**1.1.1 Mobile networks**

A multi-tier cellular network is a network that has different types of cells overlaying each other. Each type of cell differs from others by the size. The smaller the size of the cells in a 2 Will-be-set-by-IN-TECH

Various priority based call admission algorithms have been reported in the literature, as for example (Beigy & Meybodi, 2003);(Ahmed, 2005);(Ghaderi & Boutaba, 2006). They can be classified into two basic categories: (1) reservation based, and (2) call thinning schemes.

In these schemes, a subset of channels is reserved for exclusive use by handover calls. Whenever the number of calls (new calls) exceeds a certain threshold, these schemes reject new calls until the number of simultaneous calls (new calls) decreases below the threshold. These schemes accept handover calls as long as the cell has idle channels. When the number of calls is compared with the given threshold, this scheme is called call bounding (Ramjee et al., 1997); (Hong & Rappaport, 1986); (Oh & Tcha, 1992); (Haring et al., 2001); (Beigy & Meybodi, 2005). When the current number of new calls is compared with the given threshold, the scheme is called new call bounding scheme (Fang & Zhang, 2002). Equal Access sharing with reservation schemes reserve an integral number of channels or a fractional number (Ramjee et al., 1997) of channels for exclusive use by handover calls. Schemes with fractional number of guard channels have better control of the blocking probability of the new calls and the dropping probability of the handover calls than

These schemes accept new calls with a certain probability that depends on the number of ongoing calls in the cell (Ramjee et al., 1997); (Beigy & Meybodi, 2004). New call thinning schemes accept new calls with a probability that depends on the number of ongoing new calls in the cell (Fang & Zhang, 2002); (Cruz-Pérez et al., 2011). Both schemes accept

In Sections 2 and 3, we compare four basic CAC strategies by examining new call and

Section 4 deals with Dynamic reservation and Static reservation in two-tier networks. To a great extent, our purpose is a tutorial one because there are many papers on CAC schemes, but they usually contain incomparable numerical results developed by computer simulations. Similar research as our is done by (Ramjee et al., 1997). They show that the guard channel scheme is optimal for minimizing a linear objective function of call blocking and dropping probabilities. The scheme studied below appeals also to network providers in terms of

A multi-tier cellular network is a network that has different types of cells overlaying each other. Each type of cell differs from others by the size. The smaller the size of the cells in a

1. Reservation based schemes:

2. Call thinning schemes:

1. Dynamic reservation,

3. Static (fixed) reservation, 4. New call bounding scheme.

2. Fractional dynamic reservation,

**1.1 Dimensioning of multi-tier networks**

**1.1.1 Mobile networks**

schemes with integral number of guard channels.

handover calls whenever the cell has free channels.

handover call blocking probabilities for the following schemes:

maximizing the revenue obtained by simple mathematical means.

We have many types of multi-tier cellular networks all around us.

certain area is, the more channels are available for users (since the number of channels per cell is fixed). We may consider four types of cells:


Having multi-tier cellular networks increases the number of cells, which means that more users are able to use the network without being blocked, and that users in cars or any high speed vehicles are able to talk without worrying about their calls being disconnected.
