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Zhao Y.,Southwest Jiaotong University | Fang X.,Southwest Jiaotong University | Huang R.,Olympus Communication Technology of America | Fang Y.,University of Florida
IEEE Transactions on Mobile Computing | Year: 2014

Multihop cellular networks (MCNs) have drawn tremendous attention due to its high throughput and extensive coverage. However, there are still three issues not well addressed. With the existence of relay stations (RSs), how to efficiently allocate frequency resource to relay links becomes a challenging design issue. For mobile stations (MSs) near the cell edge, cochannel interference (CCI) become severe, which significantly affects the network performance. Furthermore, the unbalanced user distribution will result in traffic congestion and inability to guarantee quality of service (QoS). To address these problems, we propose a quantitative study on adaptive resource allocation schemes by jointly considering interference coordination (IC) and load balancing (LB) in MCNs. In this paper, we focus on the downlink of OFDMA-based MCNs with time division duplex (TDD) mode, and analyze the characteristics of resource allocation according to IEEE 802.16j/m specification. We also design a novel frequency reuse scheme to mitigate interference and maintain high spectral efficiency, and provide practical LB-based handover mechanisms which can evenly distribute the traffic and guarantee users' QoS. Our study shows that our scheme not only meets the requirement on coverage, but also improves the throughput while accommodating more users in MCNs. © 2014 IEEE.


Rakhshan A.,University of Massachusetts Amherst | Pishro-Nik H.,University of Massachusetts Amherst | Nekoui M.,Olympus Communication Technology of America
2015 49th Annual Conference on Information Sciences and Systems, CISS 2015 | Year: 2015

This paper studies the need for individualizing vehicular communications in order to improve collision warning systems for a highway scenario. By relating the traffic-based and communications studies, we aim at reducing highway traffic accidents. To the best of our knowledge, this is the first paper that shows how to customize vehicular communications to driver's characteristics and traffic information. We propose to develop VANET protocols that selectively identify crash relevant information and customize the communications of that information based on each driver's assigned safety index. In this paper, first, we derive the packet success probability by accounting for multiuser interference, path loss, and fading. Then, by Monte carlo simulations, we demonstrate how appropriate channel access probabilities that satisfy the delay requirements of the safety application result in noticeable performance enhancement. © 2015 IEEE.


Rakhshan A.,University of Massachusetts Amherst | Pishro-Nik H.,University of Massachusetts Amherst | Fisher D.L.,University of Massachusetts Amherst | Nekoui M.,Olympus Communication Technology of America
2013 IEEE Globecom Workshops, GC Wkshps 2013 | Year: 2013

Every year, many people are killed and injured in highway traffic accidents. In order to reduce such casualties, collisions warning systems has been studied extensively. These systems are built by taking the driver reaction times into account. However, most of the existing literature focuses on characterizing how driver reaction times vary across an entire population. Therefore, many of the warnings that are given turn out to be false alarms. A false alarm occurs whenever a warning is sent, but it is not needed. This would nagate any safety benefit of the system, and could even reduce the overall safety if warnings become a distraction. In this paper, we propose our solution to address the described problem; First, we briefly describe our method for estimating the distribution of brake response times for a particular driver using data from a Vehicular Ad-Hoc Network (VANET) system. Then, we investigate how brake response times of individual drivers can be used in collision warning algorithms to reduce false alarm rates while still maintaining a high level of safety. This will yield a system that is overall more reliable and trustworthy for drivers, which could lead to wider adoption and applicability for V2V/V2I communication systems. Moreover, we show how false alarm rate varies with respect to probability of accident. Our simulation results show that by individualizing collision warnings the number of false alarms can be reduced more than 50%. Then, we conclude safety applications could potentially take full advantage of being customized to an individual's characteristics. © 2013 IEEE.


Nekoui M.,Olympus Communication Technology of America | Huang R.,Olympus Communication Technology of America | Chu L.,Olympus Communication Technology of America
BODYNETS 2013 - 8th International Conference on Body Area Networks | Year: 2013

TDMA-based MAC schemes suit WBANs due to such networks' simple star topology and power limitations. In conventional ad hoc wireless networks, the specific arrangement of reservations within a TDMA frame is of minor importance as long as all nodes asking for a reservation are granted one within a frame interval. Yet emergency event preemptions or possible sensor-initiated and uncoordinated extensions of granted schedules, which seem inevitable for WBAN applications, make reservation arrangement an important problem. Here, such events could transgress an already scheduled reservation of maybe another node, jeopardizing the latter's transmission opportunity. This is more of an issue if we consider the power-limited nature of WBAN nodes, limiting the time they can keep awake looking forward for a maybe delayed transmission opportunity. In this paper we study the optimal arrangement of slave nodes' reservations which seeks to best fulfill the traffics' QoS requirements subject to a power consumption constraint. In that we account for nodes' reservation lengths, traffic QoS requirements, and the corresponding statistical characteristics of reservation extensions and emergencies. Our strategy protects the reservations of the more QoS-constrained of slaves' applications against the possible preemptions of others and also provides them with adequate bandwidth if they ever needed to extend their reservation on the fly. © 2013 ICST 978-1-936968-89-3.


Gudovskiy D.A.,Olympus Communication Technology of America | Chu L.,Olympus Communication Technology of America | Lee S.,Olympus Communication Technology of America
IEEE Communications Letters | Year: 2015

A novel nondata-aided feedforward algorithm for frequency and phase offset estimation of minimum shift keying (MSK)-modulated signals with joint symbol timing recovery is presented. While having relatively low complexity, it allows to operate at low signal-to-noise ratio for fully coherent demodulator. The proposed algorithm relies on a new signal transform operation that is used to extract symbol timing as well as frequency and phase offset information and a corrector that derotates the received signal prior to demodulation using the estimators' outputs. Simulation results for precoded-type MSK in an additive white Gaussian noise channel illustrate advantages of the proposed algorithm including lower variance of the symbol timing estimator compared to previous approaches. © 1997-2012 IEEE.


Ihara K.,Olympus Communication Technology of America
Asia-Pacific Microwave Conference Proceedings, APMC | Year: 2010

The author developed a GaAs wideband IQ modulator IC, which is utilized in RF signal source instruments with direct-conversion architecture. For applications requiring the precision of electric instrumentation, temperature drift is highly critical. In the author's previous studies on temperature drift mechanism of RC-CR phase shifter, equivalent parasitic capacitances are the dominant factor to cause temperature drift of phase error. The analysis was conducted by mathematical simulation where the FET as variable resistances in RC-CR phase shifter was modeled as a parallel pair of variable re- sistance and simplified parasitic capacitance while the analysis did not explain well frequency dependence of the temperature drift on the measurement. For more accurate simulation, this paper reports non-linear circuit simulation using empirically temperature-dependent non-linear FET models, where DC and non-linear AC operations are simultaneously simulated. Utilizing this method, the simulation result showed a better match with the measurement in terms of non-linear temperature dependence. © 2010 IEICE Institute of Electronics Informati.


Nekoui M.,Olympus Communication Technology of America | Chu L.,Olympus Communication Technology of America
2015 IEEE Global Communications Conference, GLOBECOM 2015 | Year: 2015

This paper proposes an optimal Admission Control (AC) policy for wireless Body Area Networks (BANs). We mathematically formulate an AC problem that captures BAN-specific characteristics such as ultra-low power consumption of sensor nodes and QoS-sensitive heterogeneous traffic types. Traffic QoS requirements along with physical BAN sensor limitations such as buffer size and energy consumption are used to determine a data flow's connection parameters. If unable to admit the new flow, the Hub initially considers adjusting some of the existing (or new) flows to free up enough bandwidth. Adjustment of a flow does not violate its QoS requirements but comes at the cost of extra energy consumption. We propose an efficient scheme that traverses viable adjustment options until the least costly is found. When adjustment does not suffice, a combination of adjusting a set of flows and terminating some of the existing ones is considered. A bandwidth-efficient algorithm is proposed that chooses to terminate the least number of flows that have lower priory than the one requesting to join. For medical-grade traffic, simulation results show a 27% increase in the number (and close to 2 levels increase in a defined priority metric) of admitted flows, at a diminutive 3% cost on the nodes' energy consumption. © 2015 IEEE.

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