airFiber - Guide to Design & Deploy NxN MIMO Multiplexor

This article describes how to properly design & deploy an airFiber NxN MIMO Multiplexor System, which allows you to combine multiple airFiber X radios on a single dish antenna for superior noise immunity performance, redundancy, and multi-Gigabit Point-to-Point (PtP) throughput.

Note: The airFiber NxN is designed for use with the airFiber 4X and 5X (AF-4X/AF-5x) radios or RocketDish antennas. The airFiber NxN is not recommended for use with the airFiber AF‑5G23-S45 antenna. If using with a RocketDish, the airFiber X Antenna OMT Conversion Kit (AF‑5G‑OMT-S45) is highly recommended for proper fitting

• Introduction
• Link Budget: Design Example
• Keeping Original Antennas
• Upgrading Antennas
• Choosing the Right Aggregation Method
• How to Install a Successful NxN System: RF Part
• How to Install a Successful NxN System: Aggregation Part

Introduction

Our airFiber NxN technology offers you flexibility to deploy dozens of collocated radios on the same tower. Additionally, by 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 selecting the right hardware for the link aggregation and the multiplexer signal loss.

Link Budget: Design Example

The airFiber NxN Multiplexers allow you to use several radios (two or four 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 (two-radio multiplexer) has a 4.1dB loss and the MPx8 (four-radio 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, let's imagine a an existing AF-5X link with AF-5G30-S45 antennas running at 47dBm EIRP. The antenna gain is set to 30dBi and specified cable loss of 1, meaning that the Tx Power is 18dBm*. And the received signal in both radios is -60dBm (which is the minimum required signal level for 8X modulation @50MHz channel width, remember to check each radio's Datasheet for other values). With this configuration, you can get around 500Mbps of REAL aggregated throughput using only 50MHz of spectrum.

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.

Note: * 18dBm is the suggested max Tx Power for 8X modulation, make sure to check your radio's Datasheet for other values. Find the device's Datasheet and other useful documentation at the bottom of each specific product's page (https://www.ui.com/products/#airfiber).

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.

Upgrading Antennas

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.

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, to double the capacity you could 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. The EdgePoint S16 (EP-S16) is a good option 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 would probably choose Layer 3 Aggregation, this means a Load-Balancing-capable router on each side. In this case, you could use the EdgePoint R8 (EP-R8): 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 by 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 used only to access the radio’s management interface.

Note: Once DATA ports are added to a LAG group you will lose access to the radio's 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.