Channel estimation for LTE downlink in High Altitude Platforms (HAPs) systems

We describe in this paper, channel estimation performance evaluation of Long Term Evolution (LTE) downlink that uses Orthogonal Frequency Division Multiplexing (OFDM) technique, which employs High Altitude Platforms (HAPs) as radio communication channel. HAPs have advantages due to unique altitude position between terrestrial and satellite systems and hence promising as alternative candidate for radio communication channel in the future. LTE is predecessor of LTE Advanced that has been selected as Fourth Generation (4G) of mobile communication systems. Channel estimation is the vital part of receiver if the system uses coherent and multi-level demodulation. Therefore, we choose two estimation methods, Least Square (LS) and Linear Minimum Mean Square Error (LMMSE), to evaluate the performance in term of Mean Square Error (MSE) and Bit Error Rate (BER) versus Signal Noise to Ratio (SNR). The evaluations are performed in different elevation angles from HAPs to user in the ground, velocities of user, and modulation orders. The performance evaluation results of MSE and BER for LMMSE are better than LS, which lower elevation angle has lower performance. Furthermore, higher velocity make increases the performance gap between elevation angles. Finally, higher modulation order also produces lower performance.