FOA Guide to Fiber Optics

Topic: Comparing DAS, Small Cells And WiFi

Table of Contents: The FOA Reference Guide

Comparing DAS, Small Cells And WiFi

If you say "wireless" to an IT or LAN person, they think WiFi. But to a telecom person. wireless means cellular. FOA's involvement is based on trying to understand the infrastructure to support wireless, OSP or premises, WiFi or cellular, tower site or small cell. We're basically outsiders on the technology side looking at how to provide the infrastructure to support them. Recently we've been trying to understand the technologies, markets and applications for both to better include the two technologies in our training and certification programs.

The initial question we had dealt with was how to distinguish DAS (distributed antenna systems for cellular) and small cells (also cellular). In most ways they seem to be very similar, except perhaps DAS is indoors and small cells outdoors. But perhaps more importantly, a DAS is usually owned by the owner of the space (building, sports facility, etc) and handles multiple service providers while small cells are owned by a service provider and carries only their service.

WiFi is generally owned by the enterprise that is using it as part of their LAN - a company or organization - and is not shared except with their employees and/or guests.

The biggest difference is costs to the users - WiFi is generally free but all cellular systems are charged by time and/or data usage. But cellular is mobile wireless - designed to serve users moving around so it can seamlessly pass a user from one cell site to another. WiFi however, assumes the user is staying within it's range and may have to log in to another WiFi access point if they move around. That mobility aspect of cellular takes some additional overhead, so WiFi generally has more bandwidth.

We've interviewed insiders in both technologies to try to understand how they work and why we should have so many options. Right off, we found that there appears to be a general lack of technical understanding about the other from almost everybody we talk to who works with one of them. And we're talking real basics - what frequencies are used, protocols, coverage, bandwidth, etc. etc. etc. Even the jargon is different, but that's not unexpected. So we've tried to consolidate information on the three different premises wireless technologies appropriate for general usage. Over time we expect to refine this comparison with more data and user feedback. (got any? send it to us)

Based on the current evaluation, WiFi is essential to premises spaces and because of the ubiquity of WiFi, it is inexpensive. However, WiFi connections for cellular mobile devices appears to have not yet been refined sufficiently to provide reliable coverage for cellular voice, but data is good and video, maybe. Given the cost structure of data plans, using cellular for video can be very expensive but WiFi is preferable since it is only limited by bandwidth.

The choice between small cell and DAS in premises spaces is simple - small cells are generally single carrier connections and that is too limiting for most users. DAS is similar technology but has the advantage of offering multiple service providers. If better cellular service is desired indoors and WiFi connections for cellular calls is unreliable, a DAS is the best solution.

Small cells appear to be a good solution for better cellular service outdoors in metropolitan areas but the capital costs for building systems is quite high - Deloitte, you might remember from an earlier FOA Newsletter, forecast a cost of over $200 billion. It makes one wonder if the carriers can make that investment while simultaneously investing in 5G.

Premises Wireless
WiFi DAS (Cellular)
Small Cell (Cellular)
Connects to: PCs, tablets, phones, many other devices Phones, tablets, some other devices Phones, tablets, some other devices
Usage Free, sponsored Paid Paid
Origin Private, LAN Public, telco Public, telco
Frequency Ranges Unlicensed
2.5GHz (802.11n, 14 - 40MHz channels, 3 max non-overlapping)
5GHz (802.11ac or 802.11n, 24 -  80 MHz channels, 23 max non-overlapping)(more bandwidth, less range)
3G:  850, 1700, 1900, 2100 MHz
4G/LTE:  600, 700, 850, 1700, 1900, 2100, 2300, 2500 MHz
CBRS (Citizens band Radio Service, shared, unlicensed): 3600 MHz, 20MHz channels,
5G: Eur: 24-27GHz, US: 37-48GHz, 71-74GHz
3G:  850, 1700, 1900, 2100 MHz
4G/LTE:  600, 700, 850, 1700, 1900, 2100, 2300, 2500 MHz
CBRS (Citizens band Radio Service, shared, unlicensed): 3600 MHz,
20MHz channels,
5G: Eur: 24-27GHz, US: 37-48GHz, 71-74GHz
Connects to: Internet Multiple telco carriers Single telco carrier
Mobility Log in to each new private system required, limited handoffs between WiFi systems or WiFi and cellular
Seamless handoffs Seamless handoffs subject to coverage
BYOD (bring your own device) OK OK Depends on service provider device connects to
Optimized for Data 3G: voice
4G/LTE/5G: data
3G: voice
4G/LTE/5G: data
Data: Max data rate: 802.11n: ~35-300Mb/s
802.11ac: ~400Mb/s - 7 Gb/s (MIMO)
4G/LTE: ~100Mb/s
5G: ~Gb/s (proposed)
4G/LTE: ~100Mb/s
5G: ~Gb/s (proposed)
Voice VoIP: good
Cellular on WiFi: not optimal, depends on device/carrier/implementation
Good with proper coverage Good with proper coverage
Video Good 4G/LTE: marginal, expensive
5G: Good (proposed), cost?
4G/LTE: marginal, expensive
5G: Good (proposed), cost?
Cabling (typical)
Fiber backbone to Cat 5, POE
Fiber, sometimes Cat 5
Fiber, sometimes Cat 5
Best for data on PCs, tablets, smartphones, good for VoIP systems, marginal on cellular devices
Best for cellular devices since can cover all service providers, not optimal for high throughput data (today, future 5G ?)
Good for cellular devices but can cover only one service provider, not optimal for high throughput data (today, future 5G ?)

Understanding 5G And 802.11ax

Within all the hype about 5G, one finds little technical details. It's either how great it's going to be or worries about the health effects. Finally, we've found some technical explanations that deal with the actual technology and why it's possible to have higher bandwidth. Interestingly, it's a lot like 802.11ax, the latest version of WiFi.

Our information on 5G came from iBwave's white paper "5G Technology Primer."  For 802.11ax, this page on technology from Ruckus called
802.11ax Fundamentals was our source. We highly recommend you read these these papers to help understand these two systems.

First, we should look at frequency ranges, what has been the center of most discussion about 5G. 5G has two frequency ranges within which cellular service providers have frequency bands licensed to them exclusively. The band now called FR1 is 450MHz to 6000 MHz and the new band is FR2, 24,250 MHz to 52,600 MHz, or as it is mostly described, 24 to 52GHz. It's the new high frequency band that has attracted most of the attention since it is more affected by the environment and more readily absorbed, with the health effects causing much controversy.
802.11ax works at the same frequency bands as earlier version of WiFI, unlicensed bands around 900MHz, 2.4 and 5GHz, although the 2.4 and 5GHz bands are generally used and the other frequencies are for specialized applications, new tech (e.g. WiGig at 60GHz) or are licensed bands. The higher frequencies are desirable because higher frequencies mean more bandwidth as described by Claude Shannon at Bell Labs 70 years ago. Higher frequencies are also problematic because they are more highly absorbed, shortening link distances and preventing signals from penetrating walls or glass for example.

The other way to send more information is to use more efficient protocols. The copper people found out long ago that one could put more information in one bit by also encoding data in the pulse height, optical transmission can also use polarization. Wireless - both cellular and WiFi - is migrating to OFDMA which stands for Orthogonal Frequency-Division Multiple Access. Both cellular and WiFi appear to operate similarly. The system can subdivide frequencies into subchannels and then divide up frames using time division multiplexing to allocate bandwidth where it is needed. Much of the additional throughput seems to come from using this option to dynamically allocate bandwidth. 802.11ax is expecting a four-fold increase in throughput.

802.11ax is using access point intelligence to manage overlaps in coverage to maximize throughput. 5G meanwhile, probably willing to spend more money on systems, appears to have decided to use phased-array antennas, where beam steering and shaping can be done dynamically to maximize signal transmission.

All this complicated tech probably shows why the 5G advocates focus on the higher frequency transmission - explaining these concepts is not easy. But what's surprising is that 5G and 802.11ax are so similar, focused on similar goals, with seemingly the biggest difference is one is on licensed frequencies and the other unlicensed. Why do we need both? Why does a building need to have both a WiFi system and a DAS? Why doe we nead outdoor WiFi? Practically every phone or tablet has the capability of connecting to either and laptops can do the same with a simple plug-in module.  Anybody care to comment?

Learn more about how small cells and other technologies contribute to "smart cities."

More On Fiber For Wireless
FTTA- Fiber To The Antenna  
Testing FTTC Fiber  
DAS - Distributed Antenna Systems  
WiFi - Premises Wireless  


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