Showing papers on "Handover published in 2001"

Distributed control algorithms for service differentiation in wireless packet networks

Abstract: This paper investigates differentiated services in wireless packet networks using a fully distributed approach that supports service differentiation, radio monitoring and admission control. Service differentiation is based on the IEEE 802.11 distributed coordination function (DCF) originally designed to support best-effort data services. We extend the distributed coordination function to provide service differentiation for delay sensitive and best-effort traffic. Two distributed estimation algorithms are proposed and analyzed. A virtual MAC (VMAC) algorithm passively monitors the radio channel and estimates locally achievable service levels. The virtual MAC estimates key MAC level statistics related to service quality such as delay, delay variation, packet collision and packet loss. We show the efficiency of the virtual MAC algorithm and consider significantly overlapping cells and highly bursty traffic mixes. A virtual source (VS) algorithm utilizes the virtual MAC to estimate application level service quality. The virtual source allows application parameters to be tuned in response to dynamic channel conditions based on "virtual delay curves". We demonstrate through simulation that when these distributed virtual algorithms are applied to the admission control of the radio channel then a globally stable state can be maintained without the need for complex centralized radio resource management. Finally, we discuss a distributed service level management scheme that builds on the proposed algorithms to offer continuous service with handoff.

Mobility management incorporating fuzzy logic for heterogeneous a IP environment

Abstract: The next generation in mobility management will enable different mobile networks to interoperate with each other to ensure terminal and personal mobility and global portability of network services. However, in order to ensure global mobility, the deployment and integration of both satellite and terrestrial components are necessary. This article is focused on issues related to mobility management in a future mobile communications system, in a scenario where a multisegment access network is integrated into an IP core network by exploiting the principles of Mobile IP. In particular, attention is given to the requirements for location, address, and handover management. In a heterogeneous environment, the need to perform handover between access networks imposes particular constraints on the type of information available to the terminal and network. In this case, consideration will need to be given to parameters other than radio characteristics, such as achievable quality of service and user preference. This article proposes a new approach to handover management by applying the fuzzy logic concept to a heterogeneous environment. The article concludes with a presentation of mobility management signaling protocols.

Enabling seamless user mobility in a short-range wireless networking environment

Abstract: The present invention provides methods, systems, and computer program instructions for enabling a variety of devices (120), particularly low-power hand-held devices, to travel seamlessly through a networking environment such as that encountered within a building by establishing connectivity to a plurality of network access points, which may be referred to as Handoff Management Points (HMPs) (110). The illusion of seamless network connectivity is provided by having these access points coordinate with a core server (100) to perform user authentication, device address assignement, and handoff services.

Optimization scheme for mobile users performing vertical handoffs between IEEE 802.11 and GPRS/EDGE networks

Abstract: The next generation wireless networks are characterised by anywhere, anytime connectivity, enhanced data services and higher data rates to enduser. New technologies such as IEEE 802.11 WLAN, Bluetooth, HIPERLAN/2, GPRS/EDGE, cdma2000 and WCDMA aim to achieve this. To facilitate new services, and make them flexible and bandwidth efficient, vertical roaming of mobile nodes is a tempting possibility for operators. Benchmarks and metrics are needed to assess these issues. The need for qualitative and quantitative results for these parameters in a real time situation is critical. One such scenario is the effect on the network performance by means of effective throughput and handoff latency perceived by the mobile user, with increasing number of active users or network load. This paper presents simulation results for mean throughput and handoff delay obtained in vertical handoff and horizontal handoff in IEEE 802.11 and GPRS/EDGE networks. An optimization scheme for mobile users performing vertical handoffs is presented with analysis.

Predictive mobility support for QoS provisioning in mobile wireless environments

Abstract: With the proliferation of wireless network technologies, mobile users are expected to demand the same quality of service (QoS) available to fixed users. This paper presents a predictive and adaptive scheme to support timed-QoS guarantees in pico- and micro-cellular environments. The proposed scheme integrates the mobility model into the service model to achieve efficient network resource utilization and avoid severe network congestion. The mobility model uses a probabilistic approach to determine the most likely cluster to be visited by the mobile unit. The admission control is invoked when a new call arrives or an existing call performs a handoff to verify the feasibility of supporting the call. The performance of the proposed schemes is compared to the shadow cluster scheme. The performance of the proposed scheme under different traffic patterns is also presented.

Estimation of Doppler spread and signal strength in mobile communications with applications to handoff and adaptive transmission

Abstract: Summary Estimation of signal strength, a measure of channel quality, and Doppler spread which is proportional to the mobile speed, are important for handoff algorithms and optimal tuning of system parameters to changing channel conditions in adaptive transmission systems. This paper provides a survey of existing techniques for estimating the statistical parameters of the mobile channel. We discuss the current state of the art in estimation of the received signal strength, mobile velocity, and other related statistical channel parameters, illustrate their performance, and compare existing techniques. The sensitivity of these schemes to modeling error owing to the presence of line of sight, directional reception, and noise is characterized analytically and illustrated by simulations. Copyright  2001 John Wiley & Sons, Ltd.

On-demand QoS routing in multihop mobile networks

Abstract: The emergence of nomadic applications have generated a lot of interest in next generation wireless network infrastructures which provide differentiated service classes. So it is important to study how the quality of service (QoS) should be guaranteed. To accomplish this, we develop an admission control scheme which can guarantee bandwidth for real-time applications in multihop mobile networks. In our scheme, a host need not discover and maintain any information of the network resources status on the routes to another host until a connection request is generated for the communication between the two hosts, unless the former host is offering its services as an intermediate forwarding station to maintain connectivity between two other hosts. This bandwidth guarantee feature is important for a mobile network to interconnect wired networks with QoS support. Our connection admission control scheme can also work in a standalone mobile ad hoc network for real-time applications. This control scheme contains end-to-end bandwidth calculation and bandwidth allocation. Under such a scheme, the source is informed of the bandwidth and QoS available to any destination in the mobile network. This knowledge enables the establishment of QoS connections within the mobile network and the efficient support of real time applications. In the case of an ATM interconnection, the bandwidth information can be used to carry out intelligent handoff between ATM gateways and/or to extend the ATM virtual circuit service to the mobile network with possible renegotiation of QoS parameters at the gateway. We examine via simulation the system performance in various QoS traffic flows and mobility environments. The "on-demand" feature enhances the performance in the mobile environment because the source can keep more connectivity with enough bandwidth to a receiver in the path-finding duration.

Method and apparatus for handoff of a wireless packet data services connection

Abstract: A novel method and apparatus is disclosed for performing seamless handoff of a mobile station (MS) between Radio Access Networks (RANs) that use different types of wireless interfaces. The described embodiments enable an MS to handoff between different RANs without causing routing ambiguity, and without substantial loss of network data. Upon moving from the coverage area of a first RAN using a first wireless interface to the coverage area of a second RAN using a second wireless interface, an MS determines whether routing ambiguity may result from the change of RAN and, based on the determination, triggers a re-registration of its network address. A foreign agent (FA) within a packet data serving node (PDSN) monitors network address re-registrations are being created for the same MS. Based on this determination, the PDSN terminates redundant R-P network connections resulting from movement of the MS between different RANs.

Efficient header handling involving GSM/EDGE radio access networks

Abstract: To facilitate handing of headers for Internet-transmissible packets, a radio access network sends to a mobile station (MS) a message which downloads configuration options for each of corresponding plural header adaptation strategies. The mobile station (MS) elects one of the plural header adaptation strategies and includes the elected strategy in a return message, whereby the radio access network configures a radio bearer for packets to be transmitted between the radio access network and the mobile station. In a first illustrated mode of implementation of the invention, the radio access network is a GSM/EDGE radio access network, with the downloading message being a radio bearer setup message and the return message sent from the mobile station to the radio access network being a radio bearer setup complete message. In a second illustrated mode of implementation of the invention, the message that downloads configuration options for each of plural header adaptation strategies is a handover command message for handing over control of the mobile station from a source radio access network to a target radio access network. In this second mode, the message which informs which of the plural strategies is elected is a handover complete message. The plural header adaptation strategies can include header compression (useful, e.g., for a multimedia service); header removal (useful, e.g., for a spectrum efficient voice packet voice bearer that reuses codec-specific channel coding); and no header adaptation.

Network resource sharing during handover of a mobile station between cellular wireless networks

Abstract: System components of cellular wireless networks are shared during and after a mobile station handover from a first cellular wireless network (system A) to a second cellular wireless network (system B). According to one aspect, layer 2/3 call control functions are anchored in a base station controller (BSC) of system A, even after a data communication is handed over from system A to system B. According to another aspect, a link layer supporting the data communication is anchored in the BSC of system A servicing the data communication. In this case, the BSC of system A interfaces with a serving BTS of system B to service the ongoing data communication. According to still another aspect, the link layer is handed over to system B but the link layer of system B continues to use a link layer transmit buffer of system A that remains in the servicing BSC of system A.

Method for autonomous handoff in a wireless communication system

Abstract: A method and apparatus for handoff to a rescue channel is introduced without the need to send and receive handoff control messages. In the preferred embodiment of the present invention, coordination of the rescue procedure at the infrastructure (450, 350, 351, 352) and mobile station (330) is provided first by disabling the mobile transmitter followed by subsequent detection of signal loss and frame erasures at the serving cells (311), then by enabling the mobile transmitter followed by subsequent detection of signal by a rescue cell (310, 312, 313, 314), and finally by enabling the rescue cell channel transmitter followed by subsequent detection and reception of signal and frames by the mobile station (330).

Handover of wireless calls between systems supporting circuit and packet call models

Abstract: An improved wireless network provides intersystem handoffs between existing circuit wireless systems and packet systems. A packet wireless system is enhanced to provide translation between circuit and packet call models. A Media Gateway translates bearer traffic between formats used in each system. The Media Gateway, a Media Gateway Control Function, and an associated Call State Control Function, cooperate to emulate the behavior of a circuit wireless system, so that when interoperating with conventional circuit systems, the packet system appears to be another circuit wireless system. Where necessary, the Media Gateway, Media Gateway Control Function, and Call State Control Function further cooperate to emulate the functions of an anchor MSC of a circuit wireless system.

Mobile communication system for accomplishing handover with phase difference of frame sync signals corrected

Abstract: A method of switching a communication channel when a mobile station moves from one service area to another service area is disclosed. The mobile station determines a difference between the transmission phase of a frame synchronizing signal received from a first base station currently holding a communication channel with the mobile station and the transmission phase of a frame synchronizing signal received from a second base station expected to newly set up a communication channel with the mobile station. The mobile station sends phase difference information representative of the above difference to the first base station via the communication channel. The first base station having received the phase difference information transfers the information to the second base station, causing it to correct the phase of data thereof to be sent to the mobile station. This successfully implements soft handover while guaranteeing the phase synchronization of frames sent from the two base stations.

Local predictive resource reservation for handoff in multimedia wireless IP networks

Abstract: This paper presents two new methods that use local information alone to predict the resource demands of and determine resource reservation levels for future handoff calls in multimedia wireless IP networks. The proposed methods model the instantaneous resource demand directly. This differs from most existing methods that derive the demands from modeling the factors that impact the demands. As a result, the proposed methods allow new and handoff calls to: (1) follow non-Poisson and/or nonstationary arrival processes; (2) have arbitrary per-call resource demands; and (3) have arbitrarily distributed call and channel holding times. The first method is based on the Wiener prediction theory and the second method is based on time series analysis. Our simulations show that they perform well even for non-Poisson and nonstationary handoff call arrivals, arbitrary per-call bandwidth demands, and nonexponentially distributed call and channel holding times. They generate closely comparable performance with an existing local method and an existing collaborative method that uses information about mobiles in neighboring cells, under assumptions for which these other methods are optimized. The proposed methods are much simpler to implement than most other existing methods with fewer capabilities.

Loss formulas and their application to optimization for cellular networks

Abstract: We develop a performance model of a cell in a wireless communication network where the effect of handoff arrival and the use of guard channels is included. Past recursive formulas for the loss probabilities of new calls and handoff calls are developed. Monotonicity properties of the loss probabilities are proven. Algorithms to determine the optimal number of guard channels and the optimal number of channels are given. Finally, a fixed-point iteration scheme is developed in order to determine the handoff arrival rate into a cell. The uniqueness of the fixed point is shown.

Handover method in wireless telecommunication systems supporting USTS

Abstract: A handover method in wireless telecommunication system supporting USTS is disclosed. The method for performing a handover of a mobile station in an asynchronous wireless telecommunication system supporting an uplink synchronous transmission scheme (USTS) mode, includes the steps of: a) performing a mode conversion of the mobile station from the USTS mode to a non-USTS mode based on a first signal measurement result from the mobile station; and b) performing a handover for the mobile station. In another embodiment of the present invention, the method further includes the step of: c) performing a mode conversion from the non-USTS mode to the USTS mode based on a second signal measurement result from the mobile station.

Seamless handoff in mobile ip

Abstract: In a system and method for handing off a mobile node in a seamless manner in a wireless access network, procedures are implemented for allowing the mobile node to synchronize the handoff with a base node (e.g., a home agent) and a correspondent node. In this way, a seamless handoff may be achieved, since few or no data packets sent between the base node or the correspondent node and the mobile node are lost. The procedures are supported by both Mobile IPv4 and Mobile IPv6 as well as Hierarchical Mobile IPv4 and Hierarchical Mobile IPv6.

An adaptive algorithm for call admission control in wireless networks

Abstract: In the present paper, we develop an adaptive algorithm for call admission control in wireless networks. The algorithm is built upon the concept of guard channels and it uses an adaptation algorithm to search automatically the optimal number of guard channels to be reserved at each base station. The quality of service parameters used in our study are the new call blocking probability and the handoff call blocking probability. Our simulation studies are performed for comparisons of the present algorithm with static guard channel policy. Simulation results show that our algorithm guarantees that the handoff blocking rate is below its given threshold and at the same time, minimizes the new call blocking rate.

Matched filter-based handoff method and apparatus

Abstract: In a cellular spread-spectrum communications network, a system and method for handing off a remote unit from a first base station to a second base station without loss of data. The remote unit receives a first spread-spectrum signal having a first signal quality from the first base station and transmits data to the first base station at a first data rate and a first power level. Responsive to monitoring the first signal quality and comparing the first signal quality to a plurality of signal qualities of a respective plurality of received-spread-spectrum signals, the remote unit initiates handoff when any of a number of predetermined criteria are met. Upon initiating handoff to the second base station, the remote unit stores the data that would otherwise have been transmitted. Once handoff is complete, the remote unit transmits the stored data to the second base station at a second data rate and a second power level, with the second data rate greater than the first data rate and the second power level greater than the first power level. Once the stored data has been transmitted, the remote unit transmits data to the second base station at a data rate and power level comparable to the first data rate and the first power level.

Apparatus, and an associated method, by which to provide temporary identifiers to a mobile node involved in a communication handover

Abstract: Apparatus, and an associated method, for a mobile communication system in which handovers of communications are effectuated between access points of the communication system as a mobile node travels there through. A manner is provided by which to perform handover evaluation functions more efficiently by performing at least some of the handover evaluations at the access point to which a mobile node is attached. And, a manner is provided by which to provide care-of-addresses formed of temporary identifiers to temporarily identify a mobile node to permit the routing of packet data thereto during a communication session.

Channel allocation for GPRS

Abstract: Based on the GSM radio architecture, the general packet radio service (GPRS) provides users data connections with variable data rates and high bandwidth efficiency. In the GPRS service, allocation of physical channels is flexible, i.e., multiple channels can be allocated to a user. We propose four algorithms for the GPRS radio resource allocation: fixed resource allocation (FRA), dynamic resource allocation (DRA), fixed resource allocation with queue capability (FRAQ), and dynamic resource allocation with queue capability (DRAQ). We develop analytic and simulation models to evaluate the performance for these resource allocation algorithms in terms of the acceptance rate of both GPRS packet data and GSM voice calls. Our study indicates that DRAQ (queuing for both new and handoff calls) outperforms other algorithms.

Method and apparatus for performing idle mode reacquisition and handoff in an asynchronous communication system

Abstract: Techniques to efficiently process paging channels in an asynchronous wireless communication system (100). In one aspect, if the base stations (104a, b, c) are not synchronized with each other and a remote terminal's (106) designated page time is different from base station to base station, the remote terminal (106) can wake up based on the earliest base station in a reacquisition search list (712) that includes candidate base stations to which the remote terminal may be handed off. In another aspect, the criteria to select base stations for evaluation as reacquisition targets may be based on the received power (512) of the base stations as well as their timing (514), both of which may be made relative to that of a preferred base station. In yet another aspect, the remote terminal may wake up multiple times in a particular paging cycle (i.e., a frame cycle or a DRX cycle) if there are one or more candidates base station to which the remote terminal may be handed off.

Method for seamless inter-frequency hard handover in radio communication system

Abstract: A method for seamless inter-frequency hard handover in a radio communication system is disclosed. The method for seamless inter-frequency hard handover includes the steps of: a) at a mobile station, blocking a first uplink carrier frequency used for communication, transmitting a direct sequence spread preamable signal through a second uplink carrier frequency for a short time, and continuously performing the communication through the first uplink carrier frequency: and h) at a target base transciever station, acquiring an uplink synchronization of a mobile station based on the preamble before performing handover.

Method and apparatus to control handoff between different wireless systems

Abstract: A wireless communications network (10) includes a first base station system (40) that performs wireless communications according to a first protocol (e.g., 1xEV-DO protocol) and a second base station system (14) that performs wireless communications according to a second, different protocol (e.g., IS-2000). A link is provided between the first and second base station systems (40, 14) to enable a network-initiated handoff procedure. If a source base station systems detects that a handoff of a mobile station to a target base station system is required, the source base station system exchanges messaging over the link with the target base station system to perform the handoff. In one example, the handoff is a hard handoff.

Method and network element for controlling handover

Abstract: The present invention relates to a method and apparatus for controlling a connection transfer in a cellular network having at least two systems, such as a GSM system and a WCDMA system. Based on a load determination, a service-based inter-system or inter-frequency handover of the connection to another system or to another carrier of the same system is initiated if the determined is below a threshold and service priorities are indicating it. If it exceeds the threshold, an additional load-based inter-system or inter-frequency handover can be initiated. If the load of the target cell is not known, a load estimation based on a learning process can be used to derive a probability of success of an interfrequency or inter-system hand-over, which may be used for deciding on the initiation of the inter-system hand-over. The learning process may be performed by evaluating preceding interfrequency or inter-system handovers to the target cell or preceding interfrequency or inter-system handovers from the target cell. Thereby, users can be shared between different radio access technologies or systems or between different carriers of one system to thereby improve network capacity and quality of service for both systems and carriers. Furthermore, unnecessary inter-system handovers can be prevented in case the load of the target cell of the other system is not known.

Performance analysis of soft handoff in CDMA cellular networks

Abstract: A unique feature of code division multiple access (CDMA) systems is the use of soft handoff between cells. Soft handoff, in general, increases the system capacity because while the link between a mobile and one base station is poor, it might be better between the same mobile and some other base station. Hence, the user may transmit at a lower power in a soft handoff situation. Teletraffic analysis of soft handoff is complex because one cannot separate transmission issues from traffic issues. Many papers in the literature have independently analyzed the effect of soft capacity and soft handoff on network performance. Some papers have analyzed the effect of soft handoff on soft capacity but there has been no proper teletraffic analysis that includes both soft capacity and soft handoff. This paper proposes a traffic model for a DS-CDMA cellular network that includes both soft capacity and soft handoff. Network performance is then computed in terms of call blocking.

Telecommunications system and method for load sharing within a code division multiple access 2000 network

Abstract: A telecommunications system and method is disclosed for load sharing within a CDMA2000 network. The queue size of a sector (or cell) is compared with a predefined threshold. If the queue size exceeds the predefined threshold, one or more mobile terminals having their Data Rate Control (DRC) pointed towards that sector are selected to discontinue using that sector. The network transmits a message to the selected mobile terminals informing the selected mobile terminals that their DRC is no longer valid. In response, the selected mobile terminals stop pointing their DRC towards that sector, which results in an interruption of the selected mobile terminal's data sessions. To continue their data sessions, each of the selected mobile terminals may initiate a “virtual” handoff to another sector.

Dynamic offset threshold for diversity handover in telecommunications system

Abstract: A telecommunications system has a source base station (BSS) and a destination base station (BSD), and a handover unit (100) having a dynamic offset threshold determination unit (102) which establishes a dynamic offset threshold for starting soft handover. When the dynamic offset threshold for soft handover is exceeded, a preliminary portion of a handover sequence is initiated at the destination base station. The preliminary portion of the handover sequence is initiated so that a time-critical handover sequence activity (such as L1 uplink synchronization) is well underway, if ot completed, by the time the soft handover is actually needed. The dynamic offset threshold for starting handover is based on a probability that the mobile station will engage in the handover. The probability is a statistical probability that handover will actually occur based on handover history of other mobile stations previously and similarly traveling and of the same signal strength. Another portion of the soft handover sequence (e.g., a remaining portion of the soft handover sequence) is initiated when the signal strength from the destination base station as received at the specified mobile station has a predetermined relationship to a fixed offset threshold.

Call admission control for mobile multimedia communications with traffic asymmetry between uplink and downlink

Abstract: The call admission control (CAC) for mobile communications is one of the most important engineering issues since it belongs to the category of resource management and the radio spectrum is a very scarce resource. In future mobile cellular systems, the CAC scheme should be efficient for multimedia services as well as for voice services. This paper proposes an advanced CAC scheme for mobile multimedia communications. A characteristic of the proposed scheme is that it takes account of the traffic (load) asymmetry between uplink and downlink in mobile multimedia environments, we evaluate the performance of the proposed scheme using Markov analysis. The performance measures on which we focus are the utilization of resources and the blocking probabilities of handoff calls and new calls. We present some numerical examples with practically meaningful parameter values. As a result, we show that the proposed CAC scheme can be a good choice for mobile multimedia systems such as the International Mobile Telecommunications-2000 systems.

Wireless base station network system, control station, base station switching method, signal processing method, and handover control method

Abstract: A wireless base station network system in which base stations arranged at a plurality of cells and a control station for controlling the base stations are connected through optical fibers by wavelength-division multiplexing transmissions. The base station is provided with a wavelength-variable transmitter for transmitting optical signals of a predetermined wavelength, and an optical coupler for multiplexing optical signals from the wavelength-variable transmitter for the wavelength-division multiplexing transmissions. The control station is provided with a plurality of optical receivers for receiving the divided and multiplexed wavelengths of the optical signals, and an optical coupler for branching the optical signals having been divided and multiplexed from the plurality of base stations, individually to the wavelengths. Where the wireless communication terminal to communicate with the base station moves to change its communicating base station, a new base station, to which the wireless communication terminal has moved, controls the wavelength of the wavelength variable transmitter and transmits the optical signal wavelength identical to that transmitted by the base station before the movement, to the control station.