Conventional capacitive touchscreens in mobile devices often malfunction in the presence of moisture, dust, or gloved hands, leading to unreliable user interactions. To overcome these limitations, we present TouchAI, a multi-modal touch detection and localization system that leverages built-in inertial sensors and audio interfaces. Running as a background process, TouchAI constantly monitors inertial measurements for potential touch input and then activates acoustic sensing only upon detected events, thus reducing power consumption and privacy concerns associated with continuous audio recording. We introduce a novel event identification method that distinguishes touch-start and touch-end instances, providing precise timing for data sampling. For fine-grained touch localization, TouchAI employs a lightweight Transformer-based classification model to capture spatiotemporal features from combined acoustic-inertial signals. Experiments on commercial smartphones demonstrate true positive rates of 95.3% and 99.1% for touch detection and event identification, respectively, at false positive rates only less than 3%. Ultimately, TouchAI achieves up to 97.0% and 86.5% localization accuracy on 4×2 and 6×3 touch input grids, respectively, confirming its practicality and effectiveness as an alternative interface under touchscreen malfunction scenarios.

The growing use of 3D point cloud data in autonomous vehicles (AVs) has raised serious privacy concerns, particularly due to the sensitive information that can be extracted from 3D data. While model inversion attacks have been widely studied in the context of 2D data, their application to 3D point clouds remains largely unexplored. To fill this gap, we present the first in-depth study of model inversion attacks aimed at restoring 3D point cloud scenes. Our analysis reveals the unique challenges, the inherent sparsity of 3D point clouds and the ambiguity between empty and non-empty voxels after voxelization, which are further exacerbated by the dispersion of non-empty voxels across feature extractor layers. To address these challenges, we introduce ConcreTizer, a simple yet effective model inversion attack designed specifically for voxel-based 3D point cloud data. ConcreTizer incorporates Voxel Occupancy Classification to distinguish between empty and non-empty voxels and Dispersion-Controlled Supervision to mitigate non-empty voxel dispersion. Extensive experiments on widely used 3D feature extractors and benchmark datasets, such as KITTI and Waymo, demonstrate that ConcreTizer concretely restores the original 3D point cloud scene from disrupted 3D feature data. Our findings highlight both the vulnerability of 3D data to inversion attacks and the urgent need for robust defense strategies.

Interest in Direct Current Power Line Communication (DC-PLC) is growing as industries seek to reduce wiring complexity and cost by combining power and data over a single medium. A programmable DC-PLC testbed is developed to enable power transfer and bidirectional communication over a shared DC power line bus. The system employs a master–slave scheme in half-duplex mode under a flexible MAC protocol, using Voltage Polarity Modulation (VPM) for downlink and Current Amplitude Modulation (CAM) for uplink. Implemented with low-cost microcontrollers, the master and slave are designed as modular units for easy connection and expansion. The platform achieves approximately 100 kbps throughput in both directions and demonstrates reliable operation with a simple polling-based MAC protocol, highlighting its potential for future DC-PLC research and applications.

Rapid growth in application bandwidth demand has challenged cellular networks to maintain high Quality of Service (QoS) using licensed spectrum alone. NR-WLAN Aggregation (NWA), standardized in 3GPP Release 16, addresses this by combining licensed and unlicensed spectrum resources. However, current flow control mechanisms are inadequate for heterogeneous dual-connectivity environments where frequent WLAN disconnections occur. This paper identifies disconnection timing prediction as a fundamental bottleneck in NWA flow control and proposes a connectivity-aware transmission volume fitting approach to minimize packet loss, reduce recovery time, and maximize throughput.

Recent advancements in Integrated Sensing and Communication (ISAC) have enabled human activity recognition (HAR) based on channel state information (CSI) from Wi-Fi signals, as a privacy-conscious and cost-effective alternative to conventional vision-based applications. With smart TV platforms increasingly crucial for home automation, Wi-Fi CSI-based HAR offers seamless integration into existing infrastructure. However, in real-world home environments, the close proximity between Wi-Fi AP and smart TV often leads to dominant Line-of-Sight (LOS) signal path, limiting multipath channel diversity and thus the HAR accuracy. To address this, we present HActiFi, an advanced HAR framework that adaptively controls CSI sampling to ensure reliable sensing without overloading the network. Our smartphone-assisted CSI injection method effectively restores recognition accuracy, and adaptive sampling dynamically optimizes throughput, ensuring robust HAR functionality while preserving streaming quality. These findings confirm that Wi-Fi CSI sensing is a scalable and privacy-conscious alternative to vision-based HAR, making it viable for real-world smart home environments.

The advent of 5G networks promises to revolutionize real-time applications with its high bandwidth capabilities. Despite this, current real-time applications such as 360-degree video conferencing and intelligent transport systems, which demand high data rates and stringent low latency, often find it difficult to satisfy their QoS needs with a single 5 G connection due to inconsistent bandwidth. As a viable option, multipath transport solutions using multiple 5G connections have emerged with recent technological advancements. In this paper, we explore real-time application performance using MPTCP over 5G multiple connections. Our real-world measurements over MPTCP across major 5G operators in South Korea reveal average frame delays exceeding 213 ms. This delay is much higher than our expectations compared to measurements over single-path TCP (SPTCP) under similar network conditions. We attribute this to the delayed reaction of the MPTCP scheduler, which relies on long-term measurements rather than adapting to recent network conditions. The delayed reaction causes sub-optimal path selection and increased latency. This paper contributes a thorough analysis of MPTCP performance degradation in real-time applications, identifies the limitations of current MPTCP schedulers, and considers potential solutions to improve their responsiveness to achieve better application latency performance.

Recent advances in electric vehicles, robots, and renewable energy have renewed interest in direct current (DC) power line communication (PLC) technology. However, existing DC-PLC systems face from several limitations, including low data rates, lack of support for duplex communication, and the absence of an effective medium access control (MAC) mechanism. To overcome these challenges, we propose D2-PLC, a novel DCPLC system that features a redesigned physical layer, enabling high-speed duplex communication over a single pair of wires supporting simultaneous power and data transmission. D2-PLC introduces voltage polarity modulation (VPM) and current amplitude modulation (CAM) for downlink and uplink communication, respectively. In addition, we develop a custom data link layer and MAC protocols to coordinate communication in a bus topology where multiple slave nodes interact with a single master node (the power source), minimizing the risk of collisions. We implement a fully functional prototype and evaluate on a 5-node testbed as well as via 256-node simulations. Results demonstrate that D2-PLC achieves a maximum data rate of ~100 kbps–260% improvement over existing solutions(Cwhile maintaining 99+% reliability. These findings highlight D2-PLC’s potential to reduce the cost and weight of battery-powered systems such as electric vehicles

There have been long efforts to refine Wi-Fi carrier sensing (CS) for more aggressive channel access, in pursuit of enhanced network performance. To this end, the recent 802.11ax amendment introduced a preamble detection (PD)-based spatial reuse, allowing concurrent transmissions between adjacent links via adjustable sensitivity levels. Against these conventional ideas, this paper presents a different perspective: Wi-Fi devices already have excessive transmission (TX) opportunities in practice, even without detecting each other under certain scenarios. We shed light on CS anomalies relevant to undetected preambles, which not only cause adjacent devices to transmit concurrently but are also triggered by the new PD-based mechanism, ultimately disrupting its intended operations. Our testbed experiments and in-depth scrutiny reveal the dominant impact of these anomalies on overall network behaviors. Based on these insights, we present two comprehensive frameworks, REFRAIN and AdOPT, to fully exploit TX opportunities enabled by the anomalies and PD-based mechanism respectively, for practical spatial reuse. Prototypes using commercialWi-Fi devices and NI USRP show the feasibility and effectiveness of our approaches. Extensive simulation results further demonstrate that REFRAIN and AdOPT achieve up to 1.94× and 1.61× higher average throughput, only with reduced transmission attempts by half, highlighting their potential to elevate network capacity and efficiency in practical Wi-Fi networks.

Due to the rapid growth of mobile traffic, network operators have difficulty investing in sufficient wireless network equipment to meet the demand for mobile traffic, especially peak demand. To maximize investment efficiency, we consider dynamic pricing that allows operators to defer infrastructure investments by spreading out peak demand. In dynamic pricing, operators announce spatiotemporal prices in advance so that mobile users move back and forth in the spatial and temporal domains to reduce peak loads. To this end, we design a decentralized partially observable Markov decision process (Dec-POMDP) framework for spatiotemporal dynamic pricing with non-linear transitions of Boltzmann rationality and nonconvex objectives. To solve the Dec-POMDP problem with only local information, we introduce a model-free, value-based, multi-agent deep reinforcement learning (DRL) algorithm, termed SHIFT, that uses centralized training and decentralized execution (CTDE). Through evaluation using real traffic data from Telecom-Italia, we reveal that SHIFT outperforms other competitive schemes in supporting multiple agents in a scalable way and reducing peak demand.

LoRa is a low-power long-range radio technology for wide-area IoT connectivity with exceptional receiver sensitivity thanks to its chirp spread spectrum (CSS) modulation. However, insufficient data rate has always been an Achilles’ heel of LoRa. This paper proposes a novel PHY-layer design, BIC-LoRa, that leverages non-linear chirp shapes as pictograph to enhance LoRa’s data rate. It employs multiple non-linear chirps for modulation whose shapes encode additional bits to boost data rate while maintaining resilience to low SINR scenarios. To the best of our knowledge, this is the first attempt to enhance the data rate of LoRa by embedding bits in the chirp shapes. Furthermore, BIC-LoRa fully leverages the characteristics of non-linear chirps, allowing it to deal with packet collisions and increase network throughput. We implement BIC-LoRa in GNURadio and MATLAB, and compare its performance against CurveALOHA and standard LoRaWAN through real experiments on USRP B210 software-defined radios. Evaluation results demonstrate that BICLoRa achieves up to 29.4% improvement in data rate for a single link and 32% improvement in overall network throughput while retaining the low SNR robustness of LoRa in real-world scenarios.

Time-slotted communication is used in countless protocols and systems. IEEE 802.15.4e time-slotted channel hopping (TSCH) is one of those examples which has shown remarkable performances in the literature. However, time-slotted systems have one fundamental drawback: a slot is predefined to be sufficiently long enough to accommodate one exchange of a maximum-sized packet and an acknowledgment. If most packets in the system are far smaller than the maximum, a significant amount of residue time within each slot is wasted, leading to corresponding loss in effective data rate. To address this fundamental challenge, we propose utility-based adaptation of slot-size and aggregation of packets (ASAP) which reduces wasted time in slotted systems to improve throughput and latency. ASAP consists of two orthogonal approaches: 1) slot-length adaptation (SLA) dynamically adapts timeslot length to actual packet size distribution and 2) utility-based packet aggregation (UPA) transmits aggregated packets in multiple consecutive slots to maximize slot utility. We case-study ASAP in the context of TSCH. We implement ASAP on real embedded devices and evaluate on large-scale testbeds using state-of-the-art schedulers to demonstrate a$2.21\times $improvement in throughput as well as a 78.7% reduction in latency.

As Wi-Fi access points (APs) are deployed more densely, the cross-technology interference (CTI) from Wi-Fi is becoming a real threat to co-existing low-power IoT protocols such as BLE. In this work, we pay attention to Wi-Fi beacons that take a substantial amount of airtime in the 2.4 GHz Industrial Scientific Medical (ISM) band. We develop B-hop, a standard-compliant framework that adjusts BLE frequency hopping to avoid expected Wi-Fi beacons in the time domain. B-hop operates on BLE master devices where Wi-Fi and BLE protocols are co-located, and it requires no modifications to Wi-Fi devices or BLE slave devices. B-hop predicts future beacon transmissions and reschedules the time domain of frequency hopping to avoid collisions. We implement a B-hop prototype using Zephyr, an open-source embedded operating system that allows us to modify necessary BLE link-layer operations. We evaluate the performance of B-hop through simulations and test-bed experiments, and demonstrate that B-hop significantly outperforms legacy BLE frequency hopping schemes that only use frequency-domain adjustment.

Multi-link operation (MLO) has recently been proposed to provide extremely high throughput by simultaneously exploiting multiple links for next generation wireless local area networks (WLANs). To transmit and receive packets using MLO, a multi-link device (MLD) should have the capability to successfully separate signals on each of the multiple links. However, if frequency separation between the two multiple links is not sufficient, the transmission of a station (STA) on an MLD causes cross-link (self) interference to other STAs on the other link on the same MLD. An STA affected by cross-link interference can not decrease its back-off counter, resulting in lower channel access probability and accordingly lower throughput compared to a legacy STA on the same link. Based on a thorough analysis, we find an appropriate contention window (CW) size of an STA on the MLD, aiming to allow it to achieve as much throughput as a legacy STA on the same link. Through extensive ns-3 simulations, we show that our proposed scheme successfully compensates for the loss of access opportunities of an STA on the MLD under cross-link interference without compromising network throughput.

Semi-supervised Learning (SSL) has received increasing attention in autonomous driving to reduce the enormous burden of 3D annotation. In this paper, we propose UpCycling, a novel SSL framework for 3D object detection with zero additional raw-level point cloud: learning from unlabeled de-identified intermediate features (i.e., "smashed" data) to preserve privacy. Since these intermediate features are naturally produced by the inference pipeline, no additional computation is required on autonomous vehicles. However, generating effective consistency loss for unlabeled feature-level scene turns out to be a critical challenge. The latest SSL frameworks for 3D object detection that enforce consistency regularization between different augmentations of an unlabeled raw-point scene become detrimental when applied to intermediate features. To solve the problem, we introduce a novel combination of hybrid pseudo labels and feature-level Ground Truth sampling (F-GT), which safely augments unlabeled multi-type 3D scene features and provides high-quality supervision. We implement UpCycling on two representative 3D object detection models: SECOND-IoU and PV-RCNN. Experiments on widely-used datasets (Waymo, KITTI, and Lyft) verify that UpCycling outperforms other augmentation methods applied at the feature level. In addition, while preserving privacy, UpCycling performs better or comparably to the state-of-the-art methods that utilize raw-level unlabeled data in both domain adaptation and partial-label scenarios.

The growing commercial interest in indoor localization-based services has stimulated the development of many indoor positioning systems. Despite extensive research on localization, system requirements, such as site survey, user intervention, or specific hardware/software, place limitations on the widespread deployment of localization. To overcome these limitations, we propose a path estimation and localization system for indoor environments, termedPYLON, that runs on a smartphone and a server without any human intervention.PYLONuses an actual floor plan and measurements from widely deployed WiFi access points (APs) and Bluetooth Low Energy (BLE) beacons to estimate the user’s path. It creates virtual rooms according to received signal strength indicator (RSSI) values and matches them to actual rooms in the real-world floor plan. After room mapping,PYLONuses door passing times to precisely refine a user’s estimated path. Unlike conventional path estimation and localization systems,PYLONworks independently of device types. We implementPYLONon five Android smartphones and conduct evaluation with three users in an office building. Our experimental results show thatPYLONachieves 97 percent floor plan mapping accuracy with a localization error of 1.42 m.

This paper studies the cross-layer challenges and performance of Hybrid Beamforming (HBF) and Multi-User Multiple-Input Multiple-Output (MU-MIMO) in 5G millimeter wave (mmWave) cellular networks with full-stack TCP/IP traffic and MAC scheduling. While previous research on HBF and MU-MIMO has focused on link-level analysis of full-buffer transmissions, this work reveals the interplay between HBF techniques and the higher layers of the protocol stack. To this aim, prior work on the full-stack evaluation of mmWave cellular networks has been extended by including the modeling of MU-MIMO and HBF. Our results reveal novel relations between the networking layers and the HBF MU-MIMO performance at the physical layer. Particularly, throughput can be increased in 5G networks by means of Space Division Multiple Access (SDMA). However, in order to achieve such benefits it is necessary to take into account certain trade-offs and the implementation complexity of a full-stack HBF solution.

Wi-Fi scanning that searches neighboring access points (APs) is an essential prerequisite for Wi-Fi operations such as initial association and handover. As the traffic demand increases, APs are more densely deployed and the number of operating Wi-Fi channels also increases, which, however, results in additional scanning delay and makes the scanning a burdensome task. In this paper, we note that the co-location of Wi-Fi protocol with BLE protocol is a common practice in IoT networks, and develop a Wi-Fi passive scanning framework that uses BLE to assist scanning. Although the framework has great potential to improve scanning performance without explicit message exchanges, there are technical challenges related to time synchronization and channel switching delay. We address the challenges and develop a practical passive scanning scheme, named BLESS-Sync. We verify its performance through testbed experiments and extensive simulations, and show that BLESS-Sync significantly outperforms legacy Wi-Fi scanning in terms of scanning delay and energy efficiency.

This work investigates a run-time scheduling system for Bluetooth Low Energy (BLE). The Bluetooth specifications propose control of the anchor point (i.e., start time of each connection event) by changing the WinOffset parameter of the control protocol data unit (PDU), which can be very useful when the master schedules multiple connections simultaneously. Since we had no access to the controller (i.e., which wraps the physical layer and link layer of Bluetooth), we could not figure out how WinOffset works or use it the way we wanted. However, with Zephyr's advent, there is room to modify the controller of BLE, and we can adjust anchor points as we want using WinOffset. To the best of our knowledge, this work is the first systematic study of this regime in the research community. We experimentally study how commercial devices actually schedule multiple connections and how this inefficient scheduling degrades BLE's performance. Based on the preliminary study, we propose BLEX that dynamically adjusts anchor points of multiple slaves to satisfy quality of service (QoS) requirements without violating the Bluetooth specifications or intervening the BLE host (i.e., software-defined higher layer). Through extensive performance evaluation on off-the-shelf BLE chips, we show that BLEX provides stable performance regardless of the traffic requirements of applications and shows significantly reduced QoS failures compared to the state-of-the-art scheduling schemes for BLE.

Internet of things (IoT) is an indispensable paradigm in today's industrial change. IoT interconnects appliances around us through the Internet, and user's private information is deeply placed inside the network. Nonetheless, security vulnerabilities in IoT have not been addressed appropriately so far due to various reasons. Even in the initial WiFi connection procedures of IoT devices, WiFi credentials can be leaked, making the WiFi access point (AP) a hacking path. We propose a secure connection scheme, termed PUP, that aims to securely and quickly connect an IoT device to the AP in proximity while improving the user experience. PUP shows perfect security performance, enabling connection time within 11 s.

The upsurge of mobile traffic volume has led to dense deployment of IEEE 802.11 wireless local area networks (WLANs). To enhance spectral efficiency in dense WLAN deployments, a new 802.11 amendment, namely 802.11ax, introduces overlapping basic service set packet detection-based spatial reuse (OBSS PD-based SR) operation. Although the OBSS PD-based SR operation enables more simultaneous transmissions among OBSSs, whether it improves network performance is highly uncertain and depends on the mutual interference among the simultaneous transmission links. In this paper, we propose a link-aware SR scheme, named LSR, that facilitates simultaneous transmissions among OBSSs considering the mutual interference. LSR efficiently exploits SR transmission opportunities by selecting the appropriate link for the SR transmission while sufficiently protecting the ongoing transmission. Moreover, the proposed method allows BSSs to coordinate with each other in a distributed manner without incurring additional control message exchange. Through extensive ns-3 simulation, we demonstrate that LSR significantly improves the network performance compared with legacy 802.11 and the OBSS PD-based SR operation.

Target wake time (TWT) has been introduced to provide the low power consumption mode for stations (STAs) with low traffic and periodic data transmissions in IEEE 802.11ax networks. The TWT operation starts with negotiating wake and doze periods between an access point (AP) and STAs. Thanks to the nature of wake and doze period negotiation, TWT operation enables time scheduled access, like time-division multiple access (TDMA) without modification overhead. In this paper, we demonstrate TWT scheduling issues that include scheduling requirements and results notifications from the AP to STAs, using standard-compliant methods. Then we establish TWT scheduling strategies by exemplifying two well-known schedulers, max-rate and proportional fairness schedulers. Through ns-3 simulation, we evaluate the performance of TWT scheduling and highlight the benefits of TWT for a large number of STAs from the fairness and power consumption perspective.

Vehicle-to-Everything (V2X) communication is a key enabling factor for fully autonomous driving vehicles. To this end, the 3GPP has introduced Cellular V2X (C-V2X) standards in Release 14. For Vehicle-to-Vehicle (V2V) communication, C-V2X provides the distributed resource allocation mode, termed Mode 4, which works for sensing-based semi-persistent scheduling. However, because of the sensing-based and distributed nature, Mode 4 suffers resource collision due to congestion, channel performance degradation due to blockage, etc. Thus, making an accurate assessment of resource use in Mode 4 becomes an important issue. To address this issue, we propose a scheme for PREdictive assessment of resource usage in C-V2V Mode 4, named PRESS. In PRESS, each vehicle leverages aggregate reselection counter information to predict the channel usage status for future resource use. With the assessment of resource usage related to the transmission time, a VUE can increase the possibility of choosing the least used resources. Through simulation, we confirm that PRESS outperforms the legacy scheme in terms of packet reception ratio.

The number of IoT devices is increasing significantly these days, especially in private spaces. The data collected in personal space may include private information. Because a lot of IoT devices use wireless channels to communicate with other devices, illegal devices (attackers) can easily access the channel. The attacker can access IoT devices and pretend to be legitimate devices. This paper proposes a novel LoS/NLoS detection based authentication scheme that aims to guarantee security while providing proper user convenience. We propose a new metric called Gap Difference of Phase (GDP) that helps to differentiate between LoS and NLoS channels. We evaluate the performance of the GDP-based LoS/NLoS detection method that also uses Support Vector Machine (SVM). As a result we confirm that our proposed method successfully differentiates between LoS/NLoS channels and achieves a balance between a high level of security and user convenience.

As the emerging Internet of Things (IoT) devices and applications flourish, demand for reliable and energy-efficient low-power wireless network protocols is surging. For this purpose, IEEE 802.15.4 standardized time-slotted channel hopping (TSCH), a promising and viable link-layer solution that has shown outstanding performance achieving over 99% reliability with low duty-cycles. However, it lacks one thing, flexibility. It is not adaptable to a wide variety of applications with varying traffic load and unpredictable routing topology due to its static timeslot scheduling. To this end, we propose OST, an On-demand Scheduling scheme for TSCH with traffic-awareness. In OST, each node dynamically self-adjusts the frequency of timeslots at run time according to time-varying traffic intensity. Moreover, it features on-demand resource allocation to handle bursty/queued packets in a timely manner. By doing so, OST aims to minimize its energy consumption while guaranteeing reliable packet delivery. We evaluate OST on a large-scale 72-node testbed, demonstrating that it achieves improvement of 60% in reliability and 52% in energy-efficiency compared to the state of the art.

For emerging high-density Wi-Fi networks, there have been plenty of studies that claim the need for more aggressive channel access to enhance spatial reuse. Against those previous ideas, this paper presents a different perspective that existing Wi-Fi devices already have excessive transmission opportunities, even without protecting each other in certain scenarios. We shed light on an anomaly within actual carrier sensing (CS) behaviors, which makes some neighboring devices become blind to each other and transmit simultaneously, due to undetected preambles. Through experimental study and analysis, we reveal both sides of the anomaly heavily affecting the overall network performance. Based on the observations, we design REFRAIN, a standard-compliant PHY/MAC framework, which copes with and further exploits the anomaly for better spatial reuse. Our prototype using NI USRP and commercial Wi-Fi devices shows the feasibility and effectiveness of our approach, while extensive simulation results demonstrate that REFRAIN achieves up to 1.57× higher average throughput by promoting valid transmissions, without modifying the 802.11 CS specification at all.

Wi-Fi devices become increasingly susceptible to mutual interference in congested network scenarios. If a device starts to receive a new frame in the presence of concurrent interference signal, its preamble reception can be seriously damaged, which spoils the channel estimation process. The resulting corrupted channel state information (CSI) causes persistent decoding errors throughout the data payload. This paper presents a comprehensive study into the impact of corrupted CSI on Wi-Fi performance. Through experimental study and link-level analysis, we verify that actual receiver performance is highly dependent on CSI acquisition at the preamble, which has never been reflected by any physical layer abstraction models. We develop a realistic model that reflects the impact of corrupted CSI on overall frame reception. Applying our model to ns-3 simulator, we revisit network performance in interference-prone scenarios, to assess consistency with real-world Wi-Fi systems.

This paper considers the problem of joint control of traffic split and cell group state decision for downlink communication via multi-connectivity in a cellular network. In this problem, a master node makes a decision on traffic split every T slots, and each secondary base station determines its cell group state between `activated' and `deactivated' to save UE power consumption. To ensure independent control of each cell group through its hosting base station, cell group state decision should be independent of each other, evolving asynchronously cell group state across cell groups. State decision for each cell group is performed dynamically according to changing environments. Such aperiodic state decision and asynchronous state evolution cause considerable difficulty in developing algorithms to solve the problem. To overcome the difficulties, we employ a frame-based Lyapunov optimization framework with variable frame sizes and develop online algorithms that are simple to implement but provably provide near optimal values. Simulation results are shown that our algorithm outperforms the other competitive schemes.

The ultra-dense network (UDN) is a promising technology that overcomes the instability of high-frequency millimeter wave (mmWave) communication in a cellular network. With a short distance between cells and variability of mmWave, a handover occurs frequently in UDN with mmWave. Hence fast handover is essential to provide reliable service. One of the important things for fast handover is prompt signaling between base stations (BSs) through backhaul. However, conventional handovers assumed backhaul has very short latency with ideal deployment. In practice, with non-ideal latency and deployment of backhaul, handover is delayed for backhaul. We find that this delayed handover led to the performance reduction of TCP, the dominant traffic of nowadays. So we propose a ProSCH, the novel handover scheme that operates on a practical backhaul network while guaranteeing TCP performance. ProSCH reduces a handover interruption time by considering the backhaul latency in the handover signaling process and uses a TCP proxy on BS to forward data without loss after handover. Through extensive ns-3 simulation, we show that ProSCH outperforms conventional schemes in terms of handover interruption time, backhaul load, throughput, and delay.

We present PC-RPL , a transmission power-controlled IPv6 routing protocol for low-power and lossy wireless networks that significantly improves the end-to-end packet delivery performance under heavy traffic compared to the standard RPL. We show through actual design, implementation, and experiments that a multihop wireless network can achieve better throughput and routing stability when transmission power and routing topology are “jointly and adaptively” controlled. Our experiments show that the predominant “fixed and uniform” transmission power strategy with “link quality and hop distance”–based routing topology construction (i.e., RPL) loses significant bandwidth due to hidden terminal and load imbalance problems. We design an adaptive and distributed control mechanism for transmission power and routing topology, named PC-RPL , on top of the standard RPL routing protocol for hidden terminal mitigation and load balancing. We implement PC-RPL on real embedded devices and evaluate its performance on a 49-node multihop testbed. PC-RPL reduces total end-to-end packet losses by approximately sevenfold without increasing hop distance compared to RPL with the highest transmission power, resulting in 17% improvement in aggregate bandwidth and 64% improvement for the worst-case node by successfully alleviating both hidden terminal and load imbalance problems.

We introduce 5G K-SimNet, a network simulator for evaluating end-to-end performance of the fifth generation (5G) cellular system.5G K-SimNet provides the features of 5G new radio (NR), 5G core, multi-radio access technology (RAT) protocol, traffic management on multi-connectivity, and software-defined network/network function virtualization (SDN/NFV). In this paper, we present the features of 5G K-SimNet, scenarios that can be simulated by using the simulator, and the simulation results.

Mobile users in an ultra-dense millimeter-wave cellular network experience handover events more frequently than in conventional networks, which results in increased service interruption time and performance degradation due to blockages. Multi- connectivity has been proposed to resolve this, and it also extends the coverage of millimeter-wave communications. In this paper, we propose a dual-connection based handover scheme for mobile UEs in an environment where they are connected simultaneously with two millimeter-wave cells to overcome frequent handover problems. This scheme allows a mobile UE to choose its serving link between the two mmWave connections according to the measured SINRs and then the corresponding base stations may forward duplicate packets to the UE. We compare our dual-connection based scheme with a conventional single-connection based scheme through ns-3 simulation. The simulation results show that the proposed scheme significantly reduces handover rate and delay. Therefore, we argue that the dual- connection based scheme helps mobile users achieve performance goals they require in ultra-dense cellular environments.

The number of IEEE 802.11 hotspots is increasing due to popularity and low price, resulting in a dense deployment of wireless local area networks (WLANs). To increase per station (STA) throughput in a densely deployed environment, a new amendment to the WLAN standard, namely, IEEE 802.11ax introduces orthogonal frequency-division multiple access (OFDMA). Especially, uplink OFDMA-based random access (UORA) enables multiple STAs to have simultaneous random access (RA) to an access point (AP) by using different subchannels. However, due to the nature of RA, UORA suffers from data collisions with the number of contending STAs. Moreover, the bandwidth underutilization problem degrades performance of UORA. In this paper, we propose a scheme, named CRUI, that substantially reduces data collisions and improves bandwidth utilization by using an extra backoff stage and opportunistic subchannel hopping. Through simulation, we demonstrate that our proposed scheme significantly improves UORA performance with lowered collision probability and improved bandwidth utilization while maintaining fairness.

The use of Bluetooth Low Energy (BLE) has been steadily increased since Bluetooth Special Interest Group (SIG) standardized BLE in 2010, and BLE performance has been improved owing to various studies. Bluetooth specification 4.2 defined only one data rate, i.e., 1 Mb/s. However, the specification 5 released in 2016 specifies 2 Mb/s and coded PHYs for higher throughput and more stable transmission, respectively. This version also allows the transmission power to be varied from -20 dBm to 20 dBm. Therefore we are enabled to use various data rates and transmission powers in BLE. However, no research has studied how to adapt these yet. In this paper, we propose an algorithm, termed $AdaptaBLE$, that selects data rate and transmission power of BLE by considering link stability and energy consumption. We implement $AdaptaBLE$ on real devices and measure its performance. As a result, we confirm that $AdaptaBLE$ successfully selects an appropriate TX power and data rate while keeping the BLE link stable.

The explosion of mobile traffic volume has led to dense deployment of IEEE 802.11 WLANs. As a consequence, periodic beacon transmissions can overwhelm the air-time, leading to significant air-time depletion for data transmissions. In this work, we develop an opportunistic air-time sharing scheme, named BeaconRider, that facilitates simultaneous data and beacon transmissions aimed at improving spectrum efficiency in dense network environments. The proposed method works for downlink communication and allows access points (APs) to coordinate with each other in a distributed manner to exploit opportunities provided by the capture effect. Our protocol is backward compatible with legacy 802.11 APs. Through experiments with a prototype implementation using off-the-shelf IEEE 802.11n dongles as well as extensive ns-3 simulation, we show that the proposed method achieves substantial performance gains that increase with the number of APs.

Cross-technology interference in the ISM band is a prevalent and challenging problem. Prior work has proposed to use busytone signaler that can protect Zigbee transmissions from WiFi interference, but only in a single-hop setting. In this work, we propose Queue-size based Busy Tone (QBT) scheme that uses novel multihop busytone scheduling and priority path selection algorithms to protect multihop Zigbee network under heavy WiFi traffic. We adopt the busytone idea from prior work, but extend it to multihop networks where data is collected from and forwarded by a number of low-power nodes. We implement QBT on a lowpower embedded platform, and evaluate through experimental measurements on a real multihop LLN testbed consisting of 30 low-power embedded nodes and one gateway with two radios, the sink and the signaler, respectively. We show that QBT improves the performance of Zigbee network under WiFi interference dramatically in terms of both reliability (up to 66.4%) and energy efficiency (up to 24.4%). We also report our findings on adjacent-channel interference among Zigbee channels, and investigate the effect of busytone on WiFi traffic as well.

The use of Bluetooth Low Energy (BLE) has steadily increased since 2010. Bluetooth specification 4.2 defined only one data rate, 1 Mb/s. However, Bluetooth specification 5 released in 2016 specifies 2 Mb/s and coded PHY for higher throughput and for more stable transmission, respectively. In addition, this version of specification defines transmission power from -20 dBm to 20 dBm. In this paper, we propose AdaptaBLE, an algorithm that selects the data rate and transmission power of BLE by considering link stability and energy consumption. We implement AdaptaBLE on real devices and measure its performance. As a result, we confirm that AdaptaBLE successfully lowers energy consumption while keeping the link stable.

We propose transmission power control algorithm for Cellular-Vehicle-to-everything (C-V2X) mode 4, based on standard-compliant sensing scheme. We show that standard resource allocation scheme for Vehicle-to-vehicle (V2V) communication mode 4, with fixed transmission power, has room for improvement. Assuming channel reciprocity, proposed algorithm estimates neighbor's SINR and controls transmission power based on the estimation. We show that proposed scheme enhances system level PRR and also, performance of the algorithm increases as vehicles get more dense.

Bluetooth and Wi-Fi are the most widely used wireless technologies because they use unlicensed spectrum and are widely deployed on the latest mobile devices. For seamless Wi-Fi connectivity in mobile environments, the mobile device should maintain the information of adjacent access points (APs) through the scanning procedure, which often consumes a significant amount of energy and time. In this paper, we develop SplitScan that enables mobile devices to share Wi-Fi scanning information with adjacent stations (STAs) via Bluetooth packet exchange. We evaluate its performance through experiment with a testbed implementation as well as extensive simulation. The results show that SplitScan saves vonsiderable energy and time during the Wi-Fi scanning process.

The coexistence problem of different wireless protocols that share a common frequency spectrum has attracted much attention owing to the proliferation of heterogeneous wireless networks in the research community. Recently, Bluetooth (BT) and Wireless LAN (WLAN) protocol stacks have been integrated as a single-chip communication module, and they now even share the antenna as well as the spectrum. In this paper, we show that this integration provides new opportunity for one protocol to better understand the other and to operate in harmony to avoid mutual interference. We develop an Opportunistic Bluetooth Transmission (OBT) scheme that enables a dual stack device having an integrated module to exploit previously-unused deferring times of the WLAN protocol. We evaluate its performance through not only model-based analysis but also practical implementation in a prototype testbed. The results show that the OBT scheme can significantly improve throughput of the dual-stack device.

The new 802.11ac standard aims at achieving Gbps data throughput for individual users by exploiting enhanced physical-layer features, such as higher modulation levels, Multiple Input Multiple Output (MIMO), and wider bandwidths. However, the heterogeneity of bandwidth in a network can cause asymmetric interferences in which certain transmissions cannot be sensed by some other nodes. As a result, the conventional Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) may not work well in 802.11ac networks. We call this the Hidden Channel (HC) problem, which is shown to be real via experiments with USRP and WARP boards. To solve this problem, we propose bandwidth adaptation based on post-CCA, which is a clear channel assessment (CCA) procedure performed aftercompleting a transmission. Post-CCA in wireless networks helps mimic the CSMA with Collision Detection (CSMA/CD) mechanism in the wired Ethernet, thus enhancing channel assessment capability. Using post-CCA, we propose Post-CCA based Bandwidth Adaptation (PoBA) that alters bandwidth and channel configuration dynamically by applying a reinforcement learning mechanism. Post-CCA and PoBA do not require any hardware modification and are also compliant with the 802.11 standards. PoBA is shown via simulation to increase network-wide throughput, channel utilization and fairness, and also lower packet error probability.

We show that a multihop wireless network can achieve better bandwidth and routing stability when transmission power and routing topology are jointly and adaptively controlled. Our experiments show that the predominant 'fixed and uniform' transmission power strategy with 'link quality and hop distance'-based routing topology construction loses significant bandwidth due to hidden terminal and load imbalance problems. We design an adaptive and distributed control mechanism for transmission power and routing topology, PCRPL, within the standard RPL routing protocol. We implement PC-RPL on real embedded devices and evaluate its performance on a 49-node multihop testbed. PC-RPL reduces total end-to-end packet losses ~7-fold without increasing hop distance compared to RPL with the highest transmission power, resulting in 17% improvement in aggregate bandwidth and 64% for the worst-case node.

For over a decade, multihop low power and lossy networks (LLNs) have mainly focused on delivering upward traffic from individual nodes to the servers for supporting remote monitoring applications. However, as part of Internet of Things(IoT), LLN applications and traffic patterns are being diversified. In this paper, we address performance issues of LLNs when delivering various traffic patterns. Specifically, we experimentally show that LLNs suffer from unreliable routes when downward traffic is dominant since current routing protocols do not utilize downward traffic for link quality update. To tackle the problem, we design a novel mechanism, named ORPL-DT, that updates link quality information by using both upward and downward traffic, and implement it on top of ORPL (defacto IPv6 opportunistic routing protocol). We evaluate its performance on a 31-node multihop testbed, showing that ORPL-DT improves performance in terms of packet delivery ratio, control overhead, and radio duty-cycle.

Jamming is one of the most famous and powerful attacks in wireless networks, and is advancing to be more stealthy and long-lasting with limited energy. Stealthy attackers transmit short jamming signals to become less detectable with less energy, and yet powerful enough to ruin the entire packet transmission procedures. For this study, we deal with three types of stealthy attacks: 'reactive jamming', 'jamming ACK', and 'fake ACK' attacks. These attacks are fatal to Low-power and Lossy wireless Network (LLN) applications because they not only interfere with communication, but also cause LLN devices to quickly drain their batteries. In this paper, we present Dodge-Jam, a light-weight antijamming technique suitable for LLN environments to address the stealthy jamming attacks with small overhead. It protects ACK exchange by switching the ACK channel calculated based on the content of a data packet. Moreover, by partitioning a packet into multiple small blocks and performing logical shifts of the blocks when retransmitting the packet, it helps the receiver recover the original packet from multiple erroneous packets. We implement Dodge-Jam on practical embedded devices, and evaluate its performance through experiments on a multihop LLN testbed. Our results show that Dodge-Jam successfully avoids many jamming attacks, recovers packets that have been jammed, and improves packet delivery performance of both singlehop and multihop networks significantly.

Bluetooth Low Energy (BLE) is one of the widely used low power wireless protocols due to its simplicity and low energy consumption. The BLE standard is being developed further to support a wide range of applications spanning smart homes, wearables, and myriad appliances as part of IoT (Internet of Things). These new applications bring forth an important challenge: connection maintenance with low energy consumption in dynamic channel environments. In this paper, we investigate effective solutions to this technical challenge. First, we show using experiments that the current design of using fixed connection intervals incurs significant performance degradation under dynamic link conditions. To overcome the problem, we mathematically find an optimal connection interval that minimizes energy consumption while maintaining connectivity for a given link condition. Then, we design a simple yet effective connection interval adaptation mechanism for BLE, named CABLE. We implement the proposed solution on real embedded devices, and using extensive testbed experiments and simulation verify that CABLE leads to significant performance improvement while providing resilient connectivity in dynamic link environments.

RPL is an IPv6 routing protocol for low-power and lossy networks (LLNs) designed to meet the requirements of a wide range of LLN applications including smart grid AMIs, industrial and environmental monitoring, and wireless sensor networks. RPL allows bidirectional end-to-end IPv6 communication on resource constrained LLN devices, leading to the concept of the Internet of Things (IoT) with thousands and millions of devices interconnected through multihop mesh networks. In this article, we investigate the load balancing and congestion problem of RPL. Specifically, we show that most of the packet losses under heavy traffic are due to congestion, and a serious load balancing problem appears in RPL in terms of routing parent selection. To overcome this problem, this article proposes a simple yet effective queue utilization based RPL (QU-RPL) that achieves load balancing and significantly improves the end-to-end packet delivery performance compared to the standard RPL. QU-RPL is designed for each node to select its parent node considering the queue utilization of its neighbor nodes as well as their hop distances to an LLN border router (LBR). Owing to its load balancing capability, QURPL is very effective in lowering queue losses and increasing the packet delivery ratio. We implement QU-RPL on a low-power embedded platform, and verify all of our findings through experimental measurements on a real testbed of a multihop LLN over IEEE 802.15.4. We present the impact of each design element of QU-RPL on performance in detail, and also show that QU-RPL reduces the queue loss by up to 84 percent and improves the packet delivery ratio by up to 147 percent compared to the standard RPL.

In time-division duplex (TDD) massive multiple-input multiple-output (MIMO) systems, the spatial multiplexing gain cannot be fully achieved since available pilot resources in each channel coherence time interval are limited. In this paper, we propose OpSAC, an Opportunistic user Scheduling algorithm that uses Aged Channel state information (CSI) to increase the spatial multiplexing gain without incurring additional pilot overhead. Assuming the base station (BS) employs precoders of maximum ratio transmission (MRT) and zero-forcing (ZF), we first derive closed- form lower bounds on the achievable sum-rate under channel aging. According to the analysis results, we develop a heuristic solution which opportunistically schedules additional users by exploiting aged CSI to enhance spectral efficiency. Through simulation, we confirm that our analysis is accurate, and show the impact of channel aging on the performance of massive MIMO systems. In addition, it is shown that OpSAC achieves near-optimal performance and considerably outperforms the conventional user scheduling algorithm that only uses current CSI.

Mobile gadgets including smartphones and laptops nowadays support both Wi-Fi and Bluetooth together. The two protocols coexist in the 2.4GHz ISM band while sharing a single antenna in order to meet constraints on form-factor. We call this kind of devices "Dual- stack devices" in this paper. Since Wi-Fi and Bluetooth on dual-stack devices work in TDM (Time Division Multiplexing) manner, the performance of Wi- Fi, specifically throughput, degrades inevitably. We propose a novel scheme, Opportunistic Antenna Utilization (OAU), which aims to improve the throughput of Wi-Fi by utilizing time assigned to yet not used for a Bluetooth streaming service. We first present measurement results showing the degradation of Wi-Fi throughput on dual-stack devices followed by a simple analysis to anticipate the expected gain of OAU. Then we verify our analysis by showing that simulation results coincide well with the analysis.

In this paper, we propose a scalable broadcast protocol, named Subcarrier-level Tone-signal based Broadcast (ST-BCAST), that disseminates a packet over OFDM-based wireless multi-hop networks in an efficient and reliable manner. Exploiting collision-resilient tone-signals and receiver-triggered forwarding decision/cancellation, ST-BCAST achieves both high packet delivery ratio and low communication overhead without using any topological information, thereby providing scalability to the network size. Under a mild assumption, ST-BCAST satisfies two sufficient conditions for reliable broadcasting: first-hop delivery condition and successful relay condition. We verify the feasibility of tone-signal generation and detection through experiments using Universal Software Radio Peripheral (USRP) devices, and show through NS-3 simulations that ST-BCAST significantly outperforms the state-of-the-art broadcast schemes in terms of packet delivery ratio and communication overhead.

In this paper, we consider a protocol architecture that enables IPv6 routing protocol for low power and lossy networks (RPL) to run on top of Bluetooth Low Energy (BLE), aiming to provide a BLE-based multi-hop IoT network. In our approach to RPL over BLE, we propose to use both of advertising and data channels of BLE to create synergistic effects between RPL and BLE to jointly achieve high energy efficiency and reliable multi-hop routing. We design an adaptation layer between BLE and RPL (ALBER) which tightly couples RPL and BLE operations together. Specifically, ALBER provides RPL control message broadcast through BLE, RPL routing metric calculation that reflects BLE link quality, and routing table update that incorporates BLE connection management. We implement ALBER in a Linux kernel to realize RPL over BLE and compare its performance with that of RPL over IEEE 802.15.4 on a multi-hop testbed network. The performance results show that our architecture is not only feasible but also provides almost perfect packet delivery performance (↑100%) and reduces dutycycle up to 32% compared to RPL over IEEE 802.15.4 under varying link dynamics. Our research shows that RPL over BLE is a promising approach which can increase the utility and impactof BLE across different application domains.

We present a transmission power control scheme for RPL, the IPv6 Routing Protocol for Low-power lossy network [9], that controls the routing topology to achieve load balancing in a low-power multihop wireless network. We show that higher-than-required transmission power results in congestion and load balancing problems under heavy traffic, and transmission power cannot be optimized for reliable packet delivery when equal power is used by all nodes. To address these issues, we propose an adaptive and non-uniform transmission power controlled RPL, called PC-RPL, that significantly improves the end-to-end packet delivery performance compared to the standard RPL.

Bufferbloat has drawn much attention in the network community for its negative impact on TCP delay performance and user QoE. Recently, it has been more commonly noted in wireless access networks, in part, due to over-provisioned buffer space. Previous works that focused only on bufferbloat prevention have suffered from either deployment or fairness problems when coexisting with conventional TCP flows. In this paper, we address the bufferbloat problem in resource-competitive environments such as Wi-Fi, and design a receiver-side countermeasure for easy deployment that does not require any modification at the sender or intermediate routers. Exploiting TCP and AQM dynamics, our scheme competes for shared resource in a fair manner with conventional TCP flow control methods and prevents bufferbloat. We implement our proposed scheme in commercial smart devices and verify its performance through real experiments in LTE and Wi-Fi networks.

In low-power wireless networks, maintaining multihop connectivity is considered effective in constructing communication routes between individual nodes to a gateway. Since sensor networks are typically used for data collection, multihop routing protocols are designed to find routes optimal in upward directions. As sensor networks become widely applied to diverse applications, efficient downward traffic delivery also becomes important. To achieve this, we consider an asymmetric transmission power-based network (APN), where a power-supplied gateway uses high-power radios to cover the entire network via single-hop transmission, whereas common nodes use low-power transmissions. For effective APN operations, we propose a single-hop downlink protocol (SHDP) that consists of direct downlink transmission, local acknowledgment, neighbor forwarding, and contention resolution among the destination’s neighbors. We evaluate SHDP through mathematical analysis, simulations, and testbed experiments. Our proposal outperforms other competitive multihop routing protocols. Specifically, SHDP shows high packet delivery performance and lowers the duty cycle greatly while reducing the packet transmission overhead by >50%.

In-band wireless full-duplex is a promising technology that enables a wireless node to transmit and receive at the same time on the same frequency spectrum. In OFDMA networks, the full-duplex transmission makes the resource allocation problem more challenging, in particular when user devices are not full-duplex capable. In this paper, we investigate the joint problem of subcarrier assignment and power allocation to maximize the sum-rate performance in full-duplex OFDMA networks. To achieve high throughput in the considered network, we propose to use a practical subcarrier assignment condition which allows a subcarrier to be allocated to a pair of uplink and downlink nodes when its inter-node channel gain is lower than its uplink channel gain. Considering this condition and the inter-node interference, we design three resource allocation algorithms which run for; i) uplink first, ii) downlink first, and iii) uplink and downlink in pair. Through simulation, we evaluate our solutions in comparison with conventional schemes with respect to performance gain.

Multi-Path TCP (MPTCP) has attracted much attention as a promising technology to improve throughput performance of wireless devices that support multi-homed heterogeneous networks. Although MPTCP provides significant increase in network capacity, it may suffer from poor delay performance since the delay tends to be aligned with the worst-performing path: packets delivered through a short-delay subflow have to wait in the reordering buffer for packets being transmitted over a long-delay subflow. In this paper, we investigate the application-level delay performance of streaming traffic over MPTCP, and develop an analytical framework to take into account non-negligible network queuing delay and the interplay of congestion control between multiple subflows. We design a simple threshold-based subflow traffic allocation scheme that aims to minimize user-level delay and develop a receiver-centric traffic splitting control (R-TSC) that can be tuned to user preferences. The client-side R-TSC solution facilitates incremental deployment of low-delay streaming service over MPTCP. Through simulation and testbed experiments using commercial LTE and WiFi networks, we demonstrate significant performance gains over the standard MPTCP protocol.

RPL is an IPv6 routing protocol for low-power and lossy networks (LLNs) designed to meet the requirements of a wide range of LLN applications including smart grid AMIs, industrial and environmental monitoring, and wireless sensor networks. RPL allows bi-directional end-to-end IPv6 communication on resource constrained LLN devices, leading to the concept of the Internet of Things (IoT) with thousands and millions of devices interconnected through multihop mesh networks. In this paper, we investigate the load balancing and congestion problem of RPL. Specifically, we show that most of packet losses under heavy traffic are due to congestion, and a serious load balancing problem exists in RPL in terms of routing parent selection. To overcome this problem, this paper proposes a simple yet effective queue utilization based RPL (QU-RPL) that significantly improves end-to-end packet delivery performance compared to the standard RPL. QU-RPL is designed for each node to select its parent node considering the queue utilization of its neighbor nodes as well as their hop distances to an LLN border router (LBR). Owing to its load balancing capability, QU-RPL is very effective in lowering the queue losses and increasing the packet delivery ratio. We verify all our findings through experimental measurements on a real testbed of a multihop LLN over IEEE 802.15.4.

Updating price tags in a large-scale market is a recurrent task, still performed manually in most markets. Given that human-errors can easily lead to customer complaints and accounting inaccuracies, the ability to autonomously reconfigure price tags can be of significant benefit. With the introduction of low-power display techniques such as electronic ink, applications of enabling electronic, wirelessly reconfigurable price tags show potential for future deployment. In this work, we examine networking architectures that can be applied in such scenarios. Through a series of preliminary pilot studies in an actual supermarket, we show that the performance of existing protocols are not ready to overcome the unique challenges of busy market environments. We identify underlying technical challenges and propose MarketNet, an asymmetric transmission power-based system designed for densely populated, obstacle-rich, downwards traffic-oriented environments. We evaluate MarketNet in a large indoor mar- ket visited by 5000+ customers per day. Our results show that MarketNet addresses the challenges of the target application and environment, while achieving higher packet delivery performance with noticeably lower radio duty-cycles than existing protocols such as RPL and SHDP.

In this demo, we present interoperability between Bluetooth Low Energy (BLE) and IPv6 routing protocol for low power and lossy networks (RPL). To make the operation of RPL over BLE feasible, we design an adaptation layer between BLE and RPL, termed ALBER. Specifically, we develop three technical features in ALBER which enable BLE to be combined with RPL. First, it broadcasts RPL control messages through BLE using advertising channels with low energy consumption. Second, it updates RPL routing table considering connection management of BLE. Lastly, it estimates link quality based on round trip time of link layer ping packets to provide routing metric for RPL. We implement our ALBER on Linux kernel. This demo will present an operation example of RPL over BLE using ALBER in a small scale multi-hop topology, where each node comprises a Raspberry Pi platform and a BLE dongle.

The major goal of IEEE 802.11ac is to provide very high throughput (VHT) performance while at the same time guaranteeing backward compatibility. To achieve this goal, 802.11ac adopts the channel bonding technique that makes use of multiple 20 MHz channels in 5 GHz band. Due to the heterogeneity of bandwidth that each device exploits, and the fixed total transmission power in the standards, a problem called `Hidden Channel' arises. In this paper, we first analyze the problem and show how the contention parameters and transmission time affect collision probability and fairness in some deployment scenarios. Then, we propose a heuristic channel allocation algorithm that aims to avoid such problematic situations effectively. Through simulations, we demonstrate that our proposed channel allocation algorithm lowers the packet error rate (PER) compared to uncoordinated and received signal strength indicator(RSSI) based allocation schemes and increases the network-wide throughput as well as the throughput of a station that experiences poor performance. This implies improved fairness performance among transmission pairs with various channel bandwidths.

Recent advances in the physical layer have demonstrated the feasibility of in-band wireless full-duplex which enables a node to transmit and receive simultaneously on the same frequency band. While the full-duplex operation can ideally double the spectral efficiency, the network-level gain of full-duplex in large-scale networks remains unclear due to the complicated resource allocation in multi-carrier and multi-user environments. In this paper, we consider a single-cell full-duplex OFDMA network which consists of one full-duplex base station (BS) and multiple full-duplex mobile nodes. Our goal is to maximize the sum-rate performance by jointly optimizing subcarrier assignment and power allocation considering the characteristics of full-duplex transmissions. We develop an iterative solution that achieves local Pareto optimality in typical scenarios. Through extensive simulations, we demonstrate that our solution empirically achieves near-optimal performance and outperforms other resource allocation schemes designed for half-duplex networks. Also, we reveal the impact of various factors such as the channel correlation, the residual self-interference, and the distance between the BS and nodes on the full-duplex gain.

In this paper, we consider the use of an electric-supplied coordinator exploiting much higher transmission power than battery-supplied nodes in low power and lossy networks (LLNs). Since the coordinator can transmit via one hop instead of multiple hops over downlink, it is possible to reduce the communication overhead significantly. To take this advantage, we propose a single hop downlink protocol (SHDP) which comprises direct downlink transmission, local acknowledgement, neighbor forwarding, and mitigation of forwarding contention. Finally, the performance of the proposed SHDP is mathematically analyzed and evaluated by computer simulation, showing significant performance improvement over conventional multi-hop routing when applied to LLNs.

In wireless networks, frame retransmission is used to increase reliability with the use of additional wireless resources. Recently, various approaches have been proposed to reduce the overhead for retransmission. However, they still suffer from performance degradation due to unpredictable wireless channel variation during a frame transmission in fast-fading environments. In this paper, we propose an in-frame rate adaptation (InFRA) scheme as a solution for mitigating the retransmission overhead. In InFRA, a receiver estimates the channel SNR of incoming symbols and feeds it back to the sender. According to the feedback information, the sender adaptively changes its symbol transmission rate during a frame transmission. In this way, InFRA significantly increases the reliability of frame transmission even when the channel state changes within a frame transmission. To evaluate the effectiveness of InFRA, we mathematically analyze its performance and compare it with the existing schemes. Finally, our simulation results show that InFRA achieves significant throughput improvements over the other competitive schemes in fast fading channel environments.

In massive multiple-input multiple-out (M-MIMO) systems, conventional sounding schemes may suffer from pilot contamination of cell edge users or a lowered number of serviced users in a multi-cell scenario. In this paper, we propose a partial sounding resource reuse (PSRR) method which aims to seamlessly guarantee the quality of service (QoS) of mobile users by mitigating the pilot contamination as well as minimize the reduction in the number of serviced users. To this end, the PSRR divides each cell area into center and edge areas, and partially reuses sounding resources among users in neighboring edge areas. We use a Markov chain model to analyze the performance of the PSRR. Then we evaluate the accuracy of our analysis through simulations, and show that the PSRR considerably improves QoS performance over the conventional schemes.

MPTCP is a promising transport technique to boost throughput of wireless multi-homed device by supporting multiple concurrent transmissions through heterogeneous wireless interfaces. As the number of concurrent subflows increase, MPTCP can achieve a linearly increasing throughput performance, but it is unclear how much improvement in the end-to-end delay performance can be attained from additional subflows. In this paper, we develop an analytical framework to understand the end-to-end delay performance of MPTCP that accounts for TCP dynamics and subflow interactions. Interestingly, it turns out that the delay performance can be even degraded with additional subflows. Considering MPTCP in heterogeneous wireless networks of Wi-Fi and LTE, we formulate a cost minimization problem subject to the end-to-end delay constraint. Based on the insight obtained from our model, we approximate the problem and develop a greedy scheme that splits traffic to minimize the cost while satisfying the delay constraints. Through simulations, we demonstrate that our proposed scheme outperforms the conventional MPTCP, and significantly improves the delay performance while lowering the user cost.

The goal of IEEE 802.11ac is to provide very high throughput~(VHT) performance while at the same time guaranteeing backward compatibility. For the goal, 802.11ac adopts the channel bonding technique that makes use of multiple 20MHz channels in 5GHz band. Due to the heterogeneity of bandwidth that each device exploits, and the fixed total transmission power, a problem called `Hidden Channel' arises. In this paper, we propose a heuristic channel allocation algorithm that aims to avoid such problematic situations. Through simulations, we demonstrate that our proposed channel allocation algorithm lowers the packet error rate~(PER) compared to uncoordinated and RSSI~(Received Signal Strength Indicator) based allocation schemes and increases the throughput of a station that experiences poor performance.

Device-to-Device (D2D) communication has become an attractive alternative in bringing popular mobile video contents much closer to the end users. However resulting interference caused by the direct communicating D2D pair demands sufficient resources as well as proper admission control mechanisms for the corresponding mode. To resolve these issues, in this paper, we suggest how source and destination end users can optimally select the corresponding operational mode between cellular and D2D modes aiming to maximize the network capacity. Further, we formulate resource block (RB) assignment as an optimization problem and design a deterministic and heuristic algorithm to approximate the optimal solution. The simulation results show a comparison of our proposed optimal and distributed heuristic mode selection with RB assignment algorithms, as well as traditional cellular and underlay D2D mode schemes. From simulation results, we show that our algorithm achieves better average uplink throughput and SINR by reducing interference.

Generating a busy tone is known as a good solution that enables a ZigBee network to coexist with any Wi-Fi network in the same ISM band. To generate a busy tone, ZigBee networks need to deploy a signaler that transmits it with the same power as Wi-Fi nodes, thus preventing other Wi-Fi nodes from accessing the corresponding channel. In this paper, we mathematically analyze the delivery ratio and delay of such a ZigBee network using a Markov chain model when busy tones are periodically generated. Based on the analysis, we derive a simple scheduling algorithm that adjusts the period of the busy tone. The analytic results are verified through simulation results which confirm that periodic busy tones enhance the performance of ZigBee transmissions.

Random backoff counter based contention schemes have some drawbacks. They are basically unfair in short periods and unable to provide differentiated services between participants. Since these drawbacks are more serious when the participants are access points rather than mobile nodes, we propose a prioritization scheme to enhance the short-term fairness and to give different priorities between them. Our proposed scheme consists of two parts: assigning higher priority to a long waiting access point and probabilistically giving one level higher priority to some access points for differentiation. Through analysis and simulation, we verify that our prioritization scheme enhances the short-term fairness and achieves the priority differentiation between participants.

In massive multiple-input multiple-out (M-MIMO) systems, the base station estimates each forward-link channel by using the reverse-link sounding pilot and the channel reciprocity property of time division duplex (TDD) operation. However, conventional non-cooperative sounding schemes, like a sounding sequence assignment scheme with reuse factor-1, cause cell edge users to suffer from pilot contamination in multi-cell scenarios. The pilot contamination problem becomes even worse in an environment where mobile users are travelling through cell edge areas frequently. To alleviate this problem, a cooperative sounding resource reuse method that assigns each cell a set of resources different from other neighboring cells by using a reuse factor-3 scheme, can be considered, but it significantly lowers the number of served users. In this paper, we propose a partial sounding resource reuse (PSRR) method which aims to seamlessly support the quality of service (QoS) of each mobile user by mitigating the pilot contamination and to minimize the reduction in the number of served users. To this end, the PSRR divides each cell area into center and edge areas, and applies a reuse factor-1 scheme for center users while a reuse factor-3 scheme for edge users. We use a Markov chain model to analyze the performance of the PSRR, and evaluate the accuracy of our analysis through simulations. Then we confirm that the PSRR considerably improves QoS performance over the conventional competitive schemes.

In wireless sensor networks, the routing control overhead could be large because multiple relays are involved in the routing operation. In order to mitigate this problem, a promising solution is to use tier-based anycast protocols. The main shortcoming of these protocols is that they can consume a much greater amount of energy as compared with other competing protocols using deterministic routing. In this paper, we analyze, in depth, a tier-based anycast protocol and develop a new technique of improving network lifetime. Our solution is guided by our analytic framework that consists of subtiering and a new forwarding protocol called 'scheduling controlled anycast protocol'. We formulate the problem for finding an optimal duty cycle for each tier with a delay constraint as a minimax optimization problem and find its solution, which we show is unique. From the analytical results, we find that the network lifetime can be significantly extended by allocating a different duty cycle adaptively for each tier under a delay constraint. Through simulations, we verify that our duty cycle control algorithm enhances the network lifetime by approximately 70% in comparison with an optimal homogeneous duty cycle allocation. Copyright © 2012 John Wiley & Sons, Ltd.

Ultra-wideband (UWB) communication is a promising technology to provide high data rates with low power consumption in wireless personal area networks. Among the standards adopting the UWB technology, Wireless USB (WUSB) running on the platform of WiMedia aims to provide high-speed wireless connectivity between mobile devices. To support reliable connectivity, data rates should be adapted according to UWB channel states that are time- varying. In this paper, we propose a novel rate adaptation scheme which considers the characteristics of WUSB protocol as well as the time-varying UWB channel. Our proposed scheme uses the channel prediction in a short time scale. Specifically, the channel state of the previous time window is used to determine the data rate of the next time window, assuming the channel similarity between the two successive time windows. Through extensive trace-driven simulations, we show that the proposed rate adaptation scheme outperforms the conventional schemes.

In this paper, we deal with a cost minimization problem for a multihomed mobile terminal that downloads and plays a video-on-demand (VoD) stream. The cost consists of the user's dissatisfaction due to playback disruptions and communication cost for downloading the VoD stream. There are three components in our approach: parameter estimation, threshold adjustment, and threshold compensation. Since we do not assume any a priori knowledge about underlying random variables, necessary parameter values are estimated online. Using the resultant estimates, we formulate the problem as a Markov decision process (MDP) problem considering as if the random variables are exponentially distributed. To solve the MDP problem efficiently, we propose a threshold adjustment algorithm that exploits some structural properties of any optimal solution that are specific to our problem. Finally, to handle the cases where the random variables are not exponentially distributed, we propose a threshold compensation algorithm to compensate for the modeling error. Through extensive simulations, we compare the performance of our scheme with those of static threshold schemes.

Abstract—Internet forums provide a varied and graceful stage for those who have hobbies or interests in common and want to share their contents of interest with each other. Traditionally they use Client-Server (CS) model. A distinct characteristic of a Internet forum is that some registered nodes1 periodically visit the forum. It implies that those nodes are regular visitors and can be considered relatively stable for some duration of time. The efficient use of these relatively stable nodes is very useful in a P2P network design, especially when the forum server is with limited bandwidth. In this paper, we propose a hybrid P2P network structure which is targeted for Internet forums. In the proposed system, the forum server maintains a list of registered nodes and classifies some nodes that are regularly visiting the forum with high prob-ability as stable nodes. The P2P network created by these stable nodes is triggered when the forum server is highly demanded due to a special event. To resolve the bandwidth shortage problem, the forum server selects stable nodes in advance, according to each node’s activity history. For the stable P2P node selection, we consider two types of mechanisms; a time period mechanism and a valid date window (VDW) mechanism, according to the considered time period. Then, we confirm that our proposed P2P model outperforms the traditional CS model through simulations. I.

Interference management is an important issue due to the wide deployment of femtocells by subscribers. An elementary solution to the interference mitigation problem is to restrict transmission of pilot signals by femto base stations (BSs) which have no serving subscribers, i.e. idle listening state operation. However, the implementation of the idle listening state in a femto BS opens a possibility of having a problem in location update because a femto BS in idle listening state and a user equipment (UE) in idle mode are not able to communicate with each other. This happens because none of these initiates communication, i.e. the deadlock problem. We consider three types of solutions to this problem; UE based, femto BS based, and network assisted solutions. Our proposed solutions handle the deadlock problem as well as the interference mitigation problem. In addition, our proposed solutions are able to be with any existing power control based interference mitigation scheme. Through simulations and numerical analysis, we show that our proposed solution considerably enhances the network capacity and save energy consumption.

Femtocells are expected as the surest way to increase the system capacity with higher-quality links and more spatial reuse in future networks. In spite of their great potential, the system capacity is highly susceptible to network density because a large portion of users are exposed to inter-cell interference (ICI). In this work, we proposed a dynamic interference avoidance scheme in densely deployed cell environments. Our proposed DDIA (Distributed Dynamic ICI Avoidance) scheme not only works in a fully distributed manner, but also controls interference link connectivity of users with high agility so that it is suited for self-organizing networks (SONs). We introduced the concept of ICI-link and two-tier scheduling in designing the DDIA scheme. To avoid ICI without any central entity, our scheme tries to harmonize all base stations (BSs) with users adaptively. Through extensive simulations, it was shown that our proposed scheme improves the throughput of users by more than twice on average compared to the frequency reuse factor 1 scheme, who are exposed to ICI while maintaining or even improving overall network performance. Our scheme operates well regardless of network density and topology.

With the multi-fold development in communication technology, there has been a rapid growth in consumption of multimedia services using mobile devices. In particular, lots of research has been done to provide multimedia services using a 3G/WLAN dual mode to mobile device users. All users download contents from content providers through cellular networks and can share their contents with their neighbors. This may lead to a situation where the cost of receiving multimedia contents is reduced owing to contents sharing. In other words, users effectively reduce the cost of receiving contents as they share some contents with neighbors. However, we believe that selfish users (or users with limited resources) are not willing to cooperate or share their contents with other users. In this paper, we propose an incentive scheme that gives the benefit of contents sharing to users in a 3G/WLAN dual mode supporting network. There are two types of users; premium users and ordinary users. Premium users can get high quality contents at the expense of spending their own money and resources of power and bandwidth, while ordinary users receive plain quality contents freely or with paying little amount of money. Our incentive mechanism designs the content provider to offer each premium user a discounted price for downloading high quality contents. Through our approach, each premium user will receive some incentive of a discounted price for receiving high quality contents in proportion to the contribution to the content provider. By doing so, the content provider can increase its total utility too. Our simulation results confirm that our proposed incentive scheme performs well.

In this paper, we propose a novel P2P VoD streaming system, named PECAN where each peer adjusts its cache capacity adaptively to meet the server's upload bandwidth constraint and achieve the fairness. For doing so, we first propose a new cache replacement algorithm that designs the number of caches for a segment to be proportional to its popularity. Second, we mathematically prove that if the cache capacity of a peer is proportional to its segment request rate, the fairness between upload and download amounts at each peer can be achieved. Third, we propose a method that determines each peer's cache capacity adaptively according to the constraint of the server's upload bandwidth. Through simulations, we show that PECAN meets the server upload bandwidth constraint, and achieves the fairness well at each peer.

Load balancing through cell-site selection in wireless networks has gained much attention as an efficient way to utilize scarce wireless resources. This paper considers a Point of Attachment (PoA) selection problem which is an extension of the cell-site selection problem. The PoA selection problem deals with an extended environment where each user device is with a different radio access technology (RAT) capability including multiple wireless network interface cards (WNICs). The goal of this paper is to formulate the problem that aims to maximize the network-wide utility under the environment of multi RATs and heterogeneous user device capabilities. To solve this problem, we first prove the problem is NP-Hard and propose a heuristic algorithm. Through extensive simulations, we evaluate the performance of our proposed algorithm against two received signal strength based approaches.

Opportunistic routing has gained much attention in recent years as a means of leveraging the broadcast nature of wireless medium. Most of the previous studies focused only on improving throughput, assuming that Best Effort traffic which is delay insensitive is delivered through opportunistic routing. However, when the delay sensitive traffic is involved, it is necessary to consider both the opportunistic gain and the delay incurred by opportunistic routing at the same time. In this paper, we analyze the relationship between these two factors and through extensive simulations confirm that our analyses are very accurate.

In IEEE 802.11 based Wireless LANs, the channel bandwidth is considered as a fixed parameter. Recently, the concept of adaptive bandwidth has been newly introduced, making it possible to allocate the channel bandwidth adaptively according to the interference type of users. Such a capability enables to enhance the previous way of channel usage where each Access Point (AP) is restricted to use a fixed bandwidth channel to serve all users. In this paper, we propose a scheme where each AP is allowed to use an adaptive bandwidth channel that is adjusted by a central controller. The channel bandwidth is determined according to whether a user to be served experiences interference or not. If the user is vulnerable to interference from other APs, not its serving AP, it is served through a channel assigned to the serving AP. On the contrary, when serving interference-free users, the AP can exploit more bandwidth which is available at the moment. In this way, our proposed scheme can enhance the spectrum utilization of interference-free users without harming the other users. Simulation results show that our scheme significantly improves the average spectrum utilization of each AP.

Two-tier overlay networks that consist of a conventional macrocell network and femtocell hotspots offer an economical solution for high user capacity and extended coverage. However, wireless interference across tiers causes significant performance degradation and restricts spectrum reuse. In this paper, we explore schemes to mitigate cross-tier interference with beamforming antennas for overlay networks. In our model, femtocells can operate with frequency spectrum that is either shared with or separated from the macrocell. The enhanced SIR from beamforming contributes to the population of femtocells with the shared spectrum, and thus improve the spectrum efficiency. Given a required SIR level, we show that which femtocells can use the shared spectrum and how much spectrum can be shared to maximize total utility. We show through a numerical performance evaluation that proposed schemes improve spectrum utilization for two-tier overlay networks.

Abstract A fully connected one‐hop ad hoc network constitutes a basic unit for managing self‐organizing networks such as IEEE 802.11 and 802.15.3 networks. Since energy efficiency is a critical issue in ad hoc networks, we develop an energy‐saving framework that includes scheduling for node‐to‐node direct communication. The scheduling is performed by a coordinator that is selected by some simple rule. We enhance IEEE 802.11 protocol by using our proposed framework, and analyze its energy efficiency in transmitting and receiving data. Through mathematical analysis, we confirm that our enhanced protocol significantly saves energy compared to the IEEE 802.11 protocol. We also investigate the robustness of our algorithm by covering the cases of uncooperative users, system malfunctioning, and channel errors. The numerical results confirm that our protocol works well under these hostile environments and maintains its advantage over the conventional scheme. Copyright © 2009 John Wiley & Sons, Ltd.

Abstract In wireless networks, maximizing throughput and minimizing energy consumption are two conflicting objectives. For elastic traffic, it is the total completion time, not the delay constraint of a single packet or the short‐term throughput requirement, that directly affects the quality‐of‐service (QoS). At the same time, the energy consumption should be minimized in order to prolong the battery lifetime of the mobile station (MS). In this paper, we propose energy efficient schedulers that consider throughput and energy saving simultaneously. Through extensive simulations, we compare the proposed schemes with the conventional scheme where a mobile terminal stays awake until all the pending packets are completely serviced. The simulation results show that our schemes outperform the conventional one in terms of utility, i.e., user satisfaction, which is defined as inversely proportional to the multiplication of weighted service completion time and energy consumption. Copyright © 2009 John Wiley & Sons, Ltd.

Due to the limited battery in wireless sensor networks (WSNs), energy efficiency is an important factor when designing a MAC protocol. To minimize energy consumption, most of MAC protocols in WSNs exploit low duty cycling. Among those, RMAC allows a node to transmit a data packet for multiple hops in a single duty cycle, which is made possible by exploiting a control frame named Pioneer (PION) for the path set up. In this paper, we present a MAC protocol called hop extended MAC (HE-MAC) that enables a node to transmit a data packet for more hops in a single duty cycle compared to RMAC. It employs an EXP (Explorer) frame to set up the path for multiple hop transmission, which contains the information about the maximum hop that a packet can travel through in a single duty cycle. Using the information in EXP and an internal state of ready-to-receive (RTR), HE-MAC extends the relay of a packet beyond the termination of the data period by two more hops compared to RMAC. Also along with our proposed adaptive sleeping method, it also reduces power consumption. We analytically obtain the packet latency in HE-MAC and evaluate the performance through ns-2 simulations. Compared to RMAC, HE-MAC shows 42.2% less power consumption and 23.6% less packet delay on average for a random topology of 300 nodes.

As the number of wireless service providers increases, competition among them is becoming stronger in wireless access networks. On the other hand, users actively change their behaviors toward the networks to get more network resources such as service time, bandwidth, capacity, etc. That is, each user will actively choose a cell or a network that offers the largest amount of resources with the lowest cost. In these environments, service providers have to consider not only technical factors but also economical factors such as revenue and user price. By controlling the pricing policy, a service provider can recruit or refuse users that are trying to associate with. In this paper, we first model the resource purchasing and pricing game scheme that takes not only revenue of a service provider but also user satisfaction into account. Assuming selfish behaviors, solution is derived using game theoretic approach. The solution produces the integrated purchasing and pricing scheme that shows cell breathing effect. We extend the model to multicell environments where a user has freedom to choose its service provider. As a user actively changes its weight of the utility function and chooses a cell to associate with, overall performance can be improved. We demonstrate the effect of load balancing with the pricing policy, and the performance improvement compared to a conventional method of association via simulation.

Although many anti-spam techniques have been developed, they have difficulty in detecting spams whose contents are altered to evade detection and in tracking spammers that are comprised of botnets. There have been a few works to resolve these limitations, but most of them are not appropriate to be deployed at a gateway for online detection. In this paper, we find network-based characteristics that spammers cannot easily distort. Based on the characteristics, we develop an algorithm applying the metrics to a large volume of traffic in real time. The scheme is efficient enough to run at the ingress point as it only needs to inspect the transport information contained in TCP/IP headers of SMTP connections.

In P2P live streaming, free-riders which do not upload data but only download them are still present. Since a greater number of viewers can generate more profit, the streaming server wants to serve the free-riders also. In this paper, we have proposed a novel P2P live streaming system, called super-peer assisted live streaming architecture (SALSA). In SALSA, super-peers, which have high upload bandwidth and serve many free-riders, are eligible to receive an incentive reward that is the ability to watch high quality videos. The server places high-quality-view-tickets at auction to make the super-peers serve free-riders more efficiently. We have proposed novel auction mechanisms and a heuristic algorithm. The simulation results showed that the proposed scheme has comparable performance to the optimal form and are able to differentiate the super-peers' video quality commensurate with their contribution level.

Over the last decade multiple-input and multiple-output (MIMO) systems have been actively researched and started to be deployed in wireless communications owing to the significant increase in channel capacity. In this paper, we propose an energy saving MAC protocol in MIMO (ESMACM) systems by focusing on energy efficiency instead of capacity maximization. ESMACM considers the energy consumption together with the tradeoff between reliability (i.e., diversity) and throughput (i.e., multiplexing gain), and dynamically chooses an appropriate number of antennas for transmission. In computing the total energy consumption, ESMACM counts circuit energy as well as transmission energy. Naturally the circuit energy consumption is directly proportional to the number of active antennas. Through numerical analysis, we confirm that our ESMACM considerably saves energy consumption compared to conventional capacity maximization schemes that use a fixed number of MIMO channels, for a given outage constraint. Our finding is that the capacity maximizing communication which possibly can be regarded best in terms of energy efficiency gives a different solution from the energy minimizing communication.

In this paper, we propose a new centralized routing protocol named WRP that aims at maximizing the network lifetime. In WRP, the sink node is assumed to be with more capabilities and basically collects each node's estimated wakeup time. This enables the sink node to estimate the wakeup times of all sensor nodes even if some of them are multi-hops away from the sink node. The estimated information is used to find a new route without flooding when some links are broken. Owing to these features, WRP solves the problem of high energy consumption mainly caused by the clock drift in ultra low duty cycled environments. It achieves longer network lifetime independently of the node density because the amount of control traffic does not increase with the node density. We investigate the performance of WRP through extensive simulations and show that WRP increases the network lifetime by more than 10 times against existing routing protocols. WRP can be a very promising routing protocol applicable to the monitoring case like AMR (Automatic Metering Reading) and AMI (Advanced Metering Infrastructure).

To create a wireless backbone network, channel allocation algorithms in mesh networks have been actively researched these days, but they still have the problem of scalability. When they operate in a centralized manner, they are not able to guarantee the upper-bound of the channel allocation time. This paper considers a new channel allocation algorithm that works under the environments of directional antennas. It allocates channels in a distributed manner and also adaptively by reflecting the traffic demand. To do so, we reconstruct the network into several groups to apply 2P MAC protocol, remove the interference caused by the directional antennas, and allocate a channel to each link without resorting to a central manager. Through simulation work, we prove that our distributed and adaptive channel allocation (DACA) achieves good performance, in terms of packet drop and channel allocation delay, compared with the other competitive channel allocation algorithms.

In wireless networks, maximizing throughput and minimizing energy consumption are two conflicting objectives. For elastic traffic, it is important to enhance the throughput since it directly affects the quality-of-service (QoS) of users. At the same time, the energy consumption should be minimized in order to prolong the battery lifetime of the mobile station. In this paper, we propose several adaptive energy saving schemes that consider throughput and energy saving simultaneously. The proposed schemes are designed for an efficient tradeoff between throughput and energy saving when transferring elastic traffic. Through extensive simulations, we compare the proposed schemes with the conventional scheme where a mobile terminal stays awake until all the pending packets are completely serviced. Our schemes outperform the conventional one in terms of utility, i.e., user satisfaction, which is defined as inversely proportional to the weighted multiplication of service completion time and energy consumption.

We design an architecture of distributed certification authority (MeCA) for wireless mesh networks (WMNs). In MeCA, the secret key and functions of certification authority are distributed over several mesh routers. For secret sharing and redistribution, we develop the fast verifiable share redistribution (FVSR) scheme. MeCA adopts the multicasting based on Ruiz tree, which is optimal in reducing the operation overhead. It can update, revoke, and verify certificates of WMN nodes in a secure and efficient manner. Simulation results show that MeCA does not disclose its secret key even under severe attacks while incurring low overhead compared to other existing schemes in mobile ad hoc networks.

Recent broadband wireless technologies such as HSDPA and mobile WiMAX achieve high data rate transmission, making wireless networking environments more similar to wired environments. As a result, wireless networks are also being exposed to DDoS attack. In this paper, we consider a possible DDoS attack in mobile WiMAX networks and solve this problem by using our proposed shared authentication information (SAI). SAI exploits unused upper 64 bits of the 128-bit cipher-based message authentication code (CMAC) which has been designed to provide the integrity of management message. In the mobile WiMAX network, the lower significant 64 bits of CMAC are truncated and used. Therefore we are able to use the upper 64 bits for our SAI while assuring the same level of security guaranteed by CMAC. Since SAI can be obtained from CMAC calculation, no additional calculations or message exchanges are required for sharing SAI and only the entity having the CMAC key can know SAI. Owing to these properties, using SAI can be a simple defense mechanism against DDoS attack without incurring overhead at access service network gateway (ASN GW) and base station (BS).

HomePlug AV (HPAV) is the standard for distribution of Audio/Video content as well as data within the home by using the power line. It uses a hybrid access mechanism that combines TDMA with CSMA/CA for MAC technology. The CSMA/CA protocol in HPAV has two main control knobs that can be used for access control: contention window (CW) size and deferral counter (DC). In this paper, we extensively investigate the impacts of CW and DC on performance through simulations, and propose an adaptive mechanism that adjusts the CW size to enhance the throughput in HPAV MAC. We find that the CW size is more influential on performance compared to the DC. Therefore, to make the network control easier, our proposal uses a default value of DC and adjusts the CW size. Our scheme simply increases the CW size if the network is too busy and decreases it if too idle. We compare the performance of our proposal with those of the standard and other competitive schemes in terms of throughput and fairness. Our simulation and analysis results show that our adaptive CW mechanism performs very well under various scenarios.

In mobile WiMAX (M-WiMAX), while generating cipher-based message authentication code (CMAC) for security, some bits of it are truncated and also while deriving a key hierarchy, some part of keying material is discarded. In this paper, we exploit these discarded information to enhance the security in M-WiMAX, and consider two cases of discarded information. Firstly, we propose to use the truncated upper 64-bits of CMAC, which we name shared authentication information (SAI), to complement the security breach in the signalling protocol which is vulnerable to DDoS attack in M-WiMAX. Secondly, we use the truncated 192-bits of master session key (MSK), which we name shared authentication key (SAK), as a temporary authentication root key for inter-domain or inter-authenticator handover. The purpose of using SAK is to reduce the latency for authentication during handover. As this paper opens a possibility of using such discarded security information for enhancing security, we may apply this approach to some other security systems in a similar way.

The duty cycle of a wireless sensor node is a key factor that determines the life time of a wireless sensor network. In general, sensor medium access control protocols reduce the duty cycle to achieve longer lifetime. However, we found out that their performance improvements substantially decrease under extremely low duty cycles (0.1%). It is with estimation of the relative clock speed between the sender and the receiver, and uses it to minimize energy consumption. It saves energy significantly well compared to the existing schemes in an order of ten times, and the performance gap increases with lowering the duty cycle.

Emerging systems like OFDMA and MIMO systems require multichannel scheduling over a wireless link. In this paper, we focus on the case that the number of channels to be assigned to a mobile terminal is limited, which we call limited matching. This case often occurs over a MIMO downlink when the number of receive antennas at a mobile user is smaller than that of transmit antennas at the base station. When the system exploits channel-aware opportunistic scheduling based on the channel feedback, finding the sum of channel gains by the limited matching is an NP-complete problem. To solve it easily, we can use the Hungarian algorithm, but its complexity is still too high and not amenable to performance analysis. Hence, we develop a heuristic algorithm, and analyze its cell throughput. Also, we investigate its performance when the channel feedback information is partially available. For analytic simplicity, we consider proportionally fair (PF) scheduling that is widely accepted as an opportunistic scheduler. Numerical results demonstrate that our heuristic limited-matching scheduling algorithm works well with partial channel feedback.

Opportunistic scheduling provides a good chance to improve wireless system performance by exploiting the underlying channel condition. There has been a lot of work on opportunistic scheduling, but the problem of finding the right feedback mechanism to convey channel information has largely been untouched. In emerging multichannel systems, the per- channel feedback induces a substantial amount of feedback overhead and requires high computational complexity. To reduce the feedback overhead, we consider an opportunistic feedback strategy that activates the channel feedback opportunistically according to the channel condition. Then, we combine the opportunistic feedback with the best-n channel feedback scheme where a mobile user chooses the best n channels and transfers this information to the base station. We analyze the throughput and the amount of channel feedback information for proportionally fair opportunistic scheduling under Rayleigh fading i.i.d. channels. The numerical results confirm that our partial feedback schemes achieve a remarkable reduction in the amount of feedback information at the cost of slight throughput degradation, thereby saving the scarce wireless uplink bandwidth and limited battery power.

As wireless networks evolve to orthogonal frequency division multiple access (OFDMA) systems, inter-cell interference control becomes a critical issue in radio resource management. The allocation of the same channels in neighbor cells cause inter-cell interference, so the channel allocation needs to be taken carefully to lower the inter-cell interference. In distributed channel allocation, each cell independently tries to allocate channels that suffer low interference level. In this paper, under the assumption of static users, we introduce the concept of interference range and use it in designing our two algorithms; basic and combined. The basic algorithm performs interference range detection and determines whether to use the considered channel, while the combined algorithm checks the channel quality in addition to detecting the interference range. The two algorithms dynamically perform channel allocation with low complexity when a systematic assistance for interference range detection is given. They show enhanced cell throughput by 14.1 % (basic) and 31.6% (combined) compared to the scheme using the frequency reuse factor 1 (FRF 1), and also perform better in terms of outage ratio and fairness.

In this paper, we consider a simple but efficient medium access control (MAC) protocol that can be used in an ad hoc network with asynchronous multi-channel environments. The approach in our proposal is to use time offset between channels where each channel has its own frame starting time. We assume that the network runs in power saving mode (PSM) of the IEEE 802.11 standard protocol which channel structure consists of beacon frame, ad hoc traffic indication message (ATIM) window, and data window. By asynchronizing beacon frame start times between channels, nodes that have no tasks involved in the current channel can switch to some other channels for more consecutive data transmission trials. Through extensive simulations, we confirm that our multi-channel access scheme results in significant throughput enhancement compared to the conventional access scheme that uses multi-channels in a synchronized manner. Combining our proposal with a power saving scheduling algorithm, we can achieve further throughput improvement. Our analysis and simulation results are used to prove the advantage of our proposals.

Random access mechanisms play an important role in wireless networks and have been extensively studied in recent years. Although many previous studies have proposed enhanced algorithms, they only considered either throughput or fairness. In this paper, we propose an efficient random access mechanism called Multi-round Collision Avoidance (MrCA). The key idea in MrCA is to avoid collisions by performing multiple contentions, each with smaller sized contention window. With this simple modification, we can significantly reduce the collision probability as well as improve the fairness. We analytically find the collision probability, and through simulations demonstrate that MrCA reduces the collision probability and increase the throughput by 25% while improving fairness compared to the IEEE 802.11 DCF with 50 contending stations. When MrCA and 802.11 DCF schemes are used with the auto rate fallback scheme, the performance gain of MrCA over 802.11 DCF increases because MrCA lowers the collision probability, which results in more accurate channel error estimation.

In this letter, we propose a power-based call admission control (CAC) scheme to accommodate multiclass traffic by directly extending the number-based CAC scheme in multicode CDMA networks, and develop some related mathematical properties. Against the conventional findings, we demonstrate that complete partitioning (CP) of the received signal power at a basestation for each traffic class can be an approach as useful as complete sharing (CS) in accommodating an appropriate number of users. The main advantage of CP scheme over CS scheme is its simplicity in resource management

Existing Internet worm research focuses either on worm detection inside an AS, or on prevention of Internet-wide worm epidemic. But of more practical concern is how to repel worm infiltration attempts at the AS boundary. In this paper, we analyze the efficacy of the general perimeter defense system operating on service registration information. When such system finds incoming packets targeting an unregistered service, it intercepts the packets and relays them to the signature generation module. While the signature is extracted, the system blocks the infiltration through blacklisting. Finally, upon the signature generation, content filtering based on the signature takes over, replacing blacklisting. Since the effectiveness of such systems depends on the type of worm, we analyze the effectiveness against the following practical worm types: random scanning TCP worms, random-start sequential scanning TCP worms, and UDP worms.

Mobile stations in the cell boundary have poor spectral efficiency due to the path loss and the interference from adjacent cells. Therefore it becomes an important issue to satisfy QoS requirements of each MS at the cell boundary. The deployment of fixed relay stations has been actively considered to solve this spectral efficiency problem at the cell boundary. In this paper, we consider some radio resource management policies that are path selection rule, frequency reuse pattern matching, and frame transmission pattern matching among cells. We evaluate performances of using relays under these policies by varying parameter values such as the relay station's position and frequency reuse factor. Through Monte Carlo simulations and mathematical analysis, we also suggest some optimal values of parameters and policies.

The OFDMA systems are emerging for future cellular networks. Creating multiple data channels, they can support the flexible frequency reuse factor (FRF). Although FRF 1 is the best choice in terms of cell throughput, it causes intercell interference at the cell boundary, thereby being unable to serve the whole cell area. Therefore it was proposed to use the FRF of greater than 3. In this paper, we develop a flexible FRF design mechanism that provides an intermediate value between 1 and 3 while the conventional schemes are dedicated to use some integer numbers only such as 3, 4, or 7. In our design, if the number of shared channels between any neighboring cells is given, we implement it simply according to a difference set. Simulation results show that a FRF of 7/4 achieves better throughput than FRF 3 and overcomes the intercell interference problem of FRF 1, so it can replace the conventional FRF such as 3. We expect that our new FRFs have the advantage in supporting smooth handoff because there are always some common channels between two neighboring cells.

In this paper, we propose a simple algorithm for detecting scanning worms with high detection rate and low false positive rate. The novelty of our algorithm is inspecting the frequency characteristic of scanning worms from a monitored network. Its low complexity allows it to be used on any network-based intrusion detection system as a real time detection module for high-speed networks. Our algorithm need not be adjusted to network status because its parameters depend on application types, which are generally and widely used in any networks such as web and P2P services. By using real traces, we evaluate the performance of our algorithm and compare it with that of SNORT. The results confirm that our algorithm outperforms SNORT with respect to detection rate and false positive rate.

This paper considers some scheduler structures that are executable in environments of multiple traffic classes and multiple frequency channels. In designing a scheduler structure for multiple traffic classes, we first propose a scheduler selection rule that uses the priority of traffic class and the urgency level of each packet. Then we relax the barrier of traffic class priority if a packet of higher priority has some room in waiting time. This gives us a chance to exploit multi user diversity, thereby giving more flexibility in scheduling. Our considered scheduler can achieve higher throughput compared to the simple extension of conventional modified largest weighted delay first (MLWDF) scheduler while maintaining the delay performance of QoS class traffic. We also design a scheduler structure for multiple frequency channels that chooses a good channel for each user as much as possible to exploit frequency diversity. The simulation results show that our proposed scheduler increases the total system throughput up to 50% without degrading the QoS performance of delay. Our schedulers are suited to be deployed for OFDMA systems like IEEE 802.16 systems that have plenty of frequency channels and use the adaptive modulation and coding (AMC) scheme.

While TCP is highly successful in the wire-line Internet, its performance fast degrades as the number of hops increases in multihop wireless networks. It is due to not only the half-duplex nature of the wireless medium, but also the congestion spreading phenomenon. Congestion in one wireless link spreads over space rather than localized to a link, causing interference to packet transmissions on neighboring links. Therefore, the space-shared feature of multihop wireless network makes congestion control different from that in wired networks. Since TCP often errs in estimating congestion level due to the wireless interference, it can overly inflate the transmission window and blast packets into the network, resulting in high level of congestion. We propose a novel algorithm to detect congestion in multihop wireless networks, which enables TCP to adjust the window size precisely. Performance evaluation through simulations confirms the advantage of our proposal in detecting spatial congestion in multihop wireless networks.

The throughput performance of the distributed coordination function (DCF) of the IEEE 802.11 MAC protocol quickly degrades as the number of contending stations increases. To solve this problem, it has been shown recently that adaptive contention window modulation based on channel idle time tracking can be used, generating near optimal throughput. In this paper, we extend the approach for the IEEE 802.11e network, where different QoS classes are defined. We show how to find the class-specific optimal contention window sizes that yield the maximum aggregate throughput while maintaining the target throughput difference between classes

Opportunistic scheduling can significantly improve wireless network performance by exploiting the feedback information that conveys the underlying channel condition. In emerging multichannel systems, the perchannel feedback induces a substantial amount of feedback overhead and requires high computational complexity. To reduce the feedback overhead, we consider an opportunistic feedback strategy that activates the channel feedback opportunistically according to the channel condition. Then, we combine the opportunistic feedback with the best-n channel feedback scheme where a mobile user chooses the best n channels and transfers this information to the base station. We analyze the throughput and the amount of channel feedback information for proportionally fair opportunistic scheduling under Rayleigh fading i.i.d. channels. The numerical results confirm that our partial feedback schemes achieve a remarkable reduction in the amount of feedback information without a significant throughput degradation, thereby saving the scarce wireless bandwidth and limited battery power.

Orthogonal frequency-division multiple access (OFDMA) systems are considered promising candidates for implementing next-generation wireless communication systems. They provide multiple channels that can be accessed via random access schemes. However, traditional random access schemes could result in an excessive amount of access delay. To address this issue, we develop a fast retrial scheme that is based on slotted Aloha and exploits the structure of OFDMA. A salient feature of this scheme is that when collisions occur instead of retrials occuring randomly in time, they occur randomly in frequency, i.e., the scheme randomly selects the subchannels for retrial. To further achieve fast access, retrials are designed to follow the 1-persistent type, i.e., no exponential backoff. To achieve the maximum throughput, we limit the maximum number of allowed retrials according to the load condition. We also consider the issue of designing for an appropriate reuse factor for random access channels in order to overcome the intercell interference problem in OFDMA multicell environments. Our finding is that full sharing, i.e., a reuse factor of one, performs best for given random access channels. Through analysis and simulation, we confirm that our fast retrial algorithm has the advantage of high throughput and low access delay, and the full sharing policy for random access channels shows high throughput as well as low collision.

As the delay is a critical QoS factor, packet scheduling over a wireless access link that often becomes congested needs to have the objective of meeting each user's delay requirement. To incorporate the delay into the scheduler design, we consider the objective of maximizing the total utility (U_T). However, since a utility-based scheduler that concerns delay requires high complexity, we introduce the concept of marginal utility. Representing the objective as minimizing the total marginal utility (M_T), we develop some related properties for maximizing U_T and minimizing M_T. For the case with fixed service time, we show that the outcome of M_T minimization becomes equivalent to that of U_T maximization. For the more complicated case of varying service time, the M_T minimization sheds light on the design of a simple scheduler. Overall, the marginal utility requires significantly low complexity for packet scheduling compared to the ordinary utility. Through simulations, we confirm that the marginal utility gives a way of flexible scheduling in meeting various delay requirements.

It is well known that opportunistic scheduling by using feedback information significantly improves wireless network performance. Most opportunistic scheduling works have focused on the case where a single channel is shared by multiple users. However, emerging wireless technologies (e.g., MIMO, OFDMA, etc.) are characterized by multiple shared channels, which complicates the problem. Moreover, it is necessary for the network to be able to provide various levels of quality of service (QoS). To address these issues, we develop a QoS-aware selective feedback model and a method to do optimal resource allocation. In our feedback model, each user chooses those channel sets that meet its QoS requirements by exploiting user diversity, thus resulting in a significant reduction in the amount of feedback information. Given the feedback channel sets for each user, the base station then distributes channels to each user with the objective of maximizing the number of accommodated users or the sum of users' utility values. We use a graph theoretic approach to solve these maximization problems by mapping them to clique searching problems. We develop some interesting theoretical results and properties but show that the complexity of this problem can be exponential in the number of channels. Thus, we also develop two suboptimal algorithms to handle the case when the number of shared channels is large. Finally, we demonstrate the efficacy of our results through an extensive numerical study

Loss differentiation is recommended as a service differentiation provided by an assured forwarding (AF) per-fop behavior (PHB) in differentiated service (DiffServ) architecture. An active queue management (AQM) technique is addressed as a suitable alternative to realize the service differentiation because the AF PHB should attempt to minimize long-term congestion while permitting short-term congestion in order to accommodate traffic bursts. In order to realize the AF PHB using an AQM scheme, it is desirable that the AQM scheme has DVO properties of sheltering and load tolerance in order to protect low drop precedence traffic and to prevent starvation of high drop precedence traffic. In this paper, we introduce another desirable property of assured drop probability. We modify an existing AQM algorithm for the property so that it assures a target drop probability in a properly provisioned network. Other properties of sheltering and load tolerance still hold for the modified AQM scheme. We evaluate it with other comparable schemes, i.e., WRED and RIO through simulation.

In this paper, we suggest a framework for power saving (PS) MAC protocol in a one hop mobile ad hoc network with a coordinator, and propose affinity based scheduling algorithm. Affinity is a novel concept that we introduce first. We define two types of affinities, i.e., node affinity and task affinity. Node affinity is defined as the weighted sum of incoming and outgoing task flows at each node, and task affinity as the sum of node affinities of source and destination nodes of each task. Our proposed scheduling algorithm has the advantage of putting more nodes into doze state for energy saving after completion of each task. To maximize the PS effect, we combine shortest job first scheduling with affinity based scheduling. We also devise an enhanced 802.11 PS MAC protocol by applying our framework and scheduling algorithm to the 802.11 MAC protocol which prevails in real world. Simulation results demonstrate that our scheduling algorithm and PS MAC protocol improve power efficiency and throughput significantly over other competitive schemes.

IEEE 802.11 wireless LANs are evolving into a high speed system by adopting MIMO technologies. Currently the standard deals with transmission for one user over a link. In this paper, we consider the MIMO technique of spatial multiplexing that enables multiple users to receive packets over the downlink simultaneously. It takes advantage of multiuser diversity in the space and time domains, supposing that each antenna independently performs link adaptation for each subchannel. Through analysis, we show that multiuser transmission has performance improvement over the single-user case. However, by using adaptive data splitting over spatial multiplexing, the performance of the single-user transmission is enhanced, and even better than that of multiuser case for small multiuser diversity. To exploit the multiuser diversity extensively, we apply a scheduling algorithm that considers channel condition of each subchannel. Simulation results show the multiuser transmission has higher link utilization than the single-user case for large multiuser diversity. To implement this, the system requires further considerations to modify ACK policy, and to mix conventional and MIMO-capable stations.

Opportunistic scheduling provides an important capability of resource management for wireless systems by taking advantage of multiuser diversity, allowing delay variation in delivering data packets. Our opportunistic scheduling aims at maximizing the utility which is usually expressed as a function of user throughput. In this paper we derive an off-line optimal scheduling policy by optimization theory, and show that the policy is also optimal in opportunistic scheduling. We extend the scheduling policy by adding QoS requirements for each user. To do so, we classify opportunistic schedulers according to QoS constraints. Their optimalities are also proved through mathematical analysis. To obtain optimal scheduling policy, the parameters related to QoS should be computed, so we propose a practical algorithm for parameter adaptation and verify its performance through simulations. The results confirm that our considered opportunistic schedulers show good fairness performance and guarantee each user's QoS without any difficulty in implementation.

We first show that various network attacks can cause fatal inflation of dynamic memory usage on packet processing computers. Considering Transmission control protocol (TCP) is utilized by most of these attacks as well as legitimate traffic, we propose a parsimonious memory management guideline based on the design of the TCP and the analysis of real-life Internet traces. In particular, we demonstrate that, for all practical purposes, one should not allocate memory for an embryonic TCP connection with roughly more than 10 seconds of inactivity.

A bandwidth-limited wireless channel can considerably improve its performance by exploiting multiple-input-multiple-output (MIMO) antennas. Combining spatial multiplexing with multiuser diversity, we develop an optimal cross-layer scheduling mechanism that executes fair scheduling at the upper layer and optimal antenna assignment at the physical layer. For fair scheduling, we propose a framework that achieves the objective of maximum capacity and proportional fairness. For optimal antenna assignment, we consider the Hungarian algorithm that maximally utilizes the characteristics of MIMO systems by adopting the graph theoretical approach. Through simulations, we demonstrate the performance of the optimal scheduling.

We introduce a utility-based radio resource management technique for multicell wireless packet networks. Assuming each base station operates to maximize its own cell utility, we try to maximize the system utility which is defined as the sum of each cell utility. By using the downlink transmit power of each base station as a control variable, we formulate a problem of system utility maximization. However, the problem is intractable because it contains non-convex functions, and, accordingly, the complexity is too high. Therefore, we first analyze a simple two-cell problem and take an intuitive approach to find its optimal solution. We extend this intuition to a general multi-cell problem and devise a simple heuristic algorithm that requires a light overhead of signaling between neighboring base stations. Through simulations, we compare, in terms of utility gain, our proposed heuristic algorithm with two competing schemes, optimal power allocation and maximum power allocation. As expected, the optimal allocation scheme shows the best performance but cannot be applied to real multi-cell problems due to its intractable complexity. Our proposed heuristic algorithm has very low complexity and its performance lies between the optimal allocation and maximum allocation schemes.

In this paper, resource allocation for heterogeneous services is studied in multiuser orthogonal frequency division multiplexing (OFDM) systems. We propose a resource allocation algorithm, which is designed to improve the system throughput while satisfying the quality of service (QoS) requirements of both the real-time and nonreal-time services. In the proposed algorithm, the resources, composed of subcarriers and transmit power, are adaptively allocated to the users based on their service types and channel states over two sequential steps: (1) resource allocation for the real-time users that minimizes the resource usage required to satisfy the data rate requirement, and (2) resource allocation for the nonreal-time users that maximizes the system throughput using the remaining resource. The performance of the proposed resource allocation algorithm is evaluated in a frequency-selective fading channel, and compared with that of a simple resource allocation algorithm. Numerical results show that the proposed algorithm provides a significant throughput gain over the conventional algorithm.

Recently cdma2000 1x EV-DO (HDR) system has begun to be deployed in some countries to support high data rate services in cellular networks. The system is originally designed to support data services, but now is expected to serve some real-time traffic including VoIP. For VoIP service with delay hound and low loss requirements, we propose a frame structure considering delay bound and a scheduling algorithm reflecting channel conditions. To schedule VoIP, we adopt the maximal rate algorithm and the proportionally fair algorithm. The proportionally fair algorithm (PF) was known to be appropriate for elastic-traffic, however, from simulation results, we conclude that the PF algorithm with the channel test is an appropriate scheduling scheme to provide QoS of VoIP. When the required slot portion of VoIP is 75%, the loss rate is about 1% on the average and 3% in the worse case. On the other hand, the maximal rate algorithm shows twice of the loss rate for the same delay bound and load. Additionally we propose a simple admission control scheme for VoIP service that controls the average portion of slots occupied by VoIP packets.

Exploiting multiple-input-multiple-output (MIMO) diversity, systems with error-prone and bandwidth-limited wireless channels can easily support reliable transmission. We develop optimal cross-layer scheduling that consists of QoS scheduling at the upper layer and optimal antenna selection at the physical layer. For QoS scheduling, we design a framework for optimal scheduling to meet users' QoS requirements. To solve this optimization problem, we consider a clique-searching algorithm for antenna selection that maximally utilizes the characteristics of MIMO systems by adopting the graph theoretical approach. As the clique searching problem becomes NP complete with the increase of transmit antennas in number, we propose a suboptimal antenna selection algorithm to deal with a large number of transmit antennas. We derive some theorems and properties for our approach and, through simulations, we demonstrate the performance of QoS scheduling which is effective to handle real-time traffic.

To provide network services consistently under various network failures, enterprise networks increasingly utilize path diversity through multi-homing. As a result, multi-homed non-transit autonomous systems (ASes) has surpassed the single-homed networks in number. In this paper, we address an inevitable problem that occurs when networks with multiple entry points deploy stateful inspection firewalls in their borders. In this paper, we formulate this phenomenon into a state-sharing problem among multiple firewalls under the asymmetric routing condition. To solve this problem, we propose a stateful inspection protocol that requires a very low processing and messaging overhead. Our protocol consists of the following two phases: 1) generation of a TCP SYN cookie marked with the firewall identification number upon a SYN packet arrival, and 2) state sharing triggered by a SYN/ACK packet arrival in the absence of the trail of its initial SYN packet. We demonstrate that our protocol is scalable, robust, and simple enough to be deployed for high speed networks. It also transparently works under any client-server configurations. Last but not the least, we present the experimental results through a prototype implementation.

We propose a new AQM algorithm that considers both the average queue length and the estimated packet arrival rate together in order to detect and control incipient congestion. It predicts the average queue length and controls it to maintain a certain reference value to achieve high link utilization and low queueing delay. Simulation results confirm the stability of our proposed algorithm under various network environments and show its performance advantages over other competitive AQM algorithms.

Abstract — Resource management in wireless networks is an important issue because of the scarceness of communication resource. So optimization schemes for efficient resource usage have been extensively researched. Throughput maximization under the condition of limited total power or power minimization under the condition of minimum bit rate are usually considered objective in many papers. These researches focused on the power allocation, but they did not consider time slot allocation which can be also used to improve the efficiency. In this paper, we introduce a time slot allocation problem for multi-user wireless networks to achieve minimum rate guarantee under the condition of fixed total power. We solve the allocation problem by using dynamic programming method, which has the complexity of where is the number of users. This complexity is lower than the non-polynomial complexity of exhaustive searching for the optimal solution. The performance of our proposed algorithm is compared with that of the waterfilling algorithm. An advantage of using the time slot optimization approach is that it can support high mobility users with QoS requirements. From simulation results, we demonstrate that our proposed algorithm shows better performance than a conventional scheme that does not use any time slot allocation. I.

CDMA data networks such as cdma2000 1x EVDO are proposed in the midst of evolving to the 3rd generation wireless networks. Basically they use time division multiplexing and rate control that need a downlink scheduling to increase the system capacity, thereby being able to support high speed data rates. As the systems will eventually support multimedia and data traffic together, we need to have a propose criterion for scheduling that can count various service requirements such as delay and loss. Therefore, we visit the concept of utility and opportunity cost considering these together. The opportunity cost is defined as the maximum utility lost among the other users by giving the current turn to a particular user. We design an algorithm to select a job for transmission with the maximum profit that is obtained by subtracting the opportunity cost form its expected utility. The simulation results show that it can support various QoS levels in terms of delay and loss for various traffic scenarios.

Cellular systems are designed to support voice service over the wireless channel but nowadays data-only networks such as cdma2000 1x EV-DO and high speed downlink packet access (HSDPA) are being deployed in the midst of evolution to the next generation wireless networks. Such systems become important because data services are essential in future wireless networks that are supposed to adopt the concept of all-IP to support integrated services. To increase the data transmission rate at downlink in cdma2000 1x EV-DO and HSDPA, the base station (BS) uses only a channel multiplexed by time division, not by code division. These systems use proportional fair scheduling to maximize throughput. While it is useful for non real time traffic, it does not provide appropriate QoS for real time services such as voice and video. Therefore we need to incorporate the multimedia QoS requirements into the design of a new scheduling algorithm. Our proposed wireless-adaptive fair scheduling (WAF) tries to allocate time slots with fair share according to the stream requirements considering the varying channel conditions to achieve good throughput. The simulation results show that our scheme can guarantee fair service and increase throughput by up to 41% compared to the purely fair (PF) scheduling scheme.

AQM attempts to provide high network utilization with low loss and delay by regulating queues at bottleneck links. While many AQM algorithms have been proposed, most suffer from instability, require careful configuration of non-intuitive control parameters, or are not practical because of slow response to dynamic traffic changes. In this paper, we propose a new AQM algorithm that combines the more effective elements of recent algorithms with a RED core. Throughput analysis and simulations, we demonstrate improved performance in stability and response time with straightforward selection parameters for both steady load and changes in loads.

The data rates of wireless networks are getting faster and faster. With this trend, IEEE 802.11a, published in 1999 to provide faster data transmission rates, is one of the strongly considered next generation wireless LAN standards. It uses CSMA/CA as the medium access control protocol and OFDM as the physical layer technology. In this paper, to enhance the throughput performance of CSMA/CA protocol in the OFDM based wireless LAN like IEEE 802.11a, we propose a new contention algorithm called parallel contention algorithm that divides the subcarriers into multiple groups to reduce the contention time. We analyze our proposed scheme by extending the Markov chain model and verify the accuracy of the analysis through the simulations. Our protocol performs well especially when the transmission speed and the number of users are getting higher, thereby achieving a better performance improvement ratio than the original IEEE 802.11a standard.

In multiple cellular CDMA systems, the channel capacity heavily depends upon the interference caused by the signal power of the other users. In this paper, we exactly quantify the cell capacity by focusing on not only the number of users but also the location of active users. To inspect the effect of multicell CDMA environments, we model three 1/6 cells divided by 60/spl deg/ sector antennas and analyzed the increased interference when a user is added to the unit of cell. Based on the capacity analysis, we propose a new call admission control scheme that uses the location information of users. Whenever a new user arrives, our scheme checks whether the admittance of that user can occur within the cell capacity. Our scheme allows more users to enter the network if they generate less interference. Therefore it has the effect of increased system capacity without sacrificing the QoS of all the other active users. Through simulations we show that the performance is improved by 10 to 20% in terms of the number of active users that can be accommodated.

Owing to the Internet's rapid expansion and fast advancing PC technology, there are many PC-based network systems now. For increasingly many applications running over the Internet, guaranteeing QoS on these PC-based systems has become an issue of some concern. In this paper, we investigate QoS failures that occur on PC-based systems and focus on one aspect of the problem that arises from coarse timer granularities. While it is usually assumed that packet schedulers in routers have sufficiently fine-grain timers, network systems frequently have timers of coarse granularity. Therefore, users cannot obtain the desired QoS even if they reserve the required bandwidth for transmission. Based on the investigation of QoS failures due to coarse timer granularities, we experiment with two methods to cure the problems. We implement them into real PC Unix-based systems and show that they can satisfy QoS requirements of TCP connections by helping them transmit the traffic at the reserved bandwidth.

CDMA systems have a trade-off relationship between the frame error rate (FER) and the number of accepted users. Therefore, the call admission control (CAC) scheme is essential for guaranteeing the FER below the required value, which is the measure of the quality of service (QoS) in the frame level. In cellular networks, the dropping probability of handoff calls is another critical measure for QoS in the call level. There has been, nevertheless, little concern for CAC schemes guaranteeing these QoS requirements simultaneously in the CDMA cellular networks. In this paper, we propose CAC that track the time-varying capacity of CDMA systems by estimating the distribution of the total received power at a base station, thereby realizing the bandwidth reservation scheme to meet the QoS requirement for handoff calls in the call level.

An important quality-of-service (QoS) issue in wireless multimedia networks is how to control handoff drops. In this paper, we propose admission control algorithms that adaptively control the admission threshold in each cell, in order to keep the handoff dropping probability below a pre-defined level. The admission threshold is dynamically adjusted based on handoff dropping events. We first present a simple admission control scheme which brings out an important performance evaluation criterion - inter-cell fairness - and serves as a reference point. We then investigate the inter-cell unfairness problem and develop two enhanced schemes to overcome this problem. The performance of these protocols is benchmarked and compared with other competitive schemes. The results indicate that our schemes perform very well while, in addition, achieving significantly reduced complexity and signaling load.

Although the application level hierarchical retransmission framework has been shown to be effective in providing reliable multicast transmission, it requires retransmission tree hierarchy construction and maintenance. If the retransmission tree is not congruent with the underlying multicast transmission tree, it results in performance degradation. For multicast networks with mobile hosts, the multicast transmission tree changes with great frequency. We examine the performance degradation due to the mobility of receivers and propose a retransmission hierarchy maintenance scheme to alleviate the problem. Simulation is done to measure the network overhead and latency of the proposed scheme. The proposed scheme is shown to exhibit significant improvement over the conventional hierarchical multicast retransmission scheme.

To support various services in the current Internet, QoS routing was proposed. QoS routing finds a path to meet the requested QoS specification for a user, reserves network resource, thereby guaranteeing the QoS for the user. Much work has been done for QoS routing in an autonomous system (AS) to make it feasible in large networks. For a large network, hierarchical QoS routing is promising candidate because it is scalable. It divides the network into several levels and routing is performed at each level. The most important factor in hierarchical QoS routing is topology aggregation, which makes lower level nodes send simplified and aggregated network topology information to upper level nodes. Therefore the topology aggregation enables QoS routing to be run in large networks while it causes some errors during the aggregation process. In this paper, we introduce a way to optimize the topology aggregation to improve the performance of QoS routing in terms of exactness. Our scheme uses the partial optimization technique instead of whole topology optimization, which is general enough to be used with other existing schemes.

In this paper, we consider a CDMA cellular network that has signal power as its scare resource and uses the multicode transmission scheme to support multiclass calls with different QoS requirements. By simply extending the number-based scheme to accommodate multiclass traffic, we present a power-based call admission control scheme. Contrary to the general fact that complete sharing (CS) achieves better utilization than complete partitioning (CP), our finding in this paper is somewhat unique. That is, the CP of signal power for each traffic class can accommodate a reasonably high number of users when compared with CS. This result allows us to use CP which is much easier than CS in terms of resource management. By adopting the CP technique for resource reservation in wireless CDMA networks, we can guarantee QoS of calls in terms of handoff drops with minimal complexity.

We introduce a fast IP table lookup algorithm that improves the table updating time as well as the IP address searching time. Because routers with Patricia trie can not support giga-bit performance, many algorithms to support giga-bit routing performance by reducing the searching time have been introduced. Most of them, however, did not considerably count the importance of the updating time. As a network often falls into unstable states, a router may generate and receive hundreds of update request messages per second. So the router should be able to update its routing table at least 1000 times per second to appropriately run in real networks. We consider the updating time as much an important factor as the searching time in proposing a flexible and fast IP lookup algorithm (FFILA). Our scheme searches the table about 3 times faster than Patricia trie. It also shows improved performance in updating time by at least 30% when compared with Patricia trie. Also as many backbone routers today have over 100,000 routing table entries and its number is still increasing due to the growth in the network size, the memory requirement for the lookup algorithm becomes more important. An additional advantage of our algorithm is in its small memory requirement, which is good to overcome the scalability problem.

We propose a new routing protocol called buffered fixed routing (BFR) for real-time applications on grid networks. While previous routing protocols for grid networks have been designed to improve the network throughput, the BFR scheme is proposed to guarantee the end-to-end packet delay and sequencing without loss by using finite buffers at each node. Thus the proposed scheme can satisfy the QoS requirements of real-time applications. The BFR scheme uses the token on the row ring to provide QoS guarantees. The performance of the BFR scheme is analyzed by using the Geom/Geom/1 queueing system under uniform traffic. In the simulation, the BFR scheme shows the zero-loss, high-throughput performance with the minimum delay variation compared to other routing protocols such as store and forward routing, deflection routing and vertical routing. In addition, it has shown the smallest average delay at intermediate and heavy loads.

While it is usually assumed that packet schedulers in routers have sufficiently fine-grain timers, network systems frequently have timers of coarse granularity. Therefore application users cannot obtain the desired QoS even if they reserve the required bandwidth for transmission. In this paper, we investigate QoS failures that occur due to coarse timer granularities. Based on the investigation, we experiment with two methods to cure the problems. We implement them in real PC Unix based systems and show that they can satisfy the QoS requirements of TCP connections by transmitting as much traffic as for the reserved bandwidth.

The assured service is a service model that can be offered within Internet differentiated services (Diff-Serv) architecture. It provides a statistical bandwidth guarantee to its subscribers, and allows the subscribers to claim a share of the excess network bandwidth in addition to the subscribed bandwidth. It has been observed that assured service does not meet the bandwidth guarantee for high-profile flows in the presence of numerous low-profile flows (such as best-effort). We demonstrate that there is an inadequacy in the packet differentiation algorithm used in the Diff-Serv routers, RIO ("RED with In and Out"), that contributes to the problem. We propose a modified RIO algorithm called RI+O to reduce the effect, and show that it significantly alleviates the problem. Our approach of modifying a router algorithm incurs much less deployment cost than other approaches.

In this paper we describe briefly a dynamic multi-path algorithm that has been considered for connection oriented asynchronous transfer mode (ATM) networks. Our scheme takes advantage of a cell multiplexing capability that has particular advantage in networks supporting variable bit rate (VBR) traffic. The fundamental objective of the scheme is to propose a congestion control based scheme that bridges the gap between routing and congestion control as the network becomes congested. The proposed routing scheme works as a shortest path first algorithm under light traffic conditions. However, as the shortest path becomes congested under unbalanced heavy traffic, the source uses multiple paths when and if available to distribute the calls and reduce cell loss. This mechanism will provide good Quality of Service for clients within the given constraints. We compare the performance of the proposed scheme with other competitive schemes. The throughput and cell loss performance are compared via simulations. These have been carried out concentrating on a five node network, each with varying traffic patterns, with the intention of gaining insight into the strengths and weaknesses of the various schemes.

In this paper we describe briefly a dynamic multi-path routing scheme that has been considered for connection oriented homogeneous high speed networks. The fundamental objective of the scheme is to bridge the gap between routing and congestion control as the network becomes congested. Because propagation delay far out shadows queueing and transmission delay in high speed networks, the proposed routing scheme works as a shortest path (minimum hop) first algorithm under light traffic conditions. However as the shortest path becomes congested, the source node uses multiple paths when and if available in order to distribute the load and reduce packet loss. The scheme is a cross between Alternate Path routing and Trunk Reservation.We compare the performance of the proposed scheme with the Shortest Path Only algorithm, the Alternate Path routing algorithm, the Random Routing algorithm, and the Trunk Reservation scheme. The throughput and packet loss performance are compared via simulations. These have been carried out concentrating on a 5 node network with varying traffic patterns, the intention being to gain insight into the strengths and weaknesses of the various schemes.