CN105187337A - OFDM decision-aided channel estimation algorithm based on repetition coding - Google Patents

Abstract

The invention relates to an OFDM decision-aided channel estimation algorithm based on repetition coding, comprising the following concrete steps of: (1) setting channel estimation H<k><n>=H<k><0>, wherein H<k><0> is initial estimation of channel; (2) according to the current channel estimation H<k><n>, calculating a symbol value X-hat<k><n> after frequency-domain equalization, and a bit soft decision value {S<k, m><n>} corresponding to the symbol; (3) performing weighted accumulation on the bit soft decision value according to a repetition coding rule; (4) calculating an erasure correction decision value {d<l><n>} according to the current bit soft decision value {LLR<l><n>}; (5) partly coding the {d<l><n>} into a to-be-mapped erasure correction bit stream {d<k, m><n>} corresponding to the nth OFDM symbol through repetition coding; (6) mapping the erasure correction bit stream {d<k, m><n>} into a transmit frequency domain symbol estimation value X-tilde<k><n>; (7) calculating a new channel estimation value; (8) updating the channel estimation value. According to the invention, the number of sample points of estimation is increased, and loss of data bandwidth caused by pilot insertion is avoided.

Description

OFDM decision-aided channel estimation algorithm based on repeated coding

Technical Field

The invention relates to an OFDM (orthogonal frequency division multiplexing) decision auxiliary channel estimation algorithm based on repeated coding, belonging to the field of low-voltage power line carrier communication.

Background

The power line carrier communication technology is a communication mode for data transmission by using a power line as a medium, and has natural advantages. With the construction of national smart power grids, power lines are favored as an economical and convenient communication medium, however, the power grid environment in China is complex, various interferences exist on power line communication channels due to interference signals generated by a plurality of electric appliances connected into the power grid, and the connected electric appliances cause changes of loads, impedances and the like, so that frequency selective fading is generated on the power line communication channels, great influence is brought to the power line communication, and particularly, the high-speed transmission of a broadband power line communication system is extremely unfavorable.

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation method used in high-speed applications, and has the advantages of converting a frequency selective channel into a flat fading channel, and using a cyclic prefix to overcome the influence of Inter-symbol interference (ISI), however, in a power line channel environment, multipath delay is unstable, the influence of multipath cannot be completely eliminated by using the cyclic prefix, frequency selective fading still exists in the system, and deep fading on some frequency bands in the OFDM system can be caused by interference introduced by some electrical appliances in the power grid, which requires an effective means to estimate channel quality and provide effective information for decoding and demodulation of the system. Meanwhile, by using the characteristics of the OFDM system, different transmission powers and bearer bit numbers can be allocated for channel gains and channel qualities of different subcarriers, and system transmission performance is optimized, which requires an accurate and real-time channel estimation means and method, especially in a power line communication environment.

At present, a plurality of broadband power line carrier communication protocols comprise ITUG.hn, HomePlugAV and the like, each physical layer data frame is generally composed of a plurality of OFDM symbols such as a leading OFDM symbol, a frame header OFDM symbol and a user data OFDM symbol, and the like. The repetition coding is a simple method for improving the communication reliability, compared with the common forward error correction coding, the coding gain is lower, but the repetition times can be flexibly configured to meet the requirement of reliable communication under different channel conditions, and meanwhile, the repetition coding also has the advantage of low decoding complexity. In practical systems, repetition coding often constitutes a serial concatenated code with forward error correction coding to achieve a balance between coding gain and implementation complexity. Repetition coding provides additional time diversity and, in addition to being used for channel coding, may also be used for channel estimation and tracking. In order to reduce the effect of frequency selective fading on repetition coding, different copies of the same transmitted bit are generally allocated to different subcarriers as much as possible. The soft decision of the bit replica received first can be weighted-averaged with the currently received bit soft decision, and then the symbol decision of the corresponding subcarrier is reconstructed for the decision-assisted estimation of the channel. Compared with the general symbol decision-assisted channel estimation, due to the existence of multiple bit copies, the accuracy of the symbol decision can be gradually improved, thereby improving the accuracy of the channel estimation.

Disclosure of Invention

The invention provides a method for carrying out weighted average by using diversity characteristics of repeated coding of a frame control head and subsequent effective carrier data and by using a soft decision result of a bit copy received firstly and a bit soft decision result received currently, and then reconstructing symbol decision of a corresponding subcarrier for auxiliary estimation of channel decision. Not only increases the number of estimated sample points, but also does not bring the loss of data bandwidth caused by inserting pilot frequency.

In order to achieve the above object, the present invention has the following technical means.

An OFDM decision-aided channel estimation algorithm based on repeated coding has a simplified system frequency domain model of,

$Y_k^m=H_{k,ideal}^n*X_k^n+W_k^n;$

wherein,in order to transmit the symbols in the frequency domain,in order to be a function of the transfer function of the channel,the method comprises the steps that frequency domain equivalent noise interference is achieved, n is an OFDM symbol serial number, and k is a subcarrier serial number; the algorithm comprises the following specific steps:

(1) order channel estimationWhereinInitial estimation is carried out on the channel; initializing coded bit soft-decision values $\left\{{\mathrm{LLR}}_l^0\right\}=0;$

(2) Based on the current channel estimateComputing frequency domain equalized symbol valuesBit soft decision value corresponding to the symbolWherein n is the OFDM symbol sequence number, k is the subcarrier sequence number, and M is the {0,1,2, …, M_kIs the bit number corresponding to the sub-carrier symbol, M_kIs the number of bits carried on subcarrier k;

(3) according to repetition coding rules, the soft decision values of the coded bits are accumulated in a weighted manner:

${\mathrm{LLR}}_{f(k,m,n)}^n=(1-w)*{\mathrm{LLR}}_{f(k,m,n)}^{n-1}+w*s_{k,m}^n;$

wherein w is a weighting coefficient, w is an element of (0, 1)]F (k, m, n) isRatio in corresponding forward error correction codeword

A special serial number; (4) according to the current bit soft decision valueCalculating erasure decision values for coded bits

<math> <mrow> <msubsup> <mi>d</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>=</mo> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mo>-</mo> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>&le;</mo> <mo>-</mo> <mi>t</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>0</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mrow> <mo>|</mo> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> </mrow> <mo>|</mo> </mrow> <mo>&le;</mo> <mi>t</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>&GreaterEqual;</mo> <mi>t</mi> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow> </math>

Wherein t is a positive number, and whether the current bit is a threshold value of an erasure bit is determined;

(5) handlePart of repeated coding is carried out to the erasure bit stream to be mapped corresponding to the nth OFDM symbol

(6) Puncturing bit streamThe symbol estimation value of the transmission frequency domain mapped toIf the erasure bit corresponding to the transmitted frequency domain symbol contains a 0 value, the estimated value of the transmitted frequency domain symbol is replaced by the Euclidean decision value of the equilibrium symbol;

(7) calculating new channel estimation values:

${\tilde{H}}_k^n=Y_k^n/{\tilde{X}}_k^n;$

(8) updating the channel estimation value:

<math> <mrow> <msubsup> <mi>H</mi> <mi>k</mi> <mrow> <mi>n</mi> <mo>+</mo> <mn>1</mn> </mrow> </msubsup> <mo>=</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> <mo>*</mo> <msubsup> <mi>H</mi> <mi>k</mi> <mi>n</mi> </msubsup> <mo>+</mo> <mi>&mu;</mi> <mo>*</mo> <msubsup> <mover> <mi>H</mi> <mo>~</mo> </mover> <mi>k</mi> <mi>n</mi> </msubsup> <mo>;</mo> </mrow> </math>

wherein mu is a smoothing coefficient, and mu belongs to (0, 1);

(9) if N < N, then N ═ N +1, go to 2) begin processing the next OFDM symbol; otherwise, ending the equalization algorithm and entering the forward error correction decoding stage.

The invention has the beneficial effects that: the algorithm of the invention utilizes the diversity characteristic of repeated coding of the frame control head and the subsequent effective carrier data, utilizes the soft decision result of the bit copy received firstly and the bit soft decision result received currently to carry out weighted average, and then reconstructs the symbol decision of the corresponding subcarrier for the auxiliary estimation of the channel decision, thereby not only increasing the number of estimated sample points, but also not bringing the loss of data bandwidth caused by inserting pilot frequency. The application of the algorithm in a power line communication system. The repeated coding and mapping can be designed separately at the receiving end, and the coding and mapping module of the transmitting end can also be multiplexed.

Drawings

Fig. 1 is a schematic block diagram of a system used in an embodiment of the present invention.

Detailed Description

The following description of specific embodiments of the present invention is provided in order to better understand the present invention with reference to the accompanying drawings.

Examples

Fig. 1 shows a schematic diagram of the system, in which the OFDM decision-aided channel estimation algorithm based on repetition coding, whose simplified system frequency domain model is,

$Y_k^m=H_{k,ideal}^n*X_k^n+W_k^n;$

wherein,in order to transmit the symbols in the frequency domain,in order to be a function of the transfer function of the channel,the method comprises the steps that frequency domain equivalent noise interference is achieved, n is an OFDM symbol serial number, and k is a subcarrier serial number; the algorithm comprises the following specific steps:

(1) order channel estimationWhereinInitial estimation is carried out on the channel; initializing coded bit soft-decision values $\left\{{\mathrm{LLR}}_l^0\right\}=0;$

(2) Based on the current channel estimateComputing frequency domain equalized symbol valuesBit soft decision value corresponding to the symbolWherein n is the OFDM symbol sequence number, k is the subcarrier sequence number, and M is the {0,1,2, …, M_kIs the bit number corresponding to the sub-carrier symbol, M_kIs the number of bits carried on subcarrier k;

(3) according to repetition coding rules, the soft decision values of the coded bits are accumulated in a weighted manner:

${\mathrm{LLR}}_{f(k,m,n)}^n=(1-w)*{\mathrm{LLR}}_{f(k,m,n)}^{n-1}+w*s_{k,m}^n;$

wherein w is a weighting coefficient, w is an element of (0, 1)]F (k, m, n) isRatio in corresponding forward error correction codeword

A special serial number; (4) according to the current bit soft decision valueCalculating erasure decision values for coded bits

<math> <mrow> <msubsup> <mi>d</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>=</mo> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mo>-</mo> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>&le;</mo> <mo>-</mo> <mi>t</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>0</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mrow> <mo>|</mo> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> </mrow> <mo>|</mo> </mrow> <mo>&le;</mo> <mi>t</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>&GreaterEqual;</mo> <mi>t</mi> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow> </math>

Wherein t is a positive number, and whether the current bit is a threshold value of an erasure bit is determined;

(5) handlePart of repeated coding is carried out to the erasure bit stream to be mapped corresponding to the nth OFDM symbol

(6) Puncturing bit streamThe symbol estimation value of the transmission frequency domain mapped toIf the erasure bit corresponding to the transmitted frequency domain symbol contains a 0 value, the estimated value of the transmitted frequency domain symbol is replaced by the Euclidean decision value of the equilibrium symbol;

(7) calculating new channel estimation values:

${\tilde{H}}_k^n=Y_k^n/{\tilde{X}}_k^n;$

(8) updating the channel estimation value:

<math> <mrow> <msubsup> <mi>H</mi> <mi>k</mi> <mrow> <mi>n</mi> <mo>+</mo> <mn>1</mn> </mrow> </msubsup> <mo>=</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> <mo>*</mo> <msubsup> <mi>H</mi> <mi>k</mi> <mi>n</mi> </msubsup> <mo>+</mo> <mi>&mu;</mi> <mo>*</mo> <msubsup> <mover> <mi>H</mi> <mo>~</mo> </mover> <mi>k</mi> <mi>n</mi> </msubsup> <mo>;</mo> </mrow> </math>

wherein mu is a smoothing coefficient, and mu belongs to (0, 1);

(9) if N < N, then N ═ N +1, go to 2) begin processing the next OFDM symbol; otherwise, ending the equalization algorithm and entering the forward error correction decoding stage.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

Claims (1)

1. An OFDM decision-aided channel estimation algorithm based on repetition coding, characterized in that: the simplified frequency domain model of the system used is,

$Y_k^m=H_{k,ideal}^n*X_k^n+W_k^n;$

wherein,in order to transmit the symbols in the frequency domain,in order to be a function of the transfer function of the channel,the method comprises the steps that frequency domain equivalent noise interference is achieved, n is an OFDM symbol serial number, and k is a subcarrier serial number; the algorithm comprises the following specific steps:

(1) order channel estimationWhereinInitial estimation is carried out on the channel; initializing coded bit soft-decision values $\left\{{\mathrm{LLR}}_l^0\right\}$ $=0;$

(2) Based on the current channel estimateComputing frequency domain equalized symbol valuesBit soft decision value corresponding to the symbolWherein n is the OFDM symbol sequence number, k is the subcarrier sequence number, and M is the {0,1,2, …, M_kIs the bit number corresponding to the sub-carrier symbol, M_kIs the number of bits carried on subcarrier k;

(3) according to repetition coding rules, the soft decision values of the coded bits are accumulated in a weighted manner:

${\mathrm{LLR}}_{f(k,m,n)}^n=(1-w)*{\mathrm{LLR}}_{f(k,m,n)}^{n-1}+w*s_{k,m}^n;$

wherein w is a weighting coefficient, w is an element of (0, 1)]F (k, m, n) isBit sequence numbers in corresponding forward error correction code words;

(4) according to the current bit soft decision valueCalculating erasure decision values for coded bits

<math> <mrow> <msubsup> <mi>d</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>=</mo> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mo>-</mo> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>&le;</mo> <mo>-</mo> <mi>t</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>0</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mrow> <mo>|</mo> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> </mrow> <mo>|</mo> </mrow> <mo>&le;</mo> <mi>t</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <msubsup> <mi>LLR</mi> <mi>l</mi> <mi>n</mi> </msubsup> <mo>&GreaterEqual;</mo> <mi>t</mi> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow> </math>

Wherein t is a positive number, and whether the current bit is a threshold value of an erasure bit is determined;

(5) handlePart of repeated coding is carried out to the erasure bit stream to be mapped corresponding to the nth OFDM symbol

(6) Puncturing bit streamThe symbol estimation value of the transmission frequency domain mapped toIf the erasure bit corresponding to the transmitted frequency domain symbol contains a 0 value, the estimated value of the transmitted frequency domain symbol is replaced by the Euclidean decision value of the equilibrium symbol;

(7) calculating new channel estimation values:

${\tilde{H}}_k^n=Y_k^n/{\tilde{X}}_k^n;$

(8) updating the channel estimation value:

<math> <mrow> <msubsup> <mi>H</mi> <mi>k</mi> <mrow> <mi>n</mi> <mo>+</mo> <mn>1</mn> </mrow> </msubsup> <mo>=</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> <mo>*</mo> <msubsup> <mi>H</mi> <mi>k</mi> <mi>n</mi> </msubsup> <mo>+</mo> <mi>&mu;</mi> <mo>*</mo> <msubsup> <mover> <mi>H</mi> <mo>~</mo> </mover> <mi>k</mi> <mi>n</mi> </msubsup> <mo>;</mo> </mrow> </math>

wherein mu is a smoothing coefficient, and mu belongs to (0, 1);

(9) if N < N, then N ═ N +1, go to 2) begin processing the next OFDM symbol; otherwise, ending the equalization algorithm and entering the forward error correction decoding stage.