| 1. |
- Axehill, Daniel, et al.
(författare)
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A Low-Complexity High-Performance Preprocessing Algorithm for Multiuser Detection using Gold Sequences
- 2008
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Ingår i: IEEE Transactions on Signal Processing. - Linköping : IEEE Signal Processing Society. - 1053-587X .- 1941-0476. ; 56:9, s. 4377-4385
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Tidskriftsartikel (refereegranskat)abstract
- The optimum multiuser detection problem can be formulated as a maximum likelihood problem, which yields a binary quadratic programming problem to be solved. Generally this problem is NP-hard and is therefore hard to solve in real time. In this paper, a preprocessing algorithm is presented which makes it possible to detect some or all users optimally for a low computational cost if signature sequences with low cross correlation, e.g., Gold sequences, are used. The algorithm can be interpreted as, e.g., an adaptive tradeoff between parallel interference cancellation and successive interference cancellation. Simulations show that the preprocessing algorithm is able to optimally compute more than 94,% of the bits in the problem when the users are time-synchronous, even though the system is heavily loaded and affected by noise. Any remaining bits, not computed by the preprocessing algorithm, can either be computed by a suboptimal detector or an optimal detector. Simulations of the time-synchronous case show that if a suboptimal detector is chosen, the bit error rate (BER) rate is significantly reduced compared with using the suboptimal detector alone.
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| 2. |
- Axehill, Daniel, et al.
(författare)
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A Preprocessing Algorithm Applicable to the Multiuser Detection Problem
- 2005
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Ingår i: Proceedings of Radiovetenskap och Kommunikation 2005. - Linköping : Linköping University Electronic Press.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper a preprocessing algorithm for binary quadratic programming problems is presented. For some types of binary quadratic programming problems, the algorithm can compute the optimal value for some or all integer variables without approximations in polynomial time. When the optimal multiuser detection problem is formulated as a maximum likelihood problem, a binary quadratic programming problem has to be solved. Fortunately, the low correlation between different users in the multiuser detection problem enables the use of the preprocessing algorithm. Simulations show that the preprocessing algorithm is able to compute almost all variables in the problem, even though the system is heavily loaded and affected by noise.
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| 3. |
- Blom, Jonas, et al.
(författare)
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Pole Placement Design of Power Control Algorithms
- 1999
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Ingår i: Proceedings of the 49th IEEE Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780355652
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Konferensbidrag (refereegranskat)abstract
- Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.
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| 4. |
- Eng, Frida, 1977-, et al.
(författare)
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Frequency Analysis using Non-Uniform Sampling with Application to Active Queue Management
- 2004
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Ingår i: Proceedings of the 2004 IEEE International Conference on Acoustics, Speech and Signal Processing. - Linköping : Linköping University Electronic Press. - 0780384849 ; , s. 581-584
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Konferensbidrag (refereegranskat)abstract
- In many real-time applications, sample values and time stamps are delivered in pairs, where sampling times are non-uniform. Frequency analysis using non-uniform data occurs in various real life problems and embedded systems, such as vibrational analysis in cars and control of packet network queue lengths. Our contribution is to first overview different ways to approximate the Fourier transform, and secondly to give analytical expressions for how non-uniform sampling affects these approximations. The results are expressed in terms of frequency windows describing how a single frequency in the continuous time signal is smeared out in the frequency domain, or, more precisely, in the expected value of the Fourier transform approximation.
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| 5. |
- Eng, Frida, et al.
(författare)
-
Frequency Domain Analysis of Signals with Stochastic Sampling Times
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In nonuniform sampling (NUS), signal amplitudes and time stamps are delivered in pairs. Several methods to compute an approximate Fourier transform (AFT) have appeared in literature, and their posterior properties in terms of alias suppression and leakage have been addressed. In this paper, the sampling times are assumed to be generated by a stochastic process. The main result gives the prior distribution of several AFTs expressed in terms of the true Fourier transform and variants of the characteristic function of the sampling time distribution. The result extends leakage and alias suppression with bias and variance terms due to NUS. Specific sampling processes as described in literature are analyzed in detail. The results are illustrated on simulated signals, with particular focus to the implications for spectral estimation.
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| 6. |
- Eng, Frida, et al.
(författare)
-
Frequency Domain Analysis of Signals with Stochastic Sampling Times
- 2008
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Ingår i: IEEE Transactions on Signal Processing. - : IEEE Signal Processing Society. - 1053-587X .- 1941-0476. ; 56:7, s. 3089-3099
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Tidskriftsartikel (refereegranskat)abstract
- In nonuniform sampling (NUS), signal amplitudes and time stamps are delivered in pairs. Several methods to compute an approximate Fourier transform (AFT) have appeared in literature, and their posterior properties in terms of alias suppression and leakage have been addressed. In this paper, the sampling times are assumed to be generated by a stochastic process. The main result gives the prior distribution of several AFTs expressed in terms of the true Fourier transform and variants of the characteristic function of the sampling time distribution. The result extends leakage and alias suppression with bias and variance terms due to NUS. Specific sampling processes as described in literature are analyzed in detail. The results are illustrated on simulated signals, with particular focus to the implications for spectral estimation.
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| 7. |
- Eriksson, Jonas, et al.
(författare)
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On Coding of Scheduling Information in OFDM
- 2009
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Ingår i: Proceedings of the 69th IEEE Vehicular Technology Conference. - 9781424425174
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Konferensbidrag (refereegranskat)abstract
- Control signaling strategies for scheduling information in cellular OFDM systems are studied. A single-cell multiuser system model is formulated that provides system capacity estimates accounting for the signaling overhead. Different scheduling granularities are considered, including the one used in the specifications for the 3G Long Term Evolution (LTE). A greedy scheduling method is assumed, where each resource is assigned to the user for which it can support the highest number of bits. The simulation results indicate that the cost of control signaling does not outweigh the scheduling gain, when compared with a simple round-robin scheme that does not need signaling of scheduling information. Furthermore, in the studied scenario, joint coding and signaling of scheduling information over all selected users is found to be superior to separate coding and signaling for each user. The results also indicate that the scheduling granularity used for LTE provides better performance than the full granularity.
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| 8. |
- Geijer Lundin, Erik, et al.
(författare)
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Adaptive Filtering Applied to an Uplink Load Estimate in WCDMA
- 2003
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Ingår i: Proceedings of the 57th IEEE Semiannual Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780377575 ; , s. 452-456
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Konferensbidrag (refereegranskat)abstract
- In the uplink of a WCDMA system, a natural choice of resource quantity is the uplink noise rise, i.e., total received power over noise power. Unfortunately this quantity is hard to measure and estimates are often noisy. This paper focuses on relative load which is closely related to the noise rise. Model-based signal processing with change detection techniques is herein used to suppress noise and minor oscillations while being alert on fast load changes. The time varying model identified in the process can also be used for prediction of future values, something which resource management algorithms can benefit from.
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| 9. |
- Geijer Lundin, Erik, et al.
(författare)
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Characterizing Uplink Load : Concepts and Algorithms
- 2004
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Ingår i: Wireless Communications Systems and Networks. - Boston : Springer US. - 0306481901 - 0306486423 ; , s. 425-441
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Bokkapitel (refereegranskat)abstract
- The maximum capacity of a CDMA cellular system’s radio interface depends on the time varying radio environment. This makes it hard to establish the amount of currently available capacity. The received interference power is the primarily resource in the uplink. Ability to predict how different resource management decisions affect this spatial quantity is therefore of utmost importance. The uplink interference power is related to the uplink load through the pole equation. In this chapter, we discuss both theoretical and practical aspects of uplink load estimation.
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| 10. |
- Geijer Lundin, Erik, et al.
(författare)
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Robust Uplink Resource Allocation in CDMA Cellular Radio Systems
- 2005
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Ingår i: Proceedings of the 44th IEEE Conference on Decision and Control and European Control Conference 2005. - Linköping : Linköping University Electronic Press. - 0780395670 ; , s. 1848-1853
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Konferensbidrag (refereegranskat)abstract
- Radio resource management (RRM) in cellular radio system is an example of automatic control. The system performance may be increased by introducing decentralization, shorter delays and increased adaptation to local demands. However, it is hard to guarantee system stability without being, too conservative while using decentralized resource management. In this paper, two algorithms that both guarantee system stability and use local resource control are proposed for the uplink (mobile to base station). While one of the algorithms uses only local decisions, the other uses a central node to coordinate resources among different local nodes. In the chosen design approach, a feasible solution to the optimization problems corresponds to a stable system. Therefore, the algorithms will never assign resources that lead to an unstable system. Simulations indicate that the proposed algorithms also provide high capacity at any given uplink load level.
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