Gyung-Ho Hwang

Fast handover scheme for real-time downlink services in IEEE 802.16e BWA system

IEEE 802.16 WirelessMAN aiming to broadband wireless access (BWA) is evolving to 4G mobile communication systems through the standardization of IEEE 802.16e supporting mobility on existing fixed WirelessMAN systems. Because IEEE 802.16e system is based on OFDM(A) technology, a mobile subscriber station (MSS) basically conducts hard handover operation when it moves to another base station (BS). Therefore, the MSS is not able to send or receive the data during handover process and these data should be delayed. As a result, real-time packet could be dropped by handover delay. In this paper, we propose an enhanced link-layer handover algorithm that an MSS can receive downlink data before synchronization with uplink during handover process. Our proposed scheme reduces data transmission delay and packet loss probability for real-time downlink service.

Adaptive random channel allocation scheme in HIPERLAN type 2

The MAC protocol of HIPERLAN type 2 is based on TDMA/TDD and resources in one MAC frame can be allocated dynamically by the access point (AP). We propose an adaptive random channel (RCH) allocation scheme for HIPERLAN type 2. The AP scheduler controls the number of RCHs in one MAC frame according to the transmission results of the previous MAC frame. The simulation results show that the proposed scheme achieves higher efficiency of resource and lower access delay than fixed RCHs allocation schemes.

Fast retransmission mechanism for VoIP in IEEE 802.11e wireless LANs

IEEE 802.11 wireless LANs provide a cheap and high data rate mobile service. Voice service through wireless LANs has became an important issue. The new IEEE 802.11e standard provides a framework to support quality of service (QoS) according to traffic type. The enhanced distributed channel access (EDCA) mechanism, which is contention-based access, has several access parameters which are able to give a higher access probability to the high priority service. Since a real time service, such as voice over IP (VoIP), has a delay constraint to guarantee QoS, fast collision resolution is required. We review the IEEE 802.11e standard and propose a new fast retransmission mechanism for VoIP packets to reduce the delay and improve the channel utilization by eliminating the overhead time for backoff procedures. Simulation results show that the proposed scheme reduces the delay and dropping probability of VoIP packets.

Adaptive random access and resource allocation scheme based on traffic load in HiperLAN type2 system

The MAC protocol of HiperLAN type2 is based on TDMA/TDD and provides access control and resource allocation schemes. We propose a scheme that provides adaptive random access and efficient resource allocation according to the traffic load for HiperLAN type2, by using access probability. The analysis and simulation results show that the proposed scheme performs better than the conventional scheme and supports priority services easily.

Distributed rate control for throughput maximization and QoS support in WCDMA system

We propose a distributed rate control scheme for throughput maximization and different QoS support of each user in the 3GPP WCDMA system using the variable spreading factor of physical channel specification. We focus on the uplink rather than downlink for the reason that the uplink resource is not used effectively by the multiple access. The base station transmits rate command bits and persistence value p considering current load and number of users with each transmission rate. And each mobile station performs the persistence test and changes transmission rate. The performance of the proposed scheme is compared with other conventional methods by simulation. The simulation results show that the proposed scheme has high throughput and supports proper differentiation according to the users QoS.

Dynamic rate control based on interference and transmission power in 3GPP WCDMA system

We propose a dynamic rate control method for throughput enhancement and different QoS support of each user in the 3GPP WCDMA system using the variable spreading factor of the physical channel specification. We focus on the uplink rather than the downlink for the reason that the uplink resource is not used effectively by the multiple access. The transmission rate of each user is controlled according to the users priority and transmission power. Also, the interference level of the other cell is considered in the case of call admission and increased transmission rate. The performance of the proposed rate control method is compared with other methods by simulation. The simulation results show proposed that the scheme has a high throughput achievement and support proper differentiation according to the users QoS.

Type II hybrid ARQ scheme based on QoS and LDPC code

There are two kinds of technique used for error control: FEC (forward error correction) and ARQ (automatic repeat request). Combining these two schemes, which is called HARQ (hybrid ARQ), makes it possible to increase the channel throughput. The error of the channel quality estimate that is used to select the MCS (modulation coding scheme) in type I HARQ can be a serious problem in scenarios when the mobile station moves at high speeds. Furthermore, in a system dominated by packet services, the interference level may be bursty, and thus it is difficult to predict the interference level. Therefore, the type II HARQ scheme is a more robust solution compared with type I HARQ. In order to improve channel throughput while at the same time satisfying quality of service (QoS) under various channel conditions, an efficient hybrid ARQ type II scheme is proposed. The optimum redundancy size for every transmission is calculated to maximize the throughput using QoS parameters, the performance of LDPC code and channel conditions. The proposed scheme, together with such benefits as QoS support, provides a way of achieving higher throughput in wireless communication systems.

Dynamic random channel allocation scheme in HIPERLAN type 2

The need for wireless high speed data transmission is increasing. HIPERLAN type 2 is an ETSI broadband wireless access network standard operating in license-exempt 5 GHz band. The MAC protocol of HIPERLAN type 2 is based on TDMA/TDD and resources in one MAC frame can be allocated dynamically by the access point (AP). We propose a dynamic random channel allocation scheme for HIPERLAN type 2. The AP scheduler controls the number of random channels (RCH) in a MAC frame according to transmission results of the previous MAC frame. The simulation results show that the proposed scheme achieves higher efficiency of resource and lower access delay than fixed RCH allocation schemes.

Mobility based dynamic multicast protocol in wireless ATM network

In this paper, we present a multicast protocol for a wireless ATM network in the case that each user has a specified mobility (high and low mobility) and it joins (or leaves) a multicast group dynamically. We use a hierarchical architecture in the ATM switch network that is inspired by the PNNI (private network-network interface) routing of the ATM Forum. The entire network is divided into many peer groups which have their own leaders. We call the peer group leader an MSA (multicast service agent). The MSA has its own logical level representing the level in hierarchy of the switches. We propose a shared tree multicast protocol to manage dynamic multicast group membership. The main contribution of this paper is that we apply a different scheme according to the mobility of members. The proposed scheme could support a better QoS by taking into consideration the mobility.