Jae Kyun Kwon

Inverse Source Coding for Dimming in Visible Light Communications Using NRZ-OOK on Reliable Links

This letter proposes an inverse source coding scheme to mitigate the severe performance degradation caused by light dimming in visible light communications using on-off keying on reliable links. The proposed scheme meets the ratio of 0s to 1s for the dimming target, and transmission efficiency approaches the theoretical maximum, entropy. It outperforms the existing time-multiplexing scheme, and the difference in performance becomes larger the more the dimming target deviates from 50%. There might be several ways to implement inverse source coding and this letter presents an example utilizing Huffman coding.

Capacity Analysis of M-PAM Inverse Source Coding in Visible Light Communications

We previously proposed inverse source coding (ISC) to maximize the transmission rate in visible light communications with dimming capability using ON-OFF keying. First, this paper extends the proposed ISC approach to -ary pulse amplitude modulation and obtains the optimal probability distributions. Then, dimming capacity is used to compare the existing analog dimming approach, the extended ISC approach, and the hybrid of these approaches. We conclude that ISC is the best approach, and threshold values for adaptive modulation are derived depending on signal quality and dimming target.

Turbo Code-Based Error Correction Scheme for Dimmable Visible Light Communication Systems

This letter presents an error correction scheme for dimmable visible light communication systems. To provide dimming control of on-off keying, the proposed coding scheme yields a codeword with the codeword weight adapted to the dimming requirement. It also allows an arbitrary value of the dimming requirement unlike existing coding schemes which have a limited support of this feature. To this end, turbo codes are employed together with puncturing and scrambling techniques to match the Hamming weight of codewords with the desired dimming rate. We demonstrate the decoding performance of the proposed coding scheme under iterative decoding and compare it with other existing error correction schemes. The simulation results prove that the proposed scheme has superior decoding performance, arbitrary dimming rate support, and diverse code rate options.

Log-likelihood ratio (LLR) conversion schemes in orthogonal code hopping multiplexing

Log-likelihood ratio (LLR) conversion schemes are proposed to reduce the effect of perforations that occur in orthogonal code hopping multiplexing (OCHM), which was previously proposed to accommodate more downlink channels than the number of orthogonal codewords. The proposed LLR conversion schemes greatly reduce the required signal-to-noise ratio (SNR) in channel decoding even when the perforation probability is high. The performance of the proposed schemes is evaluated by simulation in terms of the required E/sub b//N/sub 0/ for a 1% block error rate.

Modulation and coding for dimmable visible light communication

The recent interest in short-range optical wireless communication technology driven by the widespread deployment of solid state lighting has led to significant efforts on the standardization of visible light communication. In such efforts, the consideration of dimming support poses fundamental challenges on the VLC system design that have not been addressed elsewhere. This article overviews the technical considerations for enhancing the VLC physical layer by summarizing the state-of-the-art advancements in modulation and coding technologies dedicated to VLC systems. In addition, the technical challenges for system enhancement under lighting restrictions are described.

Color Intensity Modulation for Multicolored Visible Light Communications

This letter explains color space and signal space in visible light communications using multicolored LEDs. We propose the concept of color intensity modulation that satisfies color and dimming requirements in color space and maximizes communication capacity in signal space. The capacity values and corresponding signal constellation examples are given for orthogonal and nonorthogonal channels.

Mobility modeling and traffic analysis in three-dimensional high-rise building environments

To efficiently plan future personal communications services, we need to solve various mobility/traffic problems in one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) micro- or pico-cell environments. Although many users exhibit vertical motion inside elevators in high-rise buildings, there have been no studies regarding cell planning which take into account vertical motion with elevators. We extend the previous 3-D indoor mobility modeling by considering the proper boundary conditions on each floor and vertical motions through elevators and modeling mobility in high-rise buildings in order to estimate the number of handoffs. We then propose a blocking probability model with mobility as a traffic model in 3-D indoor environments. Using this model, we can obtain the required number of channels per cell under the given blocking probability constraint. These results can be used in planning the networks of future personal communications services.

Capacity improvement in CDMA downlink with orthogonal code-hopping multiplexing

Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E/sub b//I/sub 0/ values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCHM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E/sub b//I/sub 0/ value decrease.

Soft handoff modeling in CDMA cellular systems

We propose a new analytical soft handoff model in a rectangular cell configuration and obtain the probability distribution of the sojourn time in the soft handoff region. The movements of a mobile user are categorized into several transition cases for calculating the probability distribution. We obtain the probability distribution for each transition case and the resulting probability distribution by unconditioning the transition cases. We can derive various probability distributions by varying model parameters and observe the effects of parameters. These distributions can be utilized in characterizing various traffic characteristics such as soft handoff traffic and mean handoff rate.

Evaluation of visible light communication channel delay profiles for automotive applications

In this article, we present channel delay profiles based on simulated data regarding the practical conditions for the use of visible light communication (VLC) in automotive applications such as Intelligent Transportation Systems (ITS). Practical vehicular LED headlamp and street lamp that consider the lighting regulation for transportation are used to design the ITS scenarios based on VLC. We modeled two usage scenarios, crossroad and metropolitan street, using the CATIA V5 tool. Measurements for the VLC channel delay profile evaluation were then gathered by using a ray-tracing scheme employing commercial LightTools software under the vehicle-to-vehicle and vehicle-to-infrastructure (V2I) communication links. From the obtained channel impulse responses from both scenarios, we derived the VLC channel delay profiles. From them, we found that the common property of the delay profile was composed of dominant multiple line of sight (LOS) links and a less number of non-LOS delay taps. However, the channel delay profile for the V2I link and metropolitan scenario show more dispersive channel characteristics due to the reflection and diffusion of the visible light.