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| A publication of the National Electronics Manufacturing Center of Excellence | June 2004 |
The AN/ARS-6 includes an Antenna Set (AS), an Antenna Switching Unit (ASU), a Receiver/Transmitter (RT) Unit, a Control Display Unit (CDU), and a Remote Display Unit (RDU). The re-design activity incorporates a Commercial Off The Shelf (COTS) cPCI processor, COTS communications cards, and application specific COTS cards that use Open Architecture interfaces (i.e. USB, RS-232 and PCI). Compared to a proprietary replacement system, the COTS solution yields the enhanced function at a reduced development expense while providing the expansion capabilities and a lower total cost of ownership. Open Architecture is defined as hardware or software architecture whose specifications are available in whole or in part to the public. Open Architecture can be further defined as COTS replaceable subsystems (such as the controller and communications card in the AN/ARS-6), software operating systems (OS), and languages (such as C) with industry standard interfaces through which control and data is generated and passed. Open Architectures include those approved by various standards or trade organizations and independently designed architectures whose specifications are made public by the designers and are then placed under the control of an outside agency. All applicable aspects of the architectures (i.e. software interfaces, mechanical, electrical, timing, and protocol aspects) are defined or bounded. The use of COTS subsystems implies that there are multiple sources (vendors) for those subsystems. The dynamics of Open Architecture allow for the use of any industry standard interface between those subsystems that meets system requirements (i.e. timing and latency). The bandwidth and latency performance requirements of the AN/ARS-6 system and subsystem interfaces were analyzed to provide the minimum throughput requirement guidelines for component selection. Since Open Architecture has been defined as both industry standard hardware and software systems, the design can be partitioned so that the software is running on different platforms that are generating and passing control and data across defined interfaces. As future functions or enhancements are requested, the performance impact to the system design can easily be evaluated against the current capabilities of the system. Open Architecture allows for these future upgrades via "plug and play" type technology. Three units in the current AN/ARS-6 are being re-designed, and a fourth is under evaluation. The Receive/Transmit (RT) unit is the prime target for re-design because it is the core of the system, has the highest unit cost, and has the highest content of proprietary parts. The Control Display Unit (CDU) and Remote Display Unit (RDU) are also focuses of the re-design effort due to the high failure rates of their displays. The fourth, the Antenna Switching Unit (ASU), is under consideration for re-design for in-system operational alignment purposes. |
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The new AN/ARS-6 software system replaces the current software functions, maintains current usability, and replaces applicable hardware functions. This is accomplished with a real-time operating system (RTOS), functional applications running on the system controller, SDR, and applications running on the micro-controllers in the CDU and RDU. The Open Architecture hardware interfaces provide the base through which the three sets of discrete software packages pass data and control through a well defined messaging scheme. The following diagram (Figure 1-3) shows the high level hardware design approach used for the the RT unit. These hardware interfaces are industry standards, and the software running on the sub-systems allows for a "plug and play" method of passing control and data. The CDU and RDU functionality and size make the use of COTS solutions difficult; however, the use of standard interfaces eases development and support. In order to reduce the procurement and expense for spare parts, the CDU and RDU will use a common controller card that interfaces with the I/O and the display, and also handles the communications to and from the RT unit. The controller card senses what I/O is attached to it to in order to determine which mode (CDU or RDU) it operates in. A common bit-mapped LCD display replaces the current custom-character based displays. One source of error in the bearing calculation is the phase-delay mismatch between the two signal paths from the antennas to the receivers. If the ASU is re-designed to allow the injection of a signal into both antenna inputs, the operator would have the ability to measure and calibrate-out the phase-delay mismatch at any time, thus improving the performance of the system. The hardware components being used are COTS where applicable, and all interfaces are Open Architecture, thus ensuring that upgradability, sustainability, and cost target requirements are being met. Terminology/Definitions: |
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| The American Competitiveness Institute - - www.aciusa.org - - (610)362-1200 |  |
The AN/ARS-6 (Figure 1-1) is the airborne rescue platform part of a CSAR system, the other part being the survivor handheld radio, the AN/PRC-112. In operation, the AN/ARS-6 locates the position of the survivor’s hand-held radio/transponder by transmitting a short pseudo-random noise (PN) coded message. The AN/PRC-112 survival radio/transponder receives the coded message, recognizes its own unique identification code, and transmits a PN-coded message back to the avionics. The AN/ARS-6 processes the message from the AN/PRC-112 and computes the distance and direction to the survivor. 
The RT unit consists of a RF transmitter front end, a power amplifier, two RF receivers, a radio function, a system controller and communications cards. The requirements of the new design are to meet or exceed all current ARS-6 system requirements and specifications at one third of the current RT cost while improving the sustainability of the unit and allowing for functional enhancements. These enhancements may include SARSAT capability, the ability to locate survivors with GPS equipped radios, or the capability to triangulate the location of a beacon with the GPS locations of the aircraft. To achieve the requirements, it was decided to use the emerging software defined radio (SDR) technology, such as the SDR offered by Spectrum Signal (Figure 1-2), for the radio function.
Two of the sustainability issues being faced are having multiple sources for the various sub-systems with both long term support and the ability to provide upgrades in the future. The lack of multiple COTS solutions for the RF sub-systems presents such a challenge. The solution is to provide two options for the new design of the RF portion of the RT. The first option is to purchase individual RF sub-systems from different vendors to build into a single RF system. Vendors have been identified and evaluated who can supply low-noise amplifiers, synthesizers, mixers, digitally controlled attenuators, 10 watt class AB power amplifiers, and voltage-tuned filters for both the receiver front end and co-site filtering. The second option is to purchase an existing RF platform from a third party company and modify it to fulfill the AN/ARS-6 RF system requirements. Both options have been thoroughly studied, and are technically and financially viable solutions for the upgrade program.