This paper describes the design, analysis, and implementation of a vehicle control system using control state information obtained from a carrier phase (CP) differential global positioning system (DGPS) aided inertial navigation system (INS). Experimental data from CP DGPS/INS control experiments onboard a PATH1 vehicle is included. This testing was completed with a magnetometer sensing system onboard and running to provide a ground truth reference for comparison with the CP DGPS/INS. Navigation accuracy has previously been demonstrated at the cm level with the full navigation state updated at 150 Hz. In this article, lateral position control performance is demonstrated during challenging high-speed maneuvers with trajectory tracking accuracy at the decimeter level. During these initial experiments, the control state updated at 30 Hz. Increased trajectory following accuracy is possible, but there is an inherent tradeoff between the tracking accuracy and the ride comfort. This level of performance demonstrates that CP DGPS/INS technology has the potential to serve as one component of the reliable multisensor centimeter-level position reference system that is necessary for vehicle position control applications, including automated highway systems (AHS).
We propose and experimentally demonstrate a fast polarization tracking scheme based on radius-directed linear Kalman filter. It has the advantages of fast convergence and is inherently insensitive to phase noise and frequency offset effects. The scheme is experimentally compared to conventional polarization tracking methods on the polarization rotation angular frequency. The results show that better tracking capability with more than one order of magnitude improvement is obtained in the cases of polarization multiplexed QPSK and 16QAM signals. The influences of the filter tuning parameters on tracking performance are also investigated in detail.
We propose a simple and stable pulse compression scheme based on a filtering self-phase modulation broadened spectrum in a highly nonlinear fiber. It is found experimentally that under offset filtering the compressed pulse has a better quality compared with center filtering, such as a no pulse pedestal. Furthermore, numerical simulations reveal that the scheme has the potential to improve the pulse extinction ratio during compression. Finally, based on the obtained pulse train the 4 x 10 Gbits/s optical time-division multiplexing system is studied for verification of the high pulse quality. The compression scheme has the advantages of simple configuration, being pedestal-free, and having a high pulse extinction ratio.
Long-wavelength light-emitting diode
(LED) devices in the visible
band (>492 nm) and their applications in high-speed visible light
communication (VLC) have attracted tremendous research interest recently.
The electrical-to-optical (E-O) bandwidth of conventional c-plane long-wavelength LEDs is limited by carrier lifetime
in InGaN quantum well (QW), which is a fundamental problem limiting
the data rate of high-speed VLC systems. In order to achieve an over
GHz E-O bandwidth for applicable packaged LEDs, it is necessary to
innovate from the material level in the active region. This work aims
to break through the modulation bandwidth bottleneck of VLC systems
based on green micro-LED. Commercial LEDs suffer a very limited E-O
bandwidth due to their long radiative recombination carrier lifetime
and large resistance-capacitance delay. Herein, by the utilization
of green InGaN quantum dots (QDs) as the active region of micro-LED,
this constraint can be remarkably alleviated. Green micro-LEDs containing
five layers of InGaN QDs are fabricated, packaged, and then applied
in a line-of-sight (LOS) VLC system over a 2 m free-space channel.
The VLC system based on a single-pixel 50 and 75-μm diameter
green micro-LEDs can achieve high modulation bandwidths up to 1.22
and 1.14 GHz, respectively. Then, real-time non-return-to-zero on–off
keying (NRZ-OOK) and offline pulse-amplitude modulation four-level
(PAM-4) as two common schemes in short-distance optical communication
are adopted to evaluate the VLC system performances. A real-time 2.1
Gbps NRZ-OOK and an offline 5 Gbps PAM-4 VLC links are achieved with
BERs of 2.74 × 10–3 and 1.88 × 10–3 above the forward error correction (FEC) criterion
of 3.8 × 10–3, respectively. To the best of
our knowledge, this is the highest-recorded modulation bandwidth and
communication rate for a single-pixel green micro-LED-based VLC system.
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