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Small Cells
Dec 21st, 2013 by Dan Lampie

Small cells are currently the big buzz word in the wireless industry.  Many of the major wireless operators in the US including AT&T, Verizon Wireless, and Sprint have committed to use small cells throughout their networks.  In fact AT&T has committed to deploy 40,000 small cells by the end of 2015, which reveals that wireless operators are serious about this technology.  This begs the question what are small cells and why are they needed?

Macro vs Small Cell in New York City

 

Small cells as its name suggests are smaller cellular base stations.  By smaller this includes physical size, RF coverage area, and cost.  Another term which is used in the same context as small cells is distrusted antenna systems or DAS.  A DAS is made up of a number of small antennas nodes which then connect back via fiber to a cellular base station.  With a small cell all the intelligence is housed within the device, while a DAS node is just a dumb transmitter and receiver and the intelligence is housed at remote location.  DAS technology has been in the marketplace for a couple of years and has been successfully deployed in both outdoor and indoor environments.  Small cells are brand new to the market, and they are gaining popularly as they should be cheaper and simpler to deploy than a DAS.

DAS Node

 

The need for small cells is being driven by the surge in mobile data consumption. The popularity of smartphones and tablets means that people are consuming large amounts of data on their mobile devices.  People are not just using their mobiles devices to surf the web, but they are streaming videos and uploading pictures using applications such as Netflix, YouTube, and Instagram.  While LTE was designed to support these mobile applications, the usage is growing quicker than improvements in wireless efficiency which is making networks congested.

Source: broadband.gov

 

To better understand the situation it is important to look at the capacity of an LTE base station which is called an eNB.  LTE is similar in technology to the 802.11N Wi-Fi standard.  Both use similar modulation schemes and data transmissions technologies.  Many LTE networks in the US use 10MHz LTE carriers using a technology called frequency division duplex, or FDD.  This means that 10MHz of spectrum is used in separate downlink and uplink channels.  This allows for full duplex communication and means the total amount of spectrum that is used is 20MHz.  Wi-Fi along with some forms of LTE use a technology called time division duplex or TDD.  With this technology the downlink and uplink data is interleaved in the time domain using the same channel.

Source: blog.3g4g.co.uk

 

The standard Wi-Fi channel is 20MHz wide which uses the same amount of spectrum as a 10MHz FDD LTE carrier.  While a normal Wi-Fi access point might only serve a few people, an LTE base station has to support hundreds of users in the same bandwidth.  An LTE base station is really a high tech Wi-Fi router with advanced resource and user scheduling technology.  If a hundred people tried streaming videos from the same Wi-Fi router the performance would be mediocre, and the same holds true with LTE.  To improve performance a simple solution is to decrease the number of people using the connection.  While this might seem obvious this is one way cellular operations ensure that their networks do not become overloaded and congested.

For the last twenty years the number of cell sites has been growing while the coverage area of each cell has been shrinking.  The concept is relatively simple and is known as cell splitting.  Instead of having one large cell site which serves an area, if two smaller cell sites are used which serve the same geographical area there will be close to double the capacity.  This concept has been successfully used for a long time, but today there is so much usage in major cities that a cell site is need on every block.  It is impractical due to cost and space requirements to put conventional cellular base stations on every block.  This is why small cells are being utilized.  They allow for a denser deployment as they can be mounted on light poles and sides of buildings instead on towers or rooftops.  Instead of having one conventional cell site every four blocks, now it is possible to have a small cell on every block greatly increasing capacity.

Source: http://www.research.att.com

 

Give that small cells are a new technology there are still many questions that still need to be answered.  Will small cells be economic viable?  Will small cells be reliable?  The big question remains whether small cells are the solution to the explosive mobile data growth that is occurring.  Regardless of the success of small cells, the increase in mobile data consumption will force wireless operators to come up with innovative ways to meet mobile data demands.

A Picture Climatology
Sep 29th, 2013 by Dan Lampie

I have been meaning to add some new photos to the site for many months now.  In fact its almost been a year since I last uploaded photographs!   In the last year I was fortunate to travel both inside and outside the US, and a majority of the pictures below are from my trips.  I am still using a Panasonic ZS7 camera and I post processed the pictures in Adobe Lightroom.  Enjoy!

T-Mobile’s LTE Network using Active Antennas
Mar 26th, 2013 by Dan Lampie

Today T-Mobile officially announced the launch of its 4G LTE network.  T-Mobile might be the last of the major carriers to launch a LTE network in the US, but this has allowed T-Mobile to implement some cutting edge LTE technology into its new network.  T-Mobile is using two different equipment vendors, Ericsson and Nokia-Siemens, to power its LTE network.  In the Ericsson markets, T-Mobile is deploying a brand new technology called active antennas.  Active antennas are the evolution of cell site architecture, and offer the potential for substantial improvements in LTE performance and capacity.

T-Mobile's deploying the Ericsson AIR21 Active Antennas. This shows two building mounted sectors. Note the large depth of the antennas and how there are only two small cables to the antenna (one power and one fiber).

 

Traditional cell sites placed the base station radios at the bottom of the tower and used thick coax cables to transmit the signal to the antennas at the top.  The issue with this solution is that long runs of coax cable cause attenuation.  This means that a base station might output 20W of power, but by the time this signal reaches the antennas it is now only 15W.  The same concept is true in the uplink direction when a mobile device is transmitting to the cell site.  The uplink is usually the limiting factor in cellular communications as mobile devices can only transmit at a fraction of a watt compared to the multiple watts of a base station.  One solution to improve the uplink performance is to mount an uplink amplifier at the top of the tower, and this is known as a tower mounted amplifier or TMA.  Once the uplink signal is received by the antenna it is boosted by the TMA to help overcome the attenuation of traveling through the coax to the base station.  TMA’s are widely used by AT&T and T-Mobile on their 3G UMTS networks.

A conventional cellular antenna design. Source: Commscope

 

The evolution of the TMA was the remote radio head or RRH.  The RRH moved the entire transmit and receive radios and power amplifiers to the top of the tower.  The benefit of moving to RRHs is that signal attenuation is greatly reduced, which increases both the downlink and uplink performance.  Instead of thick coax cables, fiber and power cables are run up the tower taking up less space.  RRHs still require a small coax jumper to connect to the antennas which adds a small amount of attenuation.  RRHs are being used by most of the LTE industry, and they can be easily identified by big boxes near the antennas on top of towers.

A RRH cellular antenna design. Source: Commscope

 

The most recent technological advance, which T-Mobile is utilizing, is an integrated LTE radio inside an antenna.  This technology is known as active antennas.  The obvious benefit of this concept is completely removing coax cables from the equation, minimizing any signal attenuation.  T-Mobile is using the Ericsson AIR antennas which claim to have a 1dB improvement in the uplink over a RRH solution.  Another benefit of active antennas is the ability to better control the antenna’s beam pattern.  This allows cellular operators to more accurately define coverage areas, which can improve performance especially at the cell edge.  Additionally, in the future active antennas will allow for a concept known as beam forming.  Beam forming “steers” the antennas beam via a concept known as phase shifting.   Instead of the antenna’s beam providing coverage for an entire area, the beam is focused in the direction of each user utilizing the service at that instant.  Beam forming has the ability to greatly improve wireless performance and capacity, and it is currently used in some WiFi access points.  The issue with beam forming is that it requires a large number of radios and antennas to work to its full potential.  With today technology this results in large antenna arrays which are expensive.  While beamforming is still in its infancy, T-Mobile’s use of active antennas is paving the way on how cellular networks will be built in the future.

An Active Antenna cellular antenna design. Source: Commscope

Three Seasons
Oct 28th, 2012 by Dan Lampie

I haven’t posted for a while so I thought I would share some of the photographs I have taken in the last couple of months.  Some of my friends I suggested I use Adobe Lightroom to edit my photos, so I thought I would give it a try.  It is an easy to use program and within a couple of minutes your pictures will look amazing.  The issue with post processing software like Adobe Lightroom is that it can make any picture look good, and I feel this takes away from snapping the perfect photo.

Making Sense of Sprint’s Network Vision
Apr 7th, 2012 by Dan Lampie

A little over six months ago, Sprint-Nextel laid out its strategy for revamping its wireless network and called the plan “Network Vision.”  If you have read any of my previous articles about Sprint, you would know that Sprint has not had any real network strategy since purchasing Nextel back in 2005.  Today Sprint still has numerous sites where they have yet to combine their iDEN, CDMA/EVDO, and Clearwire’s WiMax network which has resulted in poor coverage and high maintenance and real estate costs.  Well this is all about to change with Network Vision.  After seven years without any true network plan, Sprint-Nextel has something that actually makes sense.

Sprint Network Vision Tower (Alcatel-Lucent Equipment)

 

Here is a brief overview of what “Network Vision” entails.  The website, http://s4gru.com, has some excellent detailed information on what “Network Vision” really means from a technical perspective.

- Consolidate its cell sites, by removing sites that are not needed.  Sprint currently has 68,000 sites and will reduce this by 44% to eventually remain with 38,000 sites.

* AT&T claims they have 55,000 cell sites so once Network Vision is completed its nationwide coverage will still lag behind that of AT&T.


- Shutting down iDEN and reusing the spectrum to support at least one 800MHz CDMA 1X Advanced carrier.

* Deploying a 1X carrier in the 800MHz spectrum will greatly improve the voice performance along with coverage for Sprint, especially inside buildings.

Frequency plan for new 1X advanced carriers. Source: s4gru.com

 

- Deploying a LTE carrier in a 5x5MHz channel configuration in their 1900MHz (PCS) spectrum.

* LTE is the future and this will give Sprint the opportunity to have a nationwide LTE network.
* 5MHz channels will offer only half the data speeds of the 10MHz channel that Verizon Wireless uses.  Still it will be vastly faster than EVDO with 50ms latency.
* Deploying on the 1900MHz spectrum will mean that Sprint will not have as good coverage or indoor penetration as either Verizon Wireless or AT&T which are using 700MHz.

PCS Band Plan. Source: howardforums.com


- Using Remote Radio Heads (RRH) for their existing CDMA/EVDO network and upcoming LTE network
* RRH moves the base station amplifier from the bottom of the tower to the top of the tower.  This eliminates the attenuation of long runs of coax cable up the tower.  According to this spec sheet from Andrews, 100FT of 1 ¼ coax has a loss of 1.6dB at 1900MHz, or a power loss of 31% at the top of the tower.  Thus going with the RRH solution should yield 30%+ more power output along with a 30% increase in receive power over today’s coax solution.
* This should improve coverage and performance of Sprint’s existing CDMA/EVDO network.  The combination of the 800MHz spectrum and RRH should really help Sprint’s voice coverage.

Sprint is using three RRH per face (1 for 800MHz CDMA, 1 for PCS EVDO, 1 for PCS LTE)

 

At the end of the day Sprint will have a CDMA/EVDO/LTE network, just like Verizon Wireless.  By consolidating its cell sites and turning off iDEN, Sprint will save a ton of money on operating expenses.  It is interesting that Sprint is investing a lot of time and money upgrading CDMA/EVDO instead of just focusing on deploying LTE.  Additionally, with MetroPCS, AT&T, and Verizon Wireless all committing to VOLTE it is interesting that Sprint is planning on deploying CDMA 1X Advanced for voice calls.  Sprint must have believed that its CDMA/EVDO networks could be greatly improved with Network Vision and that both these technologies will be around for some time.  Sprint has been successful at finding ways to monetize its old networks, such as offering Boost Mobile prepaid service over its iDEN network.  As postpaid customers move to LTE, Sprint could offer competitively priced but slower data services overs its CDMA/EVDO network to maximize its investment.

The one element that was left out of Network Vision is Clearwire which Sprint owns 54% of the company.  If Clearwire partnered with Sprint, like Lightsquared attempted before all their GPS interference issues, Clearwire’s network consolidation could save a great deal of money for the small carrier.  Clearwire will be upgrading its network to LTE, but it will be based on TD-LTE technology instead of FDD-LTE that all the other US carriers are using.  Clearwire’s 2.5GHz spectrum limits its usefulness to urban areas and the high cell density needed for good coverage makes network expansion expensive.  Clearwire is hoping to sell extra LTE capacity to the major wireless carriers, but using a different LTE technology and a separate frequency band than everyone else will make this difficult. While Sprint’s issues with Clearwire remain, Network Vision is a huge step in the right direction for Sprint.  One complete it will offer much greater voice coverage, improved EVDO performance, and most importantly bring Sprint into the LTE game.

A single dual band antenna supports all three technologies


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