Independent shadowing losses are often assumed for computing the frequency reuse distance of cellular mobile communication systems. However, shadowing losses may be partially correlated since the obstacles surrounding a mobile station block similarly the desired signal and interfering signals. We investigate, by computer simulation, how the shadowing correlation impacts the frequency reuse distance of a power controlled cellular system. It is pointed out that the shadowing correlation impacts the frequency reuse distance differently for the uplink and downlink.

The joint use of frequency-domain equalization and antenna diversity is presented for single-carrier (SC) transmission in a frequency-selective fading channel. Frequency-domain equalization techniques using minimum mean square error (MMSE), orthogonal restoration combining (ORC) and maximum ratio combining (MRC), those used in multi-carrier code division multiple access (MC-CDMA), are considered. As antenna diversity techniques, receive diversity and delay transmit diversity (DTD) are considered. Bit error rate (BER) performance achievable with the joint use of frequency-domain equalization and antenna diversity is evaluated by computer simulation.

Orthogonal multicode direct sequence code division multiple access (DS-CDMA) has the flexibility in offering various data rate services. However, in a frequency-selective fading channel, the bit error rate (BER) performance is severely degraded since the othogonality among spreading codes is partially lost. In this paper, we apply frequency-domain equalization and antenna diversity combining, used in multi-carrier CDMA (MC-CDMA), to orthogonal multicode DS-CDMA in order to restore the code othogonality while achieving frequency and antenna diversity effect. It is found by computer simulations that the joint use of frequency-domain equalization and antenna diversity combining can significantly improve the BER performance of orthogonal multicode DS-CDMA in a frequency-selective fading channel.

In this letter, we propose joint frequency offset and SNR estimation technique. The frequency offset may degrade the system performance greatly by deleterious effect. The proposed frequency offset estimation technique estimates frequency offset by employing the interpolation technique in the frequency domain. Also we propose SNR estimation technique using the estimated frequency offset for FFT-based system. The SNR estimated by the receiver can be used to adapt the demodulation algorithm to enhance its performance, as well as to provide the channel quality information. Simulation results show the performance of frequency offset and SNR estimator.

Multi-Carrier Code Division Multiple Access (MC-CDMA) is one of candidates for the next generation wireless communication systems. In an uplink, the MC-CDMA system suffers from the different access timing (asynchronous transmission), the different fading, and the different frequency offsets of each active user. In this paper we analyze the effects of the frequency offset compensation with MMSE-MUD (minimum mean square error based multi-user detection) for MC-CDMA in a quasi-synchronous uplink. We consider the MC-CDMA system with two subcarrier mapping schemes, the continuous mapping scheme and the discrete mapping scheme. From our theoretical analysis and computer simulation, we show that the MMSE-MUD can compensate the different frequency offsets among users. We also show that the MMSE-MUD significantly improves the bit error rate (BER) for the MC-CDMA system with the continuous mapping scheme.

This paper describes a 2.4-GHz downconverter that runs on a 1-V supply. The downconverter integrates an LNA, a quadrature mixer, a complex channel-select band-pass filter (BPF), a limiting amplifier, and a frequency doubler using 0.2-µm CMOS/SOI technology. The frequency doubler doubles the frequency deviation of FM signals as well as the frequency itself, which in turn doubles the modulation index. This improves the sensitivity of FM demodulation. The power consumption of the downconverter is 23 mW with a 1-V power supply. A bit-error-rate (BER) measurement using the downconverter and a demodulation IC shows -76.5-dBm sensitivity at a 0.1% BER.

In this paper, we propose a method of linear time-varying filtering of discrete time signals. The objective of this method is to derive a component, of an input signal, whose alias-free generalized discrete time-frequency distribution [Jeong & Williams 1992] concentrates on a specific region of a time-frequency plane. The method is essentially realized by computing an orthogonal projection of an input onto a subspace that is spanned by orthonormal signals, whose distributions concentrate on the region. We show that such orthonormal signals can be derived as eigenvectors of a matrix whose components are explicitly expressed by using the kernel of the distribution and the regions. This result shows that we can design such a filter prior to processing of the input if the specific region is given as a priori. This result is a generalization of [Hlawatsch & Kozek 1994], that is originally derived for the continuous Wigner distributions, to the discrete distributions.

Design approach to improving fmax of InP-based HBTs by combining lateral scaling (lithographic scaling) and vertical scaling (improving fT) is discussed. An HBT scaling model is formulated to provide means of analyzing the essential impact of scaling on fmax. The model was compared with measurements of single and double heterojunction bipolar transistors with different fT and various emitter sizes. While a high fmax of 313 GHz was achieved using submicron HBT with high fT, it was found that further improvement could have been obtained by reducing the emitter resistance, which has imposed considerable limit on lateral scaling.

A fully integrated RF front-end for W-CDMA applications including a low noise amplifier, a down conversion mixer, a digitally programmable gain amplifier, an on-chip VCO, and a fractional-N frequency synthesizer is designed using a 0.35-µm CMOS process. A multi-stage ring shaped on-chip LC-VCO exhibiting bandpass characteristics overcomes the limitation of low-Q components in the tank circuits and improves the phase noise performance. The measured phase noise of the on-chip VCO is -134 dBc/Hz at 1 MHz offset. The receiver RF front-end achieves a NF of 3.5 dB, an IIP3 of -16 dBm, and a maximum gain of 80 dB. The receiver consumes 52 mA with a 3-V supply and occupies only 2 mm2 die area with minimal external components.

This paper proposes a noise robust speech recognition method using prosodic information. In Japanese, the fundamental frequency (F0) contour represents phrase intonation and word accent information. Consequently, it conveys information about prosodic phrases and word boundaries. This paper first describes a noise robust F0 extraction method using the Hough transform, which achieves high extraction rates under various noise environments. Then it proposes a robust speech recognition method using multi-stream HMMs which model both segmental spectral and F0 contour information. Speaker-independent experiments are conducted using connected digits uttered by 11 male speakers in various kinds of noise and SNR conditions. The recognition error rate is reduced in all noise conditions, and the best absolute improvement of digit accuracy is about 4.5%. This improvement is achieved by robust digit boundary detection using the prosodic information.

High-frequency characteristics of SiGe heterojunction bipolar transistors with different emitter sizes are studied based on pulsed measurements. Because the self-heating effect in transistors will enhance the Kirk effect, as the devices operate in high current region, the measured cutoff frequency and maximum oscillation frequency decrease with measurement time in the pulsed duration. By analyzing the equivalent small-signal device parameters, we know the reduction of cutoff frequency and maximum oscillation frequency is attributed to the reduction of transconductance and the increase of junction capacitances for fixed base-emitter voltage, while it is only attributed to the degradation of transconductance for fixed collector current. Besides, the degradation of high-frequency performance due to self-heating effect would be improved with the layout design combining narrow emitter finger and parallel-interconnected subcells structure.

This paper considers a wireless LAN system operated in a multiple-cell environment with universal frequency reuse. A key technical goal is to increase cell-capacity within a cell. A very high-rate wireless LAN system, maximum data rates of over 100 Mbit/s, is proposed that offers an expanded signal-bandwidth compared to that specified in IEEE802.11a. The system employs OFDM and MC/CDMA signals in packet mode. It falls back from OFDM signals with low subcarrier modulation orders to MC/CDMA signals. A link level performance comparison shows that OFDM has superior performance to MC/CDMA at over 32 Mbit/s. Under 16 Mbit/s, however, MC/CDMA can establish wireless link connections unlike OFDM. Thus the fallback technique, which is triggered by the CIR environment, should select OFDM if the data rate exceeds 32 Mbit/s. It should fallback to MC/CDMA if the rate is less than 16 Mbit/s. We also evaluate the proposed scheme in a multiple-cell environment with universal frequency reuse, where the severe co-channel (other-cell) interference is present. We derive a cell capacity criterion for wireless LAN systems, and show that the proposed scheme offers a 2.2 times larger available transmission distance than the OFDM-only scheme. In addition, it is found that the proposed scheme offers a 1.3 times improvement in cell capacity compared to the MC/CDMA-only scheme, even if all other-cell interference is considered.

The rapid spread of cellular phones in recent years has facilitated not only voice communication but also Internet access via the cellular phone system, and in addition, subscriber demand has led to a diversification in the services provided. One service in high demand is the seamless use of cellular phones in both public and private wireless network areas. In the data world, there is already such an application in the form of public and private use of wireless LAN. However, an increase in the number of users would require the realization of low-cost, easy-to-install very small base stations (VSBS) that use the frequency band efficiently in order to allow private use of ordinary cellular phones. To bring such VSBS into effect, a technology that autonomously selects frequencies which do not interfere with the public communication system from out of the publicly used frequency band is essential for turning such VSBS into reality. This paper proposes a frequency selection algorithm that actively uses cellular phone features such as frequency selection and received signal level measurement, and discusses the results of verification experiments.

The complex dielectric image Green's function for metal-insulator-semiconductor (MIS) technology is proposed in this paper through dielectric image method. Then the Epsilon algorithm for Pade approximation is used to accelerate the convergence of the infinite series summation resulted from the complex dielectric image Green's function. Because of the complex dielectric permittivity of semiconducting substrate, the real and imaginary part of the resulted Green's function is accelerated by Epsilon algorithm, respectively. Combined with the complex dielectric image Green's function, the frequency-dependent capacitance and conductance of the transmission lines and interconnects based on MIS technology are investigated through the method of moments (MoM). The computational results of our method for 2-D and 3-D extraction examples are well agreement with experimental data gained from chip measurement and other methods such as full-wave analysis and FastCap.

In this paper, we derive expressions for the bit error probability of QPSK/OFDM on frequency-selective Rayleigh fading channels. In the OFDM system, ICI (interchannel interference) caused by Doppler spread of the channel degrades the error performance of the system and introduces the error floor even for coherent detection. Analysis results show that the error performance of QPSK/OFDM can be degraded as the normalized maximum Doppler frequency fD /Bsub is increased where fD is the maximum Doppler frequency and Bsub is the subchannel bandwidth. Computer simulations confirm the theoretical analysis results for BPSK and QPSK signals.

Band Division MC-CDM (BD-MC-CDM) has been proposed for high quality wireless communications and has been investigated in terms of link level performance. In this paper, we investigate frequency band and time slot selection technique from the viewpoint of system level performance in order to realize the efficient BD-MC-CDM system under cellular environments. Then a downlink frequency band and time slot selection scheme is proposed for cellular BD-MC-CDM systems. The proposed scheme selects transmission frequency band according to the signal-to-interference ratio (SIR) estimated by using the pilot signal at mobile stations and also selects transmission time slot by using the SIR threshold. Simulation results show that the proposed scheme improves the downlink throughput but degrades delay performance and it has a trade off between throughput and delay performance. By selecting suitable control parameters, the proposed scheme achieves the throughput improvement without sacrificing the delay performance.

In this letter, a receive frequency diversity technique is proposed to improve the performance of a multiplexed STBC OFDM system. Frequency diversity in the multiplexed STBC OFDM system is obtained by introducing frequency shifter in the successive STBC symbols and applying MRRC technique to regenerated and subtracted signals of the predecoded data from multiplexed STBC decoder. It is shown by computer simulation that the performance of the proposed multiplexed STBC OFDM systems with frequency diversity is improved by 5 dB at the BER of 10-3 over the existing multiplexed STBC OFDM systems with the same data rate.

This paper proposes new frame synchronizers that can achieve frame sync in the presence of a frequency offset. In particular, a maximum likelihood (ML) algorithm for joint frame synchronization and frequency estimation is developed for additive white Gaussian noise (AWGN) channels, then the result is extended to frequency selective channels. Computer simulations demonstrate that the proposed schemes can outperform existing methods when a frequency offset exists.

We propose a novel optical signal processing using an optically pumped vertical-cavity surface-emitting laser (VCSEL) with an external light input. The mode transition between a fundamental and a 1st-high-order transverse mode is induced by an external light injection. Since a single mode fiber (SMF) spatially selects a fundamental transverse mode as an output signal, we are able to realize a nonlinear transfer function, which will be useful in future photonic networks. The mode transition characteristic of a 1.55 µm optically pumped two-mode VCSEL has been simulated by using a two-mode rate equation, which includes the effects of spatial hole burning and spectral hole burning as gain saturation coefficients. We focus on the detuning effect in the injection locking. When the wavelength of an input light with a fundamental mode is slightly longer than that of a VCSEL operating in a 1st-high-order transverse mode, the transverse mode of the VCSEL is switched to a fundamental mode at a critical input power level. This gives us an ideal transfer function for 2R (reamplification and reshaping) regeneration. Also, the proposed scheme may enable polarization insensitive signal processing, which is a unique feature in surface emitting lasers.

Two simple frequency offset estimators based on projection approaches for multicarrier code-division multiple access systems are proposed, without using specific training sequences. It is not only can estimate and correct frequency offset, but also has less computational load. Several computer simulations are provided for illustrating the effectiveness of the blind estimate approaches.