WO1998015140A1

WO1998015140A1 - Two-way radio communication system

Info

Publication number: WO1998015140A1
Application number: PCT/US1997/012604
Authority: WO
Inventors: Jheroen P. Dorenbosch; Samir A. Sawaya
Original assignee: Motorola Inc.
Priority date: 1996-09-30
Filing date: 1997-07-16
Publication date: 1998-04-09

Abstract

A method and apparatus includes in a sending transceiver (225) a transmitter (206) for sending (702) a message to a receiving transceiver (122), a receiver (207) for awaiting (704) an acknowledgement of the message from the receiving transceiver within a predetermined time after sending the message, and a processing system (210) coupled to the transmitter and coupled to the receiver for transmitting (706) a command (418) to the receiving transceiver to request a repeat transmission of the acknowledgement when the acknowledgement has not been received by the sending transceiver within the predetermined time.

Description

TWO-WAY RADIO COMMUNICATION SYSTEM

Field of the Invention

This invention relates in general to radio communication systems, and more specifically to a method and apparatus for controlling transmissions in a two-way radio communication system.

Background of the Invention

Conventional two-way radio communication systems use acknowledged messaging. In such systems, messages, or message fragments, are sent to a receiving device and a positive acknowledgment (ACK) is returned to the sending device if the message or message fragment is received correctly. When data is received in error, the receiving device sends a negative acknowledgment (NAK) to request retransmission. When the retransmitted data is received correctly, the receiving device then returns an ACK to confirm reception.

In the prior art systems a message is also retransmitted when no ACK is received. An ACK may be missing for two reasons: the message was not received by the receiving device, or the response sent by the receiving device was not received by the sending device. In the latter case, even if the message had been received correctly by the receiving device, it would have been retransmitted in its entirety by the sending device. In situations where the return path is less reliable than the messaging path, the messaging path looses efficiency, due to such unnecessary retransmission of messages. Even when the inbound and outbound paths have similar reliability, inefficiencies can be considerable, since outbound and inbound fading are not always fully correlated, particularly when one of the devices is moving. Thus, what is needed is a method and apparatus that can eliminate the unnecessary retransmission of a message which results when an ACK that was sent by the receiving device is not received by the sending device. Preferably, the method and apparatus will operate in a manner that improves transmission efficiency compared to prior art systems.

Summary of the Invention

An aspect of the present invention is a method for controlling transmissions in a two-way radio communication system. The method comprises in a sending transceiver the steps of sending a message to a receiving transceiver, awaiting an acknowledgment of the message from the receiving transceiver within a predetermined time after sending the message, and transmitting a command to the receiving transceiver to request a repeat transmission of the acknowledgment when the acknowledgment has not been received by the sending transceiver within the predetermined time.

Another aspect of the present invention is a sending transceiver for controlling transmissions in a two-way radio communication system. The sending transceiver comprises a transmitter for sending a message to a receiving transceiver, a receiver for awaiting an acknowledgment of the message from the receiving transceiver within a predetermined time after sending the message, and a processing system coupled to the transmitter and coupled to the receiver for controlling the transmitter to transmit a command to the receiving transceiver to request a repeat transmission of the acknowledgment when the acknowledgment has not been received by the receiver of the sending transceiver within the predetermined time.

Another aspect of the present invention is a receiving transceiver for controlling transmissions in a two-way radio communication system. The receiving transceiver comprises a receiver for receiving a command from a sending transceiver requesting a repeat transmission of an acknowledgment to a message, a transmitter for transmitting the acknowledgment, and a processing system coupled to the receiver and coupled to the transmitter for controlling the transmitter to repeat a transmission of the acknowledgment in response to receiving the command, when the processing system has a record of having sent the acknowledgment.

Brief Description of the Drawings

FIG. 1 is an electrical block diagram of a two-way radio communication system in accordance with the present invention.

FIG. 2 is an electrical block diagram of portions of a controller and a base station in accordance with the present invention.

FIG. 3 is an electrical block diagram of a portable transceiver in accordance with the present invention.

FIG. 4 is a timing diagram of a communication protocol in accordance with the present invention.

FIG. 5 is a timing diagram depicting operation of a prior art two- way radio communication system.

FIG. 6 is a timing diagram depicting operation of the two-way radio communication system in accordance with the present invention.

FIG. 7 is a flow chart depicting operation of a sending transceiver in accordance with the present invention.

FIG. 8 is a flow chart depicting operation of a receiving transceiver in accordance with the present invention.

Detailed Description of the Drawings

Referring to FIG. 1, an electrical block diagram of a radio communication system in accordance with the present invention comprises a fixed portion 102 including a controller 112 and a plurality of base stations 116, and a portable portion including a plurality of portable transceivers 122 having acknowledge-back capability. The base stations 116 are used for communicating with the portable transceivers 122 utilizing conventional radio frequency (RF) techniques, and are coupled by communication links 114 to the controller 112, which controls the base stations 116. The hardware of the controller 112 is preferably a combination of the Wireless Messaging Gateway (WMG™) Administrator! paging terminal, and the RF-Conductor!™ message distributor manufactured by Motorola, Inc. The hardware of the base stations 116 is preferably a combination of the Nucleus® Orchestra! transmitter and RF-Audience!™ receiver manufactured by Motorola, Inc. It will be appreciated that other similar hardware can be utilized as well for the controller 112 and the base stations 116.

Each of the base stations 116 transmits RF signals to the portable transceivers 122 via a transceiver antenna 118. The base stations 116 each receive RF signals from the plurality of portable transceivers 122 via the transceiver antenna 118. The RF signals transmitted by the base stations 116 to the portable transceivers 122 (outbound messages) comprise selective call addresses identifying the portable transceivers 122, and data or voice messages originated by a caller. The RF signals transmitted by transmitters in the portable transceivers 122 to the base stations 116 (inbound messages) comprise acknowledgments that include positive acknowledgments (ACKs), negative acknowledgments (NAKs), and unscheduled messages. An embodiment of an acknowledge-back messaging system is described in U.S. Patent No. 4,875,038 issued October 17, 1989 to Siwiak et al, which is hereby incorporated herein by reference.

The controller 112 preferably is coupled by telephone links 101 to a public switched telephone network (PSTN) 110 for receiving selective call message originations therefrom. Selective call originations comprising voice and data messages from the PSTN 110 can be generated, for example, from a conventional telephone 111 coupled to the PSTN 110. It will be appreciated that, alternatively, other types of communication networks, e.g., packet switched networks and local area networks, can be utilized as well for transporting originated messages to the controller 112.

The protocol utilized for outbound and inbound messages is preferably similar to Motorola's well-known FLEX™ family of digital selective call signaling protocols. These protocols utilize well-known error detection and error correction techniques and are therefore tolerant to bit errors occurring during transmission, provided that the bit errors are not too numerous in any one code word. It will be appreciated that other similar two-way protocols can be used as well.

FIG. 2 is an electrical block diagram 200 of portions of the controller 112 and the base station 116 in accordance with the present invention. The controller 112 includes a processing system 210, a transmitter interface 204, a receiver interface 205, and a network interface 218. The base station 116 includes a base transmitter 206 and, preferably, at least one base receiver 207. For brevity within the instant application several naming conventions have been adopted. More specifically, the base transmitter 206, the base receiver 207, their respective interfaces 204, 205, and the processing system 210 grouped together are referred to as a transceiver 225. By way of example, a majority of the instant application will disclose operation of the present invention as the invention applies to outbound messages and acknowledgments thereto. For outbound messages and acknowledgments thereto, the transceiver 225 is defined as a sending transceiver, and the portable transceiver 122 is defined as a receiving transceiver. It will be appreciated by one of ordinary skill that the invention as claimed also can be applied to inbound messages and acknowledgments thereto. For inbound messages and acknowledgments thereto, the portable transceiver 122 is redefined to be the sending transceiver, and the transceiver 225 is redefined to be the receiving transceiver.

The processing system 210 is used for directing operations of the controller 112. The processing system 210 preferably is coupled through the transmitter interface 204 to the base transmitter 206 via the communication link 114. The processing system 210 preferably also is coupled through the receiver interface 205 to the base receiver 207 via the communication link 114. The communication link 114 utilizes, for example, conventional means such as a direct wire line (telephone) link, a data communication link, or any number of radio frequency links, such as a radio frequency (RF) transceiver link, a microwave transceiver link, or a satellite link, just to mention a few. The processing system 210 is also coupled to the network interface 218 for accepting outbound messages originated by callers communicating via the PSTN 110 through the telephone links 101.

In order to perform the functions necessary for controlling operations of the controller 112 and the base stations 116, the processing system 210 preferably includes a conventional computer system 212, and a conventional mass storage medium 214. The mass storage medium 214 is programmed to include, for example, a subscriber database 220, comprising subscriber user information such as addressing and programming options of the portable transceivers 122.

The conventional computer system 212 is preferably programmed by way of software included in the conventional mass storage medium 214 for performing the operations and features required in accordance with the present invention. The conventional computer system 212 preferably comprises a plurality of processors such as VME Sparc™ processors manufactured by Sun Microsystems, Inc. These processors include memory such as dynamic random access memory (DRAM), which serves as a temporary memory storage device for program execution, and scratch pad processing such as, for example, storing and queuing messages originated by callers using the PSTN 110, processing acknowledgments received from the portable transceivers 122, and protocol processing of messages destined for the portable transceivers 122. The mass storage medium 214 is preferably a conventional hard disk mass storage device.

It will be appreciated that other types of conventional computer systems 212 can be utilized, and that additional computer systems 212 and mass storage media 214 of the same or alternative type can be added as required to handle the processing requirements of the processing system 210. It will be further appreciated that additional base receivers 207 either remote from or collocated with the base transmitter 206 can be utilized to achieve a desired inbound sensitivity, and that additional, separate antennas 118 can be utilized for the base transmitter 206 and the base receivers 207. In accordance with the present invention, after the processing system 210 has controlled the transmitter 206 to send a message to one of the portable transceivers 122, the processing system 210 monitors the receiver 207 to await an acknowledgment of the message. When the acknowledgment is not received within a predetermined time, the processing system 210 controls the transmitter 206 to transmit a command to the receiving portable transceiver 122 to request a repeat transmission of the acknowledgment. Depending upon the degree of robustness desired, the processing system 210 can send explicit information with the command to identify the acknowledgment, or the acknowledgment can be identified implicitly in a predetermined manner. Examples of explicit information include (1) a time and reason for the acknowledgment, and (2) a serial number of the message that is missing the acknowledgment. An example of an implicit identification is for the portable transceiver 122 to respond with the last acknowledgment sent— provided the last acknowledgment is not more than a predetermined number of minutes, e.g., four minutes, old.

FIG. 3 is an electrical block diagram of the portable transceiver 122 in accordance with the present invention. The portable transceiver 122 comprises a transmitter antenna 302 for transmitting radio frequency (RF) signals to the base stations 116, and a receiver antenna 305 for intercepting RF signals from the base stations 116. The transmitter antenna 302 is coupled to a conventional RF transmitter 304. Similarly, the receiver antenna 305 is coupled to a conventional RF receiver 306. It will be appreciated that, alternatively, the receiver 306 and transmitter 304 can be coupled to a single transceiver antenna, which transmits and intercepts RF signals to and from the base stations 116.

Radio signals received by the RF receiver 306 produce demodulated information at the output. The demodulated information is coupled to the input of a processing system 310 for directing operations of the portable transceiver 122, and for processing outbound messages. Similarly, inbound messages are processed by the processing system 310 and delivered to the RF transmitter 304 for transmission to the base stations 116. A conventional power switch 308, coupled to the processing system 310, controls the supply of power to the RF transmitter 304 and RF receiver 306, thereby providing a battery saving function.

To perform the necessary functions of the portable transceiver 122, the processing system 310 includes a microprocessor 316, and a memory 318. The microprocessor 316 is, for example, embodied by the M68HC08 micro-controller manufactured by Motorola, Inc. The memory 318 preferably includes a conventional read-only memory (ROM) and a conventional random-access memory (RAM).

The microprocessor 316 is programmed by way of a message processing element 325 in the memory 318 to process a received outbound message element, wherein the message element is defined to be either an entire message or a portion of a message, depending upon the message type and length. In addition, the processing system 310 creates and formats inbound acknowledgments, such as positive and negative acknowledgments (ACKs and NAKs), to the message. During outbound message processing, the processing system 310 samples the demodulated signal generated by the RF receiver 306. The processing system 310 then decodes an address in the demodulated data of the outbound message, compares the decoded address with one or more addresses stored in the memory 318, and when a match is detected, continues to process the message. Using well-known techniques, the processing system 310 controls the transmitter 304 to send a negative acknowledgment (NAK) to the message when the received signal quality during reception of the message is worse than a predetermined threshold, and to send a positive acknowledgment (ACK) to the message when the received signal quality during reception of the message element is not worse than the predetermined threshold.

In one embodiment the processing system 310 maintains in the memory 318, for a predetermined time such as four minutes, a record of the last acknowledgment sent. Whenever the base stations 116 transmit a REPEAT RESPONSE command 418 (FIG. 4), the processing system 310 then accesses the record and repeats the transmission of the acknowledgment. If the predetermined time has elapsed, thereby rendering the last stored acknowledgment too old, then the processing system 310 assumes that another message must have been sent by the base stations 116 but not received by the portable transceiver 122, and the processing system 310 transmits an indication that no acknowledgment was transmitted (because no message was received). This method offers the advantage of not having to send explicit information for identifying a message which is missing an acknowledgment, but can become confused when two or more messages are sent close to one another to the same portable transceiver 122. Alternatively, a more robust system of acknowledgment identification can be utilized. For example, the REPEAT RESPONSE command 418 can include a time and cause for the acknowledgment that was missed, and the processing system 310 would try to find a corresponding acknowledgment in the record. This method is a preferred compromise between robustness and transmission overhead. Other approaches are possible as well. For example, each message can be accompanied by a serial number, and the REPEAT RESPONSE command 418 can include the serial number of the message that is missing an acknowledgment. The processing system 310 would then try to locate the acknowledgment having a corresponding serial number in the record. This method is very robust, but requires the highest transmission overhead, and uses a large amount of storage in the portable transceiver 122.

If the acknowledgment of the message is positive, the microprocessor 310 then stores the message in the memory 318, and generates a call alerting signal to alert a user that a message has been received. The call alerting signal is directed to a conventional audible or tactile alerting device 322 for generating an audible or tactile call alerting signal. On the other hand, if the acknowledgment of the message is negative, then the microprocessor 316 waits for the fixed portion 102 to resend the message.

By the use of appropriate functions provided by the user controls 320, the outbound message is recovered from the memory 318, and displayed on a display 324, e.g., a conventional liquid crystal display (LCD). Alternatively, when the message is a voice message, the message is played out on a conventional audio circuit (not shown in FIG. 3) that is included in the portable transceiver 122. Preferably, the portable transceiver 122 utilizes hardware similar to that of the Tenor™ and Tango™ personal messaging units manufactured by Motorola, Inc. of Schaumburg IL. It will be appreciated that other similar components can be utilized as well for the portable transceiver 122.

FIG. 4 is a timing diagram 400 of elements of a frame 407, 412, 414, 416, 418 of an outbound protocol and a frame 426, 428, 430 of an inbound protocol of the fixed portion 102 and the portable transceivers 122 of the radio communication system in accordance with the preferred embodiment of the present invention. The signaling format operating on the outbound and inbound channels preferably operates on independent frequencies utilizing frequency division multiplexing (FDM). Using FDM transmission, both outbound and inbound RF channel transmissions are depicted during a time interval 401.

The elements of the outbound protocol comprise an outbound sync 407, a selective call address 412, a message vector 414, an outbound message element 416, and a REPEAT RESPONSE command 418 (preferably a special type of message element 416). The outbound sync 407 provides a means for synchronization utilizing techniques well known in the art. The selective call address 412 identifies the portable transceiver 122 for which the outbound message element 416 is intended. The message vector 414 points in time within the signal format to the position of the outbound message element 416 to be received by the portable transceiver 122. The message vector 414 further provides information to the portable transceiver 122 identifying a scheduled time slot for acknowledging the message transaction. In accordance with the present invention, the REPEAT RESPONSE command 418 informs the portable transceiver 122 that an acknowledgment to a previously sent message is missing, and instructs the portable transceiver 122 to retransmit the acknowledgment. Because time is required between sending the message element 416 and determining that the acknowledgment therefor is missing, the REPEAT RESPONSE command 418 corresponding to a message element 416 is preferably transmitted in a frame that occurs after the frame in which the message element 416 was transmitted. It will be appreciated that, alternatively, the REPEAT RESPONSE command 418 can be transported in the message vector 414 instead. The elements of the inbound protocol comprise an inbound sync 426, scheduled time slots 428, and unscheduled time slots 430. The inbound sync 426 provides the base stations 116 a means for synchronization utilizing techniques well known in the art. Scheduled messages, e.g., ACKs and NAKs, commence after the inbound sync 426 at a time boundary 403. A transmission time interval 402 depicts the time interval for scheduled transmissions on scheduled time slots 428 from the portable transceivers 122. Unscheduled messages, e.g., spontaneous requests, commence after a time boundary 405 which depicts the end of scheduled transmissions from the portable transceivers 122. The duration of unscheduled transmissions on unscheduled time slots 430 is depicted by a transmission time interval 404.

Unscheduled time slots 430 may be used by any portable transceiver

122. For certain cases there may be more portable transceivers 122 attempting to utilize unscheduled time slots 430 than available. To overcome this limitation, the well-known ALOHA protocol is utilized for unscheduled messages.

FIG. 5 is a timing diagram 500 depicting operation of a prior art two- way radio communication system. In such systems when a message is received and acknowledged, and the acknowledgment is lost for any reason, then the message is retransmitted by the sending transceiver. This is inefficient, because the message was received adequately the first time and does not need to be retransmitted.

FIG. 6 is a timing diagram 600 depicting operation of the two-way radio communication system in accordance with the present invention. In this system when a message is received and acknowledged, and the acknowledgment is lost for any reason, then the sending transceiver transmits a command to the receiving transceiver to resend the acknowledgment identified in a manner described above. The receiving transceiver then retransmits the identified acknowledgment when it finds the acknowledgment in its records. This method of operation advantageously prevents wasted airtime used to transmit a message that has already been received adequately, and the longer the message, the greater the advantage. For the case in which the message was not received, the intended receiving transceiver responds to the command with an indication that no acknowledgment was transmitted.

FIG. 7 is a flow chart 700 depicting operation of a sending transceiver in accordance with the present invention. As discussed herein above, the sending transceiver can be either the transceiver 225 or the portable transceiver 122, depending upon whether the transmission direction of the message is outbound or inbound, respectively. The flow chart begins with the sending transceiver sending 702 the message to the receiving transceiver. The sending transceiver then awaits 704 an acknowledgment of the message from the receiving transceiver in response within a predetermined time after sending the message. If the acknowledgment has not been received by the sending transceiver within the predetermined time, then the sending transceiver sends 706 the REPEAT RESPONSE command 418, and the flow returns to step 704 to await the response. If the response is received in time, the sending transceiver then checks 708 the response type. If the response type is an ACK, the message was adequately received and the process ends 710. If, on the other hand, the response type is a NAK (e.g., message received, but had too many errors), then the sending transceiver resends 712 the message, and flow returns to step 704 to await the acknowledgment. It will be appreciated that conventional means, e.g., limit counters, can be utilized to control any infinite loops in the flow chart 700.

FIG. 8 is a flow chart 800 depicting operation of a receiving transceiver in accordance with the present invention. As discussed herein above, the receiving transceiver can be either the portable transceiver 122 or the transceiver 225, depending upon whether the transmission direction of the message is outbound or inbound, respectively. The flow chart begins with the receiving transceiver receiving 802 the REPEAT RESPONSE command 418. In response, the receiving transceiver identifies 804 the acknowledgment through one of the methods described herein above, and checks its records to see whether the identified acknowledgment was sent. In step 806, if the records show that the identified acknowledgment was sent, the receiving transceiver resends 808 the acknowledgment. If the records show that the identified acknowledgment was not sent, the receiving transceiver sends 810 a message to the sending transceiver indicating that no acknowledgment was sent.

Thus, it should be clear by now that the present invention provides a method and apparatus that eliminates the unnecessary retransmission of a message which results when an ACK that was sent by the receiving device is not received by the sending device. The method and apparatus operate in a manner that advantageously improves transmission efficiency compared to prior art systems.

What is claimed is:

Claims

1. A method for controlling transmissions in a two-way radio communication system, comprising in a sending transceiver the steps of: sending a message to a receiving transceiver; awaiting an acknowledgment of the message from the receiving transceiver within a predetermined time after sending the message; and transmitting a command to the receiving transceiver to request a repeat transmission of the acknowledgment when the acknowledgment has not been received by the sending transceiver within the predetermined time.

2. The method of claim 1, wherein the awaiting step comprises the step of awaiting one of a positive acknowledgment (ACK) for indicating that the message was received with adequate quality, and a negative acknowledgment (NAK) for indicating that the message was received with inadequate quality.

3. The method of claim 1, wherein the transmitting step comprises the step of including explicit information to identify the acknowledgment.

4. The method of claim 1 wherein the transmitting step comprises the step of transmitting the command without explicit information to identify the acknowledgment, and wherein an identification of the acknowledgment is predetermined.

5. The method of claim 1, wherein the sending step comprises the step of sending the message from a fixed portion of the two-way radio communication system.

6. The method of claim 1, wherein the sending step comprises the step of sending the message from a portable portion of the two-way radio communication system.

7. The method of claim 1, further comprising in the receiving transceiver the step of repeating a transmission of the acknowledgment in response to receiving the command, when the receiving transceiver has a record of having sent the acknowledgment.

8. The method of claim 1, further comprising in the receiving transceiver the step of transmitting an indication that no acknowledgment was transmitted, in response to receiving the command, when the receiving transceiver has no record of having sent the acknowledgment.

9. A sending transceiver for controlling transmissions in a two-way radio communication system, comprising: a transmitter for sending a message to a receiving transceiver; a receiver for awaiting an acknowledgment of the message from the receiving transceiver within a predetermined time after sending the message; and a processing system coupled to the transmitter and coupled to the receiver for controlling the transmitter to transmit a command to the receiving transceiver to request a repeat transmission of the acknowledgment when the acknowledgment has not been received by the receiver of the sending transceiver within the predetermined time.

10. The sending transceiver of claim 9, wherein the processing system is programmed to await one of a positive acknowledgment (ACK) for indicating that the message was received with adequate quality, and a negative acknowledgment (NAK) for indicating that the message was received with inadequate quality.

11. The sending transceiver of claim 9, wherein the processing system is programmed to transmit explicit information with the command to identify the acknowledgment.

12. The sending transceiver of claim 9 wherein the processing system is programmed to transmit the command without explicit information to identify the acknowledgment, and wherein an identification of the acknowledgment is predetermined.

13. The sending transceiver of claim 9, wherein the transmitter, the receiver, and the processing system are positioned in a fixed portion of the two-way radio communication system.

14. The sending transceiver of claim 9, wherein the transmitter, the receiver, and the processing system are positioned in a portable portion of the two-way radio communication system.

15. A receiving transceiver for controlling transmissions in a two-way radio communication system, comprising: a receiver for receiving a command from a sending transceiver requesting a repeat transmission of an acknowledgment to a message; a transmitter for transmitting the acknowledgment; and a processing system coupled to the receiver and coupled to the transmitter for controlling the transmitter to repeat a transmission of the acknowledgment in response to receiving the command, when the processing system has a record of having sent the acknowledgment.

16. The receiving transceiver of claim 15, wherein the processing system is programmed to transmit an indication that no acknowledgment was transmitted, in response to receiving the command, when the processing system has no record of having sent the acknowledgment.

17. The receiving transceiver of claim 15, wherein the processing system is programmed to identify the acknowledgment from explicit information received with the command.

18. The receiving transceiver of claim 15, wherein the processing system is programmed to identify the acknowledgment through a predetermined method when the command is received without explicit information for identifying the acknowledgment.

19. The receiving transceiver of claim 15, wherein the transmitter, the receiver, and the processing system are positioned in a fixed portion of the two-way radio communication system.

20. The receiving transceiver of claim 15, wherein the transmitter, the receiver, and the processing system are positioned in a portable portion of the two-way radio communication system.