Showing papers on "Handover published in 2009"

Vertical Handoff Decision Algorithms for Providing Optimized Performance in Heterogeneous Wireless Networks

Abstract: There are currently a large variety of wireless access networks, including the emerging vehicular ad hoc networks (VANETs). A large variety of applications utilizing these networks will demand features such as real-time, high-availability, and even instantaneous high-bandwidth in some cases. Therefore, it is imperative for network service providers to make the best possible use of the combined resources of available heterogeneous networks (wireless area networks (WLANs), Universal Mobile Telecommunications Systems, VANETs, Worldwide Interoperability for Microwave Access (WiMAX), etc.) for connection support. When connections need to migrate between heterogeneous networks for performance and high-availability reasons, seamless vertical handoff (VHO) is a necessary first step. In the near future, vehicular and other mobile applications will be expected to have seamless VHO between heterogeneous access networks. With regard to VHO performance, there is a critical need to develop algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a VHO decision algorithm that enables a wireless access network to not only balance the overall load among all attachment points (e.g., base stations and access points) but also maximize the collective battery lifetime of mobile nodes (MNs). In addition, when ad hoc mode is applied to 3/4G wireless data networks, VANETs, and IEEE 802.11 WLANs for a more seamless integration of heterogeneous wireless networks, we devise a route-selection algorithm for forwarding data packets to the most appropriate attachment point to maximize collective battery lifetime and maintain load balancing. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed algorithms.

IEEE 802.21: Media independent handover: Features, applicability, and realization

Abstract: Providing users of multi-interface devices the ability to roam between different access networks is becoming a key requirement for service providers. The availability of multiple mobile broadband access technologies, together with the increasing use of real-time multimedia applications, is creating strong demand for handover solutions that can seamlessly and securely transition user sessions across different access technologies. A key challenge to meeting this growing demand is to ensure handover performance, measured in terms of latency and loss. In addition, handover solutions must allow service providers, application providers, and other entities to implement handover policies based on a variety of operational and business requirements. Therefore, standards are required that can facilitate seamless handover between such heterogeneous access networks and that can work with multiple mobility management mechanisms. The IEEE 802.21 standard addresses this problem space by providing a media-independent framework and associated services to enable seamless handover between heterogeneous access technologies. In this article, we discuss how the IEEE 802.21 standard framework and services are addressing the challenges of seamless mobility for multi-interface devices. In addition, we describe and discuss design considerations for a proof-of-concept IEEE 802.21 implementation and share practical insights into how this standard can optimize handover performance.

Mobile communication method and mobile station

Abstract: The present invention relates to a mobile communication method in which a mobile station performs a handover from a handover source radio base station to a handover target radio base station. The mobile communication method includes the steps of: (A) acquiring, at the handover target radio base station, from the handover source radio base station or a switching center, a key for calculating a first key for generating a certain key used in a communication between the handover target radio base station and the mobile station; and (B) acquiring, at the handover target radio base station, from the switching center, a second key for calculating a first key for generating a certain key used in a communication between a next handover target radio base station and the mobile station.

Femtocell access control strategy in UMTS and LTE

Abstract: Femtocells have become an attractive device for operators to offer extended services on their licensed UMTS/LTE spectrum. In this article we focus on the access control strategy - a crucial aspect for operators to give preferential access to femtocells for their subscribers. The general issue of supporting femtocells in pre-Release 8 UMTS networks with pre-Release 8 UE is first outlined in order to help the reader understand the motivation behind some concepts introduced in 3GPP Release 8 to support femtocells. A description of the femtocell access control strategy for UMTS and LTE is then provided based on 3GPP Release 8 specifications. Finally, the issue of LTE physical cell identity confusion associated with inbound handover to femtocells (which is expected to be resolved within the 3GPP Release 9 timeline) is discussed.

Handover within 3GPP LTE: Design Principles and Performance

Abstract: The 3GPP LTE system has been designed to offer significantly higher data rates, higher system throughput, and lower latency for delay critical services. This improved performance has to be provided and guaranteed under various mobility conditions. Hence, handover (HO) and its performance are of high importance. This paper investigates the performance of the handover procedure within 3GPP LTE in terms of HO failure rate and the delay of the whole procedure. System level simulations within a typical urban propagation environment, with different User Equipment (UE) speeds, cell radii and traffic loads per cell have been performed. The entire layer 3 signalling exchanged via air interface is considered in the simulations. In addition, errors at the Layer 1 (L1) control channels are taken into account. Simulation results show that the handover procedure within 3GPP satisfies the goal of high performance mobility. Namely for cell radii up to 1 km and for UE speeds up to 120 km/h, the HO failure rate lies within the range of 0-2.2% even in high loaded systems. For medium and low loads even at speeds of 250 km/h, HO failure is below 1.3 %. In addition, simulation results show that the handover procedure is robust against L1 control channel errors.

Predictive methods for improved vehicular WiFi access

Abstract: With the proliferation of WiFi technology, many WiFi networks are accessible from vehicles on the road making vehicular WiFi access realistic. However, several challenges exist: long latency to establish connection to a WiFi access point (AP), lossy link performance, and frequent disconnections due to mobility. We argue that people drive on familiar routes frequently, and thus the mobility and connectivity related information along their drives can be predicted with good accuracy using historical information - such as GPS tracks with timestamps, RF fingerprints, and link and network-layer addresses of visible APs. We exploit such information to develop new handoff and data transfer strategies. The handoff strategy reduces the connection establishment latency and also uses pre-scripted handoffs triggered by change in vehicle location. The data transfer strategy speeds up download performance by using prefetching on the APs yet to be encountered. Experimental performance evaluation reveals that the predictability of mobility and connectivity is high enough to be useful in such protocols. In our experiments with a vehicular client accessing road-side APs, the handoff strategy improves download performance by roughly a factor of 2 relative to the state-of-the-art. The data transfer strategy further improves this performance by another factor of 2.5.

Wireless network handoff key

Abstract: The present invention provides a method and system for handoff in a wireless communication network. In one embodiment, a common handoff encryption key is generated by an authentication server and transmitted to a first access point and a second access point. The first access point transmits the handoff encryption key to a wireless terminal. The wireless terminal encrypts output data with the handoff encryption key. When the wireless terminal is associated with the second access point, the second access point decrypts data from the wireless terminal with the handoff encryption key. In a second embodiment, a handoff WEP key generation secret parameter is provided to a first and a second access point. Both access points generate a handoff WEP key as a function of the handoff WEP key generation secret parameter and an address of a wireless terminal. The first access point transmits the handoff WEP key to the wireless terminal. The second access point communicates data packets encrypted with the handoff WEP key with the wireless terminal.

Improving measurement in clinical handover

Abstract: Background: Poor clinical handover creates discontinuities in care leading to patient harm. However, the field of handover research continues to lack standardised definitions and reliable measurement tools to identify factors that would lead to harm reduction and improved safety strategies. Objective: This paper introduces a conceptual framework to underpin a research agenda around the important patient safety topic of clinical handover. Methods: Five frameworks with potential application to clinical handover were identified in a consultation process with clinicians, researchers and policy makers. Results: The framework consists of three key handover elements—information, responsibility and/or accountability and system—in relation to three key measurement elements—policy, practice and evaluation. Using this framework an analysis of current “gaps” in the measurement of handover was completed. Conclusion: The paper argues that measurement will identify gaps in knowledge about handover practice and promote rigor in the design and evaluation of interventions to reduce patient harm.

Handoff prioritization and decision schemes in wireless cellular networks: a survey

Abstract: Handoff is a key element in wireless cellular networks in order to provide quality of service (QoS) to the users and to support users' mobility. Handoff failure will result in the forced termination of an ongoing call. From the user's point of view, the service of a handoff request is more important, as the forced termination of an ongoing call is more annoying than the blocking of new calls. Therefore, in order to support QoS to the users and to provide ubiquitous coverage, the handoff procedure ought to be further investigated. This paper provides a comprehensive survey of the basic elements, the different types and phases of the handoff procedure. Moreover, particular interest has been given in the horizontal handoff execution phase by discussing and classifying the most recent handoff prioritization schemes into categories based on the concepts that these schemes adopt, e.g. channel reservation, handoff queueing, channel transferred, subrating, genetic and hybrid schemes and in the vertical handoff decision phase by presenting different decision algorithms.

Non-3gpp to 3gpp network handover optimizations

Abstract: The invention relates to a method for a handover of a mobile node from a non-3GPP to a 3GPP network, and of a mobile node, which is located in a non-3GPP/ 3GPP network. The handover is improved by discovering an appropriate MME and registering the mobile node at the discovered MME, in advance . This includes to first determine the location of the mobile node in the non-3GPP network, so as to be able to detect an MME in the vicinity of the mobile node's location. The 3GPP contexts are then transmitted to the new MME before the handover is performed. Moreover, the invention teaches to change the Serving-Gateway in the 3GPP network before performing a handover, thereby accelerating the handover. When a handover gets likely, the mobile node's location is determined and a new Serving-Gateway is selected. The data path is changed to go via the new Serving-Gateway.

Access control for macrocell to femtocell handover

Abstract: Access to a femtocell can be controlled as part of handover of a mobile device from macrocell to femtocell. Macro network platform issues a handover (HO) request towards femto network platform and a single virtual femto node, which represents a plurality of femto access points (APs). Location estimate(s) for the mobile device drives selection of a target femto AP. Selection of the target AP results in acceptance of the HO request. The mobile device also can request macro-to-femto (MTF) handover. HO neighbor list(s) is generated by decoding a network-issued identifier for each femto APs in a set of femtocells, and selectively ranking each femto AP based at least on channel quality; access privileges of the mobile device to each of the identified femto APs determines selectivity. Validation of mobile device's access right(s) drives acceptance of the MTF HO request to a top ranked femto AP.

Spectrum Handoff in Cognitive Radio Networks: Opportunistic and Negotiated Situations

Abstract: Spectrum handoff is an indispensable component in cognitive radio networks to provide resilient service for the secondary users. In this paper, we explore the spectrum handoff procedure and then propose four metrics to characterize both short-term and long-term spectrum handoff performance: link maintenance probability, the number of spectrum handoff, switching delay, and non-completion probability. In particular, the probability mass function (pmf) and the average number of spectrum handoff are developed. The tele-traffic parameters are relaxed to follow a general distribution function, which will enable a wide applicability and theoretical significance of the derived formulae. Both opportunistic and negotiated spectrum access strategies are investigated. Results show that these two mechanisms will generate significantly different performance. Numerical examples are presented to demonstrate the performance trade-off and the interaction between the primary users and the secondary users. The impact of key parameters on spectrum handoff is also discussed. The techniques as well as the results are important for evaluating the primary and second users co-existence, and hence helpful for design and optimization of cognitive radio networks.

Modeling and Analysis for Proactive-Decision Spectrum Handoff in Cognitive Radio Networks

Abstract: Spectrum handoff occurs when the primary users appear in the licensed band occupied by the secondary users. Spectrum handoff procedures aim to help the secondary users to vacate the occupied licensed spectrum and find suitable target channel to resume the unfinished transmission. In this paper, we discuss how to select the target channels to minimize the total service time with multiple spectrum handoffs. We propose a preemptive resume priority (PRP) M/G/1 queueing network model to evaluate total service time for various target channels selections. Then, we suggest a low-complexity greedy algorithm to select target channels. Numerical results show that a spectrum handoff scheme based on greedy selection strategy can reduce total service time compared to the randomly selection scheme.

Femtocell Coverage Optimization Using Switched Multi-Element Antennas

Abstract: Femtocells are low-cost, low-power cellular base stations that are deployed by the end user to supplement macrocellular coverage and provide high data rates in the customer's premises. In femtocell deployments, leakage of the pilot signal to the outside of a house can result in a highly increased signalling load to the core network as a result of the higher number of mobility events caused by passing users. In this paper, a low cost multi-element antenna solution is proposed to reduce the core network mobility signalling over previously published results using a single antenna only. Antenna gain pattern measurements of a prototype with two patches and two inverted F antennas are presented and a corresponding feeder network is discussed. Self-optimization methods are proposed that jointly select an appropriate antenna pattern and optimize the pilot power. This allows to better match the femtocell coverage to the shape of each individual house and results in an improvement of both indoor coverage and core network signalling resulting from mobility events.

Handover between macrocell and femtocell for UMTS based networks

Abstract: The femtocell networks that use home base station and existing xDSL or other cable line as backhaul connectivity can fulfill the upcoming demand of high data rate for wireless communication system as well as can extend the coverage area. Hence the modified handover procedure for existing networks is needed to support the macrocell/femtocell integrated network. Some modifications of existing network and protocol architecture for the integration of femtocell networks with the existing UMTS based macrocell networks are essential. These modifications change the signal flow for handover procedures due to different 2-tier cell (macrocell and femtocell) environment. The measurement of signal-to-interference ratio parameter should be considered for handover between macrocell and femtocell. A frequent and unnecessary handover is another problem for hierarchical network environment that must be optimized to improve the performance of macrocell/femtocell integrated network. In this paper, firstly we propose the concentrator based and without concentrator based femtocell network architecture. Then we present the signal flow with appropriate parameters for the handover between 3GPP UMTS based macrocell and femtocell networks. A scheme for unnecessary handoff minimization is also presented in this paper. We simulate the proposed handover optimization scheme to validate the performance.

Method and apparatus for automatic handover optimization

Abstract: A method for wireless communications is provided. The method includes determining a set of handover parameters that facilitate a handover between cells in a wireless network and analyzing the set of handover parameters. The method includes dynamically adjusting the parameters to mitigate handover failures between the cells.

Mobility Management Schemes at Radio Network Layer for LTE Femtocells

Abstract: Femtocell, a small cellular base station in home and small business environment, is an attractive solution for operators to improve indoor coverage and network capacity in 3G networks. However, there are technical problems due to its mass deployment. The paper presents a femtocell architecture for LTE and investigates different handover scenarios. Two mobility management schemes at radio network layer (RNL) are proposed and their signaling cost, complexity, standard impact and application scenarios are also discussed.

Improvement of LTE Handover Performance through Interference Coordination

Abstract: An Orthogonal Frequency Division Multiple Access (OFDMA) based radio-interface is specified by 3GPP for LTE system. OFDMA provides efficient spectral efficiency by reusing complete frequency band in all cells. However it projects high inter cell interference (ICI) especially on cell borders. ICI not only minimizes the cell border throughput but also effects on the handover performance in LTE. Hard handover is standardized for LTE systems using L3-filter, hysteresis, and time-to-trigger mechanisms. The UE needs to receive error free handover command message for successful handover. This becomes critical when high interference is present on cell borders. Inter cell interference coordination (ICIC) is a technique that has been proposed to overcome ICI problems. We have investigated the improvements of LTE handover performance through ICIC. We have shown that significant gain can be achieved by the use of ICIC while maintaining very low handover rates.

Seamless Indoor/Outdoor Positioning Handover for Location-Based Services in Streamspin

Abstract: This paper presents the implementation of a novel seamless indoor/outdoor positioning service for mobile usersThe service is being made available in the Streamspin system(wwwstreamspincom), an open platform for the creation and delivery of location-based services Streamspin seeks to enable the delivery of truly ubiquitous location-based services by integrating GPS and Wi-Fi location fingerprinting The paper puts focus on key aspects of the seamless handover between outdoor to indoor positioning Several different handover solutions are presented,and their applicability is evaluated with respect to positioning accuracy and battery consumption of the mobile device

Electronic software significantly improves quality of handover in a London teaching hospital

Abstract: The study compared paper-based and electronic-based medical handover with respect to quality of information transfer during hospital out-of-hours shifts, and analysed the caseload burden of the hospital night team. The participants were 1645 hospital patients transferred from the day team to the out-of-hours team over four months in 2006. Quality of information transfer was determined by clinical data handed over within pre-set fields, and caseload burden by the frequency of tasks required at handover. Handover information fields comprised patient's demographics and location, primary diagnosis, current problem, plan of action and primary care team details. Electronic handover achieved a significantly higher number of completed fields than paper-based handover. Blood collection, checking blood and X-ray results, and adjusting fluid balance and intravenous cannulation account for most of the workload during the nightshift. Electronic handover provides better continuity of care than paper-based handover, and redistribution of tasks during working hours would benefit night staff.

A History-Based Handover Prediction for LTE Systems

Abstract: Handover prediction has been considered an effective technology for improvement of LTE Handover performance Although not a few techniques have been proposed to achieve this goal including handover preparation based on cross-layer optimization and mobility prediction, the fact is that their gains are not usually so high as their cost To overcome such weaknesses, this paper proposes a simple handover prediction technique which is based on a novel user mobility model to approximate simulation the laws of user mobility actions We develop a user mobility database to assist the mobility prediction based on the user mobility history records The simulation results show that the proposed technique minimizes the number of handovers and lower the ping-pang rate in LTE system

Handover location accuracy for travel time estimation in GSM and UMTS

Abstract: Field measurements from the GSM and UMTS networks are analysed in a road traffic information context. The measurements indicate a potentially large improvement using UMTS signalling data compared with GSM regarding handover location accuracy. These improvements can be used to generate real-time traffic information with higher quality and extend the geographic usage area for cellular-based travel time estimation systems. The results confirm previous reports indicating that the technology has a large potential in GSM and also show that the potential might be even larger and more flexible using UMTS. Assuming that non-vehicle terminals can be filtered out, that vehicles are tracked to the correct route and that handovers can be predicted correctly, a conclusion from the experiments is that the handover location accuracy in both GSM and UMTS will be sufficient to estimate useful travel times, also in urban environments. In a real system, these tasks are typically very challenging, especially in an urban environment. Further, it is reasonably established that the location error will be minor for the data obtained from UMTS.

Multi-service load sharing for resource management in the cellular/WLAN integrated network

Abstract: With the interworking between a cellular network and wireless local area networks (WLANs), an essential aspect of resource management is taking advantage of the overlay network structure to efficiently share the multi-service traffic load between the interworked systems. In this study, we propose a new load sharing scheme for voice and elastic data services in a cellular/WLAN integrated network. Admission control and dynamic vertical handoff are applied to pool the free bandwidths of the two systems to effectively serve elastic data traffic and improve the multiplexing gain. To further combat the cell bandwidth limitation, data calls in the cell are served under an efficient service discipline, referred to as shortest remaining processing time (SRPT). The SRPT can well exploit the heavy-tailedness of data call size to improve the resource utilization. An accurate analytical model is developed to determine an appropriate size threshold so that data calls are properly distributed to the integrated cell and WLAN, taking into account the load conditions and traffic characteristics. It is observed from extensive simulation and numerical analysis that the new scheme significantly improves the overall system performance.

Wireless communication system and handover method therein

Abstract: A wireless communication system and handover method for the wireless communication system are provided. A handover method for a wireless communication system including a plurality of femto cells and at least one macro cell within which the femto cells are disposed includes determining, at a Radio Network Controller (RNC), a handover of a terminal to a femto base station based on a measurement report of the terminal and preset handover parameters, sending a radio link setup request message to a femto base station gateway, the radio link setup request message including a uplink scrambling code and an International Mobile Subscriber Identity (IMSI) of the terminal and a Logical Cell Identifier (LCID) of femto base stations reusing frequency of a macro base station, searching, at the femto base station gateway, for femto base stations of which LCIDs match the LCID contained in the radio link setup request message, and performing, when only one LCID-matched femto base station is discovered, the handover of the terminal to the LCID-matched femto base station.

Fourth-generation Wireless Networks: Applications and Innovations

Abstract: Fourth-Generation Wireless Networks: Applications and Innovations presents a comprehensive collection of recent findings in access technologies useful in the architecture of wireless networks. Based on research results from academia and industry, this innovative publication covers cutting-edge findings on topics such as 4G security, mobile technologies, and handover mechanisms.

Automatic handover oscillation control

Abstract: A method and apparatus are provided for use in a cellular radio communication system for adjusting a handover parameter. Information is collected regarding actual handovers that have occurred between one or more pairs of cells as well as handover failures. The collected handover information is processed to determine a handover oscillation rate or a handover cost associated with the cell pair. If the handover performance is determined to be acceptable, the determined handover oscillation rate or the determined handover cost is compared with a predetermined target handover oscillation rate or a predetermined target handover cost, respectively. One or more handover parameters associated with at least one of the cells in the cell pair is adjusted based on the comparison.

Improvements to seamless vertical handover between mobile WiMAX and 3GPP UTRAN through the evolved packet core

Abstract: Recent mobile devices are integrated with multiple network interfaces. Users want their devices connected to the network anytime anywhere. It is highly feasible for a user to change connection to another network for users that leave the service area of its current serving network, where handover needs to be executed seamlessly such that ongoing service sessions are not interrupted. The handover operation not only requires switching the interfaces within a device but also involves seamless reconfiguration of the supporting networks. In this article, an improved IP-based vertical handover technology for mobile WiMAX , 3GPP legacy systems (i.e., Global System for Mobile communications and Universal Mobile Telecommunications System), and 3G Long Term Evolution is presented, which is based on existing optimized handover techniques between mobile WiMAX and 3GPP accesses. Formerly proposed 3GPP WiMAX optimized VHO solutions introduced new elements, such as the forward attachment function and access network discovery and selection function. The ANDSF supports the discovery of target access, and the FAF provides the functionality that authenticates the UE before the execution of VHO. However, the previous technique has limitations that result in data loss and abnormal disconnection to the source access. This article provides a solution by introducing an additional network element called the data forwarding function (DFF) that eliminates the data loss during VHO execution. In addition, the DFF resolves the problem of abrupt disconnection to the source network. The simulation results show that the proposed VHO technique is effective in minimizing data loss during VHO execution between mobile WiMAX and 3GPP networks. As the proposed solution of this article is an IP based handover solution, it can be similarly applied to other communication networks.

Handover in multihop cellular networks

Abstract: This article introduces various handover scenarios in multihop cellular networks. In addition, this article presents handover schemes where relay stations are located either inside a cell or on the boundary between two adjacent cells and investigates the effects of the deployment position of relay stations to handover performance. The simulation results show that multihop cellular networks for both deployment scenarios can achieve 90 percent throughput increase over single-hop cellular networks. The results also show that the overall throughput of the multihop cellular networks with relay stations inside a cell is higher than for those with relay stations on the boundary between two adjacent cells, whereas the opposite is observed for the throughput of cell-boundary users. The intercell handover latency in multihop cellular networks is increased by 20 ~ 56 percent compared with that in single-hop cellular networks because of the increased number of handovers and signaling overhead. However, by deploying relay stations on the boundary between two adjacent cells, the service-interruption time caused by inter-cell handover is reduced by 80 percent compared with that of single-hop cellular networks.

Energy-aware network selection using traffic estimation

Abstract: This paper proposes an energy-aware handoff algorithm based on energy consumption measurements of UMTS and 802.11 WLAN networks on an Android mobile phone. The handoff algorithm uses estimation of application traffic size to find the minimum energy cost alternative by comparing the cost of using UMTS with the cost of performing an opportunistic downward vertical handoff to a WLAN and using WLAN for the transfer and the eventual upward vertical handoff back to UMTS. Our experiments show that the energy cost of UMTS is nearly equal to WLAN as a function of transfer time, but for bulk transfers, transferring a byte of data over UMTS can be over a hundred times more expensive than over WLAN. Further, we discovered that the energy cost of the vertical handoff is quite high, comparable to downloading 0.12-0.67 MB of data over UMTS. To calculate the energy cost of data transfers before they take place, we propose and evaluate a distributed traffic estimation mechanism. The mechanism can predict how much data will be transferred due to a user action (i.e. clicking of an URL link). We provide initial results on the accuracy of the mechanism. Finally, we perform a numerical analysis on the the performance of the handoff algorithm and show that it can reduce the energy consumption significantly when compared with simple policies.