GB2481575A

GB2481575A - Improvements to reception of spread spectrum signals

Info

Publication number: GB2481575A
Application number: GB1010293.7A
Authority: GB
Inventors: Mahmoud Hadef
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2010-06-18
Filing date: 2010-06-18
Publication date: 2012-01-04
Also published as: GB201010293D0; KR20110138152A

Abstract

A spread spectrum signal having a first spreading code is detected by receiving signals comprising at least the spread spectrum signal and performing a correlation operation between the received signals and a composite code, the composite code comprising a superposition of at least the first spreading code and a second spreading code. Peaks of the correlation are detected, and at least one the peaks is identified that relates to the spread spectrum signal. The first spread spectrum signal is detected on the basis of the at least one identified peak. This has an advantage that a correspondence may be determined between a peak and a spreading code within the composite code, so that for example, a delay value associated with a peak may be used for the reception and decoding of a respective signal. This method improves the speed of acquisition of the spread signals in a satellite navigation system, i.e. improving the time to first fix, TTFF.

Description

improvements to Reception of Spread Spectrum Signals

Field of the Invention

The present invention relates generally to reception of spread spectrum signals in communications systems, and more specifically, but not exclusively, to a method and apparatus for improving speed of acquisition of spread spectrum signals in a satellite navigation system.

Background of the Invention

The use of spread spectrum signals is well known in communications systems. For example, spread spectrum signals, and in particular direct sequence spread spectrum signals, are commonly used in wireless systems such as satellite navigation systems, for example Global Positioning System (GPS), and in Code Division Multiple Access (CDMA) cellular wireless systems such as Universal Mobile Telecommunications System (UMTS) and IS-95.

A direct sequence spread spectrum signal is typically formed by multiplying a signal with a spreading code comprising a sequence of chips, each chip typically having a binary value representing, for example, a modulation phase state, and the sequence of binary values in the spreading code typically being a pre-determined pseudo-random sequence that is known to a receiver of the spread spectrum signal. The multiplication of the signal with the spreading code typically has the effect of spreading the spectrum of the original signal over a wider band. Several different signals may be spread to share the same wider band, allowing multiplexing of the signals in a Code Division Multiple Access system. On reception, each spread spectrum signal is typically detected by correlating received signals with the spreading code appropriate to the signal to be received. In order to do this, it is necessary to synchronise the relative timing, that is to say a relative delay value, of the spreading code used in the correlation process on reception with the respective incoming spread spectrum signal. In a satellite navigation system such as GPS, typically spread spectrum signals transmitted from each satellite or pseudo satellite will have a respective spreading code, and each spread spectrum signal has a respective delay value and also a frequency offset value, due typically to Doppler shift.

The process of determining a delay value, and also typically a frequency offset value for reception, that is to say detection, of a spread spectrum signal, is typically part of an acquisition process that may typically proceed via successive steps of coarse and fine acquisition. Acquisition may be aided by information, for example almanac and ephemeris information, relating to spreading codes, and the motion and position of satellites in a satellite navigation system.

However, in so-called cold start acquisition, no information (neither almanac nor ephemeris) about satellites in view may be available. A search has to be performed to establish the spreading codes for visible satellites. Typically reception proceeds in a blind manner where the receiver may have to scan all possible Pseudo Random Noise (PRN) spreading codes (typically 32 codes in the case of GPS) on a case by case basis, a correlation for each spreading code being performed at each possible delay value and frequency offset value. Such a process may be critically time consuming and may considerably reduce receiver sensitivity. In fact, acquiring weak signals, found in various scenarios such as indoor and urban areas may require lengthy time integration epochs and be vulnerable to interfering signals. Since neither the visible satellite PRN code nor the status of its signal (weak, medium or strong) is known the process can easily tend to an unacceptable time to first fix (TTFF).

it is an object of the present invention to ameliorate the problems of prior art systems.

Summary of the invention

in accordance with a first aspect of the present invention, there is provided a method of detecting a spread spectrum signal having a first spreading code, the method comprising: receiving signals comprising at least said spread spectrum signal; performing a correlation operation between the received signals and a composite code, the composite code comprising a superposition of at least the first spreading code and a second spreading code; detecting a plurality of peaks of the correlation; identifying at least one of said plurality of peaks that relates to said spread spectrum signal; and detecting the first spread spectrum signal on the basis of the at least one identified peak.

This has an advantage that a single composite code may be used for correlation with received signals that may comprise one or more signals having spreading codes that are components of the composite code, which may be of value, for example, if it is not be known which of the signals having spreading codes that are components of the composite code is expected. The correlation operation with the composite code may involve fewer operations and may therefore be performed more quickly than a separate correlation operation with each of the spreading codes that form the composite code.

Preferably, the method comprises: performing said correlation operation at least for a plurality of delay values, the delay values relating to a relative timing of the received signals with respect to the composite code and each detected peak having a corresponding delay value; selecting a first of said plurality of peaks; determining a first correlation value of a correlation between the received signals and the first spreading code for a first delay value corresponding to the first selected peak; and dependent on said determined first value of the correlation between the received signals and the first spreading code being greater than a threshold value, identifying the first selected peak as relating to said spread spectrum signal.

This has an advantage that a correspondence may be determined between a peak and a spreading code within the composite code, so that for example, a delay value associated with a peak may be used for the reception and decoding of a respective signal.

Preferably, the method comprises determining a second correlation value of a correlation between the received signals and the second spreading code for a first delay value corresponding to the first selected peak; and determining said threshold value as a proportion of a sum of at least said first and second correlation values.

This has an advantage that a reliable indication may be obtained that the first selected peak relates to said spread spectrum signal.

Preferably, the method comprises determining a respective correlation value of a correlation between the received signals and each spreading code that is a component of the composite code for a first delay value corresponding to the first selected peak; and determining said threshold value as a proportion of a sum of each respective correlation value.

This has an advantage that a higher degree of certainty may be obtained that the first selected peak relates to said spread spectrum signal and not to another spread spectrum signal or to a spurious correlation.

Preferably, the method comprises selecting a peak having the highest correlation value with the composite code of said plurality of peaks as said first of said plurality of peaks.

This has an advantage that a process of identifying peaks may be carried out efficiently, by identif,'ing peaks that are most likely to correspond to correlations with spread spectrum signals first. This also has an advantage of allowing identification of peaks corresponding to stronger signals first, so that these may be removed from the received signals in order to improve the detection of weaker peaks.

In an embodiment of the invention, the method comprises: dependent on said determined first value not being greater than the threshold value, selecting another of said plurality of peaks; determining another value of a correlation between the received signals and the first spreading code for a delay value corresponding to said another selected peak; and dependent on said another determined value being greater than the threshold value, identif'ing said another selected peak as relating to said spread spectrum signal.

Preferably, the method comprises selecting a peak having the highest correlation value with the composite code of said plurality of peaks that has not been previously selected as said another of said plurality of peaks.

In an embodiment of the invention, the received signals comprise at least a second spread spectrum signal having the second spreading code, the method comprising: identifying at least a further peak of said plurality of peaks that relates to the second spread spectrum signal; and detecting the second spread spectrum signal the basis of the at least one further identified peak.

This has an advantage of allowing peaks of two spread spectrum signals to be identified using a single composite code; this may involve less computation operations that performing a separate correlation operation for each code.

In an embodiment of the invention, the method comprises: determining a second value of a correlation between the received signals and the second spreading code for a delay value corresponding to the first selected peak; and dependent on said determined second value of the correlation between the received signals and the second spreading code being greater than a second threshold value and dependent on said determined second value being greater than said determined first value, identifying the first selected peak as the further peak relating to the second spread spectrum signal.

Preferably, the method comprises determining said second threshold value as a proportion of a sum of at least said first and second correlation values.

Preferably, the method comprises identifying the first selected peak as the further peak relating to the second spread spectrum signal in further dependence on said determined second value being greater than said determined first value by at least a margin value.

This has an advantage of increasing confidence that the first selected peak is the further peak relating to the second spread spectrum signal.

In an embodiment of the invention, the method comprises: performing said correlation operation at least for a plurality of frequency offset values, wherein each of said plurality of peaks has a corresponding frequency offset value; and determining a value of the correlation between the received signals and the first spreading code for a first frequency offset value corresponding to the first selected peak.

Preferably, the method further comprises: removing a spread spectrum signal relating to a previously identified peak from the received signals; and removing a spreading code relating to a previously identified peak from the composite code.

In an embodiment of the invention, said first and second codes are pseudo-random binary codes each comprising a succession of chips, each chip having either a positive or a negative state.

In an embodiment of the invention, the method comprises superposition of the first and second codes to form the composite code by addition of respective chips of the first and second codes, such that the composite code is a multi-level code.

Preferably, the superposition of the first and second codes to form a composite code is by addition of respective chips of the first and second codes and quantisation to a binary value for each chip, such that the composite code is a binary code.

In an embodiment of the invention, the method comprises detecting fewer peaks of the cross-correlation than the number of spreading codes comprising the composite code.

This has an advantage that implementation of a correlator may be simpler while maintaining acceptable performance.

In an embodiment of the invention, the composite code comprises a superposition of at least four spreading codes.

In an embodiment of the invention, the composite code comprises a superposition of a least eight spreading codes.

In an embodiment of the invention, the method comprises detecting five or fewer peaks of the cross-correlation.

In an embodiment of the invention, said spread spectrum signal is a navigation system signal.

In an embodiment of the invention, said spread spectrum signal is a navigation system signal is a Global Positioning System signal.

In an embodiment of the invention, said spread spectrum signal is a signal of a cellular radio communication system employing code division multiple access.

In accordance with a second aspect of the present invention, there is provided a spread spectrum receiver capable of detecting a spread spectrum signal having a first spreading code, the receiver being arranged to: receive signals comprising at least said spread spectrum signal; perform a correlation operation between the received signals and a composite code, the composite code comprising a superposition of at least the first spreading code and a second spreading code; detect a plurality of peaks of the correlation; identify at least one of said plurality of peaks that relates to said spread spectrum signal; and detect the first spread spectrum signal on the basis of at least the identified peak.

Further features and advantages of the invention will be apparent from the following description of preferred embodiments of the invention, which are given by way of example only.

Brief Description of the Drawings

Figure 1 is a schematic diagram illustrating signal flow in an embodiment of the invention; Figure 2 is a flow chart illustrating an acquisition process in an embodiment of the invention; Figure 3 is a flow chart illustrating estimation of a contribution of a code to a correlation result according to an embodiment of the invention; and Figure 4 is a graph showing correlation results as a function of code delay and frequency according to an embodiment of the invention.

Detailed Description of the Invention

By way of example an embodiment of the invention will now be described in the context of a satellite navigation system, and in particular a GPS system (Global Positioning System). However, it will be understood that this is by way of example only and that other embodiments may involve other spread spectrum communication systems, such as for example cellular radio systems using Code Division Multiple Access (CDMA).

The embodiment relates to a method of speeding up a cold start acquisition process in a GPS receiver; this may also increase the receiver sensitivity.

Figure 1 shows signal flow in a receiver during an acquisition process according to this embodiment of the invention, as part of a process of detection of spread spectrum signals. Signals are received comprising spread spectrum satellite signals and converted to Inphase (I) and Quadrature (Q) components 2.

A correlation operation is performed between the components of the received signals and a composite code, the composite code comprising a superposition of spreading codes for several satellites. This correlation operation with the composite code is performed instead of performing a separate correlation operation for the code for each spread spectrum satellite signal, as would be done conventionally. The correlation operation with the composite code will typically produce several correlation peaks; these may be produced by a correlation between a received spread spectrum signal and one of the spreading codes in the composite code, or they may be spurious cross-correlations or due to interference. Peaks of the correlation having at least a given value are detected, and the peaks are then identified as to which, if any, spread spectrum signal they correspond to.

The correlation operation may be performed for a succession of relative timing relationships between the composite code used in the correlation and the received signal, that is to say for a succession of delay values. The correlation operation may typically also be performed for a succession of Doppler frequency offset values for each delay value.

Each detected peak may be identified by performing a separate correlation with each of the spreading codes in the composite code; if the correlation is greater than a threshold value the peak may be identified as relating to the signal having that spreading code. The threshold value may be expressed as a proportion of a sum of values of a correlation between the received signals and each spreading code that is a component of the composite code. This correlation with each separate spreading code need only be performed at the delay value and frequency offset value corresponding to the peak. So, it can be seen that fewer operations are typically involved in a process, according to an embodiment of the invention, involving correlating with a composite code for each possible delay and frequency offset value, and then correlating with individual spreading codes at only the delay and frequency offset values corresponding to detected peaks, than would be involved in a conventional process of separately correlating for each possible delay and frequency offset value of each individual spreading code in turn.

In searching through the detected peaks, typically the peak having the highest correlation value is selected first for identification by correlation with the individual spreading codes. Each peak in turn is then selected, typically in order of diminishing correlation value. This process may be continued until each of the spreading codes in the composite code has been associated with a peak, or until sufficient spread spectrum signals have been associated with peaks for the purposes of the receiver; this may be fewer than the number of spreading codes comprising the composite code.

Once a spreading code has been identified as relating to a detected peak, that code may be removed from the composite code. Furthermore, the signal relating to that code may be removed from, or reduced in, the incoming signals.

This may be achieved by regeneration of the signal and subtraction from the incoming signals. This may reduce spurious cross-correlations, especially if the removed or reduced signal is greater in magnitude than signals that remain to be identified.

Regarding the formation of the composite code, this may be formed by superposition of the individual spread spectrum codes of the composite code by addition of respective chips of the codes. Each chip may typically have a positive or negative state, so that in a bi-phase modulated code, the state would typically correspond to zero or 180 degrees phase, which may be represented by I or-I Addition of respective chips may then produce a multi-level code. For example, the addition of two codes would allow the states 2, 0 and -2 in the composite codes (note that the scale factor is arbitrary). The composite code would thus have both phase and amplitude modulated components. The phase and amplitude components may be used in the correlation with the incoming signal.

However, it may be advantageous in terms of simplicity of implementation to add the respective chips of the codes forming the composite code and then quantise the result to a binary value for each chip, so that the composite code is a binary code. This may be simpler in terms of hardware implementation and yet offer acceptable performance.

It has been found that it is particularly advantageous to use at least four spreading codes in the composite code, and preferably eight or more. In the particular case of a composite code comprising at least eight spreading codes, it has been found that detecting five or fewer peaks of the cross-correlation is particularly advantageous.

An embodiment of the invention will be described in more detail as follows, by reference to Figure 2; this is flow diagram an acquisition process in an embodiment of the invention, relating to the use of a set of spreading codes combined in a composite code, as previously mentioned. This process may be referred to as cluster acquisition, or cluster scan, the cluster relating to the set of spreading codes combined in a composite code. The main steps of a cluster scan process according to the embodiment of the invention as illustrated in figure 2 are as follows.

Firstly, the 32 GPS PRN codes are arranged in M clusters. Each cluster includes L different GPS codes. It should be noted that typically the more satellites are gathered in one cluster the faster is the acquisition achieved, but the lower the likelihood to detect all visible satellites. The latter effect is due to the accumulation of cross correlations and to the strong to weak signals interferences. A particularly advantageous trade off for this process, that may be referred to as repartition, is to provide 4 clusters with 8 satellites each.

Secondly, a representative composite code is generated Cm of each cluster m (ml, 2.. .M). The code is the sum (binary or decimal) of all PRN codes which constitute the cluster. The process 4 of generating this code is shown in Figure 1. The binary addition is more efficient in terms of implementation but produces more noisy acquisition output than the decimal, that is to say multi-level, one.

Then, a two dimensional (2D) acquisition process, as shown in Figure 1, is carried out for each representative composite code Cm. The dimensions are S typically time, that is to say delay value implemented by delay line 6, and frequency, typically Doppler frequency offset, implemented by estimated Doppler generation 8. For each delay and Doppler frequency offset value, an integrate and dump function 10 is performed to produce a correlation value. In total only M acquisition searches are performed instead of 32 compared to the conventional cold start search. The received IQ data is correlated first with delayed version of the code Cm then compensated with an estimated Doppler frequency. Finally, the outcome is integrated and dumped over the whole coherent time integration epoch. Typically, this procedure may be carried out over all possible code delays and estimated Doppler frequencies.

The first K maxima are selected from the 2D search outcome. A potential choice of K is the number of PRN codes forming the cluster (L).

However, considering the fact that the number of GPS satellites in view at any time on average is around 10 satellites, smaller values of K can be used. For example in case of L=8 only 5 maxima could be picked up to cover all visible satellites on this cluster.

The selected peaks do not necessarily correspond to visible satellite autocorrelations; instead it could be caused by an accumulation of cross correlations of other PRN codes or strong signal interference. So it is necessary to identify whether these peaks are due to the presence of a signal, and if this is the case which PRN is responsible.

Contributions of PRN codes forming the cluster on each peak value are then calculated. Figure 3 presents the procedure of calculating these contributions. After obtaining contributions, the percentage contk,I is calculated then the maximum percentage rnax(cont) is identified. The decision of whether the signal is available or not may be made based on max(cont). If it is larger than a chosen threshold, A, the signal is considered available. From simulation testing a particularly advantageous value for threshold A, in terms of a percentage contribution to a sum of correlations, is around 75% for L=8. If the condition is fulfilled a further fine basic acquisition confirmation is carried out.

If successful the satellite PRN which produces the maximum contribution is declared as detected and the number of detected satellites n is incremented by one. Note that the minimum number of satellites required for a three dimensional (3D) mode fix is typically 4.

Finally, after the whole scan is accomplished and if less than 4 satellites have been detected the already acquired signals are removed from the EQ data input. Then the scan process is repeated with already detected PRNs removed from the list.

To summarise, Figure 1 shows the generation process of the cluster code Cm and the corresponding 2D acquisition search and Figure 3 demonstrates the procedure of calculating the contribution of each satellite PRN on the selected peak.

Embodiments of the invention could be implemented for CDMA acquisition in general, where, conventionally, a set of PRN codes have to be searched sequentially.

So, it may be seen that embodiments of the invention use a combined code, that is to say a composite code, which represents a set of PRN codes of different satellites. The cluster scan covers a set of PRN codes to detect, in one correlation process, several peaks instead of one and save valuable time in processing. Accordingly, a search window may be used to gain valuable information regarding a set of satellites that may not be available using conventional acquisition techniques. Even though interference of strong signals can conventionally embed the weak ones and make them potentially invisible, the search according to an embodiment of the invention may result in useful data which can be used to extract the weak signals with extra processing by removing the strong signals.

The scan of a cluster may require little or no extra processing cost compared to the procedure of acquiring one satellite, so that the cluster scan method could provide a cold start fix potentially L times faster than the conventional method.

Results that have been obtained from GPS radio frequency data captured from a roof antenna and processed according to an embodiment of the invention.

Two cold start acquisitions were performed using conventional method in a first search (not shown in figure 4) and a cluster scan according to an embodiment of the invention in a second search. The same integration configuration (8ms coherent integration and 4 non-coherent accumulations) were used in both searches.

Four clusters were generated where each set includes 8 satellites. Figure 4 shows the 20 search output from the 2nd cluster scan which includes four visible satellites. As can be seen from Figure 4 that four clear peaks have obtained from only one search output. The peaks coordinates have been confirmed after they have been compared with the conventional search results.

This illustrates that that the cluster scan has managed to acquire four satellites (minimum requirement for 3D fix) in one operation instead of 8 separate searches with the same configuration settings. This means around 8 times faster process than conventional acquisition search has been achieved The above embodiments are to be understood as illustrative examples of the invention, it is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

Claims 1. A method of detecting a spread spectrum signal having a first spreading code, the method comprising: receiving signals comprising at least said spread spectrum signal; performing a correlation operation between the received signals and a composite code, the composite code comprising a superposition of at least the first spreading code and a second spreading code; detecting a plurality of peaks of the correlation; identifying at least one of said plurality of peaks that relates to said spread spectrum signal; and detecting the first spread spectrum signal on the basis of the at least one identified peak.
2. A method according to claim 1, comprising: performing said correlation operation at least for a plurality of delay values, the delay values relating to a relative timing of the received signals with respect to the composite code and each detected peak having a corresponding delay value; selecting a first of said plurality of peaks; determining a first correlation value of a correlation between the received signals and the first spreading code for a first delay value corresponding to the first selected peak; and dependent on said determined first value of the correlation between the received signals and the first spreading code being greater than a threshold value, identifying the first selected peak as relating to said spread spectrum signal.
3. A method according to claim 2, the method comprising: determining a second correlation value of a correlation between the received signals and the second spreading code for a first delay value corresponding to the first selected peak; and determining said threshold value as a proportion of a sum of at least said first and second correlation values.
4. A method according to claim 3, determining a respective correlation value of a correlation between the received signals and each spreading code that is a component of the composite code for a first delay value corresponding to the first selected peak; and determining said threshold value as a proportion of a sum of each respective correlation value.
5. A method according to any of claims 2 to 4, comprising selecting a peak having the highest correlation value with the composite code of said plurality of peaks as said first of said plurality of peaks.
6. A method according to any of claims 2 to 5, comprising: dependent on said determined first correlation value not being greater than the threshold value, selecting another of said plurality of peaks; determining another correlation value of a correlation between the received signals and the first spreading code for a delay value corresponding to said another selected peak; and dependent on said another determined correlation value being greater than the threshold value, identifying said another selected peak as relating to said spread spectrum signal.
7. A method of claim 6, comprising selecting a peak having the highest correlation value with the composite code of said plurality of peaks that has not been previously selected as said another of said plurality of peaks.
8. A method according to any of claims 2 to 7, wherein the received signals comprise at least a second spread spectrum signal having the second spreading code, the method comprising: identifying at least a further peak of said plurality of peaks that relates to the second spread spectrum signal; and detecting the second spread spectrum signal the basis of the at least one further identified peak.
9. A method according to claim 8, comprising: determining a second value of a correlation between the received signals and the second spreading code for a delay value corresponding to the first selected peak; and dependent on said determined second value of the correlation between the received signals and the second spreading code being greater than a second threshold value and dependent on said determined second value being greater than said determined first value, identifying the first selected peak as the further peak relating to the second spread spectrum signal.
10. A method according to claim 9, comprising determining said second threshold value as a proportion of a sum of at least said first and second correlation values.
11. A method according to claim 9 or claim 10. comprising identifying the first selected peak as the further peak relating to the second spread spectrum signal in further dependence on said determined second value being greater than said determined first value by at least a margin value.
12. A method according to any preceding claim, comprising; performing said correlation operation at least for a plurality of frequency offset values, wherein each of said plurality of peaks has a corresponding frequency offset value; and determining a value of the correlation between the received signals and the first spreading code for a first frequency offset value corresponding to the first selected peak.
13. A method according to any preceding claim, the method further comprising: removing a spread spectrum signal relating to a previously identified peak from the received signals; and removing a spreading code relating to a previously identified peak from the composite code.
14. A method according to any preceding claim, wherein said first and second codes are pseudo-random binary codes each comprising a succession of chips, each chip having either a positive or a negative state.
15. A method according to claim 14, wherein the method comprises superposition of the first and second codes to form the composite code by addition of respective chips of the first and second codes, such that the composite code is a multi-level code.
16. A method according to claim 14, wherein the superposition of the first and second codes to form a composite code is by addition of respective chips of the first and second codes and quantisation to a binary value for each chip, such that the composite code is a binary code.
17. A method according to any preceding claim, comprising detecting fewer peaks of the cross-correlation than the number of spreading codes comprising the composite code.
18. A method according to any preceding claim wherein the composite code comprises a superposition of at least four spreading codes.
19. A method according to any preceding claim wherein the composite code comprises a superposition of a least eight spreading codes.
20. A method according to claim 19, comprising detecting five or fewer peaks of the cross-correlation.
21. A method according to any preceding claim, wherein said spread spectrum signal is a navigation system signal.
22. A method according to claim 21, wherein said spread spectrum signal is a navigation system signal is a Global Positioning System signal.
23. A method according to any one of claim I to claim 20, wherein said spread spectrum signal is a signal of a cellular radio communication system employing code division multiple access.
24. A spread spectrum receiver capable of detecting a spread spectrum signal having a first spreading code, the receiver being arranged to: receive signals comprising at least said spread spectrum signal; perform a correlation operation between the received signals and a composite code, the composite code comprising a superposition of at least the first spreading code and a second spreading code; detect a plurality of peaks of the correlation; identify at least one of said plurality of peaks that relates to said spread spectrum signal; and detect the first spread spectrum signal on the basis of at least the identified peak.*::r: INTELLECTUAL . ... PROPERTY OFFICE Application No: GB 1010293.7 Examiner: Mr Huw Thomas Claims searched: 1-24 Date of search: 22 October 2010 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X latleast JP2003032144A (YAMADA) -See figures and EPODOC abstract.X latleast. JP07280914A (OKADA) -See figures and EPODOC abstract.A --GB2391779A (FUJITSU) -See figures 3-4, abstract and pages 19-23.A --US2008/169980 Al (UNDERBRINK) -See abstract.A --US6772065 B2 (SANMIYA) -See abstract.A --US7403583B1 (BRUENING) -See figures and abstract.Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO & US patent documents classified in the following areas of the UKCX: Worldwide search of patent documents classified in the following areas of the IPC GO1S; HO4B The following online and other databases have been used in the preparation of this search report EPODOC, WPI.Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk *.:r: INTELLECTUAL . ... PROPERTY OFFICE International Classification: Subclass Subgroup Valid From HO4B 0001/707 01/01/2006 GO1S 0019/30 01/01/2010 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk