Nak Woon Sung

A Smart Handover Decision Algorithm Using Location Prediction for Hierarchical Macro/Femto-Cell Networks

To reduce the number of unnecessary handover in hierarchical macro/femto-cell networks, it is necessary to avoid macro -> femto cell handovers of temporary femtocell visitors who stay in the femtocell for a relatively short time. In this paper, we propose a smart handover decision algorithm exploiting future mobility pattern prediction scheme to prevent macro -> femto cell handovers of such temporary femtocell visitors. Our simulation result shows that the proposed algorithm effectively reduces the number of unnecessary handovers.

Predictive Association Control for Frequent Handover Avoidance in Femtocell Networks

Appropriate base station association decisions in dense femtocell networks help to improve throughput while reducing frequent handovers of mobile stations. We consider the association control problem of mobile stations as an optimal control problem and obtain a rolling-out suboptimal control policy which is based on the predictive mobility of mobile stations. In addition, we derive a simple and lightweight online association control policy for each mobile station. The simulation results show that the proposed method provides large gain in both handover frequency and throughput over the current methods.

HW/SW codesigned implementation of IEEE 802.16 TDMA MAC for the subscriber station

The design for the TDMA MAC of the SS based on IEEE 802.16 have to meet the timing constraints for the uplink transmission, whereas for the non time-critical downlink, constraints such as implementation complexity and memory consumption have to be considered. One way to satisfy these requests is to using hardware/software codesign scheme. In this paper, we analyze the timing constraint in the SS side and determine what part should be implemented in HW. Also we present the HW/SW codesigned TDMA MAC of the SS based on the embedded system and show how we validate and implement it.

Fast intra-beam switching scheme using common contention channels in millimeter-wave based cellular systems

Millimeter wave (mmWave) cellular system has recently been introduced as an attractive approach for 5G mobile broadband communications. In the mmWave beamforming cellular systems, the user equipment (UE) can experience frequent service disruptions due to frequent switching among a plurality of beams if the UE follows the network controlled LTE handover procedures. In this paper, we shows how the mmWave beamforming cellular system can operate and which kind of new handovers UEs can experience. And we propose UE controlled beam switching mechanism based on contention based uplink channels. In this mechanism, UEs switch the serving beam to the target beam without random access delay using the pre-acquired contention based channels.

Contention based fast beam switching scheme in millimeter-wave cellular systems

Millimeter wave (mmWave) cellular system has recently been introduced as an attractive approach for 5G mobile broadband communications. In the mmWave beamforming cellular systems, the user equipment (UE) can experience frequent service disruptions due to frequent switching among a plurality of beams if the UE follows the network controlled LTE handover procedures. In this paper, we shows how the mmWave beamforming cellular system can operate and which kind of new handovers UEs can experience. And we propose UE controlled beam switching mechanism based on contention based uplink channels. In this mechanism, UEs switch the serving beam to the target beam without random access delay using the pre-acquired contention based channels.

Improving TCP Performance Using PDU Reordering in WiBro Multi FA Access Terminal

WiBro network which supports one specific channel bandwidth and frequency combination (8.75 MHz channel bandwidth at 2.3 GHz frequency) has to allow any mobile WiMax wave 1 and 2 devices to work in its cell in the future. AT using two 8.75 MHz FAs (frequency assignment) not only gives compatibility with Wave 1 and 2 devices but also supports higher data rate than AT using one 8.75 FA. However this AT does not guarantee delivering order of MAC (Medium Access Control) PDU (Protocol Data Unit) which has effect on TCP (Transmission Control Protocol) performance because of the disadvantage of TCP cumulative ACK (Acknowledge). In this paper we propose PDU reordering algorithm to improve TCP performance and AT architecture having access to two FAs at once.

Experimental Analysis for TDMA MAC Design/Implementation of the IEEE 802.16 SS

This paper presents the analysis of TDMA MAC applied to the IEEE 802.16 subscriber station and the uplink timing constraints. And this paper also shows results of the experiments with a few design approaches to check whether each design approach meets uplink timing constraints or not and which additional considerations are required. With a few experiments, although the total sum of the processing latencies of each functional component in MAC design meets the requested uplink timing, additional considerations for a burst of processing latencies with large difference from the average processing time which mainly depends on the characteristics of real-time operating system, traffic load, and the uplink burst length are needed. Considering this additional latency, this paper shows which hardware/software codesign model is analytically more suitable for TDMA MAC than that written in the software and how general partitioning criteria expression also needs to be revised to describe these characteristics.