U.S. patent application number 15/296515 was filed with the patent office on 2018-04-19 for dynamic frequency correction in delta-sigma based software defined receiver.
The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Mohiuddin AHMED, Cynthia D. BARINGER, Jongchan KANG, Yen-Cheng KUAN, James Chingwei LI, Emilio A. SOVERO, Timothy J. TALTY.
Application Number | 20180109272 15/296515 |
Document ID | / |
Family ID | 61904821 |
Filed Date | 2018-04-19 |
United States Patent
Application |
20180109272 |
Kind Code |
A1 |
TALTY; Timothy J. ; et
al. |
April 19, 2018 |
DYNAMIC FREQUENCY CORRECTION IN DELTA-SIGMA BASED SOFTWARE DEFINED
RECEIVER
Abstract
A method and apparatus for dynamically modifying filter
characteristics of a Delta-Sigma modulator to accommodate for
Doppler shift. A transceiver in a wireless cellular communication
system for adapt to changes in the RF carrier frequency for
maintaining signal integrity by applying a pilot tone in
calibration to determine a frequency shift response for a bandpass
filter. During operation, the system is operative to determine a
Doppler shift and to shift the bandpass filter in response.
Inventors: |
TALTY; Timothy J.; (Beverly
Hills, MI) ; BARINGER; Cynthia D.; (Malibu, CA)
; AHMED; Mohiuddin; (Moorpark, CA) ; KANG;
Jongchan; (Moorpark, CA) ; KUAN; Yen-Cheng;
(Los Angeles, CA) ; LI; James Chingwei; (Simi
Valley, CA) ; SOVERO; Emilio A.; (Thousand Oaks,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
DETROIT |
MI |
US |
|
|
Family ID: |
61904821 |
Appl. No.: |
15/296515 |
Filed: |
October 18, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 1/0042 20130101;
H04W 84/12 20130101; H04L 27/2601 20130101; H04B 1/0039 20130101;
H04B 7/0413 20130101 |
International
Class: |
H04B 1/00 20060101
H04B001/00 |
Claims
1. An apparatus comprising: an antenna operable to receive an RF
signal; a memory for storing a configuration parameter; a software
definable radio for configuring an initial filter response,
filtering the RF signal to generate a filtered RF signal, and for
reconfiguring the filter response in response to the configuration
parameter; and a processor 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 to couple the configuration parameter to a software
definable.
2. The apparatus of claim 1 wherein the reconfiguration the filter
involves changing the center frequency of a bandpass filter.
3. The apparatus of claim 1 wherein the determining the quality
factor involves determining a center frequency of the filtered RF
signal and comparing that to the center frequency of the initial
filter response.
4. The apparatus of claim 1 wherein the software definable radio
includes a sigma delta modulator operable to demodulate the RF
signal.
5. The apparatus of claim 1 wherein the configuring the initial
filter response involves configuring a filter bandwidth and a
filter center frequency.
6. The apparatus of claim 5 wherein reconfiguring the filter
response includes changing the filter bandwidth.
7-16. (canceled)
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates generally to wide bandwidth radio
system designed to adapt to various global radio standards and,
more particularly, to a cellular radio architecture that employs a
combination of a single circulator, programmable band-pass sampling
radio frequency (RF) front-end and optimized digital baseband that
is capable of supporting all current cellular wireless access
protocol frequency bands.
Discussion of the Related Art
[0002] Traditional cellular telephones employ different modes and
bands of operation that have been supported in hardware by having
multiple disparate radio front-end and baseband processing chips
integrated into one platform, such as tri-band or quad-band user
handsets supporting global system for mobile communications (GSM),
general packet radio service (GPRS), etc. Known cellular receivers
have integrated some of the antenna and baseband data paths, but
nevertheless the current state of the art for mass mobile and
vehicular radio deployment remains a multiple static channelizing
approach. Such a static architecture is critically dependent on
narrow-band filters, duplexers and standard-specific
down-conversion to intermediate-frequency (IF) stages. The main
disadvantage of this static, channelized approach is its
inflexibility with regards to the changing standards and modes of
operation. As the cellular communications industry has evolved from
2G, 3G, 4G and beyond, each new waveform and mode has required a
redesign of the RF front-end of the receiver as well as expanding
the baseband chip set capability, thus necessitating a new handset.
For automotive applications, this inflexibility to support emerging
uses is prohibitively expensive and a nuisance to the end-user.
[0003] Providing reliable automotive wireless access is challenging
from an automobile manufacturers point of view because cellular
connectivity methods and architectures vary across the globe.
Further, the standards and technologies are ever changing and
typically have an evolution cycle that is several times faster than
the average service life of a vehicle. More particularly, current
RF front-end architectures for vehicle radios are designed for
specific RF frequency bands. Dedicated hardware tuned at the proper
frequency needs to be installed on the radio platform for the
particular frequency band that the radio is intended to operate at.
Thus, if cellular providers change their particular frequency band,
the particular vehicle that the previous band was tuned for, which
may have a life of 15 to 20 years, may not operate efficiently at
the new band. Hence, this requires automobile manufactures to
maintain a myriad of radio platforms, components and suppliers to
support each deployed standard, and to provide a path to
upgradability as the cellular landscape changes, which is an
expensive and complex proposition.
[0004] Known software-defined radio architectures have typically
focused on seamless baseband operations to support multiple
waveforms and have assumed similar down-conversion-to-baseband
specifications. Similarly, for the transmitter side, parallel power
amplifier chains for different frequency bands have typically been
used for supporting different waveform standards. Thus, receiver
front-end architectures have typically been straight forward direct
sampling or one-stage mixing methods with modest performance
specifications. In particular, no prior application has required a
greater than 110 dB dynamic range with associated IP3 factor and
power handling requirements precisely because such performance
needs have not been realizable with complementary metal oxide
semiconductor (CMOS) analog technologies. It has not been obvious
how to achieve these metrics using existing architectures for CMOS
devices, thus the dynamic range, sensitivity and multi-mode
interleaving for both the multi-bit analog-to-digital converter
(ADC) and the digital-to-analog converter (DAC) is a substantially
more difficult problem.
[0005] Software-defined radio architectures do not currently exist
in the automotive domain, but have been proposed and pursued in
other non-automotive applications, such as military radios with
multi-band waveforms. However, in those areas, because of vastly
different waveform needs, conflicting operational security needs
and complex interoperability requirements, a zero-IF approach has
proven technically difficult. Known software defined radios have
typically focused on backend processing, specifically providing
seamless baseband operations to support multiple waveforms. The
modest performance specifications haven't demanded anything more
aggressive from front-end architectures. Straight-forward direct
sampling or 1-stage mixing methods have been sufficient in the
receiver. For software defined radios that employ delta-sigma
modulators, the component function is commonly found after a
down-conversion stage and has low-pass characteristics. With regard
to the transmitter, parallel multiple power amplifier chains to
support differing frequency bands and waveform standards have been
sufficient for meeting the requirements.
[0006] Delta-sigma modulators are becoming more prevalent in
digital receivers because, in addition to providing wideband high
dynamic range operation, the modulators have many tunable
parameters making them a good candidate for reconfigurable
systems.
SUMMARY OF THE INVENTION
[0007] In accordance with an aspect of the present disclosure, an
apparatus comprising an antenna operable to receive an RF signal, a
memory for storing a configuration parameter, a software definable
radio for configuring an initial filter response, filtering the RF
signal to generate a filtered RF signal, and for reconfiguring the
filter response in response to the configuration parameter, and a
processor 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 to
couple the configuration parameter to a software definable.
[0008] In accordance with a second aspect of the present
disclosure, a method comprising, configuring a filter response
having a first bandwidth and a first center frequency, filtering a
pilot signal having a second center frequency, determining a
frequency offset between the first center frequency and the second
center frequency, generating a configuration parameter in response
to the frequency offset, and storing the configuration parameter in
a memory.
[0009] In accordance with a third aspect of the present disclosure,
a method of configuring a software definable radio comprising
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.
[0010] In accordance with a fourth aspect of the present
disclosure, a software definable radio comprising, a source of a
pilot signal 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 operative to
generate a control signal in order to apply the pilot signal to the
filter, for determining the first center frequency and for
generating the configuration parameter in response to the first
center frequency, and a memory for storing the configuration
parameter in a memory.
[0011] Additional features of the present invention will become
apparent from the following description and appended claims, taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a block diagram of a known multi-mode,
multi-band cellular communications handset architecture;
[0013] FIG. 2 shows is a schematic block diagram of a cellular
radio front-end architecture that provides software programmable
capabilities.
[0014] FIG. 3 shows an exemplary system for dynamic frequency
correction in delta-sigma based software defined receiver.
[0015] FIG. 4 shows an exemplary method for dynamic frequency
correction in delta-sigma based SDR.
[0016] FIG. 5 shows an exemplary apparatus for dynamic frequency
correction in delta-sigma based software defined receiver.
[0017] FIG. 6 shows an exemplary method for dynamic frequency
correction in delta-sigma based software defined receiver.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0018] The following discussion of the embodiments of the invention
directed to a cellular radio architecture is merely exemplary in
nature, and is in no way intended to limit the invention or its
applications or uses. For example, the radio architecture of the
invention is described as having application for a vehicle.
However, as will be appreciated by those skilled in the art, the
radio architecture may have applications other than automotive
applications.
[0019] The cellular radio architectures discussed herein are
applicable to more than cellular wireless technologies, fur
example, WiFi (IEEE 802.11) technologies. Further, the cellular
radio architectures are presented as a fully duplexed wireless
system, i.e., one that both transmits and receives. For wireless
services that are receive only, such as global positioning system
(GPS), global navigation satellite system (GNSS) and various
entertainment radios, such as AM/FM, digital audio broadcasting
(DAB), SiriusXM, etc., only the receiver design discussed herein
would be required. Also, the described radio architecture design
will enable one radio hardware design to function globally,
accommodating various global wireless standards through software
updates. It will also enable longer useful lifespan of the radio
hardware design by enabling the radio to adapt to new wireless
standards when they are deployed in the market. For example, 4G
radio technology developments and frequency assignments are very
dynamic. Thus, radio hardware deployed in the market may become
obsolete after just one or two years. For applications, such as in
the automotive domain, the lifespan can exceed ten years. This
invention enables a fixed hardware platform to be updateable
through software updates, thus extending the useful lifespan and
global reuse of the hardware.
[0020] FIG. 1 is a block diagram of a known multi-mode, multi-band
cellular communications user handset architecture 10 for a typical
cellular telephone. The architecture 10 includes an antenna
structure 12 that receives and transmits RF signals at the
frequency band of interest. The architecture 10 also includes a
switch 14 at the very front-end of the architecture 10 that selects
which particular channel the transmitted or received signal is
currently for and directs the signal through a dedicated set of
filters and duplexers represented by box 16 for the particular
channel. Modules 18 provide multi-mode and multi-band analog
modulation and demodulation of the receive and transmit signals and
separates the signals into in-phase and quadrature-phase signals
sent to or received from a transceiver 20. The transceiver 20 also
converts analog receive signals to digital signals and digital
transmit signals to analog signals. A baseband digital signal
processor 22 provides the digital processing for the transmit or
receive signals for the particular application.
[0021] FIG. 2 is a schematic block diagram of a cellular radio
front-end architecture 30 that provides software programmable
capabilities as will be discussed 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 a range of 400 MHz-3.6 GHz. Signals received and transmitted
by the antenna structure 32 go through a multiplexer 34 that
includes three signal paths, where each path is designed for a
particular frequency band as determined by a frequency selective
filter 36 in each path. In this embodiment, three signal paths have
been selected, however, the architecture 30 could be expanded to
any number of signal paths. Each signal path includes a circulator
38 that separates and directs the receive and transmit signals, and
provides isolation so that the high power signals being transmitted
do not enter the receiver side and saturate the receive signals at
those frequency bands.
[0022] The architecture 30 also includes a front-end transceiver
module 44 that is behind the multiplexer 34 and includes a receiver
module 46 that processes the receive signals and a transmitter
module 48 that processes the transmit signals. The receiver module
46 includes three receiver channels 50, one for each of the signal
paths through the multiplexer 34, where a different one of the
receiver channels 50 is 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 at the
particular frequency band and generates a representative stream of
digital data using an interleaving process in connection with a
number of N-bit quantizer circuits operating at a very high clock
rate, as will be discussed in detail below. As will further be
discussed, the delta-sigma modulator 52 compares the difference
between the receive signal and a feedback signal to generate an
error signal that is representative of the digital data being
received. The digital data bits are provided to a digital signal
processor (DSP) 54 that extracts the digital data stream. A digital
baseband processor (DBP) 56 receives and operates on the digital
data stream for further signal processing in a manner well
understood by those skilled in the art. The transmitter module 48
receives digital data to be transmitted from the processor 56. The
module 48 includes a transmitter circuit 62 having a delta-sigma
modulator that converts the digital data from the digital baseband
processor 56 to an analog signal. The analog signal is filtered by
a tunable bandpass filter (BPF) 60 to remove out of band emissions
and sent to a switch 66 that directs the signal to a selected power
amplifier 64 optimized for the transmitted signal frequency band.
In this embodiment, three signal paths have been selected, however,
the transmitter module 48 could be implemented using any number of
signal paths. The amplified signal is sent to the particular
circulator 38 in the multiplexer 34 depending on which frequency is
being transmitted.
[0023] As will become apparent from the discussion below, the
configuration of the architecture 30 provides software programmable
capabilities through high performance delta-sigma modulators that
provide optimized performance in the signal band of interest and
that can be tuned across a broad range of carrier frequencies. The
architecture 30 meets current cellular wireless access protocols
across the 0.4-2.6 GHz frequency range by dividing the frequency
range into three non-continuous bands. However, it is noted that
other combinations of signal paths and bandwidth are of course
possible. The multiplexer 34 implements frequency domain
de-multiplexing by passing the RF carrier received at the antenna
structure 32 into one of the three signal paths. Conversely, the
transmit signal is multiplexed through the multiplexer 34 onto the
antenna structure 32. For vehicular wireless access applications,
such a low-cost integrated device is desirable to reduce parts
cost, complexity, obsolescence and enable seamless deployment
across the globe.
[0024] The delta-sigma modulators 52 may be positioned near the
antenna structure 32 so as to directly convert the RF receive
signals to bits in the receiver module 46 and bits to an RF signal
in the transmitter module 48. The main benefit of using the
delta-sigma modulators 52 in the receiver channels 50 is to allow a
variable signal capture bandwidth and variable center frequency.
This is possible because the architecture 30 enables software
manipulation of the modulator filter coefficients to vary the
signal bandwidth and tune the filter characteristics across the RF
band, as will be discussed below.
[0025] The architecture 30 allows the ability to vary signal
capture bandwidth, which can be exploited to enable the reception
of continuous carrier aggregated waveforms without the need for
additional hardware. Carrier aggregation is a technique by which
the data bandwidths associated with multiple carriers for normally
independent channels are combined for a single user to provide much
greater data rates than a single carrier. Together with MIMO, this
feature is a requirement in modern 4G standards and is enabled by
the orthogonal frequency division multiplexing (OFDM) family of
waveforms that allow efficient spectral usage.
[0026] The architecture 30 through the delta-sigma modulators 52
can handle the situation for precise carrier aggregation scenarios
and band combinations through software tuning of the bandpass
bandwidth, and thus enables a multi-segment capture capability.
Dynamic range decreases for wider bandwidths where more noise is
admitted into the sampling bandpass. However, it is assumed that
the carrier aggregation typically makes sense when the user has a
good signal-to-noise ratio, and not cell boundary edges when
connectivity itself may be marginal. Note that the inter-band
carrier aggregation is automatically handled by the architecture 30
since the multiplexer 34 feeds independent modulators in the
channels 50.
[0027] The circulators 38 route the transmit signals from the
transmitter module 48 to the antenna structure 32 and also provide
isolation between the high power transmit signals and the receiver
module 46. Although the circulators 38 provide significant signal
isolation, there is some port-to-port leakage within the circulator
38 that provides a signal path between the transmitter module 48
and the receiver module 46. A second undesired signal path occurs
due to reflections from the antenna structure 32, and possible
other components in the transceiver. As a result, a portion of the
transmit signal will be reflected from the antenna structure 32 due
to a mismatch between the transmission line impedance and the
antenna's input impedance. This reflected energy follows the same
signal path as the incoming desired signal back to the receiver
module 46.
[0028] The architecture 30 is also flexible to accommodate other
wireless communications protocols. For example, a pair of switches
40 and 42 can be provided that are controlled by the DBP 56 to
direct the receive and transmit signals through dedicated fixed RF
devices 58, such as a global system for mobile communications (GSM)
RF front-end module or a WiFi front-end module. In this embodiment,
some select signal paths are implemented via conventional RF
devices. FIG. 2 only shows one additional signal path, however,
this concept can be expanded. to any number of additional signal
paths depending on use cases and services.
[0029] Delta-sigma modulators are a well known class of devices for
implementing analog-to-digital conversion. The fundamental
properties that are exploited are oversampling and error feedback
(delta) that is accumulated (sigma) to convert the desired signal
into a pulse modulated stream that can subsequently be filtered to
read off the digital values, while effectively reducing the noise
via shaping. The key limitation of known delta-sigma modulators is
the quantization noise in the pulse conversion process. Delta-sigma
converters require large oversampling ratios in order to produce a
sufficient number of bit-stream pulses for a given input. In
direct-conversion schemes, the sampling ratio is greater than four
times the RF carrier frequency to simplify digital filtering. Thus,
required multi-GHz sampling rates have limited the use of
delta-sigma modulators in higher frequency applications. Another
way to reduce noise has been to use higher order delta-sigma
modulators. However, while first order canonical delta-sigma
architectures are stable, higher orders can be unstable, especially
given the tolerances at higher frequencies. For these reasons,
state of the art higher order delta-sigma modulators have been
limited to audio frequency ranges, i.e., time interleaved
delta-sigma modulators, for use in audio applications or
specialized interleaving at high frequencies.
[0030] The filter characteristics of a Delta-Sigma modulator may
effectively be modified in order to compensate for Doppler shift.
Doppler shift occurs when the transmitter of a signal is moving in
relation to the receiver. The relative movement shifts the
frequency of the signal, making it different at the receiver than
at the transmitter. An exemplary system according to the present
disclosure leverages the software-defined radio architecture to
quickly estimate a shift in the carrier frequency and re-center the
filter before the signal is disrupted or degraded. In normal
operation, the notch of the modulator filter is centered about 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 offset the carrier by an amount .DELTA.f causing potential
degradation to signal content with an increase in noise at one side
of the band. According to the method and system described herein,
the transceiver in a wireless cellular communication system can
adapt to changes in the RF carrier frequency and may maintain
signal integrity, by shifting the filter notch by the same amount
as the carrier frequency.
[0031] For the cellular application discussed herein that covers
multiple assigned frequency bands, a transmitter with multi-mode
and multi-band coverage is required. Also, many current
applications mandate transmitters that rapidly switch between
frequency bands during the operation of a single communication
link, which imposes significant challenges to 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 loop
bandwidth of the frequency synthesizer, around 1 MHz. Hence, the
achievable channel switching time is around several microseconds,
which unfortunately is too long for an agile radio. A fully digital
PWM based multi-standard transmitter, known in the 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
the LO sourced to enhance the switching speed, however, this design
consumes significant power and may not deliver a high frequency LO
with low spurious components. Alternately, single sideband mixers
can be used to generate a number of LOs with different center
frequencies using a common phase-lock loop (PLL), whose channel
switching times can be fast. However, this approach can only
support a limited number of LO options and any additional channels
to cover the wide range of the anticipated 4G bands would need
extra mixtures. As discussed, sigma-delta modulators have been
proposed in the art to serve as an RF transmitter to overcome these
issues. However, in the basic architecture, a sigma-delta modulator
cannot provide a very high dynamic range in a wideband of
operations due to a moderate clock frequency. It is precisely
because the clock frequency is constrained by current technology
that this high frequency mode of operations cannot be
supported.
[0032] Turning now to FIG. 3, an exemplary system for dynamic
frequency correction in delta-sigma based software defined receiver
300 is shown. The system is operative to determine a signal
response for a respective Doppler shift. For example, an example of
a Doppler shifted signal is applied to the system front end of the
receiver. The system is then operative to determine a frequency
difference in 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, thereby
shifting the filter bandwidth by an amount equal to the offset. The
system is then operative to determine in the shifted filter
frequency response has an adequate attenuation and passband
response. If so, the frequency offset value is stored in memory for
use in normal operations. 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 would is set be the frequency of an expected operating
frequency plus or minus the effects of a Doppler shift. The system
is then operative to perform an initial adjustment of the filter
according to the known pilot frequency. The DSP 330 is then
operative to generate a calibration term, such as an n-bit
calibration word. The calibration term is stored in a memory 340.
During normal receive mode operation, the system is further
operative to amend the n-bit calibration code to the tuning code
typically presented to the modulator in response to the Doppler
shift. The system may be combined using a simple adder, a
comparable adder, or implemented in software.
[0033] Turning now to FIG. 4, an exemplary method for dynamic
frequency correction in delta-sigma based SDR 400 is shown. During
calibration of the signal processing system, the method is
operative to first configure the SDR to receive a signal at an
expected carrier frequency 405. The system is then operative to
apply an RF pilot signal 410 to a signal receiving portion of the
receiver, such as at the antenna, or at the bandpass filters, or
input to the receiver, as described previously. The RF pilot signal
will have a known center frequency that is offset from the expected
carrier frequency by an amount equal to an expected Doppler shift
under operating conditions. The SDR configuration is then
configured to process the RF pilot signal. They system is then
operative to determine if the SDR configuration is suitable for
receiving the RF pilot signal 430. If the frequency response of the
SDR configuration is not suitable for properly processing the RF
pilot signal, the SDR configuration step 420 is repeated and the
SDR configuration is altered in response to the frequency response
determination. If the frequency response of the SDR configuration
is suitable for properly processing the RF pilot signal, the system
is then operative to save the configuration data associated with
the frequency of the RF pilot signal 440. For example, a frequency
offset value may be stored with the center frequency of the RF
pilot signal. Alternatively, delta signal modulation configuration
parameters may be saved to a memory along with the frequency
response of the RF pilot signal.
[0034] Turning now to FIG. 5, an exemplary apparatus for dynamic
frequency correction in delta-sigma based software defined receiver
500 is shown. The system is operative to receive a RF signal 510.
Initially the SDR 520 is 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 is different than the expected center frequency,
the DSP retrieved the appropriate saved configuration parameters
from the memory 540. These configuration parameters are used to
alter the configuration of the SDR 520 to receive a signal at the
determined center frequency of the received RF signal. The DSP 530
is then operative to process the data and determine if the signal
quality is acceptable for the determined 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 is operative to process
and decode the received RF signal with those parameters, and to
periodically check the signal quality.
[0035] Turning now to FIG. 6, an exemplary method for dynamic
frequency correction in delta-sigma based software defined receiver
600 is shown. During signal processing operations, the method is
operative 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 altered according
to the calibration word 630. The system is then operative to
process the RF signal 600. If no Doppler shift is detected, the DSP
is operative to process the RF signal 600.
[0036] As will be well understood by those skilled in the art, the
several and various steps and processes discussed herein to
describe the invention may be referring to operations performed by
a computer, a processor or other electronic calculating device that
manipulate and/or transform data using electrical phenomenon. Those
computers and electronic devices may employ various volatile and/or
non-volatile memories including non-transitory computer-readable
medium with an executable program stored thereon including various
code or executable instructions able to be performed by the
computer or processor, where the memory and/or computer-readable
medium may include all forms and types of memory and other
computer-readable media.
[0037] The foregoing discussion disclosed and describes merely
exemplary embodiments of the present invention. One skilled in the
art will readily recognize from such discussion and from the
accompanying drawings and claims that various changes,
modifications and variations can be made therein without departing
from the spirit and scope of the invention as defined in the
following claims.
* * * * *