- Email: [email protected]
Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel
G Model
ARTICLE IN PRESS
IJLEO 57177 1–6
Optik xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel
1
2
3
Q1
Lavish Kansal a,∗ , Vishal Sharma b,1 , Jagjit Singh c,1 a
4
b
5
c
6
IKG Punjab Technical University, Jalandhar, India Department of Electronics & Communication Engineering, SBSSTC, Ferozepur, India Department of Electronics and Communication Engineering, DAVIET, Jalandhar, India
7
a r t i c l e
8 21
i n f o
a b s t r a c t
9
Article history: Received 15 November 2015 Accepted 10 January 2016 Available online xxx
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20
Keywords: WiMAX OFDM DWT FFT MCM
22
1. Introduction
15 16 17 18 19
Wavelets comprise the ability to increase bandwidth efficiency in addition to higher resiliency to intersymbol interference (ISI) and inter-carrier interference (ICI). Wavelets are introduced into the wireless communication field as an orthogonal base of multi-carrier modulation and are considered as an efficient and effective measure. Fittingly, a BER and spectral efficiency estimation of discrete Fourier transform (DFT) based WiMAX structure and discrete wavelet transform (DWT) based WiMAX structure is done in this work. The evaluation is validated over Rayleigh channel using divergent digital modulation levels along with diverse convolution code (CC) rate proposed for FFT-WiMAX and WHT-WiMAX. The performance of the simulated structure is investigated via BER and spectral efficiency assessment as a function of SNR. The imitation outcome reports a significant improvement in BER and spectral efficiency for a given SNR of the simulated system using WHT-WiMAX in comparison to FFT-WiMAX. © 2016 Published by Elsevier GmbH.
Broadband wireless access (BWA) has evolved as an encouraging alternative to wide area access technological innovation to deliver high-speed mobile, as well as data access in the domestic together with small and medium sized organization enterprises. On broadband wireless access, attributable to its very own wireless characteristics, it usually is much easier to install, much easier to adapt and more reliable, and in so doing offering it the potentiality to assist customers not supported or otherwise not pleased on using the wired broadband alternatives available. BWA is standardized by IEEE 802.16 in addition to its conjoint industry association, worldwide interoperability for microwave access (WiMAX) forum assure to feature elevated data rate capabilities over hefty sites to a good amount of subscribers wherein broadband is inaccessible. The 1st description of the IEEE 802.16 standard operating in the 10–66 GHz frequency band and, also, necessitates line-of-sight (LOS) cell sites. Afterward, the standard expanded its functioning by virtue of distinct physical layer specification. The 2–11 GHz frequency band is permitting a non-line of sight (NLOS)
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Q2
∗ Corresponding author. Tel.: +91 9417700690. E-mail addresses: [email protected] (L. Kansal), er [email protected] (V. Sharma), [email protected] (J. Singh). 1 Affiliated to IKG Punjab Technical University, Kapurthala, Punjab, India.
communications, calls for methods that minimize the deterioration of fading and multipath. Acquiring the main benefit of orthogonal frequency division multiplexing (OFDM) technique the PHY could afford to deliver resilient broadband services in an intimidating wireless medium. The physical layer of the IEEE 802.16 standard centered by OFDM has already been defined in close collaboration with the European telecommunications standards institute (ETSI) high-performance metropolitan area network (HiperMAN). Consequently, the HiperMAN standard, as well as the physical layer of IEEE 802.16 based on OFDM, are approximately indistinguishable. Both of these physical layers based on OFDM will be in a position to go along with each other as well as a global system based on OFDM should surface [1]. The WiMAX forum accredited merchandises and solutions for BWA obey both the standards. The amendment of IEEE 802.16 lay down working in a frequency band 2–11 GHz named as IEEE 802.16a. Another modification of IEEE 802.16a is IEEE 802.16d was essentially regarding minimizing the power consumption of the mobile device. Further, IEEE 802.16e is a modification to IEEE 802.16-2004 featuring additional transportability [2]. To realize the technical specs of premium data rates, as well as less significant disturbance, DWT may be utilized as opposed to FFT [3]. The discrete wavelet transform (DWT) is a seemingly technologically advanced transform as opposed to the discrete Fourier transform (DFT). DWT will offer the time and frequency domain description of signals while in opposition DFT offers just the frequency domain description of signals. The attributes of the wavelet,
http://dx.doi.org/10.1016/j.ijleo.2016.01.067 0030-4026/© 2016 Published by Elsevier GmbH.
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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which include representation in time, as well as the frequency domain, orthogonality using a scale, as well as translation, emphasizes a whole new prospect in wireless communication. DWT is employed as a signal processing methodology in numerous communication sectors integrating multicarrier modulation (MCM) and Mobile wireless communication. In the initial phases, to accentuate the bandwidth efficiency, ICI as well as ISI, discrete wavelet transforms (DWT) centered OFDM was investigated. DWT-OFDM can certainly better overcome narrowband disturbance as a result of pretty high spectral containment capabilities of wavelet filters, as well as significantly more tolerant regarding ICI than standard DFT-OFDM [4]. In case of DWT-OFDM the concept of guard band (Cyclic Prefix CP) is not being utilized for wavelets; for this reason data rate will be more like compared to those of FFT practices. As a result of its improved orthogonality among spectral containment and subcarriers, OFDM drive by wavelet is anticipated to minimize the wastage of bandwidth stemming from addition of CP all of which will reduce the ISI and ICI [5]. In time variable fading channels, time changing Doppler shift arises, that will subsequently influence the orthogonality of OFDM [6]. W-OFDM assures main side lobe of far lower magnitude than that of FFT-OFDM and also being far less influenced by this shift. A pressing attribute of WOFDM is the impeccable reconstruction with lowered complication [7]. The performance of OFDM and wavelet OFDM is analyzed over power line channels, and it has been observed that wavelet OFDM offers significant improvement in terms of transmission efficiency and spectral leakage over OFDM [8]. The wavelet-based OFDM (DWT-OFDM & WPM-OFDM) provides the orthogonal basis and also satisfies the accurate reconstruction, thereby providing significant BER improvement over Fourier based OFDM [9,10]. Diverse wavelets are also being considered as an alternative to Fourier transform along with the other transforms such as DCT/DST. It has been observed that DWT/DCT/DST based OFDM is better in terms of BER performance in comparison to Fourier based OFDM [11–13]. The BER performance of wavelet based OFDM is also analyzed over flat as well as frequency selective fading channels and it has been observed that the use of wavelets influence the BER performance significantly due to their time-frequency localization property [14,15]. The overall performance of FFT-OFDM is measured against WHT-OFDM over AWGN channel and as a result of orthogonality of WHT-OFDM sub-carrier waveforms its performance is superior to FFT-OFDM [16]. The behavior of DWT-OFDM is being equated with FFT-OFDM over Rayleigh fading channel in conjunction with the effect of exponential power delay profile [17]. Use of wavelet packet modulation (WPM) for WiMAX over AWGN channel is demonstrated in [18]. A brief study of Diverse Wavelets in Orthogonal Wavelet Division Multiplex for DVB-T is presented [19]. It has been observed that Haar transform provides better performance in comparison to all other transforms in wavelet family. It has been observed that the performance of WPM based WiMAX is quite better than FFT based WiMAX. The BER performance evaluation with the help of channel estimation techniques has also been done for the comparison of conventional OFDM and wavelet based OFDM system [20]. Organization of this work is: Section 1, a basic overview of preceding work carried out on FFT-OFDM and WHTOFDM is presented. Section 2 incorporates the model description and result presentation trailed by conclusion inferred in Section 3 on the foundation of observation form the results.
2. Model description The FFT-WiMAX and WHT-WiMAX system have been simulated using MATLABTM and the overall performance is expressed using SNR vs. BER variations and SNR vs. spectral efficiency variations. The block diagram for the simulated system is depicted in Fig. 1.
At the transmitter side of the physical layer, the first process is randomization. It is indeed primarily scrambling of data to generate random arrangement to optimize coding effectiveness. In forward error correction (FEC), there exist a range of coding platform such as RS codes, convolution codes, Turbo codes and so forth. However, nonetheless in the present paper primarily RS codes and convolution codes have been utilized for simulation. RS codes fundamentally add redundancy to the data. This redundancy enhances block error reduction. RS-encoder is dependent on Galois field computation to contribute the redundancy bits. WiMAX is based on GF (28 ) that corresponds to as RS (N = 255, K = 239, T = 8) where: N = Number of bytes after encoding K = Data bytes before encoding T = Number of bytes that can be corrected Convolution code (CC) presents redundant bits into the data flow. The shift register accepts the information bits, and encoded bits are generated by using the modulo-2 addition of the contents of the shift register along with input data bits. Convolution code is utilized as desired FEC in 802.11a physical layer. The industry standard generator polynomials, g0 = 1338 and g1 = 1718, of rate R = 1/2 are utilized by convolutional code. Elevated rates such as 2/3 and 3/4, originate through it by utilizing “puncturing”. The Viterbi algorithm is employed for decoding the convolution code to get the required data bits. Interleaving strives to dispense transmitted bits in frequency or time or perhaps both of them to accomplish acceptable bit error performance after demodulation. What a sort of interleaving structure is commonly employed hinges on the channel behavior. When the system functions in the purely AWGN environment, hardly any interleaving is necessary, simply because the error distribution will not alter by relocating the bits. Modulation, as well as channel encoding, is elementary aspects of a communication system. Digital modulation is the procedure for mapping the digital data to analog form so that it could be transmitted over the channel. As a result, each and every digital communication system carries a modulator that accomplishes this task. Strongly linked to modulation is the inverse approach, referred to as demodulation, performed by the receiver to get back the transmitted digital information. The modeling of optimal demodulators is termed as detection theory. Distinct, coherent mapping employed are m-ary-phase shift keying (M-PSK) and m-ary-quadrature amplitude modulation (M-QAM). However, there exists a trade-off between, distinct mapping technology and spectral efficiency. Pilot insertion is employed for channel estimaQ4 tion & synchronization goal (Table 1). OFDM Subcarrier are generated by virtue of inverse fast Fourier transform (IFFT) which modifies the data from the frequency domain to the time domain. IFFT is incorporated in OFDM to generate subcarriers because it maintains the required frequency spacing between the subcarriers fulfilling orthogonality condition. An ordinary N-to-N point linear transformation necessitates N2 multiplications as well as additions. Nonetheless, by computing the outputs concurrently and making the most of the cyclic characteristics of the multipliers e ± j2kn/N fast Fourier transform (FFT) strategies lessen the quantity of computations to the order of N log N. The FFT is most beneficial when N is a power of 2. Numerous variants of the FFT exist, with distinct ordering of the inputs and outputs, as well as multiple usages of temporary memory. One strategy to eliminate IS1 would be to generate a cyclically lengthened guard time frame, in which every OFDM symbol is headed by a periodic extension of the signal itself. Taking into consideration the discrete-time realisation of the multi-carrier system, sampling the transmitted multi-carrier signal at a rate comparable to the data rate one retrieves a frame structure comprised of the IDFT of the
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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Fig. 1. Block diagram of WiMAX physical layer model.
Table 1 WiMAX specifications.
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3. Result discussion
Parameters
Values
NFFT Nominal channel B.W. No. of used sub-carriers Sub carrier spacing (f) Upper guard Lower guard NDC FS(sampling frequency) Tb Ratio guard time to symbol time (G) Tg = G.Tb Tsymbols = Tb + Tg Wavelet Used Convolution Code Rate Modulation Type Modulation Level Used (M) Simulated Environment Total No. of WiMAX Symbols used for Simulation
256 2.5 MHz 192 11.2 28 27 1 (prefix 128) 2.86 MHz 89 micro sec. Variable (1/2, 1/4, 1/8, 1/16, 1/32) Variable Variable Haar 1/2, 2/3, 3/4 M-PSK & M-QAM 2, 4, 16 & 64 Rayleigh Channel (NLOS) 106
data symbols and a cyclic prefix as well as wherein the OFDM frame would contain Ntotal = L + N samples. At this time, L is the number of samples replicated from the end of N sample IDFT frame and attached at the beginning of each IDFT frame. At the receiver, eliminating the guard interval will become the equivalent to eliminating the cyclic prefix, although the end results of the channel transforms into the periodic convolution of the discrete-time channel with the IDFT of the data symbols. Executing a DFT on the received samples after the cyclic prefix is neglected, the periodic convolution is transformed into multiplication, since it was the scenario for the analog multi-carrier receiver.
The orthogonality of WiMAX subcarriers will be effected by the blended outcome of the fading channel due to the time and frequency selectivity. The out-of-band side-lobes rejection is considerably more in case of several wavelet structured multi-carrier strategies in comparison to OFDM. Moreover, the resiliency against time and frequency variability of the channel is more in WOFDM. On the grounds that the resiliency offered by W-OFDM is not due to integration of GI for channel equalization, instead of that it is purely dependent upon the symbol duration in W-OFDM which in turn is inversely proportional to inverse of carrier spacing. On the other hand, because symbol overlap is hardly there in OFDM the resiliency of OFDM models to uncompensated ISI is merely influenced by the reciprocal of the carrier spacing. Eventually, as compared with OFDM, in W-OFDM systems it might be likely to achieve improved immunity to ISI by elevating the quantity of carriers. In the selective fading channel, many models may perhaps be taken into consideration to review the BER effectiveness of the systems. The BER performance of DWT-WiMAX in Rayleigh fading channel is compared with the FFT-WiMAX. This is apparent from Fig. 2.1–2.7 that WHT-WiMAX performs better than FFT-WiMAX Q5 for diverse modulation schemes since it is rather less susceptible to Doppler frequency variations. This truly originates from the deterioration in orthogonality between the carriers of FFTWiMAX consequently of the multipath wireless channel [16,17]. As an illustrated by Fig. 2.1, to achieve a BER of 10−4 , in Rayleigh fading scenario BPSK modulated with CC code rate 1/2 FFT-WiMAX necessitates SNR of 27 dB, but it is 15 dB for WHTWiMAX. For QPSK modulation with CC code rate 1/2 in Rayleigh fading scenario, FFT-WiMAX requires 33 dB of SNR, which is much less than 23 dB required in the case of WHT-WiMAX. On
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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Fig. 2. (a)–(g) SNR vs BER comparison of FFT-WiMAX and WHT-WiMAX system for Rayleigh fading channel (a) BPSK with CC 1/2 (b) QPSK with CC 1/2 (c) QPSK with CC 3/4 (d) 16-QAM with CC 1/2 (e) 16-QAM with CC 3/4 (f) 64-QAM with CC 2/3 (g) 64-QAM with CC 3/4.
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the contrary, in case of same fading scenario for same QPSK modulation but with a code rate of 3/4, FFT-WiMAX requires 38.5 dB of SNR, which is again higher than 27 dB SNR required for WHT-WiMAX. Furthermore, it has been observed that on using other modulation along with different CC code rates over
the same simulated environment, the BER performance starts degrading but can be mitigated at the cost of high SNR [16,17]. Consequently, it is summarized that WHT-WiMAX offers an improvement of 10–13 dB of SNR over FFT-WiMAX for Rayleigh fading scenarios.
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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Fig. 3. (a)–(g) Spectral efficiency comparison of FFT-WiMAX and WHT-WiMAX system for Rayleigh fading channel (a) BPSK with CC 1/2 (b) QPSK with CC 1/2 (c) QPSK with CC 3/4 (d) 16-QAM with CC 1/2 (e) 16-QAM with CC 3/4 (f) 64-QAM with CC 2/3 (g) 64-QAM with CC 3/4.
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The spectral efficiency performance of DWT-WiMAX in Rayleigh fading channel is compared with the FFT-WiMAX. This is very much from Fig. 2.8–2.14 that WHT- WiMAX outperforms the FFT-WiMAX for diverse modulation schemes since it has better BER performance. As depicted in Fig. 2.8, in order to achieve the desired
spectral efficiency in case of BPSK modulation with CC code rate 1/2 15 dB of SNR is required for WHT-WiMAX which is less than 27 dB of SNR required for FFT-WiMAX. For QPSK modulation it is very much clear from Fig. 2.9 the although the spectral efficiency is doubled in comparison to what was being obtained by
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BPSK modulation using the same CC code rate of 1/2 for both the cases. However, this elevated spectral efficiency comes at the cost of increased requirement of SNR. On doing the comparison, it is 259 clear that FFT-WiMAX requires 34 dB of SNR which is still higher 260 than 24 dB of SNR required for WHT-WiMAX. On the other side it 261 is very much clear from Fig. 2.10 that the spectral efficiency for the 262 WiMAX system can be increased for the QPSK modulation on using 263 the CC code rate of 3/4 instead of CC code rate of 1/2. However, 264 in this case also WHT-WiMAX outperforms the FFT-WiMAX as it 265 requires less SNR to achieve the required spectral efficiency. A sim266 ilar observation can be made on analyzing the simulated results for 267 Q6 other modulation schemes and CC code rates (Fig. 3). 268 257 258
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4. Conclusion
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FFT-WiMAX presents a low complexity framework as compared to WHT-WiMAX, still, the usage of CP reduces its spectral efficiency in addition to squanders transmit power. Overall performance outcome illustrates that WHT-WiMAX is a possible replacement to FFT-WiMAX but nevertheless at the expense of significantly increased the complexity of equalization. Consequently, WHTWiMAX could certainly evolve into an impressive contender for MCM in the multipath wireless channel. An enhancement of SNR in the range of 8–12 dB is reported for WHT-WiMAX to accomplish the suitable BER with different modulation schemes along with diverse CC code rate in Rayleigh fading scenarios. Furthermore, an additional SNR is required with the higher level of modulation schemes and diverse CC code rate to achieve the desired BER. Also, the spectral efficiency achieved from WHT-WiMAX is considerably more than that of FFT-WiMAX. Higher spectral efficiency can be achieved by going for higher order modulation and higher CC code rate. However, this elevated spectral efficiency can be achieved only at the cost of increased SNR values required.
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References
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[1] IEEE, Local and metropolitan area networks—part 16, air interface for fixed broadband wireless access systems, in: IEEE Standard IEEE 802.16a, IEEE, 2004. [2] IEEE, Part 11: wireless LAN medium access control (MAC) and physical layer (PHY) specifications: high-speed physical layer in the 5 GHz band, in: IEEE Standard 802.11a, IEEE, 1999.
[3] M.K. Lakshmanan, H. Nikookar, A review of wavelets for digital wireless communication, Wireless Pers. Commun. 37 (2006) 387–420. [4] N. Ahmed, Joint detection strategies for Orthogonal Frequency Division Multiplexing, RICE University, Houston, TX, April 2000, Master Thesis. [5] Z. Xiaodong, X. Pingping, Z. Guoan, B. Guangguo, Study on complex wavelet packet based OFDM modulation (CWPOFDM), ACTA Electron. Sin. 30 (4) (2002) 477–479. [6] T. Pollet, M.V. Bladel, M. Moeneclaey, BER sensitivity of OFDM systems to carrier frequency offset and wiener phase noise, IEEE Trans. Commun. 43 (1995) 191–193. [7] S. Chang, M. Lee, J. Park, A high speed VLSI architecture of discrete wavelet transform for MPEG-4, IEEE Trans. Consum. Electron. 43 (1997) 623–627. [8] S. Galli, H. Koga, N. Kodama, Advanced signal processing for PLCs: waveletOFDM, in: IEEE International Symposium on Power Line Communications and Its Applications, 2008, pp. 187–192. [9] K. Abdullah, A.Z. Sadik, Z.M. Hussain, On the DWT- and WPT-OFDM versus FFT-OFDM, in: 5th IEEE GCC Conference & Exhibition, 2009, pp. 1–5. [10] R. Asif, R.A. Abd-Alhameed, O. Oanoh, Y. Dama, H.S. Migdadi, J.M. Noars, A.S. Hussaini, J. Rodriquez, Performance comparison between DWT-OFDM and FFTOFDM using time domain zero forcing equalization, in: 2012 International Conference on Telecommunication and Multimedia, 2012, pp. 175–179. [11] D. Gupta, V.B. Vats, K.K. Garg, Performance analysis of DFT-OFDM, DCT-OFDM, and DWT-OFDM systems in AWGN channel, in: The Fourth International Conference on Wireless and Mobile Communications, 2008, pp. 214–216. [12] Z.A. Hamid, M. Samir, S.M.A. El-atty, A.E.El-Hennawy, H.E. Shenawy, S.A. Alshebeili, F.E.A. El-Samie, On the Performance of FFT/DWT/DCT-based OFDM Systems with Chaotic interleaving and Channel Estimation Algorithms, WireQ7 less Personal Communication, Vol. 78, pp 1495–1510. [13] A.H. Kattoush, W.A. Mahmoud, S. Nihad, The performance of multi wavelets based OFDM system under different channel conditions, Digital Signal Processing, Vol. 20, pp 472–482. [14] M. Oltean, M. Nafornita, Errors per scale statistics for a wavelet OFDM transmission in flat fading channels, in: 6th IEEE International Symposium on Intelligent Signal Processing, 2009, pp. 119–124. [15] M. Oltean, M. Nafornita, Wavelet OFDM performance in frequency selective fading channels, in: 8th International Conference on Communication, 2010, pp. 343–346. [16] V. Sharma, G. Singh, On BER assessment of conventional- and wavelet-OFDM over AWGN channel, Optik 125 (2014) 6071–6073. [17] V. Kumbasar, O. Kucur, Performance comparison of wavelet based and conventional OFDM systems in multipath Rayleigh fading channels, Digital Signal Process. 22 (2012) 841–846. [18] L. Na, G. Yun-Quan, D. Chun-Mei, H. Xue, Optimizing performance of WIMAX system based on WPM, in: The 7th International Conference on Computer Science & Education (ICCSE 2012), July 14–17, Melbourne, Australia, 2012, pp. 372–375. [19] S.L. Linfoot, A study of different wavelets in orthogonal wavelet division multiplex for DVB-T, IEEE Trans. Consum. Electron. 54 (August (3)) (2008) 1042–1047. [20] M.K. Gupta, S. Tiwari, Performance evaluation of conventional and wavelet based OFDM system, Int. J. Electron. Commun. 67 (2013) 348–354.
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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IJLEO 57177 1–6
Optik xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel
1
2
3
Q1
Lavish Kansal a,∗ , Vishal Sharma b,1 , Jagjit Singh c,1 a
4
b
5
c
6
IKG Punjab Technical University, Jalandhar, India Department of Electronics & Communication Engineering, SBSSTC, Ferozepur, India Department of Electronics and Communication Engineering, DAVIET, Jalandhar, India
7
a r t i c l e
8 21
i n f o
a b s t r a c t
9
Article history: Received 15 November 2015 Accepted 10 January 2016 Available online xxx
10 11 12 13 14
20
Keywords: WiMAX OFDM DWT FFT MCM
22
1. Introduction
15 16 17 18 19
Wavelets comprise the ability to increase bandwidth efficiency in addition to higher resiliency to intersymbol interference (ISI) and inter-carrier interference (ICI). Wavelets are introduced into the wireless communication field as an orthogonal base of multi-carrier modulation and are considered as an efficient and effective measure. Fittingly, a BER and spectral efficiency estimation of discrete Fourier transform (DFT) based WiMAX structure and discrete wavelet transform (DWT) based WiMAX structure is done in this work. The evaluation is validated over Rayleigh channel using divergent digital modulation levels along with diverse convolution code (CC) rate proposed for FFT-WiMAX and WHT-WiMAX. The performance of the simulated structure is investigated via BER and spectral efficiency assessment as a function of SNR. The imitation outcome reports a significant improvement in BER and spectral efficiency for a given SNR of the simulated system using WHT-WiMAX in comparison to FFT-WiMAX. © 2016 Published by Elsevier GmbH.
Broadband wireless access (BWA) has evolved as an encouraging alternative to wide area access technological innovation to deliver high-speed mobile, as well as data access in the domestic together with small and medium sized organization enterprises. On broadband wireless access, attributable to its very own wireless characteristics, it usually is much easier to install, much easier to adapt and more reliable, and in so doing offering it the potentiality to assist customers not supported or otherwise not pleased on using the wired broadband alternatives available. BWA is standardized by IEEE 802.16 in addition to its conjoint industry association, worldwide interoperability for microwave access (WiMAX) forum assure to feature elevated data rate capabilities over hefty sites to a good amount of subscribers wherein broadband is inaccessible. The 1st description of the IEEE 802.16 standard operating in the 10–66 GHz frequency band and, also, necessitates line-of-sight (LOS) cell sites. Afterward, the standard expanded its functioning by virtue of distinct physical layer specification. The 2–11 GHz frequency band is permitting a non-line of sight (NLOS)
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Q2
∗ Corresponding author. Tel.: +91 9417700690. E-mail addresses: [email protected] (L. Kansal), er [email protected] (V. Sharma), [email protected] (J. Singh). 1 Affiliated to IKG Punjab Technical University, Kapurthala, Punjab, India.
communications, calls for methods that minimize the deterioration of fading and multipath. Acquiring the main benefit of orthogonal frequency division multiplexing (OFDM) technique the PHY could afford to deliver resilient broadband services in an intimidating wireless medium. The physical layer of the IEEE 802.16 standard centered by OFDM has already been defined in close collaboration with the European telecommunications standards institute (ETSI) high-performance metropolitan area network (HiperMAN). Consequently, the HiperMAN standard, as well as the physical layer of IEEE 802.16 based on OFDM, are approximately indistinguishable. Both of these physical layers based on OFDM will be in a position to go along with each other as well as a global system based on OFDM should surface [1]. The WiMAX forum accredited merchandises and solutions for BWA obey both the standards. The amendment of IEEE 802.16 lay down working in a frequency band 2–11 GHz named as IEEE 802.16a. Another modification of IEEE 802.16a is IEEE 802.16d was essentially regarding minimizing the power consumption of the mobile device. Further, IEEE 802.16e is a modification to IEEE 802.16-2004 featuring additional transportability [2]. To realize the technical specs of premium data rates, as well as less significant disturbance, DWT may be utilized as opposed to FFT [3]. The discrete wavelet transform (DWT) is a seemingly technologically advanced transform as opposed to the discrete Fourier transform (DFT). DWT will offer the time and frequency domain description of signals while in opposition DFT offers just the frequency domain description of signals. The attributes of the wavelet,
http://dx.doi.org/10.1016/j.ijleo.2016.01.067 0030-4026/© 2016 Published by Elsevier GmbH.
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
Q3
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which include representation in time, as well as the frequency domain, orthogonality using a scale, as well as translation, emphasizes a whole new prospect in wireless communication. DWT is employed as a signal processing methodology in numerous communication sectors integrating multicarrier modulation (MCM) and Mobile wireless communication. In the initial phases, to accentuate the bandwidth efficiency, ICI as well as ISI, discrete wavelet transforms (DWT) centered OFDM was investigated. DWT-OFDM can certainly better overcome narrowband disturbance as a result of pretty high spectral containment capabilities of wavelet filters, as well as significantly more tolerant regarding ICI than standard DFT-OFDM [4]. In case of DWT-OFDM the concept of guard band (Cyclic Prefix CP) is not being utilized for wavelets; for this reason data rate will be more like compared to those of FFT practices. As a result of its improved orthogonality among spectral containment and subcarriers, OFDM drive by wavelet is anticipated to minimize the wastage of bandwidth stemming from addition of CP all of which will reduce the ISI and ICI [5]. In time variable fading channels, time changing Doppler shift arises, that will subsequently influence the orthogonality of OFDM [6]. W-OFDM assures main side lobe of far lower magnitude than that of FFT-OFDM and also being far less influenced by this shift. A pressing attribute of WOFDM is the impeccable reconstruction with lowered complication [7]. The performance of OFDM and wavelet OFDM is analyzed over power line channels, and it has been observed that wavelet OFDM offers significant improvement in terms of transmission efficiency and spectral leakage over OFDM [8]. The wavelet-based OFDM (DWT-OFDM & WPM-OFDM) provides the orthogonal basis and also satisfies the accurate reconstruction, thereby providing significant BER improvement over Fourier based OFDM [9,10]. Diverse wavelets are also being considered as an alternative to Fourier transform along with the other transforms such as DCT/DST. It has been observed that DWT/DCT/DST based OFDM is better in terms of BER performance in comparison to Fourier based OFDM [11–13]. The BER performance of wavelet based OFDM is also analyzed over flat as well as frequency selective fading channels and it has been observed that the use of wavelets influence the BER performance significantly due to their time-frequency localization property [14,15]. The overall performance of FFT-OFDM is measured against WHT-OFDM over AWGN channel and as a result of orthogonality of WHT-OFDM sub-carrier waveforms its performance is superior to FFT-OFDM [16]. The behavior of DWT-OFDM is being equated with FFT-OFDM over Rayleigh fading channel in conjunction with the effect of exponential power delay profile [17]. Use of wavelet packet modulation (WPM) for WiMAX over AWGN channel is demonstrated in [18]. A brief study of Diverse Wavelets in Orthogonal Wavelet Division Multiplex for DVB-T is presented [19]. It has been observed that Haar transform provides better performance in comparison to all other transforms in wavelet family. It has been observed that the performance of WPM based WiMAX is quite better than FFT based WiMAX. The BER performance evaluation with the help of channel estimation techniques has also been done for the comparison of conventional OFDM and wavelet based OFDM system [20]. Organization of this work is: Section 1, a basic overview of preceding work carried out on FFT-OFDM and WHTOFDM is presented. Section 2 incorporates the model description and result presentation trailed by conclusion inferred in Section 3 on the foundation of observation form the results.
2. Model description The FFT-WiMAX and WHT-WiMAX system have been simulated using MATLABTM and the overall performance is expressed using SNR vs. BER variations and SNR vs. spectral efficiency variations. The block diagram for the simulated system is depicted in Fig. 1.
At the transmitter side of the physical layer, the first process is randomization. It is indeed primarily scrambling of data to generate random arrangement to optimize coding effectiveness. In forward error correction (FEC), there exist a range of coding platform such as RS codes, convolution codes, Turbo codes and so forth. However, nonetheless in the present paper primarily RS codes and convolution codes have been utilized for simulation. RS codes fundamentally add redundancy to the data. This redundancy enhances block error reduction. RS-encoder is dependent on Galois field computation to contribute the redundancy bits. WiMAX is based on GF (28 ) that corresponds to as RS (N = 255, K = 239, T = 8) where: N = Number of bytes after encoding K = Data bytes before encoding T = Number of bytes that can be corrected Convolution code (CC) presents redundant bits into the data flow. The shift register accepts the information bits, and encoded bits are generated by using the modulo-2 addition of the contents of the shift register along with input data bits. Convolution code is utilized as desired FEC in 802.11a physical layer. The industry standard generator polynomials, g0 = 1338 and g1 = 1718, of rate R = 1/2 are utilized by convolutional code. Elevated rates such as 2/3 and 3/4, originate through it by utilizing “puncturing”. The Viterbi algorithm is employed for decoding the convolution code to get the required data bits. Interleaving strives to dispense transmitted bits in frequency or time or perhaps both of them to accomplish acceptable bit error performance after demodulation. What a sort of interleaving structure is commonly employed hinges on the channel behavior. When the system functions in the purely AWGN environment, hardly any interleaving is necessary, simply because the error distribution will not alter by relocating the bits. Modulation, as well as channel encoding, is elementary aspects of a communication system. Digital modulation is the procedure for mapping the digital data to analog form so that it could be transmitted over the channel. As a result, each and every digital communication system carries a modulator that accomplishes this task. Strongly linked to modulation is the inverse approach, referred to as demodulation, performed by the receiver to get back the transmitted digital information. The modeling of optimal demodulators is termed as detection theory. Distinct, coherent mapping employed are m-ary-phase shift keying (M-PSK) and m-ary-quadrature amplitude modulation (M-QAM). However, there exists a trade-off between, distinct mapping technology and spectral efficiency. Pilot insertion is employed for channel estimaQ4 tion & synchronization goal (Table 1). OFDM Subcarrier are generated by virtue of inverse fast Fourier transform (IFFT) which modifies the data from the frequency domain to the time domain. IFFT is incorporated in OFDM to generate subcarriers because it maintains the required frequency spacing between the subcarriers fulfilling orthogonality condition. An ordinary N-to-N point linear transformation necessitates N2 multiplications as well as additions. Nonetheless, by computing the outputs concurrently and making the most of the cyclic characteristics of the multipliers e ± j2kn/N fast Fourier transform (FFT) strategies lessen the quantity of computations to the order of N log N. The FFT is most beneficial when N is a power of 2. Numerous variants of the FFT exist, with distinct ordering of the inputs and outputs, as well as multiple usages of temporary memory. One strategy to eliminate IS1 would be to generate a cyclically lengthened guard time frame, in which every OFDM symbol is headed by a periodic extension of the signal itself. Taking into consideration the discrete-time realisation of the multi-carrier system, sampling the transmitted multi-carrier signal at a rate comparable to the data rate one retrieves a frame structure comprised of the IDFT of the
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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Fig. 1. Block diagram of WiMAX physical layer model.
Table 1 WiMAX specifications.
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3. Result discussion
Parameters
Values
NFFT Nominal channel B.W. No. of used sub-carriers Sub carrier spacing (f) Upper guard Lower guard NDC FS(sampling frequency) Tb Ratio guard time to symbol time (G) Tg = G.Tb Tsymbols = Tb + Tg Wavelet Used Convolution Code Rate Modulation Type Modulation Level Used (M) Simulated Environment Total No. of WiMAX Symbols used for Simulation
256 2.5 MHz 192 11.2 28 27 1 (prefix 128) 2.86 MHz 89 micro sec. Variable (1/2, 1/4, 1/8, 1/16, 1/32) Variable Variable Haar 1/2, 2/3, 3/4 M-PSK & M-QAM 2, 4, 16 & 64 Rayleigh Channel (NLOS) 106
data symbols and a cyclic prefix as well as wherein the OFDM frame would contain Ntotal = L + N samples. At this time, L is the number of samples replicated from the end of N sample IDFT frame and attached at the beginning of each IDFT frame. At the receiver, eliminating the guard interval will become the equivalent to eliminating the cyclic prefix, although the end results of the channel transforms into the periodic convolution of the discrete-time channel with the IDFT of the data symbols. Executing a DFT on the received samples after the cyclic prefix is neglected, the periodic convolution is transformed into multiplication, since it was the scenario for the analog multi-carrier receiver.
The orthogonality of WiMAX subcarriers will be effected by the blended outcome of the fading channel due to the time and frequency selectivity. The out-of-band side-lobes rejection is considerably more in case of several wavelet structured multi-carrier strategies in comparison to OFDM. Moreover, the resiliency against time and frequency variability of the channel is more in WOFDM. On the grounds that the resiliency offered by W-OFDM is not due to integration of GI for channel equalization, instead of that it is purely dependent upon the symbol duration in W-OFDM which in turn is inversely proportional to inverse of carrier spacing. On the other hand, because symbol overlap is hardly there in OFDM the resiliency of OFDM models to uncompensated ISI is merely influenced by the reciprocal of the carrier spacing. Eventually, as compared with OFDM, in W-OFDM systems it might be likely to achieve improved immunity to ISI by elevating the quantity of carriers. In the selective fading channel, many models may perhaps be taken into consideration to review the BER effectiveness of the systems. The BER performance of DWT-WiMAX in Rayleigh fading channel is compared with the FFT-WiMAX. This is apparent from Fig. 2.1–2.7 that WHT-WiMAX performs better than FFT-WiMAX Q5 for diverse modulation schemes since it is rather less susceptible to Doppler frequency variations. This truly originates from the deterioration in orthogonality between the carriers of FFTWiMAX consequently of the multipath wireless channel [16,17]. As an illustrated by Fig. 2.1, to achieve a BER of 10−4 , in Rayleigh fading scenario BPSK modulated with CC code rate 1/2 FFT-WiMAX necessitates SNR of 27 dB, but it is 15 dB for WHTWiMAX. For QPSK modulation with CC code rate 1/2 in Rayleigh fading scenario, FFT-WiMAX requires 33 dB of SNR, which is much less than 23 dB required in the case of WHT-WiMAX. On
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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Fig. 2. (a)–(g) SNR vs BER comparison of FFT-WiMAX and WHT-WiMAX system for Rayleigh fading channel (a) BPSK with CC 1/2 (b) QPSK with CC 1/2 (c) QPSK with CC 3/4 (d) 16-QAM with CC 1/2 (e) 16-QAM with CC 3/4 (f) 64-QAM with CC 2/3 (g) 64-QAM with CC 3/4.
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the contrary, in case of same fading scenario for same QPSK modulation but with a code rate of 3/4, FFT-WiMAX requires 38.5 dB of SNR, which is again higher than 27 dB SNR required for WHT-WiMAX. Furthermore, it has been observed that on using other modulation along with different CC code rates over
the same simulated environment, the BER performance starts degrading but can be mitigated at the cost of high SNR [16,17]. Consequently, it is summarized that WHT-WiMAX offers an improvement of 10–13 dB of SNR over FFT-WiMAX for Rayleigh fading scenarios.
Please cite this article in press as: L. Kansal, et al., Performance evaluation of FFT-WiMAX against WHT-WiMAX over Rayleigh fading channel, Optik - Int. J. Light Electron Opt. (2016), http://dx.doi.org/10.1016/j.ijleo.2016.01.067
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Fig. 3. (a)–(g) Spectral efficiency comparison of FFT-WiMAX and WHT-WiMAX system for Rayleigh fading channel (a) BPSK with CC 1/2 (b) QPSK with CC 1/2 (c) QPSK with CC 3/4 (d) 16-QAM with CC 1/2 (e) 16-QAM with CC 3/4 (f) 64-QAM with CC 2/3 (g) 64-QAM with CC 3/4.
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The spectral efficiency performance of DWT-WiMAX in Rayleigh fading channel is compared with the FFT-WiMAX. This is very much from Fig. 2.8–2.14 that WHT- WiMAX outperforms the FFT-WiMAX for diverse modulation schemes since it has better BER performance. As depicted in Fig. 2.8, in order to achieve the desired
spectral efficiency in case of BPSK modulation with CC code rate 1/2 15 dB of SNR is required for WHT-WiMAX which is less than 27 dB of SNR required for FFT-WiMAX. For QPSK modulation it is very much clear from Fig. 2.9 the although the spectral efficiency is doubled in comparison to what was being obtained by
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BPSK modulation using the same CC code rate of 1/2 for both the cases. However, this elevated spectral efficiency comes at the cost of increased requirement of SNR. On doing the comparison, it is 259 clear that FFT-WiMAX requires 34 dB of SNR which is still higher 260 than 24 dB of SNR required for WHT-WiMAX. On the other side it 261 is very much clear from Fig. 2.10 that the spectral efficiency for the 262 WiMAX system can be increased for the QPSK modulation on using 263 the CC code rate of 3/4 instead of CC code rate of 1/2. However, 264 in this case also WHT-WiMAX outperforms the FFT-WiMAX as it 265 requires less SNR to achieve the required spectral efficiency. A sim266 ilar observation can be made on analyzing the simulated results for 267 Q6 other modulation schemes and CC code rates (Fig. 3). 268 257 258
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FFT-WiMAX presents a low complexity framework as compared to WHT-WiMAX, still, the usage of CP reduces its spectral efficiency in addition to squanders transmit power. Overall performance outcome illustrates that WHT-WiMAX is a possible replacement to FFT-WiMAX but nevertheless at the expense of significantly increased the complexity of equalization. Consequently, WHTWiMAX could certainly evolve into an impressive contender for MCM in the multipath wireless channel. An enhancement of SNR in the range of 8–12 dB is reported for WHT-WiMAX to accomplish the suitable BER with different modulation schemes along with diverse CC code rate in Rayleigh fading scenarios. Furthermore, an additional SNR is required with the higher level of modulation schemes and diverse CC code rate to achieve the desired BER. Also, the spectral efficiency achieved from WHT-WiMAX is considerably more than that of FFT-WiMAX. Higher spectral efficiency can be achieved by going for higher order modulation and higher CC code rate. However, this elevated spectral efficiency can be achieved only at the cost of increased SNR values required.
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