CN101917376B - Two-stage frequency conversion method for digital down conversion system in multi-carrier digital receiver - Google Patents
Two-stage frequency conversion method for digital down conversion system in multi-carrier digital receiver Download PDFInfo
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- CN101917376B CN101917376B CN 201010241392 CN201010241392A CN101917376B CN 101917376 B CN101917376 B CN 101917376B CN 201010241392 CN201010241392 CN 201010241392 CN 201010241392 A CN201010241392 A CN 201010241392A CN 101917376 B CN101917376 B CN 101917376B
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Abstract
The invention discloses a two-stage frequency conversion method for a digital down conversion system in a multi-carrier digital receiver, which carries out down conversion operation on a digital signal by two stages. In the first stage of down conversion, all carriers are used as a whole body and are subjected to one-time down conversion by a mixer, so that frequency offsets do not exist among the carriers; and in the second stage of down conversion, the carriers have lower down conversion amplitude, cannot generate large frequency offsets and do not need decimation filters respectively. Therefore, a digital signal acquired by the down conversion system adopting the two-stage frequency conversion method has high relative frequency stability. Moreover, in the two stages of down conversion, only one decimation filter is adopted in the first stage of down conversion and when the number of the carriers is increased, only corresponding mixers are added so as to save resources of the decimation filters, reduce the volume of the system and reduce production cost.
Description
Technical field
The present invention relates to a kind of conversion method of multi-carrier digital receiver, relate in particular to the two-stage frequency conversion method of digital down conversion system in a kind of multi-carrier digital receiver.
Background technology
In recent years, along with semiconductor technology and Digital Signal Processing develop rapidly, realize that with the mode of hardware or software programming the software radio receiver of wireless receiving function all is tending towards ripe and perfect in theory and practice.Various digital technology and method have obtained extensive application.In present software radio receiver; General radio frequency (RF) signal is earlier through the extremely suitable intermediate frequency of analog down; After intermediate frequency is with analog to digital converter (ADC) digitlization, export the high-speed figure intermediate-freuqncy signal then; The operations such as frequency conversion, filtering extraction and separation of passing through digital down conversion system (DDC) again become the baseband signal of the low speed of each carrier wave, give digital signal processor (DSP) with the baseband signal of low speed at last and carry out processing such as follow-up demodulation, decoding, anti-interference, anti-fading, adaptive equalization.Therefore, digital down conversion system is one of core system of radio receiver.In the design process of present digital down conversion system; Generally all adopt the one-level conversion method; As shown in Figure 1; The one-level conversion method adopts a plurality of frequency mixers and decimation filter respectively each carrier wave in the digital signal to be carried out down-conversion and filtering extraction, and promptly each carrier wave in the digital signal need use a frequency mixer and a decimation filter at least; Adopt the one-level conversion method to have following shortcoming: 1, frequency conversion is carried out when digital signal is in High Data Rate, and frequency change is bigger after the frequency conversion, causes between each carrier wave relative frequency deviation big, makes the relative frequency stability variation of digital signal.2, each carrier wave needs corresponding decimation filter, and each decimation filter contains a considerable amount of registers and multiplier, needs a large amount of logical resources like this, and simultaneously, down conversion system can't be carried out miniaturization.And along with the increase of carrier wave number, need more decimation filter, the volume of down conversion system is also bigger, and production cost improves.
Summary of the invention
The purpose of this invention is to provide a kind of two-stage frequency conversion method that makes digital down conversion system in the multi-carrier digital receiver that the digital signal stability is high during the digital down conversion system frequency conversion, system bulk is little, production cost is low.
For realizing above-mentioned purpose, the two-stage frequency conversion method of digital down conversion system in turn includes the following steps in the multi-carrier digital receiver: step 1: one group has carrier for digital signal and gets into digital down conversion system; Step 2: one group of carrier wave is done as a whole, carried out first order down-conversion by a frequency mixer; Step 3: one group of carrier wave after the first order down-conversion is done as a wholely to carry out filtering extraction by a decimation filter; Step 4: adopt the frequency mixer identical with carrier number, each carrier wave to filter output carries out second level down-conversion respectively; Step 5: one group of carrier wave after the down-conversion of the second level carries out the time division multiplexing of each carrier wave after through one group of decimation filter, and each has the carrier wave of low speed fundamental frequency signal to separate output.One group of decimation filter comprises finite impulse response filter and root raised cosine filter in regular turn in the step 5.
The present invention compared with prior art, conversion method branch two-stage of the present invention is carried out down-conversion operation to digital signal, when first order down-conversion; Do all carrier waves as a whole; Carry out down-conversion one time by frequency mixer, do not have frequency deviation like this between each carrier wave, in the second level during down-conversion; The down-conversion amplitude of each carrier wave is less; Therefore can not produce big frequency deviation yet, need not to use respectively again decimation filter, adopt the relative frequency stability of the digital signal that the down conversion system of two-stage frequency conversion method obtains high.In addition, in the two-stage downconversion process, only need when first order down-conversion, adopt a decimation filter; And when carrier number increases,, thereby saved the decimation filter resource as long as add corresponding frequency mixer; Dwindle the volume of system, reduced production cost.
Description of drawings
Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed explanation:
Fig. 1 is the Digital Signal Processing flow chart of the one-level conversion method of prior art;
Fig. 2 is the Digital Signal Processing flow chart of two-stage frequency conversion method of the present invention.
Embodiment
Explanation of nouns among the present invention is following, Digital Down Convert: digital signal is lower than original signal through the signal frequency that obtains after the mixing, and this mixing mode becomes Digital Down Convert.Carrier wave: carrier wave is periodic electric oscillation ripple, is used for transmission signals.Frequency mixer: frequency mixer mainly comprises numerically-controlled oscillator (NCO), and signal frequency is transformed to another value by a value.Decimation filter: decimation filter is the circuit that the frequency beyond the frequency of CF or this frequency is carried out effective filtering, and its function is to obtain a CF or eliminate a CF.Root raised cosine (RRC) filter: it can form filtering to digital signal, and the compression secondary lobe reduces and disturbs, and is used for eliminating intersymbol interference.Finite impulse response filter (FIR) filter: it is an element basic in the digital information processing system, and it can have strict linear phase-frequency characteristic when guaranteeing any amplitude-frequency characteristic, and its unit sample respo is time-limited simultaneously.Be used to communicate by letter, the signal processing in field such as image processing, pattern recognition.Time division multiplexing: time division multiplexing is to adopt the different periods of same physical connection to transmit various signals, thereby has realized a plurality of digital signals of transmission on the physical connection.
As shown in Figure 2, the two-stage frequency conversion method of digital down conversion system comprises the steps: step 1 in the four carrier wave digital receivers: four have carrier for digital signal and get into digital down conversion system; Step 2: four carrier waves are done as a whole, carried out first order down-conversion by a frequency mixer; Step 3: four carrier waves after the first order down-conversion are done as a wholely to carry out filtering extraction by a decimation filter; Step 4: adopt four frequency mixer respectively each carrier wave of filter output to be carried out second level down-conversion; Step 5: four carrier waves after the down-conversion of the second level separate and export four carrier waves that have the low speed fundamental frequency signal through carrying out the time division multiplexing of each carrier wave behind finite impulse response filter and the root raised cosine filter.
Claims (2)
1. the two-stage frequency conversion method of digital down conversion system in the multi-carrier digital receiver, it is characterized in that: described method in turn includes the following steps:
Step 1: one group has carrier for digital signal and gets into digital down conversion system;
Step 2: one group of carrier wave is done as a whole, carried out first order down-conversion by a frequency mixer;
Step 3: one group of carrier wave after the first order down-conversion is done as a wholely to carry out filtering extraction by a decimation filter;
Step 4: adopt the frequency mixer identical with carrier number, each carrier wave to filter output carries out second level down-conversion respectively;
Step 5: one group of carrier wave after the down-conversion of the second level carries out the time division multiplexing of each carrier wave after through one group of decimation filter, and each has the carrier wave of low speed fundamental frequency signal to separate output.
2. according to the two-stage frequency conversion method of digital down conversion system in a kind of multi-carrier digital receiver described in the claim 1, it is characterized in that: one group of decimation filter comprises finite impulse response filter and root raised cosine filter in regular turn in the step 5.
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| CN 201010241392 CN101917376B (en) | 2010-07-30 | 2010-07-30 | Two-stage frequency conversion method for digital down conversion system in multi-carrier digital receiver |
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| CN101917376B true CN101917376B (en) | 2012-12-19 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103368880B (en) * | 2012-03-29 | 2016-04-13 | 鼎桥通信技术有限公司 | The implementation method of intermediate-frequency channel and device |
| CN109245729B (en) * | 2018-09-20 | 2021-01-26 | 电子科技大学 | 8-path parallel 2Gsps digital mixer |
| CN111327334A (en) * | 2018-12-17 | 2020-06-23 | 天津光电通信技术有限公司 | Narrow-band DDC time division multiplexing method based on FPGA |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2005041408A1 (en) * | 2003-09-25 | 2005-05-06 | Thomson Licensing S.A. | Digital rf transceiver with multiple imaging modes |
| CN201054734Y (en) * | 2007-06-28 | 2008-04-30 | 重庆会凌电子新技术有限公司 | A broad frequency monitoring receiver |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2005041408A1 (en) * | 2003-09-25 | 2005-05-06 | Thomson Licensing S.A. | Digital rf transceiver with multiple imaging modes |
| CN201054734Y (en) * | 2007-06-28 | 2008-04-30 | 重庆会凌电子新技术有限公司 | A broad frequency monitoring receiver |
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