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Spread Spectrum (SS) Radio Systems
Spread Spectrum (SS) radio system is a different type of radio than Multiple Access System (MAS) radio system. While MAS radio system operates in a licensed frequency spectrum, SS radio system operates in a license excempt spectrum (902-928 MHz or 2.4GHz). The system configuration of the SS radio system, which comprises a master and remote radios, is exactly the same as that of the MAS radio system. SS Techniques are methods by which a signal generated in a particular bandwidth is spread in the frequency domain, resulting in a signal with wider bandwidth. These wide band signals are harder to intercept and jam and are transmitted at much lower spectral power density. An SS modem can be configured for point to point, point to multipoint, broadcast mode, and as repeater.
SS radio systems are either Direct Sequence or Frequency Hopping else combination of the two. The Direct Sequence SS employs a high speed code sequence along with the information being sent to modulate the RF carrier. Frequency Hopping SS hops from frequency to frequency, the rate of hopping and order of frequencies occupied is a function of information rate. The bandwidth for 900 MHz is 12.5 kHz and 20 MHz bandwidth for 2.4 GHz. The coverage is 5-8 km for direct sequence spread spectrum radio, 16-24 km for frequency hopping spread spectrum radio which can be extended by using repeaters. The 900 MHz range allows better signal propagation than 2.4 GHz, however 2.4 GHz can support higher data rates. For 900 MHz radio the data rate is up to 19.2 kbps and T1/E1 (1.544 Mbps/2.408 Mbps for 2.4 GHz radio.
Tutorial on Spread Spectrum is available here: http://sss-mag.com/ss.html
Similar to MAS radio system, SS radio system can be used for supervisory control and data acquisition (SCADA) and distribution automation (DA) application.
Key Technology Area:
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