CN106850483B - Phase error estimation method and device for wireless communication system - Google Patents
Phase error estimation method and device for wireless communication system Download PDFInfo
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- CN106850483B CN106850483B CN201610795854.2A CN201610795854A CN106850483B CN 106850483 B CN106850483 B CN 106850483B CN 201610795854 A CN201610795854 A CN 201610795854A CN 106850483 B CN106850483 B CN 106850483B
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- 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
- H04L27/2655—Synchronisation arrangements
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2691—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation involving interference determination or cancellation
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- 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
- H04L27/2655—Synchronisation arrangements
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2692—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
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- 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
- H04L27/2655—Synchronisation arrangements
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2695—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with channel estimation, e.g. determination of delay spread, derivative or peak tracking
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/38—Demodulator circuits; Receiver circuits
- H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
- H04L27/3854—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using a non - coherent carrier, including systems with baseband correction for phase or frequency offset
- H04L27/3872—Compensation for phase rotation in the demodulated signal
Abstract
The invention discloses a phase error estimation method and a phase error estimation device for a wireless communication system. In the phase error estimation method, a pilot frequency on a pilot frequency subcarrier is extracted from a transmitting signal, and the pilot frequency is descrambled; the common phase error is calculated using the phase deflection across the plurality of pilot symbols, averaged to remove the effect of noise, and a phase error estimate on a predetermined OFDM symbol is obtained. Compared with the prior art, the phase error estimation method and the phase error estimation device provided by the invention adopt a mode of calculating phase deflection by spanning a plurality of pilot symbols and performing long-term smoothing processing, so that the accuracy of phase error estimation can be effectively improved.
Description
Technical Field
The present invention relates to a phase error estimation method, and more particularly, to a method for estimating a phase error based on estimating a phase deflection of a pilot symbol in a wireless communication system (OFDM system for short) using an OFDM technique, and a corresponding phase error estimation apparatus, and belongs to the field of wireless communication technologies.
Background
In wireless communication technology, the difference between the phase of the transmitted signal after demodulation and the ideal phase is called phase error. At the receiving end of the wireless communication system, in order to improve the receiving performance and analyze the radio frequency characteristics of the transmitting end, effective technical measures must be taken to carry out high-precision estimation and compensation on the phase error.
On the other hand, in the current 4G wireless communication system, an OFDM (Orthogonal Frequency division multiplexing) technology is a mainstream physical layer technology. The method is technically characterized in that the subcarrier resources are saved and protected through orthogonal overlapping of subcarriers, and the frequency spectrum efficiency is improved. Compared with the traditional wireless transmission technology, the OFDM system also has the following advantages: (1) good frequency selective fading resistance, and (2) simple channel equalization.
Despite the above advantages of OFDM systems, one of the most significant contributors to the overall performance of OFDM systems is the non-ideal behavior of the oscillators at the transmitting and receiving ends. At the transmitting end, the modulated signal needs to be up-converted to a radio frequency signal. At the receiving end. The radio frequency signal is to be down converted to an intermediate frequency or baseband signal. The frequencies output by the oscillators at the transmitting end and the receiving end often have difference, and after the frequency offset correction at the receiving end, residual frequency offset may exist, so that a common phase error exists on each received OFDM symbol, and the receiving performance is seriously affected.
For phase error estimation in OFDM systems, a currently common method is to embed a known pilot in the transmitted signal, and the receiving end calculates the common phase error according to the characteristics exhibited by the received pilot. This conventional method is used in chinese patent No. ZL 200410084932.5 by samsung electronics. Namely, the received front and rear pilot symbols are used for carrying out correlation operation to obtain the phase error between the front and rear OFDM symbols, and then the average of a plurality of phase errors is carried out to improve the estimation precision. In this method, the reason why the two pilot symbols before and after are selected as the basic operation set is that the correlation degree between adjacent symbols in time is the highest in consideration of the time-varying characteristic of the channel.
Further, in chinese patent application publication No. CN 101594338A, a method and apparatus for reducing common phase error is disclosed. The method adopts the data symbols after hard decision and the pilot frequency symbols to participate in phase difference estimation together so as to deal with the multipath effect. When selecting data symbol, judging interference degree, selecting symbol with smaller interference degree to improve accuracy of phase error estimation. However, in this method, hard decision of data symbols is required, so that estimation of common phase error must be performed after data demodulation, increasing complexity of the receiving end timing.
Disclosure of Invention
In view of the deficiencies of the prior art, the primary technical problem to be solved by the present invention is to provide a phase error estimation method for a wireless communication system.
Another object of the present invention is to provide a phase error estimation apparatus for a wireless communication system.
In order to achieve the purpose, the invention adopts the following technical scheme:
according to a first aspect of the embodiments of the present invention, there is provided a phase error estimation method for use in a wireless communication system using OFDM technology, comprising the steps of:
extracting pilot frequency on a pilot frequency subcarrier from a transmitting signal, and descrambling the pilot frequency;
the common phase error is calculated using the phase deflection across the plurality of pilot symbols, averaged to remove the effect of noise, and a phase error estimate on a predetermined OFDM symbol is obtained.
Preferably, the long-term smoothing of the common phase error in the time domain is performed on the measurement results of a plurality of data packets.
Preferably, the phase error estimation method is used in the application scenario of non-real-time services.
Preferably, for short data packets, the number of transmitted spectrum symbols is relatively small to ensure enough data pairs; for long data packets, the number of the transmitted spectrum symbols is relatively large to obtain the accuracy improvement under a large span.
According to a second aspect of the embodiments of the present invention, there is provided a phase error estimation apparatus for use in a wireless communication system employing OFDM technology, comprising a signal receiving unit, a calculation unit, and an output unit; wherein the content of the first and second substances,
the signal receiving unit extracts the pilot frequency on the pilot frequency subcarrier from the transmitting signal;
the calculation unit descrambles the pilot frequency, calculates a common phase error by using phase deflection across a plurality of pilot frequency symbols, and performs averaging to remove the influence of noise to obtain a phase error estimation value on a preset OFDM symbol;
the computing unit outputs the phase error estimation value to the outside through the output unit.
Preferably, the calculation unit performs long-term smoothing of the common phase error in the time domain on the measurement results of the plurality of data packets.
Compared with the prior art, the phase error estimation method and the phase error estimation device provided by the invention adopt a mode of calculating phase deflection by spanning a plurality of pilot symbols and performing long-term smoothing processing, so that the accuracy of phase error estimation can be effectively improved.
Detailed Description
The technical content of the invention is explained in detail with reference to specific embodiments.
In a 4G wireless communication system adopting the OFDM technology, there are a large number of application scenarios of non-real-time services. For example, the Wi-Fi testing apparatus receives and processes Wi-Fi signals to be measured; downloading application scenes of mass data through OFDM signals and the like. In the application scenes with low real-time requirement on signal processing, the method adopts a mode of calculating phase deflection by spanning a plurality of pilot symbols and performing long-term smoothing processing, and can effectively improve the precision of phase error estimation.
The phase error estimation method provided by the invention is explained by taking an application scenario that a Wi-Fi testing instrument receives and processes a Wi-Fi signal to be measured as an example.
Assuming that a plurality of pilot subcarriers known by a receiving end exist in a transmitted signal, in the measurement of an ieee802.11a signal, a Wi-Fi test instrument extracts pilots on 4 pilot subcarriers for an ith received OFDM symbol (i is a positive integer, the same applies below). E.g., extract pilots on pilot subcarriers-21, -7, 7, 21, respectively. In other embodiments, the pilots at different positions may be extracted on different numbers (e.g., 6 or 8) of pilot subcarriers, which is not necessarily illustrated herein.
After descrambling the decimated pilots, the common phase offset I can be estimated using the LS (least squares) method or other similar methods such as MMSE (minimum mean square error)i. In particular, the first and second (c) substrates,
first, the actual received signal is modeled as follows: where r (t) is the received signal, x (t), h (t) and
respectively, the transmitted signal, the channel impulse response and the common phase offset, and n (t) is white noise.
Secondly, the time domain signal of the ith OFDM symbol in the received signal is transformed to the frequency domain representation by FFT, and the value of the kth pilot subcarrier (k is a positive integer) can be obtained:
Ri(k)＝Xi(k)·Hi(k)·Ii,k∈[-N/2,N/2](2)
finally, using LS method, the common phase deviation I on the ith OFDM symbol can be obtainediIn which S isPIs a set of pilot subcarriers.
Since the number of pilot subcarriers on one OFDM symbol is usually very limited, the above calculation method may not sufficiently meet the requirement of the receiving end due to insufficient accuracy. In order to improve the measurement accuracy of the common phase error, the phase error estimation method further adopts the following two optimization measures on the basis of the steps:
(1) the common phase error is calculated using the phase deflection across multiple pilot symbols, averaged to remove the effects of noise.
Estimating the phase deflection of the pilot symbols to achieve phase error estimation
Considering that the influence of the time-varying channel is small in the application scenario of non-real-time traffic and the real-time requirement is low, the influence of noise can be further removed by calculating the phase deflection across multiple pilot symbols and averaging. The algorithm principle across m pilot symbols is as in equations (4) and (5), where Δ I is the phase deviation difference between adjacent pilot symbols, NsI with subscript added for the number of symbols in the whole data packetiIt represents a value on the ith OFDM symbol and m represents a positive integer.
Ii＝i·ΔI (5)
In the above optimization measures, it is necessary to select a suitable value of m for the calculation of Δ I. The selected principle is as follows: for short packets, the value of m should be relatively small to ensure that there are enough data pairs; for long packets, a larger value of m may be selected to obtain accuracy improvement over a large span.
It should be noted that the above formula (3) calculates a phase error, i.e. I, for each OFDM symboli. But only the I calculated by equation (3)iMay not be sufficiently accurate. For this purpose, the invention further uses the formulas (4) and (5) to calculate all I on the basis of the formula (3)iAfter averaging, a new I is outputi. I calculated by the formula (5)iWill be compared with I in the formula (3)iAnd is more accurate.
(2) And performing long-term smoothing processing on the measurement results of the plurality of data packets by using the common phase error in the time domain.
In the optimization measure, the characteristic that a measured piece needs to send a plurality of data packets to obtain certain measured quantity in measurement is utilized, the measurement precision of the common phase error is further improved, and the algorithm can be various, such as a first exponential smoothing method shown in formula (6) and the like, subscripts st and lt, p are added in formula (6) to represent the current value and the long-term smooth value on the p-th data packet, wherein p is a positive integer, α is a smoothing constant, and the value range is [0, 1 ].
ΔIlt,p＝α·ΔIst+(1-α)·ΔIlt,p-1(6)
Further, use Ii＝i·ΔIlt,pAnd acquiring a phase error estimated value on the ith OFDM symbol. The phase error estimation value is an optimization result obtained by adopting the phase error estimation method provided by the invention. It follows that a high accuracy of the phase error estimation can be achieved by the above described optimization measures.
It should be noted that the first exponential smoothing method used in the long-term smoothing process is only an example, and other smoothing algorithms, such as a second exponential smoothing method, a third exponential smoothing method, or a kernel smoothing method, may also be used in practice, and are not described herein again.
On the basis of the phase error estimation method, the invention further provides a phase error estimation device. The phase error estimation apparatus includes a signal receiving unit, a calculation unit, and an output unit. Wherein, the signal receiving unit extracts the pilot frequency on the pilot frequency subcarrier from the transmitting signal; after the computing unit acquires the pilot frequencies, descrambling the pilot frequencies; calculating a common phase error using the phase deflection across the plurality of pilot symbols, averaging to remove the effect of noise, wherein for the measurements of the plurality of data packets, a long term smoothing of the common phase error in the time domain is performed; through the steps, the phase error estimated value on the ith OFDM symbol is obtained. After the calculating unit obtains the phase error estimated value, the phase error estimated value is output through the output unit.
The principles and embodiments of the present invention have been described above with reference to an application scenario in a Wi-Fi test instrument. The method is mainly suitable for application scenes with low requirements on signal processing real-time performance, such as scenes in which a Wi-Fi testing instrument accurately estimates the public phase, scenes in which the public phase error of the OFDM modulation signal is measured, and the like, and only needs to be performed by a receiving end by fully utilizing the information of the whole data packet. It should be noted that the above-mentioned embodiments should be regarded as illustrative rather than restrictive, and the invention should not be regarded as being limited to the above-mentioned embodiments. In other OFDM system reception scenarios and measurement scenarios, the embodiments of the present invention may be varied accordingly.
The phase error estimation method and apparatus for wireless communication system provided by the present invention are described in detail above. It will be apparent to those skilled in the art that any obvious modifications thereto can be made without departing from the true spirit of the invention, which is to be accorded the full scope of the claims herein.
Claims (7)
1. A phase error estimation method used in a non-real-time service application scenario of a wireless communication system adopting an OFDM technology is characterized by comprising the following steps:
extracting pilot frequency on a pilot frequency subcarrier from a transmitting signal, and descrambling the pilot frequency;
calculating a common phase error using the phase deflection across the plurality of pilot symbols, averaging to remove the effect of noise by obtaining a phase error estimate on a predetermined OFDM symbol by:
Ii＝i·ΔI；
where Δ I is the phase deviation difference between adjacent pilot symbols, NsI with subscript added for the number of symbols in the whole data packetiThe value on the ith OFDM symbol is shown, and m is a positive integer and represents the number of transmitted frequency symbols.
2. The phase error estimation method of claim 1, wherein:
and performing long-term smoothing processing on the common phase error in a time domain on the measurement results of a plurality of data packets.
3. The phase error estimation method of claim 1, wherein:
in the transmitted signal, there are a plurality of pilot subcarriers known to the receiving end.
4. A phase error estimation method according to claim 1 or 2, characterized by:
for short data packets, the number of the transmitted frequency-transfer symbols is relatively small so as to ensure enough data pairs; for long data packets, the number of the transmitted spectrum symbols is relatively large to obtain the accuracy improvement under a large span.
5. A phase error estimation device, used in the non-real-time service application scene of the wireless communication system adopting OFDM technology, is characterized in that it comprises a signal receiving unit, a calculating unit and an output unit; wherein the content of the first and second substances,
the signal receiving unit extracts the pilot frequency on the pilot frequency subcarrier from the transmitting signal;
the calculation unit descrambles the pilot, calculates a common phase error using phase deflection across a plurality of pilot symbols, averages to remove the effect of noise by the following equation, obtains a phase error estimate on a predetermined OFDM symbol:
Ii＝i·ΔI；
where Δ I is the phase deviation difference between adjacent pilot symbols, NsI with subscript added for the number of symbols in the whole data packetiA value on the ith OFDM symbol is represented, m is a positive integer and represents the number of the transconductance frequency symbols;
the computing unit outputs the phase error estimation value to the outside through the output unit.
6. The phase error estimation device of claim 5, wherein:
the calculation unit performs long-term smoothing of the common phase error in the time domain on the measurement results of the plurality of data packets.
7. The phase error estimation device of claim 5, wherein:
in the transmitted signal, there are a plurality of pilot subcarriers known to the receiving end.
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| CN101499991A (en) * | 2009-03-17 | 2009-08-05 | 广东工业大学 | MIMO-OFDM system carrier frequency bias and sampling offset combined estimation method under IQ unbalance |
| CN102739579A (en) * | 2011-04-06 | 2012-10-17 | 普天信息技术研究院有限公司 | Frequency offset correction method |
| CN105490980A (en) * | 2015-12-11 | 2016-04-13 | 航天恒星科技有限公司 | Carrier wave frequency deviation estimation method and system |
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| CN101499991A (en) * | 2009-03-17 | 2009-08-05 | 广东工业大学 | MIMO-OFDM system carrier frequency bias and sampling offset combined estimation method under IQ unbalance |
| CN102739579A (en) * | 2011-04-06 | 2012-10-17 | 普天信息技术研究院有限公司 | Frequency offset correction method |
| CN105490980A (en) * | 2015-12-11 | 2016-04-13 | 航天恒星科技有限公司 | Carrier wave frequency deviation estimation method and system |
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