Design and exploitation of precoded in-band pilots for OFDM signal in cognitive radio

Spectrum sensing and signal identification at low SNR, where synchronization and demodulation are not achievable, have emerged as two of the most critical challenges in cognitive radio network. A precoded in-band pilots design for OFDM signal (PIP-OFDM) is proposed in this paper to simplify the spectrum sensing and signal identification for dynamic spectrum sharing. The actual design of pilot signal in this OFDM system contains two groups of pilot tones, i.e. uniform pilot tones and identification pilot tones. Combining the two groups of pilot tones embedded in the OFDM signal, the spectrum sensing based on detecting the energy on pilot tones achieves an exceptionally good performance. In addition, the unique identification pilot code design for each transmitter in this network makes the signal identification easy and reliable. Theoretical analysis and simulation show that this design works well in spectrum sensing and signal identification at low SNR.