The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, (MIMO-CEM), as a power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks in which relay nodes are fixed in their positions. One of the major problems hindering the real application of MIMO-CEM is to estimate MIMO channel characteristics. MIMO-CEM is based upon two contrary schemes; one is nonlinear equalization such as maximum likelihood sequence estimator, which needs accurate channel information to replicate the received signal passing through it. The other is a low resolution analog-to-digital converter (ADC), e.g., 1-bit in the default operation that removes the received signal amplitude fluctuation. In this paper, as a solution to the channel estimation problem in MIMO-CEM with low resolution ADC receiver, we propose an adaptive MIMO-CEM channel estimation scheme where iterative adaptive channel estimation is carried out to minimize the error between the received preamble signal and the replicated one. We also prove that Code Division Multiplexing (CDM) preamble transmission is effective in estimating MIMO channel parameters in the presence of large quantization noise. Computer simulation results show that MIMO-CEM with the proposed channel estimator using CDM preambles achieves identical BER performance to that with the ideal channel estimation even in presence of severe quantization noise caused by a low resolution ADC.

A wideband, low noise, and highly linear transmitter for multi-mode radio is presented. Envelope injection scheme with a CMOS amplifier is developed to obtain sufficient linearity for complex modulation schemes such as OFDM, and to achieve low noise for concurrent operation of more than one standard. Active matching technique with doubly terminated LPF topology is also presented to realize wide bandwidth, low power consumption, and to eliminate off-chip components without increasing die area. A multi-mode transmitter is implemented in a 0.13 µm CMOS technology with an active area of 1.13 mm2. Third-order intermodulation product is improved by 17 dB at -3 dBm output by the envelope injection scheme. The transmitter achieves EVM of less than -29.5 dB at -3 dBm output from 0.2 to 7.2 GHz while consuming only 69 mW. The transmitter is also tested with multiple standards of UMTS, 802.11b, WiMax, 802.11a, and 802.11n, and satisfies EVM, ACLR, and spectrum specifications.

An analog pre-distortion linearizer employing a radio frequency (RF) transistor with a self base bias control circuit is proposed. The self base bias control circuit extracts the envelope from the modulated input RF signal of the RF transistor and automatically controls its base current according to the extracted envelope. As a result, the proposed linearizer realizes positive gain deviation at high input power level. By adding a resistor between the RF transistor and the self base bias control circuit, the negative gain deviation can be derived. The design of the proposed lineaizer is described with taking the envelope frequency response of the self base bias control circuit into consideration. The fabricated linearizer achieves the adjacent channel power leakage ratio (ACLR) improvement of 8.1 dB for a 2 GHz-band, 10 W-class GaAs FET high-power amplifier (HPA) with negative gain deviation for W-CDMA base stations. It also achieves the ACLR improvement of 8.3 dB for a LDMOS HPA with positive gain deviation for the same application.

A circuit technique to correct Vdd/PM distortion and improve efficiency as supply modulation of cascode class-E PAs has been proposed. The experimental result shows that the phase distortion can be improved from 20 degrees to 5 degrees. Moreover, a system co-simulation result demonstrated that the EVM can be improved from -17 dB to -19 dB.

This paper presents the mixed time-frequency steady-state analysis method for efficient simulation of circuits whose excitation frequencies are widely separated. These circuits can be written by multitime partial differential equations. In this paper, an axis of the slow time-scale is formulated in the time domain and another axis of the fast time-scale is formulated in the frequency domain. We show that computational cost, however, is not dependent on the interval of frequencies, whereas for the harmonic balance or transient analysis, it increases as the interval of frequencies increases.

This Letter proposes an optimal gain filter for the perceptual acoustic echo suppressor. We designed an optimally-modified log-spectral amplitude estimation algorithm for the gain filter in order to achieve robust suppression of echo and noise. A new parameter including information about interferences (echo and noise) of single-talk duration is statistically analyzed, and then the speech absence probability and the a posteriori SNR are judiciously estimated to determine the optimal solution. The experiments show that the proposed gain filter attains a significantly improved reduction of echo and noise with less speech distortion.

In this paper, a criterion for nonlinear stability analysis of microwave oscillator has been devised. The circuit envelope method has been used for analyzing the perturbed circuit. The proposed approach is evaluated by analyzing the nonlinear stability of a practical FET oscillator.

In this paper, an automatic identification method based on frequency discrimination is proposed. The proposed method can be used when the received signal is a constant envelope modulation scheme. To test the proposed method PSK and FSK are considered. Using computer simulations, the performance of the proposed method was evaluated and found to be able to distinguish between PSK and FSK well even in the presence of noise.

Target shape estimation with UWB pulse radars is a promising imaging technique for household robots. We have already proposed a fast imaging algorithm, SEABED, that is based on a reversible transform BST (Boundary Scattering Transform) between the received signals and the target shape. However, the target image obtained by SEABED deteriorates in a noisy environment because it utilizes a derivative of received data. In this paper, we propose a robust imaging method with an envelope of circles. We clarify by numerical simulation that the proposed method can realize a level of robust and fast imaging that cannot be achieved by the original SEABED.

We describe an online method for selecting and annotating highlight scenes in soccer matches being televised. The stadium crowd noise and the play-by-play announcer's voice are used as input signals. Candidate scenes for highlights are extracted from the crowd noise by dynamic thresholding and spectral envelope analysis. Using a dynamic threshold solves the problem in conventional methods of how to determine an appropriate threshold. Semantic-meaning information about the kind of play and the related team and player is extracted from the announcer's commentary by using domain-based rules. The information extracted from the two types of audio input is integrated to generate segment-metadata of highlight scenes. Application of the method to six professional soccer games has confirmed its effectiveness.

A low-band spectrum envelope reconstruction method was tested to see if it could improve the sound quality of F0 modified speech with the PSOLA (Pitch Synchronous OverLap Add) method. In the conventional PSOLA method, the extracted spectrum envelope using a Hanning window with two-pitch-period length had no reliable information in the band of frequencies lower than the original F0. This problem causes sound degradation of the F0 modified speech when the F0 is shifted downward. In the proposed method, the low-band spectrum envelope was properly modified according to the F0 modification rate. The amplitude of the F0 harmonic components in the low-band were reproduced based on the spectral tilt of the spectrum envelope. Subjective listening tests suggest the proposed method yields improved sound quality than the conventional TD-PSOLA method when the downward modification rate exceeds 0.4 octave.

This paper deals with CE-SS (Constant-Envelope Spread Spectrum) signals, focusing on a novel generation technique based upon using digital processing blocks to drive a frequency modulator with a random sequence. The system described herein allows for flexibility in achieving a variety of user defined goal spectra. The foundation upon which this work is built was laid by Callegari et al. who introduced a novel synthesis procedure for 'non-stationary' modulations. This novel synthesis technique uses an iterative algorithm to arrive at an output spectrum which is a good approximation to a user-defined goal spectrum. The architecture which this paper details uses programmable logic to tune the system parameters in striving towards user defined goal spectra. The architecture can generate CE-SS waveforms whose spectra match those which the aforementioned algorithm deems achievable.

A field trial, within a suburban macro-cell environment, of a space-time (ST) equalizer for TDMA mobile communication systems is described. The ST equalizer was a cascade connection of two array processors for a four-antenna array and a two-branch-metric-combining maximum-likelihood sequence estimation (MLSE) that was designed to obtain full space- and path-diversity gains from first-arrival and one-symbol-delayed signals while suppressing excessively long-delayed inter-symbol interference (ISI). The radio frequency was 3.35 GHz, the transmission rate was 4.096 Mb/s, and the modulation was QPSK. The long-delayed ISI reduction and the space-path diversity effect of the ST equalizer was validated by Eb/N0 vs. bit-error-rate (BER) curves with respect to delay spread and antenna spacing as compared with the case of an array processor alone being used.

Signal fading due to multipath propagation severely impairs the performance of high speed mobile communication systems. The probability density function (PDF) for the envelope of the received signal using STTD (Space Time Transmitter Diversity) over correlated Nakagami fading channels with additive white Gaussian noise (AWGN) is derived in this paper. System performances of noncoherent signals over slow and flat fading channels in the presence of AWGN can be evaluated from this new PDF.

Multi-level divide-and-conquer (MDC) is a generalized divide-and-conquer technique, which consists of more than one division step organized hierarchically. In this paper, we investigate the paradigm of the MDC and show that it is an efficient technique for designing parallel algorithms. The following parallel algorithms are used for studying the MDC: finding the convex hull of discs, finding the upper envelope of line segments, finding the farthest neighbors of a convex polygon and finding all the row maxima of a totally monotone matrix. The third and the fourth algorithms are newly presented. Our discussion is based on the EREW PRAM, but the methods discussed here can be applied to any parallel computation models.

P-complete problems seem to have no parallel algorithm which runs in polylogarithmic time using a polynomial number of processors. A P-complete problem is in the class EP (Efficient and Polynomially fast) if and only if there exists a cost optimal algorithm to solve it in T(n) = O(t(n)ε) (ε < 1) using P(n) processors such that T(n) P(n) = O(t(n)), where t(n) is the time complexity of the fastest sequential algorithm which solves the problem. The goal of our research is to find EP parallel algorithms for some P-complete problems. In this paper first we consider the convex layers problem. We give an algorithm for computing the convex layers of a set S of n points in the plane. Let k be the number of the convex layers of S. When 1 k nε/2 (0 ε < 1) our algorithm runs in O((n log n)/p) time using p processors, where 1 p n1-ε/2, and it is cost optimal. Next, we consider the envelope layers problem of a set S of n line segments in the plane. Let k be the number of the envelope layers of S. When 1 k nε/2 (0 ε < 1), we propose an algorithm for computing the envelope layers of S in O((n α(n) log3 n)/p) time using p processors, where 1 p n1-ε/2, and α(n) is the functional inverse of Ackermann's function which grows extremely slowly. The computational model we use in this paper is the CREW-PRAM. Our first algorithm, for the convex layers problem, belongs to EP, and the second one, for the envelope layers problem, belongs to the class EP if a small factor of log n is ignored.

The distribution for the envelope of the received signal over frequency-nonselective slow fading channels with additive white Gaussian noise (AWGN) is derived in this paper. System performances of noncoherent M-ary signals over slow and flat fading channels in the presence of AWGN can be evaluated from the new probability density function (PDF) of the envelope.

This paper formulates problems of fitting two corresponding sets of points by translation, rotation and scaling, and proposes efficient algorithms for the fitting. The algorithms are based on the theory of lower envelopes, or Davenport-Schinzel sequences, and linearization techniques in computational geometry, and are related to dynamic furthest Voronoi diagrams.

This paper presents algorithms for computing the Minkowski sum of two polygons P and Q for a family of problems. For P being convex and Q being monotone, an algorithm is given with O (nm) time and space complexity. For both P and Q being monotone polygons, an O (nm log nm) time algorithm is presented and it is shown that the complexity of the sum is Θ (nmα(min(n,m))) in the worst case, where α() is the inverse of Ackermann's function. Finally, an O ((nm+k)log nm) time complexity algorithm is given when P is monotone and Q is simple, where k in the worst case could be Θ(n2m). The complexity of P Q is shown to be Θ(n2m) in the worst case. Here, m and n denote the number of edges of P and Q, respectively.

A kind of time domain reflectometry using deconvolution and envelope extraction process is presented for measuring microwave resonator characteristics, where data acquisition and data processing are performed entirely in the time domain. The proposed method may be used to characterize resonators which have Q values in the range between a few dozen and several hundred. The major drawback of the time domain measurement techniques is in general considered to be a low frequency resolution. In the proposed method, it is avoided skillfully.