Which A5 is right for me?

By Lee Peterson

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Mimosa’s MicroPoP model is designed to provide game-changing throughput to fixed wireless broadband end users in suburban and urban markets. We’ve seen many of our early customers able to offer services that can burst to 300 Mbps downstream and upstream! At this level, wireless ISPs can legitimately compete with DSL, cable and even fiber. 

Central to Mimosa’s MicroPop deployment model is the A5 quad-sector Access Point (AP). The A5 achieves an omnidirectional coverage pattern, but is much more efficient than a traditional omnidirectional antenna, as it consists of four independent 90° sectors that are able to selectively communicate in the direction of a given client device.

The three most common questions customers have about the A5 are mounting height, coverage radius and number of connected clients per AP, all of which we will address in this blog post. 

The Devil is in the Details

The 14 and 18 in the A5 product name refers to the antenna gain. The physical specifications of each device is below:

Product

A5-14.png

A5-18.png

Height

314 mm / 12.36 in.

668 mm / 26.29 in.

Weight

1.75 kg / 3.85 lbs

2.73 kg / 6 lbs

Gain

14 dBi

18 dBi

Vertical Beamwidth

16°

Downtilt

-4° (electronic)

Many logically assume that they will choose the A5-18 due to the additional gain over the A5-14, but it is not always the right product for every application and it depends on the deployment scenario as to which product Mimosa would suggest should be used. 

Where to Install the A5?

To achieve the highest performance possible in a MicroPop, Mimosa recommends installing the AP as close as possible to the clients. This will typically involve choosing a location within a neighborhood as a hub, where AP and backhaul products can be installed. It is usual in this scenario, for client devices to be installed in nearly the same horizontal plane as the AP. For example, the high point of a roof line might be the logical place for an AP, with Clients mounted near the roofline. This is where it is important to consider not just antenna gain, but antenna tilt. The A5-14 has a 0° tilt and a 16° vertical beamwidth on the main lobe. This is perfect for scenarios where the AP and Client have similar mounting heights above ground level (assuming mostly flat geography) and represents Mimosa’s recommendation for the most suitable application of A5-14 to support MicroPop deployments. 

Impacts of AP Installation Height

As noted, the A5-18 has higher gain than the A5-14, with a narrower beamwidth of 5° for the main lobe and a -4° tilt. The image below shows the math behind the coverage zone for installation of A5-18.

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Based on the A5-18 downtilt design, in order for a client at 600 m to be covered, the AP needs to be mounted 15.7 m higher than the client. This would represent a 4-5 story building, which is unlikely to be common in single family home suburban neighborhoods. At this same mounting height, the main lobe would begin at 138 m and peak at 225 m of horizontal distance. A client may still associate with the AP outside of this range, but on a secondary lobe with lower gain, which may not provide optimal connection quality. 

The table below show the horizontal projection of the main lobe at various mounting heights for the A5-18.

Height Δ AP-Client (m)

Main Lobe Begins (m)

Main Lobe Peak (m)

Main Lobe Ends (m)

5

44

72

191

10

88

143

382

15

132

215

573

20

176

286

764

25

219

358

955

30

263

429

1146

35

307

501

1337

40

351

572

1528

45

395

644

1718

50

439

715

1909

To summarize our mounting height recommendations:

A5-14 – Preferred for similar mounting height of AP and client radio, suitable for installation on hub premises in suburban single family home neighborhoods.
A5-18 – Above mounting height of client radio, suitable for installation on tall buildings, poles, towers or on hillsides.

What About Range?

So now that mounting height considerations are understood, it is necessary to talk about coverage radius. Mimosa recommends that the client to AP distance should not exceed 300m for the A5-14 and 600m for the A5-18. This is not the physical limit of operation for each product, but it represents where each product respectively will achieve the maximum modulation rates. This is important for a few reasons: 

  1. The maximum modulation rates are required to reach the > 600 Mbps aggregate throughout mentioned above (866 Mbps aggregate PHY, MCS 9 @ 80 MHz). Even if the service plans being offered to your end users are much lower than this peak speed, there are many benefits to airtime efficiency that can be achieved by having the clients communicate at the highest rate possible over the air. 
  2. Strong AP to client signals provide a great deal of immunity against noise in the 5 GHz spectrum. Driving a higher signal to noise ratio (SNR) provides additional noise margin to cope with a high noise floor, rain fade or interference events. It also allows the A5 Automatic Gain Control (AGC) feature to be used. This squelches out background noise by tuning the receiver to ignore signals below the client radio’s signal. 

Understanding Client Capacity

The next question this logically leads to is client count. Mimosa included a Gigabit-class network processor in the A5 in addition to the market leading Quantenna 4x4 MIMO chip we also use in our point-to-point backhaul products. This network processor provides the A5 with ample horsepower to handle many clients and the layer 2 through layer 7 features required within an advanced AP. Mimosa has confirmed A5 performance with up to 100 clients, but because A5 airtime is a shared medium, we recommend limiting deployments to 40-50 clients for an optimal user experience with regard to throughput and latency.

It is counter intuitive to many that in the MicroPoP deployment model, the client count loading per AP is often lower than rural fixed wireless deployments. This is due to the lower installation heights versus towers, and reduced number of homes within line of sight due to foliage and flatter elevation. Client counts of below 20 are often typical as a result.

If you’re unsure which A5 is right for you or would like to work with Mimosa on your network design, our support team is available to help you by emailing [email protected] or through live chat at http://help.mimosa.co.