CDMA multicarrier receiving systemTechnical field
The invention belongs to wireless mobile communications wireless access technology field, is a kind of in code division multiple access (CDMA) cellular radio Communication system, adopts the CDMA multicarrier receiving system of digital intermediate frequency mode design.
Background technology
Accompanying drawing 1 demonstrates the theory diagram of common cdma wireless receiver, mainly comprise reception antenna, radio frequency amplification and down-converter unit, intermediate frequency demodulation unit and baseband signal processing unit, the radio frequency that is connected with reception antenna amplifies and down-converter unit output intermediate-freuqncy signal, intermediate frequency demodulation unit output baseband signal.Early stage wireless intermediate-frequency receiver all adopts analogy method to realize, have problems such as costing an arm and a leg, debug complexity, along with the development of technology and technology, wireless intermediate-frequency receiver develops into digital receiver from analog receiver gradually.
Accompanying drawing 2 is present general CDMA multicarrier receiving system, and the principal character of this system is: a plurality of single carrier receiving systems are composed in parallel CDMA multicarrier receiving system.As shown in the figure, the CDMA multi-carrier signal receives through reception antenna, after passing through duplexer filtering and LNA (low noise amplifier) amplification again, be branched out in a plurality of single-carrier receivers, with a single-carrier receiver is example, this single-carrier receiver be linked in sequence radio-frequency filter 21, frequency converter 22, intermediate frequency amplifier 23, intermediate-frequency filter 24, intermediate frequency amplifier 25, A/D converter 26, quadrature demodulator 27, digital down converter 28.Wherein radio-frequency filter 21, frequency converter 22 and intermediate frequency amplifier 23 are broadband device, and intermediate-frequency filter 25 is a narrow band filter, generally select SAW (surface acoustic wave) filter for use, and the channel selection function is finished in frequency converter 22 and intermediate-frequency filter 24 actings in conjunction.Identical as for A/D converter 26, quadrature demodulator 27 and digital down converter 28 with device in the general digital if receiver.The baseband signal that each single-carrier receiver comes out demodulation remerges the unified baseband signal processing unit that is sent in back.Therefore therefrom as can be seen, this multi-carrier receiver is not a broad band multicarrier receiver truly, and this multi-carrier receiver is along with the increasing of reception carrier number, and cost and volume be multiplication thereupon also.In addition, therefore this multicarrier receiving system can't realize seamlessly transitting to the EV-DV system owing to adopt the single carrier parallel way to realize.
Summary of the invention
The present invention is exactly the shortcoming that will overcome above-mentioned prior art, a kind of wideband CDMA multicarrier receiving system truly is provided, the simulation part of whole receiving system all adopts broadband device, channel is selected by digital quadrature demodulation, numeral takes out value filtering and channel selection filter (digital FIR filter) is finished jointly, be to receive single carrier or multicarrier all adopts unified hardware platform, only need pass through software setting, can finish the receiving function of different carrier, therefore this multicarrier receiving system has with low cost, volume is little, can seamlessly transit the advantage of EV-DV.
Technological system of the present invention is achieved in that a kind of CDMA multicarrier receiving system frequently, comprise reception antenna, radio frequency amplifies and down-converter unit, four parts of intermediate frequency demodulation unit and baseband signal processing unit: described radio frequency amplifies and down-converter unit receives the radio frequency signal that receives from reception antenna, the output intermediate-freuqncy signal, comprise the radio-frequency front-end that is linked in sequence, splitter, radio-frequency filter, frequency converter, intermediate-frequency filter and intermediate frequency amplifier, it is characterized in that: its radio-frequency channel is the broadband channel, and the pass band width of intermediate-frequency filter is N*1.23MHz (N is a carrier number); Described intermediate frequency demodulation unit receives the intermediate-freuqncy signal of simulation, the output digital baseband signal, comprise the A/D converter, quadrature demodulator, Digital Down Convert, DC filtering, formed filter, channel selection filter and the AGC unit that are linked in sequence, it is characterized in that: the A/D converter of A/D converter using broadband great dynamic range, can finish the A/D mapping function of N carrier wave simultaneously.Channel is selected to be finished jointly by quadrature demodulator, Digital Down Convert and channel selection filter, quadrature demodulator can be set to centre frequency by different single carriers, Digital Down Convert filtering and channel selection filter are finished neighboring trace jointly and are suppressed, because AGC can only finish after channel is selected, so AGC adopts digital AGC mode to finish.
Channel selection filter adopts digital FIR filter;
Also include DC filter, be arranged between Digital Down Convert and formed filter, can be according to whether having DC offset circuit to accept or reject;
Described DC filter is the digital filter of isolated DC.
Described A/D converter is the A/D converter of the great dynamic range in K bit broadband, the dynamic range that analog if signal had before the described A/D converter needs M significant bit data at least, then N＞M should be arranged, if the analog if signal before the described A/D converter is a N carrier wave CDMA signal, the A/D converter must have the sampling bandwidth that satisfies analog if signal.
Described AGC adopts the unit AGC of digital mode.
As mentioned above, the present invention compared with prior art has tangible advantage and beneficial effect, because common CDMA multicarrier receiving system adopts frequency converter and intermediate-frequency filter to finish frequency jointly and selects, frequency converter is finished different single carriers and is set to centre frequency, intermediate-frequency filter is finished the neighboring trace inhibit feature, so intermediate-frequency filter is generally Surface Acoustic Wave Filter, be narrow band filter, passband is about 1.23MHz.Receive if finish multicarrier, the parallel connection of a plurality of like this single carrier receiving system must be finished jointly, along with the increase that receives multicarrier quantity, cost and volume double thereupon.Adopt the CDMA multicarrier receiving system of mode of the present invention, whole radio-frequency channel is the broadband channel entirely, the pass band width of intermediate-frequency filter is N*1.23MHz (N is a Carrier), wherein N can be by the self-defined setting of design consideration actual conditions, A/D converter using broadband great dynamic range, channel is selected to be finished by Digital Signal Processing, can finish jointly by DSP (digital signal processor) and FPGA (programming device), be that multicarrier receives or unified hardware platform is all adopted in the single carrier reception, only need to finish the reception of different carrier by changing software setting, whole system has extremely low cost, advantages such as receptivity is good, and volume is little.
Description of drawings
Fig. 1 is the theory diagram of common cdma receiver;
Fig. 2 is the CDMA multicarrier receiving system block diagram of traditional approach;
Fig. 3 is that digital demodulation of the present invention and Digital Down Convert realize block diagram;
Fig. 4 is a CDMA multicarrier receiving system block diagram of the present invention;
Specific implementation
Referring to Fig. 4, the multicarrier of CDMA shown in figure receiving system structure is made up of antenna element, radio frequency amplification and down-converter unit, intermediate frequency demodulation unit and baseband signal processing unit.Radio frequency amplifies and down-converter unit output analog if signal, intermediate frequency demodulation unit output digital baseband signal.
Radio frequency amplifies and down-converter unit comprises radio-frequency front-end 42, splitter 43, radio-frequency filter 44, frequency converter 45, intermediate-frequency filter 46 and intermediate frequency amplifier 47 compositions.
Described radio-frequency front-end 42 mainly comprises duplexer, receiving filter and LNA devices such as (low noise amplifiers), to effects such as transmitting-receiving separation, filtering and low noise amplifications.
Intermediate-frequency filter 46 general SAW (surface acoustic wave) filters that adopt, passband is N*1.23MHz.
Intermediate frequency amplifier 47 is general to be amplified to the full scale of A/D converter with the peak signal that receives or near the full scale place.
The intermediate frequency demodulation unit is received as example with one road single carrier, includes A/D converter 48, quadrature demodulator 49, digital down converter 410, DC filter 411, formed filter 412, channel selection filter 413 and AGC unit 414.Analog if signal inputs to A/D converter 48, carries out automatic gain control back output baseband signal by the AGC unit.
The A/D converter of the great dynamic range that described A/D converter 48 is broadband high-speeds, N the carrier wave of can sampling simultaneously, dynamic range can satisfy the requirement of CDMA multicarrier system to dynamic range.
Quadrature demodulator 49 in the intermediate frequency demodulation unit, digital down converter 410 and formed filter 412 are necessary links of Digital IF Processing, and the structure of general quadrature demodulator 49, digital down converter 410 is referring to Fig. 3.Quadrature demodulator 49 is with the digital baseband signal of m*chip (m*1.2288M) speed, carry out digital quadrature demodulation, demodulate digital baseband I, Q signal, deliver to and take out the value filtering device in the digital down converter 410, generally take out the value filtering device and comprise that mainly CIC (serial integration pectination) takes out the value filtering device and FIR (finite impulse response) takes out the value filtering device, digital down converter 410 is with baseband I, the Q signal value of taking out is to 8*chip (8*1.2288M) or 2*chip (2*1.2288M) speed, thereby finish anti-aliasing filter and reduce the Digital Signal Processing amount, formed filter 412 is as broad as long with the formed filter in the general digital if receiver.
Channel is selected to be finished jointly by quadrature demodulator 49, digital down converter 410 and channel selection filter 413.Quadrature demodulator 49 is with the carrier wave of required demodulation, transform to centre frequency, digital down converter 410 can play a part of neighboring trace inhibitory action, and final channel is selected to be finished by channel selection filter 413, and general channel selection filter 413 adopts digital FIR filter to realize.
AGC unit 414 adopts digital AGC mode to realize, and output RSSI (received field strength indication), and will be transported to baseband signal processing unit 427 through the baseband signal after the automatic gain control and treatment.
N such receiving element is together in parallel, just constitutes the CDMA multicarrier and receive.
Signal flow of the present invention following (referring to Fig. 4):
The wireless signal that reception antenna unit 41 receives from travelling carriage, delivering to radio frequency amplifies and down-converter unit, comprise radio-frequency front-end 42, splitter 43, radio-frequency filter 44, frequency converter 45, intermediate-frequency filter 46 and intermediate frequency amplifier 47, after carrying out radio frequency amplification and down-conversion, with RF signal transformation is intermediate-freuqncy signal, deliver to A/D converter 48 at first with the analog signal of intermediate frequency, after being transformed to digital signal, in delivering to quadrature demodulator 49, carry out quadrature demodulation, generate the I of quadrature, Q signal, digital down converter 410 is with the I of digital quadrature, Q signal carries out Digital Down Convert, to the baseband signal of down-conversion after carrying out DC filtering 411 and molding filtration 412, deliver to carry out channel selectivity filtering in the channel selection filter 413 after, deliver to again and carry out carrying out in the AGC unit 414 the automatic gain control and treatment, output meets the base band data form that base band signal process requires, and finally outputs to baseband signal processing unit 427.