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DSP apps facilitate next-gen cellphones01

Posted: 16 Jun 2003 ?? ?Print Version ?Bookmark and Share

Keywords:dsp? cellphone? mobile handset? stb? dvd player?

DSP market research firm Forward Concepts says the broad range of applications contributed to a forecast compound annual DSP growth rate of 27 percent through 2006. The standalone and embedded DSP products have been used in virtually all consumer products such as DVD players, surround-sound audio systems, STBs and in-car electronics.

One of the most challenging DSP applications is wireless handsets. Since handsets are particularly sensitive to size, cost, and power consumption, Motorola employs compact and power efficient 16bit embedded DSP sub-systems for 2G and Starcore DSP system for 3G.

To understand the functions of DSP within a wireless handset, it is useful to recapture the requirements of different GSM generations. In wireless terminology, 2G is characterized by its predominant voice applications. As consumers look for more value-added features from the wireless network, 2.5G opens up new possibilities via GPRS networks. Mobile handsets, together with WAP browsers, e-mail, multimedia messaging, start to become more like mobile entertainment and information systems. Now the upcoming technology of 2.75G brings the handset to an even higher level of data capability. The 2.75G provides data rates of up to 384Kbps, while 3G, capable of providing 2Mbps data rates, transforms the mobile handset into a small computing device, a mobile entertainment system, as well as a mobile office.

System solutions

One of the challenges in wireless multimedia applications is large objects size being run on low bandwidth. Compression technologies are critical to reduce the object size and relax the demand of wireless data bandwidth. DSP technology enhances the compression of multimedia object, making multimedia object being transferred in real-time and interactively.

In general, DSP is responsible for two types of signal processing functions. The first is to execute algorithms required by the air interface during a voice/data call and outside a voice/data call. A voice call normally requires standard specific vocoders. At the same time, DSP performs physical layer signal handling and processing such as channel coding/decoding, equalization and other algorithmic functions. In Motorola's Innovative Convergence technology, the i.250 platform, a 16bit DSP performs these functions in the background.

The second function comes from the application side. With the data capabilities offered by GPRS networks, and value-added applications--such as high quality MIDI, MP3, voice annotation and voice recognition and location services--DSP performs the entire signal processing algorithms. The provision of the optimized software to perform these value-added features allows the handset manufacturer to concentrate on man-machine interface development and related functions, without the need to develop or license these key technologies.

To ensure very low-power consumption, DSP must have the capability to gearshift the speed of the device according to the demand of these two types of functions. Further power consumption reduction can be built into the DSP software. Although Motorola's 16bit DSP architecture is essentially ROM-based, a certain amount of flexibility is provided by internal RAM. A dedicated interface between the MCU and DSP also ensures the architecture is capable of supporting the increasing data rates.

As we move toward 2.75G, DSP performs even more computationally intensive algorithms for the physical layer of the EDGE air interface. The Motorola i.275 platform leverages the DSP technology and applies it to 2.75G. In 3G, the very high data rates and the new air interface based on W- CDMA poses a challenge to system design. Motorola's i.300 3G system solution makes use of the Starcore DSP architecture that consists of four ALUs running at 200MHz. A proven technology in the wireless infrastructure system solutions arena, it is now being applied to mobile handsets. Computationally intensive algorithms, such as W-CDMA physical layer signal processing, wideband vocoders and audio processing, are performed by the DSP. In addition to 2.5G and 2.75G, R&D efforts have been underway to increase the code efficiency and MIPS, and lower power consumption for W-CDMA and application-specific algorithms.

- Stephen Lam

System and Architecture

Motorola Wireless and Broadband Systems Group, Asia-Pacific

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