Power-Domain Pilot Multiplexing for Higher CV-QKD Key Rates
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Solution Overview
Problem
Existing multiplexing schemes in continuous variable quantum key distribution (CV-QKD) systems reduce the achievable secret key rate by occupying time/frequency/polarization resources, limiting the system's efficiency and reach.
Innovation Solution
The method involves generating and transmitting pilot and quantum signals using complex multiplexing in the power dimension, allowing for efficient multiplexing without occupying time/frequency/polarization resources, and utilizing digital signal processing to recover the quantum signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing multiplexing schemes (TDM, FDM, PDM) are used to transmit pilot and quantum signals simultaneously, then physical layer synchronization, timing and carrier recovery are achieved, but time/frequency/polarization channel slots are sacrificed, significantly reducing the achievable secret key rate
Solution Approach 1:
The patent introduces power domain multiplexing as a new dimension to transmit pilot and quantum signals simultaneously without sacrificing time/frequency/polarization resources. By mapping pilot symbols to specific power levels and combining them with quantum signals in the power domain, the system achieves both synchronization and high secret key rate without the resource occupation inherent in conventional multiplexing schemes.
Solution Approach 2:
The patent segments the power domain into distinct power levels for pilot symbols and quantum signals. By dividing the power space into multiple discrete levels and assigning specific levels to pilot and quantum components, the system enables simultaneous transmission without interference, resolving the contradiction between synchronization reliability and secret key rate productivity.
2Reliability
If one of the two orthogonal polarizations is used for pilot multiplexing, then pilot signal transmission is achieved, but the quantum signal can only be transmitted through the other polarization, halving the achievable secret key rate
Solution Approach 1:
Instead of using polarization division (PDM) which restricts quantum signal transmission to a single polarization, the patent employs power domain multiplexing that allows both pilot and quantum signals to share the same polarization channel. This dimensional shift from polarization space to power space eliminates the halving effect and maintains full polarization utilization for quantum signal transmission.
3Reliability
If 50% time slots are used for time-division pilot multiplexing to minimize excess noise, then pilot signal transmission is achieved, but the secret key rate is halved
Solution Approach 1:
The patent transitions from time-domain division to power-domain multiplexing, allowing pilot and quantum signals to occupy the same time slots without mutual exclusion. By utilizing different power levels within the same time-frequency-polarization resource block, the system eliminates the need to sacrifice 50% time slots, thereby maintaining full productivity while controlling excess noise through power-level management.
Data Source
Figure 1(a)~1(c)
Figure 2(a)
Figure 2(b)
AI summary
A system, method, and signal provided, characterized by transmitting and receiving a stream of samples. On the transmitting side (Alice), generating a stream of samples for driving a transmitter, each sample having an in-phase (1) component and a quadrature (Q) component, wherein the stream of samples is generated from a stream of pilot symbols and a stream of QKD symbols, wherein the pilot symbols belong to an alphabet of M pilot symbols and the QKD symbols belong to an alphabet of N QKD symbols; mapping a pilot symbol of the stream of pilot symbols to a group of constellation points in accordance with a one-to-one mapping from the alphabet of M pilot symbols to M groups of constellation points in an I-Q space, wherein each of the M groups comprises N constellation points; and mapping a QKD symbol of the stream of QKD symbols to a constellation point in the I-Q space in accordance with a one-to-one mapping from the alphabet of N QKD symbols to the N constellation points of the group of constellation points to which the pilot symbol is mapped. On the receiving end, obtaining the stream of samples, the stream of samples representing a component of a received signal, each sample having an in-phase (1) component and a quadrature (Q) component; generating a stream of pilot symbols from the stream of samples, in accordance with a one-to-one mapping from M groups of constellation points in an I-Q space to an alphabet of M pilot symbols, wherein each of the M groups comprises N constellation points; and generating a stream of quantum key distribution (QKD) symbols from the stream of samples, in accordance with an M-to-one mapping from a set of M*N constellation points of the M groups to an alphabet of N QKD symbols, wherein the M-to-one mapping from the set of M*N constellation points to the alphabet of N QKD symbols comprises, for each respective group of the M groups, a one-to-one mapping from the N constellation points of the respective group to the alphabet of N QKD symbols.