Nicolas Malm

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

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.

Creating secondary spectrum usage opportunity for D2D communication with interference cancellation

In this demonstration, we consider secondary spectrum usage by D2D users in cellular network. Secondary usage is allowed if primary users are not impacted. We show how a Base Station (BS) creates new D2D communication opportunities on uplink resources by enabling Interference Cancellation (IC). BS can apply single-state IC when the D2D signal is strong enough. This can occur when the D2D transmitter is located near to the BS or when the BS explicitly orders D2D transmitter to increase its transmission power. This demonstration shows that D2D user successfully streams a video without influencing the cellular users live video streaming on the same spectrum resource. The demonstration is based on software defined radio platform with Universal Software Radio Peripherals (USRP) as the hardware front-ends.

Spectrum sharing in D2D enabled HetNet

This demonstration presents dynamic spectrum use by an overlay Device-to-Device (D2D) connection in a Heterogeneous Network (HetNet) environment. D2D devices can reuse the uplink resources of the cellular network. In a HetNet, the cellular users should be protected from excessive interference from the D2D connections. This is especially so for small cells as D2D transmitters may come arbitrarily close to the small cell base stations. We demonstrate how the cellular traffic can be protected by prohibiting the D2D reuse close to the cellular base stations by measuring the signal strength at the D2D devices. Our measurement results show that in the case of small cells, fast changes in the signal strength proposes challenges to the decision making algorithm. A demonstration with a software defined radio TD-LTE platform is shown.

Spectrum sharing for MTC devices in LTE

In this paper, we present practical realization of spectrum sharing scheme for machine-type communications in LTE. We demonstrate that the proposed scheme supports dynamic spectrum access for large set of low-data rate transmitters. Unlike classical random-access type communications, the new scheme avoids the need for signaling procedures that are associated with channel reservation. Moreover, compressive-sensing based algorithm is able to identify transmitting nodes and simultaneously decode multi-user data. The proposed algorithm has been implemented on software-defined radio based TD-LTE testbed.