ABSTRAKSI: Teknologi HAPS memiliki kelebihan yang dapat menutupi kekurangan dari teknologi terrestrial maupun satelit. High Altitude Platform Station memberikan keuntungan dengan adanya sinyal Line of Sight (LOS) yang diterima. Pada kondisi real di lapangan, daya yang diterima merupakan gabungan dari daya sinyal dominant/LOS dan daya sinyal multipath. Parameter yang menggambarkan perbandingan daya sinyal dominant dengan daya sinyal multipath disebut K factor. Penggabungan MIMO dan OFDM dengan kanal HAPS diharapkan akan dapat memberikan sistem komunikasi dengan kapasitas yang lebih besar dan deteksi error yang lebih kecil.
Penelitian ini menganalisis kinerja MIMO STBC 2 x 2 dan OFDM pada kanal HAPS 2.4 GHz. Sistem yang dianalisis dibatasi untuk kanal Rician fading dengan hubungan antar antena uncorrelated. Penelitian dilakukan berdasarkan pertambahan sudut elevasi antara platform HAPS dengan user terminal yang mengakibatkan bertambahnya nilai K factor dan mempengaruhi kinerja system OFDM yang terpengaruh multipath fading.
Pada sistem HAPS, nilai K factor sangat mempengaruhi performansi, semakin bertambahnya K factor (sudut elevasi semakin besar) maka semakin baik performa sistem. pada sudut elevasi 100 – 400 kinerja sistem tidak begitu berbeda jauh, tetapi setelah sudut 500 terjadi peningkatan kinerja yang cukup signifikan hingga sudut 90 0 (kf=16.8) performansinya mendekati kondisi awgn karena didominasi oleh sinyal Line Of Sight (LOS) dimana pencapaian BER 10-4 dicapai pada SNR 18 dB.Kata Kunci : HAPS, OFDM, sinyal dominant/ LOS, sinyal multipath, K factor, sudutABSTRACT: HAPS technology has some strength which covers up the weaknesses of both terrestrial and satellite technology. High Altitude Platform Station gives benefit by providing the accepted Line Of Sight (LOS) signal. In real condition in the field, the power accepted is the combination of dominant signal power/LOS and multipath signal power. A parameter which shows the comparison of dominant signal po wer and multipath signal power is called as K factor. The combination of MIMO and OFDM with HAPS channel is expected to give a communication system with larger capacity and less error detected.
This research analyzes the performance of MIMO STBC 2 x 2 and OFDM in HAPS channel 2.4 GHz. The system analyzed is limited in Rician fading channel in which the correlation between antennas is uncorrelated. This research is done based on the increasing of elevation angle between HAPS platform and user terminal which causes the increasing of K factor value and influences the performance of OFDM system affected by multipath fading.
In HAPS system, K factor value greatly affects the performance; the more K factor increases (when elevation angle is getting larger), the be tter performance of the system is. In elevation angle 100 – 400, the performance of the system is not totally different; but after the angle 500 gets an increasing performance significantly up to the angle 900 (kf=16.8), the performance gets close to the awgn condition as it is dominated by Line Of Sight (LOS) signal, in which BER 10-4 is achieved at SNR 18 dB.Keyword: HAPS, OFDM, dominant signal/LOS, multipath signal, K factor, elevation