An adaptive priori likelihood ratio (LLR) estimation method is proposed over non-Gaussian channel in the intensity modulation/direct detection (IM/DD) optical communication systems. Using the nonparametric histogram and the weighted least square linear fitting in the tail regions, the LLR is estimated and used for the soft decision decoding of the low-density parity-check (LDPC) codes. This method can adapt well to the three main kinds of intensity modulation/direct detection (IM/DD) optical channel, i.e., the chi-square channel, the Webb-Gaussian channel and the additive white Gaussian noise (AWGN) channel. The performance penalty of channel estimation is neglected.
An all optical header extraction scheme based on semiconductor optical amplifier and Mach-Zehnder-Interferometer
(SOA-MZI) with asymmetric control light was proposed and demonstrated in this paper. By theoretical analysis, we
found the proposed scheme can implement the optical header extraction more effectively. Numerical analysis and
simulation show that more than 18dB contrast ratio of the extracted header at 20Gbit/s and the suppressed payload at
80Gbit/s can be achieved. In addition, the parameters of the SOA-MZI and the input packet are discussed to optimize the
performance of the scheme and the results also indicate that the performance of the scheme is influenced greatly by the
parameters of SOA.
A all optical header extraction scheme based on semiconductor optical amplifier and
Mach-Zehnder-Interferomete (SOA-MZI) with asymmetric control light was proposed and demostrated in this paper. By
theoretical analsys, we found the proposed scheme can implement the optical pakcet header extraction more
effectively. Numerical analsys and simulation show that more than 18dB contrast ratio of the extrcacted header
at 20Gbit/s and the suppressed payload at 80Gbit/s can be achieved. In addition, the parameters of the SOAMZI
and the input packet are discussed to optimize the performance of the scheme and the results also indicate
that the performance of the scheme is influenced greatly by the parameters of SOA.
Packet scheduling plays an important role in the asynchronous optical switched networks for node performance. A
weighted scheduling algorithm based on the queue length associated with waiting delay was proposed to solve the packet
starvation of queue length weighted scheduling for the length variable OPS. The contention is resolved either in
wavelength domain by limited range wavelength converters and in time domain by fiber delay lines. The work has
contributed with a very powerful scheduling mechanism which reduces resource contention at the asynchronous OPS
core nodes and guarantees a reasonable packet delay thanks to its weighted scheduling algorithm based on queue length
and waiting delay for variable length OPS network. The scheduler calculates every input ports with N×K virtual output
queue (VOQ) weight and schedules the maximal weight queue packets to available output channel. The analysis and
simulation results show that the proposed scheduling has high throughput and low packet loss ratio.
OPS with feedback shared FDL buffer produce large voids due to FDL buffers only supplying discrete step delay and causing FDL queue virtually occupation. By analyzing the TCP traffic and ACK packets feature, the ACK packet void filling first scheduling is presented to decrease packet loss rate and to reduce the FDL voids. When the FDL buffer void size is fit for the ACK packet, the ACK packet is scheduled to FDL immediately. An ACK and non-ACK packets difference and process flow is designed according the TCP packet frame structure. Compared with the conventional FIFO scheduling and smallest FDL void first scheduling, the algorithm reduces greatly the number of ACK occupying the FDL buffer and eliminates large numbers of ACK's bad influence on efficiency of IP data transmission under different FDL buffer depth and traffic load. The results of simulation show that the proposed scheduling makes use of ACK packets first void filling scheduling mechanism to reduce FDL excess load, increases output utilization and reduce packet loss ratio for asynchronous optical network. This approach is shown to minimize the FDL numbers with the feature of high stabilization and photonic integration and to improve real time TCP traffic performance for Internet network.
An optical header extraction structure and scheme based-on SOA and improved M-Z interferometer were presented in
the paper. The parameters of improved SOA-M-Z interferometer are discussed and analyzed to optimize the performance
of optical header extraction with the proposed scheme. Numerical analysis and simulation show that more than 15dB
contrast ratio of the header extraction is achieved when the rates of header and payload are 2.5Gb/s and 40Gb/s
respectively. In addition, the system is simple structure, highly scalable and photonic integration.
The average queue delay of optical packet increases when the packets block in the virtual output queue header in the
asynchronous optical packet switching. We analyze the character of variable length Internet packet and propose the
preemptive short packets priority (PSPP) algorithm for reducing the total packet waiting time in the queue. In the PSPP
algorithm, the short packet can preempt the transmission time of the long packet and can be served first. The analysis and
the simulation shows the PSPP algorithm can make the average waiting time of the short packet decrease to zero almost
and can decrease the total packet average waiting time largely when the traffic load is middle and low. The PSPP can
guarantee the low average waiting delay for the real time TCP traffic implementation.
An optical header extraction and recognition structure was presented in the paper. The optical header is extracted by the
improved iTOAD structure with DPSK modulation, while the header recognition is realized by discrete time stretch
technology with super-continuum pulse to slow down the optical header speed for the high-speed asynchronous optical
packet switch. Analysis and Experimental results shows that the iTOAD with time stretch technique can enlarge the
output header 20dB and improve the switching ratio to 15dB when the input pulse is only 0.1pJ. By adjusting the tunable
FDL length, the two pulses after the coupler switching have the π phase shift in the iTOAD SOA. The structure can slow
down the high-speed optical header speed. Furthermore, the low speed header has the low latency time decreases
(latency time less than 100μs) and overcomes the drawbacks of time bandwidth limitation associated with dispersion in
long lengths of fiber. The system is highly scalable, lower power consumption and photonic integration.
The paper studies the performance of an all-optical packet switch (OPS) for different packet length. The packet loss ratio, considered the OPS without FDL and with FDL buffer, with different length distribution are analyzed under the Poisson arrival process and a burst super exponential arrival process respectively. The experiment and analysis show that the performance of different length packet is influence by the packet arrival process and the buffer size. When the OPS without buffer, the PLR under bursty traffic yields the higher packet loss ratio (PLR). PLR with Poisson arrival packet is not influenced by the packet length distribution, while with the super exponential traffic, the packet length distribution influences the PLR, and the fixed length packet yields higher PLR compared to the variable length exponential packet and the experiential Internet traffic. When the OPS with buffer, PLR with Poisson arrival packet yields lower than with super exponential packet under the same load, and the experiential length super exponential packet leads to highest PLR, while the fixed length Poisson process packet brings on lowest PLR.
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