GB2376380A

GB2376380A - Transmitting voice data and non-voice data in TDMA channels

Info

Publication number: GB2376380A
Application number: GB0113699A
Authority: GB
Inventors: Steven Evans; David Thomas
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 2001-06-06
Filing date: 2001-06-06
Publication date: 2002-12-11
Anticipated expiration: 2021-06-06
Also published as: GB2376380B; GB0113699D0

Abstract

A method of transmitting first data 4 from a first data source 3 and second data 6 from a second data source 5 in a time division multiple access (TDMA) system comprises transmitting the first data in predefined channels of a data frame. The second data is superimposed on at least one of the predefined channels in each data frame and the channel on which the second data is superimposed in a pseudo-random manner is varied, such that degradation of quality of service for each channel is minimised. The first data may be real time data such as voice data and the second data may be non-real time.

Description

COMMUNICATION SYSTEM This invention relates to a communication system.

In a communication system, it has been found that the efficiency of transmission can be improved by using the same channel to send speech and non real-time data, e. g. signalling data. However, this can be complex in terms of managing separation of the voice and data at the base station and may result in a perceived loss of quality in the speech transmission in particular.

Various examples of methods of sharing channels have been proposed, but these all have associated problems. One method has been proposed using dynamic coding rates in which the coding rate of data transmission is halved to allow signalling data to be transmitted and then the system reverts to full rate transmission when the signalling data stops. However, a significant drawback with this is the level of complication introduced by the need to signal between entities to track these dynamic coding rate changes and manage interactions with the associated block coding schemes. Another proposal uses spread spectrum techniques to send small amounts of signalling data to interrupt the sending of non-real-time data at the start of a talk burst. The signalling data is sent at the same time as real time data, and processing at the receiver detects the presence of signalling, separates the two signals and decodes both the data and signal.

However, this only works for a particular scenario of statistical multiplexing where both the speech and non-real-time data are associated with the same user. An extension of this concept specifies a particular channel over which all users make spread spectrum signalling. The advantage of this scheme is that a number of users may signal at the same time without the usual collision avoidance constraints. The channel used for the signalling may also be employed for user data if processing is used at the receiver to separate the signalling and data flows. The disadvantage with this method being that there is significant degradation of quality of service (QoS) for the data user on the channel used for signalling.

In accordance with a first aspect of the present invention a method of transmitting first data from a first data source and second data from a second data source in a time division multiple access (TDMA) system comprises transmitting the first data in predefined channels of a data frame; superimposing the second data on at least one of the predefined channels in each data frame; and varying the channel on

which the second data is superimposed, such that degradation of quality of service for each channel is minimised.

In accordance with a second aspect of the present invention, a time division multiple access (TDMA) communication system for transmitting data comprises a first data source, a second data source and processing means; wherein the first data source transmits first data in predefined channels of a data frame; wherein the second data source transmits second data superimposed on at least one of the predefined channels in each data frame; and wherein the processing means varies the channel on which the second data is superimposed, such that degradation of quality of service for each channel is minimised.

The present invention is able to use the same channel for transmitting both a first and second data stream, but within each frame the second data stream is transmitted on a different channel to the channel used in adjacent frames and so spreads any reduction in QoS between users.

Typically, each data frame comprises eight channels.

Preferably, the second data is superimposed in a predetermined manner defined by an algorithm. This can take various different forms. A basic example of the algorithm applies the second data to every nth channel in a continuous series of frames for an eight channel frame, n may be between 2 and 9, but preferably n is equal to 7 or 9.

Alternatively, the algorithm applies the second data to a subset of the channels of the data frame, for example, second data may be applied to one of the first four of any eight channels of any frame only.

Thus, the frame can be split into high quality and standard channels, so that the signalling is only superimposed on the standard channels.

Typically, the first data comprises user traffic, such as voice or data communications and the second data comprises signal codes.

An example of a communication system according to the present invention will now be described with reference to the accompanying drawings in which :- Figure 1 is a block diagram of a communication system according to the present invention;

Figure 2 illustrates one mode of operation of the system of Fig. 1; and, Figure 3 illustrates another mode of operation of the system of Fig. 1.

A communication system according to the present invention is shown in Fig. 1.

The system comprises a data source 1 and a data sink 2. The data source comprises a source 3 of real time data 4, such as voice and a source 5 of non-real time data 6. The two types of data 4,6 are combined in a multiplexer 7 with signalling data 8 from a processor 9, for transmission. At the sink 2, the received signal is recovered 10. The signalling data 8 is sent to a processor 11, and the stream of received data 4,6 is input to a demultiplexer 12 which splits it up again into real time data 4 and non-real time data 6 components. The data is then output 13,14 accordingly An example of such a communication system would be a mobile phone. The phone has the facility to send both voice and data and is provided with an aerial, transmitter and receiver to enable the mobile phone to receive and send messages.

A certain quality of service (QoS) is expected by users of mobile telephone systems. QoS is measurable in terms of the number of errors per channel, although for voice transmission, it tends to be more a matter of the user's perception of quality. A typical transmission arrangement is to break down a frame into eight separate channels.

Each user is allocated a channel and is able to transmit in its one allocated slot, but not the other slots. Some mobile phone systems are able to transmit in two of the slots, but in general it is only in one. Effectively, the system is modulo 8, transmit in 1, wait for 7.

The system of the present invention can be modified to operate in various modes. A first mode of operation is illustrated in Fig. 2. User data is transmitted in frames, each frame comprising 8 bits representing 8 channels. In this first mode, each different user is allocated a different channel, e. g. user 1 is allocated channel 1, user 2 is allocated channel 2 and so on. The data is transmitted on the allocated channel in each frame, as illustrated by the number of each channel, for as many frames as required to complete the message. When the system needs to send signalling data, this is superimposed on the user data. In this example, there are two sources of data shown, user 2 (15) and user 7 (16) and the signalling data 17. The signalling data 17 is superimposed on channel 1 in the first frame, channel 2 in the second frame, channel 3

in the third frame and so on until each of the 8 channels has had signalling data superimposed on it for one frame. The sequence is then repeated for as long as necessary. The advantage of superimposing data in this way is that the system knows where signalling data is going to be transmitted and only looks for it in those predefined frames. Also, by having a regular arrangement for the signalling data, the base station only has to look at predefined times, rather than continuously, which reduces the complexity of the receiver implementation. This allows the system to operate as efficiently as possible to transmit user data.

To avoid unreasonable loss of QoS, the present invention transmits the signalling information on a modulo 9 basis, i. e. transmit in 1, wait for 8. This means that the channel which is overlaid with signal data changes in a regular manner, so that no one channel suffers undue degradation. Other variations are equally possible, such as modulo 7.

A further benefit is that it is a common to reserve one channel in each frame for signalling purposes, but this invention allows that channel to be available for an additional user, so increasing the efficiency of the system.

In systems with channels of mixed QoS, an alternative mode of operation can be applied. Fig. 3 illustrates this alternative mode of operation. In this case some channels are reserved for high quality voice transmission, here channels 5 to 8 (18). The other channels, 1 to 4, are used for non-voice, user data transmission and signalling. Thus across eight frames, each of channels 1 to 4 will have signalling data superimposed twice. This will degrade the QoS more than in the first mode, but if these channels are only transmitting data, rather than voice, the effect will not appear to be significant to the user, whereas the improvement in quality of the voice transmission in its dedicated high quality channels will be noticeable. In this particular example, users 1 and 2 (19, 20) are sending data and signalling data 17 is superimposed over channels 1 to 4 in sequence, but channels 5 to 8 are kept free for high QoS voice 18 communication.

In either mode of operation, the present invention deals with degradation of QoS by changing the slot of the frame on which signal data is imposed, on a frame by frame basis. The invention is particularly applicable to global systems for mobile communication (GSM), but is also suitable for use in other systems such as communication in accordance with ANSI 136 standard, general packet radio system (GPRS), enhanced GPRS (EGPRS), enhanced data rates for GSM evolution

(EGDE) /GSM edge radio access network (GERAN), digital enhanced cordless technology (DECT) and asynchronous transfer mode (ATM). The invention is also applicable for statistical multiplexing where fast channel access is required.

Claims

1. A method of transmitting first data from a first data source and second data from a second data source in a time division multiple access (TDMA) system, the method comprising transmitting the first data in predefined channels of a data frame; superimposing the second data on at least one of the predefined channels in each data frame ; and varying the channel on which the second data is superimposed, such that degradation of quality of service for each channel is minimised.

2. A method according to claim 1, wherein each data frame comprises eight channels.

3. A method according to claim 1 or claim 2, wherein the second data is superimposed in a predetermined manner defined by an algorithm.

4. A method according to claim 3, wherein the second data is applied to every nth channel in a continuous series of frames

5. A method according to claim 4, wherein n is equal to 7 or 9.

6. A method according to claim 3, wherein the algorithm applies the second data to a subset of the channels of the data frame.

7. A method according to claim 6, wherein the second data is applied to one of the first four of any eight channels of any data frame.

8. A method according to any preceding claim, wherein the first data comprises user traffic and the second data comprises signal codes.

9. A time division multiple access (TDMA) communication system for transmitting data, the system comprising a first data source, a second data source and processing means; wherein the first data source transmits first data in predefined channels of a data frame; wherein the second data source transmits second data

superimposed on at least one of the predefined channels in each data frame; and wherein the processing means varies the channel on which the second data is superimposed, such that degradation of quality of service for each channel is minimised.