Multi-Carrier Techniques Performance on Ionospheric Channel for Delay-Sensitive Applications

Abstract

Multi-carrier modulations are widely employed in HF communications, and particularly OFDM, mainly because their ease of generation by means of DFT and also their appealing properties that can turn a selective fading channel into a set of flat channels. In order to cope with deep nulls in the channel traditional approach has been the use of channel coding and interleaving, thus causing an increase in communication delay. For delay-sensitive applications, spreading schemes over OFDM, such as OFDM-CDM can be applied. If CSI is known at transmitter, system performance can be improved by BER-optimum power loading and channel matrix SVD decomposition of OFDM-CDM signal. These techniques are well suited to delay-sensitive applications as they incur in no further delays.

Impact of CSI latency on HF multi-carrier communications for delay-sensitive applications

“…In a previous work, a scheme of power allocation over OFDM based on BER minimisation was studied [4]. There, it was shown power allocation on its own cannot overcome the stringent requirements of the HF channel, as deep nulls will cause the loss of the data in the sub-carriers affected by them.…”