Handoff Region Research Articles

Reduce The Handoff Failure By Implementing Two WLAN In Handoff Region

The problem of wireless communication is the handoff. That problem mainly shows in the urban area because limited number of Access Point (AP) and the Base Station (BS). Main problem occur when the Mobile Node (MN) are goes to out of the coverage area the MN need to make handoff because the current or old Base Station(BS) does not gives the supports. Effect of this problem is call disconnection or data loss. IEEE802.11 based wireless local area network (WLAN) are widely use to give the supports of personal or commercial basis. In the proposed work the WLAN are placed on the two adjacent cell and they are crossly connected to the BS. This WLAN are used as an AP and that AP are enhanced the signal strength of the region of handoff and increased the area of BS. This WLAN gives the services for the time of degradation until fond the new channel in the new BS or the inside of WLAN area. For this cause the failure of handoff are minimized.

QUEUEING MODEL FOR SOFT HANDOFF ANALYSIS IN CDMA BASED WIRELESS CELLULAR NETWORK

The most important feature of the mobile network is mobility. Good and continuous service in cellular mobile network can be achieved by using the procedure of handoff (or handover) from one cell to another. Soft handoff is very important feature of cellular Code Division Multiple Access (CDMA) system. In CDMA system a mobile stations (MSs) within a soft handoff region use multiple radio channels and receive their signals from multiple base stations simultaneously. In CDMA cellular system, all cells can also share the same frequency. During handoff procedure, the signaling and voice information from multiple base stations are combined at the mobile switching center (MSC). During the handoff procedure, voice and signaling information must be sent to multiple base stations and the mobile station must combine the results. Within the overlapping area (which is developed by the adjacent cells) of cells, a handset can connect to multiple base stations. In this research paper, a new soft handoff scheme for CDMA cellular network is proposed and investigated. Here we introduce the concept of overlap region between adjacent cells and develop an analytical model for soft handoff in CDMA system. In developed soft handoff model, the balking and reneging behaviors of handoff calls have also considered. Different performance measures of the soft handoff model have developed.

QoS-Aware Downlink Cooperation for Cell-Edge and Handoff Users

In this paper, we present a quality-of-service (QoS)-aware cooperative downlink scheduling approach for cell-edge and handoff users that offers more reliability and higher effective capacity. The cooperation (handoff) region is defined for active handoff users between two adjacent base stations (BSs) as a function of the user QoS requirements and network load. In addition, the proposed technique inherently acquires intercell interference (ICI) coordination by adjusting the position and size of the cooperation window suitably. Numerical results are presented showing reliability, user QoS and capacity gain performance, and the region for cooperative scheduling in a coded communication scenario. Our analysis indicates that cooperation provides relatively less gain in effective capacity, i.e., up to about 40% with respect to noncooperative handoff, when the QoS requirement is loose. On the other hand, when the QoS requirement is more stringent, the effective capacity gain can increase up to nearly 100%. Additionally, we show that, while for applications with a loose QoS requirement the cooperation window size is small, i.e., nearly 1% of the total area of the BSs participating in cooperation, it increases quite significantly, i.e., up to nearly 25%, for the applications with stringent QoS. Although the outage performance of the proposed approach is poorer than the joint transmission mode of a cooperative multipoint scheme in lightly loaded networks, its effective capacity is significantly higher under varying network traffic load and QoS constraints.

Performance analysis of forward-link capacity in multimedia CDMA systems considering macrodiversity effect

Abstract Multimedia services need macrodiversity handoff to guarantee real-time property and quality of service (QoS). Therefore, it is important to consider macrodiversity effect in calculating forward link capacity. In this paper, a novel analytic model of forward link capacity with integrated voice/data/multimedia services is developed with taking into account the effect of macrodiversity. In our analytic model, we define capacity of a system as the available peak load while maintaining a desired service quality. From the numerical results, we can see the quantitative effects of macrodiversity in system capacity. Numerical results show that forward link capacity is affected by the power distribution ratio of multipath signal, the ratio of handoff region and the combining method. Our analytic model can be extended to various environments by adjusting given parameters.

Channel Assignment Strategies for Mobile Networks Using Fuzzy Petri Nets

In mobile cellular networks, the mobile devices need to handoff to different base stations based on certain criteria. And also fuzzy Petri nets can support an effective rule to deduce the inexact information. Based on the reasons, this paper focuses on the use of fuzzy Petri nets to model the handoff region for obtaining optimal channel assignment schemes. In this paper, a fuzzy logic based scheme for selection of base station is presented. The scheme considers two cover regions, namely, dual-BSs fuzzy assignment handoff and triple-BSs fuzzy assignment handoff of each base station to arrive at a fuzzy handoff decision regarding handoff to any particular base station. For comparison, the conventional power level based handoff scheme is also considered.

Quality of service estimation for soft handoff region ratio and call admission control in CDMA cellular systems

In the operational stage of code division multiple access (CDMA) systems, the soft handoff region ratio (SHRR) is among the important parameters that guarantee the quality of service (QoS) and resource allocation. This paper analytically investigates the effects of the SHRR on QoS. In doing so, we simultaneously take into account the capacity increasing factor and traffic load variation. For this purpose, we propose a new traffic load estimation model using a semi-Markov chain in order to consider the call arrivals influenced by the SHRR under general resident time condition. We also present the calculation algorithm of the QoS measures such as the new call blocking probability (NBP) and forced termination probability (FTP) by applying the proposed model to the prioritized call admission control (CAC). The numerical result illustrates the effects of various soft handoff system parameters. Likewise, it shows that the value of SHRR has a significant impact of the QoS under the normal propagation conditions. Sensitivity analysis is also performed to show the effect of exponential cell resident time assumption. The proposed modeling is expected to provide a practical guide to improve the QoS of CDMA soft handoff systems.

Predictive handoff mechanism with real-time mobility tracking in a campus wide wireless network considering ITS

Allowing users to discover and communicate their positions in the physical world has long been identified as a key component in emerging mobile computing applications. Pervasive positioning is required for the wide scale adaptation of location awareness. Vehicular communication in a campus wide hotspot plays a major role in establishing this. To provide seamless roaming between a subnet in a hotspot and to track the position of the mobile client is the main objective of this paper. wireless local area networks (WLANs) have become the state-of-the art campus networking option in many academic and corporate campuses. As “Wi-Fi” technology becomes ubiquitous, it is important to understand trends in the usage of these networks. As the mobile clients are moving from one base station/access point to another, the conventional layer-2 handoff consumes more time in the channel-scanning process. It takes around 310 ms, which leads to a heavy packet loss in real-time applications. The proposed dynamic handoff mechanism for mobility management is designed to minimize the handoff latency in IEEE 802.11 wireless local area networks, which in turn reduces the data loss and the signalling overhead in real-time applications. In this mechanism, threshold points are considered to provide better solution for fast and ping-pong type moving clients in a campus wide network. In our approach the base station (BS) range is divided into two zones namely Z1 – Good and Z2 – Average zone based on the signal strength as well as the distance. To predict the location of the mobile client in a campus wide network, a location prediction is introduced. Based on the location of the mobile client, signal strength and capacity of the BS, the minimal required resources are proactively reserved for the mobile client. A pre hand-off initiation algorithm is triggered when the mobile unit (MU) enters the minimum threshold ( Th min ) point. The threshold points are used to provide the handoff region (signal) notification to the mobile user. The MU receives the information about the candidate BS with QoS parameters. The dynamic channel scanning is incorporated in all the access routers and the switching centre (backbone router) to provide various QoS parameters to enhance the layer-2 handoff process and thus to reduce the layer-2 handoff latency. The experimental results are compared with the conventional layer-2 handoff latency for a campus wide network. The latency time is reduced from 310 to 33 ms, which is more suitable for real-time applications in a campus wide network.

The Complementary Use of 3G WCDMA and GSM/GPRS Cellular Radio Networks

The traffic performance of integrated 3G wide-band code division multiple access (WCDMA) and GSM/GPRS network is evaluated. This type of network links two cellular radio systems which have different set of frequency bands and the same coverage size. The base station of 3G WCDMA is installed on an existing GSM/GPRS site. Dual-mode mobile terminals use handoff to establish calls on the better system. The soft handoff or inter-frequency hard handoff occurs when mobile terminals of 3G WCDMA or GSM/GPRS move between two adjacent cells, respectively. The inter-system hard handoffs are used between 3G WCDMA and GSM/GPRS systems. The data rate conversions between different systems, soft handoff region size, multiple data rate multimedia services, and the effect of the mobile terminal mobility on the user mean dwell time in each system are considered in the study. The simulation results demonstrate that a great traffic performance improvement on the complementary use of 3G WCDMA and GSM/GPRS cellular radio networks compared with the use of GSM/GPRS cellular radio networks. When high-data rate transmission is chosen for low-mobility subscribers, both the handoff failure probability, and carried traffic rates increase with the new call generation rate. However, both rates decrease conversely with the increasing new call generation rate as soon as the new call generation rate exceeds a critical value. This causes the integrated networks saturation. The higher mean speed for the mobile terminals produces lower new call blocking probabilities and total carried traffic. The new call blocking probabilities and total carried traffic increase with the size of the soft handoff region.

Introduction to a New Performance Factor of Soft Handoff for Real-Time Streaming Services

We describe a new characteristic of soft handoff, call failure when a mobile moves from the handoff region to the normal region, and introduce the metric of region-transition failure probability to more accurately assess the performance of CDMA systems that support real-time video streaming services. This characteristic has not been considered in previous research. Simulations show that this failure must be considered since it significantly degrades system performance.

A capacity acquisition protocol for channel reservation in CDMA networks

In this paper, a capacity acquisition protocol is proposed for channel reservation in CDMA networks. Under this protocol, a cell is virtually divided into three regions (i.e., inner region, forced handoff region, and active handoff region). A new call in the active handoff region works in soft handoff mode upon its admission, while a new call in the inner and forced handoff regions works in single mode. However, in the forced handoff region, calls working in single mode can be forced into soft handoff mode, when extra capacity is needed by soft handoff calls. As a result, no explicit channel reservation is required before a call enters soft handoff. By adjusting the size of the forced handoff region, the capacity acquisition can adapt to traffic load and guarantee a desired call dropping probability. To evaluate the capacity acquisition protocol, an analytical model is derived and is also validated through computer simulations. Numeric results illustrate that the capacity acquisition protocol significantly reduces the call dropping probability.

Analysis of multiservice cellular networks with asymmetrical traffic and handoff queue

The next generation mobile communication system should be able to accommodate various services, including voice and Internet dial-up. As is well known, voice service has symmetrical, i.e. equal uplink and downlink bandwidth requirements, whereas Internet dial-up traffic usually has asymmetrical, i.e. unequal uplink and downlink bandwidth requirements. Frequency division duplex (FDD) usually allocates the same bandwidth to both uplink and downlink, whereas time division duplex (TDD) can change the number of time slots allocated to uplink and downlink to allocate different bandwidth to uplink and downlink. Thus, for scenarios with asymmetrical traffic, TDD is a better solution. To provide better quality of service during handoff, make-before-break soft handoff is preferable to break-before-make hard handoff. Furthermore, as forced termination of an ongoing call is less tolerable than blocking of a new call, handoff calls are usually given priority over new calls. We consider cellular multiservice TDD networks supporting both symmetrical and asymmetrical traffic with soft handoff and handoff queueing. First, we derive the mathematical model of the considered system with multi-dimensional birth–death process. Second, since the asymmetrical traffic may lead to the waste of uplink or downlink bandwidth, the effects of the traffic mix and the number of uplink slots on the system performance are studied. Third, the comparison of TDD and FDD with the presence of asymmetrical traffic is performed. Fourth, as the handoff region area increases, more calls will enter into or originate at that region. Thus, we study the effect of handoff region area on performance. Fifth, as a handoff call that cannot obtain the required channel upon arrival will be rejected if the handoff queue is full, the effect of handoff queue size on the performance is studied.

Fast handoff scheme based on mobility prediction in public wireless LAN systems

Recently, wireless LAN systems have been widely deployed for public mobile Internet services. Public wireless LAN systems can provide high speed Internet connectivity using portable devices such as laptop computers, personal digital assistants (PDAs), etc. In public wireless LAN systems, reliable user authentication and mobility support are essential issues. However, re-authentication during handoff procedures causes long handoff latency and this affects the quality of service in real-time multimedia applications. A fast handoff scheme based on mobility prediction is proposed. In this scheme, a mobile host entering the area covered by an access point (AP) performs authentication procedures for multiple APs, rather than just the current AP. These multiple APs are selected by a prediction method called the frequent handoff region (FHR) selection algorithm, which takes into account users' mobility patterns, service classes, etc. Since a mobile host is registered and authenticated for an FHR in advance, handoff latency resulting from re-authentication can be significantly reduced. Simulation results show that the proposed scheme is more efficient than other schemes in terms of handoff delay and buffer requirements.

Multistation data fusion for code-division multiple access wireless communications

Data fusion is the study of optimal information processing in distributed multisensor environments with the benefits of more reliable detection and higher immunity to noise and sensor failures. We investi- gate applications of the data fusion principle to the handoff problem in popular code-division multiple access (CDMA) cellular wireless commu- nication networks. When a mobile station traverses a cell boundary, cell handoff is required to make the transition of a mobile between cells smoother without degrading performance. CDMA multiple access allows soft handoff, in which the signal strength of the mobile is detected and tracked by the searchers from more than one base station. The cell receiving the strongest signal strength handles signal processing. We demonstrate that the signal detection quality in the handoff region can be further improved by fusing the detected results from multiple base sta- tions. A new fusion handoff strategy is designed, and its error perfor- mance measures are derived analytically in the presence of log-normal shadowing. Theoretical fading margin analysis shows that the fusion handoff approach offers better network performance over conventional hard and soft handoffs. © 2003 Society of Photo-Optical Instrumentation Engineers.

Forward-link soft-handoff in CDMA with multiple-antenna selection and fast joint power control

We consider forward-link soft-handoff with multiple antenna selection and fast joint power control at high data rates in a cellular code-division multiple-access network, where signals are directed to a mobile station (MS) from antennas located at the same or different base stations. The total power transmitted to any mobile is divided among the active antennas selected according to the momentary channel conditions so as to maximize the signal-interference ratio at each MS. Multiple-antenna selection is used to mitigate the effects of both short- and long-term fading, and achieve the best soft-handoff with respect to system capacity and complexity. To achieve capacity gains with soft-handoff, we derive optimum handoff thresholds corresponding to the optimum handoff region in different cell environments. Numerical results demonstrate that under high Doppler spread and large handoff-delay conditions, the proposed soft-handoff employing two transmit antennas and the optimum handoff threshold achieves a significant gain in microcell environments, but not in macrocell environments.

CDMA soft handoff analysis in the presence of power control error and shadowing correlation

Soft handoff has a special importance to power controlled code division multiple access (CDMA) systems. We introduce a new analytical model for CDMA soft handoff with emphasis on interference statistics at a system level. The relationship between soft handoff and power control is further explored by integrating power control error and shadowing correlation into the model. A new forward link model is also devised to study the effects of soft handoff on forward link performance. It is observed that the performance degradation due to power control error increases with increase in soft handoff region and higher shadowing correlation lowers the interference contribution from nonhandoff mobile stations (MS). It is also found that, unlike the reverse link, the forward performance depends on both given soft handoff setting and system load.

Traffic management in a multicode CDMA system supporting soft handoffs

A traffic management scheme is proposed in a multicode code-division multiple-access system supporting soft handoff that uses guard channels and a queue for real-time traffic. Preemptive queue control gives priority to queued handoff calls. Handoff traffic is derived as a function of the new call arrival rate, the size of the soft handoff region, mobile speed, the new call blocking probability, and the handoff failure probability. System performance with K types of calls is analyzed by introducing a concept of effective channel. The effects of the number of guard channels, the number of effective channels, system capacity, and other factors are numerically investigated. The effectiveness of the proposed queue control scheme is also observed in terms of handoff processing delay.

Load analysis of the soft handoff scheme in a CDMA cellular system

In a code-division multiple-access cellular system, the soft handoff with macrodiversity is known to increase the number of available channels in each cell from the interference-reduced radio environment. This capability, however, also incurs extra load on the system due to the increase in the number of channels occupied and reserved for macrodiversity. The objective is to evaluate the associated loads, thereby enabling effective channel management. We first differentiate two kinds of loads attributable to new and handoff calls, respectively. Further dividing handoff calls into two kinds, we derive a load balance equation from which three different loads at a cell are all exactly obtained in association with the size of the soft handoff region. Comparative analysis with the case of no soft handoff region, i.e., of hard handoff, shows the appropriate proportion of channels reserved for the macrodiversity in a given soft handoff region.

Characterization of soft handoff in CDMA systems

Many analytical approaches have been proposed for handoff analysis based on hard handoff in mobile communication systems. In code-division multiple-access (CDMA) systems with soft handoff, mobile stations (MSs) within a soft handoff region (SR) use multiple radio channels and receive their signals from multiple base stations (BSs) simultaneously. Therefore, the SRs should be considered for handoff analysis in CDMA systems. An analytical model for soft handoff in CDMA systems is developed by introducing an overlap region between adjacent cells and the handoff call attempt rate and the channel holding times are derived. Applying these results to a nonprioritized CDMA system, the effects of soft handoff and the mean cell residual time are investigated and compared with hard handoff.

Network configurations for seamless support of CDMA soft handoffs between cell clusters

Current code division multiple access (CDMA) networks do not support soft handoffs between cell clusters serviced by different mobile switching centers (MSC's). Three novel network configurations are proposed to overcome this limitation. Configurations I and II employ crosslinks to allow diversity combining of signals. This is accomplished in Configuration III by linking the modified MSCs serving adjacent cell clusters. In Configuration I, a scheme which reduces the handoff blocking probability by lengthening the handoff transition time is proposed. Configuration II expands overlapping regions of adjacent cell clusters, thus enabling the use of different intercluster handoff regions for different handoff directions to prevent oscillations which may occur in Configuration I, while reducing the necessary number of intercluster handoffs. Configuration III fully shares the trunks to support the highest number of calls among all three configurations. A new mobility model for microcells is developed to enable dimensioning of the trunk groups in each configuration. For Configurations I and II, the optimal partitions of trunk groups into direct and crosslinks are determined by mathematical analyses and computer simulations. For Configuration III, the optimal number of trunks required to interconnect adjacent MSCs is investigated by computer simulations. The new call and handoff blocking probabilities in all of these configurations are compared.

Performance analysis of soft handoff in CDMA cellular networks

The code-division multiple-access (CDMA) scheme has been considered as one possible choice of the future standards for cellular networks because of its various advantages. Since there can be only one carrier frequency being used in CDMA systems, a handoff scheme with diversity, a so-called handoff, was proposed for higher communication quality and capacity. A mathematical model is developed to analyze the soft handoff process. Markov's concept is applied to describe the system's steady state statistical behavior. System performance such as blocking probability, handoff refused probability, and channel efficiency are also determined. It is concluded that the larger the area the soft handoff region is, the better users in the cellular network will feel.