United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,195,090
`
`Mar. 16, 1993
`[45] Date of Patent:
`Bolliger et a1.
`
`USOOSI95090A
`
`[54] WIRELESS ACCESS
`TELEPHONE-TO-TELEPHONE NETWORK
`INTERFACE ARCHITECTURE
`
`[75]
`
`Inventors: Brian D. Bolliger, Winfield, 111.;
`Talmage P. Bursh, Jr., South Orange;
`Marc K. Dennison, Berkeley Heights,
`both of N.J.; Michael J. English,
`Aurora, Colo.; Charles Y. Famell,
`Denver, Colo.; VMichel L. Hearn,
`Broomfield, Colo.; Richard M.
`Heidebrecbt, Boulder, Colo.; Kelvin
`K. Ho, Somerset, N.J.; Kenneth Y.
`Ho, Syosset, N.Y.; David M. Kissel,
`Boulder, Colo.; Paul E. Miller;
`Richard D. Miller, both of
`Northglenn, Colo.; Alan S. Mulberg,
`Boulder, Colo.; LaJeana N. Roberts,
`Bedminster, N.J.; Michael A. Smith,
`Westminster, Colo.; Kenneth F.
`Smolik, Naperville, 111.; Douglas A.
`Spencer, Boulder, Colo.; Kenneth W.
`Strom, Naperville, 111.; John S.
`Thompson, Boulder; Richard A.
`Windhausen, Westminster, both of
`C010.
`
`[73] Assignee: AT&T Bell Laboratories, Murray
`.
`Hill, NJ.
`
`[21] App1.No.: 727,498
`
`[22] Filed:
`
`Jul. 9, 1991
`
`.................................. H04J 31/02
`Int. Cl.5
`[51]
`[52] U.S. C1. ..................................... 370/94.1; 370/60;
`370/95.3; 379/58; 379/59; 379/60; 455/33.1;
`455/332; 455/334
`[58] Field of Search ................. 370/94.1, 60, 79, 95.3,
`370/93; 379/58, 59, 60; 455/33, 33.1—33.4
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`...................... 370/60
`4,314,367 2/1982 Bakka et al.
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`9100658
`1/1991 World Int. Prop. 0. .
`9100660
`1/1991 World Int. Prop. 0. .
`
`9107020 5/1991 World Int. Prop. 0. .
`9107030
`5/1991 World Int. Prop. 0. .
`9107036 5/ 1991 World Int. Prop. 0. .
`9107037
`5/1991 World Int. Prop. 0. .
`
`OTHER PUBLICATIONS
`
`T. H. Murray “The Evolution of DDS Networks: Part
`1”, Telecommunications, Feb. 1989, pp. 39—47.
`(List continued on next page.)
`
`Primary Examiner—Douglas W. Olms
`Assistant Examiner—Russell W. Blum
`Attorney, Agent, or Firm—David Volejnicek
`
`[57]
`
`ABSTRACT
`
`A wireless-access communications system, such as a
`CDMA cellular radio-telephone system (FIG. 2), com-
`prises a packet-switched communications network (202,
`207, 201) that interconnects cells (base stations; 202)
`with each other and with the public telephone network
`(100). Traffic of individual calls is packetized, and pack-
`et-bean'ng frames (300 in FIG. 7) of a plurality of calls
`are then statistically multiplexed and frame-relayed
`through the network to yield the high capacity, effi-
`ciency, and speed of traffic transport and handoff re-
`quired for a CDMA cellular system. At each call pro-
`cessing unit (264 in FIG. 5), individual calls are handled
`by individual service circuits (602 and 612) which per-
`form speech-processing functions such as coding and
`decoding,
`tone insertion, and echo cancellation, and
`packet-to—circuit-switched-PCM traffic
`conversion.
`Processors (602) adapt call processing unit timing to
`compensate for asynchrony between cells and call pro-
`cessing units and variations in call path transmission
`delays. Cell-to-cell communications,
`fixed call path
`addressing, and packetized control message transfers
`ensure that
`the same service circuit handles a call
`through even multiple soft handoffs (FIGS. 27—29) and
`efficiently communicates simultaneously with all cells
`involved in the handoff without involvement of system
`control entities and negative effect on system callohan-
`dling capacity. Both coded (packet-switched) and un-
`coded (circuit-switched)
`radio-telephone traffic are
`accommodated side-by-side. Wherever possible, exist-
`ing and proven technology and component units are
`used to achieve low cost and high reliability.
`
`57 Claims, 32 Drawing Sheets
`
`
`
`CLEARWIRE 1011
`
`

`

`
`Page 2
`
`5,195,090 .
`
`US. PATENT DOCUMENTS
`
`OTHER PUBLICATIONS
`
`4,494,230
`4,535,448
`4,562,572
`4,599,490
`4,617,674
`4,672,658
`4,680,786
`4,698,839
`4,726,014
`4,742,514
`4,765,753
`4,797,947
`4,894,822
`4,901,307
`4,975,939
`4,977,577
`4,984,247
`4,989,204
`5,005,171
`5,01 8,187
`5,022,024
`
`1/1985
`8/1985
`12/1985
`7/1986
`10/1986
`6/1987
`7/1987
`10/1987
`2/1988
`5/1988
`8/1988
`1/1989
`1/1990
`2/1990
`12/1990
`12/1990
`1/1991
`1/1991
`4/1991
`5/1991
`6/1991
`
`Turner .................................. 370/60
`Baxter et a].
`......
`370/85
`
`Goldman et al. ............. 370/80
`
`Cornell et a1.
`........
`179/2 EB
`
`Mangulis et al. ........... 375/1
`
`Kavehrad et a1.
`. 379/63
`
`Baker et a1. ............ 379/60
`DeVaney et al. .
`..... 379/60
`
`455/33 X
`Goldman et a1.
`.
`
`.. 370/109
`Goode et a].
`
`Schmidt ........
`379/60
`
`Labedz ............... 455/33
`
`Buhrke et a1.
`370/60
`370/18
`Gilhousen et a1.
`
`Sasaki ................
`
`375/1
`.....
`Arthur et a1.
`...... 375/1
`Kaufmann et a1.
`
`.......
`370/94.l
`Shimizu et a1.
`
`Modisette, Jr. et a]. .
`370/ 110.1
`Marinho et a1. .................. 379/60
`..................... 370/79 X
`Paneth et a1.
`
`Bell Labs News, Feb. 19, 1991, pp. 1, 4—7.
`N. S. Jayant et al., “Coding of Speech and Wideband
`Audio”, AT&T Technical Journal, vol. 69, No. 5 (Sep.-
`/Oct. 1990), pp. 25—41.
`P. Binney, “Signal-Processing Chip Boasts Design
`Breakthroughs”, Bell Labs News, Apr. 15, 1991, p. 5.
`“TDMA and FDMA: The Different Technologies Ex-
`plained”, Cordless Times. 1990 Issue 0 (Ericsson Radio
`Systems BV), pp. 10—11.
`“New Capabilities of the Definity Generic 2 Switch,”
`Definity TM 75/85 Communications System, Generic 2.
`Issue 1, (Feb., 1989).
`,
`AT&T Information Systems, Doc. #555-104—401, pp.
`2-6 to 2-15.
`
`K. W. Strom, “On the Road with Autoplex System
`1000”, AT&T Technology, vol. 3, No. 3 (1988), pp.
`42—51.
`
`W. J. Hardy et 31., “New Autoplex Cell Site Paves the
`Way for Digital Cellular Communications”, AT&T
`Technology, vol. 5, No. 4 (1990), pp. 20-25.
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 1 of 32
`
`5,195,090
`
`F]G 1
`
`PRIOR ART
`
`. MOBILE SWTCHING CENTER (NSC) b199
`
`r -------------- 1
`
`
` PUBLIC
`
`TELEPHONE
`NETWORK
`
`
`
`
`

`

`5,195,090
`
`US. Patent
`
`3991
`
`E2525..QJm53% 3:8asEN.uhm
`m_5:8...532.u«23~
`
`r.2.58
`
`one:
`
`£255:
`
`mis.fi/0use;.22.583.28%.nmgm53%\.&V2252
`
`
`
`
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 3 of 32
`
`5,195,090
`
`FIG. 3
`
`I 0 i
`
`244
`
`CHANNEL
`ELEMENTS
`
`245
`
`DSI
`INT R
`E FACE
`
`207
`
`
`
`
`
`
`CONTROLLER
`
`
`243
`DIGITAL
`
`
`
`, RADIO
`
`CLUSTER
`
`
`CTRLR.
`
`243
`
`245
`
`
`
` CHANNEL
`DIGITAL
`
`RADIO
`
`
`
`
`243
`CLUSTER CIRLR. 244
`BUS 391
`
`DIGITAL
`CHANNEL
`
`
`
`
`
`CBUS 390
`
`RADIO
`
`5ELEMENT S
`
`242
`
`031
`
`INTERFACE
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 4 of 32
`
`5,195,090
`
`{inunnunnuuuBEEFEIIIIIIIIII
`
`8—.._F—MIQIL_.-«mu
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`
`
`
`
`
`BEE;zo_mz§xu;8:52.Go:
`
`
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 5 of 32
`
`5,195,090
`
`FIG. 5
`
`SPEECH
`
`
`
`
`
`coomc
`
`
`231
`CONTROLLER
`MODULE
`
`
`133
`
`
`F"fag:—7
`
`r--
`-1
`LINTERFACEJ
`
`
`
`
`
`SPEECH
`PROC.
`
`INTERFACE
`UN”
`
`
`(no. 6)
`
`
`
`
`263
`
`210
`
`EXPAN$ON
`INTERFACE
`
`132
`
`DST
`
`210
`
`
`
`EXPANSION
`Slfégg”
`051
`I INTERFACE I. UNIT' I. INTERFACE I
`
`106
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 6 of 32
`
`5,195,090
`
`”.8302".
`
`.50
`
`5&8
`
`5&2.
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`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 7 of 32
`
`5,195,090
`
`FIC. 7
`
`300
`
`301
`
`FLAG
`
`DLCI
`
`CONTROL
`
`LEVEL-3/PACKET
`PROTOCOL
`
`302
`
`303
`
`304
`
`305
`
`FIG. 8
`
`'510
`
`
`
`BOARD ADDR.
`
`PORT ADDR.
`
`DLCI
`
`
`
`CONTROL
`
`LEVEL-S/PACKET
`PROTOCOL
`
`
`
`
`
`
`305
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 8 of 32
`
`5,195,090
`
`FIG. 9
`
`350
`
`
` PACKET TYPE
`SEQUENCE NUMBER
`
`CLOCK ADJUST
`
`AIR CRC
`
`SIGNAL QUALITY
`
`POWER CONTROL
`
`VOICE/SIGNALUNG TYPE
`
`321
`
`320
`
`322
`
`323
`
`324
`
`325
`
`326
`
`
`
`
`
`
`
`
` VOICE/SIGNALLING DATA
`327
`
`FIG. 10
`
`351
`
`PACKET TYPE
`
`MESSAGE TYPE
`
`CHANNEL ELEMENT I.D.
`
`FRAME SELECTOR I.D.
`
` 321
`
`
`
`
`331 SIGNALLING DATA
`
`
`328
`
`329
`
`330
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 9 of 32
`
`5,195,090
`
`FIG.
`
`1 1
`
`PERFORM LEVEL-2
`
`LAPD PROCESSING
`
`904
`
`906
`
`DOES FRAME
`HAVE LEVEL 3 PROTOCOL
`YES
`SELECT ASSOCIATED CALL’S STATE
`
`908
`
`910
`
`RETURN
`
`SIGNALLING
`
`
`
`
`
`
`PERFORM
`SIGNALLED
`FUNCTION
`(UPDATE CALL
`STATE/INSERT
`TONE/ADJUST
`CLOCK
`
`970
`
`
`
` THRESHOLD
`COMPARE AIR CRC AND VOICE
`QUALITY OF BOTH FRAMES
`
`
`
`
`41
`
`PACKET
`
`
`
`
`TRAFFIC
`9
`
`FRAME
`
`
`UPDATE
`MARK TRAFFIC
`FRAME AD
`CALL
`
`
`
`MARK BETTER TRAFFIC FRAME COOD
`'
`
`II’IIR'I
`
`BUFFER RETTER TRAFFIC FRAME
`FOR VOCODER
`FWSJE?
`
`946
`
`921
`
`922
`
`RETURN
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 10 of 32
`
`5,195,090
`
`FIG. 12
`
`95°
`
`952
`
`951
`
`XIh BUFFER
`EMPTY
`
`953
`
`
`PASS CONTENTS OF
`XIh BUFFER T0 VOCODER
`
`
`
`NASKING
`
`
`
`
`INVOKE VOCODER
`
`
`
`
`RETURN
`
`FIG. 13
`
`
`
`955
`
`
`REVERSE
`
`
`EDWARD
`
`SIGNALLING
`DIRECTION
`
`BOTH
`
`STORE FORWARD
`SIGNALLING
`
`956
`
`STORE
`
`
`
`
`
`
`
`964
`
`
`
`UPDATE
`
`CALL STATE
`
`
`COMPARE AIR CRC
`AND SIGNAL OUAUTY
`OF BOTH PACKETS
`
`
`958
`
`RECEIVED
`
`
`
`
`SIGNALLING
`PACKETS FROM
`
`-OTH SIDES
`
`
`YES
`
`UPDATE CALL STATE
`
`STORE
`SIGNAL ING
`
`
`
`STORE BETTER
`
`SIGNALLING
`
`
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 11 of 32
`
`5,195,090
`
`FIG. 14
`
`985
`
`SIGNALLING
`DIRECTION
`
`BOTH
`
`STORE FORWARD
`
`
`FOWARD
`
`986
`
`
` REVERSE
`
`
`
`
`SIGNALLING
`
`SIGNALLING
`
`STORE
`
`989
`
`RECEIVED
`PACKETS FRON
`
`0TH SIDES
`
`
`
`
`YES
`UPDATE CALL STATE
`
` UPDATE
`
`CALL STATE
`
`
`
`COMPARE AIR CRC
`AND SIGNAL OUAUTY
`
`OF BOTH PACKETS
`
`STORE BETTER
`
`SIGNALUNG
`
`
`
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 12 of 32
`
`5,195,090
`
`FIG. 15
`
`1 200
`
`START
`
`
`I 202
`
`
`CALL
`IN SOFT
`
`- NDOFF
`
`
`YES
`
`NO
`
`1206
`
`1204
`
`YES
`
`1 208
`
`
`
`
`IS
`
`FORWARD
`
`SICNALLINC STORED
`FOR THE CALL
`
`REQUEST FULL-RATE-
`REQUEST PARTIAL-RATE-
`ODED TRAFFIC FRAME
`CODED TRAFFIC FRAME
`
`FROM VO 0 R
`FROM V0 OIER
`
`
`1209
`
`FROM VOCODER
`
`121 I
`
`1212
`
`I
`WAP STORED POWER CONTRO
`
`FROM CAU. STATE INTO OTHER
`CELL’S PACKET
`
`1218
`
`NO
`
`
`
`
`TRAFFIC
`FRAME PARTIAL-RATE-
`CODED
`
`
`,
`
`
`‘
`IS
`
`NO
`
`FORWARD SIGNALLINC
`STORED FOR THE
`
`
`1227
`
`REQUEST FULL-RATE-
`CODED TRAFFIC FRAME
`FROM 'VOCODER
`
`GET TRAFFIC FRAME
`
`FROM VOCODER
`
`1228
`
`1 230
`
`FORMAT TRAFFIC FRAME
`
`IN LEVEL-3 PACKET
`
`1232
`
`1234
`
`1236
`
`ENCAPSULATE PACKET
`IN LAPD FRAME
`
`PREPEND BOARD
`AND PORT ADDRESS
`TO LAPD FRAME
`
`HAND MODIFIED LAPD
`FRAME OVER TO LAN
`BUS INTERFACE
`
`1238
`
`RETURN
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 13 of 32
`
`5,195,090
`
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`US. Patent
`
`Mar. 16, 1993
`
`Sheet 14 of 32
`
`5,195,090
`
`FIG. 17
`
`1050
`
`
`ADJUST CLOCK
`
`LATER
`
`MOVE
`
`
`1 052
` WHICH
`EARLIER
`
`WAY IS CLOCK TO
`
`
`
`
`
` MOVE TX_INT_X
`
`EARLIER BY TIME Y
`
`
`
`
`1060
`
`
`
`INCREASE OFFSET
`DECREASE OFFSET
`OF VOCODER OUTPUT
`
`
`OF VOCODER OUTPUT
`
`CLOCK BY TIME Y
`CLOCK BY TIME Y
`
`
`
`MOVE TX‘_INT_X
`LATER BY TIME Y
`
`1058
`
`
`
`

`

`US. Patent
`
`Mar. 16, 1993
`
`Sheet 15 of 32
`
`5,195,090
`
`
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`US. Patent
`
`h4ar.16,1993
`
`Sheet 16 of 32
`
`5,195,090
`
` E
`
`
`
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`Mar. 16, 1993
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`Mar. 16, 1993
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`US. Patent
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`Mar. 16, 1993
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`US. Patent
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`Mar. 16, 1993
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`Sheet 32 of 32
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`

`1
`
`5,195,090
`
`WIRELESS ACCESS '
`TELEPHONE-TO-TELEPHONE NETWORK
`
`INTERFACE ARCHITECTURE
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`B. D. Bolliger, T. P. Bursch, Jr., K. K. Ho, A. S.
`Mulberg, L. N. Roberts, K. F. Smolik, D. A. Spencer,
`K. W. Strom, and J. S. Thompson, “Mobile-Telephone
`System Call Processing Arrangement”, U.S. Ser. No.
`07/727,520 filed on even date herewith and assigned to
`the same assignee;
`C. Y. Farwell, M. L. Hearn, R. M. Heidebrecht, K.
`K. Ho, and D. A. Spencer, “Adaptive Synchronization
`Arrangement”, U.S. Ser. No. 07/727,491 filed on even
`date herewith and assigned to the same assignee; and
`C. Y. Farwell, M. L. Heam, R. M. Heidebrecht, K.
`K. Ho, and D. A. Spencer, “Adaptive Synchronization
`Arrangement”, U.S. Ser. No. 07/727,492 filed on even
`date herewith and assigned to the same assignee.
`TECHNICAL FIELD
`
`This invention relates to wireless-access, and particu-
`larly to cellular radio-telephone,
`telecommunications
`systems.
`
`BACKGROUND OF THE INVENTION
`
`Wireless-access telecommunications systems are well
`known in the art. They provide over-the-air (e.g., radio
`wave, infrared) connections between user communica-
`tion terminals and a communications switching and
`transport network such as the telephone network. An
`illustrative example thereof are cellular radio-telephone
`systems.
`In cellular radiodelephone systems, a plurality of
`radio cells, also referred to as base stations, are dis-
`persed through a geographical area and each provides
`radio-telephone service to radio-telephones in its vicin-
`ity, referred to as a cell zone. The cells are convention-
`ally connected to the public telephone network through
`a circuit-switched communications network known in
`the art collectively as a Mobile Telephone Switching
`Office (MTSO) or Mobile Switching Center (MSC).
`When a mobile radio-telephone crosses from one cell
`zone to another, its servicing is transferred from the cell
`serving the one cell zone to the cell serving the other
`cell zone through a process known as a “hard handoff’.
`Adjacent cell sites operate at different radio frequen-
`cies, so a “hard handoff" involves a change in the radio
`frequency that is used to service the mobile telephone.
`This change in turn requires the cellular radio-tele-
`phone system to make a second communications con-
`nection to the mobile radio-telephone and to simulta-
`neously drop the first connection. This takes time and
`uses processing capacity and switching fabric resources,
`thereby having a negative impact on the system’s call-
`carrying capacity.
`Mobile telephony is very popular, and the number of
`mobile radio-telephones is growing. This results in con-
`gestion of the presently-allocated radio-frequency spec-
`trum and a need to more efficiently use that radio-fre-
`quency spectrum. The conventional mobile radio-tele-
`phony technique, known as frequency-division multi-
`ple-access (FDMA), tries to maximize capacity by split-
`ting available bandwidth into separate channels in the
`frequency domain (e.g., into 30 KHz Channels). But the
`
`2
`radio-frequency spectrum that is allocated to mobile
`radio-telephone service is limited to 60 MHz.
`A capacity—expanding technique, known as time-divi-
`sion multipleaccess (TDMA) is known in the art and is
`a subject of technical standardization. It is a digital
`radio technique that splits each 30 KHz channel fre-
`quency into a plurality of time slots, each one or more
`of which can then act as a separate channel. The hand-
`off procedure is similar to that used for conventional
`mobile radio-telephony, so the TDMA technique can in
`many instances be handled through conventionally-
`structured radio-telephone systems with only a change-
`out ‘of the radio, i.e., the radio-frequency transmission
`and reception, equipment. But it only increases total
`system capacity approximately three-fold for mobile
`applications, which may not be adequate in many con-
`gested areas where cellular communications traffic is
`very high.
`An alternative capacity-expanding technique, known
`as code-division multiple-access (CDMA) has been
`proposed. It is a dynamic transmission-power control
`and digital direct-sequence spread-spectrum technique
`that allows reuse of the same radio-frequency spectrum
`in adjacent cells. It yields up to approximately a twenty-
`fold increase in capacity over conventional FDMA
`systems. Mobile telephones in a CDMA cellular radio-
`telephone system may undergo “hard handoff” between
`cells. But, due to the frequency reuse between adjacent
`cells, a mobile radio~te1ephone that is crossing from one
`cell zone to another may sometimes find itself commu-
`nicating with two cells on the same radio channel at the
`same time, a situation known as “soft handoff”. A whole
`sequence of “soft handoffs” may occur as a mobile
`radio-telephone moves through a series of cells.
`Handling of CDMA call capacity and “soft handoff’
`is not easily accomplished in a mobile radio-telephone
`system having the conventional FDMA architecture.
`This is due in large measure to the fact that the in-
`creased call capacity of CDMA radio systems results in
`the communications network that
`interconnects the
`cells with the public telephone network having to han-
`dle up to twenty times as many calls as before. Further-
`more there are typically many more “soft handoffs” in
`a typical CDMA system that there are “hard handoffs”
`in a conventional system and the “soft handoffs” are
`typically of longer duration than “hard handoffs”, and
`' so the demands placed by “soft handoffs” on system
`resources and processing and switching facilities are
`more extensive and acute. Handling of “soft handoffs”
`additionally requires, inter alia: routing of the duplicate
`communications received from one mobile telephone at
`the two cells to a common call-processing point in the
`system, for selection in real time of one and discarding
`of the other duplicate communication; duplication of
`return communications and routing thereof to the two
`cells; and coordination of the operations of the two cells
`so that they transmit the duplicate return communica-
`tions to the mobile telephone at the same time. Conceiv-
`able ways of meeting these requirements in convention-
`ally-architected radio-telephone systems appear to be
`awkward, inefficient, complex, and expensive.
`Furthermore, since each radio at a cell typically re-
`quires a unique trunk connection to the telephone net-
`work, handing off of a call from one radio to another
`radio requires the mobile-telephone switching fabric to
`be reconfigured to connect the new radio and trunk to
`the original network trunk connection. In conventional
`systems, the total system capacity is a function of the
`
`10
`
`15
`
`20
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`
`

`

`3
`amount of initial radio-to-network trunk connections
`the system can handle and the amount of reconfigura-
`tion (i.e. handoff) the system must perform. The recon-
`figuration requires intervention of the system control
`structures, and the length of time required for recon-
`figuring these trunks increases the complexity of these
`system control structures. CDMA systems'require es-
`tablishment of a second radio connection for “soft hand-
`off" at rates faster than those needed for traditional
`handoffs, thereby taxing or exceeding the processing 10
`and reconfiguration capabilities of systems of conven-
`tional design.
`SUMMARY OF THE INVENTION
`
`5
`
`This invention is directed to solving these and other 15
`problems and disadvantages of the prior art. According
`to the invention, there is introduced a new system archi-
`tecture for wireless-access (such as cellular radio-tele-
`phone) systems which uses packet-switching techniques
`to transport communications between the base stations 20
`(cells) and the radio-telephone call-processing and
`switching equipment. While the wireless-access voice
`communication traffic is deterministic in nature when
`speech is taking place,
`the system architecture is
`uniquely configured to permit non-deterministic, statis- 25
`tically-distributed
`packet-switching,
`techniques
`to
`transport that traffic without degradation in the voice
`quality. For purposes of this discussion and claims,
`deterministic events are events whose occurrence is
`known about and exactly anticipated prior to their oc- 30
`currence, in that they occur with regularity. In contrast,
`non—deterministic events are ones which may occur
`with irregularity, so that their precise occurrence can-
`not be predicted with exactitude.
`While the discussion of an illustrative embodiment 35
`that follows makes a distinction between level-3 “pack-
`ets" and level-2 “frames” for purposes of clarity, the use
`of the term “packet” herein and in the claims is intended
`to encompass either or both “packets” and “frames”.
`Radio-telephone call traffic is transferred in packets 40
`between cells and switching systems, and the packets of
`a plurality of calls are statistically multiplexed on the
`communications links that interconnect the cells and the
`
`switching systems. Statistically-mu]tiplexed packet
`transmissions result in highly-efficient use of the band- 45
`widths of the links and provide the throughput and
`call-handling capacity required to handle the traffic of a
`CDMA radio-telephony system. Furthermore,
`the
`packet transfers are made using the frame-relay tech-
`nique, which significantly increases transfer efficiency 50
`and throughput of the radio-telephony system by elimi-
`nating processing of packet protocols at all nodes of the
`system other than at the transfer endpoints. The packet
`transfers are advantageously made via time-division-
`multiplexed links, over channels which may be n.64 55
`Kbps wide, thereby allowing the architecture to make
`use of conventional telephony trunks for frame-relay
`transfers. In fact, the entire architecture of the system
`that interconnects cells with each other and with the
`public telephone network is ingeniously assembled from 60
`conventional and existing units wherever possible,
`thereby ensuring low system cost and high system reli-
`ability and operational confidence through the use of
`proven technology.
`The architecture is configured to provide efficient 65
`routing of traffic between a plurality of cells and a sin-
`gle call-processing unit for a call in “soft handoff.”The
`architecture thus enables a single call-processing unit to
`
`5,195,090
`
`4
`continue to handle the call from start to finish through
`numerous handoffs. This makes it possible to handle soft
`handoffs in a manner transparent to the parties to the
`call, and also simplifies the control that must be exerted
`within the system to effect the handoffs.
`This invention also solves the performance obstacles
`to “soft handoff” by utilizing the packet-routing fabric
`to establish the second CDMA radio connection. The
`radio channel unit that is initially handling the call
`passes address information to a second radio channel
`unit via a cell-to-cell data exchange. This second cell
`connects to the specified address using a virtual circuit,
`in the manner of a call establishment procedure. The
`result is a second radio connection established without
`any intervention of the main call-processing controllers.
`This reduces the load placed on these processors and
`allows for very fast radio and trunk reconfigurations.
`Though the architecture is designed for efficient han-
`dling of cellular CDMA radio-telephony traffic, the
`architecture is general and versatile enough to accom-
`modate other forms of digital voice traffic, such as
`TDMA radio-telephony traffic, or even to accommo-
`date conventional and TDMA radio-telephony traffic
`side-by-side with the CDMA traffic in the same system.
`Consequently, the architecture may be used for a wide
`variety of wireless-access telephony systems, and may
`also be used to grow existing radio-telephony systems
`by supplementing and expanding them—instead of hav-
`ing to replace them—with CDMA—capable radio-tele-
`phony equipment.
`This architecture also allows for verification of
`switch fabric connectivity in a non—disruptive fashion.
`While conventional systems require removal of a trunk
`from service, sending of specific tones over that trunk,
`and listening for those tones returning, to verify con-
`nectivity, no configuration is required with the packet
`transport system characterized above. Rather,
`test
`packets are addressed to test addresses and echoed back
`to the sender without disrupting the other frames travel-
`ing over that path. Thus, each test can be executed very
`quickly and fairly often, allowing for the near-immedi-
`ate detection of connection losses. Unlike existing sys-
`tems, a system architected according to the invention
`need not wait for a call to fail before detecting trouble.
`Specific advantageous aspects of the disclosed em-
`bodiment of the architecture are as follows:
`Call traffic units received or transmitted over the air
`are packetized by first wrapping them in a level-3 proto-
`col tailored to the application and then wrapping them
`in CCITT LAPD frames for transmission over a D51
`facility to or from a switching system.
`Information is carried to and from the switching
`system on DSl facilities in a non-channelized (“fat
`pipe”) format.
`A static addressing plan is used wherein the LAPD
`protocol Data Link Connection Identifier (DLCI) re-
`fers generally to a cluster controller at the cell in the
`forward (outbound) direction and specifically identifies
`a radio channel or channel element in the forward direc-
`
`tion, and refers generally to a speech processing unit
`(SPU) service circuit in the mobile telephone switching
`system in the reverse (inbound) direction and specifi.
`cally identifies a virtual port on the service circuit in the
`reverse direction. This static addressing plan allows
`handoffs to occur with minimal software intervention,
`greatly minimizing the handoff time for soft handoffs.
`
`

`

`5,195,090
`
`5
`Use of the static addressing plan reduces the process-
`ing needed to perform handoffs, thus increasing system
`capacity.
`Use of frame relay to perform handoffs eliminates the
`use of additional switch fabric and trunks during hand-
`off, which also increases system capacity.
`The level-3 protocol includes information to audit
`connections and to orchestrate handoffs.
`LAPD frames received from a cell are frame-relayed
`from the D81 interface associated with the cell to a port
`on a given speech processing unit service circuit based
`on LAPD link-level addressing. This frame-relaying
`connectivity accommodates variable bit~rate coding of
`the information flow received from the cell site and
`provides low delay in both forward and reverse direc-
`tions in the speech processing unit-to-cell path.
`At call set-up time, a port on a speech processing unit
`service circuit is associated with a port on a D81 inter‘
`face associated with a D81 facility connected to the
`public telephone network. Connectivity between this
`DSl interface and the speech processing unit port is
`provided on a time-division connection basis.
`The frame-relay structure allows parties to a soft-
`handoff to originate in switching modules other than
`the module in which a given call originates. Frame-
`relay connectivity is provided between switching mod-
`ules in a given switching system.
`The frame-relay structure allows for non-destructive
`auditing (verification and testing of virtual circuit paths
`through the network fabric).
`The architecture allows speech processing unit ser-
`vice circuits to be provided on an engineered basis, as
`needed for a given installation.
`The architecture allows mixing of traditional analog
`cellular traffic with CDMA or TDMA traffic within
`the same mobile telephone switching system, or a set of
`such systems. This mixing and matching allows for both
`efficient use of switching resources through shared use
`of switching fabric, and also efficient use of transmission
`resources by sharing of bandwidth with both CDMA or
`TDMA information flows in non-channelized form on
`wideband channels and traditional analog information
`flows on 64 Kbps channels.
`The architecture allows compatibility with software
`and control structures presently fielded for analog cel-
`lular applications, and allows for CDMA operation in
`conjunction with traditional operation. An evolution-
`ary path is thereby provided for evolution from all-
`analog systems to all-CDMA systems. It also efficiently
`supports the co-existence of both technologies in the
`same system.
`The architecture allows upgrades to provide for
`other digital cellular offerings, such as TDMA.
`These and other advantages and features of the inven-
`tion will become apparent from the following descrip-
`tion of an illustrative embodiment of the invention con-
`sidered together with the drawing.
`BRIEF DESCRIPTION OF THE DRAWING
`
`FIG. 1 is a block diagram of a conventional cellular
`radio-telephone system;
`FIG. 2 is a block diagram of a cellular radio-tele-
`phone system that incorporates an illustrative embodi-
`ment of the invention;
`FIG. 3 is a block diagram of a cell of the system of
`FIG. 2;
`FIG. 4 is a block diagram of a cell interconnect mod-
`ule of the system of FIG. 2;
`
`6
`FIG. 5 is a block diagram of a speech coding module
`of the system of FIG. 2;
`FIG. 6 is a block diagram of a speech processing unit
`of the module of FIG. 5;
`FIG. 7 is a block diagram of a LAPD frame of the
`system of FIG. 2;
`FIG. 8 is a block diagram of a modified LAPD frame
`of the system of FIG. 2;
`FIG. 9 is a block diagram of a level-3 protocol used
`for carrying voice and/or signalling informati