JPS634734B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a frequency fluctuation correction method that reduces frequency fluctuation correction errors. In satellite communication systems, Frequency Fluctuation Correction (AFC: Auto
A technique called Frequency Control) is used.
This is especially true in SCPC satellite communication systems that transmit low-speed signals of several kbit/s to several tens of kbit/s between a base station and many mobile stations or small stations.
It is an important issue to make the AFC correction error as small as possible. The conventional AFC method will be explained below and its drawbacks will be shown. Note that a mobile satellite communication system in which the radio frequency band between the base station and the satellite and the radio frequency band between the satellite and the mobile station are different will be described here. 1st
The figure shows the configuration of the assumed system. In FIG. 1, 1 is a base station, 2 is a pseudo mobile station, 3 is a satellite, and 4-1 to 4-N are mobile stations. In addition, _ET and _ER are the radio frequency bands transmitted from and received by the base station, _MT is the radio frequency band transmitted from the pseudo mobile station and mobile station, and _MR is the radio frequency band received by the pseudo mobile station and mobile station. be.
As shown in the figure, the system of FIG. 1 is a system in which a signal from a base station is transmitted to each mobile station, and a signal from each mobile station is transmitted to the base station. Here, the pseudo mobile station is a station that has the function of receiving the AFC pilot signal from the base station and controlling the frequency of the local oscillator of the frequency converter of the base station, and the function of transmitting the AFC pilot signal. Figure 2 shows conventional AFC from mobile station to base station.
This shows an example of the system configuration. In FIG. 2, Table 1 shows the correspondence between the numbers and names of each partial circuit on the drawing.

【table】

[Table] The operation shown in Figure 2 will be explained. A pilot signal transmitted from a pilot signal generator 1 of a pseudo mobile station is received by a base station via a satellite. Frequency fluctuation amount ΔFX Mr→E at point X of the base station at this time
is the sum of the frequency fluctuations of the local oscillators of each frequency converter that passed through, and ΔFX ΔFX Mr→E=Δ _Mrp +Δ _Mr1 +Δ _Mr2 +Δ _S +Δ _E1 +
_ΔE2 (1). The amount of frequency fluctuation at point Y is determined by AFC circuit 15.
As a result, VCO11 shifts by ΔFX Mr→E, so it becomes zero. _On the other hand, _the frequency fluctuation amount ΔFX Mi→E _of the transmission signal transmitted from the _{mobile station} at point The quantity ΔFY Mi→E is ΔFY Mi→E=ΔFX Mi→E−ΔFX Mr→E = (Δ _Mrp +Δ _Mr1 +Δ _Mr2 ) −(Δ _Mi1 +Δ _Mi2 (3). In this way, it is clear from Equation 3. The maximum amount of frequency fluctuation from each mobile station is |ΔFY Mi→E| _nax = |Δ _Mrp | +|Δ _Mr1 |+|Δ _Mr2 | +|Δ _Mi1 |+|Δ _Mi2 | (4) Therefore, the conventional AFC method has the disadvantage that it cannot correct the amount of frequency fluctuation of the pilot signal generator and the amount of frequency fluctuation at each transmission frequency converter of the pseudo mobile station and each mobile station. The aim is to improve this shortcoming,
The frequency of the pilot signal transmitted at the pseudo mobile station is intentionally shifted by the frequency variation of the receiving local oscillator, and each mobile station is intentionally shifted by the frequency variation of the incoming frequency from the base station. It transmits by shifting the transmission frequency, and its characteristics are that the base station and many slave stations are connected via communication satellites, and a pseudo station is set up near the base station, and the pseudo station is transmitted from the base station. A function of receiving a first pilot signal for frequency fluctuation correction via a communication satellite and controlling the local oscillation frequency 5 of the transmission frequency converter 4 of the base station according to the reception frequency, and the frequency change from the slave station to the base station. The frequency of the pilot signal generator 21, which has a function of transmitting a second pilot signal for fluctuation correction via a communication satellite, and provides the frequency of the second pilot signal from the pseudo station, is changed to the reception frequency converter of the pseudo station. 18 and 20, and each slave station intentionally shifts its transmission frequency by an amount corresponding to the frequency fluctuation of the first pilot signal from the base station. It is based on a frequency fluctuation correction method such as shifting the frequency. Examples will be described below with reference to the drawings. FIG. 3 shows an embodiment of the invention. The correspondence between the numbers and names of each partial circuit in FIG. 3 is summarized in Table 2.

【table】

[Table] Note that in the following explanation, the amount of frequency fluctuation of the oscillator used in the modulation circuit and the demodulation circuit is considered to be sufficiently small because the oscillation frequency is low, and will be ignored. In FIG. 3, a plurality of modulated waves for each mobile station are input from a terminal 1 of the base station, and an AFC pilot signal (one wave) output from a pilot signal generator 2 is synthesized in a circuit 3. These signals are transmitted from the base station via frequency converters 4 and 6, and received by the pseudo mobile station and each mobile station via the satellite. This signal received by the pseudo mobile station is transmitted to the frequency converter 1
The signal is frequency-converted at steps 8 and 20 and input to the AFC circuit 22 . As shown in AFC circuit 15 in Fig. 2, the AFC circuit is composed of a pilot signal detection circuit, a frequency difference detection circuit, and a VCO control voltage generation circuit, and is designed to reduce the amount of frequency fluctuation of the AFC circuit input to zero. Control VCO. Therefore, the base station
The frequency deviation amount ΔF _E1 of the VCO 5 is given by the amount of local oscillation frequency fluctuation of each frequency converter through which the pilot signal of the pilot signal generator 2 passes, ΔF _E1 = Δ _Ep + Δ ^t _E1 + Δ ^t _E2 + Δ _S1 + Δ _Mr1 + Δ _Mrp (5). Also, the frequency fluctuation amount ΔF _S of the frequency transmitted from the satellite at point B in Figure 3 is as follows: ΔF _S = ΔF _E1 − (Δ _Ep + Δ ^t _E1 + Δ ^t _E2 + Δ _S1 ) = (Δ _Mr1 + Δ _Mrp ) (6 ) becomes. Each mobile station receives a frequency having a frequency variation shown in equation (6), converts the frequency using frequency converters 27 and 29, and inputs the frequency to the AFC circuit 32. The frequency fluctuation amount at the input point of the AFC circuit 32 is determined by the frequency fluctuation amount Δ _Mi1 at the frequency converter 27 and the frequency fluctuation amount Δ Mi2 at the frequency converter 29 in addition to the frequency fluctuation amount shown in equation ( ₆₎ . Therefore, the frequency deviation ΔF _Mi of the VCO 28 becomes ΔF _Mi = (Δ _Mr1 + Δ _Mrp ) + Δ _Mi1 + Δ _Mi2 (7). Since the local oscillators of the frequency converters 29 and 31 are used in the same manner, the signal outputted to the terminal 36 has no frequency fluctuation. Furthermore, since the frequency of the local oscillator 34 is commonly used by the frequency converters 33 and 35, the signal from the terminal 37 to the base station has a frequency variation Δ _Mi3
can be canceled out, and the frequency fluctuation amount ΔF ^D _Mi at point D of the mobile station becomes ΔF ^D _Mi = (Δ _Mr1 + Δ _Mrp ) + Δ _Mi2 (8). On the other hand, regarding the pilot signal transmitted from the pilot signal generator 21 of the pseudo mobile station, the frequency fluctuation amount ΔF ^E _Mr at point E in FIG. 3 becomes ΔF ^E _Mr =Δ _Mrp +Δ _Mr1 (9). Here, since the local oscillator 24 is commonly used by the frequency converters 23 and 26, the frequency fluctuation amount Δ _Mr2 is not included in the transmission frequency fluctuation. The difference ΔF between the frequency variation of the pilot signal transmitted from the pseudo mobile station and the frequency variation of the transmission signal transmitted from the mobile station is calculated from the comparison of equations (8) and (9) as follows: ΔF=ΔF ^D _Mi − ΔF ^E _Mr = Δ _Mi2 (10), and at the worst value, |ΔF| _nax = |Δ _Mi2 | (11). This frequency fluctuation amount ΔF becomes an error frequency that cannot be corrected by AFC as explained in the conventional AFC method, but in general, since _Mi1 ≫ _Mi2 , Δ _Mi1
≫Δ _Mi2 , and as is clear from the comparison of equations (11) and (4), this method can significantly reduce the frequency fluctuation correction error than the conventional AFC method. As explained above, in the present invention, the frequency of the pilot signal transmitted from the pseudo mobile station is intentionally shifted by the amount of frequency fluctuation caused by the local oscillator of each reception frequency converter of the pseudo mobile station, and then transmitted.
Each mobile station includes the amount of frequency fluctuation in the frequency arriving from the base station in the transmission frequency to the base station, and is configured to intentionally shift the transmission frequency and transmit. This has the advantage that the difference between the frequency fluctuation and the frequency fluctuation of the pilot signal transmitted from the pseudo mobile station can be reduced, and the frequency fluctuation correction error by the AFC circuit provided in the receiving section of the base station can be reduced. In addition, the frequency of the pilot signal generator is used as the local oscillator frequency of the receiving frequency converter in the pseudo mobile station, and the frequency of one local oscillator and the local oscillator frequencies of multiple transmitting frequency converters are used in the pseudo mobile station and the mobile station. This has the advantage of reducing the number of local oscillators required. Although the present invention has been described with reference to a mobile satellite communication system, it goes without saying that the present invention can be similarly applied to a system in which a mobile station is replaced with a small station installed at a certain predetermined location.

[Brief explanation of the drawing]

Figure 1 shows an example of the configuration of a mobile satellite communication system.
The figure shows an example of the configuration of a line from a mobile station to a base station using the conventional AFC method, and FIG. 3 is a block diagram of an example of the system configuration according to the present invention. 1...Base station, 2...Pseudo mobile station, 3...Satellite, 4-1, 4-2,..., 4-N...Mobile station.

Claims (1)

[Claims] 1. A base station and a large number of slave stations are connected via communication satellites, and a pseudo station is established near the base station,
The pseudo station has the function of receiving the first pilot signal for frequency fluctuation correction transmitted from the base station via a communication satellite and controlling the local oscillation frequency 5 of the transmission frequency converter 4 of the base station according to the reception frequency. It has a function of transmitting a second pilot signal for frequency fluctuation correction from the slave station to the base station via a communication satellite,
The frequency of the pilot signal generator 21 that provides the frequency of the second pilot signal from the pseudo station is intentionally shifted by an amount corresponding to the frequency variation of the receiving frequency converters 18 and 20 of the pseudo station, and A frequency fluctuation correction method is characterized in that the transmission frequency of the slave station is intentionally shifted by an amount corresponding to the amount of frequency fluctuation of the first pilot signal from the base station. 2. The frequency fluctuation correction method according to claim 1, wherein the output frequency of the pilot signal generator 21 of the pseudo station is shared for transmission frequency conversion and reception frequency conversion in the pseudo station.