User Manual

AS4000 Wireless Local Loop
System Overview
GSI 001
605-0000-430
Issue 1.2 Date 7/4/99
Page 14 of 16
In each of the 3 cells a group of frequencies is allocated as follows:
Group 1 F1, F4, F7, F10
Group 2 F2, F5, F8, F11
Group 3 F3, F6, F9, F12
The 3 cell reuse factor that is used in CDMA systems such as AS4000 cannot be used for
other types of Wireless Access systems using TDMA or FDMA systems.
The processing gain of a spread spectrum radio system defines the level of interference that
can be tolerated by the received signal. Given a large enough processing gain a signal can be
extracted from an environment that has an interference level actually higher than the wanted
signal. As the C/I ratio defines the nearest distance at which the same Co Channel carrier
can be used, this advantage usually results in a frequency reuse for CDMA system of 3 or
less making it suitable for wide area or multi cell deployment.
The relatively low reuse distance involved in CDMA, (less than 4 cells) could, if the basic
cell size is small, as both the wanted (nearest) and unwanted (next reuse of frequency) cells
could be within the receiver range of the ST lead to the possibility of false acquisition on to
a nearby CT,. To avoid this happening AS4000 uses different PN Codes for adjacent cell
clusters.
The PN code provides the basic spreading mechanism that is inherent in CDMA systems.
The PN codes take their name from the fact that they are basically Pseudo random Noise
code sequences of a fixed length. If different PN codes are used between cells using the
same frequency then one of the three basic elements has been changed. Therefore, this
prevents false acquisition as the next reuse of frequency is seen by the system as noise and
cannot be interpreted. PN codes are chosen to have the minimum possible residual dc
component when demodulated. A limited number of these codes exist within a PN code of
given length and for the purposes of AS4000 a maximum of 7 are used. This extends the
distance between cells that are Co channel and same PN to a distance where false
acquisition should not be possible.
Allocation of Frequency and PN code will usually form part of the network planning and
will not usually be determined by an individual CT configurater.
System Management
There are two systems available for managing the AS4000 System:
AS8100 Sitespan
AS8300 Element Manager
AS8100 Sitespan is a PC-based management and control systems via which the system
administrator can test, configure and control most aspects of the AS4000 System. The
AS8100 Sitespan controller is designed to manage several sites simultaneously and uses
Windows based software as a management system.