ISSN:1124-318X    

DOI:10.1002/ett.4460120502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

摘要:

AbstractThe deployment of adaptive antennas at base stations considerably increases the spectral efficiency of wireless communication systems. To reduce the computational complexity and increase performance of space—time (ST) processing, processing may take place in reduced dimension, i. e., pre—filtering takes place which is related to linear estimation theory based on second order statistics. To this end, long—term and short—term channel estimates are integrated into specific Tx/Rx systems. In this article, we present a new ST rake structure for uplink reception in WCDMA which operates in reduced dimension. Accordingly, our approach combines short—term and long—term spatial and temporal channel properties using an eigenanalysis. By choosing dominant eigenbeams in time and space, the algorithm enhances interference suppression as well as spatial and temporal receive diversity. In contrast to previously introduced well—known receiver structures, the ST eigenrake inherently adapts to different propagation environments and achieves higher spectral efficiency than other receivers. This is illustrated by Monte—Carlo simulations.Then we extend the proposed concept to the downlink. The downlink eigenbeamformer improves closed—loop downlink diversity compared to other proposals in standardization (3GPP) which only exploit short—term channel properties. Even though the short—term feedback rate remains unchanged, additional antenna elements can be included to increase antenna and diversity gain. We also present a tracking solution to the downlink eigenbeamforming in WCDMA. To this end, we propose a distributed implementation of the eigenspace/—beam tracking at the mobile terminal and base station (BS), respectively. Moreover, the specific nature of the deployed tracking scheme offers an advantage

ISSN:1124-318X    

DOI:10.1002/ett.4460120503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

摘要:

AbstractSimple linear demodulation schemes exploiting the space and time diversity of the mobile radio channel are derived for the downlink of the Univeral Mobile Telecommunication System (UMTS) employing wideband codedivision multiple access (WCDMA). Using different stochastic models of the signals at the M × 1 receiver antennas and different objective functions including minimum—mean square error (MMSE) and maximum—likelihood approaches, we obtain time—invariant and time—variant detection schemes which make use of channel and receiver parameter estimates being calculated upon observation of a single slot. It turns out that the bit—error rate (BER) of the conventional receiver carrying out a maximum—ratio combining w. r. t. time and space can be improved considerably, where the achievable gain depends critically on the accuracy of the aforementioned estimates. Efficient ways for implementation are proposed and quantified in terms of the computational complexity. Analytical approximations and simulations of the BER for different system parameters reveal that the schemes represent means to get robust against both channel fading and multiple access interference caused by multipath

ISSN:1124-318X    

DOI:10.1002/ett.4460120504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

摘要:

AbstractDue to the increasing number of users in mobile communications and the demand for mobile multimedia services with high data rates, third generation mobile radio systems are currently one of the key communication technologies in research, development, and international standardization bodies. Smart antennas can be used to increase the capacity of wireless communication systems even further. TDD systems are particularly attractive for the employment of smart antennas, since the channel information (e. g., in terms of spatial covariance matrices) estimated on the uplink can be used directly for downlink beamforming. In this paper, we discuss efficient uplink and downlink processing techniques with smart antennas for UTRA TDD, the TDD mode of third generation mobile radio systems that is based on TD—CDMA. On the uplink, joint space—time processing is used to eliminate co—channel interference created by other users that transmit on the same frequency and in the same time slot. These joint detection techniques are efficiently implemented in the frequency domain. On the downlink, the data is only transmitted in the direction of the desired mobile user while interference in the direction of co—channel users is avoided. Moreover,short—termspatial channel estimates can be improved by projecting them into the dominant subspace of thelong—termspatial covariance matrix. System level simulations have been performed to evaluate the gain in spectral efficiency (available bit rate per bandwidth per cell) if simple downlink beamforming techniques are used at the base stations. There is a two— to three—fold spectral efficiency gain if antenna arrays ofM = 8elements are deployed in a sectorized macro—cel

ISSN:1124-318X    

DOI:10.1002/ett.4460120505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

摘要:

AbstractJoint transmission (JT), a novel downlink transmission scheme, was introduced and described in recent papers. Questions still open concern the performance assessment of JT and the comparison of JT with conventional downlink transmission schemes. In order to answer these questions, quantities termed SNR degradation and transmission efficiency are presented in this paper. Based on these quantities, exemplary system assessments and comparisons are performed, which clearly show the suitability of these measures and also the advantages of the novel downlink transmission scheme JT.

ISSN:1124-318X    

DOI:10.1002/ett.4460120506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

摘要:

AbstractWe address the problem of joint downlink beamforming and power control in wireless communication systems. The goal is to minimise the overall transmission power radiated from the base station while satisfying individual signal—to—interference levels at the mobiles. Several iterative algorithms have been proposed for this non—linear optimisation task. One important problem in this context is that for certain scenarios the problem has no feasible solution. One of the main contributions of this paper is to derive a necessary and sufficient condition for the existence of a solution. This not only gives new insight into the analytical structure of the problem, but also provides a unifying framework by which several optimisation criteria known from literature can be compared. Finally, simulations are carried out using a deterministic multi—path channe

ISSN:1124-318X    

DOI:10.1002/ett.4460120507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

摘要:

AbstractFor the simulation and design of smart antenna transmission principles in mobile radio, precise knowledge of the time—variant directional multipath structure in various radio environments is required. In this paper, a new real—time multiple—input—multiple—output (MIMO) vector radio channel sounder is described, which uses multiple antennas at the transmitter as well as at the receiver position. The proposed MIMO measurement principle can be effectively exploited to estimate the propagation direction at both ends of the wireless link simultaneously, and thus, dramatically enhance overall resolution of the multiple path parameters. Applying a proper antenna architecture and the multidimensional unitary ESPRIT algorithm, joint superresolution estimation of the direction of departure (DOD), time—delay of arrival (TDOA), Doppler shift, and direction of arrival (DOA) of the propagating waves becomes possible. The measured results can also be used directly for the simulation of combined transmit—receive diversity (MIMO) transmission principles and space—time (ST) adaptive receivers in a multi—user scenario. Results based on measurements in different locations are referenced, including a complicated indoor environment as is typical for industrial

ISSN:1124-318X    

DOI:10.1002/ett.4460120508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

摘要:

AbstractIn this paper we discuss different Radio Resource Management (RRM) strategies for smart antenna cellular networks. The focus is on adaptive strategies which combine spatial channel reuse within the cell with dynamic inter—cell channel allocation. In particular, three different SDMA channel allocation strategies are described and compared in terms of complexity as well as traffic capacity. The comparison is done by means of system simulations of a multi—cellular environment. We show that with a growing degree of freedom the RRM strategies yield better results in terms of traffic capacity while the number of handoffs per call increases and the complexity gr

ISSN:1124-318X    

DOI:10.1002/ett.4460120509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460120501

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2001

数据来源: WILEY