Young-Jong Cho

Scheduling scheme for providing QoS to real-time multimedia traffics in high-rate wireless PANs

In wireless personal area networks (WPANs), the successful design of channel time allocation algorithm is a key factor in guaranteeing the various quality of service (QoS) requirements for the stringent real-time constraints of multimedia services. In this paper we propose a dynamic channel time allocation algorithm for providing delay guarantees to multimedia traffics such as MPEG streams in the IEEE 802.15.3 high-rate WPANs. The dynamic algorithm exploits the characteristics of MPEG stream, wherein devices (DEVs) send their channel time requests near at the end of superframe. The algorithm uses mini packets for feedback control in order to deliver dynamic parameters for channel time requests from DEVs to the piconet coordinator (PNC). In this scheme, the duration of channel time allocated to a DEV during a superframe is changed dynamically depending on the MPEG frame type, traffic load and delay bound of the frame, etc. Performance of the proposed scheme is investigated by simulation. Our results show that compared to conventional scheme, the proposed scheme is very effective and has high performance while guaranteeing the delay bound.

PAMP: Power-Aware Multi-Path Routing Protocol for a Wireless Ad Hoc Network

In a wireless ad hoc network, the limited energy of the nodes is one of major challenges. Many research works are proposed to solve this issue from various aspects. Our work focuses on how to utilize the limited energy of the nodes in data delivery. By combining the concept of multi-path routing and energy reservation, the proposed scheme, PAMP ensures to make a way to delivery packets even though the nodes can not fully satisfy the energy request of the source. PAMP is designed as an extension of the existing AODV by modifying RREQ and RREP management mechanism to handle energy reservation and multiple paths. When compared with other energy-aware routing schemes and AODV, the proposed scheme gives significantly higher data reliability and network lifetime.

Admission control scheme based on priority access for wireless LANs

In order to support the quality of service (QoS) requirements at the medium access control (MAC) layer, the enhanced distributed channel access (EDCA) has been developed in IEEE 802.11e standard. However, it cannot guarantee the stringent real-time constraints of multimedia applications such as voice and video without an efficient method of controlling network loads. In this paper, we propose a measurement-based admission control scheme, which is made up of two parts: priority access and admission control. First, in order to measure the channel status per traffic type, we propose a priority access mechanism in which each priority traffic is distinguished by a busy tone, and separately performs its own packet transmission operation. Then, admission control mechanism protects existing flows from new ones, and maintains the QoS of the admitted flows based on the measured channel status information. Performance of the proposed scheme is evaluated by simulation. Our results show that the proposed scheme is very effective in guaranteeing the QoS of multimedia applications as well as in avoiding the performance starvation of low priority traffics.

Channel time allocation scheme based on feedback information in IEEE 802.11e wireless LANs

The IEEE 802.11e standard defines a set of quality of service (QoS) enhancements for wireless local area network (WLAN) applications such as voice and streaming multimedia traffic. In the standard, a new medium access control (MAC) protocol is called the hybrid coordinator function (HCF), and also a channel access scheme to transmit multimedia traffic is called the HCF controlled channel access (HCCA). In the IEEE 802.11e WLANs, to satisfy the stringent real-time constraints of multimedia services it is very important to provide an efficient method of allocating network resources. In this regard, we propose a feedback-assisted dynamic channel time allocation scheme considering the application layer information in order to achieve better performance of multimedia traffic over IEEE 802.11e HCCA under the constrained QoS requirements. Performance of the proposed scheme is investigated by simulation. Our results show that under typical channel error conditions, the proposed scheme is very effective regardless of the variation of station numbers and service intervals. Also, it yields high performances while guaranteeing the delay bound.

A distributed collision resolution scheme for improving the performance in wireless LANs

The IEEE 802.11 distributed coordination function (DCF) provides a contention-based distribution channel access mechanism for stations to share the wireless medium. However, performance of the DCF drops dramatically due to high collision probability as the number of active stations becomes larger. In this paper, we propose a simple and effective collision resolution scheme for improving the performance of the DCF mechanism. Our idea is based on the estimation of the channels contention level, by measuring duration of busy and idle periods observed on the channel at each station. In order to reduce collision probability, the proposed scheme limits the number of contending stations at the same time according to the channel contention level. Performance of the proposed scheme is investigated by numerical analysis and simulation. Our results show that the proposed scheme is very effective and improves the performance under a wide range of contention levels.

Anomaly detection of network-initiated LTE signaling traffic in wireless sensor and actuator networks based on a Hidden semi-Markov Model

LTE signaling attack is a serious threat to a wireless sensor and actuator network whose facilities are dispersed and connected with LTE technology on a large scale, in order to conduct a particular mission. An LTE attacker generates a lot of signaling initiating packets, named wakeup packets, to saturate the LTE networks resources. Existing LTE signaling attack detection schemes are merely based on measuring the mean wakeup packet generation rate. Since resulting from extensive amounts of facilities involved in a normal management process, severe fluctuations of signaling traffic are ordinarily expected in the wireless sensor and actuator network, and those mean-based schemes cannot effectively distinguish between attacks and normal traffic. In this paper, we propose an advanced LTE signaling attack detection scheme based on a Hidden semi-Markov model, which captures the spatialtemporal characteristics of normal wakeup packet generation behavior. Our proposed detector takes the log-likelihood of a nodes wakeup packet generation as the test criterion for normality. Through simulations with various parameter settings, we verified that the proposed scheme effectively distinguishes attacker nodes from normal nodes.

On the Network Coding Delay in Multi-Hop Wireless Networks with Multiple Coding Points

There have been many research works studying the network coding delay, assuming single network coding point or single hop between source and destination. In this paper, we analyze intensively the network coding delay for a multi-hop path between source and destination along which multiple coding points are permitted to reside. Firstly, extending the previous works we develop a numerical form of the network coding delay. Secondly, we present some simulation-based analysis results. The main result is that even though the increase in coding points can contribute to the reduction of network coding delay, the gain increases insignificantly as the number of coding points becomes larger.

A scalable joint routing and scheduling scheme for large-scale wireless sensor networks

The multihop configuration of a large-scale wireless sensor network enables multiple simultaneous transmissions without interference within the network. Existing time division multiple access (TDMA) scheduling schemes exploit gain based on the assumption that the path is optimally determined by a routing protocol. In contrast, our scheme jointly considers routing and scheduling and introduces several new concepts. We model a large-scale wireless sensor network as a tiered graph relative to its distance from the sink, and introduce the notion of relay graph and relay factor to direct the next-hop candidates toward the sink fairly and efficiently. The sink develops a transmission and reception schedule for the sensor nodes based on the tiered graph search for a set of nodes that can simultaneously transmit and receive. The resulting schedule eventually allows data from each sensor node to be delivered to the sink. We analyze our scheduling algorithm both numerically and by simulation, and we discuss the impact of protocol parameters. Further, we prove that our scheme is scalable to the number of nodes, from the perspectives of mean channel capacity and maximum number of concurrent transmission nodes. Compared with the existing TDMA scheduling schemes, our scheme shows better performance in network throughput, path length, end-to-end delay, and fairness index.

An Inter-Session Opportunistic Network Coding-aware Multipath Routing Protocol

An ad hoc network consists of nodes with limited energy. Therefore, the data transmission can fail abruptly due to lack of energy of transmitting node. A previous work PAMP proposed to build multiple low-energy paths to support stable packet delivery exploiting the nodes with low energy. It has energy-reservation scheme and multi-path selection scheme for stationary wireless ad hoc networks. In this paper, we propose an extended version of PAMP by incorporating network coding opportunity in path selection process. The simulation results show that our proposed scheme shows better packet delivery ratio and lower energy consumption compared with PAMP and a legacy energy-aware multipath routing protocol REAR.

A Probabilistic Routing Mechanism Considering the Encounter Frequency in the Battlefield Environment

The network nodes in a tactical network moves continuously and due to the physical and electronic obstacles, the connections are not always available. Due to the frequent disconnections, it is hard to discover the path among the nodes in a DTN. According to PROPHET(Probabilistic Routing Protocol using History of Encounters and Transitivity), one of the most well-known DTN routing protocols, a DTN node determines whom to forward a packet according to the packet delivery probability. From the viewpoint of a node, the packet delivery probability of another node is degraded while the nodes are disconnected whereas it is improved when they encounter. In this paper, we enhance the algorithm estimating the packet probability by considering the encounter count as an additional parameter. Our algorithm prefers the node that encounters the destination more frequently in selecting the next hop toward the destination. We evaluated the performance of our algorithm by simulating military operations using a DTN-dedicated simulator. Through the simulations, we show that our proposed algorithm achieve higher packet delivery ratio with similar overhead compared with PROPHET.Keywords : PROPHET(프로핏), Probabilistic Routing(확률적 라우팅), Encounter Frequency(접촉 횟수), DTN(지연내성망), Tactical Network(전술네트워크)