Showing papers on "Handover published in 1999"

Policy-enabled handoffs across heterogeneous wireless networks

Abstract: "Access is the killer app" is the vision of the Daedalus project at UC Berkeley. Being able to be connected seamlessly anytime anywhere to the best network still remains an unfulfilled goal. Often, even determining the "best" network is a challenging task because of the widespread deployment of overlapping wireless networks. We describe a policy-enabled handoff system that allows users to express policies on what is the "best" wireless system at any moment, and make tradeoffs among network characteristics and dynamics such as cost, performance and power consumption. We designed a performance reporting scheme estimating current network conditions, which serves as input to the policy specification. A primary goal of this work is to make it possible to balance the bandwidth load across networks with comparable performance. To avoid the problem of handoff instability, i.e., many mobile hosts making the same handoff decision at essentially the same time, we designed randomization into our mechanism. Given the current "best" network, our system determines whether the handoff is worthwhile based on the handoff overhead and potential network usage duration.

QoS routing in ad hoc wireless networks

Abstract: The emergence of nomadic applications have generated much interest in wireless network infrastructures that support real-time communications. We propose a bandwidth routing protocol for quality-of-service (QoS) support in a multihop mobile network. The QoS routing feature is important for a mobile network to interconnect wired networks with QoS support (e.g., ATM, Internet, etc.). The QoS routing protocol can also work in a stand-alone multihop mobile network for real-time applications. This QoS routing protocol contains end-to-end bandwidth calculation and bandwidth allocation. Under such a routing protocol, the source (or the ATM gateway) 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 addition, it enables more efficient call admission control. In the case of ATM interconnection, the bandwidth information can be used to carry out intelligent handoff between ATM gateways and/or to extend the ATM virtual circuit (VC) service to the mobile network with possible renegotiation of QoS parameters at the gateway. We examine the system performance in various QoS traffic flows and mobility environments via simulation. Simulation results suggest distinct performance advantages of our protocol that calculates the bandwidth information. It is particularly useful in call admission control. Furthermore, "standby" routing enhances the performance in the mobile environment. Simulation experiments show this improvement.

Optimized smooth handoffs in Mobile IP

Abstract: Mobile IP provides mobility support for hosts connected to the Internet without changing their IP addresses. Route optimization strategies complement Mobile IP, to alleviate triangle routing, by informing correspondent hosts of the mobile host's care-of address. We propose further strategies that are compatible with route optimization and its security model. First, foreign agents buffer packets for a mobile host and send them to its new location when it leaves. Second, hierarchical foreign agent management reduces the administrative overhead of frequent local handoffs, using an extension of the Mobile IP registration process so security can be maintained. Duplicate packets due to buffer handover are eliminated with the cooperation of mobile hosts. Simulation results show substantial performance improvements in terms of throughput, registration overhead, lost and duplicate packets during a handoff, without restrictions on physical placement of foreign agents.

IPv6 flow handoff in ad hoc wireless networks using mobility prediction

Abstract: In an ad hoc wireless network, mobile hosts are acting as routers and the network topology is constantly changing due to node mobility. The disruptions can cause serious degradation for real-time session. This paper describes a new protocol, the flow oriented routing protocol (FORP), for routing real-time IPv6 flows (e.g., voice and data) in highly mobile ad hoc wireless networks. A new concept called "multi-hop handoff" is introduced to anticipate topological changes and perform rerouting, thus limiting the disruption of a flow due to the changing topology. The performance of the proposed scheme is compared to other routing approaches.

Dynamic resource allocation schemes during handoff for mobile multimedia wireless networks

Abstract: User mobility management is one of the important components of mobile multimedia systems. In a cell-based network, a mobile should be able to seamlessly obtain transmission resources after handoff to a new base station. This is essential for both service continuity and quality of service assurance. In this paper, we present strategies for accommodating continuous service to mobile users through estimating resource requirements of potential handoff connections. A diverse mix of heterogeneous traffic with diverse resource requirements is considered. The investigate static and dynamic resource allocation schemes. The dynamic scheme probabilistically estimates the potential number of connections that will be handed off from neighboring cells, for each class of traffic. The performance of these strategies in terms of connection blocking probabilities for handoff and local new connection requests are evaluated. The performance is also compared to a scheme previously proposed by Yu and Leung (see IEEE J. Select. Areas Commun., vol.15, p.1208-25, 1997). The results indicate that using dynamic estimation and allocation, we can significantly reduce the dropping probability for handoff connections.

Communications system handoff operation combining turbo coding and soft handoff techniques

Abstract: Communication systems, including, for example, cell-based mobile communication systems, multiple satellite communication systems, or multibeam satellite systems, require reliable handoff methods between cell-to-cell, beam-to-beam, or satellite-to-satellite respectively. Recent measurement of a CDMA cellular system indicates that the system is in handoff about 30 % to 50 % of an average call period. Therefore, system reliability during handoff is one of the major system performance parameters and eventually becomes a factor in the overall system capacity. The present invention advantageously relates to novel and improved techniques for handoff in cellular communications, multibeam and multisatellite systems. The present invention combines the soft handoff mechanism with a code diversity combining technique (i.e., combining signals from multiple sources), a packet combining technique (i.e., combining multiple signals), and an iterative decoding algorithm (e.g., Turbo Coding (502)).

Communication system with fast control traffic

Abstract: A method and system for conducting rapid control traffic in a time division multiple access (TDMA) communication system comprises a base station communicating with a plurality of user stations in assigned time slots of a time frame. For bearer traffic, time slots are assigned to particular user stations for an extended duration. In unassigned time slots, the base station transmits a general polling message indicating availability of the time slot. A user station desiring to hand off communication from one base station to another uses multiple available time slots at the target base station for exchanging control traffic messages with the target base station. The next available time slot is indicated by a slot pointer in the header of each general polling message to facilitate rapid exchange of control traffic messages. During handover, the user station may establish a new link with the target base station before relinquishing the existing communication link with the old base station.

Method for inter-IP-domain roaming across wireless networks

Abstract: A method involves in integrating the communication mechanisms of IAPP and mobile IP is provided for allowing a mobile station to roam among various APs in different IP subnets. When a mobile station roams to a new IP subnet, it will issue a reassociation request to an Access Point A in the new IP subnet. In response to the reassociation request, the Access Point A will need the IP address of the previous Access Point B in the previous IP subnet to send the handoff request to the Access Point B. So, the Access Point A can find the IP address of the Access Point B via the communication mechanism of mobile IP of IP layer and then send the handoff request frame to the Access Point B. In turn, upon receiving the handoff request frame, the Access Point B deletes the record of the mobile station in the association table and then sends the handoff response frame back to the Access Point A via the communication mechanism of mobile IR. The unicast handoff response frame will be forwarded to the Access Point A. Consequently, the Access Point A can complete the handoff procedure.

Method and apparatus for providing wireless communication system synchronization

Abstract: When insufficient traffic is present in the network to maintain synchronization in this manner, other methods must be used. One approach involves making direct measurements of the timing between base stations (602, 604). This is accomplished in one of two ways. The base may interrupt its transmissions on all sectors for a short interval during which it determines the time of arrival of signals from other base stations (602, 604). Given knowledge of the other base station locations, time errors relative to all other base stations (602, 604) may be derived. Alternatively, the base may send a short signal at high power in the mobile transmit band. This time-of-arrival of this signal is measured by the surrounding base stations and the time errors between pairs of base stations are computed. In some cases, a base station (602, 604) may be isolated sufficiently from all other base stations in the network such that direct base-to-base measurement is not viable. In this case, a fixed mobile (606) is placed at a location in the handoff region between the isolated cell and another cell in the network. The fixed mobile (606) either performs measurements of base station pilots on command of the base and reports the timing information, or sends a burst transmission at a specified time and power level to be measured by the base stations.

Cell selection in mobile radio systems

Abstract: The present invention relates generally to the problem of cell selection, for e.g. cell handover, in mobile telecommunication systems, and more particularly to the problem of selecting the optimum cell among cells with differing capabilities due to different air interface modes. Known algorithms for cell selection and handover are extended by applying additional criteria that take into account the capabilities, due to different modulation and coding schemes, of the mobile station and the base stations that are possible candidates. The quality of service (“QoS”) is predicted for the different cell candidates based on a combination of signal strength or C/I, different cell capabilities, multislot capability, etc. Then the cell is selected for which the predicted QoS is maximum. In another embodiment the invention is extended by taking into account further criteria which are suitable from a system point of view, e.g. to avoid a significant increase of average outage probability or interference level. The present invention increases the use of base stations supporting high data rates. The result is an increase in overall system throughput.

Teletraffic performance evaluation of microcellular personal communication networks (PCN's) with prioritized handoff procedures

Abstract: Evaluates four handoff priority-oriented channel allocation schemes. These give priority to handoff calls by reserving channels exclusively for handoff calls. The measurement-based handover channel adaptive reassignment scheme (MHAR-A) exclusively uses reserved handover channels for newly originated calls if a certain criterion is satisfied. All four schemes studied differ from the conventional guard channel-based handover priority-oriented channel allocation scheme. To study the schemes, a personal communication network (PCN) based on city street microcells is considered. A teletraffic simulation model accommodating a fast moving vehicle is developed, and the performance parameters are obtained. The performances of all four schemes are compared with the nonpriority scheme and the conventional guard channel-based handover priority-oriented channel allocation scheme. It was found that some of the channel allocation algorithms studied improved the teletraffic capacity over the nonpriority and the conventional guard case. Also, the probability of new call blocking and carried traffic was improved for three of the schemes when compared to the conventional guard scheme. The MHAR-A scheme did not perform up to expectation. Nevertheless, it can be used to finely control the communication service quality equivalent to the control obtained by varying the number of handoff channels in a fraction of one. Increasing the number of reserved handover channels in fraction of one can never be achieved in the conventional guard channel-based handover priority-oriented channel allocation scheme.

Interference-based channel assignment for DS-CDMA cellular systems

Abstract: Link capacity is defined as the number of channels available in a link. In direct-sequence code-division multiple-access (DS-CDMA) cellular systems, this is limited by the interference present in the link. The interference is affected by many environmental factors, and, thus, the link capacity of the systems varies with the environment. Due to the varying link capacity, static channel assignment (SCA) based on fixed link capacity is not fully using the link capacity. This paper proposes a more efficient channel assignment based on the interference received at the base station (BS). In the proposed algorithm, a channel is assigned if the corresponding interference margin is less than the allowed interference, and, thus, channels are assigned adaptively to dynamically varying link capacity. Using the proposed algorithm yields more channels than using SCA in such an environment changes with nonhomogeneous traffic load or varying radio path loss. The algorithm also improves service grade by reserving channels for handoff calls.

Dynamic channel reservation based on mobility in wireless ATM networks

Abstract: We present a dynamic channel reservation scheme to improve the utilization of wireless network resources while guaranteeing the required QoS of handoff calls. The wireless channels are dynamically reserved by using the request probability determined by the mobility characteristics and channel occupancy to guarantee acceptable quality of handoff calls and keep the new call blocking probability as low as possible.

A prioritized handoff dynamic channel allocation strategy for PCS

Abstract: An analytical method is developed to calculate the blocking probability (p/sub b/), the probability of handoff failure (p/sub h/), the forced termination probability (p/sub ft/), and the probability that a call is not completed (p/sub nc/) for the no priority (NPS) and reserved channel (RCS) schemes for handoff, using fixed channel allocation (FCA) in a microcellular system. Based only on the knowledge of the new call arrival rate, a method of assessing the handoff arrival rate for any kind of traffic is derived. The analytical method is valid for uniform and nonuniform traffic distributions and is verified by computer simulations. An extension (generalization) to the nonuniform compact pattern allocation algorithm is presented as an application of this analysis. Based on this extended concept, a modified version of a dynamic channel allocation strategy (DCA) called compact pattern with maximized channel borrowing (CPMCB) is presented. With modifications, it is shown that CPMCB is a self-adaptive prioritized handoff DCA strategy with enhanced performance that can be exploited in a personal communications service (PCS) environment leading either to a reduction in infrastructure or to an increase in capacity and grade of service. The effect of user mobility on the grade of service is also considered using CPMCB.

An investigation into the functions of nurses’ communication at the inter‐shift handover

Abstract: Aims This study set out to investigate the functions of nurses’ communication at the inter-shift handover.Background The inter-shift handover should facilitate continuity in care by transferring patient information between shifts. However, nurses may also use this time for team building. Methods An observational study was conducted during six inter-shift handovers occurring on one ward in a general hospital in the UK. The data was transcribed and a thematic analysis applied. Findings The main themes related to the transfer of patient information and team building, the strongest theme being team building. Nurses were found to communicate goals and values relating to nursing practice so facilitating cohesiveness of the nursing team. Conclusions The nursing ritual of inter-shift handover serves the purpose of enhancing a shared value system amongst nurses. It should therefore not be regarded as an outdated means of communication.

Received signal quality determination methods and systems for convolutionally encoded communication channels

Abstract: Received signal quality (bit error rate) estimates for a communication channel are provided by a receiver apparatus which is connected to the communication channel and which includes a convolutional decoder providing an estimate of a transmitted data frame and an associated final decision metric. The bit error rate estimate is generated by a bit error rate estimation circuit which includes a memory containing values for mapping the final decision metric to a corresponding bit error rate estimate. The bit error rate estimate may be provided to a control node of the communication channel which may use the provided estimate to take a corrective action such as determining whether a handover to a different communication channel should be initiated based upon the bit error rate. The communication channel may be an allocated channel of a cellular radio communication network servicing a mobile terminal receiver apparatus with the control nodes being the base stations of the cellular network. The convolutional decoder may be a Viterbi decoder.

Handover queuing strategies with dynamic and fixed channel allocation techniques in low Earth orbit mobile satellite systems

Abstract: This paper deals with the performance evaluation of various resource management strategies that are suitable for low Earth orbit mobile satellite systems (LEO-MSSs). A user mobility model has been proposed and its statistical parameters have been derived. Both fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques have been considered. Moreover, in order to reduce the handover failure probability, we have assumed that interbeam handover requests which do not immediately obtain service can be queued. In particular, two different queuing disciplines have been compared: (a) the first input first output (FIFO) scheme and (b) a new technique called last useful instant (LUI) which is based on the knowledge of the maximum time within which the handover procedure must be accomplished. Implementation aspects for the LUI technique in a LEO-MSS have been discussed also in comparison with the measurement-based priority scheme (MBPS), previously proposed in the literature on this subject. The efficiency of the LUI queuing scheme as regards the FIFO technique has been investigated by simulations for both DCA and FCA techniques. An analytical approach has been also presented in order to allow the performance evaluation of the FCA scheme with different handover queuing disciplines.

An overview of cellular IP

Abstract: A number of initiatives to add mobility to the Internet and packet data services to third generation cellular systems are being considered by emerging mobile service providers as possible candidate solutions for the delivery of IP data to mobile users. Both of these two candidates have a number of shortcomings, however. Mobile IP represents a simple and scalable global mobility solution but is not appropriate in support of fast and seamless handoff control. In contrast, third generation cellular systems offer smooth mobility support but are built on complex networking infrastructure that lacks the flexibility offered by IP-based solutions. In this paper we present an overview of cellular IP which represents a 'third way' combining the strengths of bath approaches without inheriting their weaknesses. Cellular IP combines the capability of cellular networks to provide smooth fast handoff and efficient location management of active and idle mobile users with the inherent flexibility, robustness and scalability found in IP networks.

Handoff ordering using signal prediction priority queuing in personal communication systems

Abstract: Handoffs in a mobile cellular communications environment will become an increasingly important issue as cell sizes shrink to accommodate an increasingly large demand for services. A new handoff ordering method is proposed which can be used to provide rapid handovers with a smaller percentage of dropped calls than other methods. Signal prediction priority queuing (SPPQ) is a generic queuing method which can be adapted to almost any handover technique for the benefit of decreased dropped calls. In typical personal communication systems (PCSs) environment, it is shown that for realistic call-blocking probabilities (2%-6%), SPPQ leads to about 15% fewer dropped calls compared to first-in-first-out (FIFO) queuing. This benefit comes at the expense of a slight increase (<1%) in blocked call percentage. The proposed SPPQ scheme is also compared to a previously developed method called measurement-based priority scheme (MBPS), and, based on worst case scenarios, it is shown to outperform MBPS as well.

Location update method and inter core network entity handover method

Abstract: A scheme for providing a notification to a Mobile Station (MS) to initiate a location update in a mobile telecommunication system, a scheme for providing update of location of the MS to a new Core Network (CN) entity via interface between the CN entities, a scheme for providing update of location of the MS to a new CN entity via interface between a CN entity and a Serving RNC (SRNC), a scheme for providing an inter Core Network (CN) handover, e.g. inter-SGSN handover, in a mobile telecommunication system, are disclosed.

Static simulator for studying WCDMA radio network planning issues

Abstract: A static radio network simulator for studying various topics of 3rd generation WCDMA radio network planning is presented. The simulator allows analyzing coverage, capacity and quality of service related issues. Input to the simulator is the network scenario and the user information as a mobile station map. The uplink and downlink are separately analyzed and the outputs are presented in form of maps of best server, number of users, served traffic, SHO areas, AS size, SHO statistics for the area and for the users, Perch C/I plots. In the analysis, impact of the 3rd generations fast power control and soft(er) handover (SHO) possibility are taken into account by importing link level simulations into the analyses. The whole simulator is entirely based on Matlab(R) software.

A method for controlling handoff in a communication system

Abstract: A method and apparatus for controlling the transmit power of a high rate code division multiple access (CDMA) link is described. The channel condition to a subscriber unit is evaluated and the configuration of a high rate link in soft handoff is based on the channel condition. If a fading channel is detected the supplemental channels of the high rate link are transmitted from multiple base stations. If a non-fading channel is detected the supplemental channels of the high rate link are transmitted from a single base station. Parameters monitored to determine the channel condition include the pilot strength, pilot code offset and error rate.

Method and apparatus for transferring communication within a communication system

Abstract: Transferring communication within a communication system (100) occurs as follows: during communication with a serving base station (101), a handover candidate list (110) is provided to the remote unit (113). The list (110) comprises a set of neighboring base stations (102) that are capable of supporting the service requirements of the remote unit (113) and does not include any neighboring base station (111) that are incapable of supporting the current service required by the remote unit.

Synchronization of forward link base station power levels during handoff between base station sectors in a mobile radio communication system

Abstract: A method and apparatus for controlling the transmit power levels of first and second base station transceivers, wherein the first and second base station transceivers are respectively associated with first and second sectors of a cell. The received signal strength of a communication signal arriving at the mobile station is initially determined. A power control value that is based on the received signal strength is then transmitted from the mobile station to the first and second base station transceivers. A first received power control value is next generated by attempting to receive the transmitted power control value at the first base station transceiver, and a second received power control value is generated by attempting to receive the transmitted power control value at the second base station transceiver. A common transmit power value is calculated at a base station controller for the first and second base station tranceivers when the first and second received power control values are unequal. The communication signal is then transmitted from the first and second base station transceivers in accordance with the common transmit power value.

Analysis of a hierarchical cellular system with reneging and dropping for waiting new and handoff calls

Abstract: We analyze a hierarchical cellular system with finite queues for new and handoff calls. Both the effect of the reneging of waiting new calls because of the callers' impatience and the effect of the dropping of queued handoff calls as the callers move out of the handoff area are considered, besides the effect of the guard channel scheme. We successfully solve the system by adopting the multidimensional Markovian chain and using the transition-probability matrix and the signal-flow graph to obtain the average new-call blocking probability, the forced termination probability, and the average waiting time of queued new and handoff calls. We further investigate how the design parameters of the buffer sizes and guard channel numbers in macrocell and microcells affect the performance of the hierarchical cellular system. The results show that provision of a buffering scheme and guard channel scheme can effectively reduce the new call blocking probability and the forced termination probability in the hierarchical cellular system, and the effectiveness is more significant in the macrocell than in the microcells.

Forward link inter-generation soft handoff between 2G and 3G CDMA systems

Abstract: In a CDMA cellular radiotelephone system, a soft handoff (SHO) is performed when a mobile station communicates with a new inter-generation base station, without interrupting communications with the old base station. Currently, a SHO can only be used between CDMA channels having identical frequency assignments and within the same system generation (i.e., 2G2G, or 3G3G, where 2G is a second generation system, and 3G is a third generation system). The proposed IS-2000 standard for a 2G3G handoff is a hard handoff or “Break-Before-Make” procedure, which greatly reduces the quality of service (QOS). The present invention allows for SHO between second and third generation CDMA systems (2G3G and 3G2G), by modifying the proposed messaging structure. This provides a smooth service transition when a mobile station travels from one service area (i.e., 2G), to another service area (i.e., 3G), using the SHO or “Make-Before-Break” approach.

Characterization of soft handoff in CDMA systems

Abstract: 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.

System and method for effecting information transmission and soft handoff between frequency division duplex and time division duplex communications systems

Abstract: A system and method for controlling information transmission and communication handoff between frequency division multiplexing (FDD) and time division multiplexing (TDD) communication systems using any multiple access scheme is provided. The mobile unit transmits information via a current one of the FDD and TDD communication systems while it moves toward the other, or targeted one of the FDD and TDD communication systems. A pilot search signal is generated by the targeted communication system, where the pilot search signal corresponds to a transmission range of the targeted communication system. A communication handoff is initiated from the current communication system to the targeted communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal. Concurrent communications are synchronized and temporarily maintained between the mobile unit and both the current and targeted communications systems using an increased data rate for each of the communications links. When the handoff is complete, transmission between the mobile unit and the current communication system is terminated, while communication between the mobile unit and the targeted communication system is maintained when the handoff is complete.

System and method for performing an inter mobile system handover using the internet telephony system

Abstract: A telecommunications system and method is disclosed for utilizing an Internet telephony system to perform a handover of a call between different types of systems. When a serving mobile switching center (MSC) determines that there is not another MSC belonging to the same type of wireless system to which a handover can be performed, the serving MSC sends a message to an Internet Gatekeeper via an Internet Gateway for the serving MSC, inquiring whether there are any other types of wireless systems nearby. The Internet Gatekeeper maintains a database of all existing wireless systems within the area served by the Internet Gatekeeper. The Internet Gatekeeper chooses a target MSC of another wireless system (if possible), and transmits the identity of this target MSC back to the currently serving MSC. Thereafter, the currently serving MSC performs the handover to the target MSC by routing signaling messages through the Internet Gateway and the Internet Gatekeeper to the target MSC.

A fast handoff scheme for wireless networks

Abstract: In this paper, we propose a fast and efficient handoff scheme to handle the movements of mobile nodes among small wireless cells at the fringes of the Internet. Our scheme adopts a hierarchical mobility management architecture to restrict the handoff processing overheads within the vicinity of the mobile node, and uses multicast as the packet forwarding mechanism to deliver packets to multiple base stations within the vicinity of the mobile node to achieve fast handoff performance. Our scheme is based on the Internet Protocol (IP) and is compatible with Mobile IP and its route optimization option. We also present simulation results for our simulation using the Network Simulator (ns2). The simulations show that our handoff scheme is fast enough to meet the requirements of an interactive voice communication session. The first packet from the new base station arrives at the mobile node within 10 ms after the mobile node initiates a handoff. Hence our scheme is suitable for roaming mobile nodes which may encounter numerous handoffs while they are in the midst of an interactive voice communication session such as Internet telephony.