1,517 research outputs found
Modulation and coding for throughput-efficient optical free-space links
Optical direct-detection systems are currently being considered for some high-speed inter-satellite links, where data-rates of a few hundred megabits per second are evisioned under power and pulsewidth constraints. In this paper we investigate the capacity, cutoff-rate and error-probability performance of uncoded and trellis-coded systems for various modulation schemes and under various throughput and power constraints. Modulation schemes considered are on-off keying (OOK), pulse-position modulation (PPM), overlapping PPM (OPPM) and multi-pulse (combinatorial) PPM (MPPM)
Coding of PPM based modulation techniques to improve the performance of infrared WLAN's
In this communication we consider the use of PPM
based modulation methods, such as the hybrid modulation
method called Amplitude and Pulse-Position Modulation
(APPM) and Overlapping Pulse-Position Modulation
(OPPM), to improve the performance of Infrared
WLAN’s. The bandwidth eficiency expressions of these
modulation schemes are presented and compared against
the one of Pulse-Position Modulation (PPM), which
allows to conclude that both APPM and OPPM can be
used to improve the performance of PPM without
significant bandwidth expansion, using Trellis-Coded
Modulation (TCM) codes. We also derive the best codes
for some APPM and OPPM schemes, and the results
show that non-negligible coding gains without bandwidth
expansion can be obtained with trellis codes of moderate
complexity
TCM coding of PPM based modulations for Infrared WLAN's impaired by ISI
In this communication we consider the use of PPM based modulation methods, such as the hybrid modulation method called Amplitude and Pulse-Position Modulation (APPM) and Overlapping Pulse-Position Modulation (OPPM) to improve the performance of infrared WLAN’s, by the use of Trellis-Coded Modulation (TCM) codes. We describe the best
code search and results, which demonstrate that, even with trellis codes of moderate complexity, non-negligible coding gains can be obtained without bandwidth expansion. Monte Carlo simulations have been done to compare uncoded PPM against APPM and
OPPM TCM coded systems performances, on ceiling-bounce channel models for various values of delay spread. Although our
codes were derived for the AWGN channel without Inter-Symbol Interference (ISI) awareness, their behavior in multipath
dispersion channels is quite effective
Combinatorial pulse position modulation for power-efficient free-space laser communications
A new modulation technique called combinatorial pulse position modulation (CPPM) is presented as a power-efficient alternative to quaternary pulse position modulation (QPPM) for direct-detection, free-space laser communications. The special case of 16C4PPM is compared to QPPM in terms of data throughput and bit error rate (BER) performance for similar laser power and pulse duty cycle requirements. The increased throughput from CPPM enables the use of forward error corrective (FEC) encoding for a net decrease in the amount of laser power required for a given data throughput compared to uncoded QPPM. A specific, practical case of coded CPPM is shown to reduce the amount of power required to transmit and receive a given data sequence by at least 4.7 dB. Hardware techniques for maximum likelihood detection and symbol timing recovery are presented
Constellation design for future communication systems: a comprehensive survey
[EN] The choice of modulation schemes is a fundamental building block of wireless communication
systems. As a key component of physical layer design, they critically impact the expected communication
capacity and wireless signal robustness. Their design is also critical for the successful roll-out of wireless
standards that require a compromise between performance, efficiency, latency, and hardware requirements.
This paper presents a survey of constellation design strategies and associated outcomes for wireless
communication systems. The survey discusses their performance and complexity to address the need for
some desirable properties, including consistency, channel capacity, system performance, required demapping
architecture, flexibility, and independence. Existing approaches for constellation designs are investigated
using appropriate metrics and categorized based on their theoretical algorithm design. Next, their application
to different communication standards is analyzed in context, aiming at distilling general guidelines applicable
to the wireless building block design. Finally, the survey provides a discussion on design directions for future
communication system standardization processes.This work was supported in part by the Basque Government under Grant IT1234-19, in part by the PREDOC under
Program PRE_2020_2_0105, and in part by the Spanish Government through the Project PHANTOM (MCIU/AEI/FEDER, UE) under Gran
Baifuzi reduces transient ischemic brain damage through an interaction with the STREX domain of BKCa channels
Stroke is a long-term disability and one of the leading causes of death. However, no successful therapeutic intervention is available for the majority of stroke patients. In this study, we explored a traditional Chinese medicine Baifuzi (Typhonium giganteum Engl.). We show, at first, that the ethanol extract of Baifuzi exerts neuroprotective effects against brain damage induced by transient global or focal cerebral ischemia in rats and mice. Second, the extract activated large-conductance Ca2+-activated K+ channel (BKCa) channels, and BKCa channel blockade suppressed the neuroprotection of the extract, suggesting that the BKCa is the molecular target of Baifuzi. Third, Baifuzi cerebroside (Baifuzi-CB), purified from its ethanol extract, activated BKCa channels in a manner similar to that of the extract. Fourth, the stress axis hormone-regulated exon (STREX) domain of the BKCa channel directly interacted with Baifuzi-CB, and its deletion suppressed channel activation by Baifuzi-CB. These results indicate that Baifuzi-CB activated the BKCa channel through its direct interaction with the STREX domain of the channel and suggests that Baifuzi-CB merits exploration as a potential therapeutic agent for treating brain ischemia
Electrochemical sensors, MTT and immunofluorescence assays for monitoring the proliferation effects of cissus populnea extracts on Sertoli cells
<p>Abstract</p> <p>Background</p> <p>We describe the development of an electrochemical sensor array for monitoring the proliferation effects of cissus populnea plant extracts on TM4 Sertoli cells.</p> <p>Methods</p> <p>The proliferation activities of the extracts on Sertoli cells were studied using a high-throughput electrochemical sensor array (DOX-96) and the analytical sensor characteristics were compared with conventional colorimetric MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and fluorescence spectroscopy.</p> <p>Results</p> <p>This work shows that there is a definite positive trend in the proliferation effect of the extract of <it>Cissus populnea </it>on the TM4 Sertoli cells. All of the three techniques confirmed that the most effective concentration for the proliferation is 10 ppm. At this concentration, the proliferation effect was established around 120% for both DOX-96 and MTT techniques, whereas fluorescence assays showed a higher level (120-150%). DOX-96 showed a lower limit of detection (1.25 × 10(4) cells/ml); whereas the LOD recorded for both MTT and fluorescence techniques was 2.5 × 10(4) cells/ml. Visual examination of the cells by means of confocal fluorescence microscopy confirmed the proliferation of Sertoli cells as was determined using the MTT assay. This investigation provides a confident interpretation of the results and proved that the most effective concentration for the proliferation using <it>Cissus populnea </it>plant extract is 10 ppm.</p> <p>Conclusions</p> <p>Overall, the DOX results compared well with the conventional methods of checking proliferation of cells. The fascinating feature of the sensor array is the ability to provide continuous proliferation experiments with no additional reagents including 96 simultaneous electrochemical experiments. The use of the DOX-96 could reduce a typical bioassay time by 20-fold. Thus the DOX-96 can be used as both a research tool and for practical cell culture monitoring.</p
- …