Advanced receivers for high speed downlink packet access in UMTS
Başlık çevirisi mevcut değil.
- Tez No: 401353
- Danışmanlar: DR. DIRK SLOCK
- Tez Türü: Doktora
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2006
- Dil: İngilizce
- Üniversite: Ecole nationale supérieure des télécommunications-ENST
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 211
Özet
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Özet (Çeviri)
The thesis studies advanced signal processing techniques at UMTS user equipment receivers, which are particularly suited for the so-called 3.5G high speed downlink packet access services (HSDPA). In the ¯rst part, we consider families of user dedicated downlink channel esti- mation methods, which are especially bene¯cial when there is dedicated channel transmit beamforming. The methods do not assume any a priori knowledge of the path delays and the beamforming parameters and they exploit all the transmitted pilot sequences as well as the structured dynamics of the channel. We start with building least squares (LS) esti- mates of the channels associated with dedicated and common pilots in each slot. Then we improve the dedicated channel estimate quality by either jointly Kalman ¯ltering the two LS estimates or by a suboptimum cascade of weighted LS combining and one-state Kalman ¯ltering. In the latter case, the order of Kalman ¯ltering and weighted LS combining re- sults in di®ering performance and complexity in di®erent conditions. In order to obtain the estimates of the missing model parameters we incorporate the expectation maximization (EM) algorithm to the Kalman mechanism expanded with one-lag smoothing which also improves the performance compared to ¯ltering alone. In the second part we ¯rst consider a chip level HSDPA-speci¯c decision-directed normalized least mean squares (HDD-NLMS) equalization scheme which uses the previous base station chip sequence estimates as the desired responses for equalizer adaptation. Then we generalize this concept by incorporating the despreading operation. Group despreading, i.e. despreading with a partial code of PCPICH pilot sequence is a means to increase the adaptation rate and hence to increase the channel tracking capability w.r.t. the standard PCPICH symbol level LMS algorithm which does full PCPICH despreading. However, it has the risk of interference ampli¯cation which again can be compensated by incorporation of a decision directed mechanism, which estimates the ingredients of the pseudo-symbol output of the partial despreading operation using hard decisions and LMMSE weightings. Finally we propose HSDPA symbol level N-Gri±ths and HDD-NLMS equalizers which en- able adapting 16 times more frequently than the PCPICH-symbol rate adaptation. All the proposed HSDPA-speci¯c algorithms have reasonable complexity and close to Max-SINR performance in realistic working regimes. We compare the performance of the HDD-NLMS vis-µa-vis the N-Gri±ths equalizer at both chip level and HSDPA symbol level. Since the latter requires channel parameters, in order to make a fair comparison, we perturb the correct channel parameters by some amounts compliant with the performances of various channel estimation methods considered in the ¯rst part. In the last part we assess the bene¯ts of using chip equalizers w.r.t. the usage of the conventional Rake receiver and using hard decision or hyperbolic tangent symbol nonlinearities w.r.t. the usage of linear feedback operations in the context of an iterative parallel interference cancellation receiver that we derive from the polynomial expansion of the symbol level covariance matrix inverse after the ¯rst stage equalization. Since the equalizers at di®erent stages of the considered interference canceller are to be di®erent as well, in order to estimate the essential equalizer parameters of a particular stage we use the estimates from the preceding stage.
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