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In order to enhance the system capacity of wireless LANs, we propose in this paper using the frame-based adaptive multirate transmission scheme in the IEEE 802.11 and evaluate its performance. Typically, high-speed modulation schemes would require higher SNR to maintain the transmission quality and BER. The transmission rate is selected dynamically based on the detected SNR, each frame shall be transmitted at the highest available rate. The original virtual carrier sense mechanism in IEEE 802.11 is no longer suitable because the multirate hidden terminal problem. We redejke the MAC header and modifi the reservation scheme of the network allocation vector (NAV) to resolve these problems. The throughput and delay are evaluated using simulations and the results show that they can be significantly improved compared with those of the single-rate WLAN.

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Proposed is a novel structure of a cascadable photonic serial-to-parallel converter (SPC) based on the cross-phase modulation effect in a semiconductor optical amplifier for simultaneous multiple-channel optical time division multiplexed demultiplexing. The proposed SPC features cascadability, compact structure, high-speed operation, and simultaneous two-channel operation. Error-free 20 Gbit/s simultaneous two-channel demultiplexing is experimentally demonstrated.Introduction: Simultaneous multiple-channel processing, which is capable of providing several advantages such as low latency, low insertion loss, and easy synchronisation, is a key technique for optical time division multiplexed (OTDM) networks [1]. However, most of the reported OTDM demultiplexers are focused on processing individual channels using semiconductor optical amplifier (SOA)-, fibre-and electro-absorption modulator (EAM)-based optical gates [2 -4]. There are only a few approaches for multiple-channel OTDM demultiplexing. Morais et al. demonstrated a demultiplexer using both wavelength conversion and time gating techniques [5]. Uchiyama et al. reported two approaches based on cross-phase modulation (XPM) in polarisationmaintaining dispersion-shifted fibres and four-wave mixing (FWM) in SOAs [6, 7]. Furthermore, Dennis et al. employed a series of modulators to perform serial-to-parallel conversion for eight-channel full demultiplexing [8].In this Letter, we propose and demonstrate a new structure of an all-optical serial-to-parallel converter (SPC) for multiple-channel OTDM demultiplexing. The proposed SPC features cascadability, compact structure, high-speed operation, and simultaneous twochannel operation. Cascading several SPCs can provide the possibility to extend the number of ultimate outputs. A proof-of-concept experiment is carried out to demonstrate error-free operation of simultaneous two-channel demultiplexing for a 20 Gbit/s OTDM signal.

Abstract. Software testing is an important and expensive activity to the software industry, with testing accounting for over 50% of the cost of software. To ease this problem, test automation is very critical to the process of software testing. One important issue in this automation is to automatically determine whether a program under test (PUT) responds the correct(expected) output for an arbitrary input. In this paper, we model PUTs in black-box way, i.e. processing and responding a list of numbers, and design input/output list relation language(IOLRL) to formally describe the relations between the input and output lists. Given several labelled test cases(test verdicts are set), we use genetic programming to evolve the most distinguishing relations of these test cases in IOLRL and encode the test cases into bit patterns to build a classifier with support vector machine as the constructed test oracle. This classifier can be used to automatically verify if a program output list is the expected one in processing a program input list. The main contribution of this work are the designed IOLRL and the approach to construct test oracle with evolve relations in IOLRL. The experiments show the constructed test oracle has good performance even when few labelled test cases are supplied.