- Published: November 15, 2021
- Updated: November 15, 2021
- University / College: Victoria University
- Language: English
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Mobile WiMAX is a promising criterion for high informations rate nomadic communicating applications. As receiving system is mobile the multipath attenuation and Doppler frequence displacement of bearer are major factors which degrade the public presentation of the system. Hence to extenuate impacts of these two effects, we need to execute effectual channel appraisal at receiver side. In this paper we have shown comparative consequences of nomadic WiMAX Downlink system with and without consideration of channel appraisal block. The pilot agreements employed is based on Downlink Partial Usage of Subchannels ( DL-PUSC ) method.
We have performed additive insertion based on low complexness LS channel appraisal with QPSK and 16-QAM under the consideration of different Doppler displacement ( 100Hz, 200Hz and 300Hz ) in rayleigh fading channel and compared the consequences for the same with regard to BER public presentation parametric quantity. The simulation consequences shows that 6-7dB SNR difference is noted when Doppler displacement alterations 100Hz to 300Hz with increased mobility of receiving system. Besides the comparative public presentation of QPSK and 16-QAM transition strategies for LS-Based Channel Appraisal are analyzed and shown that QPSK requires 4-5dB less SNR to accomplish same BER as 16-QAM.
Keywords: Mobile WiMAX, Channel Estimation, DL-PUSC, Doppler frequence. Received: ; Revised Accepted.*Corresponding WriterSatish PatelDepartment of Electronics and Communication Engg. , Sarvajanik College of Engineering and Technology, Surat, Gujarat, IndiaElectronic mail: satish. sdp @ gmail. comIntroductionWIRELESS metropolitan country web ( Wireless MAN ) or world-wide interoperability for microwave entree ( WiMAX ) , which is defined in IEEE Std. 802. 16d/e ( Prashad et al.
, 2004, Phoung et al. , 2010 ) , is engineering that provides wireless entree for both fixed and nomadic users. This system is besides referred as Mobile WiMAX which uses extraneous frequence division multiple entree technique as a transition method. This technique is adopted from the powerful extraneous frequence division multiplexing ( OFDM ) which efficaciously mitigates the damage of the time-variant frequence selective attenuation channel ( Hwang et al. , 2009, Tolochko et al. , 2005 ) . A baseband OFDM system is shown in Figure-1. In pattern, the comparative gesture between the base and nomadic station consequences in clip fluctuations of the channel and high velocity motion causes big Doppler displacement and rapid fluctuation of channel.
Besides, channel is frequency selective and noise is added, so it becomes instead hard to gauge channel information. It can be assumed that while intersymbol intervention ( ISI ) is negligible due to infix guard interval, intercarrier intervention ( ICI ) caused by Doppler displacement can non be reduced. It is hard to gauge channel reassign map, so it is preferred to gauge channel information based on pilots in pattern. The most normally used pilot form for nomadic WiMAX is cluster based pilot allotment method harmonizing DL-PUSC subchannelization ( 2006 ) . There are many channel appraisal techniques and they are classified harmonizing to Block type and Comb type pilot interpolation techniques ( Morelli et al.
, 2001, Coleri et al. , 2002 ) . Block type pilot form is used for slow attenuation channel while comb type pilot form is used for fast fading channel. Mobile WiMAX employs 2D channel appraisal by insertion method. The most common techniques for channel appraisal are LS, MMSE, LMMSE etc ( Yu et al.
, 2012, Yucek et al. , 2007, Mohammad, et al. , 2008 ) which are fundamentally block type pilot channel appraisals. And different insertion techniques are changeless, additive, spline cubic, low base on balls insertion etc [ 6 ] which are comb type pilot appraisalsIn this paper we have performed additive insertion based on LS calculator sing consequence of different Doppler frequence displacements and compared the BER public presentation.
We have used pilot interpolation harmonizing to DL-PUSC subchannelization. The balance of this paper is organized as: system theoretical account, shannel appraisal method, simulation consequences and Discussions on consequences.
SYSTEM DESCRIPTION
The information spots provided from the beginning are converted from consecutive to parallel to organize parallel informations of some subchannels.
Each parallel subchannel modulated to complex QAM symbols of Nu active subcarriers. The modulated informations with other void bearer as guard set and DC form N subcarriers. This information sequence of length N { X ( K ) } are so fed into IDFT block symbol by symbol to transform them into clip sphere and bring forth an OFDM signal { ten ( n ) } with the undermentioned equation: ten ( n ) = IDFT { X ( K ) } = ..
. … .
.. … ..
. … .
.. …
… …
… ..
. … … ( 1 )Where N is the DFT length or the figure of subcarriers.
Figure: Baseband OFDM SystemTo forestall inter-symbol intervention ( ISI ) , a cyclic prefix of Ng samples is inserted at the beginning of every symbol. After D/A transition, the signal is transmitted through the frequence selective clip changing fading channel with linear noise. Assumed that the impulse response of the multipath attenuation channel is given by: H ( t, ) = … ..
. … … .
.. … .
.. … …
… ..
. ..
. … ..
. … ..
. … .
.. ( 2 )Where hour ( T ) and ? r are the addition and hold of the rth way, severally. The way additions h ( T ) are broad sense stationary ( WSS ) narrow-band complex Gaussian procedure and are reciprocally independent.
The standard signal, which has been corrupted by the multipath attenuation channel and contaminated by the linear white Gaussian noise can be formulated as: Y ( = … … ..
. … .
.. .
.. .
.. … .
.. ..
. … .
.. … .
.. ..
. . ( 3 )Where is the continuous-time representation of the familial discrete-time signal, x ( n ) . The standard uninterrupted clip signal so convert back to a distinct clip signal Y ( n ) , the receiving system do synchronism, downsampling, and removes the cyclic prefix. The simplified baseband theoretical account of the standard samples takes the signifier of: Y ( N ) = ..
. … … .
.. … ..
. ..
. … … .
.. .
.. … …
… … .
.. . ( 4 )Where L is the figure of sample-spaced channel lights-outs, tungsten ( n ) is linear white Gaussian noise ( AWGN ) sample with nothing mean and discrepancy of ? n2 and H ( cubic decimeter ) is the clip sphere channel impulse response ( CIR ) for the current OFDM symbol. It is assumed that clip and frequence synchronism is perfect. FFT transforms y ( n ) to the frequence sphere received basal set informations: Y ( K ) = FFT ( Y ( n ) ) = X ( K ) H ( K ) + W ( K ) …
… ..
. … …
… ..
. ..
. … ..
. … ..
. … …
… … ( 5 )Where H and W are FFT of H and tungsten severally.
Following FFT block, the pilot signals are extracted and the Channel Estimation is carried out to obtain estimated channel response A¤ ( K ) for the informations sub-channels. Then the transmitted information is estimated by equalisation procedure:..
. … .
.. …
…
…
… ..
. ..
. … .
.. ..
. … ..
. … .
.. …
… … ..
. …
… …
… … .
.. … ( 6 )After signal demapping, the beginning binary information informations are re-constructed at the receiving system end product.
CHANNEL Appraisal
Using LS estimation the channel urge can be calculated standard symbols and known pilot symbols as follow ( Mohammad et al. , 2008, Babapour et al.
, 2010 ) : A¤ p= Xp-1Y… ..
. … .
.. … …
… … .
.. … .
.. …
… …
… ..
. ..
. … …
… …
… .
.. … ..
. … … .
.. … …
… ( 7 )Where Xp is known pilot symbol and Y is the standard symbol. The advantages of the LS estimation are lower complexness and implemented easy without cognizing the channel statistics compared to progress algorithm: Minimal Mean Square Error ( MMSE ) ( Galin et al. , 2004 ) .
We have performed the channel appraisal based on Downlink Partially Used Subchannelization ( DL-PUSC ) . Harmonizing to this construct the bearers are divided in bunchs. Each bunch holding 14 subcarriers out of which two are allocated for the pilot symbols and others are for informations symbols ( 2006 ) . Figure-2 shows the bunch construction and the place of pilot symbols. Figure 2: DL-PUSC bunchsAfter this allotment the channel appraisal is performed in three stairss which are illustrated in figure 3. Three stairss can be listed as: Measure 1: LS estimation at pilot placeMeasure 2: Linear insertion on clip axisMeasure 3: Linear insertion on frequence axisFigure 3: Channel appraisal in WiMAX DL-PUSCFigure-4 can be treated as step-1 for the channel appraisal.
Dark bluish blocks can be considered as CIR at pilot place utilizing equation-7Figure 4: LS estimation at pilot placeThe additive insertion method is used to cipher channel response at kth subcarrier as ( Galin et al. , 2009 )A¤k ( K ) = A¤ ( mL+l )= A¤ P ( m ) +l/L ( A¤ P ( m+1 ) – A¤ P ( m ) ) , 0l Liter..
. …
… … .
.. … …
… .. ( 8 )Where m= 0, 1, .
. Np-1, Np= figure of pilots, L= N/Np, where N= entire figure of subcarriers. Using equation-8 we have applied additive insertion on clip axis and frequence axis to acquire estimated values of CIR at staying all information subcarriers. Time and frequence axis insertion is illustrated in figure-5 and figure-6 severally.
Figure 5: Linear insertion on clip axisFigure 6: Linear insertion on frequence axis
Simulation
Description of Simulation
The simulations have been made for WiMAX ( IEEE 802. 16e criterion ) to see system public presentation for Rayleigh Channel with and without channel appraisal block sing consequence of multipath attenuation and Doppler displacement of bearer frequence as receiving system is nomadic. The system public presentation is analyzed from BER versus SNR secret plan and besides consequence of different Doppler displacement analyzed on public presentation of system. The Mobile WiMAX Simulation parametric quantity is listed in Table 1 ( 2006 ) : Table 1: Simulation Parameters
Parameters Value
Parameters Value
FFT size ( NFFT )1024Bandwidth10MHzTransitionQPSK, 16-QAMNumber of Guard Subcarriers91+92Number of Used Subcarriers ( Nused ) including all possible allocated pilots and DC subcarrier. 841Cyclic Prefix ratio1/8Fading channelRayleighMultipath ( LOS+NLOS )3Doppler Frequency Shift100Hz, 200Hz, 300HzCarrier Frequency3. 5GHz
Simulation Consequences
A Rayleigh attenuation channel has been simulated and the information is passed through it, followed by add-on of AWGN noise. The assorted simulation parametric quantities are shown in Table-1.
Figure 6: BER public presentation of the analyzed appraisal algorithm( QPSK, Fd= 100, 200, 300Hz ) . Figure 7: Comparison of BER public presentations of No Channel Estimation, LS Based Channel Estimation and Perfect channel ( QPSK, Fd= 100, 200, 300Hz ) . Figure-6 shows the BER public presentation of nomadic WiMAX utilizing LS based additive insertion channel appraisal algorithms with QPSK transition for 100Hz, 200Hz and 300Hz Doppler displacement matching to mobility velocity of receiving system 30kmph, 60kmph and 90kmph. Its clear that analyzed appraisal algorithm perform good in all three instances but debasement in public presentation of system is noted with addition in mobility velocity.
Similar analysis is done for 16-QAM transition strategy which is shown in figure-8. The comparative analyses of BER public presentation of the Linear insertion, no channel appraisal and perfect channel conditions is shown in figure-7 with QPSK transition. Similar comparative analysis is shown in figure-9 for 16-QAM. In both instances it can be seen that without channel appraisal the BER is every bit high as around 10-0. 6 -10-0. 9 dubnium which is non suited for the practical application. Hence channel appraisal is indispensable for the practical system execution. QPSK and QAM are the two prima transition strategies for WiMAX. In general the greater the figure of spots transmitted per symbol, the higher the information rate is for a given bandwidth. Therefore, when really high information rates are required for a given bandwidth, higher-order QAM systems, such as 16-QAM is used. Finally public presentation of QPSK and 16-QAM are compared for 100Hz Doppler displacement which is shown in figure-11. This analysis shows that QPSK execute better than 16-QAM which shows QPSK is more tolerant of intervention than either 16-QAM. For this ground, whereFigure 8: BER public presentation of the analyzed appraisal algorithm( 16-QAM, Fd= 100, 200, 300Hz ) . Figure 9: Comparison of BER public presentations of No Channel Estimation, LS Based Channel Estimation and Perfect channel ( 16-QAM, Fd= 100, 200, 300Hz ) . Figure 10: BER public presentation of analyzed appraisal QPSK vs 16-QAM ( Fd= 100Hz )signals are expected to be immune to resound and other damages over long transmittal distances, QPSK is the normal pick.
Discussion
In this paper, a reappraisal of LS channel appraisal along with additive insertion and DL-PUSC frame construction is described. By sing the Mobile WiMAX parametric quantities simulation is done on MATLAB tool for OFDM system and BER public presentation is analyzed for Rayleigh melting channel with and without channel appraisal block sing QPSK and 16-QAM transition strategies. The simulation consequence shows that in instance of no channel appraisal the BER attains high value ( 10-0. 7 to 10-0. 9 ) which can non be suited for practical execution of the WiMAX system. On other manus BER is achieved with additive insertion based on LS estimation is acceptable with low complexness design of calculator. In add-on, the consequence of different mobility velocity of receiving system is analyzed on BER public presentation by changing the Doppler displacement of the bearer frequence. Simulation consequences show that as the Doppler displacement gets higher the BER public presentation degrades i. e. 6-7dB SNR difference can be seen for between Doppler displacements of 100Hz and 300Hz. Besides the public presentation of QPSK and 16-QAM are compared and conclude that QPSK is less susceptible to ISI and noise but 16-QAM is advantageous when higher information rate is demand.
