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U. Glaeser

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Modem Banks<br />

This is the first of the multi-channel DSP applications. Modem banks did not appear because of PC<br />

modems. They appeared because of the Internet (web servers) and remote workers (remote access<br />

servers). The number of required DSP MIPS is extremely high. For instance, a typical bank of 120 V90<br />

modems requires 3600 DSP MIPS (120 × ~30).<br />

DSL Modem Banks<br />

This is nothing compared to DSL, where (for instance) 30,000 DSP MIPS (120 × ~250) is required for<br />

a 120 channels S-HDSL modem bank.<br />

Broadband Line Card (Voice-over-Broadband)<br />

The most likely example of broadband line card is a DSL line card, which fills the same function as<br />

modem banks plus the typical voiceband functions (echo cancellation, voice compression, DTMF detection,<br />

fax relay) found in gateways.<br />

Gateway (Voice-over-Broadband)<br />

Under this heading are included all recent buzzword equipment such as voice-over-DSL, voice-over-IP,<br />

voice-over-Packet, etc. A gateway can be on the periphery of the network (access), in the center (core)<br />

or on customer premises (private). Its main use is to translate from a circuit network to a packet network<br />

and back. A state-of-the-art gateway SOC (System-on-Chip) targets 200 channels, which translates into<br />

4000–10,000 DSP MIPS depending on the voice compression quality. The voice quality has been the<br />

subject of a lot of debate (and hard-learnt lessons) in the IP community over the last four years.<br />

Cellular Wireless Base Station<br />

In wireless, voice quality is not a problem (relatively speaking) since compression algorithms are standardized.<br />

They require as low as 3 DSP MIPS (GSM full rate) to 30 DSP MIPS (third generation such<br />

as AMR) per channel. Cellular wireless base stations are half gateway (access to network) and half radio<br />

relay (air interface). It is this air interfaces, which presently (2001) presents a lot of challenges to the DSP<br />

world. Many MIPS-hungry techniques have been introduced (CDMA, turbo coder) and many more will<br />

be coming (smart antenna, multiple reception, software radio, etc.) over the next 20 years. In essence<br />

this is 25,000 DSP MIPS per channel. In other words, each channel requires a 25 GHz general purpose<br />

DSP. One can see the interest of application specific DSP and custom instruction set in this market.<br />

Home Gateways and “Personal Systems”<br />

A residential cordless base station is now the most common example of a “personal system.” A personal<br />

system is a device having both characteristics of telecom terminals and telecom infrastructure. It is a<br />

terminal because:<br />

1. It is sold in retail stores.<br />

2. It is targeted at a small entity (single person, family, SOHO).<br />

It is a telecom infrastructure equipment because:<br />

1. It has no human interface.<br />

2. It very often acts as a point-to-multipoint access device.<br />

© 2002 by CRC Press LLC

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