Subject : Wireless Network

Topic : Planning and Design of Wide-Area Networks

Difficulty : High

1. Requirements of wireless networks

i. A wireless network requires planning for its setup, functioning and operation.

ii. The wireless network planning process can be divided into three phases: the initial planning (dimensioning) phase, the detailed radio network planning, and the operation and optimization phase.

iii. The dimensioning phase is used to estimate the approximate number of cell sites required, base station configurations, and number of network elements in order to determine the projected costs and associated investments.

iv. In the dimensioning phase, concentration is to provide near ubiquitous coverage. When the coverage demands are met, there is focus on traffic demands.

v. Network plans change throughout the life of a wireless network. The initial focus is on coverage and expansion. For coverage, it is essential to know the link budget for both the uplink and the downlink.

vi. Link budget calculates all the power gains and power losses on both the links. This calculation helps to estimate the link capacity and hence the coverage.

vii. The detailed planning phase takes into account the real site locations, real propagation conditions, and real user distributions based on the operator’s traffic forecasts.

viii. The network operation and optimization phase deals with individual cell and system testing.

ix. Each phase requires additional support functions such as propagation measurements, key performance indicator (KPI) definitions, and so on.

x. The planning involves study of the following:

• Network topology: base-station transceiver-base station controller-mobile switching center (BTS-BSC-MSC)
• Link capacity: BTS-BSC, BSC-MSC
• BSC sizing
• MSC sizing
• The number of users
• Users’ behavior, i.e., heavy or light users
• Busy-hour traffic as a percentage of the total traffic
• Users’ distribution over the service area
• Division of the service area into zones of different traffic density
• Increase in number of users

xi. Thus, setting up a wireless network requires a study of the extent of radio coverage, the quality of service for different environments, efficient use of spectrum, and the evolution of the network.

2. Link budget analysis

A link budget is the calculation of the amount of power received at a given receiver based on the output power from the transmitter. The link budget considers all of the gains and losses that a radio wave experiences along the path from transmitter to receiver. We need to perform the calculation in both directions: from the mobile station to the base station (uplink) and from the base station to the mobile station (downlink).
We determine the maximum allowable path loss in each direction and use the lesser of the two to calculate the coverage for the cell .The link budget should include a margin to allow fading of the signal.

Below Shows Uplink budget for speech (outdoor pedestrian) service at 12.2 kbps.