51,015 research outputs found
Coherent optical communication using polarization multiple-input-multiple-output
Polarization-division multiplexed (PDM) optical signals can potentially be demultiplexed by coherent detection and digital signal processing without using optical dynamic polarization control at the receiver. In this paper, we show that optical communications using PDM is analogous to wireless communications using multiple-input-multiple-output ( MIMO) antennae and thus algorithms for channel estimation in wireless MIMO can be ready applied to optical polarization MIMO (PMIMO). Combined with frequency offset and phase estimation algorithms, simulations show that PDM quadrature phase-shift keying signals can be coherently detected by the proposed scheme using commercial semiconductor lasers while no optical phase locking and polarization control are required. This analogy further suggests the potential application of space-time coding in wireless communications to optical polarization MIMO systems and relates the problem of polarization-mode dispersion in fiber transmission to the multi-path propagation in wireless communications
Phase and Channel Estimation for High-Capacity Phase-Asynchronous Mode-Division Multiplexing Multiple-Input Multiple-Output Free-Space Optical Communications in Strong Turbulent Channels
In this paper, we propose a novel pilot-aided phase and channel estimation algorithm for coherent mode-division multiplexing multiple-input multiple-output free-space optical communication system. This algorithm enables the implementation of advanced multiple-input multiple-output decoders, leading to a significantly better bit error rate performance. This algorithm also supports phase-asynchronous light sources at each transmit and receive channel, significantly reducing the hardware requirements. Moreover, it has low computational complexity and Cramér-Rao lower bound approaching estimation performance. In our proof-of-concept experiment, we employed 10 decorrelated channels to achieve a record-high 689.2 Gbit/s/wavelength line rate in strong turbulence, verifying the feasibility of our phase and channel estimation algorithm
Digital Signal Processing for Optical Communications and Coherent LiDAR
Internet data traffic within data centre, access and metro networks is experiencing
unprecedented growth driven by many data-intensive applications. Significant
efforts have been devoted to the design and implementation of low-complexity
digital signal processing (DSP) algorithms that are suitable for these short-reach
optical links. In this thesis, a novel low-complexity frequency-domain (FD)
multiple-input multiple-output (MIMO) equaliser with momentum-based gradient
descent algorithm is proposed, capable of mitigating both static and dynamic
impairments arising from the optical fibre. The proposed frequency-domain
equaliser (FDE) also improves the robustness of the adaptive equaliser against
feedback latencies which is the main disadvantage of FD adaptive equalisers under
rapid channel variations.
The development and maturity of optical fibre communication techniques over
the past few decades have also been beneficial to many other fields, especially
coherent light detection and ranging (LiDAR) techniques. Many applications
of coherent LiDAR are also cost-sensitive, e.g., autonomous vehicles (AVs).
Therefore, in this thesis, a low-cost and low-complexity single-photodiode-based
coherent LiDAR system is investigated. The receiver sensitivity performance of this
receiver architecture is assessed through both simulations and experiments, using
two ranging waveforms known as double-sideband (DSB) amplitude-modulated
chirp signal and single-sideband (SSB) frequency-modulated continuous-wave
(FMCW) signals. Besides, the impact of laser phase noise on the ranging precision
when operating within and beyond the laser coherence length is studied. Achievable
ranging precision beyond the laser coherence length is quantified
Multiple-Access Bosonic Communications
The maximum rates for reliably transmitting classical information over
Bosonic multiple-access channels (MACs) are derived when the transmitters are
restricted to coherent-state encodings. Inner and outer bounds for the ultimate
capacity region of the Bosonic MAC are also presented. It is shown that the
sum-rate upper bound is achievable with a coherent-state encoding and that the
entire region is asymptotically achievable in the limit of large mean input
photon numbers.Comment: 11 pages, 5 figures, corrected two figures, accepted for publication
in Phys. Rev.
Explicit receivers for pure-interference bosonic multiple access channels
The pure-interference bosonic multiple access channel has two senders and one
receiver, such that the senders each communicate with multiple temporal modes
of a single spatial mode of light. The channel mixes the input modes from the
two users pairwise on a lossless beamsplitter, and the receiver has access to
one of the two output ports. In prior work, Yen and Shapiro found the capacity
region of this channel if encodings consist of coherent-state preparations.
Here, we demonstrate how to achieve the coherent-state Yen-Shapiro region (for
a range of parameters) using a sequential decoding strategy, and we show that
our strategy outperforms the rate regions achievable using conventional
receivers. Our receiver performs binary-outcome quantum measurements for every
codeword pair in the senders' codebooks. A crucial component of this scheme is
a non-destructive "vacuum-or-not" measurement that projects an n-symbol
modulated codeword onto the n-fold vacuum state or its orthogonal complement,
such that the post-measurement state is either the n-fold vacuum or has the
vacuum removed from the support of the n symbols' joint quantum state. This
receiver requires the additional ability to perform multimode optical
phase-space displacements which are realizable using a beamsplitter and a
laser.Comment: v1: 9 pages, 2 figures, submission to the 2012 International
Symposium on Information Theory and its Applications (ISITA 2012), Honolulu,
Hawaii, USA; v2: minor change
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