User guide

Understanding Bandwidth Management Link Characteristics
92
pmp-0229 (Mar 2013)
CAUTION!
2X operation requires approximately 3 to 5% more power than 1X operation.
This additional power affects the recommended maximum for power cord length
feeding the CMMmicro or CMM4. See the dedicated user guide that supports the
CMM model that you are deploying. However, 2X operation does not affect the
maximums for the CMM2.
Disabling 2X Operation
Disabling 2X operation for an SM can be helpful for alignment, troubleshooting, or preventing
frequent automatic switches between 2X and 1X, where RF conditions are only marginally
favorable to 2X. The ability to disable 2X for an SM is inherent since the 2X Operation feature
was introduced.
Disabling 2X operation for a sector can be helpful for identifying a baseline for 1X-to-2X
comparison, broader troubleshooting activities, or forcing all SMs to 1X rather than disabling 2X
in each SM. The General tab of the Configuration page in the AP provides a 2X Rate parameter:
• If you click Disable, then Save Changes and Reboot, 2X operation is disabled for the sector,
regardless of the 2X Rate setting in each SM.
• If you later click Enable, then Save Changes and Reboot, 2X operation is enabled in the
sector for SMs with 2X Rate enabled on their Configuration>General page. SMs with 2X
Rate disabled on their Configuration>General page (or P7 or P8 SMs that don’t support 2X
Rate) will only operate at 1X.
If you want to cap the bandwidth usage of certain SMs, it is generally wiser to use the Maximum
Information Rate (MIR) parameters of those SMs to do so, instead of locking down the operation
rate for the entire sector. See Maximum Information Rate (MIR) Parameters on Page 83.
3X Operation
OFDM modules offer an additional modulation scheme that provides 3X operation as an
alternative to 1X or 2X operation. In clear space, 3X operation is possible over half the range of
2X (which means it is possible over one-fourth the range of 1X). However, in NLOS installations,
multipathing may be the predominant RF issue, not free-space attenuation, so the relationship
between 1X, 2X, and 3X range may differ from clear space situations.
The effect of operation rate on the performance of OFDM modules in 10-MHz channel width
deployment is generalized in Table 23. Aggregate throughput refers to the sum of the uplink
throughput plus the downlink throughput.