Seungheon Hyeon

Implementation of an SDR system using graphics processing unit

This article presents a novel procedure of implementing software defined radio modem using a graphics processing unit instead of conventional digital signal processors and/or field programmable gate arrays. Considering that modern GPU is suitable for parallel computing due to its numerous powerful arithmetic logic units, we suggest a proper architecture of hardware and software platform for the SDR modem to be implemented on GPU. Then, we show a design example of mobile WiMAX terminal implemented on the proposed GPU platform. In our experimental tests, we observed that the GPU-driven modem is nearly 90 times faster than the conventional 8-way Very Long Instruction Word architectured DSP-driven modem for the application of Viterbi decoder implementation of mobile WiMAX terminal.

Phase Diversity for an Antenna-Array System With a Short Interelement Separation

This paper presents a simple procedure of obtaining a diversity gain in an antenna-array system with a short interelement separation, typically less than the carrier wavelength. The new technique provides a diversity gain through a noncoherent combination of received signals at each antenna element. The diversity gain arises because, as the number of signal components of the received signal at each antenna element becomes large enough and as the arrival angle of each signal component is distinct from one another, which is a general signal circumstance in most practical code division multiple access (CDMA) signal environments, the amplitudes of the received signals become nearly independent due to the phase difference among the received signals. The diversity gain was referred to as ldquophase diversityrdquo in this paper. The proposed technique is first theoretically analyzed to estimate the performance in terms of pseudorandom-noise-code acquisition, which is verified through extensive computer simulations. Then, through the experimental results that are obtained from a CDMA array-antenna base station system, it has been shown that the performance of noncoherent detection is proportionally improved to the number of antenna elements.

Novel automatic calibration technique for smart antenna systems

The problem of calibration has arisen because the phase characteristics of signal paths associated with each antenna in a smart antenna system (SAS) are different (in both receiving (RX) and transmitting (TX) modes). In this paper, we propose a simple and accurate calibration technique for eliminating the phase characteristic difference of the signal path associated with each antenna element in both RX and TX modes. Also, through the experimental data obtained from SAS, which has been implemented with the CDMA2000 1X standard, we confirm that the proposed technique has eliminated the characteristic difference.

Implementation of a smart antenna base station for mobile WiMAX based on OFDMA

We present an implementation of a mobile-WiMAX (m-WiMAX) base station (BS) that supports smart antenna (SA) functionality. To implement the m-WiMAX SA BS, we must address a number of key issues in baseband signal processing related to symbol-timing acquisition, the beamforming scheme, and accurate calibration. We propose appropriate solutions and implement an m-WiMAX SA BS accordingly. Experimental tests were performed to verify the validity of the solutions. Results showed a 3.5-time (5.5 dB) link-budget enhancement on the uplink compared to a single antenna system. In addition, the experimental results were consistent with the results of the computer simulation.

Implementation of smart antenna base station for IS-2000 1X

This paper presents performance analysis of a smart antenna base station (SABS) that has been implemented for IS-2000 1X system. The SABS introduced in this paper includes all the subsystems required in a commercial base station such as array antenna elements, RF unit, channel card, beamforming unit, GPS unit, etc. The channel card contains subsystems for generating the transmitting data, retrieving the received data, and controlling the transmitting and receiving parts. The data retrieval module, which performs the despreading function, has been realized on an FPGA board in accordance with the array structure and adaptive beamforming procedure of the proposed SABS. In order to provide a proper downlink beamforming as well as uplink beamforming, we present a novel procedure for practically usable accurate calibration. The performance analysis of the proposed SABS presented in this paper is based on experimental results provided by the commercial mobile terminals in PCS (personal communication service) frequency band.

Generalized eigen-combining algorithm for adaptive array systems in a co-channel interference environment

This paper presents a generalized eigen-combining algorithm for an adaptive array system that provides a diversity gain in angular spread, and a maximum signal-to-interference ratio (SIR) in the presence of strong interference. The proposed technique generates the maximum ratio of signal components distributed in the spatial channel subspace using channel bases that span the signal subspace and nullify the interference. Through extensive computer simulations, it is shown that the proposed algorithm represents a breakthrough in preventing performance saturation caused by strong co-channel interference.

Exploiting phase diversity for CDMA2000 1è smart antenna base stations

A performance analysis of an access channel decoder is presented which exploits a diversity gain due to the independent magnitude of received signals energy at each of the antenna elements of a smart-antenna base-station transceiver subsystem (BTS) operating in CDMA2000 1X signal environment. The objective is to enhance the data retrieval at cellsite during the access period, for which the optimal weight vector of the smart antenna BTS is not available. It is shown in this paper that the access channel decoder proposed in this paper outperforms the conventional one, which is based on a single antenna channel in terms of detection probability of access probe, access channel failure probability, and Walsh-code demodulation performance.

Implementation of 4-element beamforming antenna module for B4G base station system using GPU

This paper introduces an implementation of GPU-based beamforming antenna module consisting of 4 elements. The proposed system can be mounted on top of the next generation base station system to reduce the radiating power at the base station. The transmitting power at base station is reduced proportionally to the number of antenna elements, due to the pencil beam provided between the base station and receiving terminal. Conversely, received signal at the terminal is enhanced by 4 times if the transmit power is maintained the same. Through various experimental tests, we have verified the proposed system consisting of 4 antenna elements provides nearly 12dB improvement in the receiving power at the terminal.

Performance analysis of PN-code acquisition in a DS/CDMA smart antenna system

This paper presents a performance analysis of PN-code acquisition in a smart antenna system operating in Rayleigh fading channels with various degrees of angular spread in the arrival direction of the received signal. It was determined that the performance enhancement provided by the smart antenna system is upper- and lower-bounded by the degrees of statistical independence between channel responses associated with each of the antenna elements. The performance of PN-code acquisition in a smart antenna system is then determined in accordance with the degree of angular spread in the range determined by the upper and lower bounds. The theoretical analysis for deriving the bounds shown in this paper is verified through extensive computer simulations with various angular spreads encountered in the Rayleigh fading channel.

Performance analysis of downlink smart antenna system with auxiliary pilot in CDMA2000 IX

The auxiliary pilot has been defined in the CDMA2000 IX standard for the purpose of providing an accurate channel estimation to each of mobile terminals during the downlink beamforming. In this letter, we first analyze the multipath signal environment to verify under exactly what conditions the auxiliary pilot becomes inevitable and what happens if the auxiliary pilot is not assigned to each of the subscribers. Then, we present a systematic procedure of applying the auxiliary pilot together with a proper call processing method to handle the auxiliary pilot. Performance analysis is also given through the computer simulations and the experimental data obtained from the smart antenna base transceiver station (SA BTS) that has been implemented for the CDMA2000 IX standard.