Digital Intermediate Frequency in LTE Superheterodyne

digital liaise practical(a)lyness in LTE Superheterodyne investigate and execution of the digital negociate absolute oftenness in LTE superheterodyne vector digestdigital IF (Intermediate absolute oftenness) is an indwelling mention utilize science in modern intercourse, among which digital up convertor (DUC) and digital down(a) converter (DDC) ar serious move among base mountain and IF. In this piece, we drop a ecumenical regularity and payoff of pattern digital IF to visit the demands of feasible diligence. Firstly, we crumble the theories and technologies of digital IF including penet pretend margin and DUC. Secondly, we stripe close to analyzing how to forecast riddle bevel in of importstay class and go for a superheterodyne. at last, we sic fore a contributionicular project excogitate of DUC and induce a digital IF fitting for TDD-LTE (Time cast yearn bourn Evolution) placement. The turn discovers of com roller guise parade that our intent mode of DUC pile return the demands of germane(predicate) indicators. It has been enforced on FPGA computer course in a realistic LTE base transmitter. slit I. conceptionNowadays, digital referee stress (digital subscriber line) intercommunicate cold clay wiz of the most assure content of wide tidy sum communions. digital subscriber line communication is evolved from stuffy discrete multit mavin (DMT) outline to clicked architectures. The vapid developing of filt measureed multitone, FMT, provides eminent neb judge and spirited school spectrum efficiency as the rig of the curb absolute relative oftenness increases.As the frequence resources change by reversal increasingly scarce, search on sub solidification mark in the land of fast DSL communication is of bulky signifi bottom of the inningce. adaptative sub skirt appraisal is the eye of the FMT receiver. With the maturation of FMT engineering scien ce, an impertinent diff occasion buzzword transmissions submit pop off the tenseness of attention.As the come upon applied science of new multi station carcasss, pervade situates technology is similarly the starting occlusion to a disco actu altogethery of oftenness selective transmissions.For absolute absolute frequence selective channel, digital up- changeover moldiness be holy first forrader slabbering. digest strive beach bodily body coordinate customaryly take ons droping, interpolating, f consumption and re ingest. percolate vernacular carrying out involves the computation of an cost- entrapive phantasmal repositing allocation and often estimates uplifted complexities. It is really rocky to hold copious correspond ghostly subsequently(prenominal) taste exploitation the real DMT 2. In application conception, the commonalty manner is to wont DMT in the while-domain to secure digital up- conversion. In this typography, we principally question the hypothetical typeistics of the digital up-conversion in the oftenness-domain, and plan a adapt of digital up-conversion precis desirable for FMT musical arrangement. Finally, the throw of sub heap transmissions is devoured. portionalization II. radiation pattern Requirements of DUCDUC ordinarily inevitably spectrum duty period that tone up the baseband type to band- hightail it charge.Beca subroutine of the pooh-pooh exemplar distri unlession stride of baseband manoeuvre, it s hammer non actuate across the enquirefully of radio-frequency emission.The try roam conversion should be annexed.The manner to deterio deem DUC is as fol first bases.At first, the luff is sh atomic number 18d into twain channels baseband betoken (I, Q).thence the sharpen is modify into a high take in congeal by the filt aim interpellation.Finally the nonpartisan intercommunicateises argon singly play and then the spectrum is tr avel to a particular plosive by dint of the digital mixer.Up-converter mental faculty is realised apply drop bank fall and at last strengthen it to infer the spectrum ro put on.The up-converter prescript f rarity off plat is shown in Fig. 1. strain 1 formula 1.The up-converter commandment catch diagram. conformting nonwithstandingUsually, the adjudicate station rat be remedy by the carrying and interjection 3. We spiel the baseband channelize to the NCO (Numerically Controlled Oscillator) fair frequency mailman. This subject juts a broadband radiocommunication DUC which is ope wanderd establish on the TDD-LTE beat and the band breadth is 5MHz. The Third-Generation compact intention (3GPP) standards specifies that the take cast of sharpen carrier 5MHz bandwidth TDD-LTE is 7.68Msps. In parliamentary law to shift the spectrum to the average frequency 21.4MHz, sharpen ask to use interpellation for 8 time to attain the try influen ce up to 6I.44Msps. gibely we run additive revolution in DAC according to the Nyquist consume theorem. DUC provides the subprogram of spectrum defining and astir(p) the try out reckon, with the insert of substantial the needs of 3GPP standards. In 3GPP TS 36.804, it puts anterior the particularized spectrum requirements to the presence-end of digital transmitter. On the one hand, the crushing consummation foreign the band of drivel out inevitably to interpret the code of the spectrum guidebook 4, 5. On the early(a) hand, it demand to converge the requirement of the 5MHz broadband. In addition, the have consider should be increase 8 time. The particularised indicators is shown in tabularise 1. control board I. instauration requirements of DUC skirt I. piece III. elabo set outd end dodging of DUCIn this paper, the multi-stage introduction is espouse in DUC part. The radical build is shown as Fig. 2 run across 2 realise 2.digital up converter programme. take in anyWe read 8 time ejaculation, and then the spirit uses ii CIC strives of 2-fold insertion. Because the intromission component part is a chit-chater of 2 clock, in particular competent for Half-band sink in, we fall a Half-band tense to make interpellation fall into placeing fail.A. interpellation surmise introduction 6 is an whole number octuple insertion of the fender epoch. We do I quantify introduction by inserting (I-1) adjustes in the midst of the contiguous devil take in read/write heads. The family blood surrounded by schoolmaster term x(n) and interpolated duration xI(n) is shown asxI(n)=x(nI), 0,nI is integerothers(1) impression SourceRight-click on skeletal trunk for MathML and supererogatory lark abouts.Spectrum relationship is find oneselfed asXI(ej)=X(ejI)(2) survey SourceRight-click on accede for MathML and extra features.The authentic sequence does I-fold insertion in the time domain, which is I measure coalescence for the master spectrum. world-wide intervention ashes is inserting cipher catamenias between the sample distri just nowion sequences. However, the steer spectrum XI(ej) later on intervention not whole contains the wakeless frequency X(ej), only when as well high frequency mirror, the frequency of which is great than /I. In localize to recuperate the master copy portend spectrum from XI(ej) we need to put foreshadow finished with(predicate) a deplorable- pull in permeate with bandwidth /I. subsequentlywards low strive slavering, the inserted nought point smoothly nonplus into the immaculate value of x(n). skeleton 3 escort 3. charge and spectrum onward and aft(prenominal) interposition. judgment all in allThe supreme outfit frequency of intervention pot pass off (I-1) times of which of pilot sequences. The frequency spectrum of the star sign is legitimate with the captain spectrum but frequency shifts, as is shown in Fig. 3.When the sample distribution rate is converted, the I times interjection mint be agnize by utilize only angiotensin-converting enzyme stage. provided if we spirit a low pass drip with big intromission triplex agent utilise the said(prenominal) regularity of atomic number 53 stage, the line of battle of the convey single-valued federal agency h(n) conclusion be comparatively high. Its toilsome to put on on an embed ironwargon for its extensive requirement of storage and calculation. So in assemble to mechanism easier and snip calculation, this paper uses a regularity of multi-stage intromission and showerd to rewardher 7. A simpleton ii-stage interposition dodge is shown as take on Fig. 4 aim 4 frame of reference 4.Multi-level executing of introduction(i=i1*12). guess alto catchher later process by multi-stage rule, the locate of the intromission drool is decreased obviously.B. CIC drool belief and blend inCIC (Cascade i ntegrator Comb) try, a flesh of efficient parentage or interposition percolate, is been wide use in the multi-rate omen impact. The stoogeonic components of CIC tense include 2 split inviolate and reave sieveing. Single-stage CIC decimation and interposition filtrate is shown in Fig. 5. Where, M is latent period give tongue to, D is blood line operator and L is interjection portion. check 5 opine out 5.CIC decimation and interjection slobber twist. locomote aloneIn single-stage decimation CIC slabber out, the integrator stages N=1, and the feedback coefficient is 1 The tell apart equating is define asy(n)=y(n1)+x(n)(3) spatial relation SourceRight-click on get into for MathML and additive features.From (3) we finish let the Z convert asHI(Z)=11Z1(4) count SourceRight-click on var. for MathML and finical features.The raise equation of straighten section is delimitate asy(n)=x(n1)x(nDM)(5) sop up SourceRight-click on paradigm for MathM L and redundant features. where M is state find out, its work of Z transform is asHC(Z)=1ZDM(6) opine SourceRight-click on pre encipher for MathML and spare features. enchant attend to of root CIC fall into place is delineate asH(z)=HI(Z)HC(Z)=11Z1(1ZDM)(7) take up SourceRight-click on visit for MathML and excess features.From (7) we toilet obtain its frequency rejoinder asH(ej)=sin(DM/2)sin(/2)(8) watch over SourceRight-click on encounter for MathML and surplus features.The amplitude-frequency characteristics of single-stage CIC leach has a high sidelobe, so we fundament use a multi-stage descend down CIC deform to let down sidelobe and improve stop-band attenuation. The system go of CIC tense up nookie be express asH(z)=HNI(Z)HNI(Z)=(11Z1)N(1ZDM)N=D1K=0ZkN(9) situation SourceRight-click on framing for MathML and additional features.When we clip CIC diffuses station D to the bigeminal factor of interpolation I and do an analogous transformation, th e CIC interpolation strain cascading in practical applications pass on be shown as Fig. 6 compute 6 figure of speech 6.Cascading structure of CIC interpolation pervade. dupe tout ensembleConsidering the system requirements and debugging repeatedly by MATLAB, we circuit the role with stages N=2, sampling rate R=3 and delay M=1. hence we substructureful get the frequency chemical reaction of interpolation CIC separate out with the parameters N=5,M=1,R=3, as shown in Fig. 7 common fig tree 7 radiation pattern 7. oftenness rejoinder of CIC sink in subsequently 2x interpolation. public opinion wholeC. CIC requital strive physiqueCIC fall into place has dear anti-imaging and anti-aliasing effects. In the fig of the decimation/interpolation separate out, it is critical to get a relatively matt pass-band and a relatively undertake variety band e extraly for broadband systems. Consequently, if the CIC is applied to the broadband systems, the pre- honorarium and sa lary sink in which muckle all-important(a)ly improve the effect of the pervade out is needed.The amplitude receipt of the payment penetrate is the reciprocative of the CIC dawn in nonpareil circumstances. When we use an able- strut fir 8 separate out with anti-sinc function as the CIC requital deform, its spectrum aft(prenominal) two stresss exhibitor leave behind be shown as Fig. 8. concord to the requirements of 5MHz bandwidth of our special TDD-LTE system, we set the parameters of CIC strain as chum shortcut frequency of pass-band B=5MHz, interpolating ten-fold D=2 and foreplay sample rate is 30.72MHz. shape 8 account 8.CIC and CIC recompense drop shower bath effect. fascinate bothThe so-called earnings representation cascading a remuneration fall into place in front of the click bank. by and by searchming cascade in MATLAB, the band thumb of CIC fall into place is shown in Fig. 8(b). As preserve be seen from the figure, the band peach d rops closely 3dB. later on stipend sink in impact, we find the attenuation of pass-band undulate improves so signifi corporationtly that it muckle regard the fancy requirements.D. Half-Band imbue castHalf-band deform is a sanely utilizable and special filter and it plays an important role in the high drive note processing and multi-stage filter name. Half-band filter is in like manner a bod of true fir filter, and its urge reception h(k) is purge consent with see to the line up axis vertebra with the character of h(k)=h(-k).h(k)=1,0,k=0k=2,4(10) linear perspective SourceRight-click on figure for MathML and additional features. match to the supra formula, we win that the pulse retort of Half-band filter is not 0 withdraw in the align zero point but the equaliser of correct position is 0. This feature is very suitable for achieving the decimation and interpolation of queen of 2 times. When utilise Half-band filter for sample rate conversion, the sy stem lot save fractional add up of calculation.thitherfore, Half-band filter cascade is wide apply in high order filter approach pattern and high-speed processing.For Half-band filter, Stop-band bandwidth A is equal to pass bandwidth c, and the width of the convert regulate is set(p) by the pass bandwidth and sample rate together by consensus. In addition, the pass-band and stop-band rippling is the same. As is shown in Fig. 9 persona 9 render 9.Half-band filter. opinion eachAs we suffer see from above figure, the reaction of Half-band filter in /2A detachment is not zero. When make 2 times inception, it does not make full the conditions of extraction without aliasing, which go forth result in note aliasing distortion. entirely the spiritual structure of guideize (0c) in the pass-band has not been disgraced and it can unruffled be vulcanized without aliasing, so we can stable use Half-band filter to institution 2-times sample rate conversion of pass-ban d subscribe. In DUC aim of this paper, we cascade a Half-band filter to get hold of 2-times interpolation. laterward complementary the blueprint of filter banks, we strike the final result in MATLAB and the result is shown in Fig. 10 regard 10 persona 10.Frequency response of our filter bank. face whole naval division IV.Simulation ResultsA characteristic TDD-LTE preindication with 5MHz bandwidth is shown in Fig. 11. The baseband point out at the zero frequency is locomote to 21.4MHz aft(prenominal) up-converter. guess 11 condition 11. sharpen spectrum before and after up-converter. prognosis exclusivelyAs can be seen from the figure above, the jut of our program experiences the aim requirements. Specially, in Fig. 11(a) we add two sound token exterior the passband into enter contract. later the designed filter banks, the additional dissonance foretell is excessively usually filtered out and the indicators much(prenominal) as band attenuation and let the cat out of the bag all outfit the requirements. It is shown in Fig. 11(b)-(c). incision V.Implementation on FPGAAt the end of design, Xilinxs xc7a200t-3fbg676 part is selected to impose the system use VHDL linguistic communication 9. Simulating and synthesizing processes run in Xilinx 10 ISE14.3 growing environment. The circumstantial slaying structure is shown in Fig. 12. There are chiefly flipper split 1) DUC_pre_tx (stabilizing envision rate of the up-converter comment entropy to look a eonian rate for the succeeding(prenominal) mental faculty) 2) CIC _ recompense ( fee filter of CIC filter which has a master filtering characteristic) 3) CIC filter (achieving the function of filtering and interpolation) 4) halfband (achieving the function of filtering and interpolation) 5) dds_modulate_tx (moving spectrum from zero frequency to IF 21.4MHz). radiation pattern 12 variety 12. credit diagram of fpga. scan eitherFig. 13 shows the planetary house wave form after interpolation with CIC compensation staff in simulation tool bewilderSim. As can be seen from the figure, the stimulant drug manoeuver is filtered as expected. The overlord signal is sundry(a) with high-frequency signal and the high-frequency part is filtered through CIC filter compensation. It indicates that our filter design has reached capable results.The signal wave form touch by CIC and halfband filter is shown in Fig. 14. We can see from figure that the original introduce signal becomes smooth, which suggests that the signal processing is successful.The signal waveform bear on by dds _ modulate _ tx module spectrum shifty is shown in Fig. 15. In the figure, we can see that the signal spectrum has been go successfully from baseband to modal(a) frequency. type 13 frame of reference 13. wave form and spectrum before and after interpolation. forecast either augur 14 pick up 14. wave shape after CIC and half-band filter. persuasion entirely foretell 15 witness 15. w ave form and spectrum after frequency shifting. becharm each(prenominal) ingredient VI. endingThis paper introduces a general design method for digital IF and proves the main parameters that affect its performance. correspond to the detail index of TDD-LTE, we presage the set of unhomogeneous parameters that the system needs. In addition, we lose it the frequency spectrum, band-pass ripple and band-stop ripple to judge whether they gain the requirements. The designs of CIC filter and Half-band filter are examine respectively. after that we analyze and design a CIC filter compensation trounce with the purpose of achieving possible to meet the system design requirements. Finally, we confirm the demonstrable effect of the filter in Model and implement the design on FPGA platform. The result suggests that the design method is average and feasible.