User's Manual

66 Mercury Reference Manual 05-4446A01, Rev. C
¥ ARQEnables the Automatic Repeat Request function.
[
enable, disable; enabled]
¥ ARQ Window SizeThe maximum number of blocks to send
before receiving an acknowledgement. [
1—1024; 512]
¥ ARQ Block SizeARQ is applied to payload data in blocks of this
size. [
4—2040; 256]
¥ ARQ Block LifetimeARQ blocks are valid for this length of
time. [
0—655; 655]
¥ ARQ Transmitter DelayThe length of time the transmitter waits
before repeating an unacknowledged packet.
[
1—655; 35]
¥ ARQ Receiver DelayThe length of time the receiver waits before
repeating an unacknowledged packet. [
1—655; 35]
¥ Downlink PercentageThe percentage of link time given to
downstream traffic. It should be set to
50% when Adaptive Split is
set to
enabled. [10-90%; 50%]
¥ Adaptive SplitThe adaptive split feature provides improved
link utilitization and throughput for burst payload traffic. The
Mercury is a TDD system and normally allocates 50% of its
capacity to the downlink and 50% to the uplink. When adaptive
split is enabled, the Media Access Controller (MAC) in the
Access Point monitors the traffic flow continuously in the
downlink and uplink directions. The MAC auotmatically modi-
fies the downlink split in response to the traffic load. When
more traffic is flowing upstream, the downlink split changes to
allocate additional capacity to the uplink. When more traffic is
flowing downstream, the downlink gets additional capacity. If
TDD synchronization is used to synchronize Access Points and
minimize inter-Access Point interference, Adaptive Split should
be disabled. [
enabled, disabled; enabled]
Modulation
Protection and
Hysteresis Margins
Table 3-3 on Page 67 shows the relationship between the radios Protec-
tion Margin, Hysteresis Margin, and the SNR range allowed for each
form of modulation.
Column A lists the available modulation types for the radio, while col-
umns B and C show the minimum SNR range required to operate in each
modulation. For example, an SNR of 5.8 dB in Column B is required for
QPSK modulation with an FEC rate of 1/2. An SNR of 8.4 dB is
required for QPSK modulation with an FEC rate of 3/4.
Columns B and C have a Hysteresis Margin of 0 dB. This means there
is no overlap between the maximum SNR for BPSK (5.8 dB) and the
minimum SNR for QPSK-1/2 (5.8 dB).
Columns D and E show the SNR ranges with a Protection Margin and
Hysteresis Margin of 3 dB. The Protection Margin is added to each
value in Columns B and C to get the corresponding value in Columns D
and E. The Hysteresis Margin is then added to the Max SNR value.