This letter deals with blind multiuser detection based on the multi-channel linearly constrained constant modulus algorithm (MLCCMA) for asynchronous code division multiple access (CDMA) systems over frequency-selective Rayleigh fading channels. In conjunction with the decision-feedback generalized sidelobe canceller (DFGSC), we present an efficient approach to combat multiple access interference and intersymbol interference. Computer simulations confirm that the proposed MLCCMA-based DFGSC can significantly speed up convergence and improve the output performance.

The performance of the blind multiuser detector for a DS-CDMA system with linearly constrained constant modulus (LCCM) criterion is known to highly depend on the exact knowledge of the desired user amplitude; it is usually not available at receiver end. In this paper, we propose a novel LC adaptive CM RLS (LC-ACM-RLS) algorithm to adaptively implement the optimal solution of the LCCM receiver, and to track the desired user's amplitude, simultaneously. From computer simulations, we verify the superiority of the new proposed algorithm over the conventional LCCM-RLS algorithm for multiple access interference (MAI) suppression. Also, for time-varying channel during the adaptation processes, if the amplitude of desired user is not available and varies with time, such as hand-off and Rayleigh fading environments, we show that the proposed LC-ACM-RLS algorithm has better tracking capability compared with the conventional approaches.

A novel blind channel estimation scheme is proposed for OFDM systems employing PSK modulation. This scheme minimizes the number of possible channels by exploiting the constant modulus property, chooses a best fit over the possible channels by exploiting the finite alphabet property of information signals, and achieves competitive performance with low computational complexity. Results comparing the new scheme with the finite-alphabet based channel estimation are presented.

To support high data rate wireless communications, in this paper, based on the linearly constrained constant modulus (LCCM) criterion, the reverse link performance of the multi-carrier code division multiple access (MC-CDMA) receiver, with frequency combiner, and having smart antenna arrays beamformer in base station, has been investigated over the Rayleigh fading channel. By using the Kronecker product an equivalent direct formulation, which integrates the information of spatial-domain as well as temporal-domain, with constraint matrix could be obtained. In consequence, the modified normalized LCCM-gradient algorithm is devised to adaptively implement the direct constrained optimal weights solution of the fully space-time MC-CDMA detector. We show that the proposed method outperforms the constrained minimum output energy (CMOE) algorithm and is more robust against to the signal mismatch, due to imperfect channel and direction-of-arrival estimation used in the array beamformer.

We describe a simplified receiver structure having several receiving antennas (i.e., an adaptive array antenna system) and using time-division-multiplexing (TDM) signal processing. Three simplified receiver structures were investigated for use in the antenna system. To confirm the feasibility of using a TDM receiver, both a TDM receiver and a conventional adaptive array receiver were constructed for testing. In our proposed system, several repetitions of the constant modulus algorithm (CMA) are used to reduce co-channel interference (CCI). The frame format used for both receivers was the same as that of the personal handy phone system in Japan. The laboratory testing was done using a fading simulator to enable measurement of the bit error rate. The results are very promising and show the feasibility of the TDM receiver.

The multiple access causes an interference problem in the direct-sequence code-division multiple access systems. An efficient adaptive algorithm should be used to suppress this interference for the improvement of system performance. In this paper, the new blind adaptive method is suggested using the constant modulus algorithm for the purpose of interference suppression. Simulation results show that the converged value of signal to interference ratio for the proposed method is approximately 6 [dB] larger than that of a conventional Blind-MOE receiver in the additive white Gaussian noise channel and channel with inter-symbol interference while the signal to interference ratio improvement is almost 4 [dB] better in the Rayleigh fading channel. The suggested method is also robust to the new user interference resulting the nearly 3 [dB] improvement of the SIR value comparing with the conventional receiver. Based on these results, it is shown that the BER of the proposed receiver is lower than that of any other conventional receiver. Therefore, using the newly suggested method, the considerable performance improvement can be obtained for the DS-CDMA systems.

The constant modulus algorithm (CMA) of the adaptive array has been developed for suppressing the co-channel interference and the intersymbol interference in mobile communications. In this paper a novel CMA for the hybrid of the adaptive array and equalizer (HAE) is proposed to combat the problems of insufficient degrees of freedom and mainbeam multipath interferers. The HAE with CMA utilizes the constant modulus property for the output signal of the HAE to adjust the weight vectors of the array and equalizer simultaneously. The co-channel interferers can be canceled by the array and the multipath interferers can be removed by the array or the equalizer following the array in the HAE. Therefore, the array in the HAE with CMA may need less number of elements than that required by the CMA array which cancels both the co-channel interferers and multipath interferers. Besides, the presence of the mainbeam multipath interferers, which may seriously degrade the performance of the CMA array, has much less effect on the HAE with CMA since it can be suppressed by the equalizer instead of the array. Simulation results are presented to demonstrate the merits of the CMA for the HAE.

We have proposed a non-invasive method for diagnosis of the early stage of atherosclerosis, namely, the detection of small vibrations on the aortic wall near the heart by using ultrasound diagnostic equipment. It is, however, necessary to confirm the effectiveness of such measurement of the pulse wave velocity for quantitative evaluation of the local characteristics of atherosclerosis. It is well known that Young's modulus of a tube wall, estimated from measured pulse wave velocity, depends on inner pressure because of the non-linear relationship between the inner pressure and the change of volume in the tube. The inner pressure, however, changes during the period of one heartbeat. In this experimental study, we found for the first time that Young's modulus of the tube wall, estimated from the measured pulse wave velocity, depends not only on the diastolic pressure but also on the pulse pressure and the pressure gradient of the systolic period.

A noble blind equalization algorithm (BEA) using a single/multilevel modulus is proposed. According to the residual intersymbol interference (ISI) level of the equalizer output, the new algorithm adopts relevantly a single modulus or a multilevel modulus to form its cost function. Moreover, since the proposed approach separates complex two-dimensional signal into in-phase and quadrature components, and forms the error signals for each component, it has inherently the capability of phase recovery. Hence, it improves the performances of steady-state and recovers the phase rotation without any degradation of transient property. Simulation results confirm the effectiveness of the new approach.

In this letter, we propose a blind adaptation method for the decision feedback equalizer (DFE). In the proposed scheme, a DFE is divided into two parts: a front-end linear equalizer (LE), and a prediction error filter (PEF) followed by a feedback part. The coefficients of the filters in each part are updated using constant modulus algorithm and decision feedback prediction algorithm, respectively. The front-end LE removes intersymbol interference ISI, and the PEF with feedback part whitens the noise to reduce noise power enhanced by the LE. Pre-processing by the LE enables the DFE to equalize nonminimum phase channels. Simulation results show that the proposed scheme provides reliable convergence, and the resulting symbol error rate is much less than that of the conventional LE and very close to that of the DFE using a training sequence.

In order to estimate elasticity distribution of living soft tissue by ultrasonic pulse-echo method, we developed an algorithm by which we estimate 2-D displacement vector field from two successive rf echo data frames. The algorithm estimates a displacement vector iteratively by matching the phase characteristics of the local regions of two data frames. The estimation process is composed of coarse one and the fine one. In the coarse estimation process, the displacement is estimated by detecting the peak of the 2-D cross-correlation function. In the fine process, the displacement is estimated iteratively by shifting the 2nd frame data so that the phase characteristics matches with that of the 1st frame data. In each iterative step of both processes, the estimated displacement vector field is spatially smoothed. This proposed algorithm exhibits excellent performance in obtaining accurate and smooth distribution of displacement vector which is required to obtain strain distribution and finally shear modulus distribution. We conducted an experiment on an agar phantom which has inhomogeneous shear modulus distribution. Using the proposed method, we obtained 2-D displacement field with reasonable accuracy. We reconstructed a relative shear modulus map using axial strain assuming 1-D stress condition. The reconstructed map using the calculated axial strain through 2-D displacement estimation algorithm was satisfactory, and was clearly superior to the one through 1-D displacement estimation algorithm. The proposed 2-D displacement field estimation algorithm seems to be a versatile and powerful tool to measure strain distribution for the purpose of tissue elasticity estimation under various deformation conditions.