Design and analysis on network throughput enhancement in integrated fiber-wireless (FiWi) access networks

Abstract

Nowadays, a hybrid fiber-wireless access network (FiWi) has been proposed to integrate the optical PON network and the wireless mesh network (WMN) to provide the high bandwidth, cost efficient and ubiquitous last mile Internet access. For the PON subnetwork of FiWi networks, it consists of an Optical Line Terminal (OLT) at the central office which sends traffic received from the access network to the Internet and vice versa, an Remote Node (RN) which multiplexes the upstream traffic destinated to the OLT and vice versa, and a group of Optical Network Units (ONUs) close to users' premises which send the upstream traffic to the RN and vice versa. For the wireless subnetwork of FiWi networks, WMN is applied to support ubiquitous and flexible communications in users' premises. Generally, WMN consists of multiple gateways connected to the wired Internet, a group of wireless mesh clients that associate with those routers. In FiWi networks, the integration of PONs and WMNs enables ONUs to combine functions of both traditional ONUs in PONs and gateways in WMNs together. For the newly emerged FiWi access networks, the network throughput is a very attractive issue and hasn't been quite investigated yet. Therefore in our work, we intend to study the achievable network throughput in FiWi networks and factors that affect the throughput. Considering the specific architectural features of FiWi networks, its throughput can be affected by the following aspects: the traffic demands pattern from wireless mesh clients, the traffic routing algorithm applied in the wireless mesh subnetwork, the TDMA schedule of ONUs in the PON subnetwork and the deployment of ONUs in FiWi networks. In this work, we will address above mentioned aspects for the design and analysis on the throughput enhancement in FiWi networks. As for traffic demands from wireless mesh clients, considering traditional traffic demand that goes to the Internet, the TDMA schedule of ONUs for the upstream traffic and the routing algorithm applied in the wireless mesh subnetwork play very important roles if the high throughput is expected. In the TDMA schedule, ONUs share the uplink capacity to the OLT and each ONU can only use its assigned time slots for the upstream traffic transmission. In order to achieve higher throughput, it's better if the ONU that occupies the current transmission time slot has traffic loads for transmission, otherwise, such time slot will be wasted without any contribution to the throughput. Therefore, it's better to send traffic to the ONU whose assigned time slots are nearly coming so that the capacity assigned to that ONU can be well utilized, thus enhancing the throughput. On the other hand, at each ONU, the actual arrival rate of traffic from the wireless subnetwork has much effect on the achievable throughput. It's better if traffic goes through the wireless path with less interferences in the wireless subnetwork, which may result in higher throughput. In our work, we proposed the Interference Aware and Delay Bounded Routing (IADBR) algorithm to send traffic to the ONU from which the traffic can be sent out to the Internet as soon as possible along the wireless path with reduced interferences. We propose both centralized and distributed algorithms for IADBR and simulation results show that the distributed algorithm performs quite closely to the optimal centralized algorithm and performs much better than the shortest path algorithm. Based on above work and many other work like Alichery, Kodialam on the network throughput optimization, we observe that when only traffic that goes to the Internet is considered, the achievable network throughput of FiWi networks is quite bottle-necked by interferences in the wireless subnetwork. However, when peer-to-peer communications from one wireless client to another wireless client is introduced, the integration of PONs and WMNs in FiWi networks provides an opportunity to reduce the impact of interferences on network throughput. In traditional WMNs, peer-to-peer communication is carried in the wireless network, which is subject to interferences in wireless communications. However, in FiWi networks, such traffic can be carried through the wireless-optical-wireless mode in which the traffic is sent from the source wireless client to its nearest ONU, which is then sent to the ONU close to the destination wireless client through the PON subnetwork and then delivered to the destination wireless client. Such wireless-optical-wireless mode introduced by FiWi networks can sustain the interference in wireless subnetwork, thus improving the network throughput. In our work, we study the network throughput gain in FiWi networks subject to peer-to-peer communications compared with traditional WMNs and parameters that can affect the throughput gain. Simulation results show that with heavy peer-to-peer communication traffic, the network throughput gain in FiWi networks is significant compared with the traditional WMN. Furthermore, based on above work and other work like Sarkar on the deployment of ONUs on FiWi networks, we also observe that the ONU deployment will have great impact on the network throughput in FiWi networks considering peer-to-peer communications and the ONU deployment will be different from that when only traffic to the Internet is considered. In our work, given the distribution of wireless mesh routers, we study where to place K ONUs in FiWi networks so that the overall network throughput can be maximized considering peer-to-peer communications. We proposed a Tabu Search (TS) based heuristic for the problem solving. Simulation results show that compared to the random deployment and the fixed deployment which performs well when only traffic to the Internet is considered, Tabu Search heuristic has a much better performance with much enhanced network throughput.

Date of Award	17 Feb 2010
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Jianping WANG (Supervisor)