CiteULike: dcastro's Lim

Novel OFDM transmission scheme to overcome caused by multipath delay longer than cyclic prefix

Chiwoo Lim — 2008-07-16T11:27:19-00:00

Vehicular Technology Conference, 2005. VTC 2005-Spring. 2005 IEEE 61st, Vol. 3 (2005), pp. 1763-1767 Vol. 3.

This paper proposes the novel OFDM transmission scheme that can effectively overcome ISI by adjusting CP length. As a way of combating ISI caused by multipath delay longer than guard interval, interference canceller or powerful channel coding has been proposed. Such approaches may reduce ISI, but it needs much complex computation or considerably decreases transmission efficiency to completely eliminate ISI. In our proposed scheme, CP length can be adaptively controlled by simply adjusting sampling rate. Hence it does neither much increase receiver complexity nor decrease effective data rate, compared to the conventional schemes. Our simulation results show that by employing the proposed OFDM transmission scheme, ISI can be effectively avoided in mobile environment with various multipath delays.

Unequal Preamble Power Allocation Scheme for Frequency Offset Estimation in OFDM Based Packet Communication Systems

Jaemin Kwak — 2008-05-29T16:22:20-00:00

Future generation communication and networking (fgcn 2007), Vol. 2 (2007), pp. 536-539.

In this paper, an frequency offset estimation scheme for orthogonal frequency division multiplexing (OFDM) based packet communication systems is proposed, in which allocated powers of the short training symbols and long training symbols are different while maintaining average power of overall preamble sequence. The preamble structure considered is based on the preamble specified in IEEE802.11a and IEEE802.11p standardization group. From the simulation results, it is shown that the proposed scheme can achieve better mean squared error (MSE) performance for frequency offset estimation error than the conventional scheme.

A Novel Design of Balun using Left-Handed Transmission Line

Seungjun Lee — 2008-05-18T12:24:35-00:00

PROCEEDINGS OF ISAP2005 (2005)

A low-noise phase-locked loop design by loop bandwidth optimization

Kyoohyun Lim — 2008-05-10T14:39:00-00:00

Solid-State Circuits, IEEE Journal of, Vol. 35, No. 6. (2000), pp. 807-815.

This paper describes a low-noise phase-locked loop (PLL) design method to achieve minimum jitter from a given PLL circuit topology. An optimal loop-bandwidth design method, derived from a discrete-time PLL model, further improves the jitter characteristics of a PLL already somewhat enhanced by optimizing individual circuit components. The described method not only estimates the timing jitter of a PLL, but also finds the optimal bandwidth minimizing the overall PLL jitter. A prototype PLL fabricated in a 0.6-μm CMOS technology is tested. The measurement shows significant performance improvement by using the proposed method, The measured rms and peak-to-peak jitter of the PLL at the optimal loop-bandwidth are 3.1 and 22 ps, respectively

A Robust Statistical Approach to Non-Line-of-Sightmitigation

Chin-Heng Lim — 2008-05-07T06:40:03-00:00

Statistical Signal Processing, 2007. SSP '07. IEEE/SP 14th Workshop on (2007), pp. 428-432.

Mitigation of non-line-of-sight (NLoS) errors in the geolocation problem has received much attention. It is well-known that these errors degrade the robustness and accuracy of localization systems, whereby localization is performed using time-of-arrival (ToA) measurements. In this paper, we propose a robust approach to mitigate the NLoS effect in location estimation. The approach is based on modeling NLoS errors as contaminated Gaussian noise, which masks the unknown ToA. We then suggest a non-parametric estimate of the noise density, obtained from observations. It provides robustness against the outliers caused by the NLoS errors common in urban areas. Simulation results show an improvement over conventional approaches.