The loop of built-in modulation function
[technical field]
The present invention relates to a kind of loop of built-in modulation function; Be applied between the base station system and antenna system of mobile communication; Perhaps at base station system and tower amplifier, and the like the application scenario in, uplink/downlink signals is closed road/along separate routes.
[technical background]
In the mobile communication application; Often need be or directly the lower decline angle of antenna system is regulated through tower amplifier; Because tower amplifier and antenna system are higher apart from ground, the attendant is not easy to the maintenance of directly ascending a height, therefore; Just require to provide equipment and tower amplifier or antenna system tower under to electrically connect, then by the adjustment process of the realization of the equipment under tower relevant parameter.
Realize in the tradition lower decline angle adjusting of antenna system is mainly contained dual mode.
First kind of mode is antenna system or tower amplifier connection one cable to tower machine room lower from cat head; Electrically connect through external modulator-demodulator and controller; The adjusting that the attendant can be correlated with through controller at any time; The shortcoming of this mode is very obvious, and the laying of cable causes increasing of equipment investment cost, and it is unfavorable that operator is caused.
The second way utilizes the plain edition loop to realize, in this mode, the base station that requires to electrically connect with loop has the modulation function.When up, the attendant controls on the base station, and the modulation through the base station inputs to loop with control signal, transfers to tower amplifier or antenna system by loop and base station radio-frequency signal and direct current after synthetic, just can realize the process of modulating; In like manner, when descending, the signal of antenna system or tower amplifier is shunted to control signal, radiofrequency signal and direct current through loop, and the correlation function module of entering base station is carried out demodulation to control signal and got final product.For this mode, owing to need relevant functional module be set on the equipment of base station and so on, just limited the versatility of base station equipment, obviously do not meet the principle of modularized design.
[summary of the invention]
The object of the invention will overcome above-mentioned deficiency exactly, and a kind of modularized design principle that meets is provided, and can make the reduce investment outlay loop of built-in modulation function of cost of operator.
For realizing this purpose, the present invention adopts following technical scheme:
The loop of a kind of built-in modulation function of the present invention comprises:
First interface, when up, receive direct current and control appliance control signal input or when descending, export the feedback signal of antenna-feedback system;
Modulation-demodulation circuit is modulated to adapt to the call format of antenna-feedback system to signal the control signal of said first interface when up, when descending the feedback signal of antenna-feedback system is carried out exporting said first interface to after the demodulation;
Low pass filter carries out filtering output to the control signal after the modulation when up, when descending the feedback signal of antenna-feedback system is carried out exporting modulation-demodulation circuit to after the filtering;
Second interface, receive the input of base station radio-frequency signal when up or when descending the output radiofrequency signal give base station equipment;
The 3rd interface is exported after synthetic direct current, filtered control signal and the said radiofrequency signal when up, and the downlink time division road exports the feedback signal of antenna-feedback system to low pass filter and the radiofrequency signal that antenna-feedback system is descending exports second interface to.
Particularly, said modulation-demodulation circuit comprises:
Modulating unit is modulated signal when up;
Demodulating unit carries out demodulation to signal when descending;
Half-duplex device, the different conditions of corresponding upstream or downstream, said modulating unit of conducting or demodulating unit.
Said modulating unit comprises:
Signal source, generation is used for modulated carrier signal;
The analog switch module is modulated at the control signal of up time input on the carrier wave that said signal source produces;
Attenuation network, the signal that the analog switch module is exported carries out accomplishing modulation output after the power attenuation;
Said demodulating unit comprises:
The logarithm amplification detector, the feedback signal of the antenna-feedback system when descending carries out exporting after the demodulation;
Shaping circuit carries out shaping output to the feedback signal after the demodulation;
Be provided with an electric capacity between said second interface and the 3rd interface, this electric capacity carries out at a distance from straight-through friendship, suppresses low frequency signal the radiofrequency signal of upstream or downstream.
Said modulation-demodulation circuit and low pass filter all electrically connect with a lightning protection circuit.
Compared with prior art, the present invention possesses following advantage:
1, in loop, realized after the modulation function; The lower decline angle control appliance can directly be operated through loop, and need not lay the cable of special-purpose connection antenna-feedback system, thus; When realizing modularized design, can save the cost of investment of operator.
2, the modulating unit device used with respect to traditional ASK modulation circuit significantly reduces, and fixed the differential loss from the signal source to the output channel, makes that the power of output signal is highly stable; And can the power isolation of switch carrier signal be improved through adopting the high analog switch module of isolation, help reducing the interference of transmission course.
3, the traditional demodulation circuit generally is the combinational circuit that adopts diode detection pipe, operational amplifier and shaping comparator, and demodulating unit of the present invention compares with it, and its advantage is that device count is few, and input dynamic range is wide, and the recovering signal distortion factor is little.
[description of drawings]
Fig. 1 is circuit theory diagrams of the present invention;
Fig. 2 is the schematic diagram of modulation-demodulation circuit of the present invention;
Fig. 3 is the circuit theory diagrams of low pass filter of the present invention;
Fig. 4 is the circuit theory diagrams of lightning protection circuit of the present invention.
[embodiment]
Below in conjunction with accompanying drawing and embodiment the present invention is further described:
See also Fig. 1, the loop of built-in modulation function of the present invention has three interfaces and modulation-demodulation circuit 12, lightning protection circuit 11, a low pass filter 13 and a capacitor C.
The first interface AISG; With base station (not shown); Perhaps transfer controller (not shown) to be connected with electricity independently; And be connected with DC power supply, when up, receive direct current and control appliance control signal input or when descending feedback signal to the control appliance (base station or electricity accent controller) of output antenna-feedback system.
Modulation-demodulation circuit 12 is modulated to adapt to the call format of antenna-feedback system to signal the control signal of the said first interface AISG when up, when descending the feedback signal of antenna-feedback system is carried out exporting the said first interface AISG to after the demodulation.
The concrete composition of modulation-demodulation circuit 12 sees Fig. 2 for details, specifically comprises, and modulating unit 3, demodulating unit 4 and half-duplex device 5, modulating unit 3 is used for when up, signal being modulated; Demodulating unit 4 is used for when descending, signal being carried out demodulation; The different conditions of half-duplex device 5 corresponding upstream or downstream, said modulating unit 3 of conducting or demodulating unit 4.
Modulating unit 3 is made up of IF signal source 31, analog switch module 32 and attenuation network 33.What analog switch module 32 was selected for use is the integrated chip with low internal resistance, high-isolation, high speed switch speed; It can be according to the quick switching channel selector switch of the high-low level of control signal; Selecting through signal effectively is IF carrier wave or the signal ground that IF signal source 31 produces, and is the waveform modulated of control signal corresponding envelope signal; This envelope signal obtains the proper carrier wave power level through π type attenuation network 33 again, outputs on low-pass network and the feeder line, accomplishes modulated process.This circuit device more used than traditional ASK modulation circuit significantly reduces; And fixed differential loss from signal source 31 to output channel, make that the power of output signal is highly stable; And the isolation of the analog switch device that adopts is high, and the power isolation of switch carrier signal improves, and helps reducing the interference of transmission course.
Demodulating unit 4 is made up of logarithm amplification detector 41 and shaping circuit 42.Logarithm amplification detector 41 has adopted logarithmic amplifier; It is the function of corresponding level by linear transformation that logarithmic amplifier has input signal power; And the dynamic range of input signal is very big, can be effectively stably detects modulation signal according to the power of modulating wave envelope signal; Signal gets into shaping circuit 42 after the detection, and circuit can be adjusted the comparative level of shaping circuit adaptively according to the input signal power level, makes that circuit can be that the 20dB input signal restores by the TTL signal form to dynamic range.The traditional demodulation circuit generally is the combinational circuit that adopts diode detection pipe, operational amplifier and shaping comparator, and this circuit compares with it, and its advantage is that device count is few, and input dynamic range is wide, and the recovering signal distortion factor is little.
Half-duplex device 5 main elements are monostable flipflops.Because the transmitting-receiving of antenna-feedback system control signal is on same feeder line, to realize, so receiving and transmitting signal will transmit through time-multiplexed half-duplex form.Control switching circuit is realized the automatic conversion of receiving and transmitting signal transmission direction through the logic combination circuit of monostable burst length of adjustment and switching controls.This circuit utilizes the characteristics of monostable flipflop, and according to the source automatic switching signal transmission direction of signal, it is simple and clear to have control logic, and reliable and stable characteristics can reduce extra direction control signal line, simplifies circuit design.
Consult Fig. 3, low pass filter 13 carries out filtering output to the control signal after the modulation when up, when descending the feedback signal of antenna-feedback system is carried out exporting modulation-demodulation circuit 12 to after the filtering and carries out demodulation.It is by 13 series connection of two-stage low pass filter, and prime constitutes second-order low-pass filter 13 by L1 and C1, has higher cut-off frequency, and the main radiofrequency signal that suppresses greater than 800MHz improves the isolation between radio-frequency channel and AISG signalling channel.Back level is about 10MHz by the cut-off frequency that L2, C2 and C3 constitute third-order low-pass filter 13, mainly suppresses crosstalking of low frequency signal on the cable, reduces the distortion of modulation signal.
Please consult Fig. 1 again, the second interface BTS/Node B is connected with base station radio-frequency equipment, receives the input of base station radio-frequency signal or output when descending when up.
The 3rd interface ANT/TMA is connected through antenna-feedback system on radio frequency cable and the tower; Export after synthetic direct current, filtered control signal and the said radiofrequency signal when up, the downlink time division road exports the feedback signal of antenna-feedback system to low pass filter 13 and the radiofrequency signal that antenna-feedback system is descending exports the second interface BTS/Node B to.
Be provided with a capacitor C between said second interface BTS/Node B and the 3rd interface ANT/TMA; Its main effect is to suppress low frequency signal, partition direct current, and frequency is transmitted through being coupling between these two interfaces of it to the radiofrequency signal of 2170MHz at 800MHz simultaneously.
Said modulation-demodulation circuit 12 all electrically connects with a lightning protection circuit 11 with low pass filter 13; See Fig. 4 for details; The design of lightning protection circuit 11 has combined the lightning protection characteristics of active circuit and passive circuit; Directly adopted the Lightning Protection of passive circuit from the first interface AISG interface,, only connected the power inductance coupling on the passage respectively placing a gas discharge tube (GDT) near two input/output interface places (among Fig. 4 from IN and OUT two) to the direct current channel (passage Fig. 4 from IN to OUT) of low pass filter 13; The direct voltage loss is minimum, and this mode has been avoided the excessive problem of direct current loss that use resistance decoupling causes in traditional lightning protection circuit; Adopted the Lightning Protection of active circuit to this path of direct current regulation circuit (DC-DC) from the first interface AISG interface; In above-mentioned direct current channel, passed through first gas discharge tube (among Fig. 4 from IN) afterwards; Adopt a powerful resistance to introduce power supply, connect a Transient Suppression Diode (TVS) behind the resistance and carry out the secondary lightning protection to ground, just insert on the direct current regulation circuit then from resistance terminal as decoupling resistance; The resistance of this mode decoupling resistance is bigger; Can significantly reduce the intensity of the surging signal of input next stage circuit, protect active circuit effectively, improve the lightning protection grade of device.
The operation principle of this loop is described below.
During signal uplink; The antenna control signal that is input to the AISG interface from the base station is the form of RS485 bus signals; Through the effect of modulating unit 3, this control signal is carried out on-off keying modulation (OOK) to the carrier signal of IF, the filtering through low-pass network together with direct current then; Converge at the 3rd interface ANT/TMA again with from base station, the radiofrequency signal that is capacitively coupled to the 3rd interface ANT/TMA, three road signals are transported to base station cat head antenna-feedback system through radio frequency cable.
During signal downlink, import by the 3rd interface ANT/TMA, shunt to the second interface BTS/Node B and low pass filter 13 from the radiofrequency signal and the antenna-feedback system control signal of antenna-feedback system.The radiofrequency signal that is capacitively coupled to the second interface BTS/Node B is delivered to the radio frequency interface of base station; Another road is filtered into the IF Modulation ripple of belt controling signal through the signal of low pass filter 13; This modulating wave is through the demodulation of modulation-demodulation circuit 12; Be reduced into the sky feedforward control signal of RS485 bus signals form, give the AISG control appliance of base station then.
Loop of the present invention is compared maximum advantage and is that it has increased the modulation-demodulation circuit 12 of built-in intermediate frequency (IF) signal with the plain edition loop; Therefore; Close direct current signal and radiofrequency signal the function on road except having the plain edition loop, also have antenna feeder equipment controling signal modulation and demodulation function.Modulation function: be modulated to the antenna feeder equipment controling signal on the IF signal, close the road with direct current and radio frequency letter then; Demodulation: separate intermediate-freuqncy signal with radiofrequency signal, and demodulate control signal to antenna feeder equipment.So antenna-feedback system directly connects Smart type loop, can realize devices communicating and monitoring on base station and the tower through the rf feed cable, simplified the control connection mode of base station equipment and tower top device.