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We report on the generation of a triple-wavelength vector dark soliton in an all-fiber ring cavity of erbium-doped fiber laser mode-locked with a bismuth-doped fiber saturable absorber. The formation of the triple-wavelength vector dark soliton is due to the cross-phase coupling derived from the cavity birefringence. The mode-locked laser operated at a 1.89 MHz repetition rate with a 335 ns pulse width, and its robustness is confirmed.

•Combination of single-mode fibre with graded-indexed multimode fibre as saturable absorber.•Mode-locking operation with low threshold pump power of 41.6 mW.•Pulse energy obtained is 406.65 pJ at pump power of 84.7 mW.•The soliton laser operated at 1584.8 nm with pulse duration of 510 fs.

It is not uncommon that cellular communication infrastructures will likely be in a failure state when disaster strikes, e.g., floods, earthquakes, and forest fires. Therefore, developing an effective disaster management system is paramount to facing these critical circumstances. As a solution, unmanned aerial vehicles (UAVs) can be deployed as temporary aerial base stations to assist beyond fifth-generation (B5G) networks during and after the disaster. UAVs are increasingly used to aid the search and rescue (SAR) teams in multiple disaster management operations to improve disaster response effectiveness. However, maintaining connectivity and improving energy efficiency are indispensable to ensure continuous communication between the UAVs and SAR and prolong the network’s lifetime. This paper proposes a multi-UAV and SAR device-to-device communication model to maintain connectivity and enhance energy efficiency in multiple disaster scenarios. A clustering approach for UAV placement is utilized to improve energy efficiency, network connectivity, and coverage. We evaluate the performance of the proposed model in terms of the average capacity, energy efficiency, coverage probability and outage probability. The simulation results demonstrate an improved performance of multi-UAV and SAR collaborations and their appropriateness to support efficient and reliable disaster recovery in hard-to-reach and remote disaster areas.

We demonstrated a reliable and stable Q-switched ytterbium-doped fiber laser centered at 1069 nm by employing a segment of 11 cm thulium-doped fiber (TDF) as a saturable absorber (SA) in the ring cavity. The fiber SA has an optical absorption of 1.35 dB at the Q-switched operating regime. As we increased the pump power from 109 mW to the maximum available pump power of 206 mW, a consistent Q-switched laser with output power ranging from 1.8 to 4.8 mW was attained. The pulse width narrowed from 4.9 to 2.87 μs, whereas the repetition rate increased from 40 to 60.2 kHz. In addition, maximum pulse energy of 80.7 nJ and a maximum peak power of 28.1 mW were obtained at the maximum pump power. The signal to noise ratio (SNR) was around 47 dB. Our experimental study shows that a segment of TDF can be used as a Q-switcher in the 1 μm fiber laser cavity to facilitate a reliable and robust microsecond pulse generation.

Online bit error rate (BER) estimation (OBE) has been used as a stopping iterative turbo decoding criterion. However, the stopping criteria only work at high signal-to-noise ratios (SNRs), and fail to have early termination at low SNRs, which contributes to an additional iteration number and an increase in computational complexity. The failure of the stopping criteria is caused by the unsuitable BER threshold, which is obtained by estimating the expected BER performance at high SNRs, and this threshold does not indicate the correct termination according to convergence and non-convergence outputs (CNCO). Hence, in this paper, the threshold computation based on the BER of CNCO is proposed for an OBE stopping criterion (OBEsc). From the results, OBEsc is capable of terminating early in a varying SNR environment. The optimum number of iterations achieved by the OBEsc allows huge savings in decoding iteration number and decreasing the delay of turbo iterative decoding.

A multiwavelength Brillouin/Raman distributed Bragg reflector fiber laser operating in the S-band region is proposed and demonstrated. The laser uses a 7.7 km long dispersion-shifted fiber with an effective mode area of 15  μm^2 as the Brillouin and Raman gain media simultaneously. Two 1420 nm laser diodes with a combined power of 372 mW are used as pump sources, while a fiber Bragg grating with a center wavelength of 1500 nm is used as a reflector in the cavity. The setup is capable of generating 6 clearly defined Stokes lines at the highest pump power, spanning from 1499.8 to 1500.3 nm with the even Stokes having relatively higher peak powers, between 1.4 and 3.5 dBm as compared to the odd Stokes, which have peak powers between −4.7   and −5.0 dBm. The output of the laser is very stable and shows little to no fluctuations over a monitoring period of 50 min.

We model wireless local area network channel utilization over a finite interval through a finite time-horizon Markov (FTHM) model. By accurately capturing time-varying utilization, the FTHM model allows for generally distributed transmission-opportunity (TXOP) duration, which most existing models do not account for. An absorbing state is introduced to limit the lifetime of the counting process, resulting in a non-ergodic Markov chain that is solved via transient analysis. The model predictions for time-varying utilization are validated by simulation with errors of no more than 0.1% after eight beacon intervals. Moreover, we show that the FTHM model prediction error is below 4% for Poisson distributed and uniformly distributed TXOP durations.

Full‐duplex (FD) assisted multiple‐input–multiple‐output relaying increases the spectral efficiency through efficient spectrum utilization. The major concerns for the FD assisted relay system are the cancellation of inter‐relay interference (IRI) and relay self‐interference (RSI). Previous works were idealized only on the basis of either RSI or IRI; hence, all other realistic models to overcome the RSI or IRI were unappreciated. This paper aims to reduce the interference‐to‐signal ratio. We propose the joint relay's receive beamforming based on oblique projection to mitigate the RSI and IRI in multihop environments. Applying first orthogonal projectors to the relay's received signal, the relay's received signals are divided into interference subspace and signal subspace. Then, the desired signal is recovered from signal subspace by using oblique projection that cancels out the RSI and IRI. The geometric interpretation of oblique projection is analyzed to understand its properties. The major merit of this method is that it can be adopted even when the RSI and IRI channels are unknown. In comparison to the existing interference cancellation methods, the signal‐to‐interference ratio of our proposed method does not deteriorate even when the transmit power is high. Additionally, we demonstrate that the oblique projection output is equivalent to an orthogonal projection using geometrical interpretation, simulation, and theoretical derivation. To meet the massive wireless traffic demand in the upcoming fifth‐generation(5G) cellular networks and beyond (XG), the rapid growth of small cells is emerging as an attractive solution and deriving cellular network toward randomness and heterogeneity. Multicell Fullduplex (FD) assisted multi‐antenna relaying increases the spectral efficiency through efficient spectrum utilization. The major concerns for the relay assisted FD system is the cancellations of interferences such as inter‐relay interference (IRI) and relay‐self interference (RSI). This paper applies interference mitigation based‐on oblique projection for multiantenna FD relay to derive a general tractable model for heterogeneous networks to reduce the interference‐to‐signal ratio (ISR).