Every other week, it seems, digital signal processor vendors come up with new terms for their DSPs-such as reconfigurable processors-or are sticking to the standard techniques but making myriad implementation changes, whether through core modifications, extensions or full-blown coprocessors for dedicated functions.
Many DSPs are ideal for the functions to which they are applied, such as voice-over-packet processing in voice aggregation gateways, with its wide range of echo cancellation and codec algorithms. Contributors to this week's Focus look at how DSPs are meeting the processing demands. For example, platform architect Lloyd Palum and his colleagues at Improv Systems Inc.(Beverly, Mass.) examine the misconceptions surrounding channel density on a DSP core for voice over packet apps.
In some instances, vendors might be in danger of overstating the simplicity of their DSP approaches. Consider the plethora of vendors offering solutions that can handle baseband processing for all possible flavors of wireless LAN-802.11b, .11a, HiperLAN2 and, eventually, even 802.11g. As a result, these vendors say, anyone can quickly get to market by simply sticking their DSP next to an RF front end. Leading this charge are nBand, Systemonic, 3DSP, BOPS and others.
The gating factor for a multiband, multiprotocol radio that can handle each of the WLAN standards, however, is not the DSP but the RF front end. And meeting the power, cost, performance and footprint requirements of the WLAN market requires more than simply placing an RF section next to any DSP, as companies such as Atheros and Intersil will attest. Rather, it calls for a total systems approach, wherein the DSP's processing power compensates for the limitations of the RF section and vice versa. The result should be an optimum design to meet the market's requirements.
Recognizing the limitations of their somewhat isolationist approach, many DSP vendors are looking for a suitable RF partner with which to align themselves. Systemonic AG (Dresden, Germany) took the lead recently when it acquired Raytheon's Tondelayo two-piece 5-GHz RF chip set, along with some of Raytheon's packaging, antenna and power-amplifier technologies. Expect other DSP houses to follow suit.
Meanwhile, DSPs are bumping up against their inherent limitations in the 3G wideband CDMA basestation. Along with high overall data throughput rates and dense channel use, such systems face the problem of handling all the highly complex chip-rate processing required for any CDMA-based system.
Recently, Analog Devices Inc. (Norwood, Mass.) announced that it had added extensions to its TigerSharc line that allow the TigerSharc to handle such processing. Texas Instruments Inc. has similarly added a coprocessor to its 'C6715 to handle the same functions.
Nonetheless, FPGA companies such as Altera are pushing multiuser detection (MUD) and smart antennas for anything other than pure baseband symbol-rate decoding as well as other ancillary functions.
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