Band edge filters perform non data-aided carrier and timing synchronization of software defined radio QAM receivers

To demodulate the input signal, the receiver must align its local radio frequency oscillator with the frequency and phase of the received signal´s unmodulated carrier as well as align its sampling clock with the epochs of the underlying modulation process embedded in the received signal. When the frequency offset of the received signal is quite small phase locked loop (PLL) can be used to drive the phase error to zero, however PLLs fail to operate when the received signal has a significant frequency offset. Thus, when a significant frequency offset does exist, it must be estimated and removed prior to the PLL. Frequency locked loop (FLL) are used to accomplish this task. The maximum likelihood frequency estimator uses a frequency detector formed by a pair of band edge (BE) filters. Oddly, there is remarkably little information in the literature on the ability of the band edge filter to support the modulation timing acquisition. In this paper we show how the band edge filter can support two synchronization tasks of carrier frequency acquisition and modulation timing acquisition. We present a receiver architecture and demonstrate its ability to acquire carrier frequency and timing phase alignment without data aided observations.