GB2333420A

GB2333420A - Remote headset for a mobile phone

Info

Publication number: GB2333420A
Application number: GB9800748A
Authority: GB
Inventors: Peter Lussenhop
Original assignee: Nokia Mobile Phones Ltd
Current assignee: Nokia Oyj
Priority date: 1998-01-14
Filing date: 1998-01-14
Publication date: 1999-07-21
Also published as: GB9800748D0

Abstract

A remote headset 3 is connected via a short range radio link through transceiver 2 to the mobile phone 1. When the radio transceiver is connected to the mobile phone switches SW2 and SW3 are automatically switched from the internal loudspeaker and microphone 109, 110 to the external lines which are connected to the short range transceiver. The short range transceiver can be attached to, or part of, the battery pack. The short range transceiver detects when the mobile phone is transmitting signal bursts to the base station 100 and times the signal bursts to the headset to avoid concurrent signal bursts. The transceivers may be of the TDMA type.

Description

Device for controlling transceivers Background of the invention The present invention is generally related to radio transceivers and more particularly related to a device for the synchronisation and controlling of radio transceivers.

During the past years communication devices equipped with radio transceivers like mobile radio telephones are more and more commonly used. The usage of this communication devices has shown that it is desirable to divide this kind of communication devices into several parts. This is for example described in the patent application No. EP 976 601 05.4.

This patent application describes a concept to divide a radio telephone into a first part and a second part, wherein the first part comprises at least a power supply, a radio part (transceiver) to communicate within a radio telephone system, eg. with a base station or another radio telephone, an antenna and data transfer means to communicate with a second part. The second part comprises at least means for answering a call and data transfer means for communication with the first part. It is also possible as described within the mentioned document to divide the radio phone into more than two segments, for example to have a headset with a supplementary earpiece and a microphone which can be used conveniently by the user. The communication between the first part and the headset as the second part is also wireless based on radio transceivers within the first and the second part.

As described, the first part comprises a transceiver for communication with a radio telephone system or a base station and also comprises data transfer means for communication with the second part. This data transfer device is preferably also a radio transceiver, which communicates with the second part via another radio transceiver with which the second device is equipped.

One problem which occurs if several radio transceivers communicate with each other is, that the radio transceiver may transmit at the same time as any of the others, and even worse, two radio transceivers transmit with the same frequency and at the same time.

In commonly used Time Division Multiple Access (TDMA) systems the communication devices of one system use different transmission/reception frequencies and/or different time slots, i.e. each communication device has its own individual traffic channel. The transceivers for data transfer between the first and the second part can be designed in a way that they do not use the frequencies which are used for the communication between the first part and a base station.

But also if transceivers are located near to each other problems can occur if they transmit at the same time with different frequencies. If for example the first transceiver for communication with a base station transmits at a frequency of 900 MHz, which is eg. used for cellular radio communication systems like the GSM system and the transceivers for communication between the first and the second part of the radio telephone transmit with frequencies around 2.4 GHz, which can be used for short range radio communication between this kind of devices, undesirable disturbing frequencies are generated at M* 2.4 GHz + M*0.9 KHz.

The transmission and reception times of the transceiver which communicate with the base station are usually predetermined by the mobile radio telephone system which co-ordinates the communication between several mobile radio telephones and the basestation.

Summary of the invention According to the present invention there is provided a device for controlling transceivers of a radio communication apparatus operable in a radio system in which information is transmitted in signal bursts, the radio communication apparatus comprising a first transceiver for transmitting the signal bursts in the radio system and a second transceiver, wherein the device comprises means operable to detect propagated signal bursts from the first transceiver and control the timing of signal bursts from the second transceiver in accordance with the timing of the detected signal bursts to avoid concurrent transmissions of signal bursts from the first and second transceivers.

The device adjusts the transmission time of signal bursts of the second transceiver in a way that concurrent transmissions, ie transmission by both transceivers at the same time, are avoided.

This device can be advantageously equipped with a microwave detector which detects the radio frequency signal transmitted by the first transceiver. The detector can be constructed in a common way with an antenna and a bandpass filter followed by a diode for rectification of the radio frequency signal which passed through the band pass filter. The output of the microwave detector can be a high level signal if a radio frequency signal with the frequency of the first transceiver is detected and a low level signal, if no radio frequency signal is detected.

It would also be possible to design the receiver of the second transceiver in a way that the receiver delivers a signal to the control unit when a signal transmitted by the first transceiver is detected especially if the operating frequency of the first transceiver is near to the operating frequency of the second transceiver.

Furthermore more than one second transceiver might be attached to the first transceiver for communication eg with a headset and an extemal input device or something else.

The disclosed invention can be advantageously used for TDMA systems where signal bursts are transmitted and received in time slots during frames. If the transceivers work in a manner according to the TDMA system the frame timing of the second transceiver can be adapted to the frame timing of the first transmitter and the transmission times of the second transceiver are arranged in a way that the transmission times of both transceivers do not clash.

The control unit or the processor which receives the signals from the microwave detector can have prestored values which identify the frame length of the system the first transceiver is working with and can base the timing of the second transceiver on this value after the first signal burst from the first transceiver is detected.

Usually, for example in the GSM system, the frame lengths are fixed and the control unit needs only to know the start point of one burst in the uplink, the transmission from the first transceiver to the base station, and then the control unit can calculate the next transmission time of the first transceiver and co-ordinates the transmission time of the second transceiver.

The device can also detect the frame length/timing of the first transceiver and adapts the frame length of the second transceiver. The frame length of the second transceiver then correlates with the frame length of the first transceiver. This is necessary if the control unit does not have information about the frame length of the first transceiver. The device only needs to measure the time difference between two detected bursts of the first transceiver. Usually this time also defines the frame length of a TDMA system if the first transceiver has not changed the time slot from one frame to another which may eg. occur if the first transceiver has received a message to switch to another channel.

In a further advantageous embodiment of the invention the second transceiver forwards the frame length to a linked transceiver which then also adapts the frame length of the first transceiver to avoid collisions of the transmission of the linked transceiver with the transmission of the first transceiver.

There may also be more than one transceiver linked to the second transceiver. The second transceiver can then act as a master unit which controls the activities of several linked transceivers acting as slave transceiver.

The first transceiver can be linked to a base station which belongs to a cellular mobile telephone system. The cellular mobile telephone system predetermines the frame length and the channels the first transceiver has to use for communication within the radio telephone system, i.e. the time slots during the frames the first transceiver has to use and the frequencies are given and can only be changed on a request to the mobile radio telephone system.

Brief description of the drawings The present invention will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 is a block diagram comprising the inventive device and a system with several transceivers where this device can be used for Fig. 2 is a circuit of a microwave detector used by the invention Fig. 3 is a timing diagram showing the timings of the transceivers of Fig. 1 based on the output signal of the microwave detector of Fig.2 Detailed description of the invention Fig.1 depicts a schematic block diagram of a mobile radio telephone 1. Through antenna 101 the mobile telephone 1 communicates with a base station 100 which belongs to a mobile radio telephone system. To enable the communication with the base station 100 the mobile radio telephone 1 further comprises a radio frequency receiver Rxc 102 and a radio frequency transmitter Tx, 103. A switch SW 1, which is controlled by a control unit 106, switches antenna 101 between receiver 102 and transmitter 103. All control lines in Fig.1 are dashed.

The telephone further comprises a demodulator 104 for demodulation of the received radio frequency signal to obtain eg. a speech signal which is sent to a loudspeaker 109. For the other direction the mobile telephone comprises a microphone 110. The analogue signal of microphone 110 is sent to the modulator 105 which converts the speech signal to a digital signal and modulates the signal which is then sent by the transmitter 103 through antenna 101 to the base station 100.

The mobile radio telephone 1 further comprises a keypad to enter eg a telephone number. The mobile telephone may also contain a display 107 to show other types of information for the user. The whole system is controlled by the microcontroller 106.

The mobile radio telephone 1 is connected to a short range radio communication system based on the devices 2 and 3. Device 3 is a wireless headset comprising a loudspeaker 305 and a microphone 306. The wireless headset further comprises a radio frequency receiver Rx2 303 and a radio frequency transmitter Tx2 304. A control unit 302 controls the transmitter 303 and the receiver 304 and switches antenna 301 between the transmitter 303 and the receiver 304 with the switch SW 5.

The wireless headset 3 is connected by way of radio communication through the short range radio transceiver 2 with the antenna 206, the receiver Rx1 204 and the transmitter Tx1 205 with the mobile radio telephone 1.

The short range radio transceiver 2 is coupled to the mobile radio telephone 1 by the electrical connectors 111. In addition a mechanical connection can be used. When the short range radio transceiver 2 is coupled to the mobile radio telephone 1 the switches SW 2 and SW 3 are automatically switched from the intemal loudspeaker 109 and 110 to the external lines which connect the short range radio transceiver to the mobile radio telephone 1. This can be done eg by a mechanical solution which turns the switches SW 2 and SW 3 when the short range radio transceiver is coupled to the mobile radio telephone 1 or the connectors 111 generate an electrical signal which is sent to the control unit 106. The control unit 106 then switches the switches SW 1 and SW 2 to the external lines.

The short range radio transceiver 2 can for example be attached to the battery pack of the radio telephone or be part of the battery pack.

The short range radio transceiver 2 also comprises a control unit 203 which controls the transceiver Rx, 204, the transmitter Rx1 205 and the switch SW 4.

The control unit 203 receives the signal Ud from microwave detector 202 which is coupled to antenna 201. The antenna 201 receives radio frequency signals transmitted by antenna 101. When the microwave detector 202 detects a radio frequency signal from the mobile radio telephone 1 the detector generates a high level signal and if no signal is received a low level signal is generated.

The microwave detector 202 is shown in Fig. 2. On the left side the input line from antenna 201 is shown. The main elements of the microwave detector 202 are a band pass filter 207, comprising inductors L1 and L2, capacitors C1 and C2 and resistor R1, a detector diode D1 209 in parallel with capacitor C 3 and an amplification unit 208 comprising the integrated operational amplifier 21 wired with the resistors R2, R3, R4.

The components of the bandpass filter 207 are designed so that only radio signals can pass through which are sent out by the mobile radio telephone 1. For the GSM system this means, for example, that the bandpass is designed in a way that only frequencies around 900 MHz pass this network.

The diode D1 209 in parallel with capacitor C3 rectify and smooth the received radio frequency signal. The following block 208, comprising the operational amplifier 210 with the wiring R2, R3 and R4 which defines the amplification of the amplifier 210 delivers the signal Ud at the output. The signal Ud is a low level signal when no radio frequency signal is detected and a high level signal when a radio frequency signal is detected. The amplification unit 208 may also be followed by a threshold circuit which delivers defined high and low level signals at its output.

In Fig. 3 an example of a timing diagram of the transmitting and receiving activities of the devices 1,2 and 3 is shown, based on the receive times Rxc of receiver 102 and the transmission times Tx, of transmitter 103. Furthermore the output signal Ud of the microwave detector is shown.

In the next lines the receive time of the receiver Rx1 204 which receives radio frequency signals from the transmitter Tx2 304 and the transmission times Tax1, these signals are received by the receiver 303 Rx2.

The numbers within the diagram define numbers of the time slots of the frames of the communication system for the communication between the mobile radio telephone 1 and the base station 100. In this example the time slots 0 to 3 are used for the downlink, this means that the basestation 100 transmits signals to the mobile radio telephone 101 during these time slots. On the other hand the mobile radio telephone 1 can use the time slots 4 to 7 for the uplink, this means the mobile radio telephone transmits signals to the base station during these time slots.

The shaded boxes identify bursts with data signals which are transmitted or received by the receivers Rx or Tx.

The communication between the mobile radio telephone 1 and the base station 100 takes place within the time slots 0 for the downlink and 5 for the uplink in the beginning. These slots are predefined by the cellular radio communication system.

The other time slots can be used for the communication of the base station with other mobile radio telephones. On request of the mobile radio telephone 1 or for other reasons the cellular radio telephone system can change the time slots for the uplink and downlink.

The line Ud shows the timing of the output signal of the microwave detector. As shown at time Ti in the diagram the microwave detector generates a high level signal when a signal from the transmitter 103 (Txc) is received.

It has to be understood that the basestation 100 also transmits radio frequency signals within the frequency band which could be detected by the microwave detector 202, but the amplitude of this signal is too low to generate a high level signal at the output.

In this example the frame length and the timing of the short range radio communication system with the devices 2 and 3 is already synchronised with the frame timing of the mobile radio telephone system . Before the short range radio communication system started the transmission activities, detector 202 and control unit 203 can have observed the timing of the signal bursts transmitted from transmitter 103 and the timing was adapted in a way to avoid concurrent transmissions of signal bursts.

This means that transmitter Tx 205 transmits bursts to the receiver RX2 within time slot 4 and the receiver Rx1 204 receives bursts from the transmitter TX2 304 within time slot 3. Even though it is the case in this example it has to be mentioned that it is not necessary that the short range radio communication system has to use the same time slots for the uplink and the downlink as the mobile radio telephone system. It is only necessary to avoid that the short range radio communication system, and here particularly the transmitter 205 transmits signals at the same time as the transmitter 103.

Below the timing for Ud also the frame length of the mobile radio telephone system is shown. Provided that the mobile radio telephone system has not changed the used time slots, the frame length can be defined by the time between two rising edges of the pulses Ud.

Based on the measured frame length and the starting point of the frame the control unit 203 adapts this frame timing and enables the transmission when no transmission of transmitter 103 is expected.

The control unit 302 can also be informed of the actual frame timing. This is done by a message from the control unit 203 which is sent via transmitter 205 and receiver 303 to the control unit 302. Besides the frame length and start time also information concerning the time during this frame, when no signal should be sent, can be transferred to the control unit 302. The control unit 302 then also adapts the frame timing and enables the transmission of bursts in the time slots of a frame where collisions with transmissions from transmitter 103 are avoided.

At time T2 in the diagram of figure 3 the mobile radio telephone system has changed the time slot for transmissions from the mobile radio telephone 1 to the base station from time slot 5 to time slot 4. This means that the detector 202 detects a radio frequency signal at the same time when transmitter 205 starts to send out a burst.

The control unit 203 avoids this parallel transmission with a control signal to the transmitter 205 storing transmission in time slot 4 and waiting until the next time slot (5). The receiver 303 expected to receive a signal within time slot 4 and now sends a signal that no burst was received to the control unit 302 which puts receiver 303 to a scan mode as it is shown between T2 and T3. If this scan mode is working fast enough it can be possible to find the next burst from transmitter 205 instantly. In the example shown the receiver 303 scans the time slots for about the length of one frame until the next burst in time slot 5 is received.

The control unit 203 arranges to send the same information within the transmitted bursts until a message from the control unit 302 is received that the burst was received properly. The control units 203 and 302 now adopt the new frame timing.

The present invention may include any novel feature or combination of features disclosed herein either explicitly or implicitly or any generalisation thereof irrespective of whether or not it relates to the presently claimed invention or mitigates any or all of the problems addressed. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of invention.

Claims

Claims: 1. A device for controlling transceivers of a radio communication apparatus operable in a radio system in which information is transmitted in signal bursts, the radio communication apparatus comprising a first transceiver for transmitting the signal bursts in the radio system and a second transceiver, wherein the device comprises means operable to detect propagated signal bursts from the first transceiver and control the timing of signal bursts from the second transceiver in accordance with the timing of the detected signal bursts to avoid concurrent transmissions of signal bursts from the first and second transceivers.
2. A device according to claim 1 characterised in that signal bursts propagated from the first transceiver are detected by means of a microwave detector.
3. A device according to any of the preceding claims characterised in that said transceivers are Time Divisison Multiple Access (TDMA) - transceivers.
4. A device according to claim 4 characterised in that the device determines the timing of the transmitted signal bursts of the first transceiver and adjusts the timing of signal bursts transmitted by the second transceiver that it correlates with the first transceiver.
5. A device according to claim 4 characterised in that the second transceiver forwards the determined timing to any other transceiver.
6. A device according to any of the preceding claims characterised in that the timing of the signal bursts of the first transceiver is determined before the second transceiver starts the transmission of signal bursts.
7. A device according to any of the preceding claims characterised in that the timing of signal bursts of the second and the linked transceiver is changed when a change of the timing of the signal burst of the first transceiver is detected and a transmission of signal bursts or parts of signal bursts at the same time needs to be prevented.
8. A device according to any of the preceding claims characterised in that the first transceiver is linked to a base station which belongs to a mobile radio telephone system.
9. A device according to any of the preceding claims characterised in that the timing of transmission of the signal bursts from said first transmitter is predetermined.
10. A device according to claim 8 characterised in that the timing is predetermined by a mobile radio telephone system.
11. A radio communications apparatus operable in a system in which information is transmitted in signal bursts comprising a first transceiver for transmitting signal bursts in the system and a second transceiver, the timing of burst from the first and second transceivers being controlled by respective processors characterised in that the control unit of the second transceiver comprises means to detect propagated signal bursts from the first transmitter and the control unit of said second transceiver adjusts the timing of the signal bursts to be transmitted in accordance with the timing of the detected signal bursts to avoid concurrent transmissions of signal bursts.
12. Device according to claim 12 characterised in that the timing of signal bursts of said first transceiver is detected by means of a microwave detector.