This letter presents a lower bound and approximation for the coverage probability of the pilot channel that can be used for a CDMA downlink design. The approximation of a compound truncated Poisson distribution is used to obtain a closed form equation for the coverage probability of the pilot channel. Computer simulations show that our lower bound curve is truly less than the empirical curve, and our proposed approximation agrees well with the empirical result.

Electromagnetic shielding clothes for reducing human exposure to radio waves have been commercialized. However, their effect has so far been confirmed only in the form of the raw material. In this paper, we develop a new compact scheme for measuring electromagnetic radiations using a short dipole antenna and Gaussian pulses in order to evaluate the effect of the shielding clothes over a wide frequency range with the aid of time-domain measurements and FDTD computation. The proposed method is based on a time-domain analysis technique and pulse compression technique, which enables the user to separate the direct transmission wave from the reflection from the floor as well as from the refracted wave around the neck of the clothes. The direct advantage is that measurements can be made in an ordinary laboratory without the function of an electromagnetic anechoic chamber. Also, we can separate direct transmission wave and diffraction wave from the measurement result by using pulse compression technique, then each frequency characteristic of the shielding shirt can be evaluated. The performance of the separation is confirmed by comparing the measurements with those of a shirt with no opening. We further demonstrate the possibility of predicting the effective conductivity of the material as a function of frequency by comparing the measured results with realistic FDTD computations, which will enable us to design a shielding shirt via numerical means.

A rectangular-to-radial waveguide transformer through a crossed slot is proposed as a feeder of a radial line slot antenna (RLSA) for use in a system of solar power satellite (SPS). The transformer is analyzed and designed by using the MoM with numerical eigenmode basis functions. The measured ripple of the amplitude is 3.0 dB in the φ-direction and a 7.0% frequency bandwidth for rotating mode with the ripple below 6 dB is obtained. This bandwidth is wider than that of conventional ring slot or cavity resonator with a coaxial feeder. The antenna measurements at 5.8 GHz show reasonable rotational symmetry both in the near-field distribution and the far field radiation patterns. The reflection is -27.7 dB at the design frequency and below -15 dB in the 7.0% bandwidth. The gain of the antenna with the diameter of 300 mm is 22.7 dBi and the efficiency is 56%.

Distributed execution of a service often means that various places compete for the right to progress. If they exchange the right by explicit communication, there is a continuous flow of protocol messages. If the maximum transit delay of the communication medium is short, a better solution is to restrict progress of places to their individual time windows. The paper describes how to derive such time-sharing-based multi-party protocols for well-formed services specified in LOTOS/T+. The method is compositional with respect to the structure of the given service specification, supporting alternative, sequential, interrupt and parallel composition of services.

In this paper, we evaluate the performance of pilot channel-aided channel estimation for multicarrier direct-sequence (DS) code division multiple access (CDMA) communication system as proposed by Kondo and Milstein . We consider a multicarrier DS-CDMA system with different number of pilot and data channels. We investigate the optimum number of pilot channels for various coherence bandwidths and different number of subchannels. Keeping the total transmit bandwidth fixed, an optimum number of total subchannels and pilot channels exists under specific channel environment and transmitted energy. As the number of pilot channels increases, more accurate channel estimation is possible but the number of data channels decreases resulting a smaller diversity gain. We show that there is a tradeoff between the number of pilot channels and data subchannels, thereby requiring differing numbers of optimum pilot channels according to channel conditions.

General packet radio service (GPRS) uses a two-stage mechanism to allocate uplink radio resource to mobile stations (MSs). In stage-1, the base station (BS) assigns several packet data channels (PDCHs) to an MS. Furthermore, a PDCH may be assigned to multiple MSs. In stage-2, therefore, the BS selects one of the multiplexed MSs in a PDCH to use the radio resource. In this paper, maintaining a load balance between PDCHs in stage-1 is examined and several selection schemes to lower the mis-selection rate in stage-2 are proposed. From our simulation results, the cost deduced from the poor load balancing and selection schemes render a lower system throughput and a non-negligible increase in packet queuing delay. Among the various stage-2 selection policies, round robin with linearly-accumulated adjustment (RRLAA) has the lowest mis-selection rate and outperforms the one without any heuristic by up to 50%.

An element consist of a slot and a post is designed for canceling the reflection in a rectangular waveguide by the method of moments. For reducing the computation time in practical design of the element with a wide range of coupling strength for an array, only the axial uniform currents on the post surface are considered. This approximation is valid when the post for reflection-canceling is far enough from the slot. The post location is determined by this simple analysis for both transverse and longitudinal slots with typical coupling strength. Measured results using 4 GHz-band standard waveguides reveal that the assumption of uniform line currents on the post surface is acceptable. The design is further extended to demonstrate its applicability to a practical array design by considering a wide range of coupling strength.

This paper first presents an active integrated antenna configuration designed for broadband mobile wireless access systems using the 25-GHz band. This active integrated antenna comprises a microstrip antenna array and RF front-end circuits adopting spatial power combining schemes for reduced power consumption of the power amplifiers. Furthermore, the antenna and RF circuits are integrated into each side of a thick copper backing plate and both are connected through microstrip line /slot transitions. The developed active integrated antenna achieves the output power of 14.6 dBm and a noise figure of less than 5 dB. The wireless system using the developed active integrated antenna achieves a 6-dB improvement in the packet error rate compared to that using a passive antenna with the same array design as the active integrated antenna. Furthermore, we obtained the first license of the active integrated antenna for commercial use in high-speed wireless communication systems in Japan.

A Cyclotron Wave Converter, having decreased magnetic intensity is discussed. Two microwave cavities with uniform and quadruple (or six-pole) electric field in the gap of interaction are used to transform microwave power into the kinetic power of the electron beam fast cyclotron wave. As a result of it, magnetic flux density occurs in two (or three) times lower. The latter is very important to create a compact, powerful and efficient microwave/DC power converters operating at different frequencies including short centimetric and long millimetric wavebands.

The CDMA/NC-PRMA protocol has been proposed to deal with multimedia traffic flexibly in mobile communications systems. The Load-Balancing (LB) method has been investigated for information slot assignment in CDMA/NC-PRMA systems. However, the LB method may be not effective in multi-cell environments due to inter-cell interference although this method is effective for single cell environments. In this paper, we propose new information slot assignment methods for multi-cell environments; a total reception power based assignment method and a signal to interference ratio (SIR) based assignment method. The former one assigns information slots based on the total reception power from both inside and outside the cell for each slot in the previous frame. The latter one predicts the SIR of receiving packets and assigns information slots to MSs only when predicted SIR exceeds the target SIR. The results of computer simulation show that the proposed schemes have superior transmission performance to the conventional scheme.

This paper presents the analysis of the impedance characteristics of a sectoral cylindrical cavity-backed axial slot antenna excited by a probe. The integral equations are derived based on boundary conditions of the proposed structure and they are expressed in terms of dyadic Green functions and unknown current densities. The dyadic Green functions are obtained by using the eigenfunction expansion method together with application of scattering superposition techniques. The unknown current densities are solved by the Method of Moments. The input impedance is subsequently determined from the unknown electric current density at the probe. Numerical results of input impedance and return loss are demonstrated as functions of frequency for various parameters such as cavity length, cavity radius ratio, slot location in φ direction, slot length and probe length. Calculated results are validated by the measurements. At the operating frequency, it is found that the result is sufficiently accurate. The results from this study are very useful for the design of a sectoral cylindrical cavity-backed axial slot array antenna excited by a probe with omnidirectional beam radiation.

The proposed medium access protocol deals especially with the timely-transmission of real-time packets in wireless multimedia networks where users of many types of traffic are present. It works based on Time Division Multiple Access/Time Division Duplex (TDMA/TDD) technique and fixed-length packet switching incorporating two different policies to work differently on either non-congestion or congestion periods. In the policy to deal with congestion periods the concept of urgent packet has been introduced as any packet whose transmission deadline is on the next frame. Hence, during periods of congestion users inform to the Base Station the number and average deadline of the urgent packets in their buffers through requirement messages. According to that information the system is able to distribute its resources in a more efficient way during periods of congestion making the real-time packet loss rate decrease considerably. The simulation results show a very good performance of the method in networks where different types of traffic coexist even under high traffic-load conditions. The results also show a good trade-off characteristic between the real-time access delay and the buffer occupancy of non-real time terminals during congestion periods.

A new pilot-aided channel estimation technique is proposed and applied to wideband CDMA (WCDMA) systems. This technique is based on conventional pilot-aided decision directed (PADD) algorithms. In this letter, conventional PADD algorithms are studied extensively and a modified PADD algorithm is presented. The performance of the proposed algorithm is compared with that of conventional PADD algorithms through computer simulations in Rayleigh fading environments.

The problem of optimal placement of pilot symbols is considered for single carrier packet-based transmission over time varying channels. Both flat and frequency-selective fading channels are considered, and the time variation of the channel is modeled by Gauss-Markov process. The semi-blind linear minimum mean-square error (LMMSE) channel estimation is used. Two different performance criteria, namely the maximum mean square error (MSE) of the channel tap state over a packet and the cumulative channel MSE over a packet, are used to compare different placement schemes. The pilot symbols are assumed to be placed in clusters of length (2L+1) where L is the channel order, and only one non-zero training symbols is placed at the center of each cluster. It is shown that, at high SNR, either performance metric is minimized by distributing the pilot clusters throughout the packet periodically. It is shown that at low SNR, the placement is in fact not optimal. Finally, the performance under the periodic placement is compared with that obtained with superimposed pilots.

Turbo decoding with coherent detection requires accurate channel estimation. In this paper, we consider outer-turbo channel estimation (OTCE), which carries out iterative channel estimation before turbo decoding, and inner-turbo channel estimation (ITCE), which incorporates iterative channel estimation into turbo decoding process. The average bit error rate (BER) performances with OTCE and ITCE in a frequency nonselective Rayleigh fading channel with antenna diversity reception are evaluated by means of computer simulations to be compared. It is found that although ITCE is superior to OTCE, OTCE provides the average BER performance very close to ITCE when dual antenna diversity reception is used.

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.

This paper proposes a new method to estimate the channel impulse response for Orthogonal Frequency Division Multiplexing (OFDM) mobile radio transmission. The method employs the Recursive Least Squares (RLS) algorithm so as to exploit the correlations in frequency and time domains, and can improve the estimation accuracy. It is also applicable to both the regular and scattered pilot schemes. Computer simulations demonstrate effectiveness of the method applied to the scattered pilot scheme.

OFDM transmission performance in mobile communications suffers severe degradation caused by multipath delay difference greater than the Guard Interval (GI). This is because the excess delay results in considerable Inter-Symbol Interference (ISI) between temporally adjacent symbols and Inter-Carrier Interference (ICI) among subcarriers in the same symbol. This paper proposes a robust OFDM receiver for the scattered pilot OFDM signal that can effectively suppress both ISI and ICI by using two types of equalization and a smoothed FFT-window. In order to verify the performance of the proposed receiver, computer simulations are conducted in accordance with the scattered pilot OFDM signal format of the Digital Terrestrial Television Broadcasting (DTTB). The simulation results demonstrate that the proposed receiver shows much better performance than the conventional receiver in multipath fading environments with the delay difference greater than GI duration.

The authors propose a novel 3-way power divider named a planar cross-junction, which is used as the center feed for single-layer slotted waveguide arrays. A feeding waveguide consisting of a cascade connection of these dividers is placed at the middle of radiating waveguide in a single layer. The length of radiating waveguides is halved; the long line effect in traveling wave operation is halved and bandwidth is widened. One divider as a unit is designed by Galerkin's method of moments to suppress the reflection and to control the amplitude and the phase of the divided power into two radiating waveguides on both sides of a feed one. Two types of the cross-junction with a different divided power ratio are designed and tested by experiments in 4 GHz band. The mutual coupling effects between two adjacent cross-junctions as cascaded in a feeding waveguide of the array are predicted to be small enough; units designed here are directly applicable for a multiple-way power divider.

Adaptive prediction iterative channel estimation is presented for combined antenna diversity and coherent rake reception of direct sequence spread spectrum (DSSS) signals. Its first stage uses pilot-aided adaptive prediction channel estimation, while the succeeding iteration stages use decision feedback and moving average filtering for channel re-estimation. The bit error rate (BER) performance of DSSS signal computer simulations evaluate transmission in a frequency selective Rayleigh fading channel. It is found that the adaptive prediction iterative channel estimation is superior to the non adaptive iterative channel estimation using the conventional weighted multi-slot averaging (WMSA) filtering at the first iteration stage, particularly in a fast fading channel.