Title of Invention

METHOD AND APPARATUS FOR BANDWIDTH ESTIMATION

Abstract

A computationally efficient method and apparatus for estimating the bandwidth of a received signal. In an exemplary implementation, signal power within several selectably narrow frequency bands, each centered about a selected frequency, are calculated using only a relatively small number of arithmetic operations. Applications include using the estimated bandwidth to estimate the relative velocity between the transmitter and receiver, and modifying receiver operation based on such estimate. 1. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating each of at least a subset of the plurality of coefficients includes rotating another of the plurality of coefficients by the generating value, each of at least a subset of the plurality of coefficients is generated from the previously generated coefficient; and obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; and estimating a bandwidth of the received signal based on the power measure.

Full Text

METHOD AND APPARATUS FOR BANDWIDTH ESTIMATION BACKGROUND OF THE INVENTION 1. Related Applications [0001] The present application claims priority to U.S. Provisional Application Number 60/296,028, filed June 5, 2001. 2. FIeld of the Invention [0002] The present invention relates to wireless communications. More specifically, the present invention relates to signal reception. 3. Background information [0003] A system for mobile wireless communications may support communications between a base station and a mobile unit even when the motile unit is in, motion. For example, a system for cellular telephony may support communications even when the mobile unit is moving at a high rate of speed, such as in an automobile or on a train. [0004] Relative movement between a mobile unit: and a base station in communication may affect the characteristics of the transmission channel betw'een them, however. Specifically, this relative movement may give rise to a Doppler frequency shift that results in a spreading of the transmitted signal at the receiver. The Doppler effect may be illustrated graphically by comparing spectral plots, of a transmitted signal at the transmitter and at the receiver. For example, a pilot signal of a code-division multiple-access (CDMA) system (before pseudonoise (PN) spreading and transmission by a base station) may have a delta-function magnitude spectrum as shown in FIGURE lA. As a result of the Dopplcr effect, the spectrum of the signal as received (and after PN despreading) by a mobile unit in motion may be spread as shown in the magnitude spectrum of FIGURE IB, The bandwidth of the spreading is a function of the carrier frequency and of the relative velocity, as described by the following expression: /.=/c- (1) c whereFd is the Doppler frequency,fc is the carrier frequency, c is the speed of light, and v is the relative velocity. Expression (1) demonstrates that the bandwidth of the Doppler spreading is dependent on (and increases with) the relative velocity. In a system for- mobile wireless communications, the perc:eivedl relative velocity may be expected to change constantly. Additional discussion of the Doppler effect in wireless communications may be found in Microwave Mobile Communications, W.C. Jakes, ed., 1974 (reprinted 1994 by IEEE Pres3, Pisc;ataway, NJ) and Wireless Communications, T.S. Rappaport, Prentice- Hall, 1996. [0005] Bandwidth spreading as caused by the Doppler effect may create inaccuracies in a signal as received. Information relating to Doppler spreading of a signal may be applied within a receiver to improve reception of the spread signal (and possibly of other signals received over the same path). Unfortunately, existing methods fox bandwidth estimation are too inefficient for practi;ca]l application. What is needed is a method and apparatus to efficiently obitain a bandwidth estimate. SUMMARY [0006] A method according to an embodiment of the invention includes generating filter coefficients from a generating value, obtaining a power measure of a received signal with respect to a selected frequency, and estimating a bandwidth of the received signal based on the power measure. In obtaining; the power measure, a method includes multiplying samples of the received signal with the filter coefficients. In related embodiments, generating filter coefficients includes rotating a filter coefficient by the generating value. A method according to anothex embodiment of the invention includes obtaining; power measures of a received signal, each corresponding to a selected frequency, and estimating a bandwidth of the received signal based on the power measures. [(MDi07] A method according to another embodiment of the invention includes noiiuniformly sampling a frequency spectrum of a received signal, determiining power measures of the received signal at the sampling frecquency and obtaining an estimate of the bandwidtli of the signal based on the power measures.. In related embodiments, nonunifoimly sampling the frecquency spectrum includes filtering the received signal with filters centered at the selected sampling frequencies. [0008] A filter according to an embodiment of the invention includes a lookup table to store generating values, a first multiplier to receive a generating value and a current filter coefficient and to output a subsequent filter coeflicient, an accumulator to store the subsequent filter coefficient, a second multiplier to multiply the current filter coefficient with a sample of a received signal and to output a current filtered value, and an adder to receive the current and past filtered values and to output an accumulation signal. In related embodiments, a filter includes a power calculator to output a power measure based on a value of the accumulation signal. [0009] A system according to an embodiment of the invention includes a lookup table to store generating values, filters to output power measures, and a bandwidth estimator to output an estimate of the bandwidth of a received signal. ID related embodiments, the bandwidth estimator compares a relation between two or more power measures to a predetermined threshold and/or modifies one or more power measures based on a power measure conesponding to a frequency outside an expected bandwidth of the received signal. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIGURE. 1 is a diagram showing magnitude spectra of a signal as transmitted and as received. [0011] FIGURE 2 is a diagram showing a magnitude spectrum of a signal as received and the frequency sampling points of an eight-point discrete Fourier transform. [00121 FIGURE 3 is a diagram showing an application of a method according to an embodiment of the invention. [0013;| FIGURE 4 is a block diagram of a filter 100 according to an embodiment of the invention, [0014] FIGURE 5 is a block diagram of a structure suitable for accumulator 130 and/or 160 of filter 100. [0015] FIGURE 6 is a block diagram of a further implementation 300 of a filter 100 according to an embodiment of the invention. [0016] FIGURE 7 is a block diagram of a system 400 according to an embodiment of the invention. [0017] FIGURE 8 is a ;flowchart of a method according to an embodiment of the invention. [0018] FIGURE 9 is a flowchart of a method according to another embodiment of the invention. [00190 FIGURE l0A and l0B are flowcharts of a method according to another embodiment of the invention. [0020] FIGURE 11 is a block diagram of a further implementation 200 of a filter 100 according to an embodiment of the invention. [00.21] FIGURE 12 is a diagram showing an application of a method according to an embodiment of the invention. DETAILED DESCRIPTION [0022] In, situations where Doppler spreading may occur, a receiver may achieve better performance if it is configured to account for the current relative velocity between the transmitter and the receiver. For example, the receiver rnay' perform filtering and/or other operation according to parameters whose optimal values may change according to the relative velocity. Even in a case where Doppler spreading is taken into account, the values assigned to these parameters may be based on statistical models that correspond to one or more fixed: velocity. While this approach may yield good results when the actual relative velocity is close co a modeled velocity, it may not yield acceptable results when the relative velocity is far from a modeled velocity. [0023] Expression (1) above describes the relation between Doppler spreading bandwidth and relative velocity. As described herein, methods and apparatus for bandwidth estimation according to certain embodiments of the invention may be applied to support better receiver performance in situations » while Doppler spreading may occur. Once a bandwidth estimate is obtained, for example, demodulator performance may be improved in a system for mobile wireless communications {such as a system for cellular telephony) by tuning parameter such as filter coefficients to the corresponding velocity. In a particular example, demodulator performance may be improved in a CDMA system by tuning the coefficients of a pilot filter to correspond to the current relative velocity. A.dditional applications for bandwidth estimation as performed by methods and apparatus according to embodiments of the invention are. also possible: for example, to modify the passband of a filter to include more signal energy and/or to exclude mone noise energy. [0024] It is possible to estimate signal bandwidth by obtaining a spectrum of the received signal and determining the frequency at which signal power drops below a predetermined threshold. A spectrum of a sampled received signal may be obtained by applying an iV-point discrete Fourier transform (DFT) to a string of N consecutive samples: where p„ denotes the samples of the received signal and Xk denotes the signal power at the; discrete frequency k. [0'025] FIGURE 2 illustrates the spectrum of a received signal as obtained by applying an 8-point DFT (i.e. N = 8) to the signal (as sampled at a sampling frequency. In this case, the spectrum is presented as a magnitude spectrum for each of the two components (I and Q) of the complex received signal S10. Note that the spectrum of this illustration is derived from only eight samples, with a resulting resolution in frequency of onlyF/8. To obtain meaning ful results for a practical application, a much greater sample set and/or a much more narrow resolution may be required, with correspondingly larger computation demands.. For a sampling rate of 4800 samples/second, a 300-point D'FT would be required to achieve a resolution of 16 Hertz (corresponding to, for example, approximately five miles per hour at a carrier frecuency of 1 GHz). Although fast Fourier transform (FFT) techniques may be used to efficiently calculate a 2'-pDint DFT (for positive integer x), this computationally intensive task would still require a large amount of processing capacity for sizable values of 2x. Such a method may be impractical for real-time portable applications such as mobile wireless communications. [0026] Rather than a spectrum that is umformly sampled in frequency as produced by a DFT or FFT, it may be desirable to obtain a spectrum of a received signal that is nonuniformly sampled in frequency. For example, the bandwidth of the received signal may be known to some extent (e.g. from ■ recent observation),- and it may only be necessary to consider the received signal power at frequencies within a relatively narrow window. Narrowing of the search domain (e.g. through application of such information) may considerably reduce the amount of computation required for practical bandwidth estimation. [0027'.| In a method according to one embodiment of the invention, the calculation of expresion (2) above: is performed only for m selected values of frequency k, where m is substantially less than N. In other words, the received signal is filtered with m filters, eac;h centered about a frequency k and having an output Hk defined as follows: [0*328] In an exemplary application where /, - 4800 Hertz and iV = 4800, a VEiJlue of m = 4 may provide good results, althiough the scope of the invention indudes any ratio of ^ to A^ and any value of m that provides a computation advantage over computing', the entire N-pointDFT using a FFT technique. The m selected frequencies may be consecutive (as illustrated in FIG'URE 3 lor m = 3 and N = 8) and/or separated from one another. For example, it may be desirable to choose at least one frequency to be outside the expected bandwith of the signal (e.g. at frequency -n) in order to provide an estimate of the background noise power. It may be desired to select the m frequencies cm only one side of the spectrum (as shown in FIGURE 3) or on both sides (e.g. to estimate both bounds of an asymmetrical bandwidth). . [0029] In some cases, bandwidth estimates from only one multipath sigrial msiy be sufficient to support determination of a Doppler frequency that is ajjplicaible to multiple code channels and/or to signals iirriving over dift'erent paths. In a mssthod according to a further embodiment of the invention, improvecl performance may be achieved by combining bandwidth estimates from signals :arriving over different paths and/or carrier frequencies. [0iO3O] WTiile FFT techniques may be used to efficiently calculate an entire N-point spectrum, they are not generally applicable to calculation of m filter output Hk as described above. Because of the unavailability of these optimizations, calculation of these filter outputs may be computationally expsnsive, In a method according to another implementation of the invention, the computational complexity of the filters is reduced. We rewrite expression (3) above as where the constant tenn Ak denotes 2πk/N. Each coefficient of this finite- impolse-reaponse filter is a phase vector with unit magnitude and a phase angle of-(2πklN). Note that we may expand expression (4) as follows: Many other methods of deteraiining the Doppler frequency of the received sigr al from the power values are possible. [0038] Once the Doppler frequency fd has been estimated, the relative velocity may be estimated by applying expression (1) above. As noted herein, the receive may then apply appropriate modifications to velocity-dependent parameter in order to increase the performance of the receiver. For cases in which only one or only a few carrier frequencies fc are used, it may be convenient to store the conversion off^ to relative velocit;^ v in a lookup table. [0039.1 FIGURE 8 shows a flowchart of a method according to an emtodiment of the invention. Task P110 nonuniformly samples a spectrum of a received signal at selected frequencies. Task P120 determines power measures of the received signal relative to the selected frequencies. Task P130 estimates a bandwidth of the received signal based on the power measures. [0040] FIGURE 9 shows a flowchart of a method according to another embodiment of the invention. Task P210 receives a generating value. Task P220 generates filter coefficients from the generating value. Task P230 obtains a power measure of a received signal with respect to a selected frequency (which frequency may be established by the generating value). Task P130 estimates a bandwidth of the received signal based on the power measures. [0041] FIGURES l0A and l0B show flowcharts of a method according to another embodiment of the invention. Task P232 obtains power "■ .... t' measures of a received signal, each power measure corresponding to a selected frequency. Task P132 estimates a bandwidth of the received signal based on the power rneasures. ,is shown in FIGURE lOB, task P232 may include an arbitrary number of subtasks P240i, each including a task P210i that receives a generating value, a task P220i that generates filter coefficients from the generating value, and a task P260i that multiplies each of the filter coefficients with a corresponding sample of the received signal. [0042] In a method according to a further embodiment of the invention, one or mors windowing functions are applied to modify one or more of the m filters, to a particular example, a rectangular window of width L This. particulur v/indowing function results in a substitution of L for N in the summationindex, further reducing the computational complexity of the filter and also reducing the size of the sample set required to obtain each filter output value from N to L. For an exemplary implementation in which N = 48(N), L T.3.ay have a vaJlue in the neighborhood of A7:2 or N/4. Computational advantages may be gained in particular applications by choosing L to be an inte:ger power of two. This expression demonstrates that as L decreases, the width of the main lobe of the filter's response increases. It may be desirable to use more than one value of L among the m filters, although it should be noted that the resulting difference in the filters' frequency responses may have the effect of malcing their outputs not strictly comparable (although compensation before comparison is possible). [1044] In another method according to an embodiment of the invention., bandwidth estimation is performed in more than one stage, with different values of L, k, and/or m being used for the filters at each stage. In one two-stage example, a larger value of L, a smaller value of m, and more closely spaced values of k is used at the second stage, the values of k being selected within a narrow window of interest as indicated by the outputs of the filters of the first stage. [00415] Each of the coefficients of the filters described in expressions (5) ;md (8) has a unit magnitude. Other windowing functions may be applied that remove this property (e.g. triangular, Hanning, Hamming). FIGURE 8 shows a block diagram of an implementation 200 of filter 100 that includes a lookup table 240 configured to store the coefficients of the windowing function and a multiplier 250 to scale the filter coefficients accordingly. [0046] It may be desirable to choose a windowing function having coefficients that are positive or negative powers of two so that multiplier 250 may be implemented as a shifter: for more rapid calculation. For example, a filter's frequency response may be modified by multipl>'ing the terminal (i.e. first and last ans/or near--teiminal coefficients by Vi, W, ete. [0047] As the value of L in expression (8) increiises, more quantization error may' accumulated into the result. For a particular application, this effect may limit the maximum, value of L-even if additional computational capacity is available, .As rioted above and as illustrated in FIGURE 9, it may also be desirable to use one or more out-of-band filters (e.g. filter 6 in FIGURE 9 at frequency π) to quantify the noise within the communications system. The power value from the noise filter(s) may be subtracted from the power values fron the other filters and/or used to modify the threshold value(s) before estimation of f d. [0M8] In CDMA and other systems, a pilot signal may be used to support coherent demodulation (e.g. of phase-shift-keying modulated signals). In an exemplary application of a method or apparatus according to an embodiment of the invention, the bandwidth of a pilot filter is modified accordimg to the estimated bandwidth of the pilot signal. Such an operation may improve the quility of the resulting phase reference and improve demodulator performance. I[0049] In certain applications of a method according to an embodiment of the invention, it may be possible; to perform preprocessing operations on the received signal before bandwidth estimation. In orie example, a receiver includes an automatic gain control (AGC) circuit. Applying an AGC operation may reduce the required dynamic range of subsequent operations, such as aralog-to-digtal conversion. Once the received signal passes through the AGC circuit, however, its envelope may become relatively constant, and much of ±:e attenuation information caused by the fading channel may be lost. As the bandwith of the signal remains unchanged, however (especially for a signal transmitted with constant power and phase at least over a specified time interval, such as a pilot signal of a CDMA system), it may be possible to perform nuch a preprocessing operation upstream of a method or apparatus acccording; to an embodiment of the invention. [0050] The foregoing presentation of the described embodiments is provided to enable any person skilled in the art to make, use, or apply a method cnr apparatus for bandwidth estimation. Various modifications to the described embodiments are possible, and the principles presented herein may be applied to other embodiments as well. For example, a method or apparatus according; to an embodiment of the invention may also be extended to perform bandwidth estimation by noncoherently integrating frequency measurements acquired from more than one coherent sample set. A method or apparatus according to an embod;iment of the invention may also be implemented in part or in whole as a hard-wired circuit, as a circuit configuration fabricated into an application-specific integrated circuit, or as a firmware program loaded into non-volatile storage or a software program loaded from or into a data storage medium as. machine-readable code, such code being insitructions executable by an array of logic elements such as a microprocessor or other digital signal processing unit. [0051] A method or apparatus according to an embodiment of the invention may be used within a mobile receiver and/or a stationary receiver. Such a method or apparatus may be applied to a pilot signal to obtain a better phase reference signal for demodulation and/or to a data signal to reduce interference. Various other noise characterization techniques may also be inccrporated within such a method or apparatus to compensate for the out-of-band noise during bandwidth estimation. Although quantization noise may accumulate; for large large values of L as mentioned above, it may also be desirable to ase reduced-bit-width storage or calculation in performing certain opeaationis v/ithin implementations of a method or appairatus according to an embodiment of the invention. It is also within the scope of the invention to apply the principles set forth herein to transforms othter than the discrete Fouier transform, such as the discrete cosine transform. Thus, the present invention is not intended to be limited to the embodiments shown above but rather is to be accorded the widest scope consistent with, the principles and novel features disclosed in any fashiion herein. WE CLAIM : 1. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating each of at least a subset of the plurality of coefficients includes rotating another of the plurality of coefficients by the generating value, each of at least a subset of the plurality of coefficients is generated from the previously generated coefficient; and obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; and estimating a bandwidth of the received signal based on the power measure. 2. A method of bandwidth estimation comprising: receiving information defining a generating of value of a filter; generating a plurality of coefficients of the filter from the generating value, each of at least a subset of the plurality of coefficients being generated from the previously generated coefficient; obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; and estimating a bandwidth of the received signal based on the power measure. 3. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating value including, a phase vector of unit magnitude; obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; and estimating a bandwidth of the received signal based on the power measure. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating value includes a vector having a phase angle of magnitude (2.pi.k/N) radians, where k is the selected frequency, and wherein the number of filter coefficients L is at most equal to N/2; obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; and estimating a bandwidth of the received signal based on the power measure. The method of bandwidth estimation according to claim 4, wherein N is greater than one thousand, and wherein the number of selected frequencies is at most equal to one hundred twenty-eight. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating each of at least a subset of the plurality of coefficients includes rotating another of the plurality of coefficients by the generating value; obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; and estimating a bandwidth of the received signal based on the power measure, the estimating a bandwidth of the received signal includes comparing the power measure to a predetermined threshold. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating each of at least a subset of the plurality of coefficients includes rotating another of the plurality of coefficients by the generating value; obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; estimating a bandwidth of the received signal based on the power measure; and estimating a relative velocity between a transmitter and a receiver based on a result of said estimating a bandwidth of the received signal. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating each of at least a subset of the plurality of coefficients includes rotating another of the plurality of coefficients by the generating value; obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; estimating a bandwidth of the received signal based on the power measure; and estimating a speed of a mobile receiver based on a result of said estimating a bandwidth of the received signal. A method of bandwidth estimation comprising: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value, the generating each of at least a subset of the plurality of coefficients includes rotating another of the plurality of coefficients by the generating value; obtaining a magnitude of an output of the filter to obtain a power measure of a received signal with respect to a selected frequency, said obtaining including multiplying each of the plurality of coefficients of the filter with a corresponding sample of the received signal; estimating a bandwidth of the received signal based on the power measure; and modifying a passband of a second filter according to a result of said estimating a bandwidth of the received signal. A method of bandwidth estimation comprising: obtaining a plurality of power measures of a received signal, each power measure corresponding to one of a plurality of selected frequencies; and estimating a bandwidth of the received signal based on the power measures of the received signal, wherein obtaining each of the plurality of power measures includes: receiving information defining a generating value of a filter; generating a plurality of coefficients of the filter from the generating value; multiplying each of the coefficients of the filter with a corresponding sample of the received signal; and comparing a relation between at least two of the power estimates to a predetermined threshold. The method of bandwidth estimation according to claim 10, wherein at least one of the power measures corresponds to a selected frequency that is outside of an expected bandwidth of the received signal. The method of bandwidth estimation according to claim 11, wherein said estimating a bandwidth of the received signal includes modifying at least a subset of the plurality of power measures based on the at least one power measure that corresponds to a selected frequency that is outside of an expected bandwidth of the received signal. The method of bandwidth estimation according to claim 10, wherein said estimating a bandwidth of the received signal includes determining the greatest selected frequency for which the corresponding power estimate is greater than a predetermined threshold. iau^--' 'ftit.wi*' is i^. - . ,. • : . ..,1 . 'i ■'—-■ The method of bandwidth estimation according to claim 10, wherein said estimating a bandwidth of the received signal includes comparing a second relation between at least two of the power estimates to a predetermined second threshold. The method of bandwidth estimation according to claim 10, wherein, for each of the plurality of power measures, generating each of at least a subset of the plurality of coefficients of the filters includes rotating another of the plurality of coefficients by the generating value. The method of bandwidth estimation according to claim 15, wherein, for each of the plurality of power measures, each of at least a subset of the coefficients of the filter is generated from the previously generated coefficient. The method of bandwidth estimation according to claim 10, wherein, for each of the plurality of power measures, each of at least a subset of the coefficients of the filter is generated from the previously generated coefficient. The method of bandwidth estimation according to claim 10, wherein, for each of the plurality of power measures, the generating value defines a vector having a phase angle of magnitude (2.pi.k/N) radians, where k is the selected frequency, and wherein the number of filter coefficients is at most equal to N/2. The method of bandwidth estimation according to claim 18, wherein, for at least one of the plurality of power measures, N is greater than one thousand, and wherein the number of selected frequencies is at most equal to one hundred twenty-eight. A method of bandwidth estimation comprising: calculating at least one coefficient of at least one of a plurality of filters from another coefficient of the filter; nonuniformly sampling a frequency spectrum of a received signal at a lurality of selected frequencies by filtering the received signal with the lurality of filters, each filter being centered about one of the plurality of elected frequencies; determining a plurality of power measures of the received ignal, each power measure being relative to one of the plurality of selected requencies; and obtaining an estimate of the bandwidth of the received signal, aid estimate based at least in part on the power measures of the received ignal. the method of bandwidth estimation according to claim 20, wherein, for at one of the plurality of filters, at least a subset of the coefficients of the liter are based on a vector having a phase angle of magnitude (2.pi.k/N) adians, where k is the selected frequency, and wherein the number of oefficients of the filter is at most equal to N/2. the method of bandwidth estimation according to claim 21, wherein N is ;reater than one thousand, and wherein the number of selected frequencies is at [lost equal to one hundred twenty-eight. ^ filter comprising: a lookup table configured and arranged to store a plurality •f generating values; a first multiplier configured and arranged to receive a elected one of the generating values and a current filter coefficient and to •utput a subsequent filter coefficient; an accumulator configured and arranged 0 receive and store the subsequent filter coefficient; a second multiplier onfigured and arranged to multiply the current filter coefficient with a orresponding one of a series of samples of a received signal and to output a urrent filtered value; and an adder configured and arranged to receive the urrent filtered value and a past filtered value and to output an accumulation ignal. The filter according to claim 23, wherein the accumulator is configured and irranged to store an initial value of one. DUPLICATE The filter according to claim 23, further comprising a storage element configured and arranged to store a value of the accumulation signal in response to a latching signal, wherein the latching signal has a predetermined time relation to the initialization signal. The filter according to claim 23, further comprising a power calculator configured and arranged to output a power measure based on a value of the accumulation signal. A system for bandwidth estimation comprising: a lookup table configured and arranged to store a plurality of generating values; a plurality of filters, each filter including a first multiplier configured and arranged to receive a selected one of the generating values and a current filter coefficient and to output a subsequent filter coefficient, an accumulator configured arranged to receive and store the subsequent filter coefficient, a second multiplier configured and arranged to multiply the current filter coefficient with a corresponding one of a series of samples of a received signal and to output a current filtered value, an adder configured and arranged to receive the current filtered value and a past filtered value and to output an accumulation signal, and a power calculator configured and arranged to output a power measure based on a value of the accumulation signal; and a bandwidth estimator configured and arranged to receive the power measures of the plurality of filters and to output an estimate of the bandwidth of the received signal. The system for bandwidth estimation according to claim 27, wherein the bandwidth estimator is configured and arranged to compare a relation between at least two of the power measures to a predetermined threshold. The system for bandwidth estimation according to claim 27, wherein at least one of the power measures corresponds to a frequency that is outside of an expected bandwidth of the received signal, and wherein the bandwidth estimator is configured and arranged to modify at least a subset of the power measures based on the at least one power measure that corresponds to a frequency that is outside of an expected bandwidth of the received signal. The system for bandwidth estimation according to claim 27, further comprising a relative velocity estimator configured and arranged to output a relative velocity estimate based on the estimate of the bandwidth of the received signal.

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