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- Aronsson, Daniel, 1976-
(författare)
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Channel Estimation and Prediction for MIMO OFDM Systems : Key Design and Performance Aspects of Kalman-based Algorithms
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless broadband systems based on Orthogonal Frequency Division Multiplexing (OFDM) are being introduced to meet demands for high data transfer rates. In multiple users systems, the available bandwidth has to be shared efficiently by several users. The radio channel quality will fluctuate, or fade, as users move. Fading complicates the resource allocation, but channel prediction may alleviate this problem. A flexible and computationally inexpensive state space representation of fading channels is here used in conjunction with a Kalman filter, operating on special-purpose reference signals, to track and predict fading OFDM channels. The thesis investigates key design and performance aspects of such estimators. Taking a probabilistic approach, we interpret the output of the Kalman filter as a full representation of a state of knowledge about the fading channels, given whatever information is at hand. For systems analysis, this permits conclusions to be drawn about channel estimation and prediction performance based on only vague information about the fading characteristics of the channel rather than on actual channel measurements. This is an alternative to conducting classic simulation studies. Various reference signal designs are studied and good design choices are recommended. Superimposed reference signal schemes are also proposed for and evaluated in cases where multiple signals are received, e.g. in multi-user (MU), multi-input multi-output (MIMO), or coordinated multi-point (CoMP) settings. By using time-varying reference signals, channel estimation and prediction performance is shown to be improved considerably in crowded frequency bands. The variation of prediction performance with prediction range and Doppler spectrum characteristics is investigated. For link adaptation, we derive the appropriate metric on which adaptation decisions should be used. The probability density function for this metric is derived for general MIMO channels. Link adaptation is studied for a single link system when channel prediction and estimation errors are present, both for uncoded systems and systems using large block codes with soft decoders. Various aspects of channel model acquisition are addressed by conducting studies on measured channels. Owing to the use of special matrix structures and fast convergence to time-invariant or periodic solutions, we find the Kalman filter complexity to be reasonable for future implementation. Finally, expressions for the impact of modelling errors are derived and used to study the impact of modelling errors on channel prediction performance in some example cases.
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| 2. |
- Van Der Perre, Liesbet, et al.
(författare)
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RadioWeaves for efficient connectivity : analysis and impact of constraints in actual deployments
- 2019
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Ingår i: Conference record of the Fifty-Third Asilomar Conference on Signals, Systems & Computers. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728143002 - 9781728143019 ; , s. 15-22
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Konferensbidrag (refereegranskat)abstract
- We present a new type of wireless access infrastructure consisting of a fabric of dispersed electronic circuits and antennas that collectively function as a massive, distributed antenna array. We have chosen to name this new wireless infrastructure "RadioWeaves" and anticipate they can be integrated into indoor and outdoor walls, furniture, and other objects, rendering them a natural part of the environment. Technologically, RadioWeaves will deploy distributed arrays to create both favorable propagation and antenna array interaction. The technology leverages on the ideas of large-scale intelligent surfaces and cell-free wireless access. Offering close to the service connectivity and computing, new grades in energy efficiency, reliability, and low latency can be reached. The new concept moreover can be scaled up easily to offer a very high capacity in specific areas demanding so. In this paper we anticipate how two different demanding use cases can be served well by a dedicated RadioWeaves deployment: a crowd scenario and a highly reflective factory environment. A practical approach towards a RadioWeaves prototype, integrating dispersed electronics invisibly in a room environment, is introduced. We outline the many and diverse R&D challenges that need to be addressed to realize the great potential of the RadioWeaves technology.
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| 3. |
- Verenzuela, Daniel, 1988-
(författare)
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Analysis of Alternative Massive MIMO Designs : Superimposed Pilots and Mixed-ADCs
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of information and communication technologies (ICT) provides the means for reaching global connectivity that can help humanity progress and prosper. This comes with high demands on data traffic and number of connected devices which are rapidly growing and need to be met by technological development. Massive MIMO, where MIMO stands for multiple-input multiple-output, is envisioned as a fundamental component of next generation wireless communications for its ability to provide high spectral and energy efficiency, SE and EE, respectively. The key feature of this technology is the use of a large number of antennas at the base stations (BS) to spatially multiplex several user equipments (UEs).In the development of new technologies like Massive MIMO, many design alternatives need to be evaluated and compared in order to find the best operating point with a preferable tradeoff between high performance and low cost. In this thesis, two alternative designs for signal processing and hardware in Massive MIMO are studied and compared with the baseline operation in terms of SE, EE, and power consumption. The first design is called superimposed pilot (SP) transmission and is based on superimposing pilot and data symbols to remove the overhead from pilot transmission and reduce pilot contamination. The second design is mixed analog-to-digital converters (ADCs) and it aims at balancing high performance and low complexity by allowing different ADC bit resolutions across the BS antennas.The results show that the baseline operation of Massive MIMO, properly optimized, is the preferred choice. However, SP and mixed ADCs still have room for improvement and further study is needed to ascertain the full capabilities of these alternative designs.
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