Stepwise power control method based on mmse signal-to-noise ratio estimation

Abstract

The application provides a power control method based on MMSE signal-to-noise ratio estimation, which comprises the following steps: in the communication link establishment stage, a signal frame containing pilot subcarriers is sent from a transmitting end to a receiving end; the signal-to-noise ratio of the current link and the environmental noise level are estimated based on the signal frame received by the receiving end, and the required transmitting sound power is calculated based on the preset target signal-to-noise ratio constraint; the transmitting sound power value is mapped to the closest power level in the discrete power level set by the receiving end to generate power level indication information; the power level indication information is embedded into an acknowledgement data packet by the receiving end and fed back to the transmitting end through a reverse data link; and the transmitting end analyzes the acknowledgement data packet and extracts the power level indication information to complete the configuration of the initial transmitting power. The application periodically senses the link quality, selects the optimal transmitting power level according to the distance between nodes and the channel state, ensures the accessibility of the communication link, and effectively reduces the energy consumption in the node communication process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of network communication technology, and in particular to a power control method based on MMSE signal-to-noise ratio estimation. BACKGROUND

[0002] During the operation of UWSNs, due to the frequency-selective fading, multipath effect and node movement of seawater medium, the link quality shows a dynamic change trend. At the same time, each node in the network is usually powered by a battery, and the energy is limited. The traditional fixed transmission power strategy cannot flexibly adjust the power level according to the actual state of the link, often leading to the following problems: high power is still used when the link quality is good, causing energy waste; when the link quality is poor, the power is insufficient to guarantee the transmission reliability; fixed power is not conducive to network load balancing, affecting the overall life. Fixed power is not conducive to network load balancing, affecting the overall life. Therefore, designing a transmission power regulation mechanism with adaptive ability and channel SNR constraint guidance has become an important topic to improve network performance and energy efficiency. SUMMARY

[0003] The purpose of the present application is to provide a power control method based on MMSE signal-to-noise ratio estimation, which periodically senses the link quality, selects the optimal transmission power level according to the distance between nodes and the channel state, and effectively reduces the energy consumption in the node communication process while ensuring the reachability of the communication link.

[0004] To achieve the above purpose, the present application provides a power control method based on MMSE signal-to-noise ratio estimation, which comprises:

[0005] S11, in the communication link establishment stage, the transmitting end sends a signal frame containing pilot subcarriers to the receiving end, specifically including:

[0006] After the signal frame to be sent by the transmitting end is channel encoded and phase mapped, it is modulated onto OFDM symbols, and each OFDM symbol contains subcarriers;

[0007] For each OFDM symbol in the to-be-transmitted signal frame, a corresponding transmission vector is generated according to a preset mapping, and a transmission matrix is constructed by the transmission vector, and the expression is:

[0008]

[0009] Wherein, is the transmission matrix, is the transmission vector, is a complex field, and each transmission vector , m is the firstm one OFDM symbol;

[0010] The expression of the receiving vector of the receiving end is:

[0011]

[0012] wherein, is a receiving vector, is a Hadamard product, is a channel frequency domain response, , is an additive white Gaussian noise, , () is a normal distribution function, is a noise variance, is a unit matrix;

[0013] S12, based on the signal frame received by the receiving end, estimating the signal-to-noise ratio of the current link and the ambient noise level, and calculating the required transmitting sound power based on the preset target signal-to-noise ratio constraint;

[0014] S13, the receiving end maps the transmitting sound power value to the closest gear in the discrete power gear set, generating power gear indication information;

[0015] S14, the receiving end embeds the power gear indication information into the confirmation data packet through the reverse data link and feeds back to the transmitting end.

[0016] Further, the transmitting end sends a signal frame containing a pilot subcarrier to the receiving end, specifically including:

[0017] After the signal frame to be sent by the transmitting end is channel encoded and phase mapped, it is modulated onto one OFDM symbol, each of which contains subcarriers;

[0018] For each OFDM symbol in the signal frame to be transmitted, a corresponding transmitting vector is generated according to the preset mapping, and a transmitting matrix is constructed through the transmitting vector, the expression being:

[0019]

[0020] wherein, is a transmitting matrix, is a transmitting vector, is a complex field, and each transmitting vector , m is the m th OFDM symbol;

[0021] The expression of the receiving vector of the receiving end is:

[0022]

[0023] wherein, is a received vector, is a Hadamard product, is a channel frequency domain response, , is an additive white Gaussian noise, , () is a normal distribution function, is a noise variance, is an identity matrix.

[0024] Further, the SNR of the current link is estimated based on the received signal frame, and specifically includes:

[0025] The pilot subcarriers in the OFDM symbol in the received signal frame are collectively denoted as F The channel response at the pilot position is obtained by sampling the pilot subcarriers according to a preset rule, and the expression is:

[0026]

[0027] wherein, is a channel estimation based on least squares, is a pilot-related component, () is a received vector, () is a transmitted vector;

[0028] Based on the MMSE principle, the channel estimation expression of the pilot subcarriers is:

[0029]

[0030] wherein, is a channel estimation on all subcarriers, is a covariance matrix between the complete subcarriers and the pilot position, , is a covariance matrix of the pilot position, ;

[0031] Based on the result of the channel estimation, the MMSE SNR is calculated for each OFDM symbol, and the expression is:

[0032]

[0033] wherein, is an MMSE SNR, is a subcarrier, is the th symbol, and the ka receive vector of the sub-carrier, for the first m for the first k MMSE channel estimation value on the sub-carrier of the symbol, for the first m for the first k a transmit vector of the sub-carrier of the symbol;

[0034] Based on the MMSE signal-to-noise ratio, a sliding window average is performed on the continuous M OFDM symbols to obtain a frame-level average signal-to-noise ratio, expressed as:

[0035]

[0036] wherein, the frame-level average signal-to-noise ratio;

[0037] Based on the frame-level average signal-to-noise ratio, the signal-to-noise ratio of the current link is determined.

[0038] Further, the ambient noise level of the current link is estimated based on the signal frame received by the receiving end, specifically including:

[0039] The propagation loss of the acoustic link is established by the passive sonar equation, expressed as:

[0040]

[0041] wherein, the propagation loss, the frame-level average signal-to-noise ratio, the initial transmitted sound source level, unit , the receiver directivity gain;

[0042] NL the ambient noise level, expressed as:

[0043]

[0044] wherein, the noise power, , the time domain sampling points collected by the receiving end, the time domain sampling points, the time domain sampling points, the received signal sequence.

[0045] Further, the required transmitted sound power is calculated based on the preset target signal-to-noise ratio constraint condition, specifically including:

[0046] Based on the preset target signal-to-noise ratio, the target sound source level is calculated, expressed as:

[0047]

[0048] wherein, is a target sound source level, is a target signal-to-noise ratio;

[0049] Based on the required transmitting sound power is calculated, and the expression is:

[0050]

[0051] wherein, is the transmitting sound power.

[0052] Further, the transmitting sound power is mapped to the closest level in a discrete power level set, specifically including:

[0053] Based on the discrete power adaptive strategy of the limited levels, it is judged whether the transmitting sound power is an integer level, if yes, it is directly selected, if not, it is rounded up to the closest power level.

[0054] Further, the receiving end embeds the power level indication information into an acknowledgement data packet and feeds back to the transmitting end through a reverse data link, specifically including:

[0055] The power level indication information is encoded as a level code of a preset bit field, a data packet is generated, the level code is written in a reserved field of the data packet to generate an acknowledgement data packet, and the acknowledgement data packet is sent to the receiving end through the reverse data link.

[0056] Compared with the prior art, the beneficial effects of the present application are:

[0057] The power control method based on MMSE signal-to-noise ratio estimation provided by the present application introduces pilot subcarriers in the link establishment stage to provide initial channel references for both the transmitting end and the receiving end; the MMSE signal-to-noise ratio estimation separates the channel and the noise, so that the subsequent power calculation is based on quantifiable signal-to-noise ratio references, avoiding setting too high or too low power due to insufficient information; the continuous power requirement is mapped to discrete levels, converting complex analog adjustment into limited digital selection, reducing the implementation difficulty and control overhead; the reverse acknowledgement frame carries the level information, multiplexing the existing data link, without additional control channel to complete the closed-loop feedback; the transmitting end can configure the power according to the specified level after analyzing the acknowledgement frame, so that each power adjustment directly corresponds to the channel state change, reducing energy waste and maintaining the stability of the link. The present application periodically senses the link quality, selects the optimal transmitting power level according to the distance and channel state between nodes, ensures the reachability of the communication link, and effectively reduces the energy consumption in the node communication process. BRIEF DESCRIPTION OF DRAWINGS

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained based on the provided drawings without creative labor.

[0059] Figure 1 The flowchart of the power control method based on MMSE signal-to-noise ratio estimation provided by the embodiment of the present application is shown. DETAILED DESCRIPTION

[0060] The present application will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, and not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, not all the structures.

[0061] REFERENCE Figure 1 The embodiment provides a power control method based on MMSE signal-to-noise ratio estimation, which comprises the following steps:

[0062] S11, in the communication link establishment stage, the transmitting end sends a signal frame containing a pilot subcarrier to the receiving end.

[0063] S12, based on the signal frame received by the receiving end, the signal-to-noise ratio and the environmental noise level of the current link are estimated, and the required transmitting sound power is calculated based on the preset target signal-to-noise ratio constraint.

[0064] S13, the receiving end maps the transmitting sound power value to the closest gear in the discrete power gear set, and generates power gear indication information.

[0065] S14, the receiving end embeds the power gear indication information into the confirmation data packet through the reverse data link and feeds back to the transmitting end.

[0066] In the embodiment, in the OFDM system based on the comb-shaped pilot structure, in order to realize more accurate link quality evaluation, the initial least squares (LS) estimation at the frequency domain pilot subcarrier is used, the channel estimation value on all subcarriers is recovered through the MMSE interpolation method, and the average signal-to-noise ratio is calculated on this basis.

[0067] During the communication link establishment phase, the transmitter is completely unaware of the channel state before the link is established. It completes the initial power configuration using the tiered power control method under MMSE signal-to-noise ratio estimation. The transmitter first sends a signal frame containing pilot subcarriers. The receiver uses the MMSE principle to perform minimum mean square error estimation on the current channel to obtain the signal-to-noise ratio and ambient noise level of the current link. Under the preset target signal-to-noise ratio constraint, it back-calculates the minimum transmit acoustic power that just meets the communication quality requirements. Subsequently, the transmit acoustic power is mapped to the closest tier in the set of discrete power tiers supported by the hardware, generating the corresponding power tier indication information. This indication is then embedded into the acknowledgment data packet and fed back to the transmitter via the reverse data link.

[0068] In a preferred embodiment, the transmitting end sends a signal frame containing pilot subcarriers to the receiving end, specifically including:

[0069] The signal frame to be transmitted at the transmitting end is channel-coded and phase-mapped, then modulated onto... On each OFDM symbol, there are 1 OFDM symbol. Subcarriers;

[0070] For each OFDM symbol in the signal frame to be transmitted, a corresponding transmission vector is generated according to a preset mapping. A transmission matrix is ​​then constructed using these transmission vectors, with the following expression:

[0071]

[0072] in, For the transmission matrix, For the transmission vector, For the complex field, each transmission vector , m For the first m One OFDM symbol;

[0073] The expression for the receiver vector at the receiving end is:

[0074]

[0075] in, For the receive vector, For Hadamard product, For the channel frequency domain response, , It is additive white Gaussian noise. , () is the normal distribution function. For noise variance, It is an identity matrix.

[0076] In the embodiment, the transmitting end sends a signal frame containing pilot subcarriers in the link establishment stage, and provides the receiving end with known symbol sequences without any prior information. The receiving end directly calculates the channel gain and noise power by using the symbols, and obtains an initial signal-to-noise ratio estimation value, which lays a quantifiable and reproducible benchmark for the subsequent power control algorithm, and avoids blindly setting the transmitting power.

[0077] As a preferred embodiment, the signal-to-noise ratio of the current link is estimated based on the signal frame received by the receiving end, and specifically includes:

[0078] The pilot subcarriers in the OFDM symbol in the received signal frame are collectively denoted as F The pilot subcarriers are sampled by a preset rule to obtain the channel response at the pilot position, and the expression is:

[0079]

[0080] Among them, is the channel estimation based on least squares, is the pilot-related component, () is the received vector, () is the transmitted vector;

[0081] Based on the MMSE principle, the channel estimation expression of the pilot subcarrier set is:

[0082]

[0083] Among them, is the channel estimation on all subcarriers, is the covariance matrix between the complete subcarriers and the pilot position, , is the covariance matrix of the pilot position, ;

[0084] Based on the results of the channel estimation, the MMSE signal-to-noise ratio of each OFDM symbol is calculated, and the expression is:

[0085]

[0086] Among them, is the MMSE signal-to-noise ratio, is the subcarrier, is the th symbol, and the received vector of the k th subcarrier, is the MMSE channel estimation value of the m th symbol and the k th subcarrier, is the m th symbol, and thek a transmit vector of the subcarriers;

[0087] Based on the MMSE signal-to-noise ratio, a sliding window average is performed on the continuous M OFDM symbols to obtain a frame-level average signal-to-noise ratio, expressed as:

[0088]

[0089] wherein, is the frame-level average signal-to-noise ratio;

[0090] The signal-to-noise ratio of the current link is determined based on the frame-level average signal-to-noise ratio.

[0091] In this embodiment, the estimation is made through the pilot subcarriers in the OFDM symbol to avoid occupying unknown data bits, and the measurement is completed in the first frame, without relying on prior traffic. The pilot subcarriers are sampled through a preset rule to reduce the amount of calculation, while keeping the frequency domain sampling interval less than the coherence bandwidth to prevent loss of channel details. The MMSE principle is used to make channel estimation on the sampling points to give a frequency response value with the smallest variance under unknown noise and interference statistics, and to suppress the Gaussian noise amplification effect. After the MMSE signal-to-noise ratio is calculated for each OFDM symbol, a sliding window average is performed on the continuous OFDM symbols to smooth the burst pulse noise and retain the channel time-varying trend, and a stable frame-level average signal-to-noise ratio is obtained. The frame-level average signal-to-noise ratio is a (power-weighted) sample mean of the instantaneous in a frame, and can approximately represent the actual in a flat / slowly selective channel. The signal-to-noise ratio of the current link is determined through the frame-level average signal-to-noise ratio, which provides a single, stable and directly related metric for the actual error performance for subsequent power control, and avoids frequent power command jumps caused by instantaneous jitter.

[0092] Specifically, when the moving speed of the mobile node in the research scenario is about 1 kn. Therefore, the frame-level average signal-to-noise ratio approximately represents the signal-to-noise ratio of the current link, i.e., the actual SNR , which is used for power control and routing decision to achieve the trade-off optimization of energy efficiency and reliability in underwater acoustic communication. To ensure the actual SNR of the receiving end, the preset target signal-to-noise ratio is met, i.e., the target SNR is reached, so the transmission data can be successfully decoded, and it is necessary to dynamically adjust the transmission power according to the underwater propagation characteristics.

[0093] As a preferred embodiment, the environmental noise level of the current link is estimated based on the signal frame received by the receiving end, specifically including:

[0094] The propagation loss of the acoustic link is established through the passive sonar equation, expressed as:

[0095]

[0096] wherein, is the propagation loss, is the frame level average signal to noise ratio, is the initial transmitted sound source level, unit , is the receiver directivity gain;

[0097] NL is the ambient noise level, expressed as:

[0098]

[0099] wherein, is the noise power, , is the received time domain sampling points, is the time domain sampling point, is the received signal sequence.

[0100] In the embodiment, the propagation loss is calculated by the passive sonar equation, and the receiver only uses the existing pilot frame to solve, which saves energy and avoids interfering with other nodes. After separating the propagation loss from the total attenuation, the remaining term is the ambient noise level, which can directly correspond to the real noise floor at the receiving point at that time, eliminating the estimation bias introduced by hardware parameters such as transmission level and transducer gain. The obtained ambient noise level and signal-to-noise ratio appear in pairs within the same measurement period, providing a data basis for subsequent calculation of the required transmission sound power through the target signal-to-noise ratio, simplifying the power control algorithm. Since the passive sonar equation only depends on the distance and known frequency, the calculation result is not sensitive to channel fluctuations, which can provide a stable baseline decoupled from instantaneous fading for power level selection, preventing excessive transmission power due to mistaking deep fading as high noise.

[0101] Specifically, the calculation of the noise power is based on the noise power statistical method of the measured data. The receiver samples in the period without signal transmission, and the received signal sequence only contains background noise components.

[0102] As a preferred embodiment, the required transmission sound power is calculated based on a preset target signal-to-noise ratio constraint condition, specifically including:

[0103] Based on the preset target signal-to-noise ratio, the target sound source level is calculated, expressed as:

[0104]

[0105] wherein, is the target sound source level, is the target signal-to-noise ratio;

[0106] Based on The required transmitting acoustic power is calculated, and the expression is:

[0107]

[0108] Wherein, is the transmitting acoustic power.

[0109] In this embodiment, the target signal-to-noise ratio is taken as a hard constraint, and the target sound source level required to meet the index is first back calculated, and then the sound source level is converted into the required transmitting acoustic power. The communication quality requirement is quantified into a double index of acoustic caliber and electrical caliber at one time, which ensures that the power value directly corresponds to the link reachability threshold and leaves a compensation margin for the transducer electro-acoustic conversion efficiency, avoiding repeated iterations caused by calculating the electrical power first and then verifying whether it meets the SNR , so that the transmitting energy just enough can be given at one time in the initial chain building stage.

[0110] As a preferred embodiment, the transmitting acoustic power is mapped to the closest power level in the set of discrete power levels, which specifically includes:

[0111] Based on the discrete power adaptive strategy of limited levels, it is judged whether the transmitting acoustic power is an integer level, if yes, it is directly selected, if not, it is rounded up to the closest power level.

[0112] In this embodiment, the calculated continuous transmitting acoustic power is mapped according to the discrete power adaptive strategy of limited levels, which ensures that the power value corresponds to the quantized level actually output by the transmitter hardware, avoids the calibration complexity and temperature drift error caused by analog continuous adjustment, and the rounding up strategy ensures that the output sound level is not lower than the minimum value required by the link, so that the preset target signal-to-noise ratio is not broken through under the most simple hardware implementation, and the energy efficiency and communication reliability are considered.

[0113] Specifically, considering the complexity and energy efficiency constraints of engineering implementation, the discrete power adaptive strategy of limited levels is adopted, which, after estimating the required transmitting power, directly selects the result if it is an integer level, and rounds it up to the closest power level if it is a decimal. Table 1 lists the actual transmitting power values of the underwater acoustic communication machine under different volume settings, that is, the closest level to the estimated value is selected for transmission, which effectively simplifies the power control hardware logic and modulation system complexity while ensuring that the actual SNR of each communication link is not lower than the set threshold.

[0114] Table 1 Transmitting power corresponding to different volumes of underwater acoustic communication machine

[0115]

[0116] As a preferred embodiment, the receiving end embeds the power level indication information into an acknowledgement data packet and feeds back to the transmitting end through a reverse data link, specifically including:

[0117] The power level indication information is encoded into a level code of a preset bit field, a data packet is generated, the level code is written in a reserved field of the data packet, an acknowledgement data packet is generated, and the acknowledgement data packet is sent to the receiving end through a reverse data link.

[0118] In the embodiment, the power level indication information is encoded into a level code of a fixed length and filled into a reserved field of an acknowledgement data packet, and piggyback transmission is completed by using an ACK frame which must be returned by a link layer, without building a new control message or contending for an additional channel, so that frame format compatibility is maintained, the overhead of closed-loop power control is compressed to several bits, and fast feedback is realized under zero additional energy consumption and zero additional bandwidth.

[0119] The above only describes preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of power control based on MMSE signal-to-noise ratio estimation, characterized in that, The method comprises: S11, in the communication link establishment stage, the transmitting end sends a signal frame containing a pilot subcarrier to the receiving end, specifically comprising: The signal frame to be sent by the sending end is modulated to OFDM symbols after channel coding and phase mapping, each of the OFDM symbols contains subcarriers. For each OFDM symbol in the to-be-transmitted signal frame, a corresponding transmission vector is generated according to a preset mapping, and a transmission matrix is constructed through the transmission vector, and the expression is: Where X is the transmission matrix. For the transmission vector, For the complex field, each transmission vector , m For the first m One OFDM symbol; The expression of the receiving vector of the receiving end is: wherein is a channel frequency domain response, , is a received vector, is a Hadamard product, is an additive a Gaussian white noise, , is a normal distribution function, is a noise variance, is an identity matrix; S12, based on the signal frame received by the receiving end, the signal-to-noise ratio of the current link and the ambient noise level are estimated, and the required transmitting sound power is calculated based on the preset target signal-to-noise ratio constraint; Estimate the signal-to-noise ratio of the current link based on the signal frame received by the receiving end, specifically comprising: The pilot sub-carrier set in the OFDM symbol in the received signal frame is denoted as F The channel response at the pilot position is obtained by sampling the pilot sub-carrier set according to a preset rule, and is expressed as: wherein is a least squares based channel estimate, is a pilot related component, is a receive vector, is a transmit vector; Based on the MMSE principle, the channel estimation expression of the pilot subcarrier set is obtained as: wherein is the channel estimate over all subcarriers, is the covariance matrix between the complete subcarriers and the pilot positions, , is the covariance matrix of the pilot positions, ; Based on the results of channel estimation, the MMSE signal-to-noise ratio of each OFDM symbol is calculated, and the expression is: wherein is the MMSE signal-to-noise ratio, is the subcarrier, is the received vector for the th symbol, the k th subcarrier, is the MMSE channel estimate for the m th symbol, the k th subcarrier, is the transmitted vector for the m th symbol, the k th subcarrier; Based on the MMSE SNR, a sliding window average is performed on the consecutive M OFDM symbols to obtain a frame-level average SNR, expressed as: wherein, Sf is the frame level average signal to noise ratio; Determine the signal-to-noise ratio of the current link based on the frame-level average signal-to-noise ratio; Estimate the ambient noise level of the current link based on the signal frame received by the receiving end, specifically comprising: Establish the propagation loss of the acoustic link through the passive sonar equation, and the expression is: wherein, is the propagation loss, is the frame level average signal to noise ratio, is the initial transmitted sound source level in dB, , is the receiver directivity gain; NL For the ambient noise level, the expression is: wherein, is the noise power, , is the received signal sequence, is the number of time domain sample points, is the time domain sample point, is the received signal sequence; Calculate the required transmitting sound power based on the preset target signal-to-noise ratio constraint, specifically comprising: Based on the preset target signal-to-noise ratio, the target sound source level is calculated, and the expression is: wherein, is a target sound source level, is a target signal-to-noise ratio; Based on The required transmit acoustic power is calculated, expressed as: wherein P is the transmitted acoustic power; S13, the receiving end maps the transmitting sound power value to the closest gear in the discrete power gear set to generate power gear indication information; S14, the receiving end embeds the power gear indication information into the confirmation data packet through the reverse data link and feeds back to the transmitting end.

2. The method of claim 1, wherein the step of estimating the power level is performed by using a MMSE signal-to-noise ratio (SNR) estimation. Map the transmitting sound power to the closest gear in the discrete power gear set, specifically comprising: Based on the discrete power adaptive strategy of the limited gears, it is judged whether the transmitting sound power is an integer gear, if yes, it is directly selected, if not, it is rounded up to the closest power gear.

3. The method of claim 1, wherein the step of determining the power level is performed by a step of: determining the power level based on a MMSE signal-to-noise ratio estimate. The receiving end embeds the power gear indication information into the confirmation data packet through the reverse data link and feeds back to the transmitting end, specifically comprising: Encode the power gear indication information into the gear code of the preset bit field to generate a data packet, write the gear code in the reserved field of the data packet to generate a confirmation data packet, and send the confirmation data packet to the receiving end through the reverse data link.

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