Foreword: This whitepaper from FSMLabs describes the use of the company's RTLinux real-time Linux operating system in three research and development projects involving ad hoc wireless networking technology for military and civil service applications. The projects involve software-defined radio, saving power with directional antennas, cellular/IPv6 network interoperation. Enjoy . . . !

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Three uses of RTLinux in next-generation ad hoc wireless networking
RTLinuxPro is being used in several of the most advanced wireless communication system research and development projects — including two described here by Harris and BBN. These projects are dealing with the challenges of ad-hoc networking, mobility, and software defined radios that can select from multiple wavebands and data encodings.

Next generation wireless networking is just one of a number of fields where low microsecond hard real-time in software can provide an agile and flexible replacement for hardware devices. For example, BBN's work on antenna pointing uses smart software to get around what was an intractable power versus range tradeoff in hardware solutions.

Harris Systems tactical radio project

Tim Kaiser, WIN-T Software IPT Lead at Harris Systems, says:

At Harris we have used FSMLabs' RTLinux on two product versions of our Highband Network Waveform and Mobile Ad Hoc radio. The first version ran in a single board Pentium configuration. The follow on product runs off Dual Power PC and Quad power PC configurations. The waveform is Ad Hoc, self forming and uses Time Division Multiple Access timing to produce a 20+ Mbit/sec user throughput. This radio technology has been through a highly successful Demonstration Test — Operational Test evaluation at customer test sites. It has been enthusiastically perceived as the answer to tactical radio communications. The real time kernel provided by the RTLinux product provided deterministic timing down to microsecond granularity that is critical to the success of the waveform. The threading process allowed us to use the multiple processors concurrently to meet system performance. FSMLabs' product has been a solid platform to develop and field within our product radio. Their support of the operating system has been top notch.

More details on the Harris system can be found in this page on early stage system tests. One of the most interesting features of this system is that real-time software keeps the distributed network synchronized down to less than 10 microseconds of drift between systems world-wide. This advanced timing control uses GPS receivers, a rubidium clock, and a real-time feedback control system. The use of real-time software enables replacing fixed hardware with reconfigurable and more algorithmically rich software. A “soft radio” is far more adaptable than a “hard radio.”

BBN's antenna-pointing project

BBN, the company that originally developed the Internet, is also working on ad-hoc wireless networks with particular attention to antenna pointing and power-saving. Jason Redi, Principal Scientist in BBN's Mobility Division writes:

At BBN we have been using FSMLabs' RTLinuxPro for many years for our wireless MAC protocol efforts. RTLinux provides the rock-solid thread switching times and perfect reliability that we need to build high performance software for next generation wireless networking. When combined with the familiar Linux environment and tools, we have a hard-real time kernel that is exactly right for building high speed wireless protocols.

BBN's work on directional antennas, and further, their work on reducing power consumption, can be found here. BBN provides a summary of the first project called UDAAN.

UDAAN consists of several new mechanisms — a directional power-controlled MAC, neighbor discovery with beam-forming, link characterization for directional antennas, proactive routing and forwarding — all working cohesively to provide the first complete systems solution. We also describe the development of a real-life ad hoc network testbed using UDAAN with switched directional antennas, and we discuss the lessons learned during field trials. High fidelity simulation results, using the same networking code as in the prototype, are also presented both for a specific scenario and using random mobility models. For the range of parameters studied, our results show that UDAAN can produce up to a factor-of-10 improvement in throughput over omni-directional communications.

Lower power links are possible — and power consumption of the radios themselves can be lowered — by precise antenna control. Once you have that capability, you can also consider the type of adaptive routing that is necessary for mesh networks where the distinction between edge and core devices blurs.

Institute Eurecom's cellular/IPv6 project

The same issues show up in a third, more research oriented project based on RTLinux. This project from Sophia-Antipolis France by researchers at the Institute Eurecom combines the following:

• IPv6-based radio resource management for heterogeneous multiple radio-access technology wireless networks
• smart-antenna technology
• resource allocation and scheduling
• Quality of Service management

In one paper, these researchers cover work on:

…an experimental software radio system providing direct interconnection with an IPv6 backbone network developed in the context of several publicly-funded research projects. RF and acquisition equipment ranges from high and lowpower base-stations (Radio Gateways) to reconfigurable terminals and can be made available to the research community for experimentation with real-time radio resources. Software can be configured for both real-time deployment scenarios and radio network simulation on networked PCs. We describe issues related to interconnecting a third-generation cellular radio air-interface with an IPv6 backbone, and its consequences on wireless networking architecture.

The Eurocom work is based on RTLinuxFree — the open-source version of RTLinux — while the first two projects (which have less negotiable performance issues) are based on RTLinuxPro

More information on the Eurocom work can be found here.

Copyright FSMLabs, 2006. Reproduced by LinuxDevices.com with permission.

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