APPLICATION FOR UNITED STATES LETTERS PATENT
`
`by
`
`Krister Railh. James Ragsdale and 101111 Diachina
`
`for
`
`MULTI-RATE RADIOCOMMUNICATION SYSTEMS AND TERMINALS
`
`BURNS. DOANE. SWECKER & MATHIS. L.L.P.
`Post Office Box 1404
`
`Alexandria, Virginia 23133-1404
`(703) 836-6620
`
`Attorney's Docket No. 040010-490
`
`BROADCOM 1 0 1 2
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`-1-
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`MUL'I‘l-RATE mtocomumc‘atnotr SYSTEMS AND TERMNALS
`
`RELATED APPLICATION
`
`This application is related to 1.3.8. Patent Application Serial No.
`
`, entitled "Radiocommunication Systems and Terminals with Increased Payload
`
`Bandwidth“, which application was filed-on the same date as this application.
`
`BACKGROUND
`
`Applicant’s invention relates generally to radioconununication systems,
`
`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
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`increase capacity is to use digital conununication and multiple access techniques
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`such as TDMA. in which several users are assigned respective time slots on a
`
`single radio carrier frequency.
`.
`In North America. these features are currently provided by a digital
`
`cellular radiotelephone system called the digital advanced mobile phone service
`(D—AMPS). some of the characteristics of 'which are specified in the haterim
`
`standard lS-54B. "Dual-Mode Mobile Station-Base Station Compatibility
`
`Standard", published by the Electronic Industries Association and
`
`Telecommunications Industry Association (EINTIA). Because of a large
`
`existing consumer base of equipment operating only in the analog domain with
`
`frequency-division multiple access (PUMA). 15-548 is a dual-mode (analog and
`
`digital) standard. providing for analog compatibility in tandem with digital
`
`communication capability. For example, the 13-543 standard provides for both
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`.2.
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`FDMA analog voice channels (AVG) and TDMA digital traffic channels (DTC).
`and the system operator can dynamically rcplace-one type with the other to
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`accommodate fluctuating traffic patterns among analog and digital users. The
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`AVCs and DTCs are implemented by frequency modulating radio carrier signals.
`
`which have frequencies near 800 megahertz (MI-Ia) such that each radio channel
`
`has a spectral width of 30 kilohenz (KHz). A subsequent standard. referred to
`
`as 15-136, adds specifications for digital control channels. This standard
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`document. in particular the version identified as PIN-3474.1. dated December 15.
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`1995 and published by EINTIA. is incorporated here by reference,
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`10
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`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
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`data source. e.g.. a digitally encoded portion of a voice conversation. The time
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`slots are grouped into successive TDMA frames having a predetermined '
`
`duration. According to 18-543 and 15-136. each TDMA frame consists of six
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`15
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`consecutive time slots and has a duration of 40 milliseconds (msec). Thus, each
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`frame can carry from one to six traffic channels (e. g.. one to six radio
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`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
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`20
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`information. the number of slots used per channel depends on the source rates of
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`the speech coderldecoders (codecs) used to digitally encode the conversations.
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`Such speech (:0de can operate at either full-rate or half-rate, with full-rate
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`codecs being expected to be used until half-rate codecs that produce acceptable
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`speech quality are developed.
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`I
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`Thus, a full-rate DTC requires twice as many time slots in a given time
`
`period as a half-rate DTC. and in 13-543. each radio channel can carry up to
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`three full-rate DTCs or up to six half-rate DTCs. Each full-rate DTC uses two
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`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
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`30
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`of each TDMA frame. During each DTC time slot. 324 bits are transmitted. of
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`.3-
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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
`
`remaining bits are used for guard times and overhead signalling for purposes
`
`such as synchronization.
`
`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 radiocommunication
`
`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.
`
`These various types of information communication (also referred to herein
`
`as different “services") will likely have different optimal transmission
`
`characteristics. For example, services bemeen a remote user and the internet
`
`may benefit by providing a greater bandwidth in the downlink (i.e., from the
`
`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
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`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-
`
`136 TDMA frame) but only a full rate connection in the uplink (e.g., two time
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`10
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`15
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`20
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`slots of 81113-136 frame). This htequality between uplinlt and downlink
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`25
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`In addition to
`bandwidth is referred to herein as an "asymmetrical” connection.
`bandwidth considerations, other transmission characteristics may also be
`
`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 U2. since voice information transmission is
`
`typically not provided with a procedure for retransmission. while optimal channel
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`30
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`coding for the transmission of data, e.g, facsimile. might be rate Sid since
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`/
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`.4.
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`retransmission procedures are typically provided. Other transmission
`characteristics, for example. the ability to" tolerate delay in the reception of
`
`information, may also vary between services. All of these differences in
`
`transmission characteristics should be considered together when determining an
`
`Optimal specification for the air interface.
`
`Accordingly. it would be desirable to provide techniques for transmitting
`
`information between remote stations and the system in radioconu'nunicatiOn
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`networks that provide sufficient flexibility for the anticipated variety of
`
`information communication services described above. while also providing
`
`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 downlinlt may vary depending upon the
`
`transmission rate. For example. in a TDMA envirorunent. a first downlinlt 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. The different formats take into account
`
`the need to transmit certain types of information at only full rate. and not double-
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`10
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`15
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`20
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`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 infomiation in a fast out-of-band channel
`
`(FOG). The FCC 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
`
`0r data) being conveyed in the payload. This information can be used by the
`
`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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`-5-
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`type of payload may vary rapidly. e. g.-. on a slot-by-slot basis, or even within
`each slot.
`I
`-'
`'
`-
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`Various exemplary mapping techniques for associating the FCC
`
`information with each time slot or each blocli 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
`
`FCC information may be associated with a connection or connection which is
`
`different from that supported by the payload or data field containing the FCC.
`
`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 FCC 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.
`
`1 is a block diagram of an exemplary cellular radio telephone
`
`system in which the present invention maybe applied;
`
`FIG. ’2 illustrates an exemplary TDMA frame structure:
`
`FIG. 3 illustrates a cprrventional downlink traffic channel time slot
`
`format;
`
`FIG. 4A illustrates triple rate downlinlt framie usage;
`
`FIG. 43 illustrates full rate uplink frame usage:
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`10
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`-5.
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`FIG. 5 illustrates a base station and threemobile stations communicating
`therewith;
`3
`I
`'
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`FIG. 6 illustrates downlink time slot formats according to a first
`
`exemplary embodiment of the present invention;
`
`FIG. 7A illustrates downlink time slot formats according to a second
`
`exemplary embodiment of the present invention;
`
`FIG. TB illustrates downlink timeslot formats according to a third
`
`exemplary embodiment of the present invention;
`
`FIGS. 8A—8C illustrate exemplary mappings of FCC information to
`
`payload according to various exemplary embodiments of the present invention;
`
`FIG. 9 is a flowchart illustrating an exemplary. alternative uSage of an
`
`FOC field by a mobile station according to the present invention;
`FIG. 10 is a conventional fonnatfor all uplink traffic channel time slots:
`
`and
`
`FIG. 11 is an exemplary format for two or more uplinlt traffic channel
`
`time slots according to an exemplary embodiment of the present invention.
`
`DETAILED DESCRIPTION
`
`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 he 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 lmown in the art, as
`
`described by the above-cited U.S. patent applications and by U.S. Patent
`
`10
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`IS
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`20
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`25
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`:7-
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`No. 5.175.867 to Wells: et al.. entitled Neighbor-Assisted Handoff in a Cellular
`Communication System," and U3. Patent Apfilication No. 07f967.027 entitled
`
`“Mold-Mode Signal Processing.” which was'filed an 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
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`10
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`control channel of the base station or cell to mobiles locked to that control
`
`channel.
`
`It will be understood that the transceivers 150 and 160 can be
`
`implemented as a single device. like the traffic and control transceiver 17-0- in the
`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
`
`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 radiocomtnttnication systems generally. the interested
`
`reader is referred to U.S. Patent Application Serial No. 085441.836. 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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`-3.
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`can then read the control information transmitted on that control channel. e. 3..
`paging messages. using its traffic and control-channel transceiver 170. Then. the
`
`processing unit 180 evaluates the received control channel information, which
`
`mayr 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
`
`10
`
`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 I
`
`TDMA frame in this example has a duration of 40 msec and supports six. half-
`
`rate logical channels, three full-rate logical channels. ct greater bandwidth
`
`15
`
`channels as indicated in the following table. Each slot can. for example, have a
`
`duration of 6.6? msec and cart): 324 bits (162 symbols), which have positions in
`
`each slot that are conventionally consecutively numbered 1-324.
`
` _333_m
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`Currently. [8-136 defines a downlink DTC slot format as illustrated in
`
`FIG. 3. Therein. the numbers above each field denote the number of bits
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`25
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`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 flannel used. for example. for transmission of
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`CI
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`-9.
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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 FACCH (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 CD1. (Coded Digital Control Channel Water) 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 downlinlt
`
`format is used for each time slot in a TDMA frame. i.e., all six time slots for
`
`systems operating according to 15-136. 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. 43 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., 15-136. According to a first exemplary embodiment
`
`described below. the unused uplinlt time slots can be used to send packet data.
`
`Packet data communications support independent usage of uplink and downlinlc
`
`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 uplinlt time
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`3|]
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`ll;
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`-10.
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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. 43. 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 dowulink 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 coanection 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 downlinit 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. 3., 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 mobiie stations to return to the PCCH periodically. e.g., after
`transmitting packets 0n 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 downlinlc time slots whose data or “payload“ fields are
`
`being used to transmit information to mobile station 500. Specifically. the
`
`110me 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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`Ii}
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`_11-
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`receive triple rate downlinlt infomaIiOn.-.;FIG._6 illustrates downlinlt time slot
`formats according to this exemplary embodiment‘of the present invention.
`
`Therein. three downlinlt slot formats are illustrated for an exemplary
`
`traffic channel according to the present invention. These three slut 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 downlinlt
`
`10
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`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
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`15
`
`present invention.
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`20
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`25
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`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
`
`SACCH information in slots 2 and 3 can t: 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 central. e.g.. tearing down of a connection. However. this infonnation can
`
`be provided to the mobile station ever the control charmel at call-setup and,
`
`accordingly. need not be transmitted by the base statiOn in each downlink time.
`
`{ C)"
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`slot. Various techniques are described below to avoid problems caused by
`omitting the CDL information from some dowitlinit time slots.
`
`Omitting these fields in time slots 2 and 3 (as well as 5 and 6) provides
`
`an opportunity to inform the other mobile stations. e.g.. mobile stations 510 and
`
`520. of information pertaining to their upljnk connections, without assigning a
`
`new PDTC or forcing mobile stations 510 and 520 to revert periodically to
`
`listening to the PCCI-l. For example, the FCC fields can be used to inform
`
`mobile station 510 or mobile station 520 that a previously transmitted packet was
`
`not properly received and should he retransmitted Note that since the FCC
`
`information is "out-of-baud" (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
`
`contemplated by the present invention. For example. although the foregoing
`
`example is provided in terms of an asymmetrical connection wherein the
`
`downlink is triple rate and the uplinlt is full rate. any asymmetrical connection
`
`lends itself to application of the present invention. For example. the downlinlt
`
`may be double rate and the uplink full rate, whereupon the FOC fields would
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`10
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`15
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`replace the SACCH, CDVCC and CDL fields in only one of slots 2 and 3
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`20
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`illustrated in FIG. 6.
`Moreover, it may not be desirable to replace all three of the SACCH.
`
`CDVCC and CDL fields with FOC information. For example. it may be
`
`determined that 36 bits of FOC information is not needed. Alternatively, for
`
`compatibility reasons. it may be determined that one or more of the SACCH.
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`25
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`CDVCC and CDL fields should be maintained in each downlinlt slot. Thus. for
`
`example, downliult slot formats for the triple rate downlinklfiill rate uplink
`
`example provided above could instead be as illustrated in one of FIGS. 7A and
`
`7B. Therein, the FOC replaces only the SACCH and CDVCC in FIG. 7A and
`only the SACCH in FIG. 7B.
`'l'hose.,skilled in the art will appreciate that many
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`1 iii
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`.13-
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`more variations exist. such as time slot 2 or 3 being the “master" channel having
`the conventional slot format of F163 instead-of slot 1.
`
`As mentioned above. exemplary embodiments of the present invention
`
`wherein the base station 505 only transmits the CDVCC andlor the CDL in some
`
`downlinlr slots of a traffic channel may cause difficulties for mobile stations that
`
`expect this information in all time slots on a downlink traffic channel. For
`
`extensive information relating to the C131. and mobile functionality relating to
`
`locating digital traffic channels. the reader is referred to us. Patent Application
`
`Serial No. 081331.711 entitled "Method and Apparatus for Locating a Digital
`
`Control Channel in a Radiocornrnunication System", filed on October 31, 1994.
`
`the disclosure of which is incorporated here by reference.
`
`In brief, the (EL
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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 tones is a traffic channel.
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`According to one exemplary technique, a mobile station reads the field
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`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
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`CDVCC (implying a traffic channel per the format of FIG. 3) or a coded
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`superframe phase (CSFP) (implying a control channel per 13-136).
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`If a traffic
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`channel. the mobile station will then use the CDL information as a- pointer to
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`search another channel number, or set of channel numbers. for a control channel.
`Thus. if the CDVCC information is replaced by FOC information on
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`some downlink time slots. a conventional mobile station reading this field for
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`the purpose of identifying the channel as either a control channel or a traffic
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`channel may misidentify a traffic channel as a control channel. Alternatively. the
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`mobile station might read the FCC information as valid CDVCC data (thus
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`correctly identifying the channel as a traffic channel) and then look for the CDL,
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`which is not present (thus moving to an incorrect channel number or set to
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`search).
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`Both of these problems can be avoided according to exemplary
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`embodiments of the present invention by recognizing that both the CSFP and the
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`CDVCC according to 15-136 are 02.8) emoded 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
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`particular channel and has non«invetted checkbits, while the CSFP is a (12.8)
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`code word that has inverted checkbits and acts as an upcounter. Since the
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`universe of (12.8) codewords having these characteristics is relatively small as
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`compared with the number of total number of 12 bit binary words. gejog
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`information can heritadedistinct from the CDVCC and CSFP to avoid
`confinion. Specifically. the base station can transmit FDC information in the
`field which conventionally been used in downllnlt channels as either the CSFP or
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`the CDVCC (i.e., bits 169-131 in F1634), which is carefully tailored to avoid
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`similarity with a (12.8) codeword having these characteristics by adding tiller
`bits to distinguish therefrom as will be readily appreciated by those skilled in the
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`Of course, those mobile stations (or other receiving equipment) which are
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`designed with the present invention in mind will be aware that the SACCH,
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`CDVCC and CDL information can be located at a pie-defined full-rate portion of
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`a multi-ratc channel, which tire-defined portion is referred to herein as the
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`"master channel". The master channel may. as in the atom-described examples.
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`be transmitted on time slots 1 and 4. or alternatively on time slots 2 and 5 or 3
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`and 6.
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`In any case. a mobile station which has been suitably programmed to be
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`aware of master channels can simply tune to a master channel to find CDL
`information.
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`The present invention also has application in situations other than
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`asymmetrical datalpacltet data situations described above. For example, in order
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`to ensure complete compatibility. and for ease of implementatiou. it may be
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`desirable to adopt the downlink slot format of slot 2 in FIG. 6 for situations in
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`which packet data is transmitted in both the uplink and downlink, i.e.. for uplinlt
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`base stations according to the present invention which transmit packet data traffic
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`channels can use this downiinit format- for transmitting to mobile stations.
`Moreover, this aspect of the present hivention'is also applicable to situations
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`wherein the connection is not asymmetrical:
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`Another area in which the present invention finds application is in
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`multimedia communication. As described above. it is anticipated that future
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`radio communications will need to support intermingled voice, data and video
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`service, wherein the type of information to be transmitted may vary rapidly.
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`e.g.. time slot by time slot and wherein the different services may require
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`different levels of channel coding. One technique fordealing with this typeof
`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
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`coding. See. for example. U.S. Patent No. 5.230.003 to Dent and Raith. the
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`disclosure of which is expressly incorporated here by reference. This procedure
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`is currently used to determine whether FACCH information or voice information
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`is carried in the DATA field of a particular downlink time slot. However. as the
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`number of services expands beyond two; the complexity of discriminating
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`between services in this manner becomes excessive.
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`‘
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`Thus. according to another exemplary embodiment of the present
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`invention. the FOC fields may also serve the purpose of service type identifier.
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`In this embodiment. the FCC can provide infortnation regarding the type of
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`service which the associated payload is currently supporting. the channel coding
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`angler inurleaving associated therewith. For example. in a multimedia
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`connection information transfer may rapidly vary between voice. data and video
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`infomtation.
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`In such a case, a change in the FOC can inform the mobile station
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`of the type of information being nansmitted. so that the mobile station will know
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`how to process the received information. e.g.. how to decode the received bits.
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`As wiil be apparent from reviewing FIG. 6. FIG. 7A and F16. 7B, exemplary
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`embodiments of the present invention donotprovide FOC fields in each Lime slor
`received by the mobile station in order to maintain full-rate transmission of
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`SACCH. CDVCC and CDL. That is. using again 15-136 as an illustrative
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`example. a mobile station receiving data at triple-rate will read FOC information
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`in time slots 2. 3. S. and 6. but not slots 1 and 4. Thus, it is desirable to
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`provide a mapping between the FO