United States Patent
`Hodzic et al.
`
`[19]
`
`I 1111111111111111 11111 1111111111 1111111111 1111111111 lllll 111111111111111111
`US006097707 A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,097,707
`*Aug. 1, 2000
`
`[54] ADAPTIVE DIGITAL WIRELESS
`COMMUNICATIONS NETWORK
`APPARATUS AND PROCESS
`
`5,129,096
`5,212,805
`5,276,686
`
`7/1992 Burns ..................................... 455/33.1
`5/1993 Comroe et al. ........................ 455/33.1
`1/1994 Ito .......................................... 455/33.1
`
`[76]
`
`Inventors: Migdat I. Hodzic, 11633 Bridge Park
`Ct., Cupertino, Calif. 95014; James M.
`Brennan, 1224 Martin Ave., Apt. #5,
`San Jose, Calif. 95126
`
`[ *] Notice:
`
`This patent is subject to a terminal dis(cid:173)
`claimer.
`
`[21] Appl. No.: 08/444,553
`
`[22] Filed:
`
`May 19, 1995
`
`Int. Cl.7 ........................................................ H04J 3/16
`[51]
`[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
`
`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, 27 a], 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(cid:173)
`tively utilized. The CU adaptively manages all slot assign(cid:173)
`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 TU's.
`
`4,644,534
`
`2/1987 Sperlich ................................. 370/95.3
`
`50 Claims, 3 Drawing Sheets
`
`Ex.1013
`APPLE INC. / Page 1 of 14
`
`

`

`U.S. Patent
`
`Aug. 1, 2000
`
`Sheet 1 of 3
`
`6,097,707
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`
`Ex.1013
`APPLE INC. / Page 2 of 14
`
`

`

`U.S. Patent
`
`Aug. 1, 2000
`
`Sheet 2 of 3
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`6,097,707
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`Ex.1013
`APPLE INC. / Page 3 of 14
`
`

`

`U.S. Patent
`
`Aug. 1, 2000
`
`Sheet 3 of 3
`
`6,097,707
`
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`Ex.1013
`APPLE INC. / Page 4 of 14
`
`

`

`6,097,707
`
`1
`ADAPTIVE DIGITAL WIRELESS
`COMMUNICATIONS NETWORK
`APPARATUS AND PROCESS
`
`BACKGROUND OF THE INVENTION
`
`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
`5 which has the efficiencies of a star configuration.
`
`e. REMOTE COVERAGE
`
`1. Field of the Invention
`The present invention relates generally to the apparatus
`and methods of controlling multiple access to a communi(cid:173)
`cation network by a plurality of remote stations, and more 10
`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(cid:173)
`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.
`
`a. MOBILITY
`
`One important need is mobility. Increasingly in our soci(cid:173)
`ety there is a requirement for mobile communication sys(cid:173)
`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(cid:173)
`cations within buildings and between adjacent building
`structures without running phone lines and without interfer(cid:173)
`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(cid:173)
`point-to-point or multi-point-to-multi-point networking sys(cid:173)
`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.
`
`c. LOW COST
`
`35
`
`In cellular, star configuration, multi-point-to-point
`systems, major problems have been the fading of the broad(cid:173)
`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
`15 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(cid:173)
`cation in digital wireless networks to avoid interference and
`20 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
`25 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
`30 bandwidth which is then demodulated coherently by con(cid:173)
`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
`40 where the coverage of the major cell central unit is insuf(cid:173)
`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
`45 practical application.
`
`Cellular topology has found wide acceptance worldwide
`in multi-point-to-point and multi-point-to-multi-point net(cid:173)
`works. The use of a cellular structure in wireless commu(cid:173)
`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 50
`cellular topology because they can be formed by combining
`numerous single cells to accommodate particular applica(cid:173)
`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 55
`provide a wireless radio frequency communications network
`which can utilize the existing worldwide cellular infra(cid:173)
`structure in a variety of practical commercial applications.
`
`f. LIMITED SPECTRUM AND 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(cid:173)
`sion multiple access ("CDMA"), and time division multiple
`60 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
`
`d. EFFICIENT ORGANIZATION
`
`A star configuration is an efficient organization for con(cid:173)
`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- 65
`cerned. The remote units can communicate between each
`other via corresponding central units which can also act as
`
`Ex.1013
`APPLE INC. / Page 5 of 14
`
`

`

`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. A TDMA 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
`10 information from a different switching unit, this system does
`not describe a reservation system where requesting periph(cid:173)
`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(cid:173)
`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
`40 communication applications; to name a few.
`
`20
`
`15
`
`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 5
`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(cid:173)
`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 25
`number of subscribers. Additionally, TDMA has more flex(cid:173)
`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 30
`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 35
`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(cid:173)
`tation. Some TDM systems use a token passing ring. Others
`use fixed slot allocation or dynamic slot allocation. In a fixed 45
`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(cid:173)
`cally allocated systems, parameters, such as, the size of each
`time slot and the number of time slots allocated to a 50
`particular device may be varied. Since a device only trans(cid:173)
`mits during its allocated time slots, communication colli(cid:173)
`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
`
`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(cid:173)
`ing a total cycle time of variable duration divided into two
`phases, including an up-link phase followed by a down-link
`55 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
`60 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
`65 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.1013
`APPLE INC. / Page 6 of 14
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`

`

`6,097,707
`
`6
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram of the cellular structure of
`a wireless digital communications network employing the
`5 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
`10 3 terminal units of which only 2 terminal units are trans(cid:173)
`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
`20 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
`
`5
`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 15
`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(cid:173)
`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 25
`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 30
`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
`m~~
`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 45
`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 55
`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- 60
`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 65
`by the central unit based on the presence and amount of
`information for transmission to the remote units.
`
`35
`
`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
`50 ("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
`
`Ex.1013
`APPLE INC. / Page 7 of 14
`
`

`

`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 5
`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 10
`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 15
`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, 27 a, 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 TU 14 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, TUN in slot 25
`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 30
`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(cid:173)
`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, 40
`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 TU2 and TUN
`only and had no data message for TU 1 . 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 50
`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.
`
`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 65
`shown in FIGS. 2A, 2B. HDLC frame 40 comprises a
`plurality of individual fields wherein each field is comprised
`
`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(cid:173)
`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
`35 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
`
`6,097,707
`
`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
`20 MAC layer 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
`45 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, 27 a, the balance of those slot widths
`55 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
`60 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.1013
`APPLE INC. / Page 8 of 14
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