LGC-340/345W
7
LGIC
LG Information & Communications, Ltd.
compares this with the pre-set threshold value and then, issues out power increase/decrease commands to the
corresponding mobile station every 1.25 msec (800 times per second).
By doing so, the gain tolerance and the different radio propagation loss on the forward/backward link are
complemented.
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 mobile telephone cell site and 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. In addition, this type of variable voice encoder utilizes adaptive threshold values when 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
CDMA signals have the function of effectively protecting call confidentiality by spreading and interleaving call
information in broad bandwidth. This makes the unauthorized use of crosstalk, search receiver, and radio very
hard substantially. Also included is the encryption function on various authentication and calls specified in IS-95
for the double protection of call confidentiality.
2.5 Soft Handoff
The handoff , which is basic function of the cellular system, can maintain a call when user moves one cell site to
another. In analog cellular, the cell sites use different frequecy channel, the handoff means frequence change.
This mechanism also uses in CDMA. CDMA has many Frequency Allocation(FA)s. When the handoff carry out
between different Fas, it is called Hard Handoff. The soft handoff means the handoff without change of the FA.
During the soft hand, the cell site already in the busy state and the cell site to be engaged in the call later
participate in the call conversion. The call conversion is carried out through the original call connection cell site,
both cell sites, and then, new cell site. This method do not change frquency , so minimize call disconnection and
prevent the user from detecting the hand-off.