Tight, cool and powerful.
Building a new radio--whether a hand-held, vehicle-mounted, airborne or a shipboard type--is a task not to be taken too lightly; and none of the radio manufacturers do. No matter how much experience one has in this field, the planning and design takes some careful thought and almost always a small touch of trial and error.
The intention of this quick review is to explain the raison d'etre of a few of those components and provide a brief illustration of some of their roles.
Outside the box one usually, but not always, finds the connectors, controls, antennas and display(s). But some of what is inside the box is the focus of this discussion. The processors, the processor software and the printed circuit cards, data bus types and other components all have their specific roles. How these elements work, and their synergistic operation with other components, determines how they are chosen for a specific application.
Still Outside the Box
For reasons that are obvious to many, one finds that certain radios and specific form factors are clearly defined for a particular application and platform. Tactical handheld radios must be as small, light and powerful as possible whilst providing as many options as the mission demands. Airborne units must survive take-off and landing stresses, as well as drastic and frequent changes in altitude, temperature and pressure--here weight and size is again of supreme importance. Naval communication gear must be watertight against the high humidity levels and airborne corrosives (although most gear remains in climate-controlled spaces)--not to mention coffee-proof.
Any communication equipment that will come close to exiting the earth's atmosphere or be included in any high-altitude aircraft must contain components that are impervious to increased radiation hazards. And then there is the EMP issue (Electro-magnetic Pulse), which is emitted by a nuclear explosion (and other ad hoc weapons or devices).
Putting aside the importance of the component quality and design for a moment, the most important issue on the inside of the case is the science of keeping all of the components within the prescribed operating temperature. Three of the most popular technologies are:
conduction cooling--where the heat is physically conducted from the processor and heat-producing components to internal heat sinks, then to the chassis or directly to the chassis, which itself conducts the heat to an external cooling source or to the outside air
convection cooling--this relies on a fan, or the natural flow of air through an enclosure, to create a breeze across the components which, in turn, carries the heat externally
spray cooling--arguably one of the most controversial methods, wherein the components are encased within a closed-circuit structure. An inert, non-conducting, non-corrosive liquid is first atomised and then sprayed directly onto the components. The resulting warm 'gas' is collected from the walls of the system, routed through a thermal transfer unit and recirculated, to be sprayed again.
One other thermal management method--this example from a company called Nanocoolers--and one that warrants mention here, is known as liquid-metal cooling loops. This closed-circuit solution sees a non-toxic/non-flammable liquid metal (a gallium, indium eutectic alloy) circulated by an electro-magnetic pump through a source and an ambient heat exchanger. The benefits of this type of system is that liquid metal is said to be 65-times more thermally conductive than water (yet another popular cooling solution), and liquid-metal can cool multiple heat sources, is power efficient and can be used with slower fans or without fans at all, and is therefore a very quiet solution.
Nanocoolers has recently removed reference to the liquid-metal cooling loops from its website and is no longer actively pursuing that technology, focusing instead on its Thin Film Thermoelectric cooling solutions--a technology that will be reviewed in Armada International in the near future.
The central nervous system of any radio system--and today we speak of Software Defined Radios (SDR)--is the printed circuit board, on which sits, amongst other elements, the processor(s). Once the strict domain of the PowerPC Altivec 128-bit processor family this province is being encroached upon by FPGAs (Field-Programmable Gate Arrays)--which are user-programmable logic chips that have a lower power consumption, take up less space and are also one of the best types for prototyping certain processor designs.
Quite unlike a PowerPC or a dedicated Digital Signal Processor (DSP), the FPGA performs a number of incoming signal processing operations in parallel--executing the equivalent amount of operations that would require almost ten PowerPC processors. This sort of increase in computing power coupled with the obvious reduction in heat generation makes the inclusion of FPGAs highly attractive to board manufacturers.
The FPGA, still compared to the PowerPC chip, provides a flexible complement of external interface options with which to design sensor connections. A wide variety of developmental toolkits and libraries are available for FPGA architecture, and for designing the routing system and final application-specific software.
Security is another factor one must consider when designing a software-based radio system. Again the FPGA holds its own with the latest generations containing built-in AES decryption engines and key storage for bitstream encryption. These designs offer distinct advantages to the designer of military-grade communication systems, not the least of which is increased security against design copying, reverse engineering and tampering.
The US FCS and JTRS programmes are being built around systems containing FPGAs, as they are extremely flexible, cost less than other options and provide the requisite computational power.
Writing it Down
Designing and developing the software for digital signal processing, encryption/decription engines and other applications is key to creating a synergistic interface between the hardware and software.
When built into high-performance digital communication systems such as software-defined radios, FPGAs perform many complemental functions, such as multi-channel digital down/up conversion, matched filtering, digital pre-distortion and they manage chip-rate processing. DSP processors are often used for handling lower sample-rate tasks such as symbol encoding and decoding.
Many companies provide solutions for rapid DSP co-processing development and implementation. Xilinx supplies hardware and software development tools that allow the modelling of the FPGA-DSP system.
In 2003 the largest hybrid commercial and defence communications satellite, Optus C1--for the use of the Australian Defence Force--was launched carrying a Raytheon-built UHF payload designed with Xilinx' Virtex radiation-tolerant FPGAs.
Onboard the Optus C1, X-band telecommunications links provided via the satellite are used by the military for medium to high data-rate one- and two-way video, as well as voice and data communications. Service is provided by four 60-MHz active transponders, with an additional transponder serving as a spare.
Radiation-tolerant circuit board components for space and small form factors for the radio-in-the-hand--there is still the issue of which software to use for which application.
Mid-2005 saw Thales select the Lynux-Works LynxOS real-time operating system to power its PowerEngine7 high-performance, low-power consumption single-board computer (SBC) as a major subsystem component for a selection of airborne communication controllers.
Valerie Bertheau, Vice President of Marketing for Thales Computers commented, <<Working with a hard real-time, open standards-based OS like LynxOS enabled us to develop a turnkey product that met the stringent demands of the airborne environment>>.
LynxOS 4.0 is the real-time operating system from LynuxWorks and was designed for original equipment manufacturers to construct real-time systems. LynxOS combines hard real-time embedded technology with broad conformance to open and de facto standards such as Linux, Posix and Unix, allowing developers to build product layers on top of LynxOS that meet real-time, mission-critical application requirements.
LynuxWorks was also chosen by General Dynamics Advanced Information Systems as the embedded operating system vendor for the U.S. Army's Future Combat Systems (FCS) programme's Integrated Computer System (ICS). Under the terms of the contract, LynuxWorks' Linux-compatible LynxOS-178 safety-critical, real-time operating system is to be used to meet the network-centric operation requirements of the FCS programme, where a Linux-compatible, open standard operating system is required.
As the command, control, communications, computing, intelligence, surveillance and reconnaissance (C4ISR) infrastructure used across all FCS platforms, General Dynamics' ICS will provide computer processing, networking, information assurance, and data storage resources necessary to support the network-centric operations of the FCS.
The FCS's electronic system developers can utilize LynuxWorks' Luminosity, a Linux, Windows and Solaris-based integrated development environment (IDE) powered by the open source Eclipse IDE platform, giving developers complete control over creating, editing, compiling, managing and debugging C/C++, Ada and Java embedded and real-time applications.
Whilst this last bit of information may seem a bit heavy, it is intended to highlight the importance of a Real-Time Operating System (Rtos), as opposed to, for example, the Macintosh or Windows operating systems.
A real-time operating system is one that has been developed for real-time applications. One that facilitates the creation of real-time systems, but does not, in fact, guarantee that they are real-time; this requires correct development of the system level software. Nor does an Rtos necessarily have high throughput--rather they allow, through specialised scheduling algorithms and deterministic behaviour, the guarantee that system deadlines can be met. That is, an Rtos is valued more for how quickly it can respond to an event than for the total amount of work it can do. Key factors in evaluating an Rtos are therefore maximal interrupt and thread latency.
For digital signal processing, and other communication-related functions, one needs the operating system to react as quickly as possible.
Prime examples of an Rtos include the open source types, such as eCos, FreeRtos, Nut/OS and RTLinux--and the proprietary types include BeOS, LynxOS, MicroC/OS-II and VxWorks.
Pentek, a leader in the DSP, SDR and FPGA product field held a seminar in December 2005 titled 'Achieving SCA Compliance for Cots Software Radio Systems'. This seminar focused on the Software Communications Architecture as mandated by the Joint Tactical Radio System programme office, which provided a framework for the implementation of SDR platforms. Noted from the Pentek documents was the fact that <<[snip] many JTRS radio set developers who require FPGA or DSP devices to achieve the necessary performance levels for complex waveforms and multi-channel operation, have been faced with two choices: Either develop custom hardware and build SCA compliance into it from the ground up or buy Cots products and try to adapt the standard drivers and libraries for SCA compliance>>.
This mention illustrates the fact that software and hardware developers, even though a plethora of standards exist, are constantly working to bring top products to industry that do not require a complete rebuild of the system. The allusion to Cots products exemplifies the trend in turning away from the 'redesigning the wheel' concept.
Choosing a processor, the components, board format (including VME, cPCI, PCI, PMC, and XMC--information to be included in a later article), software and system cooling type are at the forefront when designing the electronics for a communication system. And at the pace of technology today, the idea of truly embedded electronics is not as far off as one can imagine.
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|Title Annotation:||Embedded Electronics|
|Date:||Feb 1, 2006|
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