Threshold Extending Receiver Structures for CE-OFDM

Constant Envelope OFDM (CE-OFDM) alleviates the high peak-to-average power ratio (PAPR) problem in OFDM. However, since CE-OFDM is based on angle modulation, it is susceptible to the well known threshold effect. This paper considers several threshold extending receiver structures for CE-OFDM. The simple arctangent receiver [4] is compared to the conventional limiter-discriminator type FM receiver and a second-order phase locked loop structure. A novel cycle slip eliminator (CSE) is also developed to detect and cancel cycle slips and is shown to provide significant threshold extension. It is observed that the optimum receiver design depends on the CE-OFDM modulation index. The various schemes are compared in terms of threshold extension capability and complexity for a wide range of modulation indexes.