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
When Verizon Wireless launched its 4G LTE network last year many were amazed by the speeds, but another important technological advance was forgotten, IPv6. Verizon’s LTE network assigns a mobile or datacard a NAT’ed IPv4 address and a public IPv6 address. Verizon Wireless is the first major ISP in the US to jump on the IPv6 bandwagon. IPv6 has been one of those buzzwords for many years, but in the US the large allocation of IPv4 addresses meant that there was little urgency to move to IPv6. Verizon Wireless has started the IPv6 revolution and while a limited number of sites IPv6 sites exist, this will soon change in the near future.
The easiest way to improve the throughput and reliability of mobile broadband connections is to use external antennas. This concept has been used extensively in rural areas where the only form of high speed internet is usually a 3G cellular connection. In the past this meant a directional antenna with potentially a low noise amplifier. The same concept also applies to 4G technologies such as WiMax and LTE where having a strong receive signal and most importantly a high signal to noise ratio (SNR) is essential for high data throughputs.
LTE SNR vs Throughput. Source: Ericsson
While the same general concept external antenna exists for WiMax and LTE there is one major difference, MIMO. MIMO uses two or more separate antennas to create virtual paths through the air instead of just one path with conventional 3G technologies. MIMO is extremely important as it uses multipath to greatly increase the downlink throughput. Currently only WiMax and LTE support MIMO in the downlink and most cellular operations are deploying a 2×2 MIMO solution which means two antennas are used for transmitting at the base station (cell site) and two antennas are used to receive at the mobile device (cell phone). This means to maximize your WiMax or LTE datacard throughput you must use two antennas. If you hook up only one external antenna even with the best RF conditions you will be limiting yourself to roughly half the downlink speed. This means it is extremely important two use two separate external antennas to maximize performance with WiMax and LTE.
Downlink Throughput with 2 Antennas vs 1 Antenna
Signal to Noise Ratio with different antenna configurations
Additionally, MIMO works based on the correlation of the two different receive streams sent by the two different antennas at the base station. If the receive streams are high correlated that means that the receiver in the datacard cannot differentiate the difference between both streams so there is no increase in data throughput. The high correlation is one reason why hooking up a single antenna and using a splitter to divide the signal to each antenna port at the mobile device doesn’t achieve an increase in throughput. The mobile device’s chipset will see that the signal coming into both antenna ports is roughly the same. This is why it is important to use two separate antennas. Additionally, to minimize correlation it is important to space the antennas minimally one wavelength (1.4ft for 700MHz) apart. With 3G technologies you would point your external antenna in the direction of the base station and tweak the position until you received the highest receive power. With 4G the general concept still applies but to reduce the MIMO correlation of each antenna you might have to point one antenna at a slightly different angle or use a different polarization to achieve maximum throughput.
Dual Yagi pointed directly at cell site. Good recieve signal but does't optimize MIMO correlation for my environment. Use $ software to see correlation or just run speed tests.
One Yagi pointed directly at cell site, the other pointed at a slight angle. Good recieve signal and optimizes MIMO correlation for best downlink throughput.
Both the Pantech UML290 and the LG VL600 LTE datacards on Verizon Wireless 4G LTE support external antennas. This makes hooking up external antennas a breeze, unlike many of Clear’s and Sprint WiMax cards which require soldering. Plug two pigtails into the external antenna jacks and you should be all set. Only one antenna transmits, so if you plan to connect only one antenna make sure you try both ports, or you might not be able to connect to the LTE network. To receive downlink throughputs of 20Mbps, it is important to have a signal to noise ratio of at least 15dB or higher. This can be easily checked in the Verizon Wireless VZAccess Utility.
In rural areas achieving this high signal to noise ratio far from the cell will be hard to accomplish, but even at the edge of LTE coverage 5Mbps can be achieved. It is also important to remember just not the improved data throughputs, but also the lower latency that LTE introduces. Overall, pairing external antennas with 4G technologies such as LTE can result in a substantial throughput improvement and allow you to maintain a reliable connection even in fringe signal areas.
This Sunday Verizon Wireless launches its 4G LTE network. There has been a great debate on the net regarding what is really 4G and how wireless companies are promoting their service as 4G. While the ITU determines which specifications meet the 4G standards, the term 4G refers to fourth generation wireless networks. Two big technological improvements from earlier technology in 4G are OFDM based modulation and advanced antenna techniques such as MIMO and beam forming. LTE and WiMax incorporate both these technologies and LTE Advanced and WiMax 2.0 improve on these technologies to increase the spectral efficiency. LTE Advanced and WiMax 2.0 do not introduce any ground breaking technologies instead they are just improvements to the current standards. For this reason both LTE and WiMax should be considered fourth generation wireless networks as they offer technological advantages not found in the previous generation networks.
T-Mobile and AT&T are claiming that their HSDPA+ networks provide similar performance to that of the LTE and WiMax. The HSDPA+ networks being deployed in the US offer a theoretical speed of 21Mbps which sounds impressive until you learn that Verizon Wireless’s LTE configuration using 10MHz channels with 2×2 MIMO has a theoretical speed of 73Mbps. Clearly Verizon Wireless’ LTE is in a completely different league than T-Mobile’s “4G” solution. Many reviews of Verizon Wireless’ LTE are coming back with speeds of 10Mbps which doesn’t seem that much faster compared to some people’s HSDPA+ 6-8Mbps speeds. These LTE speeds are what an average user can expect in many places, not just in perfect RF conditions under a cell where HSDPA+ can provide speeds of 6-8Mbps. In excellent RF conditions on an unloaded cell, LTE makes HSDPA+ look silly:
LTE is a very young technology and as it matures the speeds should improve closer the theoretical target. HSDPA technology has been around a long time and the hardware and software design is well understood. LTE is much more complicated, with technologies such as MIMO, and it will take some time before engineers can fully optimize the performance of the hardware and software. Even so, LTE in its current state can provide very impressive speeds when nearby a cell site. While T-Mobile claims that their “4G” network is comparable, HSDPA+ network technology will never be able to provide speeds available to either the WiMax or LTE technology path.
It has been widely agreed that Sprint’s acquisition of Nextel was one of the worst mergers in recent history. Five years after the merger, Sprint’s CDMA and Nextel’s IDEN networks are still not consolidated. This means that at a typical cell site, Sprint will have its own equipment located in outside cabinets while Nextel has its equipment in a large indoor enclosure. Additionally, Sprint and Nextel don’t share any of the same antennas or coax runs meaning for all practical purposes it is paying double in leasing costs for each cell site compared to its competitors. Even worse is the fact that Sprint and Nextel aren’t always co-located meaning that each network has vastly different coverage. Where I live Sprint has no service and so its CDMA customers roam onto Verizon Wireless. Not surprising, less than a ¼ mile away from where I live is a cell site where Nextel is located. The issue of not consolidating the CDMA and IDEN networks has resulted in lackluster coverage and additional operating costs for both services. Now that Sprint-Nextel is using Clear to launch its 4G WiMax network the issue of network fragmentation is only becoming worse. At many sites Clear is not co-locating with either Sprint or Nextel meaning additional leasing costs at each cell site. Additionally, Clear’s all IP fiber and microwave backhaul is not being used to replace the expensive and outdated T1 lines that are used to power Sprint’s CDMA and Nextel’s IDEN networks. If Sprint-Nextel utilized Clear’s backhaul it could means millions of dollars of savings while providing better performance to its subscribers. Unless Sprint-Nextel makes some major overhauls in its network design, it will soon be supporting three different networks, each based on technologies that are not compatible with each other. If Dan Hesse is to turn the company around he needs to consolidate the networks and ensure network inter-compatibility, just like the rest of the wireless industry.
