JPS6411182B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field to which the invention pertains] The present invention includes a negative feedback phase detector for a carrier suppressed signal and an acquisition tracking loop for a pseudo-noise code,
The present invention relates to a receiving device that receives a direct spread spectrum signal. [Description of the Prior Art] Conventional devices of this type include a circuit for capturing the spread spectrum code of the received signal, a synchronization detection circuit, a tracking loop for the spread spectrum code, a phase synchronization circuit for the received signal carrier, and its tracking loop. etc. have become the main components. Generally, in mobile communications, a Doppler shift (deviation) of carrier waves occurs in the communication transmission path due to the moving speed of the mobile body, so the above-mentioned receiving device requires an automatic frequency control circuit (AFC). In this case, the following (1) must be performed until the reception signal is received normally.
It is necessary to follow the steps shown in ~(9) in order. (1) Frequency search (2) AFC coarse control (3) Carrier wave regeneration (4) AFC fine control (5) Spreading code search and synchronization confirmation (6) Spreading code tracking and automatic gain using Costas loop, etc. Control (AGC) AFC control (7) Stopping AFC control (8) Changing the tracking loop filter bandwidth (9) Confirming synchronization maintenance As described above, it takes a long time to complete synchronization. Especially when the signal-to-noise ratio (S/N) is poor, a longer time is required. Recently, in order to shorten the time it takes to complete acquisition of normal reception in steps (1) to (9) above, the carrier frequency and the spreading code frequency are brought into a coherent relationship, that is, phase synchronized, and the carrier frequency is Doppler shifted ( A method is being put into practical use in which the amount of deviation (deviation) is predicted on the transmitting side and the transmitting frequency is controlled using input from the receiving device to keep it within a specific error range. The device used for this method does not require an AFC function, so
The time previously required for AFC control is shortened, and at the same time, the configuration of the device is simplified. FIG. 1 shows an example of a conventional configuration of this type of device.
A received signal (input SIG) is converted into an intermediate frequency signal by a frequency converter 1 and then gain-controlled by an AGC amplifier 2. Its output is Delay Lock Loop (DLL) 3 and correlator 4.
connected to. The error voltage output of the above DLL3 is generated by voltage controlled oscillator (VCO) 5, frequency divider (FREQDEV) 6, and spreading code generator (PN).
GEN) 7 and correlators (PSK modulators) 8 and 9 together constitute a code tracking loop. After the spread code synchronization is completed, the switch 10 is switched from the a terminal to the b terminal, and the switch 11 is further switched from the c terminal to the d terminal to maintain the code synchronization. This allows Costas Loop (Costas
The voltage controlled oscillator (VCO) 5 is controlled by the error voltage output of Loop) 12, and the frequency converter (mixer) 1
3. Signal generator 14 and bandpass filter (BPF)
15, performs a phase-locked loop of the carrier wave. By adopting such a configuration, the oscillation frequency of the voltage controlled oscillator VCO for the phase-locked loop of the carrier wave can be pulled into the lock-in range of the above loop using the Doppler shift (deviation) information of the code, and carrier wave synchronization is completed. We were able to significantly reduce the time required. However, when the above configuration is adopted, it is necessary to narrow the noise bandwidth of each detector input of the correlator output in order to use it for a line with a low (S/N) of the received signal. It is necessary to sufficiently increase the frequency stability of the voltage controlled oscillators 5 and 16. for example
If the noise bandwidth of the detector input is ±3 KHz at a reception frequency of 2 GHz band, a frequency stability of approximately ±1.2 ppm is required. In this case, if the voltage controlled oscillators 5 and 16 are housed in an active thermostatic chamber or a temperature compensated crystal oscillator (TCVCXO) is used, it is possible to satisfy the above conditions within a specific device temperature range. This is very difficult to achieve for demanding equipment. In the case of the configuration shown in Figure 1, when the spreading code is long, all codes are sent to the spreading code generator (PN GEN).
7 may take a long time to search.
In order to shorten this search time, a method called a code stagger method has traditionally been adopted. FIG. 2 shows an example of the configuration of this system. FIG. 2 shows the case where four staggers are performed. The input SIG (received signal) passes through a bandpass filter (BPF) 20 and then
The local code is divided by a phase difference of 1/4 of the total code length so that it can be detected by any one of the signal detection sequences 21a to 21d. This is the shift register (SHIFT) 22a to 22c.
This is done by shifting the phase at . In other words, the input/output of each shift register 22a to 22c is to transmit a local oscillation signal (LO SIG) to the modulator 24.
Phase shift modulation (PSK.phase-shift) from a to 24d
keying) and use it as a local code for each series circuit 21a to 21d. The outputs of the circuits 21a to 21d are detected by the A/D converter 27 by operating the circuit (1/2CHIP STEP) 25 and the switch 26, and the presence or absence of the output is detected by the processor (CPU) 28, and the received signal is For the existing series, codes with normal phases are selected by gate circuits 29a to 29d. However, although the configuration shown in Fig. 2 can perform synchronized detection of the spread code, it is necessary to separately provide a spread code tracking loop sequence and a multi-pulse detection sequence, etc., which prevents the device from becoming complicated and large. I couldn't help it. [Object of the Invention] The present invention aims to improve the above-mentioned drawbacks, and provides a method for receiving spread spectrum signals that takes a short time to complete synchronization, has a simple device configuration, has low power consumption, and can be mounted on an artificial satellite. The purpose is to provide equipment. [Summary of the Invention] The present invention provides a separately provided temperature compensation system that controls the oscillation frequency of a voltage controlled oscillator (VCO) that constitutes a spread code phase-locked loop and a carrier wave phase-locked loop until immediately before the start of a spread code or carrier acquisition operation. Achieves the desired frequency stability by phase-locking the output of a type crystal oscillator (TCXO), and simultaneously constructs a phase-locked loop for the spread code and a code pseudo-synchronization detection circuit by using each signal detection row of the code stagger. It is characterized by The present invention provides means for amplifying and frequency converting a received signal, a capture and tracking loop for a spread spectrum code corresponding to a spread spectrum signal, a carrier phase locked loop for said spread spectrum signal, and a means for superimposing or modulating said spread spectrum signal. a temperature-compensated crystal oscillator having an oscillation frequency that is approximately the same as the oscillation frequency of the voltage-controlled oscillator forming a part of the carrier phase-locked loop; and a loop for synchronizing the voltage controlled oscillator with this oscillator, and a reference for each local oscillator signal source for converting the output of the voltage controlled oscillator into the frequency of the receiver and for despreading the spread spectrum signal, and for the code acquisition tracking loop. means for multiplying, amplifying, mixing or dividing the frequency of the frequency dividing means to provide a signal source; a loop for synchronizing the voltage controlled oscillator for the spreading code acquisition and tracking to the output signal of the frequency dividing means; means for controlling the voltage controlled oscillators of each of the loops by switching between the error signal output of the two synchronized loops and the error signal output of the code capture/tracking loop; and an error signal of the code capture/tracking loop. means for controlling the carrier phase-locked loop voltage controlled oscillator by switching between an output and an error signal of the carrier phase-locked loop;
The present invention is characterized in that it includes logic circuit means such as a microcomputer that synchronizes the acquisition of the spread spectrum code and the carrier wave by all of the signal switching means described above. Furthermore, the present invention divides the received signal power into n (n=1, 2,...) before despreading the spreading code.
and means for despreading and signal detecting each of the n-divided spread signals with a 1/n code stagger, A code tracking means for selecting a code channel synchronized with the received code from each branch output of the 1/n code stagger, and a code tracking means for selecting two of the channels from each branch output of the 1/n code stagger; It may include means for leading and retarding the phase. Furthermore, the present invention may include means for switching the output of the phase advancing and phase delaying means to the branch output of the code stagger as a local code of the two signal detection sequences set for the code tracking. [Description of Embodiment] FIG. 3 is a configuration diagram of an embodiment of the present invention. The received signal (input SIG) is sent to the front end 31 of the receiving device.
The signal is subjected to frequency conversion, amplification, etc., and is connected to four subsequent signal detection trains. Each signal detection column basically consists of despreading PSK wave generators 32a to 3.
2d, correlators 33a to 33d, band wave generator 34a
~34d, amplifiers 35a~35d, square law detector 3
6a to 36d, and integral dischargers 37a to 37d
including. The PSK wave generators 32a to 32d apply the reference signal generated by the frequency synthesizer 38 to the reference signal generated by the frequency synthesizer 38.
PSK is applied using four staggered local codes from the local code generator 39. The displays A to H in the local code generator 39 represent the capture steps of each loop in the capture process shown in Table 1 below. Details of Table 1 will be explained later. The input signal for the frequency synthesizer 38 is obtained from a carrier phase locked loop voltage controlled crystal oscillator (VCXO) 40. In acquisition steps A and B in Table 1, this VCXO 40 is connected to a temperature controlled crystal oscillator (TCXO) 41 and a loop filter 4.
2. Synchronization is achieved with the oscillation frequency of the TCXO 41 by a shot loop composed of a phase detector 43 and a switch 44. At this time, the output of the VCXO 40 is divided by the frequency divider 45 to the frequency of the local code (31/(2×96) times in the embodiment), and becomes a reference signal for the short loop for generating the local code clock. This short loop is composed of a phase detector 46, a switch 47, a loop filter 48, and a VCXO 49. The output of the VCXO 49 is a T/2 phase shifter 50 (T is half the clock period).
represents the time of ), a T phase shifter 51, and a long code generator 52. Also, phase shifter 5
Each output of 0 and 51 is output from a short code generator 53,
54 respectively. Here the long code is the received signal, for example
It means the Q channel modulation code of UQPSK (unbalanced quadrature phase keying) wave, and the short code is for example
It is a 1024-bit gold code and means an I channel modulation code. The output of each code generator 52 to 54 becomes an input to a local code generator 39. In the local code generator 39, 256-stage shift registers 55a to 55c are connected in series from the output of the short code generator 53. These three connection points 56a to 56c and the shift register 55
The output of a is connected to the switching devices 57a to 57d on a one-to-one basis and simultaneously connected to the switching device 58. The output of the switch 58 is the DLL for short code phase synchronization.
The signal is input to a +T/2 phase shifter 59 and a -T/2 phase shifter 60, and a despreading PSK wave generator 61, respectively. On the other hand, the output of the long code generator 52 is
-T/2 phase shifter 90, +T/2 phase shifter 91, -2T phase shifter 92 and switch 57d, respectively. These phase shifters 59, 60, 90-91 are connected to switches 57a, 50b and 57d.
A reference signal for the PSK wave generator 61 is obtained from the frequency synthesizer 38. The output of the PSK wave generator 61 is input to a correlator 62, and the output of the correlator 62 is branched into two, and then passes through band wave generators 63a, 63b, amplifiers 64a, 64b, and square-law detector 6, respectively.
5, and connected to Costas loops 66 and 67. Costas loop 67 output and DLL comparator 68
The output of the phase detector 43 and the output of the phase detector 43 are
4 and connected to the loop filter 42.
The output of the phase comparator (DLL) 68 is also connected to the switch 47, and the output of the phase detector 46 is selected and connected to the loop filter 48. On the other hand, the outputs of the aforementioned signal detection arrays pass through a switch 80, are digitized by an A/D converter 81, and are then subjected to data processing by a microprocessor 82. The main operations of the device having such a configuration are as follows. The spread spectrum received signal subjected to Doppler correction is synchronized by searching the local codes of the four signal detection sequences and controlling the code phase by the microprocessor 82. Table 1 summarizes the operations of this apparatus during these series of acquisition processes. In acquisition steps A and B, the carrier
Tracking loop and code tracking loop are TCXO4
It operates with the output of VCXO40 synchronized to the frequency of 1. That is, in steps A and B, neither the carrier nor the code is captured, so the front end 31 and correlator 33 of the device
It is essential that the signals frequency-converted by a to 33d fall into the passbands of the bandpass converters 34a to 34d. This embodiment device is used in a system that assumes that the received signal frequency is Doppler corrected from the nominal carrier frequency to about ±700 Hz, so in order to lower the reception threshold as much as possible, the Bandwidth is 2KHz
degree

[Explanation of effects]

As explained above, the temperature compensated crystal oscillator
By adopting TCXO41 and sharing the signal detection train and code tracking loop, it is possible to switch acquisition steps at the DC level, improving reception sensitivity and shortening the time required to complete acquisition. The power consumption of the device can be reduced and the device configuration can be simplified. These advantages are particularly effective for space communication equipment mounted on artificial satellites. Since all of the series of acquisition operations described above can be performed by a microprocessor, operational complexity due to shared circuits can be completely ignored.

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams of a conventional spread spectrum signal receiving apparatus. FIG. 3 is a block diagram of an embodiment of the present invention. 1, 13... Frequency converter (mixer), 2...
AGC amplifier, 3... Delay lock loop (DLL), 4, 8, 9... Correlator, 5, 16...
Voltage controlled oscillator (VCO), 6...frequency divider,
7...Spreading code generator (PN GEN), 10,1
1...Switcher, 12...Costas loop, 14...
...Oscillator, 15... Bandwidth wave generator, 20... Bandwidth wave generator, 21... Signal detection train, 22... Shift register, 23... PN code generator, 24... PSK modulator, 25... Code transfer Phase switch, 26...switcher,
27...A/D converter, 28...Microprocessor, 29...Gate circuit, 31...Receiver front end, 32, 61...PSK modulator,
33, 62... Correlator, 34, 63... Band wave generator, 35, 64... Amplifier, 36, 65... Square law detector, 37... Integrating discharger, 38... Frequency synthesizer, 39... Local code generator, 4
0, 49... Voltage controlled crystal oscillator, 41... Temperature compensated crystal oscillator (TCXO), 42, 48... Loop filter, 43, 46... Phase detector, 4
4, 47, 57, 58, 69, 80...switcher,
45... Frequency divider, 50, 51, 59, 60, 90
~92... Phase shifter, 52-54... PN code generator, 55... Shift register, 56... Connection branch point, 66, 67... Costas loop, 68...
Comparator, 81...A/D converter, 82...Microprocessor.

Claims (1)

Claims: 1. means for amplifying and frequency converting a received signal; a spread spectrum code acquisition and tracking loop corresponding to a spread spectrum signal, including a first voltage controlled oscillator 49; and a second voltage controlled oscillator 40; a phase-locked loop that is synchronized with a carrier wave of the spread spectrum signal, and demodulation means for demodulating baseband data superimposed or modulated on the spread spectrum signal, the second voltage controlled oscillator; a temperature-compensated crystal oscillator 41 having an oscillation frequency approximately equal to the oscillation frequency of 40;
0 synchronization loop, and the output of the second voltage controlled oscillator 40 is used as a reference signal source for each local oscillation signal source for frequency conversion of the receiver and for despreading of the spread spectrum signal, and for the spread code acquisition and tracking loop. a first voltage controlled oscillator 49 included in said spreading code acquisition and tracking loop;
and a loop that synchronizes the first and second voltages by switching between each error signal output of the two synchronization loops and the error signal output of the spreading code capture and tracking loop using the temperature compensated crystal oscillator as a reference signal. means for controlling a controlled oscillator; and means for controlling a second voltage controlled oscillator 40 for the carrier phase-locked loop by switching between the error signal output of the spreading code acquisition and tracking loop and the error signal of the carrier phase-locked loop. and logic circuit means using a microcomputer for controlling signal switching of each of the means and synchronizing acquisition of a spread spectrum code and a carrier wave. 2. The acquisition and tracking loop for the spread spectrum code includes means for dividing the received signal power into n before despreading the spread code, and dividing each of the n divided spread signals by 1/n.
means for despreading and signal detection with a code stagger; and code tracking for selecting a code channel in synchronization with the received code from each branch output of the 1/n code stagger for two of the n signal detection sequences. means for leading and retarding the selected code by 1/4 of the code period; and means for switching between the output of the leading and retarding means and the branch output of the code stagger. A receiving device for spread spectrum signals as described in Range 1.