GMSK+PN遥外测体制的性能分析

Performance analysis of telemetry and ranging based on GMSK+PN technique

考虑到现有测控体制的带宽效率较低,研究基于高斯最小频移键控(Gaussian Minimum-Shift Keying,GMSK)+伪码(Pseudo-noise Code,PN)的新一代遥外测体制,以提高测控系统的带宽效率.首先描述了GMSK+PN信号的调制原理,将遥测数据的GMSK相位和伪码测距信号叠加后调制在同一载波上,实现了二者的同流传输.接着简述了GMSK+PN信号的解调原理,接收机经GMSK解调、测距信号重建和测距信号解调,得到遥测数据和伪距.然后对GMSK+PN的调制、解调进行仿真,得到了不同参数下的频谱特性、遥测误码率和测距精度等性能,并分析了性能与滤波器参数值、测距信号加权因子、测距成形脉冲、伪码码率与遥测码率的比值等参数取值之间的约束关系.最后给出调制参数的取值建议.结果表明,GMSK+PN体制具有很高的带宽效率,与现有航天测控体制相比,带宽降低22%以上,特别是在非线性信道下的优势更为明显.

In order to improve bandwidth efficiency,a novel technique based on Gaussian Minimum-Shift Keying（GMSK）＋pseudo-noise（PN）code for telemetry and ranging is studied in this paper.Firstly,we describe the modulation principle of GMSK＋PN technique which is able to transmit high rate telemetry data and ranging signal simultaneously on one frequency band by modulating high rate telemetry data and ranging signal on the same carrier wave.Then,the demodulation process of GMSK＋PN signal is depicted in chief.The telemetry data and pseudo range are obtained by a series of operations including GMSK demodulation,ranging signal reconstruction and ranging signal demodulation.Afterwards,the modulation and demodulation algorithms of GMSK＋PN signal are simulated to obtain signal spectrum,bit error rate of telemetry data and ranging precision.The bandwidth efficiency of GMSK＋PN technique is significantly increased compared with the existing TTC system.Concretely,the bandwidth of GMSK＋PN signal is just 34% compared with a system which employs spread spectrum technique for ranging and QPSK for data transmission,51%compared with a TTC and data transmission integrated system based on BPSK,78% compared with UQPSK＋PN.The simulation results are then analyzed to induce the inherent relationship between the performance and the values of the parameters including BT,raging signal weight,raging signal shaping and chip rate to telemetry data rate ratio.Finally,the recommendation of appropriate parameters for differentapplications is given.The simulation results demonstrate that the proposed GMSK＋PN technique can improve band efficiency obviously with just a little cost of bit error rate of telemetry data.Especially,the advantage of GMSK＋PN is more prominent when the signal is transmitted on a nonlinear channel.