| 1. |
- Eng, Frida, et al.
(författare)
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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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| 2. |
- Eng, Frida, et al.
(författare)
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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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| 3. |
- 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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| 4. |
- Gunnarsson, Fredrik, et al.
(författare)
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Uplink Load and Link Budget with Stochastic Noise Rise Levels in CDMA Cellular Systems
- 2005
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Ingår i: Proceedings of Radiovetenskap och Kommunikation 2005. ; , s. 491-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The limiting factor in the uplink of all CDMA cellular systems is the relation between uplink noise rise and intended coverage. In link budgets, noise rise is usually simply handled as a constant contribution to the background noise in logarithmic scale, often referred to as interference margin. In practice, however, it is not constant. We model the uplink noise rise as a lognormal distribution, and investigate the impact to link budgets. Simulations and numerical calculations show that the uplink noise rise variance does not critically affect the uplink capacity and coverage. System feasibility and its relation to the uplink load is also discussed. It is shown that approximative load expressions provides an upper bound on the uplink load and therefore they can be used to imply system feasibility. Furthermore, the uplink load expressions provide accurate approximations of the load given that the load is within the practical limits given by the link budgets.
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| 5. |
- Gustafsson, Fredrik, et al.
(författare)
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Localization Based on Observations Linear in Log Range
- 2008
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Ingår i: Proceedings of the 17th IFAC World Congress. - 9783902661005 ; , s. 10252-10257
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Konferensbidrag (refereegranskat)abstract
- AbstractReceived signal strength (RSS) is used in wireless networks as a ranging measurement for positioning and localization services. This contribution studies conceptually different networks, where neither transmitted power or the path decay constant can be assumed to be known. The application in mind is a rapidly deployed network consisting of a number of sensor nodes with low-bandwidth communication, each node consisting of a number of sensor types measuring RSS. Typical sensors measure acoustic, seismic, magnetic and IR power emitted from a target. First, a model linear in the unknown nuisance parameters (transmitted power and path loss constant) is presented and validated from real data. Then, the separable least squares principle is applied to the non-linear least squares (NLS) cost function, after which a cost function of only the unknown position is obtained. Results from field trials are presented to validate the method.
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| 6. |
- Gustafsson, Fredrik, et al.
(författare)
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Localization in sensor networks based on log range observations
- 2007
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Ingår i: 2007 PROCEEDINGS OF THE 10TH INTERNATIONAL CONFERENCE ON INFORMATION FUSION, VOLS 1-4. - : IEEE. - 9780662478300 ; , s. 1048-1055
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Konferensbidrag (refereegranskat)abstract
- This contribution presents a unified framework for localization and tracking in sensor networks based on fusing a variety of signal energy measurements as provided by for instance acoustic, seismic, magnetic, radio, microwave and infrared sensors. The received energy from such sensors generally decays exponentially, and a log range model is introduced for the sensor observations in logarithmic scale, which is linear in transmitted power and the path loss exponent. Field trial sensor data confirms the validity of the log range model. The novelty in this contribution ties in a systematic least squares approach to eliminate these nuisance parameters and also the sensor noise variances. Details on how to solve the resulting low-dimensional non-linear least squares criterion are given, and how to extend the algorithms to target tracking. Explicit formulas for the Cramer-Rao lower bound are given for both localization and tracking.
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| 7. |
- Gustafsson, Fredrik, et al.
(författare)
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Measurements used in Wireless Sensor Networks Localization
- 2009. - 1
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Ingår i: Localization Algorithms and Strategies for Wireless Sensor Networks. - : Information Science Reference. - 9781605663968 - 9781605663975 ; , s. 33-53
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Bokkapitel (refereegranskat)abstract
- Wireless sensor networks (WSN) localization relies on measurements. Availability of, and the information content in, these measurements depend on the network architecture, connectivity, node time synchronization and the signaling bandwidth between the sensor nodes. This chapter addresses wireless sensor networks measurements in a general framework based on a set of nodes, where each node either emits or receives signals. The emitted signal can for example be a radio, acoustic, seismic, infrared or sonic wave that is propagated in a certain media to the receiver. This general observation model does not make any difference between localization of sensor network nodes or unknown objects, or whether the nodes or objects are stationary or mobile. The information available for localization in wireless cellular networks (WCN) is in literature classified as direction of arrival (DOA), time of arrival (TOA), time difference of arrival (TDOA) and received signal strength (RSS). This chapter generalizes these concepts to the more general wireless sensor networks.
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| 8. |
- Gustafsson, Fredrik, et al.
(författare)
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Mobile Positioning using Wireless Networks : Possibilities and Fundamental Limitations based on Available Wireless Network Measurements
- 2005
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Ingår i: IEEE signal processing magazine (Print). - : IEEE Signal Processing Society. - 1053-5888 .- 1558-0792. ; 22:4, s. 41-53
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Tidskriftsartikel (refereegranskat)abstract
- Location in wireless networks is of increasing importance for safety, gaming, and commercial services. There are plenty of measurements available today, ranging from signal arrival times to maps of received power. It is demonstrated how fundamental the Fisher information matrix (FIM) for each measurement is to assess possible location performance. As one illustration, the FCC positioning requirements are transformed to requirements on sufficient information. Thus, it is possible to investigate whether specific sensor configurations would provide acceptable accuracy.
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| 9. |
- Amirijoo, Mehdi, et al.
(författare)
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On Self-Optimization of the Random Access Procedure in 3G Long Term Evolution
- 2009
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Ingår i: Proceedings of the 11th IFIP/IEEE International Symposium on Integrated Network Management. - : IEEE. - 9781424439232 - 9781424439249
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Konferensbidrag (refereegranskat)abstract
- Operationally efficient radio networks typically feature a high degree of self-organization. This means less planning efforts and manual intervention, and a potential for better radio resource utilization when network elements adapts its operation to the observed local conditions. The focus in this paper is selfoptimization of the random access channel (RACH) in the 3G Long Term Evolution (LTE). A comprehensive tutorial about the RACH procedure is provided to span the complexity of the selfoptimization. Moreover, the paper addresses RACH key performance metrics and appropriate modeling of the various steps and components of the procedure. Finally, some coupling between parameters and key performance metrics as well as selfoptimization examples are presented together with a feasibility discussion. The main ambition with this workshop paper is to present and define a relevant set of self-optimization problems, rather than to provide a complete solution.
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| 10. |
- Amirijoo, Mehdi, et al.
(författare)
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Towards Random Access Channel Self-Tuning in LTE
- 2009
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Ingår i: Proceedings of the 69th IEEE Vehicular Technology Conference. - 9781424425174 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Future radio access networks are expected to show a high degree of self-organization. This paper addresses self-tuning of the random access channel (RACH) in the 3G Long Term Evolution (LTE). The feasibility of self-tuning is investigated by means of simulation, where the coupling between several parameters and the performance of RACH is provided. The conclusion of the simulations is that RACH self-tuning is indeed possible given that UE assisted measurements are available for the self-tuning mechanism.
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