Multiplex communications – Diagnostic testing – Determination of communication parameters
Patent
1996-10-11
2000-10-17
Ngo, Ricky
Multiplex communications
Diagnostic testing
Determination of communication parameters
370328, 370468, 455517, 455 69, H04Q 738, H04B 726, H04L 112
Patent
active
061342203
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention is that of digital mobile radio systems. The invention applies in particular to cellular mobile radio systems such as systems conforming to the GSM (Global System for Mobile communications) standard, for example.
More particularly still, the invention concerns the exchange of digital signals, whether they constitute data or speech, in time-division multiple access (TDMA) time-division multiplex systems.
2. Description of the Prior Art
The TDMA technique divides time into frames of fixed and predetermined duration, the frames being in turn divided into time slots. Each call is associated with one or more time slots.
Thus a frame comprises N time slots that can correspond to N calls. Each receiver is able to extract the time slots addressed to it in order to reconstitute the source signal. In this way N calls can be transmitted in the same frequency band.
Where data communications are concerned, mobile radio systems like the GSM system conventionally provide two services, corresponding to two different, levels of quality. Thus, for transmission of data, the GSM system provides a first data communication mode called the full rate mode, in which a time slot is transmitted in each frame, and a second transmission mode called the half rate mode, in which the data signal is transmitted in one time slot only every two frames, on average.
In this second mode, the resource allocated to a call is halved compared to the first mode. This frees up resources for other calls.
This halving of the total bit rate of the call naturally requires modification of the channel coding used, to retain the same user bit rate, in other words, the half rate mode corresponds to channel coding with half the yield of that of the full rate mode. In the GSM system, the two modes respectively correspond to raw bit rates of 11.4 kbit/s and 22.8 kbit/s.
Consequently, the efficacy of half rate channel coding is less than that of full rate channel coding. For this reason the half rate mode can be used only when transmission conditions are good and/or the transmission quality required is average, in other words when a relatively high bit error rate can be tolerated. If the transmission channel is subject to interference and/or the data requires a higher transmission quality (i.e. a lower bit error rate) the full rate mode must be used.
According to the GSM standard, a transmission mode is chosen at the time the call is set up and is retained throughout the call. This technique has two drawbacks: the use of the half rate mode under normal conditions of operability and if the half rate mode is adopted, should the channel then be subjected to a higher level of interference, exceeding the operability limit of the system (set at a C/I value of approximately 9 dB), the call in progress is suddenly cut off; under difficult coverage conditions a value of C/I below 9 dB may be encountered; the use of the full rate mode under normal conditions of operability and if the full rate mode is adopted, should the channel subsequently be subject to a lower degree of interference, the channel coding employed is of higher quality than is required; the transmission channel is therefore unnecessarily occupied in alternate frames (causing unnecessary interference in neighboring cells).
In mobile radio systems these problems are major problems since the transmission channel changes continually with the movement of the mobile station and the movement and the activity of the sources of interference, etc. As a result, the full rate mode is usually chosen, for safety, and this leads to high and often unnecessary consumption of the transmission resource.
There are also two configurations in the case of speech signals (full rate mode and half rate mode), which correspond to the use of different speech encoders (source coding) and different channel encoders, the two pairs of encoders (source and channel) providing respective raw bit rates of 22.8 kbit/s (full rate) and 11.4 kbit/s (half rate).
Pr
REFERENCES:
patent: 5142551 (1992-08-01), Borth et al.
patent: 5327576 (1994-07-01), Uddenfeldt et al.
patent: 5404355 (1995-04-01), Raith
patent: 5490136 (1996-02-01), Sereno et al.
Source and Channel Coding for Speech in Marocell/Mcrocell/Picocell Third Generation Systems, by Tomas Sanjuan, Luis Hernandez and Jose Manuel Paez, Fourth Winlab Workshop on Third Generation Wireless Information Networks in cooperation with IEEE Vehicular Technology Society, Oct. 19-20, 1993, pp. 175-195.
Speech Coding Requirements From the Perspective of the Future, Mobile Systems, Marc Delprat, et al., IEEE Workshop on Speech Coding for Telecommunications.
Delprat Marc
Le Strat Evelyne
Alcatel Cit
Ngo Ricky
LandOfFree
Method of adapting the air interface in a mobile radio system an does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of adapting the air interface in a mobile radio system an, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of adapting the air interface in a mobile radio system an will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-476308