| 1. |
- Bengtsson, Mats, 1967-, et al.
(författare)
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Recent Advances on MIMO Processing in the SATURN Project
- 2002
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Ingår i: Proc. IST Mobile Communications Summit.
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Konferensbidrag (refereegranskat)abstract
- We highlight some recent results on the theory and algorithmsfor MIMO systems, obtained at the Royal Instituteof Technology (KTH) within the SATURN project.The paper includes a a new approximate expression forthe ergodic channel capacity of a MIMO system with correlatedfading, algorithms for MIMO beamforming underEIRP (equivalent isotropic radiated power) constraintsand a low-complexity algorithm for MIMO channel estimationin OFDM systems. Also, we show how transmitand beamformers can be determined in a decentralizedfashion without explicitly estimating the channel response.
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| 2. |
- Bergman, Svante, et al.
(författare)
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Bit and power loading for spatial multiplexing using partial channel state information
- 2004
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Ingår i: 2004 ITG. - NEW YORK : IEEE. - 0780383273 ; , s. 152-159
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Using information about the channel at the transmitter can improve the performance of Multi-Input Multi-Output (MIMO) communication systems. When perfect Channel State Information (CSI) is available at the transmitter, data can be multiplexed and optimized over independent spatial channels. However, when the available channel information is imperfect or partial, crosstalk between the spatial channels is inevitable, complicating the design of the transmitted data. This paper presents a novel practical bit and power loading algorithm, Spatial Loading based on Incomplete Channel Estimates (SLICE), that enables the use of partial CSI for spatial multiplexing. An approximation for the Bit Error Rate (BER) of the spatial channels is derived that facilitates the loading. Numerical experiments demonstrate performance improvements compared with methods that do not consider the partial information available.
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| 3. |
- Jaldén, Joakim, 1976-, et al.
(författare)
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Semidefinite Programming for Detection in Linear Systems – Optimality Conditions and Space-Time Decoding
- 2003
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Ingår i: IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 9-12
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Konferensbidrag (refereegranskat)abstract
- Optimal maximum likelihood detection of finite alphabet symbols in general requires time consuming exhaustive search methods. The computational complexity of such techniques is exponential in the size of the problem and for large problems sub-optimal algorithms are required. In this paper, to find a solution in polynomial time, a semidefinite programming approach is taken to estimate binary symbols in a general linear system. A condition under which the proposed method provides optimal solutions is derived. As an application, the proposed algorithm is used as a decoder for a linear space-time block coding system and the results are illustrated with numerical examples.
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| 4. |
- Martin, Cristoff, et al.
(författare)
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Analytic Approximations of Eigenvalue Moments and Mean Channel Capacity for MIMO Channels
- 2002
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Ingår i: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 2389-2392
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Konferensbidrag (refereegranskat)abstract
- Approximate second order moments of the squared singular values of the channel matrix of a multiple input multiple output (MIMO) system are derived. Correlation at both the receiver and the transmitter antenna arrays is allowed. The approximation converges to the true moments as either the number of transmit or receive antennas increases. Simulations indicate that the derived moments may provide a good approximation of the true moments even for realistic array sizes. As an application, an expression for the mean channel capacity is derived. The expression is simple enough to provide insight while offering promising performance when compared with simulated channel capacities.
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| 5. |
- Martin, Cristoff, et al.
(författare)
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Approximate Transmit Covariance Optimization of MIMO Systems with Covariance Feedback
- 2003
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Ingår i: Proceedings Asilomar Conference on Signals, Systems & Computers. - : IEEE. ; , s. 1047-1051
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Konferensbidrag (refereegranskat)abstract
- The data rate of a multiple input, multiple output (MIMO) communication link can be improved if knowledge about the channel statistics is exploited at the transmitter. However, many realistic system scenarios require computationally prohibitive Monte Carlo methods in order to optimize the transmit covariance for maximization of the exact mutual information. This paper instead considers an approximative approach to maximize the performance of a communication link where covariance feedback is available at the transmitter. The algorithm presented is based on an asymptotic expression of the mutual information that allows for correlation at both the transmit and the receive side of the system. From simulations we demonstrate significant gain over beamforming and pure divversity schemes in many realistic system scenarios.
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| 6. |
- Martin, Cristoff, et al.
(författare)
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Asymptotic eigenvalue distributions and capacity for MIMO channels under correlated fading
- 2004
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Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1536-1276 .- 1558-2248. ; 3:4, s. 1350-1359
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Tidskriftsartikel (refereegranskat)abstract
- Closed form approximations of the outage capacity and the mutual information between the in- and outputs of a multi-input, multi-output (MIMO) narrowband system in the presence of correlated fading are considered. First, the limiting distribution of the squared singular values of the channel matrix is derived as the number of antennas at either the transmit or receive site increases. Spatial correlation is allowed according to a realistic stochastic channel model and correlation is allowed between the transmitted signals. The derived limiting distribution has the advantage of being closed form while simulations indicate that it provides a reasonable approximation of the true distribution also for realistic antenna array sizes. Second, the channel outage capacity is derived from the limiting distribution above for the case when the number of transmit antennas is large. The resulting outage capacity has a simple form and allows for spatially correlated channel elements as well as correlation among the transmitted signals. Results from simulations and channel measurements are presented that indicate that the derived expression provides an accurate approximation of the true channel outage capacity for a wide range of realistic system conditions.
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| 7. |
- Martin, Cristoff, et al.
(författare)
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File based mobile satellite broadcast systems : Error rate computation and QoS based design
- 2004
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Ingår i: VTC2004-FALL. - NEW YORK : IEEE. - 0780385217 ; , s. 4017-4021
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Konferensbidrag (refereegranskat)abstract
- Mobile satellite broadcast systems have the potential of delivering entertainment, information and other data services with outstanding coverage and reliability. However, the long signal interruptions due to obstacles in the terminal environment that characterizes the land mobile satellite channel make the design of efficient air interfaces challenging. In this paper, a file based mobile satellite broadcast system is studied where, to overcome the signal blockages, packet time diversity is applied. Based on some simple assumptions, an analytical expression for the file error rate of the system is derived. Using this result, a design scheme is proposed that, for a given channel and file, minimizes the total number of transmitted symbols required to satisfy quality of service (QoS) constraints in terms of acceptable delay and file receive probability. The results can also be used to estimate the reduction in bandwidth requirements that can be achieved if users in demanding environments can be served using terrestrial repeaters or other means.
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| 8. |
- Martin, Cristoff, et al.
(författare)
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Joint Channel Estimation and Detection for Interference Cancellation in Multi-Channel Systems
- 2000
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Ingår i: The 10th IEEE Workshop on Statistical Signal and Array Processing. - : IEEE. ; , s. 186-190
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Konferensbidrag (refereegranskat)abstract
- Interference from other users and interference due to multipath propagation limit the capacity of wireless communication networks. As the number of users and the demand for new services in the networks increases, co-channel interference will be a limiting factor. This paper proposes an iterative structured multichannel receiver algorithm that jointly estimates the communication channels and desired data while cancelinginterference. A general way of adding training redundancy to a data frame is also introduced. From simulations the proposed method is shown to achieve low bit error rates also in the presence of strong interference. These simulations also show that by distributing the training information in a data burst elaborately further improvements in performance are achievable.
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| 9. |
- Martin, Cristoff, 1975-
(författare)
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Mobile Satellite Broadcast and Multichannel Communications : analysis and design
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, analytical analysis and design techniques for wireless communications with diversity are studied. The impact of impairments such as correlated fading is analyzed using statistical models. Countermeasures designed to overcome, or even exploit, such effects are proposed and examined. In particular two applications are considered, satellite broadcast to vehicular terminals and communication using transmitters and receivers equipped with multiple antennas. Mobile satellite broadcast systems offer the possibility of high data rate services with reliability and ubiquitous coverage. The design of system architectures providing such services requires complex trade-offs involving technical, economical, and regulatory aspects. A satisfactory availability can be ensured using space, terrestrial, and time diversity techniques. The amount of applied diversity affects the spectral efficiency and system performance. Also, dedicated satellite and terrestrial networks represent significant investments and regulatory limitations may further complicate system design. The work presented in this thesis provides insights to the technical aspects of the trade-offs above. This is done by deriving an efficient method for estimating what resources in terms of spectrum and delay are required for a broadcast service to reach a satisfactory number of end users using a well designed system. The results are based on statistical models of the mobile satellite channel for which efficient analytical design and error rate estimation methods are derived. We also provide insight to the achievable spectral efficiency using different transmitter and receiver configurations. Multiple-element antenna communication is a promising technology for future high speed wireless infrastructures. By adding a spatial dimension, radio resources in terms of transmission power and spectrum can be used more efficiently. Much of the design and analysis work has focused on cases where the transmitter either has access to perfect channel state information or it is blind and the spatial channels are uncorrelated. Herein, systems where the fading of the spatial channels is correlated and/or the transmitter has access to partial channel state information are considered. While maintaining perfect channel knowledge at the transmitter may prove difficult, updating parameters that change on a slower time scale could be realistic. Here we formulate analysis and design techniques based on statistical models of the multichannel propagation. Fundamental properties of the multi-element antenna channel and limitations given by information theory are investigated under an asymptotic assumption on the number of antennas on either side of the system. For example, limiting normal distributions are derived for the squared singular values of the channel matrix and the mutual information. We also propose and examine a practical scheme capable of exploiting partial channel state information. In both applications outlined above, by using statistical models of the channel characteristics in the system design, performance can be improved. The main contribution of this thesis is the development of efficient techniques for estimating the system performance in different scenarios. Such techniques are vital to obtain insights to the impact of different impairments and how countermeasures against these should be designed.
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| 10. |
- Martin, Cristoff, et al.
(författare)
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On robustness against burst unsynchronized co-channel interference in semi-blind detection
- 2000
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Ingår i: Conference Record of the Asilomar Conference on Signals, Systems and Computers. - : IEEE. ; , s. 946-950
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Konferensbidrag (refereegranskat)abstract
- Interference from other users and interference due to multipath propagation limit the capacity of wireless communication networks. As the number of users and the demand for new services in the networks increases, co-channel interference will be a limiting factor. This paper investigates the effects of burst unsynchronized co-channel interference on the performance of a joint channel estimation and detection algorithm. Further, the paper tries to give some insight in how to add training redundancy to a data frame in order to provide robustness against unsynchronized co-channel interference. From simulations and Cramer-Rao bound calculation we find that by using distributing training information elaborately it is possible to increase the robustness against unsynchronized co-channel interferers.
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