Sung-Joon Cho

A Study of Seamless Handover Service and QoS in Heterogeneous Wireless Networks

The integration of WLAN and beyond 3G mobile networks offers the possibility of achieving anytime and anywhere Internet access. Moreover the requests for seamless multimedia services and the quality of service (QoS) support have been one of key issues in wireless networks. Therefore the researches relative to seamless multimedia service and QoS over heterogeneous wireless networks have been progressing rapidly. In this paper, we propose interworking architecture for supporting seamless multimedia service and QoS over WLAN and WiBro networks. Based on the proposed inter-working architecture, we also provide both the seamless handover architecture such an inter-network vertical handover and the QoS-aware wireless medium access control (MAC) scheme.

The Scheme to Improve the Performance of Initial Ranging Symbol Detection with Common Ranging Code for OFDMA Systems

In orthogonal frequency division multiple access (OFDMA) systems, timing synchronization in uplink is accomplished by an initial uplink synchronization called an initial ranging process. The base stations receiver synchronizes the symbol timing to any users symbol and the other users symbols have some symbol timing offset (STO). Linear phase shift is occurred by each users STO in an OFDMA symbol. The multiple access interference (MAI) caused by the summation of each users linear phase shift degrades the performance of the ranging code detection. In this paper, we propose an initial ranging symbol structure with common ranging code for phase shift estimation and compensation

A new backoff scheme of IEEE 802.11 wireless local area networks

In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs a proposed enhanced backoff algorithm. It is considered the transmission time of TCP packet on the orthogonal frequency division multiplexing (OFDM) in AWGN channel. Also, to simulate wireless LANs system, we have assumed that three stations are operated, respectively. From the results, a proposed enhanced backoff algorithm produces a better performance than an original backoff in wireless LAN environment. Also, in OFDM/QPSK (12 Mbps and 18 Mbps) channel, we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and we can infer the correlation between packet size and the transmission time, allowing for an inference of the optimal packet size in the TCP layer

QoS-aware Wireless MAC Protocol Using Network Load Adaptation

In these days the requests for various multimedia services and the Quality of Service (QoS) support have been one of key issues in wireless data communications. Therefore the research relative to Medium Access Control (MAC) has been progressing rapidly. Especially A number of QoS-aware MAC schemes have been introduced to extend the legacy IEEE 802.11 MAC protocol which has not guaranteed any service differentiation. However, none of those schemes fulfill both QoS features and channel efficiency although these support the service differentiation based on priority. Therefore this paper studies a novel MAC scheme, referred to as Enhanced Distributed Coordination Function with Network Adaptation (EDCF-NA), for enhancements of both QoS and medium efficiency. It uses a smart factor denoted by ACK rate and Network Load Threshold (TH). In this paper, we study how the value of TH has effect on both the QoS performance and the channel efficiency via Network Simulator-2 (NS-2) simulations.

Performance Analysis of System Architecture using Wireless Relay Station and Virtual MIMO in WiBro Uplink

Introduction of Relay Station (RS) is unavoidable and wireless RS has gained more interest for next generation mobile communication systems including Wireless Broadband (WiBro) system. Also, Multi-Input Multi-Output (MIMO) scheme is an emerging technology, offering high spectral efficiency. In this paper, we propose a system architecture applying Space Time Block Coding (STBC) algorithm in RS-Base Station (BS) link and Virtual MIMO (V-MIMO) scheme in Mobile Station (MS)-RS link based on WiBro network using wireless RS. The proposed system architecture is analyzed comparing with conventional single antenna system in uplink. As a result of simulation, the proposed system architecture outperforms the 2~3dB Bit Error Rate (BER) performance in RS-BS, MS-RS, MS-RS-BS uplink. And uplink transmission capacity improved 1.7-1.8 times. The system architecture proposed in this paper, is efficient because it can improve transmission gain and system capacity without change of MS.

A study of QoS-aware MAC protocol with network adaptation

A number of QoS-aware medium access control (MAC) schemes have been introduced to extend the legacy IEEE 802.11 MAC protocol which has not guaranteed any service differentiation. However, none of those schemes fulfill both QoS features and channel efficiency although these support the service differentiation based on priority. This paper presents a novel MAC scheme for enhancements of both QoS and medium efficiency. In the proposed scheme, referred to as enhanced distributed coordination function with network adaptation (EDCF-NA), we modify the existing backoff algorithm and employ a new mechanism called inter frame space (IFS) control. These newly developed methods use smart factors denoted by ACK rate, which is involved by the entire network faults such as collisions and drops, and network load threshold (TH). In addition, our approaches are evaluated by NS-2 simulations and compared the performance of other MAC protocols

Mixed video/data transmission over indoor wireless channels using unequal error protection method

This paper provides a system level description of a mixed video/data CDMA transmission model. We propose the combination of rate compatible punctured convolution (RCPC) code for the wireless physical (PHY) layer and CDMA RAKE receiver for wireless mixed video/data traffic which can be sent over indoor wireless channels. Through numerical analysis, using a frequency selective multipath Rayleigh fading channel model, it is shown that RCPC coding at the wireless PHY layer can be effective in providing reliable wireless CDMA network. And the proposed scheme that combine RCPC coder and CDMA RAKE receiver provides a significant gain in the BER and PER performance over multipath fading channels.

Performance of 16 QAM signal with optimum code mapping and optimum threshold detection in Rician fading channel

We have analyzed the error performance of 16 QAM with optimum code mapping (OCM) and optimum threshold detection (OTD) in a Rician fading channel with and without the selective combining (SC) diversity technique. The error performance of OCM with OTD is compared to that of conventional code mapping (CCM) in a Rician fading channel. With the result of the analysis, it is found that the proposed OCM with OTD is superior to CCM with CTD. The adoption of a diversity technique with the proposed OCM with OTD can be considered as a good countermeasure for the Rician fading under a personal communication system (PCS) environment.

Network-based seamless handover framework providing QoS in heterogeneous wireless networks

In this paper, we propose the QoS-aware seamless handover framework which coordinates IEEE 802.21 Media Independent Handover (MIH) services and IETF Fast handover for MIPv6 (FMIPv6), suited for heterogeneous wireless access networks. We further evaluate the performance of the proposed framework by using numerical analysis. The proposed framework focuses on the intelligent selection of access networks depending on the QoS criteria in order to guarantee QoS. We further concentrate on the network-based service and the balance in order to facilitate the handover across heterogeneous wireless access networks. As a result, it is verified that the proposed framework significantly reduces both handover latency and signaling overhead, and thus improves QoS performance.

Improvement of TCP throughput with the snoop+/spl alpha/ protocol

The Snoop protocol is one of the ways to alleviate the effects of noncongestion-related losses on TCP performance over wireless networks. It can improve TCP performance quite well in wireless links but has a problem; when there are no duplicate ACKs, the Snoop protocol cannot notice the packet loss until the local retransmission timer is expired. This results in the degradation of TCP throughput. In this paper, we propose the Snoop+alpha protocol to solve the Snoop protocols problem. Because the Snoop+alpha agent adaptively checks packet loss whenever it receives new ACKs, it performs packet retransmission fast compared to the Snoop protocol. From the simulation results, the proposed Snoop+alpha protocol can efficiently improve TCP throughput more than the Snoop protocol. Furthermore, the degree of TCP throughput enhancement is little influenced from the fading variation