LG VX8500 Service Manual page 9

VX8500
2.3 Voice Encoder and Variable Data Speed
The bi-directional voice service having variable data speed provides voice communication which employs
voice encoder algorithm having power variable data rate between the base station and the mobile station. On the
other hand, the transmit voice encoder performs voice sampling and then, creates encoded voice packets to be
sent out to the receive voice encoder, whereas the receive voice encoder demodulates the received voice packets
into voice samples.
One of the two voice encoders described in the above is selected for use depending on inputted automatic
conditions and message/data; both of them utilize four-stage frames of 9600, 4800, 2400, and 1200 bits per
second for Cellular and 14400,7200,3600,1800 bits per second for PCS, so PCS provide relatively better voice
quality (almost twice better than the existing celluar system). In addition, this type of variable voice encoder
utilizes adaptive threshold values on selecting required data rate. It is adjusted in accordance with the size of
background noise and the data rate is increased to high rate only when the voice of caller is inputted.
Therefore, background noise is suppressed and high-quality voice transmission is possible under the
environment experiencing serious noise. In addition, in case the caller does not talk, data transmission rate is
reduced so that the transmission is carried out in low energy. This will reduce the interference on other CDMA
signals and as a result, improve system performance (capacity increased by about two times).
2.4 Protecting Call Confidentiality
Voice privercy is provided in the CDMA system by means of the private long code mask used for PN spreading.
Voice privacy can ve applied on the traffic channels only. All calls are initiated using the public long code mask
for PN spreading. The mobile station user may request voice privacy during call setup using the origination
message or page response message, and during traffic channel operation using the long code transition request
order.
The Transition to private long code mask will not be performed if authentication is not performed. To initiate a
transition to the private or public long code mask, either the base station or the mobile station sends a long code
transition request order on the traffic channel.
2.5 Soft Handoff
A handoff in which the mobile station commences communications with a new base station without interrupting
communications with the old base station. Soft handoff can only be used between CDMA channels having
identical freqeuncy assignments.
2.6 Frequency Re-Use and Sector Segmentation
Unlike the existing analog Cellular system, the CDMA system can reuse the same frequency at the adjacent cell.
there is no need to prepare a separate frequency plan. Total interference generated on mobile station signals
received from the cell site is the sum of interference generated from other mobile stations in the same cell site
and interference generated from the mobile station of adjacent cell site. That is, each mobile station signal
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