Currently,the BeiDou⁃3(BDS⁃3)precise point positioning(PPP)service(PPP⁃B2b)mostly employs the ionosphere⁃free(IF)combination model for precise timing,which tends to amplify the noise in observation values.To address this issue,this paper proposes a real⁃time BDS⁃3 precise unidirectional timing model based on uncombined(UC)observations using the BDS⁃3 PPP⁃B2b service.This model resolves the challenge of the amplified observation noise inherent in the IF combination model.The experiment involved selecting eight global navigation satellite system(GNSS)observation stations within China and collecting continuous observation data for 15 d.A comparative analy⁃sis with the traditional dual⁃frequency IF combination PPP timing model showed that the BDS⁃3 UC PPP timing based on the BDS⁃3 PPP⁃B2b service can achieve a timing preci⁃sion of 0.5 ns.In addition,it was found that due to global positioning system(GPS)satellite clock products in the BDS⁃3 PPP⁃B2b service not being unified to the standard time,the GPS IF PPP timing method based on the BDS⁃3 PPP⁃B2b service is not recommended for precise timing.In summary,the BDS⁃3 UC PPP timing model proposed in this paper is suitable for precise timing,providing observa⁃tion values with smaller noise,and its timing accuracy is comparable to that of the BDS⁃3 IF PPP,with slightly better frequency stability.
WANG YongLIU TianjunGU ShengfengGE YulongJIANG Weiping
互联网企业的发展受到科学技术以及企业内部商业模式等因素的影响,合理地对企业价值进行评估,能够帮助投资者预测其未来增长潜力和盈利能力,识别潜在的投资机会。以恺英网络为例,在介绍互联网企业特点的基础上对企业价值评估方法的适用性进行分析,选择使用FCFF(free cash flow for the firm)模型估算企业现有价值,使用B-S(black-scholes)模型来测算企业的潜在价值,最终得到企业价值评估值。结果发现,相比于传统评估方法,FCFF模型与B-S模型结合后的评估结果更接近于企业的实际价值。