# Data-Aided and Non-Data-Aided SNR Estimators for CPM Signals in Ka-Band Satellite Communications
## 1 Introduction  
Many bands can be used for satellite communication; these bands include L, S, C, Ku, and Ka bands. Adopting a high-frequency band in the construction of a broadband satellite communication network is necessary to address the issue of the limited bandwidth of satellite communication. Current high-throughput satellite (HTS) systems for broadband-distributed user access are designed following two main concepts: The use of Ka-band radio frequency (RF) links both for the forward and for the return link; The use of multispot coverage: this technique is largely applied to increase the system throughput through frequency reuse and system reconfigurability [1]. While with the exploitation of extremely high-frequency (EHF) bands (30-300 GHz) for broadband transmission over satellite links, the Q-V band (30-50 GHz) and W-band (75-110 GHz) seem to offer very promising perspectives [2]. This paper use Ka-band as the operating frequency band for satellite communication because of the advantages of the wideband, little disturbance, and small-sized terminals [3]. At frequencies beyond 10 GHz, rainfall is one of the important atmospheric parameters (hydrometeors) which causes signal degradation along both terrestrial and satellite tracks [4; 5; 6]. Therefor the rain attenuation is considered to be the main factor in Ka-band satellite communications [7; 8; 9]. Rain rate data was measured through OTT Parsival, which shows the rain rate of about 50 mm/h and attenuation of 10.7, 11.6, and 11.3 dB for 12.25, 19.8, and 20.73 GHz, respectively, for 0.01% of the time for the combined values of rain rate and rain attenuation statistics [10; 11]. The design of millimeter wave communication links and the study of propagation impairmentsat higher frequencies due to a hydrometeor, particularly rain, require the knowledge of 1-min. rainfall rate data [12; 13]. ITU-R series play an important role in prediction of rainfall attenuation. The effectiveness of ITU-RP.618-12 method is seen in which the better prediction for rain-induced attenuation and the propagation data and prediction methods required for the design of Earth-space telecommunication systems. ITU-RP.311-16 shows the data acquisition, representation and analysis of radio wave propagation studies [14]. The adaptive-coded and modulation (ACM) system is an effective measure to resist rain attenuation because it can guarantee communication quality and overcome the problem of system resource waste caused by rainfall reserve. Hence, ACM could be one of the technologies with the most potential and value. The basic principle of ACM technology in Ka-band satellite communication is to estimate the signal-to-noise ratio (SNR) at the receiver and feed the value back to the transmitter. The transmitter changes the coding and modulation mode according to the signal-to-noise ratio (SNR). The common modulation used for satellite communications mainly includes multiple phase shift keying (M-PSK) and Multiple Quadrature Amplitude Modulation (M-QAM) [15]. The limitations of these modulation techniques in the frequency band utilization restrict the development of satellite communications because of the continuous improvement of the channel bandwidth requirements of satellite communications. Continuous phase modulation (CPM) is a constant envelope continuous phase modulation signal with a wide bandwidth, high power utilization, and a certain coding gain compared with phase shift keying (PSK) modulation [16; 17]. CPM also has a larger signal state under some specific parameters, which makes a larger matched filters, leading to a high implementation complexity of optimal receiver. However, this problem can be solved with the effective choice of parameters and the use of large capacity devices. Hence, CPM has become one of the most important modulation methods in recent years. This paper uses the CPM signal to replace the PSK modulation as the main modulation mode of ACM system in Ka-band satellite communication.