EP2163059A1 - Procédé de réception d'un signal transmis multiplexe en fréquence - Google Patents
Procédé de réception d'un signal transmis multiplexe en fréquenceInfo
- Publication number
- EP2163059A1 EP2163059A1 EP08805877A EP08805877A EP2163059A1 EP 2163059 A1 EP2163059 A1 EP 2163059A1 EP 08805877 A EP08805877 A EP 08805877A EP 08805877 A EP08805877 A EP 08805877A EP 2163059 A1 EP2163059 A1 EP 2163059A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- noise
- frequency
- transmission
- frequencies
- value
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
Definitions
- the present invention relates to the reception of a frequency-multiplexed transmitted signal, and in particular but not exclusively the detection of impulsive noise in such a signal.
- impulsive noises generated for example by switching or atmospheric disturbances.
- These impulsive noises greatly parasitize the signal received, and therefore the quality of the transmission, so that methods of correcting or returning erroneous data are employed.
- the efficiency of these methods can be improved by detecting the presence of impulsive noise. Indeed, once impulsive noise detected on a received signal, it is possible to abandon or correct this signal, or to identify it as a carrier of erroneous data, in order to give less weight to these data when a decoding process.
- One of the impulse noise detection methods already known is the use of pilot carriers, which make it possible to transmit a signal carrying known data in advance of the receiver, on one or more frequencies reserved for this purpose.
- pilot carriers which make it possible to transmit a signal carrying known data in advance of the receiver, on one or more frequencies reserved for this purpose.
- the data from the pilot carriers is also disturbed, so that the receiver which recognizes that the data is affected can detect that the received signal is erroneous.
- pilot carriers A problem with the use of pilot carriers is that a number of transmission frequencies must be reserved for pilot carriers. Thus, all available frequencies for data transmission can not be used, which restricts the transmission rate. In addition, some communication standards do not specify the use of pilot carriers, and therefore do not detect impulsive noises using pilot carriers.
- the present invention aims in particular to provide a reception method for detecting an impulsive noise in a simple manner, without encumbering the transmission network.
- the subject of the invention is a method for receiving a frequency-multiplexed transmitted signal, comprising a step of measuring the noise present on at least one frequency that is not used for transmitting the signal.
- the noise measurement makes it possible to detect an impulsive noise, without occupying any of the frequencies used for the transmission of the data carried by the transmitted signal. Consequently, all the frequencies generally used for the transmission can exclusively be reserved for the transmission of useful data, since it is not necessary to reserve some of these frequencies for the pilot carriers.
- pilot carriers not only is the transmission rate not restricted by the use of pilot carriers, but the method of impulsive noise detection can also be applied to transmission methods not using pilot carriers, such as PLT powerline transmission systems.
- a “frequency not used for transmission” will preferably be a frequency having no component in the transmitted signal, not used for modulation, not carrying data, the term “data” gathering both useful data, synchronization data (including pilot carrier data) and fill data.
- the signal transmitted according to the method described above may for example be an OFDM symbol (Orthogonal Frequency Division Multiplexing).
- This OFDM symbol is distributed on a block of carriers having a certain frequency.
- Orthogonal multiplexing is an efficient method for modulating a signal since it makes it possible to distribute a signal over a large number of frequencies, these frequencies being able to be very close without interfering because they are orthogonal to one another. As a result, it is possible to transmit a maximum of information on a given portion of frequencies.
- a frequency-multiplexed transmitted signal may possibly undergo further processing between the multiplexing step and the transmission step.
- the invention may further include one or more of the following features.
- the frequency not used for the transmission of the signal is a frequency on which the transmission of the signal is defined as prohibited by an official text such as legislation.
- this frequency is defined as prohibited by a communications standard, a law, or a manufacturer's specifications, these laws reserving certain frequencies for particular applications (radio-amateurs, broadcasting, national defense, ).
- These frequencies not used for the transmission can be called for example "cut frequencies”, “forbidden frequencies”, “frequencies off”, “holes”, “notches” When transmitting a signal, nothing is said about these frequencies cut, but the received signal can still present on them of the components, due to the presence of stationary noise and possibly impulsive noise appeared during the transmission.
- the cut frequencies by measuring the power of the signal, it is possible to identify a substantial variation of the noise, which will be indicative of the appearance of a impulsive noise during transmission. Indeed, even if the cut frequencies are likely to be particularly disturbed by stationary noise, because they correspond to frequencies used for other applications, the stationary noise level is generally much lower than the noise level. an impulsive noise affecting the signal. Consequently, the measurement of a large noise value on these cut frequencies makes it possible to determine the presence of an impulsive noise on the transmitted signal, and therefore of erroneous data. However, it is possible not to use some of the cut frequencies defined in the legislation, because these frequencies are too polluted by other telecommunication systems or by electrical devices. Note that the cut frequencies may also include frequencies below or above the frequencies used for data transmission.
- the method comprises a step of comparing a measured noise value with a threshold value. This comparison will detect an impulse noise if the measured noise value is greater than the threshold value.
- the threshold value corresponds to a predetermined value of stationary noise, associated with a predetermined margin. This margin makes it possible to tolerate certain noises slightly higher than the predetermined stationary noise.
- the stationary noise value is predetermined by measuring the stationary noise present on the frequency before the transmission of the signal or during the estimation phase.
- the stationary noise or background noise
- the stationary noise is permanently present in the transmission system and varies only very little in time, so that it is considered constant at the same time. Scale of a digital communication of a few seconds, during which several thousand OFDM symbols are transmitted.
- the value of the stationary noise can be measured or calculated at a different time than during the transmission of the signal. For example, this stationary noise can be measured at the time of a connection between at least two communication terminals implementing the method described above, or periodically during the communication.
- the method comprises a step of determining the margin as a function of the value of the frequency.
- impulse noise is detected if the measured noise is greater than the threshold value and, if appropriate, one of the following steps is preferably implemented: new transmission of the data transported by the transmitted signal, -A- abandonment of the data, marking of the data, attribution to the data of a value of relevance, this value preferably being inversely proportional to the value of the noise measured.
- steps can be taken to exploit this detection to improve the quality of all the transmitted signals. Note that these operating steps can be implemented only over a certain frequency range, because the impulse noise has been detected only on some of the cut frequencies.
- the step of measuring the noise on several frequencies, in particular on a continuous range of frequencies, is implemented.
- noise is measured on a frequency band.
- the method comprises a step of estimating the impulsive noise on frequencies other than those on which the noise has been measured.
- the measurement of the noise on cut frequencies is followed by an interpolation of the value of the noise on the uncut frequencies, used for the transmission, interpolation which can be followed by a signal processing, for example the retrenchment of the estimated noise value.
- the invention also relates to a communication device comprising means for receiving a frequency-multiplexed transmitted signal, suitable for implementing a method as defined above.
- the invention further relates to a communication system comprising transmission means and means for receiving a frequency-multiplexed transmitted signal, suitable for implementing the method defined above.
- the invention finally relates to a computer program for implementing the above method, a recording medium of this program and a provision of this program for download.
- FIG. 1 is a diagram of a communication system according to a particular embodiment of the invention.
- FIG. 2 is a graph illustrating the noise of a signal received according to one embodiment of the invention, this signal not being affected by an impulsive noise;
- FIG. 3 is a graph similar to that of FIG. 2, in which the received signal is affected by an impulsive noise
- FIG. 4 is a block diagram illustrating steps prior to the method of receiving the signals illustrated in FIGS. 2 and 3; and FIG. 5 is a block diagram illustrating the method of receiving the signals illustrated in FIGS. 2 and 3.
- a communications system 10 for implementing a method according to the invention comprises two communication terminals 14, 16 connected by a transmission network 12. These terminals 14, 16, for example computers or mobile phones, each comprise a modem 18, 19, comprising means for transmitting and receiving signals.
- the transmission network 12 is an in-line carrier network (PLT).
- PKT in-line carrier network
- the network 12 makes it possible to transmit multiplexed signals in frequency.
- the transmission means of the modem 18 perform a modulation of the frequency-multiplexed message.
- the message is broken down into several groups of data, these data being successively transmitted to the terminal 16 by signals.
- data is simultaneously transmitted in parallel on different carriers, each carrier corresponding to a transmission frequency.
- OFDM OFDM multiplexing makes it possible to multiplex the transmission on orthogonal frequencies, which avoids interference between the different carriers.
- the reception means of the modem 19 of the destination terminal 16 demodulate the received signal, so as to be able to use the data carried by the OFDM symbol.
- the different data can be transmitted with redundancy, by means of coding algorithms, so that the abandonment of the data provided by an OFDM symbol is not a problem for the transmission. of the general message, since the dropped data can be retrieved from one or more other OFDM symbols.
- cut-off frequencies can not be used for the data transmission that it is desired to carry out between the terminals 14 and 16. They are defined in communication standards, in laws, or in documentation of manufacturers. Cutoff frequencies may also include frequencies below or above the frequencies used for data transmission, including frequencies that follow or precede the range of frequencies used for data transmission. The set of cut frequencies defines a band gap.
- a specification may define, in the United States, a bandgap comprising the following cutoff frequencies F: F ⁇ 2.0 MHz
- the reception means of the modem 19 are capable of detecting an impulsive noise which would have affected the transmission of one of the OFDM symbols. As will be seen in the following, if an impulsive noise is detected during the transmission of an OFDM symbol, this symbol may for example be abandoned, in whole or in a frequency range only, so that it does not affect the quality of the message transmitted.
- the representation of the power P of the signal received by the modem 19, as a function of the frequencies F, or spectral power density (DSP), has a shape similar to the spectrum 20 of FIG.
- the data of the transmitted signal is carried by frequencies, which will be called transmission frequencies.
- the transmission band is generally defined as the set of transmission frequencies used for transmission and the allocated band as the meeting of the transmission band and the forbidden band. Note that the transmission band is not necessarily continuous, it may be formed of non-contiguous subbands separated by cut frequency bands. Similarly, the bandgap is not necessarily continuous. In the above example of a specification defining the band in the United States, the band allocated may correspond to the frequency range from 70OkHz to 28MHz
- the transmission band comprising the transmission frequencies corresponds in the example of FIGS. 2 and 3 to the frequencies F such that F 1 ⁇ F ⁇ F 2 ,
- the signal power measured by the modem 19 has a lower value in the areas corresponding to the cut frequencies than in the areas corresponding to the transmission frequencies. Indeed, since the signal does not carry any data on these cut frequencies, the measured power corresponds to the power of the stationary noise present during the transmission, whereas the power measured on the transmission frequencies corresponds to the power of the stationary noise added to the power of the transmitted data-carrying signal. Therefore, the power P stat 3 measured for example at the cutoff frequency F 3 directly translates the value of the stationary noise at this frequency. It can be seen that this value P stat 3 is relatively small compared to the powers measured on the transmission frequencies Note that the stationary noise corresponds to a noise In fact, generally, this stationary noise does not vary much during the transmission of a message. transmitted
- the power of the signal is relatively large, even on the cut frequencies
- the value P 3 of the power measured at the frequency F 3 is relatively important relative to the value P stat 3 of a signal which is not affected by an impulsive noise
- the method Prior to the transmission of the signals, the method comprises steps for setting up the modem 19, illustrated in FIG. 4. These parameterization steps comprise a first step during which the terminal 16 makes an estimation request to the terminal 14. This step 30 is followed by a step 32 for transmitting, by the terminal 14, a setting signal known to the destination terminal 16. The reception 34 of this setting signal by the terminal 16 is followed by a step 36 determination of cut frequencies F 1 , or continuous intervals of cut frequencies. During this step 36, the terminal 16 may in particular refuse to consider some cut frequencies particularly polluted by other telecommunication systems. It should be noted that this step 36 for determining the cut frequencies to be used can be implemented independently of the previous steps 30 to 34, these frequencies being able for example to be pre-recorded in the modem 19.
- the reception 34 of the parameterization signal is also followed by a step 38 for measuring or calculating the value P sta t of the power of the parameterizing signal on each of the frequencies F 1 , this power reflecting the stationary noise present on the network. 12.
- the step 34 is also followed by a step 40 of determining a margin M 1 .
- This margin M 1 can depend on the frequency F 1 , so that one can provide a significant margin in the case where the frequency F 1 is very disturbed by other communication systems. Note that this step 40 can also be performed independently of steps 30 to 34, the margin can be pre-recorded, depending on whether or not the frequencies F 1 .
- Steps 34 to 40 are followed by a step 42 of calculating a threshold value.
- step 42 is calculated the value P seu, ⁇ threshold power over all frequencies F ,, cut this value corresponding to the sum of P seU ⁇ i ⁇ threshold values calculated for each frequency F 1 .
- the steps for determining the frequencies F 1, the margin M 1 and the calculation of the value P stat 1 can be carried out at other times, and differently from that described above.
- the terminal 14 transmits the corresponding OFDM symbol, which is received by the terminal 16 during a step 46.
- This reception 46 is followed by a step 48 of measuring the P 1 value of the power of the signal on each cut off frequency F 1, the P 1 values being subsequently added so as to determine a power P of the signal on all the cut frequencies, reflecting the noise of the signal.
- This measurement step 48 is followed by a step 50 of comparing the value of the power P measured with the threshold value P s ⁇ U ⁇ i stored in the modem 19.
- Step 54 can be replaced by a step of generating a request from the terminal 14 to transmit again the OFDM symbol, or by a step of marking the data affected by the impulsive noise, so as to give them less weight during the demodulation and / or decoding process and to privilege data from other OFDM symbols not affected by impulsive noise.
- Step 54 can also be replaced by a step of assigning the transmitted data a value of relevance, this value being able to be determined taking into account the value of the measured impulsive noise.
- step 54 can be replaced by an estimation step, for example by interpolation of the impulsive noise on the uncut transmission frequencies. As a result of this estimation, it is possible to process the received signal, for example by subtracting the estimated value of the noise from the received signal.
- impulse noise can be detected in a received signal simply and reliably. It should be noted that this detection can be implemented on any frequency-multiplexed transmitted signal whether the transmission uses pilot or non-pilot carriers.
- the transmission method can be implemented by a computer program installed on the terminal 16, or recorded on a separate recording medium, or downloaded.
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Quality & Reliability (AREA)
- Noise Elimination (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR0755407A FR2916920A1 (fr) | 2007-06-01 | 2007-06-01 | Procede de reception d'un signal transmis multiplexe en frequence. |
PCT/FR2008/050933 WO2009000995A1 (fr) | 2007-06-01 | 2008-05-28 | Procédé de réception d'un signal transmis multiplexe en fréquence |
Publications (1)
Publication Number | Publication Date |
---|---|
EP2163059A1 true EP2163059A1 (fr) | 2010-03-17 |
Family
ID=39166706
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP08805877A Withdrawn EP2163059A1 (fr) | 2007-06-01 | 2008-05-28 | Procédé de réception d'un signal transmis multiplexe en fréquence |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP2163059A1 (fr) |
FR (1) | FR2916920A1 (fr) |
WO (1) | WO2009000995A1 (fr) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2969435A1 (fr) * | 2010-12-20 | 2012-06-22 | France Telecom | Mesure de bruit impulsif par detection spectrale |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6452907B1 (en) * | 1998-10-15 | 2002-09-17 | Motorola, Inc. | Method for monitoring unused bins in a discrete multi-toned communication system |
US6636603B1 (en) * | 1999-07-30 | 2003-10-21 | Cisco Technology, Inc. | System and method for determining the transmit power of a communication device operating on digital subscriber lines |
-
2007
- 2007-06-01 FR FR0755407A patent/FR2916920A1/fr active Pending
-
2008
- 2008-05-28 WO PCT/FR2008/050933 patent/WO2009000995A1/fr active Application Filing
- 2008-05-28 EP EP08805877A patent/EP2163059A1/fr not_active Withdrawn
Non-Patent Citations (2)
Title |
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None * |
See also references of WO2009000995A1 * |
Also Published As
Publication number | Publication date |
---|---|
FR2916920A1 (fr) | 2008-12-05 |
WO2009000995A1 (fr) | 2008-12-31 |
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