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A new programmable AWG-Based spectral phase coding OCDMA scheme with changing phase state mechanism is configured over a fiber-to-the-home (FTTH) network. In order to improve BER and confidentiality of conventional spectral phase coding (SPC) OCDMA scheme, the proposed scheme employ complementary SPC code with Hadamard code as signature address cod...
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... the numerical results, we use the following parameters: ΔV = 2 THz ( the pulse duration of ultrafast mode lock laser τ c is equivalent to 500 fs), optical frequency f =1.9 x 10 14 Hz, the quantum efficiency of the photodetector η= 0.9, P sr = -10dBm, the bandwidth of the photodetector B p =10 GHz. As shown in Fig.4-1, BER gets worse as simultaneous users K increase. The proposed scheme adopting complementary keying improves bit error rate 260 times than the ones adopting on-off keying when K=15, and the system can supports more 9 simultaneous active users than conventional scheme under BER is 10 -5 . In the proposed scheme complementary Walsh-Hadamard code, when data bit is "1", a spectrally encoded pulse is sent; while data bit "0", we send its complement pulse. On the encoded pulse is sent only when data bit is "1". According to the Eq. (4-28), the relation between the SNR and the number of active users is shown in Fig. 4-2. Fig. 4-2. SNR versus number of number of simultaneous ...
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... critical disadvantage of TDM-EPON is a possible security threat [23] over FTTH access network, when all Ethernet frames in the downstream direction are received by each ONU. Security is a very weak part of TDM-EPON because has a broadcasting transmission in downstream channel. To enhance confidentiality of information to ensure subscriber privacy is necessary. Therefore, TDM-EPON does not seem to satisfy the secure and high-capacity FTTH access network in the future. Fig. 1-3. Upstream transmission in ...
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... the programmable complementary SPC code have been constructed in previous section, the proposed changing phase state mechanism is adopted for assigning the initial state and various shifting step to each ONU user dynamically. Fig.3-1 shows the relationship between the phase shifts and the states of the input voltage controller for the programmable SLM with three authorized ONUs. Given the unit value of phase shifts θ from 0 to π, the states of the input voltage controller S β and the shift step T s =｛-(β-1), -β, ..., 0,..., β, β−1｝for each phase shifts. The phase codeword in the different state of each user described above and the value of T s is determined based on the distance between the current phase state S β and the next phase state S β '. Fig.3-1 For example, the proposed phase codeword with different phase state are shown in Table 3-1 and Table 3-2, we assume that the shift step T s = 1 and initial phase state is S 1 , the current phase state changes from S 1 to S 2 , the ONU #1 codeword is changed from , C S P = (π, 0, π, 0) to 1 2 , C S P = (5π/4, π/4, 5π/4, ...
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... the programmable complementary SPC code have been constructed in previous section, the proposed changing phase state mechanism is adopted for assigning the initial state and various shifting step to each ONU user dynamically. Fig.3-1 shows the relationship between the phase shifts and the states of the input voltage controller for the programmable SLM with three authorized ONUs. Given the unit value of phase shifts θ from 0 to π, the states of the input voltage controller S β and the shift step T s =｛-(β-1), -β, ..., 0,..., β, β−1｝for each phase shifts. The phase codeword in the different state of each user described above and the value of T s is determined based on the distance between the current phase state S β and the next phase state S β '. Fig.3-1 For example, the proposed phase codeword with different phase state are shown in Table 3-1 and Table 3-2, we assume that the shift step T s = 1 and initial phase state is S 1 , the current phase state changes from S 1 to S 2 , the ONU #1 codeword is changed from , C S P = (π, 0, π, 0) to 1 2 , C S P = (5π/4, π/4, 5π/4, ...
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... TDM is the most popular method being considered for building an EPON infrastructure to provide FTTx services. In the downstream direction, Ethernet frames are transmitted by OLT pass through a 1: N optical splitter and reach each ONU. All of frames are broadcasted by the OLT and extracted by their destination ONU based on the media access control (MAC) address shown as Fig. ...
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... the upstream direction, signals are generated by different ONUs and they are mixed in an N: 1 optical combiner shown as Fig. 1-3. If one more than one packet arrive at the OLT simultaneously, each ONU transmits packets to the OLT and may collide with other packets. In order to avoid collisions problem, each ONU only transmits optical packet when it is allocated a time slot and it needs to transmit, and all ONUs share the upstream channel. Note that the TDM-EPON also prevents collision between downstream and upstream packets, by using 1310 nm for upstream transmission and 1550 nm for downstream transmission, ...
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... important issue is to reduce packets collision among all ONUs and realize high-speed transmission in the EPON. Both TDM and WDM are conventional systems adopted to overcome such collision problems in access network, but these systems have some limitation and weakness [27], such as TDM-EPON requires a tight control on synchronization, and WDM-EPON needs a tight control on wavelength. The OCDMA scheme is another potential multiplexing method over EPON (i.e., so-called CDM-EPON) [23]. CDM-EPON provides another dimension for multiple accesses, integrate time with optical wavelength (spectrum) domains as seen in Fig. 1-5. In the downstream traffic, each subscriber is assigned a unique signature address codes for transmission at any time. At the receiver, all the overlapping codes are detected using a single receiver and implement optical correlation processes of the underlined coding pattern. The desired data bit of each ONU then is obtained via a balanced photo-detector. Therefore, the proposed scheme will avoid the unpacking time of MAC packet coming from different ONUs, the wavelength drifts due to temperature fluctuations could be controlled entirely through the use of robust ...
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... clear explanation, we assume that code length N=8, the signature sequence for the second user is C 2 = (1, 1,-1,-1,1,1,-1,-1) and its equivalent phase code with current phase state is 2, 1 C S P = (π, π, 0, 0, π, π, 0, 0), we assume that the duration of ultrashort pulse τ c =400fs, the total bandwidth W=1.568x10 13 rad/s, and we normalized the highest amplitude of ultrashort pulse as one in the figure for clearly expression. As shown in Fig.3-4, the relation between ultrashort laser pulse and encoded signal waveform are presented in time domain. ...
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... following evaluations in Chapter 4, the proposed programmable complementary SPC scheme adopts complementary keying modulation using programmable complementary Walsh-Hadamard code and the conventional SPC scheme adopts on-off keying modulation using Walsh-Hadamard code. In Fig. 4-1, the error probability P e of the system is plotted against the number of simultaneous users K, compare to complementary keying with on-off keying, we assume that the code lengths N = 32 and the optimal threshold is ...
