CDMA technology holding point

1. CDMA is a spread spectrum communication, he has a spread spectrum communication of the following characteristics:

(1) anti-interference ability. This is the basic feature of spread spectrum communications, all communication is second to none.
(2) broadband transmission, anti-fading ability.
(3) As a result of broadband transmission, the channel of transmission of the useful signal power than the interference signal power is much lower, so it seems hidden in the noise signal in; that is, if power density is relatively low, in favor of covert signals.
(4) the use of spread spectrum code of relevance to the user's access to information intercepted by anti-capacity of the strong.
(5) to receive multiple users at the same time, to send the same time.
2. In the CDMA spread spectrum communication system, the introduction of new technology with some of the key new features:
(1) uses a variety of ways diversity. In addition to the traditional outer space diversity. As broadband transmission frequency diversity has played a role, at the same time in the base station and mobile station using the RAKE receiver technology, which is equivalent to the time diversity.
(2) the use of voice-activated technology and technology sector. Because the capacity of the CDMA system directly related to the disruption of the use of voice-activated technology sector and reduce interference, can increase the capacity of the system as a whole.
(3) the use of mobile station-assisted soft-switch. It can be achieved through the seamless switch to ensure the continuity of the call, reducing dropped calls. The switch in the region through the mobile station set to receive a number of sub-base of the signal can reduce their transmitting power, thereby reducing interference on the surrounding base stations, which will help improve the reverse way of joint coverage and capacity.
(4) the use of power control technology, this reduces the transmission power stabilization.
(5) has a capacity of soft features. In the peak traffic by raising false frame rate can be used to increase the number of channels. When the load cell adjacent to a light-weight, the weight of the load cell can reduce the transmission power of the pilot, so that users on the edge of the area due to the pilot's lack of intensity switch to the adjacent cell, so that the burden-sharing.
(6), good compatibility. CDMA because of the large bandwidth, the distribution of power in a broad spectrum, the power density so low, narrow-band interference simulation system of small, so the two can co-exist. That is, good compatibility.
(7) CDMA frequency utilization of high frequency without planning, which is one of the characteristics of CDMA.
(8) CDMA voice OCELP efficient coding. Voice encoding digital communications technology is an important issue. OCELP is the use of the code table VQ difference signal, and voice-activated in accordance with the degree of a variable rate of output signal. This sort of five-way horse is considered to be currently the most efficient encoding technology, ensuring a better quality of voice, greatly enhanced the capacity of the system. This vocoder with 8kbit / S and 13kbit / S sequences of the two rates. 8kbit / S sequence from 1.2kbit / s to 9.6kbit / s variable, 13kbit / S sequence from 1.8kbt / s to 14.4kbt / S variable. Recently, a well-8kbit/sEVRC encoders available, with 8kbit / s vocoder capacity of the characteristics of voice quality has been improved.