Differential MMSE: A New Approach for Adaptive Interference Suppression Over Time-Varying Channels

The use of the linear minimum mean square error (MMSE) criterion to design coherent adaptive receivers is a classical method for interference suppression, with applications ranging from equalization to adaptive multiuser detection for direct sequence code division multiple access (CDMA) systems. A drawback of this method is that standard MMSE adaptation is unable to track the amplitude and phase variations typical of a wireless fading channel. A classical method for noncoherent communication over such channels is differential modulation and demodulation, which obviates the need to track amplitude and phase by exploiting the fact that channel variations over successive symbols are negligible. However, there are no known methods for adaptive interference suppression for differentially modulated systems. In this thesis, this gap is filled by reformulation of the linear MMSE criterion for differential modulation. This provides the first cohesive framework for addressing the two most serious impairments of the wireless medium: interference and fading. The resulting differential MMSE receiver is obtained as a solution to an optimization problem with quadratic cost function and quadratic constraint, and is amenable to both block and recursive adaptive implementations. When the fading is frequency selective, the differential MMSE receiver provides automatic multipath combining for slow fading rates. For faster fading rates, it is necessary to extend the differential MMSE criterion to provide explicit multipath combining. A number of such extensions are proposed, notable among which is the eigen-rake receiver, which provides interference suppression and diversity combining without requiring any explicit information regarding the desired user's propagation channel. While the application explored in detail in this thesis is adaptive interference suppression for direct sequence CDMA with short spreading sequences, differential MMSE reception is equally applicable to intersymbol and cochannel interference suppression in narrowband fading channels.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Zhu, Liping Julia

Contributors dc:contributor

• Upamanyu Madhow

• Engineering, Electronics and Electrical

Language dc:language

eng

Identifier

(MiAaPQ)AAI9953189

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/81318