Implementing TD-LTE as software defined radio in general purpose processor

Abstract

Cloud radio access networks use servers that are connected to Remote Radio Heads (RRH). Base station (BS) implementation with this concept is challenging. The strict real-time nature of baseband (BB) processing seems to rule out usage of General Purpose Processors (GPP) with non-real time Operating Systems (OS). In this paper, we propose a BS architecture where most of the real-time processing is confined into a Virtual Hardware Enhancement Layer (VHEL). VHEL hides the hardware non-idealities from the software and vice versa. Possible errors due to the non-real-time OS and RRH appear as channel errors, which makes software development easier. We demonstrate the benefits of our architecture by implementing a Time-Division LTE system (TD-LTE) in C++ and running it as a user process in an Intel i7 class PC. Over-the-air transmissions are realized using USRPs. We report the performance of the implemented platform. We observe that with the given VHEL the transmitter and receiver never lose synchronization. Also the PC tends to be quick enough to feed the data; and the loss rate of subframes due to the non-real-time nature of the platform is relatively low. The proposed platform provides the possibility to implement TD-LTE on GPPs and virtual machines.