Unleash the power of modular base station design with Serial RapidIO--Part I

Michael Olsen, IDT (Integrated Device Technology, Inc.)

November 12, 2006

Michael Olsen, IDT (Integrated Device Technology, Inc.)

The modular design and manufacture of cellular base stations is essential to the cost-effective delivery of 3G mobile services such as combined video, voice and data, often referred to a "triple play." But why is modular design so important?

The ability of service providers to offer triple play services at a competitive price to the consumer is essential to realizing the return on their investment in 3G cellular, and beyond. This is driving service providers to demand significant infrastructure cost reductions from equipment providers. In fact, customers indicate that base station prices must fall by 80 percent per year. However, service providers are also demanding a major throughput increase--to 10 Gbps guaranteed--in order to deliver bandwidth-hungry services as cost-effectively as possible. The question becomes, how to reconcile the apparently conflicting objectives of cost reduction and performance increase?

Modularity certainly reduces the cost of manufacture and the cost of upgrading equipment to meet more demanding requirements in the future. However, combined with the deployment of appropriate standard application-specific system components (ASSC), it can also meet the significantly increased system performance demands. The result? The higher throughput increases the volume of services that can be processed in any given time slot, and consequently reduces the unit cost of delivering the service.

So, how do we achieve this modularity objective? The replacement of relatively expensive ASIC parts, both cell-based and FPGA, by lower cost standard components goes a long way to meeting this objective. But standard components require standard interfaces if they are to inter-operate without the use of custom-designed interfaces. The custom-designed interface is the natural enemy of efficient standard component usage, and hinders the manufacturers' ability to maximally exploit modularity.

Serial RapidIO iis an open standard interface devised to solve this problem in embedded systems. In standardizing the on-board device level interface, the Serial RapidIO standard complements other standards developed to support modularity. These include the Open Base Station Architecture Initiative (OBSAI), a system level interface standard that defines the interface between base station modules; a competing system-level interface standard, the Common Public Radio Interface (CPRI), which defines the interface between the RF and control blocks in a Universal Mobile Telecommunications System (UMTS) base station; and the Advanced Telecom Computing Architecture (ATCA), which defines a standard chassis form factor. Together, these standards define some of the critical electronic and mechanical interfaces necessary to design and manufacture a modular base station system.

This article describes the use of two Serial RapidIO-enabled ASSCs in a modular 3G base station design that boost performance by up to 20 percent and, according to base station designers, reduce the bill of materials (BOM) by 50 percent to 75 percent vs. alternative approaches. Specifically, we describe a standard ASSC, the 10 Gbps serial buffer, which eliminates a serious throughput bottleneck in the base station--the frame sample compare bottleneck; and discuss how another standard ASSC, a pre-processing switch, boosts system performance by reducing digital signal processor (DSP) loading.