Implementation of a soft LTE demonstrator

Visiting researcher: Mr Wuxiong Zhang (WiCO)
Host researcher: Dr Cheng-Xiang Wang and Dr Xuemin Hong (HWU)
Duration: 3 months
Status: Completed
 

Biography of the visiting researcher

Wuxiong Zhang received the BEng degree in Information Security from Shanghai Jiao Tong University (SJTU), Shanghai, P.R. China, in 2008. He is now a PhD candidate in communication and information system in Shanghai Research Center for Wireless Communications, which is part of Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences. Prior to that, he finished his PhD courses in University of Science and Technology of China, Hefei, Anhui province, P.R. China, in 2009. His research interests lie in the areas of communication theory, information theory and networking. Current research focuses on ad-hoc, and vehicular networks.
 

Background and motivation

Link level computer simulation has been done to evaluate the performance of RBIR/ERBIR in Wimax system, while full performance evaluation of RBIR/ERBIR, comparison of MIC, EESM, MMIB and RBIR/ERBIR with a testbed for future LTE-A system are rare and necessary.
 
Though there are some theoretical results for RBIR, while they are not sufficient to prove the performance of RBIR/ERBIR. Moreover, when doing computer simulation, the channel impulses are draw by empirical formulae, which are approximations of the real wireless environment, and thus are not accurate. So demonstrating RBIR/ERBIR in a testbed is much better to show the performance of RBIR/ERBIR, and the results will provide us insights to extend RBIR/ERBIR into more universal and realistic algorithm.

Aims and objectives

We aim to evaluation the current extension of RBIR algorithm with a testbed system to see whether it has the same benefits as with computer simulation. Based on the evaluation results, we will make some new adjustment to the parameters in the algorithm. If the final evaluation results are significant, we can further write proposals to same standard-making organisations.
 

Research activities

  1. Time & frequency domain synchronization of the PXI testbed system
    Time synchronization is the main challenge for PXI testbed system, and it is always ignored in computer based simulations. We tested two different kinds of methods for this system. The first one is for complete LTE link layer simulators. We use PXI to transmit each frame twice consecutively, and then we use PSS and CP cooperatively to find the start of the frame. Then we use CP to find fractional frequency offset, and use PSS to find integral frequency offset. The second one is based on training sequences. For both a complete LTE link layer simulators and other type of simulators, we regard the base band signals they produced to be transmitted as data payload, and add a PN or ZC sequences twice consecutively to the payload. In the receiver side, we use the training sequences to do time and frequency synchronization.
  2. Development of a simplified LTE downlink shared channel simulator
    Open source simulators, such as the LTE link and system layer simulators by Vienna university, are not easy to be applied in the PXI testbed system due to two reasons. The first is that they are based on object oriented programming method, while mathscript in Labview for PXI system does not support it. The second one is that the simulators are too complicated to be compiled into .dll files, and thus difficult to be used in Labview. The only way seems to using Matlab to get the base band signals and save them into blank files. Then use Labview to load these files and transmit them with PXI testbed, while this method is time consuming. For the simplified LTE simulator, it can be used in mathscript tool in Labview easily. This simulator realized 2X2 and 4X2 MIMO technology in both multiplexing and diversity mode. It starts from turbo coding, and both channel estimation and equalization are included.
  3. Research of ERBIR algorithm in LTE system
    I find out some technique problems of the simulator designed for this algorithm on the testbed system, and further discussions and considerations are needed before evaluating it in the testbed system in the future. And I want test it for LTE systems, so this is another reason for the design of simplified LTE simulator.

Outcomes

With this PXI testbed system, we have already demonstrated LTE SISO, MIMO downlink transmission and receiving successfully during the visit, so in the future, for 4G (and/or B4G) system, we are able to demonstrate the physical layer performance once we develop simulators for the new standards.

 

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