Showing papers on "Handover published in 1998"

Vertical handoffs in wireless overlay networks

Abstract: No single wireless network technology simultaneously provides a low latency, high bandwidth, wide area data service to a large number of mobile users. Wireless Overlay Networks – a hierarchical structure of room-size, building-size, and wide area data networks – solve the problem of providing network connectivity to a large number of mobile users in an efficient and scalable way. The specific topology of cells and the wide variety of network technologies that comprise wireless overlay networks present new problems that have not been encountered in previous cellular handoff systems. We have implemented a vertical handoff system that allows users to roam between cells in wireless overlay networks. Our goal is to provide a user with the best possible connectivity for as long as possible with a minimum of disruption during handoff. Results of our initial implementation show that the handoff latency is bounded by the discovery time, the amount of time before the mobile host discovers that it has moved into or out of a new wireless overlay. This discovery time is measured in seconds: large enough to disrupt reliable transport protocols such as TCP and introduce significant disruptions in continuous multimedia transmission. To efficiently support applications that cannot tolerate these disruptions, we present enhancements to the basic scheme that significantly reduce the discovery time without assuming any knowledge about specific channel characteristics. For handoffs between room-size and building-size overlays, these enhancements lead to a best-case handoff latency of approximately 170 ms with a 1.5% overhead in terms of network resources. For handoffs between building-size and wide-area data networks, the best-case handoff latency is approximately 800 ms with a similarly low overhead.

UMTS/IMT-2000 based on wideband CDMA

Abstract: The UMTS terrestrial radio access is based on wideband 4.096 Mchip/s DS-CDMA technology. UTRA will be connected to an evolved GSM core network for both circuit and packet services. A merger between ETSI/Europe and ARIB/Japan based on W-CDMA, a GSM core network, and a common frequency allocation according to the ITU Recommendation of 2 GHz makes a global IMT-2000 standard feasible. UTRA based on W-CDMA fully supports the UMTS/IMT-2000 requirements (e.g., support of 384 kb/s for wide-area coverage and 2 Mb/s for local coverage). Furthermore, the air interface has flexible support of mixed services, variable-rate services, and an efficient packet mode. Key W-CDMA features also include improved basic capacity/coverage performance compared to second-generation systems, full support of adaptive antenna arrays, support of hierarchical cell structures with interfrequency handover, and support of asynchronous inter-base-station operation. There have been no constraints due to the strong requirements for backward compatibility with second-generation systems. This has facilitated a high degree of flexibility and a future-proof air interface. Extensive evaluations by means of simulations and field trials have been carried out by a number of companies, and full system tests are ongoing. Consequently, W-CDMA technology can now be regarded as a mature technology, ready to provide the basis for UMTS/IMT-2000.

An adaptive bandwidth reservation scheme for high-speed multimedia wireless networks

Abstract: In the next generation high-speed wireless networks, it is important to provide quality-of-service (QoS) guarantees as they are expected to support multimedia applications. This paper proposes an admission control scheme based on adaptive bandwidth reservation to provide QoS guarantees for multimedia traffic carried in high-speed wireless cellular networks. The proposed scheme allocates bandwidth to a connection in the cell where the connection request originates and reserves bandwidth in all neighboring cells. When a user moves to a new cell and a handoff occurs, bandwidth is allocated in the new cell, bandwidth is reserved in the new cell's neighboring cells, and reserved bandwidth in more distant cells is released. The amount of bandwidth to reserve is dynamically adjusted, reflecting the current network conditions. The performance of the proposed scheme is evaluated through simulations of realistic cellular environments. The simulated network consists of a large number of cells, mobile users with various movement patterns are assumed, and a variety of multimedia applications (e.g., audio phone, video conference, video on demand, file transfer, etc.) is considered. It is shown that the proposed scheme provides small handoff dropping probability (i.e., the probability that handoff connections are dropped due to a lack of bandwidth) and achieves high bandwidth utilization.

Handoff in cellular systems

Abstract: Handoff is an essential element of cellular communications. Efficient handoff algorithms are a cost-effective way of enhancing the capacity and QoS of cellular systems. This article presents different aspects of handoff and discusses handoff related features of cellular systems. Several system deployment scenarios that dictate specific handoff requirements are illustrated. An account of handoff-related resource management tasks of cellular systems is given. Implementation of the handoff process is explained. Several mechanisms for evaluation of handoff-related system performance are described.

Method and system for mobile communications

Abstract: When a network pages the temporary user mobile identifier of a mobile station, the mobile station sends a response to the network. Next, the network checks the authenticity of the user using a ciphering key, corresponding to the temporary user mobile identifier and a random number. If the temporary user mobile identifier is authenticated, a normal incoming call acceptance procedure is executed. If the mobile station is authenticated although the temporary user mobile identifier is wrong, the network reassigns a new temporary user mobile identifier to the mobile station and stops the current communication. In communication, the network and the mobile station mutually notify encipherment-onset time and negotiate about encipherment manner with each other. In addition, diversity handover is commenced upon a call attempt. Furthermore, if a branch replacement is necessary, the current branch is replaced by new branches capable of executing the diversity handover. Additionally, when a new call occurs to or from the mobile station capable of treating a plurality of calls simultaneously, the mobile station uses the same branch structure and the same communication frequency band for all of calls. Additionally, when a new call occurs to or from the mobile station capable of treating a plurality of calls simultaneously, a branch structure and a communication frequency band, which can continue all of the calls, are selected and used. Therefore, the mobile communications system is suitable for transmission of various sorts of data in accordance with the development of multimedia.

Channel occupancy times and handoff rate for mobile computing and PCS networks

Abstract: This paper presents a study of channel occupancy times and handoff rate for mobile computing in MC (Mobile Computing) and PCS (Personal Communications Services) networks, using general operational assumptions. It is shown that, for exponentially distributed call holding times, a distribution more appropriate for conventional voice telephony, the channel occupancy times are exponentially distributed if and only if the cell residence times are exponentially distributed. It is further shown that the merged traffic from new calls and handoff calls is Poisson if and only if the cell residence times are exponentially distributed, too. When cell residence times follow a general distribution, a more appropriate way to model mobile computing sessions, new formulae for channel occupancy time distributions are obtained. Moreover, when the call holding times and the cell residence times have general (nonlattice) distributions, general formulae for computing the handoff rate during a call connection and handoff call arrival rate to a cell are given. Our analysis illustrates why the exponential assumption for call holding time results in the underestimation of handoff rate, which then leads to the actual blocking probabilities being higher than the blocking probabilities for MC/PCS networks designed using the exponential distribution approximation for call holding time. The analytical results presented in this paper can be expected to play a significant role in teletraffic analysis and system design for MC/PCS networks.

QoS routing in ad hoc wireless networks

Abstract: The emergence of nomadic applications have generated a lot of interest in wireless network infrastructures which support multimedia services. We propose a bandwidth routing algorithm for multimedia support in a multihop wireless network. This network can be interconnected to wired networks (e.g. ATM or the Internet) or stand alone. Our bandwidth routing includes bandwidth calculation and reservation schemes. Under such a routing algorithm, we can derive a route to satisfy the bandwidth requirement for the QoS constraint. At a source node, the bandwidth information can be used to decide to accept a new call or not immediately. This is specially important to carry out a fast handoff when interconnecting to an ATM backbone infrastructure. It enables an efficient call admission control. The simulation results show that the bandwidth routing algorithm is very useful in extending the ATM virtual circuit service to the wireless network. Different types of QoS traffic can be integrated in such a dynamic radio network with high performance.

Analysis of a hybrid cutoff priority scheme for multiple classes of traffic in multimedia wireless networks

Abstract: In this paper, we propose and analyze the performance of a new handoff scheme called hybrid cutoff priority scheme for wireless networks carrying multimedia traffic. The unique characteristics of this scheme include support for N classes of traffic, each may have different QoS requirements in terms of number of channels needed, holding time of the connection and cutoff priority. The proposed scheme can handle finite buffering for both new calls and handoffs. Futhermore, we take into consideration the departure of new calls due to caller impatience and the dropping of queued handoff calls due to unavailability of channels during the handoff period. The performance indices adopted in the evaluation using the Stochastic Petri Net (SPN) model include new call and handoff blocking probabilities, call forced termination probability, and channel utilization for each type of traffic. Impact on the performance measures by various system parameters such as queue length, traffic input and QoS of different traffic has also been studied.

Apparatus and method for management of resources in cellular networks

Abstract: Wireless networks require efficient mobility management to cope with frequent mobile handoff and rerouting of connections. The invention treats this problem by developing a hierarchical prediction engine that employs approximate pattern matching and Kalman filtering techniques to yield an accurate prediction of both the immediate next cell to be entered by the mobile and the overall or global route of the mobile unit in the wireless cellular network. The prediction of the mobile's future movement is used by the network to reserve resources, relieve congestion, reduce latency, and optimize the establishment of routes in the wireless cellular network.

System for automated determination of handoff neighbor list for cellular communication systems

Abstract: The system for automated determination of handoff neighbor list uses the data collected from mobile subscriber units to automatically update the handoff neighbor list. The mobile subscriber unit produces Pilot Strength Measurement (PSM) data that is indicative of the relative signal strength measured at the mobile subscriber unit from a plurality of pilot channels. The mobile subscriber unit transmits this data, along with a list of viable pilot channel candidates as determined by the mobile subscriber unit, to the base station serving the existing call. The system for automated determination of handoff neighbor list maintains a data structure that stores data indicative of the number of instances that a pilot channel is recommended, the sum of power levels that were measured by the various mobile subscriber units for these instances. This data is processed to determine a metric for each data structure in the list, with the metric in the present embodiment being a function of the number of occurrences multiplied by a weighting factor summed with the sum of power levels.

Method and an apparatus for positioning system assisted cellular radiotelephone handoff and dropoff

Abstract: A method and an apparatus is provided for acquiring satellite signals to establish the exact spatial position of a cellular radiotelephone, in order to perform a timely dropoff or smooth handoff to another base station or frequency. The cellular radiotelephone is equipped with its own positioning system which uses satellite data to determine its spatial position. The communication system is preferably a Code Division Multiple Access (CDMA) system, and the positioning system is preferably a Global Positioning System (GPS). The method of the present invention may be used to determine the base station closest to the cellular radiotelephone. In the alternative, it may be used to compute a distance between the cellular radiotelephone and a location where the quality level of the cellular radiotelephone communication signal is predicted to be less than the predetermined value, and to determine from the computed distance whether the cellular radiotelephone should be handed off.

Microcellular mobile communication system

Abstract: A microcelluar mobile communication system which performs various functions such as a centralized management of resources, a capacity increase, a Base Station Transceiver System(BTS) miniaturization, a synchronization between micro base stations, a dynamic resource management, a softer handover between cells, a grouping and ungrouping of base stations in accordance with a traffic distribution The microcelluar mobile communication system may increase the subscriber capacity, provide the high reliable service, extend the battery life of a personal station inducing low power communication and assure the radio channel capacity so that the radio multimedia service may be accomplished in the future, by maximizing the utility efficiency of radio frequency resource through cell miniaturization The microcelluar mobile communication system may be installed efficiently to an indoor, a building underground, an underground tunnel as well as an outdoor, and may compose the single cell also in the indoor

Base station transmit power control in a CDMA cellular telephone system

Abstract: A power control method in accordance with the present invention synchronizes the transmit power levels at the base stations currently serving a mobile station and an initial transmit power level of a new target base station being added in a diversity handover situation. At the beginning of the handover, a radio network controller orders the serving base stations to measure their respective transmit powers to the mobile station. Each serving base station then measures its transmit power to the mobile station and reports the power level measurements to the radio network controller. An initial transmit power setting is determined for the target base station, and new transmit power settings are determined for the serving base stations synchronized for example to a particular time (t0). At or about synchronizing time t0, the target base station transmits to the mobile station at the initial power setting, and at or about the same time, the serving base stations preferably also adjust their transmit powers toward the new values. Alternatively, the serving base stations transmit at their respective new values at or about time t0 . In a preferred embodiment of the present invention, the serving base station power adjustment is performed gradually.

Method for handover and cell re-selection

Abstract: For transmitting information about the neighbouring cells to mobile stations, a base station of a cellular radio system creates a message (27, 27') containing information about the neighbouring cells and transmits it to the mobile station. In addition to the transmission frequencies used in the neighbouring cells, the base station includes in the message other information characterizing the neighbouring cells (32a, 32b, 32c, 34). In particular, the base station includes in the message information about the quality of service offered to mobile stations by each of the neighbouring cells mentioned in the message. On the basis of the message, the mobile station makes a preliminary selection of a group of the most advantageous new cells and performs measurements among this preliminary selection in order to find a suitable new cell (41, 47). If the measurements show that there is at least one suitable new cell among the preliminary selection, the mobile station selects a new cell from this group (42). If the measurements show that there are no suitable new cells in this group, the mobile station selects a new cell from another group of cells than the preliminary selection (43, 48).

Performance analysis for a guaranteed handover service in an LEO constellation with a "satellite-fixed cell" system

Abstract: It is anticipated that the satellite component of the future universal mobile telecommunications system (UMTS) will be based (partly or totally) on non-geostationary (nonGEO) constellations of satellites to serve mixed populations of users, each category being treated through different contracts stipulating different quality of service (QoS). In particular, we envisage a high-quality premium service which guarantees the success of each handover procedure, called guaranteed handover (GH) service, and a low-cost lower quality service called regular service, where handover failures are accepted provided that the probability of a call being unsuccessful does not exceed a given value. This paper proposes a strategy which eliminates forced call terminations due to handover failures, thus allowing the GH service. This procedure applies to low Earth orbit (LEO) constellations using the satellite-fixed cell technique. An analytical model has been derived to calculate QoS parameters for a mixed population of GH and regular users. Providing both GH service to some users and regular service to other users requires an increased satellite capacity with respect to the case where all the users are served with the regular service; this capacity increase has been evaluated as a function of the percentage of GH users, the traffic load per cell, and the considered satellite mobility environment. The GH approach has been validated through the comparison with another scheme which envisages the queuing of handover requests for privileged users.

Method for CDMA handoff in the vicinity of highly sectorized cells

Abstract: A method for improved sector handoff within a sectorized communication cell utilizing a wireless communication systems. A sector handoff of a mobile radio telephone is performed in accordance with a first set of parameters if the mobile radio telephone is not in close proximity to a base antenna. Sector handoff of the mobile radio telephone is performed in accordance with a second different set of parameters when the mobile radio telephone is in close proximity of the base antenna. The second different set of parameters are utilized in close proximity to the base antenna to avoid drops and adverse handoffs in high interference, low signal strength areas and provide improved sector handoff when the mobile radio telephone encounters distorted conditions, such that improved sector handoff can be achieved.

Power control of mobile station transmission during handoff in a cellular system

Abstract: A method and apparatus for controlling the transmission power of a mobile station during handoff of a call between base stations of a cellular system A desired transmission power of a mobile station on an assigned traffic channel of a target base station is determined, and the transmission power of the mobile station is adjusted over a range of power values to be set to the desired transmission power level. The desired transmission power of the mobile station may be determined based on measurements made on the pilot channel of the target base station at the mobile station. Alternately, base station power classes may be defined for the cellular system so that each base station at which it is desired to receive mobile station transmissions at a signal level within a selected range is assigned to a power class associated with that selected range A mobile station involved in a handoff can determine the power level at which it should begin transmitting on a new traffic channel during handoff by determining the power class of the base station to which the new traffic channel is assigned.

Cellular radio access network and location updating in a cordless communications system

Abstract: A cellular radio access network and a location updating in a cordless communications system, in a cellular radio access network (1), which is connected to one or more core networks (2, 3, 4, 5) or services (SP2 to SP5), each of them having a dedicated mobility management. In a cell, identities of all those location areas are broadcast to which said cell belongs. A subscriber terminal (MS) sends to the radio access network only one location updating message irrespective of how many core networks (2, 3, 4, 5) or services (SP2 to SP5) have a simultaneously changing location area at a handover from one cell to another. On the basis of the information contained in the location updating message, the network (1) defines the core networks or services and location areas to which the location updating applies and sends a location updating message informing the new location of the subscriber or the subscriber terminal separately to each defined core network or service.

Method for determining position of mobile communication terminals

Abstract: A number of different solutions are disclosed for gathering access delay and distance measurement information for use in determining the position of a cellular mobile station (112, 160). For all of these solutions, one frequency and one uplink channel in each cell are dedicated for position determination. In one aspect of the present invention, a method is provided for determining the position of a mobile station (112, 160) using handover procedures for all of the cells or certain predefined cells in the network (100). One uplink channel is dedicated within each cell in the network (100) to be used for position determination. These positioning channels continuously listen for handover access requests. Cells detecting (124) the access bursts can measure (124) the access delay and determine the distance (128) to the requesting mobile station (112, 160). A triangulation calculation (128) is used to pinpoint the mobile station's (112, 160) position. In another aspect of the present invention, a method is provided for determining the position of a mobile station (112, 160) using position determination procedures for all of the cells or certain predefined cells in the network (100).

Analysis of a CDMA soft-handoff algorithm

Abstract: This paper analyzes the performance of a soft-handoff algorithm of the type that has been proposed in IS-95 for a code-division multiple access (CDMA) system. While the analysis is stimulated by IS-95, the focus is more on developing applicable analysis methodology rather than on specifically modeling the present IS-95 algorithm. In the soft-handoff scheme, multiple base stations are involved in the communication to and from one mobile station to improve the handoff performance on the boundaries between two base stations by providing channel diversity. On the other hand, there are additional resources used during soft-handoff. There is, thus, a tradeoff between diversity advantage and resource utilization. The analysis provides quantification for this tradeoff. The analysis is validated with simulation. The analytical results can be used to gain insight and help select the appropriate handoff thresholds.

System and method used in a mobile telecommunications network for load balancing ongoing calls between different base station controllers

Abstract: A method and system for load balancing used in a mobile telecommunications network. The load balancing system includes a mobile services switching center and a first base station controller coupled to the mobile services switching center for managing a first plurality of cells. The load balancing system further includes a second base station controller coupled to the mobile services switching center for managing a second plurality of cells, where one cell of the first plurality of cells is adjacent to one cell of the second plurality of cells. The second base station controller includes a processor responsive to receiving a first load indication message from the first base station controller in order to determine whether to handover at least one ongoing call from the one cell of the second base station controller to the one cell of the first base station controller.

System and method for soft handoff setup during system access idle handoff in a wireless network

Abstract: There is disclosed, for use in a CDMA wireless network, a base station capable of performing a soft handoff of a mobile station while the mobile station is still in the process of first accessing the wireless network. The base station comprises a receiver for receiving from the mobile station a system access message that initiates in the wireless network a system access procedure that establishes a communications channel between the mobile station and the CDMA-based wireless network. The base station also comprises a handoff controller, coupled to the receiver and receiving the system access message therefrom. The handoff controller prepares another selected base station in the CDMA-based wireless network to take control over the system access procedure by sending a handoff control message that initiates in the selected base station a handoff procedure capable of assuming control over the system access procedure. This handoff procedure is speculatively initiated in anticipation of a later handoff by the mobile station.

Providing a neighborhood zone within a mobile telecommunications network

Abstract: A neighborhood zone covering an enclosed or surrounded environment, such as a man-made building or high-rise, is defined (400) within a mobile telecommunications network by associating a plurality of base stations with respective cell areas. A same neighborhood list indicating all measurement channels being utilized within the neighborhood zone by said plurality of base stations is then further defined (400). The defined same neighborhood list is then transmitted (410) by each of the base stations within its respective coverage area. A mobile station traveling within the neighborhood zone then scans and reports measurements (420) from the indicated measurement channels to the serving mobile telecommunications network. The mobile telecommunications network then effectuates a handover (460) in accordance with the received signal measurements. An idle mobile station further utilized the measurements to effectuate a cell re-selection.

Method for transmitting measurement reports in a mobile communications system

Abstract: A service node is provided in a mobile communications network which collects radio link measurement reports which are transmitted to the service node by mobile stations. The mobile stations transmit the measurement reports in encapsulated form, in the form of SMS messages, in order to prevent the interception of the measurement report by the serving base station. The service node is able to perform handover decision algorithms using the measurement reports collected from the mobile stations in order to determine appropriate radio access nodes to be allocated to the mobile stations.

Intra-cell inter-frequency hard handoff method in a CDMA cellular system

Abstract: A method for processing a hard handoff between a moving mobile station and base stations in a code division multiple access is disclosed. In accordance with a preferred embodiment of the present invention, the method of intra-cell-inter-frequency hard handoff includes the steps of setting up a new call, confirming whether a current base station satisfies a condition of inter-frequency hard handoff and whether a currently used frequency in the base station satisfies a condition of inter-frequency hard handoff, and performing a general handoff and call processing, when both the conditions of the two confirming steps are not satisfied. If both conditions of the two confirming steps are satisfied, an output signal strength threshold value on and a distance threshold value are set. The mobile station is instructed to periodically report the base station's output signal strength. The distance between the base station and the mobile station is established and when the base station's output signal strength is less than the set threshold value hard handoff is commanded. However, if it is not less, the base station to mobile station distance is checked with respect to the set distance threshold value. On the contrary, in the event that the base station-mobile station distance is less than the set threshold value, the method returns to the step of estimating the distance between the base station and the mobile station and continues to check the output signal strength of the base station and distance between base station and mobile station.

Method and apparatus for determining a need to handoff a mobile communication signal in a wireless communication system

Abstract: In a wireless communication system, which includes a first base site (101) having an associated controller (130) and a second base site (108), a mobile station (103) responsive to the first and second base site, a method for determining a need to hard handoff a mobile communication signal (107) associated with the mobile station from the first base site to the second base site is disclosed. The method includes receiving a plurality of hard handoff candidate parameters associated with the mobile communication signal, and then measuring a plurality of scan result parameters associated with the mobile communication signal by a handoff scan receiver (304). The method further includes forwarding the plurality of scan result parameters to the controller, and then determining whether or not a hard handoff of the mobile communication signal is required based on the scan result parameters.

Performance evaluation of connection rerouting schemes for ATM-based wireless networks

Abstract: Supporting mobility in asynchronous transfer mode (ATM)-based broad-band networks with wireless access links poses many technical challenges. One of the most important of these challenges is the need to reroute ongoing connections to/from mobile users as these users move among base stations. Connection rerouting schemes must exhibit low handoff latency, maintain efficient routes, and limit disruption to continuous media traffic while minimizing reroute updates to the network switches. In this paper we propose, describe an implementation for, and experimentally evaluate the performance of five different connection rerouting schemes. We show that one of these schemes, which operates in two phases, executes very fast reroutes (with a measured latency of 6.5 ms) in a real-time phase and, if necessary, reroutes again in a nonreal-time phase to maintain efficient routing. The scheme also results in negligible disruption to both audio (e.g., a 1-in-100 chance of a single packet loss at CD-quality audio rates of 128 kb/s) and low-bit-rate video (e.g., a 2-in-100 chance of a single packet loss for 1-Mb/s video) traffic during connection rerouting. Based on these results, we conclude that simple handoff schemes coupled with a connection management architecture are sufficient for supporting low-bit-rate continuous media applications over ATM-based wireless networks.

Localised special services in a mobile communications system

Abstract: A method for controlling the local operation of a mobile station (MS). The method comprises forming a group (10) of special cells from selected network cells, and controlling the operation of the mobile station (MS) on the basis of said group (10). According to a preferred embodiment, if the old and/or new cell is a special cell, information on this is transmitted to the mobile station already in a handover command, whereby the mobile station may refuse handover.

Advanced method for executing handover

Abstract: A cellular radio system comprises base stations and mobile stations. In order to execute handover, there is chosen a group of potential new base stations and estimated the carrier to interference ratio that each potential new base station included in said group could offer. The carrier to interference ratio can be estimated separately for real-time and for non-real-time connections and/or for uplink and downlink connections.

Probabilistic routing protocol for low Earth orbit satellite networks

Abstract: Low Earth orbit (LEO) satellite networks have dynamic, yet deterministic, topologies. The time-varying connectivity pattern would result in the re-routing of all connections passing through a link that is turned off as a result of the topology change. A routing algorithm called probabilistic routing protocol (PRP) is introduced. The PRP reduces the number of re-routing attempts due to the dynamic topology of the network. During the routing phase of a newly arriving call, the PRP eliminates the links that will be turned off before the call releases the link due to call termination or connection handover. Since the algorithm has no knowledge of the call duration or exact terminal location, route usage time is only known probabilistically. The probability distribution function of the route usage time of the call is determined to realize the algorithm. Since the routing algorithm works in parallel with a handover re-routing algorithm, the application to the footprint handover re-routing protocol (FHRP) is also demonstrated. The performance of the algorithm is investigated using simulation experiments.