|||||I||
`US005521925A
`11) Patent Number:
`5,521,925
`45 Date of Patent:
`May 28, 1996
`
`5,103,445 4/1992 Ostlund .................................. 370/95.2
`5,121,385 6/1992 Tominaga et al. ...
`... 370/80
`5,200,956 4/1993 Pudney et al. .......
`370/95.3
`5,299,198 3/1994 Kay et al. .............................. 370/95.3
`Primary Examiner-Benedict V. Safourek
`Assistant Examiner-Ajit Patel
`Attorney, Agent, or Firm-Gordon R. Lindeen, III; Wanda
`K. Denson-Low
`ABSTRACT
`57)
`A system is described which integrates terminal traffic in a
`digital voice cellular radio communication system. Data is
`conveyed from remote data stations and remote radio tele
`phone stations over a reverse channel TDMA frame. The
`allocation of time slots in the reverse channel TDMA frame
`is controlled at the base station. The base station provides
`priority to radio telephones having digitized voice traffic.
`The base station assigns time slots within the reverse chan
`nel TDMA frame based upon allocation requests received
`from radio telephone stations and remote data stations.
`Remote data stations may contend on a random access for a
`minority of a set of time slots in the reverse channel data
`frame. Additionally, they may request an assigned slot by
`inserting an allocation request in a control slot of the reverse
`channel data frame. The base station allocates time slots on
`a voice radio telephone priority, and assigns any excess time
`slots to data stations waiting for access to the reverse
`channel.
`
`24 Claims, 7 Drawing Sheets
`
`O
`
`United States Patent (19)
`Merakos et al.
`
`(54) METHOD AND APPARATUS FOR
`PROVIDING MIXED VOICE AND DATA
`COMMUNICATION IN A TIME DIVISION
`MULTIPLE ACCESS RADIO
`COMMUNICATION SYSTEM
`
`(75. Inventors: Lazaros Merakos, Arlington, Mass.;
`Shrirang Jangi, Germantown, Md.,
`Fayu Li, Waltham, Mass.
`73) Assignee: Hughes Aircraft Company, Los
`Angeles, Calif.
`
`(21) Appl. No.: 118,709
`22 Filed:
`Sep. 9, 1993
`(22) File
`ep. 9,
`51) Int. Cl. ...
`-
`- -
`- - - -
`- - - - - H04J 3/16
`52 U.S. Cl. .......................... 370/953; 379/63; 455/34.1;
`455/542; 375/202
`58) Field of Search ........................ 370/941, 95.1-95.3,
`370/79, 80, 81, 85.8, 85.6, 85.7; 340/825.08;
`379/63; 455/34.1, 54.2; 375/202
`References Cited
`U.S. PATENT DOCUMENTS
`4,528.659 7/1985 Jones, Jr. ... 370/80
`4,646,294 2/1987 Eliscu et al. .............................. 370/60
`4,736,371
`4/1988 Tejima et al. .....
`... 370/95.1
`... 37055.1
`5,008,883 4/1991 Eizenhofer et al. ...
`
`(56)
`
`
`
`DATA STATION 0
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`May 28, 1996
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`FRAME 1
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`5,521,925
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`1.
`METHOD AND APPARATUS FOR
`PROVIDING MIXED VOICE AND DATA
`COMMUNICATION IN A TIME DIVISION
`MULTIPLE ACCESS RADIO
`COMMUNICATION SYSTEM
`
`RELATED APPLICATIONS
`"Method and Apparatus for Exploitation of Voice Inac
`tivity to Increase the Capacity of a Time Division Multiple
`Access Radio Communication System' Ser. No 622,232,
`filed Dec. 6, 1990, issued as U.S. Pat. No. 5,299,198 on Mar.
`29, 1994, and "Multiple Diversity Aloha Access' Ser. No.
`622,243, filed Dec. 6, 1990 now abandoned. The disclosures
`of both of these documents are hereby incorporated by
`reference herein.
`
`10
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`5
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`TECHNICAL FIELD
`The invention relates to the mobile radio telecommuni
`cation art. Specifically, a system is provided which will
`integrate data terminal communications in a cellular tele
`phone communication system.
`
`20
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`2
`with forward and reverse TDMA frames. The base station
`will manage the incoming data packets received from the
`PSTN as well as make the dynamic, on the fly reverse frame
`data slot assignments to each mobile station having a speech
`packet to transmit.
`The assignment of time slots in the reverse data frame
`results when a mobile station having a data packet issues a
`channel allocation request in a control slot of the reverse
`TDMA frame. The base station, once obtaining the alloca
`tion request, will identify an available time slot within the
`subsequent reverse data frame, and communicate the iden
`tity of that time slot to the requesting mobile in the forward
`data frame. The requesting mobile station can then transmit
`the digitized voice packet in the allotted time slot.
`In order to preserve the speech quality, the packet assign
`ment must not incur any significant delay such that the time
`between the transmission of voice packets is delayed, indi
`cating pauses of a greater length than that which were
`actually produced in the original speech. The system must
`have an adequate number of time slots to service both very
`light traffic from the mobile to the base station, as well as
`very heavy traffic.
`In the foregoing North American TDMA Digital Cellular
`Network Standard IS54, there is also a proposal to incor
`porate a data mode such that a mobile or remote data
`terminal can use any available time slots in the reverse
`frame.
`The introduction of data traffic in an essentially voice
`telecommunications system requires a protocol which will
`take into account the needs of both services. Data packets
`originating from a data terminal are not as time-sensitive to
`delays as are speech packets. Thus, it is possible to provide
`a lesser priority to data station data packets than voice
`station data packets.
`Further, in order to have a system of mixed digital voice
`packet transmission and digital data transmission, the sys
`tem must be adaptable to different traffic loads on the
`network. As channel traffic increases, the system must
`equitably distribute bandwidth to contending data stations,
`while still maintaining enough bandwidth for the higher
`priority voice stations to preserve the voice quality.
`
`SUMMARY OF THE INVENTION
`It is an object of this invention to provide for a system of
`radio communication in which digital voice as well as digital
`data may alternately use the same channel bandwidth.
`It is a more specific object of this invention to provide for
`a protocol for remote data terminals to communicate over a
`TDMA digital cellular telephone network.
`It is also a specific object of this invention to provide a
`remote data communication facility which utilizes available
`time slots in an extended time division multiple access voice
`communication system for carrying data terminal packets.
`These and other objects of the invention are provided by
`a communication protocol which permits the integration of
`data terminal traffic in a digital voice cellular radio com
`munication system. The data traffic conveyed from remote
`data stations and remote radio telephone stations to a base
`station is carried by the same reverse TDMA frame. The
`allocation of time slots for voice or data is controlled by the
`base station.
`In order to provide priority to digitized voice traffic, the
`base station includes a separate allocation que for voice
`stations desiring a time slot in the reverse data frame and a
`
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`BACKGROUND ART
`Radio telecommunications service is presently provided
`on a cellular basis to mobile telephones which communicate
`to a base station within each cellular area. A North American
`TDMA digital cellular network standard IS54 has been
`proposed, which is primarily intended to carry digitized
`voice traffic instead of analog voice traffic between the
`mobile radio telephone stations and the base stations. The
`standard seeks to conserve the scarce resource of radio
`bandwidth in the cellular networks by transmitting telephone
`speech as digitized voice packets in the time slots of a
`TDMAtime frame. The new proposed IS54 standard will
`provide for a 3:1 capacity gain over the current conventional
`Amps standard, which is documented in the TIA Standard
`IS54. The Amps-D and IS54 terminology refers to the same
`air radio interface.
`The technique described in the foregoing patent applica
`tion "Method and Apparatus for Exploitation of Voice Inac
`tivity to Increase the Capacity of a Time Division Multiple
`Access Radio Communication System' will avoid allocating
`bandwidth to the pauses which occur in speech. The system
`referred to herein as the E-TDMA(E) allots bandwidth to
`accommodate each speech burst. Each time a speech burst
`occurs, a request to allocate a time slot is generated and a
`time slot in the reverse data frame is assigned for carrying
`the digitized speech burst.
`To implement the foregoing protocol of assigning time
`slots to mobile stations when a digitized speech burst is
`created, the protocol envisions a time division multiplex
`access system having a forward TDMA frame from the base
`55
`station to each of the mobile stations and a reverse TDMA
`frame of data packets from the mobile stations to the base
`station. The time slots of the reverse TDMA frame are
`assigned by the base station as allocation requests are
`received from each mobile station which has created a
`digitized voice packet to transmit. Thus, the idle time
`represented by a speech pause does not receive any allocated
`bandwidth which would go unused.
`The system described in the aforementioned co-pending
`patent application provides a base station which manages a
`pool of transmission channels comprising a plurality of
`different carrier frequencies, each of which are modulated
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`data terminal allocation que for identifying allocation
`requests from data terminal stations requiring a time slot for
`transmitting data packets. In this way, the base station under
`software control will always give priority to voice traffic
`based on the relative contents in the voice allocation que
`versus the data terminal allocation que.
`The protocol for permitting data stations to utilize the
`reverse data frame which also carries digitized voice packets
`is responsive to changes in the level of traffic carried by the
`reverse data frames. During light traffic conditions, wherein
`there is little voice traffic, more time slots in the reverse data
`frame can be assigned to carry the data terminal traffic than
`in high traffic conditions, when the bandwidth demands of
`voice traffic must take priority.
`The protocol used by data stations for the transmission of
`data packets in the reverse channel combines three (3) basic
`mechanisms: (1) round-robin access to designated reverse
`control channel slots for sending reverse channel slot allo
`cation requests (ALLOCREQ) to the base station; (2) ran
`dom access to non-assigned reverse channel slots for the
`direct transmission of data packets without prior reverse
`channel slot assignment; and (3) a reservation process for
`assigning a reverse channel slot to a data station, which has
`successfully accessed the channel through random access.
`The round-robin (RROB) mechanism is used to guarantee
`that a data station can send an ALLOCREQ to the base
`station with a delay that does not exceed one RROB cycle,
`which consists of C consecutive reverse frames. C is a
`design parameter referring to the RROB cycle length.
`The RROB mechanism uses R slots, referred to as RROB
`slots, from the reverse pool. Each RROB slot is partitioned
`into MRROB subslots. The base station uniquely assigns to
`each data station one of the C.R.M. RROB subslots available
`in a RROB cycle, when the data station logs onto the cellular
`network. The RROB cycle length is determined by the base
`station so that the number of RROB subslots in a cycle
`exceeds by a certain small amount the number of partici
`pating data stations. When changes in the number of data
`stations occur, the base station may change the cycle length
`accordingly, and broadcast the change to the data stations in
`forward channel control slots.
`A data station transmits an ALLOCREQ in its own RROB
`subslot provided that its queue is non-empty and no reverse
`data slot has already been assigned to it.
`Data terminals may also transmit packets to the base
`station in available non-assigned reverse channel slots using
`random access. The base station will identify in control slots
`of each forward frame those slots which are available in the
`next reverse frame for random access by a data station. Thus,
`a data station having knowledge of those random access
`slots may contend with other data stations using conven
`tional contention and retry procedures for access to one of
`the random access slots.
`When a base station receives a data packet in a random
`access slot, which includes an identifier identifying which
`data station originated the data packet, it will send an
`acknowledgement in its subsequent forward frame indicat
`ing to the originating data station that the data packet was
`received.
`In high traffic conditions, wherein collisions are occurring
`at a high rate between data terminal stations trying to access
`the same random slot, a reservation system is provided
`wherein each data station may request of the base station an
`allocation of a reverse frame time slot for transmission of a
`data packet. If, after a given timeout period, random access
`attempts have not been successful, a data station may insert
`
`4
`in a subslot of the control slot of the reverse TDMA frame
`an allocation request. Each data station will have a dedicated
`subslot of each receive frame in which to communicate its
`allocation request to the base station.
`The base station, upon obtaining each allocation request,
`indicating that a data station is requesting assignment of a
`data slot in the reverse frame will place the request in the
`appropriate allocation que. When the voice traffic allocation
`que is empty, slots can be assigned which are normally used
`to carry voice packets to the waiting data stations identified
`in the data station allocation que.
`As an additional embodiment, a random access reserva
`tion may also be employed. In this mode, data stations that
`successfully contend for one of the random time slots which
`are available for use by the data stations may append an
`allocation request to its data packet. Thus, the base station,
`upon detecting a successful random access transmission of
`a data station will place an allocation request in the data
`allocation que, and in turn, assign a time slot to the request
`ing data station for use in transmitting additional packets to
`the base station.
`The mixed protocol using both random access and the
`reservation system for communicating a reverse frame allo
`cation request to the base station, permits a dynamic bound
`ary to be established for the reverse data frame.
`Thus, as the number of random available time slots in the
`reverse data frame becomes inadequate to carry data traffic
`to the base station, the base station may allocate other time
`slots when voice traffic is low.
`The foregoing protocol always provides the necessary
`priority for digitized voice packets to maintain the integrity
`of the voice traffic, while permitting the assignment of time
`slots which are not needed for voice traffic to data stations.
`DESCRIPTION OF THE FIGURES
`FIG. 1 illustrates a cellular radio telephone communica
`tion system which includes the capability of permitting data
`stations to communicate over the same channel bandwidth
`as is occupied by telephones.
`FIG. 2 shows how the time slots of the reverse channel
`TDMA are assigned between the different services.
`FIG. 3 illustrates an example of the reverse channel data
`frame used by the system of FIG. 1.
`FIGS. 4a-4d illustrates the reverse channel control slots
`which are partitioned into subslots for carrying allocation
`requests from data stations.
`FIG. 5 is a block diagram of a remote data station which
`communicates over the cellular telephone communication
`system.
`FIG. 6 is an illustration of the steps executed by the
`remote data terminal station in acquiring reverse channel
`bandwidth.
`FIG. 7 is a flow chart illustrating how the base station if
`FIG. 1 allocates reverse channel bandwidth between data
`stations and voice stations.
`FIG. 8 is an illustration of a reverse channel time frame
`in one scenario.
`FIG. 9 is the illustration of the reverse channel time frame
`in a second scenario.
`FIG. 10 is the illustration of a reverse channel frame in a
`third scenario.
`FIG. 11 is a block diagram of the base station architecture
`for affecting channel assignment in accordance with a pre
`ferred embodiment.
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Referring now to FIG. 1, there is shown an illustration of
`a mobile telephone system integrated with a remote/mobile
`data System. A base station 11 communicates with the voice
`stations 12, 13 and 14 as well as with data stations 16, 17 and
`18. The mechanism for communication is a radio link from
`the base station which can be tuned by each of the voice
`stations 12-14 and data stations 16-18.
`Traffic from the base station to each of the data stations
`16, 17 and 18 and voice stations 12, 13 and 14 is sent as
`digital packets in a forward frame of time division multiplex
`time slots which modulate the radio link. Separated from the
`outgoing forward frame 23 is a reverse frame of time
`division multiplex time slots for carrying traffic from each of
`the voice stations 12-14 and data stations 16-18 to the base
`station 11. The base station 11 is connected to a public
`service telephone network (PSTN) 20.
`The radio frequency carrier linking the base station 11
`with each of the data stations and voice stations 12-18
`employs a TDMA format, using a forward frame 22 and
`reverse frame 23. The forward frame 22 consists of a
`plurality of time slots which are divided into control slots
`carrying control information and data slots carrying either
`digitized voice or digitized digital data for either a voice
`station or data station.
`The forward and reverse frames are separated in time and
`all the stations 12, 13, 14, 16, 17 and 18 are synchronized
`with the forward and reverse frames. The base station 11
`assigns time slots in the reverse frame 23 to the data and
`voice stations to send packets of data back to the base station
`11. The system shown in FIG. 1 can use the E-TDMA
`protocol as set forth in the aforesaid co-pending patent
`application. In this protocol, speech packets from the voice
`stations 12, 13 and 14 are assigned a location in the reverse
`data frame each time they occur by issuing a new allocate
`request to the base station.
`FIG. 2 illustrates how the reverse frame time slots are
`40
`allocated between the voice stations, data stations and con
`trol slots contained in the reverse data frame. The reverse
`data frame may also include some idle slots which exist in
`a low traffic condition.
`In developing a protocol which is operable in an E-TDMA
`45
`environment, the differences between voice and data com
`munications must be appreciated. In a typical conversation,
`the average speech lasts approximately 1.5 seconds in dura
`tion. This is followed by pauses of typically 2.25 seconds
`duration, providing a 0.4 voice activity factor. E-TDMA
`50
`allots bandwidth in the way of a time slot for the speech
`bursts only, and no time slots or bandwidth is wasted on the
`pauses which naturally occur.
`If insufficient bandwidth is allotted to the voice traffic,
`voice clipping will occur, providing a disastrous effect on
`speech quality. However, delays between data station packet
`transmissions do not denigrate the quality of the data traffic
`in any material way. Thus, any protocol which adds to an
`essentially voice channel data terminal packet transmissions
`must not overload the system such that voice data packets
`suffer from delays imposed by data station traffic on the
`reverse channel data frame.
`The base station 11 in the E-TDMA system controls the
`allocation of bandwidth in the way of a TDMA time slot in
`both the forward channel 22 and reverse channel 23. As set
`forth in the aforesaid co-pending patent applications, the
`voice stations 12, 13 and 14 initiate a request for time slot
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`allotment in the reverse channel when the speech burst is
`detected and digitized. Using the contention techniques
`described in the aforementioned application, the base station
`11 will que up each request to allocate in its voice que and
`assign to each requesting station a time slot based on its
`availability in the reverse channel 23 for transmission to the
`base station 11. The slot assignment is carried by each
`forward channel frame. Each time a packet has been trans
`mitted from the voice station 12, 13 or 14 over its allotted
`time slot in the reverse channel, a deallocate is appended to
`the packet indicating to the base station 11 that it is free to
`reassign the slot to another station or the same station which
`subsequently generates a burst of digitized speech for trans
`mission to the base station 11.
`Integrating a remote data terminal capability with the
`E-TDMA voice system requires observing the protocol
`requirements for the voice stations, as well as insuring
`priority of voice traffic over data station traffic.
`Interactive data terminals are not subject to the stringent
`requirements on delays between packets. The trafficinitiated
`by a remote data terminal tends to have very low duty cycle,
`wherein a packet is produced at the speed of the user's
`typing capability. The data packets produced can be buffered
`at the data terminal and sent as bandwidth becomes avail
`able, without any serious consequences to the data service.
`Occasionally, file transfers occur from a remote data station
`to the base station, which tend to be much longer. However,
`even long file transfers can incur waits between packets
`which do not ultimately impact on the quality of the data
`transfer.
`Given the foregoing differences between transfers from
`remote data terminals and packetized speech on a speech
`burst basis, it is clear that the voice channels must have
`priority to avoid the consequences of delays between speech
`packets.
`In deciding on an appropriate protocol for carrying both
`remote data terminal traffic and remote voice radio tele
`phone traffic, the protocol must be dynamic such that it can
`adapt to the relative changes in voice traffic and data traffic
`occurring from the remote locations over the reverse chan
`nel. Providing data terminals with exactly the same protocol
`as voice terminals would result in the deterioration of the
`quality of voice traffic which, as has been noted, is delay
`sensitive. Since the delay sensitivity between the two ser
`vices is vastly different, the system which employed the
`same protocol inherently results in a loss of quality for the
`voice traffic.
`A fixed boundary approach in which certain time slots are
`allotted on a fixed basis to carry data traffic as well as voice
`traffic would resultin considerable inefficiency, as it does not
`take into account changes in traffic level which occur with
`each type of traffic, voice and data. Thus, there are periods
`of time in which the voice traffic would be very light, and
`any fixed allotment of time slots for each type of service
`would clearly result in a number of idle slots which could
`not be used by data terminals attempting to transfer files over
`the reverse channel to the base station.
`FIG. 3 illustrates the movable boundary approach imple
`mented by the present protocol as applied to the E-TDMA
`reverse channel frame.
`The E-TDMA forward and reverse channels use fre
`quency hopping and shown in the Figure are six (6) fre
`quencies and six (6) time slots, providing a total of 36 slots
`in the reverse data frame.
`Control slots are shown for the E-DTMA reverse voice
`channel as including subslots RR and RA. As explained in
`
`IPR2020-00038
`MM EX1003, Page 11
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`7
`the foregoing patent application, the RA subslots designate
`one of the following four message types: (1) reverse allocate
`request; (2) reverse deallocate request; (3) connect; and (4)
`release. The RR subslot, referred to as a reverse response
`subslot, carries the following data: (1) mobile ID message
`type; (2) DVCC; (3) CRC; and (4) FEC, all dedicated to the
`voice station protocol.
`In order to implement the data station protocol to maintain
`compatibility with the E-TDMA voice station protocol,
`more control slot overhead is needed. The control slot
`overhead necessary to implement the data station protocol is
`shown as subslots C1, C2, C3 and C4, for slot 2 as well as
`subslots C5, C6, C7 and C8 for slot 6 of frequency 6.
`The control slot overhead for the data channel protocol is
`provided such that allocate requests may be initiated at each
`of the data stations during their pre-assigned subslot. The
`base station, upon detecting the presence of a bit set in one
`of the subslots, will recognize the bit as a reverse channel
`allocate request for a specific data station.
`FIG. 3 illustrates numerous slots of the six frames marked
`as DATA. These data slots carry either digitized voice
`packets or packets from the remote data terminals, depend
`ing on the assignment given by the base station to the
`various stations having data to send.
`Two of the slots shown are marked as RANDOM and
`these two are available in this frame for random access by
`data stations. The position of each of the random slots
`available in a reverse frame is given to the remote data
`stations by the base station in control slots of the previous
`forward frame. The base station determines the location and
`number of random slots in each reverse frame from its
`knowledge of the set of reverse data slots which have not
`been assigned to a station yet. In reference to FIG. 3, data
`station terminals may contend for access to the two marked
`RANDOM slots by inserting their data packets in the
`random slot, as well as their own ID appended to the random
`packet. If the base station receives the data, and the data has
`not been subject to a collision with other data terminals
`attempting to use the two random slots, the base station will
`then acknowledge receipt of the packet.
`The remaining time slots marked DATA are partitioned by
`the base station among the radio telephones issuing voice
`packets, in accordance with the format of the EDTMA
`System and are also available for assignment to a data
`45
`terminal which have requested a slot assignment using the
`foregoing subslots. Thus, when the base station determines
`that there are an adequate number of time slots to service the
`radio telephone packets being initiated at the mobile radio
`telephones, it will assign any excess data slots to data
`terminals which are signalling their reverse allocate requests
`on the control channel subslots, C1 through C8.
`By apportioning the data slots among the competing voice
`communication demands and data terminals demands, it is
`possible to preserve the bandwidth efficiency while main
`taining adequate bandwidth for the time-sensitive voice
`communications which occur over the reverse data frame.
`The foregoing protocol combines three (3) basic mecha
`nisms for the transmission of data packets on the reverse
`channel: (1) round robin access to designated reverse control
`channel slots for sending reverse channel slot allocation
`requests (REVALREQ) to the base station; (2) random
`access to non-assigned reverse channel slots for the direct
`transmission of data packets without prior reverse channel
`slot assignment, and (3) a reservation process for assigning
`a reverse channel slot to a data station which has success
`fully accessed the channel through random access.
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`As shown in FIGS. 4A through 4D, the round robin
`mechanism, used to guarantee that a data station obtains a
`slot allocation, utilizes R slots of the reverse channel slot
`pool, referred to as RROB slots of the E-TDMA reverse
`channel frame. Each RROB slot is partitioned into M
`subslots. A round robin cycle consists of C consecutive
`frames, shown as frame 1, frame 2, frame 3 and frame 4, and
`therefore the number of RROB subslots in a RROB cycle is
`equal to N-CRM. N can be thought of as representing the
`number of locations in a conceptual ring (see FIG. 4, where
`R=1, M=4, C=4, N=16) and the RROB subslots perpool are
`thought of as RM tokens moving around the ring. Each data
`station is assigned to the lowest vacant location on the ring,
`and is synchronized to the ring when the remote data station
`first joins the network. Whenever a token comes to its
`location on the ring, the data station sends an allocate
`request to the base station, in the corresponding subslot if the
`data station que has data packets for transmission, and
`provided that no other user slot has been assigned to that
`particular data station following a previous allocation
`request.
`The base station, upon receiving an allocation request in
`the particular subslot assigned to the data station, will send
`a slot assignment (REQASGN) or, if one is not available, the
`base station will use a REQALLOCACK if the assignment
`cannot be made immediately. The base station will que up
`the request for assignment at the earliest possible time a slot
`is open.
`Each of the data stations, having received an assignment
`of a slot for its packet transmission will append a deallocate
`request (DEALLOCREQ) to the last packet of its transmis
`sion, indicating that the base station is to deallocate the slot.
`In the event either the allocation request or request
`assignment (REQASGN) is lost, the RROB cycle serves as
`a natural time out mechanism for the data station to insert its
`allocation request in its corresponding RROB subslot in the
`next RROB cycle.
`FIG. 5 is a block diagram representing the mobile/remote
`data terminal station which communicates via the forward
`and reverse data channels 22 and 23 to the base station 11 of
`FIG. 1. A data terminal 32 is shown which formulates
`packets of data, entered via a keyboard. The data terminal 32
`also includes a display for displaying incoming packets of
`digital data, as well as a buffer for storing packets awaiting
`transmission.
`The control processor 33 will control both the decoding of
`incoming frequency hopped TDMA data frames, constitut
`ing the forward frame of the forward channel 22, as well as
`encoding the outgoing packets from the data terminal 32,
`through an encoder 29. Encoder 29 inserts the outgoing data
`packet in its allocated time slot.
`When the data terminal 32 has traffic for the reverse
`channel 23, a command is sent to the control processor 33
`to either seize one of the random slots avail