802.11 standards support high data rates for a low price and thus provides an economical way for WLANs. On the other hand, 3G standards offer a much wider area of coverage that enables ubiquitous connectivity. The integration of them takes advantages from both sides and offers the possibility of achieving anywhere, anytime cost-efficient Internet access. To facilitate such integration, seamless vertical handoff is one of the major challenges because it needs to make physical movement transparent to mobile users and preserves application-level connectivity. Previous works did not consider the impact of authentication mechanisms on the performance of vertical handoff, especially on its delay. In a 3G-WLAN integration environment, since 3G and WLAN may use different authentication servers, when a mobile terminal hands over across them, certain authentication procedure needs to be performed. According to the literature, such authentication delay may be as high as hundreds of milliseconds, which is intolerable for delay-sensitive applications. We present seamless authentication protocols (SAPs) for vertical handoff in wireless heterogeneous networks, to reduce this delay. Simulation results show that SAP significantly reduces the delay caused by authentication procedures in vertical handoff.

It is well known that IEEE 802.11 provides a physical layer multirate capability and, hence, MAC layer mechanisms are needed to exploit this capability. Several solutions have been proposed to achieve this goal. However, these solutions only consider how to exploit good channel quality for the direct link between the sender and the receiver. Since IEEE 802.11 supports multiple transmission rates in response to different channel conditions, data packets may be delivered faster through a relay node than through the direct link if the direct link has low quality and low rate. In this paper, we propose a novel MAC layer relay-enabled distributed coordination function (DCF) protocol, called rDCF, to further exploit the physical layer multirate capability. We design a protocol to assist the sender, the relay node, and the receiver to reach an agreement on which data rate to use and whether to transmit the data through a relay node. Considering various issues, such as, bandwidth utilization, channel errors, and security, we propose techniques to further improve the performance of rDCF. Simulation results show that rDCF can significantly reduce the packet delay, improve the system throughput, and alleviate the impact of channel errors on fairness

It is well known that IEEE 802.11 provides a physical layer multi-rate capability, and hence MAC layer mechanisms are needed to exploit this capability. Several solutions have been proposed to achieve this goal. However, these solutions only consider how to exploit good channel quality for the direct link between the sender and the receiver. Since IEEE 802.11 supports multiple transmission rates in response to different channel conditions, data packets may be delivered faster through a relay node than through the direct link if the direct link has low quality and low rate. In this paper, we propose a novel MAC layer relay-enabled distributed coordination function (DCF) protocol, called rDCF, to further exploit the physical layer multi-rate capability. We design a protocol to assist the sender, the relay node and the receiver to reach an agreement on which data rate to use and whether to transmit the data through a relay node. Considering various issues such as bandwidth utilization and channel errors, we propose techniques to further improve the performance of rDCF. Simulation results show that rDCF can significantly improve the system performance when the channel quality of the direct link is poor.

Reducing the power consumption of the wireless network interface (WNl) is an effective way to prolong the battery lifetime of the mobile terminal. It takes some time for the WNI to transit from the power-saving mode to the active mode. This transition delay and the error-prone wireless link bring many challenges for designing power-aware and QoS-aware service models. In this paper, we present a novel power-conserving service model for streaming applications over wireless networks. At the base station side, a new scheduling algorithm, called rate-based bulk scheduling (RBS), is designed to decide which flow should be served at which time. The mobile terminal relies on a proxy to buffer data so that the WNI can sleep for a long time period to save power. To deal with channel errors, a novel adaptive technique is presented to adjust the sleep time of the WNI according to the channel condition. Through analysis, we prove that RBS can provide delay guarantee and it is more power efficient than other rate-based fair queuing algorithms. We use audio-on-demand as a case study to evaluate the performance of RBS. Experimental results show that RBS achieves excellent QoS provision for each flow and significantly reduces the power consumption.

A set of enhancements to the IEEE 802.11 standard, viz. the IEEE 802.11e have been proposed to meet the increasing demand for quality of service. The standard provides a means for service differentiation by using multiple traffic categories at each node, where each traffic category has its own individual parameters such as priority, inter-frame space and contention window size. After each successful transmission, the contention window size is decreased based on a static equation, which may result in poor channel utilization and a decrease on the system throughput. In this paper, we propose a new protocol, called enhanced distributed coordination function with dual-measurement (EDCF-DM), to address this issue. EDCF-DM is based on the idea of reducing the number of idle slots by dynamically varying the contention window size according to the current traffic state of the traffic categories at each node. Meanwhile, it carefully adapts the contention window size based on the network condition of the system to avoid incurring extra collisions. Extensive simulations are performed to evaluate the proposed protocol. Simulation results demonstrate that EDCF-DM provides a good service differentiation and outperforms the standard 802.11e in terms of channel utilization, throughput and packet delay.

The fair queuing model has been widely used to provide QoS for flows sharing a wireless channel. In fluid fair queuing, a flow cannot reclaim its service loss due to absence. As a result, fair queuing models that emulate fluid fair queuing cannot provide good service differentiation under bursty data traffic. On the other hand, strict priority queuing (SPQ) can provide good service differentiation at the cost of QoS provision. To achieve both service differentiation and QoS provision, we propose a new service model called absence compensation fair queuing. The basic idea is to allow a flow to get compensation of its service loss due to absence. Since the proposed service model is based on fair queuing, QoS provision is guaranteed. We first verify these properties by analysis, and then evaluate the performance compared to weighted fair queuing (WFQ) and SPQ. Simulation results show that our service model can provide much better service differentiation than WFQ, and outperforms SPQ in terms of QoS provision.

Many studies show that the wireless network interface (WNI) accounts for a significant part of the power consumed by mobile terminals. Thus, putting the WNI into sleep when it is idle is an effective technique to save power. To support streaming applications, existing techniques cannot put the WNI into sleep due to strict delay requirements. We present a novel power-aware and QoS-aware service model over wireless networks. In the proposed model, mobile terminals use proxies to buffer data so that the WNIs can sleep for a long time period. To achieve power-aware communication while satisfying the delay requirement of each flow, a scheduling scheme, called priority-based bulk scheduling (PBS), is designed to decide which flow should be served at which time. Through analysis, we prove that the PBS service model can provide delay assurance and achieve power efficiency. We use audio-on-demand and Web access as case studies to evaluate the performance of the PBS service model. Experimental results show that PBS achieves excellent QoS provision for each flow and significantly reduces the power consumption.

It is well known that IEEE 802.11 provides a physical layer multirate capability. In this paper, we propose a novel MAC layer relay-enabled point coordination function (PCF) protocol, called rPCF, to exploit this capability. With multiple data rates in response to different channel conditions, if the direct link has low data rate, data packets may be delivered faster through a relay node. To enable MAC layer relay, the access point needs to collect information about the channel conditions, and notify mobile nodes which data rate to use and whether to use a relay node. We design protocols to achieve this goal and refine these protocols to minimize the control overhead. Simulation results show that rPCF can significantly improve the system performance in terms of system throughput and transmission delay with a very small control overhead.

Bluetooth is a new short-range radio technology to form a small wireless system. In most of the current Bluetooth products, the master polls the slaves in a round robin manner and it may waste a significant amount of power. We propose an adaptive power conserving scheme to address this problem. The proposed solution schedules each flow based on its predictive rate and achieves power optimization based on a low-power mode existing in Bluetooth standard. Unlike other research work related to low-power, we also consider QoS of each flow. Theoretical analyses verify that our scheme can achieve throughput guarantees, delay guarantees, and fairness guarantees. Simulation results demonstrate that our scheme can save a significant amount of power compared to the round robin scheme and it shows that there exists a tradeoff between power and delay under various traffic models.

Bluetooth is a promising technology aimed at supporting short-range wireless communication. To achieve the advantage of simplicity and low-power, the master/slave model is used. However, this model has some drawbacks since no direct link exists between any two slaves in a piconet. Consequently, slave-to-slave communications must go through the master, and the master has to use extra bandwidth to forward the packets exchanged between slaves. We propose a time-slot leasing (TSL) and an enhanced TSL (ETSL) approach to address these drawbacks. Simulation results demonstrate that the TSL approach, especially the ETSL approach, can significantly improve the system performance compared to the standard master/slave model.