How to properly design and deploy an airFiber NxN system?
airFiber NxN technology offers you flexibility to deploy dozens of collocated radios on the same tower. And, using the airFiber NxN Multiplexers you can install several radios on a single antenna maximizing your infrastructure utilization and reducing operational costs, while adding extra capacity and redundancy to your wireless links. To achieve maximum performance and avoid issues, it is very important to properly design your system and consider key factors like: multiplexer signal loss and select the right hardware to do the link aggregation.
Link Budget: Design example
airFiber NxN Multiplexers allow you to use several radios (2 or 4 depending on the multiplexer model) on a single antenna, offering higher performance and redundancy to your links. However, since multiplexers are passive devices there are signal losses involved, and they must be considered in your link budget. The MPx4 (2 radios multiplexer) has a 4.1dB loss and the MPx8 (4 radios multiplexer) has 7.2dB loss, these signal losses can be entirely or partially mitigated depending on the link distance, antenna gain and required capacity.
For example, if you have an existing AF-5X link with AF-5G30-S45 antennas running at 47dBm EIRP, with antenna gain set to 30dBi and specified cable loss of 3dB (I am very conservative with my calculations so prefer to add 3dB for safe margin), which means that the Tx Power is 20dBm (Suggested Max Tx Power for 8X modulation – check radio’s datasheet for other values). And the received signal in both radios is -60dBm (which is the minimum required signal level for 8X modulation @50MHz channel width – check radio’s datasheet for other values). With this configuration, you can get around 500Mbps of REAL aggregated throughput using only 50MHz of spectrum.
Note: This example assumes no interference, if your radios receive interference you should add that value in your calculations to keep the minimum received signal value.
Now you want to offer redundancy and increase capacity, so you will install a MPx4 [2 radio multiplexer]. Let’s see two cases: keeping original antennas and upgrading antennas.
Keeping original antennas
In this case, you must add an additional 4dB loss on each side. Keeping the original EIRP level [47dBm] the radio can now transmit up to 24dBm (antenna gain 30dBm and cable loss now will be 7dB including the safe margin). We have added 4dB of extra power, but the total signal loss introduced by both multiplexers is 8dB, so the new received signal will be -64dBm (which is better than -67dBm, the minimum required signal for stable 6X modulation). Unfortunately using 24dBm of Tx Power we would be limited to 4X modulation, but reducing the Tx Power to 22dBm you can achieve stable 6X modulation, so you reduce Tx Power by 2dB, and now the EIRP level will be 45dBm, and the received signal would be -66dBm (which is enough for stable 6X modulation) and we can get around 380Mbps per link, and since now you have 2 links the total aggregated capacity would be 760Mbps and we also have the advantage of having link redundancy.
In this case, you will use the AF-5G34-S45 antenna (34dBi antenna gain), so now the multiplexer signal loss (-4dB) will be entirely compensated by the higher antenna gain (+4dB), so the EIRP level will be the same 47dBm with Tx Power of 20dBm (which is the suggested Max value for stable 8X modulation). And the received signal will still be -60dBm (which is the minimum suggested signal for stable 8X modulation), so now you keep the original capacity per link (around 500Mbps of REAL capacity), but since you have two links the maximum capacity can reach up to 1Gbps of REAL capacity, plus the benefit of link redundancy.
Interesting case: If you currently have an existing AF-5X link using AF-5G34-S45 antennas, with Tx Power of 20dBm and the received signal level is -60dBm. What can I do if I want to double the capacity? You can install another pair of AF-5G34-S45 antennas and AF-5X radios, and enable NxN checkbox in the Wireless tab of all 4 radios. With this special configuration, you don’t use any Multiplexers, but you enable the NxN mode with two separated physical links, it means using 4 radios and 4 antennas.
We have the RF part covered, now let’s decide how you will aggregate the bandwidth, there are basically two options: Layer 2 or Layer 3 aggregation.
Choosing the right aggregation method?
If you have a bridged network you should choose Layer 2 Aggregation, this means you need one LAG/Bonding-capable switch on each side. I personally recommend using the EdgePoint S16 (EP-S16) because it is a managed L2+ switch with High-Power (4 pairs for power and data) PoE outputs, so you can connect directly each AF-5X to the EP-S16, no need for external PoE Adapters.
On the other hand, if you have a routed network you probably choose Layer 3 Aggregation, this means a Load-Balancing-capable router on each side. I personally recommend using the EdgePoint R8 (EP-R8) because it is a very powerful router with advanced Load Balancing capabilities and with high-power PoE outputs, so you can connect directly each AF-5X to the EP-S16, no need for external PoE Adapters.
How to install a successful NxN system: RF part
First make sure all airFibers are running the latest firmware. Also, check that there is clear LoS (Line of Sight) and both antennas are properly aligned, which means that the current received signal should match with the expected received signal. Once the link is properly aligned, you need to choose the frequencies you will use, always try to use the cleanest available frequencies. You can easily identify them running airView for a few minutes.
Remember that selected frequencies should NOT overlap between each other, this means if you use two 50MHz channels, you can use 5500MHz and 5551MHz channels, because the first channel [5500MHz] will operate between 5475MHz and 5525MHz, and the second channel [5551MHz] will operate between 5526MHz and 5576MHz.
But you cannot use for example, channels 5500MHz and 5540MHz if both are 50MHz channel width, because they will overlap between 5515MHz and 5525MHz creating self interference. However, if you use 30MHz channels they won’t overlap because the first channel [5500MHz] will now operate between 5485MHz and 5515MHz and the second channel [5540MHz] will now operate between 5525MHz and 5565MHz.
How to install a successful NxN system: Aggregation part
If you are going to aggregate traffic based on Layer 2 Aggregation, you need to run 2 Ethernet cables per radio: one cable should be connected to the DATA port and will be member of the switch’s LAG/Bonding group; and the second cable should be connected to the radios’ Config port and WILL NOT be part of the LAG/Bonding group, but will be use only to access radio’s management interface. Note: Once DATA ports are added to a LAG group you will lose access to the radios’ management if they are not connected to a switch/router via the Config ports.
On the other hand, if you will aggregate traffic based on Layer 3 Aggregation, you need to only run one cable per radio, which must be connected to the radio’s DATA port. If you use an EdgePoint R8 or EdgeMax Router, you can easily configure the Load Balancing. To do that click on the EdgeRouter’s “Wizards” tab and select “Load Balancing 2”, specify the Ethernet interface where each radio is connected and enter the radio’s IP address on each field, then click on the Apply button.