User's Manual Part 2

05-4446A01, Rev. D Mercury Reference Manual 73
• ARQ (AP only)—Enables the Automatic Repeat Request func-
tion.
[
enable, disable; enabled]
• ARQ Window Size (AP only)—The maximum number of blocks to
send before receiving an acknowledgement. [1—1024; 512]
• ARQ Block Size (AP only)—ARQ is applied to payload data in
blocks of this size. [4—2040; 256]
• ARQ Block Lifetime (AP only)—ARQ blocks are valid for this
length of time. [0—655; 655]
• ARQ Transmitter Delay (AP only)—The length of time the trans-
mitter waits before repeating an unacknowledged packet.
[
1—655; 35]
• ARQ Receiver Delay (AP only)—The length of time the receiver
waits before repeating an unacknowledged packet. [1—655; 35]
• Downlink Percentage (AP only)—The percentage of link time
given to downstream traffic. It should be set to 50% when Adap-
tive Split is set to enabled. [10-90%; 50%]
• Adaptive Split (AP only)—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 continu-
ously in the downlink and uplink directions. The MAC automat-
ically modifies 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 addi-
tional 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 74 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.