All You Need is Unary: End-to-End Unary Bit-stream Processing in Hyperdimensional Computing

Mehran Shoushtari Moghadam, Sercan Aygun, Faeze S. Banitaba, M. Hassan Najafi

Abstract: Hyperdimensional Computing (HDC) is a brain-inspired computing paradigm introduced to achieve energy efficiency with a lightweight and single-pass training model. Hypervectors (HVs) at the heart of the HDC systems play a fundamental role in elevating the accuracy and obtaining the desired performance. Image-based HV encoding requires two types of HVs: Position and Level HVs. State-of-the-art approaches utilize pseudo-random methods for generating these HVs, which might degrade system performance and cause higher power consumption due to poor randomness in HV generation. These conventional methods require iteratively calculating orthogonal Positional HVs for acceptable accuracy. This work proposes a fast, ultra-lightweight, and high-quality HV generator incorporating low-discrepancy random sequences and the emerging unary bit-stream processing. For the first time, we employ unary computing (UC) to generate Level HVs, demonstrating that there is no need for randomness in HDC systems. We generate Position HVs using a single-source quasi-random sequence with a recurrence property. Our proposed HV generation technique improves the overall HDC accuracy by up to 6.4% for the medical MNIST dataset while reducing the power consumption of HV generation by 98%.