Sibaram Khara

K-Means Clustering in Wireless Sensor Networks

A wireless sensor network (WSN) consists of spatially distributed autonomous sensors to monitor physical or environmental conditions and to cooperatively pass their data through the network to a Base Station. Clustering is a critical task in Wireless Sensor Networks for energy efficiency and network stability. Clustering through Central Processing Unit in wireless sensor networks is well known and in use for a long time. Presently clustering through distributed methods is being developed for dealing with the issues like network lifetime and energy. In our work, we implemented both centralized and distributed k-means clustering algorithm in network simulator. k-means is a prototype based algorithm that alternates between two major steps, assigning observations to clusters and computing cluster centers until a stopping criterion is satisfied. Simulation results are obtained and compared which show that distributed clustering is efficient than centralized clustering.

Balanced Cluster Head Selection Based on Modified k-Means in a Distributed Wireless Sensor Network

A major problem with Wireless Sensor Networks (WSNs) is the maximization of effective network lifetime through minimization of energy usage in the network nodes. A modified k-means (Mk-means) algorithm for clustering was proposed which includes three cluster heads (simultaneously chosen) for each cluster. These cluster heads (CHs) use a load sharing mechanism to rotate as the active cluster head, which conserves residual energy of the nodes, thereby extending network lifetime. Moreover, it reduces the number of times reclustering has to be done and significantly increases the number of data packets sent during network operation. The results show that Mk-means (modified k-means) algorithm was found to outperform the existing clustering algorithms owing to its unique multiple cluster head methodology.

An Alternative Architecture for WLAN/GPRS Integration

In this paper, we propose a new WLAN/GPRS integration architecture from the point of view of a GPRS operators WLAN implementation. We introduce a new node, called serving GPRS access router (SGAR), and its associated protocol stack. SGAR acts as WLANs access gateway to GPRS network so that a mobile terminal (MT) can use GPRS control signaling in WLAN networks in both tight and loose coupling modes. This avoids the requirements of extensible authentication protocol (EAP), implementing RADIUS servers and using expensive SS7 signaling link. NS-2 based simulation results show that the handoff delay in the proposed SGAR based integration technique is considerably less than that with RADIUS based authentication, under increasing packet sizes and/or increasing numbers of transmitting GPRS MTs. In fact, SGAR based tight coupling reduces the latency significantly, as shown in our experimentations

Modified handoff algorithm for providing optimization in heterogeneous wireless networks

In this study, the heterogeneous wireless network is considered. Obviously, it is an integration of two different access networks, namely cellular and WLAN. In the heterogeneous wireless networks, handoff is an important process when the user moves from one network (3G) to another network (WLAN). While the user is moving, the mobile nodes (MN) move within the coverage area of WLAN and 3G with different velocities. When user migrates between heterogeneous networks, for best performance, the seamless vertical handoff (VHO) is very essential. In this paper, we propose a modified optimization (M-OPTG) based VHO or horizontal handoff (HHO) algorithm for the heterogeneous wireless networks. The performance of M-OPTG algorithm with load, battery life time, velocity and call dropping analysis have been investigated. Some of the existing VHO or HHO algorithms provide only analytical results. In this paper, we have developed a real time study using network simulator to choose the appropriate network for providing service to a MN. Our proposed (M-OPTG) VHO or HHO algorithm provides better performance on the basis of battery life time, load balancing, call dropping probability and minimizes the number of handoffs based on the velocity of the MN. The Modified OPTG algorithm not only improves the collective battery life time of a MN, but also reduces the call dropping probability and unnecessary handover.

An improved WLAN-first access scheme for UMTS/WLAN integrated system

In a tunnel-WLAN model of a UMTS/WLAN interworking system, a user always prefers to access the WLAN as soon as he/she moves to a WLAN hotspot. Thus a user never misses the higher bit rate of WLAN as long as its bandwidth is available. We have examined that overall dropping probability of a request in a mixed cell (i.e., a UMTS cell with underlying WLANs) improves if and only if the blocking probability of a request in WLAN remains lower than that in the UMTS system. Thus dropping probability increases with increasing blocking probability in WLAN. We propose a WLAN-first access scheme which transfers all blocked requests of WLAN to overlaying UMTS system, thereby preventing compulsory dropping of blocked requests in WLAN. This technique improves the request dropping probability in an entire mixed cell.

Improving Delay Performance in UMTS/WLAN Integrated Networks with Global Gateway Router

This paper presents efficient methods of vertical handoffs from UMTS to WLAN and vice versa in a loose coupling architecture. When a mobile terminal (MT) moves from UMTS to WLAN, it performs mobile IP (MIP) registration with home agent (HA). Subsequently, HA needs to perform location update signaling with UMTS network to make the MT reachable from UMTS. If HA is deployed at gateway GPRS support node (GGSN), all incoming packets from the Internet to an MT are routed via GGSN and average packet-delay increases when the MT is in loosely-coupled WLAN. MIP registration is also affected by the traffics between the Internet and UMTS. To avoid this problem, HA can be deployed in WLAN IP network, but handoff delay from WLAN to UMTS will be more because an MT cannot send MIP-registration request to HA before the establishment of PDP context in UMTS network. We propose efficient handoff methods with simple modification in GPRS tunneling protocol (GTP) and HA functionality by placing a global gateway router. Our ns-2 based simulation results show that the proposed technique improves MIP registration during handoff from UMTS to WLAN and vice versa. It also provides lower end-to-end packet delay for Internet services when an MT is residing in WLAN.

An Efficient Take-Back Call Admission Control Scheme for 3G/WLAN Integrated Cells

Capacity increases and call dropping probability decreases in a 3G cell with embedded WLAN(s) (i.e., mixed cell). Two factors reduce the 3G traffic. One, users initiate new calls through WLANs and two, ongoing sessions are handed over from 3G to WLAN. As a result, call blocking probability in 3G system decreases and overall system capacity increases with increasing WLAN coverage. It is observed that call dropping rate in an entire mixed cell decreases as long as the call blocking probability in WLAN remains less than that in the 3G system. But new call arrival rate in WLAN also increases with increasing call intercepting (CI) probability of WLAN (i.e., probability with which WLAN shares a call in a mixed cell). Thus call blocking probability in WLAN increases. At higher values of CI probability, the blocking probability of WLAN becomes more than that in the 3G system duo to rise in new calls. At this juncture, call dropping rate increases with increasing CI probability. We propose an efficient take-back call admission control (TB-CAC) scheme in which a mobile station always prefers to access WLAN and the blocked calls of WLAN are immediately taken back by 3G systems. Proposed TB-CAC scheme shows considerable improvement of call dropping rate under increasing CI probability of WLAN.

A linear model of call intercepting probability of integrated WLANs in a 3g cell

3G/WLAN integration is thought to be a viable solution for next generation heterogeneous access networks. Estimation of traffic in 3G and WLAN systems is essential to compute the performance of a 3G/WLAN mixed cell. The sharing of calls between 3G and WLAN is dependent on call intercepting (CI) probability of WLAN inside a 3G cell. CI probability is the key parameter for model based analysis of capacity gain and call dropping performance of a mixed cell. Most of the existing models do not derive CI probability. Rather the analysis has been done on the basis of assumed values of CI probability. In this article, we propose an analytical model to derive the CI probability as a function of some realistic cell parameters. The model provides linear changes of CI probability with increasing number of WLAN-hotspots. The model facilitates to represent all WLAN-hotspots by an equivalent single WLAN. Proposed model removes the error in calculating CI probability by 7.6% over existing models. The numerical results are useful to estimate the net traffic in 3G and WLAN systems of mixed cell.

A Tiered Mobility Management Solution for Cellular/WLAN Integrated Networks with Low Handoff Delay

Demand for the Internet services through GPRS/3G networks is proliferating day-by-day. But low bit rate puts constraints on multimedia or mobile business services. In contrast, Wireless Local Area Networks (WLANs) provide high bit rate with low deployment cost. Therefore, integration of these two complementary systems would be the focus of next generation wireless networks. However mobility and handoff management become the key issues for such integration. If a cellular operator deploys as Operator’s IP network (OIN), it will be connected to GPRS at Gi interface and to the Internet through firewall. Alternatively, the Internet can be connected directly at Gi interface and OIN can be connected to the Internet. These connection mechanisms restrict on scalability due to large packet forwarding delay. In this paper, we propose a new way to integrate GPRS/UMTS, OIN and the Internet for better scalability and smaller packet delay. We deploy one gateway for users of cellular (GPRSAJMTS) and WLAN host. The gateway is in OIN and is connected directly with GGSN at Gi interface. The home agent functionalities are distributed in two level hierarchies within the OIN to reduce the packet and handoff delay. The proposed architecture would be useful for large network size.

Performance analysis of the CAC scheme CARETON under mixed cell environment in overlay networks

The paper proposes a call admission control (CAC) scheme to offer best services to the users in the next generation heterogeneous networks. It optimises the available resources without compromising the interest of the service providers. It has combined the three commonly used CAC schemes – guard channel, buffer-based and priority-based schemes. It considers wireless overlay model for analysing the heterogeneity with detailed analysis of the WLAN-cellular mixed cell environment. The scheme considers differentiated services for the real time and non-real time calls to provide appropriate quality of service (QoS). The proposed scheme has been evaluated through simulation. The results show that the scheme outperforms some significant CAC schemes and shows even better performance under cellular-WLAN mixed environment due to the dual subscription of the users with dual mobile terminal.