Redline Communications Inc. AN100UXA 用户手册
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AN-100U/UX Base Station
Manual
70-00058-01-04
Proprietary Redline Communications © 2010
Page 118 of 136
April 19, 2010
7. High receiver dynamic range to address dynamic interference.
8. State of the art filtering at the RF, IF and baseband levels to reduce interference.
9. Choice of non-adaptive modulation to provide stable burst rate during periods of
rapid interference variations on the link.
7.5.2 Multipath Interference
The base station is designed with high immunity to interference and multipath signals. Its
core technology is Orthogonal Frequency Division Multiplexing (OFDM), capable of
reliable performance under multi-path and frequency selective fading known to have
severe signal fading and distortion effects in the sub-11 GHz frequencies.
core technology is Orthogonal Frequency Division Multiplexing (OFDM), capable of
reliable performance under multi-path and frequency selective fading known to have
severe signal fading and distortion effects in the sub-11 GHz frequencies.
Multipath interference is a significant problem in long-range links, and in near line-of-
sight, and non line-of-sight links. Multipath is a form of self-interference occurring when
signal reflections arrive slightly later than the primary signal. The result can be
destructive interference that can essentially null out the primary signal or overlap the
original signal such that it cannot be decoded. Multi-path interference is a problem with
long-range links where reflections off the ground, snow, and water frequently interfere
with the primary signal. It is also a problem in urban environments where the signal
reflects off buildings, trees, and roads.
sight, and non line-of-sight links. Multipath is a form of self-interference occurring when
signal reflections arrive slightly later than the primary signal. The result can be
destructive interference that can essentially null out the primary signal or overlap the
original signal such that it cannot be decoded. Multi-path interference is a problem with
long-range links where reflections off the ground, snow, and water frequently interfere
with the primary signal. It is also a problem in urban environments where the signal
reflects off buildings, trees, and roads.
OFDM breaks up the transmit signal into many smaller signals. For example, instead of
one single carrier carrying 70 Mbps of data (wireless interface rate), there are 192
separate carriers, each carrying about 364 Kbps of data (in the case of the Redline
product) in a 14 MHz bandwidth. If selective fading degrades one or two carriers, the
impact is minimal since the information is spread across the remaining carriers.
one single carrier carrying 70 Mbps of data (wireless interface rate), there are 192
separate carriers, each carrying about 364 Kbps of data (in the case of the Redline
product) in a 14 MHz bandwidth. If selective fading degrades one or two carriers, the
impact is minimal since the information is spread across the remaining carriers.
Figure 42: Op Notes:
OFDM Multiple Carriers
One key aspect of OFDM implementation is that the individual carriers overlap
significantly to preserve overall bandwidth. Normally, overlapping signals would interfere
with each other, however, through special signal processing, the carriers in an OFDM
waveform are orthogonal to each other.
significantly to preserve overall bandwidth. Normally, overlapping signals would interfere
with each other, however, through special signal processing, the carriers in an OFDM
waveform are orthogonal to each other.
Multipath interference may cause individual narrowband channels to be altogether lost.
This problem is addressed in the Redline implementation in three ways:
This problem is addressed in the Redline implementation in three ways:
1. Equalizing the received signal based on an estimate of the channel fading conditions
(restoring the faded sub-channels).
2. Interleaving the data before modulation onto the individual sub-channels (so that
adjacent data symbols do not necessarily end up on adjacent sub-channels, and
thus deep fades do not impair large chunks of the signal).
thus deep fades do not impair large chunks of the signal).
3. Convolutional encoding of the input data introduces correlations between signal
samples that are echoed on sub-channels occurring in separate parts of the
spectrum. This allows the receiver to infer the values of the signal that were
transmitted on fatally faded sub-carriers. The key advantage of multiple carriers is
that the signal is more robust to multipath disturbance, as described below.
spectrum. This allows the receiver to infer the values of the signal that were
transmitted on fatally faded sub-carriers. The key advantage of multiple carriers is
that the signal is more robust to multipath disturbance, as described below.