This paper presents a methodology of controlling the spatial correlation of BS (base station) antenna realized by a bilateral fading emulator for MIMO-OTA (Over-The-Air) testing. On the basis of Jakes theory, the base station correlation is controlled by setting the initial phases of scatterers in a two-dimensional fading emulator. The experimental results show that the designed correlation coefficient of an uplink channel using the proposed method agrees well with the theoretical value. Further, it is confirmed that the channel capacity of uplink channel can be controlled when the base station and mobile terminal correlations are changed simultaneously.
In this letter, we present a random access protocol with success priority, success prioritized distributed coordination function (SP-DCF), based on IEEE 802.11 DCF. Success stations (STAs) are prioritized contentionlessly to transmit the next data frame in the transmit queue in a random manner. We develop a performance analysis model of SP-DCF which enables us to estimate a variety of performance indexes such as the throughput or the frame discard rate (FDR) in a high accuracy for saturated wireless networks. The numerical analysis and simulation results show that the proposed SP-DCF achieves higher throughput and lower FDR as compared with the conventional DCF especially for heavily-congested wireless networks.
This paper presents multiple snapshot spatial smoothing with improved aperture (MS-SSIA) for high-resolution direction of arrival (DOA) estimation by uniform linear array (ULA). Spatial smoothing preprocessing (SSP) is often used for DOA estimation of correlated sources, but it reduces the effective array aperture and leads to low DOA estimation accuracy. SSIA and SSOA improve the problem of SSP but they have some other problems. This paper tries to improve SSIA so that it can correspond to the case of multiple snapshots, but we take a different approach with SSOA. The performance of the proposed method is evaluated through computer simulation.
N-continuous symbol padding orthogonal frequency division multiplexing (NCSP-OFDM) is a modulation technique for sidelobe suppression, which adds the correction symbol only into the guard interval to enable the seamless connection of OFDM symbols. NCSP-OFDM requires the calculation of an inverse matrix per channel estimation, and so its computational complexity is large. This paper proposes a simple method for the calculation of the inverse matrix. Numerical experiments demonstrate that the proposed method does not affect the error rate performance and effectively reduces the computational complexity.
Low power communication systems such as ZigBee enable battery-driven sensor nodes in wireless sensor networks (WSNs). Recent growing demand for transferring large amount of data across a WSN requires more energy-efficient communication schemes. Energy efficiency, evaluated in terms of energy-per-bit rate (EBR), determines the upper bound of information quantity that can be transferred while consuming all the energy stored in a battery embedded in each sensor node. TransferJet is one of the most energy efficient wireless communication schemes. It achieves 2–3 orders of magnitude lower EBR than ZigBee, at the expense of very short communication range up to a few centimeters. In this paper, we report on a preliminary experiment of energy efficient signal transmission using TransferJet devices on two-dimensional communication (2DC) system. It worked at reasonably high transmission rate of 71 Mbps with 1.7-nJ/bit EBR. We also explain the feasibility of a room-scale high-speed communication system with such a low EBR based on 2DC technology.
Recently the channel estimation method of using a time domain Training Signal (TS) for the Orthogonal Frequency Division Multiplexing (TS-OFDM) has been considered actively by many researchers as an alternative method of using pilot signals in the frequency domain. However most of them were investigated assuming the ideal symbol timing. This paper conducts the theoretical examinations for the effect of channel estimation method of using the TS method when the detected symbol timing has an offset from the ideal symbol timing. This paper also verifies the theoretical analysis by computer simulation results.
This paper proposes an identification method of anomalous traffic such as DDoS attacks. Identification results are represented as a set of aggregated flows; such as source/destination IP address ranges(prefixes), source/destination port numbers and protocols and can be used as ACL (Access Control List) rules at routers. We set requirements for the identification can be summarized as the following three conditions; 1) covering the anomalous traffic, 2) avoiding to cover normal traffic, 3) with small number of aggregated flows. To accomplish these requirements, we propose a method to generate a set of aggregate flow that achieves the highest score representing the requirements by comparing before and after attacks and searching a optimal set with dynamic programming to avoid exponential computation explosion.
In this letter, aperture efficiency of reflectarrays is enhanced using an efficient full-wave method. The full-wave method deals with the effect of real mutual coupling between all reflectarray elements exactly during its design process. Resultant long CPU time is greatly reduced by developing an efficient algorithm which is optimized for the vector supercomputer. Numerical simulation shows that the aperture efficiency of the reflectarrays can be enhanced using the proposed method. The proposed method is computationally efficient and applicable for various design targets.
In recent years, MIMO (Multi-Input Multi-Output) transmission technique has attracted increasing attention, as it can satisfy the need for exponential increase in data traffic for mobile communications, especially when used for indoor areas. In this paper, an antenna design is proposed that can operate in the 2.6 GHz and 3.5 GHz bands and produce an orthogonal bi-directional radiation pattern. Some characteristics of the proposed antenna, such as reflection coefficient (S11), transmission coefficient (S21) and far-field radiation pattern are simulated and evaluated by means of FDTD (finite-difference time-domain) methods. The results show that S11 and S21 are below −10 dB and −15 dB, and moreover, the MIMO performance can probably be improved because the difference between the two directional gain levels is achieved by approximately 15 dB when four slits are etched into the ground plane.