Testbed design for wireless communications systems assessment

Resumen

Since Marconi succeeded in carrying out the first wireless transmission in 1894, experimental research has been always linked with wireless communications. Today, most wireless communications research relies only on computer simulations. Although computer simulations are necessary and recommendable for wireless systems evaluation, they only reflect the simulation environment rather than the actual scenarios in which wireless systems operate. Consequently, it is desirable to assess wireless communications systems in real-world scenarios while, at the same time, keeping the required effort within reasonable terms. Among the different strategies suitable for undertaking such assessment, the testbed approach constitutes a simple and flexible enough solution based on the software-defined radio concept in which only the fundamental operations (usually the transmission and the acquisition) are carried out in realtime, while the remaining tasks are implemented off-line in high-level programming languages (e.g. MATLAB) and using floating point operations. The testbed approach leads to a suitable solution in terms of cost, manpower and a priori knowledge, making them affordable for small research groups with scarce resources, as in our case. In this work we introduce the GTEC MIMO testbed, which is just another multiple antenna wireless testbed based on commercial off-the-shelf hardware modules. We complement the hardware equipment with a software architecture designed to ease the utilization of the testbed as well as to simplify the software needed for the measurement process. Making use of the GTEC MIMO testbed we carried out several measurement campaigns in indoor scenarios with the objective of exploring the feasibility of blind estimation techniques of the wireless channel in Alamouti coded systems; assessing state of the art channel codes as the Serially-Concatenated Low Density GeneratorMatrix (SCLDGM); and evaluating analog joint source-channel coding. Thanks to the collaboration with the Institute of Communications and Radio-Frequency Engineering at the Vienna University of Technology, we also assessed mobile communications systems in very realistic, outdoor, urban scenarios making use of the Vienna MIMO Testbed. More specifically, we evaluated the performance of High-Speed Downlink Packet Access (HSDPA) by measuring the actual throughput of the physical layer downlink and comparing it with the estimated channel capacity as well as with the estimated maximum attainable throughput according to the HSDPA standard.