. All rights reserved. Any use is subject to the Terms of Use as given at the website. The CDMA Principle The CDMA Principle voice activity. This is coordinated between the base station and the user terminal. Lower data rates require less radio power, which reduces overall interference levels and extends battery life. In the forward direction, transmission of fewer bits per second is done by repeating the same bits over and over again at lower power, essentially increasing the processing gain by another factor of 2, 4, or 8. In the reverse direction, transmission of fewer bits per sec- ond allows the user terminal transmit only a fraction of the time. The base station does not expect transmission the other half, three-quarters, or seven-eighths of the time. Why does cdmaOne user lower power in the forward direction and intermittent transmission in the reverse direction? In the absence of any other issues, we would pre- fer to have equal power over time with more spreading gain. The CDMA channel can carry more traffic that way. This is the primary factor in the forward direction, so have the transmitter send repeating bits. However, power control is more critical in the reverse direction because of the near- far problem, and the base station can make better radio measurements when the user is transmitting at a consistent power level rather than reducing its power level every time the VAD unit notices that the speaker has paused. The base station receiver mea- sures each frame and makes a power-control determination, up or down, and this de- termination is much harder to calculate if the user terminal transmit power levels are changing because of voice activity. The reverse power-control measurement issue over- rides the preference for smooth power levels over time. As a result, in the reverse di- rection, the best option is to have the user terminal either transmit at its full-bit-rate power level or not transmit at all. In this way, overall transmit power is reduced from the user terminal without interfering with