ISIS Project: Resource Management in Wireless Communications Systems
Background
The global, heterogenous communications system is considered as the largest man-made system all categories. Due to the dramatic increase in number of users and their demand for more advanced services, the available resources have to be utilized efficiently. This is especially critical in the subset of wireless cellular communications systems, and in applications which require specific real-time behavior. The main resource management objective is to efficiently utilize the available radio spectra, while maintaining the quality of service requirements from the users.
A wireless communication system comprises many algorithms which have to be implemented in a distributed fashion but mutually affect each other. Also the information is distributed, and full observability of the system behavior is almost always not possible. Therefore, careful design and analysis of the various algorithms is crucial.
This project is carried out by Division of Communication Systems and Division of Automatic Control in cooperation with Ericsson Research. The aim is to apply methods from control theory and signal processing to different layers of wireless communications systems.
Selected Central Publications
| [C9] | F. Gunnarsson and F. Gustafsson. Power control in cellular radio systems from a control theory perspective. Survey paper. Proc. IFAC World Congress, Barcelona, Spain, Jul 2002. |
| [C12] | E. Geijer-Lundin, F. Gunnarsson, and F. Gustafsson. Uplink load estimates in WCDMA with different availability of measurements. Proc. IEEE Vehicular Technology Conference Spring, Seoul, Korea, May, 2003. |
| [C13] | E. Geijer-Lundin, F. Gunnarsson, and F. Gustafsson. Adaptive filtering applied to an uplink load estimate in WCDMA. Proc. IEEE Vehicular Technology Conference Spring, Seoul, Korea, May, 2003. |
| [C16] | F. Gunnarsson, D. Törnqvist, E. Geijer-Lundin, G. Bark, N. Wiberg, E. Englund. Uplink Transmission Timing in WCDMA. Proc. IEEE Vehicular Technology Conference, Orlando, FL, USA, October 2003. |
| [C17] | F. Gunnarsson, F. Gunnarsson, F. Gustafsson. Controlling Internet Queue Dynamics using Recursively Identified Models. Proc. IEEE Conference on Decision and Control, Maui, Hawaii, USA, Dec. 2003. |
Resource Management Algorithms
One instructive approach is to separate the resource management in layers:- Physical layer algorithms. This layer essentially directly relate to the actual radio resource utilization in terms of the transmitter powers. Therefore, power control is the key mechanism, and whether it is possible to accomodate allocated users is closely related to the momentary radio interface load situation.
- Radio link control. Datagrams are transferred over the wireless links and mechanisms ensure proper transport to the receiving end. Acknowledgements of correctly receieved data enable reliable transport.
- Radio network control. Radio network stability is monitored and controlled by managing the wireless links between users and base stations and determine whether it is possible to accomodate new users.
- Data network control. The data over the links is not continuous, and its flow depend on the behaviour of the core network run by the operator, and of other connected networks, such as the Internet. The data flow depends on both end-to-end transport protocols and on flow control mechanisms in nodes.
- Stability analysis and characterization of the physical layer power control.
- Identification and modeling of the radio network, based on control theory methodology. Primarily, the algorithms will be separated with respect to time constants, input and output signals, and physical location, to identify potential conflicts.
- Radio interface load estimation.
- Development of coordinating radio network algorithms. This also includes studying cross-couplings and conflicts between existing algorithms.
- Model data flow control to better relate to radio network and radion link control properties.
Project Overview
The projects will be described using a top down approach, from flow control of data packets sent over the wireless links, via radio interface admission control of new users and finally to control of individual transmitter powers. The overall situation is depicted in Figure 1.
Figure 1. Radio network connected to a core network and the Internet
Data flow control primarily make impacts on the core network and other connected networks, but also relates to radio network properties (ref A). Uplink load estimation and control addresses the situations at the base station, which is monitored in the RNC (Radio Network Controller), see ref B. Control of individual transmitter powers mainly deals with the situation between the base staion and the mobile situation (ref. C).
Data Network Flow Control
Many people consider 3G as the technology that makes Internet generally available to mobile users. This means that the fields of telecommunications and data communications will overlap to a greater extent than before. While the paradigm in data communications is flexibility, the key word within telecommunications is efficiency of the wireless link. Therefore, some flow control mechanisms used of wired Internet causes problems when used directly over wireless links. Furthermore, these flow control mechanisms were designed assuming different traffic characteristics than prevalent today. As always, the strength of a chain is determined by the weakest link, and in the parallel of data networks the bottleneck queue. The performance of the flow control algorithms are discussed in terms of bottleneck queue occupancy in [C2]. Bad performance is characterized by an oscillating queue occupancy with low utilization on average, while good performance show a stable and high queue occupancy. The field of data network control is "hot" within academia, and much effort is spent on modeling the control protocols and the queues of the switches and routers. The main idea with the project is to combine core knowledge in control theory and in telecommunications resource management, to form better understanding as well as better and more relevant models for the observed phenomenons. Control theory aspects of network control is discussed in [C2,C5,C6]. It is instructive to view the queue length as the controlled quantity with an associated reference signal. Good control is then identical to low queue length variance, see Figure 2.
Figure 2. Network node queue length histogram.
Active Queue Management (AQM) is a popular means to reduce the probability of overflowing queues. One example is Random Early Detection (RED), where packets are deliberately discarded in the queues with a probability increasing with the queue length. A model-based approach is presented in [C17], where the queue length is estimated and predicted to improve the AQM.
Uplink Load Estimation and Control in WCDMA
A prerequisite for proper behavior of radio network algorithms is that not more users than actually can be served are admitted into the system [C3]. This is of course intuitive, but with limited observability rather difficult to ensure. The situation is especially hard in the uplink communications from mobiles to the base stations, since the system has no absolute control of the transmitter powers of the mobiles. These depend in turn on the radio propagation conditions, which are subject to rapid changes. Easiest to implement is to associate each service with a predefined value and simply per cell sum the contributions from all connected users. This is often referred to as hard capacity. An alternative is to use a measure (soft capacity) that is related to the actual load at the base station receiver. A relevant quantity is the total received power relative to the noise power, often referred to as the noise rise, NR. This can be associated to a cell load L, which is defined by
Figure 3. Relation between noise rise and load.
Measured or estimated noise rise reflects the inter-cell dependencies, but it does not allow inter-cell contribution predictions of a user to be admitted. Therefore, methods to estimate and predict the uplink load is of importance. The initial proposal showed similar performance as hard capacity when used for admission control, but it is much easier to configure, and the configuration is independent of services and propagation conditions [C1,C4]. The methods have been further refined to improve the accuracy [C7,C8,C11]. Moreover, the methods show comparable performance using either periodic or event-triggered (currently used for handover decisions) measurements, but the latter results in much less measurement reporting [C12]. There is always a trade-off between noise suppression and fast reactions to sudden changes. This is further discussed in [C13] using advanced signal processing techniques. Flexible service realizations are needed to utilize the availability of accurate and timely information about the uplink load situations. One example is flexibility in terms of data transmision activity. To avoid excessive uplink interference it can be motivated to only transmit data when the channel is favorable. In [C16,M29], power contol information is used to determine when it is beneficial to transmit data, while aiming at a specific transmission activity controlled by the network.
Transmitter Power Control
The main resource in future 3G systems such as WCDMA is power and spectrum. Since the users share the same spectrum, power control is an important means to utilize the resources efficiently. The control of each transmitter power can be seen as distributed feedback control loops. As such, time delays, feedback bandwidth, sample rate etc. constitute fundamental limitations to the power control performance, which most naturally are analyzed using control theory methodology [J1,J3,J7,C3]. Furthermore, control theory also facilitates the control design [J2]. A compact discussion regarding the control theory aspects of power control is found in [C9, J5].Related Work
Radio link control has not been studied in detail. However, some efforts to model UMTS radio link and media access control (RLC/MAC) for network simulations using ns-2 are described in [R1]. Simplistic radio network control behavior is also implemented.Some work bridges the projects. Positioning in wireless communication networks is one example where a sensor fusion approach is used to address the problem. Since non-linearities and non-Gaussian noise are present, the particle filtering framework is plausible [J4, C10, C14]. Other work include signal processing of pilot power measurements [C15].
Publications and Reports
Journal Papers:| [J1] | F. Gunnarsson, F. Gustafsson, J. Blom. Dynamical effects of time delays and time delay compensation in power controlled DS-CDMA IEEE Journal on Selected Areas in Communications, 19(1), January 2001. |
| [J2] | F. Gunnarsson, F. Gustafsson. Time delay compensation in power controlled cellular radio systems . IEEE Communcations Letters 5(7), July 2001. |
| [J3] | F. Gunnarsson and F. Gustafsson. Convergence of some power control algorithms with time delay compensation. To appear in IEEE Transactions on Wireless Communications, 2003. |
| [J4] | F. Gustafsson, F. Gunnarsson, N. Bergman, U. Forssell, J. Jansson, R. Karlsson, and P.-J. Nordlund. Particle filters for positioning, navigation, and tracking. IEEE Transactions on Signal Processing, 50(2), Feb 2002. |
| [J5] | F. Gunnarsson, F. Gustafsson. Control theory aspects of power control in UMTS . Control Engineering Practice, 11(10), pp 1113-1125, Oct. 2003. |
| [J6] | F. Gunnarsson, J. Blom, F. Gustafsson Parameter estimation using measurements from cellular radio systems. To appear in Wireless Networks, 2003. |
| [J7] | F. Gunnarsson. Fundamental Limitations of Power Control and Radio Resource Management in Wireless Networks. To appear in Wiley Wireless Communications and Mobile Computing Journal. |
Conference Papers:
| [C1] | E. Geijer Lundin, F. Gunnarsson, F. Gustafsson. Admission Control in WCDMA Based on Relative Load Estimates . Proc. Nordic Radio Symposium, Nynäshamn, Sweden. March 2001. |
| [C2] | F. Gunnarsson, F. Gunnarsson, F. Gustafsson. TCP Performance based on Queue Occupation Proc. Nordic Radio Symposium, Nynäshamn, Sweden. March 2001. |
| [C3] | F. Gunnarsson, Fundamental Limitations of Power Control in WCDMA Proc. IEEE Vehicular Technology Conference, Atlantic City, NJ, USA, October 2001. |
| [C4] | F. Gunnarsson, E. Geijer-Lundin, G. Bark, N. Wiberg Uplink admission control in WCDMA based on relative load estimates Proc. IEEE International Conference on Communications, New York, NY, USA, April 2002. |
| [C5] | F. Gunnarsson, F. Gunnarsson, and F. Gustafsson. Aspects on performance measurements of TCP traffic and its reflections into control theory. Proc. Reglermöte, Linköping, Sweden, May 2002. |
| [C6] | F. Gunnarsson, F. Gunnarsson, and F. Gustafsson. Aspects on performance measurements of TCP traffic and its reflections into control theory. Proc. RadioVetenskaplig Konferens, Stockholm, Sweden, June 2002. |
| [C7] | E. Geijer-Lundin and F. Gunnarsson. Uplink load estimation in WCDMA. Proc. Reglermöte, Linköping, Sweden, May 2002. |
| [C8] | E. Geijer-Lundin and F. Gunnarsson. Uplink load estimation in WCDMA. Proc. RadioVetenskaplig Konferens, Stockholm, Sweden, June 2002. |
| [C9] | F. Gunnarsson and F. Gustafsson. Power control in cellular radio systems from a control theory perspective. Survey paper. Proc. IFAC World Congress, Barcelona, Spain, Jul 2002. |
| [C10] | P.-J. Nordlund, F. Gunnarsson, and F. Gustafsson. Particle filters for positioning in wireless networks. Proc. European Signal Processing Conference, Toulouse, France, Sep 2002. |
| [C11] | E. Geijer-Lundin, F. Gunnarsson, and F. Gustafsson. Uplink load estimation in WCDMA. Proc. IEEE Wireless Communications and Networks Conference, New Orleans, LA, USA, March, 2003. |
| [C12] | E. Geijer-Lundin, F. Gunnarsson, and F. Gustafsson. Uplink load estimates in WCDMA with different availability of measurements. Proc. IEEE Vehicular Technology Conference Spring, Seoul, Korea, May, 2003. |
| [C13] | E. Geijer-Lundin, F. Gunnarsson, and F. Gustafsson. Adaptive filtering applied to an uplink load estimate in WCDMA. Proc. IEEE Vehicular Technology Conference Spring, Seoul, Korea, May, 2003. |
| [C14] | F. Gustafsson and F. Gunnarsson. Positioning using Time Difference of Arrival Measurements. Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, Hong Kong, April, 2003. |
| [C15] | F. Gunnarsson. Convolutional Spatial Filtering of Pilot Power Measurements. Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, Hong Kong, April, 2003. |
| [C16] | F. Gunnarsson, D. Törnqvist, E. Geijer-Lundin, G. Bark, N. Wiberg, E. Englund. Uplink Transmission Timing in WCDMA. Proc. IEEE Vehicular Technology Conference, Orlando, FL, USA, October 2003. |
| [C17] | F. Gunnarsson, F. Gunnarsson, F. Gustafsson. Controlling Internet Queue Dynamics using Recursively Identified Models. Proc. IEEE Conference on Decision and Control, Maui, Hawaii, USA, Dec. 2003. |
Reports:
| [R1] | F. Gunnarsson, A. Björsson, B. Knutsson, F. Gunnarsson, F. Gustafsson. Radio Access Network (UTRAN) Modeling for Heterogenous Network Simulations . Technical Report, LiTH-ISY-R-2533, Aug. 2003. |
Patents:
| [P1] | F. Gunnarsson, J. Blom, F. Gustafsson. Method and System for Quality-Based Power Control in Cellular Communications Systems .US Patent US6449462. Published September 10, 2002. |
| [P2] | F. Gunnarsson, F. Gustafsson, N. Wiberg. Transmit Power Control Time Delay Compensation in a Wireless Communications System .US Patent US6493541. Published December 10, 2002. |
Master theses:
[M1] Lindquist, Erik, "Kurtosis examination in the frequency domain used in multipath detection", LiTH-ISY-EX-1602, FOA, inst 65, 1995.
[M2] Larsson, Erik, "On receiver structures for antenna diversity GSM radio base stations", LiTH-ISY-EX-1762, Ericsson Radio Systems, 1997.
[M3] Lundqvist, Fredrik, "Performance evaluation of a closed loop frequency optimization algorithm for GSM", LiTH-ISY-EX-1992, Ericsson Radio Systems, 1998.
[M4] Raismaa, Sofia, "Performance evaluation of a closed loop frequency optimization algorithm for GSM", LiTH-ISY-EX-1992, Ericsson Radio Systems, 1998.
[M5] Cassel, Magnus, "Calibration of mobile phone power", LiTH-ISY-EX-3047, Ericsson, 1999.
[M6] Johansson, Mats, "SDMA in cellular radio systems", LiTH-ISY-EX-2058, Ericsson, 1999.
[M7] Skillermark, Per, "Evaluation of transmission load dependent soft handover algorithms in WCDMA systems", LiTH-ISY-EX-2011, Ericsson, 1999.
[M8] Loh, Susanne, "A system for measuring audio in GSM", LiTH-ISY-EX-3054, Sectra, 2000.
[M9] Nilsson, Per, "Adaptive Admission and Congestion Control in WCDMA", LiTH-ISY-EX-3070, Ericsson, 2000.
[M10] Sigurdsson-Rosenberg, Erik, "Adaptive Admission and Congestion Control in WCDMA", LiTH-ISY-EX-3070, Ericsson, 2000.
[M11] Tapio, Mikael, "Adaptive equalizer functions for QAM in digital microwave radio systems", LiTH-ISY-EX-3107, Ericsson Microwave, 2000.
[M12] Frisell, Johan, "Handling conflicts in multi hop networks", LiTH-ISY-EX-3007, FOA, 2000.
[M13] Sennerbrant, Andreas, "Handling conflicts in multi hop networks", LiTH-ISY-EX-3007, FOA, 2000.
[M14] Elbornsson, Ulrika, "Detection and direction measurement of code division signals using correlation", LiTH-ISY-EX-3140, FOA, 2001.
[M15] Geijer Lundin, Erik, "Uplink Admission Control Based on Estimated Interference in WCDMA Systems", LiTH-ISY-EX-3123, Ericsson Radio System, 2001.
[M16] Backstig, Anders, "Simulation of ADSL modem in Matlab", LiTH-ISY-EX-3168, Ericsson Microelectronics, 2001.
[M17] Ekblad, Henrik, "Bluetooth Packet Reader in an OSE Environment", LiTH-ISY-EX-3131, Enea, 2001.
[M18] Gentzell, Tobias, "Bluetooth Packet Reader in an OSE Environment", LiTH-ISY-EX-3131, Enea, 2001.
[M19] Mehlqvist, Karin, "Call Gapping as Load Regulation - a Simulation in the CMS 30 Mobile System", LiTH-ISY-EX-3105, Ericsson Radio Systems, 2001.
[M20] Persson, Katarina, "TCP/IP in tactical ad hoc networks", LiTH-ISY-EX-3206, FOI 2002.
[M21] Brorsson, Jonas, "Admission Control and Downlink Scheduling for Advanced Antennas in WCDMA", LiTH-ISY-EX-3239, Ericsson Radio Systems, 2002.
[M22] Afsarinejad, Arash, "Data Synchronization using SyncML", LiTH-ISY-EX-3189, Tieto-Enator AB, 2002.
[M23] Adolfsson, Klas, "TCP performance in an EGPRS system", LiTH-ISY-EX-3163, Enea Epact, 2003.
[M24] Ahlin, Karl, "Quality of Service in IP Networks", LiTH-ISY-EX-3323, Service Network Architecture, Ericsson AB, 2003.
[M25] Brunberg, Henrik, "Distributing digital radio over an IP backbone", LiTH-ISY-EX-3317, Factum, 2003.
[M26] Fredholm, Kenth, "Implementing an application for communication and quality measurements over UMTS networks", LiTH-ISY-EX-3369, Tieto-Enator / Ericsson Research, 2003.
[M27] Nilsson, Kristian, "Implementing an application for communication and quality measurements over UMTS networks", LiTH-ISY-EX-3369, Tieto-Enator / Ericsson Research, 2003.
[M28] Tronarp, Otto, "Quality of Service in Ad Hoc Networks by Priority Queuing", LiTH-ISY-EX-3343, FOI, 2003.
[M29] Törnqvist, David, "Transmission timing in WCDMA terminals", LiTH-ISY-EX-3312, Ericsson Research, 2003.
Ongoing theses:
[M30] Wiik, Andreas, "Base station output power control for GSM", LiTH-ISY-EX-XXXX, Ericsson Radio Systems AB.
[M31] Blomberg, Petter, "Advanced Load Control in WCDMA Cellular Networks", LiTH-ISY-EX-3361, Ericsson Radio Systems AB.
[M32] Björsson, Anders, "Implementing UMTS RLC/MAC for ns-2", LiTH-ISY-EX-3414, LiTH / Ericsson Research.
[M33] Knutsson, Björn, "Emulating behavior of the radio network controller in UMTS for ns-2", LiTH-ISY-EX-3414, LiTH / Ericsson Research.
[M34] Eriksson, Jonas, "Streaming Quality of Service with HS-DSCH", LiTH-ISY-EX-3493, Ericsson Research.
[M35] Zetterberg, Kristina, "HS-DSCH in Unlicensed Frequency Bands", LiTH-ISY-EX-3490, Ericsson Research.