In this paper, we introduce the Wireless Open-Access Research Platform (WARP) developed at CMC lab, Rice University. WARP provides a scalable and configurable platform mainly designed to prototype wireless communication algorithms for educational and research oriented applications. Its programmability and flexibility makes it easy to implement various physical and network layer protocols and standards. Moreover, the online open-access WARP repository is used to document and share different wireless architectures and cross-layer designs developed at educational and research centers. This repository is a fast and easy solution for students and researchers with a wide range of backgrounds in hardware implementation and algorithm development to collaborate and initiate multi-disciplinary system designs. WARP Platform ArchitectureRice University's WARP [2] is a scalable, extensible and programmable wireless platform, built from the ground up, to prototype wireless networks. The platform architecture consists of four key components: custom hardware, platform support packages, open-access repository and research applications; all together providing a reconfigurable wireless testbed for students and faculty. Figure 1 shows the WARP board along with four daughtercards. Custom Baseband HardwareTo balance the computational needs of wireless systems operating at hundreds of Mbits/sec with the flexibility and programmability needed for wireless systems, we choose Xilinx Virtex-II Pro FPGAs as the primary communication processor on the main board. The PowerPC processors embedded in the FPGAs provide a complete embedded programming environment for MAC and network layer design. The dedicated multi-gigabit transceivers (MGTs) provide high speed board-to-board connections which make the WARP platform scalable and extendable.One of the main features of WARP hardware, which makes it distinguishable from other similar boards designed for educational purposes, is its four daughtercard slots that can be used to connect radio boards. These radio boards, designed fully by Rice University students, can be attached to the main board so that up to a 4 × 4 multiple-input multipleoutput (MIMO) system can be built. The availability of a multi-antenna radio testbed results in broader educational experiences and opportunities that enable students to understand various aspects of wireless systems such as coding, synchronization, modulation and RF IQ imbalances. Development ToolsFor physical layer design, the platform supports different levels of design flows from low level VHDL/Verilog RTL coding to system level MATLAB modeling. Xilinx "System Generator" is one of the system-level modeling tools integrated in MATLAB that provides abstractions for building and debugging high-performance DSP systems in MAT-LAB/Simulink using the Xilinx Blockset. Moreover, the WARP board supports Simulink "hardware co-simulation" that expedites the simulation and debugging steps.For MAC and network layer design, the WARP platform supports "C" based applica...

Abstract-In this paper, we present a framework for Medium Access Control (MAC) protocol development and performance evaluation. The framework, developed for the Rice University Wireless Open-Access Research Platform (WARP), allows us to interface a large class of medium access protocols with custom physical layer (PHY) implementations, thereby providing a flexible and high-performance research tool. MAC protocols for our framework are written in C and targeted to embedded PowerPC cores within the Xilinx Virtex II-Pro class of FPGAs. A key innovation is a flexible interface between the PHY and the MAC capable of exposing user-defined parameters to either layer, thus enabling cross-layer research.

Regulatory T cell (Treg) reconstitution is essential for reestablishing tolerance and maintaining homeostasis following stem-cell transplantation. We previously reported that bone marrow (BM) is highly enriched in autophagy-dependent Treg and autophagy disruption leads to a significant Treg loss, particularly BM-Treg. To correct the known Treg deficiency observed in chronic graft-versus-host disease (cGVHD) patients, low dose IL-2 infusion has been administered, substantially increasing peripheral Treg (pTreg) numbers. However, as clinical responses were only seen in ∼50% of patients, we postulated that pTreg augmentation was more robust than for BM-Treg. We show that BM-Treg and pTreg have distinct characteristics, indicated by differential transcriptome expression for chemokine receptors, transcription factors, cell cycle control of replication and genes linked to Treg function. Further, BM-Treg were more quiescent, expressed lower FoxP3, were highly enriched for co-inhibitory markers and more profoundly depleted than splenic Treg in cGVHD mice. In vivo our data are consistent with the BM and not splenic microenvironment is, at least in part, driving this BM-Treg signature, as adoptively transferred splenic Treg that entered the BM niche acquired a BM-Treg phenotype. Analyses identified upregulated expression of IL-9R, IL-33R, and IL-7R in BM-Treg. Administration of the T cell produced cytokine IL-2 was required by splenic Treg expansion but had no impact on BM-Treg, whereas the converse was true for IL-9 administration. Plasmacytoid dendritic cells (pDCs) within the BM also may contribute to BM-Treg maintenance. Using pDC-specific BDCA2-DTR mice in which diptheria toxin administration results in global pDC depletion, we demonstrate that pDC depletion hampers BM, but not splenic, Treg homeostasis. Together, these data provide evidence that BM-Treg and splenic Treg are phenotypically and functionally distinct and influenced by niche-specific mediators that selectively support their respective Treg populations. The unique properties of BM-Treg should be considered for new therapies to reconstitute Treg and reestablish tolerance following SCT.

Abstract-We present the implementation and experimental evaluation of a new, fully distributed protocol for random access systems that exploits symbol-level physical layer cooperation. By allowing single-antenna nodes to cooperate with their neighbors, MIMO-like performance is achieved. Our Distributed On-demand Cooperation (DOC) protocol is unique in its ability to realize a cooperative mode only under circumstances where cooperation can assist. Thus, under high SNR scenarios where cooperation is rarely necessary, DOC gracefully reverts to a standard CSMA/CA protocol. Our implementation of the custom DOC MAC and PHY is built on the Rice University Wireless Open-Access Research Platform (WARP). It operates in real-time without any offline processing, allowing for standalone operation and packet exchanges at timescales comparable to commercial IEEE 802.11 devices. This implementation of the DOC MAC/PHY system addresses realworld degradations like imperfections in synchronization and linklevel coordination. Extensive experimental results demonstrate that our implementation delivers substantial improvement in endto-end throughput over that of a non-cooperative link.

Abstract-We present the FPGA implementation of a MIMO and cooperative OFDM physical layer transceiver. Our transceiver is designed to support multiple antenna configurations, including SISO (single-antenna), receive switching diversity, transmit diversity using Alamouti's space-time block code and 2x2 spatial multiplexing. It also supports a fully-distributed physical layer cooperation scheme which allows two nodes to simultaneously transmit a common payload, achieving spatial diversity with only single-antenna transmissions. Our transceiver supports the common cooperative scheme of amplify-and-forward and provides a flexible interface for higher layers to enable cooperation as needed. The transceiver is implemented as a single FPGA core with a common datapath for all modes. This allows both efficient resource reuse between modes and a per-packet selection of antenna mode. This flexibility enables a wide variety of MIMO and cooperative protocols. We present architectural details of the cooperative transceiver design and early performance results using Rice University's Wireless Open-Access Research Platform (WARP).

Abstract-Wireless communication standards are developed at an ever-increasing rate of pace, and significant amounts of effort is put into research for new communication methods and concepts. On the physical layer, such topics include MIMO, cooperative communication, and error control coding, whereas research on the medium access layer includes link control, network topology, and cognitive radio. At the same time, implementations are moving from traditional fixed hardware architectures towards software, allowing more efficient development. Today, field-programmable gate arrays (FPGAs) and regular desktop computers are fast enough to handle complete baseband processing chains, and there are several platforms, both opensource and commercial, providing such solutions. The aims of this paper is to give an overview of five of the available platforms and their characteristics, and compare the features and performance measures of the different systems.

The flexible interface between the medium access layer and the custom physical layer of the Rice University Wireless Open-Access Research Platform (WARP) provides a high performance research tool for clean-slate cross layer designs. As we target a community platform, we have implemented various basic PHY and MAC technologies over WARP. Moreover, we are implementing cross-layer schemes such as rate adaptation and crosslayer MIMO MAC protocols. In this demo, we demonstrate the flexibility of the interaction between the the WARP PHY and MAC layers by showing the capability to instantaneously change the modulation scheme, disabling/enabling MAC features such as carrier sensing or RTS/CTS 4-way handshake, and different multi-rate schemes.

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