H. Le Minh

Performance Analysis of Ethernet/Fast-Ethernet Free Space Optical Communications in a Controlled Weak Turbulence Condition

The paper experimentally investigates the performance of the Ethernet and Fast-Ethernet free space optical (FSO) communications link under the influence of the weak atmospheric turbulence. A dedicated experimental indoor atmospheric chamber is used to generate and control the turbulence conditions that affect the FSO link performance. The chamber is calibrated and the measured data are verified with the theoretical prediction. We also demonstrate methods to control the turbulence levels and determine the equivalence between the indoor and outdoor FSO links. It is also observed that the connectivity of Ethernet and Fast-Ethernet links are highly sensitive to atmospheric conditions.

Characterization and performance analysis of a TOAD switch employing a dual control pulse scheme in high-speed OTDM demultiplexer

This letter presents the characterization, analysis and simulation of a novel dual control pulse (CP) scheme for the Terahertz Optical Asymmetric Demultiplexer (TOAD) switch used as a demultiplexer in optical time division multiplexing (OTDM) system. The dual-CP TOAD offers symmetrical switching window (SW) which reduces inter-channel crosstalk (CXT) in switched/demultiplexed channels, thus significantly improving the bit-error-rate (BER) and received power penalty. The improvements in CXT and received power penalty are 5 and 1.5 dB (at BER = 10-9), respectively, for demultiplexing high bit rates of 200 and 300-to-10 Gb/s.

Performance analysis for 180° receiver in visible light communications

The paper presents the concept, design and analysis for a visible light communications receiver which has a full 180° perception angle thus offering the guard against blocking and enhancing the system mobility. The proposed receiver includes seven sub-receivers with the proposed geometrical shape investigated and analyzed in MATLAB® for evaluating the received power, RMS delay spread and corresponding signal to noise ratio. The results show that the receiver is fully mobile within the test area and can handle data rates far greater than that offered by commercially available LEDs for BER ≥ 10-6.

Analysis of fog and smoke attenuation in a free space optical communication link under controlled laboratory conditions

In this paper, the attenuation of free space optical (FSO) communication systems operating at selected wavelengths of 0.83 μm, 1.31 μm and 1.55 μm in the controlled laboratory based fog and smoke environments are compared. The fog and smoke are generated and controlled homogeneously along the indoor atmospheric chamber of length 6 m. The experimental results from the selected wavelengths are compared for the continuous spectrum range (0.6 μm <; λ <; 1.55 μm) attenuation. The results show that, unlike the fog attenuation, the resultant smoke attenuation linearly decreases from the visible towards the near infrared (NIR) range from dense to light smoke conditions.

Lambertian source modelling of free space optical ground-to-train communications

There is a increasing demand for high speed data services while travelling on trains and other means of public transportation. Hence, an alternative technology to radio frequency (RF) communications called free space optics (FSO) could be used to provide truly high-speed broadband services in trains. This paper presents a Lambertian source modelling of FSO ground-to-train communication link along with its link performance analysis. Here, we investigate the use of a single optical base station (BS) that can provide the coverage range up to 75 m at 10 Mbps using on off keying (OOK) non-return to zero (NRZ) data signal with a bit error rate (BER) of 10-6.

OPN06-3: Multiple-Hop Routing Based on the Pulse-Position Modulation Header Processing Scheme in All-Optical Ultrafast Packet Switching Network

In this paper we present modeling and simulation of multiple-hop all-optical packet routing based on the pulse- position modulation header processing (PPM-HP) scheme in ultrafast optical packet switching network. Optical core node employing PPM-HP requires a dedicated routing table based on PPM scheme that will result in significantly reduced number of routing table entries. In this scheme, the header address correlation, using optical AND gates, is carried out by employing only a single bit-wise for each entry rather than a multiple-bit stream as in the existing systems thus resulting in reduced header processing time and avoiding the slow gain-recovery of AND gates. The reduced routing table also offers embedding multiple transmitting modes (unicast, multicast, broadcast) in optical layer and improves core network scalability where the number of core/edge nodes could be altered without the need for changing the number of routing table entries. The simulation results for the optical signal-to-noise ratio (OSNR) of packets at each hop are presented and compared with the theoretical calculations.

Comparison of 830 nm and 1550 nm based free space optical communications link under controlled fog conditions

In this paper, we compare the fog attenuation of free space optical (FSO) communication systems operating at infrared wavelengths of 830 and 1550 nm in the controlled laboratory based fog environment. The fog is generated and controlled homogeneously along the atmospheric chamber of length 5.5 m. The visibility (V) is measured to characterize the fog within the chamber using Koschmieder relationship at 550 nm. We show that the 1550 nm wavelength has considerably lower optical loss than 830 nm in dense to moderate fog conditions with the average loss difference of 100 dB for dense fog (V<; 70 m), 23 dB for thick fog (V = 250 m) and 8 dB for moderate fog (V= 500 m) for a link range of 1 km.

Equalization for organic light emitting diodes in visible light communications

This paper presents an effective analogue equalization approach to enhance the data modulation bandwidth of an organic light emitting diode (OLED) used for lighting and communications. The proposed approach is experimentally demonstrated to overcome the effect of the OLEDs large capacitance induced by the large emitting area panel, thus offering higher data transmission rate for visible light communications system. The measured results show that a six time increase of bandwidth can be achieved and the large-size OLED can be used for on-off-keying non-return-to-zero data communications up to 2.15 Mbit/s with the given bandwidth of 150 KHz.

Experimental investigation of the performance of different modulation techniques under controlled FSO turbulence channel

This paper experimentally investigates and compares the performance of the free space optics system employing three different modulation schemes, on-off keying (OOK) with non-return-to-zero (NRZ) and return-to-zero (RZ) and the binary phase shift keying (BPSK) operating under the turbulent atmosphere. The received average signal is measured and used to characterize the strength of the turbulence. The experiment is performed with a temperature gradient of 4 degrees at a wind velocity of 4 m/s. The temperature gradient within the controlled channel results in turbulence of a log irradiance variance of 0.002, which is classified as a very weak turbulence. The received signal eye diagram and power histograms are presented and analyzed for performance evaluation of the selected modulation schemes in the weak turbulence model.

Optimisation of Lambertian order for indoor non-directed optical wireless communication

This paper studies the optimised Lambertian order (OLO) of light-emitting diodes (LEDs) for an indoor non-directed line of sight optical wireless communication (NLOS-OWC) systems. We firstly derive an expression of the OLO from a conventional Lambertian LED model, Then, we analyse the indoor multi-cell NLOS-OWC channel characteristics including optical power distribution and multipath time dispersion for two cases of one-cell and four-cell configurations. Furthermore, we estimate the transmission bandwidth by simulating the channel frequency response. Numerical results show that, by using OLO a significant improvement of the transmission bandwidth can be achieved for in indoor NLOS-OWC systems, in particular, for multi-cell configurations.