Suckchel Yang

Adaptive discontinuous reception mechanism for power saving in UMTS

We propose the ADRX (adaptive discontinuous reception) mechanism with the EPI (extended paging indicator) for power saving in the UMTS (Universal Mobile Telecommunications System). In the proposed mechanism, DRX period for each UE (user equipment) is individually and adaptively controlled by the EPI which is decided by node B considering the current traffic situation of each UE. Simulation results show significant improvement of power saving performance by the proposed mechanism as compared to the conventional fixed DRX

An Effective MIMO–OFDM System for IEEE 802.22 WRAN Channels

We propose a closed-loop multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) transmission scheme appropriate for the IEEE 802.22 wireless regional area network (WRAN) channel environments. The proposed scheme utilizes the Grassmannian beamforming and an antenna selection algorithm to maintain bit-error-rate (BER) performance and to reduce feedback information. To further reduce the feedback information considering the channel property of the IEEE 802.22 WRAN, the proposed scheme employs an extension of the feedback period and subcarrier grouping. Simulation results in the IEEE 802.22 WRAN reference channel models indicate that the proposed MIMO-OFDM transmission scheme achieves superior BER performance and spectral efficiency than open-loop MIMO-OFDM system even considering the feedback overhead of the system.

A simple asynchronous UWB position location algorithm based on single round-trip transmission

We propose a simple asynchronous UWB (ultra wide band) position location algorithm with low complexity, low power consumption and minimal processing delay. In the proposed algorithm, UWB pulses are only twice utilized for single RTT (round-trip transmission) based on ToA (time of arrival) principle. Hence, the proposed UWB position location algorithm can decrease power consumption as well as minimize processing delay compared with basic ToA algorithm based on triple RTTs. Moreover, unlike TDoA (time difference of arrival) algorithm, the proposed algorithm can perform the position location with low complexity since it does not require strict synchronization. Nevertheless, simulation results in IEEE 802.15.4a UWB channel model reveal that the proposed UWB position location algorithm based on single RTT can achieve closely comparable position location accuracy of basic ToA and TDoA algorithms.

A rapid acquisition scheme for UWB signals in indoor wireless channels

In this work, we propose a rapid acquisition scheme for ultra wide band (UWB) signals in indoor wireless channels. The proposed acquisition scheme is based on the bit reversal search combined with a variant of the double-dwell search in which two-step thresholds and search windows are employed. Simulation results show that the proposed two-step acquisition scheme for the UWB signals can achieve remarkable reduction of the required mean acquisition time as compared to general double-dwell search schemes.

An Adaptive Discontinuous Reception Mechanism Based on Extended Paging Indicator for Power Saving in UMTS

In this paper, we propose the ADRX (adaptive discontinuous reception) mechanism with the EPI (extended paging indicator) for power saving in the UMTS (universal mobile telecommunications system). Regardless of various traffic patterns and network situations, the conventional FDRX (Fixed DRX) mechanism currently specified by 3GPP (third generation partnership projects) employs only fixed DRX period with a given DRX cycle length of the same length in which each UE (User Equipment) is to have one paging occasion with the uniquely allocated PI. However, improvement of power saving performance cannot be expected since this FDRX does not support longer DRX periods to save more power consumed in the UE for intermittent data packets. In the proposed ADRX mechanism, to solve this problem and efficiently reduce the power consumption, DRX period is easily controlled by the EPI which is decided by Node B considering the current traffic situation. In addition to its original functions to indicate paging messages, the proposed EPI also includes four extended functions; preservation, increase, decrease, and reset of the DRX periods. Simulation results reveal that the proposed ADRX mechanism achieves remarkable improvement of power saving performance as compared to the conventional FDRX mechanism. Furthermore, it is also observed that the proposed ADRX based on the EPI has a trade-off relationship between power saving performance and packet transmission reliability.

A robust joint estimator for OFDM timing and frequency offsets based on PN codes

A joint estimator for OFDM symbol timing and fractional frequency offsets is proposed based on cyclic shifting and autocorrelation properties of PN (pseudo noise) codes. In the proposed scheme, for the joint estimation of both timing and frequency offsets, a newly designed time domain preamble sequence which has the same length with the number of IFFT points and consists of twice-repeated PN codes, is utilized. Moreover, in order to achieve robustness in multipath fading channels, a new timing metric by considering delay spread of the multipath channel is also applied. Simulation results show that the proposed estimation scheme is more robust to multipath channels than the conventional OFDM symbol timing estimation schemes. Furthermore, the proposed joint estimator also provides quite reliable fractional frequency estimation.

A two-step search scheme for rapid and reliable UWB signal acquisition in multipath channels

We propose the two-step search scheme with linear search based second step (TSS-LS) by improving the conventional two-step search scheme with bit reversal search based second step (TSS-BS) for rapid and reliable acquisition of ultra wide band (UWB) signals in multipath channels. The proposed TSS-LS utilizes two different thresholds and search windows to achieve fast acquisition. Furthermore, unlike the TSS-BS in which the bit reversal algorithm is applied in both steps, the linear search is adopted for the second step in the proposed TSS-LS to correctly find the starting point in the range of effective delay spread of the multipath channels, and to obtain reliable bit error rate performance of the UWB systems.

Partitioned-SLM Scheme with Low Complexity for PAPR Reduction of OFDM Signals

In this paper, we propose P-SLM (partitioned-selective mapping) scheme with low complexity for PAPR (peak-to-average power ratio) reduction of OFDM (orthogonal frequency division multiplexing) signals. In the proposed scheme, a symbol sequence in frequency domain is partitioned into several sub-blocks, and each sub-block is multiplied by different phase sequences whose length and number are shorter and smaller than those used in the conventional SLM. Then, among statistically independent sequences in time domain generated after the IFFT (inverse fast Fourier transform) for the phase rotated sub-blocks, the sub-block combination with the lowest PAPR is selected and transmitted. Simulation results reveal that the proposed P-SLM scheme can remarkably reduce the number of IFFT calculation and multiplication than the conventional SLM without loss of PAPR reduction performance

An Effective MIMO-OFDM Transmission Scheme for IEEE 802.22 WRAN Systems

In this paper, we propose a closed-loop MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) transmission scheme that is appropriate for the IEEE 802.22 WRAN (Wireless Regional Area Network) channel environments. The proposed scheme utilizes the Grassmannian beamforming and an antenna selection algorithm proposed by the authors to maintain BER (Bit Error Rate) performance and to reduce feedback information. To further reduce the feedback information considering channel property of the IEEE 802.22 WRAN, the proposed scheme employs an extension of the feedback period. Simulation results in the IEEE 802.22 WRAN reference channel models indicate that the proposed MIMO-OFDM transmission scheme achieves superior BER performance and spectral efficiency than open-loop MIMOq-OFDM system even considering the feedback overhead of the system.

An Adaptive SLM Scheme Based on Peak Observation for PAPR Reduction of OFDM Signals

We propose an adaptive SLM scheme based on peak observation for PAPR reduction of OFDM signals. The proposed scheme is composed of three steps: peak scaling, sequence selection, and SLM procedures. In the first step, the peak signal samples in the IFFT outputs of the original input sequence are scaled down. In the second step, the sub-carrier positions where the power difference between the original input sequence and the FFT output of the scaled signal is large, are identified. Then, the phase sequences having the maximum number of phase-reversed sequence words only for these positions are selected. Finally, the generic SLM procedure is performed by using only the selected phase sequences for the original input sequence. Simulation results show that the proposed scheme significantly reduce the complexity in terms of IFFT and PAPR calculation than the conventional SLM, while maintaining the PAPR reduction performance.