Cooperative communications is a class of techniques which seek to improve reliability and throughput in wireless systems by pooling the resources of distributed nodes. While cooperation can occur at different network layers and time scales, physical layer cooperation at symbol time scales offers the largest benefit in combating losses due to fading. However, symbol level cooperation poses significant implementation challenges, especially in synchronizing the behaviors and carrier frequencies of distributed nodes.We present the implementation and characterization of a complete, real-time cooperative physical layer transceiver built on the Rice Wireless Open-Access Research Platform (WARP). In our implementation autonomous nodes employ physical layer cooperation without a central synchronization source, and are capable of selecting between non-cooperative and cooperative communication per packet. Cooperative transmissions use a distributed Alamouti space-time block code and employ either amplify-and-forward or decode-and-forward relaying.We also present experimental results of our transceiver's real-time performance under a variety of topologies and propagation conditions. Our results clearly demonstrate significant performance gains (more than 40× improvement in PER in some topologies) provided by physical layer cooperation, even when subject to the constraints of a real-time implementation. Finally, we present methodologies to isolate and understand the sources of performance bottlenecks in our design.As with all our work on WARP, our transceiver design and experimental framework are available via the open-source WARP repository for use by other wireless researchers.
Multiple input multiple output (MIMO) techniques hold the potential of dramatically increasing the data rates and spectral efficiency of wireless communications systems. Even with extensive research on the design of transmission and reception algorithms, little is known as to how much of the predicted gains are actually achievable on real wireless channels. In this paper, we present a MIMO testbed which enables the rapid prototyping of MIMO transceivers for wideband channels. Such prototypes provide experimental quantification of achievable gains from MIMO algorithms. The testbed design allows real-time operation of baseband processing and RF up/down-conversion. The choice of testbed components is made to allow maximum flexibility for research purposes, including monitoring and control of all subsystems. In addition to discussing the testbed's design, we present the implementation of two wireless systems. The first is a spread-spectrum system based on IEEE 802.11b. The second is an implementation of Alamouti's transmit diversity scheme.
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...
Bluetooth™ is a promising wireless technology designed for short-range ad hoc connections, which has many potentially useful applications. One such use is the transfer of data between two fast-moving vehicles such as automobiles. In this paper we explore the suitability of Bluetooth to make connections in highly mobile environments. In particular, we have developed a hardware testbed to make an empirical analysis of the time it takes to establish Bluetooth connections and the range at which those connections can be established. We also explore, by means of simulation, ways in which to improve connection setup times and the impact this will have on any potential data transfer.
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