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Case Study: MicroTCA Chosen for Navy Towed Sonar Array

MicroTCA offers an impressive level of compute density and a wealth of signal processing capabilities. A sonar array application leveraged those advantages to meet its performance needs.


Keywords in this Article:

  • XMC
  • PMC
  • PCI Express
  • MicroTCA
  • Ethernet
  • Enclosures
  • DSP
  • Backplanes
  • AMC
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MicroTCA has quietly been capturing mindshare amongst military system developers. To explore the technology trends that attract these engineers to MicroTCA, this case study examines how a prime military contractor chose MicroTCA over competing architectures for its naval computing application. The company was looking for a system for the signal processing of SONAR data from towed arrays or other sensors on the board. A towed array sonar system is towed behind a submarine or a surface ship in order to ensure the array's sensors are far enough away from the ship's own sound sources (Figure 1). This improves signal-to-noise ratio, making it easier to detecting faint contacts and track them.

Figure 1
A towed array sonar system is towed behind a ship in to ensure the array's sensors are far enough away from the ship's own sound sources.

For this program the requirement included a rugged front-to-rear cooled rackmount design for above and below-surface vessels with capability for a multi-gigabit backplane data transfer and failover options. Vadatech develop a 1U solution that would provide vibration and shock resistance in an isolated rack. The chassis is designed to meet MIL-STD-901D and 167A for shock/vibration and to MIL-STD-461 for EMI.

System Requirements

For the signal processing, a high-performance Xilinx FPGA Carrier in the AMC form factor was selected. With a suite of Xilinx-based FPGAs, the prime contractor was able to choose between Virtex-6, Virtex-7, Kintex-7, Zynq-7000, and Artix-7. Figure 2 shows some of the FPGA types that can be used in the AMC form factor. The engineers at the prime ended up choosing a mid-range Virtex FPGA. The carrier accepts one FPGA Mezzanine Card (FMC) for versatility and scalability. In this application, a customized FMC for beam-forming was created. Of course, Altera-based FPGAs can be used as well.

Figure 2
A variety FPGA types are available on AMC form factor modules including Virtex-6, Virtex-7, Kintex-7, Zynq-7000, and Artix-7.

Usually, the prime contractor or OEM has a preference between Xilinx or Altera. Although Xilinx is more commonly used, there are powerful AMCs using Altera chipsets. For example a communications-market Fortune 1000 company is using a 100G FPGA AMC in a currently deployed system. The 100G FPGA is out of the front panel, not across the backplane. It uses a CFP2 port and a CN6880 32-core Cavium processor. Although that application is communications market based, the example demonstrates the performance upgrade path available for future requirements in any system. The MicroTCA.0 specification is being updated to include 40GbE signaling (currently in Draft).

Processor AMC at Host

The Towed SONAR Array application also required an Intel PrAMC as a host processor. This unit provided pre-processing and acted as the system host. While high-end Haswell PCIe Gen3 processors are available in MicroTCA/AMC, the application did not require that level of performance. Therefore, a Xeon E3-1125 was selected. It provides 4 cores at 2.5 GHz with 8 MB LLC. The AMC module also has an on-board PCH with 32 Gbytes of Flash and a bank of BIOS Flash, as well up to 16 Gbytes of DDR3 memory for the Intel chip. The chassis system routed x8 PCIe Gen 3 to each of the 6 slots, providing high-speed connectivity between the AMCs. The system provides precision clocking with GPS/IEEE1588/SyncE, including a hold-over crystal for maintaining time while out of range/sight of the network.

A related program will use per VITA 57 for networking and a network interface module. Various port options are available for FMCs, including dual or quad RJ-45, SFP+, or QSFP+ cages. These provide for GbE/10 GbE/40 GbE routing in the system, respectively. For empty AMC slots, there are hundreds of off-the-shelf I/O modules, storage, graphics, networking, switches, and carriers available in the marketplace. The AMC carriers can support PMC or even XMC or, of course, FMC modules as described above. This allows for a vast ecosystem of modules to be used in near limitless configuration options. There are also double module carriers for PCIe Gen3 cards, allowing high-end commercial graphics or other boards to be incorporated into MicroTCA systems.

1U Rugged Chassis Platform

Made out of lightweight aluminum, Figure 3 shows the rugged chassis solution that was developed. To maximize performance density, it includes an integrated shelf manager and 6 AMC slots in just a 1U height. The unit has the most sophisticated clocking distribution in the market to meet the most stringent requirements such as wireless infrastructure, high speed A/D, and so on. There is also a low-jitter/low-skew backplane crossbar clock routing matrix for CLK1/CLK2/CLK3 for all AMCs, clock disciplining with arbitrary clock frequency output and holdover (Stratum-3 option) including 1PPS regeneration and holdover. The front-to-rear cooled chassis can provide Ethernet time services to the chassis networks on both the GbE and 40GbE fabrics. It can be subordinate to an external PTP or NTP master server or when the GPS receiver option is selected can act as a grand master clock utilizing the precision timing information provided via the GPS receiver and on-board disciplined oscillator.

Figure 3
This rugged chassis solution maximized performance density combining an integrated shelf manager and 6 AMC slots in just a 1U height.

The lightweight aluminum chassis has a ribbed construction and screw-down front panel tabs to meet the ruggedization requirements. Similar applications may use Vadatech's ATR-based MicroTCA solutions compliant to MicroTCA.3 for hardened conduction-cooled systems. The come in ½ and ¾ ATR sizes or can be offered in rackmount formats. The company is also developing MicroTCA.2 design for hybrid air/conduction cooling in a heat-exchanged chassis.

In deeper MicroTCA chassis via a mid-plane, it is possible to have 12 AMC slots in a 1U height. These chassis are typically approximately 600 mm deep as opposed to the more typical 300mm-475mm depths. Imagine routing x8 PCIe Gen3 to each of the 12 slots via an integrated 96-port switch. Figure 4 shows a block diagram of such a system. The performance capabilities in a 1U chassis can be very compelling in this type of configuration. It should be noted that these chassis are not designed to the rugged MIL-specs, but are used in many benign environment MIL/Aero applications.

Figure 4
Shown here is a 12 AMC slot system routing x8 PCIe Gen3 to each of the 12 slots via an integrated 96-port switch.

MicroTCA in Mil/Aero Applications

The MicroTCA architecture has been selected in several defense projects world-wide, particularly in the last 18 months. This is largely because as a rule of thumb it is between 2/3 and ½ the size, weight, and cost of competing solutions. The technological advancements for MicroTCA tend to be fast and powerful, as the architecture is used in bleeding-edge communications systems and research/physics projects. Other Mil/Aero applications include multiple radar signal processing designs, in both airborne and mobile land-based vehicles. Other implementations include naval submarine, helicopter, vehicle-based 360-degree situations awareness systems and more.

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