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
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.
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.
PCS Band Plan. Source: howardforums.com
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
Mobile security has become a growing concern with the rise of smartphones and tablets. Vulnerabilities in mobile operating systems and malicious applications are an ever increasing threat to personal information and security. Almost all of the focus for mobile security has been centered around protecting personal information stored on mobile devices. Very little research has been done in protecting cellular networks from distributed denial of service attacks, or DDoS attacks. DDoS attacks have been long used on the internet to disrupt web sites and web services. A DDoS attack is simple in theory, thousands or even millions of computers simultaneously request information from a website which overloads the servers causing the website to stop functioning.
There is a new type of DDoS attack that is possible with mobile devices called a mobile distributed attack, or mDDoS. An mDDoS attack is different from a traditional DDoS attack in that an mDDoS attack targets a cellular network, with the purpose of disrupting or even brining it down, instead of a website or web application. mDDoS attacks are possible as cellular networks can only support a very limited number of active users at a time. The number of active users at a given time varies depending on the network technology such as UMTS, EVDO, or LTE, but eventually it all comes down to the number of orthogonal codes or OFDM symbols that the different technologies utilize. Usually the small number of active users isn’t an issue as the probability that everyone on a particular cell site is updating Facebook, surfing the net, or calling Grandma at a given instant is unlikely.
When a mobile device sends a request through the airwaves to the cell site it expects to receive a response. A cell site at capacity either rejects or ignores the service request. This causes the mobile devices to retry the service request, but this time the request is sent at a higher power. When numerous mobile devices increase their transmission power it eventually creates enough interference that the base station’s capacity to serve users is severely reduced. When this happens mobile devices have a difficult time accessing the network and their data connections start to fail. Usually this is not an issue as cellular networks are designed to handle a normal traffic distribution through a process known as traffic engineering.
An mDDoS attack uses the technique of overloading the RF air interface to effectively bring down a cellular network. To execute an mDDoS attack, multiple mobile devices need to start sending data or initiate a phone call at the same instant in time. To accomplish this, a malicious app can be used to coordinate and execute the attack. The idea about how to install and spread a malicious app across millions of mobile devices is an entirely different topic, but if this can be achieved the results could be devastating. Unlike a DDoS attack where the attacking traffic can be routed by ISP’s and network operators to minimize the impact, an mDDoS attack is much harder to stop. An mDDoS attack focuses on layer 1, the RF link signaling link. Since mobile devices must follow the protocols laid out in the 3GPP and 3GPP2 standards it is difficult to engineer countermeasures.
The good news is that it is challenging to launch a successfully mDDoS attack. Most cellular networks are designed with extra capacity in mind to prevent unexpected events from causing network outages. This means that if a small number of mobiles connected to a cell site are vulnerable and an mDDoS attack is launched, it is unlikely this attack will have an impact. While mDDoS attacks are improbable, it reveals how vulnerable cellular networks are to organized attacks. To conclude, the adoption of highly advanced mobile devices such as smartphones not only increases the security threat to consumers, but also cellular network operators.
It’s hard to believe that the summer is already a distant memory. Even though I didn’t go on many photo excursions this summer, I was still able to capture a wide range of photos. I biked into Philly to get some great shots of the city, spent a night in Niagra Falls, and did some hiking in the Poconos. Enjoy
Lighting Above My Apartment. This shot was lucky, out of 100 photos only four actually captured lighting.
This was an interesting shot as at looks like morning, but actually it was pitch black and the lightning lighted the surroundings.
Niagara Falls at Dusk. I used an eight second shutter and I really like this shot as the left side of the river is peaceful while the right side is violent.
Philly!
City Hall
USS New Jersey, one of four Iowa class battle ships making it one of the most powerful battleships in the world. See the power boat along side.
Valley Forge National Park
Schuylkill River at Sun Down.
My mountain bike visiting the Liberty Bell
Hawk Mountain
How the Mountain got its name.
