CA2118717A1

CA2118717A1 - Wireless pbx system using frequency scanner for channel identification

Info

Publication number: CA2118717A1
Application number: CA002118717A
Authority: CA
Inventors: Kenneth A. Felix; Morton Stern
Original assignee: Individual
Current assignee: Motorola Solutions Inc
Priority date: 1992-08-03
Filing date: 1993-06-30
Publication date: 1994-02-17
Also published as: MX9304686A; BR9305595A; EP0614589A1; WO1994003993A1; FI941503A; EP0614589A4; JPH07504555A; FI941503A0

Abstract

WIRELESS PBX SYSTEM USING FREQUENCY SCANNER FOR CHANNEL IDENTIFICATION Abstract of the Disclosure In a wireless private branch exchange, communication network, a method and apparatus are offered for identifying network communication resources. The method includes the steps of measuring a signal quality factor of a channel of a selected spectrum and comparing the measured values with a threshold value. The method further includes the step of selecting channels, exceeding the threshold, as network communication resources. The selected spectrum is that, also used, by a local cellular communication network. Where scanning determines that a channel is not being used by the cellular system then use is permitted with the private system.

Description

2~1~717 ., - 1 -WIRE~ES~; Pl~ SYSI~ USING ~REQUENCY SCANNER FOR
CEANNEL Il)ENT~ICATION
Field of the Invention S .
The invention relates to communication ~ystems and, in specific, to wireless communication ~y~tem~ used in con,junction with private branch exchange communication systems.
Background ofthe Invention Private branch e~change communication ~y~tems (PBXs) are known. PBXs are commonly used where a discrete group of people (e.g., employees of a company) need to communicate, in large measure, wi~hin the group. A PBX, in providing service vwithin the group, i8 typically limited to a f~l~ed geographic area coincident vv~th a company facility or group of facilities.
~BX~ of~er advantages in that calls between members of 2 0 the discrete group are handled locally within the PBX and do not iDvolve an associated public switch telephone network (PSI N). :
Such local handling reduces the cost of providing communication services within the group.
2 5 PBX~ also provide other advantages, such as call blocking to specific nwnbers or groups of numbers. Csll blocking, in such case, may be used by a PBX operator to prevent long-distance calls from specific telephones or groups of telephones within the private system.
Cellular communication systems are also known.
Cellular communication systems, as opposed to PBX ~ystems, are constructed to provide communication services over broad geographic area~ through a number of base sites. Each ba~e site

3 5 v~ithin ~uch a system i~ positioned to provide service within a service coverage area, partially overlapping adjacent service coverage areas, in such a manner as to provide substantially continuous co~rerage to a communication unit passing through such an area -Communication ser~ice, within a cellular sy6tem, is provided to a communication unit on a radio channel selected from a number of communication channels (f1-fn) available ~ - -~ . ~

2~1~7~7 , within the system. Such radio channel are as~igned to communication units upon request.
Cellular communication ~yatems are typically S interconnected with the PSTN either locally, through an interconnect at each base station, or centrally, through a mobile switching center (MSC) that interfaces with a number of base sites. The interconnect with the PSTN allows a communication unit to communicate with subscribers throughout the PSTN as 10 well as other communication unita The interconnect with the PSTN also ~llows a communication unit to communicate, through PBXs with telephone users within a PBX.
While both PBX~ and cellular communication systems 15 work well in their respective market niches, instances arise where it would be advantageous to combine a PBX with a local wirelesa service, coincident with the area of the PBX ~er~ice.
Such a combination would offer the advantage of providing wirele~ communication services within the confines of a 2 0 manufacturing facility, office building, or shopping mall without the involvement of the PSTN.
Al~o, because a pnvate wireless system may find it advantageous to use cellular channels, the private wireless 2 5 system may have to coe~i~t with existing cellular facilitiea. Such a wireless PBX communication system may have to be able to select channels also being used by a local cellulsr syste~
Because of the importance of PBXs and the need for wireless communication within a PBX environment a need esists for a 3 0 means and method, of selecting cellular channels for use by a wireless PBX system, that iB non-interfenng with the cellulsr system.
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- . - . - - .. . - . ~ . -, 2~1~7~ 7 Summary of the Invention In a wireles~ private branch e~change, communication 5 network, a method and apparatus are provided for identifying network communication resources. The method includes the steps of measuring a signal quality factor of a channel of a selected spectrum and comparing the measured value~ with a threshold value. The method further includes the ~tep of 10 selecting channels, exceeding the threshold, as network communication resources. The selected spectrum is that, also used, by a local cellular communication network. Where scanning and threshold comparisons indicates that a channel is not being used by the cellular system then use is permitted 15 v~ithin the private system.

Brief Descript~on of the Drawings 2 ~
FIG. 1 illustrates, in block diagram form, a private branch eschange including a wireless communication facilities in accordance with one embodiment of the invention.
2 5 ~IG. 2 illustrates, in block diagram form, a wireless intercept bos in accordance with the invention. ~ ~
~':
Detailed Description of the Preferred Embodiment The solution to the problem of channel selection within a PBX wireless communication system lies, conceptually, in the use of a s~r~er and in the evaluation of communication resources based on signal measurements by the scanner.
3 5 Resource evaluation i~ based upon comparison of signal measurements on scanned resources with a threshold value.
The use of a scanner allows candidate resources to be evaluated . - . .~ -~
for interfering users before use is permitted within the PBX ~ - -wireles~ system. Scanning, under 8ucb a format, may be of an ~ -

4 0 entire spectrum with the results reported, en masse, to a -wireless controller or scan ung may be of individual resources under the control of the wireless controller with individual signal measurements reported back to the wireless controller for compa~ison with the threshold. - ~;

The reader's attention will fir~t be drawn to a description of function of a wireles~ PBX system. Following the description of function, channel selection will be described in accordance S with one embodiment of the invention.
FIG. 1 illustrates, in block diagram form, a PBX sy~tem, generally (10), offering wirel0s~ communication services in accordance with a preferred embodiment of the invention.
10 Included within such a system (10) is a PBX switch (11), wireles~
interfaoe bo~c (WIB) (12), ~ignaling interface (13), scan receiver controller (14), scan receiver (19), and base stations 15-18. Also shown in FIG. 1 are communication units 20-22.
l 5 PBX communication system 10 is constructed to have the functionality of routing telephone calls among subscnbers (103) and external, PSTN subscribers (not shown) and among subscribers (103). A call frG~ a wireline subscriber (103) to another wireline subscriber (103) is accomplished through 2 0 interconnect~ (102) under pror art methods within the PBX
~witch (11). Calls between an esternal, P~N subscriber and wireline aubscriber (103) i8 al~o accomplished under prior art methods within the PBX switch (11).
2 S Some subscribers (103), in accordance with one embodiment of the invention, have a dual service capability including the capacity of recei~ing (and mal~ng calls) through either wireline or wireless facilities. Such subscriber6 (103) receive wireline ser~ice through a wireline facility at a fi~ed 3 0 location (e.g., a telephone within an office) or through a wireless trsnsceiver (20-22) carned by the subscriber (103).
Such dual service capability is provided through use of the VVIB (12) interconnected with normal wireline pickup subscriber 3 5 lines (105). The WIB (12) prondes the functionality of forwarding calls directed to a wireline subsc~ber on a wireline (e.g., 106) to a wireless receiver (e.g., 20) af~cer 8 f~sed delay. (Alternatively a call may be routed fir6t to the wireless subscriber and then, after a delay, to the wireline subscriber.) The fi~ced delay allows for 4 0 receipt of the call at the fi~ed location (through wireline 106) before transfer to the wireless communication unit (20) through the W~ (12) and a base station (15, 16, 17, or 18). Coupling between W~ (12) and base stations (15-18) i8 accomplished via 2~1 ~7:17 signaling links 100, incorporating a wireless-related signaling protocol, and via subscriber links 101.
Communication units 20-22 and base stations 1~-18 are S constructed to e~cchange communicated messages at low power levels (e.g., 10 milliwatts) under a prescribed signaling protocol such as, for example, that used in the Advance Mobile Phone Ser~ice (AMPS) cellular radiotelephone ~ervice. In accordance with the preferred embodiment, communication units 20-22, 1 0 upon activation, scan a spectrum seeking a signal from any of base station~ 15-18 for service through the PBX wireless system (10). ' ' While base stations (15-18) are shown with a single 1 5 antenna ~19), the single antenna (19) of base 6tationB(15-18) is comprised of a distributed antenna network (23) coupled to the base stations (15-18) through a combiner (not shown). Also ~ -coupled to the di8tnbuted antenna network (23) through the ~ -combiner is the scan receiver (19). The independent antenna of 2 0 the distributed antenna (23) are located throughout a service coverage area of the PBX sy~tem (e.g., a floor of a building).
Other distributed antenna (23) may cover the same, or other floors.
2 5 The distributed antenna (23) simplities system de~ign in ;
that wireless aubscriber~ (20-22) may progressively transceive through different antenna of the network (23) as the subscriber (20-22) moves through a coverage area of a base station (20-22).
The distributed antenna (23) allows operation of the PBX wirele~s 3 0 network (10) without the complicated proce~s and associated - -~
hardware required by handoff from base station to bsse sta~on.
EIG. 2 generally depicts, in blocl~ diagram form, ~1VIB 12.
As shown, wireline group 104 enter~ a time slot interchange (TSI
3 5 218). In the preferred embodiment, TSI 218 may be a time slot ~ ~ ~
interchange as that having part number 8980, and manufactured ~ ~-by MITEL~9 (MllrEL is a registered trademark of MrrEL Corp., a subsidiary of British Telecom). Continuing, TSI 218 i8 al~o coupled to subscriber links 101 which interconnects WIB 12 to 4 0 base station~ 15-18. TSI 218 iB interconnected to 1/0) controller 215 which perfonns interfacing tasks between processor 206 and TSI 218. Processor 206 is coupled to a data store (209) wbich stores, inter alai, slot-to-slot connection data a~ld subscriber line-to-wireless subscriber number translation. In addition, 2~ ~717 processor 2û6 iB coupled to a program 8tore (212) which stores programs used by proce~sor 206 to perform, inter alai, TSI
control, signal digit analysis, and nng detection. Processor 206 iB coupled, via I/0 controller 203, to the Bignaling interface 13.
S Signaling interface 13 provides the requisite interface for signaling links 10C to inter-couple WIB 12 to base stations 15-18.
Signaling interface 13 accepts Big~la]ing information, from processor 206 from a selected line of wireline group 104, and u~es 1 0 this information for it~ own control and for generating the appropriate signaling messages for subscribers, for example, wirele~s subscriber 20. In addition, signaling interface 13 transmits and rece*es information to/from base stations 15-18.
I'hiB data iB primarily information which v~ill be ~ent, or has 15 been received, on a control channel, but the information content may be espanded as required. In the preferred embodiment, the type of signaliDg used in the system iB analogous to that used in the AMPS cellular radiotelephone sy~tem. In alternate embodiment, signaling ~ B 100 may carry information using a 2 0 message based protocol between signaling inter~ace 13 and base stations 15-18. Implementation of signaling interface 13 may be realized by employing any conventional micro-computer system.
As such, in thi~ embodiment, ~ignaling interface 13 would also be able to maintain call record~ and statistics as required ba~ed 2 5 upon the passage of information.
Base stations 1~18 of FIG. 1 each transmit overhead information, pages, and appropriate channel assignInents to wireless subscribers (20-22), such as wireles~ subscriber 20. In 3 0 the rever~e direction base stations (1~-18) receive page responses and call origination requests from wireless subscribers (20-22).
Signali~g linkB (100) can carry the above-me~tioned information (between base stations (15-18) and ~1VIB (12)) in the actual protocol message form as required by the wireless system, or it can be in 3 5 any of the data link protocols (e.g., high-level data link protocol (HDLC)).
Referring to FIG. 1, WIB 12 has the capability to monitor the data stream of individual trunk~ from trunk group 109. In 4 0 the preferred embodiment, trunk group 109 consists of a 2~
channel pulse coded modulated (PCM), 1.544 megabit per ~econd a!~bp~), (DS1) service. In thia scenario, the least significant bit of every si~th DS0 slot contains signaling information pertaining to trunk seizure, called number, disconnect, etc. (For further 7 1 ~
, -information, reference may be made to CClTT Bluebook ~pecification ~.704, G.733, and G.734, published November 2~, 1988 in Geneva, Switzerland.) Signaling informstion, from trunk group 109, is assembled in me~sage format and is transferred to signaling interface 13 u~ing a protocol such as HDLC. The me~sage content can be set-up in a 1 or 0" format for interpreta~ion in signaling interface 13.
Call delivery to subscriber 103 (e.g., on wireline 106) i8 as follows in accordance with the invention. When a call from an originator (for esample, from the PSl~ received by the PBX
(11), for v~ireline subscriber 103, the PBX (11) routes the call to wireline 106 as in the prior art. The WIB (12) detects a seizure (ring signal) for wireline subscriber 103 (on wireline 106) and 1 5 begins a time delay. Af~cer a f~ed delay the ~1VIB (12) dete~mines the corresponding mobile phone number of wirele~s subscriber 20 and pa~ses thi~ information to signaling interface 13 via I/O
controller 203 in the form of the actual signaling protocol (e.g., the ~DLC link protocol).

Signaling interface 13 then generates a paging message which is sent, via signaling links 100, to all base station~ 15-18 for tran~mi~sion to wireles~ subscriber 20. If one of base stations 15-18 is busy hand~ing an existing call, the busy base station will 2 5 discard the information. If a base station (15-18) is idle, i~
transmit the page as part of a control channel stream along with ~ -a sy~tem identifica~on code to which wireless sub~criber 20 attaches an association. All ba~e stations (15-18) may carry the same identifier, or different ba~e stations may carry unique 3 0 identifiers BO aB to differentiate a service or coverage areas. The wireles~ system also support~ ~lee~mode operatio~s for idle subscriber units (20-22).
While signaling information is being routed to base ~-3 5 stations 15-18, the PBX 12 recei~res information from the PSTN as r -it would for any wireline call, and sets-up the call accordingly.
The information is routed, through TSI 218, to the ba~e stations 16-18 via subscriber links 101. Upon receipt, base stations (15-18) intercept the nng signal while continuing to monitor the radio-4 0 frequency (RF) channel for a response to the page.
Wireless subscriber 20, upon receipt of the page, responds on an RF channel corresponding to an idle ba~e station (15-18) within the system (10). The idle base station (e.g., 17) which -21 ~$71~

receive8 the response, from wirele8s subscriber 20, will direct WIB 12 to a~ign the appropriate line (110) from subscriber links 101 to be interconnected with the appropriate line (106) from wireline group 104 via TSI 218. At such time as the interconnect S (between 106 and 110) iB complete the now-communicating base sta~on (17) sends an alert to wireless subscriber 20, resulting in a ring signal. When wireles~ ~ubscriber 20 answers the call, the now communicaling base station (17) will send an off-hook signal by way of subscriber link~ 101 (~ia W~ 12) to PBX 11 80 as to 10 provide the final connection and establish communication from the originator to wireless subscriber 20.
Call origination from wireless subscriber 20 to a destination ~for example at the PSTN) is accomplished as follows.
l S When not in use, wirele~s subscriber 20 resides on an idle channel that i8 tranBDlitting idle protocol. Wireless subscriber 20 monitors the protocol until such time as the protocol i8 lost or wireless subscriber 20 begins placing a call. At such time as base stations 15, 16, 17, or 18 detect an origination attempt, by wireless 2 0 subsdber 20, the corresponding base station 15, 16, 17, or 18 will drop t~e idle channel protocol and connect through to the PBX 11 via WIB 12, and more specifically, via signaling links 100. PBX
11 will prepare to receive the call from wireless subscriber 20 by connecting subscriber 20 from wireline group 104 to base station 2 5 15, 16, 17, or 18 via the appropriate line of subscriber links 101. At this point, wireless subscriber 20 can send dialing information in one of two ways.
In the first method, the origination message, sent by 3 0 wireless subscriber 20, does not contain calling information and the o~igination message simply seizes an RF channel for a call.
In this case, the corresponding base station 15, 16, 17, or 18 connects to PBX 11 by way of subscriber links 101 and waits for a dial-tone. Upon hearing a dial-tone, wireless subscriber 20 3 ~ begins using any standard dialing protocol, such as dual-tone multi-firequency (DTMF) In an alternative method, a base station 15, 16, 17, or 18 receives all the necessary calling iDformation in the origination 4 0 me~age. The corresponding base station 15, 16, 17, or 18 then goes off-hook. Upon receipt of a dial-tone from PBX 11, the corresponding base station 15, 16, 17, or 18 couples to wireles~
subscriber 20 and, at this point, the call may proceed as a nonnal wireline call 211~7~7 ::
g . ~., Channel selection, in accordance with l he in~ention, and ~ :
for assignment to the wireless subscnber (20), i~ performed by the processor (206) based upon measurements perfo~ned by the

5 scan receiver (19). Under the preferred embodiment of the invention, the processor (206) directs the scan receiver (19) to scan channel~, al80 u8et by the local cellular radiotelephone ~ :
system, for pu~pose~ of identif ying chamlels usable within the PBX wireless system (10). The processor (206) directs su~
scanning through commands generated within the processor : ~
(206) and transferred to the scan receiver controller (14) through ~ ~:
the VO controller (203) and signaling interface (13). The ~can rece*er controller (14), in tlLrn, directs scanning of channels by the scan receiver (19) based upon commands received from the l 5 processor (206).
The scan receiver (19), upon scanning channels. returns 8 signal quality factor (such as a received signal strength indicator (RSSI)) to the proces~or (206), through the 8CaI- receiver 2 0 controller (14) for each scanned channel. Signal quality factors are returned, along with a channel identifier, to the processor (206) through the signaling interface (13) and VO controller (203).
The returned signal quality factors are compared, within 2 5 1 he processor (206), with a threshold value. Cha~nels having a signal quality factor exceeding the threshold are deemed to be usable channels within the wireless system (10). A list of usable channels iB created within the data store (209) of the WIB (12).
3 0 Upon receipt of a page respon~e (or upon receipt of a request for ser~ice) the processor (206) may select a usable channel from the list within data store (209) for assignInent to the wireless gubscriber (20-22). In advance of assignInent the processor (206) may direct the scan receiver (19) to again scan the 3 5 channel in anticipation of assignment. Channels that are found ugable are assigned. Channels that are found not to be usable are removed from the list. :
Channel scanning may also occur on channels used by the 4 0 base stations (15-18) for the transmi~sion of control information.
Such ficanning v~ould occur at regular intervals to insure reliable operation of the v~ireless PBX system (10). Upon detection of interferers base stations (15-18) would change -channels for transmission of control information.

2 ~ ~ 8 ~17 - 1 o -Channel scanning and reuse of cellular channels within the PBX wirele~s system (10) beneficially allows for improved 5 communication within localized area such as shopping malls, factories, or sports facilities. Such reuse by private system~
offers the advantsge of mobile com nunication in areas that by their nature may limit interference to nearby cellular systems.
Such limited interference occurs because of the use of distributed 10 base station~ antennas and low power levels between base station and wireless unit. Where isuch private uBe i8 provided by base stations on different floors of the siame building, and limited by power levels and anteIma facilities, the private system may coexist on the ssme channel or set of channels within the same 15 system without significant mutual interference v~ithin the private system or the locial cellular syi~tem.

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Claims

1. In a wireless private branch exchange communication network located within a service coverage area of a cellular communication system ant reusing cellular communication resources, a method of identifying network communication resources, such method comprising the steps of: measuring a signal quality factor of a cellular system communication resource; comparing the measured value with a threshold value;
and when the measured value exceeds the threshold, selecting the communication resource as a network communication resource.

2. The method as in claim 1 further including repeating the measurement, comparison, and selection for each communication resource within a selected spectrum.

3. The method as in claim 2 further including transferring an identifier of selected communication resource to a network controller of the wireless communication network.

4. The method as in claim 1 further including transferring, by a network controller of the wireless communication network, an identifier of a communication resource to a scan receiver.

The method as in claim 4 further including measuring, upon receipt of the identifier, the signal quality factor of the communication resource by the scan receiver.

6. The method as in claim 5 further including transferring the measured signal quality factor of the communication resource back to the network controller.

7. In a wireless private branch exchange communication network located within a service coverage area of a cellular communication system and reusing cellular communication resources, an apparatus for identifying network communication resources, such apparatus comprising: means for measuring a signal quality factor of a cellular system communication resource; means for comparing the measured values with a threshold value; and means for selecting the communication resource as a network communication resources when the measured signal quality factor exceeds the threshold.

8. The apparatus as in claim 7 further comprising means for repeating the measurement, comparison, and selection for each communication resource within a selected spectrum.

9. The apparatus as in claim 7 further comprising means for transferring an identifier of selected communication resources to a network controller of the wireless communication network.

10. The apparatus as in claim 7 further comprising means for transferring, by a network controller of the wireless communication network, an identifier of a communication resource to a scan receiver.