Stop-on-station method and apparatus

A method for stopping on a radio station includes calculating a radio signal quality (205) using a multipath echo indicator and determining if the radio signal quality is greater than a predetermined signal quality threshold (210). A zero crossings indicator of a demodulated signal may be used (225) to reduce a false alarm rate. An apparatus includes an antenna (105), a local oscillator (110) coupled to the antenna, an analog-to-digital converter circuit (115) coupled to the local oscillator, a demodulator circuit (120) coupled to the analog-to-digital converter circuit, a signal strength determining circuit (125) coupled to the analog-to-digital converter circuit, a logarithmic circuit (150) coupled to the signal strength determining circuit, a multipath echo bandpass filter (155) coupled to the logarithmic circuit, and a stop-on-station circuit (145) coupled to the demodulator circuit, the multipath echo bandpass filter, and the logarithmic circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of communications. More particularly, the invention relates to the detection of radio stations.

2. Discussion of the Related Art

Radio stations broadcast information encoded into radio-frequency (RF) signals on a plurality of transmission schemes. These RF signals may be, for example, amplitude modulated (AM) signals or frequency modulated (FM) signals. Typically, the transmitted information is decoded into an audio signal at a radio receiver.

Modern radio receivers include seek and scan functions. These functions are initiated by a user and attempt to search for a station that meets certain criteria. A seek function searches through radio channels and stops when the receiver finds the next station. A scan function also searches though radio channels and stops at the next station, but only for a limited period of time, repeating the process until terminated by the user.

Usually, in order for seek and scan functions to find and stop at radio stations, the quality of the received RF signal is measured. A typical technique includes determining if the signal strength is greater than a predetermined magnitude. Another metric used for signal quality measurement is ultrasonic noise (USN). A problem with these metrics is that they do not satisfactorily meet the requirements for finding suitable radio stations. Moreover, even when a good quality signal is found, the encoded information may be other than an audio signal (false alarm).

Thus, there is a need for a method and/or apparatus for utilizing metrics that can satisfactorily characterize the quality of received RF signals. Further, there is a need for minimizing false alarm rates.

SUMMARY OF THE INVENTION

There is a need for the following embodiments. Of course, the invention is not limited to these embodiments.

According to an aspect of the invention, a method for stopping on a radio station includes calculating a radio signal quality using a multipath echo indicator, and stopping at the radio station if the radio signal quality is greater than a predetermined signal quality threshold.

According to another aspect of the invention, a method for stopping on a radio station includes demodulating a radio signal to produce a demodulated radio signal, calculating a zero crossings indicator of the demodulated radio signal, and stopping at the radio station if the zero crossings indicator is less than a predetermined zero crossings threshold.

According to yet another aspect of the invention, an apparatus for stopping on a radio station includes an antenna for receiving an RF signal having a plurality of radio stations, a local oscillator coupled to the antenna, an analog-to-digital converter circuit coupled to the local oscillator, a demodulator circuit coupled to the analog-to-digital converter circuit for producing a demodulated radio signal, a signal strength determining circuit coupled to the analog-to-digital converter circuit for producing a mean signal strength quantity, a logarithmic circuit coupled to the signal strength determining circuit, for producing a signal strength indicator, a multipath echo bandpass filter coupled to the logarithmic circuit for producing a multipath echo indicator, and a stop-on-station circuit coupled to the demodulator circuit and to the multipath echo bandpass filter for stopping on a radio station as a function of the signal strength indicator, the multipath echo indicator, and a zero crossings indicator of the demodulated radio signal.

These, and other, aspects and embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating various embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions and/or rearrangements may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such substitutions, modifications, additions and/or rearrangements.

DETAILED DESCRIPTION

The invention and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be understood that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those of ordinary skill in the art from this disclosure.

Exemplary embodiments of the invention include a method and/or apparatus for detecting modulated radio frequency signals, for example, FM and AM radio stations in a fixed or mobile radio environment while minimizing false alarm rates. The false alarm rate is defined herein as the rate at which the receiver stops at an unsuitable radio station during a seek, scan, or searching operation.

In one exemplary embodiment, the invention includes a multipath echo indicator to determine the quality of the radio signal and improve detection. Other embodiments of the invention may also include an adjacent station indicator to further improve detection of the radio signal by eliminating stations with high levels of interference. Additional embodiments of the invention may also include an ultrasonic noise indicator in conjunction with the multipath echo measurement and/or the adjacent station indicator to improve detection of the radio signal.

In another exemplary embodiment, the invention may include using a zero crossing (ZC) indicator of the demodulated radio signal to decrease or minimize the false alarm rate. In yet another embodiment, the invention may include using a combination of multipath echo, adjacent station, ultrasonic noise, and zero crossing indicators to perform a seek, scan, or search operation.

Referring toFIG. 1, a block diagram of a radio frequency stop-on-station circuit100is depicted according to an exemplary embodiment of the invention. A radio signal104is received by an antenna105and mixed with a local oscillator signal at a mixer110. Radio signal104may be, for example, a frequency modulated (FM) or amplitude modulated (AM) signal, or any other type of radio frequency modulated signal. The output of the mixer110is coupled to an analog-to-digital converter circuit115. The analog-to-digital converter circuit115is coupled to a demodulator120, a signal strength determining circuit125, and an adjacent band energy detector circuit130. The demodulator120is coupled to an audio and weak-signal processing circuit135, a stop-on-station circuit145, and an ultrasonic noise bandpass filter140.

The signal strength determining circuit125is coupled to a logarithmic circuit150, and the logarithmic circuit150is coupled to a multipath echo bandpass filter155. The audio and weak-signal processing circuit135, the ultrasonic noise bandpass filter140, the logarithmic circuit150, the multipath echo bandpass filter155, the adjacent band energy detector circuit130, and a program storage device165are all coupled to the stop-on-station circuit145. A microcontroller unit160is coupled to the audio and weak-signal processing circuit135and to the stop-on-station circuit145.

The analog-to-digital converter circuit115outputs in-phase (I) and quadrature phase (Q) digital signals to the demodulator circuit120, the signal strength determining circuit125, and the adjacent band energy detector circuit130. The demodulator circuit120may be, for example, an FM or an AM demodulator circuit, or any other appropriate demodulator depending upon the particular modulation scheme of radio signal104. The demodulator circuit120outputs a multiplexed signal to the audio and weak-signal processing circuit135, the stop-on-station circuit145, and the ultrasonic noise bandpass filter140. The signal strength determining circuit125outputs a sum of the squares of the in-phase and quadrature phase signals (a signal strength quantity) from the analog-to-digital converter circuit115(Received Signal Strength Indication or RSSI) to the logarithmic circuit150. The output of the logarithmic circuit150is the logarithm of the mean signal strength, i.e.: Log(RSSI).

The stop-on-station circuit145receives the signal strength indicator (Log(RSSI)) from the logarithmic circuit150, an ultrasonic noise indicator from the ultrasonic noise bandpass filter140, a multipath echo indicator from the multipath echo bandpass filter155, and an adjacent station indicator from the adjacent band energy detector circuit130. As explained below in more detail with reference to flowcharts ofFIGS. 2 and 3, one or more of these indicators may be used by the stop-on-station circuit145to calculate the radio signal quality.

The ultrasonic noise indicator may be defined as the noise in the demodulated signal that is beyond the audible frequency range. This flag is typically obtained by filtering the demodulator signal (with cutoff frequency that is well above the audible frequency range of 20 KHz). Ideally, the energy of the signal in this non-audible frequency range should be small (since information is not typically transmitted in this band) and so any deviation from this is typically used as a rough indicator of the amount distortion in the system.

The multipath echo indicator may be defined as a measure of the amount of multipath interference in the radio channel. In one embodiment, this is estimated by band-pass filtering the log(RSSI) signal. For an ideal FM signal the non-dc frequency components of the RSSI may be close to zero (since an FM signal has constant modulus) and so band-pass filtering signal gives a measure of deviation from this ideal case which is due primarily to the multipath interference in the channel. Thus, this particular flag is specific to FM systems whereas the other flags can be used for AM and FM systems.

The adjacent station indicator may be defined as a measure of the amount of interference due to the adjacent stations. This quantity is determined by estimating the relative amount of energy in the higher sub-bands of the pre-demodulated signal with respect to the desired signal energy level (of the pre-demodulated signal). In one exemplary embodiment, the adjacent channel indicator may include an IF (intermediate frequency) filter for dynamically adjusting an intermediate frequency. The IF filter may include a filter bank, a set of power/amplitude estimator circuits, and a filter control. In operation, the filter bank may generate sub-bands, each sub-band having a predetermined frequency range. The set of power/amplitude estimators may provide an estimated power/amplitude in each sub-band, and a filter control may use the power/amplitude estimates to determine the relative energies of each sub-band signal, thereby determining the adjacent channel indicator.

Still referring toFIG. 1, the stop-on-station circuit145receives the multiplexed signal from the demodulator circuit120and calculates the rate of zero crossings of the demodulated audio signal. In one embodiment, the stop-on-station circuit145calculates an average number of zero crossings, or a zero crossings indicator. The zero crossings indicator may be defined as the rate of zero-crossings in a signal. For well defined stochastic processes there may be explicit formulas for estimating the zero-crossing rate. For example, for Gaussian processes the zero-crossings rate may explicitly be computed in terms of the second-order statistics of the process. However, for empirically obtained signals, the zero crossing rate may be empirically estimated. In one embodiment, the zero-crossings rate is used as the average number of zero-crossings in an interval of time. In another embodiment, this interval of time (or window size of the observation) is programmable.

The microcontroller unit160controls the operation of the audio and weak-signal processing circuit135and of the stop-on-station circuit145. The microcontroller unit160may also control a user interface or panel (not shown). The stop-on-station circuit145may send information such as calculated indicators to the audio and weak-signal processing circuit135. The program storage media or device165may provide the stop-on-station145with instructions for performing a stop-on-station function, which may be included in a seek, scan, or search program.

In practice, the stop-on-station circuit145may be a programmable circuit, such as, for example, a microprocessor or digital signal processor-based (DSP) circuit, that operates in accordance with instructions stored in the program storage media165. The program storage media165may be any type of readable memory including, for example, a magnetic or optical media such as a card, tape or disk, or a semiconductor memory such as a PROM or FLASH memory. The stop-on-station circuit145may be implemented in software, such as, for example, a software defined radio algorithm, or the functions may be implemented by a hardware circuit, or by a combination of hardware and software.

When the stop-on-station circuit145is a programmable circuit, a program, such as that presented below and discussed in detail with reference toFIGS. 2 and 3is stored in the program storage media165to create an apparatus in accordance with an embodiment of the present invention that operates in accordance with embodiments of the methods of the present invention. In the alternative, the stop-on-station circuit145may be hard-wired or may use predetermined data tables, or may be a combination of hard-wired and programmable circuitry.

Referring toFIG. 2, a flowchart of a radio frequency stop-on-station method200is depicted according to an exemplary embodiment of the invention. The stop on station algorithm200may be performed by the stop-on-station circuit145detailed inFIG. 1.

Upon initiation of the algorithm200, the signal quality is computed in step205using an equation such as, for example:
quality=Log(RSSI)

where: quality is the radio signal quality; andLog(RSSI) is the logarithm of the radio signal strength.

In another exemplary embodiment, the signal quality may be computed in step205using another equation such as, for example:
quality=Log(RSSI)−f(echo/RSSI)

where: quality is the radio signal quality;Log(RSSI) is the logarithm of the radio signal strength; andf(echo/RSSI) is the multipath echo indicator.

In another exemplary embodiment, the signal quality may be computed in step205using another equation such as, for example:
quality=Log(RSSI)−[f(echo/RSSI)+g(adjacent station)]

where: quality is the radio signal quality;Log(RSSI) is the logarithm of the radio signal strength indicator;f(echo/RSSI) is the multipath echo indicator; andg(adjacent station) is the adjacent channel (or station) indicator.

In yet another exemplary embodiment, the signal quality may be computed in step205using another equation such as, for example:
quality=Log(RSSI)−[f(echo/RSSI)+g(adjacent station)+h(usn)]

where: quality is the radio signal quality;Log(RSSI) is the logarithm of the radio signal strength indicator;f(echo/RSSI) is the multipath echo indicator;g(adjacent station) is the adjacent channel (or station) indicator; andh(usn) is the ultrasonic noise indicator.

Other methods may also be acceptable for determining the signal quality. Next, the calculated signal quality is compared to a predetermined signal quality threshold in step210. If the signal quality is greater than the signal quality threshold, step220calculates an average of zero crossings (zero crossings indicator) of the demodulated signal, otherwise the algorithm moves on to the next station in step215. The average number of zero crossings is compared to a predetermined zero crossings threshold in step225. If the average number of zero crossings of the demodulated signal is greater than the zero crossings threshold, the algorithm tunes to the next station in step215, otherwise the current station is accepted in step230.

One exemplary embodiment includes using the stop-on-station method detailed inFIG. 2to perform a seek and/or a scan operation. When initiated by a user, the seek and/or scan operation sweeps through radio channels and stops when the receiver finds the suitable next station.

Referring toFIG. 3, a flowchart of a seek/scan algorithm300is depicted according to another embodiment of the invention. The seek/scan method300may be performed by the stop-on-station circuit145detailed inFIG. 1.

Upon initiation of the method300, a new station is tuned to in step305. Next, if a signal quality metric is to be used, as determined in step306, control passes to step310. Otherwise control passes to step365. In step310, a signal quality is calculated as Log(RSSI). Next, if a multipath echo metric will be used as determined by the algorithm in step315, the multipath echo indicator is calculated in step320and subtracted from the signal quality in step325. Otherwise control passes to step330. Next, if an ultrasonic noise metric will be used as determined by step330, the ultrasonic noise indicator is calculated in step335and subtracted from the signal quality in step340. Otherwise control passes to step345. Next, if an adjacent station metric will be used as determined by the algorithm in step345, the adjacent station indicator is calculated in step350and subtracted from the signal quality in step355. Otherwise control passes to step360.

The signal quality is compared to a signal quality threshold in step360. If the signal quality exceeds the signal quality threshold, control passes to step365. Otherwise control is returned to step305and the next station is tuned. Next, if a zero crossings metric will be used as determined by step365, a zero crossings indicator is calculated in step370and compared to a zero crossings threshold in step375. If the zero crossings indicator exceeds the zero crossings threshold, control is returned to step305and the next station is tuned. If a zero crossings metric will not be used as determined by the algorithm in step365, or if the zero crossings indicator does not exceed the zero crossings threshold as determined by step375, control passes to step380.

The method300determines whether it is performing a seek or a scan operation in step380. If a seek operation is being performed, the current station is accepted in step385and the method ends. If a scan operation is being performed, the current station is accepted in step390and control is passed to step395. In step395, if a user performs an input operation before a scan timer runs out, the method ends. Otherwise control is passed to step305and the method tunes to the next station.

One embodiment may include verifying if a Program Identification (PI) code is valid, as defined by Radio Data System (RDS) standards. A PI code verification step may be used in conjunction with the methods described above for deciding whether or not to stop at a radio station. This embodiment may use a radio signal quality criteria, a demodulated audio signal zero crossings criteria, and/or a PI code verification criteria for stopping at a radio station.

Embodiments of he invention may be implemented, for example, in a digital signal processor or in a digital intermediate frequency (DIF) radio hardware. Other embodiments of the invention may also be implemented in a software radio or a combination of DIF hardware and software radio.

The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. The term computer program, program, or software, as used herein, is defined as a sequence of instructions designed for execution on a computer system. A program, or computer program, may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system.

The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” and/or “step for.” Subgeneric embodiments of the invention are delineated by the appended independent claims and their equivalents. Specific embodiments of the invention are differentiated by the appended dependent claims and their equivalents.