GB2322525A

GB2322525A - A method of allocating a TDM communication resource

Info

Publication number: GB2322525A
Application number: GB9703667A
Authority: GB
Inventors: Andrew John Aftelak
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1997-02-21
Filing date: 1997-02-21
Publication date: 1998-08-26
Anticipated expiration: 2017-02-21
Also published as: GB9703667D0; GB2322525B

Abstract

A method of allocating a TDM communication resource comprises the steps of receiving, from a communication unit 101, a request for allocation of L time slots of a time division multiplexed (TDM) communication resource, wherein the TDM communication resource is comprised of of an M-frame repeating frame pattern and N time slots per frame and wherein L is an integer greater than or equal to 1 and N and M are integers greater than 1; and allocating, by a resource allocator 113, L time slots of the TDM communication resource such that the communication unit is allocated use of L time slots per frame and at least L + 1 different time slots are allocated in at least two different frames of the TDM communication resource. This reduces the end-to-end delays associated with allocating the same time slot(s) in each frame to a particular communication unit.

Description

A METHOD OF ALLOCATING A TDM COMMUNICATION RESOURCE Field of the Invention This invention relates to time division multiplexed (TDM) communication systems, including but not limited to allocation of communication resources in TDM communication systems.

Background of the Invention Communication systems are known to use time division multiplexed (TDM) communication resources. In a TDM system, a single channel is shared between two or more communication units, such as mobile or portable communication devices, by splitting the communication resource into two or more time slots for each frame of the communication resource.

Each communication unit is allowed at least one time slot per frame. Often, the TDM communication resource is comprised of a repeating pattern of a plurality of frames, such as 18 frames, where 17 frames are used to communicate voice information and 1 frame is used to communicate embedded signalling. Thus, every 18 frames the frame pattern repeats, thereby yielding a repeating frame pattern. In today's systems, a single request for a single slot of a TDM communication resource is assigned to one slot, the same slot, of each frame of the TDM communication resource.

For example, if each frame is split into four time slots, a first resource may include the first slot of every frame, a second resource may include the second slot of every frame, a third resource may include the third slot of every frame, a fourth resource may include the fourth slot of every frame.

In TETRA (Trans European Trunked RAdio) and GSM (Global System for Mobile communications) systems, during a fixed time period, a fixed amount of voice information is collected for transmission. Because of the compression and processing algorithms used to process the voice information into time slots suitable for transmission in these systems, extra space is available on the channel for transmission of other iWformation, such as embedded signalling information. In TETRA systems, an 18-frame repeating frame pattern consists of 17 frames for communicating voice information and 1 frame for communicating embedded signalling information. In GSM systems, an 26-frame repeating frame pattern consists of 24 frames for communicating voice information and 2 frames for communicating embedded signalling information.

Because of a mismatch between the timing of the voice frames (30 milliseconds per voice frame, two voice frames per time slot) and the TDM framing (14 1/6 milliseconds per time slot, four time slots per frame in a TETRA system), the speech is buffered such that no speech frames need be transmitted in the embedded signalling frame(s) while maintaining a constant delay incurred by each speech frame regardless of the TDM frame in which the speech frame is transmitted. As a result, a delay additional to a TDM framing structure without embedded signal information is incurred due to the buffering.

The block diagram of FIG. 1 shows an example of two different types of communications: direct and indirect. Direct communication unit 101 to communication unit 103 communications, also referred to as talkaround communications, take place over a direct communication resource 107.

Direct communications may also take place between a mobile or portable communication unit and a wireline communication unit, such as a telephone (not shown). Communication resources include wireline, frequency, frequency pair, TDM (time division multiplexed) time slot, a recurring TDMA (time division multiple access) time slot, a single-shot use of a sequence of TDMA time slots, and so forth. Indirect communication unit 101 to communication unit 103 communications, also referred to as repeated communications, take place over multiple communication resources. For example, the first communication unit 101 transmits to a base station or repeater 105 via a first communication resource 109, and the repeater 105 repeats the transmission for reception by a second communication unit 103 via a second communication resource 111.

Indirect communication unit to communication unit communications may be used, for example, when the first communication unit is incapable of direct transmission to the second communication unit.

In a first example, a first communication unit 101 communicates directly with a second communication unit 103 via a direct communication link 107. As shown in the timing diagram of a TETRA TDM communication resource in FIG. 2, in the middle section of the timing diagram labeled "Uplink," the TDM communication resource utilises an eighteen frame repeating frame pattern. Each of the frames is divided into four time slots. Voice information is transmitted in 17 frames and embedded signalling is transmitted in one frame. Shown in the upper section of FIG. 2 is a representation of voice frames as provided within a transmitter. In the example shown, the voice frames are transmitted in the first time slot of each frame. In the example shown, two voice frames are processed at the transmitter so that the resultant processed information is transmitted in one of the TDM time slots. A total of 34 voice frames comprises one repeating voice frame that is transmitted in one repeating frame pattern of the TDM communication resource. The voice frames are provided at the receiving communication unit 103 as shown in the lower section of FIG. 2.

In general, the information to be transmitted in a particular time slot must be processed before the time at which the information is to be transmitted. In addition, voice information must be held or buffered until after the embedded signalling information is transmitted. Voice frames 31 and 32 must wait until frame 18 of the TDM communication resource has been transmitted before packing the processed speech into TDM frame 1, which occurs after TDM frame 18. Thus, all the voice frames must be buffered both before and after the embedded signalling to ensure constant presentation of decoded data at the receiver and the transmitter, thereby avoiding gaps in recovered voice at the receiver. Such buffering results in a delay of 9 slots, or 127.5 milliseconds, in a direct communication.

The timing diagram of FIG. 3 shows a presentation of the same voice frame structure at a transmitter for use in an indirect transmission via an uplink (inbound communication resource) to a repeater 105, as shown in FIG.-1. The Uplink 109 incurs the same delays as the Uplink shown in FIG. 2 An indirect communication also incurs additional delays relating to transmission by the repeater 105 on the Downlink 111, because data must be presented at the repeater 105 before the time when the data is transmitted by the repeater. Consequently, the total delay for an indirect communication through a repeater 105 is seven slots plus the time of two frames, which equals 99 V6 milliseconds plus 60 milliseconds for a total of 159 V6 milliseconds. Communication delays become noticeable between 200 and 250 milliseconds, hence, the delays caused by the need to buffer information place a stringent requirement on the signal processing in infrastructured delays.

Accordingly, there is a need for a method of providing a TDM communication resource that introduces less delay end-to-end during direct and indirect communications.

Brief Description of the Drawings FIG. 1 is a block diagram of a communication system in accordance with the invention.

FIG. 2 is a timing diagram showing buffering delays in a direct communication for a TDM communication resource.

FIG. 3 is a timing diagram showing buffering delays in an indirect communication for a TDM communication resource.

FIG 4 is a timing diagram showing buffering delays in a direct communication for a TDM communication resource in accordance with the invention.

FIG. 5 is a timing diagram showing buffering delays in an indirect communication for a TDM communication resource in accordance with the invention.

Description of a Preferred Embodiment The following describes an apparatus for and method of reducing end-toend delays on both direct and indirect communications by assigning the TDM communication resource not on a same slot per frame basis, i.e., where a communication unit is given the same slot in each frame of a TDM communication resource, but rather by providing a rolling time slot, wherein the communication unit transmits in time succession on each of the time slots in a frame such the delay caused by the transmission of the embedded signalling is minimised.

A method of allocating a TDM communication resource comprises the steps of receiving, from a communication unit, a request for allocation of L time slots of a time division multiplexed (TDM) communication resource, wherein the TDM communication resource is comprised of of an M-frame repeating frame pattern and N time slots per frame and wherein L is an integer greater than or equal to 1 and N and M are integers greater than 1; and allocating, by a resource allocator, L time slots of the TDM communication resource such that the communication unit is allocated use of L time slots per frame and at least L + 1 different time slots are allocated in at least two different frames of the TDM communication resource.

A method of utilising a TDM communication resource allocation by a communication unit comprises the steps of receiving a grant of allocation of at least one time slot of a time division multiplexed (TDM) communication resource, wherein the TDM communication resource is comprised of an M-frame repeating frame pattern and N time slots per frame and wherein L is an integer greater than or equal to 1 and N and M are integers greater than 1; transmitting, by the communication unit, a first part of a message in a first time slot of a first frame of the TDM communication resource; and transmitting, by the communication unit, a second part of the message in a second time slot of the first frame of the TDM communication resource, wherein the communication unit refrains from transmitting in the first time slot of the second frame.

Additional features of the above methods may include that the communication unit transmits information in each of N frames in N different time slots. N may equal 4, and M may equal 18. The communication unit may transmit in one time slot and receive in another time slot in one frame. Voice information may be transmitted in 17 frames and embedded signalling information in 1 frame. The allocation of the TDM communication resource may comprise a repeating time slot pattern.

The repeating time slot pattern may avoid assigning two adjacent time slots to one communication unit and assign a frame for embedded signalling such that throughput delays are minimized. The repeating time slot pattern may follow any of the repeating time slot patterns as shown in Table 1, Table 2, or Table 3 below.

A timing diagram showing buffering delays in a direct communication for a TDM communication resource is shown in FIG. 4. In the preferred embodiment of the present invention, 34 voice frames, each of 30 milliseconds duration, are presented at the transmitter during each repeating voice frame pattern. The middle section of the timing diagram shows the repeating frame pattern of a 4 slot per frame TDM communication resource having anl8-frame duration in the preferred embodiment. As shown in FIG. 4, voice frames 1 and 2 are transmitted in the first time slot of the second frame of the TDM communication resource, voice frames 3 and 4 are transmitted in the first time slot of the third frame, voice frames 5 and 6 are transmitted in the first time slot of the fourth frame, and voice frames 7 and 8 are transmitted in the first time slot of the fifth time frame. At this time, the communication unit 101 begins transmitting in the next time slot, i.e., the time slot is said to roll. Voice frames 9 and 10 are transmitted in the second slot of the sixth frame, voice frames 11 and 12 are transmitted in the second slot of the seventh frame, voice frames 13 and 14 are transmitted in the second slot of the eighth frame, and voice frames 15 and 16 are transmitted in the second slot of the ninth frame.

The time slot for the communication unit 101 rolls again from the second slot to the third slot, where voice frames 17 and 18 are transmitted in the third time slot of the tenth frame, voice frames 19 and 20 are transmitted in the third time slot of the eleventh frame, voice frames 21 and 22 are transmitted in the third frame of the twelfth frame, and voice frames 23 and 24 are transmitted in the third slot of the thirteenth frame. The time slot then rolls again from the third slot to the fourth slot, where voice frames 25 and 26 are transmitted in the fourth time slot of the fourteenth frame, voice frames 27 and 28 are transmitted in the fourth slot of the fifteenth frame, voice frames 29 and 30 are transmitted in the fourth slot of the sixteenth frame, and voice frames 31 and 32 are transmitted in the fourth time slot of the seventeenth frame. The embedded signalling informatin is then transmitted, in this case in the third time slot of the eighteenth frame. The last voice frames 33 and 34 are then transmitted in the first time slot of the first frame of the next 18 frame repeating frame pattern of the TDM communication resource.

As a result of the assignment of the TDM communication resource not on a single slot per communication basis but on a rolling slot basis, the endto-end delay is less than the 127.5 milliseconds reflected in FIG. 2 for the same situation. In the case of FIG. 4, the total delay is 60 milliseconds for the time of two voice frames plus 13.3 msecs. for the time between the end of a time slot and the end of a frame plus one slot for a total of 87.5 milliseconds. Thus the present invention shortens the end-to-end delay for an 18-frame TDM communication resource, such as the one shown in FIG.

4, by 40 milliseconds. Each of the remaining time slots is similarly assigned in, as shown in Table 1 below, in a resource assignment referred to as a repeating time slot pattern. Each different letter represents a different assignment of the TDM communication resource.

TDMA | Slot 1 Slot 2 Slot 3 Slot 4 Frame 1 A D C B 2 A D C B 3 A D C B 4 A D C B 5 A B Signalling D C 6 B A D C 7 B A D C 8 B A D C 9 B A C Signalling D 10 C B A D 11 C B A D 12 C B A D 13 C B A D 14 C DSignalling B A 15 D C B A 16 D C B A 17 D C B A 18 D C A Signalling B Table 1 An example of an assignment of a TDM communication resource with rolling time slots in a system where the TDM communication resource has 26 frames per repeating frame pattern in the form of 24 frames of voice and 2 frames of embedded signalling is shown in Table 2 below. Each different letter represents a different assignment of the TDM communication resource.

Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Slot 7 Slot 8 1 A r E H D G C B F 2 A E FSIG1 D H C B G 3 A F B SIG2 E H D C G 4 B F A E H D C G 5 B F A E I GSIG1 D C H 6 B G A F CSIG2 E D H 7 C G B F A E D H 8 C G B F A E D H SIG1 9 C H B G A F E DSIG2 10 D H C G B F E A 11 D H C G B F E A 12 D ESIG2 C H B G F A 13 E ASIG1 D H C G F B 14 E A D H C G F B 15 E A D FSIG2 C H G B 16 F A E BSIG1 D H G C 17 F B E A D H G C 18 F B E A D GSIG2 H C 19 G B F A E CSIG1 H D 20 G C F B E A H D 21 G C F ~ B E A HSIG2 D 22 H C G B F A DSIG1 E 23 H D G C F B. A E 24 H D G C F B A E 25 ESIG1 D H C G B A F 26 A SIG2 E H D G C B F Table 2 In some TDM communications systems, a TDM flill-duplex scheme of assigning the TDM slots is utilised. In such a resource assignment scheme, the same communication unit will be assigned to transmit on 2 different time slots in the same frame, such as slots 1 and 3 or 2 and 4 in a four slot per frame system. Generally, a communication unit transmits in one slot and receives in another time slot at least one time slot away from the conclusion of transmission in the first time slot so that the communication unit has time to switch from transmit to receive or receive to transmit without missing the use of the beginning of the time slot. For example, in an 8 slot per frame TDM system, a communication unit may be assigned to transmit in slot 1 and receive in slot 5, transmit in slot 2 and receive in slot 6, transmit in slot 3 and receive in slot 7, or transmit in slot 4 and receive in slot 8. Similarly, a communication unit may receive in slot 1 and transmit in slot 5, receive in slot 2 and transmit in slot 6, receive in slot 3 and transmit in slot 7, or receive in slot 4 and transmit in slot 8.

The use of Table 1 above to assign TDM fill-duplex communications within a TDM communication resource requires a communication unit to transmit in one time slot and receive in the very next time slot in the same frame, i.e., in consecutive slots. Such a requirement may be difficult in some communication units that are not equipped to switch from transmit to receive in such a short time. As shown in frame 9 of Table 1, where the A designation represents the transmitting time slots and the C designation represents the receiving time slots, the communication unit will be forced to transmit in slot 2 and receive in slot 3 immediately thereafter. A similar situation occurs in frame 14, where a B and D combination is used for transmitting and receiving. In some communication units, such a resource allocation requires additional hardware to provide the required switching time in adjacent slots.

Another solution to the TDM full-duplex resource assignment switching problem described above is to provide a different assignment of the time slots. As shown in Table 3 below, no adjacent time slots in the same frame are assigned to transmit and receive in the same communication unit operating in TDM full-duplex mode. In other words, the "A" designated slots and "C" designated slots are always separated by another time slot, and the "B" designated slots and D designated slots are always separated by another time slot in the repeating time slot pattern shown. Thus, no adjacent time slots in the same frame are assigned to the same communication unit.

TDMA Slot 1 I Slot 2 I Slot 3 Slot 4 Frame 1 A D C B 2 A D C B 3 A D C B 4 A D C B 5 BSignalling A D C 6 B A D C 7 B A D C 8 B A D C 9 B A D CSignaliing 10 C B A D 11 C B A D 12 C B A D 13 C B A D 14 DSignalling C B A 15 D C B A 16 D C B A 17 D C B A 18 ~ D C B Signalling Table 3 Hence, use of the repeating time slot pattern shown in Table 3 provides an even more efficient and flexible manner for assigning a TDM communication resource while minimising required buffer delays. No additional delays result from using the repeating time slot pattern shown in Table 3 than result from using the pattern shown in Table 1.

The timing diagram of FIG. 5 shows the allocation of rolling time slots for an indirect communication, i.e., in a communication where a repeater is repeats an inbound message on an outbound communication resource.

As can be seen from FIG. 5, the total end-to-end delay in this situation is 60 milliseconds plus 13.33 milliseconds plus three time slots for a total of 115.83 milliseconds, which results in a saving of 44 milliseconds in delay time over the resource assignment shown in FIG. 3.

In the preferred embodiment, a resource allocator 113, such as a SmartZone Controller available from Motorola, Inc., receives a request for allocation of one or more slots of a TDM communication resource and in response allocates one or mroe slots of the TDM communication resource in accord with a repeating time slot patterns, such as one of the repeating time slot patterns shown in Table 1, Table 2, or Table 3.

Although the repeating time slot patterns shown and described herein begin with frame 1, because the patterns repeat, i.e., after using a repeating time slot pattern for frames 1 through 18, the same repeating time slot pattern is used again and again in succession until all information is transmitted. It is not critical in to successful practice of the present invention where in the repeating time slot pattern the sequence is begun, so long as the same pattern repeats. In other words, the beginning point of the pattern is not essential to successfully practising the present invention so long as the same pattern is repeated throughout the transmission of the message for a particular communication unit. For example, if the pattern is entered at frame 6 as shown in FIG. 3 above, and a total of 36 frames are to be transmitted, the pattern used to transmit would reflect frames 6 to 18, frames 1 to 18, and frames 1 to 5. One skilled in the art would recognise that other repeating time slot patterns exist, within the spirit and scope of the invention described and claimed herein. In addition, the invention may be successfully applied to TDM communication resources with other voice frame patterns, repeating frame patterns, number of voice frames, number of time slots per frame, number of frames, number of embedded signalling frames, and so forth.

The use of a rolling slot, as described herein, in producing a repeating time slot pattern, assigns a frame for embedded signalling such that throughput delays are minimized. For a TETRA system, the rolling slot physical communication resource offers the same service to the upper layers of a protocol stack (i.e., 17 traffic slots and one signalling slot) as the standard TETRA system, but with reduced delay. Hence, the software changes in incorporating a rolling time slot in a standard TETRA system are minimal, requiring minute change to the protocol. Further, if the pattern in Table 3 is used as described, the capabilities of the radio frequency sections of a communication unit need not be changed.

What is claimed is:

Claims

Claims 1. A method comprising: receiving, from a communication unit, a request for allocation of L time slots of a time division multiplexed (TDM) communication resource, wherein the TDM communication resource is comprised of of an M-frame repeating frame pattern and N time slots per frame and wherein L is an integer greater than or equal to 1 and N and M are integers greater than 1; and allocating, by a resource allocator, L time slots of the TDM communication resource such that the communication unit is allocated use of L time slots per frame and at least L + 1 different time slots are allocated in at least two different frames of the TDM communication resource.
2. The method of claim 1, wherein the communication unit transmits information in each of N frames in N different time slots.
3. The method of claim 1, wherein N equals 4.
4. The method of claim 1, wherein the communication unit transmits in one time slot and receives in another time slot in one frame.
5. The method of claim 1, wherein M equals 18.
6. The method of claim 5, wherein voice information is transmitted in 17 frames and embedded signalling information is transmitted in 1 frame.
7. The method of claim 1, wherein the allocation of the TDM communication resource comprises a repeating time slot pattern.
8. The method of claim 7, wherein the repeating time slot pattern avoids assigning two adjacent time slots to one communication unit.
9. The method of claim 7, wherein the repeating time slot pattern assigns a frame for embedded signalling such that throughput delays are minimized.
10. The method of claim 7, wherein each frame of the TDM communication I resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein the repeating time slot pattern is four voice frames in slot 1, five voice frames in slot 2, four voice frames in slot 3, four voice frames in slot 4, and one embedded signalling frame in slot 4.
11. The method of claim 7, wherein each frame of the TDM communication resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein the repeating time slot pattern is four voice frames in slot 1, four voice frames in slot 2, five voice frames in slot 3, four voice frames in slot 4, and one embedded signalling frame in slot 1.
12. The method of claim 1, wherein each frame of the TDM communication resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein: during frames 1 to 4, a first communication unit uses slot 1, a second communication unit uses slot 4, a third communication unit uses slot 3, and a fourth communication unit uses slot 2; during frames 5 to 9, the first communication unit uses slot 2, the second communication unit uses slot 1, the third communication unit uses slot 4, and the fourth communication unit uses slot 3; during frames 10 to 13, the first communication unit uses slot 3, the second communication unit uses slot 2, the third communication unit uses slot 1, and the fourth communication unit uses slot 4; during frames 14 to 18, the first communication unit uses slot 4, the second communication unit uses slot 3, the third communication unit uses slot 2, and the fourth communication unit uses slot 1; during frame 5, the second communication unit uses slot 1 for embedded signalling; during frame 9, the third communication unit uses slot 4 for embedded signalling; during frame 14, the fourth communication unit uses slot 1 for embedded signalling; and during frame 18, the first communication unit uses slot 4 for embedded signalling.
13. The method of claim 1, wherein each frame of the TDM communication resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein: during frames 1 to 4, a first communication unit uses slot 1, a second communication unit uses slot 4, a third communication unit uses slot 3, and a fourth communication unit uses slot 2; during frame 5, a first communication unit uses slot 1, a second communication unit uses slot 2 for embedded signalling, a third communication unit uses slot 4, and a fourth communication unit uses slot 3; during frames 6 to 8, the first communication unit uses slot 2, the second communication unit uses slot 1, the third communication unit uses slot 4, and the fourth communication unit uses slot 3; during frame 9, a first communication unit uses slot 2, a second communication unit uses slot 1, a third communication unit uses slot 3 for embedded signalling, and a fourth communication unit uses slot 4; during frames 10 to 13, the first communication unit uses slot 3, the second communication unit uses slot 2, the third communication unit uses slot 1, and the fourth communication unit uses slot 4; during frame 14, a first communication unit uses slot 4, a second communication unit uses slot 3, a third communication unit uses slot 1, and a fourth communication unit uses slot 2 for embedded signalling; during frames 15 to 17, the first communication unit uses slot 4, the second communication unit uses slot 3, the third communication unit uses slot 2, and the fourth communication unit uses slot 1; and during frame 18, a first communication unit uses slot 3 for embedded signalling, a second communication unit uses slot 4, a third communication unit uses slot 2, and a fourth communication unit uses slot 1.
14. A method comprising: receiving, by a communication unit, a grant of allocation of at least one time slot of a time division multiplexed (TDM) communication resource, wherein the TDM communication resource is comprised of an M-frame repeating frame pattern and N time slots per frame and wherein L is an integer greater than or equal to 1 and N and M are integers greater than 1; transmitting, by the communication unit, a first part of a message in a first time slot of a first frame of the TDM communication resource; and transmitting, by the communication unit, a second part of the message in a second time slot of the first frame of the TDM communication resource, wherein the communication unit refrains from transmitting in the first time slot of the second frame.
15. The method of claim 14, wherein the communication unit transmits a part of the message in each of N frames in N different time slots.
16. The method of claim 14, wherein N equals 4.
17. The method of claim 14, wherein the communication unit transmits in one time slot and receives in another time slot in one frame.
18. The method of claim 14, wherein M equals 18.
19. The method of claim 18, wherein voice information is transmitted in 17 frames and embedded signalling information is transmitted in 1 frame.
20. The method of claim 14, wherein the grant of allocation of the TDM communication resource comprises a repeating time slot pattern.
21. The method of claim 20, wherein the repeating time slot pattern avoids assigning two adjacent time slots to one communication unit.
22. The method of claim 20, wherein the repeating time slot pattern assigns a frame for embedded signalling such that throughput delays are minimized.
23. The method of claim 20, wherein each frame of the TDM communication resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein the repeating time slot pattern is four voice frames in slot 1, five voice frames in slot 2, four voice frames in slot 3, four voice frames in slot 4, and one embedded signalling frame in slot 4.
24. The method of claim 20, wherein each frame of the TDM communication resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein the repeating time slot pattern is four voice frames in slot 1, four voice frames in slot 2, five voice frames in slot 3, four voice frames in slot 4, and one embedded signalling frame in slot 1.
25. The method of claim 14, wherein each frame of the TDM communication resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein: during frames 1 to 4, a first communication unit uses slot 1, a second communication unit uses slot 4, a third communication unit uses slot 3, and a fourth communication unit uses slot 2; during frames 5 to 9, the first communication unit uses slot 2, the second communication unit uses slot 1, the third communication unit uses slot 4, and the fourth communication unit uses slot 3; during frames 10 to 13, the first communication unit uses slot 3, the second communication unit uses slot 2, the third communication unit uses slot 1, and the fourth communication unit uses slot 4; during frames 14 to 18, the first communication unit uses slot 4, the second communication unit uses slot 3, the third communication unit uses slot 2, and the fourth communication unit uses slot 1; during frame 5, the second communication unit uses slot 1 for embedded signalling; during frame 9, the third communication unit uses slot 4 for embedded signalling; during frame 14, the fourth communication unit uses slot 1 for embedded signalling; and during frame 18, the first communication unit uses slot 4 for embedded signalling.
26. The method of claim 14, wherein the TDM communication resource comprises four time slots, slot 1, slot 2, slot 3, and slot 4 in time order, and wherein: during frames 1 to 4, a first communication unit uses slot 1, a second communication unit uses slot 4, a third communication unit uses slot 3, and a fourth communication unit uses slot 2; during frame 5, a first communication unit uses slot 1, a second communication unit uses slot 2 for embedded signalling, a third communication unit uses slot 4, and a fourth communication unit uses slot 3; during frames 6 to 8, the first communication unit uses slot 2, the second communication unit uses slot 1, the third communication unit uses slot 4, and the fourth communication unit uses slot 3; during frame 9, a first communication unit uses slot 2, a second communication unit uses slot 1, a third communication unit uses slot 3 for embedded signalling, and a fourth communication unit uses slot 4; during frames 10 to 13, the first communication unit uses slot 3, the second communication unit uses slot 2, the third communication unit uses slot 1, and the fourth communication unit uses slot 4; during frame 14, a first communication unit uses slot 4, a second communication unit uses slot 3, a third communication unit uses slot 1, and a fourth communication unit uses slot 2 for embedded signalling; during frames 15 to 17, the first communication unit uses slot 4, the second communication unit uses slot 3, the third communication unit uses slot 2, and the fourth communication unit uses slot 1; and during frame 18, a first communication unit uses slot 3 for embedded signalling, a second communication unit uses slot 4, a third communication unit uses slot 2, and a fourth communication unit uses slot 1.
27. A method as substantially described herein and according to the drawings.