## 4 A Survey on Cognitive Radio Implementation Research
### ORBIT Platform from Rutgers University  
The Orbit (Open Access Research Testbed for Next-Generation Wireless Networks) testbed developed by WinLab at Rutgers University is a large-scale wireless network testbed which can be dynamically interconnected into specified topologies for wireless network experiments with reproducibility for quantitative evaluation of various new protocols, or application and system concepts [102, 103]. The radio grid emulator as shown in Figure 12 currently consists of 400 wireless nodes having 802.11a/b/g wireless cards laid out in a \(20\times 20\) grid separated by about 1 m between adjacent nodes. Each node is built on a standard PC platform with multiple wireless and wired network interfaces, some of these nodes can support mobility. The selection of a subset of grid nodes yields a configuration that aims to emulate a wireless network in the real world [102, 103, 104].  
As shown in Figure 13, the Orbit testbed uses a two-tier architecture with a lab emulator/field trial network architecture to deal with the important issue of reproducibility in experimentation, while at the same time supporting the ability to evaluate protocol and application performance in real-world  
Figure 11: Software design flow for mapping of algorithms and protocols on BEE2.  
settings [103]. A user-defined protocol is migrated to the field test after it is validated by the matrix. Users on the Internet can have remote access to the ORBIT [104].  
As shown in Figure 14, the radio nodes in ORBIT testbed form the grid and serve as the primary platform for user experiments. Each radio node is a custom wireless node which consists of: (1) 1-GHz VIA C3 processor with 512 MB of RAM and a 20 GB local hard disk, (2) two wireless mini-PCI 802.11a/b/g interfaces, and (3) two 100 BaseT Ethernet ports for experimental data and control respectively. The hardware components also include Instrumentation subsystem, Independent WLAN monitor system and support server. These components provide the testbed with power abilities such as radio measurements, MAC/network layer view of the radio grid's components and huge data storage support [102, 103, 104].  
The Orbit testbed has a software framework as shown in Figure 15, which consists of management/control software as well as user level application. The software packages and libraries support both application/protocol evaluations. These include common libraries for traffic generation, measurement collection, etc., and also provide easy hooks to enable expert users to develop their own applications, protocol stacks, MAC layer modifications and/or other experiments on the testbed. The management/control software include node handler, collection server and disk-loading server. The software for  
Figure 12: Orbit system architecture.  
Figure 13: High-level view of proposed 2-tier system architecture for ORBITs.  
radio nodes include node agent, ORBIT Measurement Library (OML) and Libmac. These components and libraries were developed based on Linux kernel 2.6.4 as the target platform to support the experiment and to provide libraries and interfaces for the user application development [102, 103, 104].  
The ORBIT testbed can be used to evaluate various concepts and network applications in real radio-device situations. However, such testbed is primarily applicable to experimentation with higher level networking protocols. The radio node is more like a computer than a real RF radio and does not have the ability to do spectrum sensing experiments. At the same time, the use of only a single vector analyzer limits the exploration of distributed spectrum sensing protocols. Also, the use of standard 100 BaseT Ethernet overhead can be a limiting factor in study of channel switching algorithms [94, 103].