Energy-efficient bit and power loading options for practical OFDM systems with pilot-aided channel estimation

In this article, we present options for energy-efficiency in adaptive bit and power loading algorithm in practical OFDM systems with imperfect Channel State Information (CSI) and pilot-aided channel estimation. We consider rate-adaptive and margin-adaptive schemes always treating energy-efficiency as the key paradigm. The studies presented aim at lowering the energy-wastage related to pilot symbols while maintaining the total transmit energy per OFDM symbol constraint. Given the energy constraints in rate-adaptive schemes, the number of pilots and their energy are chosen trading off between the Bit-Error-Rate (BER) performance and the efficiency of the spectrum usage. In margin-adaptive schemes the number of pilots and their energy are minimized to meet the required QoS parameters. We present possible options for the allocation of the available energy between pilots and data, and examine them through computer simulations in Long-Term Evolution (LTE) system scenarios.