Abstract
To foster the rollout of 5G in unserved areas, 3GPP has kicked off a study item on new radio to support nonterrestrial networks (NTNs). Due to ultra-wideband of laser, laser communication is very promising for the feeder links of NTNs; however, imprecise temporal synchronization hinders its deployment, which results from a combination of propagation delay, velocity, acceleration, and jerk of NTN platform. The prior synchronization algorithms are inapplicable to the temporal synchronization in laser communications due to the extremely high data rate and Doppler shift. This paper is devoted to addressing the temporal synchronization problem in laser communications. In particular, we first observe the sparsity of laser signal in time-frequency domain. On top of this observation, we propose a new sparsity-aware algorithm for temporal synchronization without carrier aid through sparse discrete polynomial-phase transform and sparse discrete fractional Fourier transform. Subsequently, we implement the proposed algorithm via designing a hardware prototype. To further evaluate its performance, we conduct extensive simulations, and the results demonstrate the effectiveness of the proposed algorithm in terms of good accuracy, low power consumption, and low computational complexity, suggesting its attractiveness for the feeder links of 5G NTNs.
Highlights
With the exponential growth of wireless traffic volume, new radio (NR) becomes the foundation of 5G to provide universal coverage [1, 2]
The major challenge is that the feeder links between the gateway and the nonterrestrial networks (NTNs) platforms must be broadband; i.e., the data rate should be on the order of gigabits per second (Gbps) [6,7,8]
Laser is innately of the ultra-wideband, and the laser communication is very promising for the feeder links in satisfying the data rate requirement, while it is difficult for laser communications to achieve precise temporal synchronization because of the high data rate, e.g., the order of Gbps, and the high Doppler resulting from the movement of NTN platforms [9, 10]
Summary
With the exponential growth of wireless traffic volume, new radio (NR) becomes the foundation of 5G to provide universal coverage [1, 2]. The paper [25] designed a sparse using the discrete fractional Fourier transform (DFrFT) for the temporal synchronization in the scenario with high Doppler changing rate. It is pointed out that carrier recovery is difficult to implement on laser communications for NTN platforms because of the complex structure [26] and restricts the application of the sparse transformation-domain algorithm on the feeder links of 5G NTNs. Motivated from the observations above, we employ an incoherent laser transmission system called intensity modulation direct detection (IMDD) for its simplicity and low cost [27, 28]. This paper designs a sparse transformation-domain algorithm in IMDD-based laser communications for 5G NTNs, which is of good accuracy, low power consumption, and low computational complexity.
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