147 research outputs found
Non-coherent detection for ultraviolet communications with inter-symbol interference
Ultraviolet communication (UVC) serves as a promising supplement to share the responsibility for the overloads in conventional wireless communication systems. One challenge for UVC lies in inter-symbol-interference (ISI), which combined with the ambient noise, contaminates the received signals and thereby deteriorates the communication accuracy. Existing coherent signal detection schemes (e.g. maximum likelihood sequence detection, MLSD) require channel state information (CSI) to compensate the channel ISI effect, thereby falling into either a long overhead and large computational complexity, or poor CSI acquisition that further hinders the detection performance. Non-coherent schemes for UVC, although capable of reducing the complexity, cannot provide high detection accuracy in the face of ISI. In this work, we propose a novel non-coherent paradigm via the exploration of the UV signal features that are insensitive to the ISI. By optimally weighting and combining the extracted features to minimize the bit error rate (BER), the optimally-weighted non-coherent detection (OWNCD) is proposed, which converts the signal detection with ISI into a binary detection framework with a heuristic decision threshold. As such, the proposed OWNCD avoids the complex CSI estimation and guarantees the detection accuracy. Compared to the state-of-the-art MLSD in the cases of static and time-varying CSI, the proposed OWNCD can gain ∼1 dB and 8 dB in signal-to-noise-ratio (SNR) at the 7% overhead FEC limit (BER of 4.5×10 −3 , respectively, and can also reduce the computational complexity by 4 order of magnitud
Optical Wireless Data Center Networks
Bandwidth and computation-intensive Big Data applications in disciplines like social media, bio- and nano-informatics, Internet-of-Things (IoT), and real-time analytics, are pushing existing access and core (backbone) networks as well as Data Center Networks (DCNs) to their limits. Next generation DCNs must support continuously increasing network traffic while satisfying minimum performance requirements of latency, reliability, flexibility and scalability. Therefore, a larger number of cables (i.e., copper-cables and fiber optics) may be required in conventional wired DCNs. In addition to limiting the possible topologies, large number of cables may result into design and development problems related to wire ducting and maintenance, heat dissipation, and power consumption.
To address the cabling complexity in wired DCNs, we propose OWCells, a class of optical wireless cellular data center network architectures in which fixed line of sight (LOS) optical wireless communication (OWC) links are used to connect the racks arranged in regular polygonal topologies. We present the OWCell DCN architecture, develop its theoretical underpinnings, and investigate routing protocols and OWC transceiver design. To realize a fully wireless DCN, servers in racks must also be connected using OWC links. There is, however, a difficulty of connecting multiple adjacent network components, such as servers in a rack, using point-to-point LOS links. To overcome this problem, we propose and validate the feasibility of an FSO-Bus to connect multiple adjacent network components using NLOS point-to-point OWC links. Finally, to complete the design of the OWC transceiver, we develop a new class of strictly and rearrangeably non-blocking multicast optical switches in which multicast is performed efficiently at the physical optical (lower) layer rather than upper layers (e.g., application layer).
Advisors: Jitender S. Deogun and Dennis R. Alexande
Effects of Transceiver Jitter on the Performance of Optical Scattering Communication Systems
In ultraviolet communications, the transceiver jitter effects have been
ignored in previous studies, which can result in non-negligible performance
degradation especially in vibration states or in mobile scenes. To address this
issue, we model the relationship between the received power and transceiver
jitter by making use of a moment-based density function approximation method.
Based on this relationship, we incorporate the transceiver jitter effects in
combination with Poisson distribution. The error rate results are obtained
assuming on-off key modulation with optimal threshold based detection. We
validate the error rate expressions by comparing the analytical results with
Monte-Carlo simulation results. The results show that the transceiver jitter
effects cause performance degradation especially in smaller transceiver
elevation angles or in shorter distances, which are often adopted in
short-range ultraviolet communications. The results also show that larger
elevation angle cases have a better performance with respect to anti-jitter and
may perform better compared to smaller elevation angle situations in the case
of larger standard deviation of jitter. This work studies for the first time
the transceiver jitter effects in ultraviolet communications and provides
guidelines for experimental system design.Comment: 5 pages, 2 figures, comments are welcome
Single-scatter channel impulse response model of non-line-of-sight ultraviolet communications
Previous studies on the temporal characteristics of single-scatter
transmission in non-line-of-sight (NLOS) ultraviolet communications (UVC) were
based on the prolate-spheroidal coordinate system. In this work, a novel
single-scatter channel impulse response (CIR) model is proposed in the
spherical coordinate system, which is more natural and comprehensible than the
prolate-spheroidal coordinate system in practical applications. Additionally,
the results of the widely accepted Monte-Carlo (MC)-based channel model of NLOS
UVC are provided to verify the proposed single-scatter CIR model. Results
indicate that the computational time costed by the proposed single-scatter CIR
model is decreased to less than 0.7% of the MC-based one with comparable
accuracy in assessing the temporal characteristics of NLOS UVC channels.Comment: 10 pages, 4 figure
- …