Wi-Fi-/WiMAX network selection case

In this scenario, the heterogeneous wireless environment consisting of IEEE 802.16 WiMAX network provider and two IEEE 802.11 based WLAN providers (‗A‘ and ‗B‘) are assumed. All BSs and AP‘s are in the centre of the considered cell. The network which satisfies the user requirements and the requested QoS is selected. Simulations are based on three AP‘s of each WLAN provider lie within one cellular WiMAX network. The coverage of each AP of WLAN provider ‗1‘ (A) and WLAN provider ‗2‘ (B) are assumed as 200m and 400m respectively. The coverage of WiMAX BS‘s is assumed as 1000m respectively. In the simulation scenario, a mobile user is moving clockwise at a constant speed of 10 meters per second throughout the simulation scenario shown in Figure 3.4.

The network selection decisions for this scenario can be divided into three cases:

1) When there is only one network (WiMAX) that can be chosen. This case is considered because WLAN provider ‗1‘ (A) and WLAN provider ‗2‘ (B) has less coverage area as compared to WiMAX. The WLAN providers also lie within coverage area of WiMAX.

2) Within the overlapping coverage area of WiMAX and WLAN provider ‗1‘ (A). 3) Within the overlapping coverage area of WiMAX, WLAN provider ‗1‘ (A) and

WLAN provider ‗2‘ (B).

42 The network selection for the Wi-Fi and WiMAX model can be divided into different decision points as shown below in Table 3.2.

Table 3.2 Different Decision points in the scenario

Decision Points Available Networks

D1 WiMAX

D2 WiMAX and WLAN ‗1‘ (A1)

D3 WiMAX , WLAN ‗1‘ (A1) and WLAN ‗2‘ (B1)

D4 WiMAX and WLAN ‗2‘ (B1)

D5 WiMAX

D6 WiMAX and WLAN ‗2‘ (B2)

D7 WiMAX , WLAN ‗1‘ (A2) and WLAN ‗2‘ (B2)

D8 WiMAX and WLAN ‗1‘ (A2)

D9 WiMAX

D10 WiMAX and WLAN ‗1‘ (A3)

D11 WiMAX , WLAN ‗1‘ (A3) and WLAN ‗2‘ (B3)

D12 WiMAX and WLAN ‗2‘ (B3)

D13 WiMAX

Based on Table 3.2, the network selection decisions for this scenario can be divided into four cases:

1) When there is only one network (WiMAX) that can be chosen. This case is considered because WLAN provider ‗1‘ (A) and WLAN provider ‗2‘ (B) has less coverage area as compared to WiMAX. The WLAN providers also lie within coverage area of WiMAX.

2) Within the overlapping coverage area of WiMAX and WLAN provider ‗1‘ (A). 3) Within the overlapping coverage area of WiMAX, WLAN provider ‗1‘ (A) and

WLAN provider ‗2‘ (B).

4) Within the overlapping coverage area of WiMAX and WLAN provider ‗2‘ (B).

The pair-wise comparison values between the network attributes are assumed and the equation (3.8) is applied to the network attribute values mentioned in Table 3.3 to calculate the weight of network attributes. Similarly, the equation (3.8) can also be applied to the respective network attribute values offered by different networks mentioned in Table 3.5 to calculate the relative network scores for network attributes. The ranking of networks are determined through the sum of the products of weight of each network attribute with the relative network scores for that network attribute.

43 3.6.1.1 Network Selection

User‘s preferences on network attribute are defined in Table 3.3. The pair wise comparison of available networks for each attribute i.e. Reputation (R), Cost (C), Bit rate (B) and Mobility support (M) are done based on original network parameters shown in Table 3.4 which decide the preferred network and intensity of importance. In Table 3.4, the cellular WiMAX network, WLAN provider ‗1‘, WLAN provider ‗2‘ are represented as ‗NW1‘, ‗NW2‘ and ‗NW3‘ respectively.

Table 3.3 Attribute Comparison

R C B M wi

R 1 1/3 5 1 0.232

C 3 1 5 1 0.402

N 1/5 1/5 1 1/5 0.061

M 1 1 5 1 0.305

Table 3.4 Network Parameters

NW1 NW2 NW3

R 0.3 0.4 0.5

B 2 3 5

C $1.2 $0.8 $0.9

M 0.6 0.35 0.25

For every pair wise comparison between alternative networks, the respective cost being charged is considered. When both the cost being offered is well above (or well below) the user expected value, they are equally preferred. When both costs being offered are less than the user expected value, a $1 difference in cost does not matter, but a $2 difference is considered strongly important, and a $4 difference is extreme. Whenever a network with a cost that is less than user expected value is compared with another network having cost well above user expected value, the former is extremely preferred. The network costs being offered above or below the user expected value determine the preferred network whereas their difference decides the relative importance. The network‘s parameters for each attribute can vary for different users.

44 and Mobility Support) is defined in Table 3.5 (a),(b),(c) and (d) respectively. The Relative value vector of alternative networks for each attribute is shown below in Table 3.6.

Table 3.5 Network comparisons with respect to attributes (Network preferences for attribute derived from Table 3.4)

Table 3.6 Ranking vector for alternatives with respect to each attribute

R B C M ri

NW1 0.077 0.480 0.066 0.751 0.392 NW2 0.231 0.406 0.615 0.178 0.406 NW3 0.692 0.114 0.319 0.071 0.204

The graphical representation of Table 3.6 is shown below in Figure 3.5. The network selection results based on reward index for each competing networks are shown below in Figure 3.6. The results show that network 3 never gets selected because its reward index is less than the other two competing networks. The network selection results with user preference based on attribute Reputation is shown below in Figure 3.7. In Figure 3.8, the network selection is shown with user preference on cost while Figure 3.9 and 3.10 show network selection with user preferences on Bit rate and Mobility Support respectively. It is also noted that mobile user selects high reliable WLAN ‗B‘ (NW3), when WiMAX (NW1), WLAN ‗A‘ (NW2) and WLAN ‗B‘ (NW3) are simultaneously available. Similarly the mobile user selects low price WLAN ‗A‘, when WiMAX (NW1), WLAN ‗A‘ (NW2) and WLAN ‗B‘ (NW3) are simultaneously available.

B NW1 NW2 NW3

NW1 1 1 5

NW2 1 1 3

NW3 1/5 1/3 1

(a) Bit rate

R NW1 NW2 NW3 NW1 1 1/3 1/9 NW2 3 1 1/3 NW3 9 3 1 (c) Reputation M NW1 NW2 NW3 NW1 1 5 9 NW2 1/5 1 3 NW3 1/9 1/3 1 (d) Mobility Support C NW1 NW2 NW3 NW1 1 1/9 1/5 NW2 9 1 2 NW3 5 1/2 1 (b) Cost

45 Figure 3.5 Ranking vector for alternatives with respect to each

attribute

WiMAX WLAN ‘A’ WLAN ‘B’

Decision points

46

WiMAX WLAN ‘A’ WLAN ‘B’

Decision points

Figure 3.7 Network Selection with user preference on Reputation as user rotates clockwise

WiMAX WLAN ‘A’ WLAN ‘B’

Decision points

Figure 3.8 Network Selection with user preference on Cost as user rotates clockwise

WiMAX WLAN ‘A’ WLAN ‘B’

Decision points

Figure 3.9 Network Selection with user preference on Bit rate as user rotates clockwise

47

WiMAX WLAN ‘A’ WLAN ‘B’

Decision points

Figure 3.10 Network Selection with user preference on Mobility Support as user rotates clockwise