Lars Berlemann

Radio resource sharing games: enabling QoS support in unlicensed bands

Distributed quality of service support in wireless networks that are sharing unlicensed frequency bands is an increasingly significant research problem. The spectral coexistence of dissimilar radio systems has to be addressed in the near future in concerning the widely deployed IEEE 802.11 wireless local area networks and other future radio systems operating in unlicensed or opportunistically used frequency bands. The competition between independent wireless networks for allocating a common shared radio channel is modeled in this article as a stage-based game model: players, representing wireless networks, interact repeatedly in radio resource sharing games, without direct coordination or information exchange. Solution concepts derived from game theory allow the analysis of such models under the microeconomic aspects of welfare. Decisions players repeatedly have to make are about when and how often to attempt medium access. In multistage games the players apply strategies in order to maximize their observed utility as a summarizing value for successfully supported quality of service. Strategies determine whether competing radio networks cooperate or ignore the presence of other radio networks. The traffic requirements of a player thereby decide which strategy is adequate to guarantee quality of service.

Unlicensed Operation of IEEE 802.16: Coexistence with 802.11(A) in Shared Frequency Bands

The coexistence of IEEE 802.16 (WiMAX) and IEEE 802.11 (WiFi) in shared radio spectrum is an acute problem. In license-exempt frequency bands, the frame-based medium access of 802.16 requires rigorous protection against interference from wireless local area networks in order to operate properly when sharing spectrum. We focus here on the unlicensed U-NII frequency band at 5 GHz and consider therefore the distributed medium access of 802.11(a) as competitor for spectrum utilization. We expect 802.16 systems to be available in laptops soon and then to provide wireless VoIP services that 802.11 cannot support satisfactorily well. Therefore, this paper describes approaches for enabling a reliable operation of 802.16 when sharing unlicensed spectrum with 802.11. We propose software upgrades to the medium access control of the 802.16 BS. Thereby, no 802.11 frame transmissions are required by an 802.16 system. Coexistence between 802.16 and 802.11 is enabled without any data exchange between both standards. Our solution of the described coexistence problem implies the possibility to guarantee quality-of-service within the 802.16 system although operating in unlicensed frequencies

Coexistence and Interworking of IEEE 802.16 and IEEE 802.11(e)

The coexistence and interworking of IEEE 802.16 and IEEE 802.11 is an acute problem. The frame-based medium access of 802.16 requires rigorous protection against interference from wireless local area networks in order to operate properly. The 802.11e enhancements of the medium access control of 802.11 introduce the capability to support QoS. These enhancements define a central entity as main element: the hybrid coordinator. It realizes a contention free, centrally controlled medium access and introduces QoS limitations to the contention based access of 802.11e. In this paper, a central coordinating device combines the central base station of 802.16 with the hybrid coordinator of 802.11e and is thus referred to as base station hybrid coordinator. The base station hybrid coordinator is capable to operate in an 802.16 and an 802.11(e) protocol mode in the same frequency band. The realization of the interworking between these two standards is discussed and evaluated in this paper

IEEE 802.11k: improving confidence in radio resource measurements

New radio resource measurements for the wireless local area network IEEE 802.11trade standard are defined in the standard extension IEEE 802.11k. Various types of measurements are defined that enable 802.11 stations to request measurements from other stations, for example in order to measure how occupied a frequency channel is. The measurement results are reported back to the requesting station in standardized frames. In this paper, we discuss how relevant and useful measurement results are in general. A method to estimate the confidence of such measurement results is proposed. It is proposed to apply the concept of confidence intervals to 802.11k radio resource measurements, similarly to how they are applied to stochastic simulation, where estimating the confidence of results is necessary to provide meaningful data. Our proposed method allows optimizing measurement durations and determining the optimal repetition rate of measurements. The method also allows estimating how long after the end of a measurement the reported results will represent the true reality

Strategies for distributed QoS support in radio spectrum sharing

Spectrum sharing in unlicensed bands is expected to become an increasingly significant research problem. With the proliferation of IEEE 802.11 wireless local area networks, and with other future radio systems using the unlicensed bands, spectral coexistence of dissimilar radio systems will have to be addressed. Coexistence can be achieved with the help of spectrum etiquette, or alternatively by implementing new communication protocols and defining common spectrum coordination channels. We investigate how two independent wireless networks may share spectrum without direct coordination and information exchange. We start by illustrating our previously introduced stage-based game model of such scenarios. The application of game models allows us to analyze the problem as a player competition; within radio resource sharing games, payoff-maximizing players represent wireless networks. Decisions that players repeatedly have to make are about when, and how often, to attempt medium access. We use an established notation to describe multi-stage strategies that determine a players decision-making. Should radio networks cooperate or should competing radio networks ignore the presence of other radio networks? What is the expected outcome in a repeated interaction? The paper shows that traffic requirements imposed by services and applications determine the selected strategies, which pursue cooperation or ignore other radio systems.

Behavior based strategies in radio resource sharing games

Radio resource sharing among different, co-located wireless networks operating on the same frequencies is an unsolved problem when networks operate in unlicensed frequency bands. We analyze such scenarios: in a stage-based game, wireless networks are modeled as players that attempt to meet individual quality of service requirements. Solution concepts derived from the game theory allow the analysis of such models. Games are analyzed under the microeconomic aspects of welfare, constant requirements, evolving demands, and the resulting utilities (payoffs). A multi stage game consists of repeated stages, where each stage represents the interaction of competing wireless networks for a limited duration (the duration of a single stage). Throughout the course of repeated stages, players attempt to optimize their payoffs by changing behaviors. Each player follows a strategy to determine what behavior to select in a stage, Multi stage game Nash equilibria for optimized quality of service support are determined in this paper. Results indicate that, depending on the requirements, cooperation is an achievable equilibrium that improves the overall radio resource utilization.

Policy-based reasoning for spectrum sharing in radio networks

Regulation of spectrum may undergo revolutionary changes in the near future allowing a less restricted and more flexible access to radio spectrum. Intelligent radios, or so-called cognitive radios, will realize the dynamic usage of frequency bands on an opportunistic basis, by identifying and using under-utilized spectrum. Such a flexible spectrum usage requires changes in regulation towards a more open spectrum. Policies which determine when spectrum is considered as opportunity and which define the possibilities of using these spectrum opportunities are needed. This paper discusses two approaches of different complexity that intend to enable distributed QoS support in open spectrum. These algorithms are specified as policies in a machine-understandable policy description language, such that the cognitive radio is capable of reasoning about spectrum usage. Thereby not only a multitude of policies has to be combined but also measurements of local spectrum utilization and user/operator preferences have to be taken into account

Equilibrium analysis of coexisting IEEE 802.11e wireless LANs

A model for the coexistence problem of overlapping IEEE 802.11e wireless networks is discussed in this paper. In a competition scenario of overlapping 802.11e networks, quality of service cannot be guaranteed by the 802.11e protocol. For this reason, a stage-based game structure is introduced here. Wireless networks participate in the game as players. The players are gaining in each stage a so-called utility, which is a summarizing value for the achieved quality of service. The interaction of the players within a single stage is analyzed in detail, under consideration of Nash equilibria and Pareto efficiency.

Policy Defined Spectrum sharing and medium Access for Cognitive Radios

Spectrum regulation will undergo elementary changes in the near future allowing a less restricted and more flexible access to radio spectrum. Intelligent radios, so- called cognitive radios, will realize the dynamic usage of frequency bands on an opportunistic basis, by identifying and using under-utilized spectrum. Such a flexible spectrum usage requires changes in regulation towards a more open spectrum. Policies which determine when spectrum is considered as opportunity and which define the possibilities of using these spectrum opportunities are needed. First, this article discusses an approach that intends to enable distributed QoS support in open spectrum. This algorithm is specified as policy in a machine-understandable policy description language, such that the cognitive radio is capable of reasoning about spectrum usage. Policies that enable a software defined medium access are the second focus of this article. We discuss a step towards the realization of such cognitive radios at the example of the well-known Enhanced Distributed Channel Access of IEEE 802.11e. This channel access protocol is here specified in a machine understandable policy language, instead of lengthy textual description. Such a machine-understandable description of the protocol enables cognitive radios to operate in distributed environments according to the 802.11(e) standard.

Mesh technology enabling ubiquitous wireless networks: invited paper

Todays wireless networking technology provides high data rates. With IEEE 802.11n products, data rates beyond 500Mb/s are soon feasible for Wireless Local Area Network (WLAN). Due to a standstill in standardization the project IEEE 802.15.3a it was disbanded in 2006. Companies are pushing therefore their own solutions to the Wireless Personal Area Network (WPAN) market. Shortly, 480Mb/s will be available for WPAN applications. For large scale networks, IEEE 802.16 (aka Worldwide Interoperability for Microwave Access (WiMAX)) offers a solution for the Wireless Metropolitan Area Network (WMAN) market. Besides point-to-point connections, IEEE 802.16e supports mobile connections too. With recent development, wireless technology for ubiquitous connections is available in the market. Sensitive Modulation and Coding Schemes (MCSs), Multiple Input/Multiple Output (MIMO) and other new Physical Layer (PHY) technologies provide high data rates. However, upcoming wireless technology does not increase coverage. Like preceding standards, highest data rate is only available for short range communication. Therefore, supply of large areas with high speed connections demands dense installation of backbone connected devices. While Capital Expenditure (CAPEX) for hardware is low, deployment is expensive. The Operational Expenditure (OPEX) of wired and fiber optic networks is high. Furthermore they are not as widely deployed as needed for dense installation of connection points to the core network. Hence, rollout of high speed wireless networks is delayed until a solution is provided. Relay based deployment and Mesh topology for wireless networks helps to overcome the cost barrier. With this meshing functionality, wireless networks of the IEEE 802 standard family are a promising low-cost alternative to cellular Third-Generation (3G) networks In this paper we provide insight to current activities of Institute of Electronics and Electrical Engineering (IEEE) Working Groups (WGs) regarding Mesh technology. Furthermore we show possibilities and limitations of Wireless Mesh Networks (WMNs).