| Summary: | 博士 === 國立臺灣科技大學 === 電子工程系 === 99 === To accommodate an ever increasing subscribers with prescribed quality of service(QoS), in this thesis, we propose several efficacious soft information-assisted multiuser detectors (MUDs) to reinforce the capability of interference cancellation under various emerging wireless communication systems. The investigation of this thesis includes the followings.
First, we present a new space-time two-stage receiver with the assistance of
soft information for the Alamouti space-time block code (STBC) and spatially multiplexing (SM) combined multiple-input multiple-output (MIMO) systems. The
first stage of the receiver consists of a bank of soft generalized sidelobe canceller (GSC)-based detectors to yield an initial estimate of the transmitted symbols. The groupwise detection is then conducted successively in the second stage by using the matched filters (MFs) to simultaneously detect the two consecutive symbols in one STBC block with the removal of the soft interferences in between.
Second, an alternating MUD (AMUD) for the uplink of heterogeneoussignaling
MIMO code division multiple access (CDMA) systems over multipath
fading channels is addressed, where the data are transmitted using either SM for high transmission rate or STBC for transmit diversity gains. The new MUD first separates users into two groups according to their transmission signaling schemes and then detects the transmitted symbols in each group alternately with the removal of iteratively refined soft information-assisted multiple access interference (MAI) to enhance the interference cancellation capability. Moreover, for practical low-complexity implementation, the users in each group are further partitioned into smaller subgroups based on their effective channel correlations and then detected in parallel by a bank of minimum mean-squared error (MMSE) soft detectors to further reduce the computational load.
Third, an extension of the AMUD, referred to as iterative groupwise MUD
(IGMUD), is considered for the uplink of multi-rate multi-carrier code division
multiple access (MC-CDMA) systems. The IGMUD first classifies the users into
separate groups according to their transmission rates. In each iteration, these
groups of users are detected sequentially based on a set of group detectors with the removal of MAI group by group. For practical low-complexity implementation, a partitioning scheme similar as the above is also utilized to mitigate the computational overhead.
Finally, we consider a novel subspace decomposition-based detection scheme
with the assistance of soft information cancellation in the uplink of interleaved orthogonal frequency division multiple access (OFDMA) systems. By utilizing the inherent data structure, the interference is first separated with the desired symbol and then further decomposed into one caused by the decision errors and the other one by the undetected symbols in the successive interference cancellation (SIC) scheme. With such an ingenious interference decomposition along with the soft processing scheme, the new receiver can render more thorough interference cancellation, which in turn entails enhanced system performance. Moreover, for practical implementations, we also consider to only deal with the principal components of inter-carrier interference (ICI) to reduce the computational load. Conducted simulations results show that the developed receivers can offer significant performance improvement compared with previous works in various scenarios. The corresponding low-complexity implementations are, in particular, appealing for practical applications, since they require substantially lower computational overhead with only slight performance loss.
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