HUAWEI RTN600 XPIC RADIO IMPLEMENTATION1) INTRODUCTION In a project in ‘P’ country, Huawei RTN600 XPIC radio is used to serve as aninter-province backbone for transmission network. None of engineers involved in this projecthave experience on this type of radio before and were having hard time in finding source ofreference. Therefore, it is hoped that this article could help by providing reference for otherengineers for implementing Huawei XPIC radio in other projects in future.2) PREPARATION First of all, we need to have a good understanding on how XPIC system works. There area lot of documents that discuss in theory of how XPIC system works. Therefore, there is noneed to elaborate further on that. Good reference can be easily found in Huawei supportwebsite (http://support.huawei.com). Secondly, we need to identify the difference in term of hardware of XPIC radio. For start,XPIC radio does not use IF card. It uses IFX card. Figure below shows an example of IFXcard: Figure 1: Front Panel of IFX Card At a glance, it is basically same as IF card except with 2 additional ports (as shown in redcircle) which represent ‘XPIC in’ and ‘XPIC out’. Details of how these ports should beconnected are shown in details in figure below: Vertical T Horizontal STANDBY MAIN STANDBY MAIN IFX (NCD-01-0004) M V I O IFX (NCD-01-0004) S V I O IFX (NCD-01-0004) M H I O IFX (NCD-01-0004) S H I O IDU 1 PXC SD1 1 2 PXC SCC Figure 2: Four IFX boards being used to create one 1+1 HSB XPIC configuration
From figure 2 we can see that 4 IFX boards being used to create a 1+1 HSB XPIC linkswhich provides 2 STM-1 link capacity. IFX board in slot 5 provides the 1st STM-1 while IFXboard in slot 7 provides the 2nd STM-1. These 2 boards go to different polarization at antennaport. As XPIC system works by cancelling interference produced by opposite polarization, weneed to let these 2 boards communicate. This is where this XPIC port comes into place. As wecan see from Figure 2, ‘XPIC port in’ on IFX in slot 5 is connected to ‘XPIC port out’ on IFXboard in slot 7 and vice versa. This is how to connect the XPIC ports. The connection is madeby using XPIC cable. By standard, 2 pairs of IFX cable should be supplied for each IDU. One isshort cable while the other one is long cable. Short cable is used for XPIC port connectionbetween slot 5/7 or 6/8 while the longer one can be use for XPIC connection between slot 5/6or 7/8. Next are outdoor equipments. For XPIC microwave link, dual polarized antenna is usedinstead of single polarized antenna. Dual polarized antenna can be identified from the numberof input port at the back. There will be 2 input ports, one for vertical and one for horizontal.Arrangement of these ports may be different according to different manufacturer and antennaspecifications. For example, picture 1 and 2 shows the difference in input port arrangement forAndrew VHLPX series and Andrew HPX series: Vertical input Horizontal input Picture 1: Input Port for Andrew VHLPX series
Vertical input Horizontal input Picture 2: Input Port for Andrew HPX series As we can see from both pictures above, there are no clear labels to indicate the directionof polarization for each input port. Therefore, before deploying installation teams, informationon which input port belongs to which polarization should be clearly relayed to team leaders. Also, since there will be at least 2 ODU attached to each antenna, clearly there is nospace for direct mount configuration. Therefore, ODU adapter and waveguide are required forODU-antenna connection. Picture below shows how the ODU-antenna is made for XPIC radio: Flexi waveguide ODU adapter Picture 3: Example on ODU-Antenna Connection for XPIC Radio
3) IMPLEMENTATION Implementation steps for RTN600 XPIC system are basically the same as for normalradio except when it comes to alignment and software configuration. Before starting, it isgenerally easy for anyone to make mistakes with IF cable-ODU or ODU-Antenna connectionespecially if 1+1 configuration are involved. There is no other way to avoid this except properlabeling and understanding of the system. Therefore, it is important to stress once again, briefexplanation to installation team and proper labeling guide will help a lot in XPIC radioinstallation. Proper labeling should clearly mention polarization and main/standby. Labelsshould be placed on IFX board, IF cable, ODU and waveguide. After all connections physically checked and verified, equipment can be power up andstart with initial configuration before proceed with antenna alignment. As this document willonly focus on XPIC related configuration, all other configurations such as NE and serviceconfigurations are going to be omitted. For details of these configurations, please refer to RTNconfiguration guide available from Huawei support website (http://support.huawei.com). We will use link configuration as shown in Figure 3 as an example. IDU A and B refer tosite A and B respectively. To start with, we need to configure IFX board and ODU. In this stage,just configure the IFX and ODU with all parameters such as IFX working mode, transmitfrequency, transmit power and TR spacing according to link budget. Don’t create IFX group orprotection group yet. We just need to play around with ODU switch or mute function whiledoing the alignment.
Vertical Vertical MAIN MAIN Horizontal Horizontal Vertical Vertical DIVERSITY DIVERSITY Horizontal Horizontal IFX (Standby Vertical) I O IFX (Standby Horizontal) I O IFX (Standby Vertical) I O IFX (Standby Horizontal) I O IFX (Main Vertical) I O IFX (Main Horizontal) I O IFX (Main Vertical) I O IFX (Main Horizontal) I OIDU A IDU B PXC SD1 1 2 PXC SD1 1 2 PXC SCC PXC SCC Figure 3: Sample of Board Arrangement for 1+1 SD XPIC Link V H Figure 4: Vertical and Horizontal Polarization
For alignment, there are different opinions whether to start with vertical or horizontal.Practically, it does not matter because the purpose of initial alignment is just to get dishes fromboth sites aligned. In this document, we will choose to start with vertical. There is no specificreason, just author’s preference. So, we shall start aligning main dish of site A to main dish ofsite B. To do this, ODU for standby vertical (IDU slot 7), main horizontal (IDU slot 6) andstandby horizontal (IDU slot 8) should be turned off, on both sites. Then proceed withalignment as usual. After both main dishes are aligned, next is aligning standby dish of site B to main dish ofsite A. Same thing to do. Only turn on vertical ODU. In this case, it would be IFX board on slot5 in IDU A and IFX board on slot 7 in IDU B. In SD link, main dish is aligned to main dish onopposite site while standby dish is also aligned main dish on opposite site. Due to this, leavethe main dish on site A ‘untouched’ and only aligned the standby dish on site B. Next, we canrepeat the same thing with standby dish on site A aligned to main dish of site B. After alignment is done, we will come to a stage where it is only unique for XPIC system. Itis called ‘feed horn tuning’. To further explain about why we need this ‘feed horn tuning’,please refer to Figure 4. We need to remember that this is how the wave is coming out fromthe antenna. Both waves with different polarization are transmitted at the same time. So,besides aligning the antenna, we need to align these 2 polarizations as well. What it means by‘aligning the polarization’ is that we need to ensure that horizontal and vertical waves areseparated by 90º. If not, horizontal wave will introduce interference to vertical wave and viceversa. The key of successful feed horn tuning is understanding on how XPIC system works andgood communication between team on top of the tower and team below the tower (with thelaptops). Referring back to our example (Figure 3), we should start with feed horn tuning formain antenna. To perform feed horn tuning, one site need to transmit only on vertical, and theother site need to transmit on horizontal. In this case, we will transmit vertically on site A andtransmit horizontally on site B. The respective IFX board to use is IFX board on slot 5 in IDU Aand IFX board on slot 6 in IDU B. The receive level should be differ by -30dB from what weplanned RSL in link budget. For example, if planned RSL is -35dB, we should get -65dB RSLon each antenna. In voltage conversion, if RSSI during vertical to vertical alignment is 3.8V,we should get half of it which is 1.9V. 30dB difference denotes half of the value in RSSI voltagereading. If we cant get the required RSL (with 30dB difference), then the feed horn of theantenna need to be adjusted. It can be adjusted by loosening the screw that holds theantenna’s feed horn. This will normally allow fine adjustment around +/- 5º. For example,Picture 4 and 5 will show which parts in Andrew antenna VHLPX series and HPX series thatneeds to be loosen up in order to perform the feed horn adjustment. By loosening up the screws, minor adjustment to feed horn can be done. By this time,RSSI and RSL value should be closely monitored until required value is obtained.Theoretically, the difference in RSL between vertical and horizontal polarization is called‘Cross Polarization Discrimination’ (XPD). XPD value is usually determined by antennaspecification. Some high XPD antenna has the XPD value up to 40dB. If the required XPDvalue can’t be achieved, received signal from opposite polarization will cause interference.Common symptoms are wrong received link ID and generation of MW-LOF alarm. After feedhorn tuning for main dish on both sites are completed, we can proceed with the standby dish.
Rotate +/- 5º adjustment Screws that hold feed horns. Loosen up these screws to allow feed horn adjustmentPicture 4: Feed Horn Adjustment for Andrew Antenna VHLPX Series Screws that hold feed horns. Loosen up these screws to allow feed horn adjustment Picture 5: Feed Horn Adjustment for Andrew Antenna HPX Series
Next will be software configuration. The only difference between XPIC radio and normalradio is that we have to create XPIC workgroup. However, it is advised to configure 1+1protection group first before configuring XPIC workgroup so that XPIC workgroup only need tobe created for one time. To configure XPIC workgroup, we need to identify which IFX boardbelongs to which polarization. By right, this should be determined at the very beginning of theinstallation. Nothing complicated with creating XPIC workgroup. It can be found under ‘linkconfiguration’ menu in Web LCT or T2000. As shown in Figure 5, other information should beavailable from link budget. Additional information required is only the corresponding board forvertical and horizontal polarization. Also note that by default the link ID for vertical is 1 andhorizontal is 2. After everything are configured, one should go back to ‘link configuration IF/ODUrelation’ and check whether the received link ID matched for every IFX board. Vertical shouldreceive 1 and horizontal should receive 2. If vertical is receiving 2 or horizontal is receiving 1, itmostly caused by 2 things. First is low XPD value which requires feed horn to be readjusted.Most common mistake that usually this is forgetting to tighten up the feed horn screw after feedhorn adjustment. Second is faulty IFX board. However, check and recheck the XPD valuebefore replacing any IFX board. To check the XPD value, we can play around withmute/unmute function on ODU or just switch off the ODU of opposite polarization. Also, we need to monitor the stability of the received link ID for +/- 10 minutes. It shouldbe stable and not changing from 1 to 2 or otherwise MW-LOF alarm will popped up. Figure 5: XPIC Software Configuration Example
4) SUMMARY In summary, all the steps above, to configure link as in Figure 3 for our example, can besummarized in the table below: Site A Site B Check all the cable connection Configure IF/ODU (without XPIC and 1+1 protection group)Power on ODU main vertical (IFX slot 5) Power on ODU main vertical (IFX slot 5) Main to main alignmentPower on ODU main vertical (IFX slot 5) Power on ODU standby vertical (IFX slot 7) Main to standby alignment (only move standby dish)Power on ODU standby vertical (IFX slot 7) Power on ODU main vertical (IFX slot 5) Standby to main alignment (only move standby dish)Power on ODU main vertical (IFX slot 5) Power on ODU main horizontal (IFX slot 6) Feed horn tuning for main to main dishPower on ODU main vertical (IFX slot 5) Power on ODU standby horizontal (IFX slot 8) Feed horn tuning for main to standby dish (only tune standby dish)Power on ODU standby vertical (IFX slot 7) Power on ODU main horizontal (IFX slot 6) Feed horn tuning for standby to main dish (only tune standby dish) Power on all ODU Create 1+1 protection group Create XPIC workgroup Check all the RSL and received link ID. Also monitor the stability. Table 1: Summary of Implementation Steps of XPIC Link