Mohammad Shah Alam

Bit error rate performance analysis of optical CDMA time-diversity links over gamma-gamma atmospheric turbulence channels

When we use the free space optical(FSO) communication in the near-ground, it will be great influenced by the atmospheric turbulence. There are many studies on the effects of atmospheric turbulence in FSO. Recently gamma-gamma is a widely accepted model for the optical propagating through the atmosphere in normal and strong turbulence. In order to enhance bit error rate(BER) performance influenced by turbulence-induced fading, we promote a new time-diversity scheme which use optical code division multiple access(OCDMA) as channel division code. As we know, time-diversity is an effective method to enhance the throughput performance of wireless communication system. In order to provide a higher performing and cost-efficient solution OCDMA time-diversity scheme is proposed. In this paper, we analyze the performance of the new scheme with gamma-gamma model. We first present the structure of the OCDMA time-diversity scheme. Then we present the temporal covariance of gamma-gamma model to get the independent time-interval of atmospheric turbulence. We use experiment data to confirm theoretical result. At last we give the theoretical analysis on the BER of new scheme, and use numerical results to prove the theoretical analysis. We find that the new OCDMA time-diversity scheme can enhance the BER for several orders in strong turbulence. Furthermore, the performance of the new scheme in strong turbulence is even better than the traditional scheme in normal turbulence.

IrBurst Modeling and Performance Evaluation for Large Data Block Exchange over High-Speed IrDA Links

IrBurst, recently proposed by IrDA, is a high speed information transmission protocol. In this paper, a mathematical model is developed which leads to derivation of the IrBurst throughput over the IrDA protocol stack. Based on this model, we compare the performance of IrBurst and existing OBEX protocol in order to investigate the suitability of IrBurst protocol for exchange of large data blocks over high-speed IrDA links. Furthermore, the model allows the evaluation of the impact of the link layer parameters, such as window size and frame length, and physical layer parameters, such as minimum turnaround time, on system through-put for high-speed IrDA links and in the presence of transmission errors. Consequently, an effective Automatic Repeat Request (ARQ) scheme is proposed at link layer to maximize the throughput efficiency for IrBurst protocol as well as for next generation high speed IrDA links. Simulation result indicates that employment of our proposed ARQ scheme results in significant improvement of IrBurst throughput efficiency at high bit error rates.

Performance evaluation of saturating class - C driver circuit for inductive wireless power transfer

This paper presents performance evaluation of saturating class - C driver circuit for inductive wireless power transfer. Exact link is designed following link optimization theory to select parameters of the objective circuit. By exploring specific parameters of drain to source voltage effect on overall circuit, single MOSFET is used in the proposed driver circuit design instead of two parallel MOSFETs used in conventional driver circuit. Simulation results show that the proposed driver circuit provides a significant improvement in the driver efficiency (90.34%) as well as in the overall efficiency compared to the existing driver circuit. Furthermore, from the performance comparison, it is observed that the transferred output power (14.94 mW) has also been improved considerably.

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.

A fixed assignment based window access scheme for enhancing QoS of vehicular adhoc networks

In this paper, we propose a new MAC scheme for Vehicle-to-Infrastructure (V2I) communications that ensures fairness and reassignment of unused TDMA slots. The proposed TDMA based scheduling scheme allocates TDMA slots to the vehicles evenly and continuously monitors the network for unused slots. Our scheme ensures reassignments of unused slots by using “capture effect” and “time slot reassignment” mechanism. Simulation results show that the proposed scheme outperforms the conventional protocols in terms of successfully transmitted data packets, average delay and data loss ratio.

A scheduling scheme for efficient wireless charging of sensor nodes in WBAN

This paper presents a scheduling algorithm for point to point wireless power transfer system (WPTS) to sensor nodes of wireless body area networks (WBAN). Since the sensors of wireless body area networks are continuously monitoring and sending data to remote central unit, power crisis for these sensor nodes degrades the data transfer of patient monitoring system. Although energy harvesting from ambient sources using electromagnetic induction enhances the longevity of sensor performance, continuous operation in the primary side decreases the overall efficiency. With such paradigm in sight, a framework is proposed for increasing the primary battery longevity and reducing the transmission loss, inductive power is transmitted from primary to secondary unit using medium access control (MAC) protocols for underlying the centralized scheduling opportunity in a collision free scheme for channel access of rare yet critical emergency situation. In a preliminary study, the proposed scheduling for charging sensor nodes in a wireless body area network (WBAN) is evaluated in a case consideration.

Priority Aware Interference Mitigation Techniques for Coexistence of Wireless Technologies in Smart Utility Networks

In recent years, Smart Grid (SG) is envisioned to be the next generation electric power system by replacing traditional power grid due to its advantage of using two way communications. To implement reliable SG wireless communication networks, IEEE introduced a new wireless standard (IEEE802.15.4g) for Smart Utility Networks (SUNs). However, SUN operates on 2.4 GHz unlicensed band which is overlapped with Wireless Local Area Networks (WLANs) that leads to coexistence in Smart Utility Networks. In this paper, the coexistence problem of SUN is addressed in terms of homogeneous and heterogeneous interferences. To mitigate the homogeneous interference, Contention Access Period (CAP) and Contention Free Period (CFP) of a super frame of IEEE 802.15.4g is used to access the channel using slotted CSMA/CA algorithm by modifying the Backoff Period (BP) and Clear Channel Assessment (CCA) period for different priority data. An analytical model is developed using Markov chain, through which we demonstrate the accuracy of the proposed model in terms of throughput, channel access delay, probability of successful transmission and collision for nodes with different priority data. Performance evaluation is further investigated by comparing the proposed scheme with the existing PA-MAC. A channel switching mechanism is explored to mitigate the heterogeneous interference by the prediction of Naive Bayes Classifier. Predicted result shows that proposed mechanism effectively mitigates the heterogeneous interference by choosing the non-overlapping and non-coexisting channel.

FCSEA: A Floodless Carrier-grade Scalable Ethernet Architecture

This paper proposes Floodless Carrier-grade Scalable Ethernet Architecture (FCSEA) as a completely floodless enhancement of EtherProxy to meet scalability and protection switching requirements of Ethernet in carrier networks. FCSEA uses a priority based cache retention principle, exploits attempt from end node/host to verify connectivity during commissioning and intercepts dynamic configuration (DHCP) messages to ensure an entirely floodless environment for end hosts. This work enhances the ability of EtherProxy to suppress broadcast traffic and adds protection switching support enabling it to function properly in a ring or mesh protected network. FCSEA retains EtherProxys advantages of autoconfiguration and backward compatibility with existing hardware. Simulation result and analysis with real data is presented to verify effectiveness of FCSEA and to show its suitability over recent SDN based solutions.

COASYM-MAC: A cooperative Asymmetric MAC protocol for Wireless Sensor Network

Link asymmetry, arisen from varying coverage distance between two adjacent nodes, poses a real challenge for designing efficient receiver initiated MAC protocol for extremely low duty-cycled wireless sensor networks (WSN). One of the viable solution to overcome this limitation is to exploit the benefit of cooperative communication. In this paper, we propose a cooperative MAC protocol for WSN that effectively reduces asymmetry by taking advantage of alternative paths between a pair of nodes with link asymmetry. Simulation results show that our proposed scheme achieves significant improvement in performance compared with Asym-MAC, a state-of-the-art MAC protocol for WSN with asymmetric links. This performance improvement is effectively demonstrated in terms of energy consumption, average delay per packet and packet reception ratio.

An efficient MAC protocol for provisioning fairness in vehicle to roadside communications

In this paper, we present an efficient medium access control (MAC) protocol based on IEEE 802.11 DCF, which minimizes the unfairness problem of two way vehicle ad hoc networks. Geographically highly dynamic topology in vehicle ad hoc networks lead to unfairness problem. Unfairness problem has two aspects: higher velocity vehicles cannot transmit a minimum number of packets and lower velocity vehicles cannot transmit above a minimum number of packets. To address the above mentioned issues, our proposed scheme adjusts the transmission probability for each vehicle according to its residence time by changing the value of MAC parameters dynamically. An analytical model is developed to analyze the performance of the proposed protocol in a non-saturated state. We derive the relationship between the transmission probability and the residence time. Furthermore, relation between the transmission probability and the minimum contention window size of a vehicle is also derived to correlated residence time with minimum contention window size. Analytical results show that our proposed scheme overcomes the limitations of existing MAC protocols by ensuring that packet transmission rate remains proportional to the residence time of the vehicles.