Latency Analysis in GNU Radio/USRP-based Software Radio

Abstract

Software-Defined Radio (SDR) is one of the most promising radio technologies that implements radio communication functionalities in software instead of hardware. Because of its inherent reconfigurability and flexibility, SDR systems have many prospective advantages compared to conventional radio systems. However, they also have disadvantages in terms of performance and real-time requirements. Among others, multiple heterogeneous processing units with interconnecting buses in data processing path introduce a non-negligible latency. This is due to those interconnections such as buffer delay and is beyond the unavoidable latency such as processing time and propagation delay. Several researches have investigated the latency problem as well as proposed new architectures for SDR systems. However, their studies are limited to particular SDR platforms that are not widely used in the software radio community. Our research focuses on analyzing and measuring latency on the most popular SDR system: GNU Radio software system with three versions of Universal Software Radio Peripherals (USRP) devices - USRP1, USRP2 and USRP E100. This research identifies the sources of the latency and quantifies them by using both analytical method and experimental methods. For the analysis, we identify all types of buffers in the SDR platforms as well as estimate the time that these buffers contribute. For experimental measurements, we conducted two methods to measure the latency. The first method is to calculate the Round-trip time between two SDR systems by using Linux ping utility with GNU Radio tunnel program and TUN/TAP components. The second method called hwlatency is for measuring the hardware latency. We believe this study offers the better understanding of the latency of SDR platforms and will lead to correct implementations of high-level network protocols based on SDR systems.