Tzu-Chieh Tsai

Token bucket based CAC and packet scheduling for IEEE 802.16 broadband wireless access networks

The IEEE 802.16 standard was designed for Wireless Metropolitan Area Network (WMAN). It supports QoS and has very high transmission rate. The key part of 802.16 – packet scheduling, was undefined and is an open issue. We first proposed a token-bucket based uplink packet scheduling combined with call admission control (CAC) of 802.16. Then a model of characterizing traffic flows by token bucket is presented. The simulation results show that our CAC and uplink packet scheduling can promise the delay requirement of rtPS flows and our model can predict the delay and loss of a traffic flow precisely.

CAC and Packet Scheduling Using Token Bucket for IEEE 802.16 Networks

The IEEE 802.16 standard was designed for Wireless Metropolitan Area Network (WMAN). The coverage of this new technology is expanded up to 50 km. IEEE 802.16 also has inherent QoS mechanism while the transmission rate can be up to 70Mbps. However, the main part of 802.16 - packet scheduling, was not defined and left as an open issue. In this paper, we present an uplink packet scheduling with call admission control (CAC) mechanism that is token bucket based. Also, a mathematical model of characterizing traffic flows is proposed. Simulations are carried out to validate our CAC algorithms and models. These results show that the delay requirements of rtPS flows are promised and the delay and loss can be predicted p recis e l y b y u s in g ou r math emati c al mod e ls .

Multihop wireless IEEE 802.11 LANs: a prototype implementation

We present a prototype for a new architecture, MCN (multihop cellular network), implemented over a wireless LAN platform. MCN preserves the virtue of traditional single-hop cellular networks where the service infrastructure is constructed by many bases, but it also adds the flexibility of ad-hoc networks where wireless transfer through mobile stations in multiple hops is allowed. The MCN can reduce the number of required bases or improve the throughput performance. On IEEE 802.11 compliant wireless LAN products, a bridging protocol, our BMBP (base-driven multihop bridging protocol), runs between mobile stations and access points to build bridging tables. The demonstration shows that MCN is a feasible architecture for wireless LANs.

Routing and Admission Control in IEEE 802.16 Distributed Mesh Networks

QoS provisioning in wireless mesh networks has been known to be a challenging issue. In this paper, we propose a new routing method (using SWEB as metrics) that is well-suited in IEEE 802.16 distributed, coordinated mesh mode. Also, an admission control algorithm (TAC) which utilizes the token bucket mechanism is proposed. The token bucket is used for controlling the traffic patterns for easy estimating the bandwidth required by a connection. In the TAC algorithm, we apply the bandwidth estimation by taking into account the hop count and delay requirements of real-time traffics. TAC is designed to guarantee the delay requirements of real-time traffics, and avoid the starvations of low priority traffics. With the proposed routing metrics, the admission control algorithm and the inherent QoS support for the IEEE 802.16 mesh mode, a QoS-enabled environment can be established. Finally, extensive simulations are carried out to validate our algorithms, and show good performance results.

Multihop wireless IEEE 802.11 LANs: A prototype implementation

In this paper, we present a prototype for a new architecture, MCN (Multihop Cellular Network) implemented over a wireless LAN platform. MCN preserves the virtue of traditional single-hop cellular networks where the service infrastructure is constructed by many BSs (Base Stations) but it also adds the flexibility of ad hoc networks where wireless transfer through mobile stations in multiple hops is allowed. MCN can reduce the number of required BSs or improve the throughput performance. In the prototype of MCN, a bridging protocol, BMBP (Base-driven Multihop Bridging Protocol) runs between mobile stations and access points to enable multihop routing and roaming. Demonstration show that MCN is a feasible architecture for wireless LANs.

A hierarchical simulation environment for mobile wireless networks

A hierarchical simulator has been designed for multimedia communication protocols in a wireless mobile environment. The hierarchical approach integrates performance evaluation of protocols with their implementation. The approach supports scalability studies of the protocols in an efficient manner using coarse grain models that abstract implementation details of the protocol and its execution environment by a few key parameters. Fine grain, low level models that capture implementation details are used for detailed evaluation of small networks and for automatic implementation on radio platforms. The design, evaluation, and implementation cycle is closed by feeding the measurements from the implementation back into the model to improve its accuracy. The paper describes the use of the environment in the evaluation and implementation of a cluster based multihop protocol for multimedia traffic.

An analytical model for IEEE 802.11e EDCA

Quality of service (QoS) support in wireless LAN (WLAN) is the main mission of the IEEE 802.11 group e. It uses enhanced distributed channel access (EDCA) to differentiate service of priorities by means of various inter-frame spaces (IFS) and contention windows (CW). In order to efficiently manage QoS for the IEEE 802.11e networks, throughput and MAC delay for several traffic flows from 4 different access categories (AC) should be more accurately estimated. A four-dimensional Markov model is proposed to evaluate these. The correctness of our analysis has been validated via simulation results. Throughout our model, call admission control (CAC) can be easily applied, and thus resource management for QoS support for multimedia applications is well achieved.

QoS routing in multihop packet radio environment

We present a method to compute the path bandwidth for the DSDV (destination-sequenced distance-vector) based routing algorithm. The addressed network does not necessarily have a cellular structure and could have no fixed infrastructure. This network can be either stand-alone, or connected to the wired network. Each mobile station has to relay packets for others, thus achieving multihop routing. To calculate the available bandwidth of a path in this environment, it is incorrect to simply compute the minimum bandwidth of the links along the path. There are two crucial steps in the path bandwidth computation process of this multihop environment: (1) intersecting the sets of common free slots of two adjacent links, and (2) dividing the intersection for the adjacent links to share. We present two bandwidth computation rules including the half rule and the floating rule. Numerical results are given to evaluate the performance of applying these rules to the DSDV-based QoS routing algorithm.

Reducing Calibration Effort for WLAN Location and Tracking System using Segment Technique

As mobile computing technology becomes more and more mature, people feel great interest on context-aware applications and services. Referring to context, location-aware system is one of the most important components. This paper presents a precise indoor RF-based (IEEE 802.11) locating system named precise indoor locating system (PILS). In order to acquire high level of location estimation result, a large number of training samples should be collected in offline phase. As a result, the system becomes impractical and huge number of man-power is needed. In this paper, we aim to reduce the manual effort in constructing radio map and maintain high accuracy in our system. We propose models for data calibration, interpolating, location estimation, and tracking in PILS. Wireless Channel Propagation model is also in our concern. Large scale and small scale fading are involved in the wireless channel propagation

An Adaptive IEEE 802.11 MAC in Multihop Wireless Ad Hoc Networks Considering Large Interference Range

The IEEE 802.11 standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in multihop wireless ad hoc networks, the IEEE 802.11 MAC protocol will suffer from more serious hidden terminal and exposed terminal problems than those in single hop WLANs. More specifically, it is due to the “large” interference range and the “large” carrier sensing range. In this paper, we focus on the collisions caused by the existence of large interference range in multihop wireless ad hoc networks and propose an adaptive IEEE 802.11 MAC (AMAC) that makes two simple modifications of IEEE 802.11 RTS/CTS handshake to dynamically adjust the transmission and reception according to the shared medium status near transmitter and receiver, respectively. Simulation results show that our method can lessen interferences and increase system throughput as compared with IEEE 802.11 MAC in the multihop wireless ad hoc networks.