User Manual

AS4000 Wireless Local Loop
System Overview
GSI 001
605-0000-430
Issue 1.2 Date 7/4/99
Page 13 of 16
using a code whose bit rate is much higher than the bit rate of the message (typically in the
order of 16 times). The individual bits of the code are referred to as chips.
The incoming signal at the receiver consists of the modulated message plus the channel
noise. By multiplying the same code by the incoming signal, ‘despreading’ is achieved. This
results in the unwanted noise being spread over a bandwidth equal to the noise bandwidth
plus that of the code. The use of bandpass filters effectively eliminates the noise and the
noise-free message is then extracted.
9.2 Code Division Multiple Access
In the AS4000 System, one radio channel supports 15 radio links (DS/SS transmissions)
which co-exist within the same bandwidth. To achieve this, the technique of CDMA is
employed which uses a set of orthogonal (RW) codes to modulate individual channels.
These RW codes (0 to 14), are combined with the basic spreading pseudo-random noise
(PN) codes (1 to 7) to form ordinals to reference a total of 105 spreading codes, each
having 256 bits, to modulate the digital traffic channel. The PN code and frequency channel
are used at each end of a radio link to allow transmission to occur. The use of these
parameters as a network planning tool enables the same radio channel to be re-used in a
seven-cell repeat pattern.
Omni Antenna Cell Deployment
u Non-Sectored Antenna, 4 Frequencies (RF Channels) per cell (CT),
7 PN Codes in deployment plan
PN1
PN3
PN4PN5
PN7
PN1
PN2
PN3PN6
PN7
PN1
PN2
PN3
PN4
PN5
PN6
PN7
PN2
PN4
PN5
PN6
PN1
PN3
PN4PN5
PN7
PN1
PN2
PN3PN6
PN7
PN1
PN2
PN3
PN4
PN5
PN6
PN7
PN2
PN4
PN5
PN6
1st cell frequency subset
(F1, F4, F7, F10)
2nd cell frequency subset
(F2, F5, F8, F11)
3rd cell frequency subset
(F3, F6, F9, F12)
Typical 3 Cell Repeat Pattern
Figure 11. Three Cell Repeat Pattern.