Cellular telephone data communication system and method

Abstract

The cellular telephone data communication system and method involves the use of a mobile data processing interface and a cooperating static data processing interface to effectively transmit data over a cellular telephone system. Each data processing interface includes a processor which operates in the transmitting mode to add an error control correction data format to data received from an external data source. The data is divided into packets and provided to a modem which is uniquely operated to eliminate the action of the modem scramble system and to remain active in spite of a carrier signal loss. The modem is deactivated or disconnected by a disconnect signal from the processor, and when carrier signal loss occurs, this disconnect signal is provided only after the lapse of a delay period without the resumption of the carrier signal. The error control correction data format causes a receiver to evaluate the received data for error and to retransmit an acknowledgment signal for each acceptable packet of received data. In the absence of an acknowledgment signal, the processor will again provide a data packet to the modem for retransmission. Also, the processor will determine the frequency of error in the received data from the acknowledgment signals and subsequently adjust the data packet size in accordance with this error frequency.

Description

The present invention incorporates a microfiche appendix with one microfiche having 75 frames.TECHNICAL FIELDThe 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.BACKGROUND ARTModern 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 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 ARQ (Automatic Repeat Request) or packet repeat scheme is 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 ar...

AI Technical Summary

Benefits of technology

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.

Problems solved by technology

However, the low frequency of signal quality change induced errors in a wire line environment makes this an efficient method of controlling error.

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.

However, for data communications, this "hand-off" process results in significant problem if conventional wire line modems are used.

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 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 frequently 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 transmission efficiency is reduced below an acceptable amount.

In some instances, errors may occur so often that a correct packet may never be received.

Thus, the error correction protocol present in conventional telephone modems is unable to cope with the problems presented in a cellular environment.

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.

Such systems are disclosed in U.S. Pat. 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.

Images