JP3737974B2 - Transmission / reception switching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmission / reception switching method executed in a station constituting a radio communication system in which uplink / downlink radio channels are time division multiplexed (TDD).
[0002]
[Prior art]
As an implementation form of FWA (Fixed Wireless Access) for wirelessly connecting P-MP (Point to MultiPoint) between a base station and a subscriber station, an uplink radio line that wirelessly transmits a signal from the subscriber station to the base station; A configuration in which a downlink radio channel for wirelessly transmitting a signal from a base station to a subscriber station is multiplexed by the TDD method, and signal transmission is performed between the base station and the subscriber by a burst signal under schedule management by the base station The one that adopts is being developed.
[0003]
FIG. 1 shows an outline of the system configuration. In the figure, reference numeral 10 is a base station, and 20A to 20C are subscriber stations, each having a radio frequency unit (RFU) 11 or 21 and an interface unit (IFU) 12 or 22 connected to each other by a coaxial cable 13 or 23 or the like. have. The RFU 11 of the base station 10 is provided at a high place by using a columnar structure, for example, the top of a power pole or the vicinity thereof, a rooftop of a high-rise building, etc., in order to ensure good wireless communication quality, particularly a line-of-sight range. . The IFU 12 of the base station 10 is provided in a low place where maintenance is easier, and is connected to a line on the telecommunications carrier side for connection to various networks. On the other hand, subscriber stations 20A to 20C are stations installed in FWA subscriber houses. The RFU 21 is provided by using a handrail of the balcony of the subscriber's house or on the roof so that the radio communication with the base station 10 can be satisfactorily performed. The IFU 22 is a device in the room of the subscriber's house, such as a personal computer. It is installed in the room of the subscriber's house so that it can be connected to the network.
[0004]
Wireless communication between the base station 10 and the subscriber stations 20A to 20C is performed by transmission of burst signals using uplink / downlink radio channels multiplexed according to the TDD scheme. The transmission timing of the burst signal is controlled by the IFU 12 of the base station 10 so that the ON regions do not overlap each other, that is, as shown in FIG. In addition, the multiplexing by the TDD scheme specifically includes a switch (hereinafter referred to as “TDD switch” or “TDD_SW”) for selectively connecting the transmission system circuit and the reception system circuit to the antenna. This can be realized by providing in the station 10 and the subscriber stations 20A to 20C and appropriately switching the TDD switch.
[0005]
[Problems to be solved by the invention]
In general, the control method for switching the antenna connection destination from the reception system circuit to the transmission system circuit is not limited to a device for FWA, and a transmission / reception switching switch placed in front of the antenna is transmitted according to the generation of a transmission signal. A method of switching to the system circuit side is adopted. For example, a switch switching control signal is generated in response to the generation of a transmission signal, and this switch switching control signal is transmitted to a transmission / reception switching switch superimposed on the transmission signal or by another conductor, and the switch is controlled by the switch switching control signal. There is a technique in which the signal is input to the transmission system circuit side according to the signal. By using a subcarrier having a frequency different from the carrier of the transmission signal as the switch switching control signal and superimposing it on the transmission signal, a cable dedicated to the switch switching control signal is provided separately from the cable for the transmission signal There is no need.
[0006]
However, this method is difficult to adopt in the system of FIG. 1 in which there is a transmission signal source in the IFU and a TDD switch as a transmission / reception switching switch in the RFU. For example, if the IFU generates a switch switching control signal in response to the generation of the transmission signal, the switch switching control signal is transmitted to the RFU together with the transmission signal via a coaxial cable by, for example, a subcarrier, and the RFU transmits the switch switching control signal. It is assumed that an embodiment in which detection is performed and the TDD switch is switched is adopted. In that case, generally, the time required from the detection of the switch switching control signal in the RFU to the switching of the TDD switch, compared to the time required for the transmission signal to pass through the transmission system circuit in the RFU (hereinafter referred to as “transmission system required time”). (Hereinafter referred to as “detection switching required time”) is longer, so when the leading portion of the transmission signal reaches the TDD switch, the TDD switch is not yet connected to the transmission system circuit side. For this reason, the transmission signal lacking the leading portion is transmitted wirelessly. The time required from generation of a transmission signal to generation of a switch control signal in the IFU may be a problem.
[0007]
In order to prevent the leading portion from being lost due to such a cause, in principle, if the IFU sends the switch switching control signal prior to the transmission signal by an amount exceeding the detection switching required time with respect to the transmission system required time. Good. However, since the RFU is a device that should be placed near the antenna and is generally provided outdoors, the time required for detection switching in the RFU varies depending on factors such as temperature. For this reason, the excess of the detection switching required time with respect to the transmission system required time cannot be accurately predicted by the IFU, and therefore it is difficult to realize the leading edge prevention by this principle. Further, when noise in the subcarrier frequency band enters the cable connecting the RFU and the IFU, the switch switching does not work. Furthermore, the length of the cable connecting the IFU and the RFU may be several meters in some cases but several hundred meters in other cases. -If the circuit configuration is such that the required switching time depends on the transmission signal input level to the IFU as a circuit that detects the switch switching control signal because it changes depending on the arrangement of the room equipment, etc., the influence of variations in the cable length Will receive.
[0008]
The present invention has been made in order to solve such a problem, and prevents a transmission signal head portion from being lost due to an excessive detection switching time with respect to a transmission system required time, particularly a switch from IFU to RFU. One of the purposes is to realize it without transmission of a switching control signal. Through the achievement of such an object, the present invention contributes to, for example, suppressing a transmission burst signal head portion omission in a TDD FWA using a carrier of 26 GHz band, thereby improving an effective transmission rate in a radio section. Is.
[0009]
[Means for Solving the Problems]
In order to achieve such an object, the present invention provides (1) a radio frequency unit having a TDD switch for switching and connecting an internal transmission system circuit and a reception system circuit to an antenna, and a radio frequency unit connected by a cable. And an interface unit including a transmission signal source that outputs a transmission signal modulated according to transmission information, and a radio frequency unit of a station constituting an FWA wireless communication system in which uplink / downlink radio channels are time-division multiplexed (2) When the transmission signal is supplied from the interface unit via the cable, the TDD switch is controlled so that the transmission signal is supplied to the antenna via the transmission system circuit and the TDD switch, At any other time, Lee via a cable through the TDD switch and the receiving system circuit from the antenna In reception switching method for controlling the TDD switch to the signal path leading to the interface unit is formed, and (3) a radio frequency unit detects the arrival of the transmitted signal via the cable from the interface unit, TDD switches accordingly a step of connecting to the transmission system circuit, so that the transmission signal after the above SL TDD switch is switched to the transmitting circuit side reaches the TDD switch, the transmission signal coming from the interface unit, before reaching the TDD switch in step, characterized by having a, a step of delaying by passing through a surface acoustic wave filter. More preferably, (4) an amplifier which is provided in the transmission system circuit and amplifies a transmission signal arriving from the interface unit before the TDD switch, and when the TDD switch is not connected to the amplification system circuit, the operation is stopped or the power saving operation is performed. In the transmission / reception switching method to be performed, (5) at least a delay time for the delay is set so that the transmission signal passes through the amplifier after the amplifier starts an amplification operation in a steady state.
[0010]
Thus, in the present invention, the arrival of the transmission signal is detected by the IFU, and the TDD switch is connected to the transmission system circuit accordingly. Therefore, it is not necessary to transmit a switch switching control signal from the IFU to the RFU. Further, the excess of the detection switching required time with respect to the transmission system required time is compensated by delaying the transmission signal before reaching the TDD switch, so that the transmission signal lacking its head is transmitted wirelessly. Can be prevented. A delay element necessary for this can be realized by, for example, a SAW filter. Since the SAW filter is a filter that involves electromechanical conversion, acoustic wave propagation, and mechanical-electrical conversion, it is easy to design the delay time to an extent that meets the purpose of the present invention. Further, since it is stable against environmental and weather factors such as temperature, it is excellent in terms of stability and reproducibility of the delay time. Furthermore, in a preferred embodiment of the present invention, the delay time is estimated in consideration of the time required for the amplifier in the transmission system circuit to stop operating or shift from the power saving operation state to the steady state, for example, the time when the bias circuit starts up. Is set. In such a case, it is possible to use an amplifier whose bias circuit responds at a relatively low speed. Note that stopping the operation or power-saving operation of the amplifier in the transmission system circuit at the time of non-transmission is effective in securing and improving the isolation between the transmission system and the reception system.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Since the present invention can be applied to the subscriber station of the system shown in FIG. 1, the following description shows an application example to the subscriber station, but the present invention is also applied to the base station of the system. it can. In addition, if the system requires multiplexing of TDD-based radio lines and switching by a TDD switch, there is room for applying the present invention to each station constituting the system.
[0012]
FIG. 3 shows a configuration of the subscriber station 20 according to an embodiment of the present invention. The subscriber station 20 connects the outdoor unit 21 that is an RFU and the indoor unit 22 that is an IFU via a coaxial cable 23, and the antenna 24 for wireless communication with the base station 10 is shared by the outdoor unit 21. It has a configuration for switching use. The burst modem 220 in the indoor device 22 demodulates the received burst signal received by the outdoor device 21 by the antenna 24 and supplied to the indoor device 22 via the coaxial cable 23, and the demodulation result is sent to an indoor device (not shown) such as a personal computer. A demodulating function for outputting, and a modulation function for generating a transmission burst signal modulated in accordance with the information and transmitting the information supplied from the indoor device to the outdoor device 21 via the coaxial cable 23 in order to wirelessly transmit the information from the antenna 24 have.
[0013]
The outdoor device 21 roughly includes a transmission system circuit, a reception system circuit, a control system circuit, and the like. Among them, the transmission system circuit is a system that inputs a transmission burst signal from the indoor device 22 via the coaxial cable 23 and supplies the transmission burst signal to the antenna 24. Specifically, the transmission system circuit includes a burst signal detection circuit 211, a transmission / reception branch circuit 212, a SAW filter 213, a frequency converter 210b, and a transmission high-frequency power amplifier from a connector (not shown) for connection to the coaxial cable 23. The system reaches the TDD switch 210d connected to the antenna 24 through 210c. The frequency converter 210b up-converts the transmission burst signal with the local oscillation signal supplied from the local oscillator 210a, and the transmission high-frequency power amplifier 210c power-amplifies the radio frequency transmission burst signal output from the frequency converter 210b. In the figure, 210g is a bias circuit of the amplifier 210c. In the state where the bias circuit 210g is not operating, the amplifier 210c stops the amplifying operation and the power consumption is reduced, and the impedance viewed from the TDD switch 210d increases to an extent that can be said to be substantially infinite. Can be obtained.
[0014]
The reception circuit is a system that supplies a burst signal that is wirelessly received by the antenna 24, that is, a reception burst signal, to the indoor device 22 through the coaxial cable 23. Specifically, the receiving system circuit receives from the TDD switch 210d a reception low noise amplifier 210e that amplifies the received burst signal, and frequency conversion that down-converts the received burst signal from the amplifier 210e by the local oscillation signal from the local oscillator 210a. The system reaches the connector for connection with the coaxial cable 23 through the device 210f, the transmission / reception branching circuit 212 and the burst signal detection circuit 211. The part of the receiving system circuit from the TDD switch 210d through the amplifier 210e to the power amplifier 210f and the part of the transmission system circuit from the frequency converter 210a through the amplifier 210c to the TDD switch 210d are the TDD switch 210d and the local oscillator 210a. The high frequency circuit 210 is comprised with these. The transmission / reception branch circuit 212 is a circuit that supplies a transmission burst signal supplied from the indoor device 22 side to the high frequency circuit 210 side, and supplies a reception burst signal supplied from the high frequency circuit 210 side to the indoor device 22 side. Therefore, the transmission system circuit and the reception system circuit overlap each other from the coaxial cable 23 connector to the transmission / reception branch circuit 212. In addition, the broken line in a figure has the meaning which abbreviate | omits detailed illustration.
[0015]
The control system circuit is a circuit system from the burst signal detection circuit 211 to the TDD switch 210d and the bias circuit 210g via the detection determination circuit 214 and the TDD control circuit 215. FIG. 4 shows the operation. First, when a transmission burst signal (“arrival burst signal” in the figure) arrives from the indoor device 22 via the coaxial cable 23, the burst signal detection circuit 211 generates a signal that rises at an arbitrary time constant or speed accordingly. ,Output. The reason for not standing up immediately is to maintain the noise resistance performance of detection. The detection determination circuit 214 outputs a burst transmission ON signal when the output signal of the burst signal detection circuit 211 exceeds a predetermined threshold value. In response to the burst transmission ON signal, the TDD control circuit 215 turns on the TDD_SW switching control signal. There is a processing delay in the TDD control circuit 215 or in the previous stage between the generation of the burst transmission ON signal and the turn-on of the TDD_SW switching control signal. When the TDD_SW switching control signal is turned on, the TDD switch 210d is turned on to the transmission system side, that is, the amplifier 210c side, and the supply of the power supply voltage Vdd from the bias circuit 210g to the amplifier 210c is started. Although not shown, when the output of the burst signal detection circuit 211 falls below a predetermined threshold, the burst transmission ON signal falls and the TDD_SW switching control signal is turned off, and the TDD switch 210d is turned on to the receiving system, that is, the amplifier 210e side. In addition, the supply of the power supply voltage Vdd is stopped. Therefore, in the present embodiment, the TDD switch 210d enters the transmission system side during transmission, and enters the reception system side during non-transmission including reception.
[0016]
In the present embodiment, a SAW filter 213 is provided in the transmission system circuit before the high-frequency circuit 210. The SAW filter 213 is a filter for compensating for an excess of the detection switching required time with respect to the transmission system required time. In principle, the SAW filter 213 is provided at any position after the transmission / reception branch circuit 212 and before the TDD switch 210d. Although it can be provided, the pre-up-conversion is easier to implement because the frequency band used is lower, so in this embodiment it is provided at the position shown in the figure. Here, the transmission system required time is defined as the time required for the transmission burst signal to be transmitted from the signal detection portion in the burst signal detection circuit 211 to the TDD switch 210d, and the detection switching required time is defined as the signal output from the burst signal detection circuit 211. In the case of a 26 GHz carrier FWA subscriber station, the excess time required for detection switching with respect to the transmission system required time is normally about 1 μsec. Therefore, when a high-speed response type is used as the bias circuit 210g (that is, when the rise of the “PA bias circuit output” in FIG. 4 is very steep and the slope can be regarded as infinite), the delay time of the SAW filter 213 is set. By setting the time to about 1 μsec, it is possible to compensate for an excess of the detection switching required time with respect to the transmission system required time.
[0017]
In principle, it is possible to use another type of filter or delay line instead of the SAW filter 213, but considering the installation environment of the outdoor device 21, especially the temperature change, a filter with a small delay time change with respect to the temperature change. The SAW filter 213 is preferably used. Further, the SAW device is usually designed and manufactured with various techniques for reducing the delay time except for those used for delay lines and the like. Since the delay time of about 1 μsec is a longer time as a delay time of the SAW device, that is, a delay time that can be realized without making full use of the delay time shortening technique, the SAW filter 213 in this embodiment is used for ordinary unnecessary wave prevention. Compared to a SAW filter, this can be realized easily. Of course, from the viewpoint of transmission without degrading the characteristics of the transmission burst signal, the SAW filter 213 can also have a band-pass characteristic that allows the transmission burst signal to pass and appropriately blocks unwanted radiation components. . In this case, however, it is desirable to use a flat passage phase characteristic. Further, when a low-speed response type is used as the bias circuit 210g (that is, when the rise of the “PA bias circuit output” in FIG. 4 is slow and cannot be regarded as a gradient = infinity), the time required for this rise is calculated. In consideration, the delay time by the SAW filter 213 is set longer. That is, the transmission burst signal is input to the amplifier 210c after the amplifier 210c enters the normal amplification operation state. This makes it possible to obtain the characteristic effects of the present invention while using a bias circuit 210g that responds at a relatively low speed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a system to which the present invention can be applied.
FIG. 2 is a diagram conceptually showing a burst wave.
FIG. 3 is a block diagram showing a configuration of an apparatus according to an embodiment of the present invention.
FIG. 4 is a time chart showing the operation timing of the present embodiment.
[Explanation of symbols]
10 base station, 11 RFU, 12 IFU, 13, 23 coaxial cable, 20, 20A, 20B, 20C subscriber station, 21 outdoor unit (subscriber station RFU), 22 indoor unit (subscriber station IFU), 210 high frequency circuit , 210c amplifier, 210d TDD_SW (TDD switch), 210g bias circuit, 211 burst signal detection circuit, 213 SAW filter, 214 detection determination circuit, 215 TDD control circuit, 24 antenna.

Claims (2)

A radio frequency unit having a TDD switch for switching and connecting the internal transmission system circuit and reception system circuit to the antenna;
An interface unit including a transmission signal source connected to a radio frequency unit by a cable and outputting a transmission signal modulated according to transmission information ;
With
When the transmission signal is supplied from the interface unit via the cable, the transmission signal is executed in the radio frequency unit of the station constituting the FWA wireless communication system in which the uplink / downlink wireless line is time-division multiplexed. Is controlled to be supplied to the antenna via the transmission system circuit and the TDD switch, and in other cases, a signal path from the antenna to the interface unit via the TDD switch and the reception system circuit is formed. In the transmission / reception switching method for controlling the TDD switch,
Radio frequency unit
Detecting the arrival of the transmission signal via the cable from the interface unit, a step of connecting the TDD switch to the transmitting system circuit in response thereto,
So that the transmission signal after the above SL TDD switch is switched to the transmitting circuit side reaches the TDD switch, passes the transmission signal coming from the interface unit, at the stage prior to reaching the TDD switch and the surface acoustic wave filter A step of delaying by
Reception switching method characterized by having a. The transmission / reception switching method according to claim 1,
In a transmission / reception switching method in which an amplifier which is provided in a transmission system circuit and amplifies a transmission signal arriving from an interface unit before the TDD switch is stopped or power-saving when the TDD switch is not connected to the amplification system circuit. ,
Reception switching method in which the transmission signal after the above SL amplifier starts an amplifying operation at steady state to pass the amplifier, characterized in that to set the delay time according to the delay.

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