Scalable Indoor Small Cells vs. Extending Macro Cells Indoors

August 31, 2015

Large macro base stations companies have a seemingly attractive offer for wireless operators – “Just use our macro base stations indoors! We can offer you new indoor radio heads that connect to the baseband/digital units you love, and you will be on your merry way.” The problem with this offer is that it is trying to force-fit technology designed for towers and other outdoor environments – called CPRI – into an enterprise environment.

CPRI is a standard designed to carry baseband I/Q samples from the baseband unit to a radio head. CPRI was developed so that base station OEMs could source radio transceiver units from multiple suppliers. Over time, CPRI made it possible for the radio transceivers (radio heads) to be moved from the base station chassis to the tower top, with a fiber optic cable in between. This move to remote radio heads reduced cable losses, and boosted the coverage of macro base stations. All good things.

However, CPRI was never designed to be bandwidth efficient.  A single 20 MHz LTE carrier with 2×2 MIMO requires 4.9152 Gbps of bandwidth to carry CPRI between the baseband unit and each radio head*. Considering that a 20 MHz LTE carrier can deliver up to 150 Mbps on the downlink and 50 MHz on the uplink, CPRI’s bandwidth efficiency is less than 3%. In practice, it is even lower. Some vendors compress CPRI, but compression adds cost and barely increases CPRI efficiency by a factor of 3.

The CPRI approach works fine when there is dedicated fiber between the base station and each radio head, but is not appropriate for buildings. Networks inside buildings are built with switched Ethernet. Enterprises want to connect all kinds of equipment to their Ethernet LAN – from computers and printers to Wi-Fi APs and small cells. The Ethernet LAN is the “neutral host” network infrastructure for the enterprise, and all these devices need to share the bandwidth on the LAN. Over the last 20 years, a wide range of technologies have been developed to share the LAN, from QoS to VLAN, and they were developed for a good reason: it does not make sense for enterprises to go around deploying custom cable infrastructure for every new technology they need.

Some vendors are proposing non-CPRI approaches that split baseband processing between the baseband unit and the radio head,  and are able to work on Ethernet instead of fiber. Such approaches require slightly less than 1 Gbps per radio head to carry a 20 MHz channel. Still, the throughput required on LAN increases linearly with the number of radio heads connected to the baseband unit, making it unfeasible to share the enterprise LAN.

SpiderCloud’s scalable small cell system is the only system that can serve thousands of subscribers in buildings as large as 1.5 million square feet and works on a shared enterprise LAN. In a SpiderCloud system, all baseband processing is done by its small cells, called radio nodes. Up to hundred dual carrier radio nodes are connected to SpiderCloud’s small cell controller, Services Node. The Services Node is responsible for anchoring all the user sessions, managing mobility and interference, and SON. This architecture ensures that the only traffic between SpiderCloud’s small cell and Services Node is actual user traffic, and some few hundred kbps of overhead. In other words, deploying a SpiderCloud small cell system on an Enterprise LAN is no different than deploying an enterprise Wi-Fi system. SpiderCloud’s ability to share the enterprise LAN is one of the main reasons why Cisco selected SpiderCloud to build 3G and LTE modules that clip on to Cisco’s market-leading Aironet Wi-Fi access points.

Finally, let’s consider what happens in the future with LTE-Advanced and 5G. With LTE-Advanced and 5G, operators are looking for ways to use more spectrum and more antennas. The amount of bandwidth required for CPRI scales linearly with channel bandwidth, number of channels and number of antennas. If CPRI-based approaches are struggling to, but are unable to offer 20 MHz LTE on Enterprise LANs, how will they offer LTE-Advanced and 5G? Perhaps, this is the reason why NGMN and many other organizations looking at the future of mobile networks, believe that densification using small cells is the way forward.

* This is how the math works:  30.72Msps (sampling rate) * 15b (sampling width) * 2 (I/Q) * 16/15 (1 control word per 15 data words) * 10/8 (CPRI line coding of 10b/8b) * [2 (for 2 Tx antennas) + 2 (for 2 Rx antennas)] = 4.9152 Gbps. Assuming peak cell throughput of 150Mbps in DL and 50Mbps in UL, the best-case efficiency of CPRI (bandwidth on CPRI link / actual throughput delivered by cell) is less than 3%!

– Amit Jain, Vice President of Marketing & Product Management
Twitter: @SpiderCloud_Inc

“…Just Another Brick In the Wall”?

December 12, 2014

I first heard this song in early December ’79, just after its release, now 35 years ago. We have all rebelled against something or someone at one part in our lives. “We don’t need no thought control” and “Hey! teacher! leave us kids alone!” — Pink Floyd’s music was relevant back then, and it’s relevant now. Roger Waters’s song (Education, Part II) is a protest song against rigid schooling in general and boarding schools.

Behind the brick wall, when you look beyond the one-page “Wall Mounting Kit” for easy to install radio heads (Huawei or Ericsson) you will find the undisclosed pages 2 through 99, and a long list of items needed to make radio heads (DAS) work.

Beyond the simple radio head, you’ll find dedicated cables (CPRI or Cat7a) that are connected to Indoor Radio Units (IRU), which then connects to dedicated Digital Units (DU) with maximum 12 sectors (IRU) per DU for each access technology (LTE or 3G). Each IRU connects to a DU via Fiber and the DU then connects back to the Ericsson RNC (for 3G), or the LTE EPC. Keep in mind that CPRI or Cat7a is not basic Ethernet. Nor can Radio DOT be deployed using existing Ethernet (via VLAN). It takes special handling and expertise to handle Fiber or Cat 7a cables. If you are deploying Radio Dot, Cat7a is not exactly a commonly used cable inside the Enterprise, and can cost 3-4x more per cable than Cat 5/6.

When you are maintaining or deploying DAS, your list of equipment is quite long. A plan could include over 30 different components, special cables and modules.

  • Coax, connectors, splitters or special cabling (Cat7a) which requires special handling
  • Cross band couplers, optical interfaces, boosters, housing panels, etc.
  • Master unit for optical Tx/Rx
  • Power supply and low power ‘Point of Interface’ or you may need Active DAS Tray Point of Interface
  • Male and Female connectors
  • Omni antennas, directional, MIMO or SIS0 directional
  • Coax cables and support for various type of mounts (roof, ceiling, basement, etc.), weatherproofing, sealant, etc.
  • Fiber Extenders
  • Sub-rack for the DC Remote PSU Modules
  • Tri-plexer for each access method
  • Accessory kits and stacking kits, etc.
  • AC/DC Converters for 66W or 100W
  • Fan Modules
  • And then there are the attenuators… and so on – It’s a long list

Cabling the Bricks in the Wall

On the outside, a CPRI or Cat7a cable may look similar to Cat-5/6 Ethernet, but make no mistake, it’s not. It takes a specialist to handle this, and enterprise people know this. IT people cringe when special cables are involved. Why?

Certain cables cannot be bent, crushed or “stressed”. Every cable has values for minimum bend radius and maximum “tensile loading”. (Yes – look it up if you need a good night’s sleep). Some special cables cannot hang freely for long distances or press against edges in an installation. Example: When pulling cable in conduit, all transition points must be kept smooth. In short, every cable must be treated like a baby!

As for the installation, this is where it becomes “fun.” Conduit runs are limited to 100 feet! And, you cannot have more than two 90-degree bends between pull points or boxes! Even working at night, conducting core drilling between floors for conduits with jam-packed risers in-building is also a logistics nightmare. Yes, you heard me. Electronic Industries Association/Telecommunications Industry Association 569, which is the Commercial Building Standard for Telecommunications Pathways and Spaces, even provides more granular details, if you care to find out.

And then there are building codes for optical-fiber cables, keeping in mind maximum recommended distance between main and intermediate cross-connects (4920 feet), and intermediate and horizontal cross-connects recommendations. Single-mode fiber has other regulations. In some cases, telecoms equipment is connected directly to an intermediate or main cross-connect, where connecting cables can be no longer than 98 feet.

We could go on and on. The point is, CPRI is not Ethernet. It’s not simple Cat5/6 Ethernet pull. You need experts. See a good installation checklist overview here.

“Designed by R&D for use in Labs”

If you are contemplating Ericsson’s Radio Dot, keep in mind that you will need lots of Radio Dots and special Cat7a cabling to each of the Dots to power the 100mw radio heads. To “home run” each radio Dot over Cat 7 to/from the Indoor Remote Unit (IRU) means big install cost and several racks of equipment in the data center (Enterprise), considering you can only power 8 Radio Dots per IRU (LTE or 3G) and up to 12 IRU per DU. Each 14-unit rack powers a maximum of 96 Cat7a connected 100mw Radio Heads (or 48 LTE and 48 3G 100mw radio heads). Radio Heads by access technology: If you need 3G and LTE, then you need 2 Radio Heads (one each) which means double the amount of Cat7a cable pull. In brief, 3G+LTE means two full racks (14U each) of equipment if you require maximum reach with 96 100mw radio heads for 3G and LTE coverage. Of course, you will need special installation teams since this is a complicated installation.  Each rack (14u each) limits a 3G + LTE DAS coverage (48 3G + 48 100mw radios) to a maximum 250 to 300,000 square feet. A dual-band deployment would require two full racks, and total 110-120 100mw radios, each with a Cat7a cable pull. So, when you see the Radio Dot, you may think it’s simple.  When you understand what is needed behind the wall to power the Dot, you’ll question the establishment just like Pink Floyd. You’ll soon find out that ideas designed by R&D, for use in labs, may not be suitable in real-life enterprise environments.

Ericsson image of Radio DOT posted on Twitter.
Also see

The IT Friendly Approach

SpiderCloud Wireless has an IT-friendly approach with E-RAN.  The E-RAN system is proven to scale to 100 Radio Nodes (sectors), all powered over Ethernet LAN (or VLAN) with one Services Node, which provides one secure connection to the mobile core. First to market with a dual-mode 3G/4G system, the SCRN-310 Dual-band Radio Node has been in commercial networks since June 2014. It’s the first small cell, as part of a larger system, that’s capable of connecting 32 active users via the 3G band, while at the same time connecting 32 active users (128 RRC) via the LTE band (on one integrated SoC). The same Radio Node can now be software upgraded to switch the 3G band to 4G, making it capable of dual-band 4G+4G (150 Mbps), connecting 64 active users via the same Radio Node.

A dual-band 3G+4G deployment using SpiderCloud would only require one Services Node (1 unit in a rack) and require 25-30 SCRN-310 Radio Nodes (250 mw). The cost advantage for equipment and installation (as compared to Ericsson or Huawei) vs. DAS (radio heads) is 4-5x!

The Radio Node has a pedestal base that slides into a long bracket for ceiling or wall mounting. SpiderCloud Wireless pre-bolts the pedestal base onto the extrusion plate on the Radio Node.

Radio Nodes can be mounted on a wide number of surfaces including the following typical surfaces:

  • • Light grill: Use bolts, nuts and washers to secure the mount bracket using holes in the light grill. Adjust the mounting bracket until the bracket and light grill holes align.
  • • Mount directly on the wall or ceiling: Use drywall screws to secure the mount bracket directly to sheetrock or plasterboard on the wall or ceiling.

Installing a small cell should be as easy as installing a basic enterprise Wi-Fi AP, such as using a T-rail ceiling rail to avoid drilling holes in ceiling tiles.

The Radio Node is fully compliant with the IEEE 802.3at Power Over Ethernet (PoE+) specification. Per IEEE 802.3at, use standard Cat 5e, or better, twisted-pair cable with a maximum length restriction of 100 meters (328 feet) for PoE+.

Power is distributed over two pairs of the four available pairs in Cat 5e or better cables. The Radio Node can accept power on either used, or un-used pairs.

Usage of Ethernet LAN Deployment

By usage of standard enterprise Ethernet and a Radio Node installation process that is familiar with the very large pool of Wi-Fi trained installation companies, the cost of physical installation is significantly reduced as compared to telecommunications technologies that require specialized labor.

The optimal installations share the existing enterprise transport infrastructure to enable faster installation, and reduce capital construction costs for materials.

See the 60-second installation video:

SpiderCloud’s Self Organizing Network (SON) capability configures and optimizes the small cell network to provide a high-performance mobile broadband coverage with very little user intervention. SON is a core product feature that dramatically reduces installation time, fine-tunes the network for high performance, and periodically optimizes the environment to maintain effective network operation. Without this feature, an installer would have to setup the network manually, requiring many weeks (depending on the network complexity) to create an optimal working configuration. However, as a result of this unique feature, the system is auto configured in less than an hour, thereby automating a fairly complex configuration and dramatically reducing the time-to-install.

See the 60-second installation video:

Besides reducing time-to-install, the feature ensures optimal RF coverage and handoff within the SpiderCloud network, and with macro and inter-RAT networks. During network operation, this feature continually monitors the RF environment, makes adjustments to the radio transmit power to adapt to any changes in the RF conditions, and maintains optimal network access.

No More “thought control”

So, if you agree, “We don’t need no thought control” and you’d want an IT-friendly approach to fixing in-building coverage and capacity, easy as Wi-Fi, — then you too can protest against rigid cabling and installation procedures. You have a choice. If you plan to install something in an Enterprise, look to the companies which know and understand enterprise IT requirements.

The E-RAN 3G system is already commercially proven for three years. Other SpiderCloud Wireless customers include Vodafone UK, Vodafone Netherlands, and now also Verizon Wireless, plus leading mobile operators across several continents.

Ronny Haraldsvik

Twitter: haraldsvik

Don’t forget to sign up for the December 18th Intel-SpiderCloud Webinar: “In-Building Small Cell Services Opportunities for Enterprise IT and Mobile Operators” – hosted by HeavyReading.