A dual-weighted phase error tracking method and system in OFDM systems

Abstract

This invention discloses a phase error tracking method and system based on dual weighting in OFDM systems, belonging to the field of wireless communication system technology. This application introduces a dual weighting mechanism to simultaneously evaluate and utilize static reference quality weights and dynamic measurement quality weights, thereby obtaining a more accurate estimate of channel phase error and significantly improving the performance of the communication system in harsh channel environments. Compared with the prior art, this application not only considers the quality of real-time measurement, but also incorporates the "historical" quality of the reference information used as the measurement benchmark, making the weight evaluation more comprehensive and accurate. It can effectively suppress the systematic bias introduced by the weights and prevent the propagation and contamination of errors throughout the entire data packet processing process. Moreover, in complex multipath channels, the dual weighting mechanism of this application can accurately identify and "ignore" continuously unreliable information sources, greatly enhancing the survivability of the system in harsh environments.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication system technology, specifically relating to a phase error tracking method and system based on dual weighting in OFDM systems. Background Technology

[0002] In wireless communication systems, especially those employing orthogonal frequency division multiplexing (OFDM) technology, such as high-definition digital image transmission for drones, the receiver needs to accurately track channel phase changes caused by carrier frequency offset (CFO), oscillator phase noise, and other factors.

[0003] Existing phase tracking techniques typically use a high-energy preamble (such as the Long Training Symbol, LTS in the 802.11 standard) at the beginning of the data packet to obtain initial, full-band channel state information (CSI). Subsequently, during the data transmission phase, sparse comb pilots embedded in the data are used to track the dynamic changes of the channel in real time.

[0004] A common tracking method involves calculating the phase of the pilot in each data symbol, comparing it to the phase of the corresponding pilot in the preamble to obtain the phase difference, and then estimating the common phase error (CPE) and the phase ramp caused by inter-carrier interference (ICI) by linearly fitting these phase differences (e.g., weighted least squares). In traditional weighted least squares (WLS) applications, to improve fitting accuracy, different weights are typically assigned to the pilots in the current data symbol based on their signal strength (e.g., amplitude or power). The basic idea is that pilots with high signal strength have a higher signal-to-noise ratio (SNR) and their measured phase is more reliable, therefore they should have a larger weight in the fitting; conversely, pilots with low signal strength should be given a lower weight.

[0005] However, existing technology has a critical flaw: it only considers the "real-time quality of the current measurement" while completely ignoring the "inherent quality of the reference information" used as a comparison benchmark. Specifically, if a pilot subcarrier used to establish the reference benchmark happens to fall into a deep fading point during the preamble stage, then this reference benchmark itself is "noisy" or "unreliable." All subsequent phase differences calculated based on this "noisy" or "unreliable" benchmark will carry an inherent, systematic bias, regardless of how good the pilot signal quality of the current data symbol is. This bias contaminates the entire phase tracking loop, reducing the system's demodulation performance and robustness, especially in complex multipath fading channels. Summary of the Invention

[0006] To address the problems mentioned in the background art, this invention provides a phase error tracking method and system based on dual weighting in OFDM systems. This solves the problem that existing technologies only consider the "real-time quality of the current measurement" while completely ignoring the "inherent quality of the reference information" used as a comparison benchmark. This leads to deviations in the reference benchmark contaminating the entire phase tracking loop and reducing the demodulation performance and robustness of the system.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A phase error tracking method based on dual weighting in an OFDM system includes the following steps:

[0009] S1: The receiver processes the preamble of the data packet and generates and stores the static reference quality weights related to the initial channel estimation based on the preset pilot subcarrier positions;

[0010] S2: For each OFDM data symbol in the data packet, generate dynamic measurement quality weights based on the real-time measurement values ​​of the pilot subcarrier positions preset in S1;

[0011] S3: Combine the static reference quality weight and the dynamic measurement quality weight to form a dual weighting factor. Based on the dual weighting factor, estimate the phase difference of the pilot subcarrier, and use the phase error estimation result for phase correction and equalization of OFDM data symbols.

[0012] Preferably, S1 specifically includes the following steps:

[0013] S1.1: Calculate the initial channel frequency response Hintial(k) across the entire frequency band by processing the preamble of the data packets using the receiver;

[0014] S1.2: For the preset N pilot subcarrier positions kp, extract their initial channel estimate value Hintial(kp);

[0015] S1.3: Based on the reliability of the N initial channel estimates Hintial(kp), calculate and generate N one-to-one static reference quality weights wLTF(kp) and store them in the receiver's memory.

[0016] Preferably, the reliability of the initial channel estimate is determined by its power |Hinitial(kp)| 2 Sure.

[0017] Preferably, S2 specifically includes the following steps:

[0018] S2.1: For the m-th OFDM data symbol in the data packet, N complex measurement values ​​Ypilot(kp,m) are measured at each pilot subcarrier position kp;

[0019] S2.2: Based on the reliability of the complex measurement value Ypilot(kp,m), calculate and generate N dynamic measurement quality weights wdata(kp,m).

[0020] Preferably, the reliability of real-time complex measurements is determined by their power |Ypilot(kp,m)| 2 Sure.

[0021] Preferably, S3 specifically includes the following steps:

[0022] S3.1: For each pilot subcarrier position kp, a final, double-weighted weighting factor wfinal(kp,m) is calculated by combining its corresponding static reference quality weight and dynamic measurement quality weight.

[0023] S3.2: Calculate the real-time phase difference PhaseError(kp,m) of each pilot subcarrier position kp relative to the initial reference reference;

[0024] S3.3: Use weighted least squares (WLS) to linearly fit N real-time phase differences to estimate the common phase error and phase slope of the current symbol. The weights used in the weighted least squares (WLS) fitting are weight factors wfinal(kp,m).

[0025] S3.4: Use the estimated common phase error and phase ramp to perform phase correction and equalization on the current data symbols.

[0026] A phase error tracking system based on dual weighting in an OFDM system is characterized by comprising a storage unit for storing static reference quality weights, a weight generation unit for calculating dynamic measurement quality weights, a weight merging unit for combining static reference quality weights and dynamic measurement quality weights, and a WLS solver unit for performing linear fitting, wherein the storage unit and the weight generation unit are both connected to the weight merging unit, and the weight merging unit is connected to the WLS solver unit.

[0027] Preferably, the weight generation unit includes a multi-level comparator, and the weight merging unit includes a barrel shifter.

[0028] Preferably, the WLS solver unit includes a reciprocal lookup table (LUT) and a hardware multiplier.

[0029] Preferably, the address of the inverse lookup table (LUT) is composed of the validity indicator bit of each pilot subcarrier and the weight value of the weighting factor.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] This application introduces a dual-weighting mechanism that simultaneously evaluates and utilizes static reference quality weights and dynamic measurement quality weights to obtain a more accurate estimate of channel phase error, significantly improving the performance of the communication system in harsh channel environments. Compared with existing technologies, this application not only considers the quality of real-time measurements but also incorporates the "historical" quality of the reference information used as the measurement benchmark, making the weight evaluation more comprehensive and accurate. This application can effectively suppress the systematic biases it introduces, preventing the propagation and contamination of errors throughout the entire data packet processing process. Furthermore, in complex multipath channels, the dual-weighting mechanism of this application can accurately identify and "ignore" persistently unreliable information sources, enabling the system to rely on other reliable pilots for robust tracking, greatly enhancing the system's survivability in harsh environments. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the basic framework of an OFDM receiver system;

[0033] Figure 2 This is a flowchart illustrating the process of this application. Detailed Implementation

[0034] To facilitate understanding of the technical content of this invention by those skilled in the art, the invention will be further described in detail below with reference to the accompanying drawings and specific examples. It should be understood that the specific examples described herein are merely illustrative and not intended to limit the scope of the invention.

[0035] like Figure 1 As shown, in an OFDM receiver system, a phase error tracking system based on dual weighting is set between the demultiplexer and the channel corrector.

[0036] The phase error tracking system includes a storage unit for storing static reference quality weights, a weight generation unit for calculating dynamic measurement quality weights, a weight merging unit for combining static reference quality weights and dynamic measurement quality weights, and a WLS solver unit for performing linear fitting. The storage unit and the weight generation unit are both connected to the weight merging unit, which in turn is connected to the WLS solver unit. The weight generation unit includes a multi-stage comparator for quantizing the real-time signal amplitude into weight values ​​that are powers of 2. The weight merging unit includes a barrel shifter for multiplying the static weights with the quantized dynamic weights. The WLS solver unit includes a reciprocal lookup table (LUT) and a hardware multiplier to replace the common division operation. The address of the reciprocal lookup table (LUT) is composed of the validity indicator bit of each pilot and the quantized weight value to clearly distinguish between zero and non-zero weights.

[0037] like Figure 2 As shown, a phase error tracking method based on dual weighting in an OFDM system includes the following steps:

[0038] S1: Initial channel estimation and static weight generation (preamble processing stage);

[0039] The receiver performs time-domain averaging on the two long training symbols (LTS1, LTS2) of the preamble, and then performs time-domain truncation and denoising on the averaged result (through the IFFT->truncation->FFT process) to obtain a high-precision initial channel estimate, Hintial(k). The control unit extracts the complex values ​​Hintial(kp) at four preset pilot positions and uses the CORDIC IP core to calculate the square of the amplitude of these four complex values, i.e., power |Hinitial(kp)|. 2 The four power values ​​are normalized, and the result is quantized into an M-bit fixed-point number, which is then stored as a static weight wLTF in a dedicated register set.

[0040] S2: Data symbol processing and double weighting (data symbol processing stage);

[0041] For each subsequent OFDM data symbol, perform the following pipeline operation:

[0042] (1) Real-time phase and amplitude extraction: The complex values ​​Ypilot(kp,m) on the four pilot subcarriers are fed into four parallel CORDIC IP cores. Each core simultaneously outputs the real-time amplitude Amppilot(kp,m) and the real-time phase PhaseError(kp,m).

[0043] (2) Calculation of dynamic measurement quality weight wdata(kp,m): The real-time amplitude Amppilot output by CORDIC is sent to a multi-level comparator. According to the preset amplitude threshold, the dynamic weight wdata is quantized into several integer powers of 2 (e.g., 1, 2, 4).

[0044] (3) Calculation of real-time phase error: The real-time phase error (kp,m) is calculated by using a complex multiplier (Ypilot⋅conj(Hinitial)) or a phase subtractor.

[0045] (4) Calculation of final weight wfinal: Read the static weight wLTF(kp) from the register and multiply it efficiently with wdata(kp,m) through a barrel shifter, i.e. wfinal=wLTF≪log2(wdata).

[0046] S3: High-precision WLS solution;

[0047] Weighted sum calculation: PhaseError and wfinal are fed into the WLS solver unit, which uses logic shifters and a pipelined addition tree to calculate the five weighted sum terms required by the WLS formula.

[0048] Solving for A and B: To avoid using a high-latency general-purpose divider, this embodiment employs a reciprocal lookup table (LUT) method. A lookup table stored in BRAM / ROM pre-stores the fixed-point values ​​of 1 / Denominator corresponding to all possible weight combinations. Through a lookup table plus a single hardware multiplier (DSP Slice) operation, the common phase error A (CPE) and phase ramp B (ICI) of the current symbol are efficiently calculated.

[0049] Phase correction: The solved A and B are sent to the channel corrector for phase correction of the current data symbols before equalization.

[0050] This application provides a more accurate and robust OFDM channel phase error tracking method. This method introduces a dual-weighting mechanism, simultaneously evaluating and utilizing both the "inherent quality of the reference standard" and the "real-time quality of the current measurement," thereby obtaining a more accurate estimate of the channel phase error and significantly improving the performance of the communication system in harsh channel environments. Compared with existing technologies, this invention has the following significant advantages:

[0051] Comprehensive assessment of information reliability: This invention creatively proposes and implements a dual weighting mechanism that not only considers the quality of real-time measurements, but also incorporates the "historical" quality of the reference information used as the measurement benchmark, making the weight assessment more comprehensive and accurate.

[0052] Suppressing systematic bias: By permanently deweighting the "bad" reference reference from the deep fading region, this invention can effectively suppress the systematic bias it introduces, preventing the propagation and contamination of errors throughout the packet processing process.

[0053] Enhanced system robustness: In complex multipath channels, the dual weighting mechanism of this invention can accurately identify and “ignore” persistently unreliable information sources, enabling the system to rely on other reliable pilots for robust tracking, greatly enhancing the system’s survivability in harsh environments.

[0054] Improved receiver sensitivity: More accurate phase error estimation directly translates to better error vector amplitude (EVM) and bit error rate (BER) performance, thereby statistically improving the overall sensitivity of the receiver.

[0055] Simple to implement and low cost: The core innovation of this invention lies in the algorithm level. Its hardware implementation only requires a very small increase in storage and computing resources. Compared with the complexity of the entire communication system, the cost is almost negligible, but the performance improvement is significant.

Claims

1. A phase error tracking method based on dual weighting in an OFDM system, characterized in that, Includes the following steps: S1: The receiver processes the preamble of the data packet and generates and stores the static reference quality weights related to the initial channel estimation based on the preset pilot subcarrier positions; Specifically, the following steps are included: S1.1: Calculate the initial channel frequency response across the entire frequency band by processing the preamble of the data packets using the receiver. H initial( k ); S1.2: For the preset N pilot subcarrier positions kp Extract its initial channel estimate. H initial( kp ); S1.3: Based on N initial channel estimates H initial( kp To assess the reliability of the data, N static reference quality weights are generated, each corresponding to a specific value. w LTF ( kp And store it in the receiver's memory; S2: For each OFDM data symbol in the data packet, generate dynamic measurement quality weights based on the real-time measurement values ​​of the pilot subcarrier positions preset in S1; specifically including the following steps: S2.1: For the m-th OFDM data symbol in the data packet, at each pilot subcarrier position kp Above, N complex measurement values ​​were obtained. Y pilot kp , m ); S2.2: Based on complex measurement values Y pilot kp , m To assess the reliability of the measurement quality, calculate and generate N dynamic measurement quality weights. w data kp , m ); S3: Combine the static reference quality weight and the dynamic measurement quality weight to form a dual weighting factor. Based on the dual weighting factor, estimate the phase difference of the pilot subcarriers, and use the phase error estimation result for phase correction and equalization of OFDM data symbols; specifically including the following steps: S3.1: For each pilot subcarrier position kp By combining the corresponding static reference quality weights and dynamic measurement quality weights, a final, doubly weighted weighting factor is calculated. w final( kp , m ); S3.2: Calculate the position of each pilot subcarrier kp Real-time phase difference relative to the initial reference (PhaseError) kp , m ); S3.3: Using Weighted Least Squares (WLS), a linear fit is performed on the N real-time phase differences to estimate the common phase error and phase slope of the current symbol. The weights used in the WLS fitting are weighting factors. w final( kp , m ); S3.4: Perform phase correction and equalization on the current OFDM data symbols using the estimated common phase error and phase slope.

2. The phase error tracking method according to claim 1, characterized in that, The reliability of the initial channel estimate is determined by its power | H initial( kp )∣ 2 Sure.

3. The phase error tracking method according to claim 1, characterized in that, The reliability of real-time complex measurements is determined by their power | Y pilot kp , m )∣ 2 Sure.

4. A phase error tracking system based on dual weighting in an OFDM system, used to implement the phase error tracking method according to any one of claims 1-3, characterized in that, It includes a storage unit for storing static reference quality weights, a weight generation unit for calculating dynamic measurement quality weights, a weight merging unit for combining static reference quality weights and dynamic measurement quality weights, and a WLS solver unit for performing linear fitting. The storage unit and the weight generation unit are both connected to the weight merging unit, and the weight merging unit is connected to the WLS solver unit.

5. The phase error tracking system according to claim 4, characterized in that, The weight generation unit includes a multi-stage comparator, and the weight merging unit includes a barrel shifter.

6. The phase error tracking system according to claim 5, characterized in that, The WLS solver unit includes a reciprocal lookup table (LUT) and a hardware multiplier.

7. The phase error tracking system according to claim 6, characterized in that, The address of the inverse lookup table (LUT) is composed of the validity indicator bit of each pilot subcarrier and the weight value of the weighting factor.

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