A Note about Radio Bandwidth Quality

Bandwidth quality in a radio system is normally measured in terms of bit error rate. It
can also be measured in terms of frame erasure rate—the number of frames so severely
errored they have to be discarded.
We have said that one of the key performance parameters we need to achieve is sensitivity.
This is generally measured as static sensitivity (a stationary handset) or
dynamic sensitivity (a moving handset). The reference sensitivity effectively describes
the received signal level needed to achieve a particular bit error rate. For example, the
conformance standard for GSM is -102 dBm of signal level to achieve a 1 in 103 bit error
rate. Similar performance requirements are specified for high-interference conditions
and severe multipath conditions. Delay spreads created by multipath will be relatively
small in an urban environment (typically 5 μs) and longer in hilly terrain (typically
15 μs). Channel simulations are also established for a variety of channel conditions—
for example, a rural area user traveling at 250 kmph would be an RA250 test signal.
TU3 would be typically urban, a user moving at 3 kmph. Performance requirements
are specified across a wide range of operational conditions.
The idea of static reference sensitivity being specified to deliver a 1 in 103 bit error
rate is that this equates to the same voice quality achieved by an analog cellular phone
assuming a 20 dB SINAD (signal to noise and distortion) ratio—the traditional performance
benchmark for an analog handset.
In 3G standards, static sensitivity is specified for 1 in 103 and 1 in 106 bit error rates
for a range of operational conditions. If wireless is to compete directly with wireline
connectivity, the bit error rate benchmark will need to improve to 1 in 1010, which is the
ADSL gold standard. This will represent a significant challenge. Reducing bit error
rates from 1 in 103 to 1 in 106 requires a 3 dB increase in link budget. More transmit
power, more receive sensitivity, or both will be required. Additional power can be
made available by increasing network density and improving handset performance.
There is no point in increasing bit rate if bit quality decreases. Bandwidth quality is
just as important as bandwidth quantity.