Sanjiv Tokekar

Reliability analysis of Wireless Sensor Network

Wireless sensor network (WSN) is a distributed system which possesses time varying wireless connectivity without any infrastructural backbone. Scarce energy and computation power of individual nodes, unattended and harsh operation environment, self configuration after random deployment etc complexities are known characteristic features of a WSN. Despite aforesaid constraints WSN has been evolved as a tool to bridge the gap between physical world of sensors/actuators and the virtual world of information and services. In some typical scenarios of many potential fieldspsila e.g. environmental monitoring, space explorations, military, agricultural, medical etc to name a few, WSN has been emerged as a promising technology. Sensing the environment and sending the sensed information to a remote place via sink are two primary jobs of a sensor network. These jobs are required to be done with greater reliability because some major decisions depend on the information received from WSN. The issue of quantifying reliability for a WSN is addressed in this paper.

Modeling and analysis of voice/data call admission control scheme in CDMA cellular network for variation in soft handoff threshold parameters

In CDMA cellular networks the variation in soft handoff coverage area can be taken as the parameter influencing the performance of the system. In this paper, an analytical model is developed and analyzed for the concerned target cell in CDMA cellular network. The model proposed in this paper is for integrated data and voice services. It is based on reservation for handoff voice and data calls along with call queuing scheme for handoff data calls. Preemptive priority scheme is used for handoff voice calls over ongoing data calls. Upper channel limits are set for new voice as well as data calls to give priority to handoff calls. Two dimensional Markov birth-death process is used for modeling the problem. The data handoff queue capacity is considered as function of soft handoff coverage area which depends on the two soft handoff threshold parameters T_ADD and T_DROP. Variation in these threshold parameters is stated in term of variation in handoff data call queue capacity. The performance parameters of the model mainly new voice and data call blocking probabilities and handoff voice and data dropping probabilities are analyzed for variation in upper channel limit for new voice call and handoff data call queue capacity.

A Neuro-Fuzzy Call Admission Control Algorithm for Voice/Data Traffic in CDMA Cellular Network

Soft handoff in CDMA cellular system increases system capacity as compared to hard handoff as interference is reduced by transmitting signals as lower power level. A CDMA cellular system involving integrated voice and data calls is considered in this paper. The developed model is based on priority reservation for handoff voice and data calls along with call queuing scheme for handoff data calls. Upper channel restrictions are set for new voice as well as data calls to give priority to handoff calls. For better resource management and efficient call admission to originating and handoff calls, Neuro-fuzzy call admission controller is designed. This controller uses the adaptable feature of soft handoff threshold parameters to house important voice and data calls by monitoring current new voice blocking probability, handoff data dropping probability and speed of handoff voice users. The proposed ASNFC controller is compared with non-Call admission control scheme for required QoS of the system.

Analysis of Queuing based Call Admission Control Scheme in CDMA Cellular Network for Variation in Mobility and Soft Handoff Threshold

In CDMA cellular system, the coverage area of the cell is greatly influenced by soft handoff process. The variation in soft handoff coverage area can be taken as the parameter influencing the performance parameters of the CDMA cellular system. In this paper, an analytical model is developed and analyzed for the concerned target cell in CDMA cellular network. The model proposed in this paper is based on priority reservation for handoff calls along with call queuing scheme for new as well as handoff calls. Separate queues are considered for both new as well as handoff calls. Two dimensional Markov birth-death process is used for modeling the problem. The handoff queue capacity is considered as function of soft handoff coverage area which depends on the two soft handoff threshold parameters T_ADD and T_DROP. Considering fixed cell radius, variation in soft handoff coverage area also varies the normal area for new calls. It is seen that change in normal cell area is inversely proportional to soft handoff coverage area. The effect of this variation which leads to change in handoff call queue capacity along with mobility of mobile user is analyzed for variation in network performance parameters new call blocking probability, handoff request blocking probability, new and handoff call time out probabilities and forced termination probability for handoff request. Increase in handoff call queue capacity effectively decreases handoff request blocking probability but leads to increment of new call blocking probability.

Collision Resolution Schemes with Nonoverlapped Contention Slots for Heterogeneous and Homogeneous WLANs

CSMA/CA-based DCF of 802.11 MAC layer employs a best-effort delivery model, in which stations compete for channel access with the same priority. In a heterogeneous network, providing different priorities to different applications for required quality of service is a challenging task, since heterogeneous conditions result in unfairness among stations and degradation in the throughput. This paper proposes a class of collision resolution schemes for 802.11 having contention window control with nonoverlapped contention slots. In the first scheme, window ranges of two consecutive stages are nonoverlapped, and it is called nonoverlapped contention slots (NOCS) scheme. In the other scheme, termed as NOCS-offset, an offset is introduced between window ranges of two stages. Selection of a random value by a station for its contention with discontinuous distribution results in reduced probability of collision. Analytical and simulation results show that the proposed scheme exhibits higher throughput and fairness with reduced delay and collision probability in homogeneous and heterogeneous networks. Performance of the proposed scheme is evaluated for mix traffic and high data rate environment with advanced back-off management techniques to meet the requirements of the present applications.

Class of collision resolution schemes with multistep distribution for IEEE 802.11

Traditional Medium Access Control (MAC) algorithms for Distributed Co-ordination Function (DCF) in IEEE 802.11 extend window ranges after each packet collision in the next stage. As these window ranges intersect with window ranges of other stages, the system is collision prone. This paper proposes a class of collision resolution schemes for 802.11 contention window control with multistep distribution and called as Overlapped Contention Slots with Multistep Distribution (OCS-MD). It is shown that proper selection of different steps in the distribution of OCS-MD increases the mean value of back-off counter as compared to standard Binary Exponential Back-off (BEB). This reduces probability of window intersection of different stages, resulting in lesser probability of collision. The system model is formulated for the proposed schemes. Analytical results are validated against those obtained from simulation. The performance results show that the proposed algorithm enhances the system performance in terms of throughput and collision probability with comparable mean delay and fairness than existing scheme. Moreover these schemes can be easily incorporated with little modifications in existing 802.11 standard.

A Soft Computing Based Adaptive Call Admission Control Scheme for Bi-Class Traffic in CDMA Cellular Network

Soft handoff in CDMA cellular system increases system capacity as compared to hard handoff as interference is reduced by transmitting signals as lower power level. A CDMA cellular system involving voice and data calls is considered in this paper. The model proposed in this paper is for data and voice services (Bi-class). It is based on reservation for handoff voice and data calls along with call queuing scheme for handoff data calls. Preemptive priority scheme is used for handoff voice calls over ongoing data calls. Upper channel limits are set for new voice as well as data calls to give priority to handoff calls. For better resource management and efficient call admission to originating and handoff calls, Neuro-fuzzy call admission controller is designed. This controller uses the adaptable feature of soft handoff threshold parameters to accommodate important voice and data calls. The proposed ASNFC controller is compared with the two variants of Bi-class CAC scheme. General Terms Call Admission Control, Soft Computing

Performability and survivability analysis of GSM

The concept of performability takes into accounts both availability and performance of a system [1][2] and survivability is broadly defined as the degree to which a system is able to provide critical services [3]. The ideal survivability goal is to make a network failure imperceptible to the users by providing service continuity and minimizing network congestion. This paper addresses above issues for a Global System for Mobile (GSM) network. There exist many failure scenarios in GSM networks like base transreceiver station (BTS) failure, VLR, HLR or other database failure etc. When a BTS stops all functioning, it is designated as BTS failure which is primarily considered in developing models and further analysis. Markov models have been developed for accessing the performance, availability and survivability of GSM with a scheme developed for minimizing the impact of failure. Its merits over ordinary GSM network are established in terms of performability and various attributes of survivability following general framework discussed in [Yun Liu and Trivedi, 2003].

Performability Analysis of a Fault Tolerant Sectorized Cellular Network

The concept of performability takes into accounts both availability and performance of a system. The issue of performability is very important for cellular networks due to its inherent characteristics like scarce of radio resources, high failure & outage rate and above all anytime, anywhere service expectation of the subscribers. In this work, first an algorithm is proposed for providing coverage to the users of failed cell/sector till it is repaired. The algorithm distributes the impact of a cell failure into whole network such that the fairness is maintained in the system despite the failure, thus it provides fault tolerance to the system. Then the performability of the cellular system is studied with the proposed algorithm

Adaptive soft handoff based Neuro-fuzzy call admission control scheme for multiclass calls in CDMA cellular network

Soft handoff in CDMA cellular system increases system capacity as compared to hard handoff as interference is reduced by transmitting signals as lower power level. A CDMA cellular system involving multiclass calls is considered in this paper. The type of services considered are voice and video which comes in category of real time calls. Data calls are also considered which falls in the category of non-real time calls. The developed model is based on priority reservation for handoff calls along with call queuing. Upper channel restrictions are set for new voice, video and data calls to give priority to handoff calls. For better resource management and efficient call admission to originating and handoff calls, Neuro-fuzzy call admission controller is designed. This controller uses the adaptable feature of soft handoff threshold parameters to house important real time and non-real time calls by monitoring current real time call blocking probability, handoff data dropping probability and real time handoff call dropping probabilities. The proposed ASNFC-MC controller is compared with Cut-off priority based call admission control scheme for required QoS of the system.