The cellular system goes through significant power loss due to indoor channel fading, the height of the building, wall reflections, etc. Visible Light Communication (VLC) in conjunction with the radio frequency (RF) communication can provide potential solutions to address issues wireless network is facing in the indoor environment. VLC uses existing illumination infrastructure for communication. VLC is more secure because light cannot penetrate through the wall, can offer high bandwidth and is environmentally safe green technology, unlike RF. This paper analyses and compares the RF and VLC link for indoor communication with respect to symbol-error-rate (SER) performance and power saving. The RF link path loss inside the building is modeled using WINNER-II path loss model, and VLC channel is modeled including the movement of the people. The same constellation-based modulation schemes are used in both the links for fair comparison such as binary phase shift keying (BPSK) for RF and on-o
keying (OOK) for VLC, Mthorder quadrature amplitude modulation (M-QAM) for RF and colour shift keying (M-CSK) for VLC. VLC link provides better SER performance as compared to RF link at the same signal-to-noise-ratio (SNR) for both BPSK (OOK) and 4-QAM (4-CSK) modulation schemes. There is an outstanding amount of power saving using VLC link as compared to RF link inside the room. Further, the SER gap between VLC and RF decreases as the constellation size increases.
Carrier-less amplitude and phase (CAP) modulation schemes have been actively explored in visible light communication (VLC) because of its high spectral efficiency and simpler transceiver design. Conventionally, CAP with root-raised-cosine filter (CAP-RRC) has been explored for VLC. However, in this paper, we have implemented CAP with a Gaussian minimum shift keying filter (CAP-GMSK) in order to improve the system performance. The proposed scheme is compared against CAP-RRC and baseline DCO-OFDM, on the basis of symbol error rate (SER) and peak-to-average power ratio (PAPR) performance. The result shows that as compared to DCO- OFDM, CAP-GMSK and CAP-RRC provides a SNR gain of 8 and 1 dB and PAPR improvement of 2.5 and 2.3 dB respectively.
Visible light communication (VLC) has various advantages over radio frequency (RF) communication such as ubiquity, low energy consumption, no RF radiation, and inherently secure as light does not penetrate through walls. Significant bio-medical signals including the electroencephalography (EEG) can be transferred with VLC even in places where RF is forbidden. Additionally, long-term exposure to RF radiation poses a risk to the human brain which limits the use of RF wireless wearable EEG systems. This potential advantage of VLC could help in the indoor healthcare system such as monitoring. A long-term video-EEG monitoring requires continuous monitoring by video along-with EEG signals. So, overall a significant amount of data needs to be streamed fast for real-time monitoring. A novel low-cost RF radiation-free system is proposed using VLC technology which can be integrated into a wearable EEG device. In this work, we transmit a video and multi-channel EEG signal using visible light communication. Data streams are modulated using colour shift keying (CSK) which drives the RGB LED. CSK gives double the data rate than OOK by mapping bits into a symbol. It keeps the average emitted optical colour constant during communication, thereby reduces potential human health complication related to light ashes. The proposed system aims to lower down the cost and complexity further by using single photodiode at the receiver unlike conventional CSK in IEEE 802.15.7. The receiver architecture exploits channel estimation in a better way. Computer simulations are carried out using actual raw EEG signals and video data. Simulated and theoretical SER versus SNR curves match seamlessly. The results demonstrate that at 33 dB SNR, it achieves a SER of 1x10-5. SER for different transmitter and receiver distance is also analysed. Further, the reliability and accuracy of data received at 33 dB is also discussed.
In this paper, we have proposed a novel modulation scheme for visible light communication (VLC), that has two preprocessing blocks namely, discrete Fourier transform (DFT) block and frequency domain signal shaping block, prior to conventional optical-orthogonal frequency division multiplexing (O-OFDM) modulation. Two variants of proposed scheme namely, with and without DC have been implemented so as to make it compatible with intensity modulation and direct detection (IM/DD). The results of the proposed schemes are compared against their standard O-OFDM counterparts based on peak-to-average power ratio (PAPR) and symbol error rate (SER). Results show that the proposed scheme has significantly lower PAPR and better SER as compared to corresponding O-OFDM counterpart.
Converged Fiber-Wireless (FiWi) broadband access network proves to be a promising candidate that is reliable, robust, cost efficient, ubiquitous and capable of providing huge amount of bandwidth. To meet the ever-increasing bandwidth requirements, it has become very crucial to investigate the performance issues that arise with the deployment of next-generation Passive Optical Network (PON) and its integration with various wireless technologies. Apart from providing high speed internet access for mass use, this combined architecture aims to enable delivery of high quality and effective e-services in different categories including health, education, finance, banking, agriculture and e-government. In this work, we present an integrated architecture of 10-Gigabit-capable PON (XG-PON) and Enhanced Distributed Channel Access (EDCA) that combines the benefits of both technologies to meet the QoS demands of subscribers. Performance evaluation of the standards-compliant hybrid network is done using discrete-event Network Simulator-3 (NS-3) and results are reported in terms of throughput, average delay, average packet loss rate and fairness index. Per-class throughput signifies effectiveness of QoS distribution whereas aggregate throughput indicates effective utilization of wireless channel. This work has not been reported so far to the best of our knowledge.
Orthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems because it is an effective solution to inter-symbol interference caused by a dispersive channel. Very recently a number of researchers have shown that OFDM is also a promising technology for optical communications. This paper gives a overview of OFDM for long-haul, metro/access and data center highlighting the aspects that are likely to be important in optical applications. To achieve good performance in optical systems OFDM must be adapted in various ways. The constraints imposed by optical channel are discussed and the new forms of optical OFDM which have been developed are outlined. The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset. The impairments that these cause are described and their implications for optical systems discussed.
Passive optical network based on orthogonal frequency division multiplexing (OFDM-PON) exhibits excellent performance in optical access networks due to its greater resistance to fiber dispersion, high spectral efficiency and exibility on both multiple services and dynamic bandwidth allocation. The major elements of conventional OFDM communication system are two-dimensional (2-D) signal mapper and one-dimensional (1-D) inverse fast fourier transform (IFFT). Three dimensional (3-D) OFDM use the concept of 3-D signal mapper and 2-D IFFT. With 3-D OFDM, minimum Euclidean distance (MED) is increased which results in BER performance improvement. As bit error rate (BER) depends on minimum Euclidean distance (MED) which is 15.46 % more in case of 3-D OFDM as compared to 2-D OFDM. Forward error correction (FEC) coding is a technique where redundancy is added to original bit sequence to increase the reliability of communication system. In this paper, we propose and analytically analyze a new PON architecture based on 3-D OFDM with convolutional coding and Viterbi decoding and is compared with conventional 2-D OFDM under various system impairments for coherent optical orthogonal frequency division multiplexing (CO-OFDM) without using any optical dispersion compensation. Analytical result show that at BER of 10-9, there is 2.7 dB, 3.8 dB and 9.3 dB signal-to-noise ratio (SNR) gain with 3-D OFDM, 3-D OFDM combined with convolutional coding and Viterbi hard decision decoding (CC-HDD) and 3-D OFDM combined with convolutional coding and Viterbi soft decision decoding (CC-SDD) respectively as compared to 2-D OFDM-PON. At BER of 10-9, 3-D OFDM-PON with CC-HDD gives 2.8 dB improvement in optical budget for both upstream and downstream path and gives 5.7 dB improvement in optical budget using 3-D OFDM-PON combined with CC-SDD as compared to conventional OFDM-PON system.
Passive optical network (PON) features a point-to-multi-point (P2MP) architecture to provide broadband access. The
P2MP architecture has become the most popular solution for FTTx deployment among operators. PON-based FTTx
has been widely deployed ever since 2004 when ITU-T Study Group 15Q2 completed recommendations that defined
GPON system [ITU-T seriesG.984]. As full services are provisioned by the massive deployment of PON networks
worldwide, operators expect more from PONs. These include improved bandwidths and service support capabilities
as well as enhanced performance of access nodes and supportive equipment over their existing PON networks. The
direction of PON evolution is a key issue for the telecom industry. Full Service Access Network (FSAN) and ITU-T
are the PON interest group and standard organization, respectively. In their view, the next-generation PONs are
divided into two phases: NG-PON1 and NG-PON2. Mid-term upgrades in PON networks are defined as NG-PON1,
while NG-PON2 is a long-term solution in PON evolution. Major requirements of NG-PON1 are the coexistence
with the deployed GPON systems and the reuse of outside plant. Optical Distribution Networks (ODNs) account for
70% of the total investments in deploying PONs. Therefore, it is crucial for the NGPON evolution to be compatible
with the deployed networks. With the specification of system coexistence and ODN reuse, the only hold-up of the
migration from GPON to NG-PON1 is the maturity of the industry chain. Unlike NG-PON1 that has clear goals and
emerging developments, there are many candidate technologies for NG-PON2. The selection of NG-PON2 is under
discussion. However, one thing is clear, NG-PON2 technology must outperform NG-PON1 technologies in terms of
ODN compatibility, bandwidth, capacity, and cost-efficiency.
In this paper, perfonnance of OCDMA network implemented using single wavelength with optical orthogonal codes (OOCs) and wavelength division multiplex (WDM) networks with embedded CDMA (WeCDMA) has been evaluated. Performance ofthis network is also evaluated when it is implemented with multi-wavelength optical orthogonal codes (MWOOCs) andbit stuffed unipolar m-sequence encoding schemes. In the above evaluation, the receiver is considered to be a PINphotodiodepreceededby an optical amplifier (PIN+OA). Expressions for the probability oferror are derived alter taking into consideration optical multiple access interference (0MM), optical amplifier noise andvarious sources ofreceiver noise. The numericalvalues are computed for practical values ofparameters andthe results are compared for all the above schemes. It is observed that OCDMA networks implemented using WeCDMA with OOC perfonn better thanthe single wavelengthwith OOC forthe samebandwidth expansion. It is also observedthat perfonnance of OCDMA networks using MWOOCs is better than bit stuffed unipolar rn-sequence based networks when number of simultaneous users are less, whereas for large number of simultaneous users the network perfonnance with bit stuffed unipolar msequence encoding scheme is better compared to that with MWOOCs encoding schemes.
This paper briefly describes the opto electronics activities at C-DOT. Some of the ongoing activities
which are described in this paper are design and development of Synchronous Multiplex Optical
Line terminating equipments and regenerators for 'Synchronous Optical Network', low capacity
opti cal fibre systems and optical interconnects for varying data rates.
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