This paper presents a method of spherical far-field extrapolation from near-field using phase retrieval method. The simulation results clarify that we can extrapolate far-field correctly by selecting appropriate probe scanning radius. We also present measurement to verify the simulation results.

View full abstract

Adapting a λ-tunable wavelength division multiplexing (WDM) / time division multiplexing (TDM)-passive optical network (PON) that can control huge bandwidth is an attractive candidate for accommodating the explosive growth in mobile backhaul (MBH) network traffic cost effectively. The synchronization of base stations is an important issue for MBH. However, it is hard to employ conventional time and frequency synchronization techniques over λ-tunable WDM/TDM-PON. We proposed a timestamp-based time and frequency synchronization method over a λ-tunable WDM/TDM-PON. In this letter, we describe a numerical evaluation of the synchronization performance with practical oscillators. The achieved performances are sufficient to meet the requirement of MBH.

View full abstract

Massive multi-user multiple-input multiple-output (MU-MIMO), in which access points (APs) with a lot of antennas transmit to a lot of stations (STAs) with a few antennas, is attractive for wireless LAN systems due to its potential to greatly increase throughput. However, the throughput improvement at media access control - service access point (MAC-SAP) in massive antenna systems is limited by the overhead imposed by channel state information (CSI) feedback. In this letter, we clarify the problem of CSI feedback and evaluate two frame sequences with implicit CSI feedback (ICF) for downlink (DL-) MU-MIMO systems. The use of ICF eliminates the overhead of CSI feedback because MU-MIMO precoding weight is generated from the uplink CSI using a calibation matrix that compensates the channel responce differences between the transmitter and the receiver. This letter validates the effectiveness of DL-MU-MIMO with ICF by a performance evaluation at MAS-SAP in a comparson with the conventional approach which needs CSI feedback.

View full abstract

We propose a Gilbert-Varshamov-type existential bound for the relative dimension length profile and the relative generalized Hamming weight of nested pairs of linear codes.

View full abstract

In-body wireless communication has attracted increasing attention because it can not only be used in medical application but also be combined with wireless communication to replace the existing connectivity in biological telemetry monitoring [1]. Therefore, it is possible to integrate radio frequency identification (RFID) system into a brand-new device [2]. However, it has been very difficult to combine them due to high lossy of human body. In this paper, an implantable tag antenna which is designed to match an integrated circuit (IC) chip of 9.3-j55.2Ω [3] is proposed and realized in experiment. The dimensions of proposed antenna is 15.75mm × 4mm. The impedance characteristic of proposed antenna is analyzed by finite-difference time-domain (FDTD) method. By introducing the three-layered phantom, the measurements of impedance characteristic is implemented; moreover, the maximum read range of 1.3cm is confirmed by a handy reader.

View full abstract

Digital classrooms today are commonly based on Ethernet LANs. However, use of tablets or notebooks with touch screens is also becoming increasingly popular. Many such devices do not have LAN plugs. WLANs also permit mobility which increases flexibility of educational process. This paper shows that WLANs are intrinsically less reliable and one should be careful when designing digital classrooms based entirely on WLANs. Among other conclusions, this paper shows that for classes of up to 40 students - the official upper limit for elementary school classes in Japan - one needs to split the class into at least two groups each served by a separate wireless router. Although this paper is based on the specific example of using WLANs in digital classrooms, experimental setup and findings are generic and can cover a wide range of web applications running over a shared wireless medium.

View full abstract

Guidelines for reduction of computing time of direct/iterative solver for MoM on GPU computing are reviewed. Computing time of the direct/iterative solver with and without these guidelines is compared to show the computational efficiency of GPU computing quantitatively.

View full abstract

This study examines quantitatively the requisite design area on the ground plane (GP) of a vertical U-shaped folded dipole antenna (VUFDA), and clarifies the space-saving effectiveness of the VUFDA design for mobile terminals compared to a conventional UFDA design. Our results show that the vertical deployment of the antenna element to the GP is much more effective than the horizontal deployment, not only for reducing the physical antenna area on GP, but also for saving the space which the antenna element actually requires for stable antenna operation. These results highlight the importance of evaluating carefully antenna miniaturization and actual space requirements in antenna designs intended for operation within mobile terminals.

View full abstract

ID/Locator separation architecture is proposed in order to reduce routing table size in the current Internet. In this architecture, an end-host can be identified by unique ID which is independent of its network protocol. Network protocol independency of ID provides possibility of communication with end hosts operating different network-layer protocol. This inter-layer 3 networking brings several benefits in addition to routing table size improvement, e.g. improvement of shortest path and robustness. In our previous paper, performance of inter-layer 3 networking from the viewpoint of shortest path improvement has been evaluated. In this paper, we focus on improvement of robustness brought by inter-layer 3 networking in the case of node failure. Node failure generally suffers serious degradation of connectivity because all links connected to a node are failed. Our simulation results show that significant improvement of robustness can be obtained only with small number of vertical links going through multiple network planes.

View full abstract

In this paper, we investigate a problem whether unique refractive index distribution of a gradient medium can be determined if definite optical paths in the medium are given previously. From the standpoint of transformations that leave the ray equation unchanged, general considerations reveal that the equation is invariant under a single-parameter scale transformation, and a type of local transformation parameterized by an arbitrary real function. A two-dimensional case involving the design of a gradient refractive index lens antenna reported by the author is re-examined by applying the obtained findings, and it is found that the indeterminacy with respect to the latter transformation disappears, especially in the case of the authors’ report.

View full abstract