Lecture 9: Wireless Networks Anders Västberg

Wireless Networks Provide fixed network access to a large number of stationary or mobile users. Examples: –Radio and television broadcasting systems –Mobile telephone systems (PSTN access) –Mobile broadband systems (Internet access)

Taxonomy of Wireless Networks Wireless Networks Fixed Networks Mobile Access Networks Ad Hoc Networks Cellular Networks Random Acess Networks Multihop Wireless Internets Sensor Networks [Kumar et al., 2004]

Duplex Communication Downlink: Communication from the BS to the MT. Upplink: Communication from the MT to the BS. Multiplexed by –Frequency Division Duplex (FDD) –Time Division Duplex (TDD)

Cellular System Overview [Stallings, 2005]

Radio Access Ports (RAP) Provides Wireless Connections to Mobile Terminal (MT) Service area Coverage area Area availability Population availability

Capacity System capacity –Maximum number of users that can be served –Given a certain quality level Blocking probability

Range/Interference Few RAP, Low user densities =>Range limited systems Many RAP and user terminals =>Interference limited systems

Reuse distance D R R tt tt dBW

Capacity Reuse distance Capacity only dependent on the ration between resuse distance and cell radius The system is scalable

Cell Geometry Tesselation [Stallings, 2005]

Frequency Reuse

Fixed Channel Allocation Capacity (channels/cell) Normalized resuse distance Cluster size Area Capacity (channels/a.u.)

Worst Case Downlink Scenario [Ahlin et al., 2006]

Worst Case Uplink Scenario [Ahlin et al., 2006]

Capacity increase Adding new channels –Increase C New modulation and coding schemes –Decrease  t Smaller Cells –Decrease A c –Cell splitting Divide cells into sectors –Use directional antennas

Directional Antennas Ideal sector antenna If main lobe isthe Interference power is reduced by a factor of N