• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The present invention relates to a transmitter in which channel estimation errors observed in different amplitude constellations in multi-carrier systems based on OFDM ("Orthogonal frequency-division multiplexing") are reduced by means of the channel and / or source coding performed by an generated dictionary, as well as a receiver that detects in accordance with the mentioned code dictionaries. An encoding system is selected so that the a priori probability requirements for each constellation point are met by this code.
    公开号:SE1151055A1
    申请号:SE1151055
    申请日:2010-01-25
    公开日:2012-02-13
    发明作者:Gunes Kurt；Coskun Sahin
    申请人:Turkcell Iletisim Hizmetleri Anonim Sirketi；
    IPC主号:
    专利说明:

    In addition to the repeat codes, there are also types of coding that provide security by adding information that is extra but known to the transmitted information.
    However, since more information is transmitted than the transmitted information to the channel regardless of the type of coding, an additional source utilization takes place in the channel.
    The purpose of channel coding is to ensure that the information is transmitted in the channel in an optimal way. This method often involves the conversion of analog signals such as sound or a light intensity in an image into digital signals (binary representation) and consequently the transmission of these via a modem. Channel coding is also applied in algorithms used in data compression in addition to the standard processes such as quantization and A / D conversion (analog to digital) of bits or symbol content. Standard image compression algorithms are MPEG and J PEG formatted. MPEG is used for compressing moving images as movies, while JPEG is used for compressing still images as photographs. Although the performed channel coding converts different information into digital form, the manner in which the conversion is performed will vary depending on the main purpose.
    If it is more important to protect certain information than others, for example channel coding can be performed so that it enhances the security of this information. This information can be coded using, for example, bits. Another example is encoding information, which is transmitted very often, with fewer bits.
    The symbols transmitted by the transmitter and which are defined in the receiver are referred to as "pilot symbols". These pilot symbols are coded according to the code set to be used and sent to the receiver.
    In OFDM-based systems, the entire frequency band (B Hz) is divided into N subchannels.
    In the transmitter, the incoming serial data sequence (Xn) is first subjected to error correction coding in the source and / or channel encoder (103) and then converted to a parallel structure at the serial-to-parallel converter (104). Then pilot tone (s) are added to the signal based on the communication standard used. Then a block (105) of N-point IFF T ("Inverse Fast Fourier Transform") converts the signal to the time domain. When the signal has passed through the parallel1-to-serial converter (106), a prefix and / or suf fi x is added to the signal by the cyclic pre fi x / suffix adder (107) to protect said data against channel spread. Finally, the signal is converted to analog form by passing it through a digital-to-1 analog converter (D / A converter) (108) (Figure 1). 10 15 20 25 30 Each subcarrier has a bandwidth of B / N Hz. Each subcarrier can be modulated by a digital modulation technique such as binary shift coding, M-fold phase shift coding (MPSK) or M-fold quadrature amplitude modulation (M-QAM).
    On the receiver side, the received signal must first pass through an analog-to-digital converter (A / D converter). Then the cyclic prex and / or suffix is removed from the signal to get rid of the scatter that may have been applied by the channel.
    Smoothing can be easily performed in OF DM systems on each subcarrier by using a single-pin type frequency domain equalizer (single-pin FDE, "Frequency Domain Equalizer"). Frequency domain equalizers are often used in OFDM-based systems because they are easy to implement. Channel taps are estimated based on the transmission of a known data sequence. This process is called data-assisted or pilot-based channel estimation.
    The baseband model of a transmitted OFDM symbol may be referred to as; xk = J-l fifi ggxne fi ffkfl / N, k = 0,1, ..., 1v - 1 (1) where N represents the FF T size, n indicates the frequency domain index, k indicates the time domain index and {X ,,} indicates the transmitted symbol / the bit sequence.
    The received OFDM symbol at the output of the FFT block can be designated as; -j21rkn / N Rn = Jiñg fi gg rke, n = 0,1, ..., 1v - 1 (2) where rk in equation 2 is the received symbol sample.
    The received OF DM symbol at the output of the FFT block can also be expressed as; Rn = HnXn + ln + Wn (3) In Equation 3, Hn represents the near channel pin, In represents inter-channel interference on the nth channel and Wn represents a component with additive white Gaussian noise (AWGN).
    Channel estimation is performed using the known pilot symbols. The channel estimate can basically be obtained by the following equation A Rmí Hm '- Ti (4) In equation 4, Pi denotes the izte pilot symbol. 10 15 20 25 30 If the number of pilot symbols used in the system is L, the channel pins used in the FDE can be obtained by averaging the channel estimates (5) per symbol as follows: Hn = šzël Hni (5) The samples received at the output of F DE is z = i = ïlx + Ä- "+ 321 n Hn 11 ,, n un nn (6) As can be seen from the explanations given above, the estimation error associated with the channel tap estimate, Én, causes performance degradation in OFDM systems.
    As a result of the experimental and analytical studies that have been carried out, it has been observed in prior art applications that in the OFDM-based communication methods, the noise added to the transmitted data and the interchannel interference (ICI, "Interchannel Interference") occurs more often in constellation points with high amplitudes than the points close to the origin in which the real (in-phase) and virtual (quadrature) amplitudes are zero (fi g. 3 and 4).
    Hn = Hn + AHn (7) In Equation 7, AHn represents the channel estimation error. The received symbol can then be expressed as zn = Xn -%: '- * X ,, + I§ -: + §-: (8) In equation 8 fi there is a burst that is scaled by the constellation amplitude of the transmitted symbol. To demonstrate this effect, a 64-QAM constellation is used.
    A standard 64-QAM constellation is shown in fi g. 3. The mean symbol energy in the constellation is normalized to 1. Samples received from this constellation through ideal channels with 3 pilot symbols are shown in fi g. 4. As can be seen in this ur gur, constellation points with higher arnplitude values are exposed to more noise when channeling.
    The solution methods provided in the prior art for the problem of improving the accuracy of channel estimation are generally based on the transmission of a known data sequence referred to as pilot symbols.
    One of the applications in the prior art is disclosed in U.S. Patent No. 6,327,314. This document relates to improving the channel estimation process for a more accurate channel frequency response. Another application in the prior art is disclosed in U.S. Patent Document US-2004 / 240,376. In said document, a virtual training symbol is created which is processed to correct the channel estimation error.
    SUMMARY OF THE INVENTION The object of the present invention is to provide an OFDM-based transmitter in which performance degradation arising due to channel estimation errors is reduced and a receiver operating in accordance with said transmitter.
    Another object of the invention is to provide a transmitter which takes measures against performance loss resulting from channel estimation errors, by using methods for source coding and / or channel coding.
    A further object of the invention is to minimize the number of constellation elements that are more affected by the channel estimation error in the codes revealed during channel or source coding, and thereby to reduce the performance loss resulting from the channel estimation error.
    Detailed Description of the Invention The transmitter provided to achieve the object of the present invention and the receiver operating in accordance with said transmitter are illustrated in the accompanying diagrams, in which Fig. 1 shows a block diagram of a transmitter according to the prior art.
    F ig. 2 shows a schematic block diagram of the transmitter and receiver according to the invention.
    Fig. 3 is a diagram showing the arrangement of the points in a conventional 64-QAM constellation in the prior art.
    Fig. 4 is a diagram showing the arrangement of the points in a conventional 64-QAM constellation in the prior art when noise is added to them.
    Fig. 5 is a flow chart of the method used in the transmitter.
    Fig. 6 is a flow chart for generating the dictionary used by the transmitter in the method described in fi g. 5.
    The parts of the figures have each been given a reference numeral, the designations refer to the following: 1. Receiver 2. Analog-to-digital converter 3. Cycle prefix / suf removal unit fi x 10 15 20 25 30 35 4 Serial-to -parallel-converter 5 N-FFT-block 6. Channel estimator 7 FEQ-frequency-domain-equalizer 8 Demodulator 9. Parallel-to-serial-converter 1 0. Decoder 1 1. Transmitter 12. Memory 103. Encoder 104. Serial-to-parallel converter 105. N-IFFT block 106. Parallel-to-serial converter 107. Pre-add / suf fi x 108. Add-on unit Digital-to-analog converter The transmitter (1 1) comprises a memory (12), a source and / or channel encoder (103), a serial-to-parallel converter (104), an N-IFFT block (105), a parallel-to-serial converter (106), a pre-x / suf-x adder ( 107) and a digital-to-analog converter (108).
    The symbols encoded and transmitted by the transmitter (11) according to the invention are detected by the receiver (1). The receiver (1) operating according to the transmitter (1 1) comprises an analog-to-digital converter (2), a unit (3) for removing cyclic pre fi x / suf fi x, a serial-to-1 parallel converter (4 ), an N-FFT block (5), a channel estimator (6), a frequency domain equalizer (7), a demodulator (8), a parallel-to-serial converter (9) and a source and / or channel decoder ( 10).
    Some symbols are exposed to a higher noise level due to the channel estimation error. In the present invention, symbols with a higher noise level are intended to be used to a lesser extent, in order to increase performance, while the symbols with a lower noise level are intended to be used more often. The amount of these symbols to be used is calculated according to the noise distribution, and thus the desired a priori probability values for symbols are determined.
    The transmitter (1 1) operates according to the following method: - Generates pilot symbols (201), - Measures the brush content at the channel through which the overdrive will be effected (202), 10 15 20 25 30 - Generates a dictionary in which the desired a priori probabilities for different symbols is determined according to the brush content of the channel (203), - Saves the generated dictionary in memory (12) (204), - Changes the code set to be used according to the generated dictionary (205), - Receives the uncoded data and executes channel coding according to the changed channel and / or source code set (206), - Transfer the coded data to the source and / or channel decoder (10) in the receiver (1) (207).
    The uncoded data is the data received from sources such as audio and / or video recording devices, data banks, Internet sites.
    The glossary generated in the transmitter (1 l) is generated in the source and / or channel decoder (10). The source and / or channel decoder (10) decodes the signals it detects by converting them to the nearest dictionary tower.
    The glossary is generated in the transmitter (11) by the following method: - Channel estimation errors are calculated for each point in the constellation according to the brush content of the channel (301), - The desired a priori probabilities are calculated to minimize the total error probability according to the error levels of the constellation points - The coding glossary to be used is generated according to the probabilities (303).
    In one embodiment of the invention, the source code set in the transmitter (1 1) is changed in accordance with the generated dictionary and thus source coding is performed. In this embodiment, a source encoder (103) is used as an encoder (103).
    In another embodiment of the invention, the channel code set in the transmitter (1 l) is changed in accordance with the generated dictionary and thus channel coding is performed. In this embodiment, a channel encoder (103) is used as an encoder (103).
    In the invention, it is assumed that there are M points in the constellation and the expected channel estimation error is calculated for each of the M points. As a result of these channel estimate calculations, the error probability of each point changes. The desired a priori probability values for symbols are calculated so that the total error probability is minimized. The glossary to be used in the channel and / or source coding is generated using these probabilities. 10 15 20 When symbols with high amplitudes are generated in the art, the channel estimation error increases. Therefore, it is ensured that the presence of symbols with high amplitudes is reduced in certain conditions by changing channel and / or source coding in the transmitter (11). The amount of noise in the duct is measured and the mentioned ratio is decided on in accordance with the measured results. Since the channel estimation error will increase as the noise level increases, the transmitter (11) uses the symbols near the center of the constellation more often.
    Using the channel and / or source coding dictionary generated in accordance with the measured amount of noise, symbols with high amplitudes take up less space in the coding dictionary of the information. This glossary, which is also de on the receiver's (1) page, provides a transmission that is more robust against channel estimation errors.
    It is possible to develop a wide range of embodiments of the conventional transmitter (11) and the receiver (1) operating in accordance with said transmitter. The invention may not be limited to the examples described herein and is substantially in accordance with the claims.
    权利要求:
    Claims (5)
    [1]
    A transmitter (1 1) used in OFDM communication, comprising a memory (12), a source and / or channel encoder (103), a serial-to-parallel converter (104), an N-IFFT block (105), a parallel-to-serial converter (106), a unit (107) for adding pre fi x / suf fi x and a digital-to-analog converter (108); and characterized in that it
    [2]
    2. Generates pilot symbols (201), measures the brush content at the channel through which the transmission will be effected (202), generates a glossary in which the desired a priori probabilities of different symbols are determined according to the brush content of the channel (203), saves the generated the dictionary in the memory (12) (204), changes the code set to be used according to the generated dictionary (205), receives the uncoded data and performs channel coding according to the changed code set (206), transmits the coded data to the source and / or or the channel decoder (10) in the receiver (1) (207). . A transmitter (11) according to claim 1, which calculates the channel estimation error for each point in the constellation according to the brush content of the channel (301), calculates the desired a priori probabilities to minimize the total error probability according to the error contents of the constellation points (302), and generates the coding glossary to be used according to the probabilities (303).
    [3]
    A transmitter (11) according to claim 2, which uses the source code set as the code set.
    [4]
    A transmitter (11) according to any one of the preceding claims, which uses the channel code set as the code set. 10 10
    [5]
    A receiver (1) operating in accordance with the transmitter (1 1) according to any one of claims 2-4; which receiver comprises an analog-to-digital converter (2), a unit (3) for removing cyclic pre fi x / suf fi x, a serial-to-parallel converter (4), an N-FFT block (5), a channel estimator (6), a frequency domain equalizer (7), a demodulator (8), a parallel-to-serial converter (9) and a source and / or channel decoder (10); and characterized in that it comprises a source and / or channel decoder (10) in which the generated dictionary is denoted and which decodes the signals which it detects by converting them to the nearest dictionary term.
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    同族专利:
    公开号 | 公开日
    FI20116245A|2011-12-08|
    WO2010131125A1|2010-11-18|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US6327314B1|1998-04-01|2001-12-04|At&T Corp.|Method and apparatus for channel estimation for multicarrier systems|
    US7260055B2|2003-05-30|2007-08-21|Agency For Science, Technology, And Research|Method for reducing channel estimation error in an OFDM system|CN108631879B|2018-05-14|2019-11-12|华侨大学|A kind of light orthogonal frequency division multiplexing communication method and system based on probability shaping mapping|
    US10785085B2|2019-01-15|2020-09-22|Nokia Technologies Oy|Probabilistic shaping for physical layer design|
    法律状态:
    2013-04-16| NAV| Patent application has lapsed|
    优先权:
    申请号 | 申请日 | 专利标题
    TR2009/03651A|TR200903651A1|2008-12-30|2009-05-11|OFDM is a transmitter used in communication and a receiver operating in accordance with this transmitter.|
    PCT/IB2010/050303|WO2010131125A1|2009-05-11|2010-01-25|Constellation shaping for ofdm|
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