HK1060465B

HK1060465B - A measurement technology for a radio access telecommunications terminal

Info

Publication number: HK1060465B
Application number: HK04103228.4A
Authority: HK
Inventors: Falaki Hamid
Original assignee: 日本电气株式会社
Priority date: 2002-06-06
Filing date: 2004-05-07
Publication date: 2006-09-29

Description

Measurement technique for radio access telecommunications terminal

Technical Field

The present invention relates to frequency division duplex radio access telecommunications terminals and in particular to measurement of received signal strength of a frequency channel in a transmission gap.

Background

In the Universal Mobile Telecommunications Standard (UMTS) air interface, base stations communicate continuously with User Equipment (UE). Thus, unlike the global system for mobile communications (GSM) standard, there are no discrete time slots for the UE to measure the strength of other frequency channels. However, the UMTS standard defines a period in this continuous transmission in which the transmitter and receiver within the UE are "powered down". These gaps are defined as compressed mode and therefore the UE has an opportunity to measure received signal strength on other frequency channels. If the received signal strength on a different channel is strong, the UE changes the channel as commanded by the Radio Resource Management (RRM) of the network controlling the radio link. This improves the quality of service for the UE. Furthermore, this allows the UE to roam between broadcast cells.

During compressed mode, transmission of signals from the UE can be suspended in order to reduce interference on the measured received channel.

In dual mode UEs, the UMTS standard and the GSM standard are supported. This means that measurements of the UMTS standard and the GSM standard of the received signal can be performed in compressed mode.

Thus, in compressed mode, the GSM measurement receiver is switched on to start measuring other frequency channels. However, this means that if the UE switches on the GSM measurement receiver too early, i.e. before the UMTS transmitter is "powered down", the GSM receiver will cause internal interference on the transmitted UMTS signal and therefore may require repeated data transmission. This therefore increases power consumption.

Furthermore, if measurements by the GSM measurement receiver are performed at the beginning of compressed mode gaps, interference will occur on the GSM measured signals if the UMTS transmitter is not completely powered down, and therefore repeated measurements of GSM signals may be required. This again increases power consumption in the UE.

It is therefore an object of the present invention to address these problems.

Disclosure of Invention

The present invention reduces the power consumed in a dual mode User Equipment (UE) terminal by reducing the amount of interference on a measured downlink signal. By reducing interference, the number of re-measurements of the downlink channel and data retransmissions is reduced, and thus the amount of power consumed by the UE is also reduced, thus improving battery life.

To reduce interference, the present invention determines when to begin measuring the signal strength of the downlink channel of the second signal type during a reduced power level of the transmitter.

In particular, according to a first aspect of the present invention there is provided a frequency division duplex radio access telecommunications terminal for transmitting a first signal type having a peak power level and a periodically reduced power level, and for receiving a second signal type different from said first signal type, said terminal comprising a transmitter for transmitting a transmission signal of the first type at a first frequency, the transmitter being arranged to switch between a peak power mode in which the transmission signal is transmitted at the peak power level and a reduced power mode; a receiver for receiving a second type of received signal at a second frequency different from the first frequency of the transmitted signal; a detector for measuring a signal strength of the received signal; and a controller in communication with the receiver, the transmitter and the detector, the controller being arranged to cause the detector to measure the signal strength of the received signal when the transmitter is operating in the reduced power mode and a predetermined time before the transmitter switches into said power mode.

According to a second aspect of the present invention there is provided a method of measuring the strength of a received radio signal in a mobile telecommunications signal, the method comprising the steps of: transmitting a transmission signal of a first signal type at a first frequency, the first signal type having a peak power level and a periodic reduced power level; switching a transmit signal between a peak power mode at a peak power level and a reduced power mode; receiving a second type of received signal different from the first signal type at a second frequency different from the first frequency of the transmitted signal; and measuring the signal strength of the received signal while the transmitted signal is in the reduced power mode and a predetermined time before the transmitted signal is switched to the peak power level.

Furthermore, the amount of interference on the second type of downlink signal being measured is further reduced by ordering the order in which the downlink signals are measured, with the largest interfering signals being ordered such that these measurements occur at a point in the reduced power mode of the UE transmitter that is furthest from the peak power level of the UE transmitter.

According to another aspect of the present invention there is provided a frequency division duplex radio access telecommunications terminal for transmitting a first signal type having a peak power level and a periodic reduced power level, and for receiving a second signal type different from the first signal type, the terminal comprising a transmitter for transmitting a transmission signal of the first type at a first frequency, the transmitter being arranged to switch between a peak power mode in which the transmission signal is transmitted at the peak power level and a reduced power mode; a receiver for receiving a plurality of received signals of a second type, each at one of a further plurality of frequencies different from the first frequency at which the signal was transmitted; a detector for measuring the signal strength of the received signal; and a controller in communication with the receiver, the transmitter and the detector, the controller being arranged to determine the order in which the detector measures each received signal in dependence on the degree of interference in each case between the transmitted signal and the plurality of received signals whose strengths are to be measured.

According to a fourth aspect, there is provided a method for ranking strength measurements of received radio signals in a mobile telecommunications terminal, the method comprising the steps of: transmitting a transmit signal of a first signal type at a first frequency, the first signal type having a peak power level and a periodically reduced power level; switching the transmit signal between a peak power mode and a reduced power mode at the peak power level; receiving a plurality of received signals, each received signal being at one of a further plurality of frequencies different from the first signal type, at a second frequency different from the frequency of the transmitted signal; and the order in which each received signal is measured is determined according to the degree of interference in each case between the transmitted signal and the plurality of received signals whose strengths are to be measured.

Drawings

A specific embodiment is described by way of example only and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing four broadcast cells in which User Equipment (UE) communicates with respective base stations;

FIGS. 2A and 2B illustrate exemplary Universal Mobile Telecommunications Standard (UMTS) periodic signal patterns transmitted on uplink and downlink channels, respectively;

FIG. 3 shows a more detailed timing diagram of a compressed mode transmission frame illustrating one aspect of the present invention;

fig. 4 shows a block diagram of a receiver part of a radio access telecommunications terminal of the present invention adapted to implement measurements according to the timing diagram of fig. 3;

FIG. 5 shows a flow chart for determining a preferred order in which Global System for Mobile communications (GSM) frequency channels are scanned, implementing a second aspect of the present invention; and

fig. 6 shows a processor for implementing the embodiments of fig. 3, 4 and 5.

Detailed Description

Fig. 1 shows a perspective view of four communication cells 105. Each of the communication cells 105 is generated by a first, second, third and fourth base station 110, 115, 120, 125, respectively. The cell 105 defines an area in which User Equipment (UE) can communicate with an appropriate one of the base stations 110, 115, 120, 125. In fig. 1, UE130 communicates with a fourth base station 125. It is clear that although only one single UE130 is shown communicating 140 with the fourth base station, it should be understood that in practice the fourth base station may communicate with several UEs 130. UE130 generates an "uplink" signal 140 that is transmitted to fourth base station 125 and received by fourth base station 125. The fourth base station 125 communicates with the UE130 by generating a "downlink" signal 135 that is received and processed by the UE 130. It should be noted that in this embodiment, the mobile station is capable of generating uplink signals in accordance with one of two telecommunications standards. Preferably, one standard is the global system for mobile communications (GSM) and the other standard is the Universal Mobile Telecommunications Standard (UMTS). It should be understood, however, that the present invention is not limited to GSM and UMTS standards, and that other standards, such as CDMA-2000, EGSM, etc., may be used.

Further, it should be understood that the frequencies of the uplink and downlink signals operate on different frequencies.

As is well known, the UE130 may roam between different communication cells and is therefore able to communicate with the first, second or third base station 110, 115, 120. As the UE130 moves around the current cell or enters another cell 105, downlink signals 135, 145 generated by the first, second, third or fourth base stations 110, 115, 120, 125 are received by the UE 130. Since these downlink signals are transmitted on different frequency channels, the UE130 must scan the other frequency channels in order to determine which channel is best suited for continuing communication with the base station. The UE determines this in particular from the strength of the received signal. This means that the UE130 must scan for other downlink signals on a different frequency than it is currently receiving. This scanning process is known in the art. In this case, however, this frequency sweep occurs in the compressed mode of the UMTS standard.

Figure 2 shows a typical UMTS periodic signal pattern associated with an uplink 205 and a downlink channel 210. As described above, the uplink 205 and downlink channels 210 are transmitted on different frequencies. Each period in the UMTS signal pattern consists of a length of time 225 in which peak power transmission occurs and a length of time 220 in which the transmitted power of the uplink and downlink signals is at a minimum. This minimum transmission period is referred to as compressed mode 215. The time gap in UTRAN WCDMA compressed mode can vary from 3 slots to 14 slots over one or two 10 ms frames. Higher layer parameters indicating the location and periodicity of the compressed mode in the FDD frame structure are sent by the network.

Compressed mode is a known feature of the UMTS standard. In the compressed mode, the output from the UMTS transmitter is turned off in the UE, and for the base station (node B), the transmitted signal to a particular UE is turned off (not the RF transmitter serving other UEs). WCDMA systems allow for simultaneous and non-simultaneous uplink and downlink compressed modes.

In a single mode UMTS UE, this allows the UMTS measurement receiver to measure the strength of downlink signals at different frequencies. Based on these measurements, UE130 determines whether to change the communication channel. It should be noted that the UE130 receives details of the sequence of compressed mode patterns from the base station with which it is in communication. In other words, since UE130 is first switched on or changes operating channels, UE130 requires details of the new compressed mode sequence for the uplink and downlink channels it is now communicating on. This sequence information is sent by the base station to the UE 130.

Since GSM standard signals are time-duplexed, there are defined times in which the GSM transmitter does not operate, so that the GSM measurement receiver is able to measure other GSM downlink channels. More specifically, in GSM, there are eight time slots in each GSM uplink and downlink frame. The UE is allocated one of the eight time slots for its uplink in an uplink frame and one time slot for its downlink in a downlink frame. These two time slots are allocated such that each UE is allocated one uplink time slot, which is three time slots after it receives any information from the allocated downlink time slot. Thus, the UE starts two idle slots from the moment it receives a command from the downlink or four idle slots after its uplink transmission to the network for measurement. In GSM, these idle time slots, similar to those created with compressed mode in UTRAN, are used for system measurements.

Figure 3 shows a detailed timing diagram 300 of the compressed mode transmission gap 215. As shown, the UMTS transceiver (not shown) is powered on during the time indicated at 225. However, at the ramp down point 305, the UE130 begins to enter compressed mode. Ideally, the UMTS transceiver power would drop according to dashed line 311. However, due to the parasitic characteristics of the UMTS transceiver, and in particular the capacitance, the UE130 enters the compressed mode at the second point shown at 306 in fig. 3, which is the subsequent ramp down time (defined by line 309 in fig. 3). Similarly, UE130 is powered on at a ramp up point 307 when it begins to leave compressed mode. Ideally, the transceiver will recover full power according to dashed line 325. However, due to the parasitic nature of the transceiver as previously described, full power of the transceiver does not begin (and therefore UE130 does not leave compressed mode) until point 335. This is the subsequent ramp up time (as shown by line 308 in fig. 3). The nature of the spurious features of the UMTS transceiver determine the ramp up and ramp down times, but this time can typically be 0.5 milliseconds up and 0.5 milliseconds down. This means, therefore, that there is a time gap of approximately 1 millisecond between points 306 and 307 when the UE130 is operating in compressed mode and the transceiver is tilting up or down. Note that the 15 slots in FDD WCDMA are 10 milliseconds.

Fig. 4 shows a block diagram of a receiver part of a radio access telecommunications terminal 400. Antenna 405 is coupled to receiver frame 410. As is known, the antenna 405 is arranged to receive signals using the GSM and UMTS standards. The receiver block 410 is formed by a UMTS receiver 415 and a GSM receiver 420 (detector). The UMTS receiver 415 and the GSM receiver 420 are arranged to receive signals according to the appropriate standard. The UMTS receiver 415 and the GSM receiver 420 are connected to a down-converter block 425. The down-converter block 425 is formed by a GSM down-converter 435 and a UMTS down-converter 430. Also input to down converter 425 are first and second frequency synthesizers 440 and 445. A first frequency synthesizer 440 is connected to the GSM down-converter 435 and a second frequency synthesizer 445 is connected to the UMTS down-converter 430. Although the first and second frequency synthesizers 440, 445 are shown separately, it is contemplated that they may be combined into a single frequency synthesizer. The frequency of the signals generated by the first and second frequency synthesizers 440, 445 is such that the output of the GSM and UMTS downconverters 435, 430 is a constant intermediate frequency. In other words, as the frequency of the selected downlink channel changes, the frequency of the signals generated by the first and second frequency generators 440, 445 also changes so that the output of the GSM downconverter 435 and the UMTS downconverter 430 are constant intermediate frequencies 450, 455. The baseband processor 460 includes a GSM baseband processor 465 and a UMTS baseband processor 470.

The GSM intermediate frequency 450 is input to a GSM baseband processor 465 and the UMTS intermediate frequency 455 is input to a UMTS baseband processor 470. The GSM and UMTS baseband processors 465,470 also down-convert the intermediate frequency signals to baseband signals and digitize the down-converted signals for further processing by the processors. The processor is described below with reference to fig. 6.

The functionality of the receiver portion of the UE130 in the implementation of an embodiment of the present invention will now be described with reference to fig. 3.

As previously described, the GS1X measurement receiver 420 does not measure the signal strength of other downlink frequency channels when the UMTS transmitter is transmitting at peak power 225. This is because the UMTS internal circuitry will cause interference on the GSM receiver circuitry and therefore may generate spurious signal measurements. In these cases, re-measurement or data retransmission will be required, which may reduce the battery life of the user equipment. Thus, measurements of the UMTS and GSM downlink channels are made within the time period defined between point 306 and point 307 as shown in fig. 3.

As shown in fig. 6, the processor 605 is coupled to each of the UMTS transmitter (not shown), the UMTS receiver 415, the GSM receiver 420, and the first and second frequency synthesizers 440, 445. Thus, the processor controls the operation of at least the above-described components in UE 130.

The processor 605 contains a controller 610, a logical layer 1 and protocol stack 615, and a memory 620. The protocol stack and logic layer 1615 is a programmed function that sequences commands to the controller 610 and knows the timing and order in which to manage the measurement sequence, as will be appreciated by those skilled in the art.

The protocol stack and logic layer 1615 is coupled to the controller 610. The controller is arranged to process the received digital signal and to generate a digital signal for transmission. A memory 620 is connected to the controller 610 and is arranged to store details, in particular regarding the measurement time associated with the GSM receiver 420. The estimation of the length of time that the GSM measurement receiver 420 uses to measure different downlink channels is now described.

The GSM receiver 420 is arranged to estimate the time period it takes to make signal strength measurements of other frequency GSM downlink channels. There are a number of ways in which this can be done. As an example, during testing at manufacture, the GSM receiver 420 is required to measure the strength of a particular GSM downlink frequency channel. During this time, the GSM receiver counts the number of clock pulses provided by one clock, e.g., the processor clock, that is required to enable the GSM receiver 420 to measure the signal strength of a particular frequency channel. The number of clock pulses required is then stored in a memory 620, either contained in or accessible to the processor.

Further, the processor 605 can also be arranged to check and update the stored values periodically, if needed. This periodic update has the advantage that any changes in the time used by the GSM receiver 420 to make signal strength measurements can be kept correct when the components are corrupted over time.

The processor 605 now determines the time in which the GSM receiver 420 must start scanning for other downlink frequency channels. To ensure that the GSM measurement receiver 420 stops measuring when the UE130 starts to leave the compressed mode (at the tilt up point 307) and thus mitigate the interference problem, the GSM receiver 420 preferably stops measuring at the tilt up point 307. Thus, the processor defines the most recent time that the GSM measurement receiver can start measuring. This time is defined as:

the latest time for measurement (time UE130 starts to leave compressed mode (inclined to upper point 307) -GSM receiver measurement period (1)

Because processor 605 controls when UE130 begins to leave compressed mode, it is preferable to determine the most recent time GSM measurement receiver 420 begins to measure downlink channels on different frequencies that are tilted toward upper point 307. This tilt to the upper point 307 is therefore accurately defined by the processor 605. However, it is expected that if the minimum power point 306 is well defined, for example if the ramp down time 309 is measured during manufacture and stored in memory 620, the most recent time that the GSM measurement receiver 420 starts measuring can be determined with respect to the minimum power point 306 or the ramp down time 305.

As previously described, when the UMTS transmitter transmits an uplink signal or the UMTS receiver receives a downlink signal, the GSM receiver 420 does not operate, and thus the GSM receiver enters the standby mode. Thus, there is a delay in preparing the GSM receiver 420 for signal strength measurements. This is represented in fig. 3 by the receiver warm-up time as shown by line 311. Thus, the processor would need to calculate the latest activation time for the GSM receiver 420 to provide the preparation time. Thus, the most recent activation time can be defined as:

most recent activation time (line 315) time when the UE starts to leave the compressed mode (tilt up point 307) -receiver measurement period (line 340) -receiver preparation time (line 311)

The time taken to prepare the GSM receiver 420 is estimated in a similar manner as described above with respect to the receiver measurement period (line 340). The preparation time value is also stored in memory so that the processor can access the information.

It should be noted that although this embodiment is explicitly described with respect to a GSM receiver, it is contemplated that UMTS Terrestrial Radio Access (UTRA), enhanced GSM (egsm), Personal Communication System (PCS), code division multiple access-2000 (CDMA-2000), etc. may perform measurements in compressed mode in a manner similar to that described above.

Further, it should be noted that measurements for a particular frequency channel may be performed over one or more compressed mode time periods. For example, if the period required to measure the GSM receiver signal is longer than the maximum period provided by the compressed mode set by the network, the UE130 is arranged to make measurements performed over several compressed mode gaps.

Referring now to fig. 5 by way of example, a description will now be given of an order in which channels are preferably scanned in accordance with another feature of the present invention. As previously described, the UMTS and GSM receivers 415, 420 scan for other downlink frequency channels that are different from the downlink channels utilized by the UE130 to communicate with the base station. Although the GSM receiver 420 is arranged to scan the downlink channels in the compressed mode to reduce the amount of interference on the measured signal, the interference level is determined to a maximum procedure by the frequency of the uplink signal transmitted by the UE130 and the frequency of the measured downlink signal. For example, an uplink channel that is closer in frequency to the downlink channel being measured results in a higher interference level than an uplink channel having an operating frequency that is also closer. In addition, uplink frequency channels having an operating frequency that is a harmonic of the measured downlink channel also produce a high interference level. Accordingly, the processor 605 is also configured to reduce the interference level by measuring the signal strength of the downlink channels in a particular order in the compressed mode state. The ordering is performed by the processor 605 in accordance with fig. 5, and fig. 5 shows a flow chart used by the processor 605 to determine a preferred order in which to scan the frequency channels.

The processor 605 contains a controller 610, a logical layer 1 and protocol stack 615, and a memory 620. The protocol stack and logic layer 1615 is a programmed function that sequences commands to the controller 610 and knows the timing and order in which to manage the measurement sequence, as will be appreciated by those skilled in the art. The protocol stack and logic layer 1615 is connected to the controller 610. The controller is arranged to process the received digital signal and to generate a digital signal for transmission. A memory 620 is connected to the controller 610 and is arranged to store details, in particular regarding the measurement time associated with the GSM receiver 420.

As an example of an order in which the GSM receiver 420 measures the downlink channels, if there are four, at frequency f respectively₁、f₂、f₃、f₄Is to be scanned in a compressed mode period, the logical layer 1 and protocol stack 615 is notified by the controller 610 that the GSM receiver 420 is to start measuring the signal strength of the four channels. This notification occurs at a time as defined by line 315 in fig. 3. Logical layer 1 and protocol stack 615 have a list of four channels to be scanned. This list is provided when the user equipment moves into a communication cell and starts communicating with a particular base station. In effect, the logical layer 1 and protocol stack 615 store this list as a set of numbers known in the art as Absolute Radio Frequency Channel Numbers (ARFCNs). Each of these numbers has an associated characteristic, such as the frequency of the channel carrier. The logical layer 1 and protocol stack 615 provide the controller 610 with details and order of frequency channels to be scanned by the GSM receiver 420.

The amount of interference expected to be caused by any particular channel on any other channel is determined and programmed into the logic layer 1 and protocol stack 615 at the time of manufacture.

In this example, the uplink channel operates at 900MHz, f₁Operating at 2500MHz, f₂Operating at 1800MHz, f₃Operating at 2100MHz, and f₄Operating at 800 MHz.

Thus, the protocol stack and logic layer 1615 estimates the channel f sequentially₁、f₂、f₃、f₄。

Preferably, the protocol stack and logic layer 1615 orders the channels by comparing the frequency (fi) of the scanned channels with the frequency (ft) of the uplink channel (step S1). The ranking is performed so that the scanned channels considered to be the most interfering uplink channels are ranked the highest and measured by the closest point of approach 307. Thus, in this exemplary example, the rank assigned to each channel is f₁＝1，f₂＝3，f₃2 and f₄4. Thus, due to f₄Operating on the frequency closest to the uplink channel, it is ordered as number 4 so that it is scanned closest to the tilt towards the upper point 307. Moreover, due to f₁Is ranked as 1 (and thus is the least interfering channel), so it is scanned by the closest point of approach 306 (step S2).

However, since channels with operating frequencies that are harmonics of the uplink channel add interference, the protocol stack and logic layer 1615 may incorporate weighting factors into the ordering. In this example, the weighting factor for the first harmonic (first order harmonic) is a multiplier of 2. Therefore, although f₂Previously ordered as number 3, but with the weighting factor applied, f₂Is sorted to number 6 (steps S5, S6). Since there are only four possible channels to be scanned, f₂Will be scanned by the closest point of approach 307.

Obviously, other weighting factors may also be combined. For example, a channel having an operating frequency that is the second harmonic of the uplink channel will increase interference (although the interference is not as severe as in the second harmonic case). Therefore, in this case, a weighting factor of 1.5 may be applied to the sorting (steps S7, S8). Furthermore, if the rank is reversed such that rank 1 is assigned to the most interfering signal, the weighting factor will be a divisor.

It will be apparent to those skilled in the art that interference between the GSM receiver and the UMTS receiver is further reduced by measuring the most interfering channel at a point furthest from the tilt down conversion edge of the UMTS transmitter.

Although the present invention is described with reference to dual mode UEs, it should be understood that any single mode UE using different frequency uplink and downlink channel communications and using different telecommunication standards as well as incorporating telecommunication standards for compressed mode operation such as UTRA-FDD can also use the present invention.

Claims

1. A frequency division duplex radio access telecommunications terminal for transmitting a first signal type having a peak power level and a periodically reduced power level, and for receiving a second signal type different from the first signal type, the terminal comprising:

a transmitter for transmitting a transmission signal of said first type at a first frequency, the transmitter being arranged to switch between a peak power mode in which the transmission signal is transmitted at a peak power level and a reduced power mode;

a receiver for receiving a received signal of the second type at a second frequency different from the first frequency of the transmitted signal;

a detector for measuring a signal strength of the received signal; and

a controller in communication with the receiver, the transmitter and the detector, the controller being arranged to cause the detector to measure the signal strength of the received signal while the transmitter is operating in said reduced power mode and a predetermined time before the transmitter switches to said peak power mode.

2. A terminal as claimed in claim 1, wherein the transmitter is arranged to periodically switch from the peak power mode to the reduced power mode, the controller being further arranged to cause the detector to measure received signal strength while the transmitter is operating in successive periods of the reduced power mode.

3. A terminal according to claim 1, wherein the predetermined time is dependent on the time taken by the detector to measure the signal strength of the received signal.

4. A terminal as claimed in claim 1, wherein the transmitter is arranged to transmit the transmit signal in a reduced power mode at a reduced power level.

5. The terminal of claim 1, further comprising a memory device in communication with the controller, the memory device configured to store time information relating to the predetermined time.

6. A method of measuring the strength of a received radio signal in a mobile telecommunications terminal, the method comprising the steps of:

transmitting a transmission signal of a first signal type at a first frequency, the first signal type having a peak power level and a periodic reduced power level;

switching a transmit signal between a peak power mode at a peak power level and a reduced power mode;

receiving a second type of received signal different from the first signal type at a second frequency different from the first frequency of the transmitted signal; and

measuring the signal strength of the received signal while the transmitted signal is in the reduced power mode and a predetermined time before the transmitted signal is switched to a peak power level.

7. The method of claim 6, wherein the switching step comprises periodically switching from the peak power mode to the reduced power mode, the method further comprising measuring received signal strength in successive periods of reduced power mode.

8. The method of claim 6, wherein the predetermined time is selected based on a time taken to measure a signal strength of the received signal.

9. The method of claim 6, wherein transmitting the transmit signal further comprises transmitting at a reduced power level during the reduced power mode.

10. The method of claim 6, further comprising the step of storing time information relating to the predetermined time.

11. The method of claim 10, further comprising the step of updating the stored time information.

12. A frequency division duplex radio access telecommunications terminal for transmitting a first signal type having a peak power level and a periodically reduced power level, and for receiving a second signal type different from the first signal type, the terminal comprising:

a transmitter for transmitting said first type of transmission signal at a first frequency, the transmitter being arranged to switch between a peak power mode in which the transmission signal is transmitted at a peak power level and a reduced power mode;

a receiver for receiving a plurality of received signals of said second type, each at one of a further plurality of frequencies different from said first frequency at which a signal was transmitted;

a detector for measuring a signal strength of the received signal; and

a controller in communication with the receiver, the transmitter and the detector, the controller being arranged to determine the order in which said detector measures each of said received signals in dependence on the degree of interference in each case between the transmitted signal and the plurality of received signals whose strengths are to be measured.

13. A terminal according to claim 12, wherein the controller is further arranged to order the measurements of the received signals when the transmitter is in the reduced power mode such that the measurement of the received signal with the greatest degree of interference with the transmitted signal is taken last before the transmitter switches to the peak power mode.

14. The terminal of claim 12, wherein the degree of interference is determined from at least one frequency characteristic of each of the received signals relative to the first frequency of the transmitted signal.

15. The terminal of claim 14, wherein the frequency characteristic is a frequency difference between each of the received signals and the first frequency of the transmitted signal.

16. The terminal of claim 13, wherein the frequency characteristic is harmonic signal content of the each of the received signals relative to the transmitted signal.

17. The terminal of claim 14, wherein said frequency characteristic is determined by further including a weighting factor whose value is determined using harmonic content of said each of said received signals compared to said transmitted signal.

18. A method for ranking strength measurements of received radio signals in a mobile telecommunication terminal, the method comprising the steps of:

transmitting a transmit signal of a first signal type at a first frequency, the first signal type having a peak power level and a periodically reduced power level;

switching the transmit signal between a peak power mode and a reduced power mode at the peak power level;

receiving a plurality of received signals, each received signal being at one of a further plurality of frequencies different from the first signal type, at a second frequency different from the frequency of the transmitted signal; and

the order in which each received signal is measured is determined according to the degree of interference in each case between the transmitted signal and the plurality of received signals whose strengths are to be measured.

19. The method of claim 18, wherein the ordering of measurements for each received signal when the transmitter is in a reduced power mode is such that the received signal with the greatest degree of interference to the transmitted signal occurs last before the transmitter switches to a peak power mode.

20. The method of claim 18, wherein the degree of interference is determined from at least one frequency characteristic of each of the received signals relative to the first frequency of the transmitted signal.

21. The method of claim 20, wherein the frequency characteristic is a frequency difference between each of the receive signals and the first frequency of the transmit signal.

22. The method of claim 20, wherein said frequency characteristic is harmonic signal content of said each of said received signals compared to said transmitted signal.

23. The method of claim 21 wherein said frequency characteristic is determined by further including a weighting factor whose value is determined using harmonic content of said each of said received signals compared to said transmitted signal.

24. A telecommunications system, comprising:

a terminal according to claim 1; and

a base station comprising a base station transmitter and a base station receiver, wherein said transmitter is arranged to communicate with said terminal using said first signal type and said receiver is arranged to receive signals from said terminal according to said second signal type.

25. A telecommunications system, comprising:

a terminal according to claim 12; and