Dae-Ki Hong

Robust frequency offset estimation for pilot symbol assisted packet CDMA with MIMO antenna systems

We propose frequency offset estimation and combining techniques for pilot symbol assisted (PSA) packet downlink code-division multiple access (CDMA) with multiple-input and multiple-output (MIMO) antenna systems. Orthogonal Walsh codes are used for dedicated pilot symbols at the transmit antennas. The discrete Fourier transform (DFT)-based frequency offset estimation is used for simple implementation. In addition, simple interpolation is also used for resolution improvement of the DFT. When identical frequency offset is assumed, the frequency offset estimates for each single-input single-output (SISO) sub-stream (i.e., transmit/receive antenna pair) can be combined at the receiver. Simulation results show that the estimation and combining techniques proposed deliver improvement in the frequency offset estimation performance.

A simple interpolation technique for the DFT for joint system parameters estimation in burst MPSK transmissions

In this paper, we propose a simple frequency-domain interpolation technique for the discrete Fourier transform (DFT). This interpolation technique can significantly improve the frequency and phase resolution capabilities of the DFT without increasing the size of the DFT (the number of points used for the DFT). This new technique employs a dividing point in the amplitude and phase spectra. Suitable areas of application include joint estimation of fine frequency and phase offsets in burst-mode digital transmission.

A modified covariance-based velocity estimation method for Rician fading channel

In wireless mobile communication systems, the mobile velocity or, equivalently, the maximum Doppler frequency, is very useful information to optimize the system performance. A novel velocity estimation method, based on the autocovariance of the received signal and that of the squared envelope, is proposed. The proposed estimator provides unbiased characteristics. Moreover, the proposed method does not need any other channel information such as Rician factor and angle of arrival (AoA). The performance of the proposed estimator is verified by tracking simulation in realistic cellular mobile communication scenarios.

MC-VSG BNET system for high-rate wireless personal area network applications

In this paper a multi-coded variable spreading gain (MC-VSG) CDMA system employing a binary transmission of MC signals by introducing a level clipper termed MC-VSG BNet system, is proposed for the candidate of wireless personal area network (WPAN) and 3G cellular applications. With an emphasis on the MC-VSG BNet physical layer we address the concise specification of the MC-VSG BNet system including the spreading code, level clipping, modulation, coding, frame format, and its applications. From the receiver performance based on simulation results, in addition to simple receiver structure, an acceptable performance degradation of the MC-VSG BNet system over the existing DS/CDMA system is observed, while guaranteeing a high bit rate transmission.

Analysis of a pipelined successive interference cancellation scheme for a DS/CDMA system

The bit error rate (BER) expression for a proposed pipelined successive interference cancellation (PSIC) scheme in a direct sequence/code division multiple access (DS/CDMA) system is derived analytically. The proposed PSIC scheme is a pipelined modification of a successive interference cancellation (SIC) scheme. The numerical results show that the proposed PSIC scheme outperforms the SIC scheme in viewpoints of the BER and the decoding delay performances.

Joint frequency offset and carrier phase estimation for the return channel for digital video broadcasting

This paper investigates the design of joint frequency offset and carrier phase estimation of a multi-frequency time division multiple access (MF-TDMA) demodulator that is applied to a digital video broadcasting-return channel system via satellite (DVB-RCS). The proposed joint estimation algorithm is based on the interpolation technique for two correlation values in the frequency and phase domains. This simple interpolation technique can significantly improve frequency and phase resolution capabilities of the proposed technique without increasing the number of the correlation values. In addition, the overall block diagram of a digital communications receiver for DVB-RCS is presented, which was designed using the proposed estimation algorithms.

Training sequence design and channel estimation of OFDM-CDMA broadband wireless access networks with diversity techniques

In this paper, an OFDM-CDMA system employing various diversity schemes is considered for a possible candidate of broadband wireless access networks and broadcasting applications. With an emphasis on a preamble design for multi-channel separation, we address a channel estimation based on the time-domain windowing and its imperfectness in OFDM-based multiple-antenna transmission systems. By properly designing each preamble for multiple antennas to be orthogonal in the time domain, the channel estimation can be applied to the HIPERLAN/2 and IEEE 802.11a standards in the case of more than two transmit antennas. Also, the effect of diversity techniques on the performance of OFDM-CDMA based broadband wireless access networks is investigated and the maximum achievable diversity gain for a two-path Rayleigh fading environment is evaluated. Simulation results show that the OFDM-CDMA system applying a space-time-frequency diversity with a full-rate full diversity code can give the diversity of D=4 and D=8 for both multi-user cases of maximum user and half user capacities, respectively.

Pipelined successive interference cancellation scheme for a DS/CDMA system

The bit error rate (BER) expression for a proposed pipelined successive interference cancellation (PSIC) scheme in a direct sequence/code division multiple access (DS/CDMA) system is derived analytically. The proposed PSIC scheme is a pipelined modification of a successive interference cancellation (SIC) scheme. The numerical results show that the proposed PSIC scheme outperforms the SIC scheme from the viewpoints of the BER and the decoding delay performances.

Constant-Amplitude Multicode-Biorthogonal Modulation

In this letter, a constant-amplitude biorthogonal multicode (CABM) modulation is proposed. The proposed modulation is a biorthogonal modulation scheme that employs a constant-amplitude transmission of multicode signals by introducing a simple constant-amplitude coding scheme with redundant bits. The proposed CABM modulation can provide bandwidth efficiency up to the level (i.e., 9/16) of constant-amplitude orthogonal multicode (CAOM) modulation. We prove that our encoding scheme proposed in this letter provides this constant amplitude property. The bit-error rate (BER) performance expressions and the union bounds of the proposed CABM modulation and demodulation pairs are derived analytically. The results of the computer simulation and theoretical analysis performed show that the BER performance and the hardware complexity of the proposed CABM modulation are significantly better than those of a CAOM modulation

A timing recovery for return channel of digital video broadcasting

We investigate the design of an interpolation filter of a multi-frequency TDMA (MF-TDMA) demodulator which is applied to DVB-RCS (digital video broadcasting-return channel system via satellite). If sampling is not synchronized to the data symbols, timing adjustment in the digital receiver must be performed by interpolation. It is impossible for the conventional ideal (sinc) interpolation filter coefficient actually to extend to infinity. We propose two interpolation filters (the Kaiser window interpolation filter and the sinc interpolation filter using the Kaiser window) for low side-lobes. Simulation results show that the performance improvement is realized by employing the proposed (optimal) interpolation filter.