Method and apparatus for signal processing in DECT transceivers

0001The invention relates to a method and a device for signal processing in transmitting / receiving units in DECT, where DECT stands for Digital Enhanced Cortless Telephone.

0002A transmitting / receiving unit in DECT can be a handset or a base station.

0003The DECT network is a microcellular, digital mobile network for high subscriber densities. A TDMA (Time Division Multiple Access) method is used for 10 carrier frequencies. These are in a frequency band from 1880 to 1900 MHz. A cordless telephone operating according to the DECT standard receives a bit data stream with a bit rate of 1152 kbit / s as an information signal, which is also referred to as a reception bit stream. In addition, the cordless telephone sends data with a bit rate of 1152 kbit / s as well.

0004The coding of voice data between two transmitting / receiving units working according to the DECT standard is described in ITU Recommendation G.726 <img file="EP0903948A2_D0001.tif" />Adaptive Differential Pulse Code Modulation (abbreviated ADPCM) ". Recommendation G.726 describes how to implement a 64 kbit / s pulse code modulated (PCM) channel and a linear 8 kHz pulse code modulation in a 40, 32, 24 or 16 kbit / s channel and vice versa The conversion of the PCM bit stream is done with an ADPCM data conversion technique. The relationship between the voice frequency signals and the PCM coding / decoding rules is described in ITU Recommendation G.711.

0005The mode of operation of the ADPCM encoder and decoder is shown as a block diagram in FIG. 1 of Recommendation G.726 and is described in detail on pages 2 to 13 of Recommendation G.726. The ADPCM mode of operation will therefore not be discussed further below. Details can be found in the G.726 standard.

0006If you want to transmit a modem signal via transceiver units that work according to the DECT standard, the transmission rate has so far been limited to 9600 bit / s.

0007Usually, however, only a transmission rate of 4800 bit / s can be achieved.

0008The term modem is to be understood in the entire context as a combination of modulator and demodulator. A modem should therefore include both the functionality of a fax device according to the ITU guidelines and that of a modem, for example according to the ITU standard V.34. A modem according to the present definition can send and also receive data, at the same time or in succession.

0009An object of the invention is to provide a method and a device with which the higher transmission rates for the transmission of modem signals via transceiver units which operate according to the DECT standard are possible.

0010The object is achieved by a method according to claim 1 and devices according to claims 15 and 16.

0011Thus, the method provides that at least one of the transmitting / receiving units is checked to see whether a modem signal is present and, if a modem signal is present, a switch is made to a modem operating mode.

0012The device according to the invention has a test unit in at least one of the transmitter / receiver units, the test unit checking whether there is a modem signal. Furthermore, a processing unit is provided, which is arranged downstream of the test unit and causes a change in a modem operating mode if a modem signal is present.

0013Another device according to the invention has a combined testing and processing unit, which is provided in at least one of the transmitting / receiving units. The test and processing unit checks whether a modem signal is present and initiates a change to a modem operating mode if a modem signal is present.

0014Advantageous further developments result from the dependent claims.

0015For example, it is advantageous to switch off adaptive differential pulse code modulation (ADPCM) when a modem signal is present. The result of this is that a modem which tests the line quality before the actual data transmission begins is not subject to line quality changes due to ADPCM.

0016In order to further increase the modem data signal rate, a modem waveform coding can be activated.

0017To check whether a modem signal is present, a modem pilot tone signal originating from a modem can be used.

0018There is also the possibility of using the spectrum of the transmit and / or receive signal to check whether a modem signal is present.

0019A signal strength ratio, which is evaluated at different frequencies, can be used to check whether a modem signal is present.

0020Finally, to check whether a modem signal is present, it is also possible to use pauses in the signal.

0021Instead of an automated test, you can also switch manually to the modem operating mode.

0022The transmitter / receiver units can also independently, that is separately from each other, check whether there is a modem signal.

0023Since it is advantageous that both the transmitting / receiving unit which sends the modem data and the transmitting / receiving unit which receives the modem data are informed that a modem signal is to be transmitted, the transmitting / receiving unit which has detected a modem signal can do one Transmit control signal to the further transceiver unit to indicate that a modem signal has been detected.

0024Both transmitter / receiver units can also switch to the modem operating mode by exchanging the modem signal independently without exchanging modem information.

0025In addition, the transmitting / receiving unit, which has detected a modem signal, can transmit an information signal to the further transmitting / receiving unit in order to set the data transmission rate, for example.

0026The control signal and / or the information signal can be transmitted on a communication channel or a transparent channel.

0027The transmitting / receiving unit receiving the modem signal via the air interface can be configured such that it carries out one or more actions dependent on the content of the control signal after receiving the control signal or through an independent detection of the modem signal.

0028To improve the transmission, the echo suppression can be switched off in the transmitting / receiving unit, which receives the modem signal via the air interface, when a modem signal has been detected.

0029The transmitting / receiving unit or transmitting / receiving units can be provided with a modem signal coding / decoding unit which is connected to the processing unit and is active in the modem operating mode.

0030The invention is further explained on the basis of three figures.<dl id="dl0001"><dt>Figure 1</dt><dd>shows in the form of a block diagram the inventive method for signal processing.</dd><dt>Figure 2</dt><dd>shows a modem operating mode, as it can occur in the handset or in the base station.</dd><dt>Figure 3</dt><dd>shows a modem operating mode, as it can occur in the base station.</dd></dl>

0031The invention checks whether there is a modem signal, see FIG. 1, and if this is not the case, the procedure can continue as usual. If the question "modem signal available" is answered with yes, the system switches over to a modem operating mode. At the end of the modem signal transmission process, the system switches back to the original operating mode.

0032In the modem operating mode according to FIG. 2, which occurs in the transceiver unit which transmits and / or receives the modem signal via the air interface, the adaptive differential pulse code modulation ADPCM is switched off and, if appropriate, a modem signal form coding which is optimized for the modem signal to be transmitted is switched on. The transmitter / receiver unit at DECT can be a base station, a repeater or a handset.

0033In the modem operating mode according to FIG. 3, the transceiver station is usually the base station which receives and / or transmits the modem signal via the air interface. Here the adaptive differential pulse code modulation is switched off, if necessary a modem signal form coding is switched on and additionally the echo compensation is switched off. It does not matter whether the echo cancellation is switched off last, first or at the same time as the ADPCM is switched off.

0034The modem waveform coding is to be optimized with regard to the modem signal to be transmitted and the transceiver units which operate according to the DECT standard.

0035Usually, a modem sends out a modem pilot tone signal before the actual data transmission begins, on the basis of which a subordinate unit can determine that the modem signal data transmission will soon begin. This modem pilot tone signal can be used for the invention to check whether there is a modem signal at all or whether it is a different type of signal, for example a voice signal.

0036The spectrum of the transmit and / or receive signal can be used to check whether a modem signal is present. If there is an approximately rectangular signal spectrum, a modem signal can be inferred from this. Otherwise it is assumed that there is no modem signal.

0037It is also possible to infer the signal origin from the ratio of the amplitudes of the signal at different frequencies. For example, if the amplitude of the signal under test at a low frequency differs significantly from the amplitude at a higher frequency, it will be a voice signal rather than a modem signal.

0038When checking whether a modem signal is present, signal pauses can also be used.

0039The easiest and cheapest way to switch to the modem operating mode is to initiate the change manually. This can be achieved, for example, by pressing a button or switch on the respective transceiver, by connecting the modem cable to the respective transceiver, or by pressing a certain key combination on the respective transceiver.

0040Furthermore, it is also conceivable that a transmitter / receiver unit is already integrated in the modem, which works according to the DECT standard. If this is the case, then only the transmitter / receiver unit corresponding to this transmitter / receiver unit, usually the base station, has to be informed whether a modem signal is to be transmitted. This can happen, for example, in that the transmitter / receiver unit integrated in the modern transmits a control signal to the further transmitter / receiver unit, which indicates that a modem signal is to be transmitted. In addition, of course, all other methods for modem signal detection already described above can also be used.

0041The control signal and possibly the information signal can be transmitted via a communication channel or a transparent channel.

0042The information signal can contain information about the data transmission rate to be set.