DVB-S2 Adaptive Coding and Modulation for HAP Communication System

Abstract

Combining some of the best terrestrial and satellite systems' characteristics, high altitude platforms (HAPs) have recently emerged as an alternative solution for the provision of broadband services. Characterised by challenging propagation conditions in the allocated frequency bands, they require efficient utilisation of radio interface in order to make best use of the available spectrum. This paper analyses possible utilisation of DVB-S2 standard on HAPs, focusing on the performance of its adaptive coding and modulation (ACM) procedures as a mean of maximizing the link reliability and throughput. Two distinct operating scenarios are addressed, one assuming static channel conditions with the applied rain fading and the other representing mobile channel conditions along a representative railway track. We show that by considering only a subset of transmission modes (MODCODs) defined by the DVB-S2 standard, the system could be optimized in terms of achievable spectral efficiency as well as in terms of implementation complexity. A procedure for optimal MODCOD subset selection is proposed, taking into account the predefined switching thresholds and round-trip time delay.

Target BER Driven Adaptive Coding and Modulation in HAP Based DVB-S2 System

“…The following evaluation of DVB-S2 ACM performance in mobile HAP channel is based on the simulation results provided in [9]. In particular, a subset of 7 MODCODs is considered and the SNR switching thresholds assuming target BER set to 10 -5 are used.…”

“…In Figure 6 the actual and estimated BER curves and the switches between the MODCODs are depicted for the same SNR trace as shown in Figure 4. It can be ascertained that for the target BER set to 10 -3 , the actually experienced BER ( 5.5×10 -4 ) is even lower than the targeted value, which is most likely a consequence of using the previously [9] calculated SNR switching thresholds for the target BER set to 10 -5 . For the target BER set to 10 -4 the link BER ( 1.5×10 -4 ) is just slightly above the targeted value, with the error being ascribed to BER estimation error.…”

“…It is explained into great detail in [8,9] and used in this study as follows. Concerned with mobile HAP operating environment the GW is located on HAP and a single user terminal (UT) is assumed onboard high-speed train.…”

“…On the forward link, the ACM is exploited in order to optimize the link efficiency according to changing propagation conditions. Moreover, as proposed in [9], only a subset of 7 MODCODs is considered for the operation in mobile HAP propagation environment. In particular these are QPSK 1/4, QPSK 1/2, QPSK 3/4, 8PSK 2/3, 16APSK 2/3, 32APSK 3/4 and 32APSK 9/10.…”

“…The latter is typically based on the predefined SNR switching threshold values, that can for a given target BER be obtained from simulations of MODCODs in the AWGN channel. For the case of target BER set to 10 -5 , the DVB-S2 SNR switching thresholds are provided in [9]. Efficient MODCOD switching algorithm should also take into account contributions of the effects not intended to be compensated by ACM (e.g.…”