Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth such as the particular system architecture, techniques, etc., in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
It should be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should also be understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.
As used in the present description and the appended claims, the term "if" may be interpreted as "when..once" or "in response to a determination" or "in response to detection" depending on the context. Similarly, the phrase "if a determination" or "if a [ described condition or event ] is detected" may be interpreted in the context of meaning "upon determination" or "in response to determination" or "upon detection of a [ described condition or event ]" or "in response to detection of a [ described condition or event ]".
Furthermore, the terms "first," "second," "third," and the like in the description of the present specification and in the appended claims, are used for distinguishing between descriptions and not necessarily for indicating or implying a relative importance.
Reference in the specification to "one embodiment" or "some embodiments" or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the invention. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," and the like in the specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments" unless expressly specified otherwise. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless expressly specified otherwise.
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
Fig. 1 shows a flowchart of an implementation of a low-orbit satellite communication bit timing method based on angle synthesis according to an embodiment of the present invention. By way of example and not limitation, the method may include steps S101-S104, each of which is described below.
S101, extracting the offset information of the current code element of the input signal according to the power of the input signal to obtain the offset angle representation value of the current code element.
In one possible implementation, the offset complex representation value of the current symbol may be determined according to the power of the input signal and the quantized vector of the current symbol, and then the offset complex representation value of the current symbol may be smoothly integrated and angle synthesized to obtain the offset angle representation value of the current symbol.
Illustratively, the offset complex representation value of the current symbol may satisfy the following equation:
θ=angle(α)(1.1)
θ is the offset angle representation value of the current code element, and α is the smoothing result of the current code element;
Wherein the smoothing result of the m+1th symbol satisfies the following formula:
α(m+1)=(temp(m+1)-α(m))/δ+α(m)(1.2)
delta is a smoothing coefficient, the general value is the power of 2, the hardware is convenient to realize, alpha (m+1) is the smoothing processing result of the (m+1) th code element, temp (m+1) is the offset complex representation value of the (m+1) th code element, and angle is the complex angle function.
Specifically, the angle function may be directly called in the software code or a coordinate rotation digital computing (Coordinate Rotation Digital Computer, cordic) algorithm implementation may be selected in hardware.
In one example, the input signal may be two complex signals I (m) and Q (m), and the instantaneous power of the input signal may be obtained through the square sum of the amplitudes, so as to reject the information carried by the signal.
Illustratively, the power of the mth symbol of the input signal may satisfy the following equation:
P(m)=I(m)2+Q(m)2(1.3)
Wherein P (m) is the mth symbol of the input signal.
In one example, a quantization interval can be generated according to the number n of samples per symbol, then a quantization vector is combined according to the quantization interval, a unit complex value of the quantization vector is solved through an Euler formula, and finally an inner product of the unit complex value of the quantization vector and the instantaneous power of the last symbol is made to obtain an offset complex representation value of the current symbol.
Illustratively, the quantization interval, the quantization vector, and the unit complex value of the quantization vector, i.e., the offset complex token value, may each satisfy the following formulas:
gap=2π/n(1.4)
Wherein gap is, The unit complex values of the quantization interval, the quantization vector and the quantization vector are respectively, temp (m) is the offset complex representation value of the mth code element, and P (m-1) is the instantaneous power of the mth-1 code element.
S102, correcting the offset angle representation value of the current code element through the offset angle representation value of the last code element so as to expand the sampling space to obtain the corrected offset angle representation value of the current code element.
Illustratively, the sampling space is a selectable space of sampling points.
In one possible implementation, the offset angle representation value of the current symbol may be subjected to secondary processing by using the difference between the offset angle representation values of two adjacent symbols (i.e., the adjacent angle difference) as a judgment condition, so as to ensure the stability and accuracy of the offset.
In one example, a plurality of correction preset ranges may be preset, and a corresponding preset correction value is configured for each correction preset range. When correcting the representation value of the offset angle, the difference between the representation value of the offset angle of the last code element and the representation value of the offset angle of the current code element can be firstly determined to obtain the adjacent angle difference, then the first preset range of the adjacent angle difference is determined, and finally the preset correction value corresponding to the first preset range is added or subtracted on the representation value of the offset angle of the current code element or the representation value of the offset angle of the last code element according to the positive and negative of the adjacent angle difference to obtain the corrected representation value of the offset angle of the current code element.
For example, if 4 correction preset ranges are preset, the correction preset ranges may be denoted as #1, #2, #3 and #4 in order of the size of the range boundary. The range #1 is a normal range, and if the adjacent angle difference is within the range #1, the offset angle representation value of the current symbol may be directly output as the corrected offset angle representation value of the current symbol without processing the offset angle representation value.
If the adjacent angle difference is in #2 or #4, the corrected offset angle representation value of the (m+1) th symbol can be obtained by adding or subtracting the preset correction value corresponding to #2 or #4 from the adjacent angle difference on the offset angle representation value θ (m) of the (m) th symbol.
If the adjacent angle difference is within #3, a preset correction value corresponding to #3 can be added or subtracted on θ (m) according to the adjacent angle difference, so as to obtain a corrected offset angle representation value of the (m+1) th code element.
S103, fitting the sampling center of the current code element through the corrected offset angle representation value.
In one possible implementation, the sampled fit interval may be determined prior to determining the sampling center.
In one example, the fit interval may include a plurality of consecutive symbol data, and the current symbol is not the first or last symbol of the fit interval.
In one possible implementation, after determining the fit interval, the sampling center of the current symbol may be determined, followed by step S104, described below, of selecting a sampling space by the value of the sampling center.
In one example, a difference between the first predetermined angle and the corrected offset angle characterization value may be determined to obtain a first predetermined angle difference, and a quotient of the first predetermined angle difference and the angle ratio is determined as a sampling center of the current symbol.
For example, the first preset angle may be used to determine the position of the sampling space.
Illustratively, the angular ratio is the quotient of the angular period and the ratio parameter.
In one example, to implement the proportional quantization of the subsequent fitting function sinc in hardware, the proportional parameter ω needs to be controlled to be a factor of the angular period because there are no negative values and decimal values in hardware implementation, and the maximum position sequence number of the final result needs to be added to the calculation of the sampling center in the sinc function quantization. Therefore, the difference between the second preset angle and the corrected deviation angle representation value can be determined first to obtain a second preset angle difference, and the quotient of the second preset angle difference and the angle proportion is determined as the sampling center of the current code element.
The second preset angle is the sum of the first preset angle and the maximum position number of the fitting interval.
Typically, the sample space is 1 symbol in size, and the offset angle characterization value is between 0-360 degrees. Thus, referring to fig. 2 (a), when the receiving ends are far apart, the optimal sampling point exceeds the sampling interval, and the conventional method fixes the sampling interval size to reset the offset value to zero and readjust the offset value so that the offset value is always within the interval #1, for example, from 370 degrees to 10 degrees, so that the sampling point cannot be close to the optimal sampling point. In the present invention, by correcting in step S102, when the adjacent two offset values differ greatly, the sampling space is expanded so that the sampling point can be closer to the optimal sampling point, see (b) in fig. 2, thereby enhancing the satellite positioning effect.
S104, sampling is carried out on the fitting interval based on the sampling center of the current code element to obtain sampling data of the current code element.
In one possible implementation, the current symbol data may be interpolated based on a sampling center of the current symbol to obtain the sampled data for the current symbol.
In one example, when fitting interpolation sampling is performed, sinc function proportional quantization may be performed first, and after fitting function values are obtained through a fitting function, the fitting function values are multiplied by a fitting interval to obtain sampling data of a current symbol.
Illustratively, the fit function value may satisfy SINC=sinc (-4:1/ω: 4).
By way of example, the sample data of the current symbol may satisfy the following formula:
out=SINC(i-2n:i+2n-1)×X(1.8)
wherein out is the sampling data of the current code element, i is the sampling center, and X is the fitting interval.
According to the method provided by the invention, the positions of the sampling points are regulated through the differential states of the adjacent two code element offset values, so that the sampling interval and the sampling points are expanded towards the direction of the optimal sampling point, the condition that the code elements are repeated and the code elements are missed due to the sampling offset can be avoided at lower cost, and the satellite positioning effect is enhanced.
Further, the complex vector angle (namely the offset angle representation value) is used for estimating the offset of the complex signal, so that the symbol waveform characteristic can be fully utilized, and the offset and the sampling interval can be determined by using two simple measures of condition limitation and simple integration, so that the faster convergence speed, the lower resource cost and the lower debugging cost can be obtained.
Fig. 3 is a schematic structural diagram of a low-orbit satellite communication bit timing device based on angle synthesis according to an embodiment of the present invention. By way of example, and not limitation, the apparatus 300 may be used to implement the above-described methods. The apparatus 300 may include an offset quantization unit 310, an offset correction unit 320, and a sampling unit 330.
The offset quantization unit 310 is used for extracting offset information of a current symbol of an input signal according to power of the input signal to obtain an offset complex representation value of the current symbol, the offset correction unit 320 is used for determining an offset angle representation value of the current symbol according to the offset complex representation value of the current symbol, correcting the offset angle representation value of the current symbol through the offset angle representation value of the last symbol to expand a sampling space to obtain a corrected offset angle representation value of the current symbol, wherein the sampling space is a selectable space of sampling points, and the sampling unit 330 is used for fitting a sampling center of the current symbol through the corrected offset angle representation value and sampling on a fitting interval based on the sampling center of the current symbol to obtain sampling data of the current symbol.
Specifically, the offset correction unit 320 may record the data amount using a counter, and reset the expanded sample frame back to the original position within the guard interval of the communication protocol to ensure continuous operation.
In one possible implementation, as described in the above method, the fit interval may include a plurality of consecutive symbol data, and the current symbol is not the first symbol or the last symbol in the fit interval. Accordingly, the apparatus 300 may further include a data combining unit 340. The data combining unit may be configured to combine the serial data stream into symbol data within the fitting interval for use by the sampling unit 330.
In one example, based on equation (1.8) above, the apparatus 300 may further include a sinc storage module 350.
Illustratively, SINC storage module 350 may be configured to store SINC values when i values are different. This facilitates subsequent invocation by the sampling unit 330, which can simplify the structure of the apparatus 300.
In order to better illustrate the beneficial effects of the invention, the following simulation experiments were performed:
For example, in the simulation experiment, the apparatus 300 is used as a bit timing module in a low-orbit satellite frequency hopping communication system, the modulation mode is DQPSK, and the module working clock is 122.88Mhz. The number of samples n per symbol is 12, the symbol rate is 10.24Mhz, and the sample rate is 122.88Mhz. Omega is set to 30, beta is 0, delta is 128, the whole process of the module is carried out through pipeline processing, and no communication data storage link causes no congestion. The input is two paths to form complex signals, and the quantization bit number is 16 bits.
Fig. 4 shows a comparison of the constellation before and after bit timing according to an embodiment of the present invention.
Referring to fig. 4, where (a) in fig. 4 is a DQPSK signal constellation before bit timing and (b) in fig. 4 is a DQPSK signal constellation after bit timing.
Referring to the error graphs in fig. 4 and 5, it can be seen that, in the case of QPSK modulation, with a hard decision mode adopted for 12 samples per symbol, when the signal-to-noise ratio is high, the error curve of the present invention substantially overlaps with the error curve that always maintains the optimal sampling point, and when the signal-to-noise ratio falls below 0dB, the result of the present invention starts to fluctuate and deviate from the optimal sampling point.
Fig. 6 is a schematic diagram showing a relationship between variance and signal-to-noise ratio according to an embodiment of the present invention.
Referring to fig. 6, it can be seen that the deviation variance of the sampling point deviation estimation result of the present invention is before-4 dB, the deviation is in a controllable state, and the deviation increases more significantly after-4 dB.
Fig. 7 is a schematic diagram showing a relationship between the number of convergence symbols and the signal-to-noise ratio according to an embodiment of the present invention. Where each signal to noise ratio point is averaged over 50 replicates.
Referring to fig. 7, it can be seen that the convergence speed of the present invention is slightly better than that of the generic gardner timing recovery loop gardner loop. The reason why the number of converging symbols increases significantly after-4 dB in the case of a low signal-to-noise ratio is that, on the one hand, the initial oscillation time is lengthened and, on the other hand, the increase in oscillation amplitude itself due to the influence of noise is difficult to satisfy the variance criterion considered to be converging.
Therefore, according to the method provided by the invention, the positions of the sampling points are adjusted through the differential states of the adjacent two code element offset values, so that the sampling interval and the sampling points are expanded towards the direction of the optimal sampling point, the condition that the code elements are repeated and the code elements are missed due to the sampling offset can be avoided at lower cost, and the satellite positioning effect is enhanced.
In the foregoing embodiments, the descriptions of the embodiments are focused on, and the details or descriptions of some embodiments may be found in the related descriptions of other embodiments.