From the ePMP and PMP 100 Co-location and migration recommendations guide available here.
The strategy to migrate an FSK network to an ePMP network depends on the specific deployment of the original FSK network. Factors like number of sectors per site, frequency reuse, and guard band between adjacent channels, all affect the migration strategy.
In this section some examples of migration strategies are described. The first three examples assume the typical FSK deployment with six sectors per site, using three channels. The last example assumes an FSK deployment with four sectors per site, using two channels.
Note that both the FSK system and the ePMP system recommend the use of a 5 MHz guard band between adjacent channels used in adjacent sectors. This section assumes that this guard band is used.
Example 1: 6-sector FSK to 6-sector ePMP
In this example, the existing FSK system is deployed using six sectors and three frequencies. At the end of the migration, the ePMP system also uses six sectors and three frequencies, keeping the same center frequencies and frequency planning, as shown in Figure 14.
Figure 14 - Migration from 6 FSK sectors to 6 ePMP sectors
For this migration, the FSK sectors can be replaced, one by one, with ePMP sectors using a 60⁰ sector antenna and the same 20 MHz channel bandwidth. Note that Cambium Networks offer a 90⁰ and 120⁰ sector antenna options, but any antenna with the right specifications for co-location, including a high front-to-back ratio, can be used with the connectorized ePMP AP.
Note that the front-to-back ratio of the AP antenna required for back-to-back operation of FSK APs on the same frequency is not has high as the front-to-back ratio required for back-to-back operation of OFDM APs. The reason is that the OFDM AP can operate at higher order modulation, which requires a lower interference level. For this reason, it is recommended to replace the two back-to-back APs using the same frequency at the same time, or within a short period of time. For the time during which two back-to-back sectors on the same frequency use an FSK AP on one side and an ePMP AP on the other, the ePMP AP performance is expected to be affected by the additional noise generated by the FSK AP.
Example 2: 6-sector FSK to 4-sector ePMP
In this example, the existing FSK system is deployed using six 60⁰ sectors and three frequencies. At the end of the migration, the ePMP system uses four 90⁰ sectors and two frequencies, as shown in Figure 15.
Figure 15 - Migration from 6 FSK sectors to 4 ePMP sectors
For this migration, first replace the FSK APs on one of the frequencies (60⁰ sectors), for example frequency B, with ePMP APs also on frequency B (90⁰ sectors). Note that the FSK SMs at the edge of the cells covered by frequencies A and C now experience interference from the ePMP AP on frequency B. However, if the correct guard bands are used, this interference level is very low and it does not affect the regular operation of the FSK system.
Also, as explained above, it is recommended to replace the two back-to-back APs on the same frequency within a short period of time to achieve the full capacity of the ePMP system.
Next, replace the FSK APs on frequencies A and C with ePMP APs on either frequency A or frequency C. Note that the ePMP APs will now have a different orientation compared to the two original FSK APs.
Note that the ePMP system after migration only uses two of the original three channels. After the migration is complete, the operator can:
- Use the third unused channel to update the frequency planning
- Widen either used channel to a 40 MHz channel
Example 3: 6-sector FSK to 3-sector ePMP
In this example, the existing FSK system is deployed using six 60⁰ sectors and three frequencies. At the end of the migration, the ePMP system uses three 120⁰ sectors and three frequencies, as shown in Figure 16.
Figure 16 - Migration from 6 FSK sectors to 3 ePMP sectors
For this migration, first replace two adjacent FSK APs on frequencies A and B with one ePMP AP on either frequency A or B, using a 120⁰ sector antenna. Note that the orientation of the ePMP AP is different from the orientation of the original FSK APs. One ePMP sector now covers the area originally covered by two FSK sectors.
Next, replace two adjacent FSK APs on frequencies B and C with one ePMP AP on frequency C, using a 120⁰ sector antenna. Again, one ePMP sector covers two of the original FSK sectors, and the orientation of the ePMP AP has to be changed to point towards the middle of the new 120⁰ sector.
Finally, replace the two remaining adjacent FSK APs on frequencies A and C with one ePMP AP on frequency A, using a 120⁰ sector antenna. As before, one ePMP sector covers two of the original FSK sectors.
As explained above, if during migration one ePMP sector operates with an FSK sector using the same frequency facing the opposite direction, the ePMP sector will experience additional interference until the FSK sector is replaced by an ePMP sector.
The three ePMP channels are 20 MHz wide, like the original FSK channels.
Example 4: 4-sector FSK to 4-sector ePMP
In this example, the existing FSK system is deployed using four 90⁰ sector and two frequencies. At the end of the migration, the ePMP system also uses four 90⁰ sectors and two frequencies, as shown in Figure 17.
Figure 17 - Migration from 4 FSK sectors to 4 ePMP sectors
This migration is similar to the one shown in Example 1, but with 90⁰ sectors instead of 60⁰ sectors. Each FSK AP is replaced by an ePMP AP with a 90⁰ sector antenna, using the same frequency and channel bandwidth. Again, back to back operation of an FSK AP and an ePMP AP should be avoided.