A Real Time MIMO OFDM Testbed for Cognitive Radio & Networking Research Weijun Zhu ‡ , Babak Daneshrad * , Jatin Bhatia ‡ , Jesse Chen * , Hun-Seok Kim * , Karim Mohammed * , Omar Nasr * , Sandeep Sasi ‡ , Anish Shah * , Minko Tsai* ‡ Silvus Communication Systems, Inc. Los Angeles, CA, 90064 * Wireless Integrated Systems Research (WISR) lab, UCLA, EE Dept. ABSTRACT A real time, 2 Mbps to 200 Mbps portable radio unit with MIMO and sensing capability which exposes all the PHY parameters to the higher layers will help advance experimental cognitive radio (CR), and wireless networking research. Collaboration between Silvus Communication Systems and the UCLA WISR group has resulted in the first generation radio specifically designed to meet the needs of the CR and wireless networking community. The current platform is based on a COTS FPGA platform with dual- band RF capabilities. It implements a slight variant of the 802.11n draft spec. It is a fully self contained PHY solution with over 100 unique modes of operation. Moreover it features a robust API to the MAC through which all PHY parameters can be controlled on a per-packet basis. The same API will allow the PHY to communicate channel state information, SNR, and RSSI measurements to the MAC. A 16 micro-second packet decode latency ensures that the PHY processing does not inhibit the system’s fast response to changing channel and interference conditions Categories and Subject Descriptors B.1.m [Hardware]: Miscellaneous. General Terms: Experimentation Keywords Testbeds, wireless networks, 802.11n, MIMO OFDM 1. INTRODUCTION AND MOTIVATION Development of wireless networks include many phases, but invariably verification on a practical testbed or prototype is needed to validate the theoretical and simulation work. Such prototype systems are used not only for verification of derived theory, but increasingly some concepts can only be seriously studied in practice (e.g. interference modeling). As communications theory pushes towards higher bit rates, the design and development of testbeds that can support the high throughput gets more challenging in a research environment. Consequently network and cognitive radio researchers are forced to adopt commercial platforms such as 802.11 based systems for their research needs. These platforms seldom provide the researchers full control of the RF, PHY, and lower MAC functionalities. Moreover, they do not allow any changes to the underlying framework. Our prototype system, was designed specifically to address these needs. The first version of this prototype, which is being demonstrated at WiNTECH, provides many of the above mentioned requirements. Future versions of the prototype will deliver even greater functionality and a more intuitive MAC/PHY API. 2. TESTBED HIGHLIGHTS AND FEATURES Our efforts produced a real time MIMO OFDM testbed that can satisfy the needs for both the cognitive radio community and the traditional wireless networking community. The testbed was implemented on a single Virtex-II FPGA with real time capabilities. It was developed to support a large number of permutations of physical layer modes (see table 1). It supports a slight variant of the IEEE 802.11n draft proposal [1]. Data rates supported range from as high as 200Mbps to as low as 2Mbps in an over the air bandwidth of 20 MHz, allowing prototypes for intelligent spectral allocation, high throughput testbeds, and testbeds whose main concern lies beyond raw throughput. Figure 1 shows the current form factor for the testbed. Table 1 – Radio features for first generation testbed Bandwidth 5, 10, 20 MHz Constellation size 2-, 4-, 16-, 64-QAM No. Antennas 1x1, 1x2, …, 2x4, …. 4x4 Coding Rate ½, 2/3, ¾, 5/6 Type of Antenna processing Spatial MUXing, Space-Time Coding, Diversity, Smart Ant. Spatial Multiplexing Decoder Modified MMSE Modulation OFDM (64 point FFT) No. Sp. Streams 1, 2, 4 Figure 1 – The first generation testbed (both baseband and RF) is built into a cPCI chassis measuring 17”x 8”x 12” The testbed can support any combination of the parameters shown in Table 1. These modes are defined by the MAC through an API Copyright is held by the author/owner(s). WiNTECH’06, September 29, 2006, Los Angeles, California, USA. ACM 1-59593-538-X/06/0009. 115