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BER Analysis of OFDM Systems with Varying Frequency Offset Factor over AWGN and Rayleigh Channels

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rahulmonikasharma

The document analyzes the effect of varying frequency offset on the bit error rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems over additive white Gaussian noise (AWGN) and Rayleigh channels through simulation. The simulations show that as the frequency offset increases, the BER performance of the OFDM system degrades in both channel conditions due to increased inter-carrier interference (ICI). Higher frequency offset values lead to worse performance degradation. An effective technique is needed to mitigate the impact of frequency offset on OFDM system performance.

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International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 223 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ BER Analysis of OFDM Systems with Varying Frequency Offset Factor over AWGN and Rayleigh Channels Amandeep Singh Sehmby Assistant Professor, Department of Electronics and Communication Engineering, CT Institute of Engineering, Management & Technology, Jalandhar, India singh_aman099@yahoo.com Dr. Harjit Pal Singh Assistant Professor, Department of Electronics and Communication Engineering, CT Institute of Engineering, Management & Technology, Jalandhar, India Er. Navneet Gill Assistant Professor, Department of Electronics and Communication Engineering, CT Institute of Engineering, Management & Technology, Jalandhar, India Abstract—the progressively escalating demand for tremendously high rate data transmission over wireless mediums needsresourcefulconcord of electromagnetic resources considering restrictions like power incorporation, spectrum proficiency, robustness in disparity to multipath propagation and implementation complication. Orthogonal frequency division multiplexing (OFDM) is a favorable approach for upcoming generation wireless communication systems. However its susceptibility to the frequency offset triggered by frequency difference between local oscillator of transmitter and receiver or due to Doppler shift results to Inter Carrier Interference. This delinquent of ICI results inworsening performance of the wireless systems as bit error rate increaseswith increase in value of frequency offset. In this paper simulation results aredemonstratedfor analyzing the effect of varying frequency offset factor on system’s error rate performance. Index Terms—Bit Error Ratio (BER), Inter-Carrier Interference (ICI),Additive white Gaussian Noise (AWGN), Carrier Frequency Offset (CFO). __________________________________________________*****_________________________________________________ I. INTRODUCTION The intensification in number of mobile users desires for wireless technologies that can deliver data at high speeds in a spectrally crucial manner. However, supporting such high data rates with appropriate robustness to radio channel impairments involvesjudicious excerpt of techniques. Orthogonal frequency division multiplexing (OFDM) is a multicarrier multiplexing technique, in which data is transmitted over several parallel frequency sub channels at a lower rate. It has been standardized in several wireless applications such as Digital Video Broadcasting (DVB), HIPERLAN, IEEE 802.11 (Wi- Fi), and IEEE 802.16 (WiMAX) and isused for wired applications as in the Asynchronous Digital Subscriber Line (ADSL),Digital Audio Broadcasting (DAB) and power-line communications [1,2].One of the foremost reasons to use OFDM is to step-up the robustness against narrowband interference or frequency selective fading. As every technique has its inadequacies, this technique also has problem of being sensitive towards frequency mismatch. This mismatch in frequency can either arise because of variation in local oscillator frequencies of transceivers or due to Doppler shiftinitiating carrier frequency offset. TheCFO upshots in loss of orthogonality of the subcarriers which causes ICI. This paper isoutlined in way that Section II expresses the basic description and issues of OFDM system succeeded by the system portrayal and interference scrutiny and Mathematical description of ICI is given in Section III succeeded by simulation results in Section IV. The conclusion of paper is given in Section V. II. ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING OFDM is a distinct case of multi-carrier modulation. The dictum of OFDM is to split a single high-data rate stream into a number of lesser rate streams that are transferredsimultaneouslyover some narrower sub channels which are orthogonal to each other. Henceforward it is not only a modulation technique nevertheless a multiplexing technique too. The merits of this technique that make it a desired choice over other modulation techniques are its extraordinary spectral efficiency, easier implementation of FFT, lower receiver intricacy, robustness for high-data rate transmission over multipath fading channel, high controllability for link adaptation are few benefits to list. However, it has two elementaryimpairments: 1) higher peak to average power ratio (PAPR) as paralleled single carrier signal [3]. 2) Susceptibility to phase noise, timing and frequency offsets that acquaint with ICI into the system. The carrier frequency offset is instigated by the disparity of frequencies amongst the oscillators at the transceivers, or from the Doppler spread due to the relative motion between them. The phase noise arises mainly due to imperfections of the LO in the transceiver. The timing offset emerges due to the multipath delay spread and because of it not only inter-symbol interference, but ICI also transpires. However, ICI influenced by phase noise and timing offset can completely be compensated or fixed. But the manifestation of frequency offset due to the Doppler spread or frequency shift resulting in ICI is arbitrary, henceforth only its impact can be lessened. Many diverse ICI mitigation schemes have been extensively reconnoitered to fray the Inter-Carrier Interference in OFDM systems, comprising frequency-domain equalization [4], time-domain windowing [5], and the ICI self-cancellation (SC) schemes[6]-[12], frequency offset estimation and compensation techniques[13] and so on. Amidst the schemes, the ICI self-cancellation scheme is a modest method for ICI minimization. It is a two-phase approach that uses redundant modulation to overpower ICI with ease for OFDM [18]. III. SYSTEM DEPICTION AND ICI ANALYSIS Figure1 portraits a distinctive discrete-time base-band equivalent OFDM system model. As presented, a stream of
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 224 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ input bit stream is first mapped into symbols using BPSK modulation. The symbols are modulated using IFFT on N- parallel subcarriers succeeding the serial-to-parallel (S/P) conversion. With cyclic prefix (CP) appending, the OFDM symbols are sequential using parallel to serial (P/S) conversion and referred to the channel. At the receiver, the received symbols are recaptured by S/P transformation, CP removal, FFT transformation, P/S conversion and are demapped with equivalent scheme to obtain the anticipatednovel bit stream [14][17][18]. Fig. 1 OFDM Transceiver In OFDM systems, the transmitted signal in time domain can be exhibit as: 𝑥 �� = 1 𝑁 𝑋 𝑘 𝑒 𝑗 2𝜋𝑘𝑛 𝑁𝑁−1 𝑘=0 (1) Where x (n) represents the nth sample of the OFDM transmitted signal, X (k) symbolizes the modulated symbol for the kth subcarrier and k = 0, 1... N -1, N is the total quantity of OFDM subcarriers. The received signal in time domain is specified by: 𝑦 𝑛 = 𝑥 𝑛 𝑒 𝑗 2𝜋𝑛 ∈ 𝑁 + 𝑤(𝑛) (2) Where ∈ is the normalized frequency offset known by ∈ = ∆𝑓. 𝑁𝑇𝑠 in which ∆𝑓 is the frequency difference which is either due to variance in the local oscillator carrier frequencies of transmitter and receiver or due to Doppler shift and Ts is the subcarrier frequency and w (n) is the Additive White Gaussian Noise acquainted in the channel.The outcome of this frequency offset on the received symbolstream can be implicit by considering the received symbol Y (k) on the kth subcarrier. The received signal at subcarrierindex kcan be stated as 𝑌 𝑘 = 𝑋 𝑘 𝑆 0 + 𝑋 𝑙 𝑆 𝑙 − 𝑘 + 𝑊(𝑘)𝑁−1 𝑙=0, 𝑙≠𝑘 (3) Where k = 0, 1… N-1 and X (k) S (0) is the wanted signal and 𝑋 𝑙 𝑆(𝑙 − 𝑘)𝑁−1 𝑙=0 𝑙≠𝑘 is the ICI component of acknowledged OFDM signal. ICI component S (l-k) can be given as: 𝑆 𝑙 − 𝑘 = sin ⁡(𝜋(𝑙+𝜖−𝑘)) 𝑁𝑠𝑖𝑛 (𝜋(𝑙+𝜖−𝑘)/𝑁) exp⁡(𝑗𝜋 1 − 1 𝑁 𝑙 + 𝜖 − 𝑘 ) (4) IV. RELATED WORK A simulation is directed to evaluate performance of system for input specifications given in Table 1. TABLE I INPUT PARAMETERS FOR SIMULATIONS Input Parameters Parameters Values Carrier frequency 2.3 GHz Bandwidth 10 MHz Modulation BPSK No. of Bits 51200 No. of Symbols 50 Data Sub-Carriers 512 Subcarrier Frequency 10.94 KHz Cyclic Prefix 256 OFDM Symbol Length 1280 Symbol Time 91.4 µ sec FFT Size 1024 SNR (dB) 0:2:12 Offset  0-0.2 Channel AWGN, Rayleigh Noise AWGN Fig. 2 BER performance of OFDM at 0 frequency offset in AWGN Channel. Fig. 3 BER performance of OFDM at 0.10 frequency offset in AWGN Channel. 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0.1 I/P data Modul ation S/P IFFT CP ADD P/S Channel CP Remov al S/P P/SDemod ulation O/P data FFT
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 225 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ Fig. 4 BER performance of OFDM at 0.15 frequency offset in AWGN Channel. Fig. 5 BER performance of OFDM at 0.20 frequency offset in AWGN Channel. Figure 2 to Figure 5 illustrates that as the value of frequency offset is increasing, correspondingly the bit error rate performance of standard OFDM system is degrading in AWGN channel. Fig. 6 BER performance of OFDM at 0 frequency offset in Rayleigh Channel. Fig. 7 BER performance of OFDM at 0.05 frequency offset in Rayleigh Channel. Fig. 8 BER performance of OFDM at 0.10 frequency offset in Rayleigh Channel. Fig. 9 BER performance of OFDM at 0.15 frequency offset in Rayleigh Channel. 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0.15 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0.2 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0 in Rayleigh Channel Standard OFDM at offset  = 0 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.05 in Rayleigh Channel Standard OFDM at offset  = 0.05 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.10 in Rayleigh Channel Standard OFDM at offset  = 0.10 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.15 in Rayleigh Channel Standard OFDM at offset  = 0.15 Theoretical Curve
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 226 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ Fig. 10 BER performance of OFDM at 0.20 frequency offset in Rayleigh Channel. Fig. 11 BER performance of OFDM at 0.25 frequency offset in Rayleigh Channel. Fig. 12 BER performance of OFDM at 0.30 frequency offset in Rayleigh Channel. Figure 6to Figure 12depicts that the bit error rate performance of standard OFDM system is degrades in Rayleigh channel degrades at higher values of frequency offset. It can be undoubtedly seen that OFDM system with BPSK modulation for Channel Bandwidth of 10 MHz and subcarrier 512, BER of 10-5 can be accomplished for both lower and higher values of SNR in case there is no offset in the system. But as the offset gets introduced either due to frequency dissimilarity or due to Doppler shift system’s performance starts deteriorating in terms of BER of the system. This is because the ICI component gets introduced as soon as offset occurs. It is this Inter Carrier Interference that is responsible for performance degradation of system. It can be seen from figure 2 to figure 12 that frequency offset factor deteriorates the system’s performance. The effect is much worse at higher values of offset in both channel as compared to the lower ones. An efficient, simple and effective technique is required to mitigate its effect. V. CONCLUSION This paper scrutinises the effect of varying frequency offset factor on OFDM system’s performance.The offset gets introduced either due to frequency dissimilarity or due to Doppler shift system’s performance starts deteriorating in terms of BER of the system. This is because the ICI component gets introduced as soon as offset occurs. It is this Inter Carrier Interference that is responsible for performance degradation of system. . An efficient, simple and effective technique is required to mitigate its effect. REFERENCES [1] R.W Chang, “Synthesis of band limited orthogonal signal for multichannel data transmission”, Bell syst. Tech., Vol. 45, pp.1775-1796, Dec. 1996. [2] B.RSalzberg, “Performance of an efficient parallel data transmission system”, IEEE trans. Com., Vol. Com-15, pp. 805- 813, Dec. 1967. [3] VaishaliBahl, R. Dubey, and Dalvir Kaur,” MIMO-OFDM: Foundation for Next-Generation Wireless Systems”, International Journal on Recent and Innovation Trends in Computing andCommunication(ISSN: 2321-8169(p) 1692 – 1695(0), Volume 2, Issue 6, June 2014. [4] W. G. Jeon,etal, “An equalization technique for orthogonal frequencydivisionmultiplexing systems in time-variant multipath channels,” IEEETransactions on Communications, vol. 47, no.1, pp.27-32, 2001. [5] Heung-GyoonRyu, Yingshan Li, and Jin-Soo Park, “An Improved ICIReduction Method in OFDM Communication System,” IEEETransactions on Broadcasting, vol.51, no.3, pp.395-400, 2005. [6] J. Armstrong, “Analysis of new and existing methods of reducing intercarrier interference due to carrier frequency offset in OFDM,” IEEETransactions on Communications, vol. 47, no. 3, pp.365- 369, 1999. [7] RimpyGoyal, RishavDewan,“ICI Cancellation Using Self ICI Symmetric Conjugate Symbol Repetition for OFDM System”, International Journal of Emerging Trends in Signal Processing( IJETSP ) ISSN(2319-9784) , Volume 1 , Issue 6 December 2013 [8] Yu Fu, Chi Chung Ko, “A new ICI self-cancellation scheme for OFDMsystems based on a generalized signal mapper,” in Proc. 5th WirelessPersonal Multimedia Communications, pp.995-999, Oct.2002. [9] Y. Zhao and S. Häggman, “Intercarrier interference self- cancellationscheme for OFDM mobile communication systems,” IEEE Transactionson Communications, vol.49, no. 7, pp. 1185- 1191, 2001. 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.20 in Rayleigh Channel Standard OFDM at offset  = 0.20 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.25 in Rayleigh Channel Standard OFDM at offset  = 0.25 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.30 in Rayleigh Channel Standard OFDM at offset  = 0.30 Theoretical Curve
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 227 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ [10] Li Ying-shan, etal, “ICI Compensation in MISO-OFDM SystemAffected by Frequency Offset and Phase Noise,” Journal ofCommunication and Computer, vol.5, no.12, pp.32-38, 2008. [11] Yi-Hao Peng, etal, “Performance Analysis of a New ICI-Self- Cancellation-Scheme in OFDM Systems,” IEEE Transactions onConsumer Electronics, vol.53, no. 4, pp.1333-1338, 2007. [12] Hen-GeulYeh,Yuan-Kwei Chang, and BabakHassibi,” A Scheme for Cancelling Intercarrier Interference using Conjugate Transmission in Multicarrier Communication Systems”, IEEE Trans. On wireless communication, Vol. 6, No 1, Jan 2007. [13] Q. Shi, Y. Fang, M. Wang, “A novel ICI self-cancellation scheme for OFDM systems”, in IEEE WiCom, pp.1-4, 2009. [14] AbhijeetBishnu, et al, “A new scheme ICI self-cancellation in OFDM system”, IEEE ICCSNT, 2013. [15] Eu-Suk Shim, etal, “OFDM Carrier Frequency Offset EstimationMethods with Improved Performance,” IEEE Transactions on Broadcasting, vol.53, no. 2, pp.567-573, 2007. [16] Nee, Richard van, and Ramjee Prasad. OFDM for wireless multimedia communications Artech House, Inc., 2000. [17] VaishaliBahl, Dalvir Kaur, AS Buttar,”BER Analysis of ICI Self Cancellation Schemes for OFDM Based Wireless Systems”, International Journal on P2P Trends and Technology , vol 13, no.1, pp 1 – 5, November 2014. [18] VaishaliBahl, Amandeep Singh Sehmby, and Narinder Pal Singh,” A Perlustration of ICI Self Cancellation Schemes for OFDM Systems”, Journal ofNetwork Communications and Emerging Technologies, Vol 5, Issue 2, pp 20-23 , November 2015.

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BER Analysis of OFDM Systems with Varying Frequency Offset Factor over AWGN and Rayleigh Channels

  • 1. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 223 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ BER Analysis of OFDM Systems with Varying Frequency Offset Factor over AWGN and Rayleigh Channels Amandeep Singh Sehmby Assistant Professor, Department of Electronics and Communication Engineering, CT Institute of Engineering, Management & Technology, Jalandhar, India singh_aman099@yahoo.com Dr. Harjit Pal Singh Assistant Professor, Department of Electronics and Communication Engineering, CT Institute of Engineering, Management & Technology, Jalandhar, India Er. Navneet Gill Assistant Professor, Department of Electronics and Communication Engineering, CT Institute of Engineering, Management & Technology, Jalandhar, India Abstract—the progressively escalating demand for tremendously high rate data transmission over wireless mediums needsresourcefulconcord of electromagnetic resources considering restrictions like power incorporation, spectrum proficiency, robustness in disparity to multipath propagation and implementation complication. Orthogonal frequency division multiplexing (OFDM) is a favorable approach for upcoming generation wireless communication systems. However its susceptibility to the frequency offset triggered by frequency difference between local oscillator of transmitter and receiver or due to Doppler shift results to Inter Carrier Interference. This delinquent of ICI results inworsening performance of the wireless systems as bit error rate increaseswith increase in value of frequency offset. In this paper simulation results aredemonstratedfor analyzing the effect of varying frequency offset factor on system’s error rate performance. Index Terms—Bit Error Ratio (BER), Inter-Carrier Interference (ICI),Additive white Gaussian Noise (AWGN), Carrier Frequency Offset (CFO). __________________________________________________*****_________________________________________________ I. INTRODUCTION The intensification in number of mobile users desires for wireless technologies that can deliver data at high speeds in a spectrally crucial manner. However, supporting such high data rates with appropriate robustness to radio channel impairments involvesjudicious excerpt of techniques. Orthogonal frequency division multiplexing (OFDM) is a multicarrier multiplexing technique, in which data is transmitted over several parallel frequency sub channels at a lower rate. It has been standardized in several wireless applications such as Digital Video Broadcasting (DVB), HIPERLAN, IEEE 802.11 (Wi- Fi), and IEEE 802.16 (WiMAX) and isused for wired applications as in the Asynchronous Digital Subscriber Line (ADSL),Digital Audio Broadcasting (DAB) and power-line communications [1,2].One of the foremost reasons to use OFDM is to step-up the robustness against narrowband interference or frequency selective fading. As every technique has its inadequacies, this technique also has problem of being sensitive towards frequency mismatch. This mismatch in frequency can either arise because of variation in local oscillator frequencies of transceivers or due to Doppler shiftinitiating carrier frequency offset. TheCFO upshots in loss of orthogonality of the subcarriers which causes ICI. This paper isoutlined in way that Section II expresses the basic description and issues of OFDM system succeeded by the system portrayal and interference scrutiny and Mathematical description of ICI is given in Section III succeeded by simulation results in Section IV. The conclusion of paper is given in Section V. II. ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING OFDM is a distinct case of multi-carrier modulation. The dictum of OFDM is to split a single high-data rate stream into a number of lesser rate streams that are transferredsimultaneouslyover some narrower sub channels which are orthogonal to each other. Henceforward it is not only a modulation technique nevertheless a multiplexing technique too. The merits of this technique that make it a desired choice over other modulation techniques are its extraordinary spectral efficiency, easier implementation of FFT, lower receiver intricacy, robustness for high-data rate transmission over multipath fading channel, high controllability for link adaptation are few benefits to list. However, it has two elementaryimpairments: 1) higher peak to average power ratio (PAPR) as paralleled single carrier signal [3]. 2) Susceptibility to phase noise, timing and frequency offsets that acquaint with ICI into the system. The carrier frequency offset is instigated by the disparity of frequencies amongst the oscillators at the transceivers, or from the Doppler spread due to the relative motion between them. The phase noise arises mainly due to imperfections of the LO in the transceiver. The timing offset emerges due to the multipath delay spread and because of it not only inter-symbol interference, but ICI also transpires. However, ICI influenced by phase noise and timing offset can completely be compensated or fixed. But the manifestation of frequency offset due to the Doppler spread or frequency shift resulting in ICI is arbitrary, henceforth only its impact can be lessened. Many diverse ICI mitigation schemes have been extensively reconnoitered to fray the Inter-Carrier Interference in OFDM systems, comprising frequency-domain equalization [4], time-domain windowing [5], and the ICI self-cancellation (SC) schemes[6]-[12], frequency offset estimation and compensation techniques[13] and so on. Amidst the schemes, the ICI self-cancellation scheme is a modest method for ICI minimization. It is a two-phase approach that uses redundant modulation to overpower ICI with ease for OFDM [18]. III. SYSTEM DEPICTION AND ICI ANALYSIS Figure1 portraits a distinctive discrete-time base-band equivalent OFDM system model. As presented, a stream of
  • 2. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 224 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ input bit stream is first mapped into symbols using BPSK modulation. The symbols are modulated using IFFT on N- parallel subcarriers succeeding the serial-to-parallel (S/P) conversion. With cyclic prefix (CP) appending, the OFDM symbols are sequential using parallel to serial (P/S) conversion and referred to the channel. At the receiver, the received symbols are recaptured by S/P transformation, CP removal, FFT transformation, P/S conversion and are demapped with equivalent scheme to obtain the anticipatednovel bit stream [14][17][18]. Fig. 1 OFDM Transceiver In OFDM systems, the transmitted signal in time domain can be exhibit as: 𝑥 𝑛 = 1 𝑁 𝑋 𝑘 𝑒 𝑗 2𝜋𝑘𝑛 𝑁𝑁−1 𝑘=0 (1) Where x (n) represents the nth sample of the OFDM transmitted signal, X (k) symbolizes the modulated symbol for the kth subcarrier and k = 0, 1... N -1, N is the total quantity of OFDM subcarriers. The received signal in time domain is specified by: 𝑦 𝑛 = 𝑥 𝑛 𝑒 𝑗 2𝜋𝑛 ∈ 𝑁 + 𝑤(𝑛) (2) Where ∈ is the normalized frequency offset known by ∈ = ∆𝑓. 𝑁𝑇𝑠 in which ∆𝑓 is the frequency difference which is either due to variance in the local oscillator carrier frequencies of transmitter and receiver or due to Doppler shift and Ts is the subcarrier frequency and w (n) is the Additive White Gaussian Noise acquainted in the channel.The outcome of this frequency offset on the received symbolstream can be implicit by considering the received symbol Y (k) on the kth subcarrier. The received signal at subcarrierindex kcan be stated as 𝑌 𝑘 = 𝑋 𝑘 𝑆 0 + 𝑋 𝑙 𝑆 𝑙 − 𝑘 + 𝑊(𝑘)𝑁−1 𝑙=0, 𝑙≠𝑘 (3) Where k = 0, 1… N-1 and X (k) S (0) is the wanted signal and 𝑋 𝑙 𝑆(𝑙 − 𝑘)𝑁−1 𝑙=0 𝑙≠𝑘 is the ICI component of acknowledged OFDM signal. ICI component S (l-k) can be given as: 𝑆 𝑙 − 𝑘 = sin ⁡(𝜋(𝑙+𝜖−𝑘)) 𝑁𝑠𝑖𝑛 (𝜋(𝑙+𝜖−𝑘)/𝑁) exp⁡(𝑗𝜋 1 − 1 𝑁 𝑙 + 𝜖 − 𝑘 ) (4) IV. RELATED WORK A simulation is directed to evaluate performance of system for input specifications given in Table 1. TABLE I INPUT PARAMETERS FOR SIMULATIONS Input Parameters Parameters Values Carrier frequency 2.3 GHz Bandwidth 10 MHz Modulation BPSK No. of Bits 51200 No. of Symbols 50 Data Sub-Carriers 512 Subcarrier Frequency 10.94 KHz Cyclic Prefix 256 OFDM Symbol Length 1280 Symbol Time 91.4 µ sec FFT Size 1024 SNR (dB) 0:2:12 Offset  0-0.2 Channel AWGN, Rayleigh Noise AWGN Fig. 2 BER performance of OFDM at 0 frequency offset in AWGN Channel. Fig. 3 BER performance of OFDM at 0.10 frequency offset in AWGN Channel. 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0.1 I/P data Modul ation S/P IFFT CP ADD P/S Channel CP Remov al S/P P/SDemod ulation O/P data FFT
  • 3. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 225 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ Fig. 4 BER performance of OFDM at 0.15 frequency offset in AWGN Channel. Fig. 5 BER performance of OFDM at 0.20 frequency offset in AWGN Channel. Figure 2 to Figure 5 illustrates that as the value of frequency offset is increasing, correspondingly the bit error rate performance of standard OFDM system is degrading in AWGN channel. Fig. 6 BER performance of OFDM at 0 frequency offset in Rayleigh Channel. Fig. 7 BER performance of OFDM at 0.05 frequency offset in Rayleigh Channel. Fig. 8 BER performance of OFDM at 0.10 frequency offset in Rayleigh Channel. Fig. 9 BER performance of OFDM at 0.15 frequency offset in Rayleigh Channel. 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0.15 0 1 2 3 4 5 6 7 8 9 10 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 Eb/N0 BER BER v/s SNR in AWGN Channel at  = 0.2 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0 in Rayleigh Channel Standard OFDM at offset  = 0 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.05 in Rayleigh Channel Standard OFDM at offset  = 0.05 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.10 in Rayleigh Channel Standard OFDM at offset  = 0.10 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.15 in Rayleigh Channel Standard OFDM at offset  = 0.15 Theoretical Curve
  • 4. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 226 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ Fig. 10 BER performance of OFDM at 0.20 frequency offset in Rayleigh Channel. Fig. 11 BER performance of OFDM at 0.25 frequency offset in Rayleigh Channel. Fig. 12 BER performance of OFDM at 0.30 frequency offset in Rayleigh Channel. Figure 6to Figure 12depicts that the bit error rate performance of standard OFDM system is degrades in Rayleigh channel degrades at higher values of frequency offset. It can be undoubtedly seen that OFDM system with BPSK modulation for Channel Bandwidth of 10 MHz and subcarrier 512, BER of 10-5 can be accomplished for both lower and higher values of SNR in case there is no offset in the system. But as the offset gets introduced either due to frequency dissimilarity or due to Doppler shift system’s performance starts deteriorating in terms of BER of the system. This is because the ICI component gets introduced as soon as offset occurs. It is this Inter Carrier Interference that is responsible for performance degradation of system. It can be seen from figure 2 to figure 12 that frequency offset factor deteriorates the system’s performance. The effect is much worse at higher values of offset in both channel as compared to the lower ones. An efficient, simple and effective technique is required to mitigate its effect. V. CONCLUSION This paper scrutinises the effect of varying frequency offset factor on OFDM system’s performance.The offset gets introduced either due to frequency dissimilarity or due to Doppler shift system’s performance starts deteriorating in terms of BER of the system. This is because the ICI component gets introduced as soon as offset occurs. It is this Inter Carrier Interference that is responsible for performance degradation of system. . An efficient, simple and effective technique is required to mitigate its effect. REFERENCES [1] R.W Chang, “Synthesis of band limited orthogonal signal for multichannel data transmission”, Bell syst. Tech., Vol. 45, pp.1775-1796, Dec. 1996. [2] B.RSalzberg, “Performance of an efficient parallel data transmission system”, IEEE trans. Com., Vol. Com-15, pp. 805- 813, Dec. 1967. [3] VaishaliBahl, R. Dubey, and Dalvir Kaur,” MIMO-OFDM: Foundation for Next-Generation Wireless Systems”, International Journal on Recent and Innovation Trends in Computing andCommunication(ISSN: 2321-8169(p) 1692 – 1695(0), Volume 2, Issue 6, June 2014. [4] W. G. Jeon,etal, “An equalization technique for orthogonal frequencydivisionmultiplexing systems in time-variant multipath channels,” IEEETransactions on Communications, vol. 47, no.1, pp.27-32, 2001. [5] Heung-GyoonRyu, Yingshan Li, and Jin-Soo Park, “An Improved ICIReduction Method in OFDM Communication System,” IEEETransactions on Broadcasting, vol.51, no.3, pp.395-400, 2005. [6] J. Armstrong, “Analysis of new and existing methods of reducing intercarrier interference due to carrier frequency offset in OFDM,” IEEETransactions on Communications, vol. 47, no. 3, pp.365- 369, 1999. [7] RimpyGoyal, RishavDewan,“ICI Cancellation Using Self ICI Symmetric Conjugate Symbol Repetition for OFDM System”, International Journal of Emerging Trends in Signal Processing( IJETSP ) ISSN(2319-9784) , Volume 1 , Issue 6 December 2013 [8] Yu Fu, Chi Chung Ko, “A new ICI self-cancellation scheme for OFDMsystems based on a generalized signal mapper,” in Proc. 5th WirelessPersonal Multimedia Communications, pp.995-999, Oct.2002. [9] Y. Zhao and S. Häggman, “Intercarrier interference self- cancellationscheme for OFDM mobile communication systems,” IEEE Transactionson Communications, vol.49, no. 7, pp. 1185- 1191, 2001. 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.20 in Rayleigh Channel Standard OFDM at offset  = 0.20 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.25 in Rayleigh Channel Standard OFDM at offset  = 0.25 Theoretical Curve 0 1 2 3 4 5 6 7 8 9 10 10 -5 10 -4 10 -3 10 -2 10 -1 Eb/N0(dB) BER BER of OFDM system at  = 0.30 in Rayleigh Channel Standard OFDM at offset  = 0.30 Theoretical Curve
  • 5. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 5 Issue: 7 223 – 227 _______________________________________________________________________________________________ 227 IJRITCC | July 2017, Available @ http://www.ijritcc.org _______________________________________________________________________________________ [10] Li Ying-shan, etal, “ICI Compensation in MISO-OFDM SystemAffected by Frequency Offset and Phase Noise,” Journal ofCommunication and Computer, vol.5, no.12, pp.32-38, 2008. [11] Yi-Hao Peng, etal, “Performance Analysis of a New ICI-Self- Cancellation-Scheme in OFDM Systems,” IEEE Transactions onConsumer Electronics, vol.53, no. 4, pp.1333-1338, 2007. [12] Hen-GeulYeh,Yuan-Kwei Chang, and BabakHassibi,” A Scheme for Cancelling Intercarrier Interference using Conjugate Transmission in Multicarrier Communication Systems”, IEEE Trans. On wireless communication, Vol. 6, No 1, Jan 2007. [13] Q. Shi, Y. Fang, M. Wang, “A novel ICI self-cancellation scheme for OFDM systems”, in IEEE WiCom, pp.1-4, 2009. [14] AbhijeetBishnu, et al, “A new scheme ICI self-cancellation in OFDM system”, IEEE ICCSNT, 2013. [15] Eu-Suk Shim, etal, “OFDM Carrier Frequency Offset EstimationMethods with Improved Performance,” IEEE Transactions on Broadcasting, vol.53, no. 2, pp.567-573, 2007. [16] Nee, Richard van, and Ramjee Prasad. OFDM for wireless multimedia communications Artech House, Inc., 2000. [17] VaishaliBahl, Dalvir Kaur, AS Buttar,”BER Analysis of ICI Self Cancellation Schemes for OFDM Based Wireless Systems”, International Journal on P2P Trends and Technology , vol 13, no.1, pp 1 – 5, November 2014. [18] VaishaliBahl, Amandeep Singh Sehmby, and Narinder Pal Singh,” A Perlustration of ICI Self Cancellation Schemes for OFDM Systems”, Journal ofNetwork Communications and Emerging Technologies, Vol 5, Issue 2, pp 20-23 , November 2015.