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Wireless Communications, IEEE Transactions on

Issue 12  Part 2 • Date December 2008

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Displaying Results 1 - 25 of 47
  • IEEE Transactions on Wireless Communications - Part 2 front cover

    Page(s): c1 - c3
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    Freely Available from IEEE
  • Beamforming with limited feedback in amplify-and-forward cooperative networks - [transactions letters]

    Page(s): 5145 - 5149
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (225 KB) |  | HTML iconHTML  

    A relay selection approach has previously been shown to outperform repetition-based scheduling for both amplify-and-forward (AF) and decode-and-forward (DF) cooperative networks. The selection method generally requires some feedback from the destination to the relays and the source, raising the issue of the interplay between performance and feedback rate. In this letter, we treat selection as an instance of limited feedback distributed beamforming in cooperative AF networks, and highlight the differences between transmit beamforming in a traditional multi-input single-output (MISO) system and the distributed case. Specifically, Grassmannian line packing (GLP) is no longer the optimal codebook design, and orthogonal codebooks are no longer equivalent to each other. We derive the high signal-to-noise ratio expressions for outage probability and probability of symbol error for unlimited-feedback and selection schemes, which are then used for performance comparisons. The selection protocol is compared to a limited-feedback distributed beamformer that assigns codebooks based on the Generalized Lloyd algorithm (GLA), and one that uses random beam-vectors. The main conclusion is that the performance improvement to be seen using the very complex GLA is small, and that many more feedback bits are required with random beamforming than selection for the same performance. These results indicate that the selection protocol is a very attractive protocol, with low complexity, that provides excellent performance relative to other known methods. View full abstract»

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  • A game theoretic analysis of service competition and pricing in heterogeneous wireless access networks

    Page(s): 5150 - 5155
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (319 KB) |  | HTML iconHTML  

    Next generation wireless systems will provide highspeed wireless connectivity and seamless mobility through the provisioning of heterogeneous wireless access. In such a heterogeneous wireless access environment, mobile users will be able to connect to multiple wireless networks (e.g., IEEE 802.16, cellular, and IEEE 802.11-based networks) operated by different service providers, simultaneously. We address the problem of competitive pricing in such a heterogeneous wireless access network. Each of the wireless access networks is assumed to support two types of connections, namely, premium and best-effort connections. For the premium connections, the price is fixed, while for the best effort connections it is dynamic and depends on the competitive or cooperative behavior of the service providers. A competitive pricing model for best-effort connections is developed based on a noncooperative game formulation. We first consider the case where the prices are offered to the users at the same time (i.e., a simultaneous-play game). Nash equilibrium is considered as the solution of this game. Afterwards, we consider the case where a service provider can offer its price before other providers. This is referred to as a leader-follower game for which Stackelberg equilibrium is considered as the solution. We also consider a cooperative pricing model which maximizes the total revenue of the service providers. A method for revenue sharing is presented for this cooperative pricing model. Numerical studies are carried out to evaluate the performances of the different pricing models. View full abstract»

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  • Adaptive rake combining in the soft handover region

    Page(s): 5156 - 5160
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB) |  | HTML iconHTML  

    We propose and analyze new finger assignment schemes which are applicable for RAKE reception in the soft handover region. These schemes rely on variants of the conventional generalized selection combining (GSC) and the minimum selection GSC schemes in order to choose an acceptable base station and its corresponding paths. Relying on some recently derived results on order statistics, we investigate the average error rate performance as well as the average number of estimated and combined paths of the proposed schemes over independent and identically distributed Rayleigh fading channels. The mathematical formalism is illustrated with few selected numerical results that show the tradeoff between performance and processing power consumption. View full abstract»

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  • The IEEE 802.16 mesh mode coordinated distributed scheduling can be collision free

    Page(s): 5161 - 5165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    The IEEE 802.16 mesh mode coordinated distributed scheduling has been expected to be collision free so that only one node can transmit at any transfer opportunity (TO) in the two-hop neighborhood. We will show in this paper that this collision free property is not unconditional. Assuming the common interference modeling, necessary and sufficient conditions under which the IEEE 802.16 mesh mode coordinated distributed scheduling can be collision free are identified. As the IEEE 802.16 standard defines only a framework for the mesh mode coordinated distributed scheduling, our study could provide a suggestion on how to guarantee the correct functionality. View full abstract»

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  • Performance analysis of a cross-layer handoff ordering scheme in wireless networks

    Page(s): 5166 - 5171
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (275 KB) |  | HTML iconHTML  

    In this paper we propose a cross-layer handoff ordering scheme. The frame success rate (FSR) is adopted as the basis of prioritization. Different quality of service (QoS) requirements of various applications would result in different FSR requirements. In order to indicate how critical a handoff request is, both the FSR requirement from the application layer and the FSR measurement from the medium access control layer are taken into consideration in the proposed scheme. The prioritization of handoff requests follows the most-critical-first policy. Performance analysis shows that the proposed scheme effectively reduces the forced termination probabilities. Under the same forced termination probability requirements, it could provide 1.95% to 11.13% more arrival calls compared to previous works. View full abstract»

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  • Packet-wise vertical handover for unlicensed multi-standard spectrum access with cognitive radios

    Page(s): 5172 - 5176
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    In this letter, packet-by-packet vertical handover is investigated as a means to improve the performance of unlicensed spectrum access. The analysis focuses on the optimization of a channel access strategy for a cognitive multi-standard radio node that has the capability to switch between two orthogonal uplink radio interfaces, based on long-term channel state information. The radio interfaces differ for coverage and quality of service (QoS) requirements of primary users. The proposed strategy prescribes a cross-layer selection of physical-layer (transmitting powers) and medium access control layer (handover probability) parameters and is designed to maximize secondary throughput while guaranteeing the primary QoS constraints. Analysis and numerical results bring insight into the impact of network topology, measurement errors and primary QoS constraints on the optimal system design and corresponding performance. View full abstract»

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  • Peak restoration in ofdm receiver with clipping a/d converter

    Page(s): 5177 - 5181
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    OFDM signals suffer from a large Peak to Average Power Ratio, which requires large power back-offs in the transmit and receive chains. This paper studies two digital postprocessing methods of different complexity that mitigate clipping by the analog-to-digital converter in the receiver. Clipped peaks cause spurious signals on empty subcarriers, which can be used to eliminate clipping artifacts and to recover the original signal. Simulations show that a significant reduction of 3 dB in the headroom of the A/D converter (ADC) is possible, when an elaborate MMSE clip correction algorithm is used. A simple algorithm still allows for 1 dB reduction of the headroom. As the ADC is consuming an ever increasing fraction of the total receiver power, the results are believed to be relevant for low-power design of OFDM receivers, for instance to prolong battery life during digital television reception on mobile phones. View full abstract»

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  • On capacity-optimal precoding for multiple antenna systems subject to EIRP restrictions

    Page(s): 5182 - 5187
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (223 KB) |  | HTML iconHTML  

    Ultra wideband transceivers promise multi-gigabit per second performance at power consumptions commensurate with portable devices. Future products are likely to adopt multiple antennas to maximize performance. Severe FCC EIRP restrictions impose an interesting system design constraint. In this paper, capacity optimal multiple antenna transmission schemes are investigated for EIRP restricted systems under the assumption that the channel is known at the transmitter. It is shown that per subcarrier antenna power allocation, which reduces to antenna selection at low SNR or when using one receive antenna, is optimal for some transmitter configurations. The improvements in capacity are quantified for representative channels. View full abstract»

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  • Bursty transmission and glue pouring: on wireless channels with overhead costs

    Page(s): 5188 - 5194
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (246 KB) |  | HTML iconHTML  

    Power efficiency is a capital issue in the study of mobile wireless nodes owing to constraints on their battery size and weight. In practice, especially for low-power nodes, it is often the case that the power consumed for non-transmission processes is not always negligible. In this paper, we consider the channels with a special form of overhead: a processing energy cost whenever a non-zero signal is transmitted. We show that under certain conditions, achieving the capacity of such channels requires intermittent, or `bursty', transmissions. Thus, an optimal sleeping schedule can be specified for wireless nodes to achieve the optimal power efficiency. We show that in the low SNR regime, there is a simple relation between the optimal burstiness and the overhead cost: one should use a fraction of the available degrees of freedom at an SNR level of radic2epsiv, where epsiv is the normalized overhead energy cost. We extend this result to use bursty Gaussian transmissions in multiple parallel channels with different noise levels. Our result can be intuitively interpreted as a 'glue pouring' process, generalizing the wellknown water pouring solution. We then use this approach to compute the achievable rate region of the multiple access channel with overhead cost. View full abstract»

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  • Optimal modulation and coding scheme selection in cellular networks with hybrid-ARQ error control

    Page(s): 5195 - 5201
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB) |  | HTML iconHTML  

    We propose an optimal modulation and coding scheme (MCS) selection criterion for maximizing user throughput in cellular networks. The proposed criterion adopts both the Chase combining and incremental redundancy based hybrid automatic repeat request (HARQ) mechanisms and it selects an MCS level that maximizes the expected throughput which is estimated by considering both the number of transmissions and successful decoding probability in HARQ operation. We also prove that the conventional MCS selection rule is not optimized with mathematical analysis. Through link-level and system-level simulations, we show that the proposed MCS selection criterion yields higher average cell throughput than the conventional MCS selection schemes for slowly varying channels. View full abstract»

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  • On appropriate models for characterizing hyper-rayleigh fading

    Page(s): 5202 - 5207
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (575 KB) |  | HTML iconHTML  

    Recent work presented empirical data for which the small-scale fading statistics were more severe than Rayleigh; a phenomena deemed hyper-Rayleigh fading. This paper considers whether commonly utilized small-scale propagation models can be appropriately adapted to represent this class of fading. The work argues that the most meaningful model for the hyper- Rayleigh regime is based on a physical wave model (as opposed to stochastic); in particular, the TWDP model, where Deltaap1, holds the greatest promise. The crux of the argument is that the stochastic models significantly over-predict the amount of constructive interference in comparison to what is physically realizable. View full abstract»

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  • Delay-Sum Antenna Array Reception for Transmitted-Reference Impulse Radio (TR-IR) Systems

    Page(s): 5208 - 5213
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (235 KB) |  | HTML iconHTML  

    For transmitted-reference impulse radio (TR-IR), the conventional antenna array reception will provide array gain and thus improve system bit-error-rate (BER) performance. In this paper, we propose a delay-sum antenna array autocorrelation receiver for the TR-IR systems. Simulation results show that by exploiting spatial correlations between antenna array elements, an extra system performance improvement of 1.3 dB and 2.1 dB can be achieved by the proposed receiver at BER=10-5 for the antenna array with 2 and 4 elements, respectively, in the proposed ultra-wideband channel model. View full abstract»

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  • Adaptive generalized selection combining (A-GSC) receivers

    Page(s): 5214 - 5219
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (445 KB) |  | HTML iconHTML  

    We introduce an adaptive generalized selection combining (A-GSC) receiver that can be efficiently applied in diversity rich fading environments such as in ultra-wideband applications. The branches that participate in the combining process are selected taking into account the quality of both the total combining output signal-to-noise ratio (SNR) and the individual SNR of each branch. The proposed scheme achieves better adaptation to channel conditions compared to other competing schemes such as normalized threshold GSC (NT-GSC), minimum selection GSC (MS-GSC) or minimum estimation and combining GSC (MEC-GSC), with no further complexity. The A-GSC receiver compromises between the power consumption, hardware complexity and performance gain that each additional diversity branch induces, resulting in significant savings in power and computational resources. View full abstract»

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  • Integer frequency offset recovery in OFDM transmissions over selective channels

    Page(s): 5220 - 5226
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    Carrier frequency offset (CFO) in OFDM systems is normally estimated in two steps. The fractional part of the CFO is recovered first and the remaining ambiguity is subsequently resolved by detecting the integer frequency offset (IFO). Conventional IFO recovery algorithms for OFDM signals are sensitive to multipath distortions as they are derived without explicitly taking into account the frequency selectivity of the transmission channel. In this paper, we propose a novel scheme in which the channel response and IFO are jointly estimated using a maximum likelihood (ML) approach. In doing so we exploit one or more pilot blocks placed at the beginning of the frame and carrying known symbols. Since the complexity of the resulting ML algorithm may be relatively large, we also suggest suboptimal solutions unifying various earlier proposals. Computer simulations are used to demonstrate the superiority of the proposed schemes over existing alternatives. It is shown that excellent performance can be achieved with affordable complexity even in the presence of highly dispersive channels. View full abstract»

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  • Bivariate nakagami-m distribution with arbitrary correlation and fading parameters

    Page(s): 5227 - 5232
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (347 KB) |  | HTML iconHTML  

    New, exact expressions concerning the bivariate Nakagami-m processes with arbitrary correlation and fading parameters are derived. More specifically, the following are obtained in the present work: joint moment generating function; joint probability density function; joint cumulative distribution function; power correlation coefficient; and several statistics related to the signal-to-noise ratio at the output of the selection combiner, namely, outage probability, probability density function, and mean SNR. The expressions make use of the well known generalized Laguerre polynomials. They are mathematically tractable and flexible enough to accommodate a myriad of correlation scenarios, useful in the analysis of a more general fading environment. We maintain, however, that a relation among the correlation coefficients of the corresponding Gaussian components must be kept so that convergence is attained. View full abstract»

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  • A study on channel estimation methods for time-domain spreading MC-CDMA systems

    Page(s): 5233 - 5237
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (445 KB) |  | HTML iconHTML  

    In time-domain spreading MC-CDMA systems, which are candidates for the 4G system, data and pilot symbols are spread in the time domain and code-multiplexed. To combat fading issues, we need to conduct channel estimation by using the code-multiplexed pilot symbols. In this paper, we propose a channel estimation method for highly accurate channel estimation; it is a combination of a two-dimensional channel estimation method and an impulse response-based channel estimation method. We evaluate the proposed method by computer simulations. View full abstract»

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  • On bandwidth request mechanism with piggyback in fixed IEEE 802.16 networks

    Page(s): 5238 - 5243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (209 KB) |  | HTML iconHTML  

    This paper investigates the random channel access mechanism specified in the IEEE 802.16 standard for the uplink traffic in a point-to-multipoint (PMP) network architecture. An analytical model is proposed to study the impacts of the channel access parameters, bandwidth configuration and piggyback policy on the performance. The impacts of physical burst profile and non-saturated network traffic are also taken into account in the model. Simulations validate the proposed analytical model. It is observed that the bandwidth utilization can be improved if the bandwidth for random channel access can be properly configured according to the channel access parameters, piggyback policy and network traffic. View full abstract»

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  • Joint medium access control, routing and energy distribution in multi-hop wireless networks

    Page(s): 5244 - 5249
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB) |  | HTML iconHTML  

    It is a challenging task for multi-hop wireless networks to support multimedia applications with quality-of service (QoS) requirements. This letter presents a joint cross layer optimization approach, i.e., joint medium access control, routing, and energy distribution. User satisfaction represented by user utility is maximized within the required network lifetime, given the constraints on the total available energy in the network and the minimum user rates. Although the resulting optimization problem is nonlinear and nonconvex, we prove that it is approximately equivalent to a two-step convex problem. Furthermore, we prove that the problem of maximizing network utility within achievable network lifetime is quasiconvex. View full abstract»

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  • Jointly gaussian approximation and multi-stage LLR combining in the iterative receiver for MIMO-BICM systems

    Page(s): 5250 - 5256
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB) |  | HTML iconHTML  

    In this letter, we propose a new multi-stage LLR combining (MLC) algorithm in an iterative receiver for MIMOBICM systems. This algorithm combines the soft information from different receive antennas in a multi-stage fashion, where the combining factors are derived based on the joint likelihood function of bivariate Gaussian random variables. The variance transfer (VT) function of the proposed scheme is derived for performance analysis. For slow fading channels, we show that the proposed MLC algorithm can achieve almost the same performance as the linear minimum mean square error (LMMSE) filtering approach, whereas the computation-demanding matrix inverse for LMMSE can be avoided. View full abstract»

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  • A low-complexity soft-input/soft-output multiuser detector based on local search algorithms

    Page(s): 5257 - 5262
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    In this contribution, we consider iterative multiuser detection over coded code-division multiple-access (CDMA) channels from a combinatorial optimization viewpoint and propose a low-complexity soft-input/soft-output (SISO) multiuser detector based on the k-opt local search (LS) algorithm, which was previously used for solving the traveling salesperson problem (TSP). Simulation results and complexity analysis show that the proposed detector can approach closely the performance of the full-complexity a posteriori probability (APP) multiuser detector over highly correlated convolutionally coded channels. View full abstract»

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  • Preamble-based cell identification for cellular OFDM systems

    Page(s): 5263 - 5267
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (661 KB) |  | HTML iconHTML  

    Preamble-based cell identification (CID) schemes are derived for orthogonal frequency division multiplexing (OFDM) systems. They include the optimal schemes based on the Bayesian and the maximum likelihood (ML) approaches, a suboptimal scheme that is a simplification of the ML scheme, and a differential decoding-based scheme that does not require any channel information. The complexities and performances of these CID schemes are examined and compared to existing schemes. The differential decoding-based scheme performs like the suboptimal scheme for most practical channels of interest and outperforms existing schemes, yet it is simpler to implement than the others. View full abstract»

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  • General performance analysis of TR UWB systems

    Page(s): 5268 - 5277
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (413 KB) |  | HTML iconHTML  

    A new analytical method for evaluating the bit error rate performance of a transmitted reference ultra-wide bandwidth system with an arbitrary front-end filter is derived. The method is based on expanding the received signal using the Karhunen-Loeve expansion and then evaluating the characteristic function of the receiver decision metric. This new method puts no restriction on the front-end filter type, is suitable for any arbitrary value of receiver time-bandwidth product and is highly accurate for evaluating bit error rates as small as 10-9 in both additive white Gaussian noise and fading multipath channels. The method is also extended to the case of correlated message and reference noises. The results indicate that the effect of this cross-correlation is not negligible in evaluating the bit error rate. It is found that differences in the front-end filter can lead to significant differences in the system bit error rate. View full abstract»

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  • Robust cooperative routing protocol in mobile wireless sensor networks

    Page(s): 5278 - 5285
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    In wireless sensor networks, path breakage occurs frequently due to node mobility, node failure, and channel impairments. It is challenging to combat path breakage with minimal control overhead, while adapting to rapid topological changes. Due to the Wireless Broadcast Advantage (WBA), all nodes inside the transmission range of a single transmitting node may receive the packet, hence naturally they can serve as cooperative caching and backup nodes if the intended receiver fails to receive the packet. In this paper, we present a distributed robust routing protocol in which nodes work cooperatively to enhance the robustness of routing against path breakage. We compare the energy efficiency of cooperative routing with noncooperative routing and show that our robust routing protocol can significantly improve robustness while achieving considerable energy efficiency. View full abstract»

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  • Dual-folding based rapid search method for long PN-code acquisition

    Page(s): 5286 - 5296
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (495 KB) |  | HTML iconHTML  

    For long PN-code, rapid acquisition is difficult due to large search space. To speed up the search process, extended replica folding acquisition search technique (XFAST), which directly reduces the code phases to be searched by folding local signal, provides an efficient approach to rapid acquisition. Nevertheless, after folding the correlation properties of PNcode are degraded; hence, the detection performance of XFAST to weak signal is worse than that of nonfolding methods. To improve the detection performance, a dual-folding acquisition method (DF) is proposed. By folding both incoming signal and local signal, DF extends coherent integration time to enhance detection performance and indirectly reduce mean acquisition time. Numerical results demonstrate the enhancement of the proposed method with respect to other methods such as serial search (SS), zero-padding method (ZP), and XFAST. View full abstract»

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Aims & Scope

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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Meet Our Editors

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