Chun-Ting Chou

Analysis of adaptive bandwidth allocation in wireless networks with multilevel degradable quality of service

A wireless/mobile network supporting multilevel quality of service (QoS) is considered. In such a network, users or applications can tolerate a certain degree of QoS degradation. Bandwidth allocation to users can, therefore, be adjusted dynamically according to the underlying network condition so as to increase bandwidth utilization and service providers revenue. However, arbitrary QoS degradation may be unsatisfactory or unacceptable to the users, hence resulting in their subsequent defection. Instead of only focusing on bandwidth utilization or blocking/dropping probability, two new user-perceived QoS metrics, degradation ratio and upgrade/degrade frequency, are proposed. A Markov model is then provided to derive these QoS metrics. Using this model, we evaluate the effects of adaptive bandwidth allocation on user-perceived QoS and show the existence of trade offs between system performance and user-perceived QoS. We also show how to exploit adaptive bandwidth allocation to increase system utilization (for the system administrator) with controlled QoS degradation (for the users). By considering various mobility patterns, the simulation results are shown to match our analytical results, demonstrating the applicability of our analytical model to more general cases.

The MBOA-WiMedia specification for ultra wideband distributed networks

The WiMedia Alliance is undertaking the development of an UWB-based system specification with participation from more than 170 companies. UWB technology will provide data rates up to 480 Mb/s within a range of up to 10 m. High-rate UWB will enable fast download of content from one consumer electronic (CE) device to the next in seconds instead of minutes or longer. In addition, the low-power characteristic of UWB will make possible the ubiquitous use of this technology in portable and mobile CE devices, such as cameras, MP3 players, and CD players. The WiMedia Alliance is specifying the physical layer, the MAC sublayer, and convergence layers. The WiMedia PHY layer is based on multiband orthogonal frequency-division multiplexing. The WiMedia MAC is completely distributed, making it an excellent candidate not only for the aforementioned UWB applications, but also for the next-generation MAC protocols in the domain of cognitive radios as well as in cooperative communications

Spectrum agile radio: radio resource measurements for opportunistic spectrum usage

Radio spectrum allocation is undergoing radical rethinking. Regulators, government agencies, industry, and the research community have recently established many initiatives for new spectrum policies and seek approaches to more efficiently manage the radio spectrum. In this paper, we examine new approaches, namely, spectrum agile radios, for opportunistic spectrum usage. Spectrum agile radios use parts of the radio spectrum that were originally licensed to other radio services. A spectrum agile radio device seeks opportunities, i.e. unused radio resources. Devices communicate using the identified opportunities, without interfering with the operation of licensed radio devices. The identification of spectrum opportunities is coordinated by policies, which are defined by, and under the control of, the radio regulator. Our approach is motivated by the publications of the next generation communications, XG, research project of the USA-based Defense Advanced Research Projects Agency, DARPA. We focus on IEEE 802.11k for radio resource measurements as an approach to facilitate the development of spectrum agile radios.

Cooperative communication MAC (CMAC) - a new MAC protocol for next generation wireless LANs

Reliability is a big challenge to any wireless transmission as wireless networks tend to drop a large proportion of frames due to channel errors. To improve reliability over the noisy wireless channels, forward error correction (FEC) schemes can be employed for wireless networks. Static and adaptable FEC algorithms can improve or degrade the performance of the wireless networks if their overheads are not matched properly to the underlying channel error, especially when the path loss fluctuates widely. This paper provides a new approach of alleviating the problem from a pure medium access control (MAC) centric perspective. The new MAC protocol, called cooperative MAC (CMAC) enhances the existing IEEE 802.11e wireless local area network (WLAN) MAC protocol by introducing spatial diversity which is provided via user cooperation. We prove that this protocol greatly enhances the robustness of the WLAN operation. Additionally we compare the performance of CMAC protocol with the direct and multi-hop transmissions.

An enhanced inter-access point protocol for uniform intra and intersubnet handoffs

An enhanced IEEE 802.11 inter-access point protocol (IAPP) is proposed to provide a unified solution for both intra and intersubnet handoff processes. The proposed enhancement relies on the access points (APs) interoperability with other APs, provided by the IP-based IAPP, so as to enable the intra and intersubnet link-layer frame buffering-and-forwarding. This enhancement not only eliminates frame losses during an intrasubnet handoff but, more importantly, realizes loss-free, fast intersubnet handoffs without modifying the IP-mobility protocols such as mobile IP. Our ns-2-based simulation results show that the intersubnet handoff process is transparent to the mobile hosts TCP session. Moreover, the enhanced IAPP supports higher user mobility and achieves a higher TCP throughput - up to 50 percent improvement over the original IAPP.

Spectrum agile radio: capacity and QoS implications of dynamic spectrum assignment

Radio spectrum is very scarce today because a considerable amount of the spectrum is set aside for licensed wireless applications. With the rapid growth of wireless technologies, spectrum scarcity has become a serious problem as more and more wireless applications compete for very little spectrum. On the other hand the licensed spectrum allocated to applications like television, cellular telephony and public safety show very little usage over time at different geographical locations. The evolution of newer technologies has been seriously impaired because of current regulatory constraints on the operation of these networks in licensed spectrum, such as TV bands, and is being addressed by FCC through its recent rule making. With the goal of ubiquitous communication in mind, we look into spectrum agile radio, a new technology enabled by such FCC rule making, and study its advantages over conventional radios. In this paper, we first show the utilization achievable by agile radios through simple analysis. Then we will outline two types of agile radios and derive their maximum capacities. Then we will go ahead and derive the rules that increase the spectrum utilization using agile radios. We then highlight how spectrum agile radio impacts quality of service as defined in conventional sense

Mobility support enhancements for the WiMedia UWB MAC protocol

The WiMedia Alliance is currently specifying a distributed medium access control (MAC) protocol for ultra wide band (UWB) communications in the wireless-personal-area-network (WPAN) environment. Even though this MAC protocol includes basic mechanisms to provide mobility support, such support can be improved via coordination among devices. In this paper, we propose two enhancements for mobility support in the WiMedia MAC protocol. Our enhancements are based on the beacon period (BP)-merging algorithm of the WiMedia MAC protocol with a new distributed coordination. Two cases of mobile WPANs are studied to demonstrate the effectiveness of the proposed enhancements

Peer discovery for device-to-device (D2D) communication in LTE-A networks

Device-to-device (D2D) communication is one of the key technologies in Long Term Evolution - Advanced (LTE-A) for improving network capacity and resource utilization. D2D communication can not only effectively reduce traffic loads to the core network but also reduce power consumption of user equipments (UEs), thus making it a desirable candidate for machine-to-machine communication in cellular networks. Among all functionalities required to enable D2D communication, peer discovery is arguably the most critical one. In this paper, we propose a distributed peer discovery protocol for LTE-A networks. The proposed protocol requires UEs to advertise their presence based on random access. In order to minimize resource consumption on discovery, an adaptive resource allocation algorithm based on the number of requesting D2D UEs is also proposed. Our numerical analysis shows that a very high discovery probability (e.g., 0.99) can be achieved using only 1% of the evolved Node Bs (eNBs) uplink resource.

The impact of concurrency gains on the analysis and control of multi-threaded Internet services

With the proliferation of Internet services, many solutions have emerged to provide quality-of-service (QoS) guarantees when the demands for the hosted services exceed the servers capacity. We take an analytical approach to answering key questions in the design and performance of application-level QoS techniques, especially those that are based on the multi-threading or multi-processing abstraction. Key to our analysis is the integration of the effects of concurrency into the interactions between multi-threaded services. To this end, we extend traditional time-sharing models to develop the multi-threaded round-robin (MTRR) servers, a more accurate model of operation of typical multi-threaded Internet services. For this model, we first develop powerful, yet computationally-efficient, mathematical relationships that describe the performance (in terms of throughput and response time) of multi-threaded services. We then apply optimization techniques to derive the optimal allocation of threads given specific QoS objective functions. Using realistic workloads on a typical Web server, we show the efficacy and accuracy of the proposed new methodology.

An adaptive multichannel protocol for large-scale machine-to-machine (M2M) networks

With the emergence of machine-to-machine (M2M) communications, trillions of devices will soon be interconnected to support new applications and services. The success of M2M communication relies on the scalability of underlying network architectures and protocols. In this paper, an adaptive multi-channel medium access control (MAC) protocol is proposed to address the scalability issue in M2M communications. The proposed MAC protocol enables devices to (1) real-time estimate the number of competing devices and (2) adjust their operation parameters to maximize channel utilization. Our numerical results show that the proposed protocol outperforms the existing multi-channel protocols, especially when the number of competing devices is large and fluctuates with time.