MIMO OFDM Testbed

Overview

The combination of MIMO systems with OFDM has emerged as a dominant physical layer technology in recent years. It has been adopted by different wireless standards all over the world including IEEE 802.11n (WLANs), IEEE 802.16e-2005 (WiMAX) and 3rd Generation Partnership Project’s (3GGP) Long Term Evolution (LTE). Renzym has been actively involved not only in developing communication related products but also it is also offering communication system design services and trainings. We have taken this initiative to pursue research in MIMO-OFDM technology in collaboration with different universities.

Scope of Research

The aim of research is to develop a flexible, real-time MIMO-OFDM testbed for research and rapid prototyping of wireless systems. Key research areas of focus are

  • MIMO-OFDM physical layer research with main emphasis on developing efficient and robust MIMO detection, channel estimation and synchronization algorithms.
  • Development of a GNU radio based integrated SDR framework, for both PHY and MAC, to enable rapid prototyping of MIMO-OFDM systems and network experimentations in real-time.
  • Cross-layer designs for co-operative MIMO communication and link adaptation etc.

Applications

MIMO-OFDM has been selected for supporting various wireless systems like IEEE 802.11n (WLANs), IEEE 802.16e-2005 (WiMAX) and 3rd Generation Partnership Project’s (3GGP) Long Term Evolution (LTE). Using our reference implementation of integrated PHY and MAC frameworks and prototyping capabilities of MIMO testbed, researchers can rapidly develop prototypes for these wireless networks. Specifically some of its applications are

  • Prototyping of Customer Premises Equipment (CPE) for WiMAX, User Equipment (UE) for LTE and WLAN cards for IEEE 802.11a/g/n etc after the addition of other components as per respective standard requirements.
  • Network analyzers and scanners for WiMAX and LTE Networks for optimization and fine tuning to ensure efficient network performance.
  • Furthermore it can be also used for integrated experimentation and performance evaluation of PHY and MAC layer protocols for future industry standards.

Software defined radio based approach makes MIMO testbed an ideal candidate for undergraduate and graduate labs to enable real-time communication system design.

  • Students can readily build real-time communication systems by directly applying the concepts learnt in the theory classes without requiring any hardware expertise. In addition, they can compare the theoretical performance of various techniques studied in the class with their performance in a practical environment. Such blending of theory and related practical issues is generally missing from most of the communication courses.
  • It also allows researchers working on MIMO systems to quickly experiment and test their algorithms in real-time environment with a minimum of programming effort. Most of the academic research is based on a set of assumptions that might not hold in practical sceneries. MIMO testbed provides a unique opportunity to the researchers working on algorithm development to verify their design in various practical scenarios.
  • Multi-antenna capability is also very useful in cognitive radio research where different antennas can be used to perform certain tasks simultaneously. For example one antenna can perform spectrum sensing/scanning while others can be used for communication. Furthermore wide range of spectrum can be covered for using different RF transceiver cards for different antennas.

Development Phases

The overall development of MIMO-OFDM testbed will be completed in two phases. In the first phase a low-scale 2x2 MIMO-OFDM prototype for the indoor environment will be developed. Prototype hardware will consist of USRP boards with XCVR2450 dual band, 2.4 GHz and 5 GHz, RF-transceiver cards. Furthermore a MIMO-OFDM software framework with integrated MAC and PHY support will also be will be a key outcome of this phase. This phase is expected to be completed in August 2010.

In the 2nd phase a full-scale real-time 4x4 MIMO-OFDM testbed that can process bandwidth up to 20 MHz will be developed. Currently Renzym is developing a custom 4x4 MIMO testbed hardware that will be used as target platform for this final phase. This fully functional 4x4 MIMO testbed will provide an ideal platform for research and rapid prototyping of wireless networks like WiMAX, WLAN, LTE etc.

The main idea behind this two phased approach is to concentrate on the development of robust and efficient algorithms in the first phase which is near completion now. In the 2nd phase the main emphasis will be on the efficient software/hardware partitioning and optimization of the implementation related issues so that 20 MHz bandwidth can be processed and without compromising the ease of implementation.

MIMO-OFDM SDR Framework

An open source, GNU radio based, integrated software framework for MIMO-OFDM based PHY and CSMA/CA based MAC layer is currently under development. It is basically a low scale implementation of IEEE 802.11n MIMO wireless standard and can be used to build a real-time working wireless LAN. It has been implemented in open source GNU Radio framework and its modular architecture and available APIs allow the MIMO Testbed users not only to modify the functionality of existing modules but also develop their own custom PHY and MAC layer modules. This integrated MAC and PHY reference design can be used to

  • Readily build a real-time working wireless LAN network with MIMO testbed hardware.
  • Analyze the performance of MIMO-OFDM PHY layer algorithms for channel estimation, synchronization, MIMO detection, STBC, CDD etc in real-world environment.
  • Experiment with different cross layer optimizations like co-operative MIMO, link adaptation etc for increasing network throughput.
  • Design and analyze the performance for different MAC protocols for future wireless standards.

The development work of this MIMO-OFDM framework is near completion. It will be made available to the open source community as soon as it gets ready.