I copied the following DSP tutorial from a press release from Lucent. It does a good job at describing the role of DSP in telecommunications and the difference between DSP's and the general purpose microprocessor. This is all generic info, relevant to LU DSP16000 DSP as well as TI's c6x.
BACKGROUND INFORMATION ON DIGITAL SIGNAL PROCESSORS (DSPs)
Q. How are DSPs used in wireless base stations?
A. Base stations capture voice signals from the radio waves and relay them to a telephone line. This can be a daunting task. Callers may be moving, and signal strengths can ebb and flow. Some signals may reflect off buildings and other structures, so that the base station receives both the original signal and a slightly delayed "shadow" signal. Other radio devices or even adverse weather in the cell may create intermittent noise. The challenge is to receive the user's signal, recover the voice data from the received digital stream, and pass the signal along to the system's public telephone switching office. Such signal-processing tasks, known as equalization, noise filtering, channel decoding, encryption and forward error correction, are optimally performed by DSPs.
Q. What is a DSP?
A. A DSP is a specialized semiconductor chip that performs high-speed mathematical computations with voice, data, and video signals. Used in wireless, modem, consumer electronics, and other communications devices, DSPs represent one of the fastest-growing segments of the semiconductor market.
The internal architecture of a DSP is designed to take advantage of the repetitive nature of signal processing tasks by "pipelining" the data flow, or starting one task before the preceding one is actually finished. In addition, DSPs have special processing circuits which speed up the routines commonly used in signal processing. The most common of these is known as a "MAC" or multiplier-accumulator. Within a MAC, two numbers are multiplied, and the result is added to the previous total. Lucent's new DSP16000 core and DSP16210 chip are expected to have the capability of performing up to 200 million of each multiply and accumulate functions per second. Today's DSPs can perform a MAC in one clock cycle whereas a typical microprocessor might take from 10 to 25 clock cycles. The MAC operation is fundamental to many applications in speech recognition, speech coding, noise filtering,
and telecommunications.
Q. What is the role of a DSP in a wireless telephone?
A. DSPs play two crucial roles in wireless telephone handsets. They perform a function known as "speech coding" in which the analog output from the microphone is digitized and then compressed or "coded" according to one of several available algorithms. The goal of all speech coders is to reduce the amount of data that needs to be transmitted while maintaining the maximum speech quality. Speech coding is a computationally intensive task and must be done in "real time" to maintain an interactive, natural-feeling call.
DSPs also do "channel coding." This is a function analogous to that of ordinary modems; the digitized voice signal is combined with the analog wireless radio signal for transmission. The first step in channel coding is to balance or "equalize" noise levels to obtain the best possible voice quality; then encryption may be performed; and finally, the resulting digital stream of voice data is "modulated" onto a radio frequency carrier signal. Coding, modulation, encryption, noise filtering, and equalization are functions for which a DSP chip is especially well suited. |
