|Publication number||USRE41606 E1|
|Application number||US 12/259,045|
|Publication date||Aug 31, 2010|
|Filing date||Oct 27, 2008|
|Priority date||Jan 8, 1999|
|Also published as||CA2291847A1, CA2291847C, EP1018827A1, EP1018827B1, EP1439677A1, EP1439677B1, EP1439677B9, EP1530336A1, EP1530336B1, EP1705852A2, EP1705852A3, EP1705852B1, EP1722527A1, EP1722527B1, US6654339, USRE40568, USRE41431, USRE41432, USRE41470, USRE41486, USRE41641|
|Publication number||12259045, 259045, US RE41606 E1, US RE41606E1, US-E1-RE41606, USRE41606 E1, USRE41606E1|
|Inventors||Ralf Böhnke, Thomas Dölle, Tino Puch|
|Original Assignee||Sony Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (70), Non-Patent Citations (8), Classifications (22)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Notice: More than one application has been filed for the reissue of U.S. Pat. No. 6,654,339. The reissue applications are 11/286,440, the instant application and applications 12/258,939, 12/258,984, 12/259,018, 12/258,799 and 12/259,063, all filed Oct. 27, 2008.
The present invention relates to a method for generating synchronization bursts for OFDM transmission systems, a method for synchronizing wireless OFDM systems, an OFDM transmitter as well as to a mobile communications device comprising such a transmitter.
The present invention relates generally to the technical field of synchronizing wireless OFDM (orthogonal frequency division multiplexing) systems. Thereby it is known to use a synchronization burst constructed using especially designed OFDM symbols and time domain repetitions.
Particularly from the document IEEE P802.11a/d2.0 “Draft supplement to a standard for telecommunications and information exchange between systems—LAN/MAN specific requirements—part 1: wireless medium access control (MAC) and physical layer (PHY) specifications: high-speed physical layer in the 5 GHz band” a synchronization scheme for OFDM systems is proposed. This document is herewith included by reference as far as it concerns the synchronization including the proposed implementation. Said known scheme will now be explained with reference to
The symbols t1, t2, t3, t4 are generated by means of an OFDM modulation using selected subcarriers from the entire available subcarriers. The symbols used for the OFDM modulation as well as the mapping to the selected subcarriers will now be explained with reference to FIG. 6.
Each of the short OFDM symbols t1, . . . t6 is generated by using 12 modulated subcarriers phase-modulated by the elements of the symbol alphabet:
The full sequence used for the OFDM modulation can be written as follows:
The multiplication by a factor of √2 is in order to normalize the average power of the resulting OFDM symbol.
The signal can be written as:
The fact that only spectral lines of S−24, 24 with indices which are a multiple of 4 have nonzero amplitude results in a periodicity of TFFT/4=0.8 μsec. The interval TTSHORT1 is equal to nine 0.8 μsec periods, i.e. 7.2 μsec.
Applying a 64-point IFFT to the vector S, where the remaining 15 values are set to zero, four short training symbols t1, t2, t3, t4 (in the time domain) can be generated. The IFFT output is cyclically extended to result in 6 short symbols t1, t2, t3, . . . t6. The mapping scheme is depicted in FIG. 7. The so called virtual subcarriers are left unmodulated.
The way of implement the inverse Fourier transform is by an IFFT (Inverse Fast Fourier Transform) algorithm. If, for example, a 64 point IFFT is used, the coefficients 1 to 24 are mapped to same numbered IFFT inputs, while the coefficients −24 to −1 are copied into IFFT inputs 40 to 63. The rest of the inputs, 25 to 39 and the 0 (DC) input, are set to zero. This mapping is illustrated in FIG. 7. After performing an IFFT the output is cyclically extended to the desired length.
With the proposed inverse fast Fourier transform (IFFT) mapping as shown in
Though the known synchronization scheme is very effective, it provides for disadvantage regarding the time domain signal properties.
For OFDM (or in general multicarrier signals) the signal envelope fluctuation (named Peak-to-Average-Power-Ratio=PAPR) is of great concern. A large PAPR results in poor transmission (due to nonlinear distortion effects of the power amplifier) and other signal limiting components in the transmission system (e.g. limited dynamic range of the AD converter).
For synchronization sequences it is even more desirable to have signals with a low PAPR in order to accelerate the receiver AGC (automatic gain control) locking and adjusting the reference signal value for the A/D converter (the whole dynamic range of the incoming signal should be covered by the A/D converter resolution without any overflow/underflow).
Therefore it is the object of the present invention to provide for a synchronization technique which bases on the known synchronization technique but which presents improved time domain signal properties to reduce the requirements for the hardware.
The above object is achieved by means of the features of the independent claims. The dependent claims develop further the central idea of the present invention.
According to the present invention therefore a method for generating synchronization bursts for OFDM transmission systems is provided. Symbols of a predefined symbol sequence are mapped according to a predefined mapping scheme on subcarriers of the OFDM system wherein the symbols of the predefined symbol sequence represent subcarriers with nonzero amplitudes. A synchronization burst is generated by inverse fast Fourier transforming the subcarriers mapped with a predefined symbol sequence. According to the present invention the predefined symbol sequence is optimized such that the envelope fluctuation of the time domain signal (Peak-to-average-power-ratio) is minimized.
The predefined symbol sequence can be chosen such that the following equations are satisfied for all symbols of the predefined symbol sequence:
The mapping of the symbols of the predefined symbol sequence and the Inverse Fast Fourier Transform can be set such that the resulting time domain signal of the synchronization burst represents a periodic nature.
Alternatively the mapping of the symbols of the predefined symbol sequence and the Inverse Fast Fourier Transform is set such that one burst part of the synchronization burst in the time domain is generated and the periodic nature of the synchronization burst in the time domain is achieved by copying the one burst part.
The number of symbols of a symbol sequence (n) can for example be 12.
The above equations define generally the symbol sequences according to the present invention. The pre-defined symbol sequence can therefore be for example:
A A A −A −A −A −A A −A −A A −A,
wherein A is a complex value.
Alternatively the predefined symbol sequence can be:
A −A A A −A A A A A −A −A −A,
wherein A is a complex value.
Alternatively the following predefined symbol sequence can be used:
A B −A B −A −B B A −B A −B −A
wherein A, B are complex values.
As a further alternative the following sequence can be used:
A −B −A −B −A B −B A B A B −A,
wherein A, B are complex values.
According to the present invention furthermore a method for synchronizing wireless OFDM systems is provided, wherein a synchronization burst is generated according to a method as set forth above and the synchronization burst is transmitted respectively before the transmission of data fields.
Thereby the time domain signals of the synchronization burst can be precomputed and stored in a memory, such that the computation of the time domain signal of the burst is only effected once.
According to the present invention furthermore a OFDM transmitter is provided comprising a mapping unit for mapping the symbols of a predefined symbols sequence according to a predefined mapping scheme on subcarriers of the OFDM system, wherein the symbols of a predefined symbols sequence represent the subcarriers of the OFDM system with nonzero amplitudes. Furthermore an inverse fast Fourier transforming unit is provided for generating a synchronization burst by inverse fast Fourier transforming the subcarriers of the OFDM mapped with said predefined symbols sequence. The mapping unit thereby is designed such that the resulting time domain signal of the synchronization burst represents a periodic nature. The mapping unit according to the present invention uses a predefined symbol sequence which is such that the envelope fluctuation of the time domain signal of the synchronization burst is minimized.
According to the present invention furthermore a mobile communications device such as set forth above is used.
With reference to the figures of the enclosed drawings referred embodiments of the present invention will now be explained.
According to the present invention the time domain synchronization burst structure as shown in
According to the present invention a short OFDM symbol (t1, . . . t6) consists of 12 phase-modulated subcarriers.
C00 C01 C02 C03 C04 C05 C06 C07 C08 C09 C10 C11 Seq0 A A A −A −A −A −A A −A −A A −A Seq1 A −A A A −A A A A A −A −A −A Seq2 A B −A B −A −B B A −B A −B −A Seq3 A −B −A −B −A B −B A B A B −A
Generally the predefined symbol sequence therefore is chosen such that the envelope fluctuation of the time domain signal of the synchronization burst is minimized.
Therefore generally the predefined symbol sequence is set such that the following equations are satisfied for all symbols for the predefined symbol sequence:
In the following the time domain signal properties of the new sequences according to the present invention will be shown with reference to
For simplicity we use in our demonstration the classical quadriphase symbol alphabet,
(this corresponds to φA=0.125)
Symbol A −A B −B
Table 1: Complex symbol mapping
PAPR (in decibel) is limited to 2.059 (even when using a time domain oversampling to capture the actual peak).
Further simulations have shown that not only the PAPR can be optimized but also the dynamic range of the signal should be minimized. Therefore another four sequences, with achieve a small PAPR and at the same time a small overall dynamic range are proposed further below.
Using the sequence as proposed in the state of the art the PAPR is 3.01 dB and the dynamic range (defined as the ratio of the peak power to the minimum power) is 30.82 dB (see FIGS. 9a and 9b).
Using the sequences according to the present invention and as described above the PAPR is reduced to 2.06 dB, however, the dynamic range is increased as the signal power is ‘0’ at some points.
Therefore the following four sequences are proposed as a further embodiment of the present invention:
The symbol sequence is C0, C1, . . . C11 and the mapping is:
C00 C01 C02 C03 C04 C05 C06 C07 C08 C09 C10 C11 Seq−Alt0 A A A A −A −A A −A −A A −A A Seq−Alt1 A −A A −A −A A −A −A A A A A Seq−Alt2 A B −A −B −A −B −B −A −B −A B A Seq−Alt3 A −B −A B −A B B −A B −A −B A
with A=exp (i*2*π*φA) and
Using these sequences the PAPR is reduced to 2.24 dB and the dynamic range is limited to 7.01 dB as it is shown in
The advantages are the same as described before, however, the clipping problem is further reduced due to the very limited dynamic range of the signal.
With reference to
In the transmitter the sync symbol data 1 are prepared and mapped in a IFFT mapping unit 2 to the appropriate IFFT points. The subcarriers of the OFDM system are transformed by a IFFT unit 3 and then the time domain signal is extended in a time extension unit 4 by copying parts of the signals (for example, t1, t2 are copied to t5, t6). The time extended signal is then sent to the I/Q modulator 5.
As shown in
With reference to
According to this scheme, the principle of setting only every fourth subcarrier of the OFDM system to a non-zero amplitude (see
The IFFT size is now only 16 (instead of 64 as it is the case in FIG. 7). Only one of the bursts t1, t2, . . . t6 will be generated. The other bursts can be generated by copying to retain the periodic nature of the synchronization time domain signal necessary for the correlation and synchronization on the receiving side. Therefore for example the time extension unit 4 can perform the copying of the 16-sample burst t1 generated by the IFFT 16 according to
The mapping scheme shown in
According to the present invention therefore a synchronization burst structure to be used in high speed wireless transmission systems is proposed. The synchronization burst is constructed using especially designed OFDM symbols and time domain repetitions. The resulting synchronization burst achieves a high timing detection and frequency offset estimation accuracy. Furthermore the burst is optimized to achieve a very low envelope fluctuation (Low peak-to-average-power-ratio) to reduce the complexity on the receiver and to reduce time and frequency acquisition time at the receiver.
Therefore the synchronization performance can further be improved. As with the scheme according to the present invention the envelope of the OFDM based synchronization burst in the time domain is reduced, the AGC pool-in speed at the receiver can be improved and an accurate time and frequency synchronization can be achieved. Furthermore the synchronization complexity on the receiver side can be reduced due to the reduced resolution requirements necessary due to reduced envelope fluctuation.
The advantages of the present invention can be set forth as following:
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5450456||Nov 12, 1993||Sep 12, 1995||Daimler Benz Ag||Method and arrangement for measuring the carrier frequency deviation in a multi-channel transmission system|
|US5732113||Jun 20, 1996||Mar 24, 1998||Stanford University||Timing and frequency synchronization of OFDM signals|
|US6160791||Aug 27, 1998||Dec 12, 2000||Sony International (Europe) Gmbh||Transmission system for the transmission of power control information in an OFDM system|
|US6160821||Nov 3, 1998||Dec 12, 2000||Sony International (Europe) Gmbh||Synchronization of digital communication systems|
|US6407846||Mar 16, 2001||Jun 18, 2002||All Optical Networks, Inc.||Photonic wavelength shifting method|
|US6438173||Feb 7, 2000||Aug 20, 2002||Infineon Technologies Ag||Multicarrier transmission system for irregular transmission of data blocks|
|US6452987||Nov 25, 1998||Sep 17, 2002||Lucent Technologies Inc.||Fast start-up in discrete multi-tone (DMT) based communications system|
|US6470055||Aug 9, 1999||Oct 22, 2002||Kamilo Feher||Spectrally efficient FQPSK, FGMSK, and FQAM for enhanced performance CDMA, TDMA, GSM, OFDN, and other systems|
|US6507733||Dec 15, 1999||Jan 14, 2003||Sony International (Europe) Gmbh||Three port junction receiver|
|US6535501||Nov 5, 1998||Mar 18, 2003||Sony International (Europe) Gmbh||Transmission method and transmission apparatus for transmitting signals on the basis of a OFDM/TDMA-system in a GSM/system|
|US6539215||May 25, 2000||Mar 25, 2003||Sony Corporation||Down converter and demodulator using a three port junction|
|US6545997||Feb 19, 1999||Apr 8, 2003||Sony International (Europe) Gmbh||Transmission method and transmission apparatus for transmitting signals on the basis of a OFDM/TDMA-system with pilot symbols|
|US6557139||Dec 8, 1999||Apr 29, 2003||Sony International (Europe) Gmbh||Encoding apparatus and encoding method for multidimensionally coding and encoding method and decoding apparatus for iterative decoding of multidimensionally coded information|
|US6567374||Feb 16, 1999||May 20, 2003||Sony International (Europe) Gmbh||Data and pilot mapping in an OFDM system|
|US6567383||Feb 16, 1999||May 20, 2003||Sony International (Europe) Gmbh||Header structure for TDD systems|
|US6609010||Nov 11, 1999||Aug 19, 2003||Sony International (Europe) Gmbh||Dual frequency band transceiver|
|US6650178||Dec 18, 1998||Nov 18, 2003||Sony International (Europe) Gmbh||N-port direct receiver|
|US6654339||Jan 6, 2000||Nov 25, 2003||Sony International (Europe) Gmbh||Synchronization symbol structure using OFDM based transmission method|
|US6674732||Feb 13, 1998||Jan 6, 2004||Sony Corporation||Transmitting method, receiving method, transmitter, and receiver|
|US6674817||Apr 10, 2000||Jan 6, 2004||Sony International (Europe) Gmbh||Communication device and distinguishing method for distinguishing between different data burst types in a digital telecommunication system|
|US6704562||Jun 14, 2000||Mar 9, 2004||Sony International (Europe) Gmbh||N-port receiver with RF/LO isolation|
|US6724246||Jan 22, 2001||Apr 20, 2004||Sony International (Europe) Gmbh||Demodulation structure and method|
|US6728550||Jul 7, 2000||Apr 27, 2004||Sony International (Europe) Gmbh||Coverage and cell extension in downlink power controlled wireless radio communication systems|
|US6731594||Sep 3, 1998||May 4, 2004||Sony International (Europe) Gmbh||Transmission system for OFDM-signals with optimized synchronisation|
|US6735261||Jul 7, 2000||May 11, 2004||Sony International (Europe) Gmbh||Calibration of a N-port receiver|
|US6738443||Jun 14, 2000||May 18, 2004||Sony International (Europe) Gmbh||Optimized synchronization preamble structure|
|US6748203||Sep 28, 2000||Jun 8, 2004||Sony International (Europe) Gmbh||Three port structure with modulated LO signal|
|US6803814||Feb 11, 2000||Oct 12, 2004||Sony International (Europe) Gmbh||Demodulator and method for the demodulation of modulated RF signals|
|US6917580||Jul 30, 2001||Jul 12, 2005||Sony International (Europe) Gmbh||Frequency reuse scheme for OFDM system|
|US7012882||Jul 30, 2001||Mar 14, 2006||Sony International (Europe) Gmbh||Channel estimator for OFDM system|
|US7106821||Mar 13, 2001||Sep 12, 2006||Sony Corporation||Data modulation method, data modulation device and communication device|
|US7145955||Apr 21, 2000||Dec 5, 2006||Sony Deutschland Gmbh||Optimized synchronization preamble structure|
|US7154975||Feb 22, 2000||Dec 26, 2006||Sony Deutschland Gmbh||Receiving apparatus and synchronizing method for a digital telecommunication system|
|US7184725||May 9, 2005||Feb 27, 2007||Sony Deutschland Gmbh||Pole switch down converter with symmetric resonator|
|US20040196916||Apr 20, 2004||Oct 7, 2004||Ralf Bohnke||Optimized synchronization preamble structure|
|US20060045219||Aug 23, 2005||Mar 2, 2006||Zhaocheng Wang||Backscatter interrogator reception method and interrogator for a modulated backscatter system|
|US20060133408||Nov 14, 2005||Jun 22, 2006||Juan Nogueira-Nine||Beaconless communication system|
|US20060148906||Feb 27, 2006||Jul 6, 2006||Christopher Bieniarz||Fluoroether compositions and methods for inhibiting their degradation in the presence of a lewis acid|
|US20060269008||Aug 3, 2006||Nov 30, 2006||Sony Deutschland Gmbh||Receiving apparatus and synchronising method for a digital telecommunication system|
|US20070036235||May 8, 2006||Feb 15, 2007||Sony Deutschland Gmbh||Transmitting apparatus and method for a digital telecommunication system|
|US20070115827||Dec 17, 2004||May 24, 2007||Sony Deutschland Gmbh||Wireless communication network architecture|
|CA2291847A1||Dec 6, 1999||Jul 8, 2000||Sony International (Europe) G.M.B.H.||Synchronization symbol structure using ofdm based transmission method|
|EP0836303A2||Oct 9, 1997||Apr 15, 1998||Ntt Mobile Communications Network Inc.||Reduction of peak to average power ratio in MCM systems|
|EP0869646A2||Mar 24, 1998||Oct 7, 1998||Lucent Technologies Inc.||Complementary encoding and modulation for multicarrier transmission|
|EP0982905A1||Aug 28, 1998||Mar 1, 2000||Sony International (Europe) GmbH||Universal PSK modulation apparatus and method|
|EP0984595A1||Sep 3, 1998||Mar 8, 2000||Sony International (Europe) GmbH||Blind modulation detection|
|EP0984596A1||Sep 3, 1998||Mar 8, 2000||Sony International (Europe) GmbH||Adpative PSK system and timing offset compensation circuit|
|EP0987863A1||Sep 17, 1998||Mar 22, 2000||Sony International (Europe) GmbH||Soft decision method and apparatus for 8PSK demodulation|
|EP1014562A1||Jun 16, 1999||Jun 28, 2000||Sony Corporation||Demodulator and method for the demodulation of modulated RF signals|
|EP1018827A1||Feb 22, 1999||Jul 12, 2000||Sony International (Europe) GmbH||Synchronisation structure for OFDM system|
|EP1037481A1||Mar 15, 1999||Sep 20, 2000||Sony International (Europe) GmbH||Simultaneous transmission of random access bursts|
|EP1039661A1||Mar 3, 1999||Sep 27, 2000||Sony International (Europe) GmbH||Multicast channel for a CDMA system|
|EP1065855A1||Jun 29, 1999||Jan 3, 2001||Sony International (Europe) GmbH||Adaptation of cyclic extensions in an OFDM communication system|
|EP1162764A1||Jun 5, 2000||Dec 12, 2001||Sony International (Europe) GmbH||Indoor wireless system using active reflector|
|EP1170916A1||Jul 5, 2000||Jan 9, 2002||Sony International (Europe) GmbH||Channel estimator for OFDM system|
|EP1170917A1||Jul 6, 2000||Jan 9, 2002||Sony International (Europe) GmbH||Method and device to provide an OFDM up-link using Time-Frequency interleaving|
|EP1207661A1||Nov 20, 2000||May 22, 2002||Sony International (Europe) GmbH||Adaptive subcarrier loading|
|EP1207662A1||Nov 20, 2000||May 22, 2002||Sony International (Europe) GmbH||OFDM system with antenna diversity in the transmitter and pre-equalisation|
|EP1276251A1||Jul 11, 2001||Jan 15, 2003||Sony International (Europe) GmbH||Method for calculating a weighting vector for an antenna array|
|EP1276288A1||Jul 10, 2001||Jan 15, 2003||Siemens AG||Reference symbols for channel estimation with multicarrier transmission|
|EP1379026A1||Oct 16, 2002||Jan 7, 2004||Sony International (Europe) GmbH||Dual rate wireless transmission system|
|EP1439677A1||Feb 22, 1999||Jul 21, 2004||Sony International (Europe) GmbH||Synchronisation symbol structure for OFDM system|
|EP1530336A1||Feb 22, 1999||May 11, 2005||Sony International (Europe) GmbH||Synchronization preamble structure for OFDM system|
|EP1667341A1||Jul 11, 2001||Jun 7, 2006||Sony Deutschland GmbH||Method for calculating a weighting vector for an antenna array|
|EP1705852A2||Feb 22, 1999||Sep 27, 2006||Sony Deutschland Gmbh||Synchronisation symbol structure for OFDM system|
|EP1722527A1||Feb 22, 1999||Nov 15, 2006||Sony Deutschland Gmbh||Synchronisation symbol structure for OFDM system|
|GB2320868A||Title not available|
|JP2000209183A||Title not available|
|KR100712865B1||Title not available|
|WO1998000946A2||Jun 19, 1997||Jan 8, 1998||The Board Of Trustees Of The Leland Stanford Junior University||Timing and frequency synchronization of ofdm signals|
|1||Bauml R W et al: "Reducing the Peak-To-Average Power Ratio of Multicarrier Modulationby Selected Mapping" Electronics Letters, vol. 32, No. 22, Oct. 24, 1996, p. 2056-2057, XP000643915.|
|2||Dinis R et al: "Carrier Synchronization With CEPB-OFDM" 1997 IEEE 47TH. Vehicular Technology Conference, Phoenix, May 4-7, 1997, vol. 3, No. Conf. 47, May 4, 1997, pp. 1370-1374, XP000738586 Institute of Electrical and Electronics Engineers.|
|3||*||IEEE P802.11a/D5.0, LAN/MAN Specific Requirement-Part 11: Wireless Medium Access Control (MAC) and physical layer (PHY) specifications: High Speed Physical Layer in the 5 GHz band, IEEE, 61 pages, 1999.|
|4||*||IEEE P802.11a/D5.0, LAN/MAN Specific Requirement—Part 11: Wireless Medium Access Control (MAC) and physical layer (PHY) specifications: High Speed Physical Layer in the 5 GHz band, IEEE, 61 pages, 1999.|
|5||*||Laurenti, Implementation Issues in OFDM Systems, Dissertation, 98 pages, 1998.|
|6||Mizoguchi et al: "A Fast Burst Synchronization Scheme for OFDM", IEEE, pp. 125-129, 1998.|
|7||*||Moose, A Technique for Orthogonal Frequency Division Multiplexing Frequency Offset Correction, IEEE, 7 pages, Oct. 1994.|
|8||Schmidl T M et al: "Low-Overhead, Low-Complexity Burst Synchronization for OFDM" 1996 IEEE International Conference on Communications ICC), Converging Technologies for Tomorrow's Applications Dallas, Jun. 23-27, 1996, vol. 3, Jun. 23, 1996, pp. 1301-1306, XP000625022 Institute of Electrical & Electronics Engineers ISBN: 0-7803-3251-2.|
|U.S. Classification||370/203, 375/355, 370/350, 370/208|
|International Classification||H04L27/26, H04B14/08, H04L7/08, H04L7/00, H04J11/00|
|Cooperative Classification||H04L27/2613, H04L5/0042, H04L5/0007, H04L27/262, H04L27/2626, H04L27/2657, H04L25/03343, H04L27/2662|
|European Classification||H04L27/26M2E, H04L27/26M1R3, H04L5/00A2A1, H04L5/00C3, H04L25/03B9|