HCMP or Multiple PTP links, which is the best option ?

Hi ,

In this post we are going to provide guideline for chosing between HCMP mode depolyment to using traditional multiple PTP links specifically focused for PTP 670 / PTP 700 . Using both mode have their own strategic advantage w.r.t cost, time to deploy, radio resource, debugging, radio updates etc , so we will focus on advantages of each mode of deployment and address any specific downfall as well.

Advantages of HCMP

1. Lower overall cost: Much less equipment is needed at the hub node when using HCMP. For example, a star topology with four PTP links needs four ODUs at the hub, whereas HCMP needs one ODU and a sector antenna. HCMP reduces the overall cost of equipment purchased and the cost of tower space.

2. Less space needed on the tower at the hub site: This might be an advantage if space is limited. For example at an architecturally or environmentally sensitive site.

3. More flexible allocation of resources: The total capacity of the Master can be divided unequally between the Slaves, and the allocation of resources can be reconfigured from time to time to adapt to changing traffic patterns.

4. Dynamic allocation of resources: If a Slave is configured but not in use, its share of the Master capacity can be redistributed to the active Slaves.

5. Ad hoc networks: It is more straightforward to build a temporary network in an evolving or tactical situation. A link can be installed by a single technician working at the Slave end. The capacity of the Master can be allocated to individual users as required.

HCMP makes sense in an infrastructure application where space at the hub is limited, and links are relatively short. For example, to interconnect buildings used by an organization in a city or on a campus, to interconnect small-cell base stations, or to interconnect camera towers.

HCMP also makes sense in ad hoc or tactical deployments such as disaster relief, emergency response or military operations.

Advantages of multiple PTP links

1. Higher efficiency: This arises in two ways. First, the wireless interface in HCMP has only about 80% to 90% of the efficiency of PTP, given the same modulation modes. Also, higher antenna gain at the hub end of the PTP link can allow lower link loss and thus the use of higher modulation modes compared with HCMP.

2. Higher maximum capacity: HCMP supports a single 40 MHz channel, where the aggregate capacity of the Master is divided between the connected Slaves. A multiple PTP topology could use up to 45 MHz of spectrum in each link, resulting in much higher aggregate network capacity. However, it is very rare for any site to have access to unlimited spectrum, so this advantage will not frequently be realised in practice.

3. Lower interference at the hub site: Multiple directional antennas controls interference better than one sector antenna.

4. More advantageous regulatory rules: In FCC U-NII bands, PTP links are allowed to use higher EIRP than PMP. However, in most other regulatory domains there is no distinction between PTP and PMP.

Multiple PTP makes sense in fixed infrastructure deployments needing very high capacity, or very long range, and where sufficient space is available on the tower at the hub site.

Please let us know if you have any questions related to this topic or real world deployment query (HCMP vs PTP) as well