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Showing papers on "Handover published in 1994"


Journal ArticleDOI
TL;DR: An architecture is presented for a high-speed cellular radio access network based on ATM transport technology which avoids the need to involve the network call processor for every cell handoff attempt and which can readily support a very high rate of handoffs.
Abstract: An architecture is presented for a high-speed cellular radio access network based on ATM transport technology. Central to this approach is a new concept known as the virtual connection tree which avoids the need to involve the network call processor for every cell handoff attempt. Such an approach can readily support a very high rate of handoffs, thereby enabling use of physically small radio cells to provide very high system capacity, but may occasionally cause the volume of traffic to be handled by one cell site to exceed that cell site's capacity. A simple analytical methodology is developed which can be used for admission control, the purpose of which is to limit the number of in-progress calls such that two new quality of service metrics (overload probability and average time in overload) can be kept suitably low. Finally, a general framework is presented for overall system organization and signaling. >

488 citations


Patent
28 Oct 1994
TL;DR: In this paper, the authors proposed a method and apparatus providing softer handoff of a mobile unit between sectors (50, 70 and 80) of a common base station (60) consisting of a set of demodulation elements (240A-204N).
Abstract: A method and apparatus providing softer handoff of a mobile unit (90) between sectors (50, 70 and 80) of a common base station (60). A sectorized base station (60) comprises a set of demodulation elements (240A-204N). Each demodulation element (240A-204N) may be assigned to a signal from one of a plurality of sectors. The output of the demodulators (240A-204N) are combined before the decoding process independent of the sector from which the data originated. This configuration provides improved output data reliability, more stable power control, and more efficient use of resources at the base station.

223 citations


Journal ArticleDOI
01 Sep 1994
TL;DR: In this article, a hierarchical overlaid scheme suitable for high-capacity microcellular communications systems is considered as a strategy to achieve high system performance and broad coverage, where high-teletraffic areas are covered by microcells while overlaying macrocells cover low-TEFL areas and provide overflow groups of channels for clusters of microcells.
Abstract: A hierarchical overlaid scheme suitable for high-capacity microcellular communications systems is considered as a strategy to achieve high system performance and broad coverage. High-teletraffic areas are covered by microcells while overlaying macrocells cover low-teletraffic areas and provide overflow groups of channels for clusters of microcells. New calls and handoff calls enter at both the microcell and macrocell levels. Handoff calls are given priority access to channels at each level. The layout has inherent load-balancing capability, so spatial teletraffic variations are accommodated without the need for elaborate coordination of base stations (wireless gateways). An analytical model for teletraffic performance (including handoff) is developed. Theoretical performance characteristics that show carried traffic as well as blocking, handoff failure, and forced termination probabilities are derived. Effects of nonuniform teletraffic demand and channel allocation strategies on system performance are discussed. >

190 citations


Patent
16 Oct 1994
TL;DR: In this paper, a method and system for performing an intersystem handoff of communication with a mobile station between base stations of first and second cellular systems is described, where a quantifiable parameter of a signal transmitted by a second base station of the second system is measured.
Abstract: A method and system for performing an intersystem handoff of communication with a mobile station between base stations of first and second cellular systems is disclosed herein. At the mobile station, a quantifiable parameter of a signal transmitted by a second base station of the second system is measured. When the measured value of the quantifiable parameter passes through a first predetermined level, the mobile station communicates a signal quality message via a first base station of the first system to a first mobile switching control station. A channel request message is then communicated from the first mobile switching control station to a second mobile switching control station within the second system. At the second base station, a quantifiable parameter of the signal received from the mobile station is also measured. The second base station establishes communication with the mobile station when the measured value of the quantifiable parameter passes through a predetermined level. Alternately, the signal strength of a first pilot signal transmitted by the first base station is measured at the mobile station. A handoff request message is then sent to the second base station when the measured signal strength of the first pilot signal becomes less than a second predetermined level, thereby mobile station communication to be established. The provision of a voice link between the mobile switching control stations allows for the forwarding of an existing connection between the first and second cellular systems, and enables the performance of soft intersystem handoffs.

175 citations


Patent
14 Jun 1994
TL;DR: In this paper, a lower spreading ratio is used for discontinuous transmission in CDMA communications, where the spread information only fills an information part of a frame in a compressed mode, leaving an idle part of the frame in which to perform other functions, such as evaluation of other frequencies and execution of seamless handover between frequencies.
Abstract: Introduction of discontinuous transmission in CDMA communications techniques is achieved by using a lower spreading ratio, whereby the spread information only fills an information part of a frame in a compressed mode, leaving an idle part of the frame in which to perform other functions, such as evaluation of other frequencies and execution of seamless handover between frequencies.

151 citations


Patent
17 Feb 1994
TL;DR: In this paper, a method, system, and apparatus for communication and handoff in a cellular phone system in which candidate cell units which can support communication with a mobile phone are identified.
Abstract: A method, system, and apparatus for communication and handoff in a cellular phone system in which candidate cell units which can support communication with a mobile phone are identified. Neighbor cell units which have recently supported communication with the mobile phone are also identified. Handoff threshold values for each candidate cell are determined based on the existing communication quality and whether the candidate cell is also a neighbor cell such that the handoff threshold is higher when the candidate cell is a neighbor cell. A decision to handoff is made when the improvement offered by candidate cell is greater than the handoff threshold.

140 citations


Journal ArticleDOI
01 Sep 1994
TL;DR: In this paper, the authors review the important traffic performance measures for cellular systems and the issues of channel assignment, handoff, access control, traffic modeling, and traffic management, and conclude that reuse-based networks such as FDMA and TDMA possess quite different traffic characteristics from CDMA networks.
Abstract: The paper reviews traffic-related issues in the operation of the radio interface in cellular mobile networks operating with FDMA, TDMA, or CDMA technology. The emphasis is on issues which affect the traffic performance of the network, rather than on transmission technology, or transmission quality measures such as bit error rate. The author reviews the important traffic performance measures for cellular systems and the issues of channel assignment, handoff, access control, traffic modeling, and traffic management. Traffic modeling for all types of networks is considered in some depth, both by drawing analogies with fixed-wire networks, and by considering cellular-specific modeling. From the modeling results, he concludes that reuse-based networks such as FDMA and TDMA possess quite different traffic characteristics from CDMA networks. >

126 citations


Patent
28 Oct 1994
TL;DR: In this article, a plurality of methods for achieving the soft or softer handoff process such that the performance of a system is improved are presented. But the authors do not consider the impact of the transmission power of the sector having the weakest signal strength.
Abstract: A plurality of methods for achieving the soft or softer handoff process such that the performance of a system is improved. A first method is based on delaying the softer handoff process. A second method is based on reducing the power of transmissions from the sector having the weakest signal strength. A third method is based on eliminating transmissions from the sector having the weakest signal strength. A fourth method adds a new base station or sector only when the mobile unit is in need of additional power to operate properly. In all four methods, reverse link demodulation in each sector may continue with or without the transmission of the forward link. In all four methods the operation could be based on the signal strength of the reverse link signal or the forward link. It is also possible to combine two or more of these methods to create a hybrid method.

122 citations


Patent
12 Dec 1994
TL;DR: In this paper, a cellular system transfers a call from a source base station to the target base station, where a mobile unit measures the strength of pilot signals emanating from surrounding base stations and, in response to the result of the measurement, a different frequency hand off operation is initiated by the mobile unit when all pilot signals are lower than a threshold.
Abstract: A cellular system transfers a call from a source base station to the target base station. A mobile unit measures the strength of pilot signals emanating from surrounding base stations. In response to the result of the measurement, a different frequency hand off operation is initiated by the mobile unit when all pilot signals are lower than a threshold or is initiated by a system controller with consideration being given to the frequency band occupation state of surrounding base stations and the strength information reported from the mobile unit. In a handoff operation, the mobile unit reduces a maximum data rate to modulate user information with a current used frequency and to modulate a different frequency preposition code with a primary frequency so that neighboring base stations may measure the intensity of the preposition code and the system controller can determine how the different frequency hand-off should be operated.

86 citations


Book ChapterDOI
08 Mar 1994
TL;DR: A simple model for analyzing the soft handoff, and hard handoff performance as well as quantitative performance improvement measures for the capacity of the reverse links is presented.
Abstract: We present a simple model for analyzing the soft handoff, and hard handoff performance as well as quantitative performance improvement measures for the capacity of the reverse links. The results will be based on a propagation model that represents the μth power of the distance (average path loss) and the log-normal component representing the shadowing losses.

79 citations


Patent
01 Jun 1994
TL;DR: In this article, a cell-to-cell handoff between cells of the same satellite and between cell of different satellites is proposed. But the handoff is initiated by an individual subscriber unit (ISU) based on local conditions.
Abstract: Handoff methods perform cell-to-cell handoff between cells of the same satellite and between cells of different satellites. Handoff is initiated by an individual subscriber unit (ISU) based on local conditions. Once handoff is needed, the ISU chooses a candidate cell to transfer its communication based on a dynamic handoff candidate list provided by the satellite. After selecting a candidate cell, the ISU requests handoff, the satellite or satellites perform the handoff and communication begins over a new channel in the candidate cell.

Patent
30 Sep 1994
TL;DR: In this paper, a plurality of methods for achieving the soft or softer handoff process such that the performance of a system is improved are presented. But the authors do not consider the impact of the transmission power of the sector having the weakest signal strength.
Abstract: A plurality of methods for achieving the soft or softer handoff process such that the performance of a system is improved. A first method is based on delaying the softer handoff process. A second method is based on reducing the power of transmissions from the sector having the weakest signal strength. A third method is based on eliminating transmissions from the sector having the weakest signal strength. A fourth method adds a new base station or sector only when the mobile unit is in need of additional power to operate properly. In all four methods, reverse link demodulation in each sector may continue with or without the transmission of the forward link. In all four methods the operation could be based on the signal strength of the reverse link signal or the forward link. It is also possible to combine two or more of these methods to create a hybrid method.

Proceedings ArticleDOI
08 Jun 1994
TL;DR: Important performance measures of the system such as forced termination probability, and queue lengths are obtained and solutions for some special systems such as ones with a queue only for the handoff calls and without queues for any calls were investigated.
Abstract: Studies a queueing scheme of calls in cellular radio systems where priority is given to handoff calls by assigning several channels exclusively for them. The remaining channels are shared by both the originating and handoff calls. In this scheme both the originating and handoff calls make their own queues. A handoff call queues up if on arrival it finds no idle channels. An originating call also queues if on arrival it finds that the number of available channels is less than or equal to that of the reserved channels. Important performance measures of the system such as forced termination probability, and queue lengths are obtained. Solutions for some special systems such as ones with a queue only for the handoff calls and without queues for any calls were also investigated. >

Patent
Kolio Dr. Ivanov1, Egon Schulz1
14 Feb 1994
TL;DR: In this article, a check is carried out given a mobile station traveling into A radio coverage domain of a micro cell to see whether the radio coverage of the mobile station with respect to the micro cell has significantly or insignificantly improved within a time interval.
Abstract: In A speed-dependent hand over procedure for hierarchic cell structures, a check is carried out given a mobile station traveling into A radio coverage domain of a micro cell to see whether the radio coverage of the mobile station with respect to the micro cell has significantly or insignificantly improved within a time interval. In case of a significant improvement, the micro cell is blocked for the rapidly traveling mobile station.

Journal ArticleDOI
TL;DR: A priority handoff system which has dedicated channels for handoff calls and uses a blocked call cleared (BCC) policy is analyzed and a different approach in performance analysis is used, which has low computational complexity and high accuracy.
Abstract: Handoff will become an increasingly important issue in mobile phone communications, especially in microcellular systems with the increase of handoff traffic between cells. Many approaches have been proposed for handoff analysis. In a previous analysis, it was assumed that the probability density function (pdf) of the speeds of cell-crossing terminals is the same as the pdf of the speeds of all terminals. In contrast to this assumption, we argue that both pdf's are unequal. The pdf of the speeds of cell-crossing terminals is given by a “biased sampling” formula. This boundary condition is used in our study and improves the accuracy of performance measures in handoff analysis. In previous work, a priority handoff system which has dedicated channels for handoff calls and uses a blocked call cleared (BCC) policy has been analyzed. In this paper, we use a different approach in performance analysis. The proposed approach has low computational complexity and high accuracy.

Patent
Harald Kallin1, Anna Fallgren1
12 Dec 1994
TL;DR: Several mobile assisted handoff methods for use in the cellular communication system comprising a plurality of cells are disclosed in this paper, where the quality level of each of the assigned cells is then measured by the mobile station and reported to the communication system.
Abstract: Several mobile assisted handoff methods for use in the cellular communication system comprising a plurality of cells are disclosed. First, the quality level of a cell a mobile station is presently using is measured to determine whether the quality level is above or below a threshold. If the quality level is below the threshold, a primary list of cells is assigned to the mobile station, whereas if the quality level is above the threshold, a secondary list of cells is assigned to the mobile station. The quality level of each of the assigned cells is then measured by the mobile station and reported to the communication system.

Patent
01 Nov 1994
TL;DR: In this article, a method and system for locating control channels, particularly digital control channels are described, by grouping the channels which are candidates for carrying supervisory messages in blocks indicative of their relative likehood for being used as control channels.
Abstract: A method and system for locating control channels (70), particularly digital control channels are described. By grouping the channels which are candidates for carrying supervisory messages in blocks indicative of their relative likehood for being used as control channels, a mobile station can begin its search for a control channel with channels which are most likely to actually be control channels. Placing location information on other channels allows the mobile station (120) to be redirected to a control channel when it reads one of these other channels. Similarly, by placing information describing the location of a control channel in a message associated with handoff, a mobile station avoids the necessity of having to relocate a new control channel associated with the base station to which the mobile has been handed off.

Patent
Muszynski Peter1
27 Jan 1994
TL;DR: In this paper, a semi-hard handoff procedure is employed in a CDMA cellular telecommunications system, comprising mobile exchanges (MSC), base stations (BS) and mobile stations (MS).
Abstract: In a CDMA cellular telecommunications system, comprising mobile exchanges (MSC), base stations (BS) and mobile stations (MS), a new CDMA handoff procedure, a semi-hard handoff, is employed. Semi-hard handoff takes place within one and the same border base station (BS12), located in the boundary of two service areas (SA1, SA2) which are controlled by neighbouring mobile exchanges (MSC1, MSC2). This border base station is connected to and can be accessed from both of these neighbouring mobile exchanges. The inventive semi-hard handoff is a network based handoff of the communication control functions from the first to the second neighbouring mobile exchange without interrupting the active CDMA radio communications between the border base station (BS12) and the mobile station (MS).

Proceedings ArticleDOI
08 Jun 1994
TL;DR: Two approaches are presented-one based on neuro-fuzzy methods and the other based on hidden Markov models-and it is shown that patterns are sufficiently characteristic for the proposed application.
Abstract: The GSM system provides measurement data about the radio propagation situation that is used for power control and handover decisions. Currently implemented algorithms use averages of the measurement data and comparison with thresholds for these decisions. As the variations of the measured receive levels are characteristic for the route the mobile station is travelling on, pattern recognition is proposed to determine the position of the mobile station and for handover control. Two approaches are presented-one based on neuro-fuzzy methods and the other based on hidden Markov models-and it is shown that patterns are sufficiently characteristic for the proposed application. >

Patent
07 Dec 1994
TL;DR: In this paper, a mobile-to-mobile call in a cellular communication system (402,408), where a first mobile (400) is moving from a first cell (416) to a second cell (418), and the second mobile (406) is in a third cell (428).
Abstract: Soft handoff is provided in a mobile-to-mobile call in a cellular communication system (402,408), wherein a first mobile (400) is moving from a first cell (416) to a second cell (418), and the second mobile (406) is in a third cell (428). The first mobile (400) requests a handoff from the first cell (416) to the second cell (418). In response, information regarding the call handoff is sent to the second (418) and third (428) cells. During handoff, the first (416) and second (418) cells receive radio transmission from the first mobile (400), and they both translate the transmissions into electronic data, packetize the data, and send the packetized data to the third cell (428). The third cell sends packetized data from the second mobile (406) to both the first and second cells. Further, the second mobile may also move from the third cell (428) to a fourth cell (430). The second mobile requests a handoff from the third cell to the fourth cell. Call data is sent to the fourth cell identifying the first and second cells. Call data is sent to the first and second cells identifying the fourth cell. The first and second cells thereafter transmit packetized data to the third and fourth cells, and the third and fourth cells send packetized data to the first and second cells.

Proceedings ArticleDOI
08 Jun 1994
TL;DR: In the paper, a software simulator is described that allows the design of N and H considering the handover occurrence rate and the probability of unnecessary handover, and Rectangular and exponential averaging window shapes have been considered.
Abstract: The event of handing over a call from one base station to another in a cellular mobile radio network requests the cooperation of many system elements, with a consequent load of signalling traffic. Therefore, accurate design of handover procedures must be ensured, to avoid the occurrence of forced terminations and unnecessary handovers. This can be pursued by averaging the received power samples with a window of suitable shape and length, N, and by introducing a hysteresis cycle with margin H (dB). In the paper, a software simulator is described that allows the design of N and H considering the handover occurrence rate and the probability of unnecessary handover. Rectangular and exponential averaging window shapes have been considered. >

Proceedings ArticleDOI
08 Jun 1994
TL;DR: The direction biased handoff algorithms are shown to improve cell membership properties and handoff performance by lowering the mean number of handoffs while simultaneously reducing the handoff delay.
Abstract: A novel class of direction biased handoff algorithms are proposed for improving the handoff performance in urban microcells. Multi-cell urban microcell handoff properties are derived for a cell layout with base stations at every other intersection. The direction biased handoff algorithms are shown to improve cell membership properties and handoff performance by lowering the mean number of handoffs while simultaneously reducing the handoff delay. A direction estimation technique based on the signal strength history is shown to provide improved handoff performance, especially for line of sight handoffs. >

Journal ArticleDOI
TL;DR: This paper proposes an allocation of control functions to elements of the cellular packet switch and specifies the flow of information within the switch, which relies on distributed, rather than centralized mobility management to provide prompt, accurate communications as users move about.
Abstract: Future wireless information networks will employ dense grids of base stations to support a high user population. While small cells mitigate capacity problems, lengthen battery life, and improve signal quality, the frequent movement of users across cell boundaries imposes new burdens on network controllers. Previous work suggests that a cellular packet switch, based on distributed network control, can support high density personal communications. This paper proposes an allocation of control functions to elements of the cellular packet switch and specifies the flow of information within the switch. Message flows, defined for key procedures, form the foundation of a network layer protocol. Functionality is divided into the categories of call processing (set up and release), mobility management (location updates, handover, and path optimization), and radio resource management. Central office switches perform call processing. Mobility management and radio resource management are performed by interface units of the metropolitan area network at the heart of the cellular packet switch. This architecture delivers advanced services with minimal impact on central office switch software. It also relies on distributed, rather than centralized mobility management to provide prompt, accurate communications as users move about. >

Patent
28 Apr 1994
TL;DR: In this paper, a method for determining handover between different communications systems was proposed, by reference to records of the associations of cells belonging to different systems, stored by the mobile.
Abstract: A method for determining handover between different communications systems 10, 12, 14 eg. cellular, cordless, wireless PABX. Handover may be initiated manually or automatically, by reference to records of the associations of cells belonging to different systems, stored by the mobile. The mobile can access a bulletin board which provides information on available systems and inter-system cell associations. Inter-system handover is then determined from this information. Particular cell associations include identification of domestic systems and cells on which a user is registered, identification of systems and cells from which handover commonly occurs, or which are commonly accessed, manual updates and user preferences.

Patent
16 Sep 1994
TL;DR: In this paper, a method and apparatus are presented for selective resynchronization of the cipher upon initial channel acquisition or handoff in a ciphered digital cellular communications system, where synchronization between the old channel and the new channel does not exist, the base station provides an indication along with an ITCD or handover message that re-sync is required and from the content of this message the manner in which resynchronisation is to be achieved.
Abstract: In a ciphered digital cellular communications system a method and apparatus are presented for selective resynchronization of the cipher upon initial channel acquisition or handoff. Where synchronization between the old channel and the new channel exists, the base station indicates along with an ITCD or handover message that no resynchronization is required. Where synchronization between the old channel and the new channel does not exist, the base station provides an indication along with an ITCD or handover message that resynchronization is required and from the content of this message the manner in which resynchronization is to be achieved is further indicated. By providing options for resynchronization security may be optimized or compromised for handover speed depending upon the specific requirements of the base station or the mobile station.

Proceedings ArticleDOI
01 May 1994
TL;DR: An adaptive prediction based handoff algorithm has bee proposed to reduce the number of unnecessary handoffs in a microcellular CDMA/FDMA system.
Abstract: The rapid growth in wireless personal communication networks (PCN) has placed demands on higher system capacity and performance. One way to increase the capacity of a cellular system is by reducing the size of the cells to microcells. But, in such microcellular environment the frequency of handoff also increases. Since the handoffs increase the load on the network system, they should be minimized. Generally hysteresis and averaging are used to decrease the number of handoffs. These have a deteriorating effect on the signal quality. It is important to have the right compromise between the number of handoffs and the overall received signal quality. An adaptive prediction based handoff algorithm has bee proposed to reduce the number of unnecessary handoffs. This is verified by a simulation of a microcellular CDMA/FDMA system. >

Proceedings ArticleDOI
27 Sep 1994
TL;DR: In this paper, a radio planning methodology for IS-95 based CDMA networks is presented, which is based on a comprehensive performance characterization of both the forward and reverse links over a wide array of channel conditions.
Abstract: A radio planning methodology for IS-95 based CDMA networks is presented Inherent to the planning methodology is a comprehensive performance characterization of both the forward and reverse links over a wide array of channel conditions In addition, the link margin requirements under log-normal shadowing are addressed Effects due to loading, Erlang variations and voice activity, soft and softer handoff status, forward power allocation and closed loop power control are incorporated into the network modeling The output of the planning process are CDMA specific performance maps detailing forward and reverse link coverage and availability, interference margins and handoff regions In addition, cell site specific data is derived including forward and reverse cell/sector loading, forward link power requirements and soft handoff overhead requirements >

Patent
29 Dec 1994
TL;DR: In this paper, a mobile assisted handoff of a mobile station transitioning from a CDMA portion of a cellular telecommunication network to an analog portion of the network is provided as a function of a pilot signal transmitter located at each analog cell in the analog portion.
Abstract: A mobile assisted handoff of a mobile station transitioning from a CDMA portion of a cellular telecommunication network to an analog portion of the network is provided as a function of a CDMA pilot signal transmitter located at each analog cell in the analog portion of the network. The mobile station monitors a CDMA pilot signal transmitted from each CDMA cell and each analog cell of the cellular telecommunication network, measures the signal strength of each received CDMA pilot signal and transmits the signal strength to the MTSO. The MTSO determines whether the pilot signal is associated with a CDMA base station or an analog base station. When the mobile station receives a pilot signal from an analog cell whose signal strength is above a first predetermined threshold and the received signal strengths of all pilot signals of the CDMA base stations with which the mobile station is currently in communication are below a second predetermined threshold, the MTSO directs a CDMA to analog handoff message to the mobile station.

Patent
01 Jul 1994
TL;DR: In this article, a satellite cellular communications network performs cell-to-cell handoffs between cells of different satellites (30, 32), which require resynchronization to the prospective propagation timing and Doppler frequency parameters of the prospective satellite.
Abstract: A satellite cellular communications network performs cell-to-cell handoffs between cells of different satellites (30, 32). Inter-satellite handoffs require resynchronization to the prospective propagation timing and Doppler frequency parameters of the prospective satellite. Calculation of these parameters prior to transitioning to the prospective satellite minimizes interruptions to communications. Subscriber units (24) perform handoff parameter calculations while on narrow band communications channels without occupying broadband shared acquisition resources.

Patent
Jukka Suonvieri1
30 Jun 1994
TL;DR: In this paper, the authors proposed to use the timing advance in such a manner that part of the radio capacity of a cell serves only within a given timing advance range and thereby mobile stations located within a certain area of the cell.
Abstract: The invention relates to digital time division multiple access (TDMA) radio systems, local intracell capacity allocation in such a radio system, and an intracell handover in such a radio system. In the TDMA radio system, the transmission time of a mobile station (MS1, MS2) is advanced in relation to the base station (BTS1, BTS2) of the cell (C1, C2) by a timing advance which compensates for the transmission delay caused by the distance between the base station and the mobile station. The invention utilizes this timing advance in such a manner that part of the radio capacity of a cell serves only within a given timing advance range and thereby mobile stations located within a given area of the cell.