Xpic Wb

Case Study: XPIC implementation in Maxis WB While we were implementing XPIC in Maxis West Bengal, we faced some technical issues with 7GHz XPIC links and found their workaround. This is the e-mail discussion with transmission department. 1) In 1+0 mode the HCC alarm raises and far end disappears. Reason: HCC generated due to co-channel interference. 2) Traffic disturbing alarm appears when we define in 1+1 Hot Standby. Most common alarms are: A) LOF R2L B) HCC C) Early Warning D) High BER E) IF LOS R2L F) Remote TX Switchover G) Unable to protect The order they appear is random. With these alarms the link fails to carry traffic. We checked all the H/W and done various loop test, found no problem. No XPIC specific alarms appear. Reason: Alarm A,B,C,D,E are related to interference on the non-traffic carrier signal, hence switch-over could not have happened on the stand-by radio at the near-end. 3) We found no option for space diversity (1+1SD). Reason: There is no such option for commissioning the hop with 1+1 SD. SD is a passive feature not related with MMU or RADIO configuration. 4) In some cases link carries traffic without any alarm if vertical and horizontal radios assigned different frequencies. Reason: Co-channel interference gets eliminated by applying 2 different frequencies. 5) All the alarms that come in 1+1 Hot Standby disappears if we define 1+1 Working Standby and link runs fine. Reason: In working stand-by, 2 different frequencies are used. Hence, co-channel interference does not occur. 6) We were using R12B14 SBL in one side and R12A51in other. Radio is RAU1N All 15 GHz XPIC were implemented in RAU2X and we did not face such problems in 15 GHz. Reason: The mounts were installed upright in 15GC hops!!

7) Line protection is required in MMU2F because if working MMU becomes faulty then traffic goes down. Standby MMU takes the traffic but to make that work we need to define MSP in OMS also.

General It’s very interesting to know that this problem is caused due to the improper installation of mounts on which these antennas are installed. There is nothing wrong in the installation of the hop or in the commissioning but there are other few very important steps to follow before we implement the XPIC hop.

Cause of the problem: Since the XPIC hops are dual polarised hops, there are very high chances that co-channel interference occurs if the alignment between the near-end and farend is not done properly. By properly, means that the Rx level between the Hand V- polarised radio at near end should be more than 27db in a single dualpolarised antenna. If it does not happen, then the traffic will not be through and there will be HCC and other interference related alarms in the hop. One main reason for the co-channel interference in the signal is that there is no proper signal discrimination of H- and V-pol signals between the hop. It is due to the fact that the mounts are not exactly vertical w.r.t to the ground and which gives an angular twist to the antenna and eventually to the radio waves too. When the H- and V- signals of this already tilted antenna reaches the far- end antenna ( which might also twisted from its vertical), the required discrimination of H- and V- waves does not happen. Due to this, there occurs interference in the near end antenna and it gives rise to alarms. So, to eliminate this situation, both the near-end and far-end antennas needs to be aligned w.r.t the Vertical and w.r.t to each other so as to discriminate the cross-polarization. How to do it. 1) For 0.6m dual polarised antenna with integrated splitter. There is polarization adjuster plate provided with each of the antenna (as shown in the attachment).It has to be installed at both the ends. Once the hops are installed, alignment between them has to be carried out in 3 steps. STEP-1: Normal alignment has to happen as to achieve the required planned RX level at both the ends. Both the antennae then should be locked and there should not be any horizontal or vertical movement of the antenna. STEP-2: At far-end, Polarization plate has to be adjusted with the adjuster plate so as to achieve exact level w.r.t the ground. Also, transmitter for H- Pol radio has to be disabled and only the vertical radio transmitter needs to be radiating. This step is known as Mechanical Optimization. STEP-3: At near-end, Voltmeter needs to be attached onto H-polarised radio. Fine tuning needs to be done with the help of polarity adjuster only so as to achieve the difference in the H-

signal and V-signal for more than 27db. Once this is achieved, the hop is ready for traffic loading. This step is known as Cross Polarization Discrimination Optimization. 2) For 0.6m dual polarised separately mounted antenna (polarization adjuster is not provided in this case). STEP-1: is the same as in the above case. STEP-2: Done at the far-end. Since there is no polarity adjuster in this case, the feedhorn at the back of the antenna needs to be loosened and adjusted with the spirit level so as to get the exact level. Also transmitter for H- Pol radio has to be disabled and only the vertical radio transmitter needs to be radiating. (Mechanical optimization) STEP-3: At the near-end, again the voltmeter should be attached with the H-pol radio. The feed-horn needs to be loosened and fine tune needs to be done so as to get the signal separation of more than 27db in between H- and V-pol radios. (Cross polarization discrimination optimization.) N.B: These steps need to be followed with each of the antennas at both the sides one at a time so that signal from 1 antenna does not interfere with the signals from other antenna.