Showing papers on "Handover published in 1991"

Handover and channel assignment in mobile cellular networks

Abstract: A taxonomy of channel assignment strategies is provided, and the complexity in each cellular component is discussed. Various handover scenarios and the roles of the base station and the mobile switching center are considered. Prioritization schemes are discussed, and the required intelligence distribution among the network components is defined. >

Location determination and handover in mobile radio systems

Abstract: A handover initiation system for a cellular radio network comprises means for determining both the distance of a mobile user from a cell base station based on propagation delay techniques and means for measuring the signal strength to determine the path taken by the mobile user. In a busy area microcells are constituted by single streets. The propagation characteristics of adjoining streets in a larger macrocell can be distinguished from the propagation characteristics of the street constituting the microcell such that the handover initiation of a mobile user within one of the surrounding streets can be determined.

Analysis of handover algorithms (microcellular radio)

Abstract: Handover algorithms are analyzed for a simple channel model. Three performance measures are defined: the probability of lost calls, the probability of unnecessary handover, and the probability of handover. In the design of a handover algorithm, a tradeoff between these measures has to be made since they cannot be minimized simultaneously. A particular class of algorithms, linear handover algorithms, is introduced. Performance bounds are derived, and expressions for the performance measures for linear algorithms are given. In particular, a lower bound for the probability of lost calls is derived. This bound is valid as long as the signal model is correct and is not limited to the class of linear algorithms. >

A method of operating a communications system, a communications system and a secondary station for use in the system

Abstract: A method of operating a communications system, particularly a FDM-TDD cordless telephony system, in which, in order to expedite handover, a portable secondary station builds up a record of the status and quality of the other FDM channels in the system by every 1 in n (where n is an integer greater than one) TDD frames monitoring another FDM channel. The value of n is adaptive in that, as the quality of its existing channel deteriorates, the value of n decreases, thereby updating its record more rapidly. At handover, the secondary station is able to choose immediately an acceptable alternative channel, thereby avoiding the time overhead of scanning all the other FDM channels.

Capacity of digital cellular TDMA systems

Abstract: The capacity of digital TDMA (time-division multiple-access) systems is addressed. It is projected that capacity improvement will be of the order of 5-10 times that of analog FM without adding any cell sites. For example, the North American TIA (Telecommunication Industry Association) standard offers around 50 Erlang/km/sup 2/ with a 3-km site-to-site distance. In addition, the TDMA principle allows a faster handoff mechanism (mobile assisted handoff), which makes it easier to introduce microcells with a cell radius of about 200 m. This gives substantial additional capacity gain beyond the 5-10 factor given above. TDMA makes it possible to introduce adaptive channel allocation (ACA) methods. ACA is a mechanism that provides efficient microcellular capacity. ACA also eliminates the need to plan frequencies for cells. It is concluded that the air-interface of digital TDMA cellular may be used to build personal communication networks. >

Handoff of a mobile station between half rate and full rate channels

Abstract: In a cellular mobile telephone system of the type having TDMA channels, a plurality of mobile station operate at either a full rate or a half rate. If the mobile stations are operating on the periphery of a cell they are assigned to full rate channels. If the mobile stations are operating in the vicinity of the base station, they are assigned to half rate channels. The mobile station are reassigned from full rate to half rate channels depending upon a measured parameters relating to signal strength or quality, such as the bit error rate of communications between the mobile station and the base station. If the measured bit error rate between the mobile station and a neighboring station is less than the bit error rate between the mobile station and its presently assigned base station, the mobile station is handed off to the neighboring base station.

Intra-cell call hand-over in radio communication systems with dynamic channel allocation

Abstract: The intra-cell call hand-over technique of this invention is characterized by the use of channel information from both base station and subscriber terminal in determining a standby radio traffic channel upon which to hand over a call. Communication between the base station and subscriber terminal is carried out on an inband or associated signalling channel for the selection of the standby traffic channel. The standby radio channel is the channel, which, of a set of channels under consideration by the subscriber terminal, contains the least amount of interference as measured at the subscriber terminal. The set of channels under consideration by the subscriber terminal is a subset of the entire set of channels allocated to the service. This subset is comprised of those channels having little interference as measured by the base station. The call hand-over technique thereby assures that calls proceed on channels containing little interference from the viewpoints of both base station and subscriber terminal.

Microcell system for cellular telephone system

Abstract: An improved microcell system for cellular telephone systems has a plurality of contiguous cells wherein the cells are configured in a plurality of clusters with each cell in a cluster having a different assigned set of transmission frequencies. Each of the frequencies in an assigned set for a given cell is assignable to a given mobile telephone within the cell for all locations of the mobile telephone within the cell. Frequency handoff circuitry is provided for maintaining continuous communication with mobile telephones moving from cell to cell. Each of the cells is provided with a plurality of antennas each of which is arranged and configured to limit propagation of signals substantially to one of a plurality of regions within the boundaries of the cell, which regions are substantially less in area than the area of the cell. Transmission at any one frequency of the set of transmission frequencies assigned to a cell is confined to the zone wherein the strongest signal is received from the mobile telephone to which such one frequency has been assigned. Accordingly, the clusters of cells may be arranged with a frequency reuse pattern of three and a ratio of co-channel separation to cell radius of less than four.

Handover criterion for macro and microcellular systems

Abstract: In order to realize fast handover in both microcells and macrocells, the relationship between averaging, the received signal level comparison method, and handover detection delay was analyzed. The analytical results were verified by handover simulations performed using experimental propagation data. As the criterion for accurate and stable handover in both the macrocell and the microcell, a combined handover decision is suggested which consists of long-term averaging with a small hysteresis margin and short-term averaging with a large hysteresis margin. >

Method of controlling handoff in cellular mobile radio communications system

Abstract: When communication is established using a mobile radio terminal, the speed at which the terminal is moving is measured by monitoring the Rayleigh fading of the signal strength. Using this velocity indicative parameter, a threshold level which is used to determine if a handoff is required or not, can be adjusted in a manner which renders the decision process more accurate and minimizes the number of unwarranted handoffs.

Radiotelephone locating and handoff using alternative criteria

Abstract: In a cellular mobile radiotelephone system having a plurality of cells providing radio coverage by a plurality of base stations and having a plurality of mobile stations, the location of a mobile station with respect to cell boundaries is identified using measurements, performed at the mobile station or at selected cells, of transmissions from the cells or transmissions from the mobile station. When a cell is found that meets a specified standard with respect to a call connection in progress according to a first radio-signal criterion, a handoff candidate cell is selected according a second different radio-signal criterion. When no cell is found that meets the specified standard, a cell is selected according to the first radio-signal criterion. Handoff to the selected cell is attempted if that cell is not presently handling that call. More particularly, the first radio-signal criterion may be signal strength and the second radio-signal criterion may be path loss. When a cell is found that meets the signal-strength criterion, the cell is determined to have sufficient signal strength margin so that the path loss criterion may be used instead. As mentioned above, use of the path loss criterion has the advantages of conserving power, reducing interference, and allowing effective cell boundaries to remain fixed. When no cell is found that meets the signal-strength criterion, the call connection is determined to be signal-strength limited such that the signal strength criterion is used to select the cell having the greatest signal strength.

Handoff strategies in microcellular systems

Abstract: Plausible strategies and algorithms for microcellular handoff are examined. Attention is given to such issues as propagation characteristics, C/I (carrier/interference) distribution, and handoff performance in a microcellular system. Some examples from real measurements in central Stockholm are shown, and a brief description of propagation models used in handoff simulations is presented. The handoff strategies for some contemporary systems are reviewed, and some results from simulations of mobile assisted handoff (MAHO) are shown. >

A method and apparatus for enhancing signalling reliability in a cellular mobile radio telephone system

Abstract: A method and apparatus for achieving reliable transmission of signalling messages in a cellular system in which the frequency plan, frequency/time slot allocation plan, code channel allocation plan, or dynamic/adaptive channel allocation rule of the system is violated by allowing adjacent base stations to reuse particular frequencies/time slots/channels for signalling a particular mobile station. In situations where signalling messages, such as handoff commands, which are communicated between a base station and a mobile station are not properly received by the mobile station, an alternate communications channel will be established to ensure the reception of these messages. The alternate channel is provided by repeating the message through a channel associated with a base station which has better radio characteristics. The channel selected for transmission of the message by the new base station will be on the same frequency/time slot/code as used by the established connection.

Mobile radio communication system

Abstract: In a mobile radio communication system, a mobile station (MR) constantly monitors a quality of a radio line between the mobile station and a first base station (BS1) with which the mobile station is presently communicating, detects a deterioration of the quality of the radio line between the mobile station and the first base station outside a tolerable range, successively detects field intensities of signals received from the base stations (BS2) neighboring the first base station using a free time slot which is unused by the mobile station for communication to determine a maximum field intensity, supplies to the first base station predetermined information related to a second base station (BS2) from which the signal with the maximum field intensity is received so as to make a handover request, and ends a communication with the first base station in response to a handover message. The first base station supplies a handover request message to a control station (CS) in response to the handover request from the mobile station, and the control station carries out a handover process in response to the handover request message. The handover process includes selecting a new communication channel with which the mobile station is to communicate with the second base station when the mobile station moves from a first radio zone (RZ1) to a second radio zone (RZ2), and notifying the handover message and the new communication channel to the mobile station and the first and second base stations, so that the mobile station ends the communication with the first base station in response to the handover message and starts a communication with the second base station using the new communication channel.

Method of handover and route diversity in mobile radio communication

Abstract: A method of handover and route diversity in a mobile radio communication which is less time consuming and capable of improving the frequency spectrum utilization efficiency and securing the high quality of service regardless of the moving speed of the mobile station In the method, a loop transmission line by which each base station is connected with neighboring base stations is provided; a handover information is transmitted through the loop transmission line, where the handover information is relayed by each base station from one of the neighboring base stations to another one of the neighboring base station; and the handover of a communication of a mobile station from one traffic channel of one base station to an idle traffic channel of another base station is carried out by using the handover information transmitted through the loop transmission line The method can also be applied to a route diversity reception

Performance of dynamic channel allocation in the DECT system

Abstract: The authors present the results of computer simulations of an indoor wireless PABX system conforming to the Digital European Cordless Telecommunications (DECT) standard. Of particular interest is the evaluation of the dynamic channel allocation algorithm proposed by the DECT standard. It is shown that this system is capable of meeting the expected capacity requirements for high-density indoor applications as long as there are a sufficient number of base stations on each floor of the building. System performance has been measured in terms of setup blocking, handover blocking, lost calls, cleared traffic, and carrier-to-interference ratios. >

Mobile radio handover initiation determination

Abstract: An intelligent mobile radio unit is served by one of a network of macrocells and microcells. The unit is arranged to monitor, for example, the signal strength or bit error ratio of signals transmitted from each of a set of candidate base stations of cells surrounding the serving base based on the assessment of a running average of the rise/fall in signal quality, the unit is arranged to determine from a look-up table of stored templates of conditions for handover whether a handover between base stations and bewtween macro- and microcells is

The control of handover initiation in microcells

Abstract: It is pointed out that the reliability of handover depends on many aspects of the cellular system, including the handover initiation criteria, handover protocol, and network infrastructure organization. After examining the mechanisms of handover initiation in microcellular environments, the author considers the use of a combined forward and backward handover protocol for a mixed-cell system. Network issues and the choice of mobile controlled or assisted handover are also discussed. >

On dynamic channel assignment in cellular mobile radio systems

Abstract: There are two types of strategies to assign the channels to a cell: fixed channel assignment (FCA) and dynamic channel assignment (DCA). The basic characteristics of DCA are presented in comparison with FCA. The authors introduce various DCA strategies and discuss some of most important DCA research topics currently being pursued. In particular, the authors focus on microcellular systems, including a proposed MD (moving direction) strategy. It uses the information a mobile station's (MS's) moving direction with the DCA strategy. A channel is selected among those occupied by MSs moving in the same direction with the concerned MS. In this manner, the MS can still use the same channel at the handover with high probability. DCA requires more radio equipment at each base station than FCA, and it requires elaborate channel assignment control. However, it exploits the limited frequency spectrum efficiently and has a lower forced call-termination rate than FCA when the blocking rates are equal. >

Different methods of giving priority to handoff traffic in a mobile telephone system with directed retry

Abstract: Two different ways of giving priority to handoffs in a mobile telephone system with directed retry are discussed. Directed retry considerably decreases the new calls blocking probability at the expense of the handoff failure rate. The first priority method is to reserve channels exclusively for handoff; the other is to use handoff queues. The performance of the method is analyzed by simulations. It is found that appropriately designed handoff queues can lower the handoff failure rate substantially with almost no effect on the new calls blocking probability. >

Cellular radio with microcellular/macrocellular handoff

Abstract: A cellular radio system comprises a plurality of basic stations each having a radio transceiver serving a cell of the system. A mobile station of the invention has a radio transceiver for communicating with one or other of the base stations, as well as long term averaging units (LTA0, LTA1, LTAN) for time averaging handover criterion (HOC) measurements over a first averaging period. The mobile station also includes a summer (SN) for applying a first hysteresis margin to the time averaged HOC measurements to provide a first handover indicator. The mobile station also includes short term averaging units (STA0, STA1, STAN) for time averaging HOC measurements over a second averaging period which is relatively short compared to the first averaging period, as well as a summer (SW) for applying a second hysteresis margin, which is relatively large compared to the first hysteresis margin, to the time averaged HOC measurements to provide a second handover indicator. The mobile station further includes a gate (OR1) for assessing handover requirements of the mobile station on the basis of the first and second handover indicators, whereby on the one hand relatively gradual variations in HOC can be assessed and on the other hand relatively sudden variations in HOC can also be assessed.

Method for handoff in a mobile radio communication system

Abstract: The invention relates to a method in connection with handoff from a first base station in a mobile radio communication system, in which method the signal strengths from a set of base stations surrounding a mobile station are measured in the latter. When handoff is considered to be motivated, the signal strength vector formed by the measured signal strengths is correlated with stored characteristic signal strength vectors associated with the first base station. If the correlation between measured signal strength vector and one of said stored characteristic signal strength vectors exceeds a predetermined correlation level, handoff is commanded to a predetermined second base station in the set having acceptable but not the highest signal strength in the measured signal strength vector, or is the handoff procedure interrupted and the connection between the mobile station and the first base station maintained.

Handoff procedure that minimizes disturbances to dtmf signalling in a cellular radio system

Abstract: Disturbances to DTMF signaling between mobile stations and the land-based system caused by handoff are minimized. DTMF signals are transmitted in real time between a mobile station and its associated base station. However, if during a DTMF transmission between a base station and the mobile switching center a handoff is requested, the handoff is delayed by a specified time in order to allow completion of the DTMF transmission. Alternatively, both base stations involved in the handoff transmit overlapping DTMF tones until the handoff is completed. If the handoff is requested before the start of the DTMF tone transmission, the DTMF transmission is delayed until the handoff is completed.

Handover method for radiotelephone networks

Abstract: A handover method for a cellular radiotelephone networks in which, a call having been set up with a mobile via a first transceiver of a first cell, the handover consists in handing over to a second transceiver of a second cell and in switching in the mobile from the first transceiver to the second transceiver. The switching instruction interrupts the call in a defined cut-off time interval. The instruction to hand over the call is given under conditions such that the interruption of the call which may result from the handover operation occurs during the defined cut-off time interval.

Communication transfer in a cellular radiotelephone system

Abstract: During the handoff of a mobile unit (225) between a serving or source base-site (200) and a selected target base-site, (205 or 210) the target base-site (205 or 210) is directed to tune to and monitor the mobile unit's in progress call on a serving base-site channel frequency in order to verify target cell selection immediately before the handoff. Thereafter, the mobile unit (225) is directed to tune to a selected target base-site channel by the target base-site. Next, the target base-site (205 or 210) re-tunes itself to the selected target channel frequency and continues to transmit. Upon the arrival of the mobile unit onto the selected target channel, the serving base-site channel is released.

DCAP, a decentral channel access protocol: performance analysis

Abstract: A novel decentralized channel oriented media access control protocol in combination with a direction of movement oriented channel management protocol ISMA (integrated service management protocol) is introduced. Analysis and results of performance characteristics of the protocol for direction-oriented road traffic are presented. The results show the advantages gained from the combination of ISMA and DCAP protocols. Based on knowledge of the distribution and mobility of stations, a Markov model was developed to analyze the performance of the DCAP protocol under the control of ISMA. Numerical results for handover and collision rate are presented. It is shown that under direction-oriented assignment of channels via the ISMA the DCAP protocol can hand over channels very quickly and collision probabilities are small. >

Method for effecting handoff in a multi-site communication system

Abstract: A method of effecting handoff of a communicating communication unit from a first communication resource to a second communication resource. After determining that a handoff from the first communication resource to the second communication resource should likely be made, the method makes determinations regarding relative levels of communication degradation that will likely occur when using different handoff methodologies to effect the handoff. In general, the method selects a particular handoff methodology that will provide a best level of handoff reliability while simultaneously posing at least no more than an acceptable level of communication degradation.

Handover and Channel Assjanment J in Mobile Cellular Networks Quick and timely handover has a crucial effect on how users perceive quality of service, however, handover strategies should not be too complicated.

Abstract: rhe Ph. D. degree at Georg~ Mason Unharsirys School qf lnfornlation Technology and Engineering In Farfar, Virgmia hc rapid growth in the demand for mobile communications has led the industry into intense research and development efforts toward\ a new generation of cellular systems. One of theimportant objectives in the developmentofthenewgenerationisimprovingthequalityofcellularservice,with handoversnearlyinvisiblc to the Mobile Subscriber (MS). In general, the handover function isamost frequentlyencountered network function and has direct impact on the perceived quality of servicc. It provides continuation of calls as the MS travels across cell boundaries, where new channels are assigned by thc new Base Station (BS) and the Mobile Switching Center (MSC). The system performancc characteristics include probability of blocking of new traffic, probability of forced termination of ongoing calls, delay in channel assignment, and total carried traffic. There is a tradeoff between the quality of service and implementation complcxity of the channel allocation algorithms, number of database lookups and spectrum utilization. In selecting a channcl assignment strategy, the objective is to achieve a high degree of spectrum utilization for a given quality of service with thc least possible number of database lookups and simplest possible algori thms employed at the RS and/or the MSC. Handover prioritizationschemesarechannel assignment stratcgics that allocate channels to handover requests more readily than originating calls. Prioritization schemes provide improved pcrformance at the expense of reduction in the total admitted traffic. Inthisarticle,weprovideataxonomyofthechanne1 assignmcnt strategies along with the complexity in each cellular component. Next, we consider various handover scenarios and the roles of the BS and MSC. We then discuss the prioritization schemes and define the required intelligence distribution among the network components.

An evaluation of direct sequence CDMA for future mobile communication networks

Abstract: The performance and some of the implementation aspects of a practical mobile radio communications network employing direct-sequence code-division multiple access (DS-CDMA) are examined. The use of spread-spectrum techniques results in a wideband system, thus permitting the potential exploitation of multipath signal energy and permitting a means of reducing interference arising from other users of the spectrum. An analytical performance model is developed in order to assess the spectral efficiency of a DS-CDMA communications network. The computer model permits the performance evaluation of various path diversity schemes alongside numerous digital-modulation and error-correction coding techniques while operating in a mobile radio channel. In order to substantiate the results presented, novel power control and handoff protocols are also proposed in light of the assumptions made. >

Link control in terrestrial/satellite mobile communication systems

Abstract: Algorithms and signalling requirements of procedures for link selection and handover are discussed, both for terrestrial and satellite land mobile communications. For terrestrial cellular systems the methods are well known in principle, it is argued that similar procedures could also be employed in satellite multi-beam systems. Choice of terrestrial or satellite links in integrated dual mode systems is considered in some detail.