Beam Power Adaptation Research Articles

Performance Evaluation of 5 Gbit/s and 10 Gbit/s Mobile Optical Wireless Systems Employing Beam Angle and Power Adaptation with Diversity Receivers

Over the last two decades, indoor optical wireless (OW) systems have operated typically at 30 Mbit/s to 155 Mbit/s. Here, we propose and evaluate for the first time a mobile OW system that operates at 5 Gbit/s and 10 Gbit/s. The improvements in data rates and channel bandwidth are achieved through the introduction of three approaches: angle diversity, beam angle and beam power adaptation. We propose a mobile OW system that employs beam angle and beam power adaptation in a line strip multibeam spot diffusing system configuration in conjunction with an angle diversity receiver (APA-LSMS) to mitigate the degradation due to ambient light noise, multipath dispersion and mobility. The performance of our proposed system was investigated through channel and noise modelling. Our results show that the proposed APA-LSMS at a bit rate of 30 Mbit/s achieves about 45 dB signal-to-noise ratio (SNR) gain over a power adaptive line strip multibeam system (PA-LSMS) and offers 60 dB SNR gain over a conventional diffuse system (CDS) at a 6 m horizontal separation between the transmitter and the receiver. The SNR is independent of the transmitter location and when our methods (angle diversity, beam angle and beam power adaptations) are implemented, the SNR can be maximized at the receiver for every transmitter location. The results show an increase in channel bandwidth from 36 MHz (CDS) to approximately 7.2 GHz in our proposed system (APA-LSMS). These improvements enhance our system and enable it to operate at higher data rates of 5 Gbit/s and 10 Gbit/s.

Mobile Multigigabit Indoor Optical Wireless Systems Employing Multibeam Power Adaptation and Imaging Diversity Receivers

In this paper, we introduce two novel methods (beam power adaptation and diversity imaging) to the design of optical wireless systems to improve link performance. The aim is to reduce the effect of intersymbol interference and to enhance the signal-to-noise ratio (SNR), thus enabling the system to achieve mobility while operating at high bit rates. In good agreement with previous work, the results show that the imaging conventional diffuse system (CDS) with maximum ratio combining (MRC) offers 20 dB better SNR than the nonimaging CDS. The new adaptive line strip multibeam system (ALSMS) with a new imaging diversity receiver provides an SNR improvement of 39 dB over the imaging diversity CDS when both systems employ MRC and operate at 30 Mbits∕s. This result illustrates the SNR improvement achieved through the use of our adaptive algorithm coupled with spot diffusing. The lower bit rate (30 Mbits∕s) facilitates comparison with previous work. The results also indicate that the combination of transmit power adaptation and spot diffusing coupled with imaging diversity receivers can enable fully mobile 2.5 Gbit∕s optical wireless communication. Such a 2.5 Gbit∕s system (imaging MRC ALSMS) achieved an SNR improvement of 27 dB over a lower data rate (30 Mbits∕s) nonimaging CDS.

High-Speed Spot Diffusing Mobile Optical Wireless System Employing Beam Angle and Power Adaptation and Imaging Receivers

The spot-diffusing geometry is one of the attractive configurations considered in the literature. It provides a better signal-to-noise ratio (SNR) than the conventional diffuse system (CDS), but its SNR can be degraded due to shadowing, signal blockage and mobility. Three methods: imaging reception, beam angle and beam power adaptation are introduced to the design of spot-diffusing OW systems to effectively mitigate the degradation due to mobility in the presence of ambient light noise, multipath propagation, and shadowing. The performance of our systems was evaluated through channel and noise modeling. The CDS SNR performance improves by more than 20 dB when an imaging receiver with maximum ratio combining (MRC) replaces a non-imaging receiver. A 24 dB SNR gain can be achieved when spot-diffusing is employed with an imaging MRC receiver instead of the imaging MRC CDS. In an imaging spot-diffusing system, the SNR is independent of the transmitter position and can be maximized at all receiver locations when our new methods (beam angle and beam power adaptation) are implemented. Regardless of the transmitter position, beam angle adaptation can target the spots at the optimum location that yields the best SNR at the receiver. A significant SNR improvement of 36 dB in the imaging spot-diffusing performance can be achieved when angle adaptation is introduced. Further SNR improvement of 4 dB can be obtained if the power is adaptively distributed among the spots. Furthermore, an increase in the channel bandwidth from 43 MHz (non-imaging CDS) to 8.19 GHz can be achieved through the combination of these methods (imaging reception, spot-diffusing, beam angle and beam power adaptation). The increase in channel bandwidth and SNR can enable the OW system to achieve higher data rates and 2.5 Gbit/s and 5 Gbit/s mobile OW systems are shown to be feasible. The results also prove that the influence of shadowing and signal blockage can be sufficiently combated through the use of these methods.

Beam power and angle adaptation in multibeam 2.5 Gbit/s spot diffusing mobile optical wireless system

Mobility can induce significant signal-to-noise ratio (SNR) performance degradation in optical wireless (OW) systems based on diffuse as well as spot-diffusing configurations. Two methods (beam angle and beam power adaptation) are introduced to the design of OW multibeam systems to effectively mitigate the mobility-based performance degradation in the presence of ambient light noise, multipath propagation, and shadowing. Simulation results indicate that in an angle diversity multibeam system, the SNR is independent of the transmitter position and can be maximized at all receiver locations when our new methods are implemented. A multibeam power and angle adaptive system (MBPAAS) offers a significant SNR improvement of 29 dB over the traditional line strip multibeam system (LSMS) at a transmitter-receiver separation of 6 m, when both systems employ an angle diversity receiver and operate at 50 Mbit/s. This improvement comes at the cost of complexity. The complexity can be reduced by increasing the beam angle adaptation step size from 2.3° to 26.6° resulting in a typical search time reduction from 12.5 ms to 80 μs when our modified MBPAAS replaces the main MBPAAS. However, a power penalty of 11.7 dB at receiver locations near the room edges and 1.3 dB elsewhere can be induced. An increase in the channel bandwidth from 647 MHz (LSMS) to 5.57 GHz can also be achieved when the two new methods (beam angle and beam power adaptation) are implemented. The increase in channel bandwidth and SNR can enable the OW system to achieve higher data rates and 2.5 Gbit/s and 5 Gbit/s mobile OW systems are shown to be feasible. Furthermore, simulation results prove that our modified MBPAAS can sufficiently combat shadowing and signal blockage.

Adaptive mobile multicarrier code division multiple access optical wireless systems employing a beam clustering method and diversity detection

The authors consider a mobile optical wireless system that employs an adaptive beam clustering method (ABCM) to improve system performance. Our new ABCM system offers a significant signal-to-noise ratio (SNR) improvement of 22 dB over a line strip multibeam system (LSMS) at a 6 m transmitter–receiver horizontal separation when both systems employ an 8° diversity receiver and operate at 50 Mbit/s. At the worst communication path in the 50 Mbit/s on–off keying (OOK) system, the combination of beam power adaptation, beam clustering and diversity reception can reduce the transmit power by almost 7 dB while achieving 10−9 bit error rate (BER). An increase in the channel bandwidth from 26.8 MHz (a conventional diffuse system (CDS)) to almost 8 GHz can be achieved when an 8° angle diversity ABCM system is implemented at the worst communication path. The increase in the channel bandwidth and SNR can be used to enable multiuser capabilities, in our case, by employing a multicarrier code division multiple access (MC-CDMA) scheme. At transmitter and receiver locations of (2 m, 4 m, 1 m) and (1 m, 1 m, 1 m), the MC-CDMA ABCM system achieves a BER of 5×10−10 in a four-user scenario compared to a BER of 5×10−1 when MC-CDMA CDS is considered. Furthermore, a zero forcing equalisation technique was employed to reduce multiple access interference and improve the BER performance. The results confirm that while the CDS and the LSMS systems benefit, the equalisation scheme, which increases receiver complexity, is not necessary when the ABCM replaces CDS or LSMS at the data rate considered.

Adaptive mobile optical wireless systems employing a beam clustering method, diversity detection, and relay nodes

In this paper, a novel beam power adaptation method is proposed, studied and shown to be a desirable means for improving the performance of an optical wireless (OW) system that operates under the constraints of background noise, multipath dispersion, and mobility. We propose and evaluate a new OW configuration that employs an adaptive beam clustering method (ABCM) in conjunction with diversity detection. Our goal is to reduce the effect of transmitter/receiver mobility and the associated impacts in terms of a weak received optical power and reduction in bandwidth. Previous work has shown that multiple spot diffusing techniques suffer from these two fundamental limitations associated with mobility. Our new ABCM can help overcome the impairments introduced by mobility, introduce gain in the received optical power, and increase bandwidth even at large transmitter and receiver separations. Our results indicate that, at the least successful locations, the ABCM system can reduce the signal delay spread by nearly a factor of twenty and enhance the SNR by almost 15 dB over a line strip multibeam system (LSMS). We also incorporate the concept of relaying into the Adaptive line strip multibeam system and prove that this technique can lead to considerable performance improvements.

Performance evaluation of 2.5 Gbit/s and 5 Gbit/s optical wireless systems employing a two dimensional adaptive beam clustering method and imaging diversity detection

Previous indoor mobile optical wireless systems operated typically at 30 Mbit/s to 100 Mbit/s and here we report on systems that operate at 2.5 Gbit/s and 5 Gbit/s. We are able to achieve these improvements through the introduction of three new approaches: transmit beam power adaptation, a two dimensional beam clustering method (2DBCM), and diversity imaging. Through channel and noise modeling we evaluated the performance of our systems. The performance of a novel optical wireless (OW) configuration that employs a two dimensional adaptive beam clustering method (2DABCM) in conjunction with imaging diversity receivers is evaluated under multipath dispersion and background noise (BN) impairments. The new proposed system (2DABCM transmitter with imaging diversity receiver) can help reduce the effect of intersymbol interference and improve the signal-to-noise ratio (SNR) even at high bit rate. At a bit rate of 30 Mbit/s, previous work has shown that imaging conventional diffuse systems (CDS) with maximal ratio combining (MRC) offer 22 dB better SNR than the non-imaging CDS. Our results indicate that the 2DABCM system with an imaging diversity receiver provides an SNR improvement of 45 dB over the imaging CDS with MRC when both operate at 30 Mbit/s. In the CDS system, an increase in bandwidth from 38 MHz (non-imaging CDS) to 200 MHz approximately, is achieved when an imaging receiver is implemented. Furthermore, the three new methods introduced increase the bandwidth from 38 MHz to 5.56 GHz. At the least successful receiver locations, our 2.5 Gbit/s and 5 Gbit/s imaging 2DABCM systems with MRC offer significant SNR improvements, almost 26 dB and 19 dB respectively over the non-imaging CDS that operates at 30 Mbit/s.