Showing papers on "Handover published in 2002"

Call admission control schemes and performance analysis in wireless mobile networks

Abstract: Call admission control (CAC) plays a significant role in providing the desired quality of service in wireless networks. Many CAC schemes have been proposed. Analytical results for some performance metrics such as call blocking probabilities are obtained under some specific assumptions. It is observed, however, that due to the mobility, some assumptions may not be valid, which is the case when the average values of channel holding times for new calls and handoff calls are not equal. We reexamine some of the analytical results for call blocking probabilities for some call admission control schemes under more general assumptions and provide some easier-to-compute approximate formulas.

Handover management for mobile nodes in IPv6 networks

Abstract: We analyze IPv6 handover over wireless LAN. Mobile IPv6 is designed to manage mobile nodes' movements between wireless IPv6 networks. Nevertheless, the active communications of a mobile node are interrupted until the handover completes. Therefore, several extensions to Mobile IPv6 have been proposed to reduce the handover latency and the number of lost packets. We describe two of them, hierarchical Mobile IPv6, which manages local movements into a domain, and fast handover protocol, which allows the use of layer 2 triggers to anticipate the handover. We expose the specific handover algorithms proposed by all these methods. We also evaluate the handover latency over IEEE 802.11b wireless LAN. We compare the layer 2 and layer 3 handover latency in the Mobile IPv6 case in order to show the saving of time expected by using anticipation. We conclude by showing how to adapt the IEEE 802.11b control frames to set up such anticipation.

Systems and methods for intelligent inter-system handoff

Abstract: A multi-mode mobile station performs an inter-system handoff between systems, qualified by the presence or absence of a preferred wireless communication network in a roaming lookup table (703) stored and maintained in either mobile station memory or with the network controller. In one embodiment the accurate location of the mobile unit is determined by a global position fix, after which a coverage map is consulted to verify the availability of a preferred network before initiating a background scan. In other embodiments, a learning function creates habit profiles of a subscribers regular behavior upon which the system intelligently initiates scanning for preferred network.

Context aware application level triggering mechanism for pre-authentication, service adaptation, pre-caching and handover in a heterogeneous network environment

Abstract: A network selection system that includes a mobile terminal in communication with a first network, a second network in communication with the first network and an application layer triggering mechanism that determines which one of a plurality of triggers is required in a certain set of circumstances to provide a particular application.

Authentication system for mobile entities

Abstract: Verification and authentication methods for use in mobile communications systems where base stations (110) do not have direct access to a shared secret common to a security server (101) and a mobile node (112, 114) are described. Unilateral authentication of a mobile node by a base station is augmented through the use of a mutual authentication token (MAT) generated by the security server and the mobile node as a function of the shared secret. With each handoff the MAT generated by the security server is passed from base station (110) to base station (110', 110'') via a secure communications channel. After each handoff the mobile node and new base station perform a unilateral authentication operation and establish a new encryption key that is a function of the MAT. Existence of a trust relationship between a new base station and the last base station is verified by the new base station's ability to properly encrypt data.

A dynamic call admission policy with precision QoS guarantee using stochastic control for mobile wireless networks

Abstract: Call admission control is one of the key elements in ensuring the quality of service in mobile wireless networks. The traditional trunk reservation policy and its numerous variants give preferential treatment to the handoff calls over new arrivals by reserving a number of radio channels exclusively for handoffs. Such schemes, however, cannot adapt to changes in traffic pattern due to the static nature. This paper introduces a novel stable dynamic call admission control mechanism (SDCA), which can maximize the radio channel utilization subject to a predetermined bound on the call dropping probability. The novelties of the proposed mechanism are: (1) it is adaptive to wide range of system parameters and traffic conditions due to its dynamic nature; (2) the control is stable under overloading traffic conditions, thus can effectively deal with sudden traffic surges; (3) the admission policy is stochastic, thus spreading new arrivals evenly over a control period, and resulting in more effective and accurate control; and (4) the model takes into account the effects of limited channel capacity and time dependence on the call dropping probability, and the influences from nearest and next-nearest neighboring cells, which greatly improve the control precision. In addition, we introduce local control algorithms based on strictly local estimations of the needed traffic parameters, without requiring the status information exchange among different cells, which makes it very appealing in actual implementation. Most of the computational complexities lie in off-line precalculations, except for the nonlinear equation of the acceptance ratio, in which a coarse-grain numerical integration is shown to be sufficient for stochastic control. Extensive simulation results show that our scheme steadily satisfies the hard constraint on call dropping probability while maintaining a high channel throughput.

Method and system for a handoff in a broadcast communication system

Abstract: A method and system for a handoff in a broadcast communication system is disclosed. A subscriber assisted handoff is impractical in a broadcast communication system due to e.g., a high signaling load, a difficulty to synchronize the broadcast transmission. On the other hand, the small number of broadcast channels enables the subscriber station to perform the handoff autonomously. To streamline the autonomous handoff decision process, several distinct sets of pilot identifiers and rules for transitioning among the sets are defined. To fully integrate broadcast services with the services provided by the cellular telephone systems in a subscriber environment, a methods for various handoff scenarios are analyzed.

Fast inter-ap handoff using predictive authentication scheme in a public wireless lan

Abstract: Recently, wireless LAN systems have been widely deployed for public mobile Internet services. Public wireless LAN system can provide high speed Internet connectivity using portable devices such as laptop computers, Personal Digital Assistants (PDA), etc. In the 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. In this paper, we proposed a fast Inter-AP handoff scheme based on a predictive authentication method. In our scheme, a mobile host entering the area covered by an AP, performs authentication procedures for multiple APs, rather than just the current AP. These multiple APs are selected using a 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 minimized. Simulation results show that the proposed scheme is more efficient than other schemes in terms of handoff delay and buffer requirements.

Commanding handover between differing radio access technologies

Abstract: A dual mode mobile terminal (MT) (30) is capable of communicating (e.g., with a core network) either via a first radio access network (12) having a first type radio access technology (GSM) or a second radio access network (14) having a second type radio access technology (UTRAN). When conditions warrant, a network node (26) prepares a radio access technology (RAT) handover message (3-9) for transmission to the equipment unit (UE) in conjunction with handover of the mobile terminal (MT) from the first radio access network to the second radio access network, and an associated change of operation mode of the mobile terminal (MT) from the first mode to the second mode. In accordance with the present invention, a radio access technology handover message includes a first information element representative of a first parameter from which a value of a second parameter can be derived so that the second parameter need not be included as a separate information element in the radio access technology handover message. Not including the second parameter as a separate element in the radio access technology handover message facilitates non-segmentation of the radio access technology handover message. In one aspect of the invention, the radio access technology handover message is a RRC Handover to UTRAN message; the first parameter is a Serving-Radio Network Temporary Identifier (S-RNTI 2); and, the second parameter is an information element which facilitates distribution of load and transmission of traffic in the radio access network (e.g., a Default DPCH Offset Value).

Link context mobility method and system for providing such mobility, such as a system employing short range frequency hopping spread spectrum wireless protocols

Abstract: Disclosed is a system and method for wirelessly exchanging communications with at least one mobile unit in a network that includes base stations units. The method includes receiving a wireless communication from the mobile unit, where the wireless communication is under a wireless communications protocol that does not provide for handoff of communications links between base station units. The method also includes obtaining a unique session identifier for the communication with the mobile unit, and establishing a communications link with the mobile unit, where the communications link includes link context data associated with the mobile unit. The link context data associated with the mobile unit is identified at least in part based on the unique session identifier. The method further includes determining that the mobile unit is to be handed-off, and handing off to another base station unit the communications link and link context associated with the mobile unit, where the handing off is performed without assistance of the mobile unit.

IDMP-based fast handoffs and paging in IP-based 4G mobile networks

Abstract: We consider the use of our previously proposed Intra-Domain Mobility Management Protocol (IDMP) in fourth-generation mobile networks. On evaluating the heterogeneous access technologies, cellular layouts, and application characteristics of 4G environments, we realize a need to reduce both handoff latency and the frequency of mobility-related signaling. We first present IDMP's fast intradomain handoff mechanism that uses a duration-limited proactive packet multicasting solution. We quantify the expected buffering requirements of our proposed multicasting scheme for typical 4G network characteristics and compare it with alternative IP-based fast handoff solutions. We also present a paging scheme under IDMP that replicates the current cellular paging structure. Our paging mechanism supports generic paging strategies and can significantly reduce the mobility-related IP signaling load.

Performance of handoff algorithm based on distance and RSSI measurements

Abstract: The performance of a proposed handoff algorithm based on both the distance of a mobile station to neighboring base stations and the relative signal strength measurements is evaluated. The algorithm performs handoff when the measured distance from the serving base station exceeds that from the candidate base station by a given threshold and if the measured signal strength of the adjacent base station exceeds that of the serving base station by a given hysteresis level. The average handoff delay and average number of handoffs are used as criteria for performance. Numerical results are presented to demonstrate the feasibility of the distance-based handoff algorithm, including results for an additional criterion based on relative signal strength. The proposed algorithm is compared with an algorithm based on absolute and relative signal strength measurements and with a solely distance-based algorithm. It is found that the proposed handoff algorithm performs well in a log-normal fading environment when the distance estimate error is modeled by wide-sense stationary additive white Gaussian noise.

Performance analysis on hierarchical Mobile IPv6 with fast-handoff over end-to-end TCP

Abstract: Mobile IPv4 has been considered as the de facto standard in providing Internet mobility. However, as the demand for wireless mobile devices capable of executing real-time applications increases, it is necessary to provide superior handoff latency and quality of service (QoS). Mobile IPv6 is designed to resolve these issues, and has numerous applicable optimization techniques. Two ways of reducing the handoff latency, in both IPv4 and IPv6, have been proposed in the literature. One aims to reduce the (home) network registration time while the other aims to reduce the lengthy address resolution time when in a visiting network. We present a performance analysis of the current IETF proposals, namely, the hierarchical Mobile IPv6 architecture and the fast-handoff mechanism. The former is aimed at reducing the registration time while the later in reducing the address resolution time. We show through simulation that managing the registration process in a hierarchical fashion greatly reduces the overall handoff latency. Comparatively, the fast-handoff mechanism is even more capable of reducing the handoff latency. The simple superimposition of these two frameworks produces the best overall handoff latency result. However, the overall improvement is not a simple aggregation of the individual handoff latency gains. In fact, we discovered some rather non-trivial traffic behavior when these two frameworks are combined. We identify the causes which hinder the handoff performance and hence devise a set of design guidelines to improve the handoff latency further.

Methodology for portable wireless devices allowing autonomous roaming across multiple cellular air interface standards and frequencies

Abstract: Subscriber units and base stations of telecommunication systems are equipped with RF to IF (EXA) circuit boards which provide complete flexibility for radio communication. The boards may communicate on any air interface standard (CDMA, TDMA, Bluetooth, 3G cellular, etc.) at any frequency or band of frequencies. Separate, independent forward and reverse channels may be assignment, each having its own air interface and frequency band. When a call is initiated, a set of optimum forward and reverse channels are assigned, taking into account relevant factors such as traffic, subscriber requirements for high speed data, etc., so that the channel assignment is tailored to the current communication needs. Channel assignment is updated as needs change, as other channels become available and at handoff. In a business model, air time on multiple telecommunication systems is sold to subscribers who can use this technology to roam widely. Revenue is also generated from licensing of the EXA circuit boards in subscriber units and in base stations.

Call admission control for CDMA mobile communications systems supporting multimedia services

Abstract: The call admission control (CAC) belongs to the category of resource management. Since the radio spectrum is very scarce resource, CAC is one of the most important engineering issues for mobile communications. In this paper, we propose a CAC scheme for direct sequence code-division multiple-access cellular systems supporting mobile multimedia communications services. There are multiple call classes in multimedia services and the required signal-to-interference ratio (SIR) varies with call classes. Call admission decision in the proposed scheme is based on SIR measurement. We take account of the traffic asymmetry between uplink and downlink, which is the most important characteristic of multimedia traffic. In addition, the proposed scheme guarantees the priority of handoff call requests over new call requests. We evaluate the performance of the proposed scheme using Markov analysis. The performance measures which we focus on are the system throughput and the blocking probabilities of handoff calls and new calls. The outage probability of a call in progress is also calculated, which is the probability that the measured bit energy-to-noise density ratio of the call is smaller than the required value for maintaining adequate transmission quality. We present some numerical examples with practically meaningful parameter values and, as a result, show that the proposed CAC scheme can operate well in the mobile multimedia systems such as the International Mobile Telecommunications-2000 (IMT-2000) systems.

Vertical handoff procedure and algorithm between IEEE802.11 WLAN and CDMA cellular network

Abstract: As the number of wireless subscribers rapidly increases guaranteeing the quality of services anytime, anywhere, and by any-media becomes indispensable. These services require various networks (such as CDMA2000 and Wireless LAN) to be integrated into IP-based networks, which further require a seamless vertical handoff to 4th generation wireless networks. This paper presents a seamless vertical handoff procedure between IEEE802.11 WLAN, which covers hotspot area such as offices, campuses and hotels, and the CDMA2000 cellular network that overlays the WLAN and also covers a larger area. A handoff algorithm between WLAN and CDMA2000 cellular network is proposed. In this algorithm, traffic is classified into real-time and non real-time services. Then, the beginning of handoff is decided by the handoff delay time and throughput according to traffic classes. It is also analyzed mathematically.

Method and apparatus for facilitating handovers for a group of mobile radios

Abstract: Advance handover notice is given to a "target" base station of a group of mobile radio connections that will be soon be handed over the to the target base station from a current, "serving" base station. This advance notice permits the target base station to reserve resources and prepare for the handovers of the mobile radio connections. In addition, the handover operation is initiated earlier than it would be otherwise. Early handover initiation is possible because the route of the moving vehicle is known or is predictable, and therefore, the serving and target base stations are known or may be predicted in advance. In this way, the likelihood of successful handovers with no dropped calls is increased for mobile stations moving at high speed and/or together as a group.

Method of handoff within a telecommunications system containing digital base stations with different spectral capabilities

Abstract: The present invention is directed to a digital wireless telecommunications system that includes a plurality of base station of differing spectral capabilities, and a plurality of remote stations capable of transmitting data to and receiving transmissions from the plurality of base stations. The invention herein provides a method for remote station hand-off between base stations of a narrower spectral capacity and base stations of a wider spectral capacity. A method is provided for a wireless telecommunications infrastructure to facilitate a remote station hand-off from a set of narrowband compliant base stations to at least one wideband compliant base station while a remote station is in the coverage area of both types of base stations. Additionally, the invention herein provides remote station apparatus, base station apparatus, and base station controller apparatus for performing the handoff methodology of the present invention.

Wireless base station to base station synchronization in a communication system, such as a system employing a short-range frequency hopping or time division duplex scheme

Abstract: In a network, a method is disclosed for wirelessly exchanging communications with at least one mobile unit. The network includes first and second base stations units coupled to the network, and may include a system controller. The method includes: receiving a communication signal from the second base station unit, wherein the first and second base station units are configured to employ a wireless communications protocol, and wherein the wireless communications protocol does not provide for handoff of communications links between base station units; at the first base station unit, determining if the second base station unit has been synchronized based on the communication signal; at the first base station unit, if the second base station unit is synchronized, then synchronizing an internal clock based on the synchronized second base station, wherein the synchronizing is performed without assistance from a system controller.

Forward-link scheduling in a wireless communication system during soft and softer handoff

Abstract: A method and apparatus for scheduling transmit rates and power levels for data in conjunction with a voice-data communication during conditions of soft and softer handoff. During conditions of no handoff, or hard handoff, an algorithm selects a slot reflecting a favored power level and transmission rate for transmitting the non-voice data on a supplemental channel. The slot is selected based upon the transmission power levels for voice-data transmitted by a base station to a remote station on a fundamental channel. The algorithm applies to softer handoff using information from all the sectors of a base station involved in the softer handoff. During soft handoff, instead of scheduling forward link transmission based on recent power and rate, or C/I information, data is continuously transmitted to the user at a power level based on average required power.

Icar: an integrated cellular and ad hoc relaying system

Abstract: The cellular concept was introduced for wireless communication to address the problem of having scarce frequency resource. It is based on the sub-division of geographical area to be covered by the network into a number of smaller areas called cells. Frequency reuse in the cells far away from each other increases system’s capacity. But at the same time, the cell boundaries prevent the channel resource of a system to be fully available for users. No access to Data Channels (or DCHs) in other cell by the mobile host (or MH) limits the channel efficiency and consequently the system capacity. In this dissertation, we propose a new wireless system architecture based on the integration of cellular and modern ad hoc relaying technologies, called iCAR. It can efficiently balance traffic loads and share channel resource between cells by using Ad hoc relaying stations (ARSs) to relay traffic from one cell to another dynamically. This not only increases the system’s capacity costeffectively, but also reduces transmission power for mobile hosts and extends system coverage. We analyze the system performance in terms of the call blocking probability and queuing delay using multi-dimensional Markov chains for the new call requests and the call dropping probability for handoff requests, and verify the analytical results via simulations. Our results show that with a limited number of ARSs and some increase in the signaling overhead (as well as hardware complexity), the call blocking/dropping probability in a congested cell as well as the overall system can be reduced. We also propose a seed-growing approach for ARS placement, and discuss the upper bound on the number of seed ARSs needed in the system. In order to quantitatively evaluate ARS placement strategies, we introduce the concept of a new performance metric called quality of (ARS) coverage (QoC) for the comparison of various ARS placement strategies, and propose three rules of thumb as guidelines for cost-effective ARS placement in iCAR. Furthermore, we propose the signaling and routing protocols for establishing QoS guaranteed connections for IP traffic in iCAR. In particular, we discuss how a relaying route between a MH and a BTS in a nearby cell can be established via ARSs, and evaluate the performance of the protocols in terms of request rejection rate and signaling overhead through simulations. In addition, we propose a novel concept called “managed mobility” and address the ARS mobility management in iCAR.

Apparatus and method for selecting a handoff base station in a wireless network

Abstract: An apparatus and method is disclosed for selecting a handoff target base station in a wireless network. The apparatus comprises a handoff controller within a wireless mobile station that selects an optimal target base station for handoff based on pilot signal strength measurements of at least two candidate base stations and one of: a location of the wireless mobile station, a velocity of the wireless mobile station, and a direction of motion of the wireless mobile station. The present invention uses more than just pilot strength measurements to select an optimal target base station for handoff. Incorporating position location information in the handoff decision causes the handoff decision to be more reliable. This reduces the number of unnecessary handoffs and results in better system performance.

Communication system employing multiple handoff criteria

Abstract: Disclosed herein is a communication system which manages guarantee of service (GOS) requirements for various users while efficiently managing backhaul network traffic and optimizing overall system capacity. In one aspect, armed handoff is used to transmit forward link data from a single base station to a particular mobile station as long as certain minimum requirements are met, such as minimum data throughput, minimum data rate, and GOS requirements. If these criteria are not met, soft and softer handoff can be employed to transmit forward link data from one or more base stations to a particular mobile station until the conditions for armed handoff are met. In another aspect, the test to add a base station sector to the active set differs based on whether other sectors of that base station already exist in the active set. The test is less stringent when a sector is not the first of its base station to enter the active set, and more stringent when it is the first.

On handoff performance for an integrated voice/data cellular system

Abstract: One of the key performance measures in wireless cellular systems is the handoff dropping probability. The paper studies the handoff performance for an integrated voice/data wireless cellular system. Specifically, we propose a new handoff control policy, called dual trunk reservation with queuing (DTR-Q). It uses two thresholds, one to reserve bandwidth for voice handoff, and the other for managing the data traffic. By taking advantage of the adaptiveness of data traffic, it uses a single queue to buffer the data request further in case the requested bandwidth is not available. The unique features of the proposed DTR-Q scheme are: 1) it can provide the necessary service guarantee and service differentiation for voice and data traffic; 2) it adopts a complete sharing approach that can maximize the channel utilization. We propose an analytical model to calculate the key performance measures, and thoroughly investigate system performances under a variety of system parameters.

Proactive deployment of decision mechanisms for optimal handover

Abstract: To achieve optimal selection of new access points for mobile devices (10) being located in a mobile communication environment (14), according to the present invention there is provided a method of assisting handovers for a mobile device in a mobile communication environment. It is proposed to proactively deploy a handover decision mechanism in relation to a handover and in view of the operational context of the mobile device (10). This proactively deployed handover decision mechanism is then used to determine a new access point for the mobile device (10).

Handoff in wireless mobile networks

Abstract: Mobility is the most important feature of a wireless cellular communication system. Usually, continuous service is achieved by supporting handoff (or handover) from one cell to another. Handoff is the process of changing the channel (frequency, time slot, spreading code, or combination of them) associated with the current connection while a call is in progress. It is often initiated either by crossing a cell boundary or by a deterioration in quality of the signal in the current channel. Handoff is divided into two broad categories— hard and soft handoffs. They are also characterized by “break before make” and “make before break.” In hard handoffs, current resources are released before new resources are used; in soft handoffs, both existing and new resources are used during the handoff process. Poorly designed handoff schemes tend to generate very heavy signaling traffic and, thereby, a dramatic decrease in quality of service (QoS). (In this chapter, a handoff is assumed to occur only at the cell boundary.) The reason why handoffs are critical in cellular communication systems is that neighboring cells are always using a disjoint subset of frequency bands, so negotiations must take place between the mobile station (MS), the current serving base station (BS), and the next potential BS. Other related issues, such as decision making and priority strategies during overloading, might influence the overall performance. In the next section, we introduce different types of possible handoffs. In Section 1.3, we describe different handoff initiation processes. The types of handoff decisions are briefly described in Section 1.4 and some selected representative handoff schemes are presented in Section 1.5. Finally, Section 1.6 summarizes the chapter.

Partial support of mobility between radio access networks

Abstract: Attempted utilization (by a user equipment unit which subscribes to its subscription operator network) of a restricted cell is precluded or rejected by an auxiliary operator's network, the restricted cell being any cell of the auxiliary operator network for which a subscription operator network has a competing cell. The rejected attempted utilization can be one of (1) handover to the restricted cell, and (2) cell/URA updating by the user equipment unit viathe restricted cell. Further, preclusion of attempted utilization of the restricted cell occurs when the user equipment unit attempts cell reselection.

A network architecture for MPLS-based micro-mobility

Abstract: Current mobile networks provide link-layer mobility as a mobile host changes its point of attachment within the scope of an access node, and provide wide-area mobility through global mobility protocols such as mobile IP. Several proposals have been made for an intermediate level of mobility support, called micro-mobility which addresses the issues of handover latency, signaling overhead and packet loss that are inherent in wide-area mobility protocols. We propose a new multi-protocol label switching (MPLS) based network architecture that implements intra-domain micro-mobility using label switched path (LSP) re-direction in a traffic engineered network. We introduce an enhanced label edge router (LER), called the label edge mobility agent (LEMA) and describe the operations of the network nodes in our architecture. The advantages of our approach, as compared with the existing proposals, are its distributed and scalable nature, the ability to provision for quality of service (QoS) through traffic engineering, its ease of gradual deployment, and its efficient design and handover performance.

Modeling and efficient handling of handoffs in integrated wireless mobile networks

Abstract: We propose and analyze two handoff schemes without and with preemptive priority procedures for integrated wireless mobile networks. We categorize the service calls into four different types, namely, originating voice calls, originating data calls, voice handoff request calls, and data handoff request calls and we assume two separate queues for two handoff services. A number of channels in each cell are reserved exclusively for handoff request calls. Out of these channels, few are reserved exclusively for voice handoff request calls. The remaining channels are shared by both originating and handoff request calls. In the preemptive priority scheme, higher priority is given to voice handoff request calls over data handoff request calls and can preempt data service to the queue if, upon arrival, a voice handoff request finds no free channels. We model the system by a three-dimensional Markov chain and compute the system performance in terms of blocking probability of originating calls, forced termination probability of voice handoff request calls, and average transmission delay of data calls. It is observed that forced termination probability of voice handoff request calls can be decreased by increasing the number of reserved channels. On the other hand, as a data handoff request can be transferred from a queue of one base station to another, there is no packet loss of data handoff except for a negligibly small blocking probability.