RU2140090C1 - Digital receiver of satellite radio navigation system - Google Patents

Abstract

FIELD: radio navigation. SUBSTANCE: invention refers to determination of vector of state of object by signals of satellite radio navigation system. Digital receiver of satellite radio navigation system has antenna, radio receiving part and signal processor connected in series, correlator, meter of navigation parameters, meter of vector of state, channel assignment unit connected in series, navigation information decoder, unit controlling correlator and meter of load of processor. EFFECT: enhanced precision and authenticity of determination of vector of state of objects. 1 cl, 6 dwg, 2 tbl

Description

 The invention relates to the field of radio navigation and can be used to accurately determine the state vector (spatial coordinates that make up the velocity and time vector) of various objects according to the signals of the satellite radio navigation system (SRNS).

 Known digital signal receivers SRNS GPS, designed to determine the state vector of objects [1-3] and containing an antenna, a radio receiving part, a digital signal processing unit and a microcomputer. Digital receivers of this type are characterized in that the formation of the reference signals and the calculation of the correlation of the input signal with the reference ones is carried out in the digital signal processing unit, and the navigation parameters and the state vector of the object are calculated in the microcomputer. The consequence of such a scheme for constructing digital receivers is a significant complication of the hardware with an increase in the number of parallel channels for receiving signals from navigational artificial Earth satellites (NISS).

 There are known digital receivers of SRNS GPS signals, in which, in order to simplify the hardware, the formation of reference signals and the calculation of the correlation of the input signal with the reference signals are carried out in a microcomputer [4, 5]. These digital receivers contain an antenna, a radio receiver, and a microcomputer. However, digital receivers of this type do not determine the state vector of an object in real time, which is a limitation of their use on moving objects.

 Closest to the proposed invention is a digital signal receiver SRNS GPS, described in [6]. The receiver consists of an antenna, a radio receiving part, and a microcomputer that functionally implements a correlator, a navigation parameter meter, a state vector meter, a navigation information decoder, and a channel assignment unit. The antenna of the digital receiver is designed to receive signals emitted by the GPS NIRS. The antenna output is connected to the input of the radio receiving part. The radio receiving part amplifies the signals coming from the output of the antenna, preliminary frequency selection from interference and converts the input mixture of signals and interference into digital form. From the output of the radio receiving part, digital codes are input to the signal processor, where the object state vector is calculated.

 Functional diagram of a digital receiver is presented in figure 5. The receiver consists of an antenna 1, a radio receiving part 2 and a signal processor 3, including a correlator 4, a navigation parameter meter 5, a state vector meter 6, a navigation information decoder 7 and a channel assignment unit 8.

 The device operates as follows. An additive mixture of signal and interference is received by antenna 1, in which amplification of the received mixture and preliminary frequency selection of the signal from interference occur. From the output of the antenna 1, the received signal is fed to the input of the radio receiving part 2. Radio receiving part 2 converts the input signal from a frequency of 1575.42 MHz to a frequency of 4.10 MHz and analog-to-digital quantization of the converted signal with a sampling frequency of 2.048 MHz. The choice of the method of converting the input signal to an intermediate frequency, as well as the values of the intermediate frequency and sampling frequency are due to the specific implementation of the prototype. Digital samples (samples) of the signal at an intermediate frequency in the form of a sequence of binary digits (the sign of the sample) are fed to the first input of the correlator 4, in which the processing of the received signal is divided by channels. Each channel of the correlator 4 corresponds to one NDH. According to the NISS pseudo-random sequence number (SRP) and according to this number the delay and frequency estimates received from the third output of the navigation parameter meter 5, reference signals are generated for each channel in the correlator 4 (delay and frequency estimates are used to set the initial position of the reference signals relative to of the internal time scale and their frequency, respectively) and the correlation between the reference signals and the signal fed to the first input of the correlator 4 is calculated. As a result, quadrature samples (I, Q) of the LHIS signal for each channel of the correlator 4, which are then fed to the first input of the navigation parameter meter 5. Based on the quadrature samples (I, Q) in the navigation parameter meter 5, new updated estimates of the signal delay and frequency are generated, and data symbols for the NLSS assigned to the channels of the correlator 4. In addition, the numbers of the SRP are determined by the numbers of the NLSS coming to the second input of the navigation parameter meter 5 from the output of the destination unit to channels 8, which are then used in the corrector Yator 4 for generating a reference signal. The data symbols for each NESA from the second output of the navigation parameter meter 5 are fed to the input of the navigation information decoder 7, where the navigation data (almanac, NESA ephemeris, etc.) is extracted from the binary symbol stream. According to estimates of the delay and frequency of the signal for each NESA coming from the first output of the navigation parameter meter 5, as well as the navigation data coming from the output of the navigation information decoder 7, the spatial coordinates of the object’s speed and time vector are calculated in the state vector meter 6, and Also, the calculation of the NLHA, which are in the radio visibility zone of the receiver. From the first output of the state vector 6 meter, the coordinates, speed and time are sent to the interface, and from the second output, the numbers of the visible NDH are fed to the input of the destination unit on channels 8, in which the distribution of the visible NDH across the channels of the correlator 4 is taken into account. channel status (free, search, tracking) coming from the fourth output of the navigation parameters meter 5.

 The disadvantage of the described scheme of the digital receiver is the non-optimal use of the computing resources of the signal processor when processing samples of the signal coming from the output of the radio receiving part, which leads to a limitation of the number of parallel channels for receiving signals of the NISS. The suboptimal use of computing resources lies in the fact that their distribution over the channels of the digital receiver is carried out regardless of the quality of the received signal of the NISS. Thus, when input data is redundant in any of the receiver channels, the corresponding signal processor resource is not used efficiently. An increase in the number of parallel channels for receiving NIRS signals to increase the accuracy and reliability of estimating the state vector of an object according to the described scheme is associated with significant hardware costs.

 The objective of the present invention is to provide a digital receiver of the SRNS signals, which would provide the most optimal distribution of the computing resources of the signal processor during the processing of the NLSS signals, which allows to increase the number of channels for receiving the NLSI signals and, as a result, to increase the accuracy and reliability of determining the object state vector without additional hardware costs.

 The main technical result from the implementation of the present invention is to increase the accuracy and reliability of determining the state vector of an object without increasing hardware costs due to the dynamic allocation of computing resources of the signal processor, which allows real-time, depending on the operating conditions of the receiver and the quality of the received signal, to adaptively change the number of parallel reception channels Signals NISS. The technical result is achieved due to the fact that the computing resource of the signal processor of the digital receiver of the SRNS is distributed over the channels for receiving the NIRS signals, taking into account the operating conditions of the receiver and the quality of the received signal. As a result, a free processor resource appears, which is used to receive signals of new NESS, i.e. an increase in the number of parallel channels for receiving NIRS signals, which improves the accuracy and reliability of determining the state vector of an object without additional hardware costs.

 The essence of the invention lies in the fact that the digital SRNS signal receiver contains an antenna, a radio receiver and a signal processor including a correlator, a navigation parameter meter, a state vector meter, a channel assignment unit, a navigation information decoder, a processor load meter and a correlator control unit. The antenna output is connected to the input of the radio receiving part, the output of the radio receiving part is connected to the input of the signal processor, which is also the first input of the correlator, the first output of the correlator is connected to the first input of the navigation parameter meter, and the first, second, third, fourth and fifth outputs of the navigation parameter meter are connected respectively, to the first input of the state vector meter, to the input of the navigation information decoder, to the second input of the correlator, to the second input of the channel assignment unit, and to the input of the correlator control unit. The output of the navigation information decoder is connected to the second input of the state vector meter, the second output of which is connected to the first input of the destination unit to the channels, the output of the destination unit to the channels is connected to the second input of the navigation parameter meter, the first and second outputs of the correlator control unit are connected to the control inputs of the correlator and the destination unit to the channels, respectively, and the output of the processor load meter is connected to the third input of the destination unit to the channels.

 The novelty is that the signal processor of the digital SRNS signal receiver contains a processor load meter and a correlator control unit with their new connections with other functional elements of the signal processor: the input of the correlator control unit is connected to the fifth output of the navigation parameters meter, and the first and second outputs to the control inputs of the correlator and the destination unit to the channels, respectively, the output of the processor load meter is connected to the third input of the destination unit to the channels. In addition, the correlator and channel assignment unit are controllable.

 The processor load meter is a functional element of the signal processor and is implemented as a sequence of processor instructions (programs). The processor load meter is designed to calculate the current estimate of the average value of the time interval spent by the signal processor for performing all tasks for a fixed time interval and performs the following procedures: measuring the maximum free resource of the signal processor for a fixed time interval, measuring free resource when the processor performs all tasks for this time interval and calculating the average estimate of the current load of the signal processor. The calculated estimate of the current processor load goes to the input of the destination unit to the channels.

 The correlator control unit is a functional element of the signal processor, implemented as a processor program, and is designed to calculate input data utilization coefficients for all NISS assigned to the correlator channels. The indicated coefficients are calculated for each NESA based on the measured signal-to-noise ratio coming from the fifth output of the navigation parameter meter and the calculated threshold signal-to-noise ratio, which ensures reliable operation of the phase locked loop (PLL). The calculated input data utilization coefficients go to the control inputs of the correlator and the assignment unit to the channels.

 The correlator is a functional element of the signal processor, implemented in the form of a processor program and includes a series-connected PSP generator, a mixer and an integrator with a reset, as well as a carrier frequency generator, the output of which is connected to the second input of the mixer. The correlator is designed to calculate the quadrature components of the NESA signal from the quadrature samples (samples) of the signal at the intermediate frequency coming from the output of the radio receiving part, from the SRP numbers and estimates of the delay and frequency coming from the output of the navigation parameter meter, and also from the data utilization factors for each channel coming from the output of the correlator control unit. The generated quadrature readings are fed to the input of the navigation parameter meter, where they are used to calculate new estimates of the delay and frequency of the NISH signals and to isolate the data symbols that modulate the signal emitted by the NHA.

 The channel assignment block is a functional element of the signal processor, implemented in the form of a processor program, and is designed to determine the NDIS from the receiver’s radio visibility zone, which should be assigned to the correlator channels. The assignment of the NISS to the correlator channels is carried out taking into account the current load of the signal processor coming from the output of the processor load meter, as well as the geometric factor of the working constellation of the NISS calculated on the basis of the state vector of the NISS guide cosines that are in the radio-visibility zone of the receiver.

 The description of the invention is accompanied by graphic material. Figure 1 presents the functional diagram of the receiver, implemented in accordance with the invention. On figa shows an example implementation of the radio part. On figb presents a functional diagram of the correlator. Figure 3 presents a block diagram of the algorithm of the operation of the assignment unit to the channels. In FIG. Figure 4 shows a histogram of the signal-to-noise ratio measured in the 1 Hz band for a low-orbit object. Figure 5 presents the functional diagram of the prototype.

 The proposed digital receiver (Fig. 1) consists of a series-connected antenna 1, a radio receiving part 2 and a signal processor 3, including a correlator 4, a navigation parameter meter 5, a state vector meter 6, a destination unit for channels 8 connected in series, and a navigation decoder information 7, the correlator control unit 9 and the processor load meter 10. The second output of the navigation parameter meter 5 is connected to the input of the navigation information decoder 7, the output of which is connected to the second the state vector meter 6. The third output of the navigation parameters meter 5 is connected to the second input of the correlator 4, the fourth output is connected to the second input of the destination unit to channels 8, and the fifth output is connected to the input of the control unit of the correlator 9. The output of the destination unit to channels 8 is connected to the second input of the navigation parameter meter 5, and the third input - with the output of the processor 10 load meter. The first output of the correlator control unit 9 is connected to the control input of the correlator 4, and the second output - with the control input of the assignment unit cheniya on 8 channels.

 Antenna 1 of the digital receiver is designed to receive L1-band signals (1575.42 MHz) emitted by the GPS NIRS. In the described receiver implementation, a passive antenna with a hemispherical radiation pattern and right-handed circular polarization is used. The output of the antenna 1 is connected to the input of the radio receiving part 2.

The radio receiver part 2 of the digital receiver is designed to amplify the signal from the output of the antenna 1, preliminary frequency selection from interference and converting the input mixture of signals and interference into digital form at an intermediate frequency. On figa presents a functional diagram of the radio part 2 of the described implementation of the receiver. The radio receiving part 2 consists of a series-connected reference generator (OG) 14, a gain and pre-filtering unit (BUPF) 11 and a digital processing unit (BTSO) 12, as well as a frequency synthesizer (MF) 13, the output of which is connected to the control inputs of the BUPF 11 and BCO 12, and the input with the second output of BUPF 11. In the described receiver, a 10 MHz crystal oscillator with a relative instability of 10 ^{-6 is} used as OG 14, and the BUFP 11 is implemented on the widely used VLSI GP2010 [7]. MF 13 generates from a reference frequency of 40 MHz coming from the output of the BUPF 11, the sampling frequency of the input signal 40/7 MHz. BTsO 12 is intended for converting a digital signal from the output of BUPF 11 from a complex form to preliminary buffering of quadrature samples in order to save the resources of the signal processor 3. The output of BSO 12 is quadrature samples of the input signal taken at an intermediate frequency with a sampling frequency of 40/7 MHz and packed in 32 bit words. The presence of BCO 12 in the radio receiving part 2 is due to the specific implementation of BUPF 11 and in the general case is optional. The output of the radio part 2 is connected to the input of the signal processor 3.

 The signal processor 3 (Fig. 1) of the digital receiver is designed to calculate the state vector of the object from the samples of the signal at the intermediate frequency coming from the output of the radio receiving part 2. The signal processor 3 includes a correlator 4, a meter for navigation parameters 5, a meter for state vector 6, a decoder for navigation information 7, a channel assignment unit 8, a correlator control unit 9, and a processor 10 load meter.

 Correlator 4 (Fig. 2b) for quadrature samples (samples) of the signal at the intermediate frequency coming from the output of the radio receiving part 2, according to the numbers of the SRP and estimates of the delay and frequency coming from the output of the measuring instrument for navigation parameters 5, as well as the utilization factors of the input data for each channel correlator coming from the output of the control unit of the correlator 9, calculates the quadrature components (I, Q) of the signals of the NHA, assigned to the channels. For the described implementation of the digital receiver, quadrature samples of the signal at an intermediate frequency, packed in 32-bit words, are input to the correlator 4 with a frequency of 20/7/32 MHz; SRP numbers, estimates of signal delay and frequency, as well as input data utilization coefficients, are fed to the input of correlator 4 with the frequency of the circuit of delay tracking systems (CVD) and PLL. The quadrature components of the signal (I, Q) formed by the correlator 4 with a frequency of 1 kHz are fed to the input of the navigation parameters meter 5. The functional diagram of the correlator 4 is shown in FIG. 2b. The correlator 4 includes a series-connected generator PSP 15, a mixer 17 and an integrator with a reset 18, as well as a carrier generator 16, the output of which is connected to the second input of the mixer 17.

 The SRP generator 15, using the SRP number and estimating the signal delay and frequency, forms a reference sequence of SRP samples with an sampling interval of the input signal. In the described digital receiver, the SRP generator 15 consists of an accumulative adder (phase register) and a table of preliminarily calculated SRP samples for one era of the code with a step of 1/16 of the sampling interval of the input signal. The number of generated samples of the reference memory bandwidth is defined as the product of the nominal number of memory bandwidth samples at one era of the code and the input data utilization factor. Formed readings are fed to the input of the mixer 17.

 The carrier generator 16 according to the estimate of the signal frequency generates a reference sequence of quadrature samples of the carrier frequency with a sampling interval of the input signal. In the described digital receiver, the carrier generator 16 is implemented according to the principle of direct digital frequency synthesis [8] and consists of a 32-bit phase register and a table of pre-calculated values of the sine and cosine functions with a step of π / 128. The number of generated quadrature samples of the reference carrier is defined as the product of the nominal number of carrier samples and the utilization factor of the input data. Formed readings are fed to the input of the mixer 17.

 In the mixer 17, the convolution of the quadrature samples of the signal at the intermediate frequency coming from the output of the radio receiving part 2 is calculated with the quadrature samples of the reference signal generated by the SRP and carrier generators. The convolution is calculated taking into account the utilization factor of the input data. The generated quadrature samples go to the integrator input with a reset of 18. For the described implementation of the digital receiver, the frequency of quadrature sampling is 20/7/16 MHz.

 An integrator with a reset 18 carries out the accumulation of quadrature samples coming from the output of the mixer 17 over a nominally equal interval equal to approximately one epoch of the code. The actual duration of the accumulation interval is determined by the utilization rate of the input data. The resulting quadrature samples (I, Q) are generated with a frequency of 1 kHz. Formed quadrature readings are fed to the input of the meter navigation parameters 5.

The correlator control unit 9, based on the measured signal-to-noise ratio for each NISS, coming from the fifth output of the navigation parameter meter 5, calculates the input data utilization coefficient for all the NISS assigned to the correlator channels 4. The input data utilization factor K _{i is} calculated in accordance with the formula: K _i = q _min / q _i , where q _i is the measured signal-to-noise ratio for the i-th NISS (in times); q _min - threshold signal-to-noise ratio (the minimum possible for reliable PLL operation) (times). The generated input data utilization factors K _i are supplied to the control inputs of the correlator 4 and the destination unit to channels 8.

The processor 10 load meter calculates an estimate of the average value of the time interval spent by the signal processor 3 to complete all tasks for a fixed time interval, for example, 1 second. In the described implementation of the digital receiver, the load calculation algorithm uses a 32-bit counter and time stamps (1 Hz) generated by the signal processor 3, and includes the following procedures:
1) measurement of the maximum free resource of the signal processor for a fixed time interval;
2) measurement of the current value of the free resource when the signal processor performs all tasks on a fixed time interval;
3) the calculation of the average load estimate of the signal processor.

 The first procedure is performed once at the initialization stage of the signal processor 3 and consists in calculating the maximum value of the counter for the time interval between two adjacent labels of 1 Hz. The current processor load is measured at the level of background tasks as the difference between unity and the ratio of the measured counter value between adjacent time stamps to the maximum. The measured processor load value is averaged using a first order sliding smoothing filter over 10 measurements. From the output of the load meter of the processor 10, the calculated load estimate is fed to the input of the destination unit to channels 8.

The navigational parameters meter 5, based on the measured quadrature components (I, Q) of the LHSS signal coming from the output of the correlator 4, calculates the estimate of the signal delay and frequency, the signal-to-noise ratio for the LHSS assigned to the channels of the correlator 4, and also highlights the data symbols with which it is modulated carrier frequency, for each NISS. Measurement of navigation parameters 5 includes:
1) CVD;
2) frequency-locked loop (CHAP) and PLL;
3) signal-to-noise ratio meter;
4) the synchronization scheme of the internal time scale (NW) of the digital receiver with the boundary of the data symbol.

 CVD, CHAP and PLL, as well as the synchronization circuit of the BC with the border of the symbol are implemented according to standard algorithms. A detailed description of the operation algorithms of the above schemes can be found, for example, in [8]. The measured estimates of the delay and frequency from the output of the measuring instrument for navigation parameters 5 are supplied to the inputs of the measuring device of the state vector 6 and correlator 4, the measured signal-to-noise ratio is transmitted to the input of the control unit of the correlator 9, and the data symbols for each NISS are transmitted to the input of the navigation information decoder 7. In addition to In addition, the navigation parameters meter 5, according to the NISS numbers arriving at its input from the output of the destination unit to channels 8, generates the SRP numbers for the correlator 4.

 The navigation information decoder 7 extracts navigation data (ephemeris, almanac, parameters of the ionosphere model and the onboard NW) from the binary symbol stream coming from the output of the navigation parameters meter 5 for the NISH, for the signals of which are monitored by the CVD and PLL systems.

The navigation information decoder 7 performs the following procedures:
1) the synchronization of the internal BC receiver with the beginning of the frame of the navigation message NISS;
2) decoding and data reliability control.

 In the described digital receiver, the navigation information decoder 7 is implemented based on well-known algorithms described in [9]. From the output of the navigation information decoder 7, the navigation data about the NLHA are fed to the input of the state vector meter 6.

 The state vector meter 6, based on the calculated estimates of the signal delay and frequency shift coming from the output of the navigation parameter meter 5, and also from the navigation data coming from the output of the navigation information decoder 7, calculates the spatial coordinates that make up the object’s velocity vector and time using those NISS, which were selected by the assignment unit to channels 8. In the described digital receiver, the state vector meter 6 implements the least-squares method using instantaneous measurements tions for all selected INSS. The procedure for calculating the estimate of the state vector by the least squares method is standard and is described, for example, in [10].

где K_i - коэффициент использования данных для i-го НИСЗ (K_i = 1, для НИСЗ, у которых отношение сигнал/шум не вычислено); T_max - максимально допустимая загрузка процессора; T₀ - верхняя оценка загрузки процессора одним каналом коррелятора, которая может быть получена заранее расчетным путем. В блоке 27 из сформированных наборов выделяются те, которые содержат оптимальную четвертку НИСЗ из числа назначенных на каналы. Блок 28 осуществляет выбор из выделенных наборов НИСЗ такого набора, который имеет минимальный геометрический фактор. Номера выбранных НИСЗ поступают на вход блока 29, в котором происходит распределение НИСЗ по каналам коррелятора 4. В случае T ≤ T_max в блоке 21 вычисляется N (число резервных каналов коррелятора 4) в соответствии с формулой:

где [x] - целая часть числа x. Если N ≠ 0 блок 23 по статусу каналов коррелятора, поступающему с выхода измерителя навигационных параметров 5, определяет НИСЗ, назначенные на каналы и формирует рабочее созвездие из (M+N) НИСЗ (М - текущее число каналов коррелятора), включающее назначенные на каналы НИСЗ и имеющее минимальный геометрический фактор. Номера НИСЗ сформированного созвездия поступают на вход блока 29. В противном случае (N = 0), в блоке 24 анализируется текущее число каналов коррелятора М. Если М = 4, то в блоке 25 происходит вычисление геометрического фактора рабочего созвездия и при превышении им заданного порога выбор новой оптимальной четвертки НИСЗ. Если же М > 4, то происходит переназначение НИСЗ по каналам в соответствии с описанными в блоках 26, 27 и 28 процедурами. В описанном алгоритме предполагается, что в цифровом приемнике реализованы по крайней мере 4 параллельных канала коррелятора.The assignment unit to channels 8 determines the numbers of the NISS located in the radio-visibility zone of the digital receiver, which will be used by the state vector meter 6 to determine the coordinates, velocity vector and time of the object. The block diagram of the algorithm of the operation of the assignment unit to channels 8 of the described implementation of the digital receiver is shown in Fig.3. At the input of the comparison unit 20, the current estimate of the signal processor T load calculated by the processor 10 load meter is received. In the case of T> T _max, it is necessary to reassign the LHSS through the channels of the correlator 4. For this, block 26 forms all kinds of visible LHHI combinations satisfying the inequality:

where K _i is the data utilization coefficient for the i-th NISS (K _i = 1, for the NIHS, for which the signal-to-noise ratio has not been calculated); T _max - the maximum allowable processor load; T ₀ is the upper estimate of the processor load by one channel of the correlator, which can be obtained in advance by calculation. In block 27 of those formed sets are selected those that contain the optimal fourth NDH from the number assigned to the channels. Block 28 selects from the selected NISS sets such a set that has a minimal geometric factor. The numbers of the selected NISS are fed to the input of block 29, in which the NISS is distributed over the channels of the correlator 4. In the case of T ≤ T _max, in block 21, N (the number of backup channels of the correlator 4) is calculated in accordance with the formula:

where [x] is the integer part of x. If N ≠ 0 block 23 according to the status of the correlator channels coming from the output of the navigational parameters meter 5, determines the NISS assigned to the channels and forms a working constellation from (M + N) NISS (M is the current number of correlator channels) including those assigned to the NISS channels and having a minimal geometric factor. The NISS numbers of the formed constellation are sent to the input of block 29. Otherwise (N = 0), in block 24, the current number of channels of the correlator M is analyzed. If M = 4, then in block 25 the geometric factor of the working constellation is calculated and if it exceeds the specified threshold selection of the new optimal NISS quartet. If M> 4, then there is a reassignment of the NHSS along the channels in accordance with the procedures described in blocks 26, 27 and 28. The described algorithm assumes that at least 4 parallel correlator channels are implemented in the digital receiver.

The device operates as follows. Antenna 1 receives an additive mixture of signal and interference, amplifies the received mixture and performs preliminary frequency selection of the signal from interference. From the output of antenna 1, the received signal is fed to the input of radio receiving part 2, where the input signal is converted from a frequency of 1575.42 MHz to a frequency of 4.309 MHz, analog-to-digital quantization of the converted signal with a sampling frequency of 40/7 ≈ 5.71 MHz, the formation of quadrature samples of the signal at an intermediate frequency and pre-buffering the received samples in 32-bit words. Packed into words, the signal samples at an intermediate frequency are fed to the input of the signal processor 3, which is also the first input of the correlator 4. In the correlator 4, the processing of the received signal is divided into channels. Each channel of the correlator 4 corresponds to one NDH. According to the NISS SRP number and estimates of the delay and frequency that come from the third output of the navigation parameter meter 5 corresponding to this number, reference signals are generated for each channel in the correlator 4 and the correlation between the reference signals and the signal fed to the first input of the correlator 4 is calculated. Calculation correlation of the input signal with the reference is carried out taking into account the utilization factors of the data K _i for each channel received at the control input of the correlator 4 from the first output of the correl control unit 9. 9. To calculate the quadrature samples (I, Q) of the NHSS signal in the i-th channel, the number of processed samples of the input signal is directly proportional to K _i . The calculated quadrature samples (I, Q) of the LHIS signal for each channel of the correlator 4 are fed to the first input of the navigational parameters meter 5, where new updated estimates of the delay and signal frequency, signal-to-noise ratio, and also data symbols for all LHIS corresponding to the correlator channels are generated 4. In addition, the numbers NSPZ, which are then used in the correlator 4 to form the reference signal, are determined by the numbers of the NISS entering the second input of the measuring instrument for navigation parameters 5 from the output of the destination unit to channels 8 fishing The generated estimates of the signal delay and frequency, as well as the SRP numbers from the third output of the navigational parameters meter 5 are fed to the second input of the correlator 4. The measured signal-to-noise ratio for each of the NISS assigned to the channels of the correlator 4 is fed from the fifth output of the navigational parameters meter 5 to the input of the control unit of the correlator 9, where it is used to calculate data utilization factors. The data utilization coefficient for the i-th channel is calculated in accordance with the formula: K _i = q _min / q _i , where q _i is the measured signal-to-noise ratio for the NHSS corresponding to the i-th channel of correlator 4 (times); q _min - threshold signal-to-noise ratio (the minimum possible for reliable PLL operation) (times). The data symbols for each NESA from the second output of the navigation parameter meter 5 are fed to the input of the navigation information decoder 7, where the navigation data (almanac, NESA ephemeris, etc.) is extracted from the binary symbol stream. In the state vector meter 6, the spatial coordinates that make up the object’s velocity and time vector are calculated based on the measured estimates of the delay and signal frequency for each NESS coming from the first output of the navigation parameters meter 5 and the navigation data coming from the output of the navigation information decoder 7, and also the calculation of the NLHI located in the radio visibility zone of the receiver. From the first output of the state vector 6 measuring instrument, the coordinates, speed, and time are sent to the interface, and from the second output, the numbers of the visible NLH are fed to the first input of the destination unit on channels 8, in which the visible NLH are distributed over the channels of the correlator 4.

The determination of NISS assigned to the channels of the correlator 4 is carried out taking into account the current load of the signal processor 3 coming from the output of the load meter of the processor 10, the data utilization factors K _i for each channel of the correlator 4, coming from the second output of the control unit of the correlator 9 and the channel status (free , search, tracking) coming from the fourth output of the navigation parameter meter 5.

 The technical result of the invention is illustrated by the example of the use of a digital receiver signals SRNS on low-orbit spacecraft. For the application in question, the receiver and the signal processor included in it must satisfy the radiation resistance requirements. To date, processors with up to 20 MIPs (millions of operations per second) are available on the market of radiation-resistant signal processors. For a signal processor with a capacity of 20 MIPs, no more than four parallel correlator channels can be implemented within the described receiver circuit. By simulating the motion of a low-orbit spacecraft [11] it was shown that in the radio-visibility zone of a receiver located on the spacecraft, there can be up to 8 GPS satellite navigation sensors. Therefore, the prototype does not provide the potential accuracy of determining the state vector of an object. Figure 6 presents a histogram of the distribution of the signal-to-noise ratio, measured in the 1 Hz band by a receiver located on a low-orbit spacecraft, for the NISS SRNS GPS. Analysis of the histogram shows that the average signal-to-noise ratio is in the range of 47-48 dB. This signal-to-noise ratio is redundant for estimating the delay and frequency of the NHSS signal and, therefore, can be reduced by at least 6 dB by reducing the amount of processed input data (samples) by 4 times, without compromising the accuracy of the estimation of the spacecraft state vector. On the other hand, a reduction in the amount of input data provides an additional resource for the signal processor, which can be used to process the signals of the new NISS. Since the load of the signal processor is determined mainly by the work of the correlator, and the number of operations performed by the correlator is directly proportional to the amount of processed input data, reducing the amount of input data by 4 times allows you to increase the number of tracking channels for NISS signals by the same amount. Using the present invention allows, without additional hardware costs, to implement 16 parallel channels of the correlator (on average). An increase in the number of NLHIs used to estimate the spacecraft state vector even with a decrease in the accuracy of measuring navigation parameters makes it possible to increase the accuracy of the estimate, as well as its reliability. Let us explain the above by numerical calculation.

где τ - длительность элементарного символа ПСП, м; B_DLL - односторонняя полоса ССЗ, Гц; T - постоянная времени коррелятора, с; q - отношение сигнал/шум в полосе 1 Гц. Для описываемой реализации цифрового приемника: B_DLL = 0.62 Гц, T = 0.001 с. Таким образом, σ_τ для низкоорбитального КА находится в пределах 0.37 - 0.66 м. В таблице 1 представлены значения приведенных погрешностей при использовании С/А - кода [10].It is known that the standard error (SEC) of the estimation of the state vector of the object according to the signals of the NIRS SRNS is determined by the ratio:
σ = αГσ _p ,
where α is the significance coefficient determined by the given probability of accuracy of the state vector estimate (for example, for probability 0.95, the significance coefficient is 2); G is the spatial geometric factor of the constellation, which was used to evaluate the state vector of the object; σ _p - UPC measurement of pseudorange. UPC measurement of delay (pseudorange) can be estimated from the expression:
σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{p}}$ = σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{SA}}$ + σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{iono}}$ + σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{trop}}$ + σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{m}}$ + σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{sys}}$ + σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{τ}}$ ,
where σ _SA is the error determined by selective access for civil consumers; σ _iono is the error of signal delay in the ionosphere; σ _trop - error of signal delay in the troposphere; σ _m is the error determined by multipath; σ _sys - system error (inaccuracies in the forecast of ephemeris, airborne welds, etc.); σ _τ - SKP of the noise of the receiver. The SEC of the receiver noise σ _τ is determined by the correlator and CVD parameters and can be estimated from the expression:

where τ is the duration of the elementary symbol of the SRP, m; B _DLL - single-sided CVD band, Hz; T is the correlator time constant, s; q is the signal-to-noise ratio in the 1 Hz band. For the described implementation of the digital receiver: B _DLL = 0.62 Hz, T = 0.001 s. Thus, σ _τ for the low-orbit spacecraft is in the range 0.37–0.66 m. Table 1 presents the values of the reduced errors when using the C / A code [10].

Based on the data of Table 1 and the calculation of σ _τ given above, we can conclude that a 2-fold increase in σ _τ (which corresponds to a 6 dB decrease in signal-to-noise ratio) will lead to an increase in the total SEC of only 1.006 times even in the absence of selective mode access i.e. practically does not change the accuracy of measuring pseudorange. An increase in the number of NESH used to determine the state vector of the spacecraft will lead to a decrease in the geometric factor of the constellation. Table 2 shows the dependence of the average value of the spatial geometric factor on the number of NESH used [11].

 From the data given in Table 2, it follows that with an increase in the number of NSSS used to estimate the spacecraft state vector, for example, from 4 (the minimum required number of NSSS) to 8, the geometric factor decreases by 1.34 times and, therefore, the accuracy increases as many times estimates of the state vector of the spacecraft. In addition, an increase in the number of channels for receiving NIRS signals from 4 to 8 allows the receiver to implement autonomous control of the integrity of the navigation solution through the use of an excessive number of simultaneous measurements, which increases the reliability of determining the state vector of an object.

Literature
1. Method of Doppler searching in a digital GPS receiver. U.S. Patent 4,701,934, 1987.

 2. Sequencer for a shared channel global positioning system receiver. U.S. Patent No. 5,192,957, 1993.

 3. Satellite search methods for improving time to first fix in a GPS receiver. U.S. Patent No. 5,403,347, 1995.

 4. GPS receiver and method for processing GPS signals. U.S. Patent 5663734, 1997.

 5. MicroGPS: On-orbit Demonstration of a New Approach to GPS for Space Applications / J. Srinivasan et al. ION GPS, USA, 1998.

 6.12 Channel Global Positioning System Receiver on a Programmable Platform. Accord Software & Systems Pvt. Ltd. Datasheet 1998.

 7. GP2010. GEC Plessey Semiconductors. Datasheet DS4056-2.5, 1996.

 8. Digital radio receiving systems: Reference book / M.I. Zhodzishsky, R.B. Mazepa, E.P. Ovsyannikov et al. / Ed. M.I. Zhodzishsky - M .: Radio and communications, 1990. - 208 p.

 9. ICD GPS-200 (Technical Characteristics of the NAVSTAR GPS). June 1991.

 10. Network satellite radio navigation systems / B.C. Shebshaevich et al.: Ed. B.C. Shebshaevich. - M .: Radio and communications, 1993 .-- 408 p.

 11. Considerations for The Application of GPS in Satellites: GPS System Trade Study / J.Kronman, T. McElroy. ION GPS, USA, 1994.

Claims (1)

 A digital receiver of a satellite radio navigation system comprising a series-connected antenna, a radio receiver and a signal processor including a correlator, a navigation parameter meter, a state vector meter and a channel assignment unit connected in series, the output of the channel assignment unit being connected to the second input of the navigation parameter meter, as well as a navigation information decoder, the output of which is connected to the second input of the state vector meter, and the input to the second the output of the navigation parameter meter, while the third output of the navigation parameter meter is connected to the second input of the correlator, and the fourth output is connected to the second input of the channel assignment unit, characterized in that the processor load meter and the correlator control unit are additionally introduced into it, and the output of the load meter the processor is connected to the third input of the destination unit to the channels, the first and second outputs of the correlator control unit are connected respectively to the control inputs of the correlator and the unit assignment to the channels, and input - to the fifth output meter navigation parameters.

Images