Kieran Parsons

Load balanced routing for low power and lossy networks

The RPL routing protocol published in RFC 6550 was designed for efficient and reliable data collection in low-power and lossy networks. Specifically, it constructs a Destination Oriented Directed Acyclic Graph (DODAG) for data forwarding. However, due to the uneven deployment of sensor nodes in large areas, and the heterogeneous traffic patterns in the network, some sensor nodes may have much heavier workload in terms of packets forwarded than others. Such unbalanced workload distribution will result in these sensor nodes quickly exhausting their energy, and therefore shorten the overall network lifetime. In this paper, we propose a load balanced routing protocol based on the RPL protocol, named LB-RPL, to achieve balanced workload distribution in the network. Targeted at the low-power and lossy network environments, LB-RPL detects workload imbalance in a distributed and non-intrusive fashion. In addition, it optimizes the data forwarding path by jointly considering both workload distribution and link-layer communication qualities. We demonstrate the performance superiority of our LB-RPL protocol over original RPL through extensive simulations.

Mode-evolution-based polarization rotator-splitter design via simple fabrication process

A mode-evolution-based polarization rotator-splitter built on InP substrate is proposed by combining a mode converter and an adiabatic asymmetric Y-coupler. The mode converter, consisting of a bi-level taper and a width taper, effectively converts the fundamental TM mode into the second order TE mode without changing the polarization of the fundamental TE mode. The following adiabatic asymmetric Y-coupler splits the fundamental and the second order TE modes and also converts the second order TE mode into the fundamental TE mode. A shallow etched structure is proposed for the width taper to enhance the polarization conversion efficiency. The device has a total length of 1350 µm, a polarization extinction ratio over 25 dB and an insertion loss below 0.5 dB both for TE and TM modes, over the wavelength range from 1528 to 1612 nm covering all C + L band. Because the device is designed based on mode evolution principle, it has a large fabrication tolerance. The insertion loss remains below 1 dB and the polarization extinction ratio remains over 17 dB with respect to a width variation of +/- 0.12 µm at the wavelength of 1570 nm, or +/- 0.08 µm over the entire C + L band.

Concurrent Multiband Digital Outphasing Transmitter Architecture Using Multidimensional Power Coding

All-digital outphasing transmitter architecture using multidimensional power coding (MDPC) is proposed for noncontiguous concurrent multiband transmission with a high power efficiency. MDPC transforms multiband digital baseband signals into multibit low-resolution digital signals that drive switching-mode PAs. A prototype digital outphasing transmitter consists of two 1-GHz bandwidth GaN Class-D PAs and a Chireix power combiner. The two GaN PAs are driven by bipolar radio frequency (RF) pulse-width modulation (PWM) signals, which are transformed from a concurrent dual-band LTE signal by MDPC. The dual-band LTE signal with 15-MHz aggregate channel bandwidth at 240 and 500 MHz frequency band is transmitted with -30 and -37 dBc out-of-band emissions, respectively. Digital outphasing achieves more than two times higher coding efficiency than conventional concurrent dual-band digital transmitters with the same PAs in Class-S operation. Measured power coding efficiencies of 35.4% and 47.1% are observed with outphasing bipolar and 3-level RF PWM signals respectively, which are encoded from the dual-band LTE signal.

Cycle Slip-Mitigating Turbo Demodulation in LDPC-Coded Coherent Optical Communications

We show that an iterative demodulation with soft-decision feedback information from FEC decoder can efficiently mitigate cycle slips. With 3% pilot insertion, the turbo QPSK demodulation achieves 1.05dB gain even in the presence of frequent cycle slips.

A 24-Dimensional Modulation Format Achieving 6 dB Asymptotic Power Efficiency

We propose modulation using the extended Golay code over the 24D hypercube, achieving 6 dB asymptotic power efficiency with 1 b/s/Hz/pol spectral efficiency. Noise tolerance is improved by 3 dB over DP-BPSK at a BER of 10−3.

Experimental demonstration of 24-dimensional extended Golay coded modulation with LDPC

We experimentally demonstrate ultra-long haul transmission of 24-D extended Golay coded modulation with LDPC. Compared with LDPC coded DP-BPSK, an increase of 15% in reach was shown, with a 3 dB increase in launch power margin at a transmission distance of more than 16,000 km.

Design of a 1 Tb/s Superchannel Coherent Receiver

We describe the design of a trained and pilot-aided digital coherent receiver, capable of detecting a 1 Tb/s superchannel with a single optical front-end. Algorithms for receiver training are described, which calculate the equalizer coefficients, subchannel SNRs, and centroids of the transmitted constellations. Algorithms for pilot-aided operation are then described in detail, providing pilot-aided constant modulus equalization and joint carrier-phase estimation over several coherent subchannels. We demonstrate the detection of a superchannel with net bit rate in excess of 1 Tb/s with a single coherent receiver. An 11 × 10 GBd DP-64QAM Nyquist superchannel is used, with 1.32 Tb/s gross bit rate.

Iteration-Aware LDPC Code Design for Low-Power Optical Communications

Recent low-density parity-check (LDPC) codes have shown capacity-approaching performance for various communications systems. However, their promising performance cannot always be obtained due to practical constraints, such as finite codeword length, finite iteration, finite memory, and finite precision. In this paper, we focus on a practical design method of high-performance LDPC codes under a constraint of finite-iteration decoding for low-power optical communications. We introduce an iteration-aware LDPC code design approach, which is based on decoding trajectory in extrinsic information transfer chart analysis. It is demonstrated that an LDPC code designed by the conventional curve-fitting method exhibits nearly 2 dB of penalty, when the maximum number of iterations is limited. The results suggest that the LDPC code should be adaptively changed, e.g., when the number of decoding iterations is decreased to save power consumption. We also extend our design method to a multi-objective optimization concept by taking average degrees into account, so that the threshold and the computational complexity are minimized at the same time. The proposed Pareto-optimal codes can achieve additional 2-dB gain or 50% complexity reduction at maximum, in low-power decoding scenarios.

High-Dimensional Modulation for Mode-Division Multiplexing

We explore high-dimensional modulation for mode-division multiplexed optical fiber communication systems, focusing on optimized 24-D modulation formats in six-mode fiber transmission. Compared with conventional formats, our simulations demonstrate up to 8.7 dB span loss budget improvement for 6 b/s/Hz intra-channel spectral efficiency.

A 5-level discrete-time power encoder with measured coding efficiency of 70% for 20-MHz LTE digital transmitter

This paper reports the recent development on power coding method of generating a 5-level intermediate frequency PWM-based high speed digital-RF bit train, which is used as the input switching signal for class-S digital RF power amplifiers in the digital transmitter. By introducing the discrete-time power coding process at an IF of around 60 MHz, digital transmitter at cellular bands then becomes feasible to implement with current FPGA technologies. It can lower the required sampling rate more than 10 times compared with RF carrier PWM. In addition, a linearizer is designed using a look-up-table to minimize the nonlinear coding effects of the power encoder. The demonstrator shows the state-of-the-art measured power coding efficiency of 70.47% and SNR>30dB for a 20 MHz LTE signals with PAPR of 10.25 dB at 1.9 GHz with our proposed approach.