Chapter 10

CONCLUSIONS

10.1	Problem and Selected Method..........................................	211
10.2	Summary of Results ..........................................................	212
10.3	Contributions of this Thesis .............................................	213
10.4	Further Development.........................................................	213

WIRELESS communication in unlicensed frequency bands is a challenging task when QoS is required. This thesis discusses new technologies for wireless networks and new approaches for spectrum management.

The IEEE 802.11e standard is described and analyzed with the help of a new analytical approach to approximate priorities. A mechanism to integrate other protocols such as ETSI BRAN HiperLAN/2 into 802.11e, the CCHC, is proposed as solution for coexistence and interworking of wireless networks in unlicensed bands. To analyze the CCHC coexistence, a game model is developed and comprehensively used.

10.1Problem and Selected Method

Future wireless networks will meet many technical challenges in radio resource control, especially when radio resources are shared between different networks. Considering the growth of the wireless Internet, and the increasing demands of consumer products with typical audio-/video applications that have strong QoS requirements, and considering the increasing need for information at more and more places, wireless LANs such as IEEE 802.11 are discussed in this thesis as candidate systems to provide the services needed to meet those challenges.

212	10. Conclusions

Wireless LANs operate in unlicensed bands, which makes it difficult to support QoS. However, QoS is a key requirement in future wireless networks. The coexistence of wireless networks of different or the same type operating in unlicensed bands in competition for radio resources is a key challenge in the development of future wireless networks. It is natural to approach this problem with the help of the theory of games.

“Perhaps the word ‘game’ was an unfortunate choice for a technical term. Although many rich and interesting analogies can be made to Bridge and Poker, and other parlor games, the usual sense of the word has connotations of fun and amusement, and of removal from the mainstream and the major problems in life. These connotations should not be allowed to obscure the more serious role of game theory in providing a mathematical basis for the study of [...] interaction, from the viewpoint of the strategic potentialities of individuals and groups.”

(Shubik 1982:7)

The cited statement considers human interaction, whereas in this thesis the interaction of technical systems is analyzed. However, the statement points to an often raised, but unwise concern when applying games for the analysis of technical problems. It should be emphasized in this context that “the game” is more related to strategies, whereas “the play” refers more to what is the common understanding of games between people.

Game models are developed in this thesis to analyze the CCHC coexistence. The developed methods are evaluated with stochastic simulation.

The CCHC concept relies on the upcoming enhancement of 802.11, the 802.11e. For this new protocol, an analytical model is developed and evaluated with stochastic simulation to approximate the expected achievable throughput that can be supported by 802.11e. Hence a complete analysis of this new protocol, including the analysis of the coexistence problem, is provided in this thesis.

10.2Summary of Results

802.11e will be an efficient means for QoS support in wireless LANs. It will provide mechanisms to increase the protocol efficiency and the achievable throughput. The most promising and flexible approach to support future applications are wireless LANs such as IEEE 802.11, including its enhancements to support QoS, i.e., 802.11e. Integrated into cellular networks such as Universal Mobile Telecommunications System (UMTS), wireless LANs will make these networks universal.

A new analytical model to approximate the relative priority between different access categories when 802.11e stations operate with different QoS parameters, is

10.3 Contributions of this Thesis

213

provided in this thesis. The model sufficiently approximates simulation results in nearly all scenarios.

The controlled channel access of 802.11e is analyzed by means of the analytical model, and simulation. The controlled channel access provides the means for supporting time-bounded traffic with strong QoS requirements, but does not work in coexistence scenarios. QoS support is problematic when multiple networks overlap.

This problem is discussed in detail in the context of coexisting CCHCs with the help of games. Competing networks are modeled as players. Behaviors and strategies are defined, and conditions under which a player selects certain types of behaviors are given. The concept of cooperation is discussed in the context of multi stage games. In cooperation, a CCHC seeks to establish the ability to guarantee -or at least to supportthe allocation of radio resources at the requested points in time, by considering the demands of competing CCHCs, and by implicitly negotiating the behaviors to select. It is shown in this thesis that cooperation is an achievable situation even when CCHCs are not able to communicate with each other, in many scenarios.

10.3Contributions of this Thesis

The analytical model to approximate the relative priority between different access categories will be helpful for future developments of wireless LANs.

The two simulation tools WARP2 and YouShi allow a detailed analysis of the protocol, and of the coexistence scenarios, respectively.

The games developed in this thesis, the Nash analysis of the single stage game, the strategy machines, and the discounting of payoffs are approaches that can be used for the analysis of many game problems, for example for scenarios with more than two networks operating at various channels in parallel, ad-hoc networks, and the EDCF.

10.4Further Development and Motivation

Wireless communication networks that share the frequency spectrum can be seen as forming a virtual society in the unlicensed bands. This virtual society faces many challenges that have been already analyzed for real-life societies as for example interacting nations and groups of animals such as ant colonies. The theory of games is an efficient means for analyzing such societies. When developing future flexible and adaptive wireless networks that have to operate in unlicensed bands, the models developed in this thesis may be of help. Future wireless net-

214	10. Conclusions

works will be required to act environment and interference aware when operating with shared radio resources. Such networks will be required to operate spectrum agile, with high flexibility by also considering the implications of decisions on other networks.

Further developments may focus on the application of the developed models for cellular and ad-hoc networks with a larger number of players.

The motivation for wireless communication is to facilitate the exchange of information. However, the demands for exchanging information are increasing. In our world, communication must be improved to provide a better understanding of what too often appears to be unknown, and different, simply because of lack of information. New ways to provide communication have to be found to change this. In this view, wireless communication provides great benefits to our future. Communication is one of our key means for developing our future society. Communication is life.