This letter proposes a new upgrading method to realize next-generation access networks by a lumped Raman amplifier (LRA) located at a central office (CO). An LRA can simultaneously amplifies bidirectional ten signal waves, two from 10G-EPON and eight from TWDM-PON. We estimate gains and OSNRs (optical signal noise ratios) by calculations. Finally, we made fundamental bit error rate (BER) experiments for bidirectional two 10G-EPON signals to confirm the feasibility of the proposed method. Calculated and measured results are in good agreement and we think the method can serve the next-generation PON systems.
In this paper, a fast model identification algorithm based on Givens rotation is presented for the digital predistortion (DPD) application. Because most of the computation work is operated in the hardware, the new algorithm has much faster identification speed than traditional recursive least square (RLS) method or least square (LS) method. Compared with common fast identification algorithms, the new algorithms exhibits the higher identification precision. And final experiment shows that the adjacent channel power ratio (ACPR) after the DPD with the new algorithm is -50dB, 8dB better than that with the conjugate gradient (CG) method, which verifies that the new algorithm has very good performance on both identification precision and identification speed.
As a secure communication method for wireless communication systems, we propose a method utilizing the interference alignment (IA) technique. In the MIMO interference channels, only the designated pairs of two radio stations can communicate without the interference from the other communication pairs, while a third party radio station which is not included in the IA control suffers the interference. Utilizing the property, secure communication can be realized. In this paper, we propose a new method of secure communication using IA. We examine the performance of the proposed method quantitatively by computer simulations .
As the electromagnetic (EM) environment becomes increasingly diverse, it is essential to evaluate exposures to EM waves for pregnant females and their fetuses. Therefore, we have determined the maternal and fetal specific absorption rates (SARs) of pregnant females at the 13th, 18th, and 26th gestational weeks using a high-definition numerical model of a flip phone in close proximity to the pregnant female’s abdomen. The results indicate that the difference between the simple EM source and the realictic one in the maternal and fetal SARs is within 30% in this case. Moreover, all calculated SARs were below the international safety guidelines.
An intruder detection method by using time variant Multiple Input Multiple Output (MIMO) channels has been proposed (MIMO sensor). In this letter, the detection performance using eigenvectors, which are obtained by singular value decomposition for MIMO channel matrix, is evaluated in actual indoor propagation environment. Moreover, a new diversity method using multiple eigenvectors is proposed to enhance the performance of the intruder detection using eigenvectors. Scenarios that are effective for 1st and 2nd eigenvectors is verified and the effectiveness using multiple eigenvectors is shown compared to the MIMO sensor using the channel matrix.
Tomamichel et al. improved a key rate of a Quantum Key Distribution (QKD) protocol with finite number of qubits. To compute the key rate, we need to estimate a phase error rate, which obey a hypergeometric distribution. They did not compute directly the tail probability of the hypergeometric distribution to obtain the estimate of the error rate, and they used its upper bound instead. We improve the key rate of the QKD by exact numerical computation of the tail probability. We also propose a method to decrease the computation time for exact numerical computation.
A variety of satellite missions are carried out every year. Most of the satellites yield big data, and high-performance data processing technologies are expected. We have been developing a cloud system (the NICT Science Cloud) for big data analyses of Earth and Space observations via spacecraft. In the present study, we propose a new technique to process big data considering the fact that high-speed I/O (data file read and write) is important compared with data processing speed. We adopt a task scheduler, the Pwrake, for easy development and management of parallel data processing. Using a set of long-time scientific satellite observation data (GEOTAIL satellite), we examine the performance of the system on the NICT Science Cloud. We successfully archived high-speed data processing more than 100 times faster than those on traditional data processing environments.
Low complexity equalizers are investigated for single carrier transmissions over doubly selective channels. The ZF equalizer that utilizes circulant matrices constructed from time-averaged channel coefficients exhibits good performance, keeping small computational complexity.
In this letter, we investigate energy-efficiency power allocation (PA) based on physical layer network coding (PNC) in 60GHz orthogonal frequency division multiple (OFDM) system. To optimization the energy-efficiency with required system throughput requirement, we formulate the objective task as a constrained minimization problem. The closed form minimum power allocation solutions are obtained by analyzing Karush-Kuhn-Tucker (KKT) conditions. Based on the derived solution, we propose a novel optimal energy-efficient power allocation (OE-PA) scheme. Numerical results have demonstrated the energy-efficient optimality of the derived scheme as compared to other conventional power allocation schemes.