Estimation of Diversity Improvement for Satellite-to- Helicopter Radio Channel at Ku-band Manuel Garcia Sanchez 1 , Edgar Lemos Cid 1 , Ana Vazquez Alejos 1 , Santiago Garcia Fernandez 2 1 Dept. of Teoria de la Señal y Comunicación, University of Vigo, Vigo, Spain, manuel.garciasanchez@uvigo.es 2 Centro de Medidas Electromagnéticas (CEMEDEM), Armada Española, Marín, Spain, santiagogarcia@fn.mde.es Abstract—This contribution introduces the results obtained for the satellite-to-helicopter radio channel characterization in the Ku-Band. For the wideband sounding, the results show that, in terms of wideband radio channel characterization, the root mean square delay spread was small enough to allow using 32 or 72 MHz satellite transponders with no need of equalization. Regarding the narrowband radio channel analysis, we observed two important propagation phenomena due to the rotor blades: average power attenuation related to the obstruction of the direct ray, and power level oscillation dependent on the amplitude of the received multipath components. The signal fading related to both narrowband impairments could be compensated by using the spatial diversity technique. Additionally, we also analysed the signal obtained using polarization diversity in the receiver end in a setup simulating a satellite located behind the helicopter so totally blocking the direct ray. Generally speaking, we concluded that it is possible to implement an Automatic Gain Control or time diversity to compensate the both multipath and level fading. Index Terms—K band; delay spread, diversity, Doppler, radio channel, pseudo random noise sequence. I. INTRODUCTION The helicopter-to-satellite radio channel modelling is the aim of the sub-project SICOMORO BRANCH (“Broadband RAdio chaNnel CHaracterization for Communication Systems for Emergency Environments) [1] that pretends to analyse the satellite to earth radio channel at Ku frequency band in order to design and apply novel smart antennas for emergency and disaster scenarios. For this purpose, the band 14-14.47 GHz, reserved for mobile-to-satellite link according to the ITU-R radio Regulations [2], has been used in our measurements. In literature, there are lots of models for the mobile-to- satellite channel characterization, as in [3]; however there is a gap for the characterization of the helicopter-to-satellite transmission link, and so it is only likely to find just few references regarding measurements or simulations [4] for this radio channel. Due to the time variation feature of the helicopter-to-satellite radio link, important propagation impairments could be present requiring the design of specific mitigation techniques. For instance, in [5] the important effect of the channel variability due to the helicopter blades on the Radar Cross Section (RCS) is analysed. For our study we built a wideband channel sounder valid to estimate the signal delay spread and signal fading due to the helicopter blades screening. Moreover, we analysed the Doppler spectrum and estimated the gain achieved due to the use of polarization and spatial diversity techniques. For the wideband analysis, we obtained the channel impulse response by using the data recorded with the Sweep Time Delay Cross Correlation (STDCC) sounder technique. From it, we could estimate the root mean square delay spread (IJ rms ) for the wideband radio channel characterization. We calculated the time-varying complex signal envelope by integration of h(t,τ). This complex envelope was used to obtain the signal fading and the improvement of the signal reception due to the use of diversity techniques. In the following sections, we explain the measurement system and set-up; finally we discuss the results obtained for both wideband and narrowband analysis of the helicopter-to- satellite radio channel. II. EXPERIMENTAL RADIO CHANNEL CHARACTERIZATION A. Measurement system For the wideband radio channel characterization, we used a STDCC sounder. As shown in Fig. 1 the sounder transmits a Pseudorandom Binary Sequence (PRBS), which is 2 11 -1 bit long and has 80MHz bitrate. This baseband sequence is upconverted to a radiofrequency (RF) of 14.25GHz. Later, the RF signal is amplified to reach a power of +30dBm, and it is then fed to the transmitter antenna. The receiver system ( Fig. 2) has two reception branches in order to carry out diversity analysis. For both branches the signal is received through a right or left hand circularly polarized antenna, amplified with a 36dB low noise amplifier (LNA) and downconverted to an Intermediate Frequency (IF) of 175 MHz. Finally, for each branch, the IF signal is sampled at a rate of 1.25GSps for periods of 200ms, and the sampled data are stored in a computer for offline analysis. The transmitting and the two receiving elements consist of right hand circular polarization (RHCP) antennas, except for the totally blocked case when the polarization technique is used with a right hand and a left hand circular antenna (LHPA) placed in the branches of the receiver end, with one antenna per branch. We used a rubidium clock to synchronize all the equipment. The implemented sounder has the following performance parameters: • Dynamic range (DR): 33dB. Research funded by the Spanish Government, Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, (project TEC2011-28789-C02-02), AtlantTIC Research Center and the European Regional Development Fund (ERDF). The 8th European Conference on Antennas and Propagation (EuCAP 2014) 978-88-907018-4-9/14/$31.00 ©2014 IEEE 2266