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In the last few years, optical camera communication (OCC) has benefited from built-in CMOS image sensors in smart devices. OCC is now considered a candidate for incorporation into IEEE 802.15.7r1. A major study on OCC was conducted for line-of-sight (LOS) environments. To enable users to receive OCC signals reflected from any surface easily, we considered non-LOS (NLOS) OCC in a heterogeneous reflective background in this study. A modified background subtraction method was proposed to identify the transmitted modulated signal that was recorded in an image. Then, the majority vote principle was used to restore the damaged pixels that were primarily caused by nonuniform reflection from the heterogeneous reflective background. The experimental results obtained after using a self-built NLOS OCC system demonstrated a significant improvement in the bit error rate when the proposed OCC signal recovery method was used for different distances between a smartphone and a heterogeneous reflective background.

A great deal of research has been devoted to studying indoor localization schemes for the development of location-based services. This study investigated an indoor localization system, including subsystems of nonline-of-sight (NLOS) image-sensor-based visible light communications (IS-VLCs) and the proposed $K$ -pairwise light-emitting diode (LED) image-sensor-based visible light positioning (IS-VLP), in a unified lighting environment. A smartphone received multiple LED identifiers through the designed NLOS IS-VLC and successfully performed the proposed $K$ -pairwise LED IS-VLP with $K = 3$ to achieve localization, with maximum localization errors of 2.92 and 3.54 cm being obtained for ceiling heights of 100 and 150 cm, respectively.

The visible light communication (VLC) utilising the light emitting diodes (LEDs) as transmitters has gained much interest for the indoor wireless access due to its abundance of unregulated spectrum. However, the LED non-linearities cause a detrimental non-linear distortion especially for the adoption of optical orthogonal frequency-division multiplexing (O-OFDM), which is known to suffer high peak-to-average power ratio (PAPR). Specifically, the authors consider the direct current biased O-OFDM (DCO-OFDM) to realise the O-OFDM signals. This study aims to develop the mitigation techniques for LED non-linearities at transmitter through the combined advantages of PAPR reduction and the technique of linearising the non-linear LED characteristics. The orthogonal cover code sequence is exploited to design a transform precoding to reduce the PAPR. An uncomplicated pre-distorter at transmitter is adopted to linearise the LED non-linearity. In addition, the authors propose a dynamic DC biasing method to avoid the clipping noise in DCO-OFDM. As a whole, the proposed techniques at VLC transmitter can improve the LED non-linearities even for large input signals.

By modulating the optical power of the light-emitting diode (LED) in accordance with the electrical source and using a photodetector to convert the corresponding optical variation back into electrical signals, visible light communication (VLC) has been developed to achieve lighting and communications simultaneously, and is now considered one of the promising technologies for handling the continuing increases in data demands, especially indoors, for next generation wireless broadband systems. During the process of electrical-to-optical conversion using LEDs in VLC, however, signal distortion occurs due to LED nonlinearity, resulting in VLC system performance degradation. Artificial neural networks (ANNs) are thought to be capable of achieving universal function approximation, which was the motivation for introducing ANN predistortion to compensate for LED nonlinearity in this paper. Without using additional training sequences, the related parameters in the proposed ANN predistorter can be adaptively updated, using a feedback replica of the original electrical source, to track the LED time-variant characteristics due to temperature variation and aging. Computer simulations and experimental implementation were carried out to evaluate and validate the performance of the proposed ANN predistorter against existing adaptive predistorter schemes, such as the normalized least mean square predistorter and the Chebyshev polynomial predistorter.

A simplified two-dimensional high-resolution indoor visible light positioning using smartphone image sensor is proposed in this paper. The smartphone can obtain the real coordinate of LED luminaires by the unique identification of each LED luminaires and identify its location using a captured still image. Experimental results demonstrated that the proposed two-dimensional indoor visible light positioning using smartphone image sensor achieves the maximum positioning errors of $\pmb{x}$ - axis and y-axis were within 2.27 cm and 3.87 cm, respectively, under a hexahedron positioning space with 100 cm height.

Much research has been devoted to investigating visible light signal detection using CMOS sensor embedded in smartphone under the scenario of pure white background. However, the characteristics of the reflection surface are not always homogeneous in a practical environment. This study proposed a back-ground-subtraction-like image processing for visible light signal detection under a heterogeneous background. Experimental results demonstrated that the proposed method achieved the same bit error rate and packet error rate performance no matter under the homogeneous background or the heterogeneous background.

This study uses the joint receive antenna selection and symbol detection (JRAS/SD) technique to simultaneous- ly improve the bit error rate and channel capacity while reducing the cost of the radio-frequency chains in multiple- input multiple-output (MIMO) systems. Optimal antenna selection methods in the literatureare based on the criteria of maximal capacity or minimal bit error rate. Either of these criteria requires an exhaustive search over all subma- trices in the full channel response matrix, resulting in high complexity. This study proposes a new multiobjective JRAS/SD using the cross-entropy optimizationto reduce the bit error rate while approaching the maximal channel ca- pacity in MIMO systems. Simulation results show that the proposed approach achievesimproved performance in both channel achievable rate and bit error rate performance compared with previous works. 

In this paper, we propose a low-complexity, high-efficiency two-dimensional look-up table (2D LUT) for carrying out the sum-product algorithm in the decoding of low-density parity-check (LDPC) codes. Instead of employing adders for the core operation when updating check node messages, in the proposed scheme, the main term and correction factor of the core operation are successfully merged into a compact 2D LUT. Simulation results indicate that the proposed 2D LUT not only attains close-to-optimal bit error rate performance but also enjoys a low complexity advantage that is suitable for hardware implementation.

In this paper, the effect of a power control algorithm on a Personal Access Communications System (PACS) in different propagation environments is investigated by computer simulation. The pathloss model with break point is considered in our simulation. The simulation results show that system performance in terms of outage probability can be significantly improved when a power control algorithm is employed in an uplink. Furthermore, environments with larger inner path‐loss exponents or larger outer path‐loss exponents perform better than those with smaller inner or outer path‐loss exponents. Under the constraint of an outage probability lower than 2%, it is observed that 16 carrier frequencies are sufficient for environments with inner path‐loss exponent α= 2.76 regardless of the outer path‐loss exponent values. The 16 carrier frequencies occupy a bandwidth quite consistent with the smallest channel block allocated by the FCC for licensed PCS operation.

Radio spectrum is the most valuable resource for wireless communication, thus high spectrum utilization is mostly desired to increase system economy. With an efficient frequency allocation method and an effective handoff procedure, a personal communication system can be operated with minimal number of carriers while maintaining an acceptable level of system performance, and thereby leading to a better spectrum utilization. In this paper, we study the effect of different channel selection criteria for handoff procedure on carrier planning problem with Block Oriented Network Simulator (BONeS). The results show that the C/I-based channel selection criterion leads to the best performance, and the minimal numbers of carriers required by Personal Access Communications System (PACS) are 16, 13, 10 carriers for propagation environments with path-loss exponent 2.76, 3, 4, respectively.

Future PCS (personal communication system) cellular networks will mainly be driven by high link quality, high bandwidth utilization, low power consumption and efficient network management. Power control is one of the several major techniques which could help to achieve these goals. By exploiting power control techniques, co-channel interference could be reduced and as many links as possible could be obtained with satisfactory link quality. SIR-based (signal-to-interference ratio-based) power control was proposed as a technique for managing co-channel interference in cellular radio systems. Furthermore, new distributed autonomous feedback power control methods were introduced to achieve excellent performance without the difficult centralized control used in SIR-based methods. Unfortunately, the implementation of those power control algorithms is still challenging owing to the precision of SIR. The main aim of this paper is to investigate an uplink power control algorithm which depends indirectly on the signal-to-noise ratio in the TDMA (time division multiple access) cellular system. Simulation of the prototype hardware implementation of the receiver baseband signal processing based on the PACS (personal access communications system) specification is used as the main approach to explore the performance evaluation of this power control technique. According to simulation results, suitable values of those parameters used in this power control algorithm are derived, and the minimum frequency reuse factor under different propagation environments is also obtained for PACS under power control. © 1998 John Wiley & Sons, Ltd.

The least mean square (LMS) algorithmis one of the most well-known algorithms for mobile communication systems due to its implementation simplicity. However, the main limitation is its relatively slow convergence rate. In this paper, a booster using the concept of Markov chains is proposed to speed up the convergence rate of LMS algorithms. The nature of Markov chains makes it possible to exploit the past information in the updating process. Moreover, since the transition matrix has a smaller variance than that of the weight itself by the central limit theorem, the weight transition matrix converges faster than the weight itself. Accordingly, the proposed Markov-chain based booster thus has the ability to track variations in signal characteristics, and meanwhile, it can accelerate the rate of convergence for LMS algorithms. Simulation results show that the LMS algorithm can effectively increase the convergence rate and meantime further approach the Wiener solution, if the Markov-chain based booster is applied. The mean square error is also remarkably reduced, while the convergence rate is improved.

This paper presents a straightforward and efficient reduced-complexity radial basis function (RBF)assisted decision-feedback equalizer (DFE)-based turbo equalization (TEQ) scheme, which utilizes the a priori information provided by the channel decoder to significantly reduce the computational complexity of the RBF-based DFE. The proposed scheme is capable of achieving a close performance to the Jacobian RBF DFE TEQ in the context of both binary phase-shift keying (BPSK) modulation and 4 quadrature amplitude modulation (QAM), when communicating over dispersive Rayleigh fading channels. Furthermore, it attains a factor 3 and 4.38 lower computational complexity associated with the addition/subtraction operations compared to the Jacobian RBF DFE TEQ for BPSK and 4 QAM, respectively. In addition, the complexity reduction factor associated with the multiplication/division/exp(-)/ln(-) operations is 1.14 and 2.53 for BPSK and 4 QAM, respectively.

Rapid growth in sensor technology and wireless communication has led to the development of wireless sensor networks (WSNs). Due to cost and environment concerns, the battery of sensor is not always rechargeable particularly when the network operates in an inhospitable or hostile field. This study proposed a Lifetime-Extended Uniform Distribution (LEUD) algorithm to provide ubiquitous communication in large-scale networks for a longer duration and a Modified Relative Direction-based Sensor Routing (MRDSR) scheme to solve the routing loop problem in RDSR.

In this paper, a low complexity channel estimator for MIMO OFDM systems is proposed. A frequency domain filtering scheme based on the concept of temporal windowing for noise power reduction outside the window is developed to enhance the performance of the simple Least Square estimator. This approach can eliminate the extra FFT/IFFT operations required in the conventional time domain scheme. A temporal Hamming window is adopted to further reduce the computing complexity of the frequency domain filtering. Simulation results indicate the proposed scheme can significantly improve both the NMSE and BER performance of the LS channel estimator. Compared with the time domain Most Significant Tap (MST) scheme, the proposed scheme has comparable performance but requires much less computing complexity. The proposed scheme also has the advantage in hardware implementation over the MST scheme.

An ant colony optimization (ACO) based multiuser detector assisted with a spatial diversity reception in direct-sequence code-division multiple access (DS-CDMA) is proposed. This detector combines features of joint detection and collective intelligence of ants can offer almost the same bit (BER) performance as the optimum full-search-based multiuser detector does while it can greatly reduced the computational complexity. Furthermore, the near-far resistance of the ACO-based multiuser detector is also examined. The BER performance for k = 20 remains almost the same, even when the interfering users' energy is 10dB higher, than that of the desired user.

The soft-output Viterbi algorithm (SOVA), which is a soft-input soft-output (SISO) Viterbi algorithm, is widely adopted for turbo decoding by taking advantage of its moderate complexity at the expense of some performance loss. Since the coding gain achieved by SOVA is generally about 0.7 dB less than that of maximum a posteriori (MAP) decoding, some research has been done to improve the performance of SOVA decoding for turbo codes. Bi-directional SOVA (Bi-SOVA) was proposed to be a good algorithm, approaching max-log-MAP, or even better. However, the performance improvement of Bi-SOVA degrades when the signal-to-noise ratio (SNR) gets higher and performs like a conventional SOVA. We present an improvement of the Bi-SOVA decoding scheme for turbo codes by using a scaling factors scheme. It is concluded that Bi-SOVA with scaling factor can achieve a stable performance that is better than max-log-MAP within a wide SNR range. In addition to BER performance, the computational complexity of Bi-SOVA with scaling factor is examined and discussed.

Emerging multimedia services in cellular radio systems introduces a communication scenario with variations in transmission rate and quality of service (QoS) requirement. To tackle this problem, a new application of neuro-fuzzy control to the power control strategy in multirate direct-sequence code-division multiple-access (DS/CDMA) cellular radio systems is introduced in this paper. The simulation results indicate that the neuro-fuzzy power control (NFPC) provides higher average transmission rate, lower probability of unsuccessful transmission, and less outage probability than the previous mechanisms.

A joint code division multiple access and noncollision packet reservation multiple access (JCDMA/NC-PRMA) protocol is proposed and investigated as an uplink access scheme for the third-generation mobile systems. Being the underlying TDMA architecture of the CDMA transmissions, NC-PRMA enables the base station to have a centralized control over the slot allocation policy. In order to reduce the multiple access interference (MAI) variation in CDMA transmission, load balancing (LB) slot assignment policy is proposed and evaluated. Simulation results show that considerable improvement can be achieved over the joint code division multiple access and packet reservation multiple access (JCDMA/PRMA) protocol, in which the multiple access interference variation is reduced by way of a dynamic permission probability for contending terminals.