The Subscriber Module Target Receive Level parameter (configured in the AP’s Configuration > Radio > Power Control menu) allows operators to automatically control the level of SM transmit power and signal received at the AP from registered SMs. The AP monitors the signal level received by each SM and instructs each SM to adjust transmit power levels to meet this configured receive threshold. This eliminates the need to manually adjust transmit power on SMs, especially for SMs that are very close to the sector and can potentially cause self-interference.
When should I modify the SM target receive level?
Anytime you are not installing a synchronized system with frequency re-use, we strongly recommend to change the Subscriber Module Target Receive Level parameter in order to get more power from the SM. Alternatively, you can also manually change the transmit power on the SM.
Why is the AP Power Control parameter Subscriber Module Target Receive Level important?
For network operators working in all types of radio environments, it is paramount that strict control is kept over the transmit power level of SMs. While the ePMP system supports synchronized radio transmitting and receiving, unnecessary system noise results from excessive SM transmit power levels. In other words, since co-located APs operating on the same channel “hear” SMs transmit at the same time, it is important to control the SM transmit power level automatically (referred to as Automatic Transmit Power control, or ATPC).
What factors should I consider when configuring the Subscriber Module Target Receive Level parameter?
Default Setting
By default, the Subsciber Module Target Receive Level parameter is configured on the AP with a value of -60 dBm. This setting paired with at least 3 feet of horizontal separation between co-located, co-channel APs is required to reduce AP receipt of signals from SMs in other sectors.
Adjustment Considerations
The Subscriber Module Target Receive Level may be configured from -80 dBm up to -40 dBm. Each network represents a unique case for configuring this parameter, and two important initial considerations must be made when adjusting this parameter:
- If the configured Subscriber Module Target Receive Level is set too low, link throughput may be reduced (due to Modulation and Coding Scheme requirements). Examine the SM’s Monitor > Performance page to ensure that the link is operating at the highest MCS state that the radio environment can support.
- If the configured Subscriber Module Target Receive Level is set too high, the AP will allow the SMs to transmit higher on the uplink, which may interfere and degrade the uplink performance of other sectors within radio range.
Adjustment when Operating in Noisy Environments
For radio deployments with other radio equipment reducing the quality of ePMP system uplink, increasing the Subscriber Module Target Receive Level may be necessary. By increasing this parameter the AP allows the SMs to increase power level and transmit further above the channels noise floor. When the AP receives the SM signal at a higher power level and this carrier signal is stronger than interferers the link supports higher throughput. Special care must be taken when increasing the Subscriber Module Target Receive Level parameter as allowing SMs to transmit at a higher level can increase system self-interference, thereby limiting frequency re-use for co-located sectors. Check the AP’s Monitor > Wireless page for degredation in Uplink SNR values reported for each SM.
Notes when using the ePMP eAlign feature
Automatic Transmit Power Control in an ePMP system is essential to minimizing the overall noise floor in the sector and is critical when deploying a GPS-synchronized system. When using the ePMP eAlign feature on the AP, it is important set SM parameter Tx Power Manual Limit to Max Tx Output Power and configure the SM Transmitter Output Power parameter to the maximum allowed for your region.