Dear Team, Kindly notice that XPIC links are critical links as these are high capacity with low margin, So, any small interfering signal ( external or cross-polarized ) may affect the link performance and reduce the availability. Even without interference, and link suffering from fading or any propagation problem, the XPIC links are more sensitive than the similar links without XPIC (even same distance, Tx, Rx power, modulation, capacity..Etc). So, in each XPIC links suffering from propagation problem, we have to check the three items (order is necessary): 1- Ensure the actual Rx is matched with the design: if antennas are not fully aligned, it means waste of Tx power and probability to receive signals from other adjacent channel links. 2- Interference test (external interference): to check no external signal affects the link. 3- XPD test (cross polarized interference): more effective than external interference in XPIC links, it must be exist but we must ensure its limit, if the difference if received power between V component and H component is less than the antenna XPD value, the link performance will be affected with any small fading or interference power, So, we must ensure that V receive min power from the opposite H and vice versa. The rectification of the previous points: 1- Total antenna alignment as we used to do. 2- If found interference after full alignment, planning action must be taken from design team, change the interfering frequency or the victim frequency (our link). 3- If the difference bet V and H is not greater than or equal the XPD value of antenna, need XPD Adjustment. If no problem in the previous points, preventive action must be taken against each case. How to make interference test: (as we usual do) After full alignment, we have to turn off (or mute) one side completely and check the RSL in the opposite side. And reverse direction to record RSL from both sides. Let’s agree the threshold in SDH = -90dBm and in SDH XPIC = -95dBm, if we received RSL greater than the threshold (-85 for example) we must take action.
How to make XPD test:
(after interference test, applicable for XPIC links
only) Note: Mostly the master is Vertical and slave (or sub-master) is Horizontal. Let’s consider the following XPIC link:
1- Record the RSL in normal case ( all turned ON ) in both direction and both polarizations: Rxv1, Rxh1, Rxv2, Rxh2 2- Turn off H1, then record the RSL in the opposite direction: Rxv2’ & Rxh2’. Normaly Rxv2 = Rxv2’ ( no change before and after turning H1 off ). 3- Link XPD = Rxh2 – Rxh2’, 4- Repeat the test by turning off H2, then V1 then V2 to get another 3 values for link XPD ( if Pasolink plus or V4, No need turn off the master ) Hint, Theoriticaly the 4 values of link XPD are equal and less than 30dBm ( most of Huawei antennas has XPD value 30 dbm ) . 5- If link XPD < 30dBm, link need XPD adjustment.
How to make XPD adjustment:
1- Turn off H1 and monitor H2 ( better to use LCT instead of PNMT as it has faster refresh rate ) 2- Let the technician disconnect the antenna horn partially ( just to allow a small rotation ) 3- Rotate the horn carefuly ans slowly ( clockwise or anti-clockwise ) to scan 3 or 4 degrees maximum, till reaching the min value of H2. 4- If not achieved 30 dBm difference ( in H2 reading before and after turning H1 off ), rotate the other antenna horn till achieve 30 dBm difference. 5- Recheck No change in the other V reading. And recheck turning H2,V1 and V2 off.
