FI115681B - Method and apparatus for filtering received signal - Google Patents

Description

115681

The present invention relates generally to the reception of signals, such as radio frequency signals, and in particular to the filtering of received signals.

Conventional radio-frequency receivers for use in wireless communication systems such as frequency division multiplexing, time division multiplexing, and code division multiplexing typically operate in a multi-signal environment. In such an environment, it is desirable for the receiver to have as wide a dynamic range as possible without compromising the quality of the received signal. In addition, higher dynamic range is particularly important in wide bandwidth signal receiving applications. Thus, there is a need for a device and method for filtering a received signal that provides an improved dynamic range while maintaining the quality of the received signal.

To satisfy this need, the present invention provides; There is also an apparatus and method for filtering the received signal. The apparatus comprises a compressing receiver; and an alternating frequency filter which acts to compress. : 25 controlled by the receiver. The apparatus further comprises means for: comparing the pulses in the pulse signal to t threshold and determining the frequency of the filter and

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a filter for generating an analog control signal indicative of frequency. A swap filter filters · '·· ·' 3 0 received signal. According to another aspect of the present invention, the apparatus comprises a variable frequency ·; * · filter, a first analog-to-digital converter, a dampener. and another analog-to-digital converter. The first analog-to-digital converter operates under a variable frequency filter »» * · 35 and the second analog-to-digital converter operates under an attenuator. The attenuator responds to the received signal and produces a attenuated signal.

115681 2

The method comprises the steps of: detecting a received signal; interval, determining the filter frequency based on vii-10 water and filtering the received signal at the filter frequency.

The invention itself, together with its intended advantages, will be best understood by reference to the following detailed description set forth in the accompanying drawings.

Fig. 1 is a block diagram of a preferred embodiment of a received signal filtering device.

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FIG. 2 is a block diagram of another preferred embodiment of the device for filtering a received signal.

Fig. 3 is a flowchart of a preferred embodiment of a received signal filtering method 25.

Figure 1 shows the device 10 of the received signal *. to detect and filter. The device 10 comprises an antenna 12, an input bandpass filter 14, a splitter 30 16, the compressive receiver 22 and a frequency agile filter 60. The input filter 14 is connected to an aerial 12 and the splitter 16. The apparatus 10 also comprises a splitter 16 connected in the signal branch, which comprises an amplifier 40, a filter * I * 42, a mixer 44 having a local oscillator 46, a * 115111 second amplifier 48, a second filter 50, a third amplifier 52, a third filter 54, and a delay circuit 57.

The compressing receiver 22 is coupled to a divider 16 through a mixer 18 having a local oscillator (PO) 11 and a suppressor 20 and is coupled to an alternating frequency filter 60 through digital components including threshold comparator 32, counter 34, digital control unit 36 and digital-to-analog converter. 38. The timing of the compressor-10 ringing receiver 22 is controlled by a timing circuit 30. The compressor receiver 22 comprises a mixer 24, a sweeping local oscillator 26, a frequency difference ruler 28, and a weighting filter 29.

During operation, the radio frequency (RF) input signal 13 is received by antenna 12, filtered by a filter 14, and distributed by a divider 16. The first branch of the split signal from divider 16 is mixed with mixer 18 having PO 11, damped by attenuator 20 and supplied to compression receiver 22. a second branch of the split signal is supplied to the first amplifier 40, filtered by a filter 42, mixed with a mixer 44 with the output i of a local oscillator 46, amplified by amplifiers 48 and 52, and a filter; *. 25 and 54 to produce a result signal.

While it has been contemplated that many i * .t filter and amplifier assemblies may be used, such as a single filter and a single amplifier, the serial arrangement shown in Figure 1 provides receiver 10 with the desired sensitivity and dynamic range. The output signal is delayed by a delay circuit 57 and is supplied to an alternating frequency filter 60. Of the alternating frequencies, the filter 60 is controlled by a * digital-to-analog converter 38, which is controlled by a compressor receiver 22. The output of the variable frequency filter «<, 35 60 is converted to a digital signal by analog-to-digital

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115681 4 by ADM 62 and transmitted as an output signal 64. The output signal 64 is then further processed, such as digital reverse filtering of the output signal 64, using a digital filter which is controlled by the digital control unit 36. Further processing of the output signal 64 comprises digital down-mixing, filtering and demodulation.

After the signal 13 received by the antenna 12 is detected, its frequency is downmixed by the mixer 18 and it is attenuated by the attenuator 20, the compressing receiver 22 performs frequency offset calculation of the downmixed signal to produce a pulse signal comprising several pulses. The height of each pulse corresponds to the signal strength, and the location of the pulse corresponds to the frequency of the received signal 13. Compressing receiver 22 performs a real-time Fourier conversion on the received signal and outputs a pulse signal. The compressing receiver 22 mixes the downmixed sig-20 signal with the fast-sweep local oscillator signal from the sweep oscillator 26 to produce a frequency modulated (FM) waveform i. The frequency difference delay 28 compresses each carrier in the • downmixed signal to a narrow time domain pulse. The weighting filter 29 performs a weighting filter function on the pulsed signal to delimit and generate the pulses in the pulse signal in a better way.

The delay of each output pulse from the start of the sweep of the local oscillator is proportional to the frequency of the carrier in the downmixed signal. Since the output pulse signal from the weight filter 29 is proportional to the input power of the detected radio frequency (RF) input signal 13, 35, the input frequency to be filtered is The threshold comparator 32 compares the amplitudes of at least some of the pulses in the pulse signal with the threshold. Counter 34, preferably 5 multi-event counter, determines using timer circuit 30, where pulses occur with respect to the time of start of sweep PO 26.

The digital control unit 36 then determines the frequency of the filter 10 by converting the counter output to a digital word. The digital word is converted to an analog control signal by a digital-to-analog converter 38, and the variable-frequency filter 60 filters the received signal by setting a filter at frequency 15 by the digital control unit 36. Digital control unit 36 determines the filter frequency, preferably using a look-up table, to describe the measured delay as the appropriate filter frequency. Counter 34 is triggered at the start of the scan of PO 26, and digital control unit 36 reads the counter output when threshold 20 is exceeded. Counter 34 is reset after the scan is complete. The digital control unit 36 comprises: 'preferably a controller such as Motorola, Inc., for example. available, processor and memory HC16 type:. · The wizard.

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Due to the time elapsed between the signal receiving compressor receiver 22 and the transmission of the filter frequency to the alternating frequency filter 60, the second distributed signal 30 from the second divider 16 is preferably delayed by a time 57 such that the second distributed signal arrives at the digital frequency 60 a control signal from the li-to-analog converter 38. Vaihtotaa-; ; Thus, the hair filter 60 filters the received signal 35 at a frequency calculated by the digital control unit 36.

115681 6

In the specific embodiment shown in Figure 1, the circuit 10 can be constructed with the following components: filter 14 is a Filtronix CB285 filter, divider 16 is a Mini Circuits ZFSC-2-2 type divider, mixer 18 is a Mini 5 Circuits ZFM-150 mixer and PO 11 is preferably a Panasonic ENF-VA7 series oscillator tuned to about 880 MHz. Compression Receiver 22 is a Andersen Laboratories CR-72-12-15 Compression Receiver, and Threshold Comparator 32 is an AD9696 Type 10 Comparator available from Analog Devices. The timer circuit 30 is a US-685-120 type timer circuit available from US Crystal Corp. The counter 34 is an ICM 7216B1P1 counter from Harris Semiconductor, the digital control unit 36 is the Motorola MC68HC16Z1, and the digital-to-analog converter 38 is the Burr Brown DAC600. Amplifier 15 includes two Aznac AMC155 type amplifiers in series, filter 42 is a Filtronix CB286 filter, mixer 44 is a Watkins Johnson WJ-4020 mixer, and a local oscillator 46 is a Panasonic ENF-VA7 tuned to about 930 MHz. series type oscillator. The amplifier 20 48 is a Cougar AC379 amplifier, the filter 50 is a Networks International D318 filter, and the amplifier 52 comprises two: "A Cougar AP148 series amplifier. The filter 54 is a Networks ..li 'International D319 filter. The analog-to-digital converter 62 is j '· Analog Devices AD9042 Converting Filter 25 60 is a notch filter, such as a filter that can be constructed as described in Milcom's Novel Active RF Tracking Notch Filters for Interference Suppression in HF, VHF, and UHF. Frequency Hopping Receivers, ”Conference Record 1991 30 IEEE Military Communications Conference Vol. 3 of 3, p. 956, by Masood Ghadaksak (1991).

The preferred method and apparatus for detecting and filtering a received RF signal has many good points. For example, in preferred embodiment 115681 7, the dynamic range is enhanced by protecting hardware components such as an analog-to-digital converter 62 from high saturated signals. Furthermore, the preferred embodiment may be used in multi-channel systems such as time division multiple access (TDMA), code division multiple access (CDMA) and frequency division multiple access (FDMA) systems. The preferred embodiment can be used over a wide range of RF-10 frequency bands because the input signal is mixed with the appropriate compressor receiver input frequency. Although the preferred embodiment is particularly well suited for use at cellular frequencies, it should be understood, however, that the present invention is not limited to use in the cellular frequency band.

In addition, many conventional methods of limiting the signal level 20 to a receiver detector, such as an ADM, degrade the performance of the receiver's signal-to-noise (S / N) signal and thus reduce the receiver's sensitivity. Instead, the preferred embodiment enables the processing of RF signals over the entire dynamic range in the cellular band without degrading the S / N performance. The preferred embodiment I * · .. further performs an automatic frequency control of the variable frequency filter 60. Since the alternating frequency filter 60 can be tuned throughout the desired frequency band, no fixed band-pass filters are required, and the frequencies to which the filter 60 is tuned can normally be processed as soon as the signal level has increased * "above the comparator threshold level.

; Another embodiment of the present invention is shown in FIG. 2. The same reference numerals are used for like components in each of the figures. As shown in Fig. 2, the device 100 is similar to the circuit of Fig. 1, but also includes an attenuator 70 and another analog-to-digital converter 72 coupled to attenuator 5 70. Attenuator 70 responds to received signal 13 and is coupled to delay circuit 57. Threshold 70 is selected such that the analog-to-digital converter 72 processes the largest signal received by the antenna 12 without being saturated by the converter 72. The variable frequency filter 60 protects the en-10 first analog-to-digital converter 62 from saturation.

In this device configuration, the first analog-to-digital converter 62 processes lower-level signals, and the second analog-to-digital converter 72 processes higher-level signals. Thus, the second analog-to-digital converter 15 72 is capable of processing signals having frequencies corresponding to those filtered by the alternating-frequency filter 60.

In a broadband multi-carrier environment with ADM

20 handles a plurality of RF inputs, a plurality of band-pass filters placed in front of the receiver ADM 62 protect it from saturation caused by the largest signals. This allows ADM 62 to process lower level signals. The value of the threshold setting for the suppressor 70 is:. 25 is preferably selected so that the ADM 72 can handle the mouth; the signals coming to antenna port 12 without saturating it »·.

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According to Figure 2, the RF input is supplied to two different taps. 30: a first to a compressing receiver 22 and a second to a low level receiving branch beginning at the amplifier stage 40. The third branch is formed after the delay circuit 57 «(iV ') and supplied to the threshold suppressor 70.

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Said three branches may be connected to an antenna input, a multiplexed antenna input, or they may be replicated to a plurality of receiver branches. Compressing receiver 22 performs a real-time Fourier transform on its input signals and outputs an output pulse for each input signal. The input signal of the compressor receiver 22 is rapidly mixed with the sweep PO 26 to provide an FM waveform to the mixer output 24. A Disperse Delay Line (DDL) 28 is used to compress each input signal into a narrow pulse over a time domain. The weighting filter 29 modifies the output pulse from the DDL 28 to expand the dynamic range of the compressing receiver 22. The weighting filter 29 may be integrated into the structure of the DDL 28.

The output pulse delay from the start of the PO sweep is proportional to the frequency of the input signal of the compressing receiver 22. Since the amplitude of the output pulse of the weighting filter 29 is proportional to the power of the detected input signal, then the threshold comparator 32 is used to select based on the amplitude which input frequency is to be filtered. The combination of the amplitude: "di- and delay information" is then converted to a voltage of the variable frequency filter 60.

: 25 The method for performing the conversion is to use a multi-event subtractor, '34, to correlate the input signal to the detected frequency. This is accomplished by starting counter 34 at the beginning of the scan, locking the reading when the amplitude threshold is exceeded, and resetting the counter when the scan is complete. Digital control unit 36 reads the counter output and converts it to either an analog voltage * 'or a digital word depending on the control requirements of filter 60'.

115681 10 When multiple tunable bandpass filters are used, the ADM 62 is substantially protected from a number of large RF input signals. The delay block 57 allows the compressing receiver 22 to perform detection and control the filter 60 before the ADM 62 becomes saturated. The ADM 62 processes RF signals below a predetermined threshold power level. The large RF signals above this threshold level are processed by the ADM 72, protected by the input threshold set attenuator 70. Thus, in the preferred embodiment using multiple analog-to-digital converters 62 10 and 72, the entire dynamic range of the receiver 10 is improved.

A preferred embodiment of the received RF filtering method is shown in Figure 3.

As shown in Fig. 3, method 200 begins with step 202 and comprises the steps of detecting a received signal, step 204, downconverting the received signal to produce a downconverted signal, step 206, performing a delay computation of the frequency difference 20 to produce a pulse signal comprising several pulses, step 208, the amplitudes of at least some of the pulses in the pulse signal to the threshold, step 210, measuring the delay of pulses whose S '· amplitude exceeds the threshold for a predetermined time interval, step 212, determining the filter frequency based on the delay, step 214, and filtering the received signal filter frequency, step 216. Step 216, which determines the filter frequency, may use the lookup table to describe the number of calculated pulses to the filter frequency.

The method may further comprise further steps of applying a weighting filter to the pulse signal or delaying the received RF signal before filtering the received signal at the filter frequency.

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It will be appreciated that for the purposes of this specification, the second component acts as controlled by or communicating with the first component whether the first and second components 5 are directly coupled or indirectly coupled, such as via intermediate components comprising switches operatively coupling components for a single time segment. as long as a signal branch can be found which directly or indirectly establishes a connection between the components. The variable-frequency filter 60 may function, for example, under the control of a compressor filter 22 as defined herein, although intermediate components such as comparator 32, counter 34, controller 36 15, and DAM 38 are disposed between compressor receiver 22 and filter 60.

Other advantages and modifications of the apparatus and method described above will be readily apparent to those skilled in the art. For example, although digital control unit 36 in the preferred embodiment 20 produces a digital word, digital control unit 36 may alternatively provide an analog voltage to control the filter 60 depending on the specific requirements of the filter. Also, even the best; The operation of the preferred embodiment is explained in the case of using two ana- · 25 log-to-digital converters, so the number of analog-to-digital converters used is not limiting of the present invention.

t ♦ · t »The present invention is not limited in its broader aspects. . 30, the representative device, and the descriptive signs. Various modifications and variations may be made to the above specification without departing from the scope or spirit of the present invention, and for the purpose. It is understood that the present invention encompasses all such variants and variations of * 1 1 1 · »·» • »115681 12, provided that they are within the scope of the appended claims and their equivalents.

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Claims (10)

115681 13 An apparatus for processing a received radio frequency signal (RF signal), characterized in that the apparatus comprises: a compressing receiver (22) for receiving the received radio frequency signal and for generating a pulse signal; Means (32) for comparing the pulses in the pulse signal with the threshold and determining the frequency of the filter based on the delay of the pulses exceeding the threshold and producing an analog control signal 15 indicating the filter frequency; and an alternating frequency filter (60) for receiving the control signal and filtering the delayed received signal at the filter frequency. 20 A device according to claim 1, characterized in that the compressing receiver comprises: * a mixer, a frequency difference delay module and a weighting: ·· filter; and that the mixer responds to the received signal, the frequency difference delay module operates under the mixer and the weighting filter operates the frequency difference delay module control mana 30 3. A device according to claim 2, characterized in that the compressing receiver comprises: a sweeping local oscillator unit coupled to the mixer. 35 115681 14 Device according to Claim 1, characterized in that it comprises an analog-to-digital converter controlled by an AC filter. Device according to claim 4, characterized in that it comprises a bandpass filter communicating with an alternating frequency filter and a compressing receiver. A device according to claim 1, characterized in that the device further comprises: a first analog-to-digital converter (62) operated by said variable frequency filter; an attenuator (70) responsive to the received RF signal and outputting the attenuated signal; and a second analog-to-digital converter (72) operated by said attenuator. • »; A device according to claim 6, characterized in that it comprises a controller connected to said alternating frequency filter. . ·. : 25 • · · • · A device according to claim 7, characterized in that it comprises a compressing receiver which is connected to said controller. »I * ;; / 30 A method of detecting a received signal '· *' and filtering comprising the steps of detecting a received signal and downmixing the received signal with a downmixed signal. characterized by: performing a (208) frequency difference delay computation on the down-mixed signal to produce a pulse signal comprising a plurality of pulses; Comparing (210) the amplitudes of at least some of the pulses in the pulse signal with a threshold; measuring (212) the delay of pulses whose amplitude exceeds a threshold within a predetermined time interval; The frequency of the 10 filters is determined (214) based on the pulse delay; and filtering (216) the received signal at the frequency of the filter. The method of claim 9, further comprising the step of applying a weighting filter to the pulse signal. * ia a »Si # • * ·» »• I · • · I * · • · a» • »a a *» »* a • ·! a> »i * · a ta *» a »115681 16