- Email: [email protected]
s optical CDMA over FSO communication system
G Model IJLEO-54485; No. of Pages 5
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
2.50 Gbit/s optical CDMA over FSO communication system Naresh Kumar a,∗ , Trilok Singh b a b
National Institute of Technology, Hamirpur, Himachal Pradesh, India Institute of Inorganic and Materials Chemistry, University of Cologne, D-50939, Germany
a r t i c l e
i n f o
Article history: Received 10 August 2013 Accepted 20 February 2014 Available online xxx Keywords: Optical code division multiple access (OCDMA) Free space optics (FSO) Bit error rate (BER) Pseudo orthogonal (PSO) Multi-access interference (MAI)
a b s t r a c t Optical CDMA over FSO communication system is very effective to provide high data rate transmission with very low bit error rate and low amount of multiple access interference. In this paper, we have presented optical CDMA over FSO communication system to the range of 8000 m. The simulative results reveal that the transmission distance is limited mainly by the multi-access interference (MAI) which arises when there are number of users in the system because of the fact that one user data becomes noisy for all other users in the channel. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Free space optics (FSO) communication have some distinct advantages over conventional microwave and optical fiber communication by virtue of their high carrier frequencies that permit large capacity, enhanced security and high data rate [1]. FSO is an optical communication technology that uses light propagating in free space to transmit data between two points. The technology is useful where the physical connection by the means of fiber optic cables is impractical [2,3]. FSO communication can be used in many optical links such as building-to-building, ship-to-ship, aircraft-to-ground and satellite-to-ground. In recent years, CDMA has become a very popular communication system for wireless mobile communication system for the reason of its high bit rate transmission, security, very low bit error rate and increased amount of system capacity. The use of CDMA in fiber optic communication has also become very popular for above reasons. Recently, performance evaluation of CDMA in optical terrestrial fiber is reported [4]. Now a very intelligent integration of FSO and optical CDMA is proposed and this is optical CDMA–FSO communication system [5]. Optical CDMA–FSO communication system is very effective to provide high data rate transmission with very low bit error rate and low amount of multiple access interference. A new optical CDMA time-diversity scheme could enhance the BER for several orders in strong turbulence have been presented and new scheme in strong turbulence was better
∗ Corresponding author. E-mail address: [email protected] (N. Kumar).
than the traditional scheme in normal turbulence [6]. In this paper we propose the simulative optical CDMA transmitter and receiver with free space optical communication reported in Section 2. The simulation results have been discussed in Section 3. The conclusion of our simulative results is presented in Section 4.
2. System description In the proposed optical CDMA over FSO communication system (Fig. 1), 2.50 Gbps data signal is generated with NRZ modulation. The 2.50 Gbps NRZ data signal is then modulated by means of MZM modulator and then transmitted over FSO by means of a four mode-lock lasers used to create a dense WDM multi-frequency light source of 3 mW operating at 1550.0–1551.2 nm. Then optical CDMA signal is transmitted over FSO. Here we are using 16 OC48 users requiring 16 distinct signature codes. Pseudo orthogonal (PSO) matrix codes [7] are popular for OCDMA applications primarily because they retain the correlation advantages of PSO linear sequences while reducing the need for bandwidth expansion. PSO matrix codes also generate a larger code set. An interesting variation is described in [8] where some of the wavelength/time (W/T) matrix codes can permit extensive wavelength reuse and some can allow extensive time-slot reuse. In this model, an extensive timeslot reuse sequence is used for User 1 (1 3 ; 0; 2 4 ; 0). There are four time slots used without any guard-band giving the chip period of 100 ps. At the base station, PSO code is retrieved using decoder and then optical signal is converted into electrical through APD and 2.50 Gbps optical CDMA data are recovered successfully.
http://dx.doi.org/10.1016/j.ijleo.2014.02.011 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model
ARTICLE IN PRESS
IJLEO-54485; No. of Pages 5
N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx
2 User 1
x10 3
Mach Zehnder Modulator
NRZ Modulator
Encoder Using PSO code
EDFA
Power (W)
PRBS Generator
Wavelength1
Mode-locked LASER Wavelength2
...
Optical Multiplexer
Mode-locked LASER Wavelength 4
Mode-locked LASER
1
...
Mode-locked LASER Wavelength 3
. . . . .
2
Optical Combiner
0 1547
1548
1549
1550
1551
1552
1553
1554 x10
Wavelength (m)
(a)
x10
User 16
6
NRZ Modulator
Encoder Using PSO code
5
EDFA
Power (W)
PRBS Generator
Mach Zehnder Modulator
Optical CDMA Tx FSO Channel
4 3 2
User 1 1
Decoder using PSO code
APD
BER Tester
0 1547
1548
1549
1550
1551
1552
1553
Wavelength (m)
.....
(b)
x10 7 6
User 16 Decoder using PSO code
APD
BER Tester
Opcal CDMA Rx
Power (W)
...
Optical splitter
1554 x10
5 4 3 2 1
Fig. 1. Simulation setup of optical CDMA over FSO communication system.
0 1547
1548
1549
1550
1551
Wavelength (m)
1552
1553
1554 x10
(c) 3. Results and discussion The analysis performed by observing three cases: case (I) described the analysis of optical CDMA over FSO communication system with NRZ and RZ modulation, case (II) investigated different parameters on optical CDMA over FSO communication system and case (III) gave us impact of MAI in optical CDMA over FSO communication system.
3.1. Case I. Performance investigations in optical CDMA over FSO communication system with NRZ and RZ modulation The parameters used in this case are data rate = 2.50 Gbps, aperture area = 180 cm2 , transmitted power = 3 mW, sigma add = 1.9, divergence angle = 0.25 mrad. Fig. 3(a) and (b) indicates the graph between Q value versus the transmission distance at NRZ and RZ. From results it has been observed that there is significant decrease in the value of Q factor which lies within [12.5 and 6.5] and [10.4 and 3] for transmission distance of 1000–8000 m in case of NRZ and RZ modulation, respectively. In case of BER, it has been observed that there is significant increase in the value of BER, which lies within [10−40 –10−9 ] and [10−26 –10−3 ] for transmission distance from 1000 to 8000 m in case of NRZ and RZ modulation, respectively.
Fig. 2. (a) Optical spectrum after WDM, (b) optical CDMA after coder and (c) optical CDMA after decoder.
3.2. Case II. Performance analysis of different parameter in optical CDMA over FSO communication system Fig. 4(a) and (b) indicates the graph between Q values versus the transmission distance at different transmitter power. From results it has been observed that there is significant decrease in the value of Q factor which lies within [11.3, 11, 10.8 and 10.5] and [5, 4, 3, and 1] for transmission distance of 1000–8000 m in case of 4 mW, 3 mW, 2 mW and 1 mW, respectively. In other case BER, from result it has been observed that there is significant increase in the value of BER, which lies within [10−26 , 10−27 , 10−28 , and 10−29 ] and [10−1 , 10−3 , 10−5 , and 10−6 ] for transmission distance from 1000 to 8000 m in case of 4 mW, 3 mW, 2 mW and 1 mW, respectively. Fig. 5(a) and (b) indicates the graph between Q value versus the transmission distance at different additional attenuation. From results it has been observed that there is significant decrease in the value of Q factor which lies within [11.2, 11 and 10.8] and [5.5, 4.5 and 2] for transmission distance from 1000 to 8000 m in case of −3 dBm, −5 dBm, −7 dBm, respectively. In other case BER, from result it has been observed that there is significant increase in the value of BER, which lies within [10−28 , 10−27 and 10−26 ] and [10−7 , 10−4 and 10−2 ] for transmission distance from 1000 to 8000 m in case of −3 dBm, −5 dBm, −7 dBm, respectively.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model IJLEO-54485; No. of Pages 5
ARTICLE IN PRESS N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx
3
Fig. 3. (a) Evaluation of Q value versus distance with NRZ and RZ and (b) evaluation of BER versus distance with NRZ and RZ.
Fig. 5. (a) Evaluation of Q value versus distance with different additional attenuation and (b) evaluation of BER versus distance with different additional attenuation.
Fig. 6(a) and (b) indicates the graph between Q value versus the transmission distance at different beam divergence. From results it has been observed that there is significant decrease in the value of Q factor which lies within [11, 10.2, 9.5 and 8] and [4.5, 1, 0, 0] for transmission distance from 1000 to 8000 m in case of 0.25 mrad, 0.50 mrad, 0.75 mrad and 1 mrad, respectively. In other case BER, from results it has been observed that there is significant increase in the value of BER, which lies within [10−30 , 10−27 , 10−23 and 10−20 ] and [10−6 , 10−2 , 10−2 and 10−1 ] for transmission distance from 1000 to 8000 m in case of 0.25 mrad, 0.50 mrad, 0.75 mrad and 1 mrad, respectively. 3.3. Case III. Impact of MAI in optical CDMA over FSO communication system
Fig. 4. (a) Evaluation of Q value versus distance with different power and (b) evaluation of BER versus distance with different power.
The crosstalk between different users sharing the common FSO channel known as multiple access interface is usually the dominant source of bit errors in an optical CDMA over FSO communication system [9,10]. Further, Fig. 7(a) and (b) indicates the graph between Q values and BER versus the transmission distance with and without MAI in optical CDMA over FSO system. From result it has been observed that there is significant decrease in the value of Q factor which lies within 12.5–6 in without MAI, 11–6.5 in with MAI at two users and 9–6 in with MAI at three users in the length of 1000–8000 m. In other case BER, from result it has been observed that there is significant increase in the value of BER, which lies within 10–35 to 10–9 in without MAI, 10−30 –10−10 in with MAI at two users and 10−18 –10−9 in with MAI at three users in the length of 1000–8000 m.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model IJLEO-54485; No. of Pages 5 4
ARTICLE IN PRESS N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx Eye Diagram x10-4
Signal (V)
2
1
0 0
1
2
3
4
5
6
7
8 x10-10
Time (s)
(a) Eye Diagram
x10-5 6 5
Signal (V)
4 3 2 1 0 0
Fig. 6. (a) Evaluation of Q value versus distance with different beam divergence and (b) evaluation of BER versus distance with different beam divergence.
1
2
3
4
5
6
7
8 x10-10
Time (s)
(b) lstmpEye Eye Diagram
x10-5 5 4
Signal (V)
3 2 1 0 0
1
2
3
4
5
6
7
8 x10-10
Time (s)
(c) Fig. 8. Eye diagram of received signal for single user taking NRZ signal: (a) without MAI at single user, (b) with MAI at two users, and (c) with MAI at three users.
The eye diagrams for single, double and three users are shown in Fig. 8(a–c). It has been observed that the efficiency of the system is degraded with the increase of users. Thus it is established that MAI play detrimental role in optical CDMA over FSO communication system. 4. Conclusion
Fig. 7. (a) Evaluation of Q value versus distance without and with MAI and (b) evaluation of BER versus distance without and with MAI.
The design of an optical CDMA over FSO communication system at data rate of 2.5 Gbps for 8000 m length is presented. Performance investigation on this designed optical CDMA over FSO was carried out using NRZ and RZ modulation for comparative study, with different parameters and with and without MAI. It is concluded that NRZ give us better performance as compare to RZ in optical CDMA over FSO communication system. Further transmission range also
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model IJLEO-54485; No. of Pages 5
ARTICLE IN PRESS N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx
increases with the increase in transmitter power. However, transmission range increases with the decreasing factor of attenuation and beam divergence in OCDMA over FSO communication system. It is also concluded that the efficiency of OCDMA over FSO communication system is degraded by increasing number of users. References [1] H. Willebrand, B.S. Ghuman, Free Space Optics: Enabling Optical Connectivity in Today’s Network, SAMS publishing, Indianapolis, 2002. [2] P.A. Humblet, On the bit error rate of light wave systems with optical amplifiers, J. Lightwave Technol. 9 (1991) 1576–1582. [3] N. Kumar, A.K. Sharma, V. Kapoor, Performance evaluation of free space optics communication system in the presence of forward error correction techniques, Opt. Commun. 32 (2011) 243–245. [4] S.P. Majumder, A. Azhari, F.M. Abbou, Impact of fiber chromatic dispersion on the BER performance of an optical CDMA IM/DD transmission system, IEEE Photon. Technol. Lett. 17 (2005) 1340–2134.
5
[5] T.A. Bhuiyan, S.H. Choudhury, A.R. Asif, S.P. Majumder, Performance analysis of a free space optical code division multiple access through atmospheric turbulence channel, in: Proceedings of ICCIT, World Academy of Science Engineering and Technology, vol. 56, 2009, pp. 283–286. [6] P. Liu, X. Wu, K. Wakamori, T.D. Pham, M.S. Alam, M. Matsumoto, Bit error rate performance analysis of optical CDMA time-diversity links over gamma–gamma atmospheric turbulence channels, in: Proceeding of IEEE Wireless Communications and Networking Conference (WCNC 2011), Cancun, Mexico, 2011, pp. 1932–1936. [7] A.J. Mendez, R.M. Gagliardi, H.X.C. Feng, J.P. Heritage, J.M. Morookian, Strategies for realizing optical CDMA for dense, high-speed, long span, optical network applications, IEEE J. Lightwave Technol. 18 (2000) 1685–1697. [8] A.J. Mendez, R.M. Gagliardi, V.J. Hernandez, C.V. Bennett, W.J. Lennon, Design and performance analysis of wavelength/time (W/T) matrix codes for optical CDMA, IEEE J. Lightwave Technol. 21 (2003) 2524–2533. [9] D. Sahoo, N. Kumar, D.R. Rana, 2.50 Gbps optical CDMA transmission system, Int. J. Comput. Appl. 72 (21) (2013) 20–24. [10] C.-C. Yang, J.-F. Huang, S.-P. Tseng, Optical CDMA network codes structured with M-sequence codes over waveguide-grating routers, IEEE Photon. Technol. Lett. 16 (2004) 641–643.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
2.50 Gbit/s optical CDMA over FSO communication system Naresh Kumar a,∗ , Trilok Singh b a b
National Institute of Technology, Hamirpur, Himachal Pradesh, India Institute of Inorganic and Materials Chemistry, University of Cologne, D-50939, Germany
a r t i c l e
i n f o
Article history: Received 10 August 2013 Accepted 20 February 2014 Available online xxx Keywords: Optical code division multiple access (OCDMA) Free space optics (FSO) Bit error rate (BER) Pseudo orthogonal (PSO) Multi-access interference (MAI)
a b s t r a c t Optical CDMA over FSO communication system is very effective to provide high data rate transmission with very low bit error rate and low amount of multiple access interference. In this paper, we have presented optical CDMA over FSO communication system to the range of 8000 m. The simulative results reveal that the transmission distance is limited mainly by the multi-access interference (MAI) which arises when there are number of users in the system because of the fact that one user data becomes noisy for all other users in the channel. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Free space optics (FSO) communication have some distinct advantages over conventional microwave and optical fiber communication by virtue of their high carrier frequencies that permit large capacity, enhanced security and high data rate [1]. FSO is an optical communication technology that uses light propagating in free space to transmit data between two points. The technology is useful where the physical connection by the means of fiber optic cables is impractical [2,3]. FSO communication can be used in many optical links such as building-to-building, ship-to-ship, aircraft-to-ground and satellite-to-ground. In recent years, CDMA has become a very popular communication system for wireless mobile communication system for the reason of its high bit rate transmission, security, very low bit error rate and increased amount of system capacity. The use of CDMA in fiber optic communication has also become very popular for above reasons. Recently, performance evaluation of CDMA in optical terrestrial fiber is reported [4]. Now a very intelligent integration of FSO and optical CDMA is proposed and this is optical CDMA–FSO communication system [5]. Optical CDMA–FSO communication system is very effective to provide high data rate transmission with very low bit error rate and low amount of multiple access interference. A new optical CDMA time-diversity scheme could enhance the BER for several orders in strong turbulence have been presented and new scheme in strong turbulence was better
∗ Corresponding author. E-mail address: [email protected] (N. Kumar).
than the traditional scheme in normal turbulence [6]. In this paper we propose the simulative optical CDMA transmitter and receiver with free space optical communication reported in Section 2. The simulation results have been discussed in Section 3. The conclusion of our simulative results is presented in Section 4.
2. System description In the proposed optical CDMA over FSO communication system (Fig. 1), 2.50 Gbps data signal is generated with NRZ modulation. The 2.50 Gbps NRZ data signal is then modulated by means of MZM modulator and then transmitted over FSO by means of a four mode-lock lasers used to create a dense WDM multi-frequency light source of 3 mW operating at 1550.0–1551.2 nm. Then optical CDMA signal is transmitted over FSO. Here we are using 16 OC48 users requiring 16 distinct signature codes. Pseudo orthogonal (PSO) matrix codes [7] are popular for OCDMA applications primarily because they retain the correlation advantages of PSO linear sequences while reducing the need for bandwidth expansion. PSO matrix codes also generate a larger code set. An interesting variation is described in [8] where some of the wavelength/time (W/T) matrix codes can permit extensive wavelength reuse and some can allow extensive time-slot reuse. In this model, an extensive timeslot reuse sequence is used for User 1 (1 3 ; 0; 2 4 ; 0). There are four time slots used without any guard-band giving the chip period of 100 ps. At the base station, PSO code is retrieved using decoder and then optical signal is converted into electrical through APD and 2.50 Gbps optical CDMA data are recovered successfully.
http://dx.doi.org/10.1016/j.ijleo.2014.02.011 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model
ARTICLE IN PRESS
IJLEO-54485; No. of Pages 5
N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx
2 User 1
x10 3
Mach Zehnder Modulator
NRZ Modulator
Encoder Using PSO code
EDFA
Power (W)
PRBS Generator
Wavelength1
Mode-locked LASER Wavelength2
...
Optical Multiplexer
Mode-locked LASER Wavelength 4
Mode-locked LASER
1
...
Mode-locked LASER Wavelength 3
. . . . .
2
Optical Combiner
0 1547
1548
1549
1550
1551
1552
1553
1554 x10
Wavelength (m)
(a)
x10
User 16
6
NRZ Modulator
Encoder Using PSO code
5
EDFA
Power (W)
PRBS Generator
Mach Zehnder Modulator
Optical CDMA Tx FSO Channel
4 3 2
User 1 1
Decoder using PSO code
APD
BER Tester
0 1547
1548
1549
1550
1551
1552
1553
Wavelength (m)
.....
(b)
x10 7 6
User 16 Decoder using PSO code
APD
BER Tester
Opcal CDMA Rx
Power (W)
...
Optical splitter
1554 x10
5 4 3 2 1
Fig. 1. Simulation setup of optical CDMA over FSO communication system.
0 1547
1548
1549
1550
1551
Wavelength (m)
1552
1553
1554 x10
(c) 3. Results and discussion The analysis performed by observing three cases: case (I) described the analysis of optical CDMA over FSO communication system with NRZ and RZ modulation, case (II) investigated different parameters on optical CDMA over FSO communication system and case (III) gave us impact of MAI in optical CDMA over FSO communication system.
3.1. Case I. Performance investigations in optical CDMA over FSO communication system with NRZ and RZ modulation The parameters used in this case are data rate = 2.50 Gbps, aperture area = 180 cm2 , transmitted power = 3 mW, sigma add = 1.9, divergence angle = 0.25 mrad. Fig. 3(a) and (b) indicates the graph between Q value versus the transmission distance at NRZ and RZ. From results it has been observed that there is significant decrease in the value of Q factor which lies within [12.5 and 6.5] and [10.4 and 3] for transmission distance of 1000–8000 m in case of NRZ and RZ modulation, respectively. In case of BER, it has been observed that there is significant increase in the value of BER, which lies within [10−40 –10−9 ] and [10−26 –10−3 ] for transmission distance from 1000 to 8000 m in case of NRZ and RZ modulation, respectively.
Fig. 2. (a) Optical spectrum after WDM, (b) optical CDMA after coder and (c) optical CDMA after decoder.
3.2. Case II. Performance analysis of different parameter in optical CDMA over FSO communication system Fig. 4(a) and (b) indicates the graph between Q values versus the transmission distance at different transmitter power. From results it has been observed that there is significant decrease in the value of Q factor which lies within [11.3, 11, 10.8 and 10.5] and [5, 4, 3, and 1] for transmission distance of 1000–8000 m in case of 4 mW, 3 mW, 2 mW and 1 mW, respectively. In other case BER, from result it has been observed that there is significant increase in the value of BER, which lies within [10−26 , 10−27 , 10−28 , and 10−29 ] and [10−1 , 10−3 , 10−5 , and 10−6 ] for transmission distance from 1000 to 8000 m in case of 4 mW, 3 mW, 2 mW and 1 mW, respectively. Fig. 5(a) and (b) indicates the graph between Q value versus the transmission distance at different additional attenuation. From results it has been observed that there is significant decrease in the value of Q factor which lies within [11.2, 11 and 10.8] and [5.5, 4.5 and 2] for transmission distance from 1000 to 8000 m in case of −3 dBm, −5 dBm, −7 dBm, respectively. In other case BER, from result it has been observed that there is significant increase in the value of BER, which lies within [10−28 , 10−27 and 10−26 ] and [10−7 , 10−4 and 10−2 ] for transmission distance from 1000 to 8000 m in case of −3 dBm, −5 dBm, −7 dBm, respectively.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model IJLEO-54485; No. of Pages 5
ARTICLE IN PRESS N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx
3
Fig. 3. (a) Evaluation of Q value versus distance with NRZ and RZ and (b) evaluation of BER versus distance with NRZ and RZ.
Fig. 5. (a) Evaluation of Q value versus distance with different additional attenuation and (b) evaluation of BER versus distance with different additional attenuation.
Fig. 6(a) and (b) indicates the graph between Q value versus the transmission distance at different beam divergence. From results it has been observed that there is significant decrease in the value of Q factor which lies within [11, 10.2, 9.5 and 8] and [4.5, 1, 0, 0] for transmission distance from 1000 to 8000 m in case of 0.25 mrad, 0.50 mrad, 0.75 mrad and 1 mrad, respectively. In other case BER, from results it has been observed that there is significant increase in the value of BER, which lies within [10−30 , 10−27 , 10−23 and 10−20 ] and [10−6 , 10−2 , 10−2 and 10−1 ] for transmission distance from 1000 to 8000 m in case of 0.25 mrad, 0.50 mrad, 0.75 mrad and 1 mrad, respectively. 3.3. Case III. Impact of MAI in optical CDMA over FSO communication system
Fig. 4. (a) Evaluation of Q value versus distance with different power and (b) evaluation of BER versus distance with different power.
The crosstalk between different users sharing the common FSO channel known as multiple access interface is usually the dominant source of bit errors in an optical CDMA over FSO communication system [9,10]. Further, Fig. 7(a) and (b) indicates the graph between Q values and BER versus the transmission distance with and without MAI in optical CDMA over FSO system. From result it has been observed that there is significant decrease in the value of Q factor which lies within 12.5–6 in without MAI, 11–6.5 in with MAI at two users and 9–6 in with MAI at three users in the length of 1000–8000 m. In other case BER, from result it has been observed that there is significant increase in the value of BER, which lies within 10–35 to 10–9 in without MAI, 10−30 –10−10 in with MAI at two users and 10−18 –10−9 in with MAI at three users in the length of 1000–8000 m.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model IJLEO-54485; No. of Pages 5 4
ARTICLE IN PRESS N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx Eye Diagram x10-4
Signal (V)
2
1
0 0
1
2
3
4
5
6
7
8 x10-10
Time (s)
(a) Eye Diagram
x10-5 6 5
Signal (V)
4 3 2 1 0 0
Fig. 6. (a) Evaluation of Q value versus distance with different beam divergence and (b) evaluation of BER versus distance with different beam divergence.
1
2
3
4
5
6
7
8 x10-10
Time (s)
(b) lstmpEye Eye Diagram
x10-5 5 4
Signal (V)
3 2 1 0 0
1
2
3
4
5
6
7
8 x10-10
Time (s)
(c) Fig. 8. Eye diagram of received signal for single user taking NRZ signal: (a) without MAI at single user, (b) with MAI at two users, and (c) with MAI at three users.
The eye diagrams for single, double and three users are shown in Fig. 8(a–c). It has been observed that the efficiency of the system is degraded with the increase of users. Thus it is established that MAI play detrimental role in optical CDMA over FSO communication system. 4. Conclusion
Fig. 7. (a) Evaluation of Q value versus distance without and with MAI and (b) evaluation of BER versus distance without and with MAI.
The design of an optical CDMA over FSO communication system at data rate of 2.5 Gbps for 8000 m length is presented. Performance investigation on this designed optical CDMA over FSO was carried out using NRZ and RZ modulation for comparative study, with different parameters and with and without MAI. It is concluded that NRZ give us better performance as compare to RZ in optical CDMA over FSO communication system. Further transmission range also
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011
G Model IJLEO-54485; No. of Pages 5
ARTICLE IN PRESS N. Kumar, T. Singh / Optik xxx (2014) xxx–xxx
increases with the increase in transmitter power. However, transmission range increases with the decreasing factor of attenuation and beam divergence in OCDMA over FSO communication system. It is also concluded that the efficiency of OCDMA over FSO communication system is degraded by increasing number of users. References [1] H. Willebrand, B.S. Ghuman, Free Space Optics: Enabling Optical Connectivity in Today’s Network, SAMS publishing, Indianapolis, 2002. [2] P.A. Humblet, On the bit error rate of light wave systems with optical amplifiers, J. Lightwave Technol. 9 (1991) 1576–1582. [3] N. Kumar, A.K. Sharma, V. Kapoor, Performance evaluation of free space optics communication system in the presence of forward error correction techniques, Opt. Commun. 32 (2011) 243–245. [4] S.P. Majumder, A. Azhari, F.M. Abbou, Impact of fiber chromatic dispersion on the BER performance of an optical CDMA IM/DD transmission system, IEEE Photon. Technol. Lett. 17 (2005) 1340–2134.
5
[5] T.A. Bhuiyan, S.H. Choudhury, A.R. Asif, S.P. Majumder, Performance analysis of a free space optical code division multiple access through atmospheric turbulence channel, in: Proceedings of ICCIT, World Academy of Science Engineering and Technology, vol. 56, 2009, pp. 283–286. [6] P. Liu, X. Wu, K. Wakamori, T.D. Pham, M.S. Alam, M. Matsumoto, Bit error rate performance analysis of optical CDMA time-diversity links over gamma–gamma atmospheric turbulence channels, in: Proceeding of IEEE Wireless Communications and Networking Conference (WCNC 2011), Cancun, Mexico, 2011, pp. 1932–1936. [7] A.J. Mendez, R.M. Gagliardi, H.X.C. Feng, J.P. Heritage, J.M. Morookian, Strategies for realizing optical CDMA for dense, high-speed, long span, optical network applications, IEEE J. Lightwave Technol. 18 (2000) 1685–1697. [8] A.J. Mendez, R.M. Gagliardi, V.J. Hernandez, C.V. Bennett, W.J. Lennon, Design and performance analysis of wavelength/time (W/T) matrix codes for optical CDMA, IEEE J. Lightwave Technol. 21 (2003) 2524–2533. [9] D. Sahoo, N. Kumar, D.R. Rana, 2.50 Gbps optical CDMA transmission system, Int. J. Comput. Appl. 72 (21) (2013) 20–24. [10] C.-C. Yang, J.-F. Huang, S.-P. Tseng, Optical CDMA network codes structured with M-sequence codes over waveguide-grating routers, IEEE Photon. Technol. Lett. 16 (2004) 641–643.
Please cite this article in press as: N. Kumar, T. Singh, 2.50 Gbit/s optical CDMA over FSO communication system, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.011