Multiuser CDMA. Enhancing capacity of wireless cellular CDMA. Topics Today. Dealing without multiuser reception: asynchronous CDMA SNR power balance  nearfar effect Multiuser detection (MUD) classification and properties The conventional detector (no n MUD, denotations)
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Enhancing capacity of wireless cellular CDMA
voltage at the I&D* at the decision instant
signalvoltage
ISI & noise voltage
signal power for the j:th user
channel noise
MAI
*Integrate and dump receiver
LPF
decision
phasing of
sampling
local code
Practical CDMA receiverEffective BW
is defined by:
for rectangular
spectra:
Eb/No
(=SNR1/2)
AWGN level decreases
*SNR1: received SNR without multiple access interference
Unequal received powers  the nearfar effect
The nearfar effect in asynchronous CDMA
By using the perfect power balance the number of users is
Asynchronous channel of Kusers behaves the same way as a single user channel having ISI with *memory depth of K1
*This could be generated for instance by a multipath
channel having K1 taps
Considering the whole received sequence, find the estimate for the received sequence that has the minimum distance to the allowed sequences
is the amplitude
is the spreading code waveform
is the data modulation of the k:th user
is the AWGN with N0/2 PSD
decision
decision
Conventional detection (without MUD) for multiple accessnoise
matched filter outputs
data
correlations between each pair of codes
received amplitudes
with
synchronous ch.
User 1
1
3
5
User 1
1
3
5
User 2
2
4
6
2
4
6
User 2
Asynchronous and synchronous channelWeight
multiplication
Weight
multiplication
Weight
multiplication
matched
filter
bank
R
R
R
MF
user 1
To the next stage
decision

+


Parallel interference cancellation (PIC)spreader
matched
filter
bank
decisions
and
stage
weights
+
amplitude
estimation
parallel
summer
initial
data
estimates
minimization tends to cancel MAI
PIC variations
PROS:
CONS: