Kasun Bandara

Novel colour-clustered multiuser visible light communication

Visible light has a large spectral bandwidth spanning its wavelength between about 380 and 740nm. These wavelengths create a band of colours. In this study, we propose a novel multiuser MU access scheme exploiting colour bands, which we define as colour clusters. In the proposed colour-clustered MU visible light communication system, the users are allocated into separate colour clusters, and the intensity modulated user data are transmitted through the allocated coloured beams from the red, green and blue light emitting diodes. In order to increase user capacity, a secondary user separation is performed by assigning user specific intensity levels via on-off-keying modulation. At the receiver, the primary user separation is performed by a colour sensor that is capable of distinguishing the colours between red, green and blue colour bands. A secondary user separation criterion has also been proposed. The proposed MU-visible light communication VLC system is complete in that it encompasses transmission and detection methods for multiple user access while ensuring a colour-controlled flicker-free illumination. The simulations demonstrate that the proposed MU-VLC system provides an efficient MU VLC platform with significant performances over various transmission scenarios. Copyright

PAPR reduced OFDM visible light communication using exponential nonlinear companding

In visible light communication (VLC), LEDs are used to transmit data using intensity modulation. LEDs have a limited operating voltage range and the voltage-current characteristic shows a nonlinear behavior. When an orthogonal frequency division multiplexing (OFDM) signal is used to drive these transmitter LEDs (VLC-OFDM), LED chip overheating and nonlinear distortions occur, due to high peak-to-average power ratio (PAPR) of the OFDM signal. Unlike radio frequency baseband communication systems, the VLC-OFDM signal is a real-valued signal. This would lend itself to the PAPR reduction in VLC-OFDM. In this paper, we propose to use exponential nonlinear companding transformation techniques in VLC-OFDM to reduce the PAPR. Simulation results demonstrate that with the exponential companding function employed in VLC-OFDM, the PAPR of the VLC-OFDM is significantly reduced, compared with previously considered methods.

Reduced training sequence using RLS adaptive algorithm with decision feedback equalizer in indoor Visible Light Wireless Communication channel

In this paper we present reduced training sequence in a Decision Feedback Equalizer (DFE) with Recursive Least Square (RLS) adaptive algorithm to mitigate the effect of inter-symbol interference (ISI) in an indoor Visible Light Communication (VLC) channel. We have analyzed the performance of the RLS algorithm with the DFE for the improvement of bit error rate (BER) in an indoor channel model. The wireless optical channel model consists of four sources of Light Emitting Diode (LED) transmitters that are used to illuminate the room as well as transmit data. The illumination pattern of the lights in the environment has also been considered. From this analysis, we have proven that with the proposed RLS equalizer, the training sequence can be reduced to allow more data bits to be transmitted for the identical Bit Error Rate (BER) performance.

Improved Indoor Visible Light Communication with PAM and RLS Decision Feedback Equalizer

Abstract One of the key factors that limits the data rate in visible light communication (VLC) is switching speed of the transmitter LEDs. In this paper, a multilevel pulse amplitude modulation (PAM) scheme is employed to increase the data rate significantly while maintaining the LED switching speed limitation. With the use of the multilevel PAM, the training sequence (TS) length is considerably reduced up to 1.67% of the data frame at the recursive least square decision feedback equalizer (RLS-DFE) receiver. This reduction in the TS length allows more data bits to transmit in the frame, thereby increasing the throughput. The proposed VLC system consists of four LED transmitters to transmit data while illuminating the environment at the same time in compliance with the ISO standards. Furthermore, the analysis of the outage area probability demonstrates that the proposed system supports high data rate transmission at nearly error-free rates for most areas in indoor environments.

A High Performance and Bandwidth Efficient IDMA Scheme with Large Receiver MIMO Technologies

Interleave Division Multiple access (IDMA) is a new multiple access scheme, and Multiple-Input Multiple-Output (MIMO) is an emerging technology in the wireless broadband communications. In this paper, we investigate the performance of the IDMA scheme with Large Receiver MIMO (LR-MIMO) with different antenna configurations for the multiuser detection. The bit error rate (BER) performance of the proposed system is analyzed for different channel conditions. Numerical results show that the LR-MIMO-IDMA scheme provides superior performance with the aid of MIMO detection techniques over frequency selective fading channel. Also, this scheme further enhances bandwidth efficiency by reducing the repetition length of the IDMA scheme.

On the Performance of Quasi-Orthogonal Space Time Block Coded Massive MIMO with up to 16 Antennas

Massive multiple-input multiple-output (MIMO) using a large number of antennas at both transmitter and receiver sides based on quasi-orthogonal space time block code (QOSTBC) is presented. Space-time block code (STBC) is a MIMO transmit strategy that applies transmit diversity and high reliability. QOSTBC is attractive because it achieves higher code rate than orthogonal STBC and lower decoding complexity than non-orthogonal STBC. We present the performance of massive MIMO systems using the QOSTBC with multiple antennas up to the 16 × 16 configuration. The performances of 2 × 2, 4 × 4, 8 × 8 and 16 × 16 massive MIMO systems have been presented. Simulation results show that the massive MIMO systems with QOSTBC give significant performance improvement with full rate and full diversity, compared with previously considered massive MIMO systems.

Efficient nonlinear companding scheme for substantial reduction in peak-to-average power ratio of OFDM

Orthogonal frequency division multiplexing (OFDM) produces a high peak-to-average power ratio (PAPR) that ad-versely affects high-speed OFDM data transmission. In order to reduce the high PAPR, an efficient nonlinear companding trans-form (NCT) function is proposed. With the proposed NCT function, the compression and expansion weights can be applied indepen-dently with suitably chosen function parameter values. As a re-sult, the proposed function can easily maintain the average signal power approximately unchanged during the companding process. In this regard, the proposed function is superior to previously pro-posed schemes. Also, the simulations show the outstanding PAPR reduction performance of the proposed function. It is demonstrated that the proposed scheme performs wel with nonlinear transmitter amplifiers and delivers superior error performance, compared with error function and exponential function based schemes.

Novel Nonlinear Companding Transform for Reduced Peak-to-Average Power Ratio in OFDM

Orthogonal Frequency Division Multiplexing (OFDM) is an excellent solution to overcome multipath effects and inter-symbol interference in high-speed mobile communication systems. However, OFDM inherently has a high Peak-to-Average Power Ratio (PAPR) that adversely affects the system. In this study, we propose a nonlinear companding transform scheme function, in order to reduce the high PAPR in OFDM signals. With the proposed scheme, the average power of the OFDM signal can be maintained nearly unchanged over the companding process by properly chosen values of the parameters of the companding function. One salient feature of the proposed scheme over error function based companding schemes is that the signal compression and expansion levels of the companding function can be adjusted independently, and thus it is easier to maintain the average power. With the aid of simulations, we prove that the proposed scheme has an outstanding PAPR reduction capability and it works well with nonlinear transmitter amplifiers as well. Moreover, we show that the BER performance of the proposed companding transform is superior to the one obtained from the error function companding.

On Companding Transform Techniques for OFDM Visible Light Communication over Indoor Dispersive Channels

The μ-law companding transform (CT) is proposed for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing visible light communication (VLC-OFDM) systems. The proposed PAPR reduction technique based on the μ-law CT can minimize nonlinear signal distortions and LED chip overheating problems that occur due to nonlinear characteristics of the transmitter LEDs. The performance of the proposed PAPR reduction is studied via simulations. It is verified that the proposed μ-law CT outperforms the previously proposed DFT spread (DFTS) method in VLC-OFDM systems in terms of PAPR reduction capability. The bit error rate (BER) performance of the VLC-OFDM system with the μ-law CT is also analyzed over an indoor dispersive VLC channel model.

A User-Data Division Multiple Access Scheme

The conventional Interleave Division Multiple Access (IDMA) employs interleavers to separate users, while the conventional Code Division Multiple Access (CDMA) uses user specific spreading sequences for user separation. In this paper, we propose a User-Data Division Multiple Access (UDMA) scheme that employs user data as the spreading sequence for user separation with chip-by-chip iterative multiuser detection strategy. As such, this spreading sequence is not only as random as user data and independent of current symbols, but also dynamically changes from one symbol to another according to the user data. Therefore, this spreading sequence makes unwanted detection of the data by unintended receivers practically impossible. Also, in UDMA, identical interleavers are used and thus do not require to store all interleaving patterns. The simulation results show that the proposed scheme is superior to the bit error rate (BER) performance of the system in flat fading channel.