CN101702702B

CN101702702B - Symbol synchronizing method and device and symbol receiving processing system

Info

Publication number: CN101702702B
Application number: CN2009102218700A
Authority: CN
Inventors: 李晔; 秦龙; 胡宏杰; 安东尼·宋
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2009-11-19
Filing date: 2009-11-19
Publication date: 2012-04-25
Anticipated expiration: 2029-11-19
Also published as: CN101702702A

Abstract

The embodiment of the invention discloses symbol synchronizing method and device and a symbol receiving processing system. The method comprises the steps of: receiving a signal sent by a sending terminal; obtaining position information and power information of each path in current OFDM symbols; obtaining an estimated variance for the feedback of all the OFDM symbols; obtaining the total residue interfering energy of all the paths in the current OFDM symbols according to a preset initial position aggregate or a quantized initial position ms of all FFT integrating ranges in the initial position aggregate, the obtained position information and the obtained power information of each path and the estimated variance for the feedback of all the OFDM symbols; obtaining the initial position which corresponds to the minimum interfering energy in the total residue interfering energy; and synchronizing symbols of the signal sent by the sending terminal by using the initial position which corresponds to the minimum interfering energy as a symbol timing value. The embodiment can reduce the residue interfering energy after IBI elimination and ICI reconstruction compensation under the condition that channel time-delay extension exceeds CP length.

Description

Symbol synchronization method and device, and receiving processing system

Technical Field

The present invention relates to communication technologies, and in particular, to a symbol synchronization method and apparatus, and a receiving processing system.

Background

Orthogonal Frequency Division Multiplexing (OFDM) converts a Frequency selective multipath fading channel into a flat channel in the Frequency domain, thereby reducing the influence of multipath fading and improving the spectrum utilization rate. However, the OFDM system is very sensitive to synchronization errors and has high requirements for time synchronization. In the aspect of frequency synchronization, a frequency offset introduces inter-carrier Interference (ICI), which degrades the signal-to-noise ratio of each sub-carrier, and thus degrades the transmission performance of the entire communication system. The frame synchronization error introduces Inter Symbol Interference (ISI), that is: the intersymbol interference also has a serious influence on the channel estimation. In the existing OFDM system, the following three types of synchronization methods are mainly used: symbol timing synchronization, carrier synchronization and sampling clock synchronization.

To achieve synchronization of the OFDM signal, it is necessary to find the start position of the OFDM symbol and the carrier offset. The OFDM modulation technique is a multi-carrier technique, and a multi-carrier system is more sensitive to timing offset than a single-carrier system. In a single carrier frequency domain equalization (SC-FDE) system with an OFDM system and a frequency domain equalization, ISI caused by multipath is removed by inserting a Cyclic Prefix (CP). Since the OFDM system and the SC-FDE system employ the CP, when the length of the CP is greater than the multipath delay spread of the channel, there will be a non-interference region, i.e., an ISI-free region, in the CP, the phase rotation of the useful signal can be corrected by using a frequency domain estimation method. Therefore, within the non-interference region, the OFDM symbol is not affected by ISI from the previous OFDM symbol due to a multipath channel. Outside the non-Interference region, timing errors cause Inter Block Interference (IBI) and ICI for both OFDM and SC-FDE systems. At the same time, attenuation and phase rotation of the useful signal are also caused. More seriously, it will seriously affect the performance of the channel estimator, thereby increasing the channel estimation variance.

In the prior art, a Residual Inter Symbol Interference Cancellation (RISIC) algorithm is usually adopted to reconstruct IBI caused by previous and subsequent OFDM symbols, subtract the IBI from a current OFDM symbol received signal in a corresponding integration interval, reconstruct a missing part of the current OFDM symbol, and add the missing part into a signal in the corresponding integration interval, thereby suppressing IBI and ICI.

However, when the prior art employs the RISIC algorithm to suppress IBI and ICI, the synchronization of the OFDM symbols cannot be effectively achieved when the channel delay spread exceeds the CP length, thereby reducing the receiving performance of the receiver, for example: bit error rate, symbol error rate, or block error rate performance of data transmission.

Disclosure of Invention

The embodiment of the invention provides a symbol synchronization method and device and a receiving processing system, which can reduce residual interference energy after IBI elimination and ICI reconstruction compensation under the condition that the time delay expansion of a channel exceeds the length of a CP (channel state indicator), thereby effectively realizing the synchronization of OFDM (orthogonal frequency division multiplexing) symbols and improving the receiving performance of a receiver.

The symbol synchronization method provided by the embodiment of the invention mainly comprises the following steps:

receiving a signal sent by a sending end, acquiring position information and power information of each path in a current Orthogonal Frequency Division Multiplexing (OFDM) symbol in the signal, and acquiring an estimation variance fed back by aiming at all OFDM symbols;

acquiring total residual interference energy of all paths in the current OFDM symbol according to the initial positions of all fast Fourier transform integral intervals in a preset initial position set or a quantized initial position set, the acquired position information and power information of each path and the estimation variance fed back aiming at all OFDM symbols;

acquiring an initial position corresponding to minimum interference energy in total residual interference energy;

and performing symbol synchronization on the signal sent by the sending end by taking the initial position corresponding to the minimum interference energy as a symbol timing value.

The symbol synchronization device provided by the embodiment of the invention mainly comprises:

a first obtaining module, configured to receive a signal sent by a sending end, obtain position information and power information of each path in a current OFDM symbol in the signal, and obtain an estimated variance fed back for all OFDM symbols;

a second obtaining module, configured to obtain total residual interference energy of all paths in the current OFDM symbol according to starting positions of all integration intervals in a preset starting position set or a quantized starting position set, position information and power information of each path obtained by the first obtaining module, and an estimated variance fed back for all OFDM symbols;

a third obtaining module, configured to obtain an initial position corresponding to a minimum interference energy in the total residual interference energy;

and the symbol synchronization module is used for performing symbol synchronization on the signal sent by the sending end by taking the initial position corresponding to the minimum interference energy as a symbol timing value.

A receiving processing system provided in an embodiment of the present invention includes a channel estimation device, an inter-block interference cancellation device, a cyclic prefix reconstruction device, a receiver, and a symbol synchronization device provided in the above embodiments of the present invention, wherein,

the channel estimation device is used for performing channel estimation by using the signal received by the receiving end to obtain time domain channel information of each path, wherein the time domain channel information comprises position information and channel factors of each path;

the inter-block interference elimination device is used for eliminating inter-block interference IBI of the signal after symbol synchronization of the symbol synchronization device according to the time domain channel information of each path and the decision value of the receiver aiming at the previous OFDM symbol and the next OFDM symbol of the current OFDM symbol;

the cyclic prefix reconstruction device is used for performing CP reconstruction and compensation on the signal with IBI eliminated according to the time domain channel information of each path and the decision value aiming at the current OFDM symbol sent by the receiver;

the receiver is configured to transform the time domain signal after CP reconstruction and compensation to a frequency domain, perform receiving processing, generate an estimated variance for all OFDM symbol feedbacks and send the estimated variance to the symbol synchronization apparatus, generate decision values of the front and rear OFDM symbols of the current OFDM symbol and send the decision values to the inter-block interference cancellation apparatus, and generate a decision value of the current OFDM symbol and send the decision value to the cyclic prefix reconstruction apparatus.

Based on the symbol synchronization method, the symbol synchronization device, and the receiving processing system provided by the embodiments of the present invention, the initial position corresponding to the minimum interference energy in the total residual interference energy is obtained, and the initial position corresponding to the minimum interference energy is used as a symbol timing value to perform symbol synchronization on the signal sent by the sending end.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is a timing diagram of a multipath channel received signal;

FIG. 2 is a flow chart of one embodiment of a symbol synchronization method of the present invention;

FIG. 3 is a flow chart of another embodiment of a symbol synchronization method of the present invention;

FIG. 4 is a schematic diagram of a symbol synchronization apparatus according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of another embodiment of a symbol synchronization apparatus according to the present invention;

FIG. 6 is a block diagram of an embodiment of a receiving system;

FIG. 7 is a schematic diagram of another embodiment of a receiving system according to the present invention;

FIG. 8 is a schematic diagram of symbol error rate performance improvement after the embodiment of the symbol synchronization method of the present invention is adopted;

fig. 9 is a schematic diagram of improving the performance of the block error rate after the embodiment of the symbol synchronization method of the present invention is adopted.

Detailed Description

As shown in fig. 1, a timing diagram of a signal received over a multipath channel is shown. Fig. 1 shows a useful signal composition in a multipath channel received signal under multipath delay spread, and shows IBIs caused by a previous OFDM symbol and a subsequent OFDM symbol on a current OFDM symbol, taking 3 path signals as an example. In FIG. 1, the ordinate h [ m ]]Representing a multipath channel with a minimum path position of m_minThe maximum radial position is m_max. In FIG. 1, signal 101, signal 102, and signal 103 represent path 101, path 102, and path 103 pairs, respectivelyThe corresponding signal is obtained by delaying the transmission signal according to the delay of each path. Suppose m_sThe starting position of the Fast Fourier Transform (FFT) integration interval for the nth OFDM symbol is as follows: the symbol timing position, where the nth OFDM symbol is also referred to as the current OFDM symbol. In fig. 1, horizontal dotted lines 104 and 105 represent OFDM symbols before the current OFDM symbol, horizontal dotted lines 106 and 107 represent OFDM symbols after the current OFDM symbol, and horizontal dotted lines 104 and 105 are in [ m ]_s，m_s+K-1]The integral interval part formed in the range is IBI brought by the previous OFDM symbol to the current OFDM symbol, and the horizontal dotted lines 106 and 107 are in [ m ]_s，m_s+K-1]The integration interval part formed in the range is IBI brought to the current OFDM symbol by the next OFDM symbol, and for the current OFDM symbol, the two integration intervals are missing, so that the signal (also called a path signal) corresponding to the path cannot obtain the current OFDM symbol with the complete integration interval length, or for the path signal, the CP is missing, which cannot guarantee the cyclic convolution characteristic between the transmission signal and the channel, and this may cause ICI in the frequency domain. For the signal corresponding to path 102, the signal is in the integration interval [ m ]_s，m_s+K-1]There are no front and back OFDM symbols, and therefore no IBI and ICI. The signals corresponding to path 101 and path 103 are subjected to IBI of the previous OFDM symbol and the next OFDM symbol, respectively, and ICI exists in both frequency domains.

In the embodiment of the present invention, the initial position corresponding to the minimum interference energy in the total residual interference energy is used as a symbol timing value to perform symbol synchronization on the signal sent by the sending end, so that the residual interference energy after IBI cancellation and ICI reconstruction compensation is reduced when the channel delay spread exceeds the CP length, thereby effectively achieving synchronization of OFDM symbols and improving the receiving performance of the receiver, for example: the bit error rate, symbol error rate or block error rate performance of data transmission and the like are improved. The method, the device and the system provided by the embodiment of the invention can be suitable for any communication system, such as: in the OFDM system or SC-FDE system, the multipath delay spread length is larger than the CP length, so that the CP is insufficient, and the receiver adopts the symbol synchronization of RISIC algorithm.

Fig. 2 is a flowchart of an embodiment of a symbol synchronization method according to the present invention, where the flow of the embodiment may be specifically implemented by a symbol synchronization apparatus. As shown in fig. 2, the symbol synchronization method of this embodiment may include:

and 201, receiving a signal sent by a sending end, and acquiring position information and power information of each path in a current OFDM symbol in the signal and an estimated variance fed back by aiming at all OFDM symbols.

Specifically, the estimated variance fed back for all OFDM symbols is also the estimated variance of the decision feedback time domain symbols for all OFDM symbols, wherein the decision feedback time domain symbols are also referred to as decision feedback values.

Specifically, the position information and the power information of each path may be acquired by a multipath search method or a tracking method.

202 according to the starting position m of all FFT integration intervals in the preset starting position set or the quantized starting position set_sAnd acquiring the position information and the power information of each path, and acquiring the total residual interference energy of all paths in the current OFDM symbol according to the estimation variance fed back by all OFDM symbols.

And 203, acquiring a starting position corresponding to the minimum interference energy in the total residual interference energy.

And 204, performing symbol synchronization on the signal sent by the sending end by taking the initial position corresponding to the minimum interference energy as a symbol timing value.

Specifically, the symbol timing value may be extracted from the OFDM symbol in the signal sent by the sending end according to the starting position corresponding to the minimum interference energy, so as to implement symbol synchronization on the signal sent by the sending end.

In the symbol synchronization method of the embodiment of the present invention, the initial position corresponding to the minimum interference energy in the total residual interference energy is used as a symbol timing value to perform symbol synchronization on the signal sent by the sending end, so that the residual interference energy after IBI cancellation and ICI reconstruction compensation is reduced when the channel delay spread exceeds the CP length, thereby effectively achieving synchronization of OFDM symbols and improving the receiving performance of the receiver, for example: the bit error rate, symbol error rate or block error rate performance of data transmission and the like are improved.

Fig. 3 is a flowchart of another embodiment of the symbol synchronization method of the present invention, and the flow of this embodiment may be specifically implemented by a symbol synchronization apparatus. As shown in fig. 3, the symbol synchronization method of this embodiment may include:

301, a signal transmitted by a transmitting end is received.

The received signal may be referred to as a received signal. For an OFDM system, the received signal includes a desired signal and noise. Specifically, the received signal may be expressed as:

r_n[m]＝z_n[m]+n[m] (1)

in the formula (1), r_n[m]N-th OFDM symbol representing the m-th sampling instant in the received signal, z_n[m]Useful signal in the nth OFDM symbol representing the mth sampling instant transmitted by the transmitting end, n [ m [ ]]Representing the noise in the nth OFDM symbol at the mth sampling instant. Wherein z is_n[m]Can be expressed by the following way:

in the formula (2), x_n[m]Represents the mth time domain sample signal corresponding to the nth OFDM symbol,

indicating IBI brought in by the subsequent symbol block, N indicating the symbol block length of the OFDM symbol, h m]For an equivalent discrete channel factor, it can be expressed as:

in the formula (3), m_iTime delay of i path, gamma_iδ represents the impulse function for the channel factor of the ith path.

302, obtaining the position information m of each path in the current OFDM symbol by channel estimation_iAnd channel factor gamma_iAnd according to the channel factor gamma_iObtaining power information gamma of each path_i|². Wherein i represents the ith path and is an integer greater than zero.

303, receive the estimated variance of the receiver feedback for all OFDM symbols.

At σ_n ²As the estimated variance fed back by the receiver for the nth OFDM symbol. In this embodiment of the present invention, the nth OFDM symbol is used as the current OFDM symbol.

And the estimated variance for the OFDM symbol feedback is also referred to as the estimated variance of the decision feedback symbol. Wherein, the receiver can obtain the estimated variance for all OFDM symbol feedbacks through various detection methods, for example: through the decision feedback method, the estimation variance of the OFDM symbol feedback can be obtained at the same time, and the estimation variance can be used for representing the reliability of the decision feedback of the receiver. Specifically, the receiver in the present embodiment may be an OFDM receiver.

An OFDM receiver generally consists of two parts, a detector and a decoder, and therefore, the receiver generally has two corresponding feedback modes: one is "iterative receiver" feedback, i.e., decoding feedback, which may be referred to as outer iteration; one is block decision feedback, i.e., intra-detector iteration.

The following describes how to obtain the estimated variance of the decision feedback symbol by taking decoding feedback as an example. Wherein the estimated variance of the decision feedback symbol is also referred to as the decision feedback value of the OFDM symbol. In the first iteration, except that the current OFDM symbol is the first OFDM symbol, for the current nth OFDM symbol, the decision feedback value of the previous OFDM symbol can be obtained. Estimated variance of previous OFDM symbolσ_n-1 ²Can be estimated by a detector in the OFDM receiver at the same time as the decision of the previous OFDM symbol. At this time, the decision feedback values of the current OFDM symbol and the next OFDM symbol are not yet available, and it can be assumed that

Namely: the estimated variance of the current OFDM symbol and its following OFDM symbol is equal to the power σ of the transmitted time domain symbol_s ². In the subsequent iteration, the decision feedback value of the current OFDM symbol may be the decision feedback value of the previous iteration, or may be the detector decision value updated in the current iteration, as long as the estimated variance σ of the corresponding decision feedback symbol is obtained by the estimation of the OFDM receiver_n-1 ²For both the current OFDM symbol and the OFDM symbols after the current OFDM symbol, a decision feedback value can be obtained from the previous iteration, and when the decision feedback value is obtained from the previous iteration, the corresponding symbol estimation variance σ is obtained by estimation at the same time_n ²And σ_n+1 ²And feeding back the data to the symbol synchronizer of the iteration.

Note that IBI cancellation may not be performed for the first OFDM symbol.

304 according to the starting position m of all FFT integration intervals in the preset starting position set or the quantized starting position set_sAnd respectively acquiring the total residual interference energy of all paths in the current OFDM symbol according to the position information and the power information of each path and the estimation variance fed back by aiming at all OFDM symbols.

For each starting position m of all FFT integration intervals in a preset starting position set or a quantized starting position set_sThe total residual interference energy of all paths in a current OFDM symbol can be obtained respectively.

In the embodiment of the present invention, there are various ways to obtain the total residual interference energy of all paths in the current OFDM symbol, which may be that

The above formula may also be further modified, for example as follows:

in the formula (4), ε (m)_s) For the total residual interference energy, m, of all paths in the current OFDM symbol_sFor the symbol timing position of the nth OFDM symbol, l_i(m_s) Indicating symbol timing position as m_sInterference energy of the i-th path, N_GIs the cyclic prefix CP length.

305, obtaining the minimum interference energy min epsilon (m) in the total residual interference energy_i) And according to i_o＝argminε(m_i) Obtaining the minimum interference energy min epsilon (m)_i) Corresponding start position m_o。

Wherein,

m_{o} = m_{i_{o}},

argminε(m_i) Is expressed such that ε (m)_i) The minimum parameter.

306, starting position m corresponding to the minimum interference energy in the total residual interference energy_oThe received signal is symbol-synchronized as a symbol timing value.

With the symbol synchronization method according to the above embodiment of the present invention, a series of operations such as IBI cancellation, reconstruction and compensation of a CP portion missing in a received signal, and reception processing are performed on the received signal.

If only IBIs caused by the previous OFDM symbol and the next OFDM symbol of the current OFDM symbol are considered, the received signal can be expressed as:

in the formula (5), n [ g ] represents white Gaussian noise.

Is provided with

For frequency domain decision feedback value based on nth OFDM symbolThe time domain signal obtained by fast inverse Fourier transform (IFFT) transform is:

in the formula (6), m is more than or equal to 0 and less than N, wherein N is K + N_GWhere K is the FFT integration interval length, N_GIs the CP length. The symbol synchronization is to determine the starting position of the FFT integration interval in the period of m < N which is more than or equal to 0.

Firstly, the decision feedback values of other OFDM symbols except the current OFDM symbol are utilized

Reconstruct the IBI to which the current OFDM symbol is subjected, equation (1)

And subtracting the received IBI from the received signal of the nth OFDM symbol to obtain:

<math><mrow> <msub> <mover> <mi>r</mi> <mo>^</mo> </mover> <mi>n</mi> </msub> <mo>[</mo> <mi>m</mi> <mo>]</mo> <mo>=</mo> <mi>r</mi> <mo>[</mo> <mi>m</mi> <mo>+</mo> <mi>nN</mi> <mo>]</mo> <mo>-</mo> <mi>h</mi> <mo>[</mo> <mi>m</mi> <mo>]</mo> <mo>*</mo> <munder> <mi>Σ</mi> <mrow> <mi>l</mi> <mo>&NotEqual;</mo> <mi>n</mi> </mrow> </munder> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mi>l</mi> </msub> <mo>[</mo> <mi>m</mi> <mo>+</mo> <mi>nN</mi> <mo>-</mo> <mi>lN</mi> <mo>]</mo> </mrow></math>

<math><mrow> <mo>=</mo> <mi>r</mi> <mo>[</mo> <mi>m</mi> <mo>+</mo> <mi>nN</mi> <mo>]</mo> <mo>-</mo> <munder> <mi>Σ</mi> <mi>i</mi> </munder> <munder> <mi>Σ</mi> <mrow> <mi>l</mi> <mo>&NotEqual;</mo> <mi>n</mi> </mrow> </munder> <msub> <mi>γ</mi> <mi>i</mi> </msub> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mi>l</mi> </msub> <mo>[</mo> <mi>m</mi> <mo>-</mo> <msub> <mi>m</mi> <mi>i</mi> </msub> <mo>+</mo> <mi>nN</mi> <mo>-</mo> <mi>lN</mi> <mo>]</mo> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>7</mn> <mo>)</mo> </mrow> </mrow></math>

in the formula (7), m is in the range of-N₁≤m＜N+N₂In which-N₁And N₂The first path position and the last path position of the equivalent discrete channel are respectively. It should be noted that the decision feedback value

The method is generally obtained by a receiver through a block decision feedback or iterative receiving technology, generally, the IBI suffered by the current OFDM symbol is mainly the IBI caused by the front OFDM symbol and the rear OFDM symbol, and meanwhile, when m is less than 0 or m is more than N, x is_l[m]And

are all 0, so equation (7) can be simplified as:

by substituting equation (5) for equation (8), the IBI-cancelled received signal can be obtained:

in the formula (9), e_l[m]The estimated variance of the mth decision feedback symbol for the ith OFDM symbol of the n OFDM symbols can be represented by

e_{l} [m] = x_{l} [m] - {\hat{x}}_{l} [m]

Thus obtaining the product. Specifically, the IBI to which the current OFDM symbol is subjected may be reconstructed by the inter-block interference cancellation apparatus and IBI cancellation may be performed by equation (7) or equation (9).

Furthermore, the OFDM system ensures the cyclic matrix characteristic of a time domain channel matrix through the CP action, thereby further ensuring that ICI does not exist in a frequency domain. Taking fig. 1 as an example, ICI is caused in the frequency domain because the CP in signals 101 and 103 corresponding to paths 101 and 103 is incomplete. RISIC algorithm utilizes decision feedback value of current OFDM symbol

The decision value

Specifically, the CP portion missing in the signal may be reconstructed by the receiver through a block decision feedback or iterative reception technique, and is added to the received signal after IBI removal as shown in formula (9), so as to further obtain a CP-compensated received signal, where the received signal is a time-domain signal:

in the equation (10), the second term and the third term on the right of the first equal sign are reconstruction terms of the missing CP portion at the left end and the right end of the current OFDM symbol, respectively. The second right term with equal sign is the IBI cancellation for the previous OFDM symbol from the current OFDM symbol and the reconstruction compensation for the left missing CP portion, and the third term represents the IBI cancellation for the next OFDM symbol from the current OFDM symbol and the reconstruction compensation for the right missing CP portion. Wherein m is_s≤m＜m_s+ K, corresponding to the symbol within the FFT integration window. Specifically, the cyclic prefix reconstruction device may perform CP reconstruction and compensation by equation (10), and transmit the time domain signal after CP reconstruction and compensation to the receiver.

After the CP reconstruction and compensation are performed on the received signal, the receiver may perform FFT on the CP-compensated signal, convert the time domain signal into a frequency domain signal, and perform receiving processing on the frequency domain signal, for example: demodulation, decoding, etc., generating estimated variances fed back for all OFDM symbols for symbol synchronization, generating decision values of previous and next OFDM symbols of the current OFDM symbol for IBI reconstruction and cancellation, and generating decision values of the current OFDM symbol for CP reconstruction and compensation.

First, the influence of the estimation variance fed back for all OFDM symbols due to feedback on the performance of IBI cancellation and CP reconstruction and compensation in equation (10) is analyzed. Introduction of

e_{l} [m] = x_{l} [m] - {\hat{x}}_{l} [m]

Estimator of mth decision feedback time domain symbol representing the ith OFDM symbolBy difference, then equation (10) can be expressed as:

in equation (11), the first row to the right of the equal sign represents the target signal portion, i.e.: in the nth symbol, the target signal part does not have IBI, and meanwhile, the missing CP part is reconstructed and compensated, so that the cyclic convolution characteristic is met. The other parts, namely: the second and third rows show the residual IBI and non-ideal CP reconstruction due to errors or inaccuracies in the decision feedback values. On the premise of ideal channel estimation, if the fed-back decision value is completely accurate, the parts shown in the second and third rows can be completely eliminated, that is, IBI and ICI can be ideally eliminated. In practice, however, the estimated variance of the feedback symbols is unavoidable. The embodiment of the invention can minimize residual IBI and ICI energy and eliminate the IBI and ICI to the maximum under the condition of a certain estimation variance of the feedback symbol.

According to the equation (11), the residual interference energy in each path signal can be obtained, and the time delay is m_iThe residual interference energy of the path signal of each sampling point is as follows:

from equation (12), the residual interference energy of each path is the symbol timing position m_sAs a function of (c). Wherein σ_n ²Is the estimated variance, also referred to as error, of the nth OFDM symbol, and so on.

Therefore, the total residual interference energy of all paths in the current OFDM symbol can be obtained as shown in the formula (4). Due to the estimated variance σ_n-1 ²、σ_n ²And σ_n+1 ²Determined by the detection performance of the receiver, the channel factor y_iObtaining power information gamma of each path_i|²Determined by the performance of the channel estimation device, the total residual IBI and ICI energy is therefore determined by the timing position m of the current OFDM symbol_sAnd (4) uniquely determining. The total residual interference energy epsilon (m)_s) Minimum timing position m_sAs determined symbol timing

m_{o} = m_{i_{o}},

I.e. the residual interference energy epsilon (m) after interference suppression can be minimized_s) Namely: residual interference energy epsilon (m) after interference suppression_s) To a minimum. As can be seen from equation (4), the residual interference energy ε (m) is minimized_s) M of time_sNamely:

m_{o} = m_{i_{o}},

is included in each path delay position set m_iIn (c) }.

Because iteration needs to ensure convergence, in general, in an iterative processing method of RISIC, the estimation variances of the current OFDM symbol block and the next OFDM symbol block in the iteration are the same, but different from the symbol estimation variance of the previous OFDM symbol block, that is:

definition of

Equation (4) can be simplified as:

at this time, the total residual interference energy of all paths in the current OFDM symbol can be obtained by equation (13). Then through i_o＝argminε(m_i) Obtaining the minimum interference energy in the total residual interference energy, and obtaining the starting position m corresponding to the minimum interference energy_oThe received signal is symbol-synchronized as a symbol timing value.

Fig. 4 is a schematic structural diagram of an embodiment of a symbol synchronization apparatus according to the present invention, which can be used to implement the symbol synchronization method according to the above embodiments of the present invention. As shown in fig. 4, the symbol synchronization apparatus of this embodiment includes a first obtaining module 401, a second obtaining module 402, a third obtaining module 403, and a symbol synchronization module 404. The first obtaining module 401 is configured to receive a signal sent by a sending end, where the signal is also referred to as a received signal, obtain position information and power information of each path in a current OFDM symbol in the received signal, and obtain an estimated variance fed back for all OFDM symbols. The second obtaining module 402 is configured to obtain start positions m of all FFT integration intervals in a preset start position set or a quantized start position set_sThe position information and power information of each path acquired by the first acquiring module 401, and the estimated variance fed back by all OFDM symbols, acquire the total residual interference energy of all paths in the current OFDM symbol. The third obtaining module 403 is configured to obtain the total residual interference obtained by the second obtaining module 402Starting position m corresponding to minimum interference energy in energy_s. The symbol synchronization module 404 is configured to use the starting position m corresponding to the minimum interference energy obtained by the third obtaining module 403_sThe received signal is symbol-synchronized as a symbol timing value.

Specifically, reference may be made to the relevant description in the method embodiment for processing each module in the symbol synchronization apparatus in the embodiment of the present invention.

The symbol synchronization device of the embodiment of the present invention may perform symbol synchronization on a signal sent by a sending end by using an initial position corresponding to minimum interference energy in total residual interference energy as a symbol timing value, so as to reduce residual interference energy after IBI cancellation and ICI reconstruction compensation when channel delay spread exceeds a CP length, thereby effectively implementing synchronization of OFDM symbols and improving the receiving performance of a receiver, for example: the bit error rate, symbol error rate or block error rate performance of data transmission and the like are improved.

Fig. 5 is a schematic structural diagram of another embodiment of the symbol synchronization apparatus according to the present invention, in which the first obtaining module 401 includes a receiving unit 501 and a calculating unit 502. The receiving unit 501 is configured to receive a signal sent by a sending end, that is: received signal, and position information m of each path in current OFDM symbol in received signal_iAnd channel factor gamma_iAnd the estimated variance σ of the receiver for all OFDM symbol feedback_n ². The calculating unit 502 is used for calculating the channel factor γ according to the channel factor γ received by the receiving unit 501_iObtaining power information gamma of each path_i|². Wherein i represents the ith path and is an integer greater than zero, sigma_n ²Is the estimated variance fed back for the nth OFDM symbol. According to a specific embodiment, the position information m of each path in the current OFDM symbol in the received signal_iAnd channel factor gamma_iSpecifically, the channel estimation may be performed by a channel estimation apparatus.

The symbol synchronization device according to the embodiment of the present invention shown in fig. 4 or 5 is one embodiment of the present inventionIn the middle, the second obtaining module 402 specifically obtains the position information m according to each diameter_iAnd power information | γ_i|²And the estimated variance σ fed back for all OFDM symbols_n ²Based on

Or the above equation (4) obtains the total residual interference energy of all paths in the current OFDM symbol.

As another embodiment of the present invention, in the symbol synchronization apparatus in the above-mentioned embodiment shown in fig. 4 or fig. 5, the third obtaining module 403 specifically obtains the minimum interference energy in the total residual interference energy, and obtains the minimum interference energy according to i_o＝argminε(m_i) Obtaining the radial position m corresponding to the minimum interference energy_oWherein

m_{o} = m_{i_{o}},

argminε(m_i) Is expressed such that ε (m)_i) The minimum parameter.

As another embodiment of the present invention, in the symbol synchronization apparatus of the above-described embodiment shown in fig. 4 or 5,

then, the second obtaining module 402 obtains the total residual interference energy of all paths in the current OFDM symbol based on equation (13) shown above.

Fig. 6 is a schematic structural diagram of an embodiment of a receiving processing system according to the present invention. As shown in fig. 6, the receiving processing system of this embodiment includes a channel estimation device 601, a symbol synchronization device 602, an inter-block interference cancellation device 603, a cyclic prefix reconstruction device 604, and a receiver 605. The channel estimation device 601 is configured to perform channel estimation by using a signal received by a receiving end to obtain time domain channel information of each path, where the time domain channel information includes location information and channel factors of each path. The symbol synchronization apparatus 602 is configured to receive a signal sent by a sending end, obtain position information and power information of each path in a current OFDM symbol according to time domain channel information of each path, receive an estimated variance fed back by the receiver 605 for all OFDM symbols, and perform a process on start positions m of all FFT integration intervals in a preset start position set or a quantized start position set according to the position information and power information of each path and the estimated variance fed back for all OFDM symbols_sAnd acquiring total residual interference energy of all paths in the current OFDM symbol, acquiring an initial position corresponding to minimum interference energy in the total residual interference energy, and performing symbol synchronization on a signal sent by a sending end by taking the initial position corresponding to the minimum interference energy as a symbol timing value. The inter-block interference cancellation device 603 is configured to perform IBI cancellation on the received signal after symbol synchronization by the symbol synchronization device 602 according to the time domain channel information of each path sent by the channel estimation device 601 and the decision values of the receiver 605 for the previous OFDM symbol and the next OFDM symbol of the current OFDM symbol. The cyclic prefix reconstruction means 604 is used for reconstructing a cyclic prefix according to the time domain channel information of each path sent by the channel estimation means 601 and the decision value for the current OFDM symbol sent by the receiver 605,the signal after IBI cancellation by the inter-block interference cancellation device 603 is CP reconstructed and compensated. Among them, the received signals processed by the channel estimation device 601, the symbol synchronization device 602, the inter-block interference cancellation device 603, and the cyclic prefix reconstruction device 604 are all time-domain signals, and therefore, the signal after CP reconstruction and compensation by the cyclic prefix reconstruction device 604 is also a time-domain signal. The receiver 605 is configured to perform FFT on the time domain signal sent by the cyclic prefix reconstruction device 604, transform the time domain signal after CP reconstruction and compensation into a frequency domain signal, and perform receiving processing on the frequency domain signal, for example: demodulation, decoding, etc., generates estimated variances fed back for all OFDM symbols and sends them to the symbol synchronization means 602 for symbol synchronization, generates decision values of the previous and next OFDM symbols of the current OFDM symbol and sends them to the inter-block interference cancellation means 603 for reconstruction and cancellation of IBI, and generates decision values of the current OFDM symbol and sends them to the cyclic prefix reconstruction means 604 for reconstruction and compensation of CP. Specifically, the symbol synchronization apparatus 602 may be implemented by the symbol synchronization apparatus of the embodiment shown in fig. 4 or fig. 5.

In the receiving processing system of the embodiment of the present invention, the symbol synchronization apparatus may perform symbol synchronization on the signal sent by the sending end by using an initial position corresponding to the minimum interference energy in the total residual interference energy as a symbol timing value, so that when the channel delay spread exceeds the CP length, the residual interference energy after IBI cancellation and ICI reconstruction compensation is reduced, thereby effectively achieving synchronization of OFDM symbols and improving the receiving performance of the receiver, for example: the bit error rate, symbol error rate or block error rate performance of data transmission and the like are improved.

Fig. 7 is a schematic structural diagram of another embodiment of the receiving processing system of the present invention, in which the symbol synchronization apparatus 602 is implemented by the symbol synchronization apparatus of the embodiment shown in fig. 4. The first obtaining module 401 is configured to receive a signal sent by a sending end, and obtain, according to time domain channel information of each path sent by the channel estimation apparatus 601, position information and power information of each path in a current OFDM symbol, and an estimated variance fed back by the receiving receiver 605 for all OFDM symbols. Second getThe fetching module 402 is configured to obtain start positions m of all FFT integration intervals in the preset start position set or the quantized start position set_sThe position information and power information of each path obtained by the first obtaining module 401, and the estimated variance fed back by the receiver 605 for all OFDM symbols, obtain the total residual interference energy of all paths in the current OFDM symbol. The third obtaining module 403 is configured to obtain a starting position corresponding to a minimum interference energy in the total residual interference energy obtained by the second obtaining module 402. The symbol synchronization module 404 is configured to perform symbol synchronization on a signal sent by a sending end by using the path position corresponding to the minimum interference energy acquired by the third acquisition module 403 as a symbol timing value.

As a further embodiment of the present invention, the channel estimation means 601 may be provided integrally with the symbol synchronization means 602.

Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.

The embodiment of the invention takes the initial position corresponding to the minimum interference energy in the total residual interference energy as the symbol timing value, carries out symbol synchronization on the signal sent by the sending end, and can reduce the residual interference energy after IBI elimination and ICI reconstruction compensation under the condition that the channel delay spread exceeds the CP length, thereby effectively realizing the synchronization of OFDM symbols and improving the receiving performance of a receiver.

Under the same conditions, the embodiments of the present invention respectively test the IBI and ICI suppression performance in the OFDM system based on the Worldwide Interoperability for Microwave Access (WIMAX) standard when the prior art and the embodiments of the present invention are adopted, so as to more clearly describe the beneficial technical effects of the embodiments of the present invention. The subcarrier interval of the OFDM system is 10.94kHz, the total bandwidth is 10MHz, the subcarrier number of each OFDM symbol block is 914, the CP length is 1/8 symbol period length, the adopted wireless channel is an equal-strength two-path channel, the power of the two-path channel is the same, the time delay expansion length is 17.8 microseconds, the modulation mode of the transmitted OFDM symbol is 4 Quadrature Amplitude Modulation (QAM), and the channel coding is (50, 33) Solomon codes (Reed-Solomon codes, RS for short). The test results are shown in fig. 8 and 9. Fig. 8 is a schematic diagram of symbol error rate performance improvement after the embodiment of the symbol synchronization method of the present invention is adopted. Fig. 9 is a schematic diagram of improving the performance of the block error rate after the embodiment of the symbol synchronization method of the present invention is adopted. In fig. 8 and 9, the "once-iterated optimization method" represents the once-iterated performance of RISIC tested by the symbol synchronization method according to the embodiment of the present invention; the optimization method of iterative quadratic is used for expressing the RISIC iterative quadratic performance obtained by adopting the symbol synchronization method of the embodiment of the invention; "original RISIC method of iteration once" means that adopts RISIC iteration one performance of the symbol synchronization method of the prior art; the "RISIC method for ideal decision feedback" represents the RISIC performance assuming that the decision feedback is completely correct.

Normally, 1% is selected as the operating point of the symbol error rate. As can be seen from fig. 8, under the same signal-to-noise ratio condition, the symbol error rates of the "once-iterated optimization method" and the "twice-iterated optimization method" are both lower than the "once-iterated original RISIC method", and therefore, the RISIC performance is better, and as the signal-to-noise ratio increases, the advantage of the RISIC performance brought by the "once-iterated optimization method" and the "twice-iterated optimization method" is more obvious than that of the "once-iterated original RISIC method". On 1% of working points, the RISIC performance of the optimization method of iteration once and the optimization method of iteration twice approaches the upper performance bound of the RISIC method of ideal decision feedback.

Usually, 10% is selected as the operating point of the block error rate. As can be seen from fig. 9, under the same signal-to-noise ratio condition, the block error rates of the "once-iterated optimization method" and the "twice-iterated optimization method" are both lower than that of the "once-iterated original RISIC method", and therefore, the RISIC performance is better, and as the signal-to-noise ratio increases, the advantage of the RISIC performance brought by the "once-iterated optimization method" and the "twice-iterated optimization method" is more obvious than that of the "once-iterated original RISIC method". On 10% of working points, the RISIC performance of the optimization method of iteration one and the optimization method of iteration two approaches the upper performance bound of the RISIC method of ideal decision feedback.

As can be seen from fig. 8 and 9, after the symbol synchronization method according to the embodiment of the present invention is adopted, in a scenario where the channel delay spread is larger than the CP, the RISIC performance of the original typical IBI/ICI algorithm is greatly improved, so that the performance and robustness of the corresponding receiver are improved.

Finally, it should be noted that: the above examples are only for illustrating the technical solutions of the present invention, and are not to be construed as limiting the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will understand that: modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention.

Claims

1. A method for symbol synchronization, comprising:

2. The method of claim 1, wherein obtaining the location information and power information for each path in the current OFDM symbol in the signal comprises:

obtaining position information m of each path in current OFDM symbol through channel estimation_iAnd channel factor gamma_iAnd according to the channel factor gamma_iObtaining power information gamma of each path_i|²Wherein i represents the ith path and is an integer greater than zero.

3. The method of claim 1, wherein obtaining the estimated variance for all OFDM symbol feedback comprises:

the estimated variance of the receiver feedback for all OFDM symbols is received.

4. The method of claim 2, wherein the total residual interference energy of all paths in the current OFDM symbol is obtained by:

wherein, epsilon (m)_s) Is the total residual interference energy, m, of all paths in the current OFDM symbol_sFor the symbol timing position of the nth OFDM symbol, l_i(m_s) Indicating symbol timing position as m_sInterference energy of the i-th path, | γ_i|²Is power information of each path.

5. The method of claim 2, wherein the total residual interference energy of all paths in the current OFDM symbol is obtained by:

wherein, epsilon (m)_s) For the total residual interference energy of all paths in the current OFDM symbol,for the estimated variance, N, fed back for the nth OFDM symbol_GIs the cyclic prefix CP length, m_sFor the symbol timing position of the nth OFDM symbol, | γ_i|²Is power information of each path.

6. The method according to claim 4 or 5, wherein the obtaining the starting position corresponding to the minimum interference energy in the total residual interference energy comprises:

obtaining the minimum interference energy in the total residual interference energy and according to i_o＝argminε(m_i) Obtaining the starting position m corresponding to the minimum interference energy_oWherein

argminε(m_i) Is expressed such that ε (m)_i) The minimum parameter.

7. The method of claim 5, wherein the step of removing the metal oxide is performed while the metal oxide is removed from the metal oxide

Then, obtaining the total residual interference energy of all paths in the current OFDM symbol by the following method:

wherein,

8. a symbol synchronization apparatus, comprising:

9. The apparatus of claim 8, wherein the first obtaining module comprises:

a receiving unit, configured to receive a signal sent by a sending end, and position information m of each path in a current OFDM symbol in the signal obtained through channel estimation_iAnd channel factor gamma_iAnd the estimated variance fed back for all OFDM symbols;

a calculation unit for calculating a channel factor γ from the channel factor γ_iObtaining power information gamma of each path_i|²；

Wherein i represents the ith path and is an integer greater than zero, sigma_n ²For the nth OFDM symbolThe estimated variance of the feed.

10. The apparatus according to claim 9, wherein the second acquiring means acquires the position information m of each diameter from the first acquiring means_iAnd power information | γ_i|²And the estimated variance σ fed back for all OFDM symbols_n ²Acquiring the total residual interference energy of all paths in the current OFDM symbol by the following method:

orWherein, epsilon (m)_s) Is the total residual interference energy, m, of all paths in the current OFDM symbol_sFor the symbol timing position of the nth OFDM symbol, l_i(m_s) Indicating symbol timing position as m_sInterference energy of the i-th path, N_GIs the cyclic prefix CP length.

11. The apparatus of claim 10, wherein the third obtaining module obtains a minimum interference energy of the total residual interference energy according to i_o＝argminε(m_i) Obtaining the starting position m corresponding to the minimum interference energy_oWherein

argminε(m_i) Is expressed such that ε (m)_i) The minimum parameter.

12. A device according to claim 10 or 11, characterized in that it is adapted to be used when

Then, the second obtaining module obtains the total residual of all paths in the current OFDM symbol in the following mannerAnd (4) interference energy conservation:

wherein,

13. a receive processing system, comprising: channel estimation means, inter-block interference cancellation means, cyclic prefix reconstruction means, receiver and symbol synchronization means according to any one of claims 8 to 12,