The monitoring of the Gigabit Passive Optical Networks (GPONs) is based on the optical coding (OC) technique and which is the most cost-effective monitoring technique. The performance of the OC technique relies on the design of the implemented hardware and on the design of the address code chosen. With an increasing number of GPON users, the address code selected must has the ability to support a number of code-words that are equal or larger than the available users.
The main purpose for this research is to improve the GPON monitoring system using the OC technique. This research has developed a novel spreading code family based on a prime code. The new code family is referred to as Extended Added Padded Patched Modified Prime Code “EAPP-MPC”. The proposed code has been designed to support a number of code-words that are most compatible with the GPON which is splitting the ratio in comparison with the exciting code families. EAPP-MPC increases the code utilization factor and consequently improves the spectral efficiency of the system. EAPP-MPC has a low code weight which reduces hardware complexity and results in a lower power loss. EAPP-MPC reduces energy consumption by introducing blocks of zeros into the codes by making EAPP-MPC an energy-efficient code family. The performance of the code and its probabilities has been analyzed and compared to the existing code families and the results had showed an improvement.
In addition, the research has introduced a method to manage the traffic at the monitoring layer and guaranteed that the burst of multiple users was not to collide at any time. This has been achieved by utilizing the arranging the information at the data layer to specify a fixed delay time for each user. The results indicated successful restoration of the data with the applied delays. The link status can be analyzed based on the condition of the receiving code and the received time.
Broader Research Context:
Gigabit Passive Optical Networks (GPONs) have become a popular fibre access network solution because of its service transparency, cost effectiveness, energy savings, and higher security systems over other access networks. With an increasing number of GPON users, a failure in the network will cause economic losses for operators, in addition to customer dissatisfaction. Ensuring the reliability of GPON systems is the fundamental requirement [1]. According to the Federal Communications Commission (FCC), one third of all service disturbances are due to cable issues [2]. Due to the increasing amount of interest of monitoring the physical layer of PON, the Telecommunication Standardization Sector of the International Telecommunications Union (ITU-T) had defined L.66 (2007) recommendation to allocate the U-band with wavelengths between 1625 nm to 1675 nm for PON maintenance and monitoring purposes [2]. Considering the large amount of traffic that travels over a GPON, and the large number of users, a cost-effective and reliable management system is highly desired. Several monitoring technologies have been investigated and studied. These technologies are classified into two groups: (1) Optical Time Domain Reflectometer (OTDR) based; and (2) non-OTDR based such as self-injection locked reflective semiconductor optical amplifier (SL-RSOA), Optical Frequency Domain Reflectometer (OFDR), and Optical Coding based monitoring techniques (OC). OC based technique is the most cost effective approach that use a unique code-word as a signature for each Optical network unit (ONU) are placed outside the user’s planet. Each ONU encodes the monitoring data with its code-word and reflects the data back to the central office (CO). A decoding system is implemented at the CO to decode the codes coming in from the different ONUs and a decision about the status of the links is made by the Network Management System (NMS) [2].
The key element of the PON monitoring based on OC technology relies on the structure of the hardware used (encoder and decoder) and the address code implemented.
Several research methods have been conducted to improve the PON monitoring system by improving the design of the hardware. All research has been given an address code that already existed and implemented in Optical code division multiplexing (OCDM) networks.
Various address codes of OCDM networks have been studied that includes optical orthogonal codes (OOC), quadratic congruence codes (QCC) and prime code (PC) families, such as basic PCs, modified prime codes (MPC), new-MPC (n-MPC), padded MPC (PMPC), group padded MPC (GPMPC), transposed MPC (T-MPC) and transposed sparse-padded MPC (T-SPMPC). A number of factors must be considered when designing an address code. The first factor is the code length (L) where a longer code length leads to an increase in the code cardinality (the number of active users). However, a longer code means an increase in processing. The second factor is the code weight (W) that refers to the number of 1’s in the code and the aim is to keep this factor low in order to reduce power consumption and processing. The code construction mechanism is another important factor and a simple code, in terms of construction and mathematical modelling, will be more popular and easier to implement [3]. Address codes are characterized based on two correlation functions; the auto-correlation function and the cross-correlation function. The cross-correlation function of a signal is when each signal is distinguishable from others and from their shifted versions. The auto-correlation function is defined as the cross-correlation of the signal with itself [3]. Multiple Access Interference (MAI) is a critical issue in a network with high cross-correlation. With an increasing number of simultaneous users in the network the cross-correlation function increases which leads to performance degradation [4, 5]. The correlation will improve by increasing the code length and the code weight and in this case throughput and spectral efficiency will be lower. In addition, increasing code length and code weight leads to increased complexity of the transceivers and power consumption [6].
Codes including MPC, n- MPC, PMPC and GPMPC support P2 users (9 when P = 3) with different length and weight. Other codes such as T-MPC and T-SPMPC support a larger number of users - up to 2P2, (18 when P = 3). However, this research aimed to develop a code family to support GPON splitting ratio with smaller prime number (P) and W. The proposed code, increases the number of simultaneous user dramatically up to 2(P + 1)2. It has been design to accommodate the different splitting ratio of GPON (32, 64,128) leading to increase the utilization factor and consequently improve the spectral efficiency. The performance of the code has been analyzed and compared with EAPP-MPC and MPC. A comparison of the results for EAPP-MPC and MPC, the base for many of the standard codes found today, highlights the performance advantages of EAPP-MPC. When EAPP-MPC is compared with T-SPMPC, a recently developed code that supports a large number of users with a low weight, however, the result shows that EAPP-MPC provided an improvement. The results that show with BER of 10-9 (the maximal acceptable value of BER), EAPP-MPC supports the largest number of users in comparative with other codes.
The main advantage of EAPP-MPC is its ability to support a large number of users with a smaller P and a consequently lower code weight which, leads to reduce the complexity of the hardware and lower power losses. Increase the cardinality and low weight have been achieved by dividing each code into two groups; (i) even group that consists of even sub-sequences where odd sub-sequences are patched with blocks of zeros (ii) odd group that consists of odd sub-sequences and patch the even sub-sequences with blocks of zeros then applying time shifting method for each group, where each code shifted by (P – 1) times. Another advantage of EAPP-MPC is its high energy-efficient that has obtained by patching the half sub-sequences with blocks of zeros.
GPON is a point to multi point (P2MP) connection, where, the downstream transmission is broadcasted from the optical line terminal (OLT) at the CO to all ONUs. The upstream transmission is based on a burst mode and GPON utilizes time division multiplexing access (TDMA) to manage the bursty traffic. ONUs are located at different distances from the OLT, when each ONU transmits its upstream traffic during its assigned time slot, there is a possibility for a collision as a result of the differences in the propagation delay for each ONU. In order to guarantee that the upstream transmissions do not collide, then the OLT is responsible for a ranging process during activation and registration of the ONUs. It measures the distance and assigns a specific delay time for each ONU in order to equalize its delay with other ONUs. This delay is referred to as an Equalization Time (ET).
In these examples, we have proposed a method to control burst traffic at the monitoring layer by taking the advantage of the fixed size of ONUs burst at the monitoring layer and the information of the ranging process at the data layer to sit a fixed delay time for each user. The paper shows that the data can be recovered successfully with the applied delay times and the link status can be analyzed based on the condition of the code received and the received time.
Plan for completion of thesis:
Generate the 2-D code
Implement the different scenarios of 2-D code
Publish a journal paper based on the implementation of the proposed code and provide statistical
Timeline for completion of thesis:
5. Review of literature/references
[1] R. Chandy, "Design of a reliable WDM-PON system with transmitter powered by a renewable energy source," in Transparent Optical Networks (ICTON), 2014 16th International Conference on, 2014, pp. 1-3.
[2] M. A. Esmail and H. Fathallah, "Physical layer monitoring techniques for TDM-passive optical networks: A survey," Communications Surveys & Tutorials, IEEE, vol. 15, pp. 943-958, 2013.
[3] S. Jindal and N. Gupta, "OCDMA: Study and Future Aspects," in Recent Development in Wireless Sensor and Ad-hoc Networks, ed: Springer, 2015, pp. 125-167.
[4] M. M. Karbassian and F. Kueppers, "OCDMA code utilization increase: capacity and spectral efficiency enrichment," in Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE, 2010, pp. 1-5.
[5] H. Yin and D. J. Richardson, Optical Code Division Multiple Access Communication Networks:
Theory and Applications, 1 ed., 2009.
[6] M. M. Karbassian and H. Ghafouri-Shiraz, "Capacity enhancement in synchronous optical overlapping PPM-CDMA network by a novel spreading code," in Global Telecommunications Conference, 2007. GLOBECOM'07. IEEE, 2007, pp. 2407-2411.
