Kyesan Lee

A Perturbation Analysis on the Performance of TOA and TDOA Localization in Mixed LOS/NLOS Environments

In cellular communication systems where non-line-of-sight (NLOS) channels are dominant as compared to line-of-sight (LOS) channels, a time difference of arrival (TDOA) localization method can outperform a time of arrival (TOA) localization method, although the TDOA method loses one degree of freedom in the number of usable range estimates when selecting a range estimate as the reference and doubles the variance of range sampling error when subtracting the reference range estimate. In this paper, we first show the computer simulation result on the localization performance of conventional TOA and TDOA methods in mixed LOS/NLOS environments, and then validate it by theoretical analysis. Here, we analyze the root mean square localization error by decomposing it into two factors; for one factor, which is the contribution from range sampling error, we evaluate it by the Cramer-Rao lower-bound, whereas for the other factor, which is the contribution from positively biased NLOS range error, we analyze it by perturbation method. We show that the theoretical result can well explain the localization performance by computer simulation for both the TOA and TDOA methods, and furthermore, we derive a simple condition among the number of cells, the average and variance of NLOS range error distribution which can correctly predict whether the TDOA method outperforms the TOA method or not for the case of all NLOS channels.

PAPR Reduction in SC-FDMA by Pulse Shaping Using Parametric Linear Combination Pulses

A linear combination between two intersymbol interference (ISI) free parametric linear pulses was proposed in order to obtain a new family of Nyquist pulses. The new family of pulses is utilized for pulse shaping to reduce peak-to-average power ratio (PAPR). The proposed pulse contains a new design parameter, μ, giving an additional degree of freedom to minimize PAPR for a given roll-off factor, α, and transmission scheme. While keeping the same bandwidth, the frequency responses of the proposed pulses differ with different values of the parameter μ for a fixed roll-off factor. Simulations showed that PAPR reduction is achieved when compared to that of other existing filters for the interleaved subcarrier mode of single carrier frequency division multiple access (SC-FDMA).

Performance analysis of visible light communication using the STBC-OFDM technique for intelligent transportation systems

Visible light communication (VLC) applied in an intelligent transportation system (ITS) has attracted growing attentions, but it also faces challenges, for example deep path loss and optical multi-path dispersion. In this work, we modelled an actual outdoor optical channel as a Rician channel and further proposed space-time block coding (STBC) orthogonal frequency-division multiplexing (OFDM) technology to reduce the influence of severe optical multi-path dispersion associated with such a mock channel for achieving the effective BER of 10−6 even at a low signal-to-noise ratio (SNR). In this case, the optical signals transmission distance can be extended as long as possible. Through the simulation results of STBC-OFDM and single-input-single-output (SISO) counterparts in bit error rate (BER) performance comparison, we can distinctly observe that the VLC–ITS system using STBC-OFDM technique can obtain a strongly improved BER performance due to multi-path dispersion alleviation.

PAPR reduction in single carrier FDMA uplink system using parametric linear pulses

Parametric linear pulses are implemented for pulse shaping in order to reduce peak-to-average power ratio (PAPR) in single carrier frequency division multiple access (SC-FDMA) schemes. The parametric linear pulses reduce the PAPR, while maintain the same excess bandwidth and the zero intersymbol condition; therefore, satisfying the Nyquist-I criterion. In this paper, we analytically derive the time and frequency domain parametric linear pulse (for n=1) based on the analysis from [10] and then verify the result using Scanlans [9] observations. Simulation results show that the parametric linear pulse (for n=1) has a lower PAPR compared to the PAPR of the RC filter, which is widely used in wireless communications.

Family of Nyquist-I Pulses to Enhance Orthogonal Frequency Division Multiplexing System Performance

ABSTRACT A family of Nyquist-I pulses called sinc parametric linear combination pulse (SPLCP) is proposed. It is characterized by two novel design parameters that provide additional degrees of freedom to minimize the intercarrier interference (ICI) power due to frequency offset. Moreover, it reduces the high peak-to-average power ratio (PAPR) value in orthogonal frequency division multiplexing (OFDM) systems. Several Nyquist-I pulses were recently proposed to address the subject of high sensitivity to frequency offset and high PAPR in OFDM-based transmissions. In this paper, we investigate the performance of SPLCP in terms of ICI power, signal-to-interference ratio (SIR) power, bit error rate (BER), and PAPR. We additionally examine the behaviour of SPLCP with new design parameters for a certain roll-off factor, α. We compare the performance of SPLCP with other well-known pulses. Theoretical and simulation results show that the proposed SPLCP outperforms other existing pulses in terms of ICI power, SIR power, BER, and PAPR.

PAPR Reduction in Single Carrier FDMA Uplink by Pulse Shaping Using a β-α Filter

A novel pulse shaping filter satisfying the Nyquist-I criterion was derived and implemented to reduce the peak-to-average power ratio (PAPR) over a Single Carrier Frequency Division Multiple Access (SC-FDMA) scheme. The new filter reduces the PAPR, while maintaining the same excess bandwidth and the zero intersymbol interference condition. The novel filter contains a new design parameter β to minimize PAPR, which is independent from the roll-off factor α. The minimum PAPR of the SC-FDMA scheme is linked to the value given to the parameter β for a specific roll-off factor α. Several simulations showed that PAPR is reduced greatly compared to that of the raised cosine filter, which is widely used in wireless communications. The performance of the proposed pulse shaping filter, regarding PAPR, is also compared with those of other conventional filters, demonstrating that the new filter has a superior performance.

Optimum Spread Code Applied in Indoor Visible Light Data Transmission for Optical Multipath Dispersion Reduction

Abstract In an indoor visible light communication (VLC) system, diffuse channels are very easily caused by numerous reflections of the optical signals from the obstacle surface, resulting in optical multipath dispersion which can further reduce the bit error rate (BER) performance of wireless communication system. In this paper, we investigated non-directed LOS links and optimized the design of this short-range communication model using white light-emitting diodes illumination. In our VLC system, we proposed spreading scheme to combat the severe effects of multipath dispersion. We compared the BER performances of four spread codes on the diffuse channel: pseudo random code, Walsh code, m-sequence code, and gold code. Through the analysis and comparison of simulation results, we obtained the optimum spread code, namely Walsh code, which can alleviate the serious effects of multipath dispersion.

Adaptive MMSE Equalizer for Optical Multipath Dispersion in Indoor Visible Light Communication

Abstract Multipath dispersion results from optical signals passing through more than one path. In this paper, we investigate a non-directed line of sight (LOS) model using white light emitting diode illumination. Typically in such a link, the optical signals are modeled as a reflection component and a directed LOS component over optical wireless (OW) channels. However, inter-symbol interference (ISI) induced by multipath dispersion critically influences the performance of OW communications. In this paper, we propose the adaptive minimum mean squared error (MMSE) equalizer scheme to suppress the multipath ISI, since this scheme can minimize the mean square error (MSE) between the desired equalizer output and the actual equalizer output. We compared the following two algorithms: Least mean square and recursive least square. Our computer simulations demonstrated that visible light communication using an adaptive MMSE equalizer can alleviate the serious effects of optical multipath dispersion.

Adaptive Resource Allocation for the PB/MC-CDMA System in Frequency Selective Fading Channels

We propose Adaptive Resource Allocation for the Partial Block MC-CDMA (ARA-PB/MC-CDMA) system. The ARA-PB/MC-CDMA system aims to improve total throughput performance and frequency efficiency across various channel conditions. It adaptively changes the number of blocks to improve the throughput performance and frequency efficiency according to the Signal to Interference Ratio (SIR). Therefore, the proposed system supports various Quality of Service (QoS) requirements for various SIR values.

Scalable optical relay for LED-ID systems

LED-ID (light emitting diode - identification) system typically uses line of sight (LOS) channels to achieve high data rate and bright illumination. In LOS channel, however, the LED-ID system has very narrow coverage. In cellular networks, the relay station has been introduced to improve system throughput and coverage. Accordingly, new optical relay scheme is essential to support multi-hop transmission in relay-assisted LED-ID networks. In this paper, effects of shadow region problem are investigated for LED identification (LED-ID) system in a non-line of sight (NLOS) environment. A scenario on shadow region problem is proposed, and nominal interrogation range of a desired reader is derived from this model. In order to expand the coverage of LED-ID networks, an efficient optical relay scheme is proposed and simulated by employing cooperative communication methodology. It is confirmed that the proposed technique performs well both in terms of throughput and fairness by simulation results. Also, the proposed scheme is very effective to expand coverage of LED-ID communication networks.