Mohammad A. Hoque

Multiple Radio Channel Assignement Utilizing Partially Overlapped Channels

Existing channel assignment algorithms designed for multi-radio multi-channel wireless mesh networks (MRMC-WMN) mainly deal with orthogonal or nonoverlapped channels. But in reality, the limited availability of orthogonal channel is a major issue where the network is very dense in terms of inter-nodal distances. On the other hand, partially overlapped channels (POC) are currently considered as a great potential for increasing the number of simultaneous transmissions and eventually upgrading the network capacity; especially in case of MRMC-WMN. In this paper, we address the limited orthogonal channel problem by exploring the usable POCs. The key technique lies in the fact that the interference between adjacent channels has to be considered intelligently in order to increase the overall capacity. Our contributions include a new interference model I-Matrix that helps selecting channels with less interference and a POC-based channel assignment algorithm. We evaluate the performance of our POC based algorithm in terms of capacity by comparing with the one using only orthogonal channels. Our results show capacity improvement as the increased link assignments at an average of more than 15 percent.

Exploring multiple radios and multiple channels in wireless mesh networks [Accepted from Open Call]

Much research has been performed investigating the challenging issue of efficiently utilizing the network-wide capacity available in the multihop wireless mesh networks with multiple radios and multiple channels. In this work, multihop routing and channel assignment are intertwined issues. In this article we present summaries of this work based on two broad categorizations in terms of algorithm features: centralized and distributed approaches. Due to the multiple dimensions of the topics, we subgroup the papers in terms of how the interactions between routing and channel assignments are treated. They include channel assignment based on the given connectivity graph, joint design of routing and channel assignment, routing with localized considerations on channel selection, and channel assignment with local channel usage and traffic load information. With the centralized approach, the schemes are able to target optimal channel assignment and joint design on both channel assignment and routing issues. In the distributed approach, the papers take steps focused on either route metrics or channel scheduling based on localized information about the links at each node. Comparisons and open research issues are given as the conclusion.

Efficient multi-hop connectivity analysis in urban vehicular networks

Vehicle to Vehicle (V2V) communication provides a flexible and real-time information dissemination mechanism through various applications of Intelligent Transportation Systems (ITS). Achieving seamless connectivity through multi-hop vehicular communication with sparse network is a challenging issue. In this paper, we have studied this multi-hop vehicular connectivity in an urban scenario using GPS traces obtained from San Francisco Yellow cabs. Our current work describes a new algorithm for the analysis of topological properties like connectivity and partitions for any kind of vehicular or mobile computing environment. The novel approach uses bitwise manipulation of sparse matrix with an efficient storage technique for determining multi-hop connectivity. The computation mechanism can be further scaled to parallel processing environment. The main contribution of this research is threefold. First, developing an efficient algorithm to quantify multi-hop connectivity with the aid of bitwise manipulation of sparse matrix. Second, investigating the time varying nature of multi-hop vehicular connectivity and dynamic network partitioning of the topology. Third, deriving a mathematical model for calculating message propagation rate in an urban environment.

Analysis of mobility patterns for urban taxi cabs

This paper analyzes urban taxi mobility traces obtained from San Francisco Yellow cabs. The paper presents a rigorous analysis of taxi mobility pattern with the instantaneous velocity profile, spatio-temporal distribution, connectivity of vehicle communications, clustering, hotspots and other characteristics like trip duration and empty cruise interval. The empirical data analyses presented here can be a helpful resource for wireless researchers, government organizations, taxi companies and even for the drivers or passengers. While wireless researchers can estimate the capabilities and constraints of vehicular communication from connectivity and mobility patterns, government can plan and work on issues related to implementing proper DSRC infrastructure. Finally, taxi companies and drivers can benefit from maximizing the trip revenue and minimize empty cruise time though balanced load distribution and awareness of the hotspots.

Call admission control: QoS issue for VoIP

One of the vital key elements for providing quality of service (QoS) for VoIP is the call admission control (CAC) capabilities of the session management/call session control function or gateway. Even though the network may be designed to meet a given performance and restoration objective for the engineered traffic loads, the actual traffic may be significantly higher. Without a CAC function in a VoIP network during overloads, links become congested and new calls keep getting admitted. All calls in progress, not just the new calls start dropping packets and experiencing longer delays. Contrast this to a circuit switched network, where new calls get blocked, but calls in progress experience good call quality. In the VoIP case, packet loss could become large enough that calls become unintelligible, callers hang-up their call, and most will reattempt. This paper gives an overview of potential CAC approaches, highlighting four basic alternatives; based on endpoint performance measurements, path-based bandwidth management, link-based bandwidth management, and per-call bandwidth reservation. The paper also recommends a link bandwidth management approach for its scalability and efficacy.

Performance analysis of a tree-based consistency approach for cloud databases

Cloud storage service is currently becoming a very popular solution for medium-sized and startup companies. However, there is still no suitable solution being offered to deploy transactional databases in a cloud platform. The maintenance of ACID (Atomicity, Consistency, Isolation and Durability) properties is the primary obstacle to the implementation of transactional cloud databases. The main features of cloud computing: scalability, availability and reliability are achieved by sacrificing consistency. While different forms of consistent states have been introduced, they do not address the needs of many database applications. In this paper we present a tree-based consistency approach, called TBC, that reduces interdependency among replica servers to minimize response time of cloud databases and to maximize the performance of those applications. Experimental results indicate that our TBC approach trades off availability and consistency with performance.

Modified Algorithms for Multilevel GRSB Protocol

Data aggregation is a method used in sensor networks to reduce the amount of messages transported. By aggregating, the data contained in several messages is fused into one single message. If such a message, containing the equivalent of many individual messages, is lost due to transmission errors then this has a detrimental effect on the application quality experienced. In many sensor network applications a constant supply of data is needed and therefore application quality is severely effected by excessive data loss. This paper proposes and evaluates the use of an in-network control mechanism to offset this disadvantageous effect. The control mechanism analytically calculates the correct reliability that an aggregate of given size must be forwarded at in order to meet application specific goals.

Demo: Real-time vehicle movement tracking on Android devices through Bluetooth communication with DSRC devices

This demo paper describes the architecture and communication protocols — both single hop and multi-hop — for DSRC devices. The paper also describes an Android application that enables visualization of real-time vehicle movements on Google map using DSRC and Bluetooth communication. The application receives information about position, speed and direction of mobility that multiple vehicles obtain through the GPS Receiver attached to their DSRC OBU. The android application communicates with one of the DSRC units through Bluetooth to gather real-time traces collected from all DSRC-equipped vehicles. The application displays live movement of these vehicles on Google map with their path history, speed and direction. The source code and installation files of this application will be released through the Open Source Application Development Portal (OSADP) hosted by the U.S. Department of Transportation.

Poster: Investigating Doppler Effects on Vehicle-to-Vehicle Communication: An Experimental Study

Doppler effects on vehicular communication have been theoretically modeled by many researchers. However, very limited experimental studies have been conducted to investigate the impact of Doppler shift on the vehicle-to-vehicle (V2V) communication range and reliability with high-speed mobility. The current work-in-progress research aims to quantify the impact of Doppler effects on V2V communication reliability, range, and reachability using single-hop Dedicated Short-Range Communications (DSRC) between two opposite traffic. We conducted our experiments by mounting the after-market DSRC onboard units on the dashboard of two vehicles that cross each other from opposite directions with constant relative speeds on a real interstate freeway. Our preliminary results indicate that the communication time and range drop to approximately 70% and 40% after the two vehicles cross and start moving away from each other with the average relative speeds of 110 and 140 mph, respectively. Similarly, the packet delivery ratio is also drastically reduced after the vehicles start moving away from each other. Apparently, these results indicate that there might be a strong effect of Doppler phenomena on the transmission range, packet delivery rate and the duration of the communication.

BMF-MAC: A Bidirectional Multi-flow MAC Protocol for Multihop Underwater Acoustic Sensor Networks

Due to the atypical characteristics of the physical media in underwater acoustic sensor networks (UW-ASN)--mostly because of long propagation delay, low bandwidth and high error rate--several challenges arise while designing the MAC protocol. In this paper, we propose a Bidirectional Multi-flow MAC protocol (BMF-MAC) for UW-ASN, to efficiently handle multi-hop multi-flow traffic load patterns such a way that multiple streams of data transmissions concurrently proceed while adapting with varying traffic condition. BMF-MAC supports constitution of multi-hop flows by considering all pending packets in routing layer buffer and all flow setups requests from neighbors when setting up a flow, contrary to other underwater MAC protocols. The proposed MAC introduces a data transmission technique using the bidirectional multi-flow packet method for sending multiple data packets of the same flow in the reverse direction and thus improve channel utilization. The protocol is aimed to schedule more data transmission over multiple multi-hop flows, thus permitting rapid distribution of data and reduction of latency. Results show that BMF-MAC protocol outperforms existing CMRT protocol in terms of network throughput and packet delivery latency.