In this paper, we present a low-complexity joint estimation algorithm of the direction of arrival (DOA) and time of arrival (TOA) for mobile location system, which is based on a multiple signal classification (MUSIC) algorithm. To reduce the computational overhead of conventional joint DOA/TOA estimation algorithms, the proposed approach employs two complexity reduction schemes: separation of the signal vector for individually extracting DOA/TOA and pseudo-spectrum computation with discrete Fourier transform (DFT). In addition, the loss of accuracy caused by the separation process is compensated by summing multiple pseudo-spectrums. Compared with the conventional two-dimensional (2-D) MUSIC algorithm, the proposed low-complexity algorithm not only substantially reduces the computational complexity but also provides better performance, especially in a low signal-to-noise ratio (SNR). The effectiveness of the proposed algorithm is verified by simulation results.

In this paper, we propose a computationally efficient decoding algorithm for space-time trellis codes in slow Rayleigh fading channels. The proposed scheme is based on a stack algorithm with two key ideas: (i) a variable stack size depending upon the signal-to-noise ratio to avoid the exhaustive search of paths and (ii) a normalized metric, which is defined as each cumulative path metric divided by its own length in the stack, to provide an appropriate comparison of the paths with different lengths. Simulation results demonstrate that the proposed algorithm achieves near-ML performance with significant reduction in complexity, compared with the conventional Viterbi algorithm.

We propose a novel location finding system exploiting the downlink reference signal of the Long Term Evolution (LTE) because of the absence of an efficient location finding system for the LTE. The proposed system is based on the correlation method and Chan's method for location sensing and positioning process, respectively. The conventional correlation method, however, is not matched to the LTE since the orthogonal gold sequence used for reference signal is assigned in frequency domain. Therefore, we estimate Time Difference Of Arrival (TDOA) data by cross-correlating the transmitted signal and received signal in the frequency domain. Simulation results show that the proposed system meets the Federal Communication Commission (FCC) requirement for typical Signal-to-Noise Ratio (SNR) region, and the performance can be further improved as more antennas are implemented in transmitter or receiver.

Due to high computational complexity of the optimal subcarrier allocation (SA) algorithm, various suboptimal algorithms with reduced complexity have been developed. However, since those algorithms are based on one dimensional (row or column) comparison of the channel gain, significant performance degradation is inevitable. The proposed algorithm is based on the two dimensional comparison of the channel gain to achieve higher system capacity. Simulation results demonstrate the efficacy of the proposed method.

In this paper, a computationally efficient iterative detection algorithm (IDA) for D-STTD systems is presented. To find an optimal sequence by iterative searching, the proposed scheme consists of two stages. Firstly, the IDA establishes the candidate sequences. Then, it iteratively finds an optimal sequence by examining the candidate sequences until the early termination condition is satisfied. The adaptation of the number of candidate sequences makes the proposed IDA more efficient in computational complexity. The proposed detector is shown to achieve the near-ML performance with significantly reduced complexity.

Space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) from coordinate interleaved orthogonal design (CIOD) is considered to be an effective space- time code (STC) to achieve full-rate and full-diversity with a simple maximum-likelihood (SML) decoder. However, the SML decoder cannot prevent the performance degradation completely due to time-varying effects such as co-channel interference (CCI). In this paper, we propose a decoding scheme to reduce the CCI after comparing the performance of the various STCs in time-varying environment. To fully exploit the special characteristic of the CIOD, the proposed decoding scheme consists of two stages: two symbols are decoded in advance and then used for decoding of the rest symbols in the form of interference cancellation. Simulation results demonstrate that the proposed receiver achieves significantly enhanced performance over time-varying channel compared to that of the SML. The complexity analysis of the proposed scheme and the conventional decoding schemes is also delivered.

The novel pulses, which not only meet the power spectral mask of the Federal Communications Commission (FCC) but also preserve orthonormality at the correlation receiver, have been proposed by Kim for high data rate communications in indoor ultra-wideband (UWB) systems. The proposed multiple orthonormal pulses comply with the FCC spectral mask without additional frequency shifting or bandpass filters, and furthermore, provide enhanced bit-error rate (BER) performance, compared with a well-known Gaussian monocycle and modified Hermite pulses. This paper analyzes the impact of the proposed pulses' properties, such as their auto- and cross-correlations, on the correlation receiver of the UWB system based on the pulse position modulation. The performance of the proposed pulses are compared with different waveforms under various conditions, such as multipath fading, timing mismatch, and multiuser interference. We also discuss a modulation scheme using the multiple orthogonal pulses to achieve the enhancement of data rate and the impact of the correlation characteristics of the proposed waveforms on the BER performance. Simulation results demonstrate the effectiveness of the proposed orthonormal pulses in various conditions, comparing with different waveforms