User's Manual

ECLIPSE INSTALLATION MANUAL
l Adaptive modulation maximizes use of available channel bandwidth.
l Coding provides options for maximum throughput or maximum system gain
on each modulation rate.
Adaptive Modulation (AM)
AM uses one of four automatically and dynamically switched modulations - QPSK,
16 QAM, 64 QAM, or 256 QAM. For a given RF channel bandwidth a two-fold
improvement in data throughput is provided for a change from QPSK to 16 QAM, a
three-fold improvement to 64 QAM, and a four-fold improvement to 256 QAM.
In many instances the link parameters that supported the original system gain can
be retained. For example, the antenna sizes and Tx power used for an original QPSK
link on a 7 MHz channel are unchanged when operated on 256 QAM using adaptive
modulation. The adaptive modulation engine ensures that the highest throughput is
always provided based on link quality.
Modulation switching is hitless/errorless. During a change to a lower modulation,
remaining higher priority traffic is not affected. Similarly, existing traffic is unaf-
fected during a change to a higher modulation.
Note that while adaptive modulation can also be used on PDH links and combined
PDH and Ethernet links, unlike Ethernet there is no QoS synergy on PDH con-
nections.
Ethernet connections enjoy real synergy through the QoS awareness on the DAC GE3
GigE switch, and the service provisioning provided by any MPLS or PBB-TE network
overlay. All high priority traffic, such as voice and video, continues to get through
when path conditions are poor. Outside these conditions 'best effort' lower priority
traffic, such as email and file transfers enjoy data bandwidths that can be up to four
times the guaranteed bandwidth.
DS1 connections by comparison are dropped in user-specified order when link capa-
city is reduced, and restored when capacity is increased.
Coding
Modulation code options provide two sets of modulation states, one for maximum
throughput, the other for maximum gain. These apply on each of the modulation
rates (QPSK, 16 QAM, 64 QAM, 256 QAM) to provide a total of eight modulation
states.
Maximum throughput delivers maximum data throughput - at the expense of some
system gain.
Maximum gain delivers best system gain - at the expense of some throughput.
Up to four of the eight modulation states offered with ACM can be selected for use.
For example:
l With four modulation rates, each can be set for maximum throughput or
maximum gain.
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