Opportunistic use of UMTS TDD Spectrum
© 2006, motion | mobile systems communication group | all rights reserved
To date, most UMTS deployments have focused on FDD utilizing the paired frequency bands.
Over 120 of Europe’s and Asia’s largest mobile operators have spectrum that is specifically allocated to 3G TDD technologies.
TDD fits for pico-cell hot spots, used mainly within buildings and are therefore often shielded by walls.
This results in a natural limitation of a coverage area and consequently we can predict some 5 MHz spectrum opportunities in spatial dimension for OR use.
Opportunistic use of UMTS TDD bands could be a new source of revenue for actual 3G license owners.
UMTS coverage scenarios
OR must not cause harmful interference in a UMTS.
UMTS system does not need to be changed.
UMTS sensing challenges:
UMTS is a DS-Spread Spectrum system.
Classical Energy Detector doesn't work due to low PSD of UMTS signals.
Focus on the detection of UMTS TDD signals through the use of a cyclostationary detector.
The goal is to distinguish between 2 hypotheses:
There is a fundamental tradeoff between the probability of missed detection Pm =1-Pd and the probability of false alarm.
A high Pm causes high probability of interference, on the other hand, high Pfa would result in low spectrum utilization, since false alarms increase number of wasted opportunities.
Sensing problem formulation
The Observation Time required to guarantee a sufficiently low Pmis a crucial metric to evaluate the ability of OR not to disturb the UMTS.
The Observation Time until detection the primary user is very critical because, during that time the OR is creating harmful interference to the UMTS system.
S: Spectrum Cyclic Density
α=1/T0 : Cyclic frequency
Energy detector vs. Cyclostationary detector
PSD of UMTS signal, SNR=25 dB
SCD of UMTS signal, SNR=25 dB
PSD of UMTS signal, SNR= -15 dB
SCD of UMTS signal, SNR= -15 dB
SF=16, Tobs=300 ms
[T. Weiss, F. Jondral, Spectrum Polling an innovative strategy for the enhancement of spectrum efficiency, IEEE Radio Communications, March 2004.]
Sensing Report: H0 or H1
UMTS TDD BS