We present Texas Instruments' implementation of IEEE 802.15.4e protocols (CSL and TSCH) in a multi-hop mesh. At the MAC layer, we discuss techniques which reduce radio duty-cycle in our CSL implementation. Further, we propose RPL adaptation, to operate the network in 2 phases, one with small DIO timer and another with large DIO timer to minimize the impact of RPL broadcasts. Our demo shows 10x reduction in radio power consumption resulting from careful implementation of our MAC and Routing layer techniques using TelosB motes running Contiki OS.

Sensor networks are increasingly available in home and industry automation applications. The use of battery-powered wireless sensor nodes eases network deployment, but the dynamic wireless medium, along with energy and bandwidth constraints, poses a great challenge to achieve a robust sensor network only with these nodes.

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.

A novel protocol design across the physical and MAC layers of a multiple antenna station (MIMO station) called MIMO-IC (Multiple-Input-Multiple-Output Interference Cancellation) is proposed to address the co-channel interference problem between the single antenna stations (SISO stations) and the MIMO stations. MIMO-IC enables MIMO stations to cancel interference to and from the neighboring SISO stations opportunistically so that two MIMO stations may establish a link between them along with an existing SISO link within the same contention floor without causing interference between the two links. The simulation results show that both the link throughput and the latency between two MIMO stations are improved significantly as the number of active SISO stations increases within the contention floor while the throughput of the SISO links remains unaffected. A null-forming prototype is developed using commercially available 802.11n silicon to show that the interference can be attenuated by 15dB for a static channel and by 12dB for a dynamic channel at 10 km/hr.

Conventional data networks are based on layered architectures. The introduction of wireless networks has created a need to violate this layering discipline to create cross- layer designs or adaptations. Ad-hoc implementations of such cross-layer adaptations reduce the level of modularity and abstraction in the network's implementation, giving rise to a significant increase in complexity. We present a taxonomy of possible cross-layer adaptations that is then used to derive an architecture for their implementation that significantly preserves the networks structure. We present implementation results that validate this architecture in the context of a real wireless network implementation.

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.

We address the problems of the IEEE 802.11 MAC for wireless networks by designing a MAC protocol jointly with a multiple-input multiple-output (MIMO) technique in the physical layer. We propose a new MAC protocol, mitigating interference using multiple antennas MAC (MIMA-MAC), which mitigates interference from neighboring nodes by employing the spatial multiplexing capability of MIMO. Both theoretical analysis and simulation results clearly show that the proposed MIMA-MAC system outperforms the 802.11 system in terms of the aggregate throughput of the network by mitigating interference from neighboring nodes and thereby increasing simultaneous transmissions in the network.