- Library Home /
- Search Collections /
- Open Collections /
- Browse Collections /
- UBC Theses and Dissertations /
- Blind multiuser detection for time-frequency spread...
Open Collections
UBC Theses and Dissertations
UBC Theses and Dissertations
Blind multiuser detection for time-frequency spread multicarrier CDMA Tam, Wilson
Abstract
Multicarrier transmission technology has shown tremendous potential in realizing high data rates for next generation broadband wireless communication systems. Multicarrier modulation schemes are robust to frequency selective fading which are inherent in broadband wireless channels. This thesis considers blind multiuser detection for the recently proposed time frequency spread multicarrier CDMA (TF-MC-CDMA) system in which the system uses both time and frequency domain spreading to achieve diversity in both time and frequency domains. The challenge for TF-MC-CDMA multiuser detection is to mitigate multiple access interference (MAI) in both the time and the frequency domain. The objective of this thesis is to develop and analyze the performance of blind multiuser detection algorithms for TF-MC-CDMA for three types of channel models: AWGN with MAI, slowly fading downlink Rayleigh multipath channels, and the slowly fading downlink multipath channels with Doppler shift induced intercarrier interference (ICI). A new suboptimal decoupling technique for blind multiuser detection for TF-MCCDMA in AWGN with MAI is proposed. It is found that the original TF-MC-CDMA blind multiuser detection problem can be suboptimally decoupled into two blind multiuser DS-CDMA problems. These two problems can be solved separately using blind DS-CDMA multiuser techniques. Our effort focused on using blind linear multiuser detectors in which we investigated into four types of blind detection methods: blind direct matrix inversion (DMI) method, blind CMOE RLS method, blind subspace multiuser detection method using SVD and PASTd adaptive subspace tracking. The suboptimal decoupling technique for blind multiuser detection for TF-MC-CDMA is extended to slowly fading downlink Rayleigh multipath channels known as type I detectors. Computer simulation results show that type I detectors do not work well in slowly fading multipath channels even though such a scheme provides very good performance in AWGN with MAI. In slowly fading channels, the orthogonality of the time domain signature sequences is preserved. We propose a type II detector which uses a cascade implementation with the time domain detection output acts as the input of the frequency domain detection. Computer simulations show that type II detectors provide much better performance than type I detectors. Blind multiuser detection for TF-MC-CDMA is further extended for slowly fading Rayleigh multipath channels with Doppler shift induced ICI. In mobile channels, Doppler shifts combined with multipath effects create random subcarrier frequency shifts which in turn cause subcarrier frequency mismatch. Such mismatch leads to the loss of orthogonality among subcarriers thus creating ICI. Our analysis shows that Doppler shifts induced ICI has the effect of destroying the common-channel property in downlink channels. The downlink TF-MC-CDMA signal becomes a quasi-uplink signal because of user dependent subchannel gains. The type II detector for slowly fading Rayleigh multipath channels is further extended to apply in such channels with Doppler shift induced ICI. It is shown through analysis and computer simulations that the proposed type II detectors implemented using CMOE RLS algorithm, blind subspace SVD algorithm, and the blind subspace PASTd adaptive subspace tracking algorithm, without modifications, provide robust performance in multipath channels with Doppler shift induced ICI.
Item Metadata
Title |
Blind multiuser detection for time-frequency spread multicarrier CDMA
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
2007
|
Description |
Multicarrier transmission technology has shown tremendous potential in realizing high
data rates for next generation broadband wireless communication systems. Multicarrier
modulation schemes are robust to frequency selective fading which are inherent in
broadband wireless channels. This thesis considers blind multiuser detection for the
recently proposed time frequency spread multicarrier CDMA (TF-MC-CDMA) system
in which the system uses both time and frequency domain spreading to achieve
diversity in both time and frequency domains. The challenge for TF-MC-CDMA
multiuser detection is to mitigate multiple access interference (MAI) in both the time
and the frequency domain. The objective of this thesis is to develop and analyze
the performance of blind multiuser detection algorithms for TF-MC-CDMA for three
types of channel models: AWGN with MAI, slowly fading downlink Rayleigh multipath
channels, and the slowly fading downlink multipath channels with Doppler shift
induced intercarrier interference (ICI).
A new suboptimal decoupling technique for blind multiuser detection for TF-MCCDMA
in AWGN with MAI is proposed. It is found that the original TF-MC-CDMA
blind multiuser detection problem can be suboptimally decoupled into two blind multiuser
DS-CDMA problems. These two problems can be solved separately using blind
DS-CDMA multiuser techniques. Our effort focused on using blind linear multiuser
detectors in which we investigated into four types of blind detection methods: blind
direct matrix inversion (DMI) method, blind CMOE RLS method, blind subspace
multiuser detection method using SVD and PASTd adaptive subspace tracking.
The suboptimal decoupling technique for blind multiuser detection for TF-MC-CDMA
is extended to slowly fading downlink Rayleigh multipath channels known as
type I detectors. Computer simulation results show that type I detectors do not work
well in slowly fading multipath channels even though such a scheme provides very good
performance in AWGN with MAI. In slowly fading channels, the orthogonality
of the time domain signature sequences is preserved. We propose a type II detector
which uses a cascade implementation with the time domain detection output acts as
the input of the frequency domain detection. Computer simulations show that type
II detectors provide much better performance than type I detectors.
Blind multiuser detection for TF-MC-CDMA is further extended for slowly fading
Rayleigh multipath channels with Doppler shift induced ICI. In mobile channels,
Doppler shifts combined with multipath effects create random subcarrier frequency
shifts which in turn cause subcarrier frequency mismatch. Such mismatch leads to the
loss of orthogonality among subcarriers thus creating ICI. Our analysis shows that
Doppler shifts induced ICI has the effect of destroying the common-channel property
in downlink channels. The downlink TF-MC-CDMA signal becomes a quasi-uplink
signal because of user dependent subchannel gains.
The type II detector for slowly fading Rayleigh multipath channels is further
extended to apply in such channels with Doppler shift induced ICI. It is shown through
analysis and computer simulations that the proposed type II detectors implemented
using CMOE RLS algorithm, blind subspace SVD algorithm, and the blind subspace
PASTd adaptive subspace tracking algorithm, without modifications, provide robust
performance in multipath channels with Doppler shift induced ICI.
|
Genre | |
Type | |
Language |
eng
|
Date Available |
2011-03-09
|
Provider |
Vancouver : University of British Columbia Library
|
Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
|
DOI |
10.14288/1.0101023
|
URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
|
Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.