MMSE channel estimation method of ultra-high-speed mobile communication system based on leaky cable

Abstract

The invention relates to the technical field of wireless communication transmission, and discloses an MMSE (Minimum Mean Square Error) channel estimation method of an ultra-high-speed mobile communication system based on a leaky cable. Modeling correction is carried out on an ultra-high-speed mobile communication channel based on a leaky cable, and a Doppler spectrum obtained through theoretical simulation conforms to actual measurement characteristics. Based on a demodulation reference signal DMRS in a 5G NR standard, when time domain channel estimation interpolation is carried out at a receiving end of a 5G CP-OFDM system, a channel time domain autocorrelation function used for MMSE estimation is improved according to a leaky cable-based ultra-high-speed mobile communication channel Doppler spectrum obtained through channel modeling; compared with an MMSE estimation method adopting a universal channel time domain autocorrelation function, the improved MMSE estimation method has certain performance improvement, and is suitable for ultra-high-speed mobile communication under a communication system architecture based on a leaky cable.

Description

Technical Field

[0001] The invention relates to the technical field of wireless communication transmission, and in particular to an MMSE channel estimation method of an ultra-high-speed mobile communication system based on a leaky cable. Background Art

[0002] With the development of mobile communication technology, wireless communication technology in high-speed mobile scenarios has gradually attracted attention. At present, the goal of the fifth-generation mobile communication technology is to support wireless communication at a moving speed of 500km / h, while the performance vision of the future sixth-generation mobile communication technology is expected to support wireless communication at a moving speed of 1000km / h or higher. At present, low-vacuum pipeline high-speed maglev transportation is considered to be a key technology for achieving operating speeds of 1000km / h and higher. Considering the potential safety hazards and equipment maintenance difficulties of installing antennas in pipelines in this scenario, wireless communication in pipeline scenarios based on leaky cables has significant advantages. At the same time, relevant studies have shown that wireless communication based on leaky cables has the effect of suppressing the Doppler frequency shift of the channel in mobile scenarios, so it can better support wireless communication in ultra-high-speed mobile scenarios. Summary of the invention

[0003] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide an MMSE channel estimation method for an ultra-high-speed mobile communication system based on a leaky cable, so as to solve the problem of low estimation accuracy of the leaky cable wireless communication channel in ultra-high-speed mobile scenarios in the prior art.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions: In the first aspect, the present invention provides an MMSE channel estimation method for an ultra-high-speed mobile communication system based on a leaky cable. For low-vacuum pipeline high-speed maglev transportation, when using a leaky cable for mobile communication, there are Leaking cables and There are N train antennas and N slots on each leaky cable. When OFDM is used for communication, the length of the time-domain OFDM symbol allocated to a time slot in the transmission structure configuration is , the total number of subcarriers in the frequency domain is . Corresponding train antenna l With leaky cable p Between OFDM symbols r , subcarrier k Frequency domain channel response of position It can be expressed as ; in, and are the line-of-sight component and the non-line-of-sight component respectively. According to the relevant parameters of each line-of-sight path and non-line-of-sight path, the corrected channels in the mobile scenario can be expressed as

[0005]

[0006] in, For leaking cables p To the train antenna l The Ricean factor of the link, For leaking cables p To the train antenna l The received power, M is the total number of scatterers, for A random variable uniformly distributed on , are the subcarrier spacing and OFDM symbol period configured in the system respectively; , , Leakage Cable p Slots on i To the train antenna l Amplitude attenuation factor, transmission delay and Doppler frequency shift; , , Leakage Cable p Upper slot i To the scatterer j Amplitude attenuation factor, transmission delay and Doppler frequency shift.

[0007] Preferably, in a possible implementation manner of the first aspect, the Doppler spectrum of the channel is simulated according to the modified leaky cable mobile scenario OFDM channel model, and the Doppler spectrum of the channel has a frequency There is a peak at the maximum Doppler frequency. The amplitude of the frequency components within the range is evenly distributed.

[0008] Preferably, in a possible implementation manner of the first aspect, the MMSE channel estimation is performed by a matrix W The weighted operation of the channel estimation result With the true value H The mean square error between them is the smallest, and we get W The expression is

[0009] in, is the channel LS estimation vector of the reference signal position; , They are H The autocorrelation matrix and H and The cross-correlation matrix, whose elements are calculated based on the channel autocorrelation function; , are the variance of the transmitted signal and AWGN, respectively.

[0010] Preferably, in a possible implementation manner of the first aspect, in the NR standard, a time slot uses DMRS as a reference signal for channel estimation, and a time slot is set DMRS symbols, consisting of 1 leading DMRS symbol and The corresponding resource allocation complies with NR standard TS 38.211. Based on the Doppler spectrum characteristics obtained from the OFDM corrected channel of the leaky cable in the mobile scenario, this method improves the autocorrelation function used in the MMSE channel estimation in the leaky cable scenario. , Corresponding DMRS symbol m , And data symbols r The correlation matrix elements can be expressed as

[0011]

[0012] in, , They are DMRS symbols respectively , The corresponding OFDM symbol index in the time slot, is the Doppler shift in the channel, is the OFDM symbol period.

[0013] The beneficial effects of the present invention are: providing a modeling and correction method for an OFDM wireless communication channel based on a leaky cable in a mobile scenario, which can perform mathematical analysis and theoretical simulation on the wireless communication channel based on a leaky cable in a mobile scenario, and perform targeted algorithm optimization; improving the autocorrelation function used for MMSE channel estimation by obtaining the Doppler spectrum through the corrected modeled channel, which can further improve the channel estimation accuracy of the system in the mobile scenario based on leaky cable communication, and help the system support wireless communications at higher speeds in this scenario. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 A schematic diagram of a communication system based on a leaky cable in a low-vacuum pipeline high-speed maglev transportation scenario is provided for this application.

[0016] Figure 2 A Doppler spectrum schematic diagram of a leaky cable communication channel correction model at a moving speed of 1000 km / h is provided for this application.

[0017] Figure 3 , Figure 4 A performance diagram of an improved MMSE channel estimation method is provided for this application. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Embodiment 1: The present invention provides an MMSE channel estimation method for an ultra-high-speed mobile communication system based on a leaky cable, the method comprising OFDM wireless communication channel modeling correction based on a leaky cable in a mobile scenario and an improved MMSE estimation method for leaky cable communication.

[0020] Figure 1 A schematic diagram of a communication system based on a leaky cable in a low-vacuum pipeline high-speed maglev transportation scenario is given. Based on this schematic diagram, a channel correction model of a communication system based on a leaky cable in a mobile scenario is obtained. Specifically: Total Leaking cables and Train antennas, each with a leaky cable N slots, and the total number of effective scatterers is M , evenly distributed on the inner wall of the pipe. In terms of transmission structure configuration, the time domain OFDM symbol length allocated by the system for a time slot is , the total number of subcarriers in the frequency domain is For train antennas With leaky cable Between OFDM symbols , subcarrier Frequency domain channel response of position It can be expressed as .

[0021] in, and They are line-of-sight component and non-line-of-sight component respectively.

[0022] Line of sight component By leaky cable p Each slot on To the train antenna The path components of Figure 1 The relationship between position and distance in the leaky cable p Slots on , the amplitude attenuation factor of the corresponding path , transmission delay and Doppler shift It is expressed as:

[0023]

[0024]

[0025] in, is the propagation constant, , Electromagnetic waves in the leakage cable p Up to slot i The amplitude attenuation coefficient and phase change of For leaking cables p Slot i To the train antenna l The distance For leaking cables p Slot i To the train antenna l Connections and leaky cables p The angle between the axis extension directions, is the wavelength of the leakage cable radiation field, is the carrier frequency of the leakage cable radiation field, v is the train running speed.

[0026] Similarly, the non-line-of-sight component By leaky cable p Each slot on the train reaches the train antenna through each effective scatterer. l For leaky cables p Slots on i and scatterers , the amplitude attenuation factor of the corresponding path , transmission delay and Doppler shift It is expressed as:

[0027]

[0028]

[0029] in, is the propagation constant, , Electromagnetic waves in the leakage cable p Up to slot i The amplitude attenuation coefficient and phase change of For leaking cables p Slot i To the scatterer j The distance For scatterers j To the train antenna l The distance For leaking cables p Slot i To the scatterer j Connections and leaky cables p The angle between the axis extension directions, is the wavelength of the leakage cable radiation field, is the carrier frequency of the leakage cable radiation field, v is the train running speed.

[0030] Based on the above parameters, and Respectively expressed as

[0031]

[0032] in, For leaking cables p To the train antenna l The Ricean factor of the link, For leaking cables p To the train antenna l The received power, for A uniformly distributed random variable, is the OFDM symbol, is the subcarrier position, , are the subcarrier spacing and OFDM symbol period configured in the system, , , Leakage Cable p Slots on i To the train antenna l Amplitude attenuation factor, transmission delay and Doppler frequency shift; , , Leakage Cable p Upper slot i To the scatterer j The amplitude attenuation factor, transmission delay and Doppler frequency shift are taken into account. Taking into account the time-varying situation of Doppler frequency in different OFDM symbol periods, the phase caused by Doppler frequency in the channel response is obtained by accumulating different symbols.

[0033] Figure 2 The moving speed obtained according to the channel correction model is given v =1000km / h, carrier frequency It can be seen that the channel Doppler spectrum based on leaky cable communication has a frequency There is a peak at the maximum Doppler frequency. The amplitude of the frequency components in the range is uniformly distributed. Therefore, the modified model can reflect the channel characteristics based on leaky cable communication in mobile scenarios.

[0034] The basic principle of MMSE channel estimation is through the matrix W The weighted operation of the channel estimation result With the true value H The mean square error between them is the smallest, and we get W The expression is

[0035] in, is the channel LS estimation vector of the reference signal position; , They are H The autocorrelation matrix and H and The cross-correlation matrix, whose elements are calculated based on the channel autocorrelation function; , are the variance of the transmitted signal and AWGN, respectively.

[0036] In the NR standard, the time slot uses DMRS as the reference signal for channel estimation. DMRS symbols, consisting of 1 leading DMRS symbol and The corresponding resource allocation complies with NR standard TS 38.211. When performing time domain channel estimation, the channel time domain autocorrelation function corresponding to the uniform Doppler spectrum is generally used to generate the correlation matrix to calculate W , which corresponds to the DMRS symbol m , And data symbols r The autocorrelation matrix elements can be expressed as

[0037]

[0038] in, , They are DMRS symbols respectively , The corresponding OFDM symbol index in the time slot, is the Doppler shift in the channel, is the OFDM symbol period.

[0039] Therefore, based on the Doppler spectrum characteristics obtained from the OFDM corrected channel of the leaky cable in the mobile scenario, the autocorrelation function used in the MMSE channel estimation in the leaky cable scenario is improved. The channel Doppler spectrum under the leaky cable still has uniformly distributed frequency components within the maximum Doppler frequency range, so its autocorrelation function still retains the corresponding sinc function components. At the same time, due to the obvious zero-frequency peak in the Doppler spectrum, according to the Fourier time-frequency transform relationship, it is necessary to introduce a constant component in the autocorrelation function. After amplitude normalization, the autocorrelation matrix elements obtained using the improved autocorrelation function can be expressed as

[0040]

[0041] Figure 3 , Figure 4 They were given =2, 3, the performance comparison diagram of the Normalized Mean Square Error (NMSE) channel estimation method using the improved autocorrelation function and the universal autocorrelation function. It can be seen that the two Under the configuration, the MMSE channel estimation method using the improved autocorrelation function has a certain performance improvement compared with the universal autocorrelation function, and the configuration =3, the NMSE performance is improved more significantly at the same speed. v =2000km / h as an example, when SNR=35dB, configure =2, the MMSE channel estimation method using the improved autocorrelation function has an NMSE performance improvement of about 2.46dB, while =3, it can provide about 5.81dB NMSE performance improvement. In summary, the use of improved autocorrelation function for MMSE channel estimation has better channel estimation performance at the same mobile speed, and can support communication scenarios with higher mobile speeds under fixed performance indicators. Figure 3 , Figure 4 The system parameter configuration is shown in Table 1.

[0042] Table 1 Simulation system parameter configuration

[0043] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An MMSE channel estimation method for an ultra-high-speed mobile communication system based on a leaky cable, characterized in that: The method comprises: A correction model of OFDM wireless communication channel based on leaky cable in mobile scenario is established. The model includes line-of-sight component and non-line-of-sight component. The line-of-sight component is composed of the path component from each slot on the leaky cable to the train antenna, and the non-line-of-sight component is composed of the path component from each slot on the leaky cable to the train antenna via each effective scatterer. According to the channel correction model, the amplitude attenuation factor, transmission delay and Doppler frequency shift of the path from the slot hole on the leaky cable to the train antenna, as well as the amplitude attenuation factor, transmission delay and Doppler frequency shift of the path from the slot hole of the leaky cable to the train antenna via the scatterer are calculated; Based on the channel correction model and its corresponding amplitude attenuation factor, transmission delay and Doppler frequency shift, an autocorrelation function matching the channel Doppler spectrum characteristics of leaky cable communication is generated, the elements of the channel autocorrelation matrix and cross-correlation matrix are calculated, and the channel estimation result with the minimum mean square error with the true value is calculated through weighted operation of the matrix.

2. The MMSE channel estimation method according to claim 1, characterized in that: The mobile scenarios have Leaking cables and Train antennas, each with a leaky cable N slots, the total number of effective scatterers is M , evenly distributed on the inner wall of the pipeline, the train moves along the pipeline at a speed v run; The mobile scenario uses OFDM for communication. The length of the time domain OFDM symbol allocated to a time slot in the transmission structure configuration is , the symbol period is , the total number of subcarriers in the frequency domain is , the subcarrier spacing is ; The time slot uses DMRS as the reference signal for channel estimation. DMRS symbols, consisting of 1 leading DMRS symbol and Additional DMRS symbols; When communicating, the carrier frequency selected is , the wavelength is .

3. The MMSE channel estimation method as claimed in claim 2, characterized in that: For train antennas With leaky cable , located in OFDM symbol , subcarrier Frequency domain channel response of position Expressed as ; in, and are the line-of-sight component and the non-line-of-sight component, respectively. By leaky cable p Each slot on To the train antenna The path components of By leaky cable p Each slot on i Through each effective scatterer , Arrival train antenna The path components of .

4. The MMSE channel estimation method as claimed in claim 3, characterized in that: The OFDM wireless communication channel correction method includes: For leaky cables p Slots on i , which corresponds to the amplitude attenuation factor of the line-of-sight path , transmission delay and Doppler shift for in, is the propagation constant, , Electromagnetic waves in the leakage cable p Up to slot i The amplitude attenuation coefficient and phase change of For leaking cables p Slot i To the train antenna l The distance For leaking cables p Slot i To the train antenna l Connections and leaky cables p The angle between the axis extension directions, is the wavelength of the leakage cable radiation field, is the carrier frequency of the leakage cable radiation field, v is the train running speed; For leaky cables p Slots on i and effective scatterers j , which corresponds to the amplitude attenuation factor of the non-line-of-sight path , transmission delay and Doppler shift for in, is the propagation constant, , Electromagnetic waves in the leakage cable p Up to slot i The amplitude attenuation coefficient and phase change of For leaking cables p Slot i To the scatterer j The distance For scatterers j To the train antenna l The distance For leaking cables p Slot i To the scatterer j Connections and leaky cables p The angle between the axis extension directions, is the wavelength of the leakage cable radiation field, is the carrier frequency of the leakage cable radiation field, v is the train running speed; Correspondingly, the mobile communication channel based on leaky cable is in, For leaking cables p To the train antenna l The Ricean factor of the link, For leaking cables p To the train antenna l The received power, for A uniformly distributed random variable, is the OFDM symbol, is the subcarrier position, , are the subcarrier spacing and OFDM symbol period configured in the system, , , Leakage Cable p Slots on i To the train antenna l Amplitude attenuation factor, transmission delay and Doppler frequency shift; , , Leakage Cable p Upper slot i To the scatterer j Amplitude attenuation factor, transmission delay and Doppler frequency shift.

5. The MMSE channel estimation method according to claim 4, characterized in that: The Doppler spectrum of the mobile communication channel based on the leaky cable is There is a peak at the maximum Doppler frequency, and the amplitudes of the other frequency components within the maximum Doppler frequency range are evenly distributed.

6. The MMSE channel estimation method as claimed in claim 5, characterized in that: MMSE channel estimation uses the weighted operation of the matrix W to make the channel LS estimation vector Weighted channel estimation result With the true value H The mean square error between them is the smallest; Accordingly, W The expression is in, is the identity matrix, , are the variances of the transmitted signal and AWGN, , They are H The autocorrelation matrix and H and The cross-correlation matrix, whose elements are calculated according to the channel time domain autocorrelation function; Combined with the Doppler spectrum characteristics of the mobile communication channel based on the leaky cable, the channel time domain autocorrelation function introduces a constant component based on the sinc function component; After amplitude normalization, , Corresponding DMRS symbol m , And data symbols r The elements of in, , They are DMRS symbols respectively , The corresponding OFDM symbol index in the time slot, is the Doppler shift in the channel.

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