by composing modular precompiled components into processing graphs using Python scripts. The default GNU Radio platform is the Universal Software Radio Peripheral (USRP), a configurable FPGA radio board that connects to the host. As with Sora, GNU Radio performs much of the SDR processing on the host itself. Current USRP supports USB2.0 and a new version USRP 2.0 upgrades to Gigabit Ethernet. Such interfaces, though, are not sufficient for high-speed wireless protocols in wide bandwidth channels. Existing USRP/GNU Radio platforms can only sustain low-speed wireless communication due to both the hardware constraints as well as software processing. 18 As a consequence, users must sacrifice radio performance for its flexibility.

The WARP hardware platform provides a high-performance SDR platform. 8 Based on Xilinx FPGAs and PowerPC cores, WARP allows full control over the PHY and MAC layers and supports customized modulations up to 36Mbps. A variety of projects have used WARP to experiment with new PHY and MAC features, demonstrating the impact a high-performance SDR platform can provide. KUAR is another SDR development platform. 15 Similar to WARP, KUAR mainly uses Xilinx FPGAs and PowerPC cores for signal processing. But it also contains an embedded PC as the control processor host (CPH), enabling some communication systems to be implemented completely in software on the CPH. Sora provides the same flexibility and performance as hardware-based platforms, like WARP, but it also provides a familiar and powerful programming environment with software portability at a lower cost.

The SODA architecture represents another point in the SDR design space. 14 SODA is an application domain-specific multiprocessor for SDR. It is fully programmable and targets a range of radio platforms—four such processors can meet the computational requirements of 802.11a and W-CDMA. Compared to WARP and Sora, as a single-chip implementation it is more appropriate for embedded scenarios. As with WARP, developers must program to a custom architecture to implement SDR functionality.

8. concLusion

This paper presented Sora, a fully programmable software radio platform on commodity PC architectures. Sora combines the performance and fidelity of hardware SDR platforms with the programmability of GPP-based SDR platforms. Using the Sora platform, we also present the design and implementation of SoftWiFi, a software implementation of the 802.11a/b/g protocols, and SoftLTE, a software implementation of the LTE uplink PHY.

The flexibility provided by Sora makes it a convenient platform for experimenting with novel wireless protocols. In our research group, we have extensively used Sora to implement and evaluate various ideas in our wireless research projects. For example, we have built a spatial multiplexing system with 802.11b. 19 In this work, we implemented not only a complex PHY algorithm with successive interference cancellation, but also a sophisticated carrier-counting multi-access (CCMA) MAC—implementations would not have been possible with previous PC-based software radio platforms.

Sora is now available for academic use as the MSR Software Radio Kit. 4 The Sora hardware can be ordered from a vender company in Beijing and all software can be downloaded for free from Microsoft Research website. Our hope is that Sora can substantially contribute to the adoption of SDR for wireless networking experimentation and innovation.

acknowledgments

The authors would like to thank Xiongfei Cai, Ningyi Xu, and Zenlin Xia in the Hardware Computing group at MSRA for their essential assistance in the hardware design of the RCB. We also thank Fan Yang and Chunyi Peng in the Wireless Networking (WN) Group at MSRA; in particular we have learned much from their early study on accelerating 802.11a using GPUs. We would also like to thank all members in the WN Group and Zheng Zhang for their support and feedback. The authors also want to thank Songwu Lu, Frans Kaashoek, and MSR colleagues (Victor Bahl, Ranveer Chandra, etc.) for their comments on earlier drafts of this paper.

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Kun Tan ( [e-mail]), Microsoft Research Asia, Beijing, China.

he Liu ( [e-mail]), University of California, San Diego, La Jolla, CA.

Jiansong Zhang (kuntan@microsoft. com), Microsoft Research Asia, Beijing, China.

Yongguang Zhang ( [e-mail]), Microsoft Research Asia, Beijing, China.

Ji Fang ( [e-mail]), Microsoft Research Asia and Beijing Jiaotong University, Beijing, China.

Geoffrey M. Voelker ([e-mail]. edu), University of California, San Diego, La Jolla, CA.