**3. Multi-criteria decision making methods**

The cell selection problem is about selecting one BS for handover among limited number of candidate BSs with respect to a set of different criteria. This is a typical Multiple Criteria Decision Making (MCDM) problem. In the study of decision making, terms such as MCDM is the problem of choosing an alternative solution from a set of alternatives, which are charac‐ terized in terms of their attributes [14]. The most popular classical MCDM methods are:


In this paper, we use TOPSIS as alternative score ranking based cell selection scheme and compare it with WSM, while AHP will be used for weighting the attributes or the criteria based on the importance of each criterion for the end users application.

Cell selection could be considered as an MCDM problem. For instance, suppose a user is currently connected to BS A1 and has to make a decision among two alternative candidate BSs: A2 and A3. Handover criteria considered here are CINR, BW, and congestion delay, which are denoted as: X1, X2 and X3, respectively. The decision problem can be modelled in a decision matrix Dm as shown in (1), where the capabilities of each candidate are presented.

$$\begin{array}{c c c c c c} & \mathbf{x\_1} & \mathbf{x\_2} & \mathbf{x\_3} \\ & A1 & \mathbf{x\_{11}} & \mathbf{x\_{12}} & \mathbf{x\_{13}} \\ Dm = A2 & \mathbf{x\_{21}} & \mathbf{x\_{22}} & \mathbf{x\_{23}} \\ & A3 & \mathbf{x\_{31}} & \mathbf{x\_{32}} & \mathbf{x\_{33}} \end{array} \tag{1}$$

Where *x*11 is the CINR, *x*12 is the BW and *x*13 is the congestion delay of BS A1. In similar way, *x*21, *x*22and *x*23 are the CINR, BW and congestion delay values of BS A2. In addition, *x*31, *x*<sup>32</sup> and *x*33 are the CINR, BW and congestion delay of BS A3.

Assume the user is using two types of applications; real-time application such as VoIP and non-real-time application such as Media Content Download. The traffic or application preference on handover criteria is modelled as weights assigned by the user on the criteria; for VoIP and Media Content Download which are shown in (2) and (3).

$$\mathcal{W}r = \begin{bmatrix} w\_{r1} & w\_{r2} & w\_{r3} \end{bmatrix} \tag{2}$$

$$
\Delta Wnr = \begin{bmatrix} w\_{nr1} & w\_{nr2} & w\_{nr3} \end{bmatrix} \tag{3}
$$

The CINR and congestion delay are considered as important for voice application because as studied by [15-16], to get a minimum jitter and delay the CINR has to be good enough, while the bandwidth and CINR are considered important for the non real-time application such as Media Content Download.
