TEMPERATURE CONTROLLED RADIO TRANSMITTER IN A TDMA SYSTEM

Abstract: A radio transmitter such as a mobile telephone is operating in a TDMA system. The number of slots which can be allocated for transmissions from said device is adjusted based on the ambient temperature, the amount of data to be transmitted, the channel quality, and the transmit power, such that the temperature of the device does not exceed a predetermined value.

Description: TEMPERATURE CONTROLLED RADIO TRANSMITTER IN A TDMA SYSTEM TECHNICAL FIELD OF THE INVENTION This invention relates to a radio transmitter, in particular for use in a TDMA system in which the number of time slots used for transmissions is variable. More specifically, the invention relates to handheld devices, in which heat dissipation is a major concern, and to a way of avoiding excessive heating. BACKGROUND OF THE INVENTION Many radio telecommunications systems exist, in which different users are enabled to use a single radio channel by means of TDMA (time division multiple access) . In a TDMA system, time is divided into frames, and each frame is divided into slots. One user is then able to use the same slot in each frame, for as long as is required. For example, in the GSM (Global System for Mobile Communications) system, there are eight slots in each frame. A requirement of an attractive device, such as a mobile phone or other radio communications terminal, for use in a mobile communications system, is that it should be small. Such systems can be used for voice and/or data transmissions. In the case of data transmissions, it may be advantageous for a mobile device to be able to transmit data at a higher rate than would be achievable by transmitting in just one slot per frame. Systems such as GPRS (General Packet Radio Service) , which is based on GSM, have therefore been proposed in which a mobile device can transmit data in more than one slot per frame. SUMMARY OF THE INVENTION Although in general it is advantageous to transmit data at the highest rate permitted by the radio interface, operation of a radio transmitter generates heat within the terminal. Particularly in the case of a small handheld device, the heat which is generated may be more than the device can dissipate, resulting in an increase in the temperature of the device. The present invention therefore concerns the control of radio transmissions in a way which seeks to avoid excessive heating of the transmitter. In particular aspects of the invention, the transmitter is controlled such that a maximum temperature is not exceeded. More specifically, in preferred embodiments, a number of timeslots, in which the device is to transmit, is controlled on the basis of some or all of: a total quantity of data to be transmitted; an expected transmit power level; a channel quality; and an ambient temperature, such that a maximum temperature is not exceeded. BRIEF DESCRIPTION OF DRAWINGS Figure 1 shows a mobile communications device in accordance with the invention. Figure 2 is a block schematic diagram of the device of Figure 1. Figure 3 is a graph of a temperature of a device, plotted against operating time. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a mobile phone 2, although it will be appreciated that the invention is applicable to any radio communications terminal, in particular to such terminals which primarily or exclusively transmit data rather than voice signals. The invention is of particular application where packet data are being transmitted. As is well known, the phone 2 is advantageously small and lightweight to increase its ease of use. However, a result of this is that its heat dissipation capacity is rather low. Figure 2 is a block diagram of the internal structure of the phone of Figure 1. Only parts of the phone relevant to an understanding of the present invention are shown. Otherwise the phone is conventional . The phone 2 has a data connection 4, for receiving packet data from an external device (not shown) . For example, data may be received by a wired link or by an infrared or other wireless connection. Received data are stored in a buffer 6, before conversion into a form suitable for transmission over the radio interface via transceiver circuits 8 and an antenna 10. The phone is under the general control of a processor 12, which in particular can control the number of time slots in each frame, within the TDMA system, in which the device can transmit data. Since the number of time slots allocated to a particular device is ultimately controlled by the network, a decision concerning the number of time slots in which the device should transmit data is implemented by sending an appropriate message from the device to the network. As is conventional, the processor receives control signals from the network with which it is in communication, regarding the power level at which the phone should transmit signals. For example, in general terms, in the case of a cellular mobile phone, the phone should transmit at low power when it is close to a base station, and at a higher power when it is further from a base station. Further, the phone makes channel quality measurements on a channel which has been allocated to it. The quality measurement may be signal-to-noise ratio, or bit error rate, or any convenient measure. The phone also includes two temperature sensors 14, 16, of which a first 14 may for example be located on the outer surface of the phone, and a second 16 may for example be located on an inner surface of the housing of the phone, close to the largest heat source, which will usually be the power amplifier. Thus a measured temperature value from the temperature sensor 14, indicates the ambient temperature, and a measured temperature value from the temperature sensor 16, indicates the internal temperature of the phone. Both measured temperature values are supplied to the processor 12. Figure 3 shows, schematically, the temperature of the phone, as measured by the second temperature sensor 16, during data transmission. As will be appreciated, operation of the transmit circuits of the phone, including components such as power amplifiers, generates heat within the phone. Some heat can be dissipated to the atmosphere, but some simply heats the phone, and so the temperature increases. The rate at which heat will be generated will depend on the time for which the transmit circuits are operative. Thus, if data are transmitted in more time slots of each frame, heat will be generated at a higher rate. The rate at which heat will be generated will also depend on the output power of the phone during transmission. The total amount of heat generated will depend on the total time for which the transmit circuits are operative. The rate at which heat can be dissipated will depend on the ambient temperature . In cooler conditions, heat can be lost at a greater rate than in hot conditions. Therefore, in order to ensure that a maximum temperature of the phone, as measured by the temperature sensor 16, is not exceeded, the number of time slots in each frame, used by the phone for data transmissions, is controlled. If the total amount of data stored in the buffer and awaiting transmission is sufficiently small, it may be acceptable for the number of slots to be the largest number which is available from the network. Even if heat is generated at a high rate, it will not lead to excessive heating of the phone if the duration of the transmission is short. On the other hand, if the amount of data stored in the buffer and awaiting transmission is large, excessive heating of the phone may occur if the data is transmitted at a high rate over a short period of time . In that case, it would be preferable to transmit the data at a lower rate over a longer time period. In general, the invention relates to a system in which the terminal determines a data transmission rate, for example expressed in terms of the number of slots per frame in which transmission takes place, which ensures that a predetermined maximum temperature of the phone is not exceeded. Thus, as shown in Figure 3, the temperature of the phone increases throughout the transmission, and reaches the predetermined maximum temperature only as the transmission ends. The data transmission rate can be determined on the basis of the parameters mentioned previously. For example, the terminal may have a preset maximum data rate, or w classmark" , which may be determined by such factors as the processing power of the phone, the available memory, the hardware architecture and the software used, as well as its heat dissipation properties. The actual rate set for any specific data transmission may then be reduced by an appropriate amount below this maximum rate if a large amount of data is to be transmitted, or if poor channel quality means that data may have to be retransmitted many times, or if the transmit power is expected to be above a certain level, or if the ambient temperature is above a certain level, or if more than one of these factors apply. There is thus described a terminal, and a method of operation thereof, which maximises a data transmission rate, without increasing the temperature of the terminal above a maximum level.

Claims: CLAIMS 1. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring an ambient temperature; and controlling a number of slots allocated for transmissions from said transmitter in response to the measured ambient temperature, such that a predetermined maximum temperature of the radio transmitter is not exceeded. 2. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring an ambient temperature; and controlling a number of slots allocated for transmissions from said transmitter in response to the monitored ambient temperature . 3. A radiocommunications device comprising a radio transmitter operable in a radiocommunication system defining a plurality of time slots, the device comprising: a temperature sensor for monitoring an ambient temperature; and a controller for controlling a number of slots allocated for transmissions from said transmitter in response to the monitored ambient temperature, such that a predetermined maximum temperature of the radio transmitter is not exceeded. 4. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring a total amount of data to be transmitted; and controlling a number of slots allocated for transmissions from said transmitter in response to the total amount of data to be transmitted, such that a predetermined maximum temperature of the radio transmitter is not exceeded. 5. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring a total amount of data to be transmitted; and controlling a number of slots allocated for transmissions from said transmitter in response to the total amount of data. 6. A radiocommunications device comprising a radio transmitter operable in a radiocommunication system defining a plurality of time slots, the device comprising: means for monitoring a total amount of data to be transmitted; and a controller for controlling a number of slots allocated for transmissions from said transmitter in response to the monitored amount of data, such that a predetermined maximum temperature of the radio transmitter is not exceeded. 7. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring an expected transmission output power; and controlling a number of slots allocated for transmissions from said transmitter in response to the expected transmission output power, such that a predetermined maximum temperature of the radio transmitter is not exceeded. 8. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring an expected transmission output power; and controlling a number of slots allocated for transmissions from said transmitter in response to the expected power. 9. A radiocommunications device comprising a radio transmitter operable in a radiocommunication system defining a plurality of time slots, the device comprising: means for monitoring an expected transmission output power; and a controller for controlling a number of slots allocated for transmissions from said transmitter in response to the expected power, such that a predetermined maximum temperature of the radio transmitter is not exceeded. 10. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring a transmission channel quality; and controlling a number of slots allocated for transmissions from said transmitter in response to the transmission channel quality, such that a predetermined maximum temperature of the radio transmitter is not exceeded. 11. A method of operating a radio transmitter operating in a radiocommunication system defining a plurality of time slots, the method comprising: monitoring a transmission channel quality; and controlling a number of slots allocated for transmissions from said transmitter in response to the monitored transmission channel quality. 12. A radiocommunications device comprising a radio transmitter operable in a radiocommunication system defining a plurality of time slots, the device comprising: means for monitoring a transmission channel quality; and a controller for controlling a number of slots allocated for transmissions from said transmitter in response to the monitored transmission channel quality, such that a predetermined maximum temperature of the radio transmitter is not exceeded.

Inventors: KHULLAR ANDERS, KHULLAR, ANDERS
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 2000
Main classification: H04Q7
IPC codes: H04B1, H04B7