Development of Low Power Consumption OFDM Receiver based on Joint RF and Baseband Signal Processing

正交频分复用技术（OFDM）是一种有效的技术，能够减少多径环境下由于延迟扩散而导致的性能下降，并作为地面数字电视广播和无线局域网（LAN）的传输技术，但它不能改善由于衰落而导致的性能下降。最近，日本推出了基于OFDM的手持终端数字地面电视广播技术。然而，接收器的功耗成为一个问题。接收机的射频前端组件需要低噪声系数（NF）线性放大器。一般来说，需要高功耗放大器来降低NF。此外，包含FFT处理器的基带信号处理块需要巨大的计算成本。也就是说，原则上很难降低功耗。为了降低OFDM接收机的功耗，本研究项目提出了一种自适应混合信号处理方法，该方法将包括低NF放大器在内的射频信号处理组件根据信道条件自适应控制其功耗。当通道条件良好时，射频前端放大器工作在低功率模式，当通道条件变差时，将其切换到低NF模式。为了测量信道状况，基带块测量每个OFDM子信道的信噪比（SNR），并根据测量的信噪比估计瞬时误码率。在这个项目中，我们已经证实了所提出的混合信号处理接收机能够降低功耗。

Although OFDM (Orthogonal Frequency Division Multiplex) is an efficient technique capable of reducing the performance degradation due to delay spreading in multipath environment and employed as a transmission technique for terrestrial digital television broadcasting and wireless LAN (local area network), it is not capable of improving the degradation due to fading. Recently, digital terrestrial television broadcasting for handheld terminals based on OFDM has been introduced in Japan. However, the power consumption of the receiver becomes a problem. The RF (radio frequency) front-end component of the receiver requires low noise figure (NF) linear amplifier. Generally speaking, it requires high power consumption amplifier to reduce the NF. Furthermore, the baseband signal processing block including FFT processors requires huge computational cost. That is, it is difficult to reduce the power consumption in principle.In order to reduce the power consumption of the OFDM receiver, this research project has proposed an adaptive mixed signal processing, where the RF signal processing component including low NF amplifier is adaptively controlled its power consumption according to the channel condition. When the channel condition is good, the amplifier at the RF front-end is operated in low power mode, while it is switched to low NF mode if the channel condition becomes worse. In order to measure the channel condition, the baseband block measures the signal-to-noise ratios (SNR) of each OFDM sub-channel and estimates the instantaneous bit error rate from the measured SNRs.In this project, we have confirmed that the proposed mixed signal processing receiver is capable of reducing power consumption.