AU629605B2 - Cellular telephone data communication system and method - Google Patents

Description

SHELSTON WATES PATENT ATTORNEYS CLARENCE STREET, SYDNEY o

AUSTRALIA

Cables: 'Valid' Sydney Telex:_24422 wa COMMVONWEALTH OF AUSTRAL6 9 0 FORM PATENTS ACT 1952 COM P LE T E S P E.CIF IC AT ION FOR OFFICE USE: Class nt .Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: TechnigzjLF The pr comm uni cati to a data effe ctivel;tel ephone fn, Priority: 'Related Art: 0 0 Name of Applicant: -TRUM CEL-LULAR COPMT'INICATION S 00 ~CORPORATTON- .009 Address of Applicant: 1h-Tw-rS 27- -~tmos 7:, .Fzeeway-,-Dallas,-Texa-s 720,United L4.'~ Address for Service: SHELSTON WATERS, 55 Clarence Street, Sydney 0.0 00 0 0have made t.

~e~oover conven :~00 In such sy suitable *i, provide ser modem. Wit 0 changes imdi- 0 (Automatic Convention a- 20 This requir data until packet are 0 0: frequency o: wire line er controlling Cur ren scrambled in which will a valid s conventionz scrainbler c signal is c Complete Specification for the Invention entitled: 4k-t "CELLULAR TELEPHONE DATA COMMUNICATION SYSTEM AND METHOD" The following statement is a full description of this invention, including the best method of performing it known to us:- (Divisional of 79030/87 (590,977) dated 28th September, 1987) 14

A

to receive data from which the microprocessor has A1 I 1A Cellular Telephone Data Communication System and Method Technical Field The present invention relates to telephone data communications systems generally, and more particularly to a data communication system which is adapted to effectively transmit a data stream over a cellular telephone network.

00ick round Art Modern computer and telephone system technology have made the transmission of computer originated data over conventional telephone lines a commonplace event.

In such systems, a computer is connected through a @000 suitable interface, such an a RS 232 interface, to provide serial data signals to a conventional wire line modem. With modems of this type, when signal quality ::::changes induce errors in the modem data stream, an ARO 0 (Automatic Repeat Request) or packet repeat scheme is 0 conventionally employed for controlling these errors.

This requires a complete repeat of numerous bytes of data until such time as all of the bytes of data in the packet are received correctly. However, the low frequency of signal quality change induced errors in a wire line environment makes this an efficient method of controlling error.

Current wire line modem technology provides a scrambled modulated data signal to the telephone line which will not be interpreted by telephone equipment as a valid switch command. To accomplish this, conventional wire line modems are provided with a scrambler circuit which assures that the modulated signal is continuously changing. This changing signal 00 O 00 0 o 0 0 40 000 0 0 0 00 0 ooo 0n 000 is used by to provide modulated cause the telephone e switch comn Conve ef f ectivel system for operate ef convention cellular te to and fr, between zo city with of adjoini own transm switching voice comm city passe transferre process in normally e problem fr communica significan are used.

A wir equipment 30 signal lo.

cellular t the vehic.

between cc experience telephone power tran.

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i 2 o 0 00 0000 S0 0 o o o 0 o o 0 )0 0 is used by the modem PLL (Phase Locked Loop) circuitry to provide synchronization, for without this scramble modulated signal, a static condition of the modem will cause the PLL to loose synchronization and the telephone equipment to interpret the static signal as a switch command.

Conventional telephone modems have operated effectively to interface computers with a telephone system for data transmission, but these modems do not operate effectively to provide data transmission over conventional cellular telephone equipment. In a cellular telephone system, data transmission must occur to and from a moving vehicle which may be passing between zones or cells in the system. For example, a city with cellular service is divided into a plurality of adjoining geographic cells, each of which has its own transmit/receive antenna controlled by a mobile switching office. For conventional cellular telephone voice communication, an automobile travelling through a city passes from cell to cell, and the signal is transferred from antenna to antenna. This transfer process interrupts communications for a brief period, normally a fraction of a second, and does not cause a problem for voice communication. However, for data communications, this "hand-off" process results in significant problem if conventional wire line modems are used.

A wire line modem for use with normal telephone equipment will disconnect upon experiencing a carrier 30 signal loss. Thus, such a modem, when used with a cellular telephone system, will disconnect each time the vehicle in which the modem is mounted travels between cells, for some carrier loss will always be experienced when the radio signal used for cellular telephone communication is switched between the low power transmission stations of adjacent cells.

In the cellular telephone environment, numerous 00 00 o0 0 0 0 oa" 0 0 0 0 .000 0000 errors are the probl communicat bit errors frequently transmitte and bounc shielded f error in 10 transmiss present in cellular u: environmen large and an accepta occur so received.

in convent the proble 20 Final wire lint circuitry continuou the moder employ a I the numbe error occ single bi in additi 30 scrambler errors ir These err a cellula.

the err conventio In t communica 0 0 00 0 0 0 0 0 a0 0 0 0r. 0 O0 0 00 000 9o a 0 0 00 0

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r~-arrrrrrr~---- 16 excess of 2 bits would result in no acknowledgment -3 0 0 0 o 0 q0 o b 1 0 0 errors are induced into data transmission because of the problems associated with cellular telephone communication. Echo and fading problems cause multiple bit errors in the data stream, and such problems occur frequentl~y with a moving vehicle. For example, the transmitted signal may hit a building or other obstacle and bounce erratically or fade as the vehicle is shielded from the cell antenna. This high frequency of error in the data stream~ transmitted by cellular transmission renders 'the error correction protocol present in conventional wire line modems unsuitable for cellular use. Errors occur so frequently in a cellular environment that the number of repeat requests becomes large and data transimission efficiency is reduced below an acceptable amount. In some instances, errors may occur so of ten that a correct packet may never be received. Thus, the error correction protocol present in conventional te-Lephone modems is unable to cope with the problems presented in a cellular environment.

Finally, as -previously indicated, the conventional wire line telephone modem incorporates scrambler circuitry to ensure that the modulated signal is continuously changing to provide synchronization f or the modem PLL circuitry. However, such scramblers employ a polynomial which has the effect of increasing the number of bit errors received. If a single bit error occurs during the transmission of data, that single bit error will be presented when received, but in addition, that error will propagate through the scrambler polynomial and later cause two additional errors in the received data presented to the user.

These errors, coupled with those normally inherent with a cellular telephone system, will completely overwhelm the error correction circuitry present in a conventional modem.

In the past, systems have been developed for communicating data between a plurality of geographical D0 0~ 0 000 04 zones a, Such s, 4P525,8 Aithouc data con geograp address and f adi Piasclosc-L 10 I t provide transmi system.

Ano pr ovi de data ove modem cc 20 modem i pre deter 20 carrier is Cause loss of resumes w A fL provide data ove modem con includes data sigr 30 modern.

Yet provide z data over modem conl includes said modE *000 0090 0900 0 9 0 09 9 00 0 0 0 0 0000 0 90 0 4 40 0 6 04

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17 4mn~Avecz a sliding packet -4zones and a host computer by mieans of portable radios.

Such systems are disclosed in U.S. Patent Nos.

4,525,861 and 4,545,071 to Thomas A. Freeburg.

Although these patented systems effectively provide data communications from a host computer throughout a geographical area divided into zones, they do not address the problems presented by hand-off or echoing and fading in a cellular telephone system.

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o 04 000 00 04 *0 o 4t '444 4 4440 *44' 44 4$ 0 44 4 4 41 4.4.4.4 4 *4 44 1 Disclosure of the invention It is a primary object of the present invention to provide a novel and improved method and apparatus for transmitting data signals over a cellular telephone system.

Another object of the present invention is to provide a novel and improved method f or transmitting data over a cellular telephone system by means of a modem connected to the cellular telephone system. The modem is maintained in the activated state for a predetermined time period after a loss of the system carrier signal before it is permitted to deactivate and is caused to remain in the activated state after the loss of the carrier signal if the carrier signal resumes within the predetermined time period.

A further object of the present invention is to provide a novel and improved method for transmitting data over a cellular telephone system by means of a modem connected to the cellular telephone system which includes adding error control correction data to the data signal before providing the data signal to the modem.

Yet another object of the present invention is to provide a novel and improved method for transmitting data over a cellular telephone system by means of a modem connected to the cellular telephone system which includes repetitively providing a unique data byte to said modem during a break in the data signal to the 0$ 0$ 00 0 0 0 0 00 0 0 0 000* 00 4* 0 0 4 0 4 #000 00 4 0040 0004 0000 0 0 oOOO 0000 0 0 4 00 4 4* 0 0 0 4 04 0000 00 4 modem.

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provide data ov modem C inc ude.

signal rem ovin data si 10 provide Ye pr ovide data ov modem c include modem, to the the mo consist 20 size cl quality increas f or a b,.

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com putt include 30 the com control pr ev ensi gnal period.

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pr ovi dt communi .4 cellula, 18 I.T. rnnkrpt- 1 I iir 5 o 0 ogo o o o o 0 0 00 0 0 0 II 0 o 000 0000 modem.

A further object of the present invention is to provide a novel and improved method for transmitting data over a cellular telephone system by means of a modem connected to the cellular telephone system which includes adding error control correction data to a data signal before it is provided to the modem and then removing said error control correction signal from the data signal at the receiver before the data signal is provided to a receiver use device.

Yet another object of the present invention is to provide a novel and improved method for transmitting data over a cellular telephone system by means of a modem connected to the cellular telephone system which includes providing no scrambler polynomial in the modem, but instead adding error control correction data to the data signal before providing said data signal to the modem. This error control correction signal consists of a sliding packet ARQ wherein the packet size changes or slides based on the transmission quality of the transmission. The packet size is increased for a good transmission signal and decreased for a bad transmission signal. This is combined with a forward error correction signal.

Another object of the present invention is to provide a novel and improved cellular telephone data communication system for transmitting data from a computer over a cellular telephone unit. This system includes a microprocessor which is connected between the computer and a special cellular telephone modem to control the operation of the modem. The microprocessor prevents modem disconnect upon the loss of a carrier signal for periods less than a predetermined disconnect period.

A further object of the present invention is to provide a novel and improved cellular telephone data communication system for providing communication over a cellul and a lines is con for ce which microp data s provic 10 modul a the mc transm o retrar 00 0 0 a S lines °0 and mi 00 00 S" remove 0 a00 00° before o0oo

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provic 20 commur compu 0 microp unique modem the ce theret

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provic commun 30 comput incorp adapte interf tran s associ of dat micro oo 0 0600 0060 0l 0 0 00 0 0 So a o o 00 ft I -I 19 cellular telephone call is completed, as sensed by the condit 1 I a~r~rYIII 6 oo 0 0 0 00 4 0 0 0 0 0 cellular telephone network between a portable computer and a computer connected to conventional telephone lines by use of unique modems. The portable computer is connected to a modem maintained in a unique state for cellular transmission by means of a microprocessor which controls the operation of the modem. The microprocessor adds error control correction data to a data signal from the computer before the data signal is provided to the modem. The data signal with the modulated error control correction data is provided by the modem to a cellular telephone transceiver which transmits the data to a receiving system capable of retransmitting the data over conventional telephone lines. At the central computer, a unique modem and microprocessor combination receives the data and removes the error correction control signals therefrom before providing the data signal to a use device.

Yet another object of the present invention is to provide a novel and improved cellular telephone data communication system for transmitting data from a computer over a cellular telephone unit. A microprocessor connected between the computer and a unique cellular -modem senses a static condition of the modem and provides a repetitive synchronization byte to the cellular modem during a break in the data stream thereto.

A further object of the present invention is to provide a novel and improved cellular telephone data communication system for transmitting data from a computer over a cellular telephone network which incorporates a mobile data programming interface adapted to operate with a static data programming interface. Both such interfaces operate to either transmit or receive data and cooperate with an associated external computer used to provide a stream of data to be transmitted. Each interface includes a microprocessor which is programmed to adapt the oo o o 0 0 40 0 o o a o 00 transm in the modem transm to prc commu: comipu incorE 10 adap't inter causir S envirc detect the r recei o The re and cc the da 20 accep the t ackno the e data F S data.

previ errone P 00 0 0 0 0 0 0 9 0k) 0 0 4 0 0P 0 f 1 00 0 4 00440 0 0 I 04 0 o 0 0 04 0 00 00 0 e, o o oer a 4,' Brief

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30 telep invent

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which telep invent correc I- I 19a condition that the modem PLL may lose synchronisation or of the o8 ar i I i C~P~-XILLI~lli 1 7 00 0 0 0 0 o 0 0 04 0 0 o 0 0 0 0 D0 transmitted data to the high error frequency prevalent in the cellular telephone environment and to control a modem operating in a unique mode for cellular transmission.

A still further object of the present invention is to provide a novel and improved cellular telephone data communication system for transmitting data from a computer over a cellular telelphone network which incorporates a mobile data programming interface adap'ted to operate with a static data programming interface to overcome the effects of signal error causing factors in the cellular telephone system o environment. The transmitting interface adds an error detection and correction format to the data signal and the receiving interface removes this format from a received data signal which is sent to a use device.

The receiving interface responds to the error detection and correction portion of the received signal to check the data for error and to either acknowledge receipt of acceptable data or to provide an error indication to the transmitting interface by withholding the acknowledgment. The transmitting interface evaluates the errors in the received data stream and varies a data packet repeat size for subsequently transmitted data. Also the transmitting interface retransmits previously transmitted data which was found to be erroneous at the receiving interface.

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proc trans comm" 04900 0 uv40 *00a* 0 0, 00 4 00 0 0, 0 4 0 04 4 4 l a 0 a D4 telep gener cellu tran.signe anter 14 a tran cell 20 connoper conv the tran.

14 t cony tran syst tran 30 The c be o Serv Comm syste cont cont 0 0 Brief Description of the Drawings Figure 1 is a block diagram of the cellular telephone data communication system of the present invention; Figure 2 is a diagram illustrating a manner in which the data signal to be transmitted by the cellular telephone data communication system of the present invention is modified to provide an error detection and correction capability; r j A A4 20 of the modem is. With this information, the II I V 4 m rr i c i r m ct system

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Ofl 8- Figure 3 is a flow chart showing the control functions of th. microprocessor for a transmitting interface of the cellular telelphone data communication system of the present invention; and Figure 4 is a flow chart showing the data processing function of the microprocessor for a transmitting interface of the cellular telephone data communication system of the present invention.

Best'Mode For Carrying Out The Invention The system for transmitting data over a cellular telephone network of the present invention is indicated generally at 10 in Figure 1. A vehicle mounted mobile cellular telephone system conventionally includes a transceiver 12 which transmits or receives voice signals in the radio frequency range by means of an antenna 14. Voice signals transmitted by the antenna 14 are received by an antenna 16 connected to a transceiver 18 located in a specific cell area of the cellular telephone network. The transceiver 18 is 20 connected to cellular land line equipment 20 which is operative to transmit the received signal over conventional telephone lines 22. Voice signals from the telephone lines 22 may also be transmitted by the transceiver 18 and the antenna 16 back to the antenna 14 to be provided by the transceiver 12 to a conventional mobile cellular telephone unit. The transceiver 12 is controlled by a cellular telephone system control unit 24 which is connected to the transceiver by means of a cellular telephone bus 26.

The cellular bus 26, for purposes of description, may be one which meets the AMPS (Advanced Mobile Phone Service) specifications determined by the Federal Communications Commission during test of the cellular system in Chicago. These specifications indicate that control signals between the transceiver 12 and the control unit 24 should be on an eight bit parallel a04 a 0 S 0 i S6 4 a 0 0 oi o 4 i 0 part.

diff a 24 desc Syst 269.

whir cony 10 port prog This cell 0 0 0O 0 o the the 0 4 syst S tele an e rect 20 diff betw defi :.10 cond '0 4 inte 0a 0 comn O cell Scha 0 0 impl 30 The oper cont proc anal sele data in a 1 Irll -1 I IC i; 21 system to a designated telephone number (123-4567) and the r r-pi-r i in i-riwi-irnc are zi-nrel in 1-he mirrnnrnePSSnr =Q illust- I o 1 e -il ii-- rsrLx ";'"~'~~'Y"Y~YPrUad~\fu*mrr~illll*lcYII -9- 00 00 o0 0 OQ I 4 1 ft aI 4 .0* 1

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Pt~' party line bus and that the analog signals should be a differential signal with a nominal -20 dbV level using a 24 wire interconnecting cable. A very complete description of the AMPS system is provided in 'The Bell System Technical Journal", 1979, Vol. 58, No. 1, pp 1- 269.

To this point, the cellular telephone system with which the present invention is combined is a conventional cellular telephone system, and the mobile portion of this syotem is connected to the mobile data programming interface 28 of the present i.nvention.

This mobile data programming interface includes a cellular interface 30 which renders the remainder of the mobile data programming interface compatible with the cellular bus 26 of a particular cellular telephone system. For example, with AMPS compatible cellular telephones, the cellular interface 30 would consist of an eight bit parallel I/O, port party line drivers and receivers, operational amplifiers providing 20 differential driving and receiving analog conversion between the -20 dbV signal on the cellular bus and the defined levels required by an analog switch and conditioning system 32 for the mobile data programming interface. Cellular 'interfaces of this type are known, commercially available items, as exemplified by cellular interfaces sold by Motorola Corporation of Schaumberg, Illinois, or Oki of Japan.

The analog switch and conditioning system 32 is implemented using currently known switching technology.

30 The system may incorporate CMOS analog switches operative in response to microprocessor generated control signals to switch the state of signal processing operational amplifiers. Basically, this analog switch and conditioning system operates to selectively connect various components of the mobile data processing interface to the cellular interface 30 in a manner to be described in greater detail.

044 44G 00 0 0 00 o a 0 4 4 a o oa is c for con the Thi mic.

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U-Tr 7v- 22 illustrated in greater detail in Figure 4, and for niirnnac of i-1is description, the data transmission is 11 1 N, i 10 00 00 00 0 o 0 so *o 00 0 09 0 Q' 0 0 0 0000c The heart of the mobile data programming interface is a microprocessor 34 which provides control functions for the cellular interface 30 and analog switch and conditioning system 32 as well as for other portions of the mobile data programming interface to be described.

This microprocessor my be a conventional 8/16 bit microprocessor, such as the Intel 8088 manufactured by Intel Corporation. The microprocessor includes random access (RAM) and read only (ROM) memory storage systems which contain the control and data error programs necessary to adapt computer data for cefluJar telephone transmission. The use of a separate microprocessor in the mobile data processing interface frees the limited memory which is normally available in portable computers for other uses.

A serial data stream is provided to the microprocessor 34 from an external portable computer 36 by means of r_ conventional RS 232 interface 38 included within the mobile data programming interface. Data received by the microprocessor from the portable computer 36 is provided with unique error correction signal information in the microprocessor before being provided to a modem 40.

The modem 40 may be one of a number of conventional modems used for telephone wire line transmission which has test mode capabilities for deactivating certain modem functions. A particular commercially available modem suitable for use as the modem 40 is the AMI 3530 modem manufactured by Gould Advanced Semiconductors of 3800 Bemstead Road, Santa Clara California. Modems of this type, when employed for data transmission over conventional telephone lines, will disconnect immediately in response to a carrier loss. When such modems sense a channel blanked status occasioned by a carrier loss, they provide a "break bit" output and disconnect. Also, for normal use such modems include a scrambler system which ass cha

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a 0 the a 0 to dea 00 00 be 0 00 but 00. rer moc 0000r 0 0 b000 0000J~ 0 00 00t 9 0J 0 0000 000.0 0 00i 00 0 has the thr to 0. 0 0 00 0 00a 00 0 0r 00 0 00 0.00,0 0 00O 00 0 0 OtlO 0 00a 00 0 as ant anc sui 1ir 30 the of prc to w h.

hos prc ope .1 22asignals T 7 r to keep the modem PLL in synchronization.

rlirinn 1-he nperation of the modem, the 11 assures that the data modulated signal is continuously changing, and this signal change is used by the modem PLL circuitry to provide synchronization. A nonscrambled modulated signal may be interpreted by the telephone operating equipment as a valid switch command, and this is particularly true when the modem is in the static condition. Normally the scrambler system in the modem prevents this static condition where loss of synchronization by the PLL or the interpretation of the static signal as a switch command is most likely to occur. However, modems such as the AMI 3530 incorporate a test mode of operation wherein o the miodem is prevented from disconnecting in response to carrier loss and wherein the modem scrambler can be t deactivated or defeated. Normally, such modems would be incapable of effective operation in this test mode, °o but it is the availability of this test mode that 000 renders modems of this type suitable for use as the modem The data stream from the microprocessor 34, which has been provided with unique error correction data by uo the microprocessor, is transmitted by the modem oS'' through the analog switch 32 and cellular interface to the transceiver 12. This data is then transmitted S° as a radio frequency signal by the antenna 14 to the antenna 16, where it is converted by the transceiver 18 and cellular land line equipment 20 to a signal suitable for transmission over conventional telephone lines 22. These telephone lines connect the signal to the second portion of the cellular transmission system of the present invention which is a static data programming interface 42 operative to pass data signals to and from the telephone line 22. The data signals which are passed to the telephone line originate at a host computer 44 which cooperates with the static data programming interface in a manner similar to the operation of the portable computer 36 w;ith the mobile 23 -23 rpr-ti 4 ive svnch byte is generated which is transmitted i zi tl i

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12 00 0.

0 0 0 0 0 00 co o 00 0 0000 0000 data programming interface 28.

For transmission purposes, the computer 44 provides data to an RS 232 interface 46 which in turn provides the data to a microprocessor 48. This microprocessor is identical in construction and function to the microprocessor 34, and is programmed with the same control and error correction and other programming. The microprocessor 48 adds error correction and control signals to the data provided from-the RS 232 interface, and then provides the modified data stream to a m'odem 50. The modem 50 is identical in construction and function to the modem 40, and operates to transmit the data stream b- means of an analog switch and conditioning system 52 to a conventional FCC interface 54. The FCC interface provides the data stream to the telephone lines 22 where they are sent by means of the cellular land line equipment 20 to the transceiver 18. The data is then transmitted to the transceiver 12 which provides it by means of the cellular interface 30 and the analog switch 32 to the microprocessor 34. The microprocessor then removes the error correction and control signals from the data stream and provides the data through the RS 232 interface 38 for display and use by the portable computer 36.

The static data programming intertace 42 receives data transmitted over the cellular telephone line, and this incoming data from the FCC interface 54 is fed by means of the analog switch 52 to the microprocessor 48.

Here the error and control signals are removed from the data and the data is then displayed and/or used by the computer 44. It will be noted that the static data programming interface 42 and the mobile data programming interface 28 are substantially identical in structure and operation with the exception that the static data programming interface is connected to telephone lines by an FCC interface while the mobile co *a 0 R0 0 00 00 00 00 0 6 06 0000 0 00 0 0000 data programm telephone syi mobile data pr vehicle bat conventional power bus 64 provide powe mobile data T connected to I 10 The static d similar power conventional building cont Although and the stat communicate data over a units can a cellular tel 20 data progranr interface 66 tel ephone-l conventional conditionintransmit and the transce data progra interface 7 telephone to 30 the telephor FCC interf programmin programming communicat.

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-4 i, i_ i; L 13 00 00 00 e 0 6 0 00 do 00 o 0 b 00 00 00 o 00 0 oQ 0 00-1) 0 00 data programming interface is connected to a cellular telephone system by a cellular interface. Aiso, the mobile data programming interface may be powered from a vehicle battery 60 which operates through a conventional power converter 62 to provide power to a power bus 64. This power bus 64 is connected to provide power to all of the operating units in the mobile data programming interface 28 and may also be connected to provide power to the portable computer 36.

The static data programming interface 42 includes a similar power bus, not shown, which is t nnected to any conventional power sup'ly such as the power supply in a building containing the computer 44.

Although the mobile data programming interrace 28 and the static csta programming interface 42 muut communicate with one another to effectively transmit data over a cellular telephone system, both of these units can also transmit and receive conventional cellular telephone audio transmissions. The mobile data programming interface 28 includes a telephone interface 66 which-may be connected to an external telephone-like handset 68 and which operates in conventional manner through the analog switch and conditioning system 32 and cellular interface.30 to transmit and receive audio communications by means of the transceiver 12. In a similar manner, the static data programming interface 42 includes a telephone interface 70 which may be connected to an external telephone to transmit and receive audio signals through the telephone interface, the analog switch 52 and the FCC interface 54. Thus, both the mobile data programming interface 28 and the static data programming interface 42 are adapted for normal audio communication. Like the mobile data programming interface, the static data programming interface includes a control and display section 72 which is connected to the microprocessor 48 and which operates 00 v 0 t.

4 00 09 09 6f 9 .0 0 S0 000( to receive extracted t, Both t] the static with optio block 74 i interface i include ot employed to 10 cellular p, devices kn diadlng and Before mobile dat data progr understand and modem cooperate t transmissi 20 diagramati transmitte Computer microproce.

for purpose of equal s would be dnecessarij divided by words, anL 30 each packe would norn two are sh in a packe micro proce control w data wor while byte 0000 0) 0 5900 9000 0 90 90 0 09 a 0 0 0 0 90I 0 0, S0 0 00 6. 0 0. 0 0 00C 00 0 69091 1, 00a 69b 0 2'

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1 signal is c r .i i~ 14 nO. Ct a9 a a h 4 00 a9 a fl 0 04) 4F a) a 9 a.r at S 090 a 094o to receive data from which the microprocessor has extracted the control and error signals.

Both the mobile data programming interface 28 and the static data programming interrace 42 will operate with optional equipment, and an optional equipment block 74 is shown for the mobile data programming interface in Figure 1. This optional equipment might include other modems, a microphone which may be employed to provide audio communication in place of the cellular phone 68, and various memory and encrypting devices known to the art to accomplish automatic dialing and similar functions.

Before considering in detaii the operation of tne mobile data programming interface 28 and the static data programming interrace 42, it is necessary to understand the manner in which the microprocessor 34 and modem 40 and the microprocessor 48 ano modem 5u cooperate to adapt a data signal for cellular telephone transmission. With reference to Figure 2, there is diagramatically illustrated a data document 76 to be transmitted which has originated win the portable computer 36. This data document is divided, by the microprocessor 34, into a plurality of packets 78, ana for purposes of illustration in Figure 2, four packets of equal size are shown. In actuality, a document would be divided into many more packets which would not necessarily be of equal size. Furtner, each packet is divided by the microprocessor 34 into a plurality of words, and for purposes of ilLustration in Figure 2, each packet 78 includes two words 80. Again, a packet would normally contain many more than two words, but two are shown for purposes of illustration. Each word in a packet includes three bytes a, b, ana c, ano the microprocessor 34 will determine whether the word is a control word or a data word. When the word is a data word, then bytes a and b will be data bytes, while byte c is a foward error correction (FEC) byte.

0 0p aa o t, a o, 09 0 0 4.t44 as n a 40,100 Conversely, be the con control w or FEC byte.

the FEC byt Data w stream, w asynchrono control wor 10 example of packet "en packet. Sy cyclic redu: packet "end not affect an asynch acknowledgm for byte a the FEC b 20 synchronou word", woul CRC byte f control wo byte b is The F1 to check t whether or error is d, FEC byte tc 30 a predeterr is exceede will not microproce retransmi predetermi, of bits pe occur for 4490 a bra a aad a a a a 04 a 4 a a a aa a 04.4 o bnn fln,..

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25 signal is continuously changing. This changing signal pu weL tia i In th C a 'I ct 1 15 o Co C 00 0 C~ C c CC4a 0 *0 0V Conversely, if the word is a control word, byte a will be the control word signifier, byte b will be the control word descriptor and again, byte c will be the FEC byte. Thus it will be noted that byte c is always the FEC byte for both data and control words.

Data words are always synchronous with the packet stream, while control words may or may not be asynchronous to data. An example of an asynchronous control word would be an acknowledgment word, while an example of a synchronous control word would be the packet "end" word which is the last word in every packet. Synchronous control words are added into the cyclic redundancy check (CRC) which is included in the packet "end" word, while asynchronous control words do not affect the CRC of a packet. An exemplary form for an asynchronous control word, for example, the acknowledgment word, would be a control word signifier for'byte a, the packet number for byte b, and byte c, the FEC byte. On the other hand, an example of a synchronous control word, such as the packet "end word", would be a control word signifier for byte a, a CRC byte for byte b and the FEC byte as byte c. A control word synchronous to the packet indicates that byte b is a data rather than a control byte.

The FEC byte causes the receiving microprocessor to check the data bytes in a data word and determine whether or not an error exists in that word. If an error is detected, the microprocessor 48 will use the FEC byte to correct the word at reception. However, if a predetermined error level in any word within a packet is exceeded, an acknowledgment signal for the packet will not be trahsmitted back to the transmitting microprocessor, thereby causing this microprocessor to retransmit the entire packet. For example, the predetermined error level could be a specified number of bits per word, for example 2 bits. Correction would occur for any error of 2 bits or less, but an error in 0u 0 0 00 0O 9 0044 0 00, 00 0 0040 0000 excess of being trans The m.

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0 00a 40 0 000* 0 0 0444 0040L 0 04) 044 0 00O 04) 0

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26 .d aU 4 d uL t.j b.

In the cellular telephone environment, numerous I LI communic F9(~ IIIBII~ r xr 16 o~ 0 0 00 00 oo 0o ooe 0000 excess of 2 bits would result in no acknowledgment being transmitted for the packet.

The microprocessor unit 48 operates in a manner identical to that of the microprocessor 34 to form data packets with control and data words to transmit data provided from the computer 44, and the microprocessor 34 operates in the receiving mode to check the data byte and pass acceptable data onto the computer 36. If the transmitting microprocessor 48 or 34 does not receive acknowledgment signals back from the receiving microprocessor, correction, or other procedures to be described, are initiated by the transmitting microprocessor.

Referring ba-ck to Figure 2, if the receiving microprocessor, in this example the microprocessor 48, examines a received data -word and discovers an error in excess of the predetermined error level, it will not transmit a packet acknowledgment signal to the microprocessor 34. The transmitting microprocessor 34 will, by the lack of acknowledgment signals, be informed of excess error in a data packet 78, and will operate to retransrfit this packet until the data is received in a substantially error-free or at least a correctable condition. To this point, the transmission of the data package has occurred in much the same manner as does the transmission of a data stream over a telephone wire. However, in the telephone wire environment, the error frequency is not as great as that experienced with cellular telephone transmission systems, and conseguently, a uniform packet repeat process for error correction is acceptable for wire line data transmission. This is not the case for cellular telephone transmission, because the high error frequency might well cause multiple packet repeats to such an extent that no transmission would ever occur.

Consequently, in tnis preferred embodiment the trans- -mitting microprocessor is programmed with an error 00 00 a 0 0 o 0 0 00 00 IQ* oo00 00900 0 0 0 0000 0 6 00 0 0000 0 0006 correction c size. This transmissio microproces error frequ transmitte transmits microproces packet size 10 and ddcreas a high erro minimum si continuous data st! microproce subsequent ev al uated 2, the pac transmissi 20 to a much errors are micr opr oce smaller pa In th 34 and 48 packet siz quality.

becomes packet, co 30 a cellul occurrin containin packet re would hax in the r reduce d; high err 0000 0 0 0000 0004 00 0 00 0O 0r 00 0 00a 0000 0 00~ 0000 0 W 0000 0000 0 00a 00 0 00 0 O 00n 0000 0 00I 00I 0 '1 communicating data between a Plurality of geographical .LI u said mc

I_

"II-9YIII~~~ ~UL lltii*Yi 17 00 00 0 0 0 0 o000 00 00 0 0 o 00u 00 0 0000 0000 correction capability which involves a sliding packet size. This packet size is changed in accordance with transmission quality determined by the transmitting microprocessor on the basis of an evaluation of the error frequency in signals received from previously transmitted data. The receiving microprocessor transmits a data stream to the transmitting microprocessor from which this evaluation is made. The packet size is increased for a good transmission signal and dcreased for a bad transmission signal, so that in a high error :ituation, the retransmitted packet is of minimum size. The transmitting microprocessor is continuously evaluating the number of errors in the data sti, am it receives from the receiving microprocessor, and is adjusting the packet size of subsequent transmissions in accordance with this evaluated error data. Thus, as illustrated by Figure 2, the packet size 78 might be increased during the transmission period the transmitting microprocessor to a much larger packet size 82 when transmission errors are minimal, or, conversely, the transmitting microprocessor might decrease the packet size to a much smaller packet size 84 as transmission errors increase.

In the transmission mode, both the microprocessors 34 and 48 provide a sliding packet ARQ wherein the packet size changes or slides based on the transmission quality. In a high error situation, the packet size becomes smaller and the time required to repeat a packet containing error is lessened. Consequently, in a cellular transmission situation where errors are occurring frequently, a packet of reduced size containing corrected data may be received, while if the packet remained of greater size, numerous bytes of data would have to be retransmitted until all bytes of data in the packet are received correctly. This would reduce data transmission efficiency, or in extremely high error situations, prevent the reception of a correct The 40 and during such a vehicle 28 passe The mode mode or 10 autonrat signal I disconne :00090 the res 0o 0 0 0 4 micropr data, se 'break t a the mic 00initiat modem t 20 between less th 0onseque 0 in respi the ran 0 0 period carrier by tray 04.o loss t predete 30 the modi carriez improvi loss te set by occur.

instru.

transmi D0c0 0 4 0000 o 00 v u 00 a op b 000 0 0 st 4936390

A

,fIL j. L~u.Lu±Luy a uni ue data byte to said modem during a break in the data signal to the communi

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18 correct packet. cellula The microprocessors 34 and 48 maintain the modems cellula.

and 50 on line in the event of a carrier signal loss transmi during data transmission. As previously indicated, such a carrier transmission loss occurs when the period vehicle bearing the mobile data programming interrace Thi 28 passes between cells in a cellular telephone system. mode to The modems 40 and 50 are operated normally in the test mode or a similar mode which prevents the modem from also ar automatically disconnecting in response to a carrier circuit.

signal loss. Instead, the modem is not permitted to effecti disconnect until it receives a disconnect signal from scrambl the respective microprocessor 34 or 48. This 0 microprocessor, which has been sending or receiving 0 errors 0 0 0 o data, senses the carrier signal loss when it receives a I reduce "break bit" from the associated modem, and therefore, Howev o However Sthe microprocessor recognizes a carrier loss and 0.

of the initiates a time delay period before permitting the o modem to disconnect. Generally, the hand-off period non-scr between cells of a cellular telephone system causes telepho less than a one-second carrier signal loss, and Both of 00°4°o consequently, the delay initiated by the microprocessor 00o in response to a carrier loss may be anywhere within o between the range of from two to seven seconds. This delay o* 0 Conside period is sufficient to permit reestablishment of the icropr omicropr carrier signal when the loss of carrier is occasioned 0 by travel between cells. By never allowing a carrierpresent loss to cause modem disconnect during this micropr predetermined time delay period, the time needed for signal 30 the modem to reestablish data transmission after the to keep carrier loss terminates is decreased, thereby improving overall efficiency. Thus, if the carrier the tel loss terminates during the predetermined time period is a va set by the microprocessor, modem disconnect does not however occur. On the other hand, the microprocessor will continue instruct the modem to disconnect when the datac transmission is ended by the microprocessor, when the conditi TT g communication system for providing communication over a 19 cellular telephone call is completed, as sensed by the condit cellular interface 30 or the FCC interface 54 and that t.

transmitted to the microprocessor, or when the delay condit period set by the microprocessor expires., scramh The modems 40 and 50 are not only used in the test presen mode to disable the normal modem disconnect circuitry, but when t.

also are used in a mode which disables the modem scrambler what t.

circuitry. It is important, though not essential for effective cellular data transmission to prevent the scrambler polynomial from increasing the number of bit errors received, for these additional errors further 0 0.

0 o° reduce the effectiveness of the error correction scheme. 0 However, with the scrambler defeated, the synchronization o of the modem PLL circuitry is no longer provided and the a 00 9 non-scrambled modulated signal may be interpreted by the telephone company equipment as a valid switch command.

Both of these problems are solved by the cooperation ao0 between the modem and its associated microprocessor. .4 °094 Considering the microprocessor 34 to be the transmitting °I microprocessor, all data sent by the modem 40 is first o presented to the modem by the microprocessor. The microprocessor is programmed to ensure that the data signal provided to the modem has enough changing signals to keep the modem PLL in synchronization and to prevent A the telephone switching equipment from assuming the signal is a valid switching command. It must be recognised, however, that data is not always sent by the modem 40 in a continuous stream, and that the modem is often in a static condition. It is when the modem is in this static 4 L Ior. s Lr4 2ich is pL.rora1 e tol adapt th microprocessor which is programmed to adapt the A.ii. ell L correc II HVr' 19a condition that the modem PLL may lose synchronisation or that the telephone equipment may interpret the static condition as a switch command. Normally, the modem scrambler would prevent this static condition, but in the present circuit, the transmitting microprocessor knows when the last data byte was presented to the modem and what the transmission 0 0r *o II 0 0r 00 0 0404 #4r 04 0 6 0 04 0 0 0* of the micropr conditi unique repeate transmi shut do, hereina.

stream recogni byte.

bytes, Si.

program interfa 00 recogni 04, transmi descrip herein data ani descrit but it

RE

flow cl micropx cellulE steps c control one hax .400 15 ills to Aust and inc chart c micropi instruc the por instruc 040* 0 0 0004 4000 0o 0 00 0 00 0 0 0 0 0 0 0 0 0 0 04 0 00 4 "Lsie~ ~cq" 1 .U crrectionl S IcapabilityU LU )J.UlJ l L J. L .L.L correction capability; coU1 L.

cont ~B -Y-~jl -C 8 I- i 20 no 0 0 00 9 99 of the modem is. With this information, the microprocessor determines when the modem is in a static condition, and immediately initiates the presentation of a unique byte of data to the modem. This unique byte is repeatedly presented until data is again available for transmission, or, in the alternative, until the modem is shut down. The characteristics of this unique byte, hereinafter known as the synch byte, are such that the bit stream is always changing, and the receiving modem recognizes this byte as a synch byte and not a valid data byte. These two conditions can be met by many different bytes, and the choice of which one to use is arbitrary.

Since the structure and operation of the mobile data programming interface 28 and the static data programming interface 42 are substantially the same, it will be 00 9 0 recognized that both operate in the same manner to either 0e" transmit or receive data. Therefore, for purposes of *o description, the mobile data programming interface 28 will herein be described in connection with the transmission of data and the static data programming interface 42 will be described in connection with the reception of such data, but it must noted that the roles can be reversed.

89 Referring now to Figure 3, there is illustrated a a flow chart including the basic process steps used by the microprocessor 34 in transmitting a data signal over the cellular telephone system. The coding of the process S steps of this flow chart into the instructions suitable to control the microprocessor 34 will be understandable to one having ordinary skill in the art of programming, and is illustrated in detail in the appendixed program listing to Australian Patent Specification No. 590,977 (79030/87) and incorporated herein by reference thereto. The flow chart of Figure 3 is begun at start block 86, and the microprocessor 34 is adapted to receive dialing instructions as indicated by block 88 which originate at the portable computer 36 or from some other source. These instructions command the microprocessor to connect the o o o 80 88 9 0 0 0 0 0 a 0 a 0 eo system receiv shown microV and cc to the path c transm interf 10 interf requir step i state are ir 0o mode z 8 the cE o data 1 use, t and tr o0 transc this t apparcommer.

8 the "c 8 routir Speci.

for th the NC 100 t> S6 the cdecis- 34 inL to sw: the me instru 0 0 8 0 00 60 6 0 0 06 89 8 o &o

I

34 duz I i 11control unit 24 should be on an eight bit parallel control unit 24 should be on an eight bit parallel in a ,^fa 21 0 0 o o 0 9 0 0 o 0 00 o 6 0 0 000 system to a designated telephone number (123-4567) and the received instructions are stored in the microprocessor as shown by block 90. In response to the instructions, the microprocessor then operates to cause the analog switch and conditioning system 32 to complete an instruction path to the cellular interface 30 as taught at 94. With this path completed, the microprocessor operates at 96 to transmit the stored call control signals to the cellular interface with the instructions to cause the cellular interface to send the eight bit parallel control signals required to dial the phone number 123-4567. As a first step in this transmission, the microprocessor checks the state of the cellular bus data lines. If the data lines are in use, the microprocessor enters a loop or waiting S mode and does not actuate.the AMPS interface and transmit 0 the call control signals to the cellular bus until the S data lines are not in use. When the data lines are not in use, the microprocessor will actuate the AMPS interface and transmit the call control signals to the cellular transceiver via the cellular bus. The method by which this first transmission step is implemented will be apparent to those skilled in the art on review of the commented source code implementing this step (located in the "dial.num" routine which is part of the BRIDGSUB routine) in the Appendixed program of Australian Patent Specification No. 590,977. The microprocessor then waits S for the call to be answered, and if this does not occur, the NO branch is taken from the decision block 98 to block 100 to exit from the flow chart in Figure 3. However, if the call is answered, the YES branch is taken from the decision block 98 to block 102, where the microprocessor 34 instructs the analog switch and conditioning system 32 to switch the signal path from the cellular interface to the modem 40. Subsequently, at block 104, the modem is instructed to transmit data received by the microprocessor.

The specific control functions of the microprocessor 34 during the transmission of a data stream are 00 0 0 6 0 illust.

purpos monito as dat 34, thi decisi data.

YES br discor 10 the mc switch indicthe mc micro S,0 inter befor- 60.00 06 00r 0 6 0 0 0 .C .C 06 66J 0 6000 ooo%0 0 0 0 66« 06 0 6 0 a 0 00 O3O a o d e a u' u Sc? to il micro 3 whe.

of thi the i.

will and a Austr strea 232 i indic modul other as il strec the n celil indi moder

I

in a manner to be described in greater detail.

I

us -22illustrated in greater detail in Figure 4, and for purposes of this description, the data transmission is signalmonitored as indicated by the decision block 106. As long Howeve.

as data is being transmitted through the microproces3sor microp- 34, the NO branch of the decision block 106 takes the make s decisio~i to the block 104 to continue the transmission of microp data. However, once data transmission is finished, the the tip YES branch of the decision block 106 is taken to the modem determ.

disconnect block 108 where the microprocessor instructs as id, the modem to terminate its function. Then the analog is sta switch and conditioning sytem 32 is instructed, as indicated by the block 110, to disconnect the path between the modem and the cellular interface and to reconnect the microprocessor which, 'at 112, instructs the cellular interface to hang up the telephone and terminate the call before exiting at 114.

06Referring now to Figure 4, a flow diagram is provided 0, to illustrate in detail the operation of the microprocessor 34 during the block shown at 104 in Figure 00 ~4~o 3 when data transmission is occuring. Again, the coding of the process steps used by the microprocessor 34 into the instructions suitable to control the microprocessor will be understood by one having ordinary skill in the art and are fully illustrated by the appendixed program to 0 U a Australian Patent Specification No. 590,977.

Entering the flow chart at a start block 116, a data t stream provided by the portable computer 36 through the RS 232 interface 38 is received by the microprocessor 32 as a indicated by the block 118. Next, the data signal is modulated with the error detection and correctic..- other control bytes described in connection with Figure 2, to0 as illustrated by the block 120 and the modulated data stream is stored at 122. The data is then transmitted to the modem at 124, and the modem provides the data to the cellular interface for transmission. As previously indicated, the microprocessor provides the data to the modem in a modulated signal which has enough changing use such modems include a scrambler system which I X1 22asignals to keep the modem PLL in synchronization.

However, during the operation of the modem, the microprocessor monitors the data and modem operation to make sure that the modem is not static. The microprocessor uses the transmission rate of the modem and the time when the last data byte was presented to determine when the modem is in a static condition, and as indicated by the decision block 126, when the mudem is static, the YES line to the block 128 shows that arep to Of. U a 01 00 0

CO

0 0) 0 00 00 *0 00 0 0 0 08 000

NO

inc of mi.

trz sic 'br bef th.= Si.

0 to to po bl th Th mi in at ca pr fr de fr mi 14 sE w eN O 0 0 001 0 0 0 00 00 0 0O*00.

0 00.30d 0 0* 0 0i j-i 04 operation of the portable computer 36 with the mobile 23 00 00 0 0 00 640 a o 040« repetitive synch byte is generated which is transmitted to the modem.

When the modem is not in the static condition, the NO line from the decision block 126 to the block 130 indicates that the microprocessor waits for the receipt of acknowledgment signals from the receiving microprocessor 48 for each word and packet of data transmitted. In the event of a loss of carrier signals, the microprocessors 32 and 48 respond to a "break bit" from the modem and initiate a time clock before permitting modem disconnect. As indicated by the decision block 132, when the awaited carrier signals are totally missing for a time t which is equal o to or greater than a predetermined time x, the YES line 0 to a modem disconnect block 134 is followed. At this point, the same operation which has occured with the blocks 108, 110, 112 and 114 in Figure 3 occurs, and the modem is disconnected from the cellular interface.

The cellular interface is reconnected to the microprocessor at 136 which instructs the cellular interface to perform a hang-up operation before exiting at 140.

On the other hand, if the time when no carrier signals are received is less than the S predetermined delay time period x, then the NO line from the decision block 132 to a data error frequency determination block 142 becomes relevant. Here, the frequency of data errors at the receiving data microprocessor 48 is determined and employed at block 144 to adjust the EDC packet to provide larger or smaller packets in the manner described in connection with Figure 2. Then this portion of the program is exited at 146.

The operation of the microprocessors 32 and 48 during the reception of data, evaluation of data errors and transmission of acknowledgment signals has been fully described previously. Since this operation is 0 0 0 0 0 a 0 0 d l static data programming interface is conneu-Leu tu telephone lines by an FCC interface while the mobile includes a connected t -24 similar to that which occurs with wire line and other data transmivsion systems, it will be readily understood by those having ordinary skill in the art, and the instroctions for the microprocessors are disclosed in detail by the appendixed program to Australian Patent Specification No. 550,977.

Industrial Applicability The cellular telephone data communication system of the present invention provides a cooperating mobile data programming interface and static data programming interface which operate together to perform the functions necessar' to control errors in an efficient way to permit data transmis- in the limited voice o o band available when using cellular telephirne .o technology. Since both interfaces incorporate a 0o0" microprocessor with independent firmware storage o004o capabilities, a flexible system is provided wherein various computer control devices can execute the functions provided by a cellular telephone system. At the same time, the unit permits the cellular telephone system to be employed for the conventional audio o. transmissions which the system was designed to hanole, *1 0 0 00J O OO 0 0 0 0

Claims (3)

1. An interface system for correcting error in digital data transmitted and received between first and second digital data processing units via a cellular radio celephone link established between a mobile transceiver unit which is adapted to be interfaced with the first digital data processing unit and one of a plurality of fixed transceiver units which are adapted to be interfaced with the second digital data processing unit, comprising: a mobile signal processing interface means adapted to be connected with the first data processing unit and the mobile transceiver unit for supplying in digital form the data transmitted from the second digital data processing unit via the cellular telephone system to the first digital data processing unit and for receiving in digital form data from the first digital data processing unit for transmission to the second digital ata processing unit via the cellular telephone system; a static signal processing interface means 20 adapted to be connected between the second data processing unit and the one fixed transceiver unit for supplying in digital form the data transmitted from the first digital data processing unit via the cellular telephone system to the second digital data processing unit and for receiving 25 in digital form data from the second digital data processing unit for transmission to the first digital data processing unit via the cellular telephone system: wherein each of said mobile signal processing interface means and said static signal processing interface means 30 includes microprocessor means for controlling said signal processing means, each said microprocessor means being programmed to form dividing means for dividing the data produced by the corresponding digital data processing unit into plural groups of digital data, forward error correction encoding means for generating and associating with eac signal f interfac means fo generate the micr in assoc from sai using sa. errors a. group of is below

2. An said sta to be co and the line.

3. An said sta to be co and a te 5 fixed tr digital and seco during me geograph. 10 telephoni the fixe within w. DATED th SPECTRUM ii j no on on on n o~~n oa on nrno o no o ori~s o o~ on o o ooo o o o 1 c I~ ci i I r o o 0 0 o 0oo o o a 4 40 00 I 0 t 0 I 0 0e 0« I (t I t E o 1 I 1 I o( Fell of bits per word, for example 2 bits. Correction would Consequer occur for any error of 2 bits or less, but an error in -mitting I I 26 with each group of digital data an error correcting signal for transmission to said other signal processing interface means, and forward error correcting decoding means for receiving the forward error correcting signal generated by the microprocessor of said other signal interface means in association with each group of digital data received from said other signal processing interface means and for using said forward error correcting signal to detect errors and to correct those errors in the associated group of digital data when the number of detected errors is below a predetermined amount. 2. An interface system as defined in claim i, wherein said static signal processing interface means is adapted to be connected between the second data processing unit and the one fixed transceiver unit via a telephone land line. 3. An interface system as defined in claim 2, wherein said static signal processing interface means is adapted to be connected between the second data processing unit and a telephone land line connected to the plurality of o o 5 fixed transceiver units of the cellular system so that digital data transmission and reception between the first V and second digital data processing units may continue during movement of the mobile transceiver throughout the S.geographic cells of the cellular system via a cellular telephone link between the mobile transceiver unit and St.. the fixed transceiver unit associated with the cell within which the mobile transceiver unit is moving. DATED this 5th day of August 1992 SPECTRUM INFORMATION TECHNOLOGIES, INC. Attorney: PETER HEATHCOTE Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS -d.