User's Manual

July 23, 2002 B-7
CreataLink2 XT Hardware Integrator’s Guide Appendix B
Performance Goals
Performance Goals
Network coverage is the goal of emissions control. Allowable emissions levels are a
function of radio sensitivity and the required network coverage.
Radio Performance Capabilities
Every radio technology demands certain sensitivity requirements. Wide area net-
works (WANs) require the subscriber device to be very sensitive, whereas local area
networks (LANs) operate with higher receiver signal levels.
Highly sensitive radios are more susceptible to noise from the host platform. For
example, assuming a 10 dB co-channel rejection, a less sensitive receiver tolerates
a higher level of noise.
FCC Part 15 Level Comparison
The FCC emissions limits for unintentional radiators are as follows:
• 200 µV/M between 216 MHz and 960 MHz
• 500 µV/M above 960 MHz
These limits are for measurements conducted three meters away from the device.
Compare these numbers with the receiver sensitivity. Note that even if a host is
Part 15 certified, there is still the possibility that the data transceiver will not work.
This could happen when the host has a 180 µV/M spur at a receive channel. This
would meet the FCC limit but would be 10 dB above sensitivity. If the desired
channel is at sensitivity, this would cause the data transceiver to miss pages. As a
general rule, if you provide 40 dB of margin to the FCC rules, there should be no
desense problems.
Determining Emission Level Goals
To determine the allowable emissions levels from the host device, consider the
following:
• The sensitivity of the data transceiver
• The targeted network coverage requirements
• The expected proximity of the data transceiver to the host platform noise
sources
Achieving zero desense is not a realistic goal with a cost-sensitive commercial
product. The following set of subjective levels is based on industry experience:
• Channels desensitized by less than 5 dB are acceptable.
• Channels desensitized by more than 10 dB create a noticeable problem within
the network.
• Channels desensitized by more than 20 dB are unacceptable.
Each case is different. Each air protocol reacts uniquely, and each network performs
differently under the same levels of unwanted ambient noise. Noise from the host
higher than the desense threshold level degrades performance.
Because of the restricted number of channels used for paging, narrowband
interference can cause more problems if the interference falls on a channel used by
your carrier.