ECE-T512 Wireless

Systems

Interference/Noise

Interference/Noise

Interference is the major limiting factor in cellular radioperformance particularly urban networks Voice channels Cross-talk and diminished call quality

Control channels Missed/blocked calls

Co-channel interference (CCI) is introduced when samecarrier frequency is used in different cells.

Adjacent channel interference (ACI) occurs whenneighboring cells use spectrally adjacent carrierfrequencies that spill-over into the band of interest occurs due to imperfect receive filters / image frequencyrejection

Interference/Noise

= Carrier to noise ratio = Carrier to interference ratioThresholds must be exceeded to prevent

outage:

Thermal noise outage = ON = P( < TH) CCI outage = OI = P( < TH)

Interference/Noise Thresholds

TH and TH depend on: Modulation/coding scheme

Receiver structure

Link quality measure

Propagation environment

Mobile velocity

Outage Probability

O = Outage Probability = P( < TH or < TH)General trends:

Fast mobile users Path loss/Shadowingdominant in outage probability calculations

Slow mobile users Multipath Fadingdominant in outage probability calculations

Lightly loaded systems Noise dominant Highly loaded systems Interference dominant

Interference and Cellular

System CapacityCo-channel cells - cells in a given coverage area that use

the same set of frequencies --- interference betweensignals from these cells is CCI

Thermal noise can be overcome by increasing carrierpower -- SNR increased

CCI cannot be combated in this way - increasing carrierpower also increases interference power seen by co-channel cells

Reducing CCI can be accomplished through physicalseparation of co-channel cells, specifically, byincreasing:

Q = D/R = sqrt(3N) N = cluster size

D = co-channel re-use distance

R = cell radius