Benchmark Algorithm for Asynchronous Detection of M-ASPM Packets Combined With Measuring Carrier Frequency Offset

Abstract

This paper demonstrates that in M-ary Aggregate Spread Pulse Modulation (M-ASPM) a relatively short, low-gain front portion of the transmitted packet can be used for robust asynchronous detection of the packet at low computational cost. With low processing gain, this detection is insensitive to large carrier frequency offsets (CFO) between the transmitter and the receiver, and it can be combined with measuring the CFO within the desired range and with desired precision. The subsequent costly processing of the high-gain, CFO-sensitive segments of the packet (e.g., those allocated to the synchronization and the payload) is implemented only after the detection, and the measured CFO is used for modifying the processing to prevent signal deterioration. In the receiver, only low-order matched filtering is continuously performed, and a single detection channel can be shared by multiple quasi-orthogonal channels used for payloads. This greatly economizes M-ASPM networks, especially their multi-channel, high-throughput configurations. However, since the contrast in the processing gains between different portions of the packet can exceed two orders of magnitude, matching the detection sensitivity with that of the payload, while maintaining the portion of the packet dedicated to the detection relatively small, poses a significant challenge. This paper presents the detection algorithm that overcomes this challenge, together with detailed explanation of the procedures and the tools employed in implementation of its steps. In particular, the properties, scope, and limitations of such essential algorithm components as the modulo exponential averaging (MEA) and adaptive quantile tracking filters (QTFs) for troughs are analyzed.