The system parameters used to obtain the numerical results are listed in Table
III. The quantum efficiency, average gain, excess noise factor and effective ionization ration of the APDs are η=0.6, G=40, Fe=21and ke=0.5, respectively.
The receiver noise temperature and load resistance are Tn=300K and RL=1030Ω.
The spectrum of the broadband light source is centered at 1.55µm with spectral width Δλ=30nm and coherence time is about τc≈0.267ps. The data transmission rate is 155Mbps and the electrical bandwidth of receivers is 80MHz.
Table III: Parameters used in the numerical calculation
Fig. 17 shows the number of simultaneous users that can be accommodated in the proposed system versus BER for p=7, M=3, and Ps=5dBm. For convenience of
comparison, the numerical results of the OCDMA systems using MQC codes, M-matrices codes, and 2-D perfect difference codes are also shown. As depicted in Fig. 17, the maximum number of simultaneous users that can be accommodated in the proposed system is limited to 147 due to the code size. It is clear that the proposed system can support more simultaneous users than the systems using MQC codes and M-matrices codes. Although the OCDMA system using 2-D perfect difference codes can support more simultaneous users than the proposed system, its BER is much higher and increases rapidly with the number of simultaneous users.
Fig. 17: The number of simultaneous users versus BER for p=7, M=3, and Ps=5dBm.
In Fig. 18, the source power is set to 0dBm. It shows that the OCDMA system using 2-D perfect difference codes has a dramatic performance drop because of insufficient source power.
In Fig. 19, the source power is set to -10dBm. As we can see, the performances of the systems using MQC
codes and M-matrices codes are also degraded to a unusable extent. Only the proposed system can still keep its performance in an acceptable level, i.e.
the BER is smaller than 10-9. In Fig. 8, the source power is set to -15dBm. We can find that the proposed system can still accommodate 147 simultaneous users at BER around10−9.
In Fig. 19, the BER versus the source power is shown at the number of simultaneous users equal to 130. As we can see, the systems using 2-D perfect different codes and the M-matrices codes cannot make BER lower than 10-9 when the source power is below 0dBm.
However, the proposed system can well meet this requirement even when the power is around -15dBm.
According to the numerical results shown in Figs. 17-19, it can be concluded that the proposed system is of much better performance when the optical power is low. In other words, the power demand of the proposed system is much lower than that of other systems.
Fig. 20 shows the BER of the proposed system versus the source power as the number of simultaneous users is 49 and the parameters of the PMP codes are set to (p, M) = (5, 2), (7, 3), (11, 2), or (11, 5). It is easy to find that the proposed system with the setting of (p, M) = (5, 2) needs the least source power to meet the requirement of BER=10-9 while the one with the setting of (p, M) = (11, 5) needs the most. This is because that, when the source power
is fixed, the transmitter of the proposed system using the PMP codes with (p, M)
= (5, 2) causes the least power loss during spectral encoding and thus has the largest output signal power.
As the transmitted digital data is 1, the power loss resulting from spectral encoding can be expressed as
s
loss P
Mp P p ⎟⎟⎠⋅
⎜⎜ ⎞
⎝
⎛ − −
= 21
1 .
In condition that the code length is fixed, i.e. the value of p is fixed, decreasing the value of M can reduce the encoding power loss and thus to reduce the required source power. However, decreasing the value of M will also reduce the code size and hence the number of simultaneous user that can be accommodated in the proposed system is also reduced. Therefore, there is a tradeoff in selection of the value of M.
Fig. 18: The number of simultaneous users versus BER for p=7, M=3, and Ps=0dBm.
Fig. 19: BER versus the source power as the number of simultaneous users is 130.
Fig. 20: BER versus the source power as the number of simultaneous users=49.
二、 計畫成果自評與結論 First, we have investigated the loss behavior of OPS employing PBS mechanism to provide DiffServ under Markovian modeled self-similar traffic input. The computation complexity has been shown to increase cubically as the state of MAP increases. To reduce the
computation complexity, we propose an approximate model for OPS employing PBS mechanism under Markovian modeled self-similar traffic input. Our proposed model is to retain the same high dimensional MAP for high priority traffic, but to reduce the dimension of MAP of low priority traffic following the methods in [24]. By applying the approximate model, it is obvious that the computation complexity is reduced by
8 3 = 512 times while retaining satisfactory accuracy. Accordingly, we investigate and analyze both the short term and long term performance measures. Our model is useful in performing the optimal buffer control for OPS employing PBS to provide differentiated services under self-similar traffic input. With our model and analysis, we could find out the optimal threshold level to obtain the greatest DiffServ performance and the utilization of the buffers simultaneously for OPS employing PBS mechanism under self-similar traffic input. We could also utilize the information of the mean lengths of critical and non-critical periods to be an event trigger mechanism for initializing the related call admission control schemes in OPS to improve the switching performance to greater extent.
Second, we investigate analytically the switching performance of WDM OPS employing wavelength conversion techniques under Markovian modeled self-similar traffic input. We leverage
the results of using MAPs to emulate self-similar traffic and apply them to the investigation of performance analysis of WDM OPS employing wavelength conversion techniques. Our analysis is pretty accurate and can capture the impact of self-similar traffic upon the switching performance of WDM OPS employing wavelength conversion techniques to some extent. We also propose an efficient procedure to avoid large computation efforts in solving the resultant MAP/D/c/K queues and analyze the computation complexity in a concise way. Our analysis holds good and is in line with the conclusions of other investigations made by simulations.
This feature makes our analysis valuable and useful in dimensioning WDM OPS employing wavelength conversion techniques under self-similar traffic input.
Last, we study the Spectral/time OCDMA system employing PDC. This system is applicable to the access network such as PON. In addition, we propose a novel 2-D OCDMA network architecture to further suppress PIIN and lower the demand of source power. In the proposed network architecture, the receivers are divided into p groups. The receivers in each group correspond to one code group of the PMP codes and connect to the outputs of the same star coupler. Since the cross-correlation between any two of the PMP code sequences in the same group is zero, the code sequences assigned to the receivers
in the same group are mutually orthogonal. The transmitters of the proposed network architecture only transmit the spectrally encoded signals to the receivers via the start coupler corresponding to the code group of the adopted code sequence. Hence, the receivers can use the orthogonal property of the code groups of the PMP codes to completely filter out the undesired signals sent from other users.
In this way, the MUI and PIIN caused by other users can be eliminated. Moreover, since the transmitters only need to transmit the spectrally encoded signals to one group of the receivers, the signal power lost in the start coupler can be reduced. Thus, the demand of source power is greatly reduced. According to the numerical results, it is proven that the source power of the proposed system can be much lower than that of the system using MQC codes, M-matrices codes, and 2-D perfect difference codes.
When the parameters of the PMP codes are set to p=7 and M=3, the spectral width is 30nm, and the transmission rate is 155Mbps, the proposed system can still accommodate 147 simultaneous users with the source power equal to –15dBm. Because the proposed system can function well with low source power, it is possible to employ low-cost light-emitting diodes (LEDs) in practical implementation. Moreover, by using the group orthogonal property of PMP codes, the receivers can use a set of FBGs to remove MUI and PIIN
caused by other users. Hence, the complexity of the receivers of the proposed system is lower than that of other non-coherent OCDMA systems.
Therefore, the proposed system can be used to realize a low-cost and high-performance optical access network.
三、 發表之論文
[1] Chun-Yang Chen, Chih-How Chang, Malla Reddy Perati, Shou-Kuo Shao , Jingshown Wu, ” Performance Analysis of WDM Optical Packet Switches Employing Wavelength Conversion under Markovian Modeled Self-Similar Traffic Input”, HPSR Conference, Thursday, May 31, 2007, New York, USA
[2] Chih-How Chang, Malla Reddy Perati, Shou-Kuo Shao , Jingshown Wu,” An Efficient Approximate Markovian Model for Optical Packet Switches Employing Partial Buffer Sharing Mechanism under Self-Similar Traffic Input”, HPSR Conference, Thursday, May 31, 2007, New York USA
[3] Chih-How Chang, Shou- Kuo Shao, Malla Reddy Perati and J. Wu,
“Performance Study of Various Packet Scheduling Algorithms of Variable-Packet-Length Feedback Type WDM Optical Packet Switches”, Proceeding of the Workshop on High Performance Switching and Routing, June 2006, Poznan, Poland
[4] C. H. Lin and J. Wu, “Comments on
"Novel Combinatorial Constructions of Optical Orthogonal Codes for
Incoherent Optical CDMA Systems,”
IEEE Journal of Lightwave Technology, Vol. 24, No. 2, PP. 1064, Feb. 2006 [5] Yen-Chun Liao, Chia-Chu Ho, Hen-Wai Tsao, and Jingshown Wu,
“Design and Experimental Demonstration of a Synchronous OCDMA-Based 10Gbps/1.25Gbps EPON with a Novel Synchronization Scheme”, Journal of Selected Topics in Quantum Electronics, Submitted
[6] Wen-Jeng Huang, Cheing-hong Lin, and Jingshown Wu, “Spatial/Spectral OCDMA System Using Partial Modified Prime Code and Error Correcting Code”, JLT, Submitted
[7]Chun-tao Niu, Cheing-hong Lin, and Jingshown Wu, “Novel Architecture of Non-coherent Spectral/Spatial OCDMA System Using Partial Modified Prime Codes”, JLT, Submitted
[8] Chih-How Chang, Meng-Guang Tsai, Shou-Kuo Shao, Hen-Wai Tsao, Malla Reddy Perati and J. Wu, “An Efficient Void Filling Algorithm for WDM Optical Packet Switches Operating
under Variable-Packet-Length Self-Similar Traffic,” IEICE Transaction
on Communications, Vol. E88-B, No. 12, PP. 4659-4663, Dec. 2005
[9] F. R. Gu and J. Wu, “Construction of Two-Dimensional Wavelength/Time Optical Orthogonal Codes Using Difference Family,” IEEE Journal of Lightwave Technology, Vol. 23, No. 11, PP. 3642-3652, Nov. 2005
[10] C. H. Lin, J. Wu, H. W. Tsao, and C.
L. Yang, “Spectral Amplitude-Coding Optical CDMA System Using Mach-Zehnder Interferometers,” IEEE Journal of Lightwave Technology, Vol.
23, No. 4, PP. 1543-1555, Apr. 2005 [11] Shou-Kuo Shao, Malla Reddy Perati, Meng-Guang Tsai, Hen-Wai Tsao, and J. Wu, “Generalized Variance-Based Markovian Fitting for Self-Similar Traffic Modelling,” IEICE Transaction on Communications, Vol. E88-B, No. 4, PP. 1493-1502, Apr. 2005
[12] Shou-Kuo Shao, Meng-Guang Tsai, Hen-Wai Tsao, Paruvelli Sreedevi, Malla Reddy Perati, and J. Wu, “Performance evaluation of feedback Type WDM optical routers under asynchronous and variable packet length self-similar traffic,” IEICE Transaction on Communications, Vol. E88-B, No. 3, PP.
1072-1083, Mar. 2005
[13] F. R. Gu and J. Wu, “Construction and Performance Analysis of variable-Weight optical Orthogonal Codes for Asynchronous Optical CDMA Systems,” IEEE Journal of Lightwave Technology, Vol. 23, No. 2, PP. 740-748, Feb. 2005
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