FR2830391A1 - Optimized HiperLan2 frame reception system detects burst end in Fresnel plane - Google Patents

Optimized HiperLan2 frame reception system detects burst end in Fresnel plane Download PDF

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Publication number
FR2830391A1
FR2830391A1 FR0112720A FR0112720A FR2830391A1 FR 2830391 A1 FR2830391 A1 FR 2830391A1 FR 0112720 A FR0112720 A FR 0112720A FR 0112720 A FR0112720 A FR 0112720A FR 2830391 A1 FR2830391 A1 FR 2830391A1
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Prior art keywords
modulation
characterized
frame
c100
according
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FR0112720A
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French (fr)
Inventor
Patin Frederique Ehrmann
Bars Philippe Le
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Canon Inc
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Canon Inc
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Priority to FR0112720A priority Critical patent/FR2830391A1/en
Publication of FR2830391A1 publication Critical patent/FR2830391A1/en
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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2647Arrangements specific to the receiver
    • H04L27/2655Synchronisation arrangements
    • H04L27/2668Details of algorithms
    • H04L27/2673Details of algorithms characterised by synchronisation parameters
    • H04L27/2676Blind, i.e. without using known symbols
    • H04L27/2679Decision-aided
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2647Arrangements specific to the receiver
    • H04L27/2655Synchronisation arrangements
    • H04L27/2656Frame synchronisation

Abstract

An optimized HiperLan2 frame reception system demodulates (EC330) the OFDM (Orthogonal Frequency Division Multiplexing) modulation to give a two carrier amplitude modulated signal that is demodulated (EC340) to give a signal constellation that is analyzed (EC360) in the Fresnel plane for detection (EC370) of the end of a burst when all points are within a set radius. Includes an Independent claim for mobile and base stations using the system.

Description

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 The present invention relates to an optimized reception method and device.

 The invention is described here, by way of nonlimiting example, in its application to frames received in the form of signals modulated according to an OFDM type modulation (orthogonal frequency division multiplexing, in English "Orthogonal Frequency Division Multiplex") , and more particularly, to frames conforming to the HiperLAN2 standard.

 When transmitting a message using an orthogonal frequency division modulation, the binary data of the message to be transmitted are split into data blocks. Each of these data blocks is transmitted independently and constitutes, after baseband modulation, an OFDM symbol.

 In each of these data blocks, the elements are also grouped by subsets, each subset then undergoing a cartographic report on a discrete set of points in the Fresnel space, each of these points representing a phase and an amplitude possible. This application is bijective.

 Thus, for example, in a message consisting of the following sequence {000011100100011110001010100100100 ...}, we can extract, in the order of presentation, a block of 16 binary data 0000111001000111 with which we associate the map report 1 + j, 1+ j, -1-j, 1-j, -1 + j, 1 + j, -1 + j, -1-j.

We therefore have a set of 8 complex elements of a vector V.

 These vectors are then multiplied by a fast inverse discrete Fourier transform matrix M to obtain an OFDM symbol consisting of a series of complex numbers. This symbol is transmitted after other processing.

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 The OFDM symbol is received, after passing through the transmission channel, in a demodulator, from which a vector with complex elements V 'will be extracted by multiplying the complex numbers constituting this symbol by a discrete Fourier transform matrix M', such that M. M '= Id (identity matrix). Maximum likelihood decisions on the real and imaginary part make it possible to find the initial sequence of symbols, then to restore the associated binary elements.

 For more details on this modulation technique, one can consult, for example, the work entitled "OFDM for Wireless Multimedia Communications" by Richard VAN NEE and Ranjee PRASAD published by Artech House.

 According to the HiperLAN2 standard, and as described later with reference to FIGS. 1 and 2, a HiperLAN2 frame consists of bursts, each of these bursts comprising a preamble used in particular for synchronization, this preamble being followed by OFDM symbols sent one by one. .

 During their research, the inventors found themselves confronted with the detection of the end of a burst, this detection being indeed difficult to perform quickly because the last OFDM symbol of this burst is identical to the previous ones.

 However, it is important, for several reasons, that the detection of the end of a salvo be done quickly.

 First of all, rapid detection saves processing resources of the receiver by preventing the receiver from performing unnecessary demodulation operations. This characteristic is all the more appreciable as the receiver has limited processing resources, which is the case in particular for a mobile terminal powered by battery.

 According to another aspect, the detection of the end of a burst must be rapid when the latter conditions other operations such as the reinitialization of certain parameters of the receiver or the switching from the reception mode to a transmission mode.

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 The present invention provides a reception method and device for rapidly detecting the end of a burst by analyzing the constellation obtained at the end of the demodulation phase.

 More specifically, the present invention provides a method of receiving a frame modulated according to a first modulation, the frame comprising data modulated according to a second modulation prior to the first modulation, method according to which: - the frame is demodulated according to a reverse demodulation of the first modulation, so as to obtain an intermediate signal; - The intermediate signal is demodulated according to a reverse demodulation of the second modulation, so as to obtain a constellation; - the constellation is analyzed; and detecting the end of part of the frame from the result of the analysis.

 The detection of the end of the part of the frame is thus carried out quickly, as the data is received. It also has the advantage of being able to be carried out easily, without requiring the addition of specific processing circuits.

 In a preferred embodiment, the first modulation being of the OFDM type and the frame conforming to the HiperLAN2 standard, the end of a burst of this frame is detected.

 A reception device in accordance with this preferred embodiment can advantageously be integrated into a digital signal processing apparatus further comprising a transmission device, this transmission device becoming active, for example upon detection of the end of the burst. "Downlink" of a HiperLAN2 frame.

 According to a particular characteristic, the second modulation being an amplitude modulation on two carriers in quadrature, during the analysis step, the points of the constellation are represented in a Fresnel plane, and the end of the part of the frame when all these points are inside a circle centered on the origin of the Fresnel plane and of predetermined radius depending on the second modulation.

<Desc / Clms Page number 4>

 This particular characteristic is very easy to implement and also has the advantage of being usable for different types of second modulation, when the radius of the circle is configurable.

 For the same purpose as that indicated above, the present invention also provides a device for receiving a frame modulated according to a first modulation, the frame comprising data modulated according to a second modulation prior to the first modulation.

 The device comprises: - first demodulation means adapted to demodulate the frame according to a reverse demodulation of the first modulation, so as to obtain an intermediate signal; - second demodulation means adapted to demodulate the intermediate signal according to a reverse demodulation of the second modulation, so as to obtain a constellation; - means of analysis of the constellation; and - means for detecting the end of part of the frame from the result of the analysis.

 The present invention also relates to an apparatus for processing digital signals, comprising means suitable for implementing a reception method as above.

 The present invention also relates to an apparatus for processing digital signals, comprising a reception device as above.

 The present invention also relates to a telecommunications network, comprising means suitable for implementing a reception method as above.

 The present invention also relates to a telecommunications network, comprising a reception device as above.

 The present invention also relates to a mobile station in a telecommunications network, comprising means suitable for implementing a reception method as above.

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 The present invention also relates to a mobile station in a telecommunications network, comprising a reception device such as above.

 The present invention also relates to a base station in a telecommunications network, comprising means suitable for implementing a reception method as above.

 The present invention also relates to a base station in a telecommunications network, comprising a reception device such as above.

 The invention also relates to: - a means of storing information readable by a computer or a microprocessor retaining instructions of a computer program, allowing the implementation of a reception method as above, and - a removable information storage means, partially or totally, readable by a computer or a microprocessor retaining instructions of a computer program, allowing the implementation of a reception method as above.

 The invention also relates to a computer program product comprising sequences of instructions for implementing a reception method as above.

 The special features and advantages of the receiving device, the different digital signal processing devices, the different telecommunications networks, the different mobile stations, the different base stations, the different storage means and the computer program product being similar to those of the reception method according to the invention, they are not repeated here.

 Other aspects and advantages of the invention will appear on reading the detailed description which follows of a particular embodiment, given by way of nonlimiting example. The description refers to the accompanying drawings, in which: FIG. 1 schematically illustrates a frame in accordance with the HiperLAN2 standard;

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 FIG. 2 schematically illustrates different bursts of a frame conforming to the HiperLAN2 standard; FIG. 3 is a flow diagram representing the main steps of a reception method according to the invention in a preferred embodiment; FIG. 4 schematically represents the structure of a reception device according to the present invention, in a particular embodiment; FIGS. 5a to 5d illustrate the operation of the unit for detecting an end of frame portion of FIG. 4; FIG. 6 schematically illustrates the constitution of a network station or of a digital signal processing apparatus adapted to implement a reception method in accordance with the present invention; and FIG. 7 represents in a simplified schematic form a telecommunications network in accordance with the present invention, in a particular embodiment.

 By way of illustration, the preferred embodiment is described in the case of a data transmission according to the HiperLAN2 standard.

 Figure 1 shows schematically the structure of a HiperLAN2 C100 frame (physical frame). It summarizes the information contained in the ETSI TR 101 683 V1 documents. 1.1 and ETSI 101 475 V1. 2.1.

 The frame C100 is composed of several phases C101 to C105, commonly called bursts (in English "burst"): - the general broadcast phase C101 or burst "Broadcast", located at the start of the frame C100, which contains information intended for all the receivers (transmission from the base station to the mobiles); - the "Downlink" burst Ci 02, which carries information intended for particular receivers (transmission from the base station to the mobiles);

<Desc / Clms Page number 7>

 - the C103 "direct link" burst, which allows receivers to exchange information directly, without going through a base station (transmission from mobile to mobile); - the "Uplink" C104 burst, which carries information intended for the base station (transmission from the mobile to the base station); - the “Random access” burst C105, which allows mobiles which have no channels assigned in the “Uplink” burst, to communicate with the base station.

 Each of these bursts C101 to C105 respectively comprises a header C201 to C205 called the preamble, this preamble being followed by symbols C210.

 Figure 2 shows the constitution of these different headers, which are all based on the use of particular data sequences named A, RA, B, IB, C. The content of these sequences has been determined so that they present particular properties with respect to certain mathematical operations. Reference is usefully made to the HiperLAN2 standard and to the contributions that made it possible to develop this standard, these documents being available from ETSI.

 According to a conventional diagram in OFDM, the symbols C210 comprise data D associated with a redundancy packet (or prefix), composed of the repetition of a certain number of samples of these data D.

 In the context of the HiperLAN2 standard, the D data consists of 64 samples, this prefix, designated by CP (in English "Cyclic Prefix") being the copy of the last 16 samples of the D data.

 An OFDM symbol therefore consists of 80 samples, which corresponds, according to the standard, to a duration of 4 lis.

 The flow diagram of FIG. 3 represents the main steps EC300 to EC370 of a reception method according to the invention in a preferred embodiment.

 These different steps EC300 to EC370 will be described using the example of the reception of a "broadcast" burst C101 from a HiperLAN2 C100 frame, the reception of a burst of another type being similar.

<Desc / Clms Page number 8>

 During a first step EC300, the arrival of the burst C1 01 is detected.

 This step EC300 is followed by a step EC310 during which the end of the preamble C201 of the burst C1 01 is detected.

 These two operations can be done during a synchronization step known to those skilled in the art and will not be described here.

 Step EC310 is followed by a step EC320 during which an OFDM symbol is received. As specified in the preamble to this patent application, this OFDM symbol corresponds to a binary data block having been modulated according to a second modulation such as for example an amplitude modulation on two carriers in quadrature, then at the end of this second modulation, modulated according to a first OFDM type modulation.

 The symbol received during step EC320 is then demodulated according to a reverse demodulation of the first modulation during a step EC330.

 This first demodulation step is known to those skilled in the art and will not be described in detail here.

 It is simply recalled that this first demodulation step conventionally comprises a sub-sampling and windowing step followed by a fast Fourier transformation (FFT).

 On the other hand, and in a known manner also, an OFDM symbol transmitted according to the HiperLAN2 standard comprises 64 subcarriers of which 48 are subcarriers comprising the data, 4 pilot subcarriers and 12 non-modulated subcarriers.

 At the end of the FFT, an intermediate signal is obtained comprising the complex samples transported by each of these subcarriers.

 The step EC330 is followed by a step EC340 during which the intermediate signal is demodulated according to a reverse demodulation of the second modulation so as to obtain a constellation.

 This constellation is represented in a Fresnel plane during a step EC350 following the step EC340.

<Desc / Clms Page number 9>

 Examples of representation for the second 4QAM, 16QAM and 64QAM modulations will be respectively described later with reference to FIGS. 5a, 5c and 5d.

 Step EC350 is followed by a step EC360 of analyzing the constellation.

 In the preferred embodiment described here, it is examined whether all the points of the constellation lie inside a circle C500 whose center is the origin of the above-mentioned Fresnel plane, and whose radius C ~ R predetermined depends on the second modulation.

 Such a circle C500 is shown in Figures 5a to 5d.

 In the embodiment described here, these radii are respectively: - 1, 2 in the case of a second 4QAM type modulation; - 1, 5 in the case of a second modulation of the 16QAM and 64 QAM type.

 When certain points of these constellations are not inside this circle C500, the result of the EC360 test is negative.

 This indeed means that the constellation includes points representative of data symbols.

 The EC360 test is then followed by the step EC320 already described, during which the following symbol is received in the burst C101.

 Indeed: -in the case of a second 4QAM type modulation, the coordinates of the theoretical points of the constellation are (l, j), which corresponds to a distance from the center of the Fresnel plane equal to approximately 1, 4; -in the case of a second 16QAM type modulation, the coordinates of the theoretical points of the most eccentric constellation of the center are (1, 5, 1, 5d), which corresponds to a distance from the center equal to approximately 2, 1; and in the case of a second 64QAM type modulation, the coordinates of the theoretical points of the most eccentric constellation of the

<Desc / Clms Page number 10>

 center are (1, 75, 1, 75d), which corresponds to a distance from the center equal to about 2.4.

 On the other hand, when all the points of the constellation are located inside the circle C500, this means that these points are not representative of real data symbols, but of noise, as illustrated in FIG. 5b.

 In this case the result of the EC360 test is positive. This test is then followed by step EC370 during which the end of the burst C1 01 is detected.

 FIG. 4 schematically represents the architecture of a reception device according to the present invention.

 In the description which follows, we have deliberately omitted to describe in detail certain parts of the receiver in accordance with the invention since these are known per se and are not essential to the implementation of the invention.

 At the input of the reception device illustrated in FIG. 4, the analog signal received by the radio frequency (RF) interface is sent to an automatic gain control unit C400 which makes it possible to adjust the level of the received signal.

 The signal is then sent to an analog to digital conversion unit C410 which samples the received signal and converts it into a digital signal. By way of nonlimiting example, one can choose an intermediate frequency equal to 25 MHz and an oversampling factor equal to 4, which leads to a sampling frequency of 100 MHz.

 The digital signal is then transmitted to an intermediate frequency demodulation unit C420 which brings the modulated OFDM signal around 25 MHz in baseband in a manner known per se.

 The baseband signal is then transmitted to a C425 synchronization unit. This synchronization unit C425 makes it possible in particular to detect the end of the preamble C201 of the burst "Broadcast" C1 01.

 When the C425 synchronization unit succeeds in extracting the data, the synchronized data is transmitted to a demodulator

<Desc / Clms Page number 11>

 OFDM C440 which performs the rest of the operations necessary for the recovery of this data.

 The intermediate signal from the demodulator C440 is transmitted to a detector at the end of part of the frame C445 adapted to implement the steps EC340 to EC370 previously described with reference to FIG. 3.

 The detector at the end of part of the frame C445 is in particular adapted to demodulate the intermediate signal according to a reverse demodulation of the second modulation (for example 4QAM, 16QAM, or 64QAM), to represent the constellation resulting from this demodulation in a Fresnel plane, and to check if all the points of this constellation are located in a circle whose center is the origin of the Fresnel plane and whose predetermined radius depends on this second modulation.

 When all the points of the constellation are inside the circle, the detector at the end of part of the frame C445 generates a signal C449 to reset the automatic gain control unit C400, the unit synchronization C425 and the demodulator following the first C440 modulation.

 In a known manner, the intermediate signals from the C440 demodulator are transmitted to a deinterleaving unit of the C450 subcarriers which outputs the complex signals as they were ordered at the input of the OFDM modulator.

 These signals are then transmitted to a C460 reverse cartographic reporting unit QAM, which performs a reverse cartographic reporting operation to that used at the transmitter so as to restore the binary signals as they were ordered at the input of the OFDM transmitter (reverse demodulation of the second modulation).

 FIGS. 5a to 5d illustrate the operation of the unit C445 for detecting the end of part of the frame of FIG. 4.

 FIGS. 5a, 5c and 5d illustrate the constellation corresponding to the intermediate signal at the output of the FFT, for the first OFDM symbol of data C210 after the preamble C201, respectively for a secondary modulation 4QAM, 16 QAM and 64 QAM.

<Desc / Clms Page number 12>

 These figures are shown after deletion of the cyclic prefix CP, and do not show the points corresponding to the pilot subcarriers.

 In each of these Figures 5a, 5c and 5d, there is shown an end point C501 of the constellation, that is to say a point in the constellation the furthest from the origin of the Fresnel plane.

The theoretical coordinates of point C501 are: - (1; j) in the case of the second 4QAM modulation; - (1.5; 1.5d) in the case of the second 16QAM modulation; and - (-1.75; 1.75 d) in the case of the second 64QAM modulation;
It is clearly seen, in each of FIGS. 5a, 5c and 5d that this extreme point C501 is outside the circle C500, which is characteristic of a constellation corresponding to an OFDM symbol of data.

 FIG. 5b illustrates a constellation corresponding to the intermediate signal at the output of the FFT, for the first noise symbol after the end of the data symbols C210. This figure is identical whatever the secondary modulation.

 It appears in FIG. 5b, that the end of the data C210 results in the three cases by an overwriting of the constellation around the origin of the Fresnel plane, all the points then being found inside the circle C500 (of radius 1.2 in Figure 5b).

 FIG. 6 schematically illustrates the constitution of a network station or of a digital signal processing apparatus, in the form of a block diagram.

 This station comprises a keyboard C610, a screen C609, a radio receiver C606, jointly connected to an input / output port C603 of a processing card C601.

 The processing card C601 comprises, linked together by an address and data bus C602: - a central processing unit C600; - a random access memory RAM C604; - ROM C605 read only memory; and

<Desc / Clms Page number 13>

 - the C603 input / output port.

 Each of the elements illustrated in FIG. 6 is well known to those skilled in the art of microcomputers and transmission systems and, more generally, information processing systems. These common elements are therefore not described here.

 It is further observed that the word "register" used in the description designates, in each of the memories C604 and C605, both a low-capacity memory area (some binary data) and a high-capacity memory area (allowing store an entire program).

 The random access memory C604 stores data, variables and intermediate processing results in memory registers bearing, in the description, the same names as the data whose values they store. The random access memory C604 comprises in particular: - a "received data" register, in which the binary data received are stored, in their order of arrival on the bus C602 coming from the transmission channel.

 The C605 read-only memory is suitable for keeping the operating program of the central processing unit C600, in a "Program" register.

 The read-only memory C605 also contains a register for storing the radius CR of the circle C500.

 The central processing unit C600 is adapted to implement a reception method according to the invention, as illustrated by the flowchart in FIG. 3.

 As shown in FIG. 7, a network according to the invention consists of at least one station called base station SB designated by the reference C74, and several peripheral stations called mobile terminals SPi, i = 1, ..., M, where M is an integer greater than or equal to 1, respectively designated by the references C761, C762, ..., C76M. The peripheral stations C761, C762, ..., C76M are distant from the base station SB, each linked by a radio link with the base station SB and liable to move relative to the latter.

<Desc / Clms Page number 14>

 The base station C74 can comprise means adapted to implement a reception method according to the invention or can comprise a reception device according to the invention and at least one of the mobile terminals C761 can comprise means adapted to put implement a reception method according to the invention or include a reception device according to the invention.

Claims (18)

1. Method for receiving a frame (C100) modulated according to a first modulation, said frame (C100) comprising data (D) modulated according to a second modulation prior to the first modulation, characterized in that: - demodule (EC330 ) the frame (C100) according to a reverse demodulation of the first modulation, so as to obtain an intermediate signal; - The intermediate signal is demodulated (EC340) according to a reverse demodulation of the second modulation, so as to obtain a constellation; - the constellation is analyzed (EC360); and - the end of a part (C101) of the frame (C100) is detected (EC370) from the result of the analysis.
 2. Reception method according to claim 1, characterized in that said first modulation is an OFDM type modulation.
 3. Reception method according to any one of claims 1 or 2, characterized in that the frame (C100) being in accordance with the HiperLAN2 standard, the end of a burst (C1 01) of said frame (C100) is detected. .
 4. Reception method according to any one of claims 1 to 3, characterized in that said second modulation is an amplitude modulation on two carriers in quadrature.
 5. Reception method according to claim 4, characterized in that during said analysis step (EC360), the points of said constellation are represented (EC350) in a Fresnel plane, and the end of said part is detected (C101) of the frame (C100) when all of said points are inside a circle (C500) centered on the origin of said Fresnel plane and of radius (C ~ R) predetermined depending on said second modulation.
 6. Device for receiving a frame (C100) modulated according to a first modulation, said frame (C100) comprising data (D)
<Desc / Clms Page number 16>
 modulated according to a second modulation prior to the first modulation, characterized in that it comprises: - first demodulation means (C440) adapted to demodulate the frame (C100) according to an inverse demodulation of the first modulation, so as to obtain a intermediate signal; - second demodulation means (C445) adapted to demodulate the intermediate signal according to a reverse demodulation of the second modulation, so as to obtain a constellation; - means of analysis (C445) of the constellation; and - means for detecting (C445) the end of a part (C1 01) of the frame (C100) from the result of the analysis.
 7. Reception device according to claim 6, characterized in that said first modulation is an OFDM type modulation.
 8. Reception device according to any one of claims 6 or 7, characterized in that the frame (C100) being in accordance with the HiperLAN2 standard, the detection means (C445) are adapted to detect the end of a burst ( C1 01) of said frame (C100).
 9. Reception device according to any one of claims 6 to 8, characterized in that said second modulation is an amplitude modulation on two carriers in quadrature.
 10. Receiving device according to claim 9, characterized in that said analysis means (C445) are adapted to represent the points of said constellation in a Fresnel plane, and in that said detection means (C445) are adapted detecting the end of said part (C1 01) of the frame (C100) when all of said points are inside a circle (C500) centered on the origin of said Fresnel plane and of radius (C ~ R ) predetermined depending on said second modulation.
 11. Apparatus for processing digital signals, characterized in that it comprises means suitable for implementing a reception method according to any one of claims 1 to 5.
<Desc / Clms Page number 17>
 12. Digital signal processing apparatus, characterized in that it comprises a reception device according to any one of claims 6 to 10.
 13. Telecommunications network, characterized in that it comprises means adapted to implement a reception method according to any one of claims 1 to 5.
 14. Telecommunications network, characterized in that it comprises a reception device according to any one of claims 6 to 10.
 15. Mobile station in a telecommunications network, characterized in that it comprises means suitable for implementing a reception method according to any one of claims 1 to 5.
 16. Mobile station in a telecommunications network, characterized in that it comprises a reception device according to any one of claims 6 to 10.
 17. Base station in a telecommunications network, characterized in that it comprises means suitable for implementing a reception method according to any one of claims 1 to 5.
 18. Base station in a telecommunications network, characterized in that it comprises a reception device according to any one of claims 6 to 10.
FR0112720A 2001-10-03 2001-10-03 Optimized HiperLan2 frame reception system detects burst end in Fresnel plane Pending FR2830391A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5610908A (en) * 1992-09-07 1997-03-11 British Broadcasting Corporation Digital signal transmission system using frequency division multiplex
EP0786888A2 (en) * 1996-01-29 1997-07-30 Samsung Electronics Co., Ltd. Provision of a frequency reference in a multicarrier modulation system
EP1061687A1 (en) * 1999-06-14 2000-12-20 Canon Kabushiki Kaisha Adaptation of guard interval lengths in an OFDM communication system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5610908A (en) * 1992-09-07 1997-03-11 British Broadcasting Corporation Digital signal transmission system using frequency division multiplex
EP0786888A2 (en) * 1996-01-29 1997-07-30 Samsung Electronics Co., Ltd. Provision of a frequency reference in a multicarrier modulation system
EP1061687A1 (en) * 1999-06-14 2000-12-20 Canon Kabushiki Kaisha Adaptation of guard interval lengths in an OFDM communication system

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