GB2362292A

GB2362292A - TDMA-based two-way radio systems

Info

Publication number: GB2362292A
Application number: GB0011113A
Authority: GB
Inventors: Rafael Carmon; Mark Shahaf; Nimrod Glazer
Original assignee: Motorola Israel Ltd
Current assignee: Motorola Solutions Israel Ltd
Priority date: 2000-05-08
Filing date: 2000-05-08
Publication date: 2001-11-14
Anticipated expiration: 2020-05-08
Also published as: GB0011113D0; GB2362292B

Abstract

A system for supporting TDMA transmissions from each of a plurality of transceivers, the system including a first transceiver transmitting a first transmission 14 in each of a plurality of consecutive TDMA frames 12, and at least a second transceiver transmitting a second transmission 18 in each of the plurality of consecutive TDMA frames 12, where the first and second transmissions occupy different slots within each of the plurality of consecutive TDMA frames, where the first transceiver is operative to receive the second transmission directly from the second transceiver, and where the second transceiver is operative to receive the first transmission directly from the first transceiver. Thus when the first transceiver is transmitting 14, other transceivers monitor the channel 16 and can synchronise with the first transceiver. Any transceiver can select an available slot to transmit 18. The procedure allows direct conference call arrangements to be easily set up in a TDMA system.

Description

1 0 2362292 A RADIO COMMUNICATIONS SYSTEM AND METHOD

FIELD OF THE INVENTION

The present invention relates to two-way radio systems in general, and more particularly to TDMA-based. two-way radio systems.

BACKGROUND OF THE INVENTION

In some time division multiple access (TDMA)-based two-way radio systems, such as terrestrial trunked radio (TETRA) systems, transceivers may establish voice communication with each other in trunking mode (TMO) and in direct mode (DMO). In TMO the coramunications are subject to a centralised control whereas in DMO the transceivers communicate directly with each other over the same frequency and without a control channel. The transceivers are often referred to as Mobile Stations (MSs). DMO is, by definition, half-duplex, where only one MS transmits over the common channel at any given time, with other MSs monitoring the channel and only transmitting when no other MS is transmitting.

Full-duplex and conference-type calling are not currently known for TDMA DMO twoway radio systems.

SUMMARY OF THE INVENTION

The present invention seeks to provide methods and apparatus for fullduplex directmode TDMA-based two-way radio conferencing.

There is thus provided, in accordance with a preferred embodiment of the present invention, a system for supporting TDMA transmissions from each of a plurality of transceivers, the system including a first transceiver transmitting a first transmission in each of a plurality of consecutive TDMA frames, and at least a second transceiver transmitting a second transmission in 1 each of the plurality of consecutive TDMA frames, where the first and second transmissions occupy different slots within each of the plurality of consecutive TDMA frames, where the first transceiver is operative to receive the second transmission directly from the second transceiver, and where the second transceiver is operative to receive the first transmission directly from the first transceiver.

Further in accordance with a preferred embodiment of the present invention any of the transmissions includes digital or analog audio transmissions.

Still further in accordance with a preferred embodiment of the present invention any of the transceivers receives a plurality of audio transmissions from a plurality of transceivers in a plurality of slots in at least one frame, and any of the transceivers is operative to average the plurality of transmissions to form a consolidated transmission and output the consolidated transmission.

Additionally, in accordance with a preferred embodiment of the present invention, the system further includes at least a third transceiver transmitting a third transmission in each of the plurality of consecutive TDMA frames, where the first, second, and third transmissions occupy different slots within each of the plurality of consecutive TDMA frames, and where any of the transceivers is operative to receive transmissions directly from any other of the transceivers.

There is also provided in accordance with a preferred embodiment of the present invention in a system including a plurality of transceivers including a first transceiver transmitting a first transmission in each of a plurality of consecutive TDMA frames in a direct mode, a method for full-duplex direct-mode TDMA-based two-way radio conferencing including identifying a slot in the plurality of consecutive TDMA frames in which no transmissions are present, and transmitting a second transmission in the slot in each of the plurality of consecutive TDMA fi---arnes,where the first and second transmissions occupy different slots within each of the plurality of consecutive TDMA frames, and where any of the transceivers is operative to receive transmissions directly from any other of the transceivers.

2 Further in accordance with a preferred embodiment of the present invention the identifying step includes identifying a lowest-ordered slot in which no transmissions are present.

Still further in accordance with a preferred embodiment of the present invention the transmitting step includes transmitting digital or analog voice transmissions.

Additionally in accordance with a preferred embodiment of the present invention the method further includes receiving a plurality of audio transmissions from a plurality of transceivers in a plurality of slots in at least one frame, averaging the plurality of audio transmissions to fomi a consolidated audio transmission, and outputting the consolidated audio transmission.

Moreover in accordance with a preferred embodiment of the present invention the method further includes designating the first transceiver as a master transceiver, synchronizing the plurality of transceivers to the master transceiver, and designating another of the plurality of transceivers currently transmitting in the plurality of consecutive TDMA frames as the master transceiver.

Further in accordance with a preferred embodiment of the present invention, the designating another step includes designating another of the plurality of transceivers currently transmitting in a lowest-ordered non-empty slot of the plurality of consecutive TDMA frames as the master transceiver.

Still further in accordance with a preferred embodiment of the present invention, the designating another step includes designating another of the plurality of transceivers currently transmitting in a least recently used non-empty slot of the plurality of consecutive TDMA frames as the master transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

3 Figs. IA and 1B, taken together, are a simplified graphical illustration of a full-duplex direct-mode TDMA-based two-way radio conferencing system, constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 2 is a simplified flowchart illustration of a method for implementing the system of Figs. IA and IB, the method being operative in accordance with a preferred embodiment of the present invention; Fig. 3 is a simplified flowchart illustration of a method for implementing elements of the system of Figs. IA and IB, the method being operative in accordance with a preferred embodiment of the present invention; Fig. 5 shows a schematic block diagram form radio communication apparatus in accordance with the invention; and Fig. 6 is an explanatory figure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to Figs. IA and IB, which, taken together, are a simplified graphical illustration of a full-duplex direct-mode TDMA-based two-way radio conferencing system, constructed and operative in accordance with a preferred embodiment of the present invention. In the system of Figs. IA and IB, a direct mode TDMA communications session is represented by a communications timeline 10. For purposes of the illustration, timeline 10 is shown at reference numeral 12 as having a frame comprising four slots, as is known for systems such as TETRA, although it is appreciated that a frame may comprise a different number of slots than the number shown. A transceiver, typically an MS, designated #1, is shown transmitting in slot I as is seen at reference numeral 14. All transmissions described herein typically refer to normal traffic, such as digital or analog audio or data, rather than control or signaling transmissions. For purposes of the illustration, a transmitting MS is represented by "Tx" followed by the number of the MS, and 4 a receiving MS is represented by "Rx- followed by the number of the MS. While MS #1 is transmitting in slot 1, MSs C, 3, 4, and 5 are shown monitoring the channel, as is seen at reference numeral 16. In slots 2, 3, and 4 MS #1 does not transmit, but rather monitors the channel along with MSs #2, 3, 4, and 5.

As is well known in TDMA two-way radio systems, the first MS transmitting in the channel is typically used by other MSs monitoring the channel for synchronization purposes, with the first transmitting MS being designated the "master" MS. The master MS is used to define the first slot in a frame, as well as other slot and frame characteristics. The nontransmitting MSs then derive common frame and slot timing from the master MS. Thus, in the illustration, MS #1 is designated the master MS, being the first MS to be transmitting in the frame, and MSs C, 3, 4, and 5 derive their common frame and slot reference from the transmissions of MS #1.

In accordance with the present invention, once an MS is synchronized to the master MS, it need not wait for the channel to be clear from transmissions before transmitting on the common channel. Rather, an MS may identify a slot within the TDMA frame that is free from transmissions and transmit within the free slot. Thus, in the illustration, MS #3 determines that slot 2 is not being used for transmission and therefore begins to transmit within slot 2, as is shown at reference numeral 18. As before, while MS #1 is transmitting in slot 1, MSs #2, 3, and 4 are shown monitoring the channel. With the addition of MS #3 transmitting in slot 2, MS #1 monitors the channel along with MSs #2 and 4. In this manner, slots 3 and 4 may also be used by any two of MSs #2, 4, and 5 as required for transmissions. Preferably, an MS wishing to transmit utilizes either the lowest-ordered "empty" slot in which no MS is transmitting. Once a master MS ceases transmission within a slot, the MS currently transmitting in the lowest-ordered slot or the least recently used (LRU) slot is preferably designated the master MS, with all other MSs synchronizing to the master MS in accordance with conventional techniques, as is shown with reference to Fig. 3.

The system of Figs. IA and 1B thus provides for substantially full-duplex, conferenced communications between multiple MSs in a direct-mode TDMA-based two-way radio system. Each MS is preferably adapted, in accordance with conventional techniques, to compress and/or encode outbound transmissions and decompress and/or decode multiple inbound transmissions, preferably averaging all inbound audio transmissions within a frame for consolidated output. For example, in TETRA systems, ACELP vocoders may be used. Thus, an MS that transmits in slot I and receives inbound audio transmissions in slots 2, 3, and 4 from other MSs preferably decompresses/decodes the three inbound audio transmissions and averages them before providing them for output, thus providing conference-call type communications. Conventional echo suppression and/or cancellation techniques may also be used to enhance the quality of the communications.

Fig. 2 is a simplified flowchart illustration of a method for implementing the system of Figs. IA and IB, the method being operative in accordance with a preferred embodiment of the present invention. In the method of Fig. 2, an MS wishing to transmit via a TDMA channel in direct mode listens to the channel to determine if an MS is presently transmitting (step 100). If no transmissions are detected on the channel, and therefore no MS is currently designated as the master MS, the MS begins transmitting slot-length transmissions in consecutive frames (step 110). As the first MS transmitting over the channel, the MS is designated as the master MS in accordance with conventional techniques (step 120), with the slot and frame length being determined by the master MS in accordance with default lengths known or otherwise provided to the master MS. If one or more transmissions are detected on the channel, and therefore the master MS has already been designated, the MS derives slot and frame synchronization from the master MS in accordance with conventional techniques (step 130). The MS then listens to the channel to identify one or more slots within each frame in which no transmissions are detected (step 140). The MS then selects such a slot, typically the lowest-ordered slot, and begins transmitting within the slot in consecutive frames (step 150). When not transmitting, the MS listens for other audio transmissions (step 160) within a 6 frame and preferably consolidates the inbound audio transmissions by averaging them (step 170).

The consolidated result is then output, such as via a speaker (step 180).

Figure 5 shows radio communication apparatus in the form of a two-way mobile radio (MS) 50, which operates in accordance with the invention. MS 50 comprises a microprocessor 5 1, a memory 52, an audio amplifier 53, a speaker 54, a battery 55, a key-pad 56, a display driver 57, a liquid crystal display 58, an RF power amplifier 59, an antenna switch 60, an antenna 61 and a microphone 62. These components and their functions will be familiar to the man skilled in the art and will not be described in great detail.

The microprocessor 5 1, in conjunction with the memory 52, provides the "intelligence" for controlling the operation of the MS 50. It is programmed to also provide the processing of the radio signals it receives and to also construct the signals to be transmitted. The signals are received via the antenna 61 and the antenna switch 60. When transmitting the signals pass from the microprocessor 51 to the power amplifier 59 and via the antenna switch 60 (switched by a control signal from the microprocessor) to the antenna 61.

Received signals are decoded by the microprocessor 51 and passed to the speaker 51 via the amplifier 53. Messages may also be displayed by the display 58 receiving instructions from the microprocessor 5 1.

The keypad 56 allows the user to input instructions to the MS 50 and it also includes a push to talk button (PTT). When the PTT is depressed the radio enters a transmit mode and the speech input via the microphone 62 is processed and then transmitted in the appropriate signal format.

The microprocessor is also configured to provide a combiner 63. When the MS 50 is operating in the conference call mode in accordance with the invention it is this unit of functionality that takes transmissions in the DMO time slots allocated for the conference call and combines them to be passed in combined forin to the speaker.54.

The function of the combiner 63 is depicted in Fig. 6. It will be seen that four participants in a conference call labelled I to 4 are transmitting audio information 'W', "B", "C", "D" in their respective time slots. The combiner combines these transmissions and outputs at its speaker a combined output depicted as "ABCD".

7 While the methods and apparatus disclosed herein may or may not have been described with reference to specific hardware or software, the methods and apparatus have been described in a marmer sufficient to enable persons of ordinary skill in the art to readily adapt commercially available hardware and software as may be needed to reduce any of the embodiments of the present invention to practice without undue experimentation and using conventional techniques.

While the present invention -has been described with reference to a few specific embodiments, the description is intended to be illustrative of the invention as a whole and is not to be construed as limiting the invention to the embodiments shown. It is appreciated that various modifications may occur to those skilled in the art that, while not specifically shown herein, are nevertheless within the true spirit and scope of the invention.

8

Claims

CLAIMS What is claimed is:

1. A system for supporting TDMA transmissions from each of a plurality of transceivers, the system comprising:

a first transceiver transmitting a first transmission in each of a plurality of consecutive TD11A frames; and at least a second transceiver transmitting a second transmission in each of said plurality of consecutive TDMA frames, wherein said first and second transmissions occupy different slots within each of said plurality of consecutive TD11A frames, wherein said first transceiver is operative to receive said second transmission directly from said second transceiver, and wherein said second transceiver is operative to receive said first transmission directly from said first transceiver.

2. A system according to claim 1 wherein any of said transmissions comprises digital or analog audio transmissions.

3. A system according to claim 1 wherein any of said transceivers receives a plurality of audio transmissions from a plurality of transceivers in a plurality of slots in at least one frame, and wherein any of said transceivers is operative to average said plurality of audio transmissions to form a consolidated audio transmission and output said consolidated audio transmission.

4. A system according to claim 1 and further comprising: at least a third transceiver transmitting a third transmission in each of said plurality of 9 consecutive TDMA frames, wherein said first, second, and third transmissions occupy different slots within each of said plurality of consecutive TDMA frames, and wherein said any of said transceivers is operative to receive transmissions directly from any other of said transceivers.

5. A radio communications system having a TDN4A slot structure comprising a group of transceivers grouped to participate in a conference call and being allocated slots for transmission wherein the transceivers are adapted to combine transmissions received in the slots to give a combined audio output.

6. A radio communications system as claimed in claim 5 wherein the slots allocated for transmission are allocated for direct mode operation.

7. Radio communication apparatus for use in a system as claimed in claim 5 or claim 6 comprising a combiner for combining transmissions in different slots to give a combined audio output. 8. In a system comprising a plurality of transceivers including a first transceiver transmitting a first transmission in each of a plurality of consecutive TDMA frames in a direct mode, a method for full-duplex direct-mode TDMA- based two-way radio conferencing comprising: identifying a slot in said plurality of consecutive TDMA frames in which no transmissions are present; and transmitting a second transmission in said slot in each of said plurality of consecutive TDMA frames, wherein said first and second transmissions occupy different slots within each of said plurality of consecutive TDMA frames, and wherein said any of said transceivers is operative to receive transmissions directly from any other of said transceivers.

9. A method according to claim 8 wherein said identifying step comprises identifying a lowest-ordered slot in which no transmissions are present.

10. A method according to claim 8 wherein said transmitting step comprises transmitting digital or analog audio transmissions.

11. A method according to claim 8 and further comprising: receiving a plurality of audio transmissions from a plurality of transceivers in a plurality of slots in at least one frame; averaging said plurality of audio transmissions to form a consolidated audio transmission; and outputting said consolidated audio transmission.

12. A method according to claim 8 and further comprising:

designating said first transceiver as a master transceiver; synchronizing said plurality of transceivers to said master transceiver; and designating another of said plurality of transceivers currently transmitting in said plurality of consecutive TDMA frames as said master transceiver.

13. A method according to claim 12 wherein said designating another step comprises designating another of said plurality of transceivers currently transmitting in a lowest-ordered non- empty slot of said plurality of consecutive TDMA frames as said master transceiver.

14. A method according to claim 12 wherein said designating another step comprises designating another of said plurality of transceivers currently transmitting in a least recently used non-empty slot of said plurality of consecutive TDMA frames as said master transceiver.

12 Amendments to the claims have been filed as follows Claims 1. A radio communications transceiver for use in a group communication with at least two other such transceivers using a TDMA slot structured direct mode communications method, the transceiver being operable (i) to transmit in one of a selected set of different slots of the TDMA structure and (ii) to receive communications from at least two other transceivers in at least two different slots and to combine such received communications into a single audio output.

2. A transceiver as claimed in claim 1 and wherein the transceiver is operable to transmit in a slot which is allocated according to which other transceivers in the group are already transmitting, whereby different transceivers transmit in different slots.

3. A transceiver as claimed in claim I or claim 2 and wherein the transceiver is operable to select a slot for transmission which is the lowest ordered slot of the slot structure in which no transmissions are then currently present.

4. A transceiver as claimed in claim 1, claim 2 or claim 3 and wherein the transceiver includes means for compressing and/or encoding transmitted signals and for decompressing and/or decoding received signals.

5. A transceiver as claimed in claim 1, claim 2, claim 3 or claim 4 and wherein the transceiver includes means for averaging received signals in a given frame to produce a consolidated output.

6. A transceiver as claimed inany one preceding claim and wherein the transceiver is operable for full duplex communication with other transceivers in the group.

7. A transceiver as claimed in any one of the preceding claims and wherein the k3 transceiver is such that its transmissions are in analogue form.

8. A transceiver as claimed in any one of claims 1 to 7 and wherein the transceiver is such that its transmissions are in digital form.

9. A transceiver as claimed in any one of the preceding claims and which is a mobile radio transceiver.

10. A transceiver as claimed in any one of the preceding claims and substantially as herein described with reference to the accompanying drawings.

11. A method of direct mode radio communication between transceivers in a group of at least three transceivers wherein the transceivers are as claimed in any one of the preceding claims and wherein transmissions by the transceivers are in different slots of the TDMA structure and receptions by each transceiver are such as to receive communications from at least two other transceivers in at least two different slots and to combine such received communications into a single audio output.

12. A method as claimed in claim 11 and wherein the transmissions and receptions are such that communications in different slots are on the same carrier frequency.

13. A method as claimed in claim 11 or claim 12 and wherein transmissions of the transceivers are synchronised to the transmission by the first of the transceivers to transmit in a given group communication.

14. A method as claimed in claim 13 and which is such that when the transceivers of the group are synchronised to transmission by a given transceiver designated as master transceiver and that transceiver ceases to tramit the transceivers of the group are then synchronised either to the transceiver which is transmitting in the lowest ordered slot or the transceiver which is transmitting in the least recently used slot and the transceiver to which the transceivers of the group are synchronised is designated as the master transceiver.

jk4

15. A method as claimed in any one of claims 11 to 14 and in which the TDMA slot structure is such that there are four slots per frame for communications between the transceivers.

16. A method as claimed in any one of claims I I to 15 and wherein the method comprises a group audio conference.

17. A method as claimed in any one of claims I Ito 16 and which is substantially as herein described with reference to the accompanying drawings.

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