Elektor Electronics (February 2007)

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Assuming perfect power control, the interference can be 24 Smart Antenna Engineering given by Io = (N – 1)P where N is the total number of users and P is the received signal power from each user. 10) shows the fundamental dependence of CDMA capacity not only on power control but also on interference reduction techniques such as smart antennas. Capacity can be maximized if we adjust the power control, or more broadly P, so that the SNR is exactly what is needed for an acceptable error rate. 6-Kbps data rate, we obtain an uplink pole capacity of 46 to 42, respectively.

Since this process is slow, it only compensates for the slow lognormal fading. 6 Reverse Link Closed Loop Power Control The closed loop power control attempts to balance losses between the link due to Rayleigh fading or fast fading at slow mobile speeds and interference variations due to loading once the mobile is on a traffic state. It also improves the performance of mobiles at the cell edge where the signal is weak and the interfering signals from other cells are strong. As briefly described previously, power control adjusts the transmit power of each mobile to maintain the required SNR given a specific signal quality.

Idealized models show that the capacity improvement may be as high as 20 times that of the narrowband cellular standards, such as AMPS in North America, NMT in Scandinavia, TACS in the United Kingdom, and 13 times that of TDMA. However, in practice coverage areas are highly irregular, the load is not spatially uniform and is time variant throughout the day, leading to less but still significant capacity improvements. 3 Fundamentals of CDMA The key to CDMA high capacity is the use of noise-like carrier waves.

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