Showing papers on "Handover published in 1992"

Neighbor-assisted handoff in a cellular communications system

Abstract: A handoff system where handoff requests are initiated not only by a home or serving base station, but also by neighboring base stations. As in conventional handoff, a serving base station may initiate a handoff request when the signal strength of one of its mobile stations falls below a predetermined threshold. In addition, neighboring base stations monitor the signal strength of neighboring mobile stations and request that a neighboring mobile station be handed off when that signal strength reaches a predetermined level. Thus, a handoff request may come from the serving base station because of a poor call connection or from a neighboring base station because of a possible strong call connection.

A measurement-based prioritization scheme for handovers in mobile cellular networks

Abstract: A method of improving the quality of service in mobile cellular systems based on prioritization of handover requests is presented. The objective is to improve perceived quality of cellular service by minimizing both the probability of forced termination of ongoing calls due to handover failures and the degradation in spectrum utilization. A model based on a multiple-priority nonpreemptive queuing discipline is developed. New calls are blocked if all channels are occupied. Handover requests are queued such that as soon as a channel is available, it is offered to the mobile subscriber with the measurement results closest to the minimum acceptable power level for communication. Service rate is given by channel occupancy time distribution and is assumed to be exponential. The performance of a cellular system employing the proposed handover policy is evaluated analytically and by simulation, and results are compared to those obtained when the cellular system employs nonprioritized call handling and first-in/first-out queuing discipline. This provides lower probability of forced termination and less call blocking, less reduction in traffic, and less delay. >

Wireless access telephone-to-telephone network interface architecture

Abstract: A wireless-access communications system, such as a CDMA cellular radio-telephonesystem (FIG. 2), comprises a packet-switched communications network (202, 207, 201) that interconnects cells (base stations; 202) with each other and with the public telephone network (100). Traffic of individual calls is packetized, and packet-bearing frames (300 in FIG. 7) of a plurality of calls are then statistically multiplexed and frame-relayed through the network to yield the high capacity, efficiency, and speed of traffic transport and handoff required for a CDMA cellular system. At each call processing unit (264 in FIG. 5), individual calls are handled by individual service circuits (602 & 612) which perform speech-processing functions such as coding and decoding, tone insertion, and echo cancellation, and packet-to-circuit-switched-PCM traffic conversion. Processors (602) adapt call processing unit timing to compensate for asynchrony between cells and call processing units and variations in call path transmission delays. Cell-to-cell communications, fixed call path addressing, and packetized control message transfers ensure that the same service circuit handles a call through even multiple soft handoffs (FIGS. 27 - 29) and efficiently communicates simultaneously with all cells involved in the handoff without involvement of system control entities and negative effect on system call-handling capacity. Both coded (packet-switched) and uncoded (circuit-switched) radio-telephone traffic are accommodated side-by-side. Wherever possible, existing and proven technology and component units are used to achieve low cost and high reliability.

Prioritized channel assignment in a cellular radio network

Abstract: Dimensioning procedures for prioritized channel assignment in a cellular radio network are considered. Under the cutoff priority discipline, the prioritized channel assignment procedures for a single cell and multicell system are formulated as nonlinear discrete capacity allocation problems. Exact incremental algorithms which efficiently solve the proposed problems are devised. They are based on the properties of the blocking probabilities of new calls and handoff calls. Given the number of available frequency channels together with the arrival rates and the grade of service (GOS) for both types of calls in each cell, algorithm SP1 generates an optimal channel assignment which ensures priority for handoff calls. Given the arrival rates and distinct GOSs for new and handoff calls, algorithm SP2 finds the minimum number of channels required in each cell. Algorithm MP extends algorithm SP1 to a multicell system and provides the prioritized channel assignment for all calls in the system. The algorithms are very fast and are appropriate for the fair allocation of frequency channels among cells. >

Load sharing control for a mobile cellular radio system

Abstract: In a mobile cellular radio system, load balancing is achieved by moving dynamically the borders between any two cells such that an overloaded cell becomes smaller and the neighboring cell larger. This is achieved by lowering the entering signal strength threshold for handoff to the neighboring cell and/or increasing the entering signal strength threshold for handoff from the neighboring cell. Thresholds are unique for any two cells.

The Universal Mobile Telecommunication System

Abstract: The concepts, requirements, and technologies of Europe's third generation mobile communication system-the Universal Mobile Telecommunications System (UMTS)-are discussed. The cellular architecture, radio resource, adaptive resource allocation and handover enabling techniques for realizing an effective UMTS access network are described. The modulation schemes, multiple access methods, and duplexing methods used in the third generation mobile system's flexible radio interface are also described. The architecture, mobility support, and protocol development of the UMTS fixed network are outlined. >

A method of effecting handover in a mobile multilayer cellular radio system

Abstract: A method of effecting handover in a mobile telephone system comprising fixed base stations and mobile stations. The system includes several layers of radio cells, where a cell in a given layer covers several cells in a nearest underlying or subordinate layer. A mobile station moving in a microcell may find it difficult to handover to another microcell in the same cell layer, when the signal strength of the established connection in the first microcell is rapidly weakened. No information concerning the target base station can be transmitted. According to the proposed method, handover is effected to a cell in the nearest overlying cell layer, a so-called umbrella cell, either permanently (the mobile is moving quickly) or temporarily (the mobile is moving slowly). In the latter case, handover is made back to a microcell. The handover command is either transmitted from the base station of the microcell having elevated power, or from the target base station.

Intelligent network concepts in mobile communications

Abstract: A mobile cellular network architecture that is based on intelligent network concepts is presented. Subscriber service mobility and call management attributes of the network, including location information retrieval and updating, authentication, call routing, handover, charging, and operations and maintenance, are discussed. >

Teletraffic performance of microcellular personal communication networks

Abstract: Teletraffic performance of a personal communication network (PCN) based on city street microcells catering for pedestrian mobile users is analysed. By opting for microcells, the network capacity dramatically increases as well as the spectrum efficiency, but the network must be able to accommodate substantial increases in the number and rate of call handovers. A teletraffic analysis is performed to determine the new and handover call rates as well as the channel holding time of the PCN. Next, a teletraffic model is established to determine the teletraffic performance parameters, such as the blocking probabilities of new and handover calls, the overall grade of service, the carried traffic, the channel utilisation, and the spectrum efficiency. Techniques to reduce the premature termination of calls in progress are proposed and modelled. These include reserving a set of channels exclusively for handovers at each microcell fixed station, and deploying a macrocell to overlay a microcellular cluster, where the macrocell base station is assigned channels for handover requests from mobiles who cannot be serviced by their microcell fixed stations. A large spectral efficiency of 1000 Erlang/MHz/km2 is achieved at nominal blocking probability of 2%, while the probability of premature termination is reduced to less than 10−4 in the presence of high call rates in excess of 0.06 calls/s/microcell. The results presented will assist network planners in predicting teletraffic performance.

Prioritization between handoff and new call requests in a cellular communications system

Abstract: A method and system for ensuring that handoff requests take priority over new cell requests to engage voice channels assigned to a particular target cell are provided. A certain number of channels are reserved for handoff requests. However, if no channels, reserved or unreserved, are available, handoff requests to a particular target cell are stored in a corresponding queue for a predetermined period of time. Thus, when voice channels become available, they are seized in order to satisfy the handoff requests stored in that queue. If the handoff queue is empty, new call requests to a target cell may be assigned to available voice channels.

Cellular mobile communications system using frequencies commonly shared by neighboring cells for handoff operations

Abstract: In a cellular mobile communication system, each base station is allocated common frequencies shared with other base stations in addition to unique frequencies. One of the unique frequencies is assigned by a base station to a mobile terminal in response to a call request. The field strength of a signal from that mobile terminal is detected and one of the common frequencies is assigned to it if the detected field strength becomes lower than a threshold. The base station receives a field strength signal from a neighboring station indicating the field strength of a version of the signal at the neighboring station and compares it with a threshold, and combines the signal of that mobile terminal with the version of the signal received by and relayed from the neighboring station when the field strength of that version of the signal is higher than the threshold. At the given mobile station, a signal from the base station which assigned the common frequency is combined with a signal from the neighboring station. In a modification, the field strength of signals from surrounding base stations is detected by mobile terminals and a start-of-diversity-mode request is transmitted when the field strength of one of the surrounding stations is higher than a threshold and an end-of-diversity-mode request signal is transmitted when the field strength of such a surrounding station is lower than the threshold. The base station responds to these requests for effecting diversity reception.

Network control for wireless communications

Abstract: Existing wireless network architectures and the increasing demand for cellular services are reviewed. Wireless network control tasks and the structure of a cellular packet switch (CPS) based on an optical fiber metropolitan area network (MAN) are described. Protocols for moving information through the MAN focusing on handoff, a crucial function of wireless networks, are discussed. The results of an analysis of switch performance as measured by capacity and the distribution of functionality are presented. Several open issues regarding the capability of the CPS to deliver telephone service to wireless terminals, including privacy and security issues, are discussed. >

Method of transmitting signaling messages in a mobile radio communication system

Abstract: In a mobile radio communications system, critical signaling messages, e.g., handoff messages, transmitted on a fast associated control channel and/or a slow associated control channel belonging to a digital traffic channel, are more heavily data protected than speech using convolutional coding and interburst interleaving. The coding and interburst interleaving are carried out so as to maintain compatibility with an exiting frame structure.

Resource auction multiple access (rama) : efficient method for fast resource assignment in decentralised wireless PCS

Abstract: A novel method is presented to address the need for fast and flexible access, handoff, and resource assignment in future high capacity wireless personal communications systems (PCSs). In one deterministic algorithm, called resource auction multiple access (RAMA), fast handoff, access and resource assignments are incorporated. Resource use and throughput are unaffected by heavy traffic demand as in traditional contention schemes. Using selected GSM parameters with RAMA, it is shown that, in microcells with propagation delays of 1 μs, 2160 resource assignment/s are feasible. With delays of 25 μs, 648 assignment/s are feasible.

The dynamic behavior of handoff algorithms

Abstract: The authors develop analytical models to study the dynamic behavior of handoff algorithms based on field-strength measurements in a fading environment. These models quantify the behavior of the handover algorithm as the mobile moves from one base station to another. The performance is measured in terms of the probability of correct handoff decision and the delay in handoff. The effect of algorithm parameters like averaging length and hysteresis level on these performance measures is determined. These factors interact and it is important to understand the optimizing relationships. The analysis is carried out in terms of level crossings of a stochastic process which is the difference of two processes, each representing the signal strength from a base station. >

Sequential power estimation for cellular system handoff

Abstract: Cellular handoff is improved by tailing or adapting the measurement time based on the characteristics of the received signal intensity or power. More particularly, base stations typically measure mobile signal power in order to determine the necessity for handoff and the identity of a new cell. The measurement time must be of a duration which is sufficient to characterize the environment of the mobile. In accordance with the invention, the duration of the measurement time is determined from the received signal itself. Once the duration of the measurement time is determined, that data may be passed to a target cell along with other handoff data.

Handover protocols between metropolitan area networks

Abstract: Inter-MAN handover protocols for the cellular packet switch are developed, based on interconnecting MANs via gateways. Inter-MAN handover protocols utilize the gateway to maintain a connection as a user moves across MAN boundaries. This greatly reduces the fixed-network signalling traffic while protecting information in data communications. >

A microcellular interconnection architecture for personal communications networks

Abstract: The current centralized wireless communication architectures are considered inappropriate to cope with the anticipated demand for personal communications. A distributed microcellular architecture is proposed, based on the IEEE 802.6 MAN. Initial traffic estimates indicate that the MAN would provide coverage for an urban area of 8*8 city blocks. It is shown that call control and management functions are dependent upon database distribution and class of handoff. >

Analysis of measurement based prioritization schemes for handovers in cellular networks

Abstract: A performance analysis of the first-in first-out (FIFO) and the priority queueing schemes, in comparison to the simple call handling scheme where there is no queuing, is presented. All analytical results are verified by simulation studies of the three schemes. With queuing of handovers, if all channels are occupied, new calls are blocked and handover requests are queued so that as soon as a channel is available, it is offered a handover request in the queue; new calls are blocked until the queue of handovers is emptied. In the priority queueing scheme, the mobile subscriber with the highest instantaneous priority is served first. The results indicate that the priority queueing scheme provides lower probability of forced termination and call blocking than FIFO queuing. >

Handoff in microcellular based personal telephone systems

Abstract: When using small microcells with antennas mounted at lamp post level the propagation characteristics will be very different from traditional large cells. Firstly, the so called street corner effect, i.e. 20–30 dB drop of signal level in 10–20 m, have to be considered. Very fast handoff algorithms and, maybe, new strategies will be required. Furthermore the number of handoffs per call will increase, due to the small cell size. Each handoff must therefore be made with high success rate. Secondly, the propagation is very difficult to predict since it depends to a large extent on the local environment. This makes it very difficult to find a fixed reuse plan, i.e. dynamic channel allocation (DCA) is probably required. In this paper we concentrate on the handoff issue. Some discussion on the propagation characteristics and DCA is however also made.

A personal communication network architecture using the IEEE 802.6 MAN

Abstract: The authors describe a distributed architecture based upon IEEE 802.6 metropolitan area networks (MANs) that will provide interconnection over a metropolitan area for wireless personal communications. An appropriate bridge routing strategy is suggested to interconnect the several MANs needed to cover an urban metropolitan area. A novel isochronous transport mechanism is proposed to facilitate speech silence suppression over the MAN. While a queue-arbitrated connectionless service is used for signaling over MANs to enable call setup and handoff, voice circuits are provided by means of the pre-arbitrated isochronous service. Connection issues within a metropolitan area relevant to call setup and handoff are examined. To facilitate capacity savings between voice talk spurts on the MAN, a technique is described which enables the isochronous service to accommodate data rate variations. >

Selective handover for traffic balance in mobile radio communications

Abstract: The selective handover for traffic balance (SHOT) technique, which is effective in increasing frequency efficiency for varying traffic loads, is presented. If the traffic of a cell increases temporarily such that the resource utilization rate exceeds a threshold, SHOT hands some calls over to the appropriate adjacent cells. Three algorithms are proposed and examined through computer simulations. The simulations reveal that SHOT improves the traffic performance by about 50% under the condition that offered traffic is uniformly distributed in the areas when the number of channels of each cell is ten. >

An effective prioritization scheme for handovers in cellular networks

Abstract: The authors present a method of improving the quality of service in cellular systems based on prioritization of handover requests. Handover prioritization schemes lead to a tradeoff between the improvement of the probability of successful handover and spectrum utilization. The objective is to improve perceived quality of cellular service by minimizing both the probability of forced termination of ongoing calls due to handover failures and the degradation in spectrum utilization. The authors present a handover policy based on a multiple priority nonpreemptive queueing of calls in progress. Originating calls are blocked if all channels are occupied. Handover requests are queued such that as soon as a channel is available, it is offered to the mobile subscriber with the measurement results closest to the minimum acceptable power level for communication. The queue is dynamically reordered as new measurement results are submitted. The results of the authors' simulation study show that the new scheme provides lower probability of forced termination, less call blocking, less reduction in traffic and less delay than the single priority class FIFO queueing under all traffic conditions. >

Advanced handoff control using fuzzy inference for indoor radio system

Abstract: An autonomous learning procedure fir cell boundaries is reported, and advanced handoff controls making use of the learned cell boundary are proposed. The cell boundary is learned by moving a mobile set, which has a detector showing equal signal strength along the boundary, after all the base stations have been installed. Handoff control using reliable cell boundaries can omit the exceptional transactions caused by multipath fading. Advanced controls, soft handoff without intermittence, and its extension by means of fuzzy decisions are described. >

UMTS: a third generation mobile system

Abstract: UMTS (Universal Mobile Telecommunications System) is a system capable of providing a variety of mobile services (up to 2 Mbps) now being offered by (dedicated) paging, cordless, and cellular communications systems separately. UMTS is to be operational in domestic, business, vehicular, and (multi-operator) public environments. Maximum integration with the IBCN (Integrated Broadband Communications Network, also referred to as B-ISDN) is considered. UMTS is currently under study by the RACE project 2066 (MONET) taking the work of the RACE project 1043 (UMTS) as a starting point. The paper describes new concepts in mobile system design considered for UMTS. Both radio aspects including handover and network aspects are dealt with. The relationship with the CCIR FPLMTS (Future Public Land Mobile Telecommunications System) is briefly addressed. >

Mixed cell architecture and handover

Abstract: Future personal communications and mobile radio systems will rely on a multi-cellular architecture to achieve high user capacity. In particular, the mixed cell architecture with macrocells overlaying microcells and indoor picocells appears promising. For such a system, handover techniques, band sharing strategies and ultimately the traffic performance are among the issues of utmost concern to third generation mobile system designers. The merits of a mixed cell architecture are examined. Handover strategies and procedures pertinent to a mixed cell system are reviewed together with highlights of their performance.

Techniques for cellular networks incorporating microcells

Abstract: A layered radio cell architecture is described for high capacity cellular networks, such as PCN, in which the microcells are used to increase the capacity of the system. Alternative frequency assignment schemes which support this approach are considered. A technique for handling high speed mobiles is proposed. This scheme effectively prevents handover between layers for mobiles moving too fast for the microcells and is being incorporated into phase 2 of the GSM/DCS 1800 European digital cellular/PCN standards. >

Improved gsm interference band selection and reduced power handover

Abstract: A method is offered of achieving a desired C/I ratio within a cellular system, at reduced transmitter power levels, by measuring a signal loss on a downlink between a base site transmitter (31) and mobile receiver (20) and calculating an uplink signal magnitude at a base site receiver A communication channel is then selected from a number of communication channels based upon comparison of the uplink signal magnitude with pre-measured interference levels of each channel of the number of channels to produce a desired C/I ratio

Handoff effects in microcellular systems

Abstract: A teletraffic system model has been developed for the Melbourne central business district, based on the microcellular mobile concept. A set of simulations has been developed to evaluate the implications of the use of very small cells on the traffic performance in this specified service area. This model is used to investigate the balance between the new call blocking and the handoff call blocking for such a system. >

Handover decision algorithm using power budget values

Abstract: In a cellular radio-telephone system (50), a method of selecting an appropriate handoff target where the timing advance of a mobile has exceeded a timing advance threshold, the bit error rate has risen above a BER threshold, or the signal level has fallen below an RSSI threshold. The method includes discarding signal measurements of inappropriate base sites or base sites at excessive distance and performing calculations on the remaining measurements to select an appropriate handoff target.