We describe the implementation of a novel adaptive wireless communications waveform for interference avoidance (IA) in re-configurable logic devices. While other transform domain-based IA waveforms have been suggested, the wavelet packet modulation (WPM) system described here is unique in its multiplexing of complex quadrature amplitude modulation symbols onto orthogonal wavelet packets for unrivaled time-frequency agility. We examine the realization aspects of dynamically instantiating the transmit side inverse discrete wavelet packet transform (DWPT) and receive side DWPT filter bank structures, and the WPM symbol timing recovery, in Field Programmable Gate Array (FPGA) devices. This work applies Trenas' re-configurable wavelet packet transform (WPT) architecture to a wireless communications system, draws upon Jones' theoretical foundation for orthogonally multiplexed communications, and utilizes Lindsey's WPM supersymbol tuning and Kjeldsen's WPM symbol synchronization algorithms.
The novel use of a Maximum Likelihood Decision-Directed (MLDD) synchronization scheme for a Wavelet Packet Modulation (WPM) System is discussed. MLDD synchronization allows symbol synchronization without edge detection. Multi-Carrier Modulation (MCM) techniques are being increasingly employed in military communication networks to combat time-dispersive and time-variant channel effects. One MCM method, Coded Orthogonal Frequency Division Multiplexing, has been particularly effective against multipath fading environments. Wavelet packet modulation has recently been introduced to address the need for improved transmission performance over channels with joint time and frequency interference components. Wavelet Packet Modulation's strength rests in a flexible, custom mapping of the desired signal on the communications channel at the transmitter to avoid a variety of a priori noise/interference patterns. The use of wavelet packet modulation on wireless channels has been hindered due to symbol synchronization not being achievable with conventional edge detection techniques. A MLDD receiver symbol timing recovery algorithm is presented here that should help expedite the adoption of WPM on wireless channels.