Bub-Joo Kang

On the performance of a maximum-likelihood code-acquisition technique for preamble search in a CDMA reverse link

The performance of a maximum likelihood (ML) code-acquisition technique is analyzed for slotted-mode preamble search in the code-division multiple access (CDMA) reverse link. The probabilities of detection, miss, and false alarm are derived analytically for multiple H/sub 1/ cell cases, based on the statistics of the CDMA noncoherent demodulator output in a frequency-selective Rayleigh fading channel. The probability density function (PDF) of a decision variable is also derived by considering the fading characteristics of the received signal for both single- and dual-antenna cases. The performance of the code-acquisition technique is evaluated numerically with emphasis on the effects of postdetection integration, fading rate, antenna diversity, and so on.

Hybrid acquisition in DS/CDMA forward link

The evaluation of a hybrid acquisition performance has been considered for the pilot signal in the direct sequence code division multiple access (DS/CDMA) forward link. The hybrid acquisition is introduced by the combination of two schemes, parallel and serial acquisitions. The mean acquisition time of the proposed scheme is derived by considering both case 1 (the correct code-phase offsets are included in one subset) and case 2 (the correct code-phase offsets exist at the boundary of two subsets), which are caused by the distribution of correct code-phase offsets in the subset. Detection, false alarm, and miss probabilities are derived for the cases of multiple correct code-phase offsets and multipath Rayleigh fading channel. Results are provided for the acquisition performance with respect to design parameters such as postdetection integration length in search and verification modes, subset size, and number of I/Q noncoherent correlators. Also, comparison between the hybrid acquisition and the fully parallel acquisition is provided in terms of the minimum mean acquisition time.

An adaptive channel precoded space-time transmitter for 3GPP TDD system

An adaptive channel precoded transmitter for space-time block coding based transmit diversity (STTD) is developed for a 3GPP WCDMA TDD system. Since all the functions of precoding are implemented in the base station, the channel equalization process can be left out in the mobile station. This results in the minimization of hardware complexity of the portable unit. Simulation results show that the adaptive channel precoded transmitter gives a close performance to the conventional Rake combiner.

Access channel slot acquisition in cellular DS/CDMA reverse link

This paper presents design parameters such as postdetection integration length and number of access channel message block repetitions in terms of the mean acquisition time and the mean slot acquisition time in IS-95 reverse link. The uncertainty region of the reverse link compared to that of the forward link is very small, since the uncertainty region of the reverse link is due to the cell radius. Thus the parallel acquisition technique is more efficient than the serial acquisition technique in view of the implementation and the acquisition time in the reverse link. The parallel acquisition is done by a bank of N parallel I/Q noncoherent correlators. The output characteristic of an I/Q noncoherent correlator is analyzed for the band-limited and Rayleigh fast fading channel. The independent fading of all users is assumed. The detection and no message error probabilities are derived for the multiple H/sub 1/ hypotheses and the multipath fading. The numerical results show the suboptimum choice of design parameters such as postdetection integration length and number of access channel message block repetitions in the case of a random access of a mobile station.

Performance analysis of double-dwell serial search technique in case of multiple pilot signals

In this paper, the performance of the double-dwell serial search technique is analyzed in the forward link of a cellular CDMA system in the case of multiple pilot signals. A general expression for the mean acquisition time is obtained by taking into account the multiple H/sub 1/ regions due to the pilot signals coming from different base stations. The detection and false alarm probabilities of the processor with CFAR characteristics are derived analytically in a frequency-selective Rayleigh fading channel. The performance of the code acquisition technique is evaluated numerically to investigate the effects of threshold setting, post-detection integration in the verification mode, fading rate, and so on, with an emphasis on the worst case where the mobile is located around the cell boundary.

Space-time block coding based transmit diversity using an adaptive channel precoder for WCDMA system

An adaptive channel precoded transmitter for space-time block coding based transmit diversity (STTD) is developed for a 3GPP WCDMA TDD system. Since all the functions of precoding are implemented in the base station, the channel equalization process can be left out in the mobile station. This results in the minimization of hardware complexity of the portable unit. Simulation results show that the adaptive channel precoded transmitter gives a close performance to the conventional RAKE combiner.

A maximum-likelihood technique for preamble search in a CDMA reverse link

The performance of a maximum-likelihood code acquisition technique is analyzed for slotted-mode preamble search in a CDMA reverse link. The probabilities of detection, miss, and false alarm are derived analytically for a frequency-selective Rayleigh fading channel by taking into account the fading characteristics of a received signal for both single and dual antenna cases. Numerical examples illustrate the effects of post-detection integration, fading rate, and antenna diversity on the code acquisition performance.

Performance evaluation of parallel acquisition in cellular DS/CDMA reverse link

This paper evaluates the acquisition probability and mean acquisition time of the double-dwell and single-dwell detection schemes for the parallel acquisition system, in the IS-95 reverse link. The parallel acquisition is performed by N parallel I/Q noncoherent correlators. The detection, false alarm, and missing probabilities for the single-dwell and double-dwell detection schemes are evaluated over the multiple H/sub 1/cells and multipath fading channel.

Implementation of Capacitance Measurement Equipment for Fault Diagnosis of Multi-channel Ultrasonic Probe

In this paper, we propose the method to measure the capacitances using not LCR meter but capacitance to voltage(C/V) conversion. And we design the analog MUX circuits that convert 192 channels to 6 MUX channels in order to implement the diagnosis of multi-channel ultrasonic probe. This paper derives the conversion function that converts the digital voltage of each MUX channel to the capacitance using the least squares method because the circuit characteristics that convert the voltage of each MUX channel to the capacitance are different. The developed prototype illustrates the performance test results that the measure times are measured by within 4sec and the measure error rates of maximum, minimum, and average values are within 5% in terms of the repeated measurements of all 192 channels.

Design Issues of Spectrum Sensing in Cognitive Radio Networks

This paper investigates the design issues of spectrum sensing in the cognitive radio (CR) networks of opportunistic unlicensed spectrum access. The cognitive radios can perform a communication using the incumbent user spectrum band without the interference caused by the cognitive radio users. In this case, the cognitive radios must know the real-time radio environments of the incumbent user spectrum band using the spectrum sensing, beacon signal, and geo-location database access. Then in this paper, we are going to provide spectrum sensing issues which include the sensing techniques, the regulatory requirements, the analysis of DTV detection threshold, and main considerations associated with the spectrum sensing design in cognitive radio systems. Also, this paper introduces design trade-offs in order to optimize the sensing parameters such as sensing time and sensing complexity.