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What is spread spectrum?Spreading spectrum is a technique of modulating and demodulating digital signal into broadband in order to increase the noise immunity and improve the security of data. This technique is important in wireless data communication where the loss of a single bit of data can be detremental to the quality of entire data of communication. Two different basic techniques of spreading sprectrum are available today. One is direct sequence spread spectrum (DSSS) where data stream is spread in spectrum as the name implies. Another technique is frequency hopping (FH) where each data frame switches (i.e.hops) its RF frequency in pseudo random sequence as the name implies. Other spread spectrum techniques in use are code-division-multiple-access (CDMA) and OFMD. Siliconians supports DSSS technology. In DSSS, each bit of data is modulated with a pseudo noise (PN) code and then fed to RF module for air transmission. The signal after spreading looks very like random noise signal. A length of PN code is determined at system architecture level, and is any number between 11 to several hundreds. Siliconians uses 2-bit symbol technique where a pair of data bits are modulated with a set of 32 bit long PN codes. Despreading reverses the process of spreading. Noise-like signal is demodulated with a set of PN codes and then the original data are recovered. This technique of spread spectrum allows high quality data communication in noisy environment where peak power of noise might be greater than that of data. This advantage gain comes at the expense of broadening the communication bandwidth. For this reason, spread spectrum communication requires broadband communication band, mostly in ISM band. ISM band is a RF channel specially allocated by FCC for unlicensed communiation. Currently 900M hz band and 2.4M band are allowed in the United States. An RF module for a spread spectrum communicaton device should be able to handle broadband signal. This makes DSSS radio design more challenging than that of narrow band communication. Fortunately several RF IC companies have recently introduced IC chips specifically designed for ISM band communication.The comparison of DSSS technology vs. FH technology is complex and often confusing even to communication experts. It suffices to say that wireless local area network (WLAN) protocols (IEEE802.11x) are mostly based on DSSS. Digital cordless phones use DSSS by necessity while well-publicized Bluetooth is based on FH. In general, DSSS has higher efficiency and is not limited by speed limitation. The drawback is this is more expense to implement because of its complexity compared to FH. Siliconians products resolves this barrier of complexity of DSSS with ASIC solution. All complex DSSS circuitry is implemented by hardware on silicon and is easily controlled by software. This allows low cost solution for production and quick design turn around time. Further information about spread spectrum technology can be found by searching the topics in Internet. One such site is listed below. This site does not have any business relationship with Siliconians.
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