A Study on Log-Likelihood Ratio Setting for Superposed Multicarrier Transmission
Details
Superposed multicarrier transmission scheme is known to improve frequency utilization efficiency where several wireless systems share spectrum. On superposed band, log likelihood ratio (LLR) cannot be set correctly because of interference, which results in BER (Bit Error Rate) degradation. To suppress the effect of interference, forward error correction (FEC) metric masking is proposed. In this technique, LLRs that correspond to superposed band is set to zero, because received bits that correspond to superposed band is unreliable. This scheme requires superposed band detection and does not consider channel estimation error. We proposed an iterative esimation technique for undesired signal power in [6]. Although, this scheme does not require superposed detection beforehand, due to the estimation error of undesired signal power, BER is degraded. In this report, we propose an estimation technique for undesired signal power and superposed band to calculate LLR correctly. This scheme estimates superposed band within 1 packet and using the information about superposed band, undesired signal power is estimated using pilot symbols. Simulation results show that as the number of pilot symbols increases, BER performs better than [6] and gets closer to the BER when the estimation of undesired signal power is perfect.
