Jeng Ji Huang

Uplink capacity enhancement for an integrated HAPS-terrestrial CDMA system

The integration of a high altitude platform station (HAPS) with existing terrestrial communication systems would be beneficial as several kinds of wireless services can be easily extended into remote areas. In this letter, we first examine the uplink capacity of a sharing-band overlaid HAPS-terrestrial code division multiple access (CDMA) system and an improved version using a doughnut-like cell model. Numerical results indicate that the uplink capacity is poor under both the proposals due to serious inter-system interference. To mitigate this problem, a ring structure is proposed for HAPS when integrated with a terrestrial cellular system

Designing a fair scheduling mechanism for IEEE 802.11 wireless LANs

A fair scheduling mechanism called distributed elastic round robin (DERR) is proposed in this letter for IEEE 802.11 wireless LANs operated in a distributed manner. To quantify the fairness, we not only derive its fairness bound, but also observe the fairness through ratios of throughput and weight using a simulation approach. By numerical comparisons among DERR, distributed deficit round robin (DDRR), and IEEE 802.11e, we demonstrate that DERR outperforms the other two mechanisms in performance and fairness.

Capacity Enhancement for Integrated HAPS-Terrestrial CDMA System

In this paper, we consider the uplink capacity of an integrated high altitude platform station (HAPS)-terrestrial code division multiple access (CDMA) system in which sharing band overlay configuration is used. To increase system capacity, an enhancement is investigated by assuming that directional antenna is used for high mobility users to access to the HAPS. This will lead to a reduction of not only the interference from HAPS to terrestrial, but also the interference from terrestrial to HAPS as the uplink power to HAPS can accordingly be increased. Numerical results are obtained analytically and it is shown that the system capacity can be enhanced significantly under the proposed scheme

An MSI-Based Scheduler for IEEE 802.11e HCCA

Variable bit rate (VBR) traffic may have a wide range of packet sizes and generation intervals. While the former can be handled in the IEEE 802.11e uplink scheduling, e.g., by adapting transmission opportunity (TXOP) durations according to backlogged traffic reports, the latter may cause packet losses if service intervals of the scheduling do not fit the generation intervals. In this paper, a scheduler that employs adaptive maximum service interval (MSI) is proposed to fix this problem, while attempting to minimize scheduling overheads.

A Scheduling-Based Delay-Tolerant Power Saving Scheme for the IEEE 802.16e Wireless MAN

When the system load is high or congestion occurs, a base station (BS) in the IEEE 802.16e metropolitan area network (MAN) is not able to transmit all buffered packets to mobile stations (MSs) within a frame interval, resulting in extra energy consumption for MSs to wake up for receiving pending packets. To save energy for such a situation, we first propose a scheduling- based delay-tolerant traffic indication message (D-TIM) scheme to enable a BS to properly schedule queued packets for non-real-time variable rate (NRT-VR) and best effort (BE) using information of delay threshold (DT), which can be derived from QoS parameters, and to determine the time offset between the frame in which an MS has to wake up and the frame containing a TIM message. With the time offset, MSs are able to wake up more precisely so that energy can be efficiently saved and less packet delay can be reached. Furthermore, two variants of D- TIM are also proposed for solving the problem of higher jitter to the unsolicited grant service (UGS). Through simulation, we demonstrate that D-TIM outperforms other related schemes in the literature in terms of energy efficiency and packet delay and the two variants reduce jitter greatly as compared to D-TIM while maintaining good energy efficiency and less packet delay.

An Efficient Channel Scan Scheduling Algorithm for VoIP Handoffs in WLANs

To guarantee seamless handoffs between access points (APs) is one of the most decisive factors in providing realtime applications such as voice over Internet protocol (VoIP) in IEEE 802.11 networks. It is because in wireless local area networks (WLANs) there is no specific control channel for executing a handoff process and a mobile station (MS) has to search for new APs from channel to channel by temporarily disconnecting its association with the old AP. While previous studies are mainly focused on how to reduce the handoff latency, in this paper a channel scanning algorithm is proposed to schedule suitable time for performing a handoff process efficiently. In the proposed algorithm, the voice activity is taken into consideration, and the handoff process is performed during silent periods. Extensive simulations are conducted to investigate the performance of the proposed algorithm in terms of the handoff success probability and the packet loss rate, and the results obtained in this paper can serve as a good reference for the system design.

A Dynamic Resource Reservation Scheme Designed for Improving Multicast Protocols in HMIPv6-Based Networks

This paper aims at proposing a dynamic resource reservation scheme to enhance wireless multicasting protocols run in the hierarchical mobile IP version 6 (HMIPv6) based networks. The novelty of this scheme relies on techniques of dynamic resource reservation, priority, pre-registration, and path prediction, which are used to improve wireless multicasting and guarantee service continuity. Through numerical examples, we demonstrate that the proposed scheme performs well in terms of robustness, adaptiveness, and quality of service (QoS) guarantee

A scheme to reduce merging collisions in TDMA-based VANETs

It is well known that a time division multiple access (TDMA)-based medium access control (MAC) is advantageous in many aspects in vehicular ad hoc networks (VANETs). These include its ability to prevent the hidden-terminal problem, and the guarantee of strict quality-of-service (QoS) for providing real-time applications. However, time slot assignments to vehicles could suffer from an unstable problem, called merging collisions. This problem is due mainly to the changing network topology of a VANET, which can be characterized by vehicles joining into or leaving from a cluster of vehicles. In this paper, we focus on the problem of unstable time slot assignments facing several existing TDMA approaches, and a scheme is proposed to effectively alleviate this problem.

Interference Reduction for Terrestrial Cellular CDMA Systems via High Altitude Platform Station

In a cellular code division multiple access (CDMA) system, uplink capacity is limited by interference. For a ground-based CDMA system or a high altitude platform station (HAPS) CDMA system, the interference is contributed by users in the same cell and in other cells. In this paper, a novel scheme is proposed to reduce both the same-cell and other-cell interferences in a cellular CDMA system. The proposed scheme attempts to lower the required transmitting power for each user by integrating terrestrial base stations (BSs) with a HAPS to provide two separate paths for signal reception. Numerical results show that the total interference is significantly reduced and the uplink capacity is improved under the proposed scheme, compared to either a HAPS CDMA system or a ground-based CDMA system.

A new method to improve the performance of TCP SACK over wireless links

In this paper, a new method to improve TCP SACKs performance over wireless links is presented. The proposed method attempts to differentiate congestion and corruption loss by the use of tagged segments. Whenever a congestion loss occurs at a router, a tagged segment is dropped at the router and a notification is generated. Loss of the tagged segment is eventually detected by the TCP to serve an indication of congestion. When the tagged segment is not lost due to congestion, its survival then further serves as a trial signal for the TCP to detect corruption loss. Contrasting to most existing approaches employing explicit notification; our method is attractive in that it requires no modification to the receiving end. Simulation results show that our method significantly improves the performance of TCP SACK over both low and long delay noisy links.