See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/279869147
Secure MDM-OFDM-Ro-FSO System Using HG Modes ARTICLE · JUNE 2015 DOI: 10.2174/2210327905999150521110316
READS
53
3 AUTHORS, INCLUDING: Angela Amphawan
Sushank Chaudhary
Massachusetts Institute of Technology
Universiti Utara Malaysia
76 PUBLICATIONS 173 CITATIONS
20 PUBLICATIONS 14 CITATIONS
SEE PROFILE
All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
SEE PROFILE
Available from: B B Gupta Retrieved on: 28 November 2015
Send Orders for Reprints to
[email protected] International Journal of Sensors, Wireless Communications and Control, 2015, 5, 13-18
13
Secure MDM-OFDM-Ro-FSO System Using HG Modes Angela Amphawan1,*, Sushank Chaudhary1 and Brij B. Gupta2 1
Integrated Optics Group, School of Computing, Universiti Utara Malaysia, Sintok, Malaysia; 2National Institute of Technology Kurukshetra, India Abstract: Radio-over-free-space-optics (Ro-FSO) is a promising technique to distribute radio frequency (RF) signals over the atmosphere using optical carriers. In this work, we designed a 60Gbps-120GHz OFDM-Ro-FSO transmission system in conjunction with mode division multiplexing. Three independent 40 GHz radio signal are optically modulated at 20 Gbps and transported over a secure free-space link of 50 km by mode division multiplexing of three Hermite-Guassian modes HG 00, HG 01 and HG 02.
Keywords: Hermite-Gaussian modes, Mode division multiplexing, OFDM, Ro-FSO. 1. INTRODUCTION The last decade has seen tremendous development in the growth of broadband access networks around the globe. The interest for faster data rates in the evolution towards 5G wireless systems has brought rapid innovation in new optical technologies to accommodate the rise in number of subscribers. The growth of Internet traffic together with an increase in the number and range of new services have placed pressure on legacy low-speed optical networks. This calls for effective modern optical communication systems that support high transmission rates and enhanced coverage. It has been very difficult for the International Telecom Unions (ITU) to allocate the limited RF Spectrum among the operators due to the explosive growth of subscribers every year. The ITU has reported 7.5 billion cellular subscribers in 2013 [1]. Ro-FSO is a promising technology for increasing broadband penetration, enabling transmission of multiple RF signals via a high-speed optical carrier without expensive optical fiber cabling *Address correspondence to this author at the Integrated Optics Group, School of Computing, Universiti Utara Malaysia, Sintok, Malaysia; Tel: +604 928 4000; Fax: +604-928 5067; E-mail:
[email protected]
2210-327/15 $58.00+.00
or licensing for RF solutions. Ro-FSO harness merits of both radio-over-fiber (RoF) and freespace-optics (FSO) technologies. In FSO links, transportation of signals is carried out through the atmosphere instead of an expensive optical fiber, thus eliminating the need for costly cabling of fiber optics in sparsely-populated rural areas. Another main advantage of FSO is that contrary to RF communications, no license is required for transmission in FSO [2]. Thirdly, in some rural areas where current wireless radio technology are inaccessible such as hilly terrains and areas far from radio base stations, FSO technology may be integrated with existing mobile cellular radio technology to promote more rapid deployment of a ubiquitous wireless architecture. Although FSO guarantees high speed data rates, there are some challenges such as scintillations, and atmospheric turbulences which need to be addressed in order to improve the signal-to-noise ratio (SNR) of the FSO link [3-4]. Hence by integration of RoF to FSO, referred to as Ro-FSO, a ubiquitous platform for seamless integration with RF wireless networks may extend the achievable capacity of current wireless networks rapidly and cost effectively [5].
© 2015 Bentham Science Publishers
14
International Journal of Sensors, Wireless Communications and Control, 2015, Vol. 5, No. 1
OFDM is an established approach for overcoming multipath fading. It works by transporting data over a huge number of sub-carriers separated by precise frequencies with overlapping bands. The orthogonality of the sub-carriers is ensured through Fast Fourier Transform (FFT) calculations. Hence, by adopting OFDM with FSO, long haul transmissions with higher data rates can be achieved [6-11]. Eigenmomdes are used in mode division multiplexing (MDM) to drive the propagation of a number of channels on different modes generated by various mechanisms such as spatial light modulators [12-15], optical signal processing [16-18], few mode fiber [19, 20], photonic crystal fibers [21] and modal decomposition methods [22-24]. In this work, we have presented 3 20Gbps-40GHz secure OFDM-Ro-FSO channels by adopting mode multiplexing scheme using HermiteGuassian modes, not reported in any prior work. The remainder of the paper is organized as follows: Section II elucidates the main principles of
Fig. (1). Proposed Ro-FSO transmission system.
Amphawan et al.
the MDM-OFDM model and simulation parameters. Section III describes the results and discussions, followed by the conclusion in Section IV. 2. SYSTEM DESCRIPTION The proposed secure OFDM-Ro-FSO transmission system, modeled in OptiSystemTM software, is illustrated in Fig. (1). Three independent fourlevel quadrature modulation OFDM channels, each carrying 20Gbps-40GHz signal are modulated over an optical spatial carrier by modal multiplexing on three laser modes HG mode 00, HG mode 01 and HG mode 02 and are transmitted over a FSO link of 50km. The HG mode is described mathematically as: m,n (r,) = H m (
x y 2y y )H n ( )exp( 2 )exp( j ) woy Rox Roy woy 2
exp( j
2x x2 )exp( 2 ) wox wox 2
2
(1)
Secure Hybrid MDM-OFDM-Ro-FSO International Journal of Sensors, Wireless Communications and Control, 2015, Vol. 5, No. 1 15
(a)
(b)
(c) Fig. (2). Excited HG Modes (a) HG 00 (b) HG 01 (c) HG 02.
A continuous wavelength (CW) laser and HG mode generator are used to excite HG modes as shown in Fig. (2). A 4-QAM sequence generator is used to generate 20 Gbps of data using 2 bits per symbol which is further modulated using OFDM 512 sub-carriers and 1024 FFT points. These OFDM signals are again modulated at 7.5 GHz using a QM modulator at 40 GHz. The QM signal is modulated by a LiNb modulator driven by a CW source on HG modes and transmitted over a FSO link. The link equation for the received power is given by [11].
d R2 R R/2 PRe ceived = PTransmitted 10 2 (dT + R)
(2)
where defines receiver aperture diameter , is the transmitter aperture diameter, is the beam divergence, R is the range, is the atmospheric attenuation. At the reception side, the mode is retrieved based on mean-squared error minimization of the optical signal using a mode-indexed semiconductor optical amplifier (SOA) with an injection current of 0.5A. The FSO transmitter aperture and receiver aperture is set to 20 cm and 30 cm respectively. A 40 GHz signal is again added after photodiode for the down conversion of signal. This electrical signal is then fed to a QM demodulator followed by OFDM modulator and QAM decoder for the recovery of data. The atmospheric turbulences emulate clear weather conditions.
16
International Journal of Sensors, Wireless Communications and Control, 2015, Vol. 5, No. 1
Amphawan et al.
Fig. (3). Evaluation of SNR and total received power under clear weather conditions.
(a)
(b)
(c)
Fig. (4). Constellation measured at 50km (a) HG mode 00 (b) HG mode 01 (c) HG mode 02.
3. RESULTS AND DISCUSSION In this section, the results from our simulation are presented and discussed. Fig. (3) reveals the SNR and total received power for our proposed Ro-FSO transmission system under clear weather conditions. It is observed from the Fig. (3) (a) that the value of SNR for HG mode 00 is computed as 38.11dB, 36.11dB and 25.11dB; for HG mode 01 as 31.12dB, 17.22dB and 11.16dB and for HG mode 02 as 36.22dB, 26.11dB and 20.34dB at a FSO link of 10km, 40km and 50km respectively. Consequently, the value of total received power for HG mode 00 is computed as -54.11dBm, -
68.54dBm and-74.11dBm; for HG mode 01 as 68.12dBm, -82.11dBm and -88.32dBm; for HG mode 02 as -59.43dBm, -73.11dBm and 79.11dBm at the transmission link of 20km, 40km and 50km respectively. This indicates that under clear weather conditions, the channel propagating HG mode 00 prolongs to 50km, the channel propagating HG mode 01 prolongs to 25km and the channel propagating HG mode 02 prolongs to 40km with acceptable SNR and total received power. It also indicates that HG mode 01 is more affected by fading compared to HG mode 00 and HG mode 02. The constellations and RF spectrum at the receiver measured at a distance of
Secure Hybrid MDM-OFDM-Ro-FSO International Journal of Sensors, Wireless Communications and Control, 2015, Vol. 5, No. 1 17
(a)
(b)
(c) Fig. (5). RF Spectrum measured at 50km (a) HG 00 Mode (b) HG 01 Mode (c) HG mode 02.
50km under clear weather conditions are shown in Fig. (4) and Fig. (5). It is observed from Fig. 4(a), (b) and (c) that the constellation diagram for the channel propagating HG mode 01 is more distorted compared to the constellation diagrams for the channels carrying HG mode 00 and HG mode 02. Similarly, the RF spectra measured at 50km reported in Fig. 5(a), (b) and (c) shows that the received power for the channel propagating HG 01 mode is less compared to the received power carrying HG mode 00 and HG mode 01 due to multipath fading.
FSO link of 50km under clear weather conditions. From our results, it is concluded that HG mode 01 is more affected by severe multipath fading compared to HG mode 00 and HG mode 01. Under clear weather conditions, the achievable distance for the channel propagating HG mode 00 is 50km compared to the achievable distance by the channels propagating HG mode 01 and HG mode 02 which achieve a distance of 25km and 40km respectively with acceptable SNR and total received power. CONFLICT OF INTEREST
CONCLUSION AND SCOPE FOR FUTURE WORK
The authors confirm that this article content has no conflict of interest.
In this work, mode division multiplexing is adopted for transmitting 3 x 20 Gbps - 40 GHz secure OFDM radio subcarriers using optical HG mode 00, HG mode 01 and HG mode 02 over a
ACKNOWLEDGEMENTS Declared none.
18
International Journal of Sensors, Wireless Communications and Control, 2015, Vol. 5, No. 1
REFERENCES [1]
[2]
[3] [4]
[5]
[6]
[7]
[8]
[9] [10]
[11]
[12]
[13]
Facts and figures. Brahima Sanou, International Telecommunication Union 2013. Avaliable From: http://www.itu.int/en/ITU-D/Statistics/Documents/ facts/ICTFactsFigures2013-e.pdf. Hamed Al-Raweshidy, Shz K. eds. Radio over fiber technologies for mobile communications networks. 1st ed. Artech house universal communication sereise 2002. Chaudhary S, Amphawan A. The role and challenges of free-space optical systems. J Opt Commun 2014; 327-34. Chaudhary S, Amphawan A, Nisar K. Realization of free space optics with OFDM under atmospheric turbulence. Optik - Int J Light and Electron Optics 2014; 125(18): 5196-98. Dat PT, Shah A, Kazaura K, et al. An innovative technology for ubiquitous communication using radio on FSO links. Proceeding of International Conference on Advanced Technologies for Communications; 2008 oct 124-127. Bekkali A, Naila CB, Kazaura K, Wakamori K, Matsumoto M. Transmission analysis of OFDMbased wireless services over turbulent radio-on-FSO links modeled by Gamma–Gamma distribution. IEEE Photon J. 2010; 2(3): 510-20. Djordjevic IB, Vasic B, Neifeld MA. LDPC-coded OFDM for optical communication systems with direct detection. IEEE J Sel Topics Quantum Electron. 2007; 13(5): 1446-54. Cvijetic, Neda, DayouQian, Ting W. 10Gb/s freespace optical transmission using OFDM. Proceeding of Optical Fiber Communication Conference; 2008. Optical Society of America, OFC/NFOEC 2008. Mostafa A, Steve H. In-field demonstration of OFDM-over-FSO. IEEE Photon Technol Lett 2012; 24(8): 709-11. Kolev DR, Wakamori K, Matsumoto M. Transmission analysis of OFDM-based services over line-ofsight indoor infrared laser wireless links. J Lightw Technol 2012; 30(23): 3727-35. Refai HH, SlussJr JJ, Refai HH. The transmission of multiple RF signals in free-space optics using wavelength division multiplexing. Proc. SPIE Atmospheric Propagation II; 2005 May 25;-28; Orlando, Florida, USA: 2005. Carpenter J, Wilkinson TD. All optical modemultiplexing using holography and multimode fiber couplers. J Lightw Technol 2012; 30(12): 1978-84.
Received: October 16, 2014
[14]
[15] [16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
Amphawan et al.
Amphawan A. Holographic mode-selective launch for bandwidth enhancement in multimode fiber. Opt Express 2011; 19(10): 9056-65. Amphawan A. Binary spatial amplitude modulation of continuous transverse modal electric field using a single lens for mode selectivity in multimode fiber. J Mod Opt 2012; 59(5): 460-69. Amphawan A. Binary encoded computer generated holograms for temporal phase shifting. Opt Express 2011; 19(23): 23085-96. Ark SO, Kahn JM, Ho KP. MIMO signal processing for mode-division multiplexing: An overview of channel models and signal processing architectures. IEEE Signal Process Mag 2014; 31(2): 25-34. Ryf R, Randel S, Gnauck AH, et al. Space-division multiplexing over 10 km of three-mode fiber using coherent 6 6 MIMO processing. Proceeding of Optical Fiber Communication Conference, Optical Society of America, IEEE 2011. Amphawan A, Mishrab V, Nisara K, Nedniyomc B. Real-time holographic backlighting positioning sensor for enhanced power coupling efficiency into selective launches in multimode fiber. J Mod Opt 2012; 59(20): 1745-52. Tsekrekos CP, Syvridis D. All-Fiber broadband lp02 mode converter for future wavelength and mode division multiplexing systems. IEEE Photon Technol Lett 2013; 24(18): 1638-41. Amphawan A, Chaudhary S, Chan VWS. 2 x 20 Gbps - 40 GHz OFDM Ro-FSO transmission with mode division multiplexing. Journal of the European Optical Society - Rapid publications 2014; 9 Available at: http://www.jeos.org/index.php/jeos_rp/article/view/1 4041 [Accessed 17 Oct. 2014] Amphawan A, Nedniyom B, Nashwan MA. Samman A. Selective excitation of LP01 mode in multimode fiber using solid-core photonic crystal fiber. J Mood Opt 2014; 60(20): 1675-83. Kaiser T, Flamm D, Schroter S, Duparre M. Complete modal decomposition for optical fibers using CGH-based correlation filters. Opt Express 2009; 17(11): 9347-55. Amphawan A, O'Brien D. Modal decomposition of output field from holographic mode field generation in a multimode fiber channel. Proceedings of the IEEE International Conference on Photonics; 2010 July 5-7; Langkawi: IEEE 2010. Shapira O, Abouraddy AF, Joannopoulos JD, Fink Y. Complete modal decomposition for optical waveguides, Phys Rev Lett 2005; 94(14).
Revised: January 16, 2015
Accepted: March 02, 2015
