GB2391428A

GB2391428A - Adjusting for temperature variation and oscillator aging during radio frequency tuning

Info

Publication number: GB2391428A
Application number: GB0217275A
Authority: GB
Inventors: Klaus Martin Tetz; Hartmut Koenig; Reinhard Seiler; Moshe Ben-Ayun; Leif Petersen; Mark Rozental
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2002-07-25
Filing date: 2002-07-25
Publication date: 2004-02-04
Anticipated expiration: 2022-07-25
Also published as: GB2391428B; GB0217275D0

Abstract

A portable radio communications unit includes temperature measuring means operable coupled to a signal processor. Which is able to control a radio frequency generator. A memory element stores data relating to frequency versus temperature and the signal processor adjusts the radio frequency signal in response to the measured temperature using the stored data. Factory values of frequency versus temperature are initially stored in the memory element, but these are updated when the radio communications unit is in contact with an external reference signal, such as that of a base station. In this way aging of the oscillator may also be compensated for (Figure 2 is a flow chart depicting the method of this second aspect) This is of particular use when a radio communications unit is out of range of a base station and in direct communication with another portable radio unit. With no strong reference frequency to correct to, the oscillator requires accuracy.

Description

CM00687M/CT/GB/Tetz - 1 FREQUENCY TUNING IN A WIRELESS COMMUNICATION UNIT

Field of the Invention

This invention relates to synchronisatior. between wireless communication units. The invention is applicable to, but not limited to, a wireless cor, munication unit fine-tuning its frequency generation circuit for direct communication with another 10 communication unit.

Background of the Invention

Wireless co.mmunication systems, for example cellular 1> telephony or primate mobile radio communications systems, typically provide for radio telecommunication links to be arranged between a plurality of base transceiver stations (BTSs) and a plurality of s bscriber units, often termed mobile stations (MSs).

20 The term mobile station generally includes both hand-

portable and vehicular mounted radio units.

The communication link from a BTS to a MS is generally referred to as a downlink communication channel.

2> Conversely, the communication link from a MS to a BTS is generally referred to as an up-link communication channel. In a wireless communication system, each BTS has 30 associated with it a particular geographical coverage area (or cell). The coverage area defines a particular

CM00687M/CT/GB/Tetz - 2 geographic range that the BTS can maintain acceptable communications with MSs operating in its serving cell.

Often these cells combine to produce an expanded system coverage area, with the infrastructure supporting 5 respective cells interconnected via centralized switching equipment. The coverage area is typically determined by a receiver's ability to receive and decode very low-level signals from 10 the transmitting unit. In a wireless private mobile radio (PMR) communication system, it is known that a MS may operate outside of a dedicated network coverage area by communicating in a direct communicator. 1luk with at least one other MS. Such a communication mode is 15 generally referred to as a Dlrect Mode of Operation (DMO). DMO is similar to the back-to-back operation of conventional half-duplex two-way radio schemes used by many existing private mobile radio (PMR) systems such as that of the emergency services. This term is in contrast 20 to Trunked mode operation (TMO) that enables the MS to work within a network's coverage, with communications tofrom the MS controlled and facilitated by a switching and management infrastructure (SwMI) via the serving BTS.

25 Ir. the field of this invention wireless communication

urn's, operating in (or having access to) a bunked radio or cellular phone system, use a broadcast reference frequency signal to calibrate their operating (transmit/receive frequency. The broadcast signal is 30 generally transmitted from one or more BTSs. In this manner, the wireless communication units use the

'- CM00687M/CT/GB/Tetz - 3 broadcast reference frequency signal in order to synchronize their internal frequency generation circuits.

The units synchronize their operating frequency to match the system frequency, prior to entering into a com.municatlon. With all wireless _ommunlcatiGn units synchronized In this manner, an improved system performance can be achieved.

Nevertheless, it takes a finite amount of time for a 10 wireless communication unit to synchronize its operating frequency. The 'tuning' time depends upon a number of factors, for example, the signal strength of transmissions and the amount of frequency shift (offset) of the receiver to the base station transmitter. Hence, 15 it is hugely beneficial for the wireless communication unlays initial operating frequency to be as close to the reference signal as possible, to speed up the synchronisation process.

20 Furthermore, this approach to synchronization is not applicable to wireless units that are operating outside of the coverage area provided by the TOO BTSs, for example when operating in DMO. Hence, when a MS operates in DMO, there is no system controller, and therefore no 25 guaranteed reference frequency signal, Lo enable synchronization between wireless communication units.

It is known that speedy synchronization for wireless communication units operating in DMO is an essential 30 performance factor. In direct mode operation (DMO) two radios can directly communicate to each other without

CM00687M/CT/GB/Tetz - 4 using a base station, assuming that they can synchronize their operating frequencies. In this mode, one radio typically takes over the role of a 'masher' communication unit. The master communication unit dictates the timing 5 and frequency of signals between the two communication units. That means the second 'slave' radio communication unit has to synchronies its transmissions Lo the carrier signal of the master communication unit lO A major problem associated with DMO operation is that the master radio unit only uses default frequency tuning parameters to set its radio frequency, and therefore the master frequency. A consequent, second, problem is that the frequency of the reference oscillator IS temperature 15 dependent. Therefore, the carrier frequency used by the communication unit cannot be guaranteed to be stable, as even though a default frequency value is selected, t still varies with temperature. A third problem is that the frequency of the wireless communication unit's 20 internal reference oscillator also varies during the lifetime of the oscillator.

Hence, in practice, a slave communication unit may well have to adjust its operating frequency by a significant 25 amount, In order to take into account the frequency draft of the master communication unit's oscillator due to the aforementioned problems.

The current solution used to address these problems, for 30 example to support the TETRA RF DMO specification, is to

use expensive, high-accuracy reference oscillators.

CM00687M/CT/GB/Tetz In the factory, the reference oscillator is tuned for optimal radio performance. The tuning parameters are stored in a nonvolatile storage in the radio. These 5 parameters are static. They are typically never changed during the radio's life cycle. Unfortunately, these high-specification, high-cost oscillator solutions still

fail to cake into account the temperature and ageing dependency of the reference oscillator.

Thus, a need has arisen to provide a wireless comm.unication Init, and in particular, a method of frequency tuning a wireless communication unit wherein the aforementioned disadvantages may at least be 15 alleviated.

Statement of Invention

In accordance with a first aspect of the present 20 invention, there is provided a wireless communication unit, as claimed in claim 1.

In accordance with a second aspect of the present invention there is provided a method Of tuning a 2) frequency of a wireless communication unit, as claimed in Claire 9.

In accordance with a third aspect of the present invention, there is provided a storage medium storing 30 processor implementable instructions cr associated data, as claimed in Claim 16.

CM00587M/CT/GB/Tetz - 6 - Further aspects of the present invention are defined in the dependent Claims.

5 Brief Description of the Drawings

Exemplary embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: FIG. l shows a block diagram of a wireless communication unit adapted to support the various inventive concepts of a preferred embodiment of the present invention; and 15 FIG. 2 shoves a flowchart of the frequency tuning process in accordance with the preferred embodiments of the present Invention.

Description of Preferred Embodiments

In summary, the preferred method of synchronlsation

between two wireless communication units, such as two DMO communication units, is for both wireless communication units to adapt their initially selected operating 25 frequencies based on a temperature measurement in the wireless communication unit. The selection is made using a iook-up table of operating frequency versus temperature stored In the wireless communication unit.

30 In an enhanced embodiment of the present invention, the impact of oscillator (or any other frequency generation

CM00687M/CT/GB/Tetz component) ageing is negated by continuously re-

calibrating the selected operating frequency. The re-

calibration process is achieved using a reference transmission from a centralized (TMO) source, such as a 5 BTS. These accurate reference signals are preferably accessed as soon as the wireless communication unit IS switched on, if the DMO unit is within coverage range or a reference frequency signal transmission. In tithe preferred embodiment of the present invention, the 10 reference frequency signal transmissions are accessed periodically thereafter.

Referring now to FIG. 1, a block diagram of a wireless subscribed communication unitJmobile statics (MS) 100, 15 adapted to support the inventive concepts of the preferred'. embodiments of the present invention, is shown.

The Ma loo contains an antenna 102 preferably coupled to a duplex filter or circulator or antenna switch 104 that 20 provides isolation between receive and transmit chains within ME 100.

The receiver chain includes scanning receiver front-end circuitry 106 (effectively providing reception and 25 filtering of the received signal). The received, filtered signal is input to a frequency generation/conversion circuit 128 that includes a reference oscillator (not shown), signal mixing elements (not shown), etc. as known in the art. The frequency 30 generation/conversion circuit 128 is serially coupled to a signal processing function (generally realised by a

- - CM00687M/CT/GB/Tetz - 8 digital signal processor (DSP)) 103 via a baseband (back-

end) processing circuit 107.

A controller 1L4 is operably coupled to the frequency 5 generation/conversion circuit 128. Receive bit-error-

rate (BER) or rame-error-rate (FEW) calculations or similar link-q-ality measurement data may be obtained by the processor 108 via a received signal strength indication (RSSI) 112 function. The RSSI 112 function is lO operably coupled to the scanning front-end circuit 106.

A memory device 116 stores a wide array of MS-specific data, for example decoding/encoding functions, frequency and timing information for the communication unit, etc. 15 A timer 11& IS operably coupled to the controller 114 to control the timing of operations, namely the transmission or reception of time-dependent signals, within the MS lOO.

As known in the art, received signals that are processed by the signal processing function are typically input to 20 an output device, such as a speaker or visual display unit (VDU).

The transmit chain essentially includes an input device 120, such as a microphone, coupled in series through a 25 processor iO8, transmitter/modulation circuitry 122, Frequency generation/conversion circuit 128 and a power amplifier 124. The processor 108, transmlLter/modulation circuitry- 122 and the power amplifier 124 are operationally responsive to the controller. An output 30 from the power amplifier is coupled to the duplex filter or circulator or antenna switch 204, as known in the art.

CM00687M/CT/GB/Tetz In accordance with a preferred embodiment of the present invention, temperature measurement means 130 have been provided, operably coupled to the frequency 5 geleration/conversion circuit 128. In this manner, a temperature of one or more components or functions of the frequency generation/conversion circuit 128 can be measured. In this regard, the temperature measurements may be viewed as being made for a 'portion' of the 10 wireless communication unit. The temperature measurements are provided to the signal processing function 1Q8, so that the signal processing functlor 108 can select an initial operating frequency- for the wireless communication unit 100. If the temperature IS varies, the signal processing function 10& may select another operating frequency and/or adjust the frequency generation/converelon circuit 128 accordingly.

A preferred example of performing the temperature 20 measurement would be to use a readily available integrated circuit (IC) that converts a temperature to a voltage signal. This analogue signal may then be analogue-to-digitally (A/D) converted and forwarded to the controller (108). Preferably, the IC performing the 25 temperature measurement is located directly adjacent the reference oscillator circuit. In the preferred embodiment of the present invention, the temperature Is measured once per minute, which is deemed regular enough due to the high temperature hysteresis of the chassis.

30 Preferably, the result of the temperature measurement is translated into a particular temperature range (e.. 20

CM00687M/CT/GB/Tetz den in the table would represents a temperature range of 15-24 deg. Celsius).

Clearly, for other wireless communication products, other 5 temperature measurement techniques or circuits may be used. Furthermore, the temperature measurement device/element may be placed in other locations, for example above or below the reference oscillator circuit or any other frequency dependent element. Alec, other 10 temperature measurement rates and accuracy of the temperature recording Any be used, dependent upon the particular needs of the wireless communication product.

It is envisaged that any component or aspect of the l5 wireless communcatlon unit that affects an operating frequency of the wireless com, -,unlcaton, when undergoing a change in temperature, may be measured. In this manner, a determination of frequency drift based on temperature, may be made by the signal processing 20 function 108.

The memory device 116 has also been adapted to include a look-up table storing operating frequency versus temperature information for the wireless communication 25 unit loo. It is also envisaged that the memory device 116 may contain temperature versus frequency correction parameters, including, for example, a direction in which a frequency has to be corrected and a number of reference oscillator steps to be used to correct an operating 30 frequency. In this manner, the signal processing function 108 accesses the memory device and

CM00687M/CT/GB/Tetz - 11 obtains selects an operating frequency dependent upon a temperature measurement. The signal processing function id then tunes/sets the frequency operation of the wireless communication unit lOO, based on this temperaue measurement. If both wireless communication units follow the same tuning methodology, the selection of a same, or close, operating frequency can be achieved much more quickly, and more accurately, than known techniques. Furtnefn-ore, in the enhanced embodiment, che signal processor function 108 monitors a reference frequency in a servlug wireless communication unlc. Inls mor.ltorl'.g process is preferably performed soon after the:ireless 15 communication unit is switched On, and period rally thereafter. In this enhanced embodiment, by comparing the wireless communication unit's selected operating frequency with the system's (BTS's) highly accurate reference frequency, a frequency difference may be Q determined. The signal processing function 108 may then re-program the memory device 116 if the frequency difference exceeds a threshold value. In effect, the re-

programming operation re-calibrates the operating frequency, for a particular temperature.

In the preferred embodiment of the present invention, the minimal resolution of the reference oscillator is 30Hz for a THE TETRA product and 35Hz for an 800MHz TETRA product. The maximum allowed frequency shift for 30 synchronization with the BTS is +/-800Hz. In the preferred embodiment, a maximum of about +/-lOOHz (three

i al CM00687M/CT/GB/Tetz reference oscillator steps, 3*30Hz for UHF, 3*35Hz for 800MHz) is allowed. Whenever the frequency shift exceeds three steps, the frequency correction parameters are updated with the actual temperature measured. Clearly, a 5 skilled art-sap would realise that for other wireless products, alternative resolutions/thresholds may be applied dependent upon the particular circumstances.

A large difference indicates a substantial drift of the 10 wireless communication unit's operating frequency. As the operating frequency has been selected for a particular temperature measurement, the drift can be assumed to be substantially due to ageng of one or more components in the frequency generation/conversion circuit 15 128.

The re-calibration procedure solves the problem of ageing dependency of the reference oscillator in the following manner. Whenever the wireless communication unit 100 is 20 switched on, the scanning front-end circuit 106, under control of controller 114, locks on to a base station signal. Concurrently, or close thereto, the radio temperature of any functions/components associated with setting the correct RF frequency of the wireless 25 communication unit are measured. If the reference requency value(s) differ(s) substantially from that already stored in the memory device 116, the frequency value(s), for one or more measured temperatures, are updated to adjust the operating frequency to the measured 30 reference frequency.

al CM00687M/CT/GB/Tetz - 13 It is envisaged that the adjustments may be made to, say, a multiplying factor or steering line voltage in the frequency generation circuit, so that the adjustment of the generated operating frequency tunes the operating 5 frequency to substantially match the reference frequency.

It is within the contemplation of the invention that a threshold may be used to determine whether an update operation is required. For example, if there is a minor 10 frequency difference between the operating frequency and the reference frequency where the difference does not exceed a frequency threshold value, no frequency update IS performed on the look-up table. However, where the difference between the frequencies is significant enough 15 to affect the chances of a speedy and accurate communication link being set up, i.e. the difference exceeds a frequency threshold value, a frequency value update process s performed on the ookup table.

20 Therefore, after a period of time a look-up table of temperature versus frequency (oscillator tuning) values may be generated, to reflect the frequency tuning requirements of the wireless communication unit 100.

Advantageously, by continuing to make comparisons between 25 the measured reference frequency and the unit's operating frequency measurements, coupled with concurrent temperature measurements, ageing effects of the oscillator/frequency generation circuitry can be accounted for.

- - CM00687M/CT/GB/Tetz It is envisaged that the look-up table could take the form shown below in Table 1: Table 1:

Temperature [deg. C] |Oscillator Tuning [hex] : -30 $FF(*)

i -20 $04

1 1

-10 $05

1 1 - O 1 $06

i a_ 1 +10 $08

_ _

+20 ', $OS 1

l +30 $09.

+40. $ 9

I +50 $0A I

+6Q $FF(*) I

1 1 Where: (*) indicates that no value has been stored for this temperature so far 10 Hence, when the wireless communication unit 10G is subsequently switched on, the preferred tuning values are extracted from Table 1 in memory device 116 and are used by the signal processing function 158 ( for both the master and slave wireless communication unit) to lS initially set the unit's operating frequency.

Only when no parameters are stored in the table, for example as shown with '$ff' or with a new radio or where no value is available for the measured temperature of +60

- CM00687M/CT/GB/Tetz deg. C, is the default value from a factory tuning process used. As both master and slave units preferably use their respective frequency tuning process according to Table 1, when operating in DMO mode, a mulch closer 5 initial operating frequency between the two units IS achieved. In an alternative embodiment, the signal processor function 1Q in the transmit chain may be implemented as 10 distinct from the signal processor function 108 in the receive chain. Alternatively, a slugle processor 108 may be used to Implement the processing of both transmit and receive signals, as shown in F G. 1.

15 Of course, the various components within the As lOQ mall be realised in discrete or integrated component form.

Furthermore, it is within the contemplation of the invention that the MS 100 may be any wireless communication device, such as a portable or mobile PER 20 radio, a mobile phone, a personal digital assistant, a wireless laptop computer, etc. More generally, any re-programming or adaptation of one or more software algorithms in the signal processor 25 function 103 or data banks or memory device 116, may be implemented In any suitable manner. For example, a new signal processor function or memory device may be added to a conventional wireless communication unit 105.

Alternatively, existing parts of a conventional wireless 30 communication unit may be adapted, for example by reprogramming one or more processors therein. As such,

CM00687M/CT/GB/Tetz - 16 the required adaptation may be implemented in the form of processor-implementable instructions stored on a storage medium, such as a floppy disk, hard disk, PROM, RAM or any combination of these or other storage multimedia.

The preferred embodiment of the present invention is described with reference to the T=TRA standard, and in particular the TETRA DMO standard. However, it is within the contemplation of the invention that the inventive 10 concepts described herein apply to any wireless communication system, particularly those where a direct communication mode is provided.

It is within the contemplation of the invention that the 15 processor 108 physically tunes!se_s its frequency generation circuit In a similar manner to any other known wireless communication unit, for example by adjusting a voltage on a steering line. All frequency adjustments are typically based upon a common reference oscillator 20 frequency of, say, 15.8 MHz. However, in accordance with the preferred embodiment, such a tuning process is 'in response to' the stored oscillator frequency values with respect to temperature of the wireless communication unit 100. Furthermore, these values are preferably 9 continuously updated to account for ageing in the frequency generation!conversion components.

Referring now to FIG. 2, a flowchart 200 of the preferred tuning operation is described. The flowchart commences 30 with a measurement of the wireless communication unit's temperature, as shown in step 205. A determination is

- CM00687M/CT/GB/Tetz - 17 then made as to whether a frequency (or tuning parameter such as a corresponding steering line voltage) is available for the measured temperature, as in step 210.

If a preferred frequency is not avail-able for that 5 ie..perature, in step 210, the pre-set, default factory tuning parameters are used as an initia_ setting for the frequency generation circuit, as shown in step 215.

However, if a frequency for the measured temperature is available from the memory device, in step 210, the IQ corresponding frequency settings are used to adjust/set the wireless communication unit's operating frequency in step 220. In this r,anner, an improved initial frequency setting is used, based on a temperature measurement.

15 Periodically, a scanning front-end circuit of the w reless communicat on unit searches for a BIS reference (carrier) signal, to obtain an accurate frequency indication, as in step 225. Once an accurate BTS reference signal has been found, a calculation of a 20 frequency shift required to align the wireless communication unit to the BTS's frequency is determined, in step 230. A temperature measurement IS (substantially) concurrently performed.

25 If an operating frequency is not available, in step 235, or the operating frequency of the wireless communication unit is sufficiently close to the BTS's reference frequency that only a minor frequency adJustmen_ may be required, no update of the look up table s performed.

t CM00687M/CT/GB/Tetz 18 However, if there is a sufficient difference between the operating frequency of the wireless communication unit and the Pleasured reference frequency of the BTS signal, the look-up table is preferably updated with the revised 5 frequency Devalue, (of corresponding steering line voltage) for the measured temperature, in step 240.

It is envisaged that such temperature measurements continue to be made, dependent upon a tamer function 10 (say, initiated by timer 118 of FIG. 1) . By measuring the temperature shift over a period of time, a determination can be made as to whether the temperature of the wireless communication unit is stable or not, as in step 245. If it is, the operating frequency is 15 assumed stable, and no further updates to the look-up table are needed at that tlmA. However, if the temperature of the wireless -ommunication unit is constantly varying, measurements of the temperature in step 250 and the BTS's reference frequency in step 230 2n are continuously performed. In this manner, the effect of temperature on the operating frequency can be determined by comparing it to the BTS's reference frequency signal.

25 It will be understood that the frequency tuning mechanism described above provides at least the following advantages: (i) Temperature and agelng dependencies of the reference oscillator are eliminated; 30 (ii) Cheaper reference oscillators, operating with less accuracy can be used;

) CM00687M/CT/GB/Tetz (iii) More consistent radio performance over a longer time period can be achieved; (iv) More consistent radio performance over temperature variations can be achieved; and 5 (v) A faster lock process can be achieved, which is particularly beneficial when the radio is operating in a DMO mode.

Apparatus of the invention In summary, a wireless communication unit has been

described that includes a radio frequency generation circuit for generating a radio frequency signal to be used by the wireless communication unit. A signal 15 processor is operably coupled to the radio frequenc-

generation circuit for adjusting the radio frequency signal. Temperature measurement Means, operably coupled to the signal processor, measure and inform the signal processor of a temperature of a portion of the wireless 20 communication unit. A memory element, operably coupled to the signal processor, stores one or more frequency values corresponding to respective one or more temperatures. The signal processor adjusts or sets the radio frequency signals in response to the measured 25 temperature, based on a correso^-nding frequency indicated in the memory element. In this manner, the operating frequency of =he communication unit is adjusted or set in accordance with a temperature of, say the unit's reference oscillator.

Method of the invention

CM00687M/CT/GB/Tetz - 20 In summary, a method of tuning or setting a radio

frequency signal of a v-.'ireless communication unit has been described. The method includes the step of 5 treasuring a temperature of a portion of said wireless communication unit. One or more frequency values corresponding to respective one or more temperature measurements are stored in a memory element in the wireless communication unit. A radio frequency signal is 1Q generated based on the temperature measurement.

Whilst specific, and preferred, implementations of the present invention are described above, it is clear that one skilled in the art could readily apply variations and 15 modifications of such inventive concepts.

Linus a wireless communication unit, and a method for tuning a radio frequency signal in a wireless communication unit have been provided where the 20 disadvantages described with reference to prior art

arrangements have been substantially alleviated.

Claims

CM00687M/CT/GB/Tetz - 21 Claims 1. A wireless communication unit Riggs

comprising: a radio frequency generation circuit (128) for 5 generating a radio frequency signal to be used by the wireless communication un t; a signal processor (108) operably coupled to the radio frequen--generation circuit for adjusting said radio frequency signal; and 10 temperature measurement means (130), operably coupled to the signal processor (108), for measuring and informing said signal processor (108) of a temperature of a portion of the wireless communication unit; the wireless communication unit (100) characterized by: lo a memory element!116), operably coupled to said signs- processor (108), storing one or more frequency values corresponding respectively to one or more temperatures; wherein said signal processor adjusts or sets said 20 radio frequency signal, In response to the measured temperature, based on a corresponding frequency indicated in the memory element (116).
2. The wireless communication unit (100) according to 95 Claim 1, wherein the said memory element is udateable during communication with a base station or repeater.
3. The wireless communication unit (loo) according to claim 1, further characterized by:

an. 3 CM00687M/CT/GB/Tetz - 22 a radio receiver, operably coupled to said signal processor (108), for receiving a reference frequency signal from a serving communication unit; wherein said signal processor (108): 5 determines a frequency of said received reference frequency signal, obtains a temperature measurement of said port-on of a wireless communication unit at a substantially concurrent time as said reference frequency 10 is being determined, and stores in said memory element (116) said determined reference frequency as a frequency corresponding to said ten,perature measuremen_, for subsequent use in adjusting or setting a red o frequency 15 signal of said frequency generation circuit.
4. The wireless communication unit (100) according to any preceding Claim, comprises means for overwriting said one or more frequency values corresponding to 20 respectively one or more temperature measurements in said memory element (116).
5. The wireless communication unit (100) according to claim 4, wherein the values stored within the said memory 25 element (116) are over- written sufficiently often to compensate substantially for all ageing effects of the frequency generation circuit and/or wireless communication unit components.

30
6. The wireless communication unit (100) according to any preceding Claim, wherein said memory element (116)

- - CM00687M/CT/GB/Tetz À 23 contains temperature versus frequency correction parameters, including, for example, a direction in which a frequency has to be corrected and a number of reference oscillator steps to be used to correct an operating 5 frequency.
7. The wireless communication unit (100) according to Claim 1, wherein said signal processor (108) selects a radio frequency signal based on factory default settings 1(] if one or both of the following conditions prevail: (i) No temperature measurement is available; or (ii) No frequency value has been stored for the measured temperature reading.

15
8. The wireless communication unit!100) according to any of the preceding Clalms, wherein the wireless communication unit (100) is one of a portable or mobile (PMR) radio, a mobile phone, a personal digital assistant, a wireless capable laptop computer.
9. A method of tuning or setting a radio frequency signal of a wireless communication unit, the method characterized by the following steps: measuring (205) a temperature of a portion of 25 said wireless communication unit; storing, in a memory element in said wireless communication unit, one or more frequency values corresponding to respective one or more temperature measurements; and

CM00687M/CT/GB/Tetz - 24 generating a radio frequency signal to be used by said wireless communication unit based on said temperature measurement.

5 10. A method of tuning or setting a radio frequency signal of a wireless communication unit according to Claim 9, wherein said step of generating a radio frequency signal generates an initial operating frequency signal, the method further characterized by the step of: LO adjusting said initial operating frequency signal based on stored frequency value for the measured temperature. 11. The method of tuning or setting a radii frequency 1: signal of a wireless communication unfit according to Clalm 9 or Claim 10, the method further characterized by the steps of: receiving (225) a reference Frequency signal from a serving communication unit; and 20 updating (240) a frequency value in said memory element with a value corresponding to said reference frequency at a measured temperature.

12. The method of tuning or setting a radio frequency 95 signal of a wireless communication unit according to Claim 11, wherein said step o-= updating is performed if a frequency difference between said operating frequency- and said reference frequency signal exceeds a threshold.

30 13. The method of tuning or setting a radio requency signal of a wireless communication unit according to

CM00687M/CT/GB/Tetz - 25 Claim 11 or Claim 12, the method further characterized by the step of: calculating <230) a frequency shift to align said operating frequency of said wireless - mmunication unit 5 to said reference frequency; and adjusting said operating frequency of said tireless communication unit to operate at said reference frequency. 10 14. The method of tuning or setting a radio frequency signal of a wireless communication unit according to any of preceding Clai..s 8 to 12, the method further charactersed by the steps of: determining (210! whether a frequency value is 15 available for said measured temperature) and: using (215, a pre-set default frequency as an initial frequency setting, if said frequency value or said measured temperature is not available) or using (220) said frequency value from said 2Q memory element as an initial frequency setting if said frequency value fur said measured temperature is available. 15. The method of tuning or setting a radio frequency 2- signal of a wireless communication unit according to any -f preceding Claims 9 to 14, the method further characterized by the step of: continuing to measure said temperature and said reference frequency if said temperature of the wireless 30 communication unit is constantly varying; and

CM00687M/CT/GB/Tetz updating stored frequency values in said memory device, as appropriate, in response to said continued measurements. S 16. A storage r,edium ills, storing processor iplementable instructions for controlling a processor to = carry out the method of any of claims 9 to 15.

17. A wireless communication unit (TOG) substantially 10 as hereinbefore described with reference to, and/or as illustrated by, FIG. - of the accompanying drawings.
10. A method of tuning a frequency of a wireless communication unit '200) substantially as hereinbefore 15 described with reference to, and/or as al ustrated by, FIG. 2 of the accompanying drawings.