Kwok-Wah Hung

Design algorithms for multihop packet radio networks with multiple directional antennas stations

A protocol called the simple tone sense (STS) protocol is designed for multihop packet radio networks (PRNs) with multiple directional antennas stations. The protocol can minimize transmission interference by using a group of tones to identify the active neighbors. A variation of the STS protocol called the variable power tone sense (VPTS) protocol is also designed to further reduce interference. Algorithms for assigning tones and for determining the orientation and broadcasting angles of the directional antennas are designed. Design examples are given. Simulation result shows that the STS protocol gives better throughput-delay performance than the busy-tone multiple access protocol, especially when the traffic is heavy. The VPTS protocol gives still better throughput-delay performance than the STS protocol. >

Design of node configuration for all-optical multi-fiber networks

It is cost-effective to install multiple fibers in each link of an all-optical network, because the cost of fibers is relatively low compared with the installation cost. The resulting network can provide a large capacity for good quality of service, future growth, and fault tolerance. If a node has more incoming/outgoing fibers, it requires larger optical switches. Using the current photonic technology, it is difficult to realize large optical switches. Even if they can be realized, they are expensive. To overcome this problem, we design a node configuration for all-optical networks. We exploit the flexibility that, to establish a lightpath across a node, we can select any one of the available channels in the incoming link and any one of the available channels in the outgoing link. As a result, the proposed node configuration requires significantly smaller optical switches while it can result in nearly the same blocking probability as the existing one. We demonstrate that a good network design is to adopt the proposed node configuration and slightly more fibers in each link, so that the network requires small optical switches while it has a small blocking probability.

The coded tone sense protocol for multihop spread-spectrum packet radio networks

The use of spread-spectrum techniques in packet radio networks allows overlapping of packet transmission by assigning a different code to each transmitted signal. The authors have designed an algorithm for assigning codes to the stations such that these codes can be reused beyond their interference range. This algorithm can reduce the number of spreading codes required to 20%-35% of the number of stations in the network. Using the code assignment algorithm on slotted ALOHA, the resulting CSA/n protocol can give 42% to 80% performance improvement over the SA protocol. The authors also propose the coded tone sense (CTS) protocol, which can further reduce the number of codes required. From simulation results, it was found that CTS has a much better performance than the BTMA (busy tone multiple access) protocol. For a 80-station network using only five codes, the maximum throughput of CTS is found to be 73% to 80% higher than that of BTMA. It was found that the CSA (coded slotted ALOHA) and CTS protocols are particularly attractive for densely populated networks.<<ETX>>

An efficient code assignment algorithm for multihop spread spectrum packet radio networks

Multihop spread-spectrum packet radio networks (PRNs) with a large number of stations would require a large number of codes, even with code reuse beyond the interference range. It is important to find an efficient algorithm for assigning as few codes to the PRN stations as possible, since the smaller the number of codes used the smaller the bandwidth needed. The code assignment problem in transformed to the familiar graph coloring problem. A heuristic code assignment algorithm, making use of some special properties of PRNs, is designed. A lower bound on the chromatic number, which is the minimum number of codes required, is obtained. The performance of this algorithm is assessed by making comparisons to the bound as well as to one of the best heuristics for graph coloring.<<ETX>>

Contention resolution in the loop-augmented ShuffleNet multihop lightwave network

In ShuffleNet multihop lightwave networks with hot-potato routing, when two or more packets simultaneously arrive at a given node and contend for the same outgoing link to achieve minimum distance routing, then all but one will be misrouted to links which produce longer paths to the destination. In this paper, we propose a new topology for multihop lightwave networks, called loop-augmented ShuffleNet, which can shorten the alternate path traveled by misrouted packets. The loop-augmented ShuffleNet is constructed with slight change in the ShuffleNet connectivity while retaining the simple addressing and self-routing properties. Compared with ShuffleNet, the network performance is greatly improved by reducing the expected number of hops using this new network design.

Design algorithms for multihop packet radio networks with multiple directional antenna stations

The simple tone sense (STS) protocol is designed for multihops PRNs (packet radio networks) with multiple directional antenna stations. The protocol can minimize transmission interference by using a group of tones to identify the active neighbors. A variation of the STS protocol, the variable power tone sense (VPTS) protocol, is also designed to further reduce interference. Algorithms for assigning tones and for determining the orientation and broadcasting angles of the directional antennas are designed. Design examples are given. Simulation shows that the STS protocol performs better than the BTMA (busy tone multiple access) protocol, especially when the traffic is heavy. VPTS, however gives still better throughput performance.<<ETX>>