Abstract
In order to achieve multi-gigabit transmission (projected for 2020) for the use in interplanetary communications, the usage of large number of time slots in pulse-position modulation (PPM), typically used in deep-space applications, is needed, which imposes stringent requirements on system design and implementation. As an alternative satisfying high-bandwidth demands of future interplanetary communications, while keeping the system cost and power consumption reasonably low, in this paper, we describe the use of orbital angular momentum (OAM) as an additional degree of freedom. The OAM is associated with azimuthal phase of the complex electric field. Because OAM eigenstates are orthogonal the can be used as basis functions for N-dimensional signaling. The OAM modulation and multiplexing can, therefore, be used, in combination with other degrees of freedom, to solve the high-bandwidth requirements of future deep-space and near-Earth optical communications. The main challenge for OAM deep-space communication represents the link between a spacecraft probe and the Earth station because in the presence of atmospheric turbulence the orthogonality between OAM states is no longer preserved. We will show that in combination with LDPC codes, the OAM-based modulation schemes can operate even under strong atmospheric turbulence regime. In addition, the spectral efficiency of proposed scheme is N2/log2N times better than that of PPM.
Highlights
Power-efficient modulation schemes, such as pulse-position modulation (PPM), are widely adopted in current deep-space optical communications [1,2,3,4,5,6]
The ability to generate/analyze states with different orbital angular momentum (OAM), by using interferometric or holographic methods [9,10,11,12,13] allows the realization of deep-space/near-Earth optical communication systems with ultra-high photon efficiencies expressed in terms of number of bits per photon
We studied the use of OAM as an additional degree of freedom for modulation and multiplexing in deep-space and near-Earth applications
Summary
Power-efficient modulation schemes, such as pulse-position modulation (PPM), are widely adopted in current deep-space optical communications [1,2,3,4,5,6]. 2. Deep-space and near-Earth optical Communications based on LDPC-coded OAM modulation. Such a mode detector will have N outputs that correspond to N-projections along OAM modes After this generic description of OAM based deep-space/near-Earth optical communication systems, we provide more details of OAM transmitter and receiver. The signals are modulated, mode multiplexed and sent over the deep-space or near-Earth optical channel (see Fig. 1). When the deepspace/near-Earth optical communication system is based on N-dimensional transmitter and receiver shown, the corresponding signal constellation point is defined as. The current deep-space optical communications are based on PPM, and in order to achieve the multi-Gb/s data rate, predicted by Hemmati in [5], a huge number of time-slots will be needed in PPM, which introduces too stringent requirements from implementation point of view
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