Mobile devices performing mission-critical functions at the tactical edge, such as those employed by first responders, military personnel, and law enforcement, operate in environments that are vastly different from enterprise computing environments. In spite of the differences in resource availability, threat models, vulnerabilities, information formats, and communication protocols, there is a great advantage to (and great demand for) enabling information exchange between the tactical edge and enterprise environments. Creating a specialized mobile version of each desired service that incorporates an appropriate level of security protection and quality of service (QoS) for the tactical users is one possibility. Such an approach is not cost effective, however, as the market for a given tactical application is small compared to the commercial user base for mobile applications and services. Furthermore, the need for information or services from the enterprise by tactical users can be too ad hoc and time critical, e.g., during disaster response, to support developing a specialized version. Finally, service specialization for mobile web access covers only one of multiple information dissemination and access patterns that arise in tactical operations. This paper presents the design and a prototype implementation of a gateway solution that provides secure tactical-enterprise information exchange and handles the differences in resource availability, QoS requirements, communication formats, and protocols.

Increasingly wireless networks use multi-antenna nodes as in IEEE 802.11n and 802.16. The physical layer (PHY) in such systems may use the antennas to provide multiple streams of data (spatial multiplexing) or to increase the robustness of fewer streams. These physical layers also provide support for sending packets at different rates by changing the modulation and coding of transmissions. Rate adaptation is the problem of choosing the best transmission mode for the current channel and in these systems requires choosing both the level of spatial multiplexing and the modulation and coding. Hydra is an experimental wireless network node prototype in which both the MAC and PHY are highly programmable. Hydra's PHY is essentially the 802.11n PHY, and currently supports two antennas and the same modulations and codings as 802.11n. Because of limitations of our hardware platform, the actual rates are a factor of 10 smaller than 802.11n. The MAC is essentially the 802.11 MAC with extensions, including the ability to feedback channel state or rate information from the receiver. Hydra was designed to allow experimentation with real radios, PHYs, and network stacks over real-world channels and it is well suited to studying rate adaptation in multi-antenna systems. To allow controlled experimentation, we also have the ability to perform experiments over emulated channels using exactly the same MAC and PHY used for RF transmissions. We present rate control experiments based on transmission over both real and emulated channels. Our experiments include measurements for single antenna systems and two antenna systems using a single or multiple spatial streams. We study rate adaptation algorithms using both explicit and implicit feedback from the receiver. A novel aspect of our results is the first experimental study of adaptation between single and multiple spatial streams for 802.11n style systems.

Hydra is a flexible wireless network testbed being developed at UT Austin. Our focus is networks that support multiple wireless hops and where the network, especially the MAC, takes advantage of sophisticated PHY techniques, such as OFDM and MIMO. We argue that for this domain simulation alone is not adequate and that working prototypes are needed to validate algorithms and protocols. Hydra nodes consist of a flexible RF front-end and a general purpose machine with a software based MAC and PHY. Using the frameworks of the Click modular router and GNU radio and coding in C++ makes it relatively easy to implement working prototypes of cross-layer designs that require custom MACs and PHYs. We present the architecture and implementation of Hydra, as well as a preliminary cross-layer design experiment for a rate-adaptive MAC. These early results show Hydra is a capable prototyping tool for wireless network research.