The Effect of Tandem Band and Amplitude Limiting on the Eb/No Performance of Minimum (Frequency) Shift Keying (MSK)
The Effect of Tandem Band and Amplitude Limiting on the Eb/No Performance of Minimum (Frequency) Shift Keying (MSK)
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DOI：
10.1109/tcom.1974.1092108
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发表时间：
1974-10
期刊：
影响因子：
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通讯作者：
H. Mathwich;J. F. Balcewicz;M. Hecht
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文献类型：
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作者：
H. Mathwich;J. F. Balcewicz;M. Hecht
最小（频移）键控（MSK）是一种数字调制技术，它可以被看作是峰值频率偏差精确等于\pm(1/4)R_{L}的频移键控（FSK），其中rl是链路比特率，也可以看作是偏移键控的四相移键控调制。在调制器和解调器之间没有带宽或幅度限制的情况下，MSK的E_{b}/N_{0}性能与相干检测的二相移键控（PSK）相同。本文简要回顾和定义了MSK。然后提出了一种系统模型，其中在理想调制器和解调器之间插入一个发射带限滤波器、一个硬限幅器和一个接收带限滤波器的串联组件。该模型旨在模拟实际链路（如航天器到地面链路），其中信道带宽（B_{c}）约束很重要，RF处的后调制滤波是不可取的，并且需要通过作为幅度限制器的高效发射机进行传输。然后通过分析得出了由于带宽和幅度限制而导致的E_{b}/N_{0}退化。仅限带就会对每个正交相量所携带的数据产生码间干扰，但在所使用的假设集下不会产生互相串扰。在限幅的情况下，存在一种互相串扰机制。推导了几种周期波形的平均符号失真、符号能量降低和噪声降低。对于3db带宽（B_{L} / rl）比至少为0.6的复合系统，理论E_{b}/N_{0}的衰减小于1db。然后，对带限和随后的硬限幅发射机的后调制频谱进行了参数化实验数据的报告。本文还介绍了使用带限滤波器、限幅器和第二个带限滤波器的串联组件测量E_{b}/N_{0}退化的数据。限幅器大大增加了主瓣以外的谱旁瓣的电平。研究发现，对于所有传输带通滤波的显著值加上随后的限幅，99%的传输能量包含在bc = 1.1 rl内。此外，当bl大于0.65 rl时，E_{b}/N_{0}的衰减很小（十分之一分贝）。当B_{L} = 0.55 R_{L}时，E_{b}/N_{0}发生快速降解。这些数据适用于带-带-幅-带有限系统模型。放置在发射和接收滤波器之间的限幅器如所预测的那样引起数据符号形状的互相串扰和畸变；然而，在研究的情况下，由限幅效应本身引起的E_{b}/N_{0}退化（这是b L的函数）从未超过0.3 ~ 0.5 dB。
Minimum (frequency) shift keying (MSK) is a digital modulation technique which can be viewed either as frequency-shift keying (FSK) with peak frequency deviation precisely equal to \pm(1/4)R_{L} where R L is the link bit rate or as an offset-keyed quaternary phase-shift-keyed modulation. In the absence of bandwidth or amplitude limiting between the modulator and the demodulator, the E_{b}/N_{0} performance of MSK is identical to that of coherently detected binary phase-shift keying (PSK). This paper briefly reviews and defines MSK. It then presents a system model in which a tandem assembly of a transmit band-limiting filter, a hard limiter, and a receive band-limiting filter are interposed between an ideal modulator and demodulator. This model is aimed at simulating actual links (such as spacecraft-to-ground links) in which channel bandwidth (B_{c}) constraints are important, postmodulation filtering at RF is objectionable, and transmission through efficient transmitters which operate as amplitude limiters is a requirement. An analysis then derives the E_{b}/N_{0} degradation due to both bandwidth and amplitude limiting. Band limiting alone causes intersymbol interference on the data carried by each of the quadrature phasors but no interphasor crosstalk under the set of assumptions used. With amplitude limiting also present, an interphasor crosstalk mechanism exists. The average symbol distortion, symbol energy reduction, and noise reduction are derived for several periodic waveforms. For composite systems with 3-dB bandwidth (B_{L}) -to-R L ratios of at least 0.6, the theoretical E_{b}/N_{0} degradation is less than 1 dB. Parametric experimental data are then reported on the postmodulation spectrum of a transmitter with band limiting plus subsequent hard amplitude limiting. Data are also presented on the E_{b}/N_{0} degradation measured using tandem assemblies of a bandlimiting filter, an amplitude limiter, and a second band-limiting filter. The amplitude limiter substantially increases the level of the spectral side lobes beyond the main lobe. It was found that for all significant values of transmit bandpass filtering plus subsequent amplitude limiting, 99 percent of the transmitted energy is contained within B c = 1.1 R L . Further, little E_{b}/N_{0} degradation (tenths of a decibel) was measured if B L was greater than 0.65 R L . A rapid degradation of E_{b}/N_{0} occurred when B_{L} = 0.55 R_{L} . These data apply for the band-band-amplitude-band limited system model. The amplitude limiter placed between the transmit and receive filters caused interphasor crosstalk and distortion of the data symbol shapes as predicted; however, E_{b}/N_{0} degradation caused by the amplitude-limiting effects by themselves (which are a function of B L ) never exceeded 0.3 to 0.5 dB for the cases studied.