GB2281157A

GB2281157A - Gain control using sampling suitable for TDMA systems

Info

Publication number: GB2281157A
Application number: GB9416082A
Authority: GB
Inventors: Michael Reiner; Ulrich Langewellpott
Original assignee: AEG Mobile Communication GmbH
Current assignee: AEG Mobile Communication GmbH
Priority date: 1993-08-16
Filing date: 1994-08-09
Publication date: 1995-02-22
Anticipated expiration: 2014-08-09
Also published as: IT1274600B; DE4327541A1; GB9416082D0; GB2281157B; FR2709215B1; ITMI941722A1; ITMI941722A0; FR2709215A1

Description

2281157 Process for Automatic Regulation of the Amplification in a

Receiver In conventional receivers of analogue operation, processes for automatic regulation of amplification in a receiver are widely known. In modern receivers with digital signal processing, such as receivers in TDMA- systems, there are particular requirements for amplification regulation which are not met by conventional concepts.

In wide band TDMA-systems, such as the cellular GSM-system, 10. several parties have access to the same frequency channel which is subdivided into time slots allocated to individual parties. The time slots are periodically repetitive frames, such that a communication link in a frequency channel between two participating stations is periodically 15. interrupted by information exchanged between other stations in other time slots of the same frequency channel. This other information.may have greatly varying field strengths and these must not affect the amplification regulation of the receivers operating in other time slots. Conversely,

20. the receiver must be sufficiently quick enough to respond to variations in the field strength of the signal received in the allocated time slot; the fluctuations may, for example, occur due to multipath propagation and corner cutting, in particular in mobile radio-telephone operation.

25. In TDMA-systems, the situation may occur where nothing is transmitted in particular time slots, because, for example, the transmitter is switched off, when information is not transmitted, for example in pauses in speech. The amplification regulation in the receiver must only take into 30. account those time slots allocated to the relevant receiver, must, however, conversely, not respond to time slots in which nothing is transmitted, otherwise the amplification would be inappropriately adjusted up.

The purpose of the invention is to indicate a process for automatic amplification regulation in a receiver, suitable for digital amplification control.

This purpose is achieved by the characteristics indicated

Claims

5. in Claim 1. Useful executions of the invention are the object of the

associated claims.

The process in accordance with the invention can be applied usefully to TDMAsystems, is, however, not limited to these. However, with reference to a TDMA-system using a preferred 10. type of execution and with reference to the drawings, further details will be given. The following drawings show:

Fig. 1 a block circuit diagram of part of receiver relevant to the invention; is.

Fig. 2 a block circuit diagram comparable to Fig. 1, for a receiver suitable for DTX operation, and Fig. 3 a diagram of a given curve of the amplification to be set, dependent upon the level of signal reception.

In the process in accordance with the invention, the 20. absolute reception performance or the level of the signal received is measured once per time slot, whilst taking into account the relevant amplification set and a value representing the level is stored. This may take place logarithmically in order to achieve a considerable reduction in the numeric range necessary for representing the possible level of reception. Reception performance may, for example, be calculated according to A/D-change. As a rule, an A/Dconverter has a limited numeric range. Logarithmisation takes account of this and is carried out with the aid of a 30. table. (The effect of the amplification set can then be determined simply by adding the relevant logarithmic amplification value.

A If, in accordance with Fig. 1, the amplification factor to be set is calculated from the reception levels of the last N time slots, an average is obtained which takes into account the last N reception level. The amplification is 5. set in accordance with a characteristic curve which may be linear, and thus in the simplest case a straight line.

In the case of very small reception performance, a smaller level control may be selected, as the smallest possible reception output is limited by the noise level and with a 10. further decrease in output, reception is no longer possible. This means that the maximum required amplification is limited. The minimum amplification is obtained from the maximum possible reception level. These observations result in a characteristic curve in accordance with Fig. 3 which 15. moves into constant values at its upper and lower end.

It is particularly useful, if the amplification for the next time slot is determined according to the maximum value of the signal level received in the last N time slots. The advantage of this measure is that signal obliteration in 20. individual time slots, due, for example, to multipath reception, does not affect amplification regulation. Thus not too large a dynamic reserve need be provided in case of an increase in output after signal obliteration. By evaluating the maximum, when the mean reception performance increases, the reaction time of the amplification regulation of a single time slot is obtained. If the reception performance falls, the reaction time is N time slots.

25.

The optimum level control of the receiver should lie 30. somewhat below the maximum possible level control in order to have at disposal the necessary reserve.

In the simplest case, determining the level in the last N time slots can be achieved with the aid of the circuit in accordance with Fig. 1, according to which the values representing the signal level are shifted by a shift register, the cells of which are connected parallel to an evaluating circuit, of which the outgoing signal determines the amplification factor. The evaluating circuit may be a simple averaging circuit, or, as explained in the useful type of execution referred to lastly, such a circuit which 10. determines the maximum level under the last N levels determined.

In mobile communication networks the situation often occurs where for a short time during an established connection, no useful information is transmitted, for example in pauses in 15. speech. In a telephone conversation, as a rule, only one of the participants speaks. In order to minimize samechannel interference, i.e. interference on the same frequency due to more remote transmitting stations, it is useful to switch off the transmitter in such periods of 20. speech pause. This is called DTX (Discontinuous Transmission). For the receiver, however, at certain intervals, certain control or regulating information must be transmitted, for example in order to maintain synchronisation in the receiver. This means that at certain 25. intervals, even if no useful information is transmitted, a signal (control information) must be transmitted to maintain, in an orderly manner, the connection to the receiver addressed. In the GSMsystem, a fixed time-slot pattern known to the receiver is used, i.e. there are time 30. slots reserved for transmitting such control information and which cannot be affected by DTX, i.e. in these (time slots) a signal is transmitted in any case.

In accordance with one type of execution of this invention, when the receiver in such a system is operated, the 1 A -5 amplification of the receiver is regulated not only with the relevant N last time slots being taken into account, during which useful information was transmitted, but also with time slots in which control information of the type previously 5. mentioned being taken into account. Here, the levels of the control signals are determined and the M last values obtained therefrom are stored and taken into account when the amplification factor is set. In this way, an increase in amplification of the receiver in periods during which 10. nothing is transmitted, is avoided. The amplification is consequently only increased if the level of these control signals is correspondingly low.

The arrangement shown in Fig. 2 as a block circuit diagram is suitable for carrying out this process, according to 15. which not only the level values obtained in the useful signal time slots are fed to the evaluation circuit, but also the last M level values of the control signals transmitted in the special time slots. For this there is a second shift register with M cells, in which only the 20. level values of the control signals are fed in, controlled via a switch. The shift register cells are connected parallel to the evaluation circuit and their values are processed along with the level values obtained from the useful signals.

Claims 5.

10.

15.

20.

25.

30.

1 Process for the automatic regulation of amplification in a receiver, characterized in that the level of a signal received by the receiver is measured at certain intervals whilst the amplification set in the receiver is taken into account and a value representing the level measured is stored, and the amplification for a particular future period is determined from the N last values stored, where N > 1.

Process in accordance with Claim 1, characterized in that the amplification for a particular future period is determined from the maximum of the N last values stored.

3.

4.

Process in accordance with one of the claims above, characterized by its use in TDMA-system, and furthermore, in that the level is measured in the time slots allocated to the receiver.

Process in accordance with Claim 3, in which in particular time slots allocated to the receiver there is no reception signal when no information has to be transmitted, and in which in other time slots, likewise allocated to the receiver, a signal (control or useful information) is always transmitted, characterized in that the levels of the time slots which always contain a signal are measured whilst taking into account the amplification set in the receiver and a value representing the level measured is stored separately, and the amplification for a particular future time slot is determined from the stored N last level values of all time slots and the stored M last levels of the time slots in which a signal is always transmitted, where M > 1.

1 7- 5.

5.

10.

Process in accordance with Claim 4, characterized in that the amplification is determined from the maximum of the stored N last level values of all time slots allocated to the receiver and the stored M last level values of the time slots in which a signal is always transmitted.

6. Process in accordance with Claim 2 or 5, characterized in that the amplification is determined with the aid of a given curve, representing a correlation between the level measured and the amplification to be set.

Process in accordance with Claim 6, characterized in that the curve is linear.

8. Process in accordance with Claim 6, characterized in that the curve has a linear section which merges into limited, constant values at its upper and lower end.

9. Process in accordance with Claim 3, characterized in that the amplification is not changed within a time slot.

10. Process in accordance with one of the preceding claims, 20. characterized in that the scanning values of the reception signal are digitalized and the level of the reception signal is determined from the digital scanning values.