DE102006019889A1 - Digitally modulated carrier signal receiver circuit, has control device arranged such that adjustment of filter function of matched filter to different interval lengths is enabled based on output signal of evaluation device - Google Patents

Digitally modulated carrier signal receiver circuit, has control device arranged such that adjustment of filter function of matched filter to different interval lengths is enabled based on output signal of evaluation device

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Publication number
DE102006019889A1
DE102006019889A1 DE200610019889 DE102006019889A DE102006019889A1 DE 102006019889 A1 DE102006019889 A1 DE 102006019889A1 DE 200610019889 DE200610019889 DE 200610019889 DE 102006019889 A DE102006019889 A DE 102006019889A DE 102006019889 A1 DE102006019889 A1 DE 102006019889A1
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Germany
Prior art keywords
signal
matched filter
baseband signal
filter
receiver circuit
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DE200610019889
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German (de)
Inventor
Thomas Duda
André Dr. Neubauer
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Infineon Technologies AG
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Infineon Technologies AG
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Priority to DE200610019889 priority Critical patent/DE102006019889A1/en
Publication of DE102006019889A1 publication Critical patent/DE102006019889A1/en
Application status is Withdrawn legal-status Critical

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/01Equalisers
    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03HIMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00Networks using digital techniques
    • H03H17/02Frequency selective networks
    • H03H17/0248Filters characterised by a particular frequency response or filtering method
    • H03H17/0254Matched filters
    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03HIMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00Networks using digital techniques
    • H03H17/02Frequency selective networks
    • H03H17/0294Variable filters; Programmable filters

Abstract

The The invention relates to a digital receiver circuit for receiving a receive signal which is a base band signal encoding a bitstream digitally modulated carrier signal is which receiver circuit, a matched filter for filtering the baseband signal separated from the carrier signal by means of a filter function adapted to the pulse shape of the baseband signal, a clock recovery unit supplied with the baseband signal for recovering the clock Takts from the baseband signal and a downstream of the matched filter Scanning unit for sampling the filtered baseband signal by means of of the recovered Takts, which is characterized in that the Matched Filter to its filter function to different interval lengths of Bit periods of the baseband signal is suitably adapted to the matched Filter a signal evaluation device for evaluation of the filtered Baseband signal is connected downstream and one with the signal evaluation and the matched filter control means is arranged, which is so effectively coupled with the matched filter that based an output signal of the signal evaluation device an adaptation the filter function of the matched filter to different interval lengths of Bit periods of the baseband signal takes place.

Description

  • The The present invention is in the field of digital circuit technology and relates to a digital receiver circuit, in which the received signals by means of a signal relationship matched filter receive filtered.
  • at wireless transmission digital information, as in telephone and Internet communication or Radio networks (for example, WLAN) is the case, it is common practice a digital information signal (baseband signal) an analog carrier signal modulate. For this purpose, digital modulation methods such as ASK (Amplitude Shift Keying), FSK (Frequency Shift Keying), PSK (Phase Shift Keying), GFSK (Gaussian Frequency Shift Keying), PAM (Pulse Amplitude Modulation), PCM (Pulse Code Modulation) and various variants used hereof.
  • exemplary ASK and FSK are closer here explained become. Thus, ASK (German "amplitude shift keying") is a digital form of conventional Amplitude modulation. In this case, the amplitude of the carrier signal changed according to the bitstream to be modulated, that is, the digital values (in binary Case zero or one), discrete amplitude values are assigned. The simplest form of ASK is the so-called on-off-keying (OOK), in which a signal is transmitted at a digital one and at a digital zero no signal transmitted in other words, becomes a zero-amplitude signal. OOK has However, the disadvantage that you can never tell for sure if the transmitter failed, or really a bitstream with only digital Zeros is transmitted. If several amplitude levels are used in ASK, then per Clock also transmitted several bits become. For example, ASK is being used in transmission today the radio clock synchronizing radio signal used.
  • Rated (German "Frequenzumtastung") is a digital Form of conventional Frequency modulation. Here, the frequency of the carrier signal changed according to the bit stream, this means, in binary Case the digital values become zero and one discrete frequency values assigned. To the transfer rate to increase, you can also use several discrete frequency values with FSK. For example, if four different frequencies are used, so can transmitted two bits per clock become. While ASK is rarely used today, FSK is very common in wireless telecommunications technology, such as in local wireless networks (WLAN) used.
  • Becomes now such as for example by means of ASK or FSK in digital Transferring the form modulated signal wirelessly is the task Recipient to recover the transmitted bit stream as error free as possible. In the receiver For this purpose, the received signal is first switched to one for analog-to-digital conversion suitable signal strength scales, since A / D converters usually have a limited dynamic range. After separating the Baseband signal from the carrier signal takes place afterwards a filtering of the baseband signal, in particular line distortions to compensate and disturbances abzuseparieren. The filtered baseband signal then becomes one Clock recovery device fed to one to recover the data suitable sampling frequency for a filter downstream Detecting scanner. By means of the obtained sampling frequency The filtered input signal is then in the scanner tastes and so on the original recovered coded data stream. This is in an additional Decision maker discriminates (decided) whether a signal is present at all or not.
  • Now is a wireless signal transmission always with signal interference connected veschiedenster kind, which add up to the useful signal. These disorders can in natural Way in the transmission arise or by resistance noise, transistor noise and the like be more conditional. They are stored in the useful signal component as so-called "white noise" (Gaussian noise) and can a data recovery oppose when they reach a size which, for example, half a signal amplitude of the useful signal component equivalent. The receive filter is therefore the most important task to separate this noise from the useful signal component, wherein the receiving filter should be dimensioned so that the broadband noise at the receiver input preferably is blocked while at the same time an optimum signal component for the detection of the data can happen.
  • In Modern digital receive circuits become noise filtering mostly signal- or noise-adjusted filters (also matched filters or correlation filter called) used. Here you basically go away that the shape of the baseband signal is known in the receiver and that only has to decide whether the received signal this known baseband signal contains or not.
  • In other words, with the matched filtering, the filtering is adapted to the transmitted signal pulse shape. For recovering the bit data stream, the output of the receive filter is sampled in accordance with the recovered clock at the time point T (at the end of the symbol period or bit period). The preset pulse shape of the matched filter is usually a time-inverted version of the transmitted pulse shape. So if the transmitted pulse shape h (t) is defined as h (t) for 0≤t≤T, (1) where the period from 0 to T represents a bit period, then an ideal response of the matched filter h m (t) H m (t) = h (T - t) for 0 ≤ t ≤ T (2)
  • Such signal processing has two advantages. One advantage is that typical pulse shapes have a low-pass response, so that by filtering the received signal with a matched filter in the receiver, the frequencies containing the baseband signal (payload) are passed while the remaining frequencies are attenuated. Matched Filtering thus limits the scope of the noise spectrum, which is forwarded to subsequent stages in the receiver. Another advantage is that a matched filter correlates the received signal with the transmitted pulse shape over the symbol period T. Since passing a signal r (t) through a filter h m (t) is a convolution operation, the corresponding convolution of these two signals is
    Figure 00040001
    where y (t) is the sampled ("sampled") output of the matched filter at time T.
  • Since the response of the matched filter has been given as h m (t) = h (T-t) in equation (2) above, by substituting equation (2) into equation (3),
    Figure 00050001
    Equation (4) is the cross-correlation of r (t) sampled at time T with h (t) for a delay 0. Thus, matched filtering effects a correlation of the received signal with the matched filter, thereby increasing the correlation gain by integrating the received signal energy while taking the White noise with zero mean can be achieved.
  • nowadays especially in digital ASK modulation techniques and FSK, mostly rectangular pulse shapes for transmission a bitstream.
  • In such an example, a signal reception by means of a conventional receiver circuit with a matched filter will be explained in more detail, with reference to the 1A to 1F is taken.
  • First illustrated 1A schematically a possibility of digitally encoding a binary logical pair (zero and one) by means of a so-called "Manchester coding" in which at a digital zero in the middle of a bit period, a signal transition from a low signal level ("low") a high signal level ("high") and at a digital one a signal transition from high to low is encoded.
  • For wireless signal transmission, a square-wave signal representing a bit data stream is modulated onto an analog signal carrier, for example by means of FSK, and received after transmission by the matched-filter receiver. After separation of the baseband signal and the carrier signal, the baseband signal containing the encoded data stream is applied to the input of the matched filter. The input signal of the matched filter is in 1B exemplified.
  • 1C shows, according to the ideal input signal, an optimum output signal of the matched filter, which is obtained at a uniform data rate and a duty cycle of about 50%.
  • In 1D the takeover clock recovered from the receive signal in a clock recovery device, which is used to sample the filter output signal, is shown.
  • 1E shows the amplitude values which are obtained by applying the in 1D obtained takeover act.
  • In 1F Finally, the recovered polarities of the transmitted bit data stream are shown. Obviously, the recovered polarities agree with the in 1B by "0" and "1" symbolized bit sequence.
  • Now but occurs in the wireless signal transmission usually the Case on that the Matched Filter applied square wave signal in its shape opposite originally to generate the bit data stream generated square wave signal due of disorders changed may be, as already explained. So in particular the data rate and interval lengths of bit periods (duty cycle) of the originally generated Square-wave signal of the bit data stream deviate.
  • As a result, the object of the present invention is to provide a matched-filter receiver for a digital to provide a modulated received signal in which the problem of faulty recovery of bit data in the coded bit data stream of the baseband signal due to an irregular data rate or different interval lengths (duty cycle) of bit periods can be avoided.
  • These Task is achieved by a receiver circuit with the characteristics of the independent Claim solved. Advantageous embodiments of the invention are characterized by the features the dependent claims specified.
  • According to the invention is a digital receiver circuit indicated for receiving a digitally modulated received signal, wherein the received signal in conventional Way of a baseband signal encoding a digital bit stream, that an analog carrier signal is modulated. In the baseband signal is usually a Bit during a respective bit period (T).
  • The inventive receiver circuit includes a matched filter for filtering of the carrier signal separate baseband signal by means of a to the selected pulse shape the baseband signal matched filter function. The receiver circuit according to the invention is still with a clock recovery device to recover a sampling clock from the baseband signal, and a bit data recovery means (Sampling / decision means) for sampling the filtered baseband signal by means of the recovered Clock signal and discriminating bit data from the bit stream Mistake.
  • The inventive receiver circuit is now characterized by the fact that the Matched Filter for adapting its filter function to different interval lengths (Duty Cycle) of bit periods of the bit data stream of the baseband signal in suitable manner is formed. Here is a signal output of the matched filter with a signal evaluation device for evaluation the filtered baseband signal connected. In addition, one with the Signal evaluation unit and the matched filter connected control device arranged which is so coupled with the matched filter, on the basis of an output signal of the signal evaluation device an adaptation of the filter function of the matched filter to different ones interval lengths (Duty Cycle) of bit periods of the baseband signal can be done. Here, an adaptation of the filter function of the matched filter in particular done in such a way that the filter function as long changed is evaluated until an output signal of the matched filter the signal evaluation device assumes a maximum signal value.
  • at the signal evaluation device is preferably a Signal energy evaluation device, which for detecting and evaluating the signal energy of the baseband signal is designed to be suitable. In this way, the filter function of the matched filter can be simpler Way to varying interval lengths (Duty cycle) of bit periods of the baseband signal to be adjusted.
  • Thus, according to the invention advantageously an adaptation of the filter function of the matched Filters on a disturbed Baseband signal in which the bit data stream is different interval lengths (Duty cycle) of bit periods done.
  • According to the invention, the matched filter is designed to adapt its filter function to different interval lengths (duty cycle) of bit periods of the bit data stream of the baseband signal in a suitable manner. For this purpose, the matched filter can be equipped with an adaptation device for adapting the filter radio tion at different interval lengths of bit periods of the baseband signal to be equipped. Alternatively, it is also possible for the matched filter to comprise a plurality of (for example three) separate matched-filter units, each of which is suitable for filtering the baseband signal. In this case, the matched filter units are provided with mutually different filter functions, which are adapted to different interval lengths (duty cycle) of bit periods. In the latter case, the control device is advantageously coupled to the matched filter in such a way that, on the basis of an output signal of the signal evaluation device, a selection of a matched filter unit takes place whose filter function is suitable for a respective interval length (duty cycle) of bit periods of the baseband signal ( that is, for example, gives a maximum signal energy of the output signal of the matched filter).
  • Of Furthermore, the invention relates to a method for operating a as described above, digital receiver circuit in which an adaptation on the basis of an output signal of the signal evaluation device the filter function of the matched filter to different interval lengths (Duty Cycle) of bit periods of the baseband signal.
  • If the matched filter with a plurality of matched filter units for filtering the baseband signal by means of different interval lengths filter functions adapted to bit periods of the baseband signal is provided, preferably on the basis of an output signal the signal evaluator a selection of matched filter units corresponding to respective interval lengths (duty cycle) of bit periods of the baseband signal.
  • The Invention will now be described by way of exemplary embodiments explained in more detail, wherein Reference to the attached Drawings is taken. Show it:
  • 1A - 1F schematic diagrams of the successive processing of the baseband signal in a conventional receiver circuit;
  • 2 a schematic representation for illustrating the structure of an embodiment of the receiver circuit according to the invention;
  • 3 a schematic representation for illustrating the structure of another embodiment of the receiver circuit according to the invention.
  • The 1A - 1F were already explained at the beginning, so that can be dispensed with a further description at this point.
  • It will now be related to the 2 taken. 2 shows a schematic structure of a first embodiment of the receiver circuit according to the invention, wherein for the sake of simplicity, only for the understanding of the invention essential circuit components are shown. Thus, the receiver circuitry is constructed to receive and process both digital ASK encoded signals and digital FSK encoded signals. This is the FSK-coded received signal 2 first an FSK demodulator 3 supplied for demodulation. Then it will be a mixer (multiplexer or signal selection circuit) 4 fed. The mixer 4 , which further ASK-coded received signals 1 supplied, serves to distinguish the FSK and ASK-coded received signals. From the mixer 4 then the received signals are a matched filter 5 fed to filter received signals by means of a matched to the pulse shape of the baseband filter function.
  • The Matched Filter 5 is a signal detector 6 downstream, which discriminates whether a signal is present or not. In parallel with the signal detector 6 is a clock recovery device fed with an output signal of the signal detector 7 for recovering the clock from the baseband signal. To recover the bit data stream from the filtered baseband signal is the signal detector 6 furthermore a scanning device 8th connected in series. In the scanner 8th are using the clock in the recovery device 7 recovered takeover clock bit data recovered from the baseband signal. Integrated in the scanner 8th is also a logical data processing device 9 , such as a logic chip, a data decoder or the like.
  • In the receiver circuit according to the invention, the output signal of the matched filter 5 a signal energy evaluation device connected in parallel with this 10 for detecting and evaluating the signal energy of the output signal of the matched filter 5 fed.
  • In the illustrated embodiment of the receiver circuit according to the invention is the matched filter 5 provided with a filter function for filtering the separated from the carrier signal baseband signal. Here is the matched filter 5 designed to adapt its filter function to different interval lengths (duty cycle) of bit periods of the bit data stream of the baseband signal in a suitable manner. For this purpose, the matched filter 5 equipped with an adaptation device for adapting its filter function to different interval lengths of bit periods of the baseband signal, wherein an adaptation of the filter function of the matched filter 5 based on output signals of the signal energy evaluation device. For this purpose, a signal output of the signal evaluation device 10 with the matched filter 5 connected. For example, the filter function is adapted in such a way that, detected by the signal energy evaluation device, an output signal of the matched filter 5 has a maximum signal energy. In this way, the filter function of the matched filter 5 be adapted in a simple manner to varying interval lengths (duty cycle) of bit periods of the baseband signal.
  • 3 illustrates an alternative embodiment of the receiver circuit according to the invention, wherein for the sake of simplicity only the difference in the structure of the receiver circuit to the receiver circuit of 2 is shown and otherwise on the under 2 made statements made reference.
  • Accordingly, the matched filter 5 is built from a plurality of n (n is a natural number greater than 1) separate matched-filter units. In 3 are exemplary three matched filter units 11 . 12 . 13 shown. The matched filter units are provided with filter functions that differ from each other, which are adapted to different interval lengths (duty cycle) of bit periods. The matched filter units are each signal energy evaluation units 14 . 15 . 16 which are each fed with output signals of the matched-filter units, and are suitable for detecting and evaluating the signal energy of the output signals of the matched-filter units. Furthermore, the signal energy output units are a matched filter unit selection means 17 downstream, which is so operatively coupled to the matched filter units, that on the basis of output signals of the signal energy evaluation units, a selection of a matched filter unit suitable for a respective interval length of bit periods can take place.
  • 1
    ASK signal
    2
    FSK signal
    3
    FSK demodulator
    4
    mixer
    5
    Matched filter
    6
    signal detector
    7
    Clock recovery device
    8th
    scanning
    9
    logical Data processing device
    10
    Signalenergieauswerteeinrichtung
    11
    Matched filter unit
    12
    Matched filter unit
    13
    Matched filter unit
    14
    Signalenergieauswerteeinrichtung
    15
    Signalenergieauswerteeinrichtung
    16
    Signalenergieauswerteeinrichtung
    17
    Matched filter unit selector

Claims (6)

  1. A digital receiver circuit for receiving a received signal, which is a carrier signal digitally modulated with a bitstream encoding base band signal, which receiver circuit, a matched filter ( 5 ) for filtering the baseband signal separated from the carrier signal by means of a filter function adapted to the pulse shape of the baseband signal, a clock recovery unit fed with the baseband signal (US Pat. 7 ) for recovering the clock from the baseband signal, and a sampling unit connected downstream of the matched filter ( 8th ) for sampling the filtered baseband signal by means of the recovered clock, characterized in that - The matched filter is adapted to its filter function at different interval lengths of bit periods of the baseband signal, - the matched filter is followed by a signal evaluation device for evaluating the filtered baseband signal, and - a control device connected to the signal evaluation device and the matched filter is arranged with the Matched filter is so effectively coupled that on the basis of an output signal of the signal evaluation device, an adaptation of the filter function of the matched filter to different interval lengths of bit periods of the baseband signal.
  2. receiver circuit according to claim 1, characterized in that the matched filter with an adaptation device for adapting the filter function different interval lengths is equipped with bit periods of the baseband signal.
  3. receiver circuit according to claim 1, characterized in that the matched filter a plurality of matched filter units for filtering the baseband signal by means of a filter function adapted to the pulse shape of the baseband signal , wherein the filter functions to different interval lengths of Bit periods of the baseband signal are adjusted.
  4. receiver circuit according to claim 3, characterized in that the control device is so effectively coupled with the matched filter that based on a Output signal of the signal evaluation device a selection of a Matched filter unit with one at an interval length of Bit periods of the baseband signal matched filter function done can.
  5. Method for operating a digital receiver circuit according to claim 1, wherein on the basis of an output signal of the signal evaluation device an adaptation of the filter function of the matched filter to an interval length of Bit periods of the baseband signal takes place.
  6. The method of claim 6, wherein the matched Filter with a plurality of matched filter units for filtering the baseband signal by means of a to the pulse shape of the baseband signal matched filter function is provided, based on an output signal the signal evaluator a selection of a matched filter unit with one at an interval length matched by bit periods of the baseband signal filter function he follows.
DE200610019889 2006-04-28 2006-04-28 Digitally modulated carrier signal receiver circuit, has control device arranged such that adjustment of filter function of matched filter to different interval lengths is enabled based on output signal of evaluation device Withdrawn DE102006019889A1 (en)

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5563907A (en) * 1995-01-04 1996-10-08 Interdigital Technology Corporation Variable bandwith spread spectrum device and method

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5563907A (en) * 1995-01-04 1996-10-08 Interdigital Technology Corporation Variable bandwith spread spectrum device and method

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