DYNAMIC FREQUENCY CORRECTION IN A DELTA-SIGMA-BASED SOFTWARE-DEFINED RECEIVER

Abstract

Device comprising: an antenna (32) capable of receiving a radio frequency (RF) signal; a memory (340) for storing a configuration parameter; a software-definable radio device (300) for configuring an initial filter response, for filtering the RF signal to produce a filtered RF signal, and for reconfiguring the filter response in response to the configuration parameter, wherein the software-definable radio device (300) includes a delta-sigma modulator (320) that is functional to demodulate the RF signal, and wherein the software-definable radio device (300) is configured to apply a pilot tone (310) at a known frequency to the delta-sigma modulator (320); and a processor (330) capable of processing the filtered RF signal, determining a quality factor of the filtered RF signal, retrieving the configuration parameter in response to the quality factor, and coupling the configuration parameter to a definable software.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] This invention relates generally to a broadband radio system designed to adapt to various global radio standards, and more particularly to a cellular radio architecture using a combination of a single circulator, a programmable band-pass sampling radio frequency (RF) front-end, and an optimized digital baseband capable of supporting all current mobile access protocol frequency bands. Explanation of the state of the art

[0002] Conventional mobile phones use various operating modes and bands, supported in hardware by integrating multiple different radio front-end and baseband processing chips into a single platform, such as tri-band or quad-band user handsets supporting a Global System for Mobile Communications (GSM), Global Packet Radio Service (GPRS), etc. Common mobile receivers have integrated some of the antenna and baseband data paths, but the current state of the art for mass mobile and vehicular radio deployments remains a multiple static channelization approach. Such a static architecture critically depends on narrowband filters, Dopplers, and standard-specific downconversion to intermediate frequency (IF) stages.The main disadvantage of this static, channelized approach is its inflexibility with changing standards and operating modes. As the wireless industry has evolved from 2G, 3G, 4G, and beyond, each new waveform and mode required a redesign of the receiver's RF front end and an expansion of the baseband chipset capability, necessitating a new handset. For automotive applications, this inflexibility to support new applications is prohibitively expensive and a nuisance to the end user.

[0003] Providing reliable wireless access for the automotive industry is challenging from an automaker's perspective, as mobile connectivity methods and architectures vary worldwide. Furthermore, standards and technologies are constantly changing and typically have a development cycle many times faster than the average vehicle lifespan. In particular, current RF front-end architectures for automotive radios are designed for specific RF frequency bands. Dedicated hardware tuned to the correct frequency must be installed on the radio platform for the specific frequency band on which the radio is to operate.Therefore, when mobile operators change their respective frequency bands, the vehicle that was designed for the previous band, which may have a lifespan of 15 to 20 years, may not operate efficiently on the new band. Therefore, this requires automakers to manage a variety of radio platforms, components, and suppliers to support each deployed standard and provide a path to expandability as the mobile landscape changes.

[0004] Known software-defined radio architectures have typically focused on seamless baseband operations to support multiple waveforms and adopted similar downconversions in baseband specifications. Similarly, the transmitter side typically used parallel power amplifier chains for different frequency bands to support different waveform standards. Thus, the receiver front-end architectures typically feature simple direct sampling or single-stage mixing techniques with modest power specifications. In particular, there has been no need to date for an application requiring a dynamic range exceeding 110 dB, with the associated IP3 factor and power consumption requirements, as these performance requirements were not feasible with complementary metal-oxide-semiconductor (CMOS) analog technologies.It is not obvious how these metrics can be achieved using existing architectures for CMOS devices, so dynamic range, sensitivity, and multimode connectivity are a much more difficult problem for both the multi-bit analog-to-digital converter (ADC) and the digital-to-analog converter (DAC).

[0005] Currently, software-defined radio architectures do not exist in the automotive sector, but have been proposed and pursued in other non-automotive applications, such as military radios with multiband waveforms. However, in these areas, a zero-IF approach has proven technically challenging due to the widely varying waveform requirements, conflicting operational reliability requirements, and complex interoperability requirements. Known software-defined radios have typically focused on backend processing, specifically providing seamless baseband operations to support multiple waveforms. The modest performance requirements have not placed more aggressive demands on front-end architectures. Simple direct sampling or one-stage mixing techniques have been sufficient in the receiver.In software-defined radios using delta-sigma modulators, the component function is typically found after a downconversion stage and exhibits low-pass characteristics. Regarding the transmitter, parallel multiple power amplifier chains supporting different frequency bands and waveform standards are sufficient to meet the requirements.

[0006] Delta-sigma modulators are becoming increasingly common in digital receivers because the modulators not only provide wideband, high dynamic range operation but also have many adjustable parameters, making them suitable for reconfigurable systems.

[0007] CN101729082A discloses a center frequency adjusting apparatus and a method thereof for a communication receiver, and more particularly, a center frequency adjusting apparatus and a method thereof for adjusting a center frequency of an analog filter of the communication receiver based on a received signal.

[0008] US20120082100A1 discloses techniques for the detection, dynamic allocation, and sharing of available spectrum by cognitive radio systems. In some cases, RF carriers (e.g., secondary carriers or secondary cells) are not permanently assigned to base stations, user equipment, or the network. The base station can request the allocation of secondary carriers with a reservation request. The allocated secondary carriers can be released and made available for assignment to another base station or a radio access network.

[0009] WO2003090373A1 discloses a method and apparatus for dynamically adjusting parameters of a pilot signal filter. An incoming signal containing a pilot signal is filtered using non-identical filters, and the magnitudes of the filtered signals are compared to estimate a bandwidth of the pilot signal.

[0010] US20110200077A1 discloses a delta-sigma modulator (DSM) with a loop in which an output signal from a quantizer is digitally processed and fed back to an analog filter via a digital-to-analog converter. The quantizer quantizes an analog signal from an analog filter section to output a digital signal. The digital signal from the quantizer is digitally processed in a first-order recursive filter circuit, wherein the first-order recursive filter circuit comprises an amplifier and a delay element.

[0011] US20100166124A1 discloses a radio frequency (RF) receiver comprising an analog receiver circuit and a digital receiver circuit. The analog circuit of the receiver is located in a first integrated circuit, and the digital circuit of the receiver is located in a second integrated circuit. The second integrated circuit is connected to the first integrated circuit via a one-bit digital interface. The receiver receives an RF signal and processes the received RF signal to generate a digital signal. The analog circuit of the receiver provides the digital signal to the digital circuit of the receiver. The digital circuit of the receiver includes a digital downconverter circuit that mixes the digital signal with an intermediate frequency (IF) local oscillator (LO) signal to generate a digital downconverted signal.The digital circuit of the receiver circuit includes a digital filter circuit that filters the down-converted digital signal to produce a filtered digital signal. SUMMARY OF THE INVENTION

[0012] According to one aspect of the present disclosure, an apparatus comprises an antenna for receiving an RF signal, a memory for storing a configuration parameter, a software-definable radio for configuring an initial filter response, for filtering the RF signal to generate a filtered RF signal, and for reconfiguring the RF filter response in response to the configuration parameter, wherein the software-definable radio includes a delta-sigma modulator operable to demodulate the RF signal, and wherein the software-definable radio is configured to apply a pilot tone at a known frequency to the delta-sigma modulator, and a processor for processing the filtered RF signal, determining a quality factor of the filtered RF signal, retrieving the configuration parameter in response to the quality factor, and coupling the configuration parameter to definable software.

[0013] According to a second aspect of the present disclosure, a method for configuring a software-definable radio comprising applying a pilot tone at a known frequency to a delta-sigma modulator, retrieving a first configuration parameter, configuring a filter response in response to the first configuration parameter, filtering an RF signal, determining an offset between a center frequency of the RF signal and a center frequency of the filter response, retrieving a second configuration parameter associated with the offset, reconfiguring the filter response in response to the second configuration parameter, and filtering the RF signal.

[0014] According to a third aspect of the present disclosure, a software-definable radio device comprises a source of a pilot signal operable to generate a pilot signal at a first center frequency, a filter having a configurable filter response responsive to a configuration parameter, a processor generating a control signal to supply the pilot signal to the filter, for determining the first center frequency and for generating the configuration parameter responsive to the first center frequency, a memory for storing the configuration parameter in a memory, and a delta-sigma modulator operable to demodulate an RF signal.

[0015] Further features of the present invention will become apparent from the following description and the appended claims in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a known multimode multiband mobile radio handset architecture; Fig. Figure 2 shows a schematic block diagram of a mobile front-end architecture that provides software-programmable functions. Fig. Figure 3 shows an example of a system for dynamic frequency correction in a delta-sigma-based receiver. Fig. Figure 4 shows an example of a method for dynamic frequency correction in a delta-sigma-based SDR. Fig. Figure 5 shows an example of a device for dynamic frequency correction in a delta-sigma-based receiver. Fig. 6 shows an example of a method for dynamic frequency correction in a delta-sigma-based software-defined receiver. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The following discussion of embodiments of the invention directed to a cellular architecture is merely exemplary in nature and is not intended to limit the invention or its applications or uses in any way. For example, the radio architecture of the invention is described as an application for a vehicle. However, as will be appreciated by those skilled in the art, the radio architecture may also provide applications other than automotive.

[0017] The cellular architectures discussed herein are not only applicable to cellular technologies such as Wi-Fi (IEEE 802.11). Furthermore, the cellular architectures are presented as a full-duplex radio system, i.e., a radio system that both transmits and receives. For receive-only wireless services, such as GPS (Global Positioning System), GNSS (Global Navigation Satellite System), and various entertainment devices such as AM / FM, Digital Audio Broadcasting (DAB), SiriusXM, etc., only the receiver design discussed herein would be required. Furthermore, the described radio architecture design enables a globally functional design for radio hardware that can be adapted to various global cellular standards through software updates. It also enables a longer service life of the radio design, as the radio can adapt to new radio standards upon market launch.For example, developments in 4G radio technology and frequency allocations are highly dynamic. As a result, radio hardware currently in use on the market can become obsolete after just one or two years. For applications such as those in the automotive sector, the lifespan can be over ten years. This invention makes it possible to make a fixed hardware platform updatable through software updates, thus extending the service life and global reuse of the hardware.

[0018] Fig. Figure 1 is a block diagram of a known multimode, multiband cellular handset architecture 10 for a typical cellular phone. The architecture 10 includes an antenna structure 12 that receives and transmits RF signals on the frequency band of interest. The architecture 10 also includes a switch 14 at the front end of the architecture 10 that selects which particular channel the transmitted or received signal is currently for and passes the signal through a dedicated set of filters and duplexers, represented by box 16 for the respective channel. Modules 18 provide multimode and multiband analog modulation and demodulation of the received and transmitted signals, separating the signals into phase and quadrature-phase signals, which are transmitted to or received by a receiver 20. The receiver 20 also converts analog received signals to digital signals and digital transmitted signals to analog signals.A baseband digital signal processor 22 provides the digital processing of the transmit or receive signals for the respective application.

[0019] Fig. Figure 2 is a schematic block diagram of a cellular radio front-end architecture 30 that provides software-programmable capabilities, as explained in detail below. The architecture 30 includes an antenna structure 32 capable of receiving and transmitting the cellular frequency signals discussed herein, such as in the 400 MHz - 3.6 GHz range. The signals received and transmitted by the antenna structure 32 pass through a multiplexer 34 with three signal paths, each path dedicated to a specific frequency band determined by a frequency-selective filter 36 in each path. In this embodiment, three signal paths were chosen, but the architecture 30 could be expanded to include any number of signal paths.Each signal path includes a circulator 38 that separates and routes the receive and transmit signals and provides isolation so that the high power signals to be transmitted do not penetrate the receiver side and saturate the receive signals on these frequency bands.

[0020] The architecture 30 also includes a receive module 44 located behind the multiplexer 34, a receive module 46 that processes the received signals, and a transmit module 48 that processes the transmitted signals. The receive module 46 includes three receiver channels 50, one for each of the signal paths through the multiplexer 34, with another receiver channel 50 connected to a different one of the circulators 38, as shown. Each of the receiver channels 50 includes a delta-sigma modulator 52 that receives the analog signal in the respective frequency band and generates a representative digital data stream using an interleaving technique in conjunction with a series of N-bit quantization circuits operating at a very high clock rate, as explained in detail below.As discussed further below, the delta-sigma modulator 52 compares the difference between the received signal and a feedback signal to generate an error signal representative of the received digital data. The digital data bits are provided to a digital signal processor (DSP) 54, which extracts the digital data stream. A digital baseband processor (DBP) 56 receives and operates the digital data stream for further signal processing in a manner well known to those skilled in the art. The transmit module 48 receives digital data transmitted from the processor 56. The module 48 includes a transmitter circuit 62 with a delta-sigma modulator that converts the digital data from the digital baseband processor 56 into an analog signal.The analog signal is filtered by a tunable bandpass filter (BPF) 60 to eliminate band emission and then passed to a switch 66, which routes the signal to a selected power amplifier 64 optimized for the frequency band of the transmitted signal. In this embodiment, three signal paths were chosen, but the transmit module 48 could be implemented using any number of signal paths. The amplified signal is sent to the respective circulator 38 in the multiplexer 34, depending on the frequency being transmitted.

[0021] As will be apparent from the following discussion, the configuration of architecture 30 provides software-programmable capabilities through high-performance delta-sigma modulators that provide optimized performance in the signal range of interest and can be tuned over a wide range of carrier frequencies. Architecture 30 complies with current cellular access protocols in the 0.4–2.6 GHz frequency range by dividing the frequency range into three non-continuous bands. However, it should be noted that other combinations of signal paths and bandwidth are, of course, possible. Multiplexer 34 implements frequency-domain demultiplexing by routing the RF carrier received at antenna structure 32 into one of the three signal paths. In contrast, the transmit signal is multiplexed onto antenna structure 32 by multiplexer 34.For in-vehicle wireless access applications, such a low-cost integrated device is desirable to reduce parts costs, complexity, and obsolescence, and enable seamless global deployment.

[0022] The delta-sigma modulators 52 can be positioned near the antenna structure 32 to convert the received RF signals directly into bits in the receiver module 46 and bits into an RF signal in the transmitter module 48. The primary advantage of using the delta-sigma modulators 52 in the receiver channels 50 is to enable variable signal acquisition bandwidth and variable center frequency. This is possible because the architecture 30 allows software manipulation of the modulator filter coefficients to vary the signal bandwidth and tune the filter characteristics across the RF band.

[0023] Architecture 30 allows for varying the signal acquisition bandwidth, which can be used to receive continuous carrier-aggregated waveforms without additional hardware. Carrier aggregation is a technique that combines the data bandwidths of multiple carriers for normally independent channels for a single user to achieve significantly higher data rates than a single carrier. Along with MIMO, this feature is a requirement in modern 4G standards and is enabled by the orthogonal frequency division multiplexing (OFDM) family of waveforms, which enable efficient spectral utilization.

[0024] The architecture 30, through the delta-sigma modulators 52, can handle precise carrier aggregation scenarios and band combinations through software tuning of the bandpass bandwidth, thus enabling multi-segment sensing. The dynamic range decreases at larger bandwidths as more noise is injected into the sampling bandpass. However, it is assumed that carrier aggregation is typically useful when the user has a good signal-to-noise ratio, rather than cell boundary edges, where connectivity itself may be marginal. Note that interband carrier aggregation is automatically handled by the architecture 30 because the multiplexer 34 injects independent modulators into the channels 50.

[0025] The circulators 38 route the transmit signals from the transmit module 48 to the antenna structure 32 while enabling separation between the high-power transmit signals and the receive module 46. Although the circulators 38 provide significant signal separation, there is port-to-port leakage within the circulator 38, which represents a signal path between the transmit module 48 and the receive module 46. A second undesired signal path arises from reflections from the antenna structure 32 and possibly other components in the receiver. As a result, a portion of the transmit signal is reflected from the antenna structure 32 due to a mismatch between the line impedance and the antenna input impedance. This reflected energy follows the same signal path as the desired incoming signal back to the receive module 46.

[0026] The architecture 30 is also flexibly adaptable for other wireless communication protocols. For example, a pair of switches 40 and 42 controlled by the DBP 56 may be provided to route the receive and transmit signals via dedicated fixed RF devices 58, such as a Global System for Mobile Communications (GSM), an RF front-end module, or a Wi-Fi front-end module. In this embodiment, some selected signal paths are implemented via conventional RF devices. Fig. 2 represents only one additional signal path, but can be extended to any number of additional signal paths depending on the use and area of ​​application.

[0027] Delta-sigma modulators are a well-known class of devices for implementing analog-to-digital converters. The fundamental properties utilized are oversampling and error feedback (delta), which are accumulated (sigma), to convert the desired signal into a pulse-modulated stream, which can then be filtered to read the digital values, while effectively reducing noise through reshaping. The main limitation of known delta-sigma modulators is the quantization noise during the pulse conversion process. Delta-sigma converters require large oversampling ratios to generate a sufficient number of bitstream pulses for a given input. In direct conversion schemes, the sampling rate is greater than four times the RF carrier frequency to simplify digital filtering. Therefore, the required multi-GHz sampling rates have limited the use of delta-sigma modulators in higher-frequency applications.Another approach to noise reduction is the use of higher-order delta-sigma modulators. However, while canonical first-order delta-sigma architectures are stable, higher orders can be unstable due to tolerances at higher frequencies, especially the tolerances at higher frequencies. For these reasons, higher-order delta-sigma modulators are limited to audio frequency ranges, i.e., time-interleaved delta-sigma modulators for use in audio applications or special interleaving at high frequencies.

[0028] The filter characteristics of a delta-sigma modulator can be effectively modified to compensate for Doppler shifts. Doppler shifts occur when the transmitter of a signal moves relative to the receiver. The relative motion shifts the frequency of the signal, making it different at the receiver than the transmitter. An exemplary system according to the present disclosure utilizes the software-defined radio architecture to quickly estimate a carrier frequency shift and recenter the filter before the signal is interrupted or attenuated. During normal operation, the modulator filter notch is centered around the expected carrier frequency of the received signal, with the signal band information centered around the carrier frequency and not exceeding the bandwidth of the modulator filter.A Doppler shift would compensate for the carrier by an amount Δf, resulting in a potential degradation of the signal content with an increase in noise on one side of the band. According to the method and system described herein, the receiver in a wireless cellular communication system can adapt to changes in the RF carrier frequency and maintain signal integrity by shifting the filter notch by the same amount as the carrier frequency.

[0029] For the mobile radio application discussed here, which covers multiple assigned frequency bands, a transmitter with multimode and multiband coverage is required. Many current applications also require transmitters that can rapidly switch between frequency bands during operation of a single communication link, which poses a significant challenge for typical local oscillator (LO)-based transmitter solutions. This is because the switching time of the LO-based transmitter is often determined by the LO channel switching time under the control of the frequency synthesizer's loop bandwidth around 1 MHz. The achievable channel switching time is thus a few microseconds, which is unfortunately too long for an agile radio. A fully digital PWM-based multi-standard transmitter known in the prior art suffers from high distortion, and the channel switching time is still determined by the LO at the carrier frequency.A DDS can be used as an LO source to increase switching speed, but this design consumes considerable power and may not provide high-frequency LOs with low spurious components. Alternatively, single-sideband mixers can be used to generate multiple LOs with different center frequencies via a common phase-locked loop (PLL), whose channel switching times can be fast. However, this approach can only support a limited number of LO options, and additional channels to cover the wide spectrum of expected 4G bands require additional mixing. As discussed, sigma-delta modulators have been proposed in the prior art as RF transmitters to address these problems. However, in its basic architecture, a sigma-delta modulator cannot provide very high dynamic range in wideband operation due to a moderate clock frequency.Precisely because the clock frequency is limited by current technology, this high-frequency operating mode cannot be supported.

[0030] Referring now to Fig. 3 illustrates an exemplary system for dynamic frequency correction in the delta-sigma-based software-defined receiver 300. The system is operative to determine a signal response for a corresponding Doppler shift. For example, an example Doppler shift signal is attached to the system front end of the receiver. The system is then operative to determine a frequency difference between the expected carrier frequency and the Doppler-shifted carrier frequency. Once this difference is determined, the difference is applied as an offset to the filter response, shifting the filter bandwidth by an amount equal to the offset. The system is then operative to determine in the shifted filter frequency response whether sufficient attenuation and a sufficient passband response are present. If so, the value of the frequency offset is stored for use in normal operation.According to an exemplary embodiment, during a system configuration mode, a pilot tone 310 at a known frequency is applied to the delta-sigma modulator 320. The pilot tone is the frequency of an expected operating frequency plus or minus the effects of a Doppler shift. The system is then operated to perform an initial adjustment of the filter to the known pilot frequency. The DSP 330 is then capable of generating a calibration term, such as an n-bit calibration word. The calibration term is stored in a memory 340. During normal receive operation, the system is further capable of adjusting the n-bit calibration code to the tuning code typically presented to the modulator in response to the Doppler shift. The system can be implemented using a simple adder, a comparable adder, or in software.

[0031] With reference now to Fig. Figure 4 illustrates an exemplary method for dynamic frequency correction in a delta-sigma-based SDR 400. During calibration of the signal processing system, it is possible to first configure the SDR to receive a signal having an expected carrier frequency 405. The system is then capable of applying an RF pilot signal 410 to a receiving portion of the receiver, such as the antenna or bandpass filters, or the receiver input, as previously described. The RF pilot signal has a known center frequency offset from the expected carrier frequency by an amount corresponding to an expected Doppler shift under operating conditions. The SDR configuration is then configured to process the RF pilot signal. The system is then operative to determine whether the SDR configuration is suitable for receiving the RF pilot signal 430.If the frequency response of the SDR configuration is not suitable for correct processing of the RF pilot signal, the SDR configuration step 420 is repeated and the SDR configuration is modified according to the determined frequency response. If the frequency response of the SDR configuration is suitable for correct processing of the RF pilot signal, the system can save the configuration data with the frequency of the RF pilot signal 440. For example, a frequency offset value can be saved with the center frequency of the RF pilot signal. Alternatively, the configuration parameters for the delta signal modulation can be stored in a memory along with the frequency response of the RF pilot signal.

[0032] Referring now to Fig. Figure 5 illustrates an exemplary apparatus for dynamic frequency correction in delta-sigma-based software-defined receiver 500. The system is operative to receive an RF signal 510. The SDR 520 is initially configured to receive the RF signal at an expected frequency. The SDR processes the received RF signal 510 and couples the filtered and demodulated data to the DSP 530. The DSP processes the data and determines the signal quality or a quality factor of the signal. If the signal quality is below an acceptable quality threshold, the DSP attempts to determine the center frequency of the received RF signal. If the determined center frequency differs from the expected center frequency, the DSP retrieves the appropriate stored configuration parameters from memory 540.Using these configuration parameters, the SDR 520's configuration is changed to receive a signal with the specific center frequency of the received RF signal. The DSP 530 then processes the data and determines whether the signal quality is acceptable for the specific center frequency. If not, the process is repeated with different configuration parameters until the signal quality is acceptable. Once an acceptable configuration is established, the system can process and decode the received RF signal using these parameters and periodically check the signal quality.

[0033] Referring now to Fig.Figure 6 illustrates an exemplary method for dynamic frequency correction in the delta-sigma-based software-defined receiver 600. During signal processing, the method operates to receive an RF signal 605 at the frequency band of interest. The delta-sigma modulator is configured to receive the RF signal 605 at the frequency band of interest 610. A DSP is then used to determine if a Doppler shift is present on the RF signal 620, thereby changing the expected carrier frequency. If a Doppler shift is detected, a pre-stored calibration word is extracted from memory, and the delta-sigma modulator response is changed according to the calibration word 630. The system is then operable to process the RF signal 600. If no Doppler shift is detected, the DSP operates to process the RF signal 600.

[0034] As is well known to those skilled in the art, the various steps and methods discussed herein to describe the invention may relate to operations utilized by a computer, processor, or other electronic computing device that manipulates and / or alters data using electrical operations. These computers and electronic devices may include various volatile and / or non-volatile memories, including a non-transitory computer-readable medium having an executable program stored thereon, including various codes or executable instructions capable of being executed by computers or processors, where the memory and / or computer-readable medium may be any and all forms and types of memory and other computer-readable media.

[0035] The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. Those skilled in the art will readily appreciate from the above discussion and the accompanying drawings and claims that various changes, modifications, and variations may be made therein without departing from the spirit and scope of the invention as defined in the following claims.

Claims

[1] Device comprising: an antenna (32) operable to receive a radio frequency (RF) signal; a memory (340) for storing a configuration parameter; a software-definable radio (300) for configuring an initial filter response, for filtering the RF signal to generate a filtered RF signal, and for reconfiguring the filter response in response to the configuration parameter, wherein the software-definable radio (300) includes a delta-sigma modulator (320) operable to demodulate the RF signal, and wherein the software-definable radio (300) is configured to apply a pilot tone (310) at a known frequency to the delta-sigma modulator (320); and a processor (330) operable to process the filtered RF signal, determine a quality factor of the filtered RF signal, retrieve the configuration parameter in response to the quality factor, and couple the configuration parameter to definable software. [2] The apparatus of claim 1, wherein reconfiguring the filter response includes changing the center frequency of a bandpass filter. [3] The apparatus of claim 1, wherein determining the quality factor includes determining a center frequency of the filtered RF signal and comparing it to the center frequency of the initial filter response. [4] The apparatus of claim 1, wherein configuring the initial filter response includes configuring a filter bandwidth and a filter center frequency. [5] The apparatus of claim 4, wherein reconfiguring the filter response includes changing the filter bandwidth. [6] A method for configuring a software-definable radio device, comprising: - applying a pilot tone (310) at a known frequency to a delta-sigma modulator (320); - retrieving a first configuration parameter; - configuring a filter response in response to the first configuration parameter; - filtering an RF signal; - determining an offset between a center frequency of the RF signal and a center frequency of the filter response; - retrieving a second configuration parameter associated with the offset; - reconfiguring the filter response in response to the second configuration parameter; and - filtering the RF signal. [7] A software-definable radio device (300) comprising: - a source of a pilot signal (310) operable to generate a pilot signal at a first center frequency; - a filter having a configurable filter response in response to a configuration parameter; - a processor (330) generating a control signal to apply the pilot signal to the filter to determine the first center frequency and to generate the configuration parameter in response to the first center frequency; - a memory (340) for storing the configuration parameters in a memory; and - a delta-sigma modulator (320) operable to demodulate an RF signal. [8] The software definable radio (300) of claim 7, wherein the processor (330) is operable to determine a second center frequency, retrieve a second configuration parameter associated with the second center frequency, and couple the second configuration parameter to the filter. [9] The software definable radio (300) of claim 8, wherein the filter is operable to reconfigure a filter response in response to the second configuration parameter.

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