In a Long-Term Evolution system, a transmitter can appropriately transmit layered data streams via multiple antennas with the help of a precoding matrix. The precoding matrix can be selected using the feedback precoding matrix indicator information from the receiver. Different precoding matrixes will affect the system capacity and bit error rate performance dramatically. In this paper, we propose a low complexity precoding matrix selection method based on trace calculation of the MIMO channels’ eigenvalue. The method will have almost the same capacity as the maximum mutual information (MI) method, as well as the low computational complexity advantage. Simulation results show that the proposed method requires less than 20% calculations needed by the maximum MI method.
This letter is concerned with distributed estimation in a Gaussian sensor network operating under a semi-orthogonal multiple-access channel (MAC). In such a semi-orthogonal MAC, all sensors are divided into groups and signals from the sensors in each group are directly combined (opposed to be coherently combined) and then transmitted on one orthogonal channel to a fusion center (FC). The behavior of the average distortion in terms of the number of sensors, namely the scaling law, is analyzed. The analytical derivation and simulation results show that the semi-orthogonal MAC with adaptive sensor grouping can achieve the optimal scaling law while requiring only a small amount of feedback from the FC to the sensors.
In this letter, radiation pattern of a dipole array antenna coupled to a two-wire transmission line is numerically investigated. The effect of array spacing on the main beam direction of the array antenna is shown. In addition, it is shown that the endfire radiation of the array antenna can be suppressed when series inductors are loaded with the two-wire transmission line.
In our recently proposed reduced-complexity near-maximum likelihood block signal detection employing QR decomposition and M-algorithm (QRM-MLBD) for broadband single-carrier (SC) block transmission, unreliable symbol candidates are removed from the symbol tree based on the hard-decision minimum mean square error based frequency-domain equalization (MMSE-FDE). In this paper, to further remove the unreliable symbol candidates and consequently reduce the computational complexity, we introduce a soft-decision MMSE-FDE based selection of reliable symbol candidates into reduced-complexity QRM-MLBD. It is shown that the soft-decision MMSE-FDE based selection significantly reduces the computational complexity while achieving a bit error rate (BER) performance similar to the original QRM-MLBD.
Tor (The Onion Router) realizes that anonymous web surfing without revealing the user’s identity. However, A. Panachenko et al. reveals that an onion router that directly communicates with a user can infer which website a user accesses by leveraging site-specific traffic features, e.g., volume and time, and this attack is called the fingerprinting attack. In this paper, we propose a countermeasure against the fingerprinting attack by obfuscating site-specific traffic features. The idea is to establish two distinct Tor connections and to separately request text-based contents and image-based one through them. We show the effectiveness of our scheme with experiments.
This paper proposes a meta-surface for a miniaturized unit cell that consists of a double-layered Frequency Selective Surface (FSS) and the ground plane. Additional miniaturization of the unit cell is achieved by sliding one layer of the double-layered FSS in the polarization direction of an incident wave. Moreover, the unit cell becomes smaller than half the size of a conventional single-layered meta-surface by using the double-layered FSS.
MIMO technology has been widely used for several years for the purpose of improving communication speed and communication capacity. However, if MIMO antenna is mounted closely, radiation efficiency and throughput of MIMO are decreased due to strong mutual coupling. In this paper, a decoupling method using meander branch antenna is proposed. It is confirmed that the mutual coupling is reduced and the radiation efficiency is increased by utilizing this method. Moreover, further developing this method, it is confirmed that a decoupling bandwidth can be enhanced.
This paper proposes matching method based on image impedances for near field MIMO. In this letter, matching method, which can realize matching of all port at the same time by extending image impedances theory, is proposed. Numerical analysis and experimental results demonstrate the proposed matching method is effective in enhancing the channel capacity of the near field MIMO, where facing antennas strongly couple to each other.