Modular, Scalable, High-Performance Architecture Ideal for LTE Applications
As MicroTCA moves to 100G and with ATCA’s large bandwidth, these systems will continue to provide solutions for LTE/4G and other requirements for many years to come.
As LTE/3G/4G systems continue along their evolution path, they will require key elements. The constant battle is packing more performance into less rack space. Proprietary or in-house solutions can fix a hole in a provider’s requirement, but they rarely achieve a long-term strategic approach to remain at the forefront of technology, have a wealth of options to adjust to market demands, and minimize costs and time-to-market.
Modular open standard architectures (MOSA) such as MicroTCA and AdvancedTCA have tailored offers for various communications systems and LTE in particular. Femto cell and most pico cell LTE applications tend to utilize less bandwidth and management functions. But micro and macro cell systems require higher performance and functionality in the system. These size LTE systems would benefit from elements such as:
- High bandwidth (high-speed fabric interface to 10Gb per lane and specification in committee to do 40Gb Ethernet)
- 100G line cards (out the front panel ports)
- Scalability as requirements progress
- High availability (99.999% uptime)
- System and shelf management
- Chassis locators
- Hot swappability and failover
- Modular open architecture
- Large ecosystem of products and vendors
Both MicroTCA and AdvancedTCA (ATCA) meet these design objectives. MicroTCA in particular has improved significantly in the last 5 years or so. In the early days, too many vendors rushed substandard products to the market that often didn’t meet the specification. This left a sour taste for those who dipped their toes with the wrong suppliers. Today, the experts who have been successful in deploying quality solutions are left standing. The performance has significantly shifted to include 100G line cards and full backplane systems with 40G traffic being finalized (a 40GbE specification is in committee).
MicroTCA is smaller (approx. 75mm wide x 30mm tall x 180mm deep boards) than ATCA, offering significant performance in a small space. It is typically more much more cost-effective, especially for smaller systems. AdvancedTCA uses larger boards for even more processing power, but in a 355mm wide by 30mm tall x 280mm deep size. MicroTCA stemmed from ATCA, where advanced mezzanine cards (AMCs) are plugged into a carrier card. In the PCI Industrial Computer Manufacturer’s Group (PICMG), they realized that you can plug these AMCs directly into a backplane. They added a MicroTCA carrier hub for the shelf management and built-in complete redundancy and failover options to ensure high availability. See Figure 1 for a chart showing the MicroTCA specification family and its connection to AdvancedTCA.
|Figure 1: This model from PICMG’s MicroTCA Application Guide show the various types of MicroTCA formats. The same AMCs from ATCA carriers are used for MicroTCA systems. Photo courtesy of PICMG, from PICMG’s MicroTCA Application Guide.|
With its versatile, modular open standard design, MicroTCA is used in a wide range of applications. This includes telecommunications, military/aerospace, enterprise networking, industrial automation, medical, transportation, energy and more. By configuring highly diverse collections of AMCs in a modular MicroTCA shelf, many different application architectures can be easily realized. The AMCs plug into the chassis and come in various types with functions such as processing, networking, graphics, storage, shelf management and more. The shelf management is a key area of the specification. It can be used to access information about the current state of the shelf or the carrier, obtain information such as the FRU population, or monitor alarms, power management, current sensor values and the overall health of the shelf. Today’s shelf management software GUIs can be very powerful, providing a virtual carrier and FRU construct for a simple, effective interface. See Figure 2 for an example.
|Figure 2: The GUI of this shelf management software shows a virtual carrier and FRUs. Each FRU can be selected for a visual representation of the status, along with resource navigation trees, sensor reading and monitoring graphs, etc.|
The common elements defined by MicroTCA are capable of interconnecting these AMCs in many interesting ways—powering and managing them, all at high efficiency and low cost. The flexibility of protocols includes:
- AMC.0 base specification
- AMC.1 PCIe
- AMC.2 GbE and 10GbE
- AMC.3 SAS/SATA
- AMC.4 Serial RapidIO
The MicroTCA ecosystem offers a wealth of Intel-, Freescale- and Cavium-based processors and Xilinx and Altera FPGAs. Aside from a full ecosystem of chassis, NICs, A/D and D/A converters, there are application-ready platforms (ARPs) that are specific for the LTE market.
There are MicroTCA-based ARPs now available in the marketplace. They are designed for the LTE market, but still have the flexibility of a modular system that allows various configurations and performance options. For example, if an application requires heavy data and signal capture, it will have more FPGA and A/D conversion (using standard AMC carriers). If connectivity and throughput are more prevalent, the same chassis will have more network processing units (NPUs) in the AMC format. With a proprietary solution, you typically will not have the breadth of choices for these FPGAs combined with cutting-edge processors, shelf management, etc. Even with a MicroTCA ARP from one vendor, the Linux OS doesn’t discriminate any software layer on top. The engineer can still design in modules from a different supplier. So the variety of choices remains, which has the ancillary benefit of a faster time-to-market.
LTE is based on an IP network with voice traffic supported as voice over IP (VoIP), providing improved integration with other multimedia services. LTE improves spectral efficiency, increases mobility and reduces the cost of data transport, and provides better integration with other open standards. The Open Base Station Architecture Initiative (OBSAI) and the Common Public Radio Interface (CPRI) are other standards that define the interface and modules of base stations for commonality.
Micro and macro cell LTE applications need to cover the 4 x 4 multiple-input, multiple-output (MIMO) requirements and have more antennas to reach all three 120-degree sectors in the roughly 200m-10 Km radius. The 20, 40 MHz band of microcells and 60-75 MHz for macro put more demands on the system. Thus, to achieve the speed requirements and intercommunication/management of all nodes, MicroTCA is a great fit. The architecture’s GbE and 10GbE (with roadmap right around corner to 40GbE) are attractive, plus the ability to run PCI Express for Gen 3 PCI Express across the fat pipes. By utilizing the extended fabric option, you can double up the ports of 10GbE across 8 lanes for aggregate bandwidth of 80GbE. For A/D conversion, there are standard FMCs across FPGA-based carriers with Virtex-7 processing support and up to 2 GB DDR3 memory. Network interface cards (NICs) provide various panel formats for up to 12 GbE ports or 14-port managed layer 2 switches. There are a wealth of standard AMCs with LC, SPF, SPF+, QSPF, QSPF+ options as well as zQSPF+ and CFP2 for 100G out the front panel ports.
For Layer 1 processing, a DSP AMC with software can provide the frequency processing including OFDMA/SCFDMA, PUSC and diversity combining (MRC), etc. The layer 2 processor and software can provide the core processing and MAC level controls and scheduling. The processors can also include several optimized software drivers for the specific hardware.
When side-to-side cooling is acceptable and a deeper chassis is not an issue (600mm), then it is possible to have up to 12 AMC slots in a 1U high 19-inch rackmount chassis. AMC boards plug from both the front and rear of the chassis. If depth is an issue or front to rear cooling is required, chassis with front-plug only cooling can be incorporated. See Figure 3 for a photo showing the three types of chassis.
|Figure 3: The same base 1U form factor chassis can come in various configurations depending on the LTE application requirements. This includes cooling configurations in front-to-rear or side-to-side, and module plugging in both front and rear or only in the front of the chassis.|
The AdvancedTCA architecture is also well-suited for LTE systems, particularly for more demanding applications. With 40G speeds across each lane, performance is quite high. The architecture was designed with built-in redundancy, shelf management and hot swappability. For LTE applications, utilizing a Xeon-based or other powerful ATCA processor for the deep packet inspection and other heavy processing along with AMCs for I/O and other functionality would be ideal. The AMCs provide the I/O and a wealth of standard options in the single width, mid-size. Without having to use carriers, an LTE system could have pluggable AMCs into the backplane for A/D conversion and a load of FPGAs. (If a carrier is used, you can fit up to 8 AMCs in the single width, compact-size, which has less functionality and less products in the market than the mid-size.) Combining the versatile mix of features in a low profile platform would provide tremendous design versatility and performance. See Figure 4 for an example of a 3U hybrid ATCA/MicroTCA chassis platform.
|Figure 4: By combining the pure processing power of ATCA with the versatility of AMC modules in one chassis, the user has a wealth of standard options for various LTE applications in one standard architecture.|
LTE for today and tomorrow
MicroTCA and AdvancedTCA are open-standard architectures that provide versatility, modularity, scalability and high performance. As MicroTCA moves to 100G and with ATCA’s large bandwidth, these systems will continue to provide solutions for LTE/4G and other requirements for many years to come.
Justin Moll is director of marketing for VadaTech, Inc. With over 15 years of embedded computing experience, Justin has previously worked in director and management-level positions for electronics packaging companies. He has a BS in business administration from the University of California, Riverside. Justin is active in the PICMG and VITA communities and has chaired various marketing groups. He can be reached at Justin@vadatech.com