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BER performance for PSK-OFDM optical link over Exponentiated Weibull atmospheric turbulence
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摘要
本文研究了指向误差、气动光学效应及Exponentiated Weibull大气湍流联合效应对OFDM光链路通信性能的影响。其中OFDM链路采用PSK调制，应用Meijer G函数推导得到多载波条件下总平均误码率的闭合表达式。根据平均误码率闭合表达式进行了仿真，分析了不同大气湍流强度、PSK调制阶数、抖动标准差和波束宽度对误码率的影响。通过仿真分析证明基于Exponentiated Weibull大气湍流模型，在不同湍流强度条件下误码率随着发射功率的增加改善近似。当抖动标准差小于0.7及调制阶数小于4时，增大发射功率对改善链路误码率效果明显。
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关键词:
- 误码率 /
- Exponentiated Weibull分布 /
- 指向误差 /
- 正交频分复用 /
- PSK
Abstract
Aiming at the combined effects of the Exponentiated Weibull atmosphere turbulence, aero-optical effects and pointing errors on space optical links, the bit error rate (BER) performance of the orthogonal frequency division multiplexing (OFDM) optical communication link is investigated. OFDM links adopted PSK modulation. The closed-form expression for average bit error rate is derived based on a Meijer's G function. The relationship between the BER performance and the transmitted optical power under different parameters such as the atmosphere turbulence, the normalized jitter standard deviation and the normalized beam-width is analyzed by simulation. The results show that the BER performance is similarly improved in different intensity turbulence by increasing the transmitted optical power. The BER performance is obviously improved by increasing the transmitted optical power when the normalized jitter standard deviation is less than 0.7 and the modulation order is less than 4.
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Overview
Overview: Laser communication has many advantages, such as large bandwidth, high speed, fast and simple deployment and free band. Compared with traditional radio communication, it has a wider application prospect in civilian and military applications. However, in aviation laser communication, aircraft flight at an altitude of 7 km~10 km, airborne laser link is extremely easy to be influenced by the atmospheric turbulence intensity fluctuation in the receiving end, at the same time, the atmospheric boundary layer around the plane generated by the aero optical effects on the laser signal transmission will be affected. Orthogonal frequency division multiplexing (OFDM) is a multi carrier modulation mode, which modulates multiple independent data streams through multiple subcarriers with different frequencies. It has good anti frequency selective fading, narrow band interference and high channel utilization. OFDM subcarrier can use many different modulation modes. The two main modulation modes are multilevel quadrature amplitude modulation (MQAM) and multiple phase-shift keying modulation (MPSK). The quadrature amplitude modulation (QAM) demodulator needs to detect the phase and amplitude at the same time, and phase shift keying (PSK) demodulation only needs to detect the phase. In 2012, Barrios R and Dios F first proposed the Exponentiated Weibull atmospheric turbulence model for the weak to strong turbulence and the average aperture. Therefore, aiming at the characteristics of Aeronautical laser communication, based on the Exponentiated Weibull distribution atmospheric turbulence model, the joint pointing error is used to study the performance of OFDM system with PSK modulation mode. Aiming at the combined effects of the Exponentiated Weibull atmosphere turbulence, aero-optical effects and pointing errors on space optical links, the bit error rate (BER) performance of the OFDM optical communication link is investigated. OFDM links adopted PSK modulation. The closed-form expression for average bit error rate is derived based on a Meijer’s G function. The relationship between the BER performance and the transmitted optical power under different parameters such as the atmosphere turbulence, the normalized jitter standard deviation and the normalized beam-width is analyzed by simulation. The results show that the BER performance is similarly improved in different intensity turbulence by increasing the transmitted optical power. The BER performance is obviously improved by increasing the transmitted optical power when the normalized jitter standard deviation is less than 0.7 and the modulation order is less than 4. In practical application, the derived average error rate closed expression can be used to estimate the performance of the system and provide reference for the design of the aviation laser communication system.
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图 1 当Cn2=1×10-14，M=4，σs/r=0.5，wz/r=1时，不同传输距离下平均误码率与发射功率的关系
Figure 1. Average BER versus the transmitted power Pt for the different propagation distance when M is 4, Cn2=1×10-14, the normalized jitter σs/r is 0.5 and the normalized beam width wz/r is 1
图 2 当L=50 km，M=4，σs/r=0.5，wz/r =1时，不同湍流强度下的平均误码率与发射功率的关系
Figure 2. Average BER versus the transmitted power Pt for the different turbulence strengths when L is 50 km, M is 4, the normalized jitter σs/r is 0.5 and the normalized beam width wz/r is 1
图 3 当L=50 km，Cn2=1×10-14，σs/r=0.5，wz/r=1时，副载波不同M-PSK调制下的平均误码率与发射功率关系
Figure 3. Average BER versus the transmitted power Pt for M-PSK when L is 50 km, the normalized jitter σs/r is 0.5 and the normalized beam width wz/r is 1, Cn2 is 1×10-14
图 4 当L=50 km，Cn2=1×10-14，M=4，wz/r=1时，不同σs/r比值下的平均误码率与发射功率的关系
Figure 4. Average BER versus the transmitted power Pt for the different normalized jitter when L is 50 km, M is 4 and the normalized beam width wz/r is 2, Cn2 is 1×10-14
图 5 当L=50 km，Cn2=1×10-14，M=4，σs/r=0.5时，不同ws/r比值下的平均误码率与发射功率的关系
Figure 5. Average BER versus the transmitted power Pt for the different normalized beam width when L is 50 km, M is 4 and the normalized jitter σs/r is 0.5, Cn2 is 1×10-14
表 1 仿真参数
Table 1. Simulation parameter
参数 值 波长(λ)/nm 1550 OFDM信号持续时间(Ts)/ms 1 接收孔径/cm 10 PD负载阻抗(RL)/Ω 50 PD响应度(ρ)/(R/A/W) 0.8 
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