Jung-Shyr Wu

Hot-spot traffic relief with a tilted antenna in CDMA cellular networks

Direct-sequence code division multiple-access (DS-CDMA) cellular networks are highly promising in terms of their potential to provide more capacity than an advanced mobile phone system (AMPS). However, heterogeneous traffic loading causes traffic congestion in a CDMA hot-spot. This paper presents a tilted antenna mechanism for sectored cells in CDMA cellular networks to relieve the congestion in a hot-spot sector. The fixed antenna-tilted mechanism, which only tilts the hot-spot antenna, can provide the merit of traffic balancing. Besides, we design a dynamic antenna-tilted mechanism in which tilting the antennas of the hot spot and its adjacent cell sectors is based on varying the signal-to-noise ratio (SNR). The dynamic mechanism can automatically tilt the antenna corresponding to the variation of traffic. Consequently, more capacity can be provided than in a fixed tilting mechanism, which only tilts the hot-spot antenna. Another benefit is the traffic-balancing effect with a tilted-antenna mechanism that reduces the transceivers of a hot-spot base station. Therefore, extra facilities are unnecessary for the hot spot than for a normal or light traffic sector.

Performance study for a microcell hot spot embedded in CDMA macrocell systems

The code-division multiple-access (CDMA) system can provide more capacity than other systems, and the hierarchical layer of cells is required for system design. However, the problem is whether the same radio frequency (RF) channels used in a CDMA overlayed/underlayed macrocell and microcell structure also obtain a high capacity as in the homogeneous structure. We investigate the interference of uplink and downlink from both the microcell and macrocell under a hierarchical structure. A downlink power control scheme and two power control methods for the uplink are also considered. Performance measures such as blocking probability, C/I, capacity, and service hole area are also obtained by computer simulation. Besides, some extra efforts for a microcell are also noted, such as more power need to be transmitted by a microcell base station (BS) if the same RF channels are used in the hierarchical structure. The capacities of macrocell and microcell in the overlaying/underlaying structure are limited by the uplink and downlink, respectively. With downlink power control, the microcellular capacity can be increased. However, the combination of downlink power control for the microcell and C/I uplink power control for the macrocell causes the overall system capacity to significantly increase.

A Channel Access Scheme to Compromise Throughput and Fairness in IEEE 802.11p Multi-Rate/Multi-Channel Wireless Vehicular Networks

Wireless access in vehicular environment (WAVE) architecture of intelligent transportation system has been standardized in the IEEE 802.11p specification. The WAVE network supports the features of multi-rate and multi-channel and it is going to be widely deployed in realistic roadway environments in order to provide traffic information and convenient services. However, the adopted contention-based medium access control protocol, which confronts the performance anomaly problem, would severely downgrade transmission efficiency between road-side-unit (RSU) and on-board-unit (OBU) because they may use diverse data transmission rates to access channel. As a solution, this paper proposes the vehicular channel access scheme (VCAS) to group a number of OBUs with similar transmission rates into one channel to optimize the channel throughput, while the group sizes of channels are controlled in order to fulfill the fairness requirement. To flexibly compromise the tradeoff between throughput and fairness, a marginal utility model is proposed in this paper. Simulation results demonstrate that the proposed VCAS with marginal utility provides a flexible way to handle versatile vehicular scenarios.

Performance improvement for a hotspot embedded in CDMA systems

The CDMA system can provide more capacity than other systems and the hierarchical layer of cells is required for system design. However, the problem is whether the same RF channels used in CDMA overlayed/underlayed macrocell and microcell structure also obtain a high capacity as in the homogeneous structure. In this study, we investigate the interference of uplink and downlink from both the microcell and macrocell under a hierarchical structure. Downlink power control scheme and two power control methods for uplink are also considered. Performance measures such as blocking probability, C/I, capacity and service hole area are also obtained by computer simulation. With downlink power control, microcellular capacity can be increased. However, combining of downlink power control for microcell and C/I uplink power control for macrocell causes the overall system capacity to significantly increase.

Mobile IPv6 Mobility Management in Integrated Wi-Fi and WiMAX Networks

The MIPv6 has been proposed to solve the problem of mobility in mobile networks by handling routing of IPv6 packets to mobile nodes that handover across the visited and home networks. However, the MIPv6 introduce long handover delay and signaling load. The HMIPv6 can solve the problem by splitting the handover management to macro-mobility and micro-mobility schemes. Although much research was focused on modified MIPv6 to get better efficient performance, there are few papers to discuss admission control when considering handover and mobility management. In this paper, we extend HMIPv6 binding update message to support CAC schemes. These CAC schemes can reduce the probability of the handoff dropping and cell overload, and limit the new call blocking probability. We also propose our schemes to a realistic scenario in integrated Wi-Fi and WiMAX networks.

Agent-Based Scheduling Scheme for IEEE 802.11p Wireless Vehicular Networks

The wireless access in vehicular environment (WAVE) architecture of intelligent transportation system (ITS) has been standardized in the IEEE 802.11p specification and it is going to be widely deployed in many roadway environments in order to provide prompt emergency information and internet services. A typical WAVE network consists of a number of WAVE devices, in which one is the road-side-unit (RSU) and the others are on-board-units (OBUs), and supports one control channel (CCH) and one or more service channels (SCH) for OBUs to access. The CCH is used to transport the emergency messages and service information of SCHs and any SCH is used to carry internet traffic of OBUs. However, the IEEE 802.11p contention-based medium access control protocol would downgrade transmission efficiency when the number of OBUs served by a RSU is large and all WAVE devices equipped with a single transceiver access to the same SCH. Synchronizing all WAVE devices to periodically and equally access the CCH and an SCH will cost as much as 50% channel resource wastage on SCH. As a solution, we propose an efficiency-improvement scheme, namely agent-based scheduling (ABS) scheme, which promotes the SCH throughput by means of choosing one OBU to be the agent to schedule the other OBUs contending the access opportunities on one SCH to access the other SCH served by RSU in a contention-free manner. Numerical results and simulation results demonstrate that the proposed scheme indeed improves the standard transmission efficiency.

Listening Interval Spreading Approach (LISA) for Handling Burst Traffic in IEEE 802.16e Wireless Metropolitan Area Networks

The mobile wireless metropolitan area network (WMAN) architecture imposes a demanding power management requirement on mobile stations (MSs) in order to prolong the lifetime of MS. The base station (BS) will functionally serve as a buffer for non-real-time traffic distribution to the multiple MSs associated with it, and thus naturally provide MSs with the power saving capability. However, the power management scheme in IEEE 802.16e standard, which was designed for handling sleep pattern of non-real-time traffic, often use timeout approach to trigger sleep mode, as a certain idle time prior entering sleep mode will render a potential latency and limit the overall power saving capacity. Moreover, the fast growing sleeping window would cause long packet reception delay. As a solution, we propose a new scheme, namely listening interval spreading approach (LISA), which redistributes the idle periods and a number of interim listening periods in order to reduce the response time of interactive traffic, such as HTTP applications. As confirmed by the performance evaluation, the proposed LISA can achieve significant response time reduction as well as better power saving efficiency than standard.

Performance study of multi-channel access schemes in two-tier CDMA cellular systems

According to Wu and Chung (1996), system performance and capacity degrade due to co-channel interference between microcells and macrocells in hierarchical structure if the same channel is used. In order to avoid co-channel interference, different channels are assigned for macrocells and microcells. This paper proposes three multi-channel access schemes in which the same channel can be used in the macrocell and hot-spot (or microcell) simultaneously. Using the proposed multi-channel access schemes, we can avoid co-channel interference between a macrocell and hot-spot and provide more capacity.

Performance study of traffic balancing via antenna-tilting in CDMA cellular systems

CDMA cellular networks are very promising to provide more capacity than the AMPS system. However, heterogeneous traffic loading will cause traffic congestion in hot-spots with the CDMA system. In this paper, the tilted antenna mechanism for sectored cells in CDMA cellular networks is provided to relieve congestion in the hot-spot sector. The proposed mechanism which tilts the hot-spot antenna can meet the blocking probability of the hot-spot sectors and the adjacent sectors below 1%. Besides congestion relief for the hot-spot, another benefit is the traffic balancing effect with a tilted antenna mechanism that will reduce the transceivers of the hot-spot base station so that one need not provide more extra facilities for hot-spots than for normal or light traffic sectors.

Coordinated scheduling scheme for IEEE 802.11p wireless vehicular networks using centralized scheduling of IEEE 802.16e wireless metropolitan area networks

The IEEE 802.11p architecture imposes a demand- ing reliable transmission requirement on both road-side-unit (RSU) and on-board-unit (OBU) in order to provide emergency messages, traffic information, and internet services. The IEEE 802.16e network, which has been designed as a centralized control system to provide the mobile services in a metropolitan area network (MAN), can assist the WAVE network to fulfill the requirement. As all OBUs equip with both IEEE 802.11p and IEEE 802.16 transceivers, the deficiency of the IEEE 802.11p contention-based medium access control protocol can be curbed by using the IEEE 802.16e centralized scheduling scheme. As a solution, we propose a novel scheme, namely coordinated scheduling scheme (CSS), which allows the IEEE 802.11p OBUs to access service channels in a contention-free manner by means of IEEE 802.16 centralized scheduling. As confirmed by the performance evaluation, the proposed CSS can achieve significant throughput improvement, as compared with the IEEE 802.11p standard.