Next-generation mobile communication networks are supposed to provide various high capacity multimedia services to mobile users using various kinds of access networks. Among them, the WiNGS system developed by ETRI as one of 4G mobile system provides high performance RATs (Radio Access Technology) and network architecture with IP connectivity for merging them. In this paper, we propose a new link layer Selective-Repeat Automatic Repeat Request (SR-ARQ) mechanism that solves packet re-ordering problems during handovers and enhances handover performance in WiNGS system. In the proposed mechanism, we adopt an adaptive timer in the sending node in order to prevent unnecessary packet retransmission during handovers, and a delayed NAK scheme in the receiving node to prevent detection of temporal packet reordering due to handover delay. We implemented the proposed SR-ARQ mechanism in ns-2 simulator for performance evaluation. The simulation results show that the proposed SR-ARQ enhances handover performance for the WiNGS system by preventing unnecessary retransmission and reordering.

This paper describes a shared medium access protocol for residential home and small business customer ATM network application with distributed multimedia services. This protocol offers global fairness for the whole network and, at the same time, offers a local priority mechanism for different traffic on each node. The traffic of B-ISDN services is characterized for real or non-real time multimedia, which means the local priority mechanism is very important for different traffic in a node to support real time multimedia traffic effectively. Simulation results show this protocol has higher performance than already announced protocols. This paper also shows a hardware structure of the high-speed ATM MAC (HAM) protocol.

This paper proposes a method of reducing the cell loss probability by interleaving the header and data bits in wireless ATM networks where bit errors are likely to occur in bursts. Analytic modeling of the proposed method and a subsequent calculation shows a substantial improvement in cell loss probability due to burst errors, which has been also verified by computer simulation. This paper also proposes a header interleaving expansion method and techniques of applying the interleaving method to physical layer protocols. The proposed methods are easily applicable to the B-ISDN physical layer protocol and have a small processing delay.

For the existing shared medium access protocol, a serious problem is the performance decreasing against the increasing distance and speed in the shared medium high speed LAN/MAN application, caused by the overhead of access control. In this paper, a new protocol is proposed to reduce the overhead using distributed access function. It uses distributed cycle reset function and token reset function at the same time. That is the reason why the proposed protocol is named Distributed Cycle Reset (DCR) protocol. The proposed protocol combines merits of the distributed cycle reset algorithm and the centralized reset algorithm on the basis of cycle concept controlling bandwidth usage for each terminal. Simulation result shows the performance of this protocol increased throughput comparing with other similar protocols.

Two low-redundancy codes for in-band pilot insertion are introduced. KF10 suppresses the baseband PAM and the modulated QAM signal power at the Nyquist frequency so that the dual-pilot tone calibration technique of recent interest can be arranged to convey both a symbol timing and a carrier reference to the receiver. OF00 suppresses the signal power at zero as well as the Nyquist frequency and allows the utilization of a triple-pilot scheme which provides, in addition to a symbol timing, a carrier reference with no 180 degrees phase ambiguity.>

Techniques for varying duobinary and modified duobinary, which are two of the most important partial-response codes, to limit their run lengths without destroying their minimum bandwidth property, are introduced. One of the example codes is the first run-length-limited variant of duobinary ever known, and the other two are already publicized variants of modified duobinary, but are described either in more detail or from a different point of view. Performance figures of the three codes such as power spectrum, eye width, and error probability are experimentally confirmed to be acceptable for all engineering purposes.

By generalizing a concept on a power spectral zero at the Nyquist frequency, a condition for the line codes' capability to signal with the minimum bandwidth is established. From the condition, lower bounds of eyewidth are obtained for various values of a new system parameter called intersymbol interference sum variation (ISV). As an application of the condition, the nonminimum-bandwidth bipolar code is modified to a minimum-bandwidth code, which can be directly used in conventional bipolar signaling systems with increased bandwidth efficiency.