“Toward a Framework for Power Control in Cellular Systems” By Zvi Rosberg and Jens Zander EE 360 May 16, 2001 Timothy J. Peters

Outline Purpose of power control Dominant factors affecting power control Measurable information Algorithm requirements Public knowledge bank Analysis and Conclusion

Purpose of Power Control Alleviate co-channel and cross-channel interference to increase resource sharing Resources are generally shared using orthogonal or semi-orthogonal techniques

Purpose of Power Control Orthogonal techniques are not perfect; Interference results Causes of interference: –FDMA ( Doppler shift, imperfect technology) –TDMA (Imperfect sync, multipath, incorrect time slots) –Spread Spectrum (Multipath, near-far, imperfect sync)

Dominant Factors Affecting Power Control Signaling, modulation scheme, and multiple access method Link orientation (uplink or downlink) Environment morphology and topology Speed of mobile terminals Cell hierarchy Connection type (Continuous or discontinuous)

Dominant Factors Affecting Power Control Signaling, modulation scheme, and multiple access method Example: –Narrowband TDMA signal (e.g. GSM) will have few interfering signals –CDMA signal (e.g. IS-95) will have many interfering signals –RESULT: Gaussian statistics may be applicable for the CDMA signal, making power control easier

Dominant Factors Affecting Power Control Link orientation (uplink or downlink) Example: –Base stations are usually stationary and elevated. –Mobile units are moving and are located among many obstacles. –Asymmetry of broadcast and MAC channel –RESULT: Uplink and downlink experience different shadowing and multipath which affects power control.

Dominant Factors Affecting Power Control Environment morphology and topology Example: –Outdoor rural environments are dominated by line-of- sight, with large obstacles at great distances. –Outdoor urban environments are influenced by reflections from corners and line-of-sight. –Indoor environments are affected by shadowing from walls –RESULT: Different environments have different interference statistics, which affects power control.

Dominant Factors Affecting Power Control Speed of mobile terminals Example: –With fast-moving mobiles, shadowing may not be a problem. –Slow-moving or stationary mobiles will be affected by shadowing. –RESULT: Interference statistics are dependent on the speed of the mobile, which affects power control. * “Broadband Communications on the Highways of Tomorrow ”

Dominant Factors Affecting Power Control Cell hierarchy Example: –A system may contain macro cells composed of micro cells composed of pico cells. –Transmission is constrained by the different power limits and resources available within each cell. –RESULT: Interference will be asymmetric, resulting in a different statistical model.

Dominant Factors Affecting Power Control Connection type (Continuous or discontinuous) Example: –Voice traffic is continuous and delay constrained. –Data (packet switched) is bursty and somewhat delay constrained. –RESULT: Interference is affected by the nature of the traffic.

Measurable Information For practicality, power control algorithm should be distributed and use only local information Measurements and power updates must be “fast enough” Subject to measurement errors, sampling errors, and information aging

Algorithm Requirements Fixed or variable increments Fixed or variable time steps Distributed and asynchronous updates Stability of the control process Ease of implementation and robustness

Public Knowledge Bank Power control and many other parameters require full system simulation Each research group creates its own unique simulation scenario No “benchmark” scenario exists Authors propose an open and public knowledge bank to allow researchers to compare their models

Analysis and Conclusion Power control is a complex problem, affected by many factors System simulations have become complicated and time consuming “Knowledge Bank” will not work due to code compatibility issues, profit takers, and egos, among other reasons