UC4G Testbed and Technology Demonstration

Introduction

Due to the absence of openly accessible platforms for rapid emulation and/or experimentation of mobile wireless systems, research work on wireless communications systems has been conducted predominantly using simulations. However, even today’s most sophisticated simulators can only provide limited fidelity to real-world systems due to their use of commonly-used simplified assumptions about wireless propagation channels and interfering conditions, etc. In addition, simulations usually fall short of addressing important practical issues such as synchronisation, implementation impairments, real-time requirements, and hardware complexity. Consequently, there is an increasing need in the research community to be able to conduct investigations of various advanced wireless technologies in real-world broadcast conditions.       

 
Motivated by this, the UK-China Science Bridges: R&D on (B)4G Wireless Communications (UC4G) project set up an ambitious goal to provide an open testing facility for wireless communication systems. This testing facility, the UC4G UK testbed, aims to facilitate researchers to perform a variety of physical layer tests. The testbed will not only serve to inspire innovations with real-world experimentation but will also encourage proof-of-concept, technology transfer, and commercialisation of the latest wireless inventions and innovations.
 
 
It is envisioned that the UC4G testbed will be developed in two stages. During the first stage, the UC4G UK testbed will be developed at Heriot-Watt University (HWU), Edinburgh in order to test technologies such as the novel technique known as, ‘spatial modulation’, which is a multiple-input/multiple-output (MIMO) technique that has never been demonstrated experimentally before. Along with this, various MIMO long term evolution (LTE) standards are also being investigated. During the second stage, the UC4G UK testbed will be connected to other testbeds in the UK and China to form a complete UC4G testbed. As a “Network of Testbeds”, the complete UC4G testbed will consolidate existing testbed resources and make these precious resources more accessible to eligible researchers in the UK and China.
 

UC4G UK testbed

The 4x2 MIMO testbed was set up at HWU in March 2011. It is based on the, ‘PXI’ products of National Instruments Ltd. The left figure below depicts the hardware of the testbed, while the right figure is a schematic of the hardware architecture of the testbed. The testbed consists of five major components: a 4-channel transmitter (Tx), a 2-channel receiver (Rx), a 6 TB hard-drive array, known as a, ‘RAID’ array, and two personal computers (PCs), which are built into the chassis that house the Tx and Rx units. The Tx, Rx and PCs are interconnected through a hub to form a local area network (LAN).
 
 
The specifications of the testbed are:
  • Support of up to 4x2 synchronous one-way (simplex) MIMO communication  
  • Tx frequency range: 85MHz to 6.6GHz
  • Tx RF bandwidth: 100 MHz
  • Max. Tx power: 10 dBm
  • Rx frequency range: 10MHz to 6.6GHz
  • Rx bandwidth (3dB): 50MHz
  • Rx typical spurious-free dynamic range (SFDR): 80dB
  • Embedded FPGAs (Xilinx Virtex 5) at both the Tx and Rx for real-time signal processing
  • Qual-core i7 Processor at both the Tx and Rx for control and signal processing 
  • RAID storage capacity: 6 TB (12 x 500) GB drives
  • RAID I/O speed: 750 Mbytes/s
Since the testbed was first set up in March 2011, continuous efforts have been made to develop its functionalities and also to demonstrate advanced (B)4G technologies. Offline demonstrations refer to those that are facilitated by MATLAB software in conjunction with the testbed itself while online (or real-time) demonstrations refer to those that are implemented in the FPGA boards also in conjunction with the testbed itself. The key milestones to date are:
  • Offline demonstration of 4x2 MIMO LTE multiplexing systems with signal or image transmission
  • Offline demonstration of 4x2 MIMO LTE diversity systems with signal or image transmission
  • Offline demonstration of the novel spatial modulation technique with signal or image transmission 
  • Real time demonstration of single-input/single-output (SISO) OFDM wireless LAN systems

Ongoing and planned developments on the testbed include:

  • Offline demonstration of spatial modulation techniques compared with other MIMO techniques
  • Real-time demonstration of a 2x2 wireless LAN system
  • Real-time channel emulator
 

A NovelTechnology Demonstration - Spatial Modulation

Among the many transmission techniques that exploit multiple antennas at the transmitter and/or receiver, Spatial Modulation (SM) is a novel and recently proposed technique that utilises multiple–antenna transmission to realise an entirely new modulation concept. SM offers improved data rates (multiplexing gain), compared to Single-Input Single-Output (SISO) systems, and robust error performance even in correlated channel environments. The system complexity is significantly lower than that of other spatial multiplexing techniques such as BLAST (Bell labs layer space time). SM exploits the uniqueness and randomness properties of the wireless channel for communication. This is achieved by adopting a simple but effective coding mechanism that establishes a one-to-one mapping between blocks of information bits to the transmitted and the spatial positions of the transmit antennas in the antenna array.

 
It has now been possible to demonstrate on the UC4G testbed for the first time ever that SM and a variant of SM called trellis-coded SM work in practice. Quite significantly, this has not been demonstrated anywhere else before, although many research groups around the world now work on SM. As a result, the practical feasibility of one of the UC4G project’s IPRs has been successfully demonstrated. Also, given the strengths of the SM technique, it is expected to be a key contender for physical layer techniques for beyond 4th generation (B4G) wireless communications standards. This therefore has the potential to put the UC4G testbed at the forefront of essential contributors to future wireless communications standards. As a consequence, at present the UC4G project consortium is seeking an industrial partner to help commercialise the technology.
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