United States Patent (19)
`Hodzic et al.
`
`USOO6097707A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,097,707
`*Aug. 1, 2000
`
`54 ADAPTIVE DIGITAL WIRELESS
`COMMUNICATIONS NETWORK
`APPARATUS AND PROCESS
`
`7/1992 Burns ..................................... 455/33.1
`5,129,096
`5,212,805 5/1993 Comroe et al. .
`... 455/33.1
`5,276,686
`1/1994 Ito .......................................... 455/33.1
`
`*
`
`Notice:
`
`76 Inventors: Migdat I. Hodzic, 11633 Bridge Park
`Ct., Cupertino, Calif. 95014; James M.
`Brennan, 1224 Martin Ave., Apt. #5,
`San Jose, Calif. 95.126
`This patent is Subject to a terminal dis-
`claimer.
`21 Appl. No.: 08/444,553
`1-1.
`22 Filed:
`May 19, 1995
`(51) Int. Cl. .................................................. H04J 3/16
`52 U.S. Cl. .......................... 370/321; 370/337; 370/347;
`455/54.1; 455/57.1
`58 Field of Search .................................. 370/24, 26, 29,
`370/18, 55.3, 68.1, 77, 85.2, 79, 85.3, 84,
`94.1, 94.3, 85.7, 95.1, 85.8, 95.2, 95.3,
`100.1, 103, 104.1, 105,105.1, 379/58,
`63, 59; 340/825.06, 825.07, 825.08; 455/33.1,
`33.4, 16, 15, 49.1, 51.1, 54.2, 53.1, 54.1,
`57.1; 375/200, 202, 205
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,644,534 2/1987 Sperlich ................................. 370/95.3
`
`
`
`Primary Examiner Benedict V. Safourek
`Assistant Examiner Ricky Q. Ngo
`Attorney, Agent, or Firm Donald J. Lisa
`57
`ABSTRACT
`A Single channel wireleSS digital communication network
`10 has a cellular topology which includes a central unit
`12) ("CW") controlling communications with a plurality of
`remote units 14 (“TU”) in a star configuration. Network
`acceSS is Synchronously controlled through a time division
`multiplexed cycle 20 of variable total duration having an
`up-link phase 21 of a variable number of fixed size time
`slots 25, 27, 27a), each pre-assigned by reservation by a
`remote unit, and a down-link phase 22 of a variable
`number of variable size slots (31a, 31b) which are adap
`tively utilized. The CU adaptively manages all slot assign
`ments according to a variety of parameters. RU up-link Slot
`reservations are confirmed by the CU in a variety of ways.
`During the up-link phase, RU’s which did not reserve a slot
`on the previous up-link cycle are temporarily Suspended and
`are then polled or periodically tested for re-entry. A repeater
`unit 15 (“RU”) having a back-to-back coupled ccu-tu pair
`operates as a minicell within the major cell where major cell
`coverage is not broad enough to reach all major cell TUS.
`
`50 Claims, 3 Drawing Sheets
`
`Ex.1028
`APPLE INC. / Page 1 of 14
`
`

`

`U.S. Patent
`
`Aug. 1, 2000
`
`Sheet 1 of 3
`
`6,097,707
`
`32
`GUARD tiME-
`
`2O
`
`23
`such FRAME
`2
`WTC x/RX1
`24
`25
`TU DAA
`
`
`
`TU 2 DATA
`
`Switch c/RXN
`
`
`
`Ex.1028
`APPLE INC. / Page 2 of 14
`
`

`

`U.S. Patent
`
`Aug. 1, 2000
`
`Sheet 2 of 3
`
`6,097,707
`
`Fig. 2A
`
`M
`
`
`
`42 43
`
`44
`
`45
`
`40
`
`49
`
`5O
`
`Ex.1028
`APPLE INC. / Page 3 of 14
`
`

`

`U.S. Patent
`
`Aug. 1, 2000
`
`Sheet 3 of 3
`
`6,097,707
`
`
`
`Ex.1028
`APPLE INC. / Page 4 of 14
`
`

`

`6,097,707
`
`1
`ADAPTIVE DIGITAL WIRELESS
`COMMUNICATIONS NETWORK
`APPARATUS AND PROCESS
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates generally to the apparatus
`and methods of controlling multiple access to a communi
`cation network by a plurality of remote Stations, and more
`particularly, to a non-contention, digital, wireleSS System in
`which all Stations share one channel and a central Station
`Synchronously controls access through a cyclic, time divi
`Sion multipleX process.
`2. Discussion of Background and Prior Art
`Modern communications Systems must be designed to
`meed a wide variety of practical applications which have
`varying needs.
`
`15
`
`a MOBILITY
`One important need is mobility. Increasingly in our Soci
`ety there is a requirement for mobile communication SyS
`tems which eliminate expensive wire pulling, Such as, in
`multi-building and various campus environments.
`There is a need for and it is an object of the present
`invention to provide omnidirectional short range communi
`cations within buildings and between adjacent building
`Structures without running phone lines and without interfer
`ences from the wall or building structures.
`b. DIGITAL
`Digital communications Systems are dramatically pushing
`out our communications frontiers because of the flexibility
`and reliability of digital techniques. Nevertheless, in multi
`point-to-point or multi-point-to-multi-point networking SyS
`tems between multiple radio units, there is a need for and it
`is an object of the present invention to provide Such a System
`which handles digitized Video, audio and data at error-free
`and higher through-put rates.
`
`25
`
`35
`
`40
`
`2
`repeaters. Constant monitoring of remote units by the central
`control improves the reliability of the network. There is a
`need for and it is an object of the present invention to
`provide a wireleSS, Single channel, media access control
`which has the efficiencies of a Star configuration.
`e. REMOTE COVERAGE
`In cellular, Star configuration, multi-point-to-point
`Systems, major problems have been the fading of the broad
`cast Signals at the far corners or remote areas of a covered
`region and interference from multiple transmissions.
`Spread Spectrum technology is well known and has been
`available since World War II. Spread spectrum is a technique
`that uniformally distributes the information bandwidth of a
`data Signal Over a frequency range that is much larger than
`required for transmission. The technique adds redundancy to
`the Signal, which allows data to be recovered in the presence
`of Strong interfering Signals. It has wide commercial appli
`cation in digital wireleSS networks to avoid interference and
`provide reliable Signal detection in the presence of multiple
`Signal Sources. Two fundamental techniques for Spreading
`the digital bandwidth over a wide spectrum are well known
`and include direct-Sequence and frequency hopping. In the
`basic direct-Sequence technique, a base band data Signal is
`combined with a pseudo-random noise (“PRN") code using
`an exclusive-OR (“XOR”) gate.
`The out-put is a combined signal with a “chipping rate'
`much faster than the data-Signal rate which spreads the
`Signal over a frequency range larger than the data-Signal
`bandwidth which is then demodulated coherently by con
`ventional techniques at the receiver end.
`Thus, in spread spectrum the data and Spread signals are
`combined. The spreading Signal dominates the content. The
`combined Signal looks like noise, but is correlatable because
`the spread spectrum has a unique code that can be detected
`and demodulated.
`In a typical multi-point-to-multi-point System the central
`control unit functions as a repeater for remote terminal units
`where the coverage of the major cell central unit is insuf
`ficient to reach all remote units within the major cell.
`There is a need for and it is an object of the present
`invention to provide the advantages of Spread Spectrum and
`repeater capability in a digital wireleSS network of broad
`practical application.
`f. LIMITED SPECTRUMAND MEDIA ACCESS
`CONTROL
`The limited Spectrum for radio frequency broadcasting
`has long been a major problem for communications Systems.
`The need to effectively and efficiently use existing spectrum
`has spawned many new types of Systems and capabilities.
`Multi-point-to-point wireleSS Systems have created multiple
`acceSS problems as multiple units contend for channel
`availability. Single channel Systems have aggravated the
`need for good multiple access control of the media. Numer
`ous channel access Schemes are well known including
`frequency division multiple access (“FDMA"), code divi
`sion multiple access (“CDMA"), and time division multiple
`access (“TDMA”).
`In FDMA, the total spectrum assignment is divided into
`channels in the frequency domain. A major disadvantage of
`the FDMA system is that it requires considerably more
`equipment at the base Station to handle a given number of
`Subscribers.
`CDMA is the characteristic form of multiple access that is
`used for Spread spectrum Systems. In these Systems each unit
`
`C. LOW COST
`Cellular topology has found wide acceptance Worldwide
`in multi-point-to-point and multi-point-to-multi-point net
`45
`WorkS. The use of a cellular structure in wireleSS commu
`nications Systems eliminates the need for telephone lines and
`cable lines. A vast infra-Structure of cellular radio towers
`now exist worldwide.
`Wireless networks are especially well adapted for use in
`cellular topology because they can be formed by combining
`numerous Single cells to accommodate particular applica
`tions. Different cells would use different spreading codes to
`minimize the potential interference problems. There is a
`need for and it is an object of the present invention to
`provide a wireleSS radio frequency communications network
`which can utilize the existing Worldwide cellular infra
`Structure in a variety of practical commercial applications.
`d. EFFICIENT ORGANIZATION
`A Star configuration is an efficient organization for con
`trolling multiple access of numerous remote units in a Single
`cell communication Scheme. The central unit acts as the
`control or master while the remote or terminal units act as
`Slaves So far as channel access and Scheduling are con
`cerned. The remote units can communicate between each
`other via corresponding central units which can also act as
`
`50
`
`55
`
`60
`
`65
`
`Ex.1028
`APPLE INC. / Page 5 of 14
`
`

`

`3
`is assigned a unique randomized code Sequence, different
`from all other users. Spread spectrum Systems utilize a
`Single wide band carrier, and, thus, in CDMA Systems a
`large number of users can transmit Simultaneously, resulting
`in the bandwidth being very wide when compared to either
`TDMA or FDMA
`The problem with CDMA is that the spreading signal
`requires more bandwidth. A Second major problem with
`CDMA is “near-far’ affect in which mobiles close to the
`base drown out those which are far away. Another problem
`is that diverse communications traffic needs may require
`different bandwidth and performance requirements to coex
`ist within a given network. Thus, a multi-access protocol
`must be capable of Satisfying Such diverse requirements.
`There is a need for and it is an object of the present invention
`to provide the advantage of CDMA in a wireless system
`where its disadvantages are minimized.
`With TDMA the channels are multiplexed by time divi
`Sion So that each channel accesses the full bandwidth for a
`short time slot. The total number of simultaneous users is
`limited by the number of time slots that are available and
`users only use the channel during specific time slots. The
`major advantage of TDMA systems over FDMA is the
`reduced cost of central Site equipment, which arises because
`each radio channel is effectively shared by a much larger
`number of Subscribers. Additionally, TDMA has more flex
`ibility and is more open to technology change. Santa Maria
`and Lopez-Hernandez, Wireless LAN Systems, Artech
`House. Inc. (1994). At p. 210-212. Thus, there is a need for
`and it is an object of the present invention to apply the
`advantages of TDMA to a digital wireleSS Single channel
`non-contention communication network.
`The world's most widely used digital cellular system is
`the European standard known as GSM which originally
`stood for Groupe Special Mobile, but now stands for Global
`System for Mobile communications and is designed to allow
`Subscribers to use the same terminal equipment throughout
`all the territories where GSM has been adopted. This system
`is a fully digital network in the 900-MHz band. However,
`the GSM is not a Single channel non-contention network.
`Single-channel non-contention Systems relieve Subscriber
`devices operating on the network from having to detect
`collisions. Cyclic TDM approaches is one Such implemen
`tation. Some TDM Systems use a token passing ring. Others
`use fixed slot allocation or dynamic Slot allocation. In a fixed
`Slot allocation System, regularly occurring time slots in a
`repetitive framed Sequence are dedicated to specific devices
`operating on a network for their transmission. In dynami
`cally allocated Systems, parameters, Such as, the Size of each
`time slot and the number of time slots allocated to a
`particular device may be varied. Since a device only trans
`mits during its allocated time slots, communication colli
`sions generally do not occur. See Budin U.S. Pat. No.
`5,276,703 (4:11-21).
`Multi-point digital wireleSS communications networks are
`also well known. In one system to Gilbert U.S. Pat. No.
`5,297,144 a non-contention based, Single optical-infrared
`channel, Star configuration network using a central Station to
`control access of multiple remote Stations in a cyclic,
`synchronized, TDMA process is described. This patent
`describes a reservation period and a polling period protocol
`during which reserving Stations from the first period are
`polled Sequentially for data transfer in the Second period.
`The System does not describe a wireleSS radio frequency link
`and Suffers from less than optimal utilization of the channel.
`In another system to Ahl U.S. Pat. No. 5,313,461 a single
`channel, Spread spectrum, Star network, wireless, digital
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6,097,707
`
`4
`communication network is described in which the common
`resource is adaptively shared as a function of traffic going to
`and from the remote units. ATDMA process is disclosed in
`which Segments of user data are analyzed by the System with
`respect to content and amount and slices are dynamically
`and adaptively assigned based on that analysis. While time
`Slices which will not be used during a particular frame due
`to the lack of or the repetitive nature of information from a
`particular Switching unit can be temporarily used to transfer
`information from a different Switching unit, this System does
`not describe a reservation System where requesting periph
`erals can reserve a slot for a Subsequent cycle, nor a
`Suspending of inactive remote units with provision for their
`Subsequent re-entry.
`Thus, there is a need for and its is an object of the present
`invention to provide an adaptive proceSS for assigning
`up-link slots based on advance reservation by remote units
`and to optionally manage the allocation of available capacity
`to Served units.
`Due to the adaptive nature of the present invention, there
`is a need for and it is an object of the present invention to
`provide the overall network with a dynamic reconfiguration
`capability where one or more of the remote units can be
`removed from the network or inserted back into it without
`disturbing the normal network operations Such that removed
`remote units do not waste any System bandwidth which
`contributes to efficient use of communication linkS.
`There is also a need for and it in a further object of the
`present invention to provide a flexible adaptive network that
`has the capability to be easily reconfigured to meet a wide
`range of applications, while providing long range (over 20
`miles) and high data through-put. Typical proprietary
`(Vertical) applications include general Security (audio,
`CCTV, alarm, etc) and Security for high-rise buildings and
`gated communities; utilities, traffic management; rural tele
`communications, and ATM monitoring, to name a few.
`Typical Subscriber (horizontal) applications include remote
`access to on-line Services (Internet, etc.); remote access to
`corporation networks, and general mobile wireleSS data
`communication applications, to name a few.
`SUMMARY OF THE INVENTION
`Set forth below is a brief Summary of the invention which
`achieves the forgoing and other objects and advantages in
`accordance with the purposes of the present invention as
`broadly described herein.
`One aspect of the invention is in a Single channel, Star
`configuration, wireleSS digital communication network of
`cellular topology wherein a central control unit is radio
`frequency linked to a plurality of remotely controlled units
`and multiple access is Synchronously controlled by the
`central unit through a time division multiplexed cycle hav
`ing a total cycle time of variable duration divided into two
`phases, including an up-link phase followed by a down-link
`phase, each phase having a plurality of time slots in which
`information is transferred between units, wherein the
`improvement comprises in the up-link phase, a variable
`number of fixed size time slots, each pre-assigned on request
`of a remote unit in a prior up-link phase for the next up-link
`phase, and in the down-link phase, a variable number of
`variable size time slots.
`A feature of this aspect of the invention is the request
`being in the form of a flag Set in an information frame
`transmitted by the requesting remote unit to the central unit
`in the prior up-link phase.
`In this aspect of the invention a Synchronization frame is
`transmitted Simultaneously to all remote units at the begin
`
`Ex.1028
`APPLE INC. / Page 6 of 14
`
`

`

`S
`ning of each up-link phase, and an acknowledgement frame
`is transmitted Simultaneously to all remote units in the
`network at the end of each up-link phase. The up-link time
`Slots within which each remote unit transmits information to
`the central unit are of equal duration.
`A confirmation signal in the acknowledgement frame
`broadcast by the central unit is addressed to and received by
`each remote unit for whom a slot has been allocated in the
`next up-link cycle. Thus, each remote unit is able to locate
`its pre-assigned time slot in an up-link cycle, for example, by
`Simply counting the number of remote units Scheduled by
`the central unit for transmission ahead of itself in the up-link
`cycle .
`A further feature of this aspect of the invention is that the
`number of down-link time slots is managed by the central
`unit according to of the number of remote units for whom
`the central unit has information to be transmitted, and the
`Size of a down-link slot for a remote unit is similarly
`managed according to the payload Scheduled by the central
`unit for the remote unit.
`Another aspect of the invention is a Suspend mode omit
`ting assignment of an up-link time slot in the next up-link
`phase for any remote unit which did not request one in a
`current up-link phase.
`A feature of this aspect of the invention is that Suspended
`Stations are queried in any of a number of ways to determine
`whether they are ready to re-enter the up-link phase of the
`network, Such as, by a polling Signal transmitted by the
`central unit to each Suspended remote unit to indicate
`reservation of an up-link slot for the remote unit in the next
`up-link phase. The polling Signal may be a confirmation bit
`Set by the central unit in the acknowledgement frame
`transmitted by the central unit to all remote units at the end
`of an up-link phase.
`A further feature of this aspect of the invention is that the
`polling Signal may be transmitted every k cycles to each
`Suspended remote unit to indicate reservation of an up-link
`Slot for the remote unit in the next up-link phase, where k is
`an integer.
`A further aspect of the invention is the network operating
`in a spread spectrum.
`Another aspect of the invention is the central unit and its
`asSociated plurality of remote units forming a major cell
`with a repeater unit having a local remote unit-local central
`unit pair coupled back to back to operate as a mini-cell
`within the major cell. The local remote unit operates on the
`Same spread spectrum code as the major cell central unit,
`and the local central unit operates on a different spread
`Spectrum code.
`A further feature of this aspect of the invention is frames
`from the major cell central unit received by the local remote
`unit of the back to back pair are passed through a UART
`channel of the local remote unit to a UART channel of the
`local central unit which in turn acts as a central unit to other
`remote units in the minicell, and Vice versa, whereby the
`local remote unit also acts as a regular remote unit also in the
`major cell.
`Thus, in Summary, a major aspect of one embodiment the
`invention is the variable number of up-link slots is adap
`tively allocated by the central unit on demand by remote
`units with non-requesting units being temporarily Suspended
`from the up-link phase of the network until ready to re-enter.
`A further aspect of the present invention is the variable
`number and Size of down-link slots is adaptively allocated
`by the central unit based on the presence and amount of
`information for transmission to the remote units.
`
`6
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic diagram of the cellular structure of
`a wireleSS digital communications network employing the
`present invention.
`FIG. 2 is a Schematic diagram of a complete cycle of a
`wireleSS communications network employing the present
`invention showing an up-link phase and a down-link phase
`of an adaptive time division multipleX access process having
`3 terminal units of which only 2 terminal units are trans
`mitting in the cycle presented.
`FIG. 2A is a Schematic representation of the channel
`frame format used in the multiple-access Signalling protocol
`of the present invention shown in FIG. 2.
`FIG. 2B is a schematic representation of a 2-byte, 16 bit
`control field format used in an HDLC frame format of the
`present invention shown in FIG. 2A.
`FIG. 2C is a schematic representation of a 2-bit
`acknowledgement/confirmation field format used in the data
`packet field of an HDLC frame format use by a central
`control unit of the present invention.
`FIG. 3 is a timing diagram for a typical cycle for an
`adaptive time division multiple acceSS protocol using the
`present invention.
`FIG. 4 is a Schematic diagram of a minicell within a major
`cell of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`The detailed description is divided into five sections.
`Section 1 describes an overview of the network. Section 2
`sets forth an overview of the adaptive time division multiple
`access (“TDMA) media access control ("MAC") layer
`protocol of the present invention. Section 3 describes the
`frame formats used. Section 4 describes the Scheduling
`method on the shared radio channel. Section 5 presents the
`method for operating a Repeater Unit 15 explaining how a
`repeater can relay information from one remote region to a
`CCU 12 and vice versa.
`
`1. OVERVIEW OF WIRELESS NETWORK
`TOPOLOGY
`
`As shown in FIGS. 1 and 4 wireless network 10 of the
`present invention is based on a cellular topology. A Single
`cell 11 includes a region covered by a Single radio broadcast
`service. The cell 11 includes a single Central Control Unit
`(“CCU”) 12 and plurality of remote or terminal units
`(“TUS”) 14 each of which is radio frequency linked 13 to the
`CCU 12. In areas of the cell 11 where the radio coverage
`does not reach a particular Terminal Unit, a Repeater Unit
`(“RU”) 15 is used to relay frames between remote TUs 14a
`and 14b and the CCU 12.
`
`2. OVERVIEW OF TIME DIVISION MULTIPLE
`ACCESS MEDIA ACCESS CONTROL
`PROTOCOL
`AS shown in FIG. 1, a Single wireleSS cell 11 including a
`single CCU 12 and multiple TUs 14 is arranged in a star
`configuration. The CCU 12 is the cell controller. A TU 14
`radio frequency linked 13 to CCU 12 represents a data
`terminal device, Such as, a computer, a digital camera, a
`digital monitor, a computer terminal or the like. Media
`acceSS control protocol for the present invention employs an
`adaptive TDMA process or cycle 20. The cycle 20 of typical
`Scheduling for media access is depicted in FIG. 2. A total
`
`6,097,707
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Ex.1028
`APPLE INC. / Page 7 of 14
`
`

`

`6,097,707
`
`15
`
`25
`
`35
`
`40
`
`7
`cycle is divided into two phases, an up-link phase 21
`followed immediately by a down-link phase 22. The total
`cycle duration is variable as explained below.
`The up-link phase 21 of the cycle 20 starts with the CCU
`12 broadcasting a synchronization frame, ("Synch') 23. All
`TUs 14 in the cell 11 use the Synch frame 23 to schedule
`their access to the shared channel. AS described below in
`greater detail, TU’s 14 will know how many other TU's 14
`are Scheduled ahead of themselves in an up-link phase, and
`will be able to count slots to find their assigned slot to
`transmit in. TUs 14 are required to monitor the channel and
`determine whether the CCU 12 had allotted an up-link slot
`for them in the next up-link cycle. As will be seen below, this
`task is accomplished by a TU's receipt of an addressed
`confirmation bit set in the acknowledgement frame 29 by
`CCU 12. The CCU 12 Switches to a receive mode 24 after
`transmitting the Synch frame 23. (FIG. 3). The protocol
`provides for a specific time slot 25, 27a, allocated by the
`CCU 12 by demand (e.g. by request or reservation) from a
`TU 14 in a prior up-link phase for the next up-link phase.
`Each up-link slot is of equal duration or Size during which
`a single data frame is transmitted from the TU14 to the CCU
`12. Only during its allotted up-link time slot is a TU allowed
`to transmit. For example, as shown in FIG. 2, TU 1 is only
`allowed to transmit in slot 25, TU 2 in slot 27, TU in slot
`27a etc. If a TU, for some reason, misses the Synch frame
`23, it loses its turn to transmit during the current cycle 20.
`When all selected TUs 14 finish transmitting their frames,
`they revert to the receive mode and the CCU 12 Switches to
`the transmit mode 28. (FIG. 3). As described below in
`greater detail the CCU 12 broadcasts a Special fixed size
`Acknowledgement ("Ack”) frame 29 directed from the CCU
`12 to all TUS 14.
`Next, the down-link phase 22 immediately follows. The
`CCU 12 follows the Ack frame 29 by broadcasting down
`link data frames 31 directed to the respective TUs 14 for
`whom the CCU has traffic. During the down-link phase the
`total number of down-link slots is variable. The CCU 12
`may transmit Zero frames up to the number of TUS in its cell,
`with a maximum of one frame per TU. These frame slots,
`however, are of variable sizes depending on the size of the
`payload (presence and amount of information) intended to
`be transmitted by the CCU 12 to each respective TU 14 for
`whom it has traffic. As seen in FIG. 2 the CCU 12 has
`downloaded data frames of different sizes for TU and TU
`only and had no data message for TU. Upon completion of
`the transmission of data frames to the TUS 14, the CCU 12
`Sends the next Synch frame 23 to Start another up-link phase
`21 of a new cycle 20. Different cycles 20 may have different
`total durations of time. In this manner a CCU 12 acts as a
`frame relay between TUs 14 in the same cell, as well as with
`TUs 14 that may reside in different cells (not shown). In the
`latter case, the local CCU 12 forwards frames 31 to a remote
`CCU 12 (not shown) where the target TU 14 (not shown) is
`located.
`
`45
`
`50
`
`55
`
`3. FRAME FORMATS
`The MAC layer protocol employs three types of frames:
`Synch 23, Data 31, and Ack 29. The digital hardware used
`in the preferred embodiment is a Motorola 68302 processor.
`However, other processors are known and may also be used
`Such as an Motorola 68360. Since transmission over the
`radio channel preferably employs the HDLC capabilities of
`the Motorola 68302, all frame formats are based on the
`format of an HDLC frame 40 one embodiment of which is
`shown in FIGS. 2A, 2B. HDLC frame 40 comprises a
`plurality of individual fields wherein each field is comprised
`
`60
`
`65
`
`8
`of a number of 8-bit bytes. Applicant Stresses, however, that
`this format is only one of many that are conventional and
`will work in the protocol of the present invention. AS Seen
`in FIG. 2A HDLC frame 40 has as its first field a header or
`preamble 41, followed by a special beginning frame or start
`delimiter field 42 of 1-byte, followed by a 2-byte destination
`address field 43, followed by a 2-byte source address field
`44, followed by a frame length field 45, followed by a
`variable length information field 46 which includes a two
`part control field 47, having a 1-byte control field portion
`47a and a 1-byte type field portion 47b, and a variable length
`data packet 48, followed by a 4-byte frame check Sequence
`or CRC field 49, and terminated by an end frame or end
`delimiter field 50 of 1-byte. As more fully described below
`and as Seen in FIG. 2, to identify each frame type, the type
`field 47b of the control field 47 of an HDLC frame 40 is
`programmed with a Special code for each type as more fully
`described below. The data field of the HDLC frame 40 is
`used to carry the relevant information for the respective
`MAC layer frame.
`a SYNCHRONIZATION FRAME
`A CCU 12 broadcasts a Synch frame 23 at the beginning
`of each up-link phase 21 of cycle 20. In destination address
`field 43, HDLC frame 40 uses the FFFF hex address for
`broadcast addressing to be received by all Stations. The
`HDLC type field 47b is programmed for the Synch frame
`with the identification byte AD hex. The identification flag
`field 47b consists of four repeats of the type field code AD
`hex, namely: ADADADAD hex. Additionally, a 32-bit iden
`tification flag (not shown) is also used in the HDLC data
`field 48 for redundant recognition of the Synch frame 23. (It
`is important that no remote unit 14 miss the Synch frame 23
`which synchronizes the entire network.) These identification
`flags can be used to recognize the Synch frame even if the
`HDLC frame has CRC errors. The CRC field 49 is generated
`automatically by the Motorola 68302 when its Serial Control
`Channel, SCC, is programmed in the HDLC mode.
`b. DATA FRAME
`The HDLC Data frame 40 has a variable size data packet
`field 48 ranging between 23 octets and 128 octets. It is
`generated in the CCU 12 to forward data to a TU 14 during
`down-link phase 22. When used by the CCU 12, the Data
`frame 40 has a variable length data packet field 48 which is
`reflected in the variable size of the down-link slots 31. It also
`is generated in the TU 14 to send data to the CCU 12 during
`up-link phase 21. When used by the TU 14, the Data frame
`40 has a data packet field 48 of variable length, but which
`is restricted by the fixed size of the up-link slots 25, 27.
`Thus, if a TU 14 uses only a few of the octets in the HDLC
`data packet field 48 of a data frame 40 which do not fully
`occupy up-link slots 25, 27a, the balance of those slot widths
`would be unused. Conversely, if the length of the data packet
`field 48 of a data frame 40 was so long that the data frame
`40 exceeded the length of slot 25, 27, 27a, duration, some of
`the data would be lost.
`The 2-byte 16-bit HDLC frame 40 destination 43 address
`field is used to identify the CCU 12 address when data is
`directed from a TU 14 to CCU 12, while it is used to identify
`the selected TU 14 address when data is directed from CCU
`12 to TU 12.
`The 2-byte, 16-bit HDLC frame 40 control field 47,
`shown generally at 51 in FIGS. 2A, 2B, is used to indicate
`the Status of the last transaction and the data-link Sequence
`number in control field 47a, and the type of data frame in
`
`Ex.1028
`APPLE INC. / Page 8 of 14
`
`

`

`6,097,707
`
`9
`type field 47b. As seen in FIG. 2B control field 47.51 is
`programmed as follows:
`Bit 0 is a data link acknowledgement (“DLack”). In the case
`of data frames from a TU 14 to a CCU 12, a zero indicates
`a TU14’s positive acknowledgement of receipt of CCU
`12’s data frame 31. This field is ignored in the case of data
`frames from the CCU 12 to a TU 14 (The CCU 12 uses
`the acknowledgment frame 29 to acknowledge all trans
`missions from all TUs 14 at once).
`Bit 1 is used by a TU 14 in the present up-link phase 21 to
`make a request or reservation, directed to the CCU 12, for
`allocation of a slot 25, 27, 27a during the next up-link
`phase 21 of the next cycle 20.
`Bits 2-4 are reserved for future use.
`Bits 5-7 contain the data link sequence number of the frame,
`each bit of which can take the values: 0, 1, 2, and 3.
`Bits 8-15 contain the frame type identification field. The
`content of this frame is a Sync frame (AD hex), or
`indicates if the frame contains data (10 hex), ack only, (01
`hex), or data plus a piggybacked ack (11 hex).
`The HDLC frame 40 data field 48 has a variable size of
`up to 122 octets of which 18 are reserved for higher level
`protocols and 104 for actual transport level data. Informa
`tion is encapsulated inside the HDLC frame data field.
`
`c. ACKNOWLEDGMENT/CONFIRMATION
`FRAME
`This frame format 40 is