Real-Time Experimental Demonstration of Multi-band CAP Modulation in a VLC System with Off-the-Shelf LEDs

We demonstrate, for the first time, m-CAP modulation using off-the-shelf LEDs in a VLC in real time experimental setup using field programmable gate arrays based in universal software radio peripherals (USRPs). We demonstrate transmission speeds up to ~30 Mb/s can be achieved, which supports high definition television streaming.Comment: 2 pages, 4 figures, IEEE INFOCOM Demonstration

Real Time Implementation of CAP Modulation With “Better-Than-Nyquist” Pulse Shaping in Visible Light Communications

In this letter we experimentally verify a real-time implementation of the ‘better-than-Nyquist’ pulse shape in carrier-less amplitude and phase (CAP) modulation in the context of a visible light communications system. We use two National Instruments universal software radio peripherals (USRPs) as a transmitter and receiver working independently. Previously reported experimental work on pulse shaping in CAP is also verified in real time, showing lower error vector magnitudes (EVM) can be obtained at shorter filter lengths using the better-than-Nyquist pulses in place of the conventionally used square-root raised cosine as the basis function of the signal. We show that a real time EVM penalty is an additional 3% EVM in the worst case and is a result of synchronisation offset at the receiver

On the Implementation of Carrierless Amplitude and Phase Modulation in Visible Light Communication

OAPA Carrierless amplitude and phase modulation (CAP) is one of the spectrally efficient schemes that has been proposed to tackle the limited modulation bandwidth challenge in visible light communication (VLC). The VLC technology leverages existing lighting fixtures to provide wireless data communication, which makes it attractive for many applications. However, the commercially available white LEDs that are predominantly employed in VLC offer low modulation bandwidths that limit the achievable data rate. Thus, CAP modulation is employed to improve achievable data rate, primarily due to its implementation simplicity and high spectral efficiency. The CAP scheme also has a special feature in that it can be implemented as a single band or a multiband scheme which provides design flexibility. This paper presents an in-depth study of the implementation of CAP in LED-based VLC systems, highlighting the unique features that make it specially suited for VLC applications. Furthermore, a comprehensive investigation is carried out regarding the design parameters of the CAP modulation transceiver, its benefits and techniques to mitigate the challenges of CAP-based VLC systems

Hybrid Free-Space Optical and Visible Light Communication Link

V součastnosti bezdrátové optické komunikace (optical wireless communication, OWC) získávají širokou pozornost jako vhodný doplněk ke komunikačním přenosům v rádiovém pásmu. OWC nabízejí několik výhod včetně větší šířky přenosového pásma, neregulovaného frekvenčního pásma či odolnosti vůči elektromagnetickému rušení. Tato práce se zabývá návrhem OWC systémů pro připojení koncových uživatelů. Samotná realizace spojení může být provedena za pomoci různých variant bezdrátových technologií, například pomocí OWC, kombinací různých OWC technologií nebo hybridním rádio-optickým spojem. Za účelem propojení tzv. poslední míle je analyzován optický bezvláknový spoj (free space optics, FSO). Tato práce se dále zabývá analýzou přenosových vlastností celo-optického více skokového spoje s důrazem na vliv atmosférických podmínek. V dnešní době mnoho uživatelů tráví čas ve vnitřních prostorech kanceláří či doma, kde komunikace ve viditelném spektru (visible light communication, VLC) poskytuje lepší přenosové parametry pokrytí než úzce směrové FSO. V rámci této práce byla odvozena a experimentálně ověřena závislost pro bitovou chybovost přesměrovaného (relaying) spoje ve VLC. Pro propojení poskytovatele datavých služeb s koncovým uživatelem může být výhodné zkombinovat více přenosových technologií. Proto je navržen a analyzovám systém pro překonání tzv. problému poslední míle a posledního metru kombinující hybridní FSO a VLC technologie.The field of optical wireless communications (OWC) has recently attracted significant attention as a complementary technology to radio frequency (RF). OWC systems offer several advantages including higher bandwidth, an unregulated spectrum, resistance to electromagnetic interference and a high order of reusability. The thesis focuses on the deployment and analyses of end-user interconnections using the OWC systems. Interconnection can be established by many wireless technologies, for instance, by a single OWC technology, a combination of OWC technologies, or by hybrid OWC/RF links. In order to establish last mile outdoor interconnection, a free-space optical (FSO) has to be investigated. In this thesis, the performance of all-optical multi-hop scenarios is analyzed under atmospheric conditions. However, nowadays, many end users spend much time in indoor environments where visible light communication (VLC) technology can provide better transmission parameters and, significantly, better coverage. An analytical description of bit error rate for relaying VLC schemes is derived and experimentally verified. Nonetheless, for the last mile, interconnection of a provider and end users (joint outdoor and indoor connection) can be advantageous when combining multiple technologies. Therefore, a hybrid FSO/VLC system is proposed and analyzed for the interconnection of the last mile and last meter bottleneck

High Speed Optical Links Using CAP Modulation and Novel Equalisation Techniques

High speed optical links suffer from inter-symbol-interference (ISI) due to their limited bandwidth. Equalisation is typically used to mitigate ISI and therefore improve the link capacity. This dissertation explores novel equalisation techniques for carrierless amplitude and phase (CAP) modulation based optical communication systems including OM4 based and plastic optical fibre (POF) based links. An 850 nm VCSEL based OM4 link using CAP-16 scheme is studied. For the first time, the CAP equaliser, is proposed to mitigate both crosstalk channel interference (CCI) and ISI in the link at the receiver side. Performance comparisons are studied between the CAP-16 scheme using CAP equaliser and a conventional equaliser, pulse amplitude modulation (PAM-4) scheme, and discrete multitone (DMT) scheme. CAP based data transmission of 112 Gb/s is achieved over 150 m OM4 fibre with this novel equaliser, while the conventional equaliser can only support over 1 m OM4 fibre and fails to recover the signals at the same data rate. In addition, this novel equaliser provides a 1.2 dB and 1.7 dB improvement in receiver sensitivity over PAM-4 and DMT schemes, respectively, at 112 Gb/s over 100 m OM4 fibre. A novel pre-CAP-equaliser solving CCI at the transmitter side is also proposed. Data transmission of 56 Gb/s over 100 m OM4 fibre is reported experimentally with an improvement of 0.7 dB in receiver sensitivity compared to using the CAP equaliser at the receiver side. A simulation study shows a 2 dB improvement in receiver sensitivity at 112 Gb/s over 100 m OM4 fibre. Furthermore, an artificial neural network (ANN) equaliser in conjunction with the CAP equaliser structure is explored in a VCSEL based OM4 fibre link in order to further mitigate the nonlinear impairments. For 112 Gb/s data transmission over 100 m OM4 fibre, a 2.4 dB improvement of receiver sensitivity is achieved compared to the CAP equaliser. In addition to the electrical equalisers, a monolithically integrated silicon optical equaliser consisting of three taps is used for 50 Gb/s data transmission. After 10 km standard single mode fibre (SSMF), error free eye diagrams at the receiver are demonstrated. A μLED based POF link based on an APD receiver is also investigated with the CAP equaliser at the receiver side. Data transmission rates of 4 Gb/s over 25 m and 5 Gb/s over 10 m POF links are demonstrated with this equaliser while the conventional equaliser can only support 4 Gb/s over 10 m and fails to recover the signals for 5 Gb/s data transmission

Enhanced carrierless amplitude and phase modulation for optical communication systems

This thesis develops and investigates enhanced techniques for carrierless amplitude and phase modulation (CAP) in optical communication systems. The CAP scheme is studied as the physical layer modulation technique due to its implementation simplicity and versatility, that enables its implementation as a single carrier (CAP) or multi-carrier technique (m-CAP). The effect of timing jitter on the error performance of CAP is first investigated. The investigation indicates that synchronization is a critical requirement for CAP receiver and as a result, a novel low-complexity synchronization algorithm is developed with experimental demonstration for CAP-based visible light communication (VLC) systems. To further reduce the overall link complexity, a fractionally-spaced equalizer (FSE) is considered to mitigate the effects of inter-symbol interference (ISI) and timing jitter. The FSE implementation, which eliminates the need for a separate synchronization block, is shown through simulation and VLC experimental demonstration to outperform symbol-spaced equalizers (SSE) that are reported in literature for CAP-based VLC systems. Furthermore, in this thesis, spectrally-efficient index modulation techniques are developed for CAP. The proposed techniques can be divided into two broad groups, namely spatial index CAP (S-CAP) and subband index CAP (SI-CAP). The proposed spatial index techniques leverage the fact that in VLC, multiple optical sources are often required. The spatial CAP (S-CAP) transmits CAP signal through one of Nt available LEDs. It is developed to reduce equalization requirement and improve the spectral efficiency of the conventional CAP. In addition to the bits transmitted through the CAP symbol, the S-CAP encodes additional bits on the indexing/spatial location of the LEDs. The generalised S-CAP (GS-CAP) is further developed to relax the S-CAP limitation of using a single LED per symbol duration. In addition to the S-CAP scheme, multiple-input multiple-output (MIMO) techniques of repetitive-coded CAP (RC-CAP) and spatial multiplexing CAP (SMux-CAP) are investigated for CAP. Low-complexity detectors are also developed for the MIMO schemes. A key challenge of the MIMO schemes is that they suffer power penalty when channel gains are similar, which occur when the optical sources are closely located. The use of multiple receivers and power factor imbalance (PFI) techniques are proposed to mitigate this power penalty. The techniques result in significant improvement in the power efficiency of the MIMO schemes and ensure that the spectral efficiency gain is obtained with little power penalty. Finally, subband index CAP (SI-CAP) is developed to improve the spectral efficiency of m-CAP and reduce its peak-to-average power ratio (PAPR). The SI-CAP encodes additional information bits on the selection of ‘active’ subbands of m-CAP and only modulate data symbols on these ‘active’ subbands. The error performance of the proposed SI-CAP is evaluated analytically and verified with computer-based simulations. The SI-CAP technique is also experimented for both VLC and step-index plastic optical fibre (SI-POF) communication links. The experimental results show that for a fixed power efficiency, SI-CAP achieves higher data rate compared tom-CAP. For example, at a representative bit error rate (BER) of 10-5, the SI-CAP achieves a data rate and power efficiency gain of 26:5 Mb/s and 2:5 dB, respectively when compared to m-CAP. In addition, an enhanced SI-CAP (eSI-CAP) is developed to address the complexity that arises in SI-CAP at higher modulation order. The results of the experimental demonstrations in VLC and 10 m SI-POF link shows that when compared with m-CAP, eSI-CAP consistently yields a data rate improvement of between 7% and 13% for varying values of the SNR