As a typical planar antenna in Japan, a microstrip antenna and radial line slot antenna are chosen and some original technologies are introduced for them. About the microstrip antenna, the analyzing method is described first and the method based on the theory of microstrip planar circuit born in Japan is introduced. According to the formulas derived by this method, the design procedure considering the bandwidth is established. In addition, it is shown clearly that a microstrip antenna can produce the circular polarizations at two kinds of frequencies with a single feed. Furthermore, two kinds of broadband techniques born in Japan are picked up. About other unique microstrip antennas, they may be introduced in a suitable section each time. As for the RLSA, the history on invention is briefly presented. The radiation mechanisms depending on the slot-set arrangement and the excitation mode are discussed. The slot-coupling analysis to simulate the excitation of a two-dimensional uniformly-excited slot array is explained. The simple design based on the operation with traveling-wave propagation is also described. The technical progress to keep high efficiency in a wide gain range for satellite-TV reception is reviewed. Extensions of the RLSAs to millimeter-wave bands and plasma etching systems are finally summarized.

Broadband fixed wireless access (FWA) systems offer significantly higher bit rates than current cellular systems to which adaptive arrays are partly applied. Digital beam forming is being eagerly explored on account of its flexibility, but it will be difficult to apply to the high-speed systems, because its digital signal processing requires huge resources and power consumption. Conventional phased arrays, on the other hand, utilize phase shifters through RF or IF signal lines, but the phase shifters are usually both bulky and expensive. The authors propose an adaptive array steered by IF local signal phase shifters in this paper. The phase shift and the frequency shift of the signal from each antenna element can be simultaneously accomplished at the down conversion stage by the phase-controlled local signal. A prototype receiver operated in the K-band with the proposed configuration and its beam pattern measurement results are also described.

We create a practical method to set the segment size of the Welch FFT for wideband and long-term spectrum usage measurements in the context of hierarchical dynamic spectrum access (DSA). An energy detector (ED) based on the Welch FFT can be used to detect the presence or absence of primary user (PU) signal and to estimate the duty cycle (DC). In signal detection with the Welch FFT, segment size is an important design parameter since it determines both the detection performance and the frequency resolution. Between these two metrics, there is a trade-off relationship which can be controlled by adjusting the segment size. To cope with this trade-off relationship, we define an optimum and, more easy to analyze sub-optimum segment size design criterion. An analysis of the sub-optimum segment size criterion reveals that the resulting segment size depends on the signal-to-noise ratio (SNR) and the DC. Since in practice both SNR and DC are unknown, proper segment setting is difficult. To overcome this problem, we propose an adaptive segment size selection (ASSS) method that uses noise floor estimation outputs. The proposed method does not require any prior knowledge on the SNR or the DC. Simulation results confirm that the proposed ASSS method matches the performance achieved with the optimum design criterion.

The architecture and control procedure for a direct conversion receiver are investigated for a linear modulation scheme. The proposed design techniques maintain receiver linearity despite various types of signal distortion. The techniques include the fast gain control procedure for receiving a control channel for air interface connection, DC offset canceling in both analog and digital stages, and 2nd-order intermodulation distortion canceling in an analog down-conversion stage. Experimental and computer simulation results on PHS (Personal Handy-phone System) parameters, showed that required linear modulation performance was achieved and thus the applicability of the proposed techniques was demonstrated.

In direct communication, terminals that are close to each other can communicate directly without traffic going through centralized controller such as a base station (BS). This brings several advantages. We study direct communication with localized distribution, so that users tend to gather around some areas (clusters/hot-spots) within the cell such as buildings. Previous analysis about clustering has focused on one dimensional scenarios. Here we present theoretical analysis of direct communication with two dimensional clustering. Additional analysis is presented for direct communication with correlated clusters. With correlated clusters some pairs of source and destination clusters are more probable than other pairs. According to our best knowledge, this is the first time that theoretical analysis is presented about clustering and correlated clusters in two dimensional scenarios. Simulations confirm the validity of the analysis. In addition to the exact results, we also suggest using the point-based approximation to rapidly and easily obtain results. The numerical results show that the gains from direct communication, in terms of blocking probability and carried traffic, depend on the offered traffic. Additionally, correlation in cluster selection is shown to significantly improve performance. Point-based approximation is shown to be very useful when the number of clusters is large.

This paper presents a novel design method for reducing the complexity of the design procedure for diversity antennas on the hand-held phone. Recently, antenna selection diversity has been widely used for hand-held phones in order to overcome a problem of fading. A monopole antenna and an inverted-F antenna are the typical combination for this purpose. In the case of the conventional design method, the mutual coupling between two antennas are used for improving the diversity performance. However, strong mutual coupling often makes the diversity antenna design difficult and degrades the radiation performance. The proposed design method suppresses this coupling by tuning the terminating impedance on the unselected antenna and improves the diversity performance by modifying the shape of inverted-F antenna. The validity of the proposed method is investigated under the effect of the user's hand and head by FDTD simulation.

This paper investigates the use of cooperative spectrum sensing (CSS) to detect primary user (PU) signals during spectrum sharing between the PU and the secondary user (SU). In particular, we employ a variant of CSS (which achieves space diversity), called weighted gain combining CSS (W-CSS), which has the potential to achieve increased diversity gain and enhance detection performance. In a typical W-CSS system, the SU needs to obtain the PU signal power information in order to set the proper weight value. However, as it is hard for the SU to ascertain whether the PU is present or absent, this is difficult to obtain. To address this problem, a PU signal power estimation algorithm is introduced. In addition, we also analyze the statistics of the estimator and derive the detection probability of the W-CSS when the PU signal power estimation algorithm is applied. The analysis and related simulation results reveal that the detection probability of the proposed W-CSS under time-variant Rayleigh fading asymptotically approaches the detection probability in an additive white Gaussian noise channel as the number of antennas is increased. This also follows results from our Monte Carlo simulations, showing that multiple antenna elements could suppress the effect of Rayleigh fading. In short, the accuracy of the estimation algorithm is affected by channel variation (especially in the case of fast Rayleigh fading). Hence, to address this problem, we employ multiple antenna elements with a square-law combining energy detector in the W-CSS.

In this paper, we propose a novel highly reliable packet transmission protocol for ad-hoc wireless networks without deciding the route from a source node to a destination node in advance. The proposed protocol uses distributed surrounding nodes as transmitters of the retransmission packet when the transmitted packet contains an error. In this protocol, when a packet is not correctly received at the destination node, the source node and the surrounding nodes that have correctly received the packet simultaneously retransmit the same data packet to the destination node. The transmitting timing is triggered by the control packet transmitted from the source node. These operations are repeated until the packet reaches to the destination node like automatic repeat request (ARQ). Moreover, the retransmitted packet is encoded by one branch of the space time block code (STBC) for improving the performance with the network diversity effect. We call this method as STBC Distributed ARQ scheme. The performance of the proposed scheme is evaluated by the computer simulations.

A miniature transceiver, including highly integrated MMIC front-end, for 1.9 GHz band personal handy phone system(PHS) has been developed. The terminal, adopting direct conversion transmitter and receiver technology, consists of four high-density RF circuit modules and a digital signal processing LSI with 2.7 V power supply. The four functional modules are a power amplifier, a transmitter,a receiver, and a frequency synthesizer. Each functional module includes one IC chip and passive LCR components connected with solder bumps on module substrate. The experimental miniature PHS handset has been fabricated to verify the design concepts of the miniature transceiver. The total volume of the developed PHS terminal is 60cc, including the 12cc front-end which comprises the four RF functional circuit modules. The air interface connection with the PHS base station simulator has been confirmed.

Hop-timing detection is of extreme importance for the reception of frequency hopping (FH) signals. Any error in the hop-timing detection has a deleterious effect on the performance of the receiver in frequency hopping (FH) communication systems. However, it is not easy to detect the hop-timing under low signal to noise power ratio (SNR) environments. Adaptive array antennas (AAA) have been expected to improve the performance of FH communication systems by beamforming for the direction of arrival of the desired signal. Since the conventional AAA exploits at least the coarse synchronization for dehopping of FH signals before achieving the beamforming, any fault in the hop-timing detection causes the deterioration of the performance of AAA. Using AAA based on the constant modulus algorithm (CMA), this paper proposes a new method for blind beamforming and hop-timing detection for FH signals. The proposed method exploits both the spatial and temporal characteristics of the received signal to accomplish the beamforming and detect the hop-timing without knowing any a priori information such as fine/coarse time synchronization and training signal. The performance verifications of the proposed method based on pertinent simulations are presented.

A Direct Radiating Array Antenna (DRAA) concept has been introduced to international satellite communications in order to achieve multiple shaped beams which are electrically reconfigurable. The subject of this paper is to describe the new design method for a reconfigurable DRAA. The design procedure consists of three steps, 1) derivation of the initial array layout using Fourier transform method (FTM) , 2) array shape rearrangement, 3) optimization of the final array excitation with the modified constraint least mean square (MCLMS) algorithm. At the first step, it is necessary to derive the initial array layout for the desired shaped beam with respect to array shape, number of antenna elements, and excitation distribution. For this purpose, a new closed form solution of FTM using N-polygonal desired coverage is used. At the second step, the array shape is rearranged to fit the beam forming network (BFN) configuration which can reduce insertion loss and influence on frequency variation sensitivity. At the third step, the array excitation is optimized using MCLMS which is exploited to satisfy the power sum constraints caused by the restriction of the BFN configuration. The design method provides useful insight regarding the layout design of a DRAA with well-shaped coverages, the low insertion loss of the BFN and the high sidelobe isolation characteristic. The design of the reconfigurable DRAA with the specified multiple shaped (beams is demonstrated and compared with the experimental model.

Based on the MSN algorithm, an adaptive algorithm capable of controlling antenna patterns by phase weight only is derived. Then, an algorithm for phase nulling convenient in case not needing adaptive weight control is derived. This algorithm with null directions only being the parameter is convenient for pattern synthesis and pattern improvement. Finally, two examples are presented to demonstrate usefulness and validity of the technique.

In this paper, we propose a soft decision based cooperative sensing method for cognitive radio (CR) networks for opportunistic frequency usage. To identify unused frequency, CR should exploit sensing technique to detect presence or absence of primary user and use this information to opportunistically provide communication among secondary users while performance of primary user should not be deteriorated by the secondary users. Because of multipath fading or shadowing, the detection of primary users may be significantly difficult. For this problem, cooperative sensing (CS), where gathered observations obtained by multiple secondary users is utilized to achieve higher performance of detection, has been investigated. We design a soft decision based CS analytically and analyze the detector in several situations, i.e., signal model where single-carrier case and multi-carrier case are assumed and two scenarios; in the first scenario, SNR values of secondary users are totally equal and in the second scenario, a certain SNR difference between secondary users is assumed. We present numerical results as follows. The first scenario shows that there is little difference between the signal models in terms of detection performance. The second scenario shows that CS is superior to non-cooperative sensing. In addition, we presents that detection performance of soft decision based CS outperform detection performance of hard decision based CS.

This paper investigates a signal detection method with a RAKE combiner for the case wherein the receiving signals use the same spreading code. In the case where multiple user interference with the same spreading code (MUI-SC) occurs, blind channel estimation is difficult and as far as we know has not been investigated. To tackle the issue of MUI-SC, we propose two blind channel estimation methods based on the multimodulus algorithm (MMA), i.e., MMA-IQ and MMA-I methods. When a one dimensional modulation scheme, such as differential binary phase-shift keying (DBPSK), is used, the output of the MMA-IQ channel estimation method can, under MUI-SC, have two states. The first state is that the channel estimate corresponds to a channel response for one of the received signals, and the second state is that the channel estimate corresponds to combined channel responses for two of the received signals. This is because the MMA-IQ uses two degrees of freedom (both axes in the IQ-plane), however one DBPSK signal uses only one degree of freedom. In the case of the second state, it is possible to detect two signals/packets at once. However, in the MMA-IQ, the receiver has to recognize the state of the channel estimate before the signal detection, thus we also propose a state recognition method. In the MMA-I channel estimation method, only the I-axis is used thus the channel estimate always corresponds the case with one signal. Numerical results show that the average number of detected packets of the MMA-IQ is more than that of the MMA-I in high signal-to-noise power ratio case. In addition, several aspects of the MMA-I and MMA-IQ based RAKE signal detection methods are shown.

Spread Spectrum (SS) has been widely used for various wireless systems such as cellular systems, wireless local area network (LAN) and so on. Using multiple antennas at the receiver, two-dimensional (2D) RAKE is realized over the time- and the space-domain. However, it should be noted that the 2D-RAKE receiver must detect the bit timing prior to the RAKE combining. In case of deep fading, it is often difficult to detect it due to low signal-to-noise power ratio (SNR). To solve this problem, we propose a new blind 2D-RAKE receiver based on the constant modulus algorithm (CMA). Since it does not need a priori bit timing detection, it is possible to compensate frequency selective fading even in very low SNR environments. The proposed method is particularly suitable for the software defined radio (SDR) architecture. The performance of the proposed method is investigated through computer simulations.

This paper proposes a MAC protocol for efficient broadcasting in wireless ad hoc networks. Pure flooding leads to serious redundant broadcasts, packet contention and packet collisions, known as the broadcast storm problem. This paper focuses on how to reduce the redundant broadcasts. Several protocols to achieve efficient broadcasting have been proposed. However a trade-off exists between the reachability and the broadcasting ratio, which is the ratio of the number of the broadcasting nodes to the number of received nodes. This paper proposes a new MAC protocol for on-demand broadcasting, which is referred to as dialogue-based protocol in order to resolve the trade-off. The dialogue-based protocol employs additional massages which are called as request packets and reply signals. They are exchanged in an on-demand manner, in order that relay candidate nodes recognize its neighbor nodes status whether they have already received the broadcast packets. Finally, by computer simulations, this paper presents that the dialogue-based scheme combines high reachability with low broadcasting ratio by using the low additional massages.

Wireless ad hoc communications such as ad hoc networks have been attracting researchers' attention. They are expected to become a key technology for "ubiquitous" networking because of the ability to configure wireless links by nodes autonomously, without any centralized control facilities. Adaptive array antennas (AAA) have been expected to improve the network efficiency by taking advantage of its adaptive beamforming capability. However, it should be noted that AAA is not almighty. Its interference cancellation capability is limited by the degree-of-freedom (DOF) and the angular resolution as a function of the number of element antennas. Application of AAA without attending to these problems can degrade the efficiency of the network. Let us consider wireless ad hoc communication as a target application for AAA, taking advantage of AAA's interference cancellation capability. The low DOF and insufficient resolution will be crucial problems compared to other wireless systems, since there is no centralized facility to control the nodes to avoid interferences in such systems. A number of interferences might impinge on a node from any direction of arrival (DOA) without any timing control. In this paper, focusing on such limitations of AAA applied in ad hoc communications, we propose a new scheme, Forward Interference Avoidance (FIA), using AAA for ad hoc communications in order to avoid problems caused by the limitation of the AAA capability. It enables nodes to avoid interfering with other nodes so that it increases the number of co-existent wireless links. The performance improvement of ad hoc communications in terms of the number of co-existent links is investigated through computer simulations.

Cognitive radio (CR) systems aim for more efficient spectrum utilization by having so called secondary users (SUs) transmit on a frequency band reserved for licensed primary users (PUs). The secondary transmissions are allowed provided that no harmful interference will be caused to the PUs. SU terminals with multiple antennas can employ transmit power control with transmit precoding in order to control the interference levels. In most of the existing works, perfect channel state information (CSI) is assumed to be available for the SUs. However, in practical systems where perfect CSI is not available, the SUs are not able to guarantee that the interference constraints are sufficiently satisfied. In this paper, we investigate the problem of spectrum sharing for multiantenna CR systems using estimated CSI. Due to the random nature of the estimation error, we set a probabilistic interference constraint and, in order to satisfy it, provide a density function for the interference power. In addition, we present a power control framework for the SU to meet the probabilistic interference constraint.

M-ary/SS is a version of Direct Sequence/Spread Spectrum (DS/SS) aiming to improve the spectral efficiency employing orthogonal codes. However, due to the auto-correlation property of the orthogonal codes, it is impossible to detect the symbol timing by observing correlator outputs. Therefore, conventionally, a preamble has been inserted in M-ary/SS signals. In this paper, we propose a new blind adaptive array antenna for M-ary/SS systems that combines signals over the space axis without any preambles. It is surely an innovative approach for M-ary/SS. The performance is investigated through computer simulations.

In relation to the Software Defined Radio (SDR) concept, an experimental simulation system was developed. Likewise, verification tests were performed in order to validate the envisaged SDR certification processes including its development, certification, distribution, and software installation assuming the future possibility of exchanging the software in the field.