KEYWORDS: Detection and tracking algorithms, Interpolation, Signal detection, Telecommunications, Error analysis, Technology, Demodulation, Signal to noise ratio, Satellite communications, Receivers
Frequency hopping (FH) communication system is known as an important direction of research in the field of satellite communication. Timing synchronization, as the process in which signal timing error is eliminated, serves as the basis for the realization of FH synchronization and data transmission, enabling it to be one of the key technologies of the whole system. Due to the characteristics of short frame burst possessed by the FH system, it is required that the system should complete the detection and tracking of signal timing error quickly, which requires high performance of timing synchronization. Through the improvement in the Gardner timing error detection algorithm, as well as use of the shifting of sampling position and interpolation with fixed fractional interval, there is the design of an open-loop timing synchronization algorithm with low complexity and strong real-time performance. With this algorithm, the system can have a bit error rate (BER) lower than 10-7 and no data loss with a clock deviation of 1ppm. Experimental results demonstrate the performance of the algorithm, the algorithm ensures low complexity and no data loss during synchronization process.
Terahertz (THz) communication is becoming a promising technology for 6G communication system to realize Tbps data rate to support emerging ultra-high-speed applications. Benefit from the high spectrum efficiency and anti-multipath fading capability, Orthogonal Frequency Division Multiplexing (OFDM) technique has obtained significant attention in terahertz communication system. However, one major challenge of high frequency OFDM systems is the phase noise. The general solution is to insert pilots in subcarriers to estimate and compensate for phase noise which causes a waste of spectrum resources. To tackle this challenge, we firstly propose a pilot generation method based on Cyclic Code Shift Keying (CCSK) to transmit more information while estimating the phase noise. Furthermore, a constellation diagram design method with anti-phase noise based on Archimedes spiral is proposed to greatly reduce the power of the pilot signal. Simulation results illustrate that the pilot pattern designed in this paper can improve the spectrum efficiency, and the spiral constellation shows superior Symbol Error Rate (SER) performance even when the average pilot power is much lower than the signal average power, about 2.7dB of EbN0 gain is obtained at a SER of 10-2.
The frequency-hopping (FH) method is widely applied in broadband satellite communication systems because of its low interception rate and good anti-jamming performance. In order to design an FH system, the core issue to be considered is synchronization. For a frequency-hopping time-division multiple access (FH-TDMA) system set in satellite optical communication or satellite wireless communication with large orbital angular momentum (OAM), imperceptible changes in carrier frequencies due to the network properties of large bandwidth, low signal-to-noise ratio (SNR), and high-frequency will cause large equivalent doppler frequency shift of the baseband signal, manifesting ‘linear inconsistence’ in the FH pattern of the network. Furthermore, the receiver of such a system needs to be robust to adapt to complex and harsh environments of noise interference for the purpose of fast synchronization and tracking progress. This paper proposes an open-loop carrier synchronization and tracking method based on dichotomous iterations by establishing a maximum likelihood (ML) doppler frequency shift estimation model. This method realizes the multidimensional search for frequencies and phases at low SNR. Compared with traditional open-loop carrier synchronization methods, this method can be functional based on mere complex multiplications and additions and can realize high accuracy frequency offset estimation of data at normalized frequency offset within 4.8e-4.
KEYWORDS: Telecommunications, Demodulation, Modulation, Quadrature amplitude modulation, Receivers, Field programmable gate arrays, Technology, Design and modelling, Analog to digital converters, Computer simulations
In terahertz digital wireless communication systems, the performance of the demodulation system in the receiver directly affects the quality of the communication. Channel equalization technology is regarded as an important part of the receiver counteracting damage to terahertz communication system caused by Inter-Symbol Interference (ISI) produced by timing sampling deviation, channel distortions and the nonideal in-band response of ADC and terahertz devices. Compared with non-blind equalization, blind equalization can equalize the channel by using the prior information of the received sequence itself only and does not require pre-training data. The most commonly used blind equalization algorithm is Constant Modulus Algorithm (CMA), while it does not perform well in non-constant modulus modulation. CMA-Assisted Decision Adjusted Modulus Algorithm (CADAMA) can effectively solve the above problem. Furthermore, traditional serial equalization algorithms are no longer applicable due to the serious imbalance between terahertz band high-speed demodulation requirements and available computing resources. Therefore, this paper develops a high-speed parallel CADAMA equalization scheme for high-order QAM modulation. The general architecture of its implementation which can be widely used in terahertz demodulation systems is presented. Meanwhile, this paper gives the simulation results of the convergence performance of the parallel equalizer and compares with the serial algorithm to analyze the loss caused by parallelization, which demonstrates the effectiveness and reliability of the parallel equalization algorithm. Finally, the high-speed parallel blind equalization algorithm is implemented in FPGA and applied to the high-speed terahertz band online demodulation system at 15 gigabits per second (Gbps) data rate, 64QAM modulation.
KEYWORDS: Renewable energy, Wind energy, Solar energy, Solar radiation models, Data transmission, Binary data, Wireless communications, Internet, Antennas, Systems modeling
Wireless backhauling with renewable powered base stations (BSs) provides an attractive and cost-effective solution to enabling ultra dense cellular networks to meet the ever-increasing traffic demands of massive Internet of Things applications. To address the spectrum shortage in wireless backhaul networks, we propose to offload the delay-tolerant data traffic to the shared spectrum bands and jointly consider BSs' energy consumption, spectrum allocation, and data routing to maximize the amount of delivered data. Numerical results demonstrate that the adopted sequential fixing algorithm implements a near-optimal solution and our scheduling strategy significantly outperforms the conventional strategies which only considers spectrum allocation. Moreover, the impacts of resources availability on the performance of obtained strategies are analyzed.
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