In this paper, penetration phenomenon of an early-time (E1) high altitude electromagnetic pulse (HEMP) into dispersive underground multilayer structures is analyzed using electromagnetic modeling of wave propagation in frequency dependent lossy media. The electromagnetic pulse is dealt with in the power spectrum ranging from 100kHz to the 100MHz band, considering the fact that the power spectrum of the E1 HEMP rapidly decreases 30dB below its maximum value beyond the 100MHz band. In addition, the propagation channel consisting of several dielectric materials is modeled with the dispersive relative permittivity of each medium. Based on source and channel models, the propagation phenomenon is analyzed in the frequency and time domains. The attenuation levels at a 100m underground point are observed to be about 15 and 20dB at 100kHz and 1MHz, respectively, and the peak level of the penetrating electric field is found 5.6kV/m. To ensure the causality of the result, we utilize the Hilbert transform.

In this letter, a codebook based multiuser MIMO precoding scheme is proposed for a space-division multiple access (SDMA) system with limited feedback. Focusing on the case of SDMA systems with two transmit antennas, a precoder codebook design is proposed based on the idea that a precoder inducing larger fluctuations in the signal to interference and noise ratio (SINR) at each link can lead to a larger gain in terms of multiuser diversity. It is shown that the proposed multiuser MIMO precoding outperforms existing multiuser MIMO techniques in terms of the average system throughput.

This paper presents an analysis of the effects of RF filter characteristics on the system performance of an impulse radio. The impulse radio system transmits modulated pulses having very short time duration. Information can be extracted in the receiver side based on the cross-correlation between received and reference pulses. Accordingly, the pulse distortion due to in-band group delay variation can cause serious degradation in system performance. In general, RF band pass filters inevitably cause non-uniform group delays to the signal passing through the filter that are proportional to its skirt characteristic due to its resonance phenomenon. In this work, a small signal scattering parameter, S21, which is a frequency domain parameter, and its Fourier transform are utilized to characterize the output pulse waveform under the condition that the input and output ports are matched. The output pulse waveform of the filter is predicted based on the convolution integral between the input pulse and filter transfer function, and the analysis result is compared with previously reported experimental result. The resulting bit error rate performances in a bi-phase modulation and a pulse position modulation based impulse radio system are also calculated. Moreover, improvement of system performance by the pulse shaping method, a potential solution for pulse waveform distortion, is analyzed.

A precise analysis of the capacity of a wireless downlink packet data system with a fair scheduler is presented. We assume the use of a transmit diversity scheme is operating at each link under the assumption of spatially correlated Rayleigh fading. Numerical results show that spatial fading correlation of the channel improves the capacity of multiuser diversity by reducing the space diversity gain of transmit diversity in each link.

In this letter, base station placement is automatically determined from pre-defined candidate sites using a genetic approach, and the transmit power is obtained taking the interference situation into account in cases of interference-dominant systems. In order to apply a genetic algorithm to the base station placement problem, a real-valued representation scheme is proposed. Corresponding operators such as crossover and mutation are also introduced. The proposed algorithm is applied to an inhomogeneous traffic density environment, where a base station's coverage may be limited by offered traffic loads. An objective function is designed for performing the cell planning in a coverage- and cost-effective manner.

This paper describes the measurements made in an urban canyon environment of a relay network scenario to determine the capacity of the multiple-input-multiple-output (MIMO) channel. While varying antenna number and spacing, we measure the channel matrices in the 3.7 GHz band using a 44 switching MIMO channel sounder. The results show that antenna spacing is shown to have less impact than signal-to-noise (SNR) on MIMO channel capacity in a line-of-sight (LOS) environment when physical antenna spacing is selected at four wavelengths. As a result, in an urban MIMO LOS scenario, a base station can provide sufficient data throughput to relay station because most links from base station to relay station have LOS environment and are free from restriction of antenna spacing.

We propose a modified orthogonal transmit diversity (OTD) scheme, which can simultaneously achieve full path diversity and temporal diversity by using symbol splitting. Our proposed method is comparable to space-time spreading (STS) in performance and superior to STS in the cost and efficiency of base station RF devices.

In this paper, several spiral inductors with various ground clearance structures and turns were investigated to achieve noise suppression up to the fourth harmonic (3.2 GHz) regime of DDR3-1600. Their performances were characterized in terms of their capability to effectively suppress simultaneous switching noise (SSN) in the frequency region of interest. For a wider noise suppression bandwidth, a spiral inductor with large ground clearance, which provides a high self resonance frequency (SRF) as well as high inductances, was implemented. The proposed spiral inductor exhibited good noise suppression characteristics in the frequency domain and achieved 50% voltage fluctuation reduction in the time domain, compared to the identical 4-turn spiral without pattern ground structure.

In this letter, a new CCM material, adding Ni powder to a conventional CCM, for X-band applications is designed and analyzed to improve the SE. To obtain the SE of the fabricated CCM accurately, material constants of the CCM of the permittivity and permeability were extracted using transmission/reflection measurements. Using the material constants derived from the measurement, the SE was calculated and the results were verified using a commercial full-wave three-dimensional electromagnetic wave simulator. The SE of the proposed the CCM was improved by approximately 4 dB in the X band compared to that of a conventional CCM. The CCM proposed in this paper can be applied as a shielding material as well as for housing of various communication systems and electrical instruments.

We proposed and analyzed a fiber-reinforced ceramic (FRC) composite for a protection layer on top of an antenna mounted on the outer surface of aircraft. The manufactured FRC is a single-layered flat construct. To analyze the performance of the FRC, we extracted the material constant using the transmission/reflection (T/R) method. We described the relation between the pressure and strength of the FRC radome with respect to mechanical properties and analyzed the insertion loss with respect to electrical properties. We evaluated the characteristics of the FRC radome in conjunction with the horn antenna and showed that the analytic results for the FRC radome agree with the experiment results.

In this letter, the system capacity of multiuser diversity combined with spatial multiplexing schemes is analyzed. An analytic expression is derived for the ergodic system capacity with multiuser scheduling and dual multi-input multi-output (MIMO) systems by using a tight lower bound of the link capacity. The proposed analytic approach is verified through comparisons between analytic and simulated results, and is shown to make fairly precise predictions of the ergodic system capacity and the scheduling gains even when the numbers of antennas and users are small.

A low-loss ultra-wide band (UWB) filter is presented, which uses miniaturized parallel coupled line along with an standard printed circuit board (PCB) technology. By analyzing even- and odd-mode impedances (in comparison with conventional parallel coupled lines) of miniaturized parallel coupled line, this structure provides tight coupling, thus, relaxing the requirements on physical dimensions width and spacing when designing broadband filters. A bandpass filter for Mode 1 (the first 3 sub-bands) in the 3.1-5 GHz band for Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) UWB is realized and compared with a conventional parallel coupled line filter. The experimental results show as much as 0.9 dB insertion loss improvement over the conventional counterpart.

To improve path loss estimation, a ray tracing method for inhomogeneous building surfaces and its verification are presented in this paper. Considering real building surfaces with many heterogeneous materials, the effective specular reflection based on a physical optics (PO) approximation is modeled and applied to the reflection in a ray tracing method. To verify the proposed method, measurement at 2.7 GHz is performed in a complex urban environment. Comparisons between the measurements and the ray tracing results are made in LOS and NLOS environments.

Based on the substrate integrated waveguide (SIW) technology, a new type of varactor-tuned radial power divider has been developed with a single bias supply. The varactors are used as tuning elements and allow for a frequency agile behavior. In addition, bandwidth characteristics have been analysed with group-delay. It has been measured with a single bias supply ranging from 6 V to 12 V that the center frequency of the power divider can be adjusted from 6.6 GHz to 7.2 GHz (600 MHz, 11.5%) while maintaining a low insertion loss (< 1 dB) in the passband.