): 256 - 258
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB) |  | HTML iconHTML  

    In WiMAX networks, a bandwidth request-grant process is required for uplink operation. However, the process is not optimized for TCP, since the uplink ACK stream is disrupted due to the following: (a) The process consists of several stages which in turn introduce big transmission delay; and (b) it requires additional uplink bandwidth which is significant compared to the ACK packet size. In this paper, the authors propose a new ACK transmission scheme, where ACK packets are combined with a bandwidth request (BR) header. Through simulation, it is demonstrated that the proposed scheme reduces the overheads of TCP-ACK transmissions effectively. View full abstract»

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  • Closed-form error analysis of the non-identical Nakagami-m relay fading channel

    Publication Year: 2008 , Page(s): 259 - 261
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    We present closed-form expressions for the average bit error probability (ABEP) of BPSK, QPSK and M-QAM of an amplify-and-forward average power scaling dual-hop relay transmission, over non-identical Nakagami-m fading channels, with integer values of m. Additionally, we evaluate in closed-form the ABEP under sufficiently large signal-to-noise ratio for the source-relay link, valid for arbitrary rn. Numerical and simulation results show the validity of the proposed mathematical analysis and point out the effect of the two hops unbalanced fading conditions on the error performance. View full abstract»

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  • Implementing TCP flow-level fairness using 802.11e in a multi-radio mesh testbed

    Publication Year: 2008 , Page(s): 262 - 264
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    TCP is known to be subject to poor performance in multi-hop mesh networks. While most work has focused on interference and related issues, we note that cross-layer interactions can also induce considerable unfairness. In this paper, we propose a simple 802.lie scheme to mitigate these interactions and regulate TCP fairness in a flexible manner. The practical effectiveness of the approach is confirmed in a multi- hop, multi-radio testbed. View full abstract»

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  • Optimal time-division for bidirectional relaying using superposition encoding

    Publication Year: 2008 , Page(s): 265 - 267
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (110 KB) |  | HTML iconHTML  

    Bidirectional wireless communication between two nodes is enabled by a half-duplex relay node using a two-phase decode-and-forward protocol. In the first phase, the messages of two nodes are transmitted to the relay node, which broadcasts a superposition of the re-encoded messages in the succeeding phase. Individual mean transmit power constraints averaged over both phases are considered so that they are inversely proportional to the time division between the phase. An equivalent characterization of the achievable rate region with optimal time division is presented. Moreover, it is proved that the rate region is convex, which makes efficient algorithmic optimization solutions feasible. View full abstract»

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  • Peak-to-average power ratio and power efficiency considerations in MIMO-OFDM systems

    Publication Year: 2008 , Page(s): 268 - 270
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (149 KB) |  | HTML iconHTML  

    Peak-to-average power ratio (PAR) reduction is a powerful tool that can increase power efficiency and reduce distortion noise in MIMO-OFDM systems. Various PAR metrics have been used in the MIMO-OFDM literature without justifications regarding the physical mechanisms that support those PAR definitions. In this paper, we show that in order to deliver high power efficiency, two MIMO-OFDM linear-scaling schemes are possible: one that scales all MIMO branches with the same factor and another that uses a different scaling factor for each branch. For each system, we derive a meaningful PAR metric that should be used. View full abstract»

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  • Randomized cyclic delay code for cooperative communication systems

    Publication Year: 2008 , Page(s): 271 - 273
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (202 KB) |  | HTML iconHTML  

    We deal here with distributed cooperative communication systems in which a single source transmits its information with the help of multiple relays to a destination. Specifically, we consider decode and forward relay networks based on orthogonal frequency division multiplexing (OFDM). Most previous work needs a priori information for antenna allocation to obtain cooperative diversity advantages. We propose a simple method that does not require additional information in order to coordinate relay transmission. Our main proposal is to retransmit randomly cyclic-shifted sequences of the received symbol at relays. Simulation results verify that full gain in diversity is achieved when the number of subcarriers is sufficiently large. View full abstract»

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  • Scheduler for IEEE 802.16 networks

    Publication Year: 2008 , Page(s): 274 - 276
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB) |  | HTML iconHTML  

    The IEEE 802.16 standard was designed to support real-time and bandwidth demanding applications with quality of service (QoS). Although the standard defines a QoS signaling framework and five service levels, scheduling disciplines for these service levels are unspecified. In this paper, we propose a scheduling scheme for the uplink traffic which is fully standard-compliant and can be easily implemented in the base station. Simulation results show that this scheme is able to meet the QoS requirements of the service flows. View full abstract»

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  • Multi-cell uplink-downlink beamforming throughput duality based on Lagrangian duality with per-base station power constraints

    Publication Year: 2008 , Page(s): 277 - 279
    Cited by:  Papers (14)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (90 KB) |  | HTML iconHTML  

    Despite significant research efforts in beamforming, the maximum achievable downlink throughput with beamforming in a multi-cell environment is not available due to difficulty in finding optimal downlink beamforming. Thus, to reformulate the problem into a more solvable form, we derive dual uplink throughput optimization problem to multi-cell downlink beam- forming throughput maximization with per-base station (BS) power constraints based on Lagrangian duality. The optimal downlink beamforming is shown to be a minimum mean squared error (MMSE) beamforming in the dual uplink. It is also shown that the dual uplink problem achieves the same optimal throughput as the primal downlink problem. View full abstract»

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  • Outage probability analysis of a MIMO relay channel with orthogonal space-time block codes

    Publication Year: 2008 , Page(s): 280 - 282
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (110 KB) |  | HTML iconHTML  

    We investigate the performance of a cooperative multiple-input multiple-output (MIMO) relay channel in which the source and relay use the same orthogonal space-time block code (OSTBC) for transmission whereas the relay and destination use maximum-ratio-combining (MRC) for reception. Considering that perfect channel state information is available at the relay and destination, we derive a closed-form expression for the outage probability of the destination signal-to-noise ratio (SNR) in terms of the confluent hypergeometric function of two variables in a Rayleigh flat-fading environment. The validity of the closed-form expression is confirmed with the numerical results. View full abstract»

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  • Performance comparison of OFDM bandwidth request schemes in fixed IEEE 802.16 networks

    Publication Year: 2008 , Page(s): 283 - 285
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB) |  | HTML iconHTML  

    IEEE 802.16 standard specifies two contention based bandwidth request schemes working with OFDM physical layer specification in point-to-multipoint (PMP) architecture, the mandatory one used in region-full and the optional one used in region-focused. This letter presents a unified analytical model to study the bandwidth efficiency and channel access delay performance of the two schemes. The impacts of access parameters, available bandwidth and subchannelization have been taken into account. The model is validated by simulations. The mandatory scheme is observed to perform closely to the optional one when subchannelization is active for both schemes. View full abstract»

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  • Distributed utility-maximization using a resource pricing power control in uplink DS-CDMA

    Publication Year: 2008 , Page(s): 286 - 288
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (103 KB) |  | HTML iconHTML  

    This letter considers a distributed utility maximization power control scheme in uplink DS-CDMA systems. Maximizing a utility function is solved by Lagrangian dual decomposition, where the Lagrangian multiplier can be considered as a resource price charging to users. By adjusting the price in a distributed fashion, the proposed algorithm results in a bang- bang type power control, 'maximum power transmission' or 'shutdown'. Numerical result shows that the proposed algorithm achieves around 95% of the optimal utility maximization with a modest computational burden. View full abstract»

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  • Delay constrained optimal resource utilization of wireless networks for distributed control systems

    Publication Year: 2008 , Page(s): 289 - 291
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (183 KB) |  | HTML iconHTML  

    An optimal resource utilization framework to analyze the impact of end-to-end delay thresholds on the wireless network throughput is developed. In contrast to conventional networks where lumped transmission and queuing delays are used to model the end-to-end delay, the proposed framework models these delay components separately to analyze their relative contribution to the end-to-end delay when stringent delay thresholds are used. A 'log' utility maximization problem is formulated and its distributed implementation using dual decomposition is proposed. Our optimization results show that decreasing the delay threshold leads to larger contribution from the transmission delay to the end-to-end delay. View full abstract»

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  • An efficient decoding algorithm for QO-STBCs based on iterative interference cancellation

    Publication Year: 2008 , Page(s): 292 - 294
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB) |  | HTML iconHTML  

    We propose an efficient decoding algorithm targeted for quasi-orthogonal space-time block codes which can be viewed as an iterative extension of the parallel detection algorithm using iterative interference cancellation. The essence of the algorithm is in the realization of the fact that the number of candidate symbols at the end of each interference cancellation iteration reduces very quickly, and that no more than two iterations are required. View full abstract»

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Editor-in-Chief
George K. Karagiannidis
Aristotle University of Thessaloniki
Greece