RU2110149C1 - Receiver for signals of satellite navigation systems - Google Patents

Abstract

FIELD: preliminary information processing circuits of receiver of two different satellite navigation systems. SUBSTANCE: signal receiver has antenna, low-noise amplifier, mixer, intermediate-frequency amplifier, reference temperature- stable oscillator, complex signal processing circuit. Goal of invention is achieved by introduced input feeder, wide-band filter of preliminary selection, second low-noise amplifier, first and second band-pass filters, unit of automatic gain control and frequency generator. This results in possibility to receive and process signals from various modern space navigation systems without redundant receiving channels, by means of single receiving circuit. EFFECT: increased functional capabilities, decreased group delay, increased precision, simplified design, decreased power consumption. 6 dwg

Description

 The invention relates to satellite radio navigation and can be used in primary information processing paths of receiver indicators of two mutually-out of sync satellite radio navigation systems (SRNS).

 A known receiver [1], which contains an antenna, a low noise amplifier (LNA), a filter of the first mirror channel (FZK 1), a mixer, a frequency multiplier n times, a filter, a preliminary amplifier of the first intermediate frequency, a filter of the second mirror channel (FZK 2), the second mixer, the second frequency multiplier by a factor of m, the input of which receives a signal from the output of the fine grid synthesizer, the second intermediate frequency amplifier, covered by an automatic gain control (AGC) circuit. This device can only receive signals from only one navigation system (either a Glonass-type system or a Global Positioning System-like system (GPS-global navigation system Navstar), which is a serious drawback, as duplication of receiver equipment is required in case of receiving signals spacecraft (SC) of two radio navigation systems.In addition, the use of two frequency multipliers (respectively n and m times) leads to a significant increase in the level of phase noise of the receiving path, which reduces the signal-to-noise ratio at the output of the device and, as a result, the accuracy indicators of the measurement vector of the entire receiver-indicator.

These disadvantages are partially eliminated in the Texas Instruments multiplex receiver (USA) [2], which includes an antenna, an antenna amplifier, a frequency selector f ₁ and f ₂ , an L frequency converter, an integrated frequency control generator f ₁ and f ₂ , a synthesizer frequencies, a correlator and a frequency converter, an analog-to-digital converter (ADC) and a preprocessing device. It should be noted that the structural diagram of the receiver [2] shows some other blocks, which are not components of the receiver itself, but implement the function of tracking meters and therefore will not be considered here.

The advantage of this device is the ability to work with spacecraft GPS "Navstar" according to the general use code (C / A - code) and high-precision P-code at a frequency of f ₁ and f ₂ (respectively 1575.42 MHz and 1227.6 MHz). However, the presence of multiplexing leads to a decrease in the signal-to-noise ratio, while the loss is approximately 1.5 dB per channel. In addition, the receiver [2] cannot simultaneously receive and process the signals of two satellite radio navigation systems of the Glonass type and the Navstar type.

The closest in technical essence to the present invention is a combined receiver of signals from the GPS spacecraft "Navstar", "Glonass" [3], containing an antenna, a low-noise amplifier, a diplexer, a signal splitter, a down-converter of signals from spacecraft of the Glonass type system, a down-converter of spacecraft signals of a Navstar system, a reference thermostatic generator, a receiver of spacecraft signals of the Glonass system operating on a frequency x L ₁ and L ₂ (respectively by C / P and P-codes) as an optional, optionally supplied unit; a four-channel receiver of signals from spacecraft (SC) of the Glonass system, operating according to the general application code C / A, a receiver of signals from the spacecraft GPS Navstar system, operating at frequencies L ₁ and L ₂ (respectively, according to C / A and P-codes) as an optional, optionally supplied unit; six-channel GPS satellite receiver Navstar, operating according to the general application code C / A. In each of the four channels of the receiver of the Glonass system, additional amplification and filtering of the intermediate frequency is performed, as well as analog-to-digital conversion, and each channel of this system, unlike GPS Navstar, requires the use of a separate intermediate frequency, since each satellite emits a signal its intermediate frequency.

 The advantage of the combined receiver [3] lies in the possibility of working with the signals of two satellite radio navigation systems - Glonass and Navstar. This ensures the continuity and high accuracy of the measurement of the vector of navigation parameters by the receiver indicators in which this receiver is used.

 However, the prototype device [3] has a number of significant drawbacks, since the ability to work on the spacecraft signals of two SRNSs is achieved due to the two-channel reception equipment separate for each spacecraft system, which leads to a noticeable complication and increase in the overall dimensions of the receiver. In addition, the use of a diplexer in the prototype device leads to energy losses and complicates control in the time sharing mode to ensure operation on each of the channels for receiving signals from spacecraft.

In the inventive device, the ability to solve the following problems:
- the ability to receive and process signals from the spacecraft of the Glonass and Navstar radionavigation systems using a single receive path, i.e. without duplication of reception channels;
- the implementation of the specified receiver can be achieved using one mixer and an intermediate frequency amplifier, which will simplify the device as a whole and reduce additional energy losses that occur during additional transformations of the input signal;
- improve the accuracy of the receiver by reducing the group delay time when transmitting signals from satellite radio navigation systems such as Glonass and GPS Navstar.

 These advantages over the prototype are achieved due to the fact that the signal receiver of satellite radio navigation systems containing an antenna, a low noise amplifier, a mixer, an intermediate frequency amplifier, a reference thermostatic generator, an input feeder, a broadband filter preselector, a second low noise amplifier, the first and second are additionally introduced bandpass filters, automatic gain control unit, frequency synthesizer and complex signal conversion unit. The antenna output is connected to the input of the input feeder, the output connected to the input of a broadband filter-preselector, the output of which is in turn connected to the first input of the first low-noise amplifier. The output of this low-noise amplifier (LNA) is connected to the input of the first band-pass filter, the output of which is connected to the first input of the low-noise amplifier. The output of the second LNA is connected to the first input of the mixer, the output of which is connected to the input of the second bandpass filter connected by the output to the input of the intermediate frequency amplifier. The output of the intermediate frequency amplifier is connected simultaneously to the information input of the complex signal conversion unit and the input of the automatic gain control (AGC) unit, and the output of the AGC block is connected simultaneously to the second input of the first LNA, the second input of the second LNA and the second input of the intermediate frequency amplifier. The output of the reference thermostatic generator is connected to the input of the frequency synthesizer, the first output of which is connected to the second input of the mixer, and the second and third outputs of the frequency synthesizer are connected respectively to the first and second inputs of the complex signal conversion unit, thereby providing quadrature digital samples of the processed signal at the output of the receiver .

 In FIG. 1 is a functional diagram of a signal receiver of satellite radio navigation systems; in FIG. 2 is a diagram of a frequency synthesizer; in FIG. 3 is a functional diagram of a multi-stage frequency divider; in FIG. 4 (a, b, c) - respectively, the amplitude-frequency, phase-frequency characteristics and the characteristic time of the group delay of a broadband filter-preselector; in FIG. 5 - amplitude-frequency characteristic of the band-pass filter of the intermediate frequency path; in FIG. 6 is an embodiment of a complex signal conversion unit.

 According to the invention, the signal receiver of satellite radio navigation systems (figure 2) contains an antenna and an input feeder 1, the output of which is connected to the output of the broadband filter preselector 2, the output connected to the first input of the first low-noise amplifier 3. The output of the low-noise amplifier 3 is connected to the input of the band-pass filter 4 the output of which is connected to the first input of the second low-noise amplifier 5, connected by the output to the first input of the mixer 6, to the second input of which the first output of the frequency synthesizer 7 is connected, which in this case is the function of a local oscillator. The input of the frequency synthesizer 7 is connected to the output of the reference thermostatic generator 8. The output of the mixer 6 is connected to the input of the band-pass filter 9, which ensures the separation of signals from the Glonass and Navstar spacecraft at the difference (intermediate) frequency. The output of the bandpass filter 9 is connected to the first input of the intermediate frequency amplifier 10. The output of the intermediate frequency amplifier 10 is connected simultaneously with the input of the complex signal conversion unit 11, the output of which serves as the output of the inventive device, as well as with the input of the automatic gain control unit 12. The outputs of the latter are connected respectively to the second input of the intermediate frequency amplifier 10, the second input of the second low-noise amplifier 3 and the second input of the low-noise amplifier 5.

 The frequency synthesizer 7 (figure 1, 2) contains a pulse phase detector 13, the first input of which receives a signal from the output of the thermostatic generator 8. The output signal from the output of the thermostatic generator 8 also goes to the first input of the frequency detector 14. The outputs of the phase detector 13 and the frequency the detector 14 is connected respectively to the first and second inputs of the adder 15, the output of which is connected to the input of the low-pass filter 16 (LPF). The output of the low-pass filter 16 is connected to the input of a voltage controlled oscillator 17, the output of which in turn is connected simultaneously to the input of the mixer 6, thereby providing a 1440 MHz local oscillator signal, as well as to the input of a multi-stage frequency divider 18, thereby forming an active frequency synthesizer.

 A multi-stage frequency divider 18 (Fig. 2,3) contains a T-trigger 19, the clock input of which is connected to the output of a voltage controlled oscillator (VCO) 17 and is the input of a multi-stage frequency divider 18.

 The direct output of the T-flip-flop 19 is connected to the clock input of the T-flip-flop 20, and the inverse is connected to the input of the counter-divider 21 (P = 72), the output of which is connected respectively to the second inputs of the pulse phase detector 13 and the frequency detector 14. Inverse output of the flip-flop 20 connected simultaneously with the input of the T-trigger 22 and the first input of the 3-I 23. The output of the T-trigger 22 is connected simultaneously to the input of the T-trigger 24 and the second input of the 3-I 23. The output of the T-trigger 24 is connected simultaneously to the third input of the element 3-I 23 and the first input of the analog-digital control converter 11. The direct output of the T-flip-flop 20 is connected to the synchronization input of the T-flip-flop 25, the output of which is connected to the synchronization input of the T-flip-flop 26, the output of which is connected to the second control input of the analog-to-digital converter 11. The output of the 3-I 23 element is connected to the inputs the reset of the T-flip-flops 25 and 26. The signals that are removed from the output of the T-flip-flops 25 and 26 are fed to the corresponding control inputs of the analog-to-digital converter 11 with a quarter-time offset from each other, thereby providing a square hydrochloric input processing.

 Figure 4 (a, b, c) shows the amplitude-frequency and phase-frequency characteristics, as well as the time delay characteristic of the group delay of the broadband filter preselector 2 (Cauer filter preselector).

 In FIG. 5 shows the amplitude-frequency characteristic of a cascade band-pass filter 9, which provides filtering of the mirror noise of the radio path and separation (selectivity) of the signals of the spacecraft of the Glonass and Navstar systems.

Block complex signal conversion 11 (Fig.1.6) contains comparators 27, 28 and 29, the first input of which receives a signal from the output of the amplifier 10 of the intermediate frequency. The second input of the comparator 27 is connected to a positive potential that determines the threshold comparison voltage (U _por1 ); the second input of the comparator 28 is connected to a negative potential that determines the threshold comparison voltage (U _por2 ); the second input of the comparator 29 is connected to the zero potential, which also determines the threshold comparison voltage (U _por3 ). The outputs of the comparators 27 and 28 are connected respectively to the first and second input of the OR element 30, the output of which is connected simultaneously with the information input of the D-flip-flops 31 and 32. The output of the comparator 29 is connected simultaneously to the information inputs of the D-flip-flops 33 and 34. The clock inputs of the triggers 31 and 33 are simultaneously connected to the output of the T-flip-flop 24, and the clock inputs of the D-flip-flops 32 and 34 are simultaneously connected to the output of the T-flip-flop 26. The outputs of the D-flip-flops 31 and 33 form the first (sine) pair of samples, and the outputs of the D-flip-flops 32 and 34 form a second (cosine) pair tschetov Q ₁ and Q ₂ output of the digital information signal.

 The inventive device operates as follows.

где P_i(t) - псевдослучайная огибающая i-го КА, = 1...n;
D_i(t) - навигационное сообщение i-го КА;
φ_i•L₁ и φ_i•L₂ - начальные фазы принимаемых сигналов;
ω_i•L₁ и ω_i•L₂ - несущие частоты в диапазонах L₁ и L₂ от i-го космического аппарата;
t - текущее время.At the antenna input of the receiver, signals from the spacecraft of two satellite radio navigation systems Glonass and Navstar S _L are received simultaneously, which in the two received frequency ranges L ₁ and L ₂ have the form:

where P _i (t) is the pseudo-random envelope of the i-th spacecraft, = 1 ... n;
D _i (t) - navigation message of the i-th spacecraft;
φ _i • L ₁ and φ _i • L ₂ are the initial phases of the received signals;
ω _i • L ₁ and ω _i • L ₂ - carrier frequencies in the ranges L ₁ and L ₂ from the i-th spacecraft;
t is the current time.

 The amplitude-frequency characteristic of the receiving path of the claimed device is determined by the frequency spectra of the received signals. The signal spectrum of the Navstar GPS satellite system when working with the C / A general-use code is (1575.42-1) MHz, and the spectrum of the GLonass satellite system signals with the C / A and P-code is (1602-1620 , 6) MHz.

 This means that the total frequency band of the received signals is equal to 1574.42 ≤ Δf ≤ 1620.6 MHz, i.e. The occupied frequency band Δf is approximately 50 MHz. The received signals from the antenna enter the input feeder 1, which is a quarter-wave segment of the coaxial line closed on one side and serves to coordinate the parameters of the antenna and the input circuits of the receiver. From the output of the feeder 1, the signals are fed to the input of the broadband filter-preselector 2, which serves to limit the frequency band of the received signals in the range of 1574.42-1621 MHz. The specified filter, made on microstrip lines, implements an elliptical 5th order Cauer bandpass filter. Figure 4, a presents the amplitude-frequency characteristic of this filter, and figure 4, b - its phase-frequency characteristic. As can be seen from FIG. 4b, the broadband filter preselector 2 has an important advantage, namely, the almost linear phase in the passband of the filter, which is a great advantage when working with complex phase-shift keyed signals received from satellites. This leads, for example, to the fact that the filter preselector 2 has the same linear group delay time τ in the passband equal to about 2.5 ns (Fig. 4 c). Such an implementation leads to the fact that there is no need to use a special calibrator to ensure the same group delay time τ for all signals received from the spacecraft. From the output of the filter preselector 2, the signal is fed to the input of a low-noise amplifier 3, the output of which is connected to the input of a band-pass filter 4, the output signal of which is fed to the input of the second low-noise amplifier 5.

 The bandpass filter 4 is designed to eliminate additional ripple in the obstacle bar of the broadband filter-preselector 2, as well as for decoupling between low-noise amplifiers 3 and 5. The main amplification of the receiving path is provided by low-noise amplifiers 3 and 5, which are based on gallium arsenide transistors with a Schottky barrier . The parameters of low-noise amplifiers 3 and 5: a gain of 35 dB, a range of received frequencies of 1 ... 8 GHz with uneven amplitude-frequency characteristics of 1 dB and a noise figure of 1.1 dB.

Next, the signal from the output of the LNA 5 is fed to the input of the mixer 6, made according to the balanced circuit and representing a linear frequency shift converter, i.e., at the output of block 6, the signal of the difference frequency f _pr = f _s - f _{p is extracted} , but it remains linearity of group delay time τ for all received signals.

 The output of the mixer 6 is connected to the input of the band-pass filter 9, the amplitude-frequency characteristic of which is presented in Fig.5. It represents two sequentially connected third-order Bessel filters with a linear phase-frequency characteristic tuned to the frequencies of the signals of the spacecraft of the Navstar GPS system, i.e. on the frequency (133-137 MHz) and the Glonass system, i.e. frequency (157-181 MHz), thereby providing processing of input information in a wide frequency band. The output of the bandpass filter 9 is connected to the first input of the intermediate frequency amplifier 10 to further amplify the input signal. To ensure the constancy of the gain within the specified limits, a block 12 of automatic gain control is used, covering LNA 3 and 5, an amplifier 10 of an intermediate frequency.

The output signal of the intermediate frequency amplifier 10 is fed to the input of the complex signal conversion unit, which implements quadrature processing of the input information by supplying rectangular pulses with a quarter-period shift to the control inputs of this node, while a sine wave is generated at the outputs I ₁ , I ₂ , and at the outputs Q ₁ and Q ₂ is the cosine component of the input information signal.

Compared with the prototype device [3] in the inventive receiver of satellite radio navigation signals, the following advantages are achieved:
a) providing the ability to receive and process signals of two satellite radio navigation systems, i.e. "Glonass" and GPS "Navstar" systems, using one receiving path, which means that a significant simplification of the receiving equipment has been achieved;
b) the implementation of the receiver can be carried out using one conversion to an intermediate frequency for the purpose of further digital processing of signals received from the spacecraft of satellite radio navigation systems, while the supply of local oscillator signals and control of the complex signal conversion unit. The use of a pulse phase and frequency detector in the frequency synthesizer protects the device from false captures at multiple frequencies of a voltage-controlled generator, and thereby ensures high reliability and accuracy of the circuit;
c) the inventive device provides higher accuracy of reproducing input information than the prototype device due to the use of filters with elliptic approximation, which provides a linear phase-frequency characteristic and, as a result, the same and minimum group delay time for all received signals. Thus, the tasks are completed.

Claims (1)

 A signal receiver of satellite radio navigation systems, comprising an antenna, a low noise amplifier, a mixer, an intermediate frequency amplifier, a reference thermostatic generator, characterized in that it further comprises a broadband filter preselector, a second low noise amplifier, a first and second bandpass filters, an automatic gain control unit, a synthesizer frequencies, a complex signal conversion unit, the output of the antenna feeder connected to the input of a broadband filter preselector, the output connected to the first input of the first low-noise amplifier, the output of which is connected to the input of the first low-pass filter, the output connected to the first input of the second low-noise amplifier, the output connected to the first input of the mixer, the output of which is connected to the input of the second low-pass filter, the output connected to the first input of the intermediate frequency amplifier the output of which is connected simultaneously with the information input of the complex signal converter unit and the automatic gain control unit, the output of the automatic A gain control is connected simultaneously with the second input of the first low-noise amplifier, the second input of the second low-noise amplifier and the second input of the intermediate-frequency amplifier, while the output of the reference thermostatic generator is connected to the input of the frequency synthesizer, the first output of which is connected to the second input of the mixer, and the second and third outputs frequency synthesizer connected respectively to the first and second inputs of the complex signal conversion unit.

Images