MXPA99006033A - Compensation for mobile assisted handoff measurement inaccuracies - Google Patents

Abstract

A mobile assisted handoff (MAHO) signal strength measurement is ordered by the cellular telephone system for not only the currently used traffic channel (108) and the reference (control) channels of neighboring cells (104), but also for the reference (control) channel of the current cell (106). These MAHO measurements are reported (110) to the system where a compensation factor (112) is determined which accounts for the use of different modulation schemes and/or hyperbands by system traffic and control channels. The compensation factor is calculated by subtracting the MAHO measurement made on the reference channel of the current cell from the MAHO measurement made on the traffic channel of the current cell. The calculated compensation factor is then added (114) to each of the MAHO measurements made on the reference channels for each of the neighboring cells to generate compensated signal strength measurements. The compensated measurements are then compared (116) to the MAHO measurement made on the traffic channel (in view of a predetermined hysteresis) to determine whether a handoff (118) to one of the neighboring cells should be made.

Description

COMPENSATION FOR IMPRECISIONS OF MOBILE ASSISTANCE TRANSFER MEASUREMENT BACKGROUND OF THE INVENTION Technical Field of the Invention Xa present invention is related to cell phone r-edes and, in particular, to a process for the transfer of mobile assisted assistance (.MAHO) within a network -le t-aléíano cell phone .

Description of the Technique-Relative Now we now refer to Figure 1, where we see an aschemic view of a cell phone system 10 that includes a plurality of 12 individual cells. Each cell i2 operates with a set of allocated channels. -In-sis or ace cominicaciones not .mj-tlti lexados. ciialquijer --- rocuencia -determinada comprises a channel, -In communication systems muítiplajeados, _sin j-anbargo. each frequency - is divided into a plurality of time slots comprising the channels, _the channel set assigned to each step 12 ------- cliry'-e ciiar-do - 3 - exLQS a. channel of o-? t ßi 'O - 3 - P ip 1! »? _.- dp a reference channel - pilot and / or measurement operation on either or both, an analog and / or a digital mode, and a plurality of trafic (or voice) channels (TCHs) also operable in either or both modes, analogously digital. The assigned channel sets are different for adjacent cells 12, and these sets are not repeated except for cells that are sufficiently far apart from one another to reduce the adjacent channel probability or co-channel interference to the channel. A station 14 ?? base that includes a plurality of I? O -shown transceivers) capable of operating independently in each of the set of -as .. assigned assigned to each of the cells (a set of channels per station of .-- - ase ). Through the r-ansceptore - the bastion BStations 14 are coupled in communications to a variety of mobile stations 16 operating within the area of the associated cell 12, the control channels in the set of channels assigned to each call 12 are used to carry the system control sánalos between station 14 of Jetase and the stations -1-5. Mobiles closely located, -these control signals include signals from IZ Lamada. call- -subsequences of location registration, voice channel assignments, maintenance instructions, and -output selection- or reselection instructions. The multiplicity of traffic channels in the assigned channel set-to each stream 12 are used to carry voice or subscriber data communications as well as system pass-through communications to the base station 14 and mobile stations 15 placed in close proximity, Xaa stations 14 of -basa aa communicate additional via signaling links and voice trunks 22 with a central control station, commonly referred to as a switching center 18 -mobile, which operates to control the operation of a portion of the system l, -In particular, the center 18 ds .mobile switching operates to connect -selectively voice communications and subscriber data to the stations 1.6 -mobiles through the stations 14 of nase. At the same time, the mobile switching center 18 controls the system operation -by means of and in response to 1-the transmission of control signals through the control channels to establish the so-called traffic channels. aa originate from or terminate at the stations 1-5 -mobiles, -the IB switching center also control, through and in response to -the transmissions d & control channel and trauco, as well as the measurements made in the control and trafic channels, to the transfer of a s-uscrlptor communication from a trauco channel of a cell 12 to a tragic channel of another cell to -as measured the station 1.6.mobile of the sponsor moves through the area of cellular service during a - á - communication in process, -It now provides a brief description of the handover process. A call communication in progress is being carried out by a selected trafic channel, as the mobile station 16 moves around the EXB &; of a dioxide coverage of a cell 12 currently airing, the mobile station makes signal-resistance measurements both to the currently used traffic channel and a reference channel of the included control channels (also referred to as co-ordinates). a pilot channel or channel gives -measurement) for each of the surrounding cells -are listed in a neighbor list supplied to the mobile station through the center or switching -mobile, at the same time, the base station 14 for the cell 12 which serves can make uplink signal rasistance measurements in the currently used trauco channel, When the mobile station -16 moves -to the rail of cell 1-2 -which currently serves, the system evaluation of the resistors of downlink and uplink signal measurements for the currently used trafic channel and the signal resistances. Downlink measurement for the control channels (-re-farenx-ia) of the c Eldas circundantes provides an indication that a handover is necessary, Xn that point, the system identifies cells 12 candidate potentiators for handover and requests that the base station 14 for these calls make and report on uplink signal strength measured with respect to .al current traffic channel. Once all the uplink and downlink signal strengths have been determined, the system selects a new cell 1-2 (and the associated base station 14) to handle the call continuation, iin the game traffic channel. of channels assigned to the new cell -12 issued to Xueqo- selects, and an order is transmitted from the mobile switching center 18 through the current traffic channel by ordering the mobile station to commute the calls to the trauco selected in the new cell, at-the same time, the mobile switching center 1-8 redirects the call from-station 1A from .base in Z to old .cell 1-2 to .la station 14 from Jbaae to the fact that the new cell completes the handover process, J In some cell phone systems, traffic channels and control channels use different types of signal modulation schemes, for example, in a digital cellular phone system such as that proposed by the digital advanced mobile phone service (X-AMPS), the traffic channels use quadrature phase shift keyboard (QPSK), and when measuring monos (reference, or pilot) of . control channels use frequency shift keyboard. (.ESK) as their respective schemes of jodulation, It has been observed, without amb.ar.go, that in some cases the significant discrepancies in signal strength measured downlink made by IdAHD may exist between the traffic channel of the the cell that serves and the control channel of a neighboring cell. These discrepancies have been linked, at least in part, to the differences in modulation types used in the signals. -Additionally? , with specific reference to cellular systems that support a plurality of -hyperbanda communications (for example, operation to both BDO -Mhz and 190.0 -MHz), it has been observed that significant discrepancies to -signal resistance -link measurement Downstream made by .MAHO. may exist between the traffic channel of the airing cell operating in a hyper band and the control channel of a neighboring cell operating in another band. , -Now reference is made to Zía Xigura 2 where it -shows one. graph illustrating a comparison of downlink signaling resistance measurements - made by a station - mobile in a reference channel (control) against a traffic channel, the graph in Figure .2 is generated from - an experiment that records downlink signal strength measurements in the reference (control) channel of the serving cell and the traffic channel of the cell currently serving for all mobile station handover requests made during a period of Twenty-four hours, in the experiment, the reference (control) channel used frequency shift keying modulation (PSK), and the traffic channel used modulation in quadrature phase shift keying (QPSK), and both channels They were in the same - hyperbande. Xas-recorded measurements for each handover were compared (ie, control channel signal resistance for the cell, which serves less traffic channel signal strength for the cell it serves), with comparison results during the period of 24-hour test used to generate a probability density function (pdf). The peak of the probability density function illustrates a large number of handover cases where the mobile station downstream channel signal strength measurements with respect to. the cell that airs are between four and five decibels -4-5 -E ---- P -Ke-nos-that the me- ücions --- 'gives signal strength of reference channel (control) of descending eznlace of the station zsióvll with respect to the cell of target. Similar results have been observed when the reference channel '(control) of the serving cell and the traffic channel of the currently serving cell use different hyperbands, It has been further observed that said modulation and / or hyperband differences in resistance Downlink measurement signal made by MAHO can adversely impact the operation of the cell phone system. For example, discrepancies, when not counted during the handover processing of the system, can cause oscillating handovers (i.e., ping-pong) as the mobile station moves along the boundary between two adjacent cells. There is a need for a mechanism that allows the cell phone system to consider the modulation scheme and the discrepancies influences by hyperband in downlink signal strength measurements made by MAHO. Reference is now made to Figure 3, where shows one. graphic that illustrates one. comparison of downlink signal strength measurements made by a mobile station in a traffic channel against another traffic channel, La. graph of Figure 3 is generated a. from an experiment that records downlink signal strength measurements - 3 - in LUÍ first channel of traffic of the cell that is going and a second channel of traffic of the cell that is currently airing in relation to the requests of transfer of station -mobile made during a period of one-and-a-half hours, in the experiment, each one of the First and second traffic channels used modulation to quadrature phase shift key (OPSK), and each was within the same hyperband. Xas recorded measurements for each handover were compared (ie aañ-ai resistance of first traffic channel for the cell that serves least signal strength of second traffic channel for the cell it serves), with the comparison results through of the twenty-four hour test period used to generate a probability density function (pdf). Xa peak of probability density function illustrates a large number of handover cases wherein measurements of signal strength of the first channel of mobile station downlink traffic with respect to resistance measurements gives a signal of second channel of traffic and the cell that serves with respect to the cell that serves are almost ZLas jr-ismas. This shows that the downlink signal resistance measurements for -traffic channels that use the same QPSK modulation scheme are comparable, similar results occur with the with respect to you evaluate the -FSK modulation when comparing the measurements, of downlink safari resistance in a first control channel of the serving cell and a second control channel of the current-serving current, COMPENDIUM OF THE INVENTION In order to address the above problem, a mobile-assisted handoff signal (MAHO) signal-mobile signaling resistance is ordered by a cellular telephone system not only for the currently used traffic channel and the reference channels (control ) of the surrounding cells, but also for the reference channel (control) of the current flow, - a compensation factor is then determined by the system to take into account the use of diierant.es modulation schemes. and / or hyperhandas through traffic channels and system control, XI -compensation factor is calculated by subtracting the MAHO measurements made in the reference channel of the current cell from the MAHO measurements made in the traffic channel of the ctual cell, XI compensation factor .calculated then added to each of the MAHD measurements made in the reference channels for each of the surrounding cells to generate -measurement is compensated signal strength, the compensated measurements are then used in place of the control channel measurements made by conventional MAHD to make the handover determination, BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the method and apparatus of the present invention can be gained by reference to the following Detailed Description when taken in conjunction with the accompanying drawings, in which; Xa Xigur 1 (previously described) is - a schematic diagram of a cell phone system; Xa Xigure 2 (previously described) is - a density graph that illustrates a comparison of downlink signal strength measurements. -by means of a mobile station in a reference channel (control) of a white balance against a traffic channel of a cell currently serving; Xa Fig. 3 (previously described) is a graph of density illustrating a comparison of downlink signal strength measurements made by a mobile station in a tragic channel of a white cell against a traffic channel of a stream that currently serves; and, Xa Xigiira 4 is a signal flow diagram and network operation illustrating the handover process in accordance with Z. The present invention, DETAILED DESCRIPTION OF THE DRAWINGS Reference is now made to the Figure, where ae - shows a flow diagram illustrating the handover of a mobile station 15 from a first cell 12 (1) (serving) to a -second cell 12 (2) (.of blank) in accordance with the present invention, A call l? D communication is being carried through a traffic channel selected from the first cell 1 (1), Xe sends a-message lJQ-2 to the mobile-station IB including a list of surrounding 12 cells and the channels assigned to them that the mobile station must explore in order to make -downlink signal -resistance measurements. Xe conformance with the procedure - of handoff assisted by known mobile, this neighbor list identifies the relational channels (control) for some of the cells 1-2 (-) -12 () that surround Z to calda -12 (1) which, at present, is in accordance with the present invention, this neighboring list message 10.2 further includes, as an iden.tifi.cado of the channels to explore and make -measurements of signal resistance,? l reference channel (control ) of the. cell 12 (1) currently serving, Xn the case that the neighboring list is complete, the channel of reiarancia (control) of the cell. Z12 (1) currently serving is specified as a temporary substitution, Xn response to the neighboring list, mobile station 16 makes 10 a measurements of signal strength in the reference channels (r.nn rnlj par?, some of the neighboring cells X2 (2) -12 (4), and also makes a measurement 106 of signal resistance in the reference channel (control) of the cell 12 (1) currently serving. The mobile station 16 still additionally makes a resistance measurement 108 of downlink signal in the currently used traffic channel of the serving cell 12 (1) carrying the call communication 100. All the previous mobile assisted transfer (MAHO) measurements are then reported to the cellular system through station 14 of hase for cell 12 (1) currently serving. The base station 14 then calculates (action 112) a modulation scheme compensation factor (C) of the .MAHD measurements, Xas -measurements comprised: the downlink signal strength measurement (SSra). made by the received mobile station made, in the currently used traffic channel of cell 12 (1) serving the carrying. 1-0.0 call communication; and, the signal (SSca-) signal resistance 1? - .candente an the reference channel (---- ontrol) of the fall 1-2 (1) gue -serve -actually. Xn parjü-cular the compensation factor measures the difference between these two .ritions as follows: C = .SSTCH - SSCCK - for the flow that sees - Certain assumptions are made with respect to the operation of -system with respect to the calculation of the compensation factor, - It is assumed that the same -m scheme is used. --- dilation (for example, XSK) through the reference channels (control) for certain of the cells -12 (-2) -12 () surrounding and the channel of xe.feren.cia (control) of cell 12 (1) currently serving, -e It further assumes that the effective radiated energy for the cell transceivers is substantially the same. XI -compensation factor - consequently provides information regarding? schema, modulation and / or discrepancies influences by .hyperbanda. in downlink signal strength measurements made in .MAHD, Xa station 14 (1) of .base then add (action 114) the compensation value (C) to each of the station 16 -mobile reported in the -designations of resistivity of signal of bonding made in the channels of ignorance (control) for certain of the cells 12 (2) -12 (4) surrounds to generate compensating compensated backbone channel-link signal strength measurements, the link reference signal resistor measurements descandent--. compensated with xaspec.to to certain of Xas cells 1-2 (-2) -1-2 (4) surrounding and then compare (action .116) with the measurement 10B of xe-siafencia-downlink signal p- ox.tada by the. Mobile IB station - made in the traffic channel currently used in Z to cell 12 (1) which air carries the call IDO communication, the comparison generally comprises the subtraction of the 10-8 measurement of signal strength - downstream link traffic channel (.more some hysteresis value) of each of the compensated downslope xane channel channel aane resistance measurements. - From this comparison, station 14 of -base determines the first a transfer is necessary (action 118). based on the results of subtraction, second, station 14 of base determines in which cell or ceids could and / or should occur preferably the transfer (action 1-20) based on the relative magnitudes of the -results of the subtraction process, Xn this example, ae a-upone -qua la. ermin base station 1.4, ZL18, which requires a soft handoff, since the channel measurement gives traffic. Most hxstóxesis does not exceed. Control channel measurement compensated. -It also supposes that one should be added. 12 of cell 12 (2) as regards the preferred Manco transfer for transfer because it has the greatest difference in Z measurements, request 122 for transfer including information that includes an identification of cell 12 (1) currently serving, the traffic channel that is being used for communication with the mobile station 1.6 in cell 12 (1), the time slot (for a digital traffic channel) that carries the cellular communication, and cell 12 ( 2) of .white for handover, is then sent through station 1.4 (1) of .base to mobile service switching center 1.8, XI center .18mobile switch then - points 12 A to. calda 12 (2) of white requesting allocation (and reservation) of a channel of irá-ficD (and xanura of time in the ism for a channel of digital traffic) for transfer, and it is informed 12-6 of the allocation of the channel of traffic in cell 1212) of .white, then one is sent. -signal 128 to station .16 (1) z ovll through Zla station 1 (1) of base for the current 12 (1) that is currently serving, including a -pass command that instructs the mobile station to switch to allocated traffic channel (and time slot in it, if appropriate) in Zla cell 12 (2) of .white. The mobile station 1B (1) is then tuned to and has access 130 to the assigned traffic channel (in the appropriate time slot). When the base station 14 (29 detects access to the mobile station (action 132), the mobile switching center 18 is informed 13 A and the call XQO 'is switched 135 through the base station 1A (2). to complete the handover procedure, Xa above description is only an example of the procedure used to make the determination to institute a handover, Xesde then, it will be understood that the determination in its place can be done through other system nodes, talas co or in the connected base station controller to the base station 1A in the base 1 itself in the mobile switching center 18 n place in the base station as described, Xn such cases * ZAS. MAHD measurements are sent via the station 14 of -basa for another node calculation of the compensation factor, determination of compensated control channel output signal resistance measurements, and determination of whether the transfer should occur and who should aar! transfer. The exposure of the base station processing is only an illustration of the operating system, and it makes an assessment of the performance and evaluation of MAHD measurements. It presents a number of benefits to others. To solve the problem of discrepancy in the signal readability measurement, Ximaero, Zla accuracy of .MAHD measurement is improved regardless of variations in the accuracy of individual mobile station, XI -compensation factor is defined as a -base of pass-through transfer and individual mobile station, -Second-. There is no impact on the hardware or aoitware of the mobile station implementing this solution, Xe this way, or to xequiare at xegress -not reprogramming of the mobile stations. Tareero, it turns out-improved pass-through operation of using the compensation factor to consider the discrepancies influences of modulation scheme and / or hyperband in downlink signal strength measurements made by MAHO, even though a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying drawings and has been. described in the above Detailed Description, it will be understood that the invention is not limited to the described mode, but is capable of numerous rearrangements, modifications and substitutions without abandoning the spirit of the invention as set forth by the following claims,

Claims (2)

REI INDICATIONS

1 - A method for assisting a mobile station with a tripping step related to signal resistance measurement, comprising the steps of; making resistance measurements of the downlink received signal in a reference channel for each of a plurality of surrounding cells; making resistance measurements of the downlink received signal in a traffic channel it handles, a call communication in transit for the mobile station within a. currently serving cell; .Does .alphase resistance tests received from downlink in a reference channel for a cell, which currently serves; and reporting the downlink signal strength measurements made, 2, - The method of claim 1, wherein the reference channel comprises a measurement channel, 3, - The method of claim 1, wherein in channel of reference comprises a pilot channel, 4, - The method of claim 1, wherein the reference channel comprises a control channel, - The method of claim 1, wherein the reference channels for the cells serving currently and surrounding uses a first modulation scheme, and the traffic channel for the cell that airves currently uses a second scheme, of different modulation, 6. - XI method of claim .5, wherein the first modulation scheme comprises the displacement key of fr..mienni a (FSK) and Í.1 seg ndo f. < Modulation scheme comprises quadrature phase shift key (QPSK). 7 - The method of claim 1, wherein the channels for the currently serving cell use a first hyperband, and the channels for at least one of the surrounding cells use a second different hyperband. 8. The method of claim 7, wherein any of the first or second hyperband is at approximately 1900 MHz. and the other one of the first or second hybrids is at approximately 800 MHz. 9 - A list of neighbors for transmission to a mobile station identifying a plurality of channels for the mobile station for making downlink signal strength measurements, the list of neighbors including: an identification of a plurality of reference channels, the reference channels comprising the reference channels for each, one of a plurality of surrounding cells; an allocation of a channel of tolerance for one. cell that I am currently airliving. 10, - XI method of claim 9, wherein the reference channel comprises a measurement channel, 11. - XI method of claim 9, wherein the reference channel comprises a pilot channel, 12, - the method of claim 3, wherein the reference channel comprises a control channel, 1, - Xa list as in Claim 3 - which includes - in addition; an -identification of a traffic channel that handles an anonymous call communication for the mobile station within the cell currently airing, 1A, - The method of claim 1-3, wherein the reference wells for the current and surrounding airwaves use a first flow control scheme and the traffic channel for the cell currently airing use a second different modulation scheme, 1-5, - Xl method of claim 14, where the primar modulation scheme comprises frequency shift key (XSK) and the second modulation scheme comprises ztass shift key in quadrature (QP-SK), 15, - XI method of claim 1., wherein the channels for the cell currently serving use a first hyperband, and the channels for when one of the surrounding cells uses a second, iiipexband different 17, - XI method of claim 16, wherein any one of the first or second hyper-band. it is at approximately 1-90-0 -MHz, and the other of the first or second. Hyperbande is a. Approximately 8-0-0 JMHz, 18, - A method for evaluating aañal resistance measurements related to handover done by station -mobile-, comprising the steps of: receiving resistance measurements of received downlink signal -made by the mobile station; a reference channel for each of a plurality of surrounding cells; a relay-traffic channel that handles a call-in-transit communication for the. mobile station - inside the cell that currently serves; and a reference channel for the cell that is currently airing; calculate a compensation factor for, -retake the measurement of xassence. of downlink signaling done by mobile station in the reference channel for the cell currently serving the measurement of downlink signal strengths made by mobile station in the traffic channel that handles the. call communication in transit within the cell currently serving; and adding the factor rie compensation to each, one of the downlink signal strength measurements made by mobile station in the reference channels, for surrounding cells in order to generate compensated downlink signal resistance measurements, 19, - The method as in claim 18, further including the step of comparing the compensated downlink signal strength measurements to the downlink link signal resistance measurement made by the mobile station in the traffic channel handling the downlink communication. call, in transit within Zla cell currently serving in order to identify the need to transfer station -mobile to one of the surrounding cells, 20. - The method of claim 18, wherein the delay channel comprises a measurement channel. -twenty-one. - XI method of claim 18, wherein the reference channel comprises a pilot channel, 22, - XI method of claim 1., where the z-channel has a control channel, -

2-3. - XI method of the. Claim 18, wherein the reference channels for, the cells serving acts and the surrounding uses a first modulation scheme, and the traffic channel for the currently serving cell uses a different modulation scheme. , -24, - XI method of claim 23, wherein the first, modulation scheme comprises key frequency shift (XSK) and the second scheme, modulation comprises quadrature phase shift key (QPSK), , - XI method of claim 18, wherein the channels for the cell that currently serves use a first hyperband, and the channels for, when hands one of the surrounding cells use a second -hypexband different, 26. - XI method is claim 25, wherein any of the first or second Jxiperbanda is at approximately 150.0 Mhz, and the other of the first or-second hyperband is. at approximately 800 -MHz,