QUALCOMM, INCORPORATED CDMA TECHNOLOGIES 5775 MOREHOUSE DRIVE SAN DIEGO, CA 92121 http://www.cdmatech.com/about_us/contact.jsp
ENABLING THE FUTURE OF COMMUNICATIONSTM
CSM2000™CELL SITE MODEM
QUALCOMM CDMA TECHNOLOGIES HTTP://WWW.CDMATECH.COM
Overview
The CSM2000™ device, developed by QUALCOMM Incorporated, is a
CDMA digital baseband modem which replaces QUALCOMM’s
previous generation of Cell Site Modem™ (CSM™) devices, the
CSM1.0™ and CSM1.5™ devices. The previous CSM devices
supported only one Forward Link and one Reverse Link channel per
device. The CSM2000 device has been enhanced to support eight
Forward Link channels and eight Reverse Link channels.
The CSM2000 device provides QUALCOMM’s CDMA licensees with an
IS-95A compliant system capable of supporting both 9.6 kbps and
14.4 kbps channels. The CSM2000 device is made up of eight
integrated Channel Elements. Each Channel Element is accessed as if
it were a single CSM1.0 or CSM1.5 device. This allows the CSM2000
device to be controlled by software written for the CSM1.0 or CSM1.5
devices with only minor changes.
Performance
The high integration of the CSM2000 device allows a substantial
savings in power consumption. The CSM2000 device provides more
than 75% power savings when replacing eight CSM1.0 devices and
more than 50% power savings when replacing eight CSM1.5 devices.
Improvements in the demodulator of the CSM2000 device provide up
to 1.2 dB of improvement over the CSM1.0 and CSM1.5 devices. This
reduces the output power required from the mobile unit, resulting in
improved Reverse Link system capacity and increased battery life in
the mobile unit.
Channel Element Functions
Searcher
The searcher selects an antenna set for a search and programs the
position and size of the search window. Then, the searcher initiates the
search and finds the largest multipath peaks within the search
parameter set. Normally, the searcher operates continuously; while the
results from a search are read, the next search is already underway.
For acquisition searches, the searcher results can be used to detect
the presence of a mobile attempting to access the CDMA network. For
demodulator multipath searches, fingers may be assigned to the
reported paths to improve the demodulator performance of the rake
receiver.
Four Fingers
The four fingers make up a front-end interface to the demodulator.
The fingers provide timing, Walsh chip accumulation and Walsh chip
storage for the demodulation process. The fingers may be
programmed to accept data from the same or different antenna
sources.
Demodulation Processor
The demodulation processor performs Fast Hadamard Transforms for
the searcher and the four fingers. It also performs optimal soft
combining of data from the fingers and performs power calculations,
including lock detection and power control decisions.
CSM2000 Transmit Chain Diagram
CSM2000™CELL SITE MODEM
Channel
Element
0
Channel
Element
1
Channel
Element
6
Channel
Element
7
Receive
Samples
Microprocessor
Interface
Transmit
Chain
Outputs
Transmit
Chain
Inputs
Tx Tx Tx Tx
CSM2000
QUALCOMM, INCORPORATED CDMA TECHNOLOGIES 5775 MOREHOUSE DRIVE SAN DIEGO, CA 92121 http://www.cdmatech.com/about_us/contact.jsp
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ENABLING THE FUTURE OF COMMUNICATIONSTM
CSM2000™CELL SITE MODEM
QUALCOMM CDMA TECHNOLOGIES HTTP://WWW.CDMATECH.COM
Deinterleaver & Viterbi Decoder
The deinterleaver is used to reverse the interleaving performed by the
mobile unit. Interleaving provides protection against burst errors and
fades.
The Viterbi decoder, using the Viterbi algorithm, optimally decodes the
convolutional coding from the mobile unit. Quality bits and Cyclic
Redundancy Check (CRC) bits are used to verify the quality of the
decoded data.
PN Sequence Generators
There are several Pseudorandom Noise (PN) generators within the
CSM device. The PN sequences generated are the I channel, Q
channel and long code sequences for both Forward and Reverse Link
processing.
Encoder & Interleaver
The encoder takes Forward Link data frames, convolutionally encodes
them, and performs symbol repetition for bit rates less than full rate.
The encoder also automatically generates CRCs for the frames that
require them.
The interleaver is used to provide time diversity in
transmitted symbols, thereby providing protection
from relatively long transmission fades and burst
errors. The effects of the interleaver are reversed in
the mobile unit deinterleaver.
Modulator
The modulator contains three individually programmable sections that
generate Forward Link information streams from the interleaver output.
The symbols from the interleaver are scrambled with the long code PN
sequence and punctured with power control bits, if appropriate. The
punctured symbols are covered with the proper Walsh code and
spread with the I and Q PN sequences. The resulting chips are then
bandlimited with FIR filters and multiplied by a programmable gain
factor. Each of the three transmit sectors can be driven by a particular
section of the modulator, the sum of all three sections or zero.
Transmit Summer
The transmit summer of each Channel Element combines its outputs
with the outputs of the previous Channel Element and passes the
result to the next Channel Element. Channel Element 0 receives its
inputs from the CSM2000 device pins, and Channel Element 7 sends
its result to the CSM2000 device pins. This allows the transmit chains
of several CSM2000 devices to be tied together. Each Channel
Element in the chain can be programmed to do any one of these three
things:
• Pass the samples on its cascade inputs straight through to its
outputs
• Ignore the samples on its cascade inputs and only output the
samples it generated
• Sum the samples it generates with the samples on its cascade
inputs
The transmit summer adds a parity bit to the output samples and can
also do parity checks on the cascade input samples. If the samples fail
the parity check, the transmit summer can automatically ignore those
samples.
Copyright © 2004 QUALCOMM Incorporated. All rights reserved. QUALCOMM is a
registered trademark, and CSM2000, Cell Site Modem, CSM, CSM1.0, and CSM1.5
are trademarks of QUALCOMM Incorporated. All other trademarks and service marks
are the property of their respective owners. Data subject to change without notice.
Printed in USA 2/2004 CSM2000-SS X7
Searcher
Demodulation
Processor
Deinterleaver
&
Viterbi Decoder
P/N
Sequence
Generator
RXI
RXQ
TX Data
Packets Modulator Transmit
Summer
Encoder
&
Interleaver
Cascade
I,Q Inputs
TXI,
TXQ
RX Data
Packets
Four Fingers
CSM2000 Channel Element Functional Block Diagram
