Modulation Strategy
Modulation Strategy classify Tow parts :
1) Fixed modulation. 2) Adaptive modulation (AM)
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1) Fixed modulation.
Fixed modulation refers to a modulation policy in which a modulation scheme is adopted invariably to provide constant air interface bandwidth for a running radio link.
2) Adaptive modulation (AM) .
The adaptive modulation (AM) technology adjusts the modulation scheme automatically based on channel quality.
Modulation Scheme and Air-interface Capacity
When the channel quality is good (such as on days when weather conditions are favorable), the equipment adopts a high-efficiency modulation scheme to transmit more user services. This improves transmission efficiency and spectrum utilization of the system.
When the channel quality deteriorates (such as on days with adverse weather), the equipment adopts a low-efficiency modulation scheme to transmit only higher-priority services within the available bandwidth while discarding lower-priority services. This method improves anti-interference capabilities of the radio link, which helps ensure the link availability for higher-priority services.
Modulation Scheme Shift and Service Priorities
In Integrated IP microwave mode, the equipment supports the AM technology. With configurable priorities for E1 services and packet services, the transmission is controlled based on the service bandwidth and QoS policies corresponding to the current modulation scheme. The highest-priority services are transmitted with precedence.
Priorities of E1 services
The priorities of E1 services are assigned based on the number of E1 services that each modulation scheme can transmit. When modulation scheme switching occurs, only the E1 services whose number is specified in the new modulation scheme can be transmitted and the excess E1 services are discarded.
Priorities of packet services
With the QoS technology, packet services are scheduled to queues with different priorities. The services in different queues are transmitted to the microwave port after running the queue scheduling algorithm. When modulation scheme switching occurs, certain queues may be congested due to insufficient capacity at the air interface. As a result, certain services or all the services in these queues are discarded.
Adaptive Modulation
Figure 1 shows the service changes caused by shifts among six modulation schemes as an example. The orange part indicates E1 services. The blue part indicates packet services. The closer the service is to the outside of the cylinder in the figure, the lower the service priority. Under all channel conditions, the service capacity varies according to the modulation scheme. When the channel conditions are unfavorable (during adverse weather conditions), lower-priority services are discarded.
Characteristics
The AM technology has the following characteristics:
The lowest-efficiency modulation scheme (also called reference scheme or modulation scheme of guaranteed capacity) and the highest-efficiency modulation scheme (also called nominal scheme or modulation scheme of full capacity) used by the AM can be configured.
For modulation schemes that Integrated IP microwave IF boards support,
In AM, when modulation schemes are switched, the transmit frequency, receive frequency, and channel spacing remain unchanged.
In AM, modulation schemes are switched step-by-step.
In AM, modulation scheme switching is hitless. When the modulation scheme is downshifted, high-priority services will not be affected when low-priority services are discarded. The switching is successful even when 100 dB/s channel fast fading occurs.
Example Cnfiguration The AM technology in Huawei optix RTN 950A
Networking diagram of the AM function
Conclusion
* The fixed Modulation used in areas with good weather conditions to keep the data transfer rate the same.
* The Adaptive Modulation is used when weather conditions are bad and there is high fading, so the modulation changes to keep the necessary data rate.
