Byung-Han Ryu

Urgency and Efficiency based Packet Scheduling Algorithm for OFDMA wireless system

In this paper, we propose an urgency and efficiency based wireless packet scheduling (UEPS) algorithm that is able to schedule real time (RT) and non-real time (NRT) traffics at the same time. The UEPS algorithm is designed to support wireless downlink packet scheduling in OFDMA system which is a strong candidate wireless system for the next generation mobile communications. The UEPS algorithm uses the time-utility function as a scheduling urgency factor and the relative status of the current channel to the average one as an efficiency indicator of radio resource usage. The design goal of the UEPS algorithm is to maximize throughput of NRT traffics with satisfying QoS requirements of RT traffics. Simulation study shows that the UEPS algorithm is able to give better throughput performance than existing wireless packet scheduling algorithms such as proportional fair (PF) and modified-largest weighted delay first (M-LWDF) while satisfying QoS requirements of RT traffics such as the average delay and the packet loss rate under various traffic loads.

Urgency and efficiency based wireless downlink packet scheduling algorithm in OFDMA system

In this paper, we exploit how to provide quality of service at the downlink in the OFDMA wireless communication systems. The OFDMA, also referred to as multiuser-OFDM, is considered as a strong candidate wireless system for the next generation mobile communications. Since there are a variety of traffic demands for real-time and non-real-time traffics in the next generation mobile communications, especially at the downlink from a base station, scheduling of such downlink traffic packets is expected to be a key function for QoS provisioning to users. One such scheduling algorithm designed not only to support multiple users simultaneously but also to offer real-time and non-real-time services to a user at the same time is the urgency and efficiency based packet scheduling (UEPS) algorithm [S. Ryu et al., 2005]. The UEPS algorithm uses the time-utility function as a scheduling urgency factor and the relative status of the current channel to the average one as an efficiency indicator of radio resource usage. The design goal to maximize throughput of non-real-time traffics with satisfying QoS requirements of real-time traffics.

Analysis of handover failures in LTE femtocell systems

In this paper, we evaluate handover (HO) performance when user equipment (UE) moves between femto cell and macro cell in long term evolution (LTE) systems. The focus is on the HO performance for inbound and outbound mobility which corresponds to handoff between the femtocell and the macro cell. Due to the severe signal-to-interference noise ratio (SINR) degradation near the edge area of femtocell, HO triggering for inbound and outbound mobility needs to be carefully selected than that of the macro cell. Too late HO triggering leads to radio link failures (RLF), whereas too early HO triggering causes ping-pong HO. In this paper, we take the neighbouring cell configurations into account to keep the allowable RLF rate and low ping-pong rates. We propose a cell-types adaptive handover margins algorithm, which assigns different handover margins in line with neighbouring cell types. Simulation results indicate that the low ping-pong rate and the low RLF rate are achieved simultaneously by using the proposed algorithm.

Inbound Mobility Management on LTE-Advanced Femtocell Topology Using X2 Interface

The femtocell access point of LTE-Advanced system, which can be deployed under macrocell coverage, was applied to the paper. The paper consists of two analyses which are the interference impact by the femtocell and the macrocell at a user equipment and the load impact to the control plane in evolved packet core network by X2 and S1 handover signaling messages. On the results of investigations by performance simulations with regard to the receiving power and signal-to-noise ratio at a user equipment side, the unavailable zone to the inbound handover from macrocell to femtocell occurred due to a severe intercell interference depending on a femtocell topology. Therefore, we found that an intercell interference coordination between macrocell and femtocell in order to make an inbound handover is needed and that X2 interface is the better solution rather than S1 interface for an inbound handover by investigating the X2 and S1 handover procedure of 3GPP. Ultimately, it is shown that the X2 interface between macrocell and femtocell can play an important role in an high reliable inbound handover and a simple interference control implementation on femtocell environment.

Traffic characteristics based performance analysis model for efficient random access in OFDMA-PHY system

Currently, IEEE 802.16a wireless MAN supports the contention based OFDMA-CDMA ranging subsystem for ranging operation (Initial Ranging, Periodic Ranging, Bandwidth Request)[1]. This system uses essentially the slotted ALOHA protocol. However, the number of code-slots/frame for random access transmission tends to be much greater than one and a simple Markov chain analysis may not be numerically feasible. At the same time, the frame size in number of code-slots may be dynamically adjusted based on the traffic load. In order to evaluate delay-throughput performance and stability measure of the random access protocol, we first examine the possible traffic load to be carried throughput the ranging subchannel. We the present performance analysis and numerical examples.

The impact of cloud base station's coordinated multi-point schemes on mobility performance

The so-called cloud base station considered as a kind of distributed antenna system can faciliate the fast coordination among cells and also enlarge its scale by using many remote radio heads. Hence, these characteristics can widen the application region of the special coordinated multi-point scheme that fast coordination among cells should be imperative, which may be brings benefits to the overall system performance. The objective of this paper is to investigate the mobility performance according to the scale of cloud base station applying the coordinated multipoint joint processing scheme compared with the mobility performance of non-CoMP. To grasp the impacts on mobility performance, three mobility metrics (radio link failure, HO failure, ping-pong) are used and their results mean that the combination between cloud base station architecture and coordinated multi-point joint processing scheme may bring the rise of mobility performance.

Power Efficient Frequency Domain Packet Scheduling for OFDMA Systems

As the enormous development of IT technology, the convergence technology enlarges its research areas. Recently, OFDMA which was widely used in satellite and wireline communications is applied to broadband wireless communication systems. In order to employ the OFDMA to next generation mobile systems, throughput maximization and power efficient control mechanism is needed. This paper proposes the multilevel scheme for the power efficient feedback of channel state information without degrading system performance. Also, we propose a sub-optimal resource allocation scheme based on a greedy algorithm which guarantees fairness with reduced complexity. Proposed scheme is evaluated by system level simulation which uses a spatial channel model and the results show that the proposed scheme follows proportional fair throughput and reduces signaling overheads for feedback.

PI-PD Controller for Adaptive and Robust Active Queue Management for Internet Congestion Control

Since random early detection (RED) was proposed in 1993, many active queue management (AQM) algorithms have been proposed to support better end-to-end Transmission Control Protocol (TCP) congestion control. In this article, the authors introduce and analyze a feedback control model of the TCP/AQM dynamics. Then they suggest the concept of an AQM algorithm that can detect and avoid congestion proactively. Finally, they propose the proportional-integral (PI) proportional-derivative (PD) controller using proportional-integral-derivative (PID) feedback control to overcome the reactive control behavior of existing AQM proposals. The PI-PD controller is able to provide proactive congestion avoidance and control using an adaptive congestion indicator and a control function. A comparative simulation study under a variety of network environments shows that the PI-PD controller outperforms RED and the PI controller in terms of the queue length dynamics, the packet loss rates, and the link utilization.

Design of performance analysis model for efficient random access protocol in CDMA based OFDMA-PHY system

Currently, IEEE 802.16a wireless MAN supports the contention based OFDMA-CDMA ranging subsystem for ranging operation (initial ranging, periodic ranging, bandwidth request). This system is basically similar to slotted ALOHA (K. Leonard and S.S. Lam, April 1975), but the frame size (code-slot/frame) allocated for random access or ranging request is relatively big and can be altered by the dynamic adjustment of downlink and uplink subframe size on the MAC frame of OFDMA-PHY system. In this paper, the design performance analytical model for correct interpretation of ranging subsystem is presented. Until now, the Internet traffic study have achieved wire net, but there is still a need for Internet traffic study that correctly reflects the radio environment. In this paper, the performance analysis result of this paper can perform the reference mark for random access protocol in OFDMA-CDMA ranging system. Traffic modeling can also be used to prepare the network resources in radio networks

Performance evaluation for low bit-rate voice traffic in IMT-2000 network

We present the system performance when the voice traffic is constructed as the ATM Adaptation Layer type 2 (AAL-2) and then it is transmitted to the base station controller (BSC) from the base station transceiver subsystem (BTS) in the International Mobile Telecommunication-2000 (IMT-2000) network. We first describe the configuration of the BTS and the BSC, and then model them as a queueing network. Through a simulation study, we present the timeout time that should be set for multiplexing the user packets at the line interface unit (LIU) and evaluate the processing capacity of the call control blocks and the transmission efficiency of the physical links. Finally, we present the transmission delay time from the radio channel element (RCE) to the selector & transcoder subsystem (STS) for the offered traffic which can be simultaneously accommodated on one E1 link.