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WSD Feature Article

Base Station Boosts Cellular Communications

BY Cheryl Ajluni

Flanked By Hardware, Software, And Middleware, This Software-Defined, Radio-Based Platform Offers A Cost-Effective And Quick Means Of Migrating To 3G.


The migration to 3G functionality reveals a number of interesting obstacles for today's wireless carriers, developers, engineers, equipment vendors, and network operators. How, for example, do you cost-effectively transition from a 2G or 2.5G network to a 3G one, while maintaining consistency and quality of service for cellular customers? To say the least, this has been a difficult issue to address. Work in the area of software-defined radios (SDRs) has opened the doorway to one potential solution: a base station that can dynamically support multiple cellular services or protocols. With this approach, network operators would be able to minimize changes to existing infrastructure while still providing the end user with quick access to new functionality.

While the concept of the SDR is compelling, its implementation has been slow in coming. Luckily, for today's wireless engineers, a viable alternative has emerged. It's based on an innovative view of the SDR, and it promises to enable rapid deployment of 3G wireless services and applications. Called SpectruCell, it hails from an Australian company called Advanced Communications Technologies (ACT).

SpectruCell is a proprietary and patent-pending SDR wireless base-station technology. A SpectruCell network is comprised of general-purpose signal-processing boards running software that defines cellular-protocol functionality. It's deployed on an industry-standard Compact PCI platform, so operators can add or remove processing cards as needed.

A network operator might, for example, deploy a SpectruCell base station with only two or three processing cards in a cell site. As the number of customers grows, or if the operator wants to support multiple services/operators, it simply adds more processing cards. A management engine eases the burden of upgrading the hardware by eliminating the need for operator configuration. Instead, the SpectruCell operating system automatically recognizes the fact that a new card or cards are present. It just adds them to the pool of available processing power.

SpectruCell is targeted at mobile network operators and equipment vendors, wireless engineers, and application developers. In addition to supporting existing 2G and 2.5G net-works, it provides a viable migration path to 3G wireless networks, services, and applications. As a software-defined platform technology, the same SpectruCell infrastructure can support multiple protocols simultaneously. In other words, an operator can support GSM, CDMA, W-CDMA, 3G, and UMTS all on the same base station. Having such a broad customer profile will significantly reduce the cost of providing next-generation services. In fact, the network rollout cost is reduced by about 25% compared to current hard-ware base stations.

JUST THE FACTS

SpectruCell is comprised of three main components: hardware, middleware, and software. The hardware component comprises high-speed signal-processing cards and tunable digital up-and/ or downconverters. What makes this hardware component unique is its SDR implementation. Unlike traditional SDRs, which are implemented using arrays of digital signal processors (DSPs), SpectruCell relies on a combination of DSPs and reconfigurable processors (RCPs) from Chameleon Systems ( http://www.chameleonsystems.com ). This combination culminates in an SDR platform for both chip-and symbol-rate processing.

Each SpectruCell signal-processing card consists of four processing stripes. A stripe is defined as one DSP and one RCP. Every processing stripe can handle 2 Mb of data throughput, independent of the front-end air interface. The air interfaces are defined by application code that runs on each stripe. This code is managed by the SpectruCell middleware, which runs on a Linux operating system (FIG. 1). It is CORBA-based, and expands on initiatives set forth by both the JTRS and the Software Defined Radio Forum.A domain manager helps facilitate the registration of all hardware and software resources. It matches the applications to available processing resources and then loads them into the SpectruCell system.

The object-based application code, or software, that provides air-interface functionality makes up the last component of the SpectruCell system. ACT currently offers patent-pending implementation methods for cellular protocols like GSM and IS95 (CDMA) deployed on a SDR processing platform. Apart from those air-interface applications, and others like CDMA2000 and UMTS, SpectruCell supports management and billing interfaces.

As explained by Simon Cleary, Vice President of Research and Development at ACT, "An application developer may choose to develop a real-time fraud-detection application to sit at the base station. Or, as IP is pushed further out the network, more and more applications will reside in the base station. SpectruCell has been designed to facilitate this movement through the published API and development suite available in the SpectruCell SDK."

A suite of design tools currently being developed by ACT will make application development for the SpectruCell platform even easier. Included in this suite will be a simulator, emulator, reference design, high-level API, and source code. Scheduled for shipment in the first quarter of 2002, these development tools will allow application developers to focus on the higher-layer, application-specific functions of their development. They won't have to worry about such things as the choice of operating system, device drivers, FPGA development, on-board switching integration, or digitization. All of this functionality will be supplied in SpectruCell through reconfigurable modules that the developer can include in their system-level design.

What does all of this mean? Essentially, the SpectruCell hardware takes a wide-band RF front end of 25 MHz, downconverts and digitizes it, and then feeds it into the SpectruCell processing farm. Once there, all tasks—such as linearization, filtering, and channelization—are defined in software. They may then be dynamically altered as needed (FIG. 2).

According to Jason May, ACT's Chief Technology Officer, "Traditional hardware-defined solutions do not allow you the flexibility of, say, dynamically changing your CDMA search space once an application is deployed in the field. In this example, a solution using Qualcomm hardware-defined chip sets cannot change these characteristics once deployed. SpectruCell has been designed for this, and allows a developer to tweak their application once it is deployed."

UNDERSTANDING ITS UNIQUENESS

There are many unique aspects to the SpectruCell offering, not the least of which is its role as a platform for seamless migration from 2G to 3G. With a flexible, software-based processing platform, cellular protocols can be uploaded to a base station as demand dictates. Because services can be deployed virtually instantaneously over existing infrastructure, operators are able to better maintain their investments. Network bugs, deployment parameters (performance tweaks), and diagnostic routines simply become software programs that can be remotely monitored, controlled, and deployed.

Wireless design engineers can use the company's base framework as the vehicle from which to quickly deploy applications. Rather than spending time understanding the hardware subsystem, they can focus their attention on what they do best—develop software applications.

As an added benefit, the platform has been designed to focus on Quality of Service (QoS) delivery. This will become an especially crucial feature as mobile Internet Protocol (IP) services evolve. Aiding in this process is SpectruCell's management engine, which partitions off sections of the base station to perform specific functions. Such a capability can be used to provide support for either multiple protocols or multiple network operators, the latter of which is referred to as mobile virtual-network operator (MVNO). A SpectruCell-based network can even deliver cellular services for more than one operator or spectrum licensee over more than one protocol.

One of the main benefits of this platform is its cost effectiveness. The price of a SpectruCell-based system is comparable to competing hardware-based solutions. A fully populated Compact PCI Frame (4 IF cards, 8 signal-processing cards, 2 control cards, 1 network card, 1 management CPU) can be configured or reconfigured dynamically in one of the following ways: • 96 GSM channels (frequency reuse of 2) = 48 channels, 8 users/channel = 384 users • 16 CDMA 2000 carriers (120-Km cell size) = 16 carriers, 32 users/carrier = 512 CDMA 2000 users • 4 UMTS carriers = 4 carriers, 64 users/carrier = 256 UMTS users • 48 GSM channels (frequency reuse of 2) = 24 channels, 8 users/channel = 162 GSM users, 8 CDMA 2000 carriers (120-Km cell size) = 8 carriers, 32 users/carrier = 256 CDMA2000 users, 1 UMTS carriers = 1 carrier, 64 users/carrier = 64 UMTS users.

Given a fully configured CompactPCI rack, cost will be approximately $150,000 (US dollars) for the base-station components. This is for a scalable 2G-, 2.5G-, and 3G-capable system that allows for virtual networks and simultaneous multiple-protocol support. It also looks to be virtually future-proof. For a less powerful SpectruCell system, the cost is significantly lower. As a base entry point, an operator can deploy a SpectruCell micro-cell system and upgrade it to a macro by slotting in more signal-processing cards as demand requires.

Once services have been deployed for two or more operators over shared infra-structure, the cost of the network for each operator is dramatically lowered. For example, a shared network with three operators results in network ownership that costs approximately one-third of what they would spend to deploy their own network.

Of course, all of these benefits do not come without a price. Committing functionality in software, as is the case with the SpectruCell platform, means a speed sacrifice. A purely hardware-based solution, after all, will always be more efficient than a software one due to the effort in obtaining efficient use of processing resources. But the cost effectiveness and flexibility of SpectruCell, coupled with the recent improvements in compiler technology and processor speed, seem to minimize this concern. The platform's real limiting factor is the RF spectrum, as newer technologies will seek to gain higher spectral efficiency from standards-based air interfaces.

While SpectruCell is a proprietary solution, the company is working within the confines of an emerging SDR Forum specification. Once the final specification gets approved, ACT plans to publish an interface to it. ACT will begin shipping pre-production hardware, along with software-development kits, in the second quarter of 2002. Live field trials with at least one major national operator are also set to begin in the second quarter. They will be conducted in the US.

Advanced Communications Technologies,
Level 20
350 Queen Street
Melbourne, Australia;
[phone]
FAX: [phone],
http://www.adcomtech.net.

ACT—USA, Inc. (ADVC)
19200 Von Karman Avenue
Suite 500
Irvine, CA 92612
[phone]
FAX: [phone]

copyright WIRELESS SYSTEMS DESIGN (DECEMBER 2001)

imho, Jerome