ISCO and Blackfin® Suppress Interference between Cell Phones and Basestations

ISCO International designs, manufactures, and distributes products that improve what is known in cellular industry as the "reverse link" the signals mobile devices send to wireless basestations. ISCO products, when deployed as network-wide solutions, are designed to improve the quality, coverage, and capacity of a wireless operator's network.

One ISCO product in particular, the Adaptive Notch Filter (ANF) platform, identifies and suppresses interference signals that are within the RF passband of mobile devices. These in-band interference signals are especially prevalent in Code Division Multiple Access (CDMA) mobile systems, and are extremely difficult to control using conventional means. In fact, ISCO's patented ANF solution is the only in-band interference solution commercially available in the marketplace today. It successfully enables wireless operators to realize significant, consistent gains in performance throughout their in-band channels.

"...Blackfin offers the best price/performance of any of the processors we researched. We were impressed with Blackfin's combination of signal processing and control processing. Blackfin will also enable us to reduce our part count as we go from an analog to a digital approach."
Sean Cordone,
Director of Engineering

Until now, ISCO's ANF product has been implemented using analog components. As available technology advanced, ISCO recognized the cost, performance, and time-to-market advantages of replacing these components with software-based digital processing algorithms, especially in anticipation of the increased system demands brought about by 2.5G and 3G cell phone architectures. The company researched the available products and chose a Blackfin ADSP-BF533 processor from Analog Devices, Inc. (ADI). Blackfin offered the best price/performance and flexibility of any processor on the market for ISCO's signal processing application.

Millions of Cell Phones
Consider that today there are approximately a hundred million digital cellular phones in use, being serviced by slightly over a million basestations. The most popular architecture currently in use in North America is CDMA. CDMA allows many users to share a broad spectrum at the same time and operates in the 800MHz band and 1.9GHz PCS band. It is less costly to implement than Global System for Mobile (GSM), which is primarily used in Europe, and Time Division Multiple Access (TDMA), a satellite and cellular phone technology that interleaves multiple digital signals onto a single high-speed channel. CDMA spreads the voice stream over the full 1.25MHz bandwidth of the CDMA channel, coding each stream separately so it can be decoded at the receiving end.

Unfortunately, noise is a common problem that often plagues the CDMA architecture. The causes of noise are many. Certainly, the fact that the RF spectrum is overcrowded with cell phones is part of the problem more cell phones, more noise. But public service networks such as fire and safety networks are another contributing factor as they use RF devices that generate cross talk interference from adjacent channels, when a device communicating on one frequency gets bounced around or phase shifted.

Generations of Cell Phone Service

The first generation (1G) of mobile cellular communications systems was analog, and was primarily used for voice. It was introduced in the late 1970s, early 1980s.

Starting in the 1990s, the second-generation (2G) systems were introduced – GSM, TDMA and CDMA – that used digital encoding. 2G systems were used mostly for voice.

A variety of 2G+, or 2.5G, technologies have been deployed that provided faster e-mail and Internet access.

Third generation (3G) is designed for high-speed multimedia data and voice and is also expected to provide advanced global roaming.

More Calls, More Money
Without question, wireless operators need an effective and economic reverse-link solution (the ability for a basestation to detect and process a signal from a portable device). ISCO's solutions improve network performance by identifying and mitigating reverse link limitations. With strong subscriber cell phone growth and the emerging demand for 2.5G and 3G wireless services, ISCO planned to extend its reverse-link solution – the ANF product – to stay ahead of the market.

ISCO's ANF product is essentially a smart filter on the reverse link that "intelligently" identifies the meaningful portion of the signal and the part that is unwanted interference. The ANF then passes the useful part of the signal and eliminates the interference. "A high-quality customer experience is fundamental to a cell phone operator's success," said Sean Cordone, Director of Engineering, ISCO. "By taking interference out of their networks, we reduce the dropped calls and ineffective attempts that are the principle source of frustration for mobile phone users."

ISCO's next-generation ANF product will adopt an all-digital approach using a digital receiver front end, with the spectrum interference analysis algorithm executed in software running on the Blackfin processor. "We decided to go 'digital' for increased flexibility, horsepower, and speed," said Cordone. "We saw a good match for what we want to do with ADI products for a number of reasons. Blackfin offers the best price/performance of any of the processors we researched. We were impressed with Blackfin's combination of signal processing and control processing. Blackfin will also enable us to reduce our part count as we go from an analog to a digital approach."

Blackfin processors are designed to meet the computational demands and power constraints of today's embedded audio, video, and communications applications. The processors deliver breakthrough signal processing performance and power efficiency with a RISC programming model, allowing flexible resource allocation between hard real-time signal processing tasks and non real-time control tasks. System control tasks can often run in the shadow of signal processing tasks. The Blackfin processor's unique combination of processing attributes eliminates the need for separate digital signal and control processors, which reduces bill of material costs and greatly simplifies hardware and software design tasks.

Time to Market
As it is for many companies, time to market is crucial for ISCO. To that end, the company is using a whole suite of tools from ADI to speed the development process. The first is ADI's VisualDSP++ software development and debugging environment (IDDE), which enables efficient management of projects from start to finish from within a single interface. The project development and debugging environments allow movement quickly and easily between editing, building, and debugging activities. Cordone says ISCO is also depending on ADI's universal serial bus emulator and high-performance in-circuit emulator (ADDS-HPUSB-ICE) to "bring up the board" using the familiar JTAG interface.

ISCO has already proven itself in the market. The company's ANF system completes the reverse-link identification/suppression process in less than 20 milliseconds per CDMA carrier. It simultaneously suppresses up to three interferers, addressing the strongest interference signals first. It improves site coverage and capacity, and it extends handset battery life. With Blackfin inside, ISCO will eliminate network interference faster, enabling wireless operators to handle more calls and offer more sophisticated services to consumers. For consumers that means fewer dropped calls and better reception.

For more information about ISCO International, visit their Web site at

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