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Plenary Lecture

MIMO Transmission in IEEE802.11a WLAN

Dr. Zoran Stamenkovic
System Design/Wireless Broadband Communication Systems
IHP GmbH, Frankfurt (Oder)
Germany
E-mail: stamenko@ihp-microelectronics.com

Abstract: MIMAX is a communication solution based on MIMO technology. In contrast to the approaches used by the conventional MIMO technology trend, e.g. 802.11n or LTE, MIMAX proposes to move signal processing functionalities from the digital baseband to the RF analogue front end, reducing the complexity of the system its costs and the overall system power consumption. In order to achieve these results MIMAX implements signal processing close to the transmitting and receiving antennas exploiting synergies in the radio access. MIMO processing is carried out in the analogue front-end by customised integrated circuits. These system blocks are able to weight the transmitted and received signals coherently in order to achieve the maximum performance during data transmission process. The challenge in designing these analogue weighting circuits consists in achieving a reproducible signal processing as in digital hardware. These circuits are assembled on a front-end PCB, which can be connected to a customised antenna array. MIMAX solution implements new MIMO algorithms able to exploit spatial diversity from the new front-end architecture.
The talk starts by giving an overview of the complete system architecture and its functional building blocks. The specifications are derived from the used wireless technology (IEEE 802.11a) and summarised on a system level. The MIMO signal processing concept is described too. The system performance evaluation is presented next. It is based on the analysis of processing gains and link budget. The use of multiple antennas provides several benefits in comparison to conventional single antenna 802.11a transceivers. In order to extract these gains, the baseband processor includes two new blocks equipped with optimal algorithms: the MIMO channel estimation block and the RF weight selection block. The link budget is calculated for a wireless system in an indoor environment based on the standard IEEE 802.11a. The next part describes baseband architecture and frame formats. The baseband architecture of transceiver takes the 802.11a standard as a reference and provides new MIMO functionalities. We focus on the specifications of the new blocks for the baseband processor, mainly the channel estimation block and the RF weights selection block. Furthermore, we consider the modifications needed in the 802.11a format frames to add the new MIMO functionalities. Two different frame formats are used. The first one is exactly the 802.11a frame. On the other hand, the new frame format is needed only for MIMO channel estimation in order to get the optimal set of RF weights. The transmission schemes, channel estimation, and robustness issues are discussed too. The basis for the MAC protocol is the well-established WLAN standard IEEE 802.11 Medium Access Control protocol. This standard MAC protocol needs a few extensions to handle special MIMO features. We discuss the new MAC functionalities imposed by the MIMO baseband processor. The MAC is implemented on a suitable FPGA platform, which allows easy testing and bug fixing. The part on analogue front-end architecture gives an overview of the applied concept of direct conversion for receiving and transmitting to further enhance the requirement of lowest complexity and power consumption.

Brief Biography of the Speaker: Dr. Zoran Stamenković is with IHP GmbH, Frankfurt (Oder), Germany. He received his Ph.D. degree in electronic engineering from the University of Niš, Serbia in 1995.
His research interests include wireless SOC design, HDL modelling, logic synthesis, chip layout, and IC yield modelling and prediction. He has leaded the EU funded project on a wireless MIMO system (MIMAX) at IHP GmbH. Currently he is in charge for the project on a vehicle wireless camera system funded by the German State of Brandenburg.
Dr. Stamenković has published a book on IC yield, six chapters in prestigious monographs, and more than 80 scientific journal and conference papers.