GB2409606A

GB2409606A - Cellular network identification and acquisition

Info

Publication number: GB2409606A
Application number: GB0329830A
Authority: GB
Inventors: Richard Ormson; Frederic Gabin; Darioush Downer; Nigel Legg
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2003-12-23
Filing date: 2003-12-23
Publication date: 2005-06-29
Anticipated expiration: 2023-12-23
Also published as: GB2409610A; GB0329830D0; GB2409610B; GB2409606B; GB0414200D0

Abstract

A mobile radio communications device seeking connection to a network of a first radio access technology (RAT), such as WCDMA, scans a plurality of frequency bands to determine a signal characteristic for each band, such as signal strength, and analyses the characteristic of a plurality of frequency bands to identify a block of bands having a uniform characteristic, implying that a WCDMA has been located. Then, an attempt is made to connect at a centre frequency of the identified block of frequency bands. Alternatively, where at least two RATs, such as GSM and WCDMA, operate with partially overlapping frequency bands, signal characteristics of the common frequency bands may be determined and an attempt to connect on a first of the frequency bands in accordance with a first of the RATs is made. If the attempt fails, an attempt is made to connect to the same frequency band in accordance with a second of the RATs before attempting to correct to a second of the frequency bands.

Description

CELLULAR NETWORK ACQUISITION

METHOD AND APPARATUS

The present invention relates to a method and apparatus for use in network acquisition for mobile radio communications devices.

Mobile radio communications devices, such as cell phones, have become increasingly popular and widely adopted and in many instances have become a prime means of communication both for business and domestic 1 0 purposes.

As such usage becomes more widespread, potentially disadvantageous limiting features of such devices become more apparent. For example, when a cell phone is first turned on, network acquisition procedure has to be conducted so that the cell phone can acquire the appropriate communications network and subsequently take part in a communications exchange over that network.

The period between turning the cell phone on, and actually acquiring the network, does not generally go unnoticed by the user. This period represents dead-time as far as the user is concerned since no other operations over and above network acquisition are conducted during that period.

The longer the time period required to acquire the network, the more likely this period is to be noticed by the user and so lead to irritation.

Also, the network acquisition procedure requires the cellular communication device to expend a significant amount of power relative to the power requirements arising merely when in an idle or communicating mode.

Indeed, in view of the different mobile communication modes that have arisen for such devices, and the subsequent requirement for cell phone handsets to offer dual mode, and indeed multi-mode, operability, it is considered that it will become increasingly necessary for each handset to search for more than one network. Thus, the eventual delays in network acquisition and related potential user irritation are likely to become more frequently experienced.

Network acquisition procedures generally require a search through a set of frequencies in an attempt to identify the most suitable cell of each network.

The set of frequencies is defined in accordance with each mode as a particular band of frequencies. This initial search is a relatively simple one employing characteristics such as signal strength, or a derivative thereof, and which leads to the cells being ranked in an order based on the characteristic.

With regard to known multi-mode arrangements, the cellular handset is arranged to search one entire Radio Access Technology (RAT) at a time and the relative priority with which the RATs are searched is set within the handset.

Thus, for example with a dual mode GSM/\NCDMA handset, a search for WCDMA cells will only commence if no suitable cells are found when searching all of the ranked frequency bands for GSM cells.

The present invention seeks to provide for cellular network acquisition procedures and arrangements offering specific advantages as compared with current acquisition techniques.

The present invention advantageously arises from the recognition that for a mobile handset arranged to operate with at least two RATs having at least some overlapping frequencies, the signal characteristic determined during the search in relation to one of the RATs may in fact be originating from the other RAT.

If this is indeed the case, then any attempt to decode cell information or to camp onto the cell will fail until the correct RAT is identified. al

According to a first aspect of the present invention there is provided a network search method for use in a mobile radio communications device seeking connection to a network of a first radio access technology and comprising scanning a plurality of frequency bands to determine a signal characteristic for each band, analysing the said characteristic for a plurality of said bands to identify a block of bands having a substantially uniform characteristic, and attempting to connect to the network at a frequency substantially at the centre of the said identified block of frequency bands.

This aspect of the present invention is particularly advantageous in that through analysing the block of bandwidths, it becomes possible to readily identify whether an appropriate RAT is being searched and, if so, the likely centre frequency thereof. This assists in preventing power and time wastage arising in attempting to connect to frequencies not at the centre of the said block of frequencies.

Advantageously, the method includes the step of identifying a plurality of blocks and the further step of sorting the said blocks into a ranked order in particular based on the relative values of the characteristic.

As such, the method advantageously allows for the step of attempting to connect to the centre frequency of each of said blocks in accordance with the ranked order.

The said characteristic of each signal can comprise signal strength or a derivative thereof.

In accordance with the above-mentioned aspect of the invention, if no suitable block of a plurality of bandwidths is identified, the method advantageously includes the step of searching for a second, or further, RAT.

With such an arrangement, the frequency bands are searched according to the second RAT and in a ranked order dependent upon a characteristic such as signal strength or a derivative thereof.

The invention is particularly advantageous when employed in a mobile radio communications device offering at least dual mode GSM/\NCDMA operability wherein WCDMA comprises the first RAT mentioned above and GSM the second.

Also according to this first aspect of the present invention, there is provided a mobile radio communications device arranged for connection to a network of a first radio access technology, and including means for scanning a plurality of frequency bands to determine a signal characteristic for each band, means for analysing the said characteristic for a plurality of bands to identify a block of bands having a substantially uniform characteristic, and means for connecting to the frequency substantially at the centre of the said identified block of frequency bands.

The device can include means for identifying a plurality of blocks and for sorting the said block into a ranked order.

As such, the device can then be arranged to connect to the centre frequency of each of said blocks in accordance with the ranked order.

The device of course can include means for performing the various method steps noted above.

According to another aspect of the present invention there is provided a network search method for use in mobile radio communications device arranged for connection to networks of at least two radio access technologies operating with at least partially overlapping frequency bands, determining signal characteristic of the common frequency bands, attempting to connect on a first of the plurality of bands in accordance with a first of the plurality of radio access technologies, and if the said attempt to connect to the first of the said plurality of bands in accordance with the first radio access technology fails, attempting to connect to the said first of the plurality of bands in accordance with a second of the plurality of radio access technologies before attempting to connect to a second of the plurality of bands.

This aspect of the present invention is particularly advantageous in that, in accordance with the invention, it is identified that, while conducting, for example, a signal level search in accordance with one of two possible RATs the signal being analysed might actually be arising in accordance with the other of the two RATs.

Advantageously, should an attempt to connect to the first of the plurality of bandwidths in accordance with both of the radio access technologies fail, the search is then to be repeated, for each band in turn and for each of the RATs.

Of course, the plurality of bands can be ranked in accordance with the respective levels of the signal characteristics concerned.

The said signal characteristic may comprise signal strength or a derivative thereof.

It should be appreciated that the search on one of the RATs can be performed in accordance with the first aspect of the present invention as defined above.

The invention can also provide for a corresponding mobile radio communications device including means for connection to networks of at least two radio access technologies operating with at least partially overlapping frequency bands, means for determining a signal characteristic of the \ common frequency bands means for connecting on a first of the plurality of bandwidths in accordance with a first of the plurality of radio access technologies, and if the said attempt to connect to the first of the said plurality of bands in accordance with the first radio access technology fails, the device being arranged to connect to the said first of the plurality of bands in accordance with a second of the plurality of radio access technologies, before attempting to connect to a second of the plurality of bands.

As mentioned before while conducting, for example, a signal level search in accordance with one of the two possible RATs the signal being analysed might actually be arising in accordance with the other of the RATs.

Also, the search in accordance to one of the two RATs can be performed in accordance with a device of the hrst aspect of the present invention as defined above.

Referring to the above-mentioned first aspect of the present invention, can be employed as part of a method for determining which of the plurality of RATs a mobile radio communications device should attempt connection to and based on the uniformity of the signal characteristic with frequency.

In particular, the method can include the step of determining whether or not the distribution of the characteristic over frequency is relatively uniform, or random.

If the distribution is uniform then the method includes the step of determining that the radio access technology is likely to be a first of the plurality of two radio access technologies. If, however, the distribution of the characteristic with frequency is more random in nature, then the method includes the step of identifying, and seeking connection to, a second of the plurality of radio access technologies.

Advantageously, this aspect of the invention can comprise a method employed as a means for determining whether the radio access technology to which the handset can connect comprises GSM or WCDMA.

As before, the said signal characteristic can advantageously comprise signal strength or a derivative thereof.

The basis of the invention is now described by reference to a dual mode (GSM/WCDMA) handset.

Under current 3 GPP specifications, such a handset is required to search the first of the two entire Radio Access Technologies (RATs) at a time.

The relative priority of the two RATs is set within the handset and, in this example, the handset will first search for a GSM connection or WCDMA connection, and will then only look at the second of the RATs during initial selection if no suitable cells are found on the first of the RATs.

An initial search is generally simple involving reference to signal strength, or a derivative thereof, and sales are generally ranked in order of signal strength such that the cell offering the strongest signal strength is assessed first for suitability. The present invention identifies that potential problems might arise when any two or more radio systems offer operation in the same, or at least partially overlapping, frequency band.

For example, 3 GPP standards have recently added support for WCDMA in the GSM 1800 and 1900 bands.

According to the present invention, it has been identified that signal strength figures that might be detected during the search on one of the RATs, may in fact turn out to be originating for a cell of the other RAT. On this basis any attempt to decode cell information or camp onto the cell of the first RAT will of course fail.

In one particular aspect of the present invention, the method and apparatus is proposed that advantageously takes account of the different bandwidths employed in accordance with the two RATs GSM and WCDMA.

As known, GSM employs a 200kHz band, while WCDMA employs 5MHz band.

On this basis, for any given frequency on which an appropriate signal power level is determined in accordance with the present invention using a 200kHz band raster scan, there will be a 1 in 25 chance of that frequency actually forming the centre frequency of a larger WCDMA band.

Since it will only prove possible to connect to the WCDMA network if the centre frequency is employed, the invention advantageously provides for a mechanism for establishing whether or not the frequency located is in fact likely to be the centre frequency to thereby prevent the need to search the other twenty-four possible frequencies which would represent 24 fruitless attempts wasting both time and power resources.

This aspect of the present invention takes advantage of the fact that within WCDMA, the distribution of power over the 5MHz bandwidth is relatively even so that it can be determined if a 5MHz block of frequencies in the initial search is found which have, within a certain tolerance, a uniform power level, this can be taken as a determination that a WCDMA band has been located, and the centre frequency established accordingly.

Although it might be considered that such a method and arrangement could lead to erroneous results if a GSM deployment could be seen at the same power level over a 5MHz band. Such GSM employment is extremely improbable in practice. In particular for the following reasons.

Frequencies are block allocated to networks, so to get 5MHz at the same power level would need a network to allocate 25 GSM contiguous channels to one cell which is never done, or 25 contiguous channels to adjacent cells covering the same area. Thus the only place where this can happen is in an area with coverage from more than one cell. Even then only a specific location would receive the same power on a band this wide originating from more than one base station, and that position would constantly change as the transmission levels and fading paths altered.

Also, it is normally only the CO channel on each cell is transmitted at full power and the other channels are sent at a variation of this. So for a network in normal operation power spikes will be evident on the CO channels if the band is in use by GSM, but no such spikes will be evident on a WCDMA band.

Thus, it will be appreciated that the present invention advantageously employs the realization that, for example, a WCDMA signal could be detected by a GSM RSSI scan and which is elaborated further as follows.

Turning first to the analogue section of a GSM receiver, this can simplistically be considered as a frequency shifter serving to select a block of spectrum several kHz in width, for example 280kHz, from the larger GSM band and to shift this in frequency so that the block runs from zero to 280 kHz.

While the methods of achieving this vary, such as the use of direct conversion radios, and ones with intermediate frequencies, the net effect is the same regardless of the method used. As the radio is just a frequency shifter, and the selected 280kHz block contains radio energy, this will be passed to the base band stage. It is noted that the radio is not concerned with modulation method employed and simply passes the radio signal to the base band for processing.

Consideration is now given to the case where the selected 280 kHz block is in fact part of a WCDMA 5MHz band. Given that the WCDMA system produces a spectrum where the entire 5 MHz band contains substantially uniform levels of power, the 280 kHz block will contain radio power, and that power will be passed through the GSM radio and output to the base band as a O to 280 kHz signal.

It is noted that the GSM radio gives two outputs corresponding to I and Q channels. However, splitting the input signal in two paths and mixing both with a reference frequency generate these and the difference is that in one case the reference frequency is phase shifted. It should be appreciated that radio energy still passes through this process even if it is not GSM. This can be identified by inputting random noise into a GSM radio, I and Q signals will still be output.

Turning now to consideration of the Radio Signal Strength Indication (RSSI) measurement in the Digital Signal Processor (DSP)/Communication Signal Processor (CSP), once the GSM radio completed its handling of the signal, the analogue base band takes over. For an RSSI measurement the process is very simple. Firstly a pair of analogue to digital converters measure the voltages on the I and Q paths. Then these are Route Mean Square (RMS) combined to give an indication of the power present. The process is repeated for a number of samples and the results averaged so as to provide for the RSSI power.

In the case where the signal being received is in fact WCDMA, radio power will still be received as described above. The RSSI measurement will therefore still indicate the level of radio power in the spectral block to which the radio is tuned, regardless of whether or not this is GSM.

The invention is described further hereinafter by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic flow diagram illustrating a method in accordance with one aspect of the present invention; Fig. 2 is a flow diagram illustrating a variation of the aspect illustrated in accordance with Fig. 1; Fig. 3 is a flow diagram illustrating a method according to an embodiment of another aspect of the present invention; and Fig. 4 is a schematic diagram of a handset embodying the present invention.

Turning now to Fig. 1, there is illustrated, in a flow diagram form, a network search method according to an embodiment of the present invention.

The method commences at 10 with a scan of the frequencies of the signals received at the handset using a 200kHz raster scan and once the scan is complete, the results are analysed at 12 in an attempt to identify blocks of twenty-five-200kHz bands exhibiting substantially the same signal strength within a predetermined tolerance range dB.

If the analysis at 12 identifies such a block of twenty-five-200kHz bands, then the method branches at 14 to step 16 at which the plurality of blocks, indeed if the plurality of such blocks is identified, are sorted in an ranked order determined by signal strength.

At 18, the block exhibiting the strongest signal is then selected and an attempt at step 20 is made to camp on the centre of the block in accordance with WCDMA procedures.

At 22, the success of the attempted camp-on is determined and if identified as successful, the method concludes at step 24 in that the handset can enter its idol mode.

If, however, the WCDMA camp-on procedure was identified as not being successful at step 22, a search is made at step 26 for any further blocks of twenty-five-200kHz bands and if such further blocks are found, the next block in the ranked order is selected at 28 and a WCDMA camp-on procedure is attempted on that next block.

The loop identified by steps 22, 26, 28 and 20 is repeated for all of the blocks identified in an attempt to achieve a successful camp-on for WCDMA and subsequent entry of the handset into its idol mode at step 24.

Returning to step 14 however, if no blocks of twenty-five-200kHz bands are found with substantially the same power level at step 12, or indeed the search of all blocks as exhausted without a successful WCDMA camp-on procedure at step 26, the method can be arranged to proceed via step 30 in which all of the 200kHz bands are sorted by signal strength and then a conventional camp-on procedure can be followed for each of the radio access technologies concerned at 32 and if camp-on proves successful for one of the radio access technologies, then the device enters its idle mode.

Turning now to Fig. 2, there is illustrated the operation of a handset in accordance with a multimode device.

The method illustrated in Fig. 2 commences in a similar manner as that illustrated in Fig.1 in that an initial 200kHz raster scan is conducted at step 34 in an attempt to look for blocks of a plurality, i.e. n, of 200kHz frequency bands with a substantially uniform power at step 36.

If any such blocks are located at step 38, then a determination is made as to the number of 200kHz frequency bands within such one or more blocks at step 40.

The method then proceeds either by way of processing chains 42, 44 or 46, dependent upon the number of 200kHz frequency bands found in the blocks.

This aspect of the present invention is particularly advantageous in that it employs the signal strength characteristic, or derivative thereof, to identify the width of the block of substantially common signal strength, in order to determine to which of a plurality of radio access technologies, the identified signal might belong.

In this manner, potentially wasteful attempts to connect to an incorrect and inappropriate radio access technology can be limited and even prevented altogether.

Again, at step 38 should no block of a plurality of 200kHz frequency bands be identified, standard camp-on procedures can then be pursued in which the 200kHz frequency bands are ranked in order of signal strength and the camp-on procedure attempted in accordance with radio access technology in turn.

As will be appreciated, the arrangement of Fig. 2 advantageously employs the realization that each radio access technology generally employs a fixed frequency band per channel and this frequency band generally varies between the technologies. Thus, as illustrated, it is possible to discern a WCDMA channel with a bandwidth of 5kHz, from a COMA 20001x channel with a bandwidth of 1.25kHz from a COMA 20003x channel with a bandwidth of 3. 75kHz, from a IS-136 channel with a bandwidth of 1.6kHz, from a GSM with a width of 200kHz and so on.

The present invention is particularly advantageous in accelerating the initial acquisition of network and also leading to power savings.

Turning now to Fig. 3, there is illustrated another aspect of present invention which also leads to improved efficiency for network acquisition. In situations where it is identified that two or more radio systems may be operating within the same frequency, this aspect of the present invention provides for a simultaneous dual RAT search which allows for potentially quick identification of the appropriate RAT than is currently employed.

Rather than searching each RAT in turn for a full range of ranked frequencies, this aspect of the present invention processes each of the ranked frequency signals the first for one of the RATs, and then for the other RAT, before moving on to a similar attempt for the next in the ranked signals.

Turning therefore in particular to Fig. 3, the mechanism again commences with a 200kHz raster scan of all available frequencies at step 50, which frequencies are then ranked at step 52 in accordance with the identified power levels of each of the 200kHz bands.

At step 52, the strongest of the ranked signals is selected and an attempt to camp on the network in accordance with that signal, in accordance with a first of a plurality of RATs is made at step 56.

If such an attempt to camp on this signal by means of the first RAT is found not to be successful at step 58, then the success of the attempt to camp on the other of the plurality of RATs at step 60 is determined at step 62.

As will be seen from Fig. 3, if either of the attempted camp-on's in accordance with the two RATs, is determined as being successful at steps 58, 62 respectively, then the device enters its idle mode at 64.

If, however, an attempt to camp on the first of the ranked signals in accordance with both of the RATs is not successful, then the method proceeds to step 66 where it is determined whether or not any of the ranked 200kHz signal bands remain for further camp-on attempts. If no such further frequency bands remain, then it is determined at step 68 that the device is out of coverage and the method returns to step 50 to repeat the initial 200kHz raster scan as and when appropriate.

However, if further signals within the ranked order remain, then the method proceeds via step 70 to step 56 to attempt a camp-on using the first RAT and then, as before, if that attempt is not successful, the mechanism requires an attempt in accordance with the second RAT before looking to the next signal in the ranked series of 200kHz bands.

It will therefore be appreciated that this aspect of the present invention is particularly advantageous in that, through conducting an attempt to camp-on all the different RATs in turn, for each of the ranked frequency signals identified from the initial 200kHz raster scan, then it is likely that a successful camp-on will be achieved in accordance with the appropriate RAT in a more time and power efficient manner than is currently achieved through known camp-on procedures.

Turning now to a further aspect of the present invention, the invention can advantageously employ the power distribution of frequency to establish the identity of a particular RAT that is being operated in a locality of the handset. By means of such efficient identification, the handset can then completed omit attempts to camp on to the signal in accordance with other RATs. It is by simple form, that this aspect of the present invention identifies that power distribution and determines the degree of uniformity of such power distribution over frequency.

The arrangement identifies that, in order to discern between two RATs, it will be possible to establish whether the uniformity of the power distribution is above or below a threshold level: the position above or below the threshold level thereby indicating which radio access technology should be employed.

For example WCDMA employs a relatively uniform power distribution such that, through analysing the power distribution and frequency, it will be possible to identify whether or not the signals received belong to the WCDMA radio systems. Alternatively, GSM signals are somewhat more random in their power distribution and so any random signals falling below the aforementioned threshold, can be identified as belonging to that second, for example GSM, radio access technology and an appropriate camp-on procedure can be pursued.

This aspect of the present invention provides for a particularly advantageous front-end to a search procedure since it can provide for a relatively efficient and speedy determination of the likely most appropriate radio access technology in respect of which the initial campon procedure should be conducted.

Fig. 4 provides a schematic illustration by way of a functional diagram of a cellular phone handset embodying the present invention. There is illustrated a handset 50 comprising GSM 52, WCDMA 54 and any other required radio sections 46 each of which is associated with respective antenna 58,62,66 and analogue digital conversation circuitry 60,64,68 which feed into common signal processing arrangement 70. In practice however, it should be appreciated that those radio hardware components may be shared between the different radio systems since, in example, only a single antenna may be employed.

As will be appreciated, the processing provided within 70 is arranged to be controlled so as to employ the measurement results in a manner achieving the functionality described hereinbefore.

Of course, it will be appreciated that the present invention can employ a combination of one or more of the above-mentioned procedures and mechanisms as required so as to provide for a particularly efficient, and yet quick, network search procedure and mechanism.

Claims

Claims 1. A network search method for use in a mobile radio communications

device seeking connection to a network of a first radio access technology and comprising scanning a plurality of frequency bands to determine a signal characteristic for each band, analysing the said characteristic for a plurality of said bands to identify a block of bands having a substantially uniform characteristic, and attempting to connect to the network at a frequency substantially at the centre of the said identified block of the frequency bands.
2. A method as claimed in Claim 1, and including the step of identifying a plurality of blocks and the further step of sorting the said blocks into a ranked order.
3. A method as claimed in Claim 2, and including the step of attempting to connect to the centre frequency of each of said blocks in accordance with the ranked order.
4. A method as claimed in Claim 1, 2 or 3, wherein the said characteristic comprises at least a derivative of signal strength.
5. A method as claimed in Claim 1, 2, 3 or 4, wherein if no suitable block of a plurality of bandwidths is identified, the method includes the step of searching for a network of another radio access technologies.
6. A mobile radio communications device arranged for connection to a network of a first radio access technology, and including means for scanning a plurality of frequency bands to determine a signal characteristic for each band, means for analysing the said characteristic for a plurality of bands to identify a block of bands having a substantially uniform characteristic, and means for connecting to the frequency substantially at the centre of the said identified block of frequency bands.
7. A device as claimed in Claim 6 and including means for identifying a plurality of blocks and for sorting the said blocks into a ranked order.
8. A device as claimed in Claim 7, and including attempting connection to the centre frequency of each of said blocks in accordance with the ranked order.
9. A device as claimed in Claim 5, 6, 7 or 8, wherein the said characteristic comprises at least a derivative of signal strength.
10 A device as claimed in Claim 6, 7, 8 or 9, and including means for searching for another radio access technology.
11. A network search method for use in mobile radio communications device arranged for connection to networks of at least two radio access technologies operating with at least partially overlapping frequency bands determining signal characteristics of the common frequency bands attempting to connect on a first of the plurality of bands in accordance with a first of the plurality of radio access technologies, and if the said attempt to connect to the first of the said plurality of bands in accordance with the first radio access technology fails, attempting to connect to the said first of the plurality of bands in accordance with a second of the plurality of radio access technologies, before attempting to correct to a second of the plurality of bands.
12. A method as claimed in Claim 11 and including the steps of attempting to connect to each of the plurality of frequency bands in turn for each radio access technology.
13. A method as claimed in Claim 11 or 12, and including the method of Claims 1, 2, 3, 4 or 5, for searching one of the radio access technologies.
14. A mobile radio communications device including means for connection to networks of at least two radio access technologies operating with at least partially overlapping frequency bands, means for determining a signal characteristic of the common frequency bands, means for connecting on a first of the plurality of bandwidths in accordance with a first of the plurality of radio access technologies, and if the said attempt to connect to the first of the said plurality of bands in accordance with the first radio access technology fails, the device being arranged to connect to the said first of the plurality of bands in accordance with a second of the plurality of radio access technologies, before attempting to connect to a second of the plurality of bands.
15. A device as claimed in Claim 14, and arranged to connect to each of the plurality of frequency bands in turn with each radio access technology.
16. A mobile radio communications device substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

16. A device as claimed in Claim 14 or 15, and combined with the device of Claims 6, 7, 8, 9 or 10.

17. A method as claimed in Claim 1, and forming part of a method of determining to which of a plurality of radio access technologies received network signals belong.

18. A method as claimed in Claim 17, and including identifying the radio access technology on the basis of the degree of variation of the characteristic with frequency.

19. A device as claimed in Claim 6, and including means for determining to which of a plurality of radio access technologies a received network signal belongs.

20. A device as claimed in Claim 19, and arranged to identify the radio access technology on the basis of the degree of variation of the characteristic with frequency.

21. A network search method for use in a mobile radio communications device and substantially as hereinbefore described with reference to, and as illustrated in Fig. 1, Fig. 2 and Fig. 3 of the accompanying drawings.

22. A mobile radio communications device substantially as hereinbefore described with reference to Fig. 1, Fig. 2 and Fig. 3 of the accompanying drawings.

Claims 1. A network search method for use in a mobile radio communications device seeking connection to a network of a first radio access technology and comprising scanning a plurality of frequency bands to determine a signal characteristic for each band, analysing the said characteristic for a plurality of said bands to identify a block of bands having a substantially uniform characteristic, and attempting to connect to the network at a frequency substantially at the centre of the said identified block of the frequency bands.

2. A method as claimed in Claim 1, and including the step of identifying a plurality of blocks and the further step of sorting the said blocks into a ranked order.

3. A method as claimed in Claim 2, and including the step of attempting to connect to the centre frequency of each of said blocks in accordance with the ranked order.

4. A method as claimed in Claim 1, 2 or 3, wherein the said characteristic comprises at least a derivative of signal strength.

5. A method as claimed in Claim 1, 2, 3 or 4, wherein if no suitable block of a plurality of bandwidths is identified, the method includes the step of searching for a network of another radio access technologies.

6. A mobile radio communications device arranged for connection to a network of a first radio access technology, and including means for scanning a plurality of frequency bands to determine a signal characteristic for each band, means for analysing the said characteristic for a plurality of bands to identify a block of bands having a substantially uniform characteristic, and ma means for connecting to the frequency substantially at the centre of the said identified block of frequency bands.

7. A device as claimed in Claim 6 and including means for identifying a plurality of blocks and for sorting the said blocks into a ranked order.

8. A device as claimed in Claim 7, and including attempting connection to the centre frequency of each of said blocks in accordance with the ranked order.

9. A device as claimed in Claim 5, 6, 7 or 8, wherein the said characteristic comprises at least a derivative of signal strength.

10 A device as claimed in Claim 6, 7, 8 or 9, and including means for searching for another radio access technology.

11. A method as claimed in Claim 1, and forming part of a method of determining to which of a plurality of radio access technologies received network signals belong.

12. A method as claimed in Claim 11, and including identifying the radio access technology on the basis of the degree of variation of the characteristic with frequency.

13. A device as claimed in Claim 6, and including means for determining to which of a plurality of radio access technologies a received network signal belongs. )3

14. A device as claimed in Claim 13, and arranged to identify the radio access technology on the basis of the degree of variation of the characteristic with frequency.

15. A network search method for use in a mobile radio communications device and substantially as hereinbefore described with reference to, and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.