156	7. The Game Model

one hand to prevent the opponent from successful allocation by taking an action that reduces the observed payoff of the opponent. On the other hand, a temporary withdraw of allocations may be preferred by a player, in order to let the opponent player achieve a maximum utility. In any case, it is of importance that a player has knowledge about the current demands, which is realized by applying the predictor.

There are other ways to predict the demands the opponent player has which may lead to more accurate results, as they have been used in a different context in Kyriazakos (1999) and Mangold and Kyriazakos (1999).

The improvement of the estimation method to predict demands from the history of allocations is not within the scope of this thesis. Possible improvements of the prediction accuracy by for example averaging the history of past observations within a number of SSGs. See Berlemann (2002) for an in-depth analysis of the prediction as well as a discussion of the gain of a common spectrum coordination channel that allows information exchange between players, and thus eliminates the need for the mutual prediction of demands. This gain is given through the limitations of the predictor. The less accurate the prediction, the more helpful becomes a spectrum coordination channel that is common to all players.

7.5Concluding Remark

When viewing the CCHC coexistence problem as a game of players, several questions can be answered by applying the model, such as whether there exists a stable operation point, whether this stable point is unique, whether the dynamic system actually converges to this point, and if it converges, how fast does it converge.

In the context of the wireless LAN 802.11e, it is important to understand the level of QoS that can be supported by overlapping QBSSs that operate on a shared medium in the unlicensed band. Further, as part of the MSG discussion, it is beneficial to analyze possible behaviors of overlapping networks. With the help of the game model, sharing rules, or a spectrum etiquette can be defined for particular frequency bands and radio systems.

The fundamental question is which action should be taken by each player in order to meet their requirements as close as possible in the presence of competing players.

This problem exists regardless of the ability of players to exchange information about their individual requirements. Solutions to this problem are developed in the following chapters.

7.5 Concluding Remark

157

SSG n										demanded (--)
one
										and observed (-)
within										← allocations of
										player 1
TXOPs										demanded (--)
		resource allocation interval D2(n),								and observed (-)
		demanded by player 2 in SSG n								← allocations of
0	20	40	60	80	100	120	140	160	180	player 2
										200
				time [ms]

1

resource allocation interval

0.8of player 1 that is predicted by player 2 for SSG n+1

0.6
ACF		ACF (right hand
0.4		←side) that player 2
		calculates from the
0.2		observation of
		player 1

00	20	40	60	80	100	120	140	160	180	200
					time [ms]
1
0.8			resource allocation interval
	D2(n)		D2(n+1) of player 2 that is
		predicted by player 1 for SSG n+1
0.6
ACF										ACF (right hand
0.4										←side) that player 1
										calculates from the
0.2										observation of
										player 2
00	20	40	60	80	100	120	140	160	180	200
					time [ms]

Figure 7.10: An SSG example illustrating the prediction of the opponents demand with the help of the resource allocation interval predictor. Top: resource allocations of two players within one SSG n, duration 200 ms. Center and bottom: right hand sides of the auto correlation functions that are used to predict the upcoming actions of player 1 and player 2, respectively.