JP2002084209A - Afc system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AFC system by which a base station can easily correct a frequency offset of a received wireless signal without the need for using an inexpensive variable frequency local oscillator of an analog circuit or the like. SOLUTION: A multi-direction multiplex wireless system is adopted for communication between a base station 100 (not shown) and subscriber stations 200 (200a) by using a TDMA signal. The base station 100 uses a frequency offset detection means to detect a frequency offset of a wireless signal received from the subscriber station 200a and allows a TDMA circuit means to multiplex information of the detected frequency offset with the TDMA signal and the base station 100 transmits the multiplexed signal to the subscriber station 200a. A frequency offset information demultiplexer circuit 30 of the subscriber station 200a demultiplexes the frequency offset information and a frequency offset correction circuit 23 inversely offsets a frequency of base band data of a prescribed frame on the basis of the demultiplexed frequency offset information so as to bring the frequency of the transmitted wireless signal within a specified frequency range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AFC system capable of appropriately controlling the frequency of a radio signal transmitted to an opposite station in a digital radio communication system, and more particularly to an AFC system suitable for a multidirectional multiplex radio system.

[0002]

2. Description of the Related Art In digital radio communication, if the frequency of a received signal (reception frequency) deviates from the correct frequency (there is a frequency offset), delays in carrier synchronization and BE.
This results in degradation of received data quality such as degradation of R (bit error rate). This phenomenon is particularly significant in systems with low transmission rates. For example, in the TDMA (Time Division Multiple Access) type multi-directional multiplex radio system shown in the embodiment of the present invention in FIG. 1, the base station 100 transmits a plurality of subscriber stations 200 (200a to 200n: ) Is synchronously detected by the subscriber station 200,
The uplink radio signal transmitted from the subscriber station 200 to the base station 100 is subjected to delay detection in the base station 100. However, the problem of the synchronization range in the downlink and the problem of the deterioration of the BER characteristic in the uplink are becoming important. come.

In the conventional digital radio communication, in a synchronous detection type receiving apparatus (such as the subscriber station 200), the receiving apparatus itself converts the local oscillation frequency to the receiving frequency by a carrier recovery circuit using a PLL (phase synchronization) circuit or the like. There is a method of synchronizing (for example, Japanese Unexamined Patent Publication No. 6-61998: Synchronization pull-in method for digital radio equipment). Further, it is difficult for a delay detection type receiving apparatus (such as the base station 100) to correct the frequency of a radio signal received by its own apparatus to an appropriate frequency. In the case of the TDMA system (for example, the multi-directional multiplex radio system shown in FIG. 1) in which a burst-like received radio signal transmitted in a time-division manner from each of A variable frequency oscillator is added to each device to control the oscillation frequency of the oscillator on the transmitting station side according to the frequency offset information sent from the base station to the own station device, or use a crystal oscillator with a thermostat as the source oscillation. Therefore, it was necessary to precisely control the frequency of the radio signal.

[0004]

As described above, in the conventional digital radio communication system, in order to correct or eliminate the frequency offset of the received radio signal, both the receivers of the communicating radio stations need to have a PLL oscillator or the like. It was necessary to additionally provide an expensive analog oscillator such as a variable frequency oscillator or a high-accuracy crystal oscillator with a thermostat. In particular, under the condition that a preamble code cannot be added to a burst-like data signal for reasons such as an increase in transmission efficiency, such as in the uplink of a TDMA multi-directional multiplex radio system, the radio frequency is high and the reception received by the base station is high. In a situation where the frequency offset of the signal cannot be ignored, the provision of a variable frequency local oscillator has the disadvantage of being expensive.

Accordingly, the present invention overcomes the above-mentioned disadvantages of the prior art in digital radio communication systems and eliminates the need for expensive analog oscillators such as variable frequency local oscillators or crystal oscillators with constant temperature ovens. An object of the present invention is to provide an AFC system that can easily correct a frequency offset of a radio signal.

[0006]

A first aspect of the AFC system according to the present invention is to use a base station that transmits a TDMA signal by a radio signal, and a radio signal that receives the TDMA signal and is different from the radio signal. An AFC system for a wireless communication network comprising a subscriber station transmitting a data signal to the base station in a defined frame of a TDMA signal, wherein the base station performs a frequency offset of a radio signal received from the subscriber station. And a TDMA circuit for multiplexing the detected information of the frequency offset into a data signal of a predetermined frame of the TDMA signal, wherein the subscriber station receives a signal from the base station. Frequency offset information separating means for separating the information of the frequency offset from a predetermined frame of the TDMA signal,
Frequency offset correction means for reversely offsetting the frequency of the baseband data of the predetermined frame based on the separated information of the frequency offset, and setting the frequency of the wireless signal to be transmitted within a specified range.

In the first of the AFC systems, the wireless communication network includes one base station and a plurality of subscriber stations for transmitting the wireless signals having substantially the same frequency. Multi-directional multiplexing, wherein each of the subscriber stations broadcasts a data signal through a corresponding frame of the TDMA signal, and each of the subscriber stations transmits a data signal to the base station through a corresponding frame of the TDMA signal. A configuration that is a wireless system can be adopted.

[0008] The second type of the AFC system can adopt a configuration in which a preamble code is not added to a data signal transmitted by the subscriber station.

A third type of the AFC system is that the radio signal transmitted from the subscriber station is subjected to four-phase modulation, and the frequency offset correcting means separates the orthogonal baseband data from the two orthogonal baseband data. It is possible to adopt a configuration in which a sine wave component and a cosine wave component of the frequency of the frequency offset are subjected to a complex operation to shift the frequency of the baseband data by the frequency of the inverse offset.

A fourth aspect of the AFC system is that the subscriber station includes a demodulator for demodulating the received TDMA signal, and the frequency offset information is created based on a demodulation phase error of the demodulator. Can be taken.

A fifth aspect of the AFC system can have a configuration in which the frequency offset correction circuit is a digital signal processing circuit arranged before a modulator that modulates baseband data.

The second of the AFC systems according to the present invention is TDM.
A base station for transmitting the A signal by a radio signal;
A plurality of subscriber stations for receiving an MA signal through a predetermined frame and transmitting a data signal to the base station in a predetermined frame of a TDMA signal using a radio signal having substantially the same frequency as the radio signal. An AFC system for a multi-directional multiplex radio system comprising: a base station, wherein the base station detects frequency offset of a radio signal received from the subscriber station, and information of the detected frequency offset. TDMA circuit means for multiplexing the TDMA signal into a data signal of a predetermined frame, wherein each of the subscriber stations separates the frequency offset information from the predetermined frame of the TDMA signal received from the base station. Frequency offset information separating means, and a frame rate of a frame determined based on the separated frequency offset information. Scan and band reverse offset frequency of the data, and a frequency offset correction means for the defining the frequency of the radio signal to be transmitted.

The third of the AFC systems according to the present invention is an AFC system of a multi-directional multiplex radio system in which a base station and a modulator and a receiver of a subscriber station communicating with the base station in a TDMA system both use a common local system. And the subscriber station is
Frequency offset information detecting means for detecting frequency offset information from a frequency shift of a radio signal received from the base station, and the frequency using a digital signal processing circuit arranged before a modulator for modulating baseband data. Frequency offset correction means for reversely offsetting the frequency of the baseband data based on the offset information and setting the frequency of the radio signal to be transmitted within a prescribed range.

A fourth aspect of the AFC system according to the present invention is an AFC system of a digital wireless system in which a first wireless station communicates with the first wireless station using digital wireless signals, wherein the first wireless station communicates with the first wireless station. A station for detecting a frequency offset of a radio signal received from the second radio station, and multiplexing the detected information of the frequency offset to another data signal to the second radio station; Frequency offset information transmitting means for transmitting, wherein the second radio station separates the frequency offset information received from the first radio station from the data signal, The radio signal to be transmitted with the frequency of the baseband data to be transmitted to the first radio station inversely offset based on the obtained information of the frequency offset. And a frequency offset correction means for within a specified frequency.

[0015]

According to the AFC system of the present invention, in a digital radio communication system, each lower radio station has a local oscillator of a transmission / reception section so that a frequency offset in a demodulation section of an opposing upper radio station is minimized. This is a method of giving a frequency offset in advance by the transmitting unit of the own station so as to cancel the value obtained by adding the frequency offset of According to the present invention, when a frequency offset is given by this transmission unit, this is realized in digital signal processing by a digital circuit arranged before the modulator of the transmission unit, and an expensive analog oscillator such as a variable frequency oscillator is used. Is not required.

The AFC system according to the present invention is suitable for a multi-directional multiplex radio system for performing TDMA communication. The carrier frequency shift (offset) of a TDMA frame (received signal) received by a base station from each of the subscriber stations. , Respectively, and returns these frequency offset information to each of the subscriber stations.The subscriber station receiving the information transmits a frequency offset that cancels this frequency offset in a signal frame given in advance. In the base station, a received signal without a frequency offset can be obtained.

[0017]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the AFC system according to the present invention. FIG. 1 shows a TDMA multidirectional multiplex radio system.

This multi-way multiplex radio system is based on a base station 1
00 to the plurality of subscriber stations 200 (200a to 200n: n is plural).
Broadcasting is performed by the M method. Each of the subscriber stations 200 receives a data signal of a predetermined TDM frame among the transmitted radio signals, and demodulates the data signal by a synchronous detection method. Each of the subscriber stations 200 has a TDMA having the same frame configuration as the TDM frame.
A (digital) radio signal is transmitted to the base station 100 at substantially the same frequency as the radio signal from the base station 100 using different frames having different frames. The frequencies of these radio signals generally differ slightly from the specified frequencies (frequency offsets) because the source oscillator for generating the radio signals is different. Base station 10
0 demodulates the data signal of the corresponding frame for each of the subscriber stations 200 by the differential detection method. Note that radio signals are often quadrature modulated by PSK modulation or the like. Further, a data signal transmitted by the subscriber station 200 is often not added with a preamble code in order to increase transmission efficiency.

FIG. 2 shows a base station 1 in the embodiment of FIG.
FIG.

The base station 100 is one of the subscriber stations 200,
For example, a predetermined TDM sent from the subscriber station 200a
The radio signal (uplink signal) of the A frame is received by the antenna 7. The received reception signal S1 is input to the receiver 8 via the duplexer 6. The receiver 8 frequency-mixes the received signal S1 and a local oscillation signal (local signal) S2a supplied by the local oscillator 12 and amplifies the signal to a predetermined level to generate a baseband (BB) digital signal S3. The digital signal S3 is a demodulator 9 of the delay detection system.
Supplied to

The demodulator 9 reproduces (demodulates) the digital signal S3 and converts the reproduced data signal S4 to TDMA.
Output to the receiving circuit 10. The TDMA receiving circuit 10 separates the data signal S4 on the time axis, converts the TDMA frame into a frame for line concentrating processing, and outputs the processed data to the exchange 1 via the line concentrating circuit 2. I do. Here, the demodulator 9 outputs the digital signal S3a before demodulation to the frequency offset detection circuit 11 simultaneously with the reproduction (demodulation) of the digital signal S3. The frequency offset detection circuit 11 detects the deviation (rotation angle θ) of the ideal point of the eye pattern of the digital signal S3, that is, the demodulation phase error, and detects the rotation angle θ and the digital signal S3.
Then, a carrier (frequency or carrier frequency) offset Δf of the received signal S1 is calculated from the clock frequency of No. 3 and converted into a digital signal corresponding to the amount of the frequency offset. The frequency offset (frequency offset information) S5 of the received signal S1 converted into the digital signal is TDMA
Output to the transmission circuit 3.

On the other hand, base station 100 converges data from exchange 1 by concentrator 2 and outputs the data to TDMA transmitter 3. The TDMA transmission circuit 3 multiplexes the frequency offset S5 from the frequency offset detection circuit 11 in addition to converting the data from the line concentrating processing frame into a TDMA frame and multiplexing the data from the line concentrating circuit 2 on the time axis. Further, waveform shaping is performed. The multiplexed and waveform-shaped data signal S6 is supplied to the modulator 4. Modulator 4
Modulates the local oscillation signal S2b output from the local oscillator 12 with the data signal S6. This modulation method is 4PSK modulation. Note that the local oscillation signal S2b is
The frequency may be the same as 2a or different from each other. The transmission signal S7 modulated by the data signal S6 is
The transmission signal S amplified and frequency-limited by the transmitter 5
7a. The transmission signal S7a is further supplied to the antenna 7 through the antenna duplexer 6, and is transmitted from the antenna 7 to the plurality of subscriber stations 200, that is, the downstream lower stations, as radio signals.

FIG. 3 is a configuration diagram of an example of the subscriber station 200 (200a) in the embodiment of FIG. This figure shows a subscriber station 200a as a representative of a plurality of subscriber stations 200.

The subscriber station 200a receives the down-link radio signal transmitted from the base station 100 by the antenna 27 and generates a reception signal S11. The reception signal S11 is supplied to the receiver 28 via the antenna duplexer 26. The receiver 28 frequency-mixes the received signal S11 with a local oscillation signal (local signal) S12a generated by the local oscillator 32 and downconverts the signal to generate a baseband signal S13 of a predetermined TDM frame. The baseband signal S13 is supplied to the demodulator 29. The demodulator 29 outputs the baseband signal S
13 is demodulated by a synchronous detection method to generate a demodulated signal S14. The demodulated signal S14 is output from the frequency offset information separation circuit 3
Sent to 0.

The frequency offset information separating circuit 30 separates the data signal multiplexed into the TDM frame from the base station 100 and the frequency offset information (S5), and outputs the separated data signal S15 to the TDMA receiving circuit 31 for frequency offset. The information S16 is output to the frequency offset correction circuit 23. The frequency offset information (S5) may be inserted at a predetermined position in the frame. The data signal S15 is subjected to the separation of the data signal converged by the TDMA receiving circuit 31 and the frame conversion from the radio frame to the frame for the subscriber circuit. It is output to the subscriber circuit 21.

On the other hand, the data signal from the subscriber circuit 21 is subjected to frame conversion from a frame for the subscriber circuit to a TDMA frame, data multiplexing and waveform shaping by the TDMA transmission circuit 22, and then to the frequency offset correction circuit 23. Is output. The frequency offset correction circuit 23
In accordance with the frequency offset information S16, an inverse frequency offset is given to the waveform-shaped data signal S17 from the TDMA transmission circuit 22. The inverse offset referred to here is the frequency offset (S
5) means a frequency offset that cancels out. That is, the signal processing is to correct the frequency offset of the digital signal S3 supplied to the demodulator 9 of the base station 100 to substantially zero or within a specified range. Note that this inverse offset is performed before the modulator 24 that converts the transmission signal S19 to the transmission frequency, that is, in the baseband region.

The modulator 24 modulates the carrier signal S12b generated by the local oscillator 32 with the inversely offset data signal S18 to generate a transmission signal S19. Although the modulator 24 in the present embodiment is a quadrature modulator, the modulation method is not limited to this modulation method. Transmission signal S19
Is transmitted through a transmitter 25 that performs amplification and frequency limitation and an antenna duplexer 26, and is transmitted as an antenna 2 as a transmission signal S19a.
7 is supplied. The antenna 27 transmits the transmission signal S19a to the base station 100 as an uplink radio signal.

As described above, in the multi-directional multiplex radio system described with reference to FIGS. 1 to 3, the base station 100 detects the frequency offset of the radio signal from the subscriber station 200 for each TDMA frame, and The frequency offset information is transmitted to each of the base stations 200, and the subscriber station 200 transmits a transmission signal having a frequency obtained by applying an inverse offset of the frequency offset of the own station. As a result, the demodulator 9 of the base station 100 has no frequency offset. Delay detection can be performed on the signal. Since the reverse offset can be performed by digital signal processing of the baseband signal, the multidirectional multiplex radio system has an effect that AFC (automatic frequency control) can be activated without adding an expensive analog oscillator. .

In addition, since a frequency pull-in operation is not required for a phase synchronization method of a demodulator by carrier recovery using a PLL circuit or the like which is conventionally known, a preamble code is added to a data signal of a TDMA frame in order to increase transmission efficiency. There is also an effect that the AFC can be operated early and effectively even if the AFC cannot be added.

In the present embodiment, a multi-directional multiplex radio system is taken as an example.
It is needless to say that the present invention is also effective for a general digital wireless system with one-to-one communication.

In the base station 100, a delay detection system which is convenient for demodulating a radio signal with a frequency offset from a plurality of subscriber stations 200 is used. It is possible to detect the offset, and there is no necessity to be limited to the differential detection method to detect the frequency offset.

FIG. 4 is a block diagram showing in detail the features of the present invention in the subscriber station 200a. In FIG. 4, TDMA
The transmission circuit 22 and the frequency offset correction circuit 23 are shown in detail. FIG. 5 is a diagram for explaining the operation of the frequency offset correction circuit 23 shown in FIG.

The TDMA circuit 10 of the TDMA transmission circuit 22
1 multiplexes a data signal or the like (BB signal) to be transmitted supplied from the subscriber circuit 21 according to various timing signals or the like, and converts the multiplexed signal into a radio (TDMA) frame format. Here, the modulator 24 performs four-phase PSK modulation (4PSK modulation).
K), the output is two data strings (digital 2
S101a and S101b. P
channel transmission filter (TX-FIL) 102 and Qch
The transmission filter (TX-FIL) 103 of the
The waveforms of the signals 101a and S101b are respectively shaped by digital signal processing, and the data signals S102a and S102b expressed by a plurality of bits are output to the complex multiplication circuit 104 of the frequency offset correction circuit 23. Now, the data sequence S102a is represented by a function P (t), and the data sequence S102b is represented by a function Q (t).

In the frequency offset correction circuit 23, the frequency offset information S16 separated from the data signal S15 is input to the frequency offset information updating circuit 109. The frequency offset information updating circuit 109 updates the currently held frequency offset information (S16) at a certain period. This information update cycle is
At least, the radio signal from the subscriber station 200a is transmitted to the base station 1
00 and the frequency offset S5
Is detected, the information is multiplexed into a data signal S6 which is a transmission signal to the subscriber station 200a, separated at the subscriber station 200a, and the frequency offset information updating circuit 109 is again transmitted.
It must be longer than the round trip time for the navel response to return.

The frequency offset information updating circuit 109
Adding the updated update offset information S103 to the adding circuit 11
0 is sent to one input terminal. The output of the addition circuit 112 is
An address signal S104 of the sine wave generator (SIN-GEN) 112 and the cosine wave generator (COS-GEN) 113 is used. The flip-flop circuit (F / F) 111 is
The address signal S104 is delayed by one sample and fed back to the other terminal of the adder circuit 110. And
The adding circuit 110 adds the currently held frequency offset information (S16) and the newly input frequency offset information S16 to calculate a total frequency offset amount. That is, the address signal S104 currently held in the flip-flop circuit 111 is applied to the subscriber station 200a.
Frequency offset information S16 added to the transmission signal S19 on the side, and the frequency offset information S16 separated from the data signal S15 is further corrected (reverse offset).
Frequency offset information to be performed.

The update of the frequency offset (Δf) will be additionally described. In the subscriber station 200a, the value to be inversely offset changes due to some factors such as the environmental temperature where the apparatus is placed. When the reverse offset amount decreases, the correction amount further increases by adding the reverse offset amount. If the value of the reverse offset is excessive, the correction amount decreases.

The address signal S104 output from the adder circuit 110 is a sine wave generator (SIN-GEN) 112
And a cosine wave generator (COS-GEN) 113. The angular frequency of the carrier signal having the frequency of the inverse (frequency) offset −Δf is 2πΔf = Δω. Therefore,
The sine wave generator 112 generates a sine wave S105 represented by SIN (Δωt) in response to the input of the address signal S104. The cosine wave generator 113 generates a cosine wave S106 represented by COS (Δωt). The sine wave S105 and the cosine wave S106 are supplied to the complex operation circuit 104, respectively.

The complex operation circuit 104 calculates the orthogonal function P
Sine wave SIN orthogonal to (t) and function Q (t)
(Δωt) and the cosine wave COS (Δωt) are subjected to a complex operation according to the following equation to perform the inverse offset of the function P (t) and the function Q (t).

((P (t) + jQ (t)) × (COS
(Δωt) −jSIN (Δωt)) (COS (Δωt)
Since −jSIN (Δωt)) is exp (−jΔωt), the above equation can be expressed as the following equation.

((P (t) + jQ (t)) × exp (−jΔωt) That is, the above equation is an orthogonal function ((P (t) + jQ (t)) which is the data signals S102a and S102b to be transmitted.
This shows that the complex operation circuit 104 generates the data signals S107a and S107b in which the frequency of the data signal is inversely offset by the frequency Δf. Note that the above-described complex operation can be performed by a digital signal processing circuit using a gate array. FIG. 5 shows how the data signals S107a and S107b are inversely offset in the (-) frequency direction by this complex operation.

Data signal S107a reversely offset
And S107b are digital-to-analog converters (D / A
A) The signals are converted into analog signals by 105 and 106, respectively. These analog signals are waveform-shaped by low-pass filters 107 and 108, respectively, to become data signals S18 (S18a and S18b), and the data signal S18 is supplied to the modulator 24 as a modulation signal.
Since the data signal S18 has an inverse frequency offset, the transmission signal S19 output from the modulator 24 is
The frequency offset notified from the base station 100 is canceled and corrected.

As described above, the frequency offset correction of the transmission radio signal by the frequency offset correction circuit 23 of the subscriber station 200 can be performed by the digital signal processing circuit in the baseband region disposed before the modulator 24. It does not require the addition of an expensive analog oscillator, is inexpensive and only slightly increases the size of the gate array, absorbs all of the above-mentioned radio frequency deviations, and has no frequency offset in the demodulator 9 of the base station 100. The digital signal S3 can be obtained.

FIG. 6 is a block diagram showing a subscriber station 200A in another embodiment of the AFC system according to the present invention.

The subscriber station 200A which is one of the plurality of subscriber stations 200 realizes the acquisition of the frequency offset information S16 by the demodulator 29 and the frequency offset information separation circuit 30 in FIG. I have.
Further, the local oscillator 32 includes a local oscillation signal S12A supplied to the receiver 28 and a carrier signal S1 supplied to the modulator 24.
The frequency of 2B is the same frequency (common local method). The other configuration and functions of the subscriber station 200A are the same as those of the subscriber station 200a, and thus the description is omitted. Also, base station 1
00A (not shown) has the same configuration and function as the base station 100 except that the local oscillator 12 of the base station 100 shown in FIG. 2 employs a common local system for supplying the modulator 4 and the receiver 8 with oscillation signals of the same frequency. Same as station 100.

As described above, when both opposing stations use the common local system, the frequency deviation of the signal received from the opposing station (eg, base station 100A) and the local station (eg, subscriber station 200A) ) Indicates the same or very high correlation with the frequency deviation of the received signal. In this case, the subscriber station 200A can detect the frequency offset information S16A from the data signal S13 received by the receiver 28 of the own station without receiving the frequency offset information from the base station 100.

That is, the demodulator 29A synchronously detects the baseband signal S13, which may be affected by the frequency offset, by the detection circuit 40 to generate the data signal S15.
The carrier reproducing circuit 41 using the Costas method or the like reproduces the carrier S108 from the data signal S15. At this time, the APC voltage generated in the Costas loop or the like is converted into a digital signal, and frequency offset information S16A is obtained. By supplying the frequency offset information S16A to the frequency offset correction circuit 23, the AFC method according to the embodiment of FIG. 6 can obtain the same frequency offset correction effect as that of the embodiment of FIG.

[0048]

As described above, according to the present invention, the TDMA
A first radio station transmitting a signal by a radio signal; and a first radio station receiving the TDMA signal and using a radio signal of a frequency different from the radio signal to convert a data signal in the predetermined frame of the TDMA signal into the first radio station. An AFC system for a wireless communication network including a second wireless station transmitting to a wireless station, wherein the first wireless station detects a frequency offset of a wireless signal received from the second wireless station. Detecting means, and TDMA circuit means for multiplexing the detected information of the frequency offset into a data signal of a predetermined frame of the TDMA signal, wherein the second wireless station receives a signal from the first wireless station. Frequency offset information separating means for separating the information of the frequency offset from a predetermined frame of the TDMA signal, based on the separated information of the frequency offset. Frequency offset correcting means for reversely offsetting the frequency of the baseband data of the determined frame and setting the frequency of the radio signal to be transmitted within a prescribed range, such as a variable frequency local oscillator or a crystal oscillator with a thermostat. There is an effect that it is possible to provide an AFC system capable of easily and inexpensively correcting the frequency offset of the received radio signal in the first radio station without adding an expensive analog oscillator.

Also, this AFC system can be used even if it is not possible to add a preamble code to the data signal of the TDMA frame in order to increase the transmission efficiency from the second wireless station.
There is also an effect that C can be operated effectively.

Further, in the AFC system, for example, by inserting a frequency offset correction circuit realized by digital signal processing into the transmission BB circuit of the second radio station,
Only by slightly increasing the size of / A, the total of the deviations of the radio frequencies in one round of the radio station can be absorbed, and a reception signal having no frequency deviation can be obtained in the receiving-side demodulator of the second radio station. This has the effect.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an AFC system according to the present invention.

FIG. 2 is a configuration diagram of a base station 100 in the embodiment of FIG.

FIG. 3 shows a subscriber station 200 (2) in the embodiment of FIG.
FIG. 100A is a configuration diagram of an example.

FIG. 4 is a configuration diagram showing in detail a characteristic portion of the present invention in the subscriber station 200a.

5 is a diagram for explaining an operation of the frequency offset correction circuit 23 shown in FIG.

FIG. 6 is a configuration diagram showing a subscriber station 200A in another embodiment of the AFC system according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 base station 1 exchange 2 concentrator circuit 3 TDMA transmission circuit 4 modulator 5 transmitter 6 antenna duplexer 7 antenna 8 receiver 9 demodulator 10 TDMA reception circuit 11 frequency offset detection circuit 12 local oscillator 200 (200a to 200n, 200A) Subscriber station 21 Subscriber circuit 22 TDMA transmission circuit 101 TDMA circuit 102, 103 Transmission filter (TX-FIL) 23 Frequency offset correction circuit 104 Complex multiplication circuit 105, 106 Digital / analog converter (A /
D) 107, 108 Low-pass filter 109 Frequency offset information update circuit 110 Addition circuit 111 Flip-flop circuit (F / F) 112 Sine wave generator (SIN-GEN) 113 Cosine wave generator (COS-GEN) 24 Modulation Devices 25, 32 local oscillator 26 antenna duplexer 27 antenna 28 receiver 29, 29A demodulator 30 frequency offset information separation circuit 31 TDMA reception circuit 40 detection circuit 41 carrier reproduction circuit

Claims (12)

[Claims] A base station for transmitting a TDMA signal by a radio signal; a base station for receiving the TDMA signal and transmitting a data signal in a predetermined frame of the TDMA signal by using a radio signal having a frequency different from the radio signal. An AFC system of a wireless communication network including a subscriber station transmitting to a base station, wherein the base station detects a frequency offset of a radio signal received from the subscriber station;
The information of the detected frequency offset is stored in the TDMA
TDMA for multiplexing with a data signal of a predetermined frame of a signal
Circuit means, wherein the subscriber station receives the TDMA from the base station.
Frequency offset information separating means for separating the information of the frequency offset from a predetermined frame of the signal, and inversely offsetting the frequency of the baseband data of the predetermined frame based on the separated information of the frequency offset;
An AFC system comprising: a frequency offset correction unit for setting a frequency of the wireless signal to be transmitted within a specified range. 2. The wireless communication network includes one base station and a plurality of subscriber stations for transmitting the wireless signals having substantially the same frequency, wherein the base station includes a plurality of subscriber stations. A multi-directional multiplex radio system in which each of the subscriber stations transmits a data signal to the base station through a corresponding frame of the TDMA signal. The AFC method according to claim 1, wherein: 3. The AFC system according to claim 1, wherein a preamble code is not added to a data signal transmitted by the subscriber station. 4. The radio signal transmitted from the subscriber station is subjected to four-phase modulation, and the frequency offset correction means outputs a sine of a frequency of the frequency offset separated from two orthogonal baseband data. 3. The AFC method according to claim 1, wherein a complex operation is performed on a wave component and a cosine wave component to shift a frequency of the baseband data by an inverse offset frequency. 5. The TDMA received by the subscriber station.
3. The AFC system according to claim 1, further comprising a demodulator for demodulating a signal, wherein the frequency offset information is created based on a demodulation phase error of the demodulator. 6. A base station for transmitting a TDMA signal by a radio signal, and determining the TDMA signal by receiving the TDMA signal through a predetermined frame and using a radio signal having substantially the same frequency as the radio signal. A plurality of subscriber stations for transmitting data signals in said frames to said base station in a multi-directional multiplex radio system, wherein said base station comprises a frequency offset of a radio signal received from said subscriber station. Frequency offset detection means for detecting
The information of the detected frequency offset is stored in the TDMA
TDMA for multiplexing with a data signal of a predetermined frame of a signal
Circuit means, each of said subscriber stations receiving said TD from said base station.
Frequency offset information separating means for separating the information of the frequency offset from a predetermined frame of the MA signal, and inversely offsetting the frequency of the baseband data of the frame determined based on the separated information of the frequency offset;
An AFC system comprising: a frequency offset correction unit for setting a frequency of the wireless signal to be transmitted within a specified range. 7. A radio signal transmitted from the subscriber station is subjected to four-phase modulation, and the frequency offset correction means outputs a sine of a frequency of the frequency offset separated from two orthogonal baseband data. 7. A circuit for performing a complex operation on a wave component and a cosine wave component to shift the frequency of the baseband data by an inverse offset frequency.
AFC method as described. 8. The AFC system according to claim 1, wherein said frequency offset correction means is a digital signal processing circuit arranged before a modulator for modulating said baseband data. . 9. An AFC system of a multi-directional multiplex radio system in which a base station and a modulator and a receiver of a subscriber station communicating with the base station in a TDMA system both use a common local system. Using frequency offset information detection means for detecting frequency offset information from the frequency deviation of the radio signal received from the base station, and a digital signal processing circuit disposed before the modulator for modulating the baseband data. An AFC system comprising: a frequency offset correction unit that reversely offsets the frequency of the baseband data based on frequency offset information and sets the frequency of the wireless signal to be transmitted within a prescribed range. 10. An AFC system of a digital radio system in which a first radio station and said first radio station communicate using digital radio signals, wherein said first radio station is said second radio station. Frequency offset detecting means for detecting a frequency offset of a radio signal received from a station; frequency offset information transmitting means for multiplexing the detected information of the frequency offset into another data signal and transmitting the multiplexed information to the second radio station; Frequency offset information separating means for separating the information of the frequency offset received from the first wireless station from the data signal, and the information of the separated frequency offset. A frequency that reversely offsets the frequency of baseband data to be transmitted to the first wireless station based on the frequency and makes the frequency of the wireless signal to be transmitted within a prescribed range. AF, characterized in that it comprises a offset compensation means
C method. 11. A radio signal transmitted from the second radio station is subjected to four-phase modulation, and the frequency offset correcting means outputs a frequency of the frequency offset separated from two orthogonal baseband data. 2. A circuit for performing a complex operation on a sine wave component and a cosine wave component of the baseband data to shift the frequency of the baseband data by an inverse offset frequency.
1. The AFC method according to 1. 12. The AFC system according to claim 10, wherein said frequency offset correction means is a digital signal processing circuit arranged before a modulator for modulating said baseband data.