(Regular Paper) 21 3, 2016 5 (JBE Vol. 21, No. 3, May 2016) http://dx.doi.org/10.5909/jbe.2016.21.3.391 ISSN 2287-9137 (Online) ISSN 1226-7953 (Print) FBMC/OQAM a), b), a), a) A Study of Iterative Channel Estimation and Equalization Scheme of FBMC/OQAM in a Frequency Oversampling Domain YongJu Won a), JongGyu Oh b), JinSeop Lee a), and JoonTae Kim a) FBMC/OQAM(Filterbank multicarrier on offset-quadrature Amplitude Modulation) OFDM/QAM(Orthogonal frequency division multiplexing on Quadrature Amplitude Modulation) CP(Cyclic Prefix). OFDM/QAM. FBMC/OQAM. OFDM/QAM. Abstract FBMC/OQAM(Filterbank multicarrier on offset-quadrature Amplitude Modulation) system is a multicarrier modulation which is not need to use cyclic prefix(cp). The CP of OFDM/QAM (orthogonal frequency division multiplexing on Quadrature Amplitude Modulation) system decreases data transmission rate. However, SER(symbol error rate) performance of FBMC/OQAM system is worse than OFDM/QAM system with frequency 1-tap equalization scheme in the frequency selective channel. In this paper, an iterative channel estimation and equalization scheme is performed in a frequency oversampling domain about each sub-channel of FBMC/OQAM system and SER performance using computer simulation is shown. Using the proposed scheme, the SER performance approaches to that of OFDM/QAM system in a frequency selective channel. Keyword: FBMC, OFDM/OQAM, Channel estimation, Iterative Channel equalization a) (Department of Electronic Engineering, Konkuk University) b) (Korea Electronics Technology Institute) Corresponding Author : (Joon Tae Kim) E-mail: jtkim@konkuk.ac.kr Tel: +82-2-458-9714 ORCID: http://orcid.org/0000-0001-6953-5482 2015 () (R0101-14-0189, ). This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (R0101-14-0189, Development of the next generation convergence broadcasting and monitoring systems combined with the networks) in 2015. Manuscript received February 25, 2016; Revised April 12, 2116; Accepted April 12, 2016.
(JBE Vol. 21, No. 3, May 2016). OFDM/QAM(Orthogonal frequency division multiplexing on Quadrature Amplitude Modulation) [1][2] [3][4]. QAM (Sub-carrier) (Rectangular function) (Prototype filter). CP(Cyclic Prefix) ISI(Inter-Symbol Interference) ISI ICI(Inter-Carrier Interference) [5]. CP.. OFDM/QAM CP CP. CP ISI ICI [6] OFDM/QAM ISI CP. OFDM/QAM CP OFDM/OQAM (OFDM on Offset-Quadrature Amplitude Modulation) [7]. 1 CP ISI ICI OFDM/QAM. OFDM/OQAM 1 QAM. OQAM [7]. OFDM/ OQAM CP OFDM/QAM. OFDM/OQAM OFDM/QAM 1. OFDM/OQAM Fig. 1. The conceptional diagram of OFDM/OQAM system
., FBMC/OQAM [8]. (OFDM/ OQAM FBMC/OQAM.) [9] FBMC/OQAM Extended FFT(Extended Fast Fourier Transform) polyphase network. FBMC/OQAM OFDM/ QAM,..,,.. (Real orthogonality) [8].., FBMC/OQAM OFDM/QAM. FBMC/OQAM. (Auxiliary Pilot : AP) [10]. OFDM/QAM. FBMC/ OQAM OFDM/QAM. FBMC/OQAM (frequency oversampling domain). FBMC/ OQAM OFDM/QAM Brazil-D TU(Typical Urban)-6.. 2 FBMC/ OQAM 3 FBMC/ OQAM. 4, OFDM/QAM. II. FBMC/OQAM OFDM/QAM QAM (1) [5]. OFDM/QAM QAM,, OFDM/QAM. (1) OFDM/QAM
(JBE Vol. 21, No. 3, May 2016) OFDM/ QAM.. ISI, OFDM/QAM CP ISI, CP. FBMC/OQAM (2) ISI, OFDM/QAM CP [7]. FBMC/OQAM, QAM OQAM, OQAM (3). m od FBMC/OQAM,., OQAM. [9] (4). cos,. ISI ICI, OFDM/QAM,. 1. [9] Table 1. Frequency coefficients of the prototype filter [9] 1 1 - - - - 1. (4) 256, 2-(a), (b). OFDM/QAM. FBMC/OQAM 2-(a). OFDM/QAM 1 FBMC/OQAM, 2-(b). (frequency oversampling rate). OFDM/QAM IFFT(Inverse-Fast Fourier Transform), FBMC/OQAM [9] PPN (Poly Phase Network) FFT
5 4 Time Impulse response of Prototype Filter K = 1(OFDM/QAM) K = 2 K = 3 K = 4(This paper) 1 Frequency Impulse response & Coefficients of Prototype Filter K = 1(OFDM/QAM) K = 2 K = 3 K = 4(This paper) 0.8 3 Value 2 Magnitude 0.6 1 0.4 0 0.2-1 0 100 200 300 400 500 600 700 800 900 1000 Time 0-2 -1 0 1 2 Sub-channel Index (a) (b) (c) 2. : (a), (b) (c) ( ) [9] Fig. 2. The responses of the prototype filter depend on the overlapping factor K and the frequency response of filterbank (a) Time impulse response, (b) Frequency response, (c) Frequency response of filterbank( ) [9] FFT. FFT 4 1 [9]. FBMC/OQAM 2-(c). 3 3. IFFT Fig. 3. Inverse-FFT module in the transmitter 4. Offset-QAM Fig. 4. Offset-QAM scheme
(JBE Vol. 21, No. 3, May 2016) ( ). IFFT. CP OFDM/QAM FBMC/OQAM 4 QAM Offset-QAM [7]. FBMC/OQAM, OQAM (5) [7]. 1 2 [9]. (5) 2. frequency de-spreading Table 2. The result of frequency de-spreading process about neighboring sub-channels in the receiver OQAM 0 0.0006-0.0001 0 0 0-0.0001 0.0006 0 0.0054 j0.0429-0.1250 -j0.2058 0.2393 j0.2058-0.1250 -j0.0429 0.0054 0-0.0668 0.0002 0.5644 1 0.5644 0.0002-0.0668 0 0.0054 -j0.0429-0.1250 j0.2058 0.2393 -j0.2058-0.1250 j0.0429 0.0054 0 0.0006-0.0001 0 0 0-0.0001 0.0006 0 5. De-Overlapping FFT Fig. 5. De-Overlapping operation and Extended FFT module in the receiver
.,,. (5). real orthogonality, [7]. FBMC/OQAM 5 Sliding. FFT,, [9]. III. FBMC/OQAM FBMC/OQAM 3 4. FBMC/OQAM 6., index., ( 6 )., FBMC/OQAM OFDM/QAM., OQAM,, [10]. (6) [10]. index,. 6. Frequency de-sreading Fig. 6. The result of the frequency de-spreading process in the receiver
(JBE Vol. 21, No. 3, May 2016) r mp n p n m p n p (8),. [10].,,.. 2.. (9) [10]. (9) 7 Neighboring Data 7 Auxiliary Pilot. IV.. (8). FBMC/OQAM [9] 7. Fig. 7. The placement and calculation sub-channel index of auxiliary pilot 8. Fig. 8. Channel estimation in the frequency oversampling domain
[11]. (8) cubic spline 8. OQAM, OQAM FFT,, (10). 9-(b). (10) (8),. (10)., (10), (11). (10). 10 FBMC/OQAM. 10-(a) FBMC/OQAM de-overlapping FFT Frequency de-spreading (7).. 10-(b). 10-(b) FBMC/OQAM. (a) (b) 9. FBMC/OQAM : (a), (b) Fig. 9. The FBMC/OQAM channel equalizer using extended-fft module : (a) Frequency one-tap equalizer, (b) Frequency oversampling domain equalizer
(JBE Vol. 21, No. 3, May 2016) (a) (b) 10. FBMC/OQAM : (a), (b) Fig. 10. Channel equalizer for the FBMC/OQAM system : (a) Frequency one-tap equalizer, (b) Iterative channel equalizer for the frequency oversampling domain FFT sub-carrier Frequency de-spreading... Channel Store/Modification. Time Interpolation Frequency Interpolation Sub-carrier Channel Equalizer Frequency de-spreading (10). Channel Store/Modification (11). (10). 11., (8). FBMC/ 11. Fig. 11. The flow chart of the proposed channel estimation and equalization algorithm OQAM OFDM/QAM.
V. FBMC/OQAM FBMC/OQAM OFDM/QAM DVB-T2 [3] 3. 12 Brazil-D TU(Typical Urban)-6 symbol error rate. 12-(a) 1024 OFDM/QAM 3. Table 3. Transmission parameters for the computer simulation Parameter Value Fading Model SubChannel Number 1024 or 4096 - Transmission Bandwidth(MHz) 6 Pilot Spacing in Freq., Time Domain (sub-channels) BrazilD Channel Path Delay[us] [0.15, 0.63, 2.22, 3.05, 5.86, 5.93] BrazilD Channel Path Power[dB] [-0.1, -3.8, -2.6, -1.3, 0.0, -2.8] BrazilD Constellation Mapping 4, 4 256 QAM TU6 Channel Path Delay[us] [0.0, 0.2, 0.5, 1.6, 2.3, 5.0] TU6 Channel Path Power[dB] [-3.0, 0.0, -2.0, -6.0, -8.0, -10.0] TU6 Channel mobile velocity(km/h) 210 TU6 Constellation Mapping 16 QAM Static Rayleigh 10 0 SER Performances over BrazilD Channel 10 0 SER Performances over TU6 Channel SER (Symbol Error Rate) 10-1 FBMC 1024 1Tap FBMC 1024 Oversampling FBMC 1024 Oversampling 2nd Iter FBMC 1024 Oversampling 3rd Iter FBMC 1024 Oversampling 5th Iter FBMC 4096 1Tap FBMC 4096 Oversampling FBMC 4096 Oversampling 2nd Iter FBMC 4096 Oversampling 3rd Iter OFDM 1024 OFDM 4096 0 5 10 15 20 25 30 35 SNR (Signal to Noise ratio) SER (Symbol Error Rate) 10-1 10-2 FBMC 1024 1Tap FBMC 1024 Oversampling FBMC 1024 Oversampling 2nd Iter FBMC 1024 Oversampling 3rd Iter FBMC 4096 1Tap FBMC 4096 Oversampling 3rd Iter OFDM 1024 OFDM 4096 0 5 10 15 20 25 30 35 SNR (Signal to Noise ratio) 12. Brazil-D TU-6 (Symbol Error Rate) : (a) Brazil-D, (b) TU-6 Fig. 12. Symbol error rate performances under Brazil-D, TU-6 channel : (a) Brazil-D channel, (b) TU-6 channel
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