Multihop optical network with convolutional coding SuFong Chien, Kenzo Takahashi, and Satya Prasad Majumder Faculty of Engineering, Multimedia University, 63100 Cyberjaya, Selangor, Malaysia sfchien@mmu.edu.my Received 7 August 2001 We evaluate the bit-error-rate (BER) performance of a multihop optical ShuffleNet with and without convolutional coding. Computed results show that there is considerable improvement in network performance resulting from coding in terms of an increased number of traversable hops from a given transmitter power at a given BER. For a rate-1/2 convolutional code with constraint length K = 9 at BER = 10 -9 , the hop gains are found to be 20 hops for hot-potato routing and 7 hops for single-buffer routing at the transmitter power of 0 dBm. We can further increase the hop gain by increasing transmitter power.  2001 Optical Society of America OCIS codes: 060.0060, 060.4510. 1. Introduction Use of a multihop optical network with wavelength-division multiplexing is one solution for high-speed broadband communication systems (over 100 Gb/s). Many network topologies have recently 1 been proposed for the multihop network, in particular for regular two-connected systems such as ShuffleNet and the Manhattan street network. The nodes in such networks are linked to other nodes by optical fiber lines that can provide tremendous bandwidth, as much as several tens of terabits/s. One advantage of these networks is that they do not need rapidly tunable transceivers or extensive transmission coordination. In such a network, packets traveling from one node to another are routed through an intermediate node in a series of hops on the fiber, each hop using one of many different channels that are wavelength multiplexed onto the optical fiber. Hence tagged packets could be collided by flowing through existing or newly generated packets in the network node. To enhance the performance of these networks, a simple and fast routing scheme, the so-called hot-potato (H-P) routing scheme, has been proposed. This scheme has little effect on the throughput-delay performance, but it may require that packets take more hops to reach their destination. To resolve the hop delay caused by this scheme, a single-delay-line optical buffer strategy has been proposed as an alternative, and results show that it could efficiently reduce hop delay. 2 However, both routing schemes resolve another issue, i.e., that the traveling of the packet in a high-speed optical network is limited by the accumulation of noise such as the optical amplifier’s amplified spontaneous emission (ASE) noise and cross talk resulting from the optical crossbar routing switch. 3 In this paper, performance analysis is carried out for an optical ShuffleNet to evaluate the effect of accumulated ASE and cross talk on the bit-error-rate (BER) performance with per-hop loss compensation with optical amplifiers. We extend the BER performance evaluation by employing a convolutional coding system in the network nodes to investigate the efficacy of coding in reducing the required signal power for a given BER compared with the previous results in an uncoded system. 4 These new results may lead to using the coding system in multihop optical network nodes. 2. Network Model The topology of the 24-node ShuffleNet, as well as the node architecture, is illustrated in Fig. 1. There are only two add–drop optical crossbar switches (A/D) equipped in each node, a pair of optical transceivers and an electronic input buffer to store incoming cells. 34953 January 2002 / Vol. 1, No. 1 / JOURNAL OF OPTICAL NETWORKING 66