Kai-Yeung Siu

Bio: Kai-Yeung Siu is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Asynchronous Transfer Mode & Throughput. The author has an hindex of 19, co-authored 57 publications receiving 2266 citations.

Efficient memoryless protocol for tag identification (extended abstract)

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 reader's 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.

Dynamic assignment of orthogonal variable-spreading-factor codes in W-CDMA

Abstract: This paper presents an optimal dynamic code assignment (DCA) scheme using orthogonal variable-spreading-factor (OVSF) codes. The objective of dynamic code assignment is to enhance statistical multiplexing and spectral efficiency of W-CDMA systems supporting variable user data rates. Our scheme is optimal in the sense that it minimizes the number of OVSF codes that must be reassigned to support a new call. By admitting calls that would normally be blocked without code reassignments, the spectral efficiency of the system is also maximized. Simulation results are presented to show the performance gain of dynamic code assignment compared to a static assignment scheme in terms of call blocking rate and spectral efficiency. We also discuss various signaling techniques of implementing our proposed DCA scheme in third-generation wideband CDMA systems.

Efficient memoryless protocol for tag identification

Abstract: The invention features a method and system for identifying a plurality of tags using an efficient memoryless protocol. The system includes a reader and a plurality of tags. The reader is adapted to maintain an ordered set of query strings; select a string from the set of query strings; broadcast a query message containing the selected string or a portion of the selected string to the tags; and receive a response from one of the tags. The tags operate without batteries and are adapted to respond to the selected string broadcast by the reader. Accordingly, the tag identification methods are efficient in terms of both time and communication complexities.

New dynamic algorithms for shortest path tree computation

Abstract: The open shortest path first (OSPF) and IS-IS routing protocols widely used in today's Internet compute a shortest path tree (SPT) from each router to other routers in a routing area Many existing commercial routers recompute an SPT from scratch following changes in the link states of the network Such recomputation of an entire SPT is inefficient and may consume a considerable amount of CPU time Moreover, as there may coexist multiple SPTs in a network with a set of given link states, recomputation from scratch causes frequent unnecessary changes in the topology of an existing SPT and may lead to routing instability We present new dynamic SPT algorithms that make use of the structure of the previously computed SPT Besides efficiency, our algorithm design objective is to achieve routing stability by making minimum changes to the topology of an existing SPT (while maintaining shortest path property) when some link states in the network have changed We establish an algorithmic framework that allows us to characterize a variety of dynamic SPT algorithms including dynamic versions of the well-known Dijkstra, Bellman-Ford, D'Esopo-Pape algorithms, and to establish proofs of correctness for these algorithms in a unified way The theoretical asymptotic complexity of our new dynamic algorithms matches the best known results in the literature

Performance of a new Bluetooth scatternet formation protocol

Abstract: 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

On the capacity of a cellular CDMA system

Abstract: It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

Mobile ad hoc networking: imperatives and challenges

Abstract: Mobile ad hoc networks (MANETs) represent complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self-organize into arbitrary and temporary, ‘‘ad-hoc’’ network topologies, allowing people and devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster recovery environments. Ad hoc networking concept is not a new one, having been around in various forms for over 20 years. Traditionally, tactical networks have been the only communication networking application that followed the ad hoc paradigm. Recently, the introduction of new technologies such as the Bluetooth, IEEE 802.11 and Hyperlan are helping enable eventual commercial MANET deployments outside the military domain. These recent evolutions have been generating a renewed and growing interest in the research and development of MANET. This paper attempts to provide a comprehensive overview of this dynamic field. It first explains the important role that mobile ad hoc networks play in the evolution of future wireless technologies. Then, it reviews the latest research activities in these areas, including a summary of MANETs characteristics, capabilities, applications, and design constraints. The paper concludes by presenting a set of challenges and problems requiring further research in the future. � 2003 Elsevier B.V. All rights reserved.

OFDM for Wireless Communications Systems

Abstract: Written by leading authority Ramjee Prasad, this timely new work offers a complete understanding of OFDM technology and applications in wireless communications systems, placing emphasis on wireless LANs and PANs. OFDM is a key technology for beyond 3G communications, promising robust, high capacity, high speed wireless broadband multimedia networks. In this practical resource, established and new technologies are explained clearly and comprehensively, from OFDM basics to a detailed account of a new technique, hybrid OFDM CDMA slow frequency hopping. The book offers an in-depth treatment of the underlying technologies and applications of PANs and describes and evaluates a practical OFDM system concept. Invaluable for wireless engineers and researchers, this cutting edge new book is a must-have for anyone who needs to understand this critical technology and its implementation in WLANs and WPANs.

Efficient Object Identification with Passive RFID Tags

Abstract: Radio frequency identification systems with passive tags are powerful tools for object identification. However, if multiple tags are to be identified simultaneously, messages from the tags can collide and cancel each other out. Therefore, multiple read cycles have to be performed in order to achieve a high recognition rate. For a typical stochastic anti-collision scheme, we show how to determine the optimal number of read cycles to perform under a given assurance level determining the acceptable rate of missed tags. This yields an efficient procedure for object identification. We also present results on the performance of an implementation.

Dynamic power allocation and routing for time-varying wireless networks

Abstract: We consider dynamic routing and power allocation for a wireless network with time-varying channels. The network consists of power constrained nodes that transmit over wireless links with adaptive transmission rates. Packets randomly enter the system at each node and wait in output queues to be transmitted through the network to their destinations. We establish the capacity region of all rate matrices (/spl lambda//sub ij/) that the system can stably support-where /spl lambda//sub ij/ represents the rate of traffic originating at node i and destined for node j. A joint routing and power allocation policy is developed that stabilizes the system and provides bounded average delay guarantees whenever the input rates are within this capacity region. Such performance holds for general arrival and channel state processes, even if these processes are unknown to the network controller. We then apply this control algorithm to an ad hoc wireless network, where channel variations are due to user mobility. Centralized and decentralized implementations are compared, and the stability region of the decentralized algorithm is shown to contain that of the mobile relay strategy developed by Grossglauser and Tse (2002).