Mobile interaction is fundamentally tied to the screen, requiring users to look at and physically touch their devices by tapping on-screen controls. We introduce AcouLetter, a system for recognizing fine-grained, mid-air alphabetic thumb gestures above the screen that enables one-handed and non-contact input. Our method fuses acoustic signals with inertial sensor data to discern the subtle characteristics of each letter gesture, capturing the dynamics of the hand’s motion. We employ a multi-stage architecture that integrates a convolutional network for acoustic features and a transformer-based network for inertial data. AcouLetter first detects the initiation of the gesture using inertial measurements, determines which hand holds the phone, and then classifies the specific letter among 27 classes, including the 26 letters of the alphabet and a null gesture. The system achieves high accuracy and demonstrates robust performance even under ambient noise while a user is standing or walking. Since letter-shaped gestures are meaningful and readily recognizable, they support an intuitive system of expressive shortcuts in which letters act as mnemonics for complex functions. A user study further confirmed the practicality of this approach for one-handed, contact-free interaction. Our results demonstrate that this expressive alphabetic gestural interface is a feasible new modality for commodity smartphones.

Emotional voice conversion (EVC) aims to modify the emotional style of speech while preserving its linguistic content. In practical EVC, controllability, the ability to independently control speaker identity and emotional style using distinct references, is crucial. However, existing methods often struggle to fully disentangle these attributes and lack the ability to model fine-grained emotional expressions such as temporal dynamics. We propose Maestro-EVC, a controllable EVC framework that enables independent control of content, speaker identity, and emotion by effectively disentangling each attribute from separate references. We further introduce a temporal emotion representation and an explicit prosody modeling with prosody augmentation to robustly capture and transfer the temporal dynamics of the target emotion, even under prosody-mismatched conditions. Experimental results confirm that Maestro-EVC achieves highquality, controllable, and emotionally expressive speech synthesis.

Wi-Fi channel state information (CSI)-based gesture recognition systems have recently gained significant attention. One major challenge faced by these systems is that CSI measurements are affected by various conditions, including environmental factors and user orientation, leading to degraded sensing performance in unseen environments. Due to this challenge, most existing systems require multiple transceivers placed only a few meters apart from each other, and users are required to perform gestures within the proximity of these transceivers. Despite these systems robustly sensing users, their sensing range and mobility are severely restricted. In this article, we propose UbiGest, a smartphone-based gesture recognition system. UbiGest leverages beacon frames from multiple nearby APs over adjacent channels, enabling ubiquitous gesture recognition while mitigating the effects of the environment, user position, and user orientation. The system, even with limited computational resources, extracts features from noisy CSI data collected from a smartphone and robustly classifies a user’s gesture. By incorporating few-shot learning, the system maintains its robustness in challenging conditions, such as in entirely new environments with only one or two available APs. The extensive experimental results demonstrate that UbiGest achieves an accuracy of 95.3% in in-domain evaluation and 92.6% in cross-domain evaluation, on average.

Wireless video multicast over IEEE 802.11 WLANs is a viable approach to bridging the gap between limited wireless resources and the ever-increasing mobile video traffic demand. However, existing wireless multicast mechanisms have several limitations, such as low spectral efficiency, high feedback overhead, and lack of consideration of the frame aggregation feature of current WLANs. In this paper, we propose FlexVi, a flexible wireless multicast solution for efficient video streaming over WLANs. Considering the frame aggregation of the current WLANs, FlexVi allows an access point to dynamically adjust the data rate on the basis of three factors: available wireless bandwidth, heterogeneity of the channel qualities among the clients, and the priorities among the video frames in terms of video quality. In addition, by harnessing the orthogonality of the subcarriers in the orthogonal frequency division multiplexing, FlexVi enables multiple clients to deliver their feedback to an access point simultaneously without collision, which results in very low feedback overhead. We verified the feasibility of FlexVi through experiments on a software defined radio platform. We also conducted an extensive simulation study and found that FlexVi outperforms the latest wireless multicast mechanisms.

A wide bandwidth through the channel bonding of IEEE 802.11ac significantly increases the capacity of wireless transmissions. However, multicast traffic is simply transmitted using a narrow 20 MHz bandwidth because the access point (AP) is agnostic to the supportable bandwidth information of clients in a multicast group. This paper proposes WiderCast which enables channel bonding for multicast in IEEE 802.11ac WLANs. In WiderCast, the AP scales the bandwidth for multicast transmissions according to the supportable bandwidths of multicast clients. To enable bandwidth negotiation between the AP and clients without high control overhead, WiderCast employs a novel bandwidth signaling scheme, in which multicast clients can simultaneously deliver their supportable bandwidth information to the AP without collision. We verified the feasibility of WiderCast with a prototype on software-defined radio. We also conducted an extensive simulation study demonstrating that WiderCast achieves higher throughput and improved video quality than traditional wireless multicast. To the best of our knowledge, this is the first work to take into account channel bonding for wireless multicast in WLANs.

Breathing pattern and heart rate can be major indicators of a person's physical condition, and an easy way to measure the vital signs can be useful in health monitoring. In this paper, we propose a new method for identifying the changes in breathing and heart rate pattern of a person using commercial WiFi devices. The amplitude of signal waves can represent the periodic up-and-down chest movements caused by breathing and heartbeat, and prominent changes of the signal pattern can be detected by using the Dynamic Time Warping algorithm. We verified the feasibility of the proposed method in real testbeds and evaluated the method through various experiments with 10 participants. The proposed method achieves 94% accuracy in identifying a subjects physical status. This low-cost method will be useful for monitoring our health in everyday life.

In order to manage data center networks, distributed SDN controllers such as ONOS controller have been researched and used. In this paper, we propose simple live distributed controller migration scheme and design the orchestrator for this scheme. This scheme basically transfers an distributed SDN controller from the overloaded physical machine to the under-loaded physical machine. According to experimental results, a data center network is broken without our scheme when computing load increases. On the other hands, our proposed scheme reduces an average delay as well as avoids a breakdown of the data center network.

With the advancement and development for more than two decades, WiFi has become an indispensable infrastructure in most of indoor venues. Indoor localization using this pre-existing infrastructure has been studied in the literature and is proven practically feasible, which mostly relies on WiFi fingerprints and the corresponding radiomap database. Since the radiomap essentially tells which APs are available and how strong their signals are at positions in the venue, this information can usefully utilized to “steer” to a better AP for the purpose of increasing the user throughput, which we call Guided Tour of Handoff Steering (GUT) in this paper. This steering is not much different from a conventional handoff, but it does not need an expensive scanning process owing to the radiomap, thus some additional handoffs are allowed than conventional handoffs. This leads to higher throughput, because a client can switch to a better AP whenever available. Based on an extensive experiment in a large-scale indoor venue of 119,685m2with 1,734 APs, it is observed that GUT achieves as much as 84% higher throughput, but the number of handoffs increases only a few. This result supports that the handoff steering is not as expensive as the conventional handoff in terms of latency and traffic.

Due to the low-speed GPS transmission and poor signal quality, localization is considered an expensive operation in battery-operated smartphones. This is even worse for apps that need a single location fix such as Foursquare and Flickr rather than continuous navigation because it cannot exploit the less-demanding “warm start” mode of GPS operation. This paper proposes GPS-Tether (GTR) which shares and reuses the known GPS coordinates among mobile devices in the proximity. Benefiting from unremitting Wifi discovery behaviors of smartphones, GTR does not need an additional protocol and does not disrupt operations of non-GTR clients. Experiments based on Samsung Galaxy smartphones and Monsoon Power Monitor show that GTR can extend smartphones battery usage as much as 19% compared to Assisted GPS (A-GPS). One important design goal is that it should require minimal changes for the implementation of GTR, which has been accomplished by incorporating the Wifi virtualization technique.

While numerous efforts have been made to save energy of “client” devices but it has not been addressed for access points (APs) as they are assumed to be supported by AC power. This paper proposes E-MAP, which is an energy saving algorithm for a tethering smartphone that plays a role of mobile AP (MAP) temporarily. It saves MAP's energy by introducing the sleep cycle as in power save mode (PSM) in 802.11 but successfully keeps clients from transmitting while it sleeps. One important design goal of E-MAP is backward compatibility, i.e., it requires no modification on the client side and supports PSM and adaptive PSM (A-PSM) as well as normal constant awake mode (CAM) clients. Experiments show that E-MAP reduces the energy consumption of a Wifi tethering smartphone by up to 54% with a little impact on packet delay under various traffic patterns derived from real-life traces.

Power saving mode mechanism in IEEE 802.11 is designed for reducing power consumption by switching WiFi interface of mobile device between active-state and sleep-state alternately. Since the power consumption in active-state is significantly higher than that in sleep-state, switching between both states should be done carefully; e.g., low priority packets such as delay tolerant packet should not trigger switching to active-state for increasing power saving effect. Delay tolerant traffic, however, also equally affects behaviors of the mechanism since the mechanism is operated within the MAC layer. To overcome this issue, we propose Scrooge which separates delay tolerant traffic from delay sensitive traffic to prevent delay tolerant traffic from impacting on behavior of power saving mechanism. Thus, delay tolerant packets never affect the behavior of power saving mode mechanism. Our prototype implementation improves power saving performance by up to 95% without significant transmission delay under common applications' traffic patterns.

A wireless distribution system (WDS)-based wireless local area network (WLAN) is composed of a base access point (AP) which is connected to wired line and one or more linked APs which are connected to the base AP or other linked APs via wireless links. Usually, WLAN stations try to associate with an AP from which the stations receive the strongest signal strength. However, in WDS-based WLANs, the base AP may provide higher throughput than linked APs although the signal strength of base AP is weaker than those of linked APs. In this paper, we propose a new medium access scheme in which each station uses an AP that can provide the highest throughput to improve the capacity of WDS-based WLANs. To implement the proposed scheme, no modification is required to stations, while some modifications are required to APs. Our experiment and simulation results show that the proposed scheme achieves improved throughput performance over existing schemes.

This paper proposes an energy-saving bit-rate adaptation algorithm for Software-defined Radio (SDR)-based wireless systems, called Joint Rate and Voltage Fallback (JRF). It exploits the unused network time in underutilized networks by using a lower bit-rate than what an underlying rate adaptation algorithm such as Auto-rate Fallback (ARF) or Robust Rate Adaptation Algorithm (RRAA) dictates. While slow or low bitrate communication potentially consumes more energy due to its extended communication time, it saves energy in SDR due to the possibility of reducing the speed and the voltage of the microprocessor that runs the SDR software. The net result favors a lower rate communication in terms of energy performance. To analyze the tradeoff quantitatively, this paper evaluates the computational complexity of SDR communication software by using BBN 802.11b implementation in GNU Radio. Moreover, for an extensive evaluation, we conducted the simulation study based on OPNET, which shows that JRF improves energy cost by as much as 78.0% compared to No Rate and Voltage Scaling (NoRVS) and as much as 51.3% compared to Independent Rate and Voltage Scaling (IRVS).

Being readily available in most of 802.11 radios, multirate capability appears to be useful as WiFi networks are getting more prevalent and crowded. More specifically, it would be helpful in high-density scenarios because internode distance is short enough to employ high data rates. However, communication at high data rates mandates a large number of hops for a given node pair in a multihop network and thus, can easily be depreciated as per-hop overhead at several layers of network protocol is aggregated over the increased number of hops. This paper presents a novel multihop, multirate adaptation mechanism, called multihop transmission opportunity (MTOP), that allows a frame to be forwarded a number of hops consecutively to minimize the MAC-layer overhead between hops. This seemingly collision-prone nonstop forwarding is proved to be safe via analysis and USRP/GNU Radio-based experiment in this paper. The idea of MTOP is in clear contrast to the conventional opportunistic transmission mechanism, known as TXOP, where a node transmits multiple frames back-to-back when it gets an opportunity in a single-hop WLAN. We conducted an extensive simulation study via OPNET, demonstrating the performance advantage of MTOP under a wide range of network scenarios.

Recently, wireless communication methods that exploit the broadcast nature of the wireless medium have been attracting growing attention. Among these methods, opportunistic routing and network coding are regarded as the most promising techniques. While there have been some attempts to combine opportunistic routing with network coding to capture the advantages of both techniques, none of these attempts has considered bit-rate selection for data transmission in multi-rate wireless networks. In this paper, we study the potential benefits of the combination of opportunistic routing and network coding with the bit-rate selection mechanism from an optimization perspective. We develop a theoretical model and algorithm for finding the optimal forwarding scheme for a multi-rate combination of opportunistic routing and network coding in a given network. MIT Roofnet trace-based simulations show that considering bit-rate selection in combination with opportunistic routing and network coding has substantial benefits in terms of the expected transmission time compared to multi-rate opportunistic routing, multi-rate network coding, and a fixed-rate combination approach.

IEEE 802.16 OFDMA systems have gained much attention for their ability to support high transmission rates and broadband access services. For multiuser environments, IEEE 802.16 OFDMA systems require a resource allocation algorithm to use the limited downlink resource efficiently. The IEEE 802.16 standard defines that resource allocation should be performed with a rectangle region of slots, called a burst. However, the standard does not specify how to construct bursts. In this paper, we propose a heuristic burst construction algorithm, called HuB, to improve the downlink capacity in IEEE 802.16 OFDMA systems. To increase the downlink capacity, during burst constructions HuB reduces resource wastage by considering padded slots and unused slots and reduces resource usage by considering the power boosting possibility. For simple burst constructions, HuB makes a HuB-tree, in which a node represents an available downlink resource and edges of a node represent a burst rectangle region. Thus, making child nodes of a parent node is the same as constructing a burst in a given downlink resource. We analyzed the proposed algorithm and performed simulations to compare the performance of the proposed algorithm with existing algorithms. Our simulation study results show that HuB shows improved downlink capacity over existing algorithms.

The legacy multicasting over IEEE 802.11-based WLANs has two well-known problems-poor reliability and low-rate transmission. In the literature, various WLAN multicast protocols have been proposed in order to overcome these problems. Existing multicast protocols, however, are not so efficient when they are used combining with the frame aggregation scheme of IEEE 802.11n. In this paper, we propose a novel MAC-level multicast protocol for IEEE 802.11n, named Reliable and Efficient Multicast Protocol (REMP). To enhance the reliability and efficiency of multicast services in IEEE 802.11n WLANs, REMP enables selective retransmissions for erroneous multicast frames and efficient adjustments of the modulation and coding scheme (MCS). In addition, we propose an extension of REMP, named scalable REMP (S-REMP), for efficient delivery of scalable video over IEEE 802.11n WLANs. In S-REMP, different MCSs are assigned to different layers of scalable video to guarantee the minimal video quality to all users while providing a higher video quality to users exhibiting better channel conditions. Our simulation results show that REMP outperforms existing multicast protocols for normal multicast traffic and S-REMP offers improved performance for scalable video streaming.

Wireless mesh networks (WMNs) have received an increasing interest for broadband Internet accesses. Today's IEEE 802.11 PHY and MAC standards offer multiple channels and data rates. One of challenging issues in WMNs is to exploit multiple channels and data rates for high performance WMNs. Channel assignments control the trade-off between node connectivity and channel diversity. In multi-rate WMNs, low-rate links severely affect the capacity of high-rate links, known as rate anomaly. In this paper, we propose a distributed family-based channel assignment (FCA) protocol to separate different data rate links using multiple channels so that rate anomaly is mitigated. FCA assigns channels for rate separation and improves node connectivity and channel diversity of WMNs by using a new channel assignment and routing metric and heuristic algorithms. Simulation and experiment results verify the potential of FCA for IEEE 802.11 multi-radio WMNs.

Wireless multihop communication is becoming more important due to the increasing popularity of wireless sensor networks, wireless mesh networks, and mobile social networks. They are distinguished from conventional multihop networks in terms of scale, traffic intensity and/or node density. Being readily-available in most of 802.11 radios, multirate facility appears to be useful to address some of these issues and is particularly helpful in high-density scenarios where inter-node distance is short, demanding a prudent multirate adaptation algorithm. However, communication at high bit rates mandates a large number of hops for a given node pair and thus, can easily be depreciated as per-hop overhead at several layers of network protocol is aggregated over the increased number of hops. This paper presents a novel multihop, multirate adaptation mechanism, called Multihop Transmission OPportunity (MTOP), that allows a frame to be forwarded a number of hops consecutively but reduces the MAC-layer overhead between hops. This seemingly collision-prone multihop forwarding is proven to be safe via analysis and USRP/GNU Radio-based experiment. The idea of MTOP is in clear contrast to, but not mutually exclusive with, the conventional opportunistic transmission mechanism, referred to as TXOP, where a node transmits multiple frames back-to-back when it gets an opportunity. We conducted an extensive simulation study via ns-2, demonstrating the performance advantage of MTOP under a wide range of network scenarios.

Wireless Mesh Networks (WMNs) have emerged to provide cost-effective broadband Internet accesses. Today's IEEE 802.11 PHY and MAC specifications support multi-channel and multi-rate capabilities. Designing an efficient channel assignment protocol utilizing available channels and data rates is a hot issue to leverage the network capacity. In multi-rate networks, low-rate links severely decrease the capacity of high-rate links, known as performance anomaly. In this paper, we design a Cooperative Channel Assignment (CoCA) protocol to address the performance anomaly in WMNs. For the channel assignment of family architecture, CoCA utilizes the Estimated Delivery Time (EDT) metric and the balancing algorithm. With the EDT metric, CoCA separates different rate links via multiple channels. By using the balancing algorithm, CoCA also increases throughput fairness. Our simulation results show that CoCA outperforms the existing well-known channel assignment protocols for WMNs.

In this paper, we address the issue of per-station fairness in IEEE 802.11-based wireless local area networks (WLANs). Although the IEEE 802.11 Distributed Coordination Function (DCF) has been designed to provide a fair channel access for all competing stations, it does not guarantee fairness between uplink and downlink flows in infrastructure mode WLANs. In the literature, several solutions have been proposed, where they give a higher channel access priority to an access point (AP) in order to avoid the starvation of downlink flows. However, we found that existing solutions cannot guarantee per-station fairness when uplink and downlink flows coexist in a station. In this paper, we propose a new MAC protocol for IEEE 802.11 WLANs, which aims at providing a fair medium access for all stations regardless of the direction of flows. In the proposed protocol, stations are classified into four states according to their traffic patterns, and they access the medium in different ways according to their states. The proposed protocol is fully backward compatible with the IEEE 802.11 standard and it does not include any complex scheduling algorithm. We evaluated the performance of the proposed protocol via extensive simulations and experiments in a real test-bed. Compared to existing work, the proposed protocol shows improved fairness performance in resource sharing among WLAN stations.

In this paper, we propose a new MAC protocol, called proxy relay-enabled MAC (PR-MAC), to improve the capacity of multi-rate WLANs. PR-MAC introduces a new entity called proxy relay point (PRP), which serves as a relay between the AP and stations. The cooperation of the AP with PRP replaces direct transmissions for low-rate stations with fast two-hop transmissions while the stations think that they communicate directly with the AP. Our experiment and simulation results showed that PR-MAC can significantly improve the throughput of legacy stations without any modification on the MAC operation of the stations.

Abstract With the rapid growth of mobile Internet, offering seamless connectivity in different types of wireless networks is an important feature in next generation wireless networks (4G networks). Mobile IP (MIP) is expected to play a key role to handle the movements of mobile nodes (MNs) in 4G networks. However, MIP suffers from long handoff latency since it is designed to support the macromobility of a MN. Therefore, it is necessary to devise a scheme that provides currently deployed networks with backward compatibility and that offers seamless connectivity during MIP handoffs across the heterogeneous wireless networks. In this paper, we propose a client‐based vertical handoff system for multi‐networks to provide end‐users with seamless connectivity across heterogeneous wireless networks. Our proposed system is designed as a common network interface at a client side and provides transparent service to IP/MIP layers regardless of used wireless technologies. With this system, we also present vertical handoff performance over a loosely coupled cdma2000/WLAN experimental test‐bed. The experimental results show that our system enables a MN to handoff seamlessly across different types of wireless networks without any modifications to the existing IP/MIP stack and core network. Copyright © 2008 John Wiley & Sons, Ltd.

With the rapid growth of wireless communication technologies, the demands for large-scale wireless networks have been emerged. One promising solution is the hierarchical architecture that consists of global and local wireless networks. The service discovery is a key issue to meet a vast amount of service demands from mobile nodes. However, under dynamic wireless networks, node failures severely affect the performance of service discovery protocols. Therefore, in this paper, we propose the directory hopping (DH) protocol for efficient service discoveries in dynamic large-scale networks. Basically, DH utilizes the directory for low-overhead service discoveries and periodically moves the directory to other operating nodes. In addition, it provides a fast and efficient recovery mechanism for node failures in dynamic network environments. Through extensive simulations, we show that the proposed DH protocol outperforms existing service discovery schemes.

Wireless network coding (WNC) has been considered as a promising solution with its capability of improving the overall performance of wireless mesh networks. A problem caused when WNC is employed in multi-rate wireless networks is that the link status between the relay node and intended receivers of a coded packet is mutually different. Even though there are links that support higher transmission rates, the relay node must transmit the coded packet at the lowest transmission rate among intended links' rates for the successful reception at all intended receivers. In this paper, we propose a WNC scheme that is combined with Forward Error Correction (FEC) to alleviate the problem explained above. The proposed scheme tries to transmit coded packets with a transmission rate higher than the lowest transmission rate so that the time required to transmit coded packets is reduced. However, it may increase the error rate. To compensate for the increased error rate, we use adaptively controlled FEC code. Our simulation study results show that the proposed scheme can increase the network coding gain compared to existing schemes.

Wireless Mesh Networks (WMNs) support the cost-effective broadband access for Internet users. Although today's IEEE 802.11 PHY and MAC specifications provide multi-channel and multi-rate capabilities, exploiting available channels and data rates is a critical issue to guarantee high network performance. In multi-rate wireless networks, high-rate links heavily suffer from performance degradation due to the presence of low-rate links. This problem is often referred to as performance anomaly. In this paper, we propose a Rate-Based Channel Assignment (RB-CA) algorithm to alleviate performance anomaly in multi-channel multi-rate WMNs. By exploiting multiple channels, the proposed algorithm alters a low-rate single-hop path to a high-rate multi-hop path. With RB-CA, a large volume of traffics in WMNs can be simultaneously delivered from or to the Internet via multiple non-overlapping channels as well as high-rate links. Extensive ns-2 simulation experiments have been performed to evaluate the performance of RB-CA and compared it with the existing WMN architecture. Our simulation results show that RB-CA outperforms existing scheme in terms of packet delivery ratio and end-to-end delay.

Discovering currently available radio access networks (RANs) is one of the most challenging issues in the heterogeneous wireless network environment. Especially, discovering WLANs, which support high data rates but have limited service coverage, has a significant effect on the energy consumption of multi-mode terminals (MMTs). In this paper, we propose three WLAN discovery schemes which are based on the upcoming IEEE 802.21 standards. In the proposed schemes, a MMT exploits the information on neighboring WLANs from a MIH information server to discover available WLANs as soon as possible while minimizing energy consumption. Our simulation results show that the proposed schemes can enhance the performance of MMTs in terms of energy consumption and the detection time of WLANs compared to conventional WLAN discovery schemes.

Designing scheduling algorithms that are simple to implement along with the process for servicing packets with low computation complexity is necessary to provide Quality- of-Service (QoS) for high-speed wireless networks. The ordinary frame-based scheduling algorithms are well-known for providing fair service with constant time complexity (O(l)), however, they have limitations of not being able to properly handle location-dependent burst errors in wireless networks. To utilize the advantage of frame-based scheduling algorithms, we propose a newCompensationModelwhich is based onLead-lagModel, to provide smooth compensation, so that frame-based scheduling algorithms can guarantee fairness and reduce delay in error-prone wireless channels. Through the analytical model and simulation studies, we show that frame-based scheduling algorithms withCompensationModelcan provide smaller delay bound and better fairness in wireless networks. Our belief is that the proposed frame-based scheduling algorithm (WFRR) based on the gracefulCompensationModelcan be a strong candidate for the scheduling algorithm in high speed wireless networks since the proposed algorithm has low computational complexity, is simple to implement, and has the ability to handle channel errors.

With the rapid growth of mobile Internet, offering seamless connectivity and high-speed multimedia services in different types of wireless networks are important features in next generation wireless networks (4G networks). Many researchers envision that the 4G networks will consist of many radio access technologies which integrate into all IP-based networks while providing seamless handoffs across the heterogeneous wireless networks. Mobile IP is a prominent solution to handle mobile nodespsila movement in IP-based networks. However, Mobile IP suffers from long handoff latency since it is designed to support the macromobility of a mobile node. Therefore, it is necessary to devise a scheme that offers seamless connectivity during Mobile IP handoffs across the heterogeneous wireless networks. In this paper, we propose a client-based handoff management system for multi-networks to provide end-users with seamless connectivity across heterogeneous wireless networks. Our proposed system is designed as a common network interface at a client side and provides transparent services to IP/MIP layers regardless of used wireless technologies. With this system, we also present vertical handoff performance over a loosely coupled cdma2000/WLAN experimental test-bed. The experimental results show that our system enables a mobile node to handoff seamlessly across different types of wireless networks without any modifications to the existing IP/MIP stack and core network.

In the next-generation networks, guaranteeing QoS is one of the important factors, which allows QoS supportable networks such as UMTS and 802.16e to be deployed together. Under such networks, a mobile node (MN) with multiple interfaces demands for the QoS service continuity during a handover. The 802.21 framework enables MNs to freely move in multiple networks. However, supporting QoS service continuity remains as a problem to be solved. In this paper, we propose a network-initiated handover based on the 802.21 framework to provide the QoS service continuity in UMTS/802.16e networks. To support the QoS service continuity, we design a detailed handover procedure that consists of three steps; QoS measurement, passive reservation, and activation. Through our performance evaluation, we show that the proposed handover scheme provides the QoS service continuity of MNs during a handover in terms of guaranteed data rates and latency.

Wireless Mesh Networks (WMNs) has recently evolved into a hot issue to support high network capacity in wireless access networks. Although IEEE 802.11 PHY and MAC specification support up to 3 and 12 multiple non-overlapping channels according to IEEE 802.11b/g and IEEE 802.11a, respectively, it is a critical issue to exploit all channels to accommodate a large volume of network traffics in WMN. In this paper, we proposed a channel assignment scheme using the local channel information for multi-channel WMNs. In the proposed scheme, nodes perform only channel switching without channel scanning during data communication with neighbors operating on different channels. Our simulation study results show that the proposed scheme achieves improved throughput performance over existing schemes.

To provide Internet connectivity to mobile ad hoc networks, several solutions have been proposed. Most of the proposals focus on the suitable and optimal gateway selection and handover schemes in accordance with the network status and node mobility. However, since an integration of the Internet and ad hoc networks is a function of the network layer, they do not consider characteristics of lower layers such as a multichannel capability. If the operating channels of each gateway are different, mobile nodes connecting to one gateway cannot receive any messages from other gateways, and thus they cannot perform handovers to other gateways. In this paper, we propose a new handover scheme for hybrid ad hoc networks in multi-channel environments. We revise and extend the previously proposed handover schemes namely the forced handover and optimized handover. We also studied the performance of the proposed two schemes through ns-2 simulations.

In this paper, we define a resource allocation problem focusing on the scheme minimizing energy consumption of subscribers in uplink subframe of the IEEE 802.16 OFDMA systems. In order to clearly formulate the relation between the uplink resource allocation and energy efficiency of subscribers, we use the multiple choice knapsack (MCK) problem, which is proved to be an NP-hard problem. Instead of finding an optimal solution, we seek a suboptimal solution. Based on the problem formulation, we adopt the existing solution of the Multiple Choice Knapsack problem to solve the resource allocation problem. The suboptimal solution adaptively uses the modulation and coding scheme defined in the IEEE 802.16 systems to minimize the required transmission power while guaranteeing QoS. Our simulation results show that the suboptimal algorithm can reduce the energy consumption up to 53% compared to the channel state information (CSI) scheme, which determines the modulation and coding level only considering the channel state information.

The IEEE 802.11e is the extension to enhance the wireless medium access control (MAC) quality of service (QoS) for applications requiring real time services. The IEEE 802.11b is also one of the extensions with the higher and multiple data transmission rates according to the channel condition. However, when the IEEE 802.11e WLANs are used with multi-rate scheme, they suffer unfairness in terms of throughput. In this paper, we propose a rate adaptive transmission opportunity (TXOP) to solve the unfairness with the performance. Our simulation results show that the proposed scheme provides better fairness.

The IEEE 802.16e system supporting mobility on fixed wireless-MAN systems is supposed to be a mobile broadband wireless access (BWA) and evolve into 4G mobile communication systems. Although the system already defines its own mobility management algorithm, a network layer handover algorithm should be defined to support the mobility of mobile stations in the Internet. There are many active researches on how to apply the L3 handover protocol over the existing IEEE 802.16e L2 handover scheme, but most of the previous works have focused on the timing of L3 handover messages over the IEEE 802.16e L2 handover messages. In this paper, we propose a new handover scheme for fast mobile IPv6 over the IEEE 802.16e system. By integrating FMIPv6 with IEEE 802.16e system efficiently, the proposed scheme can minimize not only L3 handover latency but also packet losses.

Mobile IPv6, which is a protocol being standardized by IETF for global IP mobility support, is expected to play a key role for future all-IP wireless networks. As the demands for delay sensitive real-time applications increase, the handover latency of mobile IPv6 becomes inadequate for these applications. There have been many proposals, such as fast handovers for mobile IPv6 (FMIPv6), to tackle this problem. However, FMIPv6 only concentrates on the protocol operation while it does not address other issues, such as radio access discovery and candidate access router discovery, that are critical to the handover performance of FMIPv6. Therefore, in this paper, we propose ARIP (access router information protocol), which performs a candidate access router discovery and a radio access network discovery in one protocol suite, to provide an efficient handover framework for MIPv6 and FMIPv6. ARIP is designed to cope with heterogeneous networks as well as homogeneous networks and to be closely coupled with FMIPv6 to provide an efficient handover operation. The performance evaluation of MIPv6, FMIPv6, and FMIPv6 with ARIP is performed in an actual network environment and the performance results show that FMIPv6 with ARIP gives the best performance in terms of handover latency

There has been much research effort to exploit the multi-rate capability of WLANs to improve performance. While these approaches focused on exploiting good channel conditions for direct transmission between stations, there are no considerations of performance degradation by low rate transmissions due to poor channel conditions. Thus, we propose a frame relay based MAC protocol, termed FR-MAC, to tackle this issue and to improve network performance. The key idea of FR-MAC is that the time required to transmit a frame using an intermediate station as a relay can be much smaller than the direct transmission at a lower rate, if the intermediate station between the source and the receiver can relay the frame at higher rates. Simulation results show that the proposed protocol improves network performance and the amount of improvement significantly increases as the number of relayed stations and the payload size are increased.

In ad hoc networks, broadcasting is one of the important communications patterns frequently used. Straight-forward broadcast is usually known to be very expensive and results in serious redundancy, contentions, and collisions. The phenomenon is referred to as broadcast storm problem. In this paper, we propose a forwarding set selection scheme and efficient schemes to broadcast with transmission power control in multi-hop ad hoc networks. Our simulation study shows that the proposed schemes reduce the broadcast latency, the number of collisions, average power consumption, etc.

Abstract The IEEE 802.11 standard specifies the point coordination function (PCF) in the media access control (MAC) sublayer for the transfer of real‐time traffic, such as voice. The transfer of real‐time traffic over wireless LANs is rapidly gaining acceptance, but little work has been done concerning the efficient use of IEEE 802.11 PCF mode to support voice‐over‐IP (VoIP) services. In this paper, we propose adaptive polling MAC schemes for IEEE 802.11 MAC. The proposed schemes achieve bandwidth efficiency by reducing the number of polls required for the uplink voice packet transmissions using a talkspurt detection algorithm. We analyze the applicability of the proposed schemes to IEEE 802.11 WLANs and compare them with other related works. Copyright © 2004 John Wiley & Sons, Ltd.

Recently, many on-demand routing protocols for ad-hoc networks have been proposed, but most of these works have been done on the basis of the IEEE 802.11 standard that supports a single transmission rate. In ad hoc networks supporting the multi-rate transmission scheme, which is referred to as dynamic rate shifting in the IEEE 802.11 standard, few performance studies on ad-hoc routing protocols have been performed. In this paper, we extensively study the impact of dynamic rate shifting on the performance of ad-hoc routing protocols in various situations in multi-rate WLANs environments. Our question is whether the dynamic rate shifting scheme supported by the IEEE 802.11 standard affects the relative performance of the routing protocols being studied. We have extended the ns-2 network simulator to accurately model the IEEE 802.11b wireless LAN standard, and simulated the performance of two ad hoc routing protocols over each of networks supporting single rate and multi-rate transmissions.

In this paper, we propose an efficient multicast routing protocol based on mobile IP standard in wireless mobile networks. A mobile host that is located in a foreign network receives a tunneled multicast datagram from a multicast agent, which is located in a remote network or local network. While receiving a tunneled multicast datagram from a remote multicast agent, the local multicast agent starts a multicast tree join operation if the mobile host is expected to remain the network relatively long period of time, while it does not start multicast tree join operation if the mobile host is expected to remain the network relatively short period of time. The proposed protocol tries to maximize the number of unnecessary multicast tree join operations. We examined performance of the proposed protocol by simulation under various environments and we got good performance results.

Most of recent research results on TCP performance in wireless networks have a limitation that they assume a single TCP connection. When multiple TCP connections are concentrated in a base station (BS), it is liable to be a bottleneck and the difference of network bandwidth between wired and wireless links aggravates the situation. The BS experiences frequent congestions and eventually lead to performance degradation. Furthermore, it is difficult to guarantee fairness among multiple TCP connections. To meet both of the challenges, we propose a flow control scheme called feedback-based snoop (F-Snoop). F-Snoop provides the TCP sender with BS buffer state information via TCP ACKs explicitly in real time so that the TCP sender can increase its transmission window size to fill the network pipe, while regulating packet transmission rate to avoid buffer overflow at the BS. The performance is evaluated by simulation using ns-2 and the results show that the F-Snoop not only achieves improvement in throughput but also fairly allocates the available wireless bandwidth to all TCP connections.

In this paper, a new reliable transport protocol called rate-control snoop is proposed for improving TCP performance over error-prone wireless links. It is implemented at a base station where it performs rate-based transmission control based on characteristics of a data path. The proposed protocol monitors every packet that passes through the path and asks the sender to reduce the transmission rate when packet losses are detected only at a wired link. The performance of the proposed protocol is evaluated by simulations and it shows better throughput than TCP Reno, TCP-Snoop, and end-to-end rate control TCP.

The presence of location-dependent and burst errors in wireless networks introduces difficulties in developing packet fair queuing (PFQ) algorithms for wireless networks. We introduce a new theoretical model to build PFQ algorithms for both wired and wireless networks and an algorithm to approximate the proposed model. The proposed model has some advantages in its application to wireless networks: self-detection of the session state and self-compensation. The proposed algorithm provides all expected characteristics of wireless PFQ: short-term fairness to error-free flows and long-term fairness to error-bounded flows; short-term throughput bounds to error-free flows and long-term throughput bounds to error-bounded flows; delay bounds to error-free flows; graceful service compensation and degradation. The algorithm is called WMRPS, wireless modified rate proportional server, based on the rate proportional server of D. Stiliadis and A. Varma (see IEEE/ACM Trans. on Networking, vol.6, no.2, 1998).

The routing protocols designed for wired networks can hardly be used for mobile ad-hoc networks due to unpredictable topology changes, and thus several routing protocols for mobile ad-hoc networks have been proposed. The goal of this paper is to select the most reliable route that is impervious to failures by topological changes by mobile nodes' mobility. To select a reliable route, we introduce the concept of stable zone and caution zone, and then apply it to the route discovery procedure of the existing on-demand routing protocol (i.e. AODV). The concept of the stable zone and caution zone, which are located in a mobile node's transmission range, is based on a mobile node's location and mobility information received by Global Positioning System (GPS). The proposed protocol was evaluated by simulation in various conditions and we got an improved performance.

All-to-all personalized communication commonly occurs in many important parallel algorithms, such as FFT and matrix transpose. This paper presents new algorithms for all-to-all personalized communication or complete exchange in multidimensional torus- or mesh-connected multiprocessors. For an R/spl times/C torus or mesh where R/spl les/C, the proposed algorithms have time complexities of O(C) message startups and O(RC/sup 2/) message transmissions. The algorithms for three- or higher-dimensional tori or meshes follow a similar structure. Unlike other existing message-combining algorithms in which the number of nodes in each dimension should be a power-of-two and square, the proposed algorithms accommodate non-power-of-two tori or meshes where the number of nodes in each dimension need not be power-of-two and square. In addition, destinations remain fixed over a larger number of steps in the proposed algorithms, thus making them amenable to optimizations. Finally, the data structures used are simple, hence making substantial savings of message-rearrangement time.

Providing a multicast service to mobile hosts is difficult due to frequent changes of mobile host location and group membership. To overcome the difficulty, several multicast protocols for mobile hosts have been proposed. But they include glitches such as a non-optimal delivery route, duplicated datagrams, and overheads caused by the frequent reconstruction of a multicast tree. We summarize these problems and propose an efficient multicast protocol. The proposed protocol reduces the data delivery path length and decreases not only the amount of duplicated data but also multicast traffic load. The performance of the proposed protocol was evaluated by simulation and we got an improved performance.

Providing multicast service to mobile hosts is difficult due to frequent changes of mobile host location and group membership. To overcome the difficulty, several multicast protocols for mobile hosts have been proposed. Although the protocols solve several problems inherent in multicast routing proposals for static hosts, they still have problems such as non-optimal delivery path, datagram duplication, etc. In this paper, we summarize these problems of multicast routing protocols and propose an efficient multicast protocol using a multicast agent in wireless mobile networks, where a mobile host receives a tunneled multicast datagram from a multicast agent located in a network close to it or directly from the multicast router in the current network. While receiving a tunneled multicast datagram from a remote multicast agent, the local multicast agent starts multicast join process, which makes the multicast delivery route optimal. The proposed protocol reduces data delivery path length and decreases not only the amount of duplicate copies of multicast datagrams but also multicast traffic load. We examined and compared the performance of the proposed protocol and existing protocols by simulation under various environments and we got an improved performance over the existing proposals.

This paper presents a software-based approach to fault-tolerant routing in networks using wormhole or virtual cut-through switching. When a message encounters a faulty output link, it is removed from the network by the local router and delivered to the messaging layer of the local node's operating system. The message passing software can reroute this message, possibly along nonminimal paths. Alternatively, the message may be addressed to an intermediate node, which will forward the message to the destination. A message may encounter multiple faults and pass through multiple intermediate nodes. The proposed techniques are applicable to both obliviously and adaptively routed networks. The techniques are specifically targeted toward commercial multiprocessors where the mean time to repair (MTTR) is much smaller than the mean time between router failures (MTBF), i.e., it is sufficient to tolerate a maximum of three failures. This paper presents requirements for buffer management, deadlock freedom, and livelock freedom. Simulation results are presented to evaluate the degradation in latency and throughput as a function of the number and distribution of faults. There are several advantages of such an approach. Router designs are minimally impacted, and thus remain compact and fast. Only messages that encounter faulty components are affected, while the machine is ensured of continued operation until the faulty components can be replaced. The technique leverages existing network technology, and the concepts are portable across evolving switch and router designs. Therefore, we feel that the technique is a good candidate for incorporation into the next generation of multiprocessor networks.

The interprocessor complete exchange communication pattern can be found in many important parallel algorithms. In this paper, we present algorithms for complete exchange on 2D mesh-connected multiprocessors. The unique feature of the proposed algorithms is that they are configurable where the time for message startups can be traded against larger message sizes. At one extreme, the algorithm minimizes the number of message startups at the expense of an increased amount of time spent in message transmission. At the other extreme, the time spent in message transmission is reduced at the expense of an increased number of message startups. The structure of the algorithms is such that intermediate solutions are feasible, i.e., the number of message startups can be increased slightly and the message transmission time is correspondingly reduced. The ability to configure these algorithms enables the algorithm characteristics to be matched with machine characteristics based on specific overheads for message initiation and link speeds to minimize overall execution time. In effect, the algorithms can be configured to strike the right balance between direct and message combining approaches on a specific architecture for a given problem size. We believe these algorithms are distinguished by this ability and contribute to efficient portable implementations of complete exchange algorithms.

Complete exchange communications are found necessary in many important parallel algorithms. This paper presents algorithms for complete exchange for 2D torus-connected multiprocessors. The proposed algorithms are unique in that they are configurable while trading the time for message startups against larger message sizes. At one extreme, the algorithm minimizes the number of message startups at the expense of increased message-transmission time. At the other extreme, the message-transmission time is reduced at the expense of increased number of message startups. The algorithms are structured such that intermediate solutions are feasible, i.e., the number of message startups can be increased slightly and the message-transmission time is correspondingly reduced. The ability to configure these algorithms makes the proposed algorithms distinct from others and leads to efficient portable implementation of complete exchange algorithms.

This paper presents new algorithms for all-to-all personalized exchange in multidimensional torus-connected multiprocessors. Unlike existing message-combining algorithms in which the number of nodes in each dimension should be power-of-two and square, the proposed algorithms accommodate non-power-of-two tori where the number of nodes in each dimension need not be power-of-two. In addition, destinations remain fixed over a larger number of steps in the proposed algorithms, thus making them amenable to optimizations. Finally, the data structures used are simple, hence making substantial saving of message-rearrangement time.

All-to-all communication patterns occur in many important parallel algorithms. This paper presents new algorithms for all-to-all communication patterns (all-to-all broadcast and all-to-all personalized exchange) for wormhole switched 2D/3D torus- and mesh-connected multiprocessors. The algorithms use message combining to minimize message start-ups at the expense of larger message sizes. The unique feature of these algorithms is that they are the first algorithms that we know of that operate in a bottom-up fashion rather than a recursive, top-down manner. For a 2/sup d//spl times/2/sup d/ torus or mesh, the algorithms for all-to-all personalized exchange have time complexity of O(2/sup 3d/). An important property of the algorithms is the O(d) time due to message start-ups, compared with O(2/sup d/) for current algorithms. This is particularly important for modern parallel architectures where the start-up cost of message transmissions still dominates, except for very large block sizes. Finally, the 2D algorithms for all-to-all personalized exchange are extended to O(2/sup 4d/) algorithms in a 2/sup d//spl times/2/sup d//spl times/2/sup d/3D torus or mesh. These algorithms also retain the important property of O(d) time due to message start-ups.