BAR CODE LABEL
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`U.S. PATENT APPLICATION
`
`SERIAL NUMBER
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`08/725,643
`
`FILING DATE
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`GLASS
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`GROUP ART UNIT
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`10/15/96
`
`455
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`2611
`
`ALEX K. RAITH, DURHAM, NC;
`GARNER, NC.
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`JAMES RAGSDALE, RALEIGH, NC; JOHN DIACHINA,
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`*JO0NTINUING DATA*********************
`VERIFIED
`
`**FOREIGN/PCT APPLICATIONS************
`VERIFIED
`
`FOREIGN FILING LICENSE GRANTED 01/29/97
`
`INDEPENDENT
`CLAIMS
`
`FILING FEE
`RECEIVED
`
`ATT-ORNEY DOCKET NO.
`
`12
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`1$2,632.00
`
`02 755 5-801
`
`RqNALD L GRUDZ IECKI
`BURNS DOANE SWECKER & MATHIS
`P P0 B0X1404
`A EXANDRIA VA 22313-1404
`
`M LTI-RATE RADIOCOMMUNICATION
`
`SYSTEMS AND TERMINALS
`
`This
`isaetf
`that annexed hereto is a true copy from the records of the United States
`nd Ctraemark Office of the application which is identified above.
`Patenta
`By auth rity of the
`COMMI SIONER OF PATENTS AND TRADEMARKS
`
`Date
`
`ICertifying
`
`Officer
`
`

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`ABSTRACT
`Variances in bandwidth used by a radiocommunication connection are
`adapted to by changing the type of information being transmitted. For example,
`in a TDMA environment, a first downlink time slot associated with a double- or
`triple-rate connection may have a first format, while a second time slot associated
`with the same connection may have a second format different from the first
`format. Bandwidth in the second (or third) time slot can be used to carry
`information in a fast out-of-band channel (FOC). The FOC may provide
`information relating to the same connection as the payload or data field in that
`time slot, e.g., a service type identifier which informs the mobile or base station
`of the type of information (e.g., voice, video or data) being conveyed in the
`payload. Alternatively, the FOG information may be associated with a
`connection or connections which are different from that supported by the payload
`or data field containing the FOG.
`
`

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`'A 1996
`
`q5p
`t
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`APPLICATION FOR UNITED STATES LETTERS PATENT
`
`by
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`Krister Raith, James Ragsdale and John Diachina
`
`for
`
`MULTI-RATE RADIOCOMMUNICATION SYSTEMS AND TERMINALS
`
`BURNS, DOANE, SWECKER & MATHIS, L.L.P.
`Post Office Box 1404
`Alexandria, Virginia 22313-1404
`(703) 836-6620
`
`Attorney's Docket No. 027555-801
`
`

`
`MULTI-RATE RADIOCOMMUNICATION SYSTEMS AND TERMINALS
`
`RELATED APPLICATION
`This application is related to U.S. Patent Application Serial No. L1Z.
`entitled "Radiocommunication Systems and Terminals with Increased Payload
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`Bandwidth", which application was filed on the same date as this application.
`
`BACKGROUND
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`Applicant's invention relates generally to radiocommunication systems,
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`e.g., cellular or satellite systems, that use digital traffic channels in a multiple
`access scheme, e.g., time division multiple access (TDMA) or code division
`multiple access (CDMA).
`The growth of commercial radiocommunications and, in particular, the
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`explosive growth of cellular radiotelephone systems have compelled system
`designers to search for ways to increase system capacity without reducing
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`communication quality beyond consumer tolerance thresholds. One way to
`increase capacity is to use digital communication and multiple access techniques
`such as TDMA, in which several users are assigned respective time slots on a
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`single radio carrier frequency.
`In North America, these features are currently provided by a digital
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`cellular radiotelephone system called the digital advanced mobile phone service
`(D-AMPS), some of the characteristics of which are specified in the interim
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`standard IS-54B, "Dual-Mode Mobile Station-Base Station Compatibility
`Standard", published by the Electronic Industries Association and
`Telecommunications Industry Association (EIA/TIA). Because of a large
`existing consumer base of equipment operating only in the analog domain with
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`frequency-division multiple access (FDMA), IS-54B is a dual-mode (analog and
`digital) standard, providing for analog compatibility in tandem with digital
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`communication capability. For example, the IS-54B standard provides for both
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`FDMA analog voice channels (AVC) and TDMA digital traffic channels (DTC),
`and the system operator can dynamically replace one type with the other to
`accommodate fluctuating traffic patterns among analog and digital users. The
`AVCs and DTCs are implemented by frequency modulating radio carrier signals,
`which have frequencies near 800 megahertz (MH-z) such that each radio channel
`has a spectral width of 30 kilohertz (KHz). A subsequent standard, referred to
`as IS-136, adds specifications for digital control channels. This standard
`document, in particular the version identified as PN-3474. 1, dated December 15,
`1995 and published by EIA/TIA, is incorporated here by reference.
`In a TDMA cellular radiotelephone system, each radio channel is divided
`into a series of time slots, each of which contains a burst of information from a
`data source, e.g., a digitally encoded portion of a voice conversation. The time
`slots are grouped into successive TDMA frames having a predetermined
`duration. According to IS-54B and IS-136, each TDMA frame consists of six
`consecutive time slots and has a duration of 40 milliseconds (msec). Thus, each
`frame can carry from one to six traffic channels (e.g., one to six radio
`connections). The number of connections which can be supported by each
`TDMA frame depends on the desired information transmission rate. For
`example, if the connections are used to support the transmission of voice
`information, the number of slots used per channel depends on the source rates of
`the speech coder/decoders (codecs) used to digitally encode the conversations.
`Such speech codecs can operate at either full-rate or half-rate, with full-rate
`codecs being expected to be used until half-rate codecs that produce acceptable
`speech quality are developed.
`
`Thus, a fuill-rate DTC requires twice as many time slots in a given time
`period as a half-rate DTC, and in IS-54B3, each radio channel can carry up to
`three full-rate DTCs or up to six half-rate DTCs. Each full-rate DTC uses two
`slots of each TDMA frame, i.e., the first and fourth, second and fifth, or third
`and sixth of a TDMA frame's six slots. Each half-rate DTC uses one time slot
`of each TDMA frame. During each DTC time slot, 324 bits are transmitted, of
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`which the major portion, 260 bits, is due to the speech output of the codec,
`including bits due to error correction coding of the speech output, and the
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`remaining bits are used for guard times and overhead signalling for purposes
`such as synchronization.
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`In addition to voice information being transmitted on the traffic channels,
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`various other types of data can and will be transmitted thereon. For example,
`facsimile (fax) transmissions are commonly supported by radiocommunication
`systems. Similarly, packet data transmissions, which divide information streams
`into packets rather than providing dedicated (i.e., "connection-.oriented"~)
`
`channels for each information stream, will be supported in radiocomununication
`systems. Other types of information transmission, e.g., video or hybrid voice,
`data and video to support internet connections, will likely be supported in the
`future.
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`These various types of information communication (also referred to herein
`
`as different "services") will likely have different optimal transmission
`characteristics. For example, services between a remote user and the internet
`may benefit by providing a greater bandwidth in the downlink (i.e., from the
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`internet to the remote station) than in the uplink, since many users spend a
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`significant portion of their connection time downloading information from the
`internet rather than uploading thereto. Thus, it may be desirable in such cases to
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`allocate a triple rate connection in the downlink (e.g., all six time slots of an IS-
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`136 TDMA frame) but only a full rate connection in the uplink (e.g., two time
`slots of an IS-136 frame). This inequality between uplink and downlink
`In addition to
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`bandwidth is referred to herein as an "asymmetrical" connection.
`bandwidth considerations, other transmission characteristics may also be
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`impacted. For example, different services may require different degrees of error
`protection. Thus, for example, an optimal channel coding for the transmission of
`voice information might be rate 1/2 since voice information transmission is
`typically not provided with a procedure for retransmission, while optimal channel
`coding for the transmission of data, e.g, facsimile, might be rate 5/6 since
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`retransmission procedures are typically provided. Other transmission
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`characteristics, for example, the ability to tolerate delay in the reception of
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`information, may also vary between services. All of these differences in
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`transmission characteristics should be considered together when determining an
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`optimal specification for the air interface.
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`Accordingly, it would be desirable to provide techniques for transmitting
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`information between remote stations and the system in radiocommunication
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`networks that provide sufficient flexibility for the anticipated variety of
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`information communication services described above, while also providing
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`sufficient compatibility with existing technology so that equipment used by the
`existing consumer base will not become obsolete.
`
`SUMMARY
`According to exemplary embodiments of the present invention, the type of
`
`information transmitted in the uplink or downlink may vary depending upon the
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`transmission rate. For example, in a TDMA environment, a first downlink time
`slot associated with a double- or triple-rate connection may have a first format,
`while a second time slot associated with the same connection may have a second
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`format different from the first format. The different formats take into account
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`the need to transmit certain types of information at only full rate, and not double-
`or triple-rate.
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`According to some exemplary embodiments, bandwidth in the second (or
`third) time slot can be used to carry information in a fast out-of-band channel
`(FOC). The FOC may provide information relating to the same connection as
`the payload or data field in that time slot, e.g., a service type identifier which
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`informs the mobile or base station of the type of information (e.g., voice, video
`
`or data) being conveyed in the payload. This information can be used by the
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`receiving equipment to aid in processing the information conveyed in the
`payload, e.g., by knowing the channel coding rate. These exemplary
`embodiments find particular application to multimedia communications where the
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`type of payload may vary rapidly, e.g., on a slot-by-slot basis, or even within
`each slot.
`
`Various exemplary mapping techniques for associating the FOC
`information with each time slot or each block of data which may be interleaved
`over two or more time slots are also described herein. These exemplary
`mapping techniques also account for the fact that there may not be FOC
`information provided in each time slot.
`According to other exemplary embodiments of the present invention, the
`FOC information may be associated with a connection or connection which is
`different from that supported by the payload or data field containing the FOC.
`For example, in asymmetrical connections, e.g., where a mobile station transmits
`in a different number of slots per frame than it receives, a downlink channel may
`carry payload to a first mobile station in the data fields in several time slots of a
`frame but the FOC may provide control information to one or more other mobile
`stations which are not interested in the payload. All of these mobile stations may
`share the same frequency on the uplink, e.g., the one or more other mobile
`stations may transmit packet data and use the FOC to receive retransmission
`requests.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The features and advantages of Applicants' invention will be understood
`by reading this description in conjunction with the drawings, in which:
`FIG. e'ls a block diagram of an exemplary cellular radio telephone
`system in whic,h- the present invention may be applied;
`FIG. P2 illustrates an exemplary TDMA frame structure;
`FIG. Y'illustrates a conventional downlink traffic channel time slot
`format;/
`FIG. 4 1 jdstrates triple rate downlink frame usage;
`FI.P) illustrates full rate uplink frame usage;
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`FIG. 5 illustrates a base station and three mobile stations communicating
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`therewith;
`FIG., 6 illustrates downlink time slot formats according to a first
`exemplary embodiment of the present invention;
`FIG. 7Aillustrates downlink time slot formats according to a second
`exemplary embodiment of the present invention;
`FIG. 7B illustrates downlink time slot formats according to a third
`exemplary embodiment'of the present invention;
`FIGS. 868'illustrate exemplary mappings of FOC informnation to
`payload according to various exemplary embodiments of the present invention;
`flowchart illustrating an exemplary, alternative usage of an
`FIG. 9/is
`FOC field by mobile station according to the present invention;
`FIG. 10 is a' conventional format for all uplink traffic channel time slots;
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`and
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`FIG. 41 is an exemplary format for two or more uplink traffic channel
`time slots according to an exemplary embodiment of the present invention.
`
`DETAILED DESCRIPTION
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`The following description is scripted in terms of a cellular radiotelephone
`system, but it will be understood that Applicant's invention is not limited to that
`environment. Also, the following description is in the context of TDMA cellular
`communication systems, but it will be understood by those skilled in the art that
`the present invention may apply to hybrid access methodologies, e.g,. those
`including TDMA and Code Division Multiple Access (CDMA).
`FIG. 1 represents a block diagram of an exemplary cellular mobile
`radiotelephone system, including an exemplary base station 110 and mobile
`station 120. The base station includes a control and processing unit 130 which is
`connected to the MSC 140 which in turn is connected to the PSTN (not shown).
`General aspects of such cellular radiotelephone systems are known in the art, as
`described by the above-cited U.S. patent applications and by U.S. Patent
`
`

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`-7-
`
`No. 5,175,867 to Wejke et al., entitled "Neighbor-Assisted Handoff in a Cellular
`Conmunication System," and U.S. Patent Application No. 07/967,027 entitled
`"Multi-Mode Signal Processing," which was filed on October 27, 1992, both of
`which are incorporated in this application by reference.
`The base station 110 handles a plurality of traffic channels through a
`
`traffic channel transceiver 150, which is controlled by the control and processing
`unit 130. Also, each base station includes a control channel transceiver 160,
`which may be capable of handling more than one control channel. The control
`channel transceiver 160 is controlled by the control and processing unit 130.
`The control channel transceiver 160 broadcasts control information over the
`control channel of the base station or cell to mobiles locked to that control
`It will be understood that the transceivers 150 and 160 can be
`channel.
`implemented as a single device, like the traffic and control transceiver 170 in the
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`mobile station, for use with control channels and traffic channels that share the
`same radio carrier frequency.
`The traffic channels can be used in a dedicated, connection-oriented
`manner to transmit information, e.g., for a voice connection, where each channel
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`is used continuously for a period of time to support transmission of a single
`stream of information or in a packet-oriented manner where each channel can be
`used to send independent units of information associated with different
`information streams. When used in the former sense, control channels and
`traffic channels will be referred to herein as DCCHs and DTCs, respectively.
`When used in the latter sense, control channels and traffic channels will be
`referred to herein as PCCHs or PDTCs, respectively. For more information
`regarding packet data radiocommunication systems generally, the interested
`reader is referred to U.S. Patent Application Serial No. 08/544,836, entitled
`"Packet Channel Feedback", filed on October 18, 1995, the disclosure of which
`is expressly incorporated here by reference.
`After an idle mobile station 120 has located a control channel, e.g., by
`using digital control channel location information found on a traffic channel, it
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`can then read the control information transmitted on that control channel, e.g.,
`paging messages, using its traffic and control channel transceiver 170. Then, the
`processing unit 180 evaluates the received control channel information, which
`may include, for example, paging messages or requests to measure signals
`strengths on identified channels. When a connection between the mobile station
`120 and the system is desired, the transceiver 170 will tune to an appropriate
`traffic channel as described below.
`An exemplary organization of the information transmitted on each radio
`channel, i.e., the channel bursts, or time slots, in accordance with Applicant's
`invention is shown in FIG. 2. The consecutive time slots on a radio channel are
`organized in TDMA frames of, for example, six slots each so that a plurality of
`distinct channels can be supported by a single radio carrier frequency. Each
`TDMA frame in this example has a duration of 40 msec and supports six half-
`rate logical channels, three full-rate logical channels, or greater bandwidth
`channels as indicated in the following table. Each slot can, for example, have a
`duration of 6.67 msec and carry 324 bits (162 symbols), which have positions in
`each slot that are conventionally consecutively numbered 1-324.
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`jUsed Slots
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`1,4
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`1,4,2,5
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`1,4,2,5,3,6
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`Number of Slots
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`11
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`2
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`4
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`6
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`Rate
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`half
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`full
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`double
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`triple
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`Currently, IS-136 defines a downlink DTC slot format as illustrated in
`FIG. 3. Therein, the numbers above each field denote the number of bits
`associated therewith. For example, the SYNC field is used for synchronization
`equalizer training and time slot identification. The SACCH (Slow Associated
`Control Channel) is a signalling channel used, for example, for transmission of
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`control and supervision messages between the mobile station and the base station.
`The two DATA fields are used to transmit the 'payload" of the slot, e.g., user
`information or control channel information as part of the FACCHI (Fast
`Associated Control Channel). The CDVCC (Coded Digital Verification Color
`Code) is a cell identifier that identifies the base station which is transmitting to
`the mobile station. The CDL (Coded Digital Control Channel Locator) is a
`pointer which can be used to indicate on which frequency, or set of frequencies,
`a digital control channel is likely to be found. Conventionally, this downlink
`format is used for each time slot in a TDMA frame, i.e., all six time slots for
`systems operating according to IS-136. According to the present invention,
`however, it may be desirable to provide alternative slot formats to accommodate
`the different communication services provided above.
`Consider again the situation where it is desirable to provide a triple rate
`connection in the downlink (i.e., base-to-mobile direction) and a full rate
`connection in the uplink (i.e., mobile-to-base direction). This situation is shown
`in FIGS. 4A and 4B. Therein, FIG. 4A illustrates a downlink frame wherein all
`six time slots are allocated to a particular mobile, as denoted by the cross-
`hatching of each of time slots 1-6. FIG. 4B illustrates a corresponding uplink
`frame. Note that only slots 1 and 4 are allocated to the particular mobile station
`which is using all of the time slots of FIG. 4A. Thus, the remaining time slots
`2, 3, 5 and 6 are unallocated and, conventionally, would go unused.
`Bandwidth being a precious commodity, exemplary embodiments of the
`present invention provide techniques for using unallocated bandwidth in a single
`link without adversely impacting compatibility with existing air interface
`specifications, e.g., IS-136. According to a first exemplary embodiment
`described below, the unused uplink time slots can be used to send packet data.
`Packet data communications support independent usage of uplink and downlink
`frequencies. Accordingly, packet data can be sent on the unused time slots in the
`uplink from one or more other mobile stations to the base station. Consider
`Figure 5. Therein, mobile station 500 is allocated the downlink and uplink time
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`slots illustrated in FIG. 4A and 4B for communicating with base station 505. To
`fully utilize the bandwidth resources according to the present invention, another
`mobile station 510 transmits packet data to base station 505 in a PDTC
`comprising time slots 2 and 5 of FIG. 4B, while a third mobile station 520
`transmits packet data to base station 505 on a PDTC comprising time slots 3 and
`6.
`
`If either of the mobile stations 510 and 520 require downlink bandwidth,
`then a downlink channel may be assigned on some other frequency, since mobile
`station 500 is using all of the time slots of the frequency represented by FIG.
`4A. Alternatively, it may be the case that, for a particular time period during a
`packet data connection which is referred to herein as an "activity burst", one or
`both mobile stations 510 and 520 only need to transmit packet data and,
`therefore, do not require downlink bandwidth for the purposes of receiving
`packet data. Nonetheless, mobile stations 510 and 520 will still need to receive
`overhead information from base station 505, e.g., relating to which packets were
`not received and whether each mobile station is allowed to transmit in a
`particular frame. Assigning a downlink PDTC purely for the transmission of
`such overhead information is spectrally inefficient. One solution would be to
`provide this overhead information to mobiles 510 and 520 on a PCCH and
`require the mobile stations to return to the PCCII periodically, e.g., after
`transmitting packets on the PDTC during the activity burst which lasts, for
`example, one second.
`However, according to exemplary embodiments of the present invention,
`another technique for providing overhead information to mobile stations 510 and
`520 using one or more downlink time slots whose data or "payload" fields are
`being used to transmit information to mobile station 500. Specifically, the
`downlink time slot format illustrated in FIG. 3 can be altered to (1) provide
`overhead information regarding packet data communications to mobile stations
`510 and 520, without (2) significantly altering mobile station 500's ability to
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`receive triple rate downlink information. FIG. 6 illustrates downlink time slot
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`formats according to this exemplary embodiment of the present invention.
`Therein, three downlink slot formats are illustrated for an exemplary
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`traffic channel according to the present invention. These three slot formats might
`correspond, for example, to slots 1, 2 and 3 of FIG. 4A. Slots 4, 5 and 6 would
`have the same format as slots 1, 2 and 3, respectively for this exemplary
`embodiment. Unlike conventional systems, e.g., those currently specified by IS-
`136, the downlink formats illustrated in FIG. 6 differ within the frame.
`Specifically, while time slot 1 has the same slot format as conventional downlink
`traffic time slots (see, e.g., FIG. 3), time slots 2 and 3 differ in that the
`SACCH, CDVCC and CDL fields of slot 1 have each been replaced by an FOC
`(fast out-of-band channel) field. It will be noted that, for the purposes of
`simplicity, the RSVD bit illustrated in FIG. 3 has been omitted. However, this
`bit may also be reserved and included in downlink slot formats according to the
`present invention.
`In the example described above, mobile station 500 is using a triple rate
`downlink connection, i.e., it is reading the data fields of each of time slots 1, 2
`and 3 in FIG. 6. However, some of the other fields provided in the conventional
`downlink time slot format of FIG. 3 need not be transmitted in each time slot
`under these circumstances. For example, the type of overhead signalling that
`occurs on the SACCH is such that mobile station 500 need not receive the
`SACCH at triple rate. That is, mobile station 500 may only need to receive one
`SACCH burst every three time slots. Thus the field that is normally used for
`SACCHZ
`information in slots 2 and 3 can be replaced by FOC information
`according to the present invention. The CDVCC field includes information that
`aids in the identification of the radio link and is conventionally used for radio
`link control, e.g., tearing down of a connection. However, this information can
`be provided to the mobile station over the control channel at call-setup and,
`accordingly, need not be transmitted by the base station in each downlink time
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`slot. Various techniques are described below to avoid problems caused by
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`omitting the CDL information from some downlink time slots.
`Omitting these fields in time slots 2 and 3 (as well as 5 and 6) provides
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`an opportunity to inform the other mobile stations, e.g., mobile stations 510 and
`520, of information pertaining to their uplink connections, without assigning a
`new PDTC or forcing mobile stations 510 and 520 to revert periodically to
`listening to the PCCII. For example, the FOG fields can be used to inform
`mobile station 510 or mobile station 520 that a previously transmitted packet was
`not properly received and should be retransmitted. Note that since the FOG
`information is "out-of-band' (i.e., is not encoded as part of the data), mobile
`stations 510 and 520 advantageously need not be aware of the channel coding and
`interleaving needed to read the data fields in time slots 2 and 3.
`Many variations of the foregoing exemplary embodiment are possible and
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`contemplated by the present invention. For example, although the foregoing
`example is provided in terms of an asymmetrical connection wherein the
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`downlink is triple rate and the uplink is full rate, any asymmetrical connection
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`lends itself to application of the present invention. For example, the downlink
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`may be double rate and the uplink full rate, whereupon the FOC fields would
`replace the SACCH, CDVCC and CDL fields in only one of slots 2 and 3
`illustrated in FIG. 6.
`Moreover, it may not be desirable to replace all three of the SACCH,
`CDVCC and CDL fields with FOG information. For example, it may be
`
`determined that 36 bits of FOG information is not needed. Alternatively, for
`
`compatibility reasons, it may be determined that one or more of the SACCH,
`CDVCC and CDL fields should be maintained in each downlink slot. Thus, for
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`example, downlink slot formats for the triple rate downlink/full rate uplink
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`example provided above could instead be as illustrated in one of FIGS. 7A and
`7B. Therein, the FOG replaces only the SACCH and CDVCC in FIG. 7A and
`only the SAGGCH in FIG. 7B. Those skilled in the art will appreciate that many
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`more variations exist, such as time slot 2 or 3 being the "master' channel having
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`the conventional slot format of FIG. 3 instead of slot 1.
`As mentioned above, exemplary embodiments of the present invention
`wherein the base station 505 only transmits the CDVCC and/or the CDL in some
`downlink slots of a traffic channel may cause difficulties for mobile stations that
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`expect this information in all time slots on a downlink traffic channel. For
`extensive information relating to the CDL and mobile functionality relating to
`locating digital traffic channels, the reader is referred to U.S. Patent Application
`Serial No. 08/331,711 entitled "Method and Apparatus for Locating a Digital
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`Control Channel in a Radiocommunication System", filed on October 31, 1994,
`In brief, the CDL
`the disclosure of which is incorporated here by reference.
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`field is used by unconnected mobile stations (e.g., at power-up) to locate a
`control channel if the first channel to which it tunes is a traffic channel.
`
`According to one exemplary technique, a mobile station reads the field
`corresponding to the CDVCC in the time slot to which it first tunes on a
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`frequency. This conventional mobile station will identify this field as either a
`CDVCC (implying a traffic channel per the format of FIG. 3) or a coded
`superframe phase (CSFP) (implying a control channel per IS-136). If a traffic
`channel, the mobile station will then use the CDL information as a pointer to
`search another channel number, or set of channel numbers, for a control channel.
`Thus, if the CDVCC information is replaced by FOC information on
`
`some downlink time slots, a conventional mobile station reading this field for
`the purpose of identifying the channel as either a control channel or a traffic
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`20
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`channel may misidentify a traffic channel as a control channel. Alternatively, the
`mobile station might read the FOC information as valid CDVCC data (thus
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`25
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`correctly identifying the channel as a traffic channel) and then look for the CDL,
`which is not present (thus moving to an incorrect channel number or set to
`
`search).
`
`Both of these problems can be avoided according to exemplary
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`30
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`embodiments of the present invention by recognizing that both the CSFP and the
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`

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`CDVCC according to IS-136 are (12,8) encoded data words, i.e., 8 bits of data
`encoded to 12 bits that have particular characteristics. Specifically, the CDVCC
`is a 12,8) code word that remains the same in each time slot associated with a
`particular channel and has non-inverted checkbits, while the CSFP is a (12,8)
`code word that has inverted checkbits and acts as an upcounter. Since the
`
`universe of (12,8) codewords having these characteristics is relatively small as
`compared with the number of total number of 12 bit binary words, the FOG
`information can be made distinct from the CDVCC and CSFP to avoid
`confusion. Specifically, the base station can transmit FOG information in the
`field which conventionally been used in downlink channels as either the CSFP or
`the CDVCC (i.e., bits 169-181 in FIG.3), which is carefully tailored to avoid
`similarity with a (12,8) codeword having these characteristics by adding filler
`bits to distinguish therefrom as will be readily appreciated by those skilled in the
`
`art.
`
`Of course, those mobile stations (or other receiving equipment) which are
`designed with the present invention in mind will be aware that the SACCH,
`CDVCC and CDL information can be located at a pre-defined full-rate portion of
`
`a multi-rate channel, which pre-defined portion is referred to herein as the
`"master channel". The master channel may, as in the afore-described examples,
`be transmitted on time slots 1 and 4, or alternatively on time slots 2 and 5 or 3
`
`In any case, a mobile station which has been suitably programmed to be
`and 6.
`aware of master channels can simply tune to a master channel to find CDL
`information.
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`5
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`10
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`15
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`20
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`The present invention also has application in situations other than
`asymmetrical data/packet data situations described above. For example, in order
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`25
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`to ensure complete compatibility, and for ease of implementation, it may be
`desirable to adopt the downlink slot format of slot 2 in FIG. 6 for situations in
`which packet data is transmitted in both the uplink and downlink, i.e., for uplink
`and downlink PDTCs as well as downlink DTCs and uplink PDTCs. That is,
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`base stations according to the present invention which transmit packet data traffic
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`

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`channels can use this downlink format for transmitting to mobile stations.
`Moreover, this aspect of the present invention is also applicable to situations
`wherein the connection is not asymmetrical.
`Another area in which the present invention finds application is in
`multimedia communication. As described above, it is anticipated that future
`radio communications will need to support intermingled voice, data and video
`service, wherein the type of information to be transmitted may vary rapidly,
`e.g., time slot by time slot and wherein the different services may require
`different levels of channel coding. One technique for dealing with this type of
`situation is to use call control signalling (e.g., over the FACCH) to identify
`which type of instantaneous service is to be supported over the channel. Another
`alternative is simply to allow the base station to transmit information pertaining
`to different services on a slot-by-slot basis, and require the mobile station to
`discriminate between the different services based on the differences in channel
`coding. See, for example, U.S. Patent No. 5,230,003 to Dent and Raith, the
`disclosure of which i