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

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 mode and does not actuate the AMPS interface and transmit the call control signals to the cellular bus until the 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 microfiche Software Appendix. The microprocessor then waits 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 FIG. 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 illustrated in greater detail in FIG. 4, and for purposes of this description, the data transmission is monitored as indicated by the decision block 106. As long as data is being transmitted through the microprocessor 34, the NO branch of the decision block 106 takes the decision to the block 104 to continue the transmission of data. However, once data transmission is finished, the YES branch of the decision block 106 is taken to the modem disconnect block 108 where the microprocessor instructs the modem to terminate its function. Then the analog switch and conditioning system 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.

Referring now to FIG. 4, a flow diagram is provided to illustrate in detail the operation of the microprocessor 34 during the block shown at 104 in FIG. 3 when data transmission is occurring. 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.

Entering the flow chart at a start block 116, a data stream provided by the portable computer 36 through the RS 232 interface 38 is received by the microprocessor 32 as indicated by the block 118. Next, the data signal is modulated with the error detection and correction and other control bytes described in connection with FIG. 2, 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 signals 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 modem is static, the YES line to the block 128 shows that a 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 to or greater than a predetermined time x, the YES line 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 FIG. 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 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 FIG. 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 descrbed previously. Since this operation is similar to that which occurs with wire line and other data transmission systems, it will be readily understood by those having ordinary skill in the art, and the instructions for the microprocessors are disclosed in detail by the appendixed program.

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 necessary to control errors in an efficient way to permit data transmission in the limited voice band available when using cellular telephone technology. Since both interfaces incorporate a microprocessor with independent firmware storage 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 transmissions which the system was designed to handle.

Claims

1. A method for transmitting data from a transmitting station over a cellular telephone system to a receiving station by means of a modem connected to said cellular telephone system which is operative in an activated state to modulate a carrier signal for said cellular telephone system with a data signal, said method including the steps of placing said modem in the activated state, providing a data signal to said activated modem, maintaining said modem in the activated state for a predetermined time period after a loss of said carrier signal before permitting said modem to deactivate, and causing said modem to remain in said activated state after the loss of said carrier signal if said carrier signal resumes within said predetermined time period.

2. The method of claim 1 which includes adding an error control correction data format to said data signal before providing said data signal to said modem.

3. The method of claim 1 which includes repetitively providing a unique data byte to said modem during a break in said data signal.

4. The method of claim 2 wherein the addition of said error control correction format involves dividing data to be transmitted into a plurality of data packets, each data packet including a plurality of data words, the number of data words in a data packet determining the size of the data packet, providing said data signal to said modem for transmission to said receiving station, examining the data words in each received data packet at the receiving station for error and determining which data words are acceptable, transmitting an acknowledgment signal to the transmitting station for each acceptable data word, determining from the transmitted acknowledgment signals which data packets were received with unacceptable errors and retransmitting said unacceptable data packets, and determining the frequency of error in said received data packets from said acknowledgment signals and adjusting the size of subsequent data packets to be transmitted in accordance with said error frequency.

5. The method of claim 4 which includes decreasing the size of subsequent data packets to be transmitted as the frequency of error in received data packets increases and increasing the packet size of subsequent data packets to be transmitted as the frequency of error in received data packets decreases.

6. The method of claim 4 which includes sensing a complete loss of said carrier signal for a predetermined period at said transmitting station and initiating said predetermined time period in response to said loss to maintain said modem in the activated state.

7. The method of claim 6 which includes causing said modem to disconnect and terminate transmission to said receiving station of all data packets if the signal is not resumed within said predetermined time period.

8. The method of claim 7 which includes operating said modem without a scrambler polynomial and continuously changing said data signal provided to said modem for modem synchronization.

9. The method of claim 8 which includes repetitively providing a unique data byte to said modem during a break in said data signal to prevent the modem from entering a static condition.

10. A method for transmitting data between a transmitting station and a receiving station using a cellular network which includes dividing data to be transmitted into a plurality of data packets, each data packet including a plurality of data words, the number of data words in a data packet determining the size of the data packet, transmitting said data packets to the receiving station, examining the data words in each received data packet for error and determining which data words are acceptable, transmitting an acknowledgment signal to the transmitting station for each acceptable data word packet, determining from the transmitted acknowledgment signals which data packets were received with unacceptable errors and retransmitting said unacceptable data packets, and determining the frequency of error in said received data packets from said acknowledgment signals and adjusting the size of subsequent data packets to be transmitted in accordance with said error frequency.

11. The method of claim 10 which includes decreasing the size of subsequent data packets to be transmitted as the frequency of error in received data packets increases and increasing the packet size of subsequent data packets to be transmitted as the frequency of error in received data packets decrease.

12. A signal processing interface for communicating data from a data source over a cellular telephone system to a receiving means via a cellular telephone radio carrier signal comprising processing means connected to receive data from said data source, said processing means operating to form said data into a data signal format to be transmitted as a data signal, the data signal format including blocks of data, at least one acknowledgment signal to be retransmitted by said receiving means back to said processing means upon receipt of each of said data blocks, cellular telephone transmission means operative upon receipt of said data signal format to transmit said data signal to said receiving means, and modem means connected to said signal processing means and said cellular telephone transmission means and operative to receive said data signal containing said data signal format from said processing means and to provided said data signal for transmission to said cellular telephone transmission means, said modem means being operative to disconnect from said cellular telephone transmission means in response to a disconnect signal and inoperative to disconnect in response to a loss of said cellular telephone radio carrier signal, said processing means operating to provide a disconnect signal to said modem means when a delay period subsequent to a loss of said cellular telephone radio carrier signal has elapsed without the resumption of said cellular telephone radio carrier signal.

13. The signal processing interface of claim 12 wherein said modem means operates without a scrambler polynomial, said processing means operating to continuously change said data signal to provide synchronization for said modem means.

14. The signal processing interface of claim 13 wherein said processing means operates in response to a break in said data to repetitively provide a unique data byte to said modem means for the duration of said break in the data.

15. A cellular telephone data communication system for communicating data from a data source over a cellular telephone system having a mobile transceiver unit operative to transmit and receive cellular telephone signals and a plurality of fixed transceiver units connected to transmit signals over a conventional telephone line system comprising a mobile signal processing interface means connected to said mobile transceiver unit and operative to communicate data from a data source to said mobile transceiver unit for transmission via a cellular telephone radio carrier signal or to receive a transmitted data signal from said mobile transceiver unit, and a static signal processing interface means connected to said conventional telephone line system and operative to communicate data from a data source over said conventional telephone line system to one of said fixed transceiver units for transmission via a cellular telephone radio carrier signal to said mobile unit or to receive a transmitted data signal via said conventional telephone line system, each said mobile signal processing interface means and static signal processing interface means being operative in a transmitting or receiving mode while the other operates in the opposite mode and each including signal processing and control means connected to receive data from a respective data source in the transmitting mode, said signal processing and control means also being operative in the receiving mode to receive a data signal from the associated mobile transceiver unit or associated conventional telephone line system, and modem means connected to said signal processing and control means, the signal processing and control means of the mobile or static signal processing interface means operating in the transmitting mode being operative to receive data from the associated data source and to form data into a data signal format to be transmitted as a data signal to the modem means connected thereto, said modem means being operative to disconnect in response to a disconnect control signal and inoperative to disconnect in response to a loss of said cellular telephone radio carrier signal, the signal processing and control means operating to provide a disconnect control signal to the modem means connected thereto when a delay period subsequent to a loss of said radio carrier signal has elapsed without the resumption of said telephone radio carrier signal.

16. The cellular telephone data communication system of claim 15 wherein the data signal format is formed by the signal processing and control means for the mobile or static signal processing interface means operating in the transmitting mode by dividing data to be transmitted into a plurality of data packets, each data packet including a plurality of data words, the number of data words in a data packet determining the size of the data packet, the signal processing and control means for the mobile or static signal processing interface means operating in the receiving mode being operative to receive and examine the data words in each transmitted data packet for error to determine which data words are acceptable and to transmit an acknowledgement signal for each acceptable data word packet to the transmitting mobile or static signal processing interface means, the signal processing and control means for the transmitting mobile or static signal processing interface means operative to receive and determine the frequency of error in said received data packets from said acknowledgment signals and to adjust the size of subsequent data packets to be transmitted in accordance with said error frequencey.

17. The cellular telephone data communication system of claim 16 wherein the signal processing and control means for the transmitting mobile or static signal processing interface means operates to control the size of subsequent data packets inversely to the error frequency detected thereby.

18. A data processing interface for operation in a transmitting mode for transmitting data from a data source over a cellular telephone system to a receiving means via a cellular telephone radio carrier signal comprising processing and control means connected to receive data from said data source, said processing and control means operating to form said data into a data signal format to be transmitted as a data signal, said data signal format including a plurality of data packets, each said data packet including a number of data and control words, the number of words in a data packet determining the size of the data packet, each said data packet including an error control correction data format having at least one acknowledgement section, the acknowledgement section adapted to be retransmitted by said receiving means as an acknowledgment signal when an acceptable data packet is received by said receiving means, and modem means connected to said processing and control means to receive said data signal therfrom, said modem means being operable to modulate said cellular telephone radio carrier signal with said data signal and to provide said modulated signal to said cellular telephone system, said modem means receiving the acknowledgment signals transmitted by the receiving means and operating to provide such acknowledgment signals to said processing and control means, the processing and control means determining from said acknowledgment signals the frequency of error in the received data packets and adjusting the size of subsequent data packets in the data signal in accordance with said error frequency.

19. The data processing interface of claim 18 wherein said processing and control means determines from the acknowledgment signals which data packets were received with unacceptable errors and provides said data packets to said modem means for retransmission by said cellular telephone system.

20. The data processing interface of claim 19 wherein said modem means operates without a scrambler polynomial, said processing and control means operating to continuously change the data signal to provide synchronization for said modem means.

21. The data processing interface of claim 19 wherein said modem means operates without a scrambler polynomial, said processing and control means operating in response to a break in the data from said data source to repetitively provide a unique data byte to said modem means for the duration of said break in the data.

22. The data processing interface of claim 19 wherein said modem means is operative to disconnect from said cellular telephone system in response to a disconnect signal and inoperative to disconnect in response to a loss of a cellular telephone radio carrier signal, said processing and control means operating to provide a disconnect signal to said modem means when a delay period subsequent to a loss of said cellular radio carrier signal has elapsed without the resumption of said cellular telephone radio carrier signal.

23. The data processing interface of claim 22 which is operative in a receiving mode to receive a data signal transmitted by said cellular telephone system, said modem means receiving the data signal from said cellular telephone system and providing said data signal to said processing and control means, the processing and control means operating to examine the data words in each received data packet for error to identify acceptable data words and providing an acknowledgment signal to said cellular telephone system for each acceptable data word, the processing and control means operating to remove the error control correction data format from said data section.

24. The data processing interface of claim 23 wherein said modem means operates without a scrambler polynomial, said processing and control means operating to continuously change said data signal to provide synchronization for said modem means.

25. The data processing interface of claim 24 wherein said processing and control means operates in response to a break in the data from said data source to repetitively provide a unique data byte to said modem means for the duration of the break in said data.

26. An interface system for correcting error in digital data transmitted and received between first and second digital data processing units via a cellular radio telephone link established between (1) a mobile transceiver unit which is adapted to be interfaced with the first digital data processing unit and (2) one of a plurality of fixed transceiver units which are adapted to be interfaced with the second digital data processing unit, comprising:

(a) 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 data processing unit via the cellular telephone system;

(b) a static signal processing interface means 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 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 includes: microprocessor means for controlling respectively said mobile signal processing interface means and said static signal processing interface 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 each group of digital data an error correcting signal for transmission to the other of said mobile signal processing interface means and said static signal processing interface means, and forward error correcting decoding means for receiving the forward error correcting signal generated by the microprocessor of the other of said mobile signal processing interface means and said static signal processing interface means in association with each group of digital data received from the other of said mobile signal processing interface means and said static 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.

27. An interface system as defined in claim 26, 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 unit. 28. An interface system as defined in claim 27, 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 fixed transceiver units of the cellular system so that digital data transmission and reception between the first and second digital data processing units may continue during movement of the mobile transceiver throughout the geographic cells of the cellular system via a cellular telephone link between the mobile transceiver unit and the fixed transceiver unit associated with the cell within which the

mobile transceiver unit is moving. 29. A data transmission system for transmitting data from a data source to a data receiver over a radiotelephone system in which errors may occur at a varying error rate, the data transmission occurring in a data stream comprising a plurality of data packets, with the radiotelephone system including at least one portable transceiver unit operative to transmit and receiver radiotelephone signals and a plurality of fixed transceiver units connected to receive signals from a conventional telephone line system and transmit the signals to the portable transceiver unit and also to receive signals from the portable transceiver unit and transmit the signals to the conventional telephone line system, with the data receiver including a protocol decoding circuit that is in signal communications connection with at least one of the fixed transceiver unit, comprising:

a portable signal processing interface means adapted to be connected to the portable transceiver unit and operative to transmit data from the data source to the portable transceiver unit, said portable signal processing interface means including a signal processing means for implementing an error-handling data transmission protocol, including

an error compensation protocol portion which adapts signal formatting of the transmitted data stream to minimize the propagation of data errors beyond the protocol decoding circuit, said error compensation protocol portion being effective for frequencies of error of less than a predetermined error rate, and

an error limiting protocol portion which is operationally effective to vary, in response to changes in the radiotelephone system error rate, the size of the data packets transmitted, thereby reducing the quantity of data affected by errors occurring at frequencies greater than said predetermined error rate, said error correction protocol portion operating at least when the radiotelephone system error rate exceeds said predetermined error rate. 30. The data transmission system of claim 29 wherein the error compensation protocol portion further includes a forward error correction protocol which is enabled to correct errors occurring at a specified frequency which is not greater than the error rate capacity of the error compensation protocol portion. 31. The data transmission system of claim 29 wherein the sizes of the packets transmitted are varied within predetermined limits during operation of the error correction protocol portion. 32. The data transmission system of claim 31 wherein the packet sizes are increased when the error rate of the radiotelephone system decreases, and decreased when the said error rate increases. 33. The data transmission system of claim 32 wherein a forward error correction protocol is included in the error compensation protocol portion to minimize the propagation of errors occurring at a specified frequency which is less than the predetermined error rate.