Massive data traffic demand for satellite networks has been increased with the emergence of global broadband services. Due to limited onboard processing capacity and imbalanced distribution of global traffic, severe link congestion may occur in hot spots, deteriorating the performance of the whole network. A link cost modification applied in load balancing algorithm based on artificial bee colony is proposed for routing and wavelength assignment problem to distribute traffic in advance. Moreover, congestion avoidance based on wavelength utilization is designed for unexpected congestion to minimize the adverse impact of congestion on network performance. Experiment results show that the method we proposed realizes high performance in communication success rate and average transmission delay and also achieves the maximum utilization of wavelength utilization under the condition of low blocking rate and the equalization of traffic load.
In this paper, Radio over Fiber (RoF) system of generalized frequency division multiplexing (GFDM) and orthogonal frequency division multiplexing (OFDM) based on geometric shaping (GS) 16QAM is established on MATLAB and Optisystem platform. The transmission signals consist of a GFDM signal and a OFDM signal with bandwidth of 5GHz and 2.5GHz respectively. The frequency interval between the two signals is 10GHz. They were then transmitted onto carriers with a frequency of 60GHz by a quadrature modulator, the central frequencies of the two signals are 60GHz, 70GHz respectively. The transmission distance through single mode fiber (SMF) is 16km. Furthermore, we study the bit error rate performance of the proposed scheme combined with low density parity check (LDPC) codes. In the end of the paper, we analyze the performance of the proposed RoF system and be verified through MATLAB and Optisystem joint simulation that the proposed GFDM scheme with LDPC-GS-16QAM outperforms GFDM scheme with regular 16QAM by at least 15.3dB at bit error rate (BER) of 10−5 .
Aiming at the problem of lightweight and miniaturization of satellite optical communication terminals and intersatellite optical communication in multi-layer satellite networks, The beaconless light tracking and acquisition technology in satellite optical communication is researched and analyzed. The link margin of the satellite laser link under direct detection mode is analyzed , the track and the capture process is designed, the influence of satellite platform attitude error, inter-satellite link communication distance and other factors on capture time and capture probability are simulated and analyzed. The scheme designed uses the active side to emit signal light to scan the FOU, and the passive side uses the capture. The way the detector gaze is captured, ie the gaze-scan capture method. The research shows that in the designed multi-layer satellite network optical communication scenario, the acquisition time of GEO satellite to MEO satellite and GEO satellite to LEO satellite communication is 2034 seconds and 351 seconds respectively, and the capture probability is 95.28% and 99.99% respectively. The acquisition time of MEO satellite and LEO satellite communication is 216 seconds, and the probability of capture is 87.32%, which can meet the requirements of optical communication links of different orbit satellites in multi-layer satellite networks.
In order to solve the problem of endurance of high-speed mobile multi-UAV in Ad Hoc networks with frequent network topology changing, this paper proposes a weighted clustering algorithm based on node energy (EWCA). In this algorithm, we use a multi-parameter weighted clustering algorithm, which improve the node degree difference and node residual energy calculation methods, and study the similarity between the adjacent nodes in terms of speed, direction, etc. The simulation studies the inter-cluster switching rate, the number of nodes and the performance of the minimum lifetime of network node. The results show that, compared with the highest node degree algorithm (HIGHD), adaptive security clustering algorithm (SWCA) and weighted clustering algorithm (WCA), the proposed algorithm can reduce the number of clusters, improve the stability of clustering, and the survival time of drones, and improve the network's endurance.
In the future, with multiple services and large-capacity access network scenarios, the network load is often high but the bandwidth is limited. On the situation, based on the software-defined TDM-PON access network architecture and network traffic prediction-correction model, a dynamic bandwidth allocation algorithm is proposed. In the algorithm, a prediction model is used to predict traffic information and a correction mechanism is used to correct the prediction model. After analyzing the global information of the network, the algorithm provide corresponding bandwidth management policies based on business priorities according to different network load conditions. We compare this algorithm with IPACT algorithm, unused prediction algorithm and neural network prediction without correction. It proves that the algorithm guarantees the service quality requirements of different priority services when the bandwidth is limited and the network load is high, and it performs better in terms of average packet delay, bandwidth utilization, etc. Simulation shows, compared with the traditional strategy, the average packet delay is reduced by 70%, and the bandwidth utilization is increased by 19%.
As a resolve to high complexity of user selection and different users with different requirements of QoS(Quality of Services) optimization of multi-user selection with criterion of SLNR based on QoS is proposed in this paper with maximization of SLNR(Signal-to-leakage and Noises Ratio) as standard and different settlements of scheduling for different kinds of users in MIMO (Multiple-input multiple-Output) system. The simulation compares this algorithm with round robin scheduling and leakage based user scheduling. The results show the proposed optimization is much better not only in channel capacity but also in throughput and BER (Bit error rate) than these two algorithms.
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