United States Patent [191
`Quick, Jr.
`
`[54]
`
`RANDOM ACCESS COMMUNICATIONS
`CHANNEL FOR DATA SERVICES
`
`[75] Inventor:
`
`Roy F. Quick, Jr.. San Diego. Calif.
`
`[73]
`
`As signee :
`
`Qualcomm Incorporated. San Diego.
`Calif.
`
`Appl. No.: 412,648
`Filed:
`May 17, 1995
`
`Int. Cl.6 ............................. .. H04J 13/00; H04Q 7/30
`US. Cl. ............ ..
`. 370/342; 370/349; 455/383
`Field of Search ............................. .. 370/18. 50. 95.1.
`370/953; 375/200. 205; 455/381 38.2.
`38.3; 340/ 825.44
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,241,542
`5,384,777
`5,491,837
`
`8/1993 Natarajan et a1. ................... .. 370/953
`1/1995 Ahmadi et a1.
`.. 370/953 X
`2/1996 Haartsen .......................... .. 370/953 X
`
`FOREIGN PATENT DOCUMENTS
`
`0642283 3/1995 European Pat. Off. ....... .. H04Q 7/22
`9405095 3/1994 WIPO ............................ .. H04B 7/24
`
`OTHER PUBLICATIONS
`
`Giuseppe Bianchi et 211. “Dynamic Channel Allocation
`Procedures for Packet Data Services over GSM Networks”.
`[88 ’95, vol. 1. Apr. 1995. pp. 246-250.
`
`200
`
`‘
`
`US005673259A
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,673,259
`Sep. 30, 1997
`
`Frank Mademann. “General Packet Radio Service-a
`Packet Mode Service within the GSM". [SS ’95, vol. 1. Apr.
`1995. pp. 36-40.
`
`Primary Examiner—Melvin Marcelo
`Attorney, Agent, or Firm-Russell B. Miller; Roger W.
`Martin
`
`ABSTRACT
`
`[57]
`In a digital communication system for communicating digi
`tal information. the digital communication system having a
`forward link and a reverse link. a system and method for
`communicating a data packet. The system comprises a
`communicating transceiver. from among a number of digital
`transceivers. for sending the data packet on a random access
`channel over the reverse link and for receiving the digital
`information from the forward link. The system also com
`prises a base station for receiving the data packet on the
`random access channel from the reverse link and for sending
`the digital information over the forward link. The digital
`transceivers share the random access channel. The digital
`transceivers have a bandwidth demand. The system may also
`include a dedicated channel for communicating the data
`packet between the communicating transceiver and the base
`station and a processor for switching from the random
`access channel to the dedicated channel when the bandwidth
`demand exceeds a ?rst threshold. and for switching from the
`dedicated channel to the random access channel when the
`bandwidth demand drops below a second threshold. The
`system is well suited for use in CDMA applications.
`
`48 Claims, 19 Drawing Sheets
`
`204
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`US. Patent
`
`Sep. 30, 1997
`
`Sheet 1 of 19
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`5,673,259
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`

`
`US. Patent
`
`Sep. 30, 1997
`
`Sheet 2 0f 19
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`5,673,259
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`

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`U.S. Patent
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`Sep. 30, 1997
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`U.S. Patent
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`US. Patent
`
`Sep. 30, 1997
`
`Sheet 9 of 19
`
`5,673,259
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`602
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`FIG 7 A
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`
`US. Patent
`
`Sep. 30, 1997
`
`Sheet 10 0f 19
`
`5,673,259
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`
`US. Patent
`
`Sep. 30, 1997
`
`Sheet 11 0f 19
`
`5,673,259
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`
`US. Patent
`
`Sep. 30, 1997
`
`Sheet 12 of 19
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`5,673,259
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`

`
`US. Patent
`
`Sep. 30, 1997
`
`Sheet 13 of 19
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`5,673,259
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`US. Patent
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`Sep. 30, 1997
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`Sheet 15 of 19
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`5,673,259
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`US. Patent
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`Sep. 30, 1997
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`Sheet 16 of 19
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`U.S. Patent
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`Sep. 30, 1997
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`5.673.259
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`l
`RANDOM ACCESS COMMUNICATIONS
`CHANNEL FOR DATA SERVICES
`
`BACKGROUND OF THE INVENTION
`I. Field of the Invention
`
`The present invention relates to a random access com-
`munications channel for data services. More particularly. the
`present
`invention relates to a method for sharing the
`resources of existing channels in a cellular telephone com-
`munications system among a large number of packet data
`users. each having a variable and unpredictable demand for
`transmission resources.
`
`ll. Description of the Related Art
`Cellular telephone systems have traditionally provided
`voice services. patterned on the land telephone system
`model. In that model. a user places a call by requesting a
`connection between one telephone terminal and another
`such terminal. Once the connection is established. it remains
`in place until the calling party or the called party requests
`that the connection be released. While the connection is
`established.
`the telephone system dedicates system
`resources. such as trunk bandwidth.
`to the call. The
`resources are dedicated at all times. regardless of whether
`the callers talk or are silent. The system resources are not
`shared among calls.
`The land telephone model is followed in conventional
`cellular systems. For example. two systems that follow that
`model are the Advanced Mobile Phone System (“AMPS”)
`cellular system described in “Mobile Station/Land Station
`Compatibility Specification.” ANSI/EIA/TIA—553
`(September 1993). and the time division multiple access
`(“TDMA”) system. described in “Cellular System Dual-
`Mode Mobile Station/Base Station Compatibility Standard.”
`EIAIFIA/IS-54-B (September 1992). The code division
`multiple access (“CDMA”) cellular system. described in
`“Mobile Station/Base Station Compatibility Standard for
`Dual—Mode Wideband Spread Spectrum Cellular System.”
`TIA/'EIA/[S-95. Telecommunications Industry Association
`(July 1993). allows sharing of radio bandwidth. but follows
`the land telephone model for connections between the
`mobile switching center (“MSC”) and the public switched
`telephone network (“PSTN”).
`The CDMA system described above uses a 1.23 MHz
`bandwidth to serve multiple calls. using a CDMA scheme.
`Each user is assigned a unique code. All user terminals
`sharing the radio channel transmit simultaneously. and the
`receivers use the unique code to identify and decode a signal
`from the terminal that is to be received. The process is
`limited by the interference generated by the other transmit-
`ters. So long as the desired signal can be maintained
`sufficiently strong relative to the total interference. the signal
`can be successfully demodulated. When the number of users
`exceeds the CDMA channel’s capacity. however. the nec-
`essary signal strength cannot be maintained This CDMA
`cellular system provides for a total of 64 forward link
`channels per cell in each 1.23 MHz band. Experiments have
`shown that such a system can support more than 60 simul-
`taneous calls per cell in the 1.23 MHz bandwidth under
`benign propagation and interference conditions.
`The CDMA cellular telephone system also provides a
`means of serving a large population of cellular telephone
`units. most of which are idle. i.e.. not involved in a call.
`These idle units monitor a special control channel known as
`the “Paging Channel." which continuously transmits system
`information and paging messages. Paging messages are used
`to inform a mobile terminal that a caller wishes to establish
`
`2
`a call connection to the mobile. Each Paging Channel has
`one or more associated “Access Channels." The Access
`Channels use multiple-access protocols. by which the
`mobile terminals transmit call requests (originations) and
`answer paging messages. When a connection is established.
`the cellular base station assigns the mobile station a dedi-
`cated “'l'l'aflic Channel” to carry the voice information for
`the duration of the call.
`
`The CDMA system was designed to exploit the idleness
`of the mobile terminals. If this were not so. the number of
`mobile terminals supported would be limited to fewer than
`64 per cell. because of the limited number of channels
`provided in the system design. Because most terminals are
`idle. the system can support several orders of magnitude
`more mobile terminals per cell. thereby justifying the choice
`of 64 channels as an upper limit.
`Users of packet data services often utilize system
`resources in a manner that varies over the course of the
`packet data session. File transfers. e-mail. and infomtation
`retrieval are examples of packet data services that follow
`this pattern. For these services. a few packets are sent while
`the user selects the file. e-mail. or other information to be
`retrieved. then a long sequence of packets is sent or received
`while the information is transferred.
`
`In other types of data packet services. only a few packets
`are sent during an exchange of data. and the exchanges occur
`on an irregular basis. Examples of such services include:
`credit verification. message and paging services. order entry.
`and delivery routing.
`The manner in which these two types of data packet
`services utilize resources suggests that a packet service
`should provide two basic service modes. First. for those
`cases where large amounts of data are to be transferred. a
`service mode should be available that optimizes the data
`throughput. Second. for cases where packet transmission is
`infrequent and irregular. dedicating a channel assignment to
`each user would be wasteful of system resources. because
`the dedicated channels would be unused most of the time.
`For this second case.
`then. a service mode should be
`available that optimizes the sharing of resources. i.e.. opti-
`mizing channel usage. It should be possible for a packet
`service to switch between the two modes in response to
`usage demand.
`including CDMA.
`Conventional cellular systems.
`however. have neither the capability to efiiciently and effec-
`tively handle both types of data packet services. nor the
`capability to switch between the two. While the CDMA
`Trafiic Channels do provide dedicated channel assignments
`and can thus be used to handle high-throughput packet
`service to prevent the throughput reduction resulting from
`channel sharing. they are inefficient for low throughput.
`irregular and infrequent data packet transmissions. Thus. a
`multiple-access protocol is required for a service mode that
`optimizes sharing of resources.
`Despite providing multiple—access protocols. the existing
`CDMA Paging and Access Channels operate in a manner
`that is not well suited to data packet services. For example.
`those channels can support only a small packet size. which
`reduces the efiective throughput of the channel because each
`packet contains header information as overhead. This over-
`head occupies a greater fraction of the available channel
`bandwidth when the packets are small.
`Furthermore.
`the Paging and Access Channels cannot
`support long packet sizes because of their access methods.
`The Access Channel provides no power control feedback
`that would allow the base station to maintain the mobile
`
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`5.673.259
`
`3
`terminal’s signal strength in an acceptable range during a
`prolonged transmission. Instead. mobile terminals simply
`transmit messages repeatedly. with increased transmit power
`on successive attempts. until the base station acknowledges
`reception of the message. Because longer messages are more
`susceptible to errors caused by interference or fading. the
`mobile terminal’s power level may reach very high levels
`when attempting to send a long message. This would result
`in excessive interference to other users during the transmis-
`sion. On the Paging Channel. moreover. long packets cannot
`be supported because of the structure of the channel. Mes-
`sages are limited to a maximum of 255 octets. and no
`mechanism exists for fragmenting longer messages.
`The Access Channel also is incapable of identifying
`multiple propagation paths. On Trafiic Channels. each of the
`mobile terminals has a unique spreading code that is used by
`the base station to identify and exploit multiple propagation
`paths. using a signal combining method On the Access
`Channel. in contrast. all mobile terminals use the same
`spreading code for transmissions. making multiple propa-
`gation paths indistinguishable from transmissions from
`other mobile terminals.
`In some present systems. it is possible to provide con-
`nectionless data services. based on the delivery of individual
`data packets from many users who transmit data packets in
`bursts. Such services preferably do not utilize fixed alloca-
`tions of communication resources and allow the sharing of
`such resources among multiple users.
`In many present
`communications systems. and in particular digital cellular
`systems and CDMA cellular. however. no capability exists
`to provide for communication of data packets from many
`bursty users. In such systems. eflicient support for connec-
`tionless data services requires changes in the access methods
`used on the radio channel and in the land network.
`
`Therefore. a need exists for a random access data packet
`channel that can share communication channel resources
`among a large number of bursty packet data users. each
`having a variable and unpredictable demand for transmis-
`sion resources. and for a way to switch between such a
`random access channel and a dedicated data channel. A need
`also exists for a coding scheme that can be used to identify
`users on the random access channel and a scheme for
`overlaying the random access channel with control channels.
`
`SUMMARY OF THE INVENTION
`
`Accordingly. the present invention is directed to a random
`access channel for packet data services in a wireless com-
`munications system that substantially obviates one or more
`of the problems due to the limitations and disadvantages of
`the related art.
`
`Additional features and advantages of the invention will
`be set forth in the description that follows and in part will be
`apparent from the description. or may be learned by practice
`of the invention. The objectives and other advantages of the
`invention will be realized and attained by the apparatus
`particularly pointed out in the written description and claims
`of this application. as well as the appended drawings.
`To achieve these and other advantages. and in accordance
`with the purpose of the invention as embodied and broadly
`described herein.
`in a digital communication system for
`communicating digital information. the digital communica-
`tion system having a forward link and a reverse link. the
`invention is a system for communicating a digital data
`packet. The system of the present
`invention comprises
`digital transceivers for sending the digital data packet on a
`random access channel over the reverse link and for receiv-
`
`4
`information from the forward link. The
`ing the digital
`system further comprises a digital base station for receiving
`the digital data packet on the random access channel from
`the reverse link and for sending the digital information over
`the forward link. wherein the digital transceivers make
`packet service requests on the random access channel and
`thereby share the random access channel.
`In another aspect. in a digital communication system for
`communicating digital information. the digital communica-
`tion system having a forward link and a reverse link. the
`present invention is a method for communicating a digital
`data packet. The method comprises sending the digital data
`packet on a random access channel over the reverse link and
`receiving the digital information from the forward link by a
`number of digital transceivers. The method further com-
`prises receiving the digital data packet on the random access
`channel from the reverse link and sending the digital infor-
`mation over the forward link by a digital base station.
`wherein the digital
`transceivers make packet service
`requests on the random access channel and thereby share the
`random access channel.
`
`In another aspect. in a digital communication system for
`communicating digital information. the digital communica-
`tion system having a digital transceiver and a digital base
`station. the digital transceiver having a bandwidth demand.
`the present invention is a system for communicating digital
`data packets. The system of the present invention comprises
`a random access channel and a dedicated channel for com-
`municating the digital data packets between the digital
`transceiver and the digital base station. The system further
`comprises a processor for switching from the random access
`channel to the dedicated channel if the bandwidth demand
`exceeds a first
`threshold level and from the dedicated
`channel to the random access channel if the bandwidth
`demand below a second threshold level and/or if the digital
`transceiver is highly mobile. frequently moving from the
`coverage area of one base station to the coverage area of
`another.
`
`In yet another aspect, in a digital communication system
`having a broadcast channel for communicating system infor-
`mation and an access channel for making access requests.
`the system information including paging messages.
`the
`digital communication system including a plurality of trans-
`ceivas each having a specific long code. the present inven-
`tion is a system for communicating a digital data packet. In
`the system of the present invention. a communicating trans-
`ceiver from among the plurality of transceivers initializes a
`packet service request. requests a searcher reservation on the
`access channel. and sends the digital data packet over a
`random access channel using the specific long code corre-
`sponding to the communicating transceiver to obtain a coded
`digital data packet. The system comprises a base station.
`including a plurality of searchers and a controller for locat-
`ing a free searcher from the plurality of searchers and for
`sending to the free searcher the specific long code corre-
`sponding to the communicating transceiver. Further. the
`base station assigns the free searcher to the communicating
`transceiver and receives the coded digital data packet from
`the communicating transceiver over the random access
`channel. The plurality of transceivers share the random
`access channel.
`
`In all of the systems and methods described above and in
`the following description. the digital data can be communi-
`cated over the digital cellular communications system using
`code division multiple access (CDMA). CDMA is a spread
`spectrum method of multiplexing transmissions by encoding
`the transmissions so that they are each distinctive. CDMA
`
`

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`5.673.259
`
`5
`multiplexing permit a larger number of transceivers (i.e..
`mobile telephone units) to communicate within a commu-
`nication network than would other wise be possible without
`this spread spectrum technique.
`It is to be understood that both the foregoing general
`description and the following detailed description are exem-
`plary and explanatory only and are not restrictive of the
`invention. as claimed.
`
`The accompanying drawings are included to provide a
`further understanding of the invention and are incorporated
`in and constitute a part of this specification. to illustrate the
`embodiments of the invention. and.
`together with the
`description. to explain the principles of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features. objects. and advantages of the present
`invention will become more apparent from the detailed
`description set forth below when taken in conjunction with
`the drawings in which like reference characters identify
`correspondingly throughout and wherein:
`FIG. 1 is a schematic overview of an exemplary mobile
`cellular telephone system.
`FIG. 2 is a schematic overview of the process of searcher
`reservation in accordance with the present invention.
`FIG. 3 is a schematic overview of the process of switching
`between a random access channel and a dedicated channel
`for reverse link communications in accordance with the
`present invention.
`FIG. 4 illustrates a Long Code Mask used on a forward
`link Packet/Paging Channel.
`FIG. 5A and FIG. SB illustrates the structure of the
`forward link Packet./Paging Channel in accordance with the
`present invention.
`FIG. 6A and FIG. 6B illustrates the structure of the Packet
`Subchannel of the Packet/Paging Channel of the present
`invention.
`FIGS. 7A—7C illustrate the half-frame structure of the
`Packet Subchannel of the present invention.
`FIG. 8 shows the structure of messages sent on the Packet
`Subchannel.
`
`FIG. 9 illustrates the synchronization of a random access
`channel (or Reverse Packet Channel) in accordance with the
`present invention.
`FIG. 10 illustrates the structure of transmissions sent on
`the Reverse Packet Channel of the present invention.
`FIG. 11 illustrates the message portion of a transmission
`sent on the Reverse Packet Channel of the present invention.
`FIGS. 12A—l2C are flow diagrams illustrating an exem-
`plary mobile station searcher management scheme in accor-
`dance with the present invention.
`FIGS. 13A—13E are flow diagrams illustrating an excru-
`plary base station searcher management scheme in accor-
`dance with the present invention.
`
`DETAILED DESCRIPTION OF THE
` D EMBODIMENTS
`
`Reference will now be made in detail to the present
`preferred embodiments of the invention. examples of which
`are illustrated in the accompanying drawings. Wherever
`possible. the same reference numerals will be used through-
`out the drawings to refer to the same or like parts.
`In accordance with the present invention. in a digital
`communication system for communicating digital informa-
`
`6
`tion having a forward link and a reverse link. a system and
`method are provided for communicating digital data pack-
`ets. The system comprises digital transceivers. for-example.
`mobile cellular telephones. for sending the digital data
`packets on a random access channel over the reverse link
`and for receiving digital information from the forward link
`The system also comprises a digital base station for receiv-
`ing the digital data packet on the random access channel
`from the reverse link and for sending digital information
`over the forward link. The digital transceivers make packet
`service requests on and thereby share the random access
`channel.
`I. SYSTEM DESIGN
`
`A. Applications
`An exemplary embodiment of a terrestrial digital cellular
`mobile telephone system in which the present invention may
`be embodied is illustrated in FIG. 1 and designated generally
`by reference numeral 100. The digital communication sys-
`tem illustrated in FIG. 1 may utilize TDMA. CDMA. or
`other digital modulation techniques in communications
`between the remote user units 102.104 (which may be fixed
`or mobile and may also be referredto as mobile stations) and
`the cell- sites (or base stations) 108. For the remainder of this
`description. the terms “cell-site” and “base station” will both
`be used to refer to terrestrial transceivers that communicate
`over-the-air with remote andlor mobile units. It
`is not
`intended. however. that the present invention be limited to
`cellular systems and thus to cell-sites. Cellular systems in
`large cities may have hundreds or thousands of mobile
`telephones 102 and many ce1l—sites 108. Nevertheless. the
`present system is not limited to mobile telephones 102 and
`may be used to interconnect a hired position cellular com-
`munications device 104. For example, a cellular transceiver
`104 can be supplied at abuilding in order to send and receive
`data and/or voice communications between some device in
`the building and a switching station 110 that collects the
`data. Transmissions from the cell-sites 108 to the remote
`user units 102. 104 are sent on a forward link 120. while
`transmissions in the opposite direction are sent on a reverse
`link 130. The cell sites 108 are coupled to the switching
`station 110 Via backhaul 140 or may be linked to the
`switching station 110 over-the-air.
`An example of such a use would be a company that has
`many vending machines throughout a wide area and that
`needs to monitor the requirements of those vending
`machines. The vending machines could be equipped with a
`digital cellular transceiver 104 that can send and receive data
`to and from the switching station 110. including whether the
`machine is empty. which slots are empty. whether the supply
`is running low. and whether the machine has malfunctioned.
`In such an application. the vending machines would not need
`to communicate large amounts of data at any one time. but
`rather only short packets. such as status reports and
`malfunctions. and then only sporadically. With many vend-
`ing machines needing to comrnnnicate data packets to the
`switching station 110. and vice versa. it would be ineflicient
`and impractical to have the vending machines communicate
`over a dedicated communication channel. in which system
`resources would be dedicated to each vending machine that
`required channel time.
`A more eflicient approach is to provide a random access
`channel over which the vending machines can communicate
`with the switching station 110. With a random access
`channel. the vending machines could request channel time
`only when they need it. Because the vending machines
`require channel time only infrequently and briefly. literally
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`5.673.259
`
`7
`thousands of vending machines could share a single random
`access channel without significant transmission delays due
`to the random access channel being busy.
`Another application in which a random access channel on
`a digital cellular system is useful would be where a fleet of
`taxicabs reports information back to a dispatcher. Each
`taxicab must keep the dispatcher apprised. for example. of
`the cab’ s location and availability and must monitor requests
`for service. As with the vending machine example. many
`cabs must communicate with the dispatcher. but only with
`data packets that are sent sporadically. Accordingly. in this
`example as well. a random access channel would more
`efficiently serve the communications needs of the taxicab
`fleet and dispatcher than would a dedicated data channel.
`Furthermore. the cabs could be equipped with a voice/data
`transceiver so that they can communicate by voice with the
`dispatcher when needed and send and receive data from the
`dispatcher. Communicating both voice and data over the
`same system is made possible by the use of a digital system.
`for in such systems both the voice and data transmissions are
`in digital format.
`Therefore. in accordance with the present invention. a
`system for communicating short digital data packets over a
`random access channel is provided within the system 100 of
`FIG. 1. An additional feature of the system of the present
`invention is the ability to send digital data packets over a
`dedicated data channel
`in the system 100. To facilitate
`sending digital data packets over the random access and
`dedicated channels. the present invention includes means for
`switching between the random access and dedicated data
`channels. depending on the bandwidth demand of the user
`(or mobile unit) that is communicating data packets. The
`details of the present invention. including the means for
`switching between the random access and dedicated data
`channels. will be described in detail below.
`While applicable to any digital communications system.
`the system of the present invention is particularly well suited
`to the use of CDMA techniques. In a CDMA system. a “User
`Specific Long Code" is used to encode data and voice
`transmis