Yaw-Wen Kuo

Maximum rectangle-based down-link burst allocation algorithm for WiMAX systems

The IEEE 802.16e standard known as Mobile WiMAX has recently been introduced. Because of the high data throughput and low cost of deployment, it becomes one of the leading solutions for wireless broadband services. Mobile WiMAX makes use of Orthogonal Frequency-Division Multiple Access (OFDMA) digital modulation scheme as the transmission method. The standard specifies that a data burst in the downlink subframe needs to be mapped into a time and frequency domain with a rectangular shape, but how the data bursts are organized to minimize the wasted space is not detailed. Many burst mapping algorithms have been proposed by researchers in these late years. This paper presents an efficient packing algorithm which achieves high throughput, reduces the number of unused slots, and minimizes the mapping information overhead. We compare the performance of our proposed algorithm with that of eOCSA, a high-performance packing algorithm recently presented by other researchers. Simulation results show that our proposed algorithm outperforms eOCSA.

A Data Mapping Algorithm for Two-Level Requests in WiMAX Systems

The IEEE 802.16e standard known as Mobile WiMAX has recently been introduced. It is considered as one of the most promising wireless access technologies supporting high data throughput with low cost of deployment. Mobile WiMAX makes use of Orthogonal Frequency-Division Multiple Access (OFDMA) digital modulation scheme as the transmission method. With the constraint requires that all requests have to be mapped as a rectangle, it is shown that finding an optimum mapping solution is an NP-complete problem. Many burst mapping algorithms have been proposed, but none considered the case with prioritized requests. This paper presents an efficient packing algorithm for two-level requests with two targets: (1) map high (MUST part) priority data as much as possible; and (2) achieve high efficiency, reduces the number of unused slots, and minimizes the mapping information overhead. Simulation results show that the proposed algorithm achieves high efficiency.

A framework to approximate the delay distribution for IEEE 802.11 DCF protocol

This paper presents a framework to approximate the distribution of the frame delay in the IEEE 802.11 WLAN. Two schemes are also provided to demonstrate the trade-off between complexity and accuracy. Based on the simulation results, scheme 1 can approximate the delay distribution well and scheme 2 is very fast. For the WLAN networks with delay QoS requirement, this paper provides an efficient method to develop admission control algorithm or tune system parameters.

Throughput analysis for wireless LAN with frame aggregation under mixed traffic

Frame aggregation is a mandatory feature of the high throughput wireless LAN MAC to improve the performance. Frame aggregation can be implemented at MAC or PHY layer. However, implementing only one type of aggregation will be more cost-effective. This paper derives an upper bound of MSDU throughput (MT) for the two types of aggregation under mixed traffic.

A Downlink Mapping algorithm for two-level requests in IEEE 802.16e systems under AMC mode

This paper proposes a downlink mapping algorithm for two-level requests in Orthogonal Frequency Division Multiple Access based IEEE 802.16e systems under the Adaptive Modulation and Coding (AMC) mode by which the modulation and coding scheme (MCS) of a user may be different for available subchannels. Given a set of requests each with two priorities, the proposed algorithm efficiently allocates a two-dimensional (time and frequency) burst with a suitable MCS to each user to maximize the system throughput with service differentiation. Simulation results show that the proposed algorithm outperforms the Efficient Downlink Mapping Allocation (EDMA) algorithm [5] in terms of the throughput of high priority data, but slightly sacrifice in overall throughput. The proposed algorithm can improve up to 98.8% more the average allocated ratio of urgent data than the EDMA.

Delayed Contention DCF MAC Protocol for IEEE 802.11 Wireless LANs

This paper proposes a new MAC protocol called delayed contention DCF (DC-DCF) with a built-in traffic shaping feature for IEEE 802.11 wireless LANs. By suspending a number of active stations, the new protocol significantly reduces the probability of collision and provides better quality of service. The complexity of implementing such a protocol is low and the related parameter is easily determined. Simulation results show that the proposed protocol outperforms DCF in terms of throughput, the probability of collision, and average delay.

An efficient downlink mapping algorithm for AMC mode in WiMAX systems

This paper proposes an efficient downlink resource allocation scheme for Orthogonal Frequency Division Multiple Access based WiMAX systems using the Adaptive Modulation and Coding mode operation. Given a set of user requests, the proposed algorithm determines the modulation scheme and allocates a two-dimensional (time and frequency) burst to each user. It is known that finding the optimal solution for such a resource allocation problem is NP-complete. To reduce the computation complexity, this paper proposes a heuristic solution. Compared with the Efficient Downlink Bandwidth Allocation (EDBA) algorithm [6], the proposed scheme achieves higher channel utilization and system throughput with similar execution time. Simulation results show that the average channel utilization of the proposed scheme is about 75~85% and that of EDBA is about 60~70%.

User grouping and adaptive modulation for downlink MC-CDMA systems

In this paper, we propose the user grouping and adaptive modulation algorithms for downlink Multi-Carrier Code Division Multiple Access (MC-CDMA) systems. Under a frequency-selective fading channel, we adaptively assign users into groups by their channel state information (CSI) such that spectrum efficiency is improved and BER is reduced. After grouping, we assign bit loading and allocate transmission power for each user according to its effective channel response. Our scheme aims at maximizing total system data rate under both the total power and the BER bound constraints. Simulation results show that our scheme outperforms at bit error rate and data rate.

Fixed contention window backoff scheme for the contention-based IEEE 802.11 MAC

In order to develop a contention-based MAC with quality of service (QoS) guarantee based on the distributed coordination function (DCF), we investigate the backoff scheme. We optimize the channel utilization with the constraint that delay requirement is guaranteed. Based on our analysis data, we propose the fixed contention window backoff (FCWB) scheme to get the best performance. The optimal performance can be simply achieved by setting the minimum contention window and the transmission opportunity (TXOP) to the values derived from our procedure.

An Analysis of Channel Utilization for the IEEE 802.11 with Aggregation

The IEEE 802.11 MAC provides a method for multiple users to share the wireless media. The channel utilization is limited because of protocol overhead no matter how fast the payload is transmitted. To increase utilization, frame aggregation is a straightforward way to improve the channel efficiency. This paper presents an analytic method to estimate the utilization for RTS/CTS-based contention access mechanism with unidirectional or bidirectional aggregation. Simulation results are also provided to show the accuracy of the analytic model