Microwave link feature

A microwave link is the channel that is used to transmit the information between stations. To double the transmission capacity with channel unchanged, reduce the interference of a transmitter to adjacent systems and the residual bit error rate, and adjust the modulation scheme based on the quality of channels.

XPIC

The cross-polarization interference cancellation (XPIC) technology is used together with the co-channel dual-polarization (CCDP) technology. Application of the two technologies doubles the transmission capacity with channel conditions unchanged. The XPIC technology works with the co-channel dual-polarization (CCDP) technology so that the transmitter transmits two electromagnetic waves whose polarization directions are orthogonal to each other to the receiver over the same channel. The receiver recovers the original two channels of signals after canceling the interference between the two electromagnetic waves through the XPIC processing.

System Configuration:

The OptiX RTN 980 supports one to seven XPIC workgroups. The OptiX RTN 950 supports one to three XPIC workgroups. The OptiX RTN 910/905 2A/905 1C supports one XPIC workgroup. Each XPIC workgroup uses one frequency and consists of the following items:
- Two XPIC IF boards/Two OptiX RTN 905 1C IDUs/One OptiX RTN 905 2A IDUs
- Two ODUs
- One dual-polarized antenna in separate mounting mode or one dual-polarized antenna with an OMT (orthogonal mode transducer) in direct mounting mode
When one XPIC group is configured, two OptiX RTN 310 NEs need to be configured on each XPIC site. Each XPIC group uses one frequency and requires the following hardware configurations:
- Two OptiX RTN 310 NEs
- One dual-polarized antenna mounted separately or one dual-polarized antenna mounted directly with an orthogonal mode transducer (OMT)
- One XPIC cable

Purpose:

The XPIC technology is used to double the link transmission capacity over the same channel.

ATPC

Automatic transmit power control (ATPC) is an important function of a microwave transmission system. This function reduces the residual bit error rate (BER) and transmitter's interference to neighbor systems. ATPC is a method of adjusting transmit power based on the fading of transmit signal detected at the receiver.

When the ATPC function is enabled, the following conditions are possible:

If the receive signal level (RSL) at the receiver is 2 dB lower than the central value of the ATPC upper threshold and the ATPC lower threshold, the receiver notifies the transmitter of an increase in the transmit power. Therefore, the RSL can be within the value range that has a bias of ±2 dB from the central value of the ATPC upper threshold and the ATPC lower threshold.
NOTE:
- If the actual transmit power of the ODU reaches the preset maximum transmit power whereas the RSL at the receiver fails to be within the value range that has a bias of ±2 dB from the central value of the ATPC upper threshold and the ATPC lower threshold, adjustments are no longer made.
- The preset maximum transmit power of the ODU should not be more than the rated maximum transmit power of the ODU.
- If the maximum transmit power of the ODU is not set, the transmit power of the ODU can increase at most to the rated maximum transmit power of the ODU.
If the RSL at the receiver is 2 dB higher than the central value of the ATPC upper threshold and the ATPC lower threshold, the receiver notifies the transmitter of a decrease in the transmit power. Therefore, the RSL can be within the value range that has a bias of ±2 dB from the central value of the ATPC upper threshold and the ATPC lower threshold.

Purpose:

The ATPC technology enables a transmitter to automatically change its output power within the ATPC control range based on the change in the RSL of a receiver. In this way, the RSL of the receiver remains in a fixed range, and the interference with the neighboring system and the residual error rate are reduced.

AM

The adaptive modulation (AM) function is a main characteristics in Integrated IP radio mode. The AM function helps to adjust the modulation scheme based on the quality of channels. After the AM technology is used, at the same channel spacing, the microwave service bandwidth varies with the modulation scheme. The higher the modulation efficiency, the higher the bandwidth of the transmitted services.

When the channel quality is satisfactory (such as on days weather conditions are favorable), the equipment adopts a high-efficiency modulation scheme to transmit more user services. In this manner, the transmission efficiency and the spectrum utilization of the system are improved.
When the channel quality deteriorates (such as on days there is a storm or fog), the equipment adopts a low-efficiency mode to transmit only the services with a high-efficiency priority within the available bandwidth and to discard the services with a lower priority. In this manner, the anti-interference capability of the radio link is improved and the link availability of the services with a high-efficiency priority is ensured.

NOTE:

The Integrated IP radio equipment supports the AM technology, in which the priorities of E1 services and packet services can be set. With the AM technology used, service transmission is controlled based on the service bandwidth and QoS policy corresponding to the current modulation scheme. The service with the highest priority is transmitted with preference.

Purpose:

When the AM function is enabled for a radio link, link availability for higher-priority services is ensured and bandwidth utilization is greatly improved.

AMAC

Adaptive modulation and adaptive channel space (AMAC) is the enhancement of AM. If the lowest-order modulation scheme is set to QPSK Strong, the AM feature downshifts the modulation scheme to QPSK Strong when channel quality deteriorates. Then, the AC function downshifts the channel spacing. The equipment uses the available bandwidth to transmit high-priority services, reducing the impact of channel quality deterioration on service signals.

NOTE:

OptiX RTN 380 supports AMAC.

Feature Dependencies and Limitations

Table 1 describes the dependencies and limitations of XPIC, ATPC and AM.

**Table 1** Feature Dependencies and Limitations
Feature	Self-limitations	Dependencies and limitations with other features
XPIC	Inter-NE configuration: Fort RTN 900s, an XPIC group can be configured only on one NE. Inter-NE configuration is not allowed. For RTN 310, inter-NE configuration is allowed. IF cable length: The maximum difference between the IF cables in two polarization directions of an XPIC group cannot exceed 12 meters in length. Mix of different board types: If an ISV3 board and an ISX2 board form an XPIC group, the ISV3 board must work in IS2 mode. If the link in one polarization direction of an XPIC group fails, the link in the other polarization direction also fails.	One XPIC group cannot form a 1+1 HSB, 1+1 FD, or 1+1 SD protection group. Members of an XPIC group that consists of ISX2/ISV3 boards can be configured into an N+1 protection group. Note that members in an XPIC group can be configured into only the same N+1 protection group. LAG: You can manually create a load-sharing link aggregation group (LAG) using the two member links in an XPIC group. If N+0 non-protection links are member links in multiple XPIC groups, you can manually create a load-sharing LAG that consists of all member links in the XPIC groups. If four member links in two XPIC groups are 4+0 non-protection links, you can manually create a load-sharing LAG that consists of the four member links. The Ethernet header compression mode, guaranteed E1/STM-1 capacity, E1 priority (enabled or disabled), and full E1 capacity parameters must be consistently set for members in a LAG. If the two members in an XPIC group are ISX2/ISV3 boards inserted in paired slots, the two boards can form a physical link aggregation (PLA) group. You can create an enhanced physical link aggregation (EPLA) group using the two member links in an XPIC group. If four member links in two XPIC groups form 4+0 non-protection links, you can create an EPLA group to protect the four links. If two of the 3+0 non-protection links are member links in an XPIC group, you can create an EPLA group to protect all links.
ATPC	-	The ATPC parameters, such as ATPC status (enabled or disabled) and ATPC adjustment thresholds, must be consistently set for members in an N+1 protection group. XPIC can work with ATPC. However, it is not recommended that you use the two functions together. When using the two functions together, pay attention to the following points: The ATPC parameters, such as ATPC status (enabled or disabled) and ATPC adjustment thresholds, must be consistently set for links in the horizontal and vertical polarization directions in an XPIC group. The difference between the ATPC upper threshold and the ATPC lower threshold must be minimized (5 dBm is recommended). AM can work with ATPC. However, it is not recommended that you use the two functions together. When using the two functions together, pay attention to the following points: The ATPC lower threshold must be greater than the AM sensitivity in AM full capacity mode plus 14 dB. AM sensitivity indicates the AM receive power in the case of AM modulation scheme shift. The ATPC upper threshold must be 5 dBm greater than the ATPC lower threshold. The AM booster function must be disabled.
AM	If the AM feature is AM and AMAC features are enabled, configuring quality of service (QoS) for transmitted Ethernet services is recommended. When a microwave link works in a lower-order modulation scheme, QoS allocates available bandwidth so that higher-priority Ethernet services are transmitted first. Enable AM before enabling the E1 service priority. An Integrated IP radio with the channel spacing of 3.5 MHz does not support the AM feature. AM booster	AM can work with 1+1 protection. AM can work with N+1 protection. In this case, AM parameters must be consistently set for members in the N+1 protection group. When the AM function is used with N+1 protection, the members must be enabled or disabled with E1 service priority simultaneously. When the E1 service priority is enabled, the maximum E1 capacity must be consistently set for the members. Cross polarization interference cancellation (XPIC) can work with AM. However, it is not recommended that you use the two functions together. When using the two functions together, ensure that the AM parameters are consistently set for the links in the horizontal and vertical polarization directions in an XPIC group. Microwave ports that support AM can be configured into a LAG at air interfaces. The AM attribute and E1 priority must be set to the same values for the IF ports in a LAG.