CA2106761C - Reduced noise interference during handoff - Google Patents
Reduced noise interference during handoffInfo
- Publication number
- CA2106761C CA2106761C CA002106761A CA2106761A CA2106761C CA 2106761 C CA2106761 C CA 2106761C CA 002106761 A CA002106761 A CA 002106761A CA 2106761 A CA2106761 A CA 2106761A CA 2106761 C CA2106761 C CA 2106761C
- Authority
- CA
- Canada
- Prior art keywords
- audio path
- station
- coverage area
- base
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
- H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
- H03G3/34—Muting amplifier when no signal is present or when only weak signals are present, or caused by the presence of noise signals, e.g. squelch systems
- H03G3/342—Muting when some special characteristic of the signal is sensed which distinguishes it from noise, e.g. using speech detector
Abstract
A radiotelephone system reduces noise interference during handoff by muting the audio path of a receiver employed in a target base-station (135). After receiving a handoff request message, a target base-station (135) mutes the target audio path and determines if the target audio path had been enabled by an undesired interfering signal having a common SAT. If the target audio path had been enabled by an interfering signal having a common SAT, the target base-station (135) will use the SAT and the received signal strength indication (RSSI) of the desired transmission of the subscriber (125) to enable the target audio path. Once the SAT and RSSI are present and adequate the target audio path is enabled, the source audio path is coupled to the target audio path, and the subscriber (125) is handed off from the source base-station (130) to the target base-station (135) without a third party experiencing an objectionable noise blast.
Description
WO 92/19077 PCl'/US92/01S47 6 7 :~ 1 REDUCED NOISE INTERFERENCE
DURING HANDOFF
Field of ~he Invention The invention relates generally to cellular radiotelephone s~ e~"s and more specifically to cellular 10 radiotelephone Sy5tell1S having noise interference during communication handoff.
Background of the Invention Cellular radiotelephone sysle.ns employ radio ~ce ~c-? having ~ery high sensi~ ics. This high sensili~ is required in radiotelephone receivers to maintain com~nunication throughout a particular coverage .
20 arca, but such high sensidvity can also result in ocgali~e system pcrformancc. In analog radiotelcphone S~StC~I.S, particular cclls arc indi~id~ ed employing a specific supcrvisory audio tone (SAT) which distinguishes voice communication channels from thcir sullo:-nding neighbor 2 5 voicc communication ~b---tls. Reccive.~ used in these SJSt~ S dctect thc SAT n~Qd~ ed on a radio Lc~l~ency (RF) carrier and couplc an audio path within the receivers to land-line t~lep~re ne~ o.~s accordingly. Problems arisc, ~:. cver, whcn the high sensitivity receivers detect a 30 undcsilcd, low-level RF carrier having a common SAT.
These undesired RF carriers might occur in systems where frequency reuse is utilized, intermod~ tion distortion is high, and adjacent channel interference is present.
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WO g2/19077 PCI/US92/01547 ., ~ .
~ ~ ~ 6 7 ~ ~ 2 ~;
Detection of these undesired, low-level RF carriers having a common SAT presents a major problem during handoff in a cellular radiotelephone system. When the receiver receives the undesired signal, the receiver audio 5 path is enabled, allowing ~arely quieted discrimin~tor noise (due to low received signal strength) to be output to the phone line of the channel. This noise can be summed into a conversation during a channel handoff on the bridge between the source base~station and a target base-station.
10 When the noise i5 summed into the conversation, an objectionable noise blast occurs.
Thus, a need exists which enables a high sensitivity receiver to comple~e c~mmunication hai~doff without substantial noise interference.
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Summary of the Invention A ncc;~cl rcduccs noise interference during 20 communication handoff. The l~cc;~or has a switched audio path to convey at least an audio signal to a destination telephone system. The rcceive. acccpts a desircd radio frequency signal having at least the audio signal and a - covcrage area identification value n-odulatcd Ihc~on, 2 S d~ .,-oJ~ tes the desired radio frequency signal to produce signals ~ s~nti~lQ at least the audio signal and the ' coverage area identification value, and dcte.. --lncs a signal quality value of the desired radio ~.c~uen~,y signal. The receiver providcs a prcdct~r...incd coverage area value, -3 0 CG-~p~rCS the demodulated coverage area identification value to the predetermined coverage area value, disables the switched audio path, and detc.,-.ines when the s~ chcd audio path has been enabled by an WO 92/19077 PCl'/US92/01547 ~ e r~ ~'!r!~
3 f- .~ 3 S V-~
undcsi-ed radio frequency signal. The receiver then e~ablcs the switched audio path ~csponsive to the signal quality value determination and the companson if the switched audio path has been enabled by an undesired 5 radio frequency signal.
' "''' ':' Detailed Dcs~ ,tion of The Drawings FIG. 1 gencrally depicts base-stations coupled to an EMX in a radiotele~p~ ~ system that may be used to employ the prcscnt invention.
PIG. 2 gènerally depicts in bloc~ form a base-station controller (BSC) and transceivers located within the base-15 st~io~S of ~IG. 1 and used to iplcl.,ent the present in~cntion.
FIG. 3 illustratcs a ~roicc channcl controllcr (VCC) locatcd within thc BSC of FIG. 2 and uscd to control the scanning and voice lranscc;~c-s found in FIG. 2.
FIG. 4 gencrally dcpicts a schcmatic diagram of a ccc-~ter cmployed to dcmodulatc a radio frcqucncy (RF) signal and dct~....;nc a tcccivcd signal strength indication (RSSI) of the sigDal in a~c3rdance with the invention.
FIG. 5 gcnerally depicts in flow diagram form the 2 5 stcps a basc-stadon undcrgocs to reduce noise inte,îerence during handoff in accordance with the invention.
FIG. 6 gcncrally dcpicts in flow diagram form the steps a base-station undcrgocs to conlilm a mobile's arrival on a targct channcl in ~c~ancc with the invention. ~
~ ~ -~ ~ ~ Detailcd Dcsc,il~ion of a Preferred Embodiment ;~ ~
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wo 92/l9077 Pcr/usg2/o1547 ~ o ~ ~ 1 4 FIG. 1 generally depicts a cellular network which may employ the present in-rention. Cellular networks may incorporate as many different cells as is required to ;~rco.--...odate the coverage area. ~or example, a cell 100 5 typically covers only a small portion of the total coverage area in largc cellular systems. As the cellular networlc grows in a particular coverage area, frequency reuse becGmes an important parameter tha~ is used to accommodate all the subscr~bers necessary. ~eturning to 10 FIG. 1, a first coverage area or cell 100 usin,g a supervisory audio tone of SATl is bounded by six neighboring cells, but ~' only two neighboring cells are shown for explanation ywyOSCS. A second cover2gs area or neighbonng cell 10 has a SAT of SAT2 while still another neighboring cell 110 15 has a SAT of SAT3. Each of these cells has itS own base-stadon, which is requi~ed to co...~--u.-ic~e to a subscriber 125. In the source cell 100, a source base-stadon 130 communicates to a subscriber 125 on a radio frequency (RP) signal. SAT1 is modulated on the RP signal by thc 2 0 source base-station 130 and is demodulatcd by thc subscriber 125. SATI is used by the subscriber 125 to idendfy the sourcc cell 100 the subscriber 125 is located within. In sectorized cells (not shown), a similar method of commu~iratiQr ~ansf~r (called a port change) is used when 2 5 the subs ,~-ber 125 moves from sector to sector within a gi~en cell.
Each base-station within a particular cell in a cellular r,cl~.o.~ is cQ~ ceted to an EMX 120 switch, available from Motorola, Inc. and described in Motorola Instruction 3 0 l~r~u~l No. 68P81054E59 published by Motorola Service Publiratior~c, Scha~mburg, IL. The EMX 120, and more particularly the three party circuit (not shown) in the EMX
120, is the interface bet~.een the base-stations within the , .
W O 92/19077 PC~r/US92/0~547 5 2 1 ~ 6 J s~
cells and the public switched telephone network (PSTN), ;
which is the land-line system. The EMX 120 also serves as a junction point bel~. ccn basc-stations in a cellular network. For examplc, as the subscriber moves throughout S the source cell 100, the basc-station 130 continuously monitors thc f~,CeiVed signal strcngth indicq.~ion (RSSI) of the subscriber 125. As the subscriber 125 moves away from the base-station 130, the RSSI of the subscriber 125 eventually falls below a transfer threshold. The source 10 base-station 130, via the EMX 120, sends a message, which includes the source RSSI measure~lent~ to all neighboring cells, but again for the example only neighboring cells 105, 110 are shown. If target base-stqtior~c 135, 140 receive the ll~ns~icsion of the subscriber 125 and if the handoff 15 criterion is met for the particular cell 105, 110, the target base stP~ions 135, 140 will send a response to the EMX 120 noting such. Targct base-stadon 13S.140 will meet the handoff critcrion if tne RSSI measured at the target base-stations 135, 144, plus some byste.~,s;s value is greater 2 0 than thc RSSI measured by the source base-stadon 130.
The hyst~,~esis ~alue is used by neighboring base-stations , 135, 140 to take into account the physically dif~nt locations of the target base-stations 135, 140 with respect ~ -to the source b~se stq.~ion 130.
At this point, the EMX 120 d<te.. inss which of the target cells 105 or 110 is a better cqnAid2te for handoff. If for example, target base-station 135 in cell 105 RSSI
measurement plus hysteresis was higher than that of base-station 140 in cell 110, cell !05 would be a better 30 candidate. In this scenario, the EMX 120 sends a responce to the target base-station 135 in cell 105 to determine if there is an idle channel available for colnm~lnic~ion. If there is, the t rget base-station 135 sets-up the chqnnel, '~ ' .
WO 92/19077 PCI'/US92/01547 ' ~ 7 ~ :L 6 begins tr~ncmicsion and notifies the EMX 120 of the channel and SAT information. The EMX relays the channel and SAT information to the source base-station 130, the source base-station 130 instructs the subscriber unit 125 S to tune to the new cl~ n~l and to change SAT to SAT2, and the subscriber 125 begins to communicate to the target base-station 135 in cell 105. At this point, the subscriber -125 is det~ ed to have arrived in cell 105 by the- use of SAT2.
1 0 Each of the basP-stations 130, 135, 14~, 145, and 150 includes a plurality of transmitters and receivers for operating on at least one duplex signalling channel and a plurality of duplex voic~ chann~ls. One com/en~ional system employs transmitters and receivers of the type 1 5 described in Motorola Instruction Manual No.
68P81058E32-A pU~liC~d by Motorola Service Publications, Schaumburg, IL., in 1989. FIG. 2 generally depicts transcci~ and ~s~ci~ted controlling hardware within one base-stadon. A baso-site cohtroller (BSC) 200 typically consists of four cards and plo~idcs thc interface bctween bas~-st;~;ons 130, 135, 140, 145, and 150 within cells and tbe EMX 120. A BSC 200 is con~sed of a cell-site controUer (CSC) 203, a voice channel controller (VCC) 212, a signalling cl~n~l controller (SCC) 206, and an c~ctend multiple port intc,.r~e (EMPI) (not shown). An identical secondary set of cards can be employed to provide BSC redundancy. Together, these cards provide voice channel ac~ignmert~ signalling channel control, performance monitoring, and other control functions that arc used by the EMX 120 to initiate calls, dete.n.ine Ct'~''r'&l allocation, and make handoff decisions.
VCC 212 controls the primary voice transceivers 222-225 and the sc~nni-~g receiveI 221. FIG. 3 generally .
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WO 92/19077 PCI'/US92/01547 7 ~18 ~
depicts a block diagram of a VCC 212 which may be employed to i,..ple-~.Pnt the present invention. The central processing unit (CPU 306) may be a micloproccssor such as MC6809 available from Motorola, Inc. This CPU 306 is is S used to control the y.i-..aI~ voice c}~ cl transceivers 222-225 and scanning receiver(s) 221 in accordance with plog..ll..."cd steps storcd in RAM and EPROM 312. In a nonl~,dundant configuration of the present invention, VCC
212 may control up to 30 cl~qn-els of radio cq~.ip.~lent and 1 0 one scanning lecciv~r employing SSDA 310, voice transceiver interface 320, and scanning receiver interface 322. Signalling data encoding and decoding is controlled ~ -via SSDA 308 and signalling enco~ g and recovery interface 318. T.anscei-~e,s are selected by enable drivers 1 5 324 which is controlled by CPU 306 via pc~iphc.al interface, ~pto~s (PIA) 314. In the redundant configuration reqbiring two VCCs, each transcc;~r (being dual ported) can communicate with both V.CCs. Under normal opcrating conditions, each VCC acdvely controls half 20 of the channcls whilc c~changing control and status ~ ssag~s with thc other half. Interfacc to a redundant CSC
is accomplishcd via ADLC 304.
A tl~n~ t~d signal from a subscriber unit 125 cnters onc of voice transcci~c.. 222-225 via a matrix RF
25 board (not shown). FIG. 4 gencrally depicts a schc-~q~;c diagram of tCCC.~'~Cr hard- ~., c...plo~ed to dcmodulate the transmitted signal from thc subscriber 125 and determine a signal quality valuc or signal strcngth indication (SSI) of the signal. RefelTing to FIG. 4, thc .ccc;-c. has as input an 3 0 cvcn and odd signal for div~i.sil~r rcccpdon p~..ycses. An even mixer/IF board 405 accepts the even signal while an odd mixer/lF board 410 accepts the odd signal. Both mixer/lF boards 405,410 have an input from a side-step ..
' ' .' ' . ,. . .. ... . , ..... , ,, . .,, . .. . . ",. - , , . ~, ,, .. , . .. i.. .. . ... .. . . . . . .. .
W O 92/19077 PC~r/US92/01547 2~ ~7~ 8 synthesizer 400 which acts as a first local oscillator (LO) for mi~ing pu",oses. An injection/amplifier board 415 provides another input to each mixer/IF board 405,410 and acts as a second LO for mixing purposes. The IF ICs 445, 450, which in the preferred embo~limPrt are part number TDA 1576 available from Signetics, provide limiting, quadrature detection, and amplification to yield an audio output signal which is further amplified and fed to a audio control board 420 for processing. SSI detection is 1 0 performed by CilCuilly internal to the IF ICs 445, 45û and by discrete SSI detection range extension circuitry. The outputs of IF ICs 445, 450 individually provide linear SSI
signals. These SSI signals are fed to ~he audio coil~ol board 420 wherc they are used to drive a diversity switch 1 5 425, which in turn is used to enableldisable an audio switch 430. Output from the audio switch 430 is the audio ;~ which rcy.~sents the communicadon &om the subscriber 125. This audio is output to the EMX 120 via conventional phone lines.
When the subscribcr 125 reaches thc boundary of the source cell 100, a comm ~;c~ion transfer or ~ off is rc~1.,ir~d as the subscriber 125 enters a r~Pi&hboring target cell 105. As handoff occurs, noise resultirlg from target channel SAT falsing may be in~rod,.ced Target cbDn~l SAT falsing appears when an interferer is present in the systcm witb the same SAT tonc-as the arri~ing mobile. For example, cell 155 in FIG. I has the id~ Dl SAT tone, SAT2, as cell I05 thus, if a signal l.~n~ red by the base-stadon 150 in cell 155 propag~t~s to the point where base-station 135 in cell 105 may receive it, the probability of that trans~itted signal er~bling the audio lines in the ~ce;ve. of base-station 135 is high. Other forms of undesired signals occur due to frequency reuse, wo 92/ l 9077 p~T/uss2/o 1 s47 2 ~
intermodul~ion distortion and adJacent channel intelle.ence. The interferer can cause the SAT detector on the target channel to report a false SAT i~ r~ion~ The SAT falsing opens the receive audio on the target channel 5 and introduces noise into the handoff until the desired mobile arrives on channel.
Returning to FIG. 2, voice transceivers 222-225 typically mute the audio path in response to either of two events. The first event is under hardware control. When 1 0 voice transceivers 222-225 no longer detect SAT, the receive audio path is muted by enabling audio switch 430.
The second event is a sofl-.~e controlled switch. When lhe audio switch 430 is en~ble~l the audio path in the voice transceiver 218 is muted. The switch overrides the 1 5 ha~dwarc SAT detect status. Therefore, the audio path in thc voice transceivcrs 222-225 can be forced to mute regardless of the SAT status. This function l~lo~idcs the basis for the target channel SAT falsing soludon in accordance with the in~ention. An algorithm is used in the 20 BSC 200 which has the ability to distinguish between an interferer signal and the desired mobile on the target c~nnel As a result, the audio path in the voice transceivers 222-225 will remain muted until it is dctc"..ined that the desired unit has arrived on channel.
25 When this occurs, the audio switch 430 will be disabled and the recei~e audio path in the voice l.ansceivers 222-225 will be opencd and closed based on the hard~.a.e SAT
detect status.
Noise in~e.re.ence during ~ndoff is reduced in 30 accordance with the invention as follows. The subscriber - 125 is continuQltsly mori~ored by the source base-station 130 for SSI. The base-station 130 in cell 100 has SATl which distinguishes cell 100 from its neighboring cells.
wo 92/19077 PCr/l,lS92/~1547 21~7~ ~ lo When the SSI being measured by the base-station 130 falls below a ~ doff threshold, the base-station 130 sends a handoff request m~ss~pe to the EMX 120. The EMX 120 sends a meSs~e to neighboring target base-stations 135, 140 in cells 105, 110 ~es~ccti~cly. Neighboring cells sullounding the source cell 100 receive the handoff measulc,...~,nt re~..cst message. Continuing, base-stations 135, 140 make a SSI measulGlllcnt of the transmission of the subscriber 125 and dete,.l.ine if the handoff cnterion is met. For e~mple. if base-station I35 in cell 105 meets the h~n~Qff criterion, the base-station 135 will send a response to the EMX 12û noting such. If the target base-stations are not viable candidates for handoff, they will not lespond to the EMX 120.
At this time, the EMX 120 sends a message to the best candidate targct base-station 135 requesting it to deterrninc if an idle channel exists. If an idle channel does exis~, the target base~station 13S returns a message to the EMX 120 containing the idle channel information, including channel frcquencg and SAT2. To complete the handoff - procedure, the EM~C 120 sends thc idle channel information to the source base-station 130 which in turn broadc~sts the information to thc subscriber 125. The subscriber 125 will tune to the new channel frequency, will changc SAT from 25 SAT1 to SAT2, and begin co~.unica~ion to the target base-stadon 135 in cell lOS. The threc party circuit (not shown) - in thc EMX 120 s--t~hcs the land-line ccr-7~tion from the audio path of the sourcc base-station 130 to the audio path of the targct base-station 135 to co.nplet- the handoff.
3 0 Previously, handoff occulled regardless of the status ~, of the audio path of the idle target chiannel. If the audio path was open, disc~ tor noise would be summed into a conversation via the three party circuit (not shown) '.
. ~. ,i .. , .... .. " ... .. ~ . . .: .. . ... . .... .
WO 92/19077 PC~/US92/01547 .
2 1 ~ ~ 7 ~
during h~-~doff, resultirlg in an objectionable noisc blast to the using parties. In accordance with the invention, the target base-station 135 mutes thc audio path, determines if the audio path of the chosen idle target chqnne1 was 5 enabled by detection of an undesired signal having a co.l..non SAT, and if it was, uses the SAT and the RSSI of the subscriber 125 transmission to enable the audio path for handoff.
If the most recent idlc target cl'qnnel SAT status 10 returns a positive SAT ir~ica~ion, then an intc.rcrer is present on the idle target voice channel. When this occurs, the VCC 212 triggers two concu.,cnt events: a SSI
qu~l;fic~ion time-out and the SSI q~tqlific~tion task. The SSI qu-q-lificvqtion time-out is a safety valve to ensure that 15 the audio path of thc idle target channel does not remain muted. This taslc is only e-Yecuted when thc intc.l~.ing signal has a strong SSI and thc BSC 200 is unable to distinguish thc ioterfcrer from the desired subscriber 125 transmission. Thc dme-out value iep~sents a worst case 2 0 arriva1 scenario, and in the p,ef~ ,d embodiment may be in the range from 300-2000 m;~ e~nds.
The SSI qrql;r;~ task is run by VCC 212 periodically to eYqmire the SSI of the trq-~C~nis$ion by the subscriber 125. The SSI quqlifirq~ion task is intended to 25 p~o~,idc a high degree of confidence that the subscriber 125 has arrived or has begun co,.~ ;on on the target channel.- Refernng to FIG. 4, the SSI is det~,.n~incd by mixcr/A.nr!ifi~r boards 405, 410 and sent to the audio control board 420 where the inforrnation is routed to the 30 data distribution board 435 within one of the voice transccivcrs 222-225. The data distribution board 435 serves as the interface point betwcen the voice sceivers 222-225 and the VCC 212. The VCC 212 7 ~ ~
c~ pa~s the subscriber SSI with the interferer SSI plus a downloaded SSI offset. The downloaded SSI offset is stored in RAM and EPROM 312 and cu..~nlly represents compes~s~ion for variations in signal strength of up to 7 S dB. Thc com~rc~ti~r may be higher in future implementations.
If VCC 212 detc...~ es the subscriber SSI is greater than the intelÇe,~c. SSI plus the downloaded SSI offset, the SSI qu~lific~tion timc-out is cancelled, and VCC 212 sends a 10 disable mute message to the target voice transceiver. This message enables the first positive SAT update message from the target voice llanscciver to send a handoff complete message to the FMX 120. If the SSI qualification time-out expires before VCC 212 detc.,.lines the subscriber 15 SSI is greatcr than thc inte,~-~r SSI plus the-downloaded SSI offset, VCC 212 sends the same disable mutc mPss~ge to the target voice transcei~rer. Again, this ~ ss~~c e-~?bks the first pGSili~C, SAT updatc .--~ssagc &om the target voice transceivcr to send a handoff complete message to the EMX
20 r20.
PIG. S generally depicts in flow diagram form the steps a base-station 135 undcrgocs to reduce noise nterforence during handoff in accordance with the invention. The p~cess starts at 500 by receiving at 503-a 25 desired RF signal having at least the audio signal and a coveragc area idc~l;r~r~lion value mQdnl~tçd thereon. The base-station 135 then demodul~t~!s at 506 the desired RF
signal to produce signals ~cpresenting at least the audio signal and the coverage arca iden-ifi~q~ion value and de,t~.. nincs at 509 a signal quality value of the desired RF ~-signal. A l~dctc.-".ncd coverage area value is provided at 512 and CG.I.pa~Cd at 515 to the demod~ ted coverage area iden-ific~tioh value. The base-station 135 disables at .
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1 3 2 5 ~ ~ 7 $ ~
518 the switched audio path, determines at 521 when the swi~ched audio path has been enabled by an undesired RF
signal, and enables at 524 the s~vitchcd audio path in response to the signal quality dete. n~ination 509 and the S co.npaiison 515 when the switchcd audio path has been enabled by an undesired RF signal.
FIG. 6 generally depicts in flow diagram form the steps a base-station undergoes to confirm a mobile's arrival on a target ch~nnP~I in acco.dance with the invention. The 10 process starts by selectir~g at 600 a target channel at a target base-station 135. The base-station 135 asserts at 603 a soflwale mute and waits at 606 up to ~50 mi~ ecs)~.;s ~fo~e ta~ing a "sn~rs~ot" or poll of the transceiver 222-225 SSI and SAT. A test is, performed at 15 609 to det~.lincd if SAT is present during the snapshot.
If it is not present, thc base-station 135 sets at 612 a best case arri~ral timcout and performs at 615 another test to detem~incd if thc timcout has eAp;~d. If it has, the softwarc mute is un-asserted at 618 and handoff procccds as normal. If it has not eApired, thc test at 615 is 1'epc3~e~ ;
until it has eApired.
If SAT is prescnt during thc sn~rshot in test 609, a SSI quqlfflration tin~eout is set at 621 and thc status alg~.ith... or SSI q~ ficq~iqr task r~siding in RAM and 25 EPROM 312 of the VCC 212 is invoked. A test is pc.roi".ed at 624 to dct~....ine if the SSI qu~!ific?tion !;...e~l,( has A~;~eCl. If it has, the softwarc mute is un-assc.~d at 618.
If has not cxpired, a test is performcd at 627 to determine if the sampled SSI is grcater than or cqual to the inte.Ierer 30 SSI plus some va. r~le ~. If it is not, the process ~.~ocecds back to test 624 to det~,.lnil1e if the SSI qu~lification I; eou~ has expired. If the sampled SSI is greater, the ba$e-station dete.",-nes at 633 if the sr~pshot had a good '.
WO 92/19077 PCr/US92/01547 5 ~ ~1 SAT. If it did not, the test at 624 is repeated. If it did, the soflwaie mute is un-asserted at 618 and handoff proceeds as norrnal. Using these stcps, noise inte~rence in the form of a noisc blast is reduced during the handoff process.
S What I claim is:
: '
DURING HANDOFF
Field of ~he Invention The invention relates generally to cellular radiotelephone s~ e~"s and more specifically to cellular 10 radiotelephone Sy5tell1S having noise interference during communication handoff.
Background of the Invention Cellular radiotelephone sysle.ns employ radio ~ce ~c-? having ~ery high sensi~ ics. This high sensili~ is required in radiotelephone receivers to maintain com~nunication throughout a particular coverage .
20 arca, but such high sensidvity can also result in ocgali~e system pcrformancc. In analog radiotelcphone S~StC~I.S, particular cclls arc indi~id~ ed employing a specific supcrvisory audio tone (SAT) which distinguishes voice communication channels from thcir sullo:-nding neighbor 2 5 voicc communication ~b---tls. Reccive.~ used in these SJSt~ S dctect thc SAT n~Qd~ ed on a radio Lc~l~ency (RF) carrier and couplc an audio path within the receivers to land-line t~lep~re ne~ o.~s accordingly. Problems arisc, ~:. cver, whcn the high sensitivity receivers detect a 30 undcsilcd, low-level RF carrier having a common SAT.
These undesired RF carriers might occur in systems where frequency reuse is utilized, intermod~ tion distortion is high, and adjacent channel interference is present.
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~: ~
WO g2/19077 PCI/US92/01547 ., ~ .
~ ~ ~ 6 7 ~ ~ 2 ~;
Detection of these undesired, low-level RF carriers having a common SAT presents a major problem during handoff in a cellular radiotelephone system. When the receiver receives the undesired signal, the receiver audio 5 path is enabled, allowing ~arely quieted discrimin~tor noise (due to low received signal strength) to be output to the phone line of the channel. This noise can be summed into a conversation during a channel handoff on the bridge between the source base~station and a target base-station.
10 When the noise i5 summed into the conversation, an objectionable noise blast occurs.
Thus, a need exists which enables a high sensitivity receiver to comple~e c~mmunication hai~doff without substantial noise interference.
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Summary of the Invention A ncc;~cl rcduccs noise interference during 20 communication handoff. The l~cc;~or has a switched audio path to convey at least an audio signal to a destination telephone system. The rcceive. acccpts a desircd radio frequency signal having at least the audio signal and a - covcrage area identification value n-odulatcd Ihc~on, 2 S d~ .,-oJ~ tes the desired radio frequency signal to produce signals ~ s~nti~lQ at least the audio signal and the ' coverage area identification value, and dcte.. --lncs a signal quality value of the desired radio ~.c~uen~,y signal. The receiver providcs a prcdct~r...incd coverage area value, -3 0 CG-~p~rCS the demodulated coverage area identification value to the predetermined coverage area value, disables the switched audio path, and detc.,-.ines when the s~ chcd audio path has been enabled by an WO 92/19077 PCl'/US92/01547 ~ e r~ ~'!r!~
3 f- .~ 3 S V-~
undcsi-ed radio frequency signal. The receiver then e~ablcs the switched audio path ~csponsive to the signal quality value determination and the companson if the switched audio path has been enabled by an undesired 5 radio frequency signal.
' "''' ':' Detailed Dcs~ ,tion of The Drawings FIG. 1 gencrally depicts base-stations coupled to an EMX in a radiotele~p~ ~ system that may be used to employ the prcscnt invention.
PIG. 2 gènerally depicts in bloc~ form a base-station controller (BSC) and transceivers located within the base-15 st~io~S of ~IG. 1 and used to iplcl.,ent the present in~cntion.
FIG. 3 illustratcs a ~roicc channcl controllcr (VCC) locatcd within thc BSC of FIG. 2 and uscd to control the scanning and voice lranscc;~c-s found in FIG. 2.
FIG. 4 gencrally dcpicts a schcmatic diagram of a ccc-~ter cmployed to dcmodulatc a radio frcqucncy (RF) signal and dct~....;nc a tcccivcd signal strength indication (RSSI) of the sigDal in a~c3rdance with the invention.
FIG. 5 gcnerally depicts in flow diagram form the 2 5 stcps a basc-stadon undcrgocs to reduce noise inte,îerence during handoff in accordance with the invention.
FIG. 6 gcncrally dcpicts in flow diagram form the steps a base-station undcrgocs to conlilm a mobile's arrival on a targct channcl in ~c~ancc with the invention. ~
~ ~ -~ ~ ~ Detailcd Dcsc,il~ion of a Preferred Embodiment ;~ ~
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wo 92/l9077 Pcr/usg2/o1547 ~ o ~ ~ 1 4 FIG. 1 generally depicts a cellular network which may employ the present in-rention. Cellular networks may incorporate as many different cells as is required to ;~rco.--...odate the coverage area. ~or example, a cell 100 5 typically covers only a small portion of the total coverage area in largc cellular systems. As the cellular networlc grows in a particular coverage area, frequency reuse becGmes an important parameter tha~ is used to accommodate all the subscr~bers necessary. ~eturning to 10 FIG. 1, a first coverage area or cell 100 usin,g a supervisory audio tone of SATl is bounded by six neighboring cells, but ~' only two neighboring cells are shown for explanation ywyOSCS. A second cover2gs area or neighbonng cell 10 has a SAT of SAT2 while still another neighboring cell 110 15 has a SAT of SAT3. Each of these cells has itS own base-stadon, which is requi~ed to co...~--u.-ic~e to a subscriber 125. In the source cell 100, a source base-stadon 130 communicates to a subscriber 125 on a radio frequency (RP) signal. SAT1 is modulated on the RP signal by thc 2 0 source base-station 130 and is demodulatcd by thc subscriber 125. SATI is used by the subscriber 125 to idendfy the sourcc cell 100 the subscriber 125 is located within. In sectorized cells (not shown), a similar method of commu~iratiQr ~ansf~r (called a port change) is used when 2 5 the subs ,~-ber 125 moves from sector to sector within a gi~en cell.
Each base-station within a particular cell in a cellular r,cl~.o.~ is cQ~ ceted to an EMX 120 switch, available from Motorola, Inc. and described in Motorola Instruction 3 0 l~r~u~l No. 68P81054E59 published by Motorola Service Publiratior~c, Scha~mburg, IL. The EMX 120, and more particularly the three party circuit (not shown) in the EMX
120, is the interface bet~.een the base-stations within the , .
W O 92/19077 PC~r/US92/0~547 5 2 1 ~ 6 J s~
cells and the public switched telephone network (PSTN), ;
which is the land-line system. The EMX 120 also serves as a junction point bel~. ccn basc-stations in a cellular network. For examplc, as the subscriber moves throughout S the source cell 100, the basc-station 130 continuously monitors thc f~,CeiVed signal strcngth indicq.~ion (RSSI) of the subscriber 125. As the subscriber 125 moves away from the base-station 130, the RSSI of the subscriber 125 eventually falls below a transfer threshold. The source 10 base-station 130, via the EMX 120, sends a message, which includes the source RSSI measure~lent~ to all neighboring cells, but again for the example only neighboring cells 105, 110 are shown. If target base-stqtior~c 135, 140 receive the ll~ns~icsion of the subscriber 125 and if the handoff 15 criterion is met for the particular cell 105, 110, the target base stP~ions 135, 140 will send a response to the EMX 120 noting such. Targct base-stadon 13S.140 will meet the handoff critcrion if tne RSSI measured at the target base-stations 135, 144, plus some byste.~,s;s value is greater 2 0 than thc RSSI measured by the source base-stadon 130.
The hyst~,~esis ~alue is used by neighboring base-stations , 135, 140 to take into account the physically dif~nt locations of the target base-stations 135, 140 with respect ~ -to the source b~se stq.~ion 130.
At this point, the EMX 120 d<te.. inss which of the target cells 105 or 110 is a better cqnAid2te for handoff. If for example, target base-station 135 in cell 105 RSSI
measurement plus hysteresis was higher than that of base-station 140 in cell 110, cell !05 would be a better 30 candidate. In this scenario, the EMX 120 sends a responce to the target base-station 135 in cell 105 to determine if there is an idle channel available for colnm~lnic~ion. If there is, the t rget base-station 135 sets-up the chqnnel, '~ ' .
WO 92/19077 PCI'/US92/01547 ' ~ 7 ~ :L 6 begins tr~ncmicsion and notifies the EMX 120 of the channel and SAT information. The EMX relays the channel and SAT information to the source base-station 130, the source base-station 130 instructs the subscriber unit 125 S to tune to the new cl~ n~l and to change SAT to SAT2, and the subscriber 125 begins to communicate to the target base-station 135 in cell 105. At this point, the subscriber -125 is det~ ed to have arrived in cell 105 by the- use of SAT2.
1 0 Each of the basP-stations 130, 135, 14~, 145, and 150 includes a plurality of transmitters and receivers for operating on at least one duplex signalling channel and a plurality of duplex voic~ chann~ls. One com/en~ional system employs transmitters and receivers of the type 1 5 described in Motorola Instruction Manual No.
68P81058E32-A pU~liC~d by Motorola Service Publications, Schaumburg, IL., in 1989. FIG. 2 generally depicts transcci~ and ~s~ci~ted controlling hardware within one base-stadon. A baso-site cohtroller (BSC) 200 typically consists of four cards and plo~idcs thc interface bctween bas~-st;~;ons 130, 135, 140, 145, and 150 within cells and tbe EMX 120. A BSC 200 is con~sed of a cell-site controUer (CSC) 203, a voice channel controller (VCC) 212, a signalling cl~n~l controller (SCC) 206, and an c~ctend multiple port intc,.r~e (EMPI) (not shown). An identical secondary set of cards can be employed to provide BSC redundancy. Together, these cards provide voice channel ac~ignmert~ signalling channel control, performance monitoring, and other control functions that arc used by the EMX 120 to initiate calls, dete.n.ine Ct'~''r'&l allocation, and make handoff decisions.
VCC 212 controls the primary voice transceivers 222-225 and the sc~nni-~g receiveI 221. FIG. 3 generally .
~ . ~ i ?;
WO 92/19077 PCI'/US92/01547 7 ~18 ~
depicts a block diagram of a VCC 212 which may be employed to i,..ple-~.Pnt the present invention. The central processing unit (CPU 306) may be a micloproccssor such as MC6809 available from Motorola, Inc. This CPU 306 is is S used to control the y.i-..aI~ voice c}~ cl transceivers 222-225 and scanning receiver(s) 221 in accordance with plog..ll..."cd steps storcd in RAM and EPROM 312. In a nonl~,dundant configuration of the present invention, VCC
212 may control up to 30 cl~qn-els of radio cq~.ip.~lent and 1 0 one scanning lecciv~r employing SSDA 310, voice transceiver interface 320, and scanning receiver interface 322. Signalling data encoding and decoding is controlled ~ -via SSDA 308 and signalling enco~ g and recovery interface 318. T.anscei-~e,s are selected by enable drivers 1 5 324 which is controlled by CPU 306 via pc~iphc.al interface, ~pto~s (PIA) 314. In the redundant configuration reqbiring two VCCs, each transcc;~r (being dual ported) can communicate with both V.CCs. Under normal opcrating conditions, each VCC acdvely controls half 20 of the channcls whilc c~changing control and status ~ ssag~s with thc other half. Interfacc to a redundant CSC
is accomplishcd via ADLC 304.
A tl~n~ t~d signal from a subscriber unit 125 cnters onc of voice transcci~c.. 222-225 via a matrix RF
25 board (not shown). FIG. 4 gencrally depicts a schc-~q~;c diagram of tCCC.~'~Cr hard- ~., c...plo~ed to dcmodulate the transmitted signal from thc subscriber 125 and determine a signal quality valuc or signal strcngth indication (SSI) of the signal. RefelTing to FIG. 4, thc .ccc;-c. has as input an 3 0 cvcn and odd signal for div~i.sil~r rcccpdon p~..ycses. An even mixer/IF board 405 accepts the even signal while an odd mixer/lF board 410 accepts the odd signal. Both mixer/lF boards 405,410 have an input from a side-step ..
' ' .' ' . ,. . .. ... . , ..... , ,, . .,, . .. . . ",. - , , . ~, ,, .. , . .. i.. .. . ... .. . . . . . .. .
W O 92/19077 PC~r/US92/01547 2~ ~7~ 8 synthesizer 400 which acts as a first local oscillator (LO) for mi~ing pu",oses. An injection/amplifier board 415 provides another input to each mixer/IF board 405,410 and acts as a second LO for mixing purposes. The IF ICs 445, 450, which in the preferred embo~limPrt are part number TDA 1576 available from Signetics, provide limiting, quadrature detection, and amplification to yield an audio output signal which is further amplified and fed to a audio control board 420 for processing. SSI detection is 1 0 performed by CilCuilly internal to the IF ICs 445, 45û and by discrete SSI detection range extension circuitry. The outputs of IF ICs 445, 450 individually provide linear SSI
signals. These SSI signals are fed to ~he audio coil~ol board 420 wherc they are used to drive a diversity switch 1 5 425, which in turn is used to enableldisable an audio switch 430. Output from the audio switch 430 is the audio ;~ which rcy.~sents the communicadon &om the subscriber 125. This audio is output to the EMX 120 via conventional phone lines.
When the subscribcr 125 reaches thc boundary of the source cell 100, a comm ~;c~ion transfer or ~ off is rc~1.,ir~d as the subscriber 125 enters a r~Pi&hboring target cell 105. As handoff occurs, noise resultirlg from target channel SAT falsing may be in~rod,.ced Target cbDn~l SAT falsing appears when an interferer is present in the systcm witb the same SAT tonc-as the arri~ing mobile. For example, cell 155 in FIG. I has the id~ Dl SAT tone, SAT2, as cell I05 thus, if a signal l.~n~ red by the base-stadon 150 in cell 155 propag~t~s to the point where base-station 135 in cell 105 may receive it, the probability of that trans~itted signal er~bling the audio lines in the ~ce;ve. of base-station 135 is high. Other forms of undesired signals occur due to frequency reuse, wo 92/ l 9077 p~T/uss2/o 1 s47 2 ~
intermodul~ion distortion and adJacent channel intelle.ence. The interferer can cause the SAT detector on the target channel to report a false SAT i~ r~ion~ The SAT falsing opens the receive audio on the target channel 5 and introduces noise into the handoff until the desired mobile arrives on channel.
Returning to FIG. 2, voice transceivers 222-225 typically mute the audio path in response to either of two events. The first event is under hardware control. When 1 0 voice transceivers 222-225 no longer detect SAT, the receive audio path is muted by enabling audio switch 430.
The second event is a sofl-.~e controlled switch. When lhe audio switch 430 is en~ble~l the audio path in the voice transceiver 218 is muted. The switch overrides the 1 5 ha~dwarc SAT detect status. Therefore, the audio path in thc voice transceivcrs 222-225 can be forced to mute regardless of the SAT status. This function l~lo~idcs the basis for the target channel SAT falsing soludon in accordance with the in~ention. An algorithm is used in the 20 BSC 200 which has the ability to distinguish between an interferer signal and the desired mobile on the target c~nnel As a result, the audio path in the voice transceivers 222-225 will remain muted until it is dctc"..ined that the desired unit has arrived on channel.
25 When this occurs, the audio switch 430 will be disabled and the recei~e audio path in the voice l.ansceivers 222-225 will be opencd and closed based on the hard~.a.e SAT
detect status.
Noise in~e.re.ence during ~ndoff is reduced in 30 accordance with the invention as follows. The subscriber - 125 is continuQltsly mori~ored by the source base-station 130 for SSI. The base-station 130 in cell 100 has SATl which distinguishes cell 100 from its neighboring cells.
wo 92/19077 PCr/l,lS92/~1547 21~7~ ~ lo When the SSI being measured by the base-station 130 falls below a ~ doff threshold, the base-station 130 sends a handoff request m~ss~pe to the EMX 120. The EMX 120 sends a meSs~e to neighboring target base-stations 135, 140 in cells 105, 110 ~es~ccti~cly. Neighboring cells sullounding the source cell 100 receive the handoff measulc,...~,nt re~..cst message. Continuing, base-stations 135, 140 make a SSI measulGlllcnt of the transmission of the subscriber 125 and dete,.l.ine if the handoff cnterion is met. For e~mple. if base-station I35 in cell 105 meets the h~n~Qff criterion, the base-station 135 will send a response to the EMX 12û noting such. If the target base-stations are not viable candidates for handoff, they will not lespond to the EMX 120.
At this time, the EMX 120 sends a message to the best candidate targct base-station 135 requesting it to deterrninc if an idle channel exists. If an idle channel does exis~, the target base~station 13S returns a message to the EMX 120 containing the idle channel information, including channel frcquencg and SAT2. To complete the handoff - procedure, the EM~C 120 sends thc idle channel information to the source base-station 130 which in turn broadc~sts the information to thc subscriber 125. The subscriber 125 will tune to the new channel frequency, will changc SAT from 25 SAT1 to SAT2, and begin co~.unica~ion to the target base-stadon 135 in cell lOS. The threc party circuit (not shown) - in thc EMX 120 s--t~hcs the land-line ccr-7~tion from the audio path of the sourcc base-station 130 to the audio path of the targct base-station 135 to co.nplet- the handoff.
3 0 Previously, handoff occulled regardless of the status ~, of the audio path of the idle target chiannel. If the audio path was open, disc~ tor noise would be summed into a conversation via the three party circuit (not shown) '.
. ~. ,i .. , .... .. " ... .. ~ . . .: .. . ... . .... .
WO 92/19077 PC~/US92/01547 .
2 1 ~ ~ 7 ~
during h~-~doff, resultirlg in an objectionable noisc blast to the using parties. In accordance with the invention, the target base-station 135 mutes thc audio path, determines if the audio path of the chosen idle target chqnne1 was 5 enabled by detection of an undesired signal having a co.l..non SAT, and if it was, uses the SAT and the RSSI of the subscriber 125 transmission to enable the audio path for handoff.
If the most recent idlc target cl'qnnel SAT status 10 returns a positive SAT ir~ica~ion, then an intc.rcrer is present on the idle target voice channel. When this occurs, the VCC 212 triggers two concu.,cnt events: a SSI
qu~l;fic~ion time-out and the SSI q~tqlific~tion task. The SSI qu-q-lificvqtion time-out is a safety valve to ensure that 15 the audio path of thc idle target channel does not remain muted. This taslc is only e-Yecuted when thc intc.l~.ing signal has a strong SSI and thc BSC 200 is unable to distinguish thc ioterfcrer from the desired subscriber 125 transmission. Thc dme-out value iep~sents a worst case 2 0 arriva1 scenario, and in the p,ef~ ,d embodiment may be in the range from 300-2000 m;~ e~nds.
The SSI qrql;r;~ task is run by VCC 212 periodically to eYqmire the SSI of the trq-~C~nis$ion by the subscriber 125. The SSI quqlifirq~ion task is intended to 25 p~o~,idc a high degree of confidence that the subscriber 125 has arrived or has begun co,.~ ;on on the target channel.- Refernng to FIG. 4, the SSI is det~,.n~incd by mixcr/A.nr!ifi~r boards 405, 410 and sent to the audio control board 420 where the inforrnation is routed to the 30 data distribution board 435 within one of the voice transccivcrs 222-225. The data distribution board 435 serves as the interface point betwcen the voice sceivers 222-225 and the VCC 212. The VCC 212 7 ~ ~
c~ pa~s the subscriber SSI with the interferer SSI plus a downloaded SSI offset. The downloaded SSI offset is stored in RAM and EPROM 312 and cu..~nlly represents compes~s~ion for variations in signal strength of up to 7 S dB. Thc com~rc~ti~r may be higher in future implementations.
If VCC 212 detc...~ es the subscriber SSI is greater than the intelÇe,~c. SSI plus the downloaded SSI offset, the SSI qu~lific~tion timc-out is cancelled, and VCC 212 sends a 10 disable mute message to the target voice transceiver. This message enables the first positive SAT update message from the target voice llanscciver to send a handoff complete message to the FMX 120. If the SSI qualification time-out expires before VCC 212 detc.,.lines the subscriber 15 SSI is greatcr than thc inte,~-~r SSI plus the-downloaded SSI offset, VCC 212 sends the same disable mutc mPss~ge to the target voice transcei~rer. Again, this ~ ss~~c e-~?bks the first pGSili~C, SAT updatc .--~ssagc &om the target voice transceivcr to send a handoff complete message to the EMX
20 r20.
PIG. S generally depicts in flow diagram form the steps a base-station 135 undcrgocs to reduce noise nterforence during handoff in accordance with the invention. The p~cess starts at 500 by receiving at 503-a 25 desired RF signal having at least the audio signal and a coveragc area idc~l;r~r~lion value mQdnl~tçd thereon. The base-station 135 then demodul~t~!s at 506 the desired RF
signal to produce signals ~cpresenting at least the audio signal and the coverage arca iden-ifi~q~ion value and de,t~.. nincs at 509 a signal quality value of the desired RF ~-signal. A l~dctc.-".ncd coverage area value is provided at 512 and CG.I.pa~Cd at 515 to the demod~ ted coverage area iden-ific~tioh value. The base-station 135 disables at .
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W O 92/19077 PC~r/US92/Ot547 ' :
1 3 2 5 ~ ~ 7 $ ~
518 the switched audio path, determines at 521 when the swi~ched audio path has been enabled by an undesired RF
signal, and enables at 524 the s~vitchcd audio path in response to the signal quality dete. n~ination 509 and the S co.npaiison 515 when the switchcd audio path has been enabled by an undesired RF signal.
FIG. 6 generally depicts in flow diagram form the steps a base-station undergoes to confirm a mobile's arrival on a target ch~nnP~I in acco.dance with the invention. The 10 process starts by selectir~g at 600 a target channel at a target base-station 135. The base-station 135 asserts at 603 a soflwale mute and waits at 606 up to ~50 mi~ ecs)~.;s ~fo~e ta~ing a "sn~rs~ot" or poll of the transceiver 222-225 SSI and SAT. A test is, performed at 15 609 to det~.lincd if SAT is present during the snapshot.
If it is not present, thc base-station 135 sets at 612 a best case arri~ral timcout and performs at 615 another test to detem~incd if thc timcout has eAp;~d. If it has, the softwarc mute is un-asserted at 618 and handoff procccds as normal. If it has not eApired, thc test at 615 is 1'epc3~e~ ;
until it has eApired.
If SAT is prescnt during thc sn~rshot in test 609, a SSI quqlfflration tin~eout is set at 621 and thc status alg~.ith... or SSI q~ ficq~iqr task r~siding in RAM and 25 EPROM 312 of the VCC 212 is invoked. A test is pc.roi".ed at 624 to dct~....ine if the SSI qu~!ific?tion !;...e~l,( has A~;~eCl. If it has, the softwarc mute is un-assc.~d at 618.
If has not cxpired, a test is performcd at 627 to determine if the sampled SSI is grcater than or cqual to the inte.Ierer 30 SSI plus some va. r~le ~. If it is not, the process ~.~ocecds back to test 624 to det~,.lnil1e if the SSI qu~lification I; eou~ has expired. If the sampled SSI is greater, the ba$e-station dete.",-nes at 633 if the sr~pshot had a good '.
WO 92/19077 PCr/US92/01547 5 ~ ~1 SAT. If it did not, the test at 624 is repeated. If it did, the soflwaie mute is un-asserted at 618 and handoff proceeds as norrnal. Using these stcps, noise inte~rence in the form of a noisc blast is reduced during the handoff process.
S What I claim is:
: '
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A receiver which reduces noise interference during communication handoff, the receiver having a switched audio path to convey at least an audio signal to a destination telephone system, the receiver comprising:
accepting means for accepting a desired radio frequency signal having at least the audio signal and a coverage area identification value modulated thereon;
demodulating means for demodulating said desired radio frequency signal to produce signals representing at least the audio signal and said coverage area identification value;
first determining means for determining a signal quality value of said desired radio frequency signal;
providing means for providing a predetermined coverage area value;
comparing means for comparing said demodulated coverage area identification value to said predetermined coverage area value;
disabling means for disabling said switched audio path;
enabling means for enabling said switched audio path responsive to said comparing means;
second determining means for determining when said switched audio path has been enabled by an undesired radio frequency signal;
overriding means for overriding said enabling means to assert disablement of said switched audio path when said switched audio path has been enabled by an undesired radio frequency signal; and unasserting means for unasserting the disablement of said switched audio path disabled by said overriding means, responsive to said first determining means and said comparing means.
accepting means for accepting a desired radio frequency signal having at least the audio signal and a coverage area identification value modulated thereon;
demodulating means for demodulating said desired radio frequency signal to produce signals representing at least the audio signal and said coverage area identification value;
first determining means for determining a signal quality value of said desired radio frequency signal;
providing means for providing a predetermined coverage area value;
comparing means for comparing said demodulated coverage area identification value to said predetermined coverage area value;
disabling means for disabling said switched audio path;
enabling means for enabling said switched audio path responsive to said comparing means;
second determining means for determining when said switched audio path has been enabled by an undesired radio frequency signal;
overriding means for overriding said enabling means to assert disablement of said switched audio path when said switched audio path has been enabled by an undesired radio frequency signal; and unasserting means for unasserting the disablement of said switched audio path disabled by said overriding means, responsive to said first determining means and said comparing means.
2. The receiver of claim 1 wherein said first determining means further comprises means for providing at least one communication handoff threshold.
3. The receiver of claim 2 wherein said unasserting means further comprises means for unasserting the disablement of said switched audio path when said signal strength value is greater than said at least one communication handoff threshold and when said demodulated coverage area identification value essentially equals said predetermined coverage area value.
4. The receiver of claim 1 wherein said comparing means further comprises means for comparing said demodulated coverage area identification value to one of at least a first, second, and third predetermined coverage area values.
5. A base-station employing a receiver which reduces noise interference during communication handoff, the base-station employed in a radiotelephone system, the receiver having a switched audio path to convey at least an audio signal to a destination telephone system, the base-station comprising:
receiving means for receiving a desired radio frequency signal having at least the audio signal and a coverage area identification value modulated thereon;
demodulating means for demodulating said desired radio frequency signal to produce signals representing at least the audio signal and said coverage area identification value;
first determining means for determining a signal quality value of said desired radio frequency signal;
providing means for providing a predetermined coverage area value;
comparing means for comparing said demodulated coverage area identification value to said predetermined coverage area value;
disabling means for disabling said switched audio path;
enabling means for enabling said switched audio path responsive to said comparing means;
second determining means for determining when said switched audio path has been enabled by an undesired radio frequency signal;
overriding means for overriding said enabling means to assert disablement of said switched audio path when said switched audio path has been enabled by an undesired radio frequency signal; and unasserting means for unasserting the disablement of said switched audio path disabled by said overriding means, responsive to said first determining means and said comparing means.
receiving means for receiving a desired radio frequency signal having at least the audio signal and a coverage area identification value modulated thereon;
demodulating means for demodulating said desired radio frequency signal to produce signals representing at least the audio signal and said coverage area identification value;
first determining means for determining a signal quality value of said desired radio frequency signal;
providing means for providing a predetermined coverage area value;
comparing means for comparing said demodulated coverage area identification value to said predetermined coverage area value;
disabling means for disabling said switched audio path;
enabling means for enabling said switched audio path responsive to said comparing means;
second determining means for determining when said switched audio path has been enabled by an undesired radio frequency signal;
overriding means for overriding said enabling means to assert disablement of said switched audio path when said switched audio path has been enabled by an undesired radio frequency signal; and unasserting means for unasserting the disablement of said switched audio path disabled by said overriding means, responsive to said first determining means and said comparing means.
6. The base-station of claim 5 wherein said first determining means further comprises means for providing at least one communication handoff threshold.
7. The base-station of claim 6 wherein said unasserting means further comprises means for unasserting the disablement of said switched audio path when said signal strength value is greater than said at least one communication handoff threshold and when said demodulated coverage area identification value essentially equals said predetermined coverage area value.
8. The base-station of claim 5 wherein said comparing means further comprises means for comparing said demodulated coverage area identification value to one of at least a first, second, and third predetermined coverage area values.
9. A radiotelephone system having reduced noise interference during communication handoff, the radiotelephone system having a source base-station communicating with a subscriber unit in a first coverage area, the source base-station having a source audio path to convey an audio signal, the subscriber unit requiring communication handoff from the source base-station to a target base-station in a second coverage area, the target base-station having a target audio path to convey an audio signal, the radiotelephone system comprising:
receiving means, at the target base-station, for receiving a desired radio frequency signal having at least a coverage area identification value modulated thereon;
demodulating means, at the target base-station, for demodulating said desired radio frequency signal to produce at least one signal representing said coverage area identification value;
first determining means, at the target base-station, for determining a signal quality value of said desired radio frequency signal;
providing means, at the target base-station, for providing a predetermined coverage area value;
comparing means, at the target base-station, for comparing said demodulated coverage area identification value to the predetermined coverage area value;
disabling means, at the target base-station, for disabling the target audio path;
enabling means, at the target base-station, for enabling said target audio path responsive to said comparing means;
second determining means, at the target base-station, for determining when said target audio path has been enabled by an undesired radio frequency signal;
overriding means, at the target base-station, for overriding said enabling means to assert disablement of said target audio path when said target audio path has been enabled by an undesired radio frequency signal;
unasserting means, at the target base-station, for unasserting the disablement of said target audio path disabled by said overriding means, responsive to said first determining means and said comparing means; and coupling means for coupling said source audio path to said enabled target audio path.
receiving means, at the target base-station, for receiving a desired radio frequency signal having at least a coverage area identification value modulated thereon;
demodulating means, at the target base-station, for demodulating said desired radio frequency signal to produce at least one signal representing said coverage area identification value;
first determining means, at the target base-station, for determining a signal quality value of said desired radio frequency signal;
providing means, at the target base-station, for providing a predetermined coverage area value;
comparing means, at the target base-station, for comparing said demodulated coverage area identification value to the predetermined coverage area value;
disabling means, at the target base-station, for disabling the target audio path;
enabling means, at the target base-station, for enabling said target audio path responsive to said comparing means;
second determining means, at the target base-station, for determining when said target audio path has been enabled by an undesired radio frequency signal;
overriding means, at the target base-station, for overriding said enabling means to assert disablement of said target audio path when said target audio path has been enabled by an undesired radio frequency signal;
unasserting means, at the target base-station, for unasserting the disablement of said target audio path disabled by said overriding means, responsive to said first determining means and said comparing means; and coupling means for coupling said source audio path to said enabled target audio path.
10. A method of reducing noise interference during communication handoff in a base-station, the base-station employed in a radiotelephone system and incorporating a receiver having a switched audio path to convey at least an audio signal to a destination telephone system, the method comprising the steps of:
receiving a desired radio frequency signal having at least the audio signal and a coverage area identification value modulated thereon;
demodulating said desired radio frequency signal to produce signals representing at least the audio signal and said coverage area identification value;
determining a signal quality value of said desired radio frequency signal;
providing a predetermined coverage area value;
comparing said demodulated coverage area identification value to said predetermined coverage area value;
disabling said switched audio path;
enabling said switched audio path responsive to said step of comparing;
determining when said switched audio path has been enabled by an undesired radio frequency signal;
overriding said step of enabling to assert disablement of said switched audio path when said switched audio path has been enabled by an undesired radio frequency signal; and unasserting the disablement of said switched audio path disabled in said step of overriding, responsive to said step of determining a signal quality value and said step of comparing.
receiving a desired radio frequency signal having at least the audio signal and a coverage area identification value modulated thereon;
demodulating said desired radio frequency signal to produce signals representing at least the audio signal and said coverage area identification value;
determining a signal quality value of said desired radio frequency signal;
providing a predetermined coverage area value;
comparing said demodulated coverage area identification value to said predetermined coverage area value;
disabling said switched audio path;
enabling said switched audio path responsive to said step of comparing;
determining when said switched audio path has been enabled by an undesired radio frequency signal;
overriding said step of enabling to assert disablement of said switched audio path when said switched audio path has been enabled by an undesired radio frequency signal; and unasserting the disablement of said switched audio path disabled in said step of overriding, responsive to said step of determining a signal quality value and said step of comparing.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US683,001 | 1991-04-10 | ||
| US07/683,001 US5239675A (en) | 1991-04-10 | 1991-04-10 | Reduced noise interference during handoff |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2106761A1 CA2106761A1 (en) | 1992-10-11 |
| CA2106761C true CA2106761C (en) | 1998-04-28 |
Family
ID=24742147
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002106761A Expired - Fee Related CA2106761C (en) | 1991-04-10 | 1992-03-02 | Reduced noise interference during handoff |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US5239675A (en) |
| JP (1) | JP2632441B2 (en) |
| KR (1) | KR970002759B1 (en) |
| CN (1) | CN1027849C (en) |
| BR (1) | BR9205867A (en) |
| CA (1) | CA2106761C (en) |
| GB (1) | GB2270818B (en) |
| MX (1) | MX9201668A (en) |
| MY (1) | MY107863A (en) |
| WO (1) | WO1992019077A1 (en) |
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| JP2972445B2 (en) * | 1992-07-17 | 1999-11-08 | 日本電気通信システム株式会社 | Electric field level measurement method |
| US5918184A (en) * | 1992-09-21 | 1999-06-29 | Lucent Technologies Inc. | Method and apparatus for detecting a supervisory audio tone |
| JP3483295B2 (en) * | 1994-04-15 | 2004-01-06 | 富士通株式会社 | Peripheral zone carrier monitoring method and mobile station |
| US5649290A (en) * | 1994-12-14 | 1997-07-15 | Lucent Technologies Inc. | Handover method based upon channel quality |
| US5586338A (en) * | 1994-12-22 | 1996-12-17 | Bell Atlantic Mobile Systems, Inc. | System identification (SID) list for selecting operating frequencies |
| US5613204A (en) * | 1994-12-22 | 1997-03-18 | Bell Atlantic Mobile Systems, Inc. | Beacon system for roaming cellular stations |
| US5797095A (en) * | 1995-12-15 | 1998-08-18 | Telefonaktiebolaget Lm Ericsson | Supervisory audio tone-signalling tone(SAT-ST) handling |
| US5878342A (en) * | 1995-12-15 | 1999-03-02 | Telefonaktiebolaget Lm Ericsson | Supervisory audio tone (SAT) approximation in an analog cellular mobile radio telephone system |
| GB2330485B (en) * | 1997-10-16 | 2002-05-29 | Motorola Ltd | Background noise contrast reduction for handovers involving a change of speech codec |
| JP3464150B2 (en) * | 1998-07-29 | 2003-11-05 | 沖電気工業株式会社 | Mobile communication receiver |
| US8195187B2 (en) | 2001-06-25 | 2012-06-05 | Airvana Network Solutions, Inc. | Radio network control |
| US8160020B2 (en) * | 2001-06-25 | 2012-04-17 | Airvana Network Solutions, Inc. | Radio network control |
| US20050037757A1 (en) * | 2003-08-12 | 2005-02-17 | Samsung Electronics Co., Ltd. | Mobile communication system for handoff between heterogeneous mobile communication networks and handoff method using the same |
| US7127955B2 (en) * | 2004-03-12 | 2006-10-31 | Bondhus Corporation | Torque limiting handle |
| CN101142839B (en) * | 2005-03-14 | 2013-04-24 | 艾利森电话股份有限公司 | Method, system and node for improved handover of communication system |
| US8099504B2 (en) | 2005-06-24 | 2012-01-17 | Airvana Network Solutions, Inc. | Preserving sessions in a wireless network |
| US20060291420A1 (en) * | 2005-06-27 | 2006-12-28 | Dennis Ng | Network-initiated dormant handoffs |
| US7751835B2 (en) | 2005-10-04 | 2010-07-06 | Airvana, Inc. | Non-circular paging areas |
| US8094630B2 (en) * | 2005-12-16 | 2012-01-10 | Airvana Network Solutions, Inc. | Radio frequency dragging prevention |
| US8145221B2 (en) | 2005-12-16 | 2012-03-27 | Airvana Network Solutions, Inc. | Radio network communication |
| US8619702B2 (en) | 2005-12-16 | 2013-12-31 | Ericsson Evdo Inc. | Radio network control |
| US8085696B2 (en) | 2006-07-14 | 2011-12-27 | Airvana Networks Solutions, Inc. | Dynamic modification of route update protocols |
| US8843638B2 (en) | 2007-12-13 | 2014-09-23 | Ericsson Evdo Inc. | Handing off active connections |
| US8185120B2 (en) | 2010-03-26 | 2012-05-22 | Microsoft Corporation | Cellular service with improved service availability |
| US11490301B1 (en) * | 2020-11-10 | 2022-11-01 | T-Mobile Innovations Llc | Delaying handovers based on intermodulation distortion |
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| US3819872A (en) * | 1972-07-10 | 1974-06-25 | Bell Telephone Labor Inc | Mobile telephone cellular switching system |
| US4025853A (en) * | 1976-02-12 | 1977-05-24 | Bell Telephone Laboratories, Incorporated | Method and apparatus for radio system cochannel interference suppression |
| US4229620A (en) * | 1978-11-09 | 1980-10-21 | Bell Telephone Laboratories, Incorporated | Mobile radiotelephone station two-way ranging system |
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| US5001742A (en) * | 1990-01-29 | 1991-03-19 | At&T Bell Laboratories | Baseband signal processing unit and method of operating the same |
-
1991
- 1991-04-10 US US07/683,001 patent/US5239675A/en not_active Expired - Lifetime
-
1992
- 1992-03-02 JP JP4509937A patent/JP2632441B2/en not_active Expired - Fee Related
- 1992-03-02 BR BR9205867A patent/BR9205867A/en not_active IP Right Cessation
- 1992-03-02 KR KR1019930703042A patent/KR970002759B1/en not_active IP Right Cessation
- 1992-03-02 CA CA002106761A patent/CA2106761C/en not_active Expired - Fee Related
- 1992-03-02 GB GB9320107A patent/GB2270818B/en not_active Expired - Fee Related
- 1992-03-02 WO PCT/US1992/001547 patent/WO1992019077A1/en active Application Filing
- 1992-03-25 MY MYPI92000505A patent/MY107863A/en unknown
- 1992-04-09 CN CN92102616A patent/CN1027849C/en not_active Expired - Fee Related
- 1992-04-10 MX MX9201668A patent/MX9201668A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BR9205867A (en) | 1994-08-02 |
| JPH06506806A (en) | 1994-07-28 |
| KR970002759B1 (en) | 1997-03-10 |
| CA2106761A1 (en) | 1992-10-11 |
| GB2270818B (en) | 1995-06-14 |
| CN1027849C (en) | 1995-03-08 |
| GB9320107D0 (en) | 1994-01-05 |
| US5239675A (en) | 1993-08-24 |
| CN1070297A (en) | 1993-03-24 |
| MY107863A (en) | 1996-06-29 |
| WO1992019077A1 (en) | 1992-10-29 |
| JP2632441B2 (en) | 1997-07-23 |
| GB2270818A (en) | 1994-03-23 |
| MX9201668A (en) | 1992-10-01 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |