Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Particular function performed
Patent
1997-05-28
1999-11-16
Malzahn, David H.
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Particular function performed
G06F 1710
Patent
active
059874856
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to adaptive digital filters, in particular for use in radio receivers.
Conventional adaptive digital filters are known, for example, from digital signal processing by E C Ifeachor and D W Jervis, 1993 Addison-Wesley Publishers Limited. These filters suffer the disadvantage that filter coefficients are all updated and stored before use in modulating received data samples. This procedure necessarily involves writing the coefficients to memory and reading all the coefficients from memory before filtering. This makes the adaptive filter relatively slow, or requires additional circuitry for the separate up-dating of coefficients.
The present invention is defined in the claims to which reference should now be made.
The present invention provides a method of adaptive digital filtering comprising first steps each of adapting a filter coefficient dependent on a received data sample, and second steps each of applying an adapted filter coefficient to a received data sample, in which the first and second steps are timed such that adapted filter coefficients and modulated data samples are alternatively determined. In consequence, each adapted filter coefficient can be provided for immediate use in filtering without needing to be held in a memory.
Coefficients are adapted according to an error derived from a previous filtering operation for use in the next filtering operation. Each filtering operation is on successively later received data samples.
The present invention also provides an adaptive digital filter comprising filter means and adaptive means, the adaptive means being operative to adapt a filter coefficient to provide an adapted coefficient, the filter means being operative to apply an adaptive filter coefficient to a received data sample, the operation of the filter means and adaptive means being timed such that adaptive filter coefficients and modulated data samples are alternately provided. In this way, an adapted filter coefficient may be read into the filter means one clock cycle after having been determined. An adapted filter coefficient can, at a predetermined time, both be read by the filter means and written to a memory for later use.
The present invention also provides a receiver including a novel adaptive digital filter as outlined above. The receiver could be for radio or telecommunications, in particular for time division multiplex (TDM) and/or Time division multiple access (TDMA) communications. The receiver can be a base station receiving TDMA communications from subscriber units which can be at fixed locations.
The present invention also relates to corresponding methods of radio reception.
The present invention preferably provides the advantage of increased data throughput through simple adaptive digital filters.
A preferred embodiment of the present invention will now be described by way of example and with reference to the drawings in which:
FIG. 1 is a simple block diagram illustrating an adaptive filter; and
FIG. 2 is a block diagram of an adaptive filter according to the present invention.
As shown in FIG. 1, an adaptive filter 1 comprises a digital filter 2 connected with adaptive means 4. Data samples D are received and applied to the digital filter 2 and a filtered output signal FIR.sub.result is provided. The previous filter coefficients C.sub.n applied by the filter 2 are adapted, i.e. updated, dependent on an error E which is the difference between received and expected filter outputs FIR.sub.result to provide adapted filter coefficients C.sub.n '. These adapted coefficients C.sub.n ' are applied to filter out any systematic errors received in data samples D. The filter 2, which is a multi-tap (e.g. 8-tap) filter, acts to provide an output FIR.sub.result according to the equation ##EQU1## where C.sub.n ' are the updated filter coefficients and D.sub.N+n+2 are the data samples, N denoting the first data sample in the combined adaption and filtering process.
The filter acts in response to a complex error signal E where the error E is deduced as follows:
Th
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Jin Yun Zhang et al, "Realization and Implementation of Adaptive State-Space Recursive Filters", pp. 956-959, IEEE, 1989.
Ionica International Limited
Malzahn David H.
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