Ching Law

Efficient memoryless protocol for tag identification (extended abstract)

This paper presents an efficient collision resolution protocol and its variations for the tag identification problem, where an electromagnetic reader attempts to obtain within is read range the unique ID number of each tag. The novelty of our main protocol is that each tag is memoryless, i.e., the current response of each tag only depends on the current query of the reader but not on the past history of the readers queries. Moreover, the only computation required for each tag is to match its ID against the binary string in the query. Theoretical resulst in both time and communication complexities are derived to demonstrate the efficiency of our protocols.

Performance of a new Bluetooth scatternet formation protocol

A Bluetooth ad hoc network can be formed by interconnecting piconets into scatternets. The constraints and properties of Bluetooth scatternets present special challegnes in forming an ad hoc network efficiently. In this paper, we evaluate the performance of a new randomized distributed Bluetooth scatternet formation protocol. Our simulations validate the theoretical results that our scatternet formation protocol runs in O(log n) time and sends O(n) messages. The scatternets formed have the following properties: 1) any device is a member of at most two piconets, and 2) the number of piconets is close to be optimal. These properties can avoid overloading of any single device and lead to low interference between piconets. In addition, the simulations show that the scatternets formed have O(log n) diameter. As an essential part of the scatternet formation protocol, we study the problem of device discovery: establishing multiple connecitons with many masters and slaves in parallel. We investigate the collision rate and time requirement of the inquiry and page processes. Deducing from the simulation results of scatternet formation and device discovery, we can verify that the total number of packets sent is O(n) and demonstrate that the maximum number of packets sent by any single device is O(log n). At last, we give estimates of the total time requirement of the protocol and suggest further improvements

Distributed construction of random expander networks

A novel distributed algorithm for constructing random overlay networks that are composed of d Hamilton cycles is presented. The protocol is completely decentralized as no globally-known server is required. The constructed topologies are expanders with O(log/sub d/ n) diameter with high probability. Our construction is highly scalable because both the processing and the space requirements at each node grow logarithmically with the network size. A new node can join the network in O(log/sub d/ n) time with O(d log/sub d/ n) messages. A node can leave in O(1) time with O(d) messages. The protocol is robust against an offline adversary selecting the sequence of the join and leave operations. We also discuss a layered construction of the random expander networks in which any node can be located in O(log n) time. The random expander networks have applications in community discovery, distributed lookup service, and dynamic connectivity.

A Bluetooth scatternet formation algorithm

A Bluetooth ad hoc network can be formed by interconnecting piconets into scatternets. The constraints and properties of Bluetooth scatternets present special challenges in forming an ad hoc network efficiently. We present and analyse a new randomized distributed algorithm for Bluetooth scatternet formation. We prove that our algorithm achieves O(log n) time complexity and O(n) message complexity. We show that: (1) in the scatternet formed by our algorithm, any device is a member of at most two piconets; (2) the number of piconets is close to being minimal.

A new Bluetooth scatternet formation protocol

A Bluetooth ad hoc network can be formed by interconnecting piconets into scatternets. The constraints and properties of Bluetooth scatternets present special challenges in forming an ad hoc network efficiently. In this paper, we present and analyze a new randomized distributed protocol for Bluetooth scatternet formation. We prove that our protocol achieves O(logu2009n) time complexity and O(n) message complexity. The scatternets formed by our protocol have the following properties: (1) any device is a member of at most two piconets, and (2) the number of piconets is close to be optimal. These properties can help prevent overloading of any single device and lead to low interference between piconets. We validate the theoretical results by simulations, which also show that the scatternets formed have O(logu2009n) diameter. As an essential part of the scatternet formation protocol, we study the problem of device discovery: establishing multiple connections simultaneously with many Bluetooth devices. We investigate the collision rate and time requirement of the inquiry and page processes. Our simulation results indicate that the total number of packets sent is O(n) and that the maximum number of packets sent by any single device is O(logu2009n).

Online routing and wavelength assignment in single-hub WDM rings

We present new theoretical results on the performance limits of online routing and wavelength assignment (RWA) algorithms in a single-hub wavelength division multiplexing (WDM) ring network architecture. A routing and wavelength assignment (RWA) algorithm is said to be online if at each point in time, the algorithm assigns a route and a color to the current connection request based only on past information, without knowledge of future requests. We study the throughput performance of deterministic online RWA algorithms in terms of competitive ratio, i.e., the maximum ratio of the throughput of an optimal off-line algorithm to that of an online algorithm over any satisfiable sequence of requests. We show that the competitive ratio for the min-hop algorithm is exactly 2. When there are sufficient wavelengths, smaller competitive ratio W/(W+1-N) can be achieved by the greedy-complete algorithm for infinite-duration requests, and by the pair-complete algorithm for uniform-duration requests, where W is the number of wavelengths and N is the number of nodes. In the general case where requests can have arbitrary durations, we prove that a natural deterministic online algorithm can achieve a competitive ratio of 1+2g, where g>1 is the ratio of the longest duration of any request to the shortest duration of any request. These results exhibit the performance tradeoffs among the number of nodes, the number of wavelengths, and the range of request durations.

Online routing and wavelength assignment in WDM rings

We present new theoretical results on the performance limits of on-line routing and wavelength assignment (RWA) algorithms in a single-hub wavelength division multiplexing ring network architecture. An RWA algorithm is said to be on-line if at each point in time, the algorithm assigns a lightpath to a current connection request based only on past information and with no knowledge whatsoever about the future requests. We derive tight bounds on the throughput performance of an on-line min-hop algorithm in comparison with that of an optimal off-line algorithm. In addition, we show that when there are sufficiently many nodes in the ring, the min-hop algorithm achieves the best possible throughput performance among all on-line RWA algorithms. On the other hand, when the number of nodes is not greater than the number of wavelengths in the ring, an on-line algorithm that minimizes the maximum load of the network is shown to achieve better throughput performance than the min-hop algorithm.