Orthogonal convolutional modulation for UWB-impulse radio systems: performance analysis and adaptive schemes

In the context of UWB (ultra-wide band) impulse radio (IR) heterogeneous low data-rate networks, the need for coding/modulation schemes amenable of both coherent and noncoherent detection has emerged. The rationale is the potential coexistence of different classes of nodes, characterized by different complexity and performances. In such scenario, one of the main technical challenges is the design of efficient coding/modulation schemes incorporating forward error correction (FEC) and spreading capabilities, thus providing the necessary processing and coding gain, to guarantee robust communications. In this work, we introduce novel coding schemes exploiting the trellis structure of orthogonal convolutional codes for generating time-hopping sequences suitable for UWB-IR, while simultaneously mapping the information bits onto the transmitted waveforms. Namely, we present a new class of orthogonal convolutional modulation (OCM) schemes, highlighting the trade-offs in terms of coherent vs. non-coherent detection performance. Then we develop an adaptive OCM scheme (AOCM) for application to broadcast transmission in heterogeneous UWB-IR networks, illustrating advantages in terms of energy savings and potential drawbacks.