CN109831821B

CN109831821B - A satellite mobile communication terminal

Info

Publication number: CN109831821B
Application number: CN201910201157.3A
Authority: CN
Inventors: 周微; 张庆业; 张洁; 王广远
Original assignee: CETC 54 Research Institute
Current assignee: CETC 54 Research Institute
Priority date: 2019-03-18
Filing date: 2019-03-18
Publication date: 2021-06-22
Anticipated expiration: 2039-03-18
Also published as: CN109831821A

Abstract

The invention discloses a satellite mobile communication terminal, which belongs to the technical field of satellite mobile communication. The device performs the following steps: (1) the accelerator demodulates the wireless signal received by the radio frequency to complete the offset estimation of timing and frequency; (2) uses the timing estimation information to adjust the timer module to complete the timing synchronization process, and at the same time the frequency The information is sent to the digital down-conversion processing unit to complete the frequency compensation of the baseband demodulation; (3) In the idle standby state, the periodic downlink receiving method with large intervals is used to achieve synchronous tracking; (4) In the service state, the frequency estimation update of the current service is used. Frequency drift rate, and use the timing drift rate parameter to complete the real-time tracking compensation of timing and frequency in the weak signal state. The invention can effectively complete the tracking compensation of timing and frequency under no signal or weak signal, and can effectively reduce the link receiving failure and the large-scale deviation of the transmission signal frequency.

Description

Satellite mobile communication terminal

Technical Field

The invention belongs to the technical field of satellite mobile communication, and particularly relates to a satellite mobile communication terminal.

Background

In satellite mobile communication systems, the TDMA/FDMA technical scheme is generally adopted. The frame structure of a TDMA (Time Division Multiple access) system is composed of an ultra-high frame, a super-frame, a multi-frame, a frame and a Time slot number. The satellite mobile communication uses the GEO geostationary orbit satellite transponder as a relay station to complete the communication between the terminal and the ground station, and requires that all signals of the terminal are received and transmitted to be aligned at a satellite port, so the ground terminal of the satellite mobile communication system has the characteristics of independent uplink and downlink communication, large transmission delay, large timing drift and frequency offset and the like compared with the ground mobile communication. However, the inevitable shielding of the terminal during the ground movement will cause the signal to weaken for a while, and the difference in velocity during the movement will affect the demodulation reception of the channel.

At present, no detailed description is provided for a timing and frequency tracking method in satellite mobile communication in the prior art, the prior art mainly depends on the stability of a crystal oscillator of equipment and the control of temperature to ensure the stability of the timing and frequency of a terminal, and the method has high requirements on hardware conditions.

Disclosure of Invention

In view of the above, the present invention provides a satellite mobile communication terminal, and the terminal and the method thereof do not depend on hardware conditions, but use a software control manner to complete timing and frequency tracking compensation in the absence of signals or weak signals, so as to effectively reduce link reception failure and large-scale drift of the frequency of the transmitted signals.

In order to achieve the purpose, the invention adopts the technical scheme that:

a satellite mobile communication terminal comprises a CPU, a baseband satellite communication accelerator, a timer module, a digital down-conversion processing module and an uplink transmission frequency compensation module, wherein the baseband satellite communication accelerator comprises a baseband demodulation module, wherein:

the baseband satellite communication accelerator demodulates the radio signals received by radio frequency to complete frequency estimation and timing estimation;

the CPU utilizes the timing estimation information to adjust the timer module to complete the timing synchronization process, and simultaneously sends the frequency estimation information to the digital down-conversion processing module to complete the frequency compensation of the baseband demodulation; in the idle standby state, the CPU adopts a large-interval periodic downlink receiving mode to carry out synchronous tracking, and utilizes the prior timing estimation information to calculate the timing drift rate during the interval period to carry out periodic timing compensation; in a service state, the CPU estimates and updates the frequency drift rate by using the frequency of the current service, and completes real-time tracking compensation of timing and frequency in a signal shielding or weak state by using a timing drift rate parameter;

the timing and frequency compensation method comprises the following steps:

(1) inputting each burst downlink baseband signal S into a baseband satellite communication accelerator, and outputting a timing estimation delta T and a frequency estimation delta F by a baseband demodulation module of the baseband satellite communication accelerator;

(2) when the network searching is completed and the system is read, the broadcast control channel stage is once regulated by using 8 XK frame interval to estimate the timing of N frames₁、ΔT₂、....、ΔT_NMaking statistics to obtain initial frequency drift rate

Wherein, the broadcast channel 8 frames are updated once, and K is more than or equal to 1;

(3) after the network access is finished and the standby idle low-power consumption state is carried out, a CPU keeps timing tracking synchronization, and a broadcast control channel is configured at intervals of M frames for receiving, wherein M is more than or equal to 32; specifically, the timing estimation Δ T output in step (1) is used, the timing drift rate Δ T ' at M frame intervals is calculated in an averaging manner, and Δ Time _ rate obtained in step (2) is corrected in real Time by using Δ T ', and the correction value is Δ Time _ rate ':

ΔTime_rate’＝α·ΔTime_rate+(1-α)·ΔT’，α∈[1.0，1.5]，

the CPU utilizes the delta Time _ rate' to carry out timing tracking compensation of an idle state;

(4) in a voice or data service working state, carrying out N-frame statistical averaging on frequency estimation delta F output by a baseband demodulation module to obtain an average value delta F ', wherein N is more than or equal to 8, the frequency drift rate output in an N-frame interval range is delta Freq _ rate, and the delta Freq _ rate is delta F'/N; if the channel demodulation is correct, the CPU adopts delta F' to perform uplink and downlink frequency tracking compensation, otherwise, the CPU adopts delta Freq _ rate estimated and output by the last N frame interval to perform uplink and downlink frequency tracking compensation;

(5) in the working state of voice or data service, timing tracking compensation is performed by using the timing estimation delta T output by the baseband demodulation module, which specifically comprises the following steps: if the channel demodulation is correct, the CPU adjusts the timing module by adopting the delta T value; otherwise, the timing tracking compensation is performed with the value of α × Δ Time _ rate, α ∈ [1.0,1.5 ].

The beneficial effect who adopts above-mentioned technical scheme to obtain lies in:

1. the invention calculates the periodic timing drift frequency and the frequency drift frequency based on the demodulation processing module of the downlink channel of the satellite mobile communication system, is particularly suitable for the demodulation threshold with low signal-to-noise ratio, namely, the tracking compensation of the timing and the frequency is completed under the state of signal shielding or weak, can prevent the step of receiving loss of a link after the signal recovery and the large-range deviation of the frequency of an uplink sending signal, and can meet the change curve of characteristic frequency and intermittent frequency.

2. The invention does not depend on hardware conditions, but adopts a software control method, can effectively finish the tracking compensation of timing and frequency under no signal or weak signal, and can effectively reduce the failure of link reception and the large-range drift of the frequency of the transmitted signal.

Drawings

FIG. 1 is a schematic block diagram of an embodiment of the present invention;

FIG. 2 is a frame plan diagram of a satellite mobile communication system according to an embodiment of the present invention;

FIG. 3 is a diagram of a timing estimation drift rate unit for a broadcast channel in an embodiment of the present invention;

FIG. 4 is a diagram of a traffic state timing estimation and frequency estimation compensation unit according to an embodiment of the present invention;

FIG. 5 is a graph of standard variation of frequency and timing during a characteristic state in an embodiment of the present invention;

FIG. 6 is a graph of frequency and timing measurements during steady state in an embodiment of the present invention;

FIG. 7 is a graph of frequency measurements during a feature state according to an embodiment of the present invention;

FIG. 8 is a graph of frequency measurements during an intermittent state in an embodiment of the present invention;

FIG. 9 is a graph of frequency measurements and a mean and root mean square statistical table of timing errors during steady state, feature, and intermittent states in an embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

A satellite mobile communication terminal comprising a CPU, a baseband satellite communication accelerator, a timer module, a digital down-conversion processing module, and an up-transmission frequency compensation module, the baseband satellite communication accelerator comprising a baseband demodulation module, wherein:

the CPU utilizes the timing estimation information to adjust the timer module to complete the timing synchronization process, and simultaneously sends the frequency estimation information to the digital down-conversion processing module to complete the frequency compensation of the baseband demodulation; in the idle standby state, the CPU adopts a large-interval periodic downlink receiving mode to carry out synchronous tracking, and utilizes the prior timing estimation information to calculate the timing drift rate during the interval period to carry out periodic timing compensation; in the service state, the CPU estimates and updates the frequency drift rate by using the frequency of the current service, and completes real-time tracking compensation of timing and frequency in the signal shielding or weak state by using the timing drift rate parameter.

A timing and frequency tracking compensation method for a satellite mobile communication terminal as described above, comprising the steps of:

(2) after the network searching is completed, entering a broadcast control channel stage of a reading system, carrying out timing adjustment once by using a frame interval of 8 multiplied by K, and carrying out statistics on timing estimation delta T to obtain an initial frequency drift rate delta Time _ rate; wherein, the broadcast channel 8 frames are updated once, and K is more than or equal to 1;

(3) after the network access is finished and the standby idle low-power consumption state is carried out, a CPU keeps timing tracking synchronization, and a broadcast control channel is configured at intervals of M frames for receiving, wherein M is more than or equal to 32; the specific mode is that the timing estimation delta T output in the step (1) is utilized, the timing drift rate delta T 'under the M frame interval is calculated in an averaging mode, the delta Time _ rate obtained in the step (2) is corrected in real Time by utilizing delta T', the corrected value is delta Time _ rate ', and the CPU utilizes the delta Time _ rate' to carry out timing tracking compensation of an idle state;

Specifically, referring to fig. 1, the satellite communication baseband demodulation module receives and outputs timing estimation information Δ T and frequency estimation information Δ F in a downlink direction, where Δ T is sent to the timer module for timing adjustment, and Δ F needs to be sent to the digital down-conversion module for demodulation and also needs to be sent to the uplink transmission frequency compensation module for uplink frequency synchronization compensation.

Referring to the frame schedule of satellite mobile communication of fig. 2, 8 frames of BCCH (Broadcast Control Channel) are received once, so that the timing drift rate is estimated using a frame interval of 8 × K (K ≧ 1).

Referring to fig. 3, assuming that the adjustment values of each interval are Δ Tb1, Δ Tb2, …, Δ TbN, the frequency drift rate Δ Time _ rate (unit: number of primary clocks/frame) of the broadcast BCCH is:

after entering the idle state, the terminal configures the BCCH channel for maintaining the timing synchronization and the frame period of the M (M is greater than or equal to 32) frame period, and at this time, the same method is used to statistically calculate the timing drift rate of the M frame interval as follows:

ΔTime_rateM＝ΔTbM/M (2)

wherein Δ TbM is a timing estimation value of BCCH broadcast after an interval of M frames under standby low power consumption, and then the current real-Time iterative update correction value Δ Time _ rate' is:

ΔTime_rate’＝α·ΔTime_rate+(1-α)·ΔTime_rateM (3)

referring to fig. 4, in the working state of voice or data service, the baseband demodulation module outputs a timing Δ Td and an estimated frequency Δ Fd per frame in real time, where the estimated frequency output is an average estimated value output of N frames (N ≧ 8) each time, and then the frequency drift rate Δ Freq _ rate is Δ Fd/N (unit: Hz/frame) within an interval range of N frames, and a sliding frame statistical method is adopted to average the latest K times (K ≧ 3) for smooth output design, that is:

when the frequency change is in a steady state, the statistically averaged frequency drift rate Δ Freq _ rate _ avg value converges to about 0. The specific frequency tracking compensation method comprises the following steps: if the channel demodulation is correct, the CPU adopts the delta Fd to carry out the frequency tracking compensation of the uplink and the downlink; if the channel demodulation is incorrect, the CPU processor adopts the delta Freq _ rate _ avg output by the N frame interval estimation under the condition of the last signal to carry out the uplink and downlink frequency tracking compensation.

Still referring to fig. 4, in the working state of voice or data service, the timing tracking compensation method is as follows: if the channel demodulation is correct, the CPU adjusts the timing module by adopting the delta Td value of the current frame; if the channel demodulation is incorrect, the delta Time _ rate parameter is adopted, and the timing tracking compensation is carried out by using the alpha multiplied by the delta Time _ rate value, wherein the alpha value is related to the terminal type and the transmission bandwidth of the current channel, and the value range of the alpha value is [1.0,1.5 ].

The above embodiments implement timing and frequency tracking compensation in satellite mobile communications, which can satisfy the timing and frequency measurement variation graphs of the satellite mobile standard of fig. 5. Fig. 6, 7 and 8 show the timing and frequency tracking curves of the terminal in steady state, characteristic and intermittent states in the beijing tel laboratory network access certification test, respectively, and fig. 9 is a frequency measurement graph and a mean and root mean square statistical table of timing errors during the steady state, characteristic and intermittent states. Therefore, the invention achieves the corresponding design standard, and the terminal obtains good communication effect in the actual satellite.

Claims

1. a satellite mobile communication terminal, is characterized in that, comprises CPU, baseband satellite communication accelerator, timer module, digital down-conversion processing module and uplink transmission frequency compensation module, and described baseband satellite communication accelerator comprises baseband demodulation module, wherein :

The baseband satellite communication accelerator demodulates the wireless signal received by the radio frequency to complete the frequency estimation and timing estimation;

The CPU uses the timing estimation information to adjust the timer module to complete the timing synchronization process, and at the same time sends the frequency estimation information to the digital down-conversion processing module to complete the frequency compensation of the baseband demodulation. In the service state, the CPU uses the frequency of the current service to estimate and update the frequency drift rate, and uses the timing drift rate parameter to calculate the timing drift rate in the signal state. Real-time tracking compensation of timing and frequency under occlusion or weak state;

The way of timing and frequency compensation is:

(1) Input the downlink baseband signal S in every burst into the baseband satellite communication accelerator, and output timing estimation ΔT and frequency estimation ΔF by the baseband demodulation module of the baseband satellite communication accelerator;

(2) After searching the network and entering the stage of reading the broadcast control channel of the system, use the 8×K frame interval to make a timing adjustment, and perform statistics on the timing estimates ΔT ₁ , ΔT ₂ , . . . , ΔT _N of N frames to obtain the initial Frequency drift rate

N≥8; among them, the broadcast channel is updated once every 8 frames, K≥1;

(3) After the network is completed and the standby idle low power consumption state is completed, the CPU maintains timing tracking synchronization, and configures broadcast control channel reception at an interval of M frames, M≥32; Calculate the timing drift rate ΔT' at the M frame interval in an average manner, and use ΔT' to correct the ΔTime_rate obtained in step (2) in real time, and the correction value is ΔTime_rate':

ΔTime_rate'=α·ΔTime_rate+(1-α)·ΔT', α∈[1.0,1.5],

The CPU uses ΔTime_rate' to perform timing tracking compensation in the idle state;

(4) In the working state of voice or data service, perform statistical averaging of N frames on the frequency estimate ΔF output by the baseband demodulation module to obtain the average value ΔF', where N≥8, the frequency drift rate output within the N frame interval is ΔFreq_rate, ΔFreq_rate=ΔF'/N; if the channel demodulation is correct, the CPU uses ΔF' to track and compensate the frequency of the uplink and downlink; otherwise, the CPU uses the ΔFreq_rate output by the last N frame interval estimation to track the frequency of the uplink and the downlink. compensate;

(5) Under the working state of voice or data service, use the timing estimate ΔT output by the baseband demodulation module to perform timing tracking compensation, specifically: if the channel demodulation is correct, the CPU uses the ΔT value to adjust the timing module; otherwise, use the ΔT value to adjust the timing module. The value of α×ΔTime_rate performs timing tracking compensation, α∈[1.0,1.5].