Pulse or digital communications – Miscellaneous
Reexamination Certificate
2000-06-07
2004-11-16
Corrielus, Jean B. (Department: 2734)
Pulse or digital communications
Miscellaneous
C708S311000, C455S166100
Reexamination Certificate
active
06819731
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to British Application No. 9913154.2 filed 08 Jun. 1999.
BACKGROUND OF THE INVENTION
The invention to which this application relates is a method for undertaking a search for a carrier frequency especially, but not exclusively, in relation to digital tuners.
Conventionally the method for undertaking a frequency searching procedure on digital tuners follows the known steps of scanning the entire frequency range of the tuner, typically starting from the minimum frequency value through to the maximum frequency value.
This search reveals whether a lock, or signal, is detected and when a carrier frequency “lock” is detected, the corresponding parameters of the lock such as centre frequency and symbol rates are determined and stored. The search is continued through the frequency range for all the carrier frequencies in the range.
For Zero interference (IF) the frequency of the local oscillator can typically be within the tolerance of the carrier frequency and the symbol rate obtained corresponds to the flat region of the frequency response centred on the carrier frequency. When the carrier frequency is close to the incoming frequency, the carrier signal lies in the “pull-in” range of the PLL and the loop is phased locked.
In practice it is possible for this searching procedure, which is searching for frequency carriers in a digital tuner, to mistakenly lock to an analogue carrier which gives an incorrect reading, wastes time in the searching procedure and is inefficient. In addition to the above, a false lock can occur on digital carriers when phase lock has been detected but the correct control frequency has not been reached. This situation can occur in QPSK tuners for frequency offsets that are multiples of 1/4T where T is the QPSK symbol duration. Offsets that are not multiples of 1/4T are difficult to predict.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a method for searching which allows for the searching of digital carrier frequency locations in a frequency range in an efficient, timely manner.
In a first aspect of the invention there is provided a method for searching the frequency range of a device said method including the steps of estimating the initial starting frequency for a digital carrier by dynamic real-time pre-processing of the spectrum profile and then obtaining successive samples of the frequency range from the start position for the carrier until the centre frequency for the carrier is located.
Typically the start point estimation and search for the location for the centre frequency is repeated for each digital carrier in the frequency range.
The subsequent use of centre frequency estimation of each digital carrier by overall pattern analysis of their corresponding frequency response also allows a reduction in the search time as not all of the frequency range needs to be searched in a progressive manner as is currently the case.
The solution can be accomplished in one embodiment by employing general pattern recognition techniques, one example of which is Neurocomputing utilizing neural net techniques, that is, a computer architecture in which processing can learn by trail and error, in which the each apparatus and system is pre-programmed to be able to distinguish and reject analogue carrier frequencies which are found in, for example, digital tuners and subsequently estimate the local oscillator locking frequency for the digital carriers. The progressive frequency estimation is achieved by an overlapping windowing function in which the parameters in each overlapping window constitute a subset of the input vector to the system. It should however be clear that any suitable general pattern recognition techniques can be used as required.
The use of the successive samples allows intra-layer propagation of input parameters in each layer to develop an integrated representation of the spectral profile for the digital carrier.
By training the system to recognise and ignore analogue carrier profiles which tend to have a different profile than digital carriers, and then subsequently estimating the initial Local Osc. (LO) frequency for lock within the specified tolerance or very close estimation prior to the search routine and which estimation acts as the start point from which the search begins for each digital carrier, and which functions can be performed simultaneously, so the search can be performed more efficiently and quickly than with the conventional searches which progressively move through the frequency range.
In one embodiment the system can predict the centre frequency estimations of all digital carriers for respective channels and hence the start position for the search for each digital carrier, prior to the search commencing. Indeed, in one preferred embodiment there need not be search performed for those digital carriers where the estimated centre frequency value lies within the tolerances of the predesignated centre frequency value for that carrier.
The system of this invention therefore reduces the possibility of locking to analogue carriers, and has the potential of significantly reducing the time required to perform a search in comparison to the current digital carrier frequency “search & lock” procedure.
In an alternative embodiment a simpler technique can be utilised which involves the use of the estimated parameters in the process to refer to a table of information and, from that information the estimated digital carrier frequency value can be obtained. These tables of information are generally known as “look-up” tables.
In a further aspect of the invention there is provided a method for searching the frequency range of a digital data receiving device, said method including the steps of, estimating the initial starting frequency for a digital carrier in the range by dynamic real-time pre-processing of the spectrum profile and then locating the centre frequency for the carrier and identifying and disregarding analogue carrier frequencies in the range.
Typically by first distinguishing between analogue and digital carriers and ignoring or rejecting the analogue carriers so the time for the search of the frequency range can be considerably reduced.
REFERENCES:
patent: 5128625 (1992-07-01), Yatsuzuka et al.
patent: 5666062 (1997-09-01), Takahashi et al.
patent: 5699385 (1997-12-01), D'Sylva et al.
patent: 2000-134174 (2000-05-01), None
patent: WO 99/26339 (1999-05-01), None
Derwent Publication No. 200-393125, Derwent Week 200034, Orthogonal frequency division multiplex transmission system receiver for domestic broadcast system, has microprocessor to indicate detected frequency of analog carrier signal.
Corrielus Jean B.
Head Johnson & Kachigian
Pace Micro Technology Plc.
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