Makoto Taromaru

Enhanced Reactance-Domain ESPRIT Algorithm Employing Multiple Beams and Translational-Invariance Soft Selection for Direction-of-Arrival Estimation in the Full Azimuth

An enhanced reactance-domain estimation of signal parameters via rotational invariance techniques (RD-ESPRIT) algorithm is proposed for direction-of-arrival (DoA) estimation in the full-azimuth plane. Unlike the classical RD-ESPRIT algorithm, the proposed method employs a generalized RD correlation matrix combined with soft selection. The proposed algorithm is expected to allow estimating more than one signal DoA with improved estimation precision. The generalized RD correlation matrix is formed by utilizing a number of beam patterns greater than or equal to the number of array elements. The soft selection employed in the enhanced RD-ESPRIT consists of two steps. First, the estimates obtained by applying the generalized RD-ESPRIT to three translational-invariance configurations are gathered to form a set of DoA estimate candidates. Second, selection functions based on a modified MUSIC function are used to select the DoA estimates from among the estimate candidate set. The proposed algorithm is investigated through computer simulations with a seven-element electronically steerable parasitic array radiator (ESPAR) antenna. The simulation showed that the proposed algorithm can perform effective DoA estimation of up to four incoming signals in the full-azimuth plane with slightly improved DoA-estimation precision. So far, the classical RD-ESPRIT is not effective because it can estimate up to one signal DoA. Moreover, the proposed method showed robust estimation capability for up to two incoming signals. A robust estimation refers to the fact that a number of DoA estimates equal to the number of incoming signals can always be selected from trial to trial. A one-signal estimation experiment was conducted in an anechoic chamber with a fabricated seven-element ESPAR antenna. In general, the proposed algorithm showed as accurate estimation precision as the classical algorithm. In particular, using soft selection instead of hard selection increases the estimation precision, whereas augmenting the number of beam patterns brings an increase in the estimation precision only when used with hard selection.

Wireless secret key generation exploiting the reactance-domain scalar response of multipath fading channels : RSSI interleaving scheme

A secure communication scheme that uses the random fluctuation of the natural environment of communication channels is studied and an improved scheme for the secret key generation is proposed. We have been developing a novel secret key generation and agreement scheme that uses the fluctuation of channel characteristics with an Espar (electronically steerable parasitic array radiator) antenna. This antenna consists of a single central active element surrounded by parasitic elements loaded with variable reactors. Using an Espar antenna, we can increase the fluctuation of the channel characteristics and acquire the undulated RSSI (received signal strength indicator) profile in a short time to generate a randomized secret key. We acquire more randomized and stronger secret keys generated from the interleaved RSSI values in this scheme. As a result of experiments on the prototype system in which the IEEE 802.15.4/ZigBeetrade wireless PAN (personal area network) chip is mounted, we confirmed that the probability of success for key generation was estimated to exceed 99.998% when 128-bit secret keys are changed every two seconds and that the generated secret keys were sufficiently random to pass the FIPS (Federal Information Processing Standards) PUB 140-2 statistical test for random numbers

Optimal Frame Splitting for Downlink MIMO Channels With Distributed Antenna Arrays

A frame-splitting (FS) scheme is proposed to exploit spatial diversity in the downlink wireless transmission from a base station (BS) to a mobile station (MS) that has multiple receive antennas. The BS has multiple geographically distributed arrays, each consisting of multiple transmit antennas. The scenario comprises a number of downlink multiple-input-multiple-output (MIMO) channels from different BS arrays to an MS with mutually independent Rayleigh-fading processes. A data frame from the BS for the MS is split into portions, which are consecutively transmitted from multiple BS arrays. For the FS transmission scheme, the distribution of information capacity is formulated on the basis of the FS fractional lengths of the portions. Analytical evaluation of the outage probability reveals the optimal setting of FS fractional lengths for the maximum diversity advantage based on knowledge of the long-term average signal-to-noise ratios (SNRs) of the downlink MIMO channels.

Experimental Proof of Electrically Invisible State of Inductively Loaded Dipole and Proposal of Electrically Invisible Meander-Lines

We examine that an inductively loaded dipole becomes electrical invisible showing that the influence on a nearby antennas input impedance and on its radiation pattern (scattering) are minimized. We also verify that the direction of the current reverses on the electrically invisible dipole so that the integral of the dipole current becomes zero. By making an inductive load with a distributed constant line, we fabricate an electrically invisible dipole without using chip devices and evaluate its performance. Furthermore, we propose electrically invisible conductor lines formed by connecting these electrically invisible dipoles in series using open stubs as connectors, and analytically examine their invisible state

Performance of Angle Switch Diversity Using ESPAR Antenna for Mobile Reception of Terrestrial Digital TV

Using a computer simulation, we investigate the mobile reception quality of terrestrial digital broadcasting with switch diversity in consideration of channel estimation errors caused by switching. Generally, the bit error rate (BER) performance of antenna switch diversity is degraded by abrupt phase changes due to switching. In this paper, we demonstrate that the switching rate of diversity decreases by 60% and the BER performance improves when using a directional antenna. We use an ESPAR (electrically steerable parasitic array radiator) antenna as the directional antenna. A switching beam pattern along the direction of travel, in particular, gives the best BER performance, and when the maximum Doppler frequency is 20 Hz, the maximum diversity gain is about 4 dB at a BER of 10-2.

Proposal of band-limited divided-spectrum single carrier transmission for dynamic spectrum controlled access in ISM band

A single carrier transmission system is proposed. It is a dynamic spectrum access system designed for ISM bands where various radio systems are operating. The proposed system divides the spectrum of the single carrier modulation into a few “subspectra” and allocates them for fragmented vacant spectra, which are called “white space” in the band. Not FFT/IFFT operations for each signal block with cyclic prefix, but band-limiting filters, of cosine roll-off characteristics for example, are adopted for the spectrum dividing in order to reduce ACPR (or ACLP, adjacent channel leakage power ratio). Simulation results show that PAPR (peak-to-average power ratio) of the transmitted signal can be reduced by limiting the number of the spectrum division within a few pieces. The proposed system utilizes the remaining vacant spectra thoroughly so that it copes with the increasing demand of spectrum use expected in ISM bands toward the ubiquitous network world in the near future.

Performance of adaptive array antenna with widely spaced antenna elements

Adaptive array antenna is receiving attention because it can suppress interference waves coming from other cells. We investigate performance of adaptive array antenna with widely spaced antenna elements. We show that at a base station the adaptive array antenna with wide element spacing has better bit error rate performance due to space diversity effect than the one with narrow element spacing under co-channel interference and multipath fading environment.

Achieving the Lowest Outage Probability for Multi-Phase Cooperative Wireless Networks

The performance of a multi-phase cooperative communication is studied in a wireless network. Each node is a mobile module having multiple antennas (MA) or a group of sensors forming a virtual antenna array (VAA). The scenario comprises a number of multiple-input multiple-output (MIMO) channels with mutually independent Rayleigh fading processes. A data frame from a signal source node is split into portions. Each portion is transmitted from a distinct node in a sequential manner to the destination node. First, we give the criterion on how to select wireless nodes for achieving the lowest outage probability of information capacity. Second, the analytical expressions of the optimal frame splitting (FS) ratios are derived for arbitrary signal-to-noise (SNR) situations. This is fulfilled by employing Gaussian approximations of those random MIMO channel capacities. Finally, we examine the optimal FS ratios in high-SNR regime. The theoretical results are useful to designing cooperative communication protocols.

Downlink control channel transmission with antenna directivity switching or space diversity at base stations

A strategy to improve the transmission quality of the downlink control channel in mobile communications is proposed. In this strategy, the base station transmits control channel bursts repeatedly with switching of antenna directivity or with an omnidirectional antenna for space diversity. The effect is evaluated by computer simulation, and it is shown that the proposed strategy is effective. The directivity pattern conditions suitable for this strategy are considered. The effect of the proposed method is confirmed by field experiments.

A basic study on EER transmitter with burst-width envelope modulation based on triangle-wave PWM

The improvement of efficiency on power amplifiers (PAs) has been a major assignment from dc to microwave region. The class-E and F PAs, overdriven amplifiers with harmonics control are well known scheme to obtain the high efficiency on microwave PA. However, significant deterioration as same as the conventional amplifier is specifically inevitable issue in the linear operation. These facts draw efficiency reduction and modulation inaccuracy on the high backoff modulation such as OFDM. Recently, EER (envelope elimination and restoration) and polar modulation are widely researched as a solution for these issues. In this work, a novel EER transmitter with burst-width modulation driven class-E amplifier system is verified on 64 QAM signal of 2.3GHz. As a result, it is confirmed that basic parameters on PA, EVM and ACLR are simultaneously improved.