WIRELESS NETWORKS AND PROTOCOLS

Home Work - IISavitha Chintakindi

10829871

Problem Definition:

In this homework we study the wireless network design. In particular, we concentrate on the design of access network for the cellular networks. We investigate on cellular tower placement and explore ways of cost reduction and improved availability. We use the roadmap (satellite and other views as well) information in and around of Denton for placing the BTS’s.

Maps and BTS’s location:

In the following maps 1 and 2 all the BTS’s are connected to the central office (CO). The central office is denoted in oval shape painted in blue and CO is written on it. The BTS’s connection to the CO is denoted by black line. There are 2 CO’s and are connected in a two way. Based on the scales I’ve taken I divided the map into two parts where there are CO’s in each of them and the CO’s are connected using a two way link.

Calculation:

Given:

Radius of each cell 100-500m

Total available spectrum: 100 MHz

Bandwidth needed per user: 30 kHz

Frequency reuse factor (assumed to be) 5

Number of simultaneous users for 100 MHz= (100*10^6)/ (30*10^3) =3333.33 users.

Total population of Denton is 117,187. Hence using only one large power base station is not sufficient. It is advisable to use large number of small power base stations depending on the population in that area, as the frequency can be reused and large number of customers can be supported.

The frequency reuse factor assumed is 5.

No. of subscribers = 20,000 (assumed value)

Frequency reuse factor (N) = 5;

Thus total numbers of users supported are

Total available spectrum (W) = 100MHz

Each cell has spectrum (W/N) = 100MHz/5 = 20MHz

Bandwidth for each call (B) = 30KHz

Simultaneous user for each cell= 20 MHz/30KHz = 667

Simultaneous Users for one cluster=667*5= 3335

The total area of Denton= 89.316 sq miles.

Given each cell radius=100mts-500mts = 0.0621371 miles - 0.310686 miles

Area of the hexagonal cell (approx.) =0.3 sq mi

Distance between Co-channels (min.-max.)= 0.24miles -1.20 miles

Assumptions for number of subscribers in different areas based on zip codes and number of BTS’s: (approximate values)

Denton 76201(Zip code): 6500 subscribers out of 26,938 population

Total number of BTS’s required = 10

Denton 76205(Zip code): 3000 subscribers out of 19,628 population

Total number of BTS’s required = 4

Denton 76207(Zip code): 2000 subscribers out of 9143 population

Total number of BTS’s required = 3

Denton 76208(Zip code): 2500 subscribers out of 19,762 population

Total number of BTS’s required = 4

Denton 76209(Zip code): 3950 subscribers out of 24,581 population

Total number of BTS’s required = 6

Denton 76210(Zip code): 2000 subscribers out of 38,354 population

Total number of BTS’s required = 3

Distance between each base station is approximately 2-3 miles

Distance between base station and central office (average) is approximately 6 miles

Bandwidth for a 2G for each cell = 0.064*667 = 42.68 Mbps

Number of T1’s for a 2G network for each BTS = 42.68/1.544= 28 (approx..)

Total cost of the network, this includes the cost between the BTS’s to the CO’s and also between the CO’s. The network constructed here is a star network. Hence,

Nlink number of transmission links, Tlink Termination cost, Flink fixed cost, Mlink per mile costs, D distance on average between the stations.

Cs = 30*[28(150+50)+2*15*6+(28-10)*15*6] = $60000 /-

SNR (Min.-Max.):

When the SNR is larger better performance is provided. There less interference and high signal strength.

The values used below are purely based on assumptions.

Let Sr be the signal to interference ratio, d1, d2, be the distances from desired and interfering base stations respectively.

Then the value of Sr=( d2/ d1)2

Let d1= 0.4 miles, d2= 0.1 miles

Sr = 0.0625 Minimum Sr

Let d1= 0.1 miles, d2= 0.4 miles

Sr = 16 Maximum Sr

Improving Analysis/Cost:

Analysis can be improved by taking fewer assumptions. Cost can be improved by correctly utilizing the bandwidth.

Conclusion:

This design placed all the base stations in the city of Denton and also connected them to the Central Offices. Even both the CO’s are connected. The cost analysis of the whole star network is determined. The values and estimations used in this work are based on assumptions.