Multiplexing Access Passive Optical Network Research Articles

Joint Resource Allocation and Software-Based Reconfiguration for Energy-Efficient OFDMA-PONs

The widely deployed passive optical network (PON) is a cost-effective way to create a front/backhaul carrier for ubiquitous wireless access connectivity. To hide the difference of frame formats and multiplexing methods, an orthogonal frequency division multiplexing access PON (OFDMA-PON) was proposed. In upstream transmission, multiple optical network units (ONUs) from the same segment or residential area can transmit data through a shared group of orthogonal low-bitrate subcarriers (SCs) during different time slots (TSs) within the entire transmitting period. In downstream transmission, the optical line terminal can send control signaling of reconfiguring ONUs’ parameters so that SCs can be reallocated among segments, thus sleeping segments with empty data load while ensuring service continuity. Though energy savings can be ensured for upstream data transmission by using existing solutions, only frequency and time domains are involved. It is meaningful for us to make the flexible and energy- efficient configuration of transmitting power and modulation level assigned for ONUs in terms of improving energy efficiency. In this paper, we investigate joint resource allocation for energy-efficient upstream data transmission in OFDMA-PONs, with the help of software-based ONU reconfiguration. We formulate the problem, and the upper bound of energy saving is also derived. To solve the problem in a short span of time, we propose a novel heuristic algorithm whose effectiveness has been demonstrated by extensive simulations.

A low-overhead switched-mode Energy saving strategy for OFDMA-PON downstream transmission

Abstract Green networks and energy saving have become important topics of worldwide concern and attracted intensive attention from both academia and industry. As orthogonal frequency division multiplexing access passive optical network (OFDMA-PON) employs more advanced and energy-consuming digital signal processing (DSP) techniques than other PON systems, it is of critical importance to improve the energy efficiency of OFDMA-PONs. In this paper, we propose a switched-mode energy saving strategy with low overhead for OFDMA-PON downstream transmission. By embedding information in the short training sequences (STSs) of the OFDM frame preamble, the STSs serve a twofold purpose: providing time synchronization and carrying the information with regard to the destination of the frame, hence eliminating the need for extra upper-layer control or information exchange between OLT and ONU. As STS is an inherent part of the OFDM frame, the proposed scheme requires little extra overhead in transmission time and hardware cost. The ONU continues the subsequent processing only when it is the intended receiver, while the unintended ONUs drop the frame and stands by to save energy. In order to achieve a tradeoff between energy saving and delay performance, the scheme switches between single-ONU mode and team mode where either a single ONU or a team of ONUs are the targeted receivers. We verify the feasibility of proposed scheme through experiments and evaluate the performance in terms of energy saving and packet delay by simulations. The results indicate that substantial energy can be saved compared with conventional OFDMA-PON systems.

Randomized Dynamic Bandwidth Allocation Algorithm for Upstream Access in OFDMA-PON

A randomized dynamic bandwidth allocation algorithm for upstream access in an orthogonal frequency division multiplexing access passive optical network (OFDMA-PON) system is proposed. According to theoretical analysis, the proposed algorithm has low computational complexity and strong throughput reliability. From the simulation results, compared with the existing algorithms, the novel proposed algorithm has higher throughput and lower average packet delay.

Physical-layer energy-efficient receiving method based on selective sampling in orthogonal frequency division multiplexing access passive optical network

We propose a physical-layer energy-efficient receiving method based on selective sampling in an orthogonal frequency division multiplexing access passive optical network (OFDMA-PON). By using the special designed frame head, the receiver within an optical network unit (ONU) can identify the destination of the incoming frame. The receiver only samples at the time when the destination is in agreement with the ONU, while it stays in standby during the rest of the time. We clarify its feasibility through an experiment and analyze the downstream traffic delay by simulation. The results indicate that under limited delay conditions, ∼60% energy can be saved compared with the traditional receiving method in the OFDMA-PON system with 512 ONUs.

Forward error correction loading for power budget improvement of orthogonal frequency division multiplexing access-passive optical network

We propose and experimentally demonstrate a novel loading scheme to improve the maximum system power budget for orthogonal frequency division multiplexing access-passive optical network (OFDMA-PON). For the downstream traffic, optical network units (ONUs) with asymmetric distribution fiber lengths are paired together, and information for the paired ONUs is loaded into the same OFDM signal by forward error correction loading combined with bit and power loading scheme. Power budgets of ONUs with long distribution fiber lengths can be improved at the cost of the power budget degradation of ONUs with short distribution fiber lengths, while maintaining the data rates for both ONUs. Besides, the total number of subcarriers used in downstream OFDM signal remains unchanged. A proof-of-concept experiment is performed to demonstrate the feasibility of the proposed scheme. A maximum of 80 km transmission and a 1∶128 split ratio is achieved by the scheme, which improves the maximum system power budget by ∼4 dB than traditional methods.

Full-asynchronous gigabit-symmetric DPSK downstream and OOK upstream OCDMA-PON with source-free ONUs employing all-optical self-clocked time gate

We propose an asynchronous gigabit-symmetric optical code division multiplexing access passive optical network (OCDMA-PON) in which optical network units (ONUs) are source-free. In the experiment, we demonstrate a duplex OCDMA system with a 50 km 10 Gbit/s/user 4-user DPSK-OCDMA downlink and a 50 km 10 Gbit/s/user 4-user OOK-OCDMA uplink and error-free duplex transmissions are achieved. Besides, we investigate an all-optical self-clocked time gate, which is used for the signal regeneration of decoded signals and ensures asynchronization in the up/downstream transmissions. Furthermore, we evaluate the power budget of the proposed duplex transmission.