WO2010139248A1

WO2010139248A1 - Mehtod and apparatus for soft demodulation for quadrature amplitude modulation in mobile television service

Info

Publication number: WO2010139248A1
Application number: PCT/CN2010/073224
Authority: WO
Inventors: 曹南山; 李强; 邱宁; 陈力; 张涛; 游月意; 姚扬中
Original assignee: 中兴通讯股份有限公司
Priority date: 2009-05-31
Filing date: 2010-05-25
Publication date: 2010-12-09
Also published as: CN101902429B; CN101902429A

Abstract

A method and an apparatus for soft demodulation for Quadrature Amplitude Modulation (QAM) in mobile television service are provided. In the method, according to the channel estimation value of each subcarrier of Orthogonal Frequency Division Modulation (OFDM) symbols to be demodulated at present, amplitude decision threshold for each subcarrier of the OFDM symbols to be demodulated is determined, and soft information values of low bits in the constellation diagram corresponding to each subcarrier are calculated by using the amplitude decision threshold for each subcarrier. By using the method of the present invention, the accuracy of signal demodulation can be increased, and with time domain filtering of channel estimation values of OFDM symbols and frequency domain filtering of each subcarrier signal of OFDM symbols, noise is further suppressed, signal noise ratio of soft demodulation signal and decoding capability of the receiving end are improved.

Description

Soft demodulation method and device for orthogonal amplitude modulation in mobile TV service

Technical field

The invention relates to the field of wireless communication technologies, in particular to a soft solution of 16QAM (Quadature Amplitude Modulation, QAM, or quadrature amplitude modulation) in a mobile TV service of China Mobile Multimedia Broadcasting (CMMB). Adjustment method and device.

Background technique

Mobile TV is a service that watches TV with a mobile phone with video support. At present, there are three main ways to realize the mobile TV service: (1) Based on mobile network implementation. At present, the mobile TV services launched by US and Chinese operators mainly rely on existing mobile networks. In China, both China Mobile and China Unicom have adopted mobile streaming technology based on their General Packet Radio Service (GPRS) network and Code-Division Multiple Access (CDMA) IX network. Launched a mobile TV business. (2) Based on satellite implementation. Such an implementation method provides downlink transmission to realize a mobile-type mobile TV service through satellite, and the user can realize reception of multimedia data by integrating a module that can directly receive satellite signals on the mobile terminal. Typical technologies include the European S_DVB standard and the Japanese and Korean S_DMB standards. (3) Implementation based on terrestrial digital broadcasting network. Such implementation technologies are mainly generated for terrestrial digital broadcast television, and the frequencies used are generally broadcast television bands.

The CMMB technology was proposed by the State Administration of Radio, Film and Television and was promulgated as an industry standard in October 2006. It uses a combination of S-band high-power satellites and terrestrial equal-frequency supplementation network technology, combining single-directional broadcasting and two-way interaction to achieve national coverage of the whole world and national roaming. This standard is applicable to broadcast systems that transmit multimedia signals such as television, radio, and data information over satellite or terrestrial radio frequencies in the 30Mhz ~ 3000Mhz frequency range.

According to the provisions of the first part of the GY/T220 mobile multimedia broadcasting standard (broadcast channel frame structure, channel coding and modulation), forward error correction coding, interleaving and constellation are performed on the input data stream from the upper layer on the mobile TV service signal transmitting end. After mapping, it is multiplexed with discrete pilots and continuous pilots. Together, and adding 4, and adding 4 Orthogonal Frequency Division Multiplexing (OFDM) effective subcarriers are mapped to OFDM symbols by inverse Fourier transform (IFT). In the receiving end of the mobile TV service signal, after converting the received signal into a frequency domain signal, the received OFDM symbol is first demodulated. The CMMB standard stipulates that the receiving end must support Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), and 16QAM modulation. The 16QAM constellation mapping method is as shown in FIG. 1. Each constellation point corresponds to 4 bits, which are followed by a highest bit (b3), a second highest bit (b2), a second lower bit (b1), and a lowermost bit (b0). The soft information of the high two bits 3 and 2) can be directly obtained by phase demodulation, and the soft information of the lower two bits (ie, bl and b0) needs to be obtained by amplitude demodulation.

When the mobile TV service signal is modulated, BPSK technology and QPSK technology are used to phase-modulate only the signal, and 16QAM not only performs phase modulation, but also performs amplitude modulation. Therefore, when the receiving end performs 16QAM demodulation, it is not only necessary to analyze the phase information of the signal, but also to analyze the amplitude information of the signal. In the prior art, when the receiving end performs 16QAM demodulation on the mobile TV service signal, the average power of the statistical signal is generally used, and the decision threshold for obtaining the phase soft information and the amplitude soft information is determined according to the statistical average power of the signal. In the class method, the signal within a certain time span needs to be preserved and processed, and the average power of the signal is calculated according to the signal. Since the OFDM system is a multi-carrier system, the wireless channel may have time selective fading and frequency selective fading. The decision threshold corresponding to different carriers at different times may have drastic changes. Although the average power calculation decision threshold is statistically correct, it is not optimal.

Summary of the invention

The invention provides a soft demodulation method and device for orthogonal amplitude modulation in a mobile TV service, thereby improving the accuracy of signal demodulation.

In order to solve the prior art problem, the present invention provides a soft demodulation method for orthogonal amplitude modulation in a mobile phone television service, including: according to a channel estimation value of each subcarrier in an OFDM symbol currently being demodulated, Determining the amplitude decision threshold of each subcarrier in the OFDM symbol to be demodulated, and calculating the low bit in the constellation corresponding to each subcarrier by using the amplitude decision threshold of each subcarrier Soft information value.

The above method can also have the following characteristics:

Performing a filtering process on the channel estimation value of the OFDM symbol to be demodulated, and determining, according to the channel estimation value of the OFDM symbol to be demodulated, a threshold decision threshold of each subcarrier in the OFDM symbol to be demodulated, according to The amplitude decision threshold of each subcarrier calculates the soft information value of the low bit in the constellation corresponding to each subcarrier.

The filtering process may include:

Time domain filtering of the channel estimate of the OFDM symbol to be demodulated based on channel estimates of the first N demodulated OFDM symbols using a time domain filter; or

Frequency domain filtering of the channel estimate of the OFDM symbol to be demodulated by a frequency domain filter; or

Performing time domain filtering on the channel estimation value of the OFDM symbol to be demodulated according to channel estimation values of the first N demodulated OFDM symbols by using a time domain filter, and then using a frequency domain filter to solve the to-be-solved Frequency domain filtering of channel estimates of modulated OFDM symbols; or

Performing frequency domain filtering on the channel estimation value of the OFDM symbol to be demodulated by using a frequency domain filter, and then using a time domain filter to calculate the channel estimation value of the first N demodulated OFDM symbols. Time domain filtering of channel estimation values of modulated OFDM symbols;

The time domain filter satisfies the following conditions: for a dynamic channel, ensuring that a maximum Doppler spread of the dynamic channel is located within a passband of the current domain filter; and the frequency domain filter is based on a maximum time of the transport channel The extension spread determines the bandwidth of this frequency domain filter.

The step of calculating the soft information value of the low bit in the constellation corresponding to each subcarrier by using the amplitude decision threshold of each subcarrier may include: performing 16-bit quadrature amplitude modulation on the OFDM symbol to be demodulated In the case of performing modulation, the difference between the real part absolute value of the data of each subcarrier in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier is used as the soft information of the second lower bit of the subcarrier. And determining, as the soft information of the lowest bit of the subcarrier, the difference between the absolute value of the imaginary part of the data of each subcarrier in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier.

The determining of the amplitude decision threshold of each subcarrier in the OFDM symbol to be demodulated may include: In the case where the OFDM symbol to be demodulated is modulated by 16-bit quadrature amplitude modulation, the product of the modulus value of the channel estimation value of each subcarrier in the OFDM symbol to be demodulated and llsqrt is taken as this sub The amplitude decision threshold of the carrier, ^rt represents the square root operation.

The invention also provides a soft demodulation device for orthogonal amplitude modulation in a mobile phone television service, which is located in a mobile terminal supporting a mobile TV service, the soft demodulation device comprising: a channel estimation value storage module connected in sequence, and an amplitude decision threshold Determining a module and a low bit soft information determining module; wherein the channel estimation value storage module is configured to store a channel estimation value of each subcarrier in the orthogonal frequency division multiplexing OFDM symbol to be demodulated;

The amplitude decision threshold determining module is configured to determine a magnitude decision threshold of each subcarrier in the OFDM symbol according to a channel estimation value of each subcarrier in the OFDM symbol;

The low bit soft information determining module is configured to calculate a soft information value of a low bit in the constellation corresponding to each subcarrier according to the amplitude decision threshold of each subcarrier.

The soft demodulation device may further include a filtering module respectively connected to the channel estimation value storage module and the amplitude determination threshold determining module;

The channel estimation value storage module may be further configured to store the OFDM symbol to be demodulated

Channel estimation values for N demodulated OFDM symbols;

The filtering module is configured to filter a channel estimation value of the OFDM symbol to be demodulated;

The amplitude decision threshold determining module may be configured to determine a magnitude decision threshold of each subcarrier in the OFDM symbol to be demodulated according to the channel estimation value of the filtered OFDM symbol to be demodulated.

The filtering module may include a connected time domain filtering unit and a frequency domain filtering unit, where the time domain filtering unit is configured to: use a time domain filter according to channel estimation values of the first N demodulated OFDM symbols Decoding the channel estimation value of the demodulated OFDM symbol for time domain filtering, or performing frequency domain filtering on the frequency domain filtering unit according to channel estimation values of the first N demodulated OFDM symbols by using a time domain filter The channel estimation value of the OFDM symbol to be demodulated is subjected to time domain filtering; wherein, the time domain filter satisfies the following condition: for the dynamic channel, ensuring that the maximum Doppler spread of the dynamic channel is located in the passband of the current domain filter within;

The frequency domain filtering unit is configured to: use the frequency domain filter to pair the OFDM symbol to be demodulated The channel estimation value is subjected to frequency domain filtering, or the frequency domain filter is performed on the channel estimation value of the OFDM symbol to be demodulated by the time domain filtering unit by using a frequency domain filter; the frequency domain filtering The bandwidth of the frequency domain filter is determined based on the maximum delay spread of the transport channel.

The low bit soft information determining module may be configured to: in the case where the OFDM symbol to be demodulated is modulated by 16-bit quadrature amplitude modulation, the real part of the subcarrier data in the OFDM symbol to be demodulated is absolute The difference between the value and the amplitude decision threshold of the subcarrier is used as the soft information of the second lowest bit of the subcarrier, and the absolute value of the imaginary part of the subcarrier data in the OFDM symbol to be demodulated is compared with the amplitude of the subcarrier. The difference of the value decision threshold is used as the soft information of the lowest bit of this subcarrier.

The amplitude decision threshold determining module may be configured to set a modulus value of a channel estimation value of each subcarrier in the OFDM symbol if the OFDM symbol to be demodulated is modulated by 16-bit quadrature amplitude modulation The product of 1 Ι ϋ) is used as the amplitude decision threshold of this subcarrier, and wrt represents the square root operation.

By using the method of the invention, the accuracy of signal demodulation can be improved, and the noise can be further suppressed by performing time domain filtering on the channel estimation value of the OFDM symbol and frequency domain filtering on each subcarrier signal in the OFDM symbol. The signal-to-noise ratio of the soft demodulated signal improves the decoding performance of the receiving end.

BRIEF abstract

1 is a schematic diagram of 16QAM constellation mapping in a mobile TV service in the prior art;

Figure 2 is a structural diagram showing the structure of a soft demodulation device in the embodiment;

3 is a flowchart of a 16QAM soft demodulation method in Embodiment 1;

4 is a schematic diagram showing the structure of a time domain IIR filter in the embodiment.

Preferred embodiment of the invention

In QAM modulation and demodulation, among the N bits indicated by each constellation point in the constellation diagram, the upper N/2 bits are called high bits, and the lower N/2 bits are called low bits. Taking 16QAM as an example, the four bits b3, b2, bl and b0, b3 and b2 corresponding to each constellation point in the constellation diagram are called high bits, and bl and b0 are called low bits. As shown in FIG. 2, the soft demodulator device for orthogonal amplitude modulation in a mobile terminal supporting mobile TV service includes: a channel estimation value storage module connected in sequence, a filtering module, an amplitude decision threshold determining module, and a low bit soft An information determining module, and a high bit soft information determining module connected to the channel estimation value storage module; the filtering module further includes a connected time domain filtering unit and a frequency domain filtering unit; the channel estimation value storage module may further determine the threshold value threshold Modules are directly connected;

The channel estimation value storage module is configured to store a channel estimation value of each subcarrier in the orthogonal frequency division multiplexing OFDM symbol to be demodulated, and a channel estimation of the N demodulated OFDM symbols before the current OFDM symbol to be demodulated Value

The filtering module is configured to perform time domain or frequency domain or time-frequency filtering processing on the channel estimation value of the OFDM symbol to be demodulated, and send the filtered data to the amplitude determination threshold determining module;

The time domain filtering unit in the filtering module is configured to: time-domain filter the channel estimation value of the OFDM symbol to be demodulated according to channel estimation values of the first N demodulated OFDM symbols by using a time domain filter, or Performing time domain filtering on the channel estimation value of the OFDM symbol to be demodulated by the frequency domain filtering unit according to the channel estimation values of the first N demodulated OFDM symbols by using a time domain filter; The domain filter satisfies the following conditions: For a dynamic channel, the maximum Doppler spread of the dynamic channel is guaranteed to be within the passband of the current domain filter;

The frequency domain filtering unit in the filtering module is configured to: perform frequency domain filtering on the channel estimation value of the OFDM symbol to be demodulated by using a frequency domain filter, or perform the frequency domain filtering on the time domain filtering unit by using a frequency domain filter The channel estimation value of the OFDM symbol to be demodulated in the time domain is subjected to frequency domain filtering; and the frequency domain filter determines the bandwidth of the frequency domain filter according to the maximum delay spread of the transmission channel.

The amplitude decision threshold determining module is configured to: determine, according to a channel estimation value of each subcarrier in the OFDM symbol to be demodulated, an amplitude decision threshold of each subcarrier in the OFDM symbol; Demodulating a channel estimation value of the OFDM symbol to determine an amplitude decision threshold of each subcarrier in the OFDM symbol to be demodulated; where the OFDM symbol to be demodulated is modulated by 16-bit quadrature amplitude modulation, The product of the channel estimation value of each subcarrier in the OFDM symbol and the product of 2/^rt(10) is used as the amplitude decision threshold of the subcarrier, and ^rt represents the square root operation.

The low bit soft information determining module is configured to calculate, according to the amplitude decision threshold of each subcarrier, a soft information value of a low bit in the constellation corresponding to each subcarrier, where the to-be-demodulated In the case where the OFDM symbol is modulated by 16-bit quadrature amplitude modulation, the difference between the real part absolute value of the subcarrier data in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier is used as the subcarrier. Soft information of the second lower bit, the difference between the absolute value of the imaginary part of the subcarrier data in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier is used as the soft information of the lowest bit of the subcarrier .

The high bit soft information determining module is configured to obtain a soft information value of a high bit in the constellation corresponding to each subcarrier according to the OFDM symbol data to be demodulated, wherein the OFDM symbol to be demodulated is a 16-bit orthogonal amplitude In the case of modulation for modulation, the real part of the OFDM symbol data to be demodulated is taken as the soft information of the highest bit (b3), and the imaginary part of the OFDM symbol data to be demodulated is used as the soft information of the next highest bit (b2). .

Embodiment 1

As shown in FIG. 3, the method for soft demodulation of the quadrature amplitude modulation at the receiving end of the mobile TV service includes the following steps:

Step 301: Determine, according to a channel estimation value of each subcarrier in the OFDM symbol to be demodulated, an amplitude decision threshold of each subcarrier in the OFDM symbol.

Taking 16QAM as an example, the amplitude decision threshold of each subcarrier in the OFDM symbol to be demodulated is the product of the modulus value of the channel estimation value of this subcarrier and 1Ι ϋ), indicating the square root operation.

Step 302: Calculate, according to the amplitude decision threshold of each subcarrier, a soft information value of a low bit in the constellation diagram corresponding to each subcarrier;

Taking 16QAM as an example, step 302 specifically includes: taking the difference between the real part absolute value of the subcarrier data in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier as the second low bit (bl) of the subcarrier. And the soft information, the difference between the absolute value of the imaginary part of the subcarrier data in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier is used as the soft information of the lowest bit (b0) of the subcarrier.

Step 303: Obtain a soft information value of a high bit in a constellation corresponding to each subcarrier according to the OFDM symbol data currently being demodulated. The process ends.

Taking 16QAM as an example, the real part of the OFDM symbol data to be demodulated is taken as the soft information of the highest bit (b3), and the imaginary part of the OFDM symbol data to be demodulated is taken as the next highest bit (b2). Soft information.

The method of calculating the soft information values of the highest bit and the next highest bit in this step 303 is the same as in the prior art.

Embodiment 2

The difference between the second embodiment and the first embodiment is that before step 301, the

Channel estimation value of N demodulated OFDM symbols before OFDM symbol Processing step of IIR (Infinite Impulse Response) filtering in time domain for the channel estimation value of the OFDM symbol to be demodulated, the method in Embodiment 2 Specifically include:

The receiving end of the mobile TV service buffers the channel estimation value of the OFDM symbol to be demodulated and the channel estimation value of the first N demodulated OFDM symbols of the OFDM symbol to be demodulated; N is an integer greater than or equal to 1. In order to ensure the real-time performance of mobile TV services, the preferred value of N is 1;

The channel estimation value of the OFDM symbol to be demodulated is time-domain filtered according to the channel estimation values of the N demodulated OFDM symbols preceding the OFDM symbol to be demodulated;

For a typical AWGN channel, a static Rayleigh channel, or a static channel with deep and deep echoes, the memory length of the IIR filter (or the bandwidth of the IIR can be reduced) can improve the demodulation performance; specifically, according to the static channel The maximum Doppler spread determines the IIR bandwidth, ensuring that the bandwidth is greater than the maximum Doppler spread. The IIR bandwidth can be very narrow.

For dynamic Rayleigh channels, the bandwidth of the IIR filter can be determined based on the maximum Doppler spread of the channel to ensure that the maximum Doppler spread is within the passband.

The time domain filter structure is shown in Figure 4. The subcarriers at the same position of the two OFDM symbols are weighted and output, and the filter coefficient a controls the memory length of the filter. Different coefficients a can be designed according to different channel types to get the best performance under different channels. For example, the filter coefficient a = 0.125 can be used in the AWGN channel.

After performing the above-described time domain filtering on the channel estimation values of the demodulated OFDM symbols, the processing procedures described in steps 301, 302, and 303 are sequentially performed.

Embodiment 3

The third embodiment differs from the first embodiment in that before step 301, a processing step of performing FIR (finite impulse response) filtering on the OFDM symbol to be demodulated is added, and the method in the third embodiment is specific. include: The channel estimation values on the respective subcarriers of the demodulated OFDM symbol are subjected to FIR low pass filtering in the frequency domain. The filter order and characteristics can be designed according to the specific situation. For different channels, the bandwidth of the FIR filter can be determined according to its maximum delay spread, and the bandwidth is guaranteed to be larger than the maximum delay spread.

When the channel estimation values of the respective subcarriers in the OFDM symbol are subjected to FIR filtering in the frequency domain, the M subcarriers before and after the subcarriers may be taken and averaged for each subcarrier as the output value of the subcarrier, the foremost and last M of the OFDM symbol. The subcarriers are not filtered, and M is an integer greater than zero.

After performing the above-described frequency domain filtering on the channel estimation values of the demodulated OFDM symbols, the processing procedures described in steps 301, 302 and 303 are sequentially performed.

Embodiment 4

In the fourth embodiment, the time domain filtering process described in the second embodiment and the frequency domain filtering process described in the third embodiment may be sequentially performed before the step 301 of the first embodiment, or may be implemented in sequence before the step 301 of the first embodiment. The time domain filtering process described in Example 2 and the frequency domain filtering process described in Embodiment 3 are performed.

In the fourth embodiment, filtering is performed from two latitudes in the time domain and the frequency domain, respectively, which can effectively suppress noise, improve the signal-to-noise ratio of the soft demodulation, and thereby improve the demodulation performance.

In summary, the method of the present invention can effectively operate in various channel conditions. For static or slow-changing channels, the decoding performance of the receiver can be effectively improved by increasing the memory length of the time-domain filter. For the fast-changing channel, noise suppression can be further performed by the frequency domain filter to improve the decoding performance of the receiver.

It is a matter of course that the invention may be embodied in various other forms and modifications without departing from the spirit and scope of the invention.

Industrial applicability

Compared with the prior art, the method of the present invention can improve the accuracy of signal demodulation, and can further improve the time domain filtering of the channel estimation value of the OFDM symbol and the frequency domain filtering of each subcarrier signal in the OFDM symbol. The noise is suppressed, the signal-to-noise ratio of the soft demodulated signal is improved, and the decoding performance of the receiving end is improved.

Claims

Claim

1. A soft demodulation method for quadrature amplitude modulation in a mobile TV service, including:

Determining, according to a channel estimation value of each subcarrier in the OFDM symbol to be demodulated, an amplitude decision threshold of each subcarrier in the OFDM symbol to be demodulated, and determining a threshold by using an amplitude of each subcarrier The soft information values of the low bits in the constellation corresponding to each subcarrier are calculated separately.

2. The method according to claim 1, wherein before the step of determining a magnitude decision threshold of each subcarrier in the OFDM symbol to be demodulated, the method further comprises:

Filtering channel estimation values of the OFDM symbols to be demodulated;

The determining the amplitude decision threshold of each subcarrier in the OFDM symbol to be demodulated comprises: determining, according to the channel estimation value of the OFDM symbol to be demodulated, the amplitude decision of each subcarrier in the OFDM symbol to be demodulated Threshold.

3. The method according to claim 2, wherein the performing the filtering process comprises: using a time domain filter to channel the OFDM symbol to be demodulated according to channel estimation values of the first N demodulated OFDM symbols Estimating the value for time domain filtering; or

The time domain filter satisfies the following conditions: for a dynamic channel, ensuring that a maximum Doppler spread of the dynamic channel is located within a passband of the current domain filter;

The frequency domain filter determines the bandwidth of the frequency domain filter based on the maximum delay spread of the transmission channel.

4. The method of claim 1, 2 or 3, wherein The step of calculating the soft information value of the low bit in the constellation corresponding to each subcarrier by using the amplitude decision threshold of each subcarrier includes: performing, by the 16-bit orthogonal amplitude modulation, the OFDM symbol to be demodulated In the case of modulation, the difference between the real part absolute value of the data of each subcarrier in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier is used as the soft information of the second lower bit of the subcarrier. The difference between the absolute value of the imaginary part of the data of each subcarrier in the OFDM symbol to be demodulated and the amplitude decision threshold of the subcarrier is used as the soft information of the lowest bit of the subcarrier.

5. The method according to claim 1, wherein the determining the amplitude decision threshold of each subcarrier in the OFDM symbol to be demodulated comprises:

In a case where the OFDM symbol to be demodulated is modulated by 16-bit quadrature amplitude modulation, a modulus value of a channel estimation value of each subcarrier in the OFDM symbol to be demodulated is 2 / ^ rt (10) The product of ) is used as the amplitude decision threshold of this subcarrier, and ^rt represents the square root operation.

6. A soft demodulation device for orthogonal amplitude modulation in a mobile TV service, located in a mobile terminal supporting a mobile TV service, the soft demodulation device comprising: a channel estimation value storage module sequentially connected, an amplitude determination threshold determination module, and Low bit soft information determining module; wherein

The channel estimation value storage module is configured to store a channel estimation value of each subcarrier in an orthogonal frequency division multiplexing OFDM symbol to be demodulated;

The amplitude decision threshold determining module is configured to determine a magnitude decision threshold of each subcarrier in the OFDM symbol according to a channel estimation value of each subcarrier in the OFDM symbol to be demodulated;

The low bit soft information determining module is configured to calculate soft information values of low bits in the constellation corresponding to each subcarrier according to the amplitude decision threshold of each subcarrier.

The soft demodulation apparatus according to claim 6, further comprising a filtering module respectively connected to the channel estimation value storage module and the amplitude decision threshold determining module;

The channel estimation value storage module is further configured to store channel estimation values of the N demodulated OFDM symbols before the OFDM symbol to be demodulated;

The amplitude decision threshold determining module is configured to be based on the filtered OFDM symbol to be demodulated The channel estimate determines an amplitude decision threshold for each subcarrier in the OFDM symbol to be demodulated.

8. The soft demodulation apparatus according to claim 7, wherein the filtering module comprises a connected time domain filtering unit and a frequency domain filtering unit;

The time domain filtering unit is configured to: perform time domain filtering on the channel estimation value of the OFDM symbol to be demodulated according to channel estimation values of the first N demodulated OFDM symbols by using a time domain filter, or use a time interval The domain filter performs time domain filtering on the channel estimation value of the OFDM symbol to be demodulated by the frequency domain filtering unit according to the channel estimation values of the first N demodulated OFDM symbols; The domain filter satisfies the following conditions: For a dynamic channel, the maximum Doppler spread of the dynamic channel is guaranteed to be within the passband of the current domain filter;

The frequency domain filtering unit is configured to: perform frequency domain filtering on the channel estimation value of the OFDM symbol to be demodulated by using a frequency domain filter, or perform time-division filtering on the time domain filtering unit by using a frequency domain filter The domain-filtered channel estimation value of the OFDM symbol to be demodulated is subjected to frequency domain filtering; wherein the frequency domain filter determines the bandwidth of the frequency domain filter according to the maximum delay spread of the transmission channel.

9. The soft demodulating device according to claim 6, 7 or 8, wherein

The low bit soft information determining module is further configured to: if the OFDM symbol to be demodulated is modulated by 16-bit quadrature amplitude modulation, each subcarrier of the OFDM symbol to be demodulated The difference between the absolute value of the real part of the data and the amplitude decision threshold of the subcarrier is used as the soft information of the second lowest bit of the subcarrier, and the imaginary part of the data of each subcarrier in the OFDM symbol to be demodulated is absolutely The difference between the value and the amplitude decision threshold of this subcarrier is taken as the soft information of the lowest bit of this subcarrier.

10. The soft demodulation device according to claim 6, wherein

The amplitude decision threshold determining module is configured to determine an amplitude decision threshold of each subcarrier in an OFDM symbol to be demodulated by: modulating the OFDM symbol to be demodulated by 16-bit quadrature amplitude modulation In the case, the product of the channel estimation value of each subcarrier of the OFDM symbol and the product of 2 / ^ rt (10) is used as the amplitude decision threshold of the subcarrier, and sqrt represents the square root operation.