Chih-Chiang Wu

IMT-advanced relay standards [WiMAX/LTE Update]

There are two candidates for IMT-Advanced (4 G) standards, LTE-Advanced by 3 GPP and 802.16 m by IEEE. This article focuses on relay architectures in 16 m and LTE-A, and discusses design principles and trade-offs leading to decisions in each standards group. Basically, 16 m relay and LTE-A Release 10 relay are very similar technologies where the relay is essentially an orthogonal frequency-division multiple access base station with a wireless backhaul link. However, some open issues, such as mobility, power saving, multihop architecture, transparent relaying, multi-arrier transmission, and cooperative transmission, are still left as challenges for engineers and researchers. This article provides insights to both relay standards that could be helpful for readers to fully comprehend practical ways of incorporating relays into 4 G wireless broadband networks.

Using grey prediction theory to reduce handoff overhead in cellular communication systems

A novel handoff algorithm based on grey theory is being proposed for reducing the handoff overhead in cellular communication environment. The design of the methods is intended to be used under a log-normal fading environment. The grey prediction model is used to predict the received signal strength indicator (RSSI) values from two base stations (BS). The decision whether performing handoff is based on the predictive RSSI value, the received RSSI value and n-1 past RSSI values. By changing the handoff probability of two regions (divided by the middle point of two separated BSs), the position of first handoff to be executed will close to the middle point of two separated BSs. The simulation results show that the proposed algorithm with grey theory obtains excellent performance because it not only minimizes the number of performing handoff, but also has a very short calculating time.

Design and implementation of a reservation-based MAC protocol for voice/data over IEEE 802.11 ad-hoc wireless networks

IEEE 802.11 is a standard, which specifies both the medium access control (MAC) and physical layers (PHY) for wireless local area networks (LANs). However, it cannot support real-time services for ad hoc networks. We propose a distributed bandwidth reservation protocol (DBRP), which is compliant with the IEEE 802.11 standard, to support both non-real-time (data) and real-time (voice) traffic over an ad hoc WLAN. The simulation results show that DBRP can provide a high channel utilization as well as a high quality of service (QoS). We also realize our proposed DBRP over a WLAN adapter and the measured results show that the DBRP performs much better then the conventional IEEE 802.11 standard.

A smart photonic ATM switch architecture with compression strategy

Generally, the limitations of optical delay line and link capacity limit the switching efficiency in the photonic asynchronous transfer mode (ATM) switch. Under the constraints, a smart photonic ATM switch designed for high-speed optical backbone network should have some fast switching strategies so that the congestion can be avoided or reduced. In this paper, we mill propose a novel smart photonic ATM switch architecture with a novel compression strategy. In the smart architecture, while more than two frames are destined for the same destination, the losers will be queued and compressed to reduce the degree of congestion. Therefore, not only the total switching time (TST) can be reduced but also the scarce buffer is able to store more incoming cells. To meet the high-speed switching performance, a simple and efficient compression decision algorithm (CDA) is proposed. The timing of employing compression strategy and the saturated performance of proposed strategy are analyzed. Simulation results show that compared to the conventional photonic ATM switch without compression strategy, the proposed strategy offers a much better performance in terms of queueing delay.

A new contention-based CSMA protocol for star networks

This paper proposes a new protocol, called CSMA with adaptive reservations by interruptions (CSMA/ARI), to enhance the carrier sense multiple access with collision detection (CSMA/CD) protocol. The proposed CSMA/ARI protocol allows active stations to contend/reserve channel capacity by sending requests during a successful ongoing frame transmission. To avoid corrupting the ongoing frame, for shorter frames, we scarify the precision of error detection by allocating a partial cyclic redundancy check (CRC) field for contention. The performance of the proposed protocol is studied by simulation and compared with the CSMA/CD and CSMA/RI with MAC delay, and channel utilization. Simulation results demonstrate that CSMA/ARI always offers better performance than CSMA/CD and CSMA/RI.