There are several types of competing technology for the small cell, some of which are more directly related to coverage problems, others to capacity overload.
Here we consider several directly competing technical solutions for the mobile network operator.
Almost every smartphone has WiFi built in. These automatically seek out and use Wi-Fi where it is available, often providing a faster, more responsive data service than the outdoor mobile network. This can work well when stationary and visiting the same places (home, work, cafe etc.), but often requires entering a password for each new location. Battery consumption can be much higher when using Wi-Fi, resulting in much shorter battery life than when using a 3G small cell.
Some smartphones can also use Voice over IP (VoIP) applications such as Skype, Truphone or Viber to make voice calls using Wi-Fi. These applications may not fully integrate with the phone's built in address book, operate using a different phone number or identity or handle voicemail or messages differently when out of Wi-Fi range. In 2014, the introduction of Wi-Fi calling to the iPhone and Android makes the operation more seamless, but quality (especially in public areas) remains a concern.
Some operators actively encourage their smartphone customers to use Wi-Fi where possible. For example, ATT Wireless provide free access to over 20,000 WiFi hotspots in public areas. But the vast majority of traffic through Wi-Fi occurs at home or in the office, helping to reduce the strain on the mobile networks.
US cable operators also operate large Wi-Fi networks, sharing access to more than 50,000 for their subscribers. China Mobile has more than 2.2 million. The largest aggregated Wi-Fi network is FON, with over 13 Million (October 2014).
UMA dual-mode phones
A special type of Wi-Fi capable phone uses the UMA (Unlicenced Mobile Access) standard to operate seamlessly with the mobile phone system, effectively extending the same service over Wi-Fi with the same phone number, text messaging, voicemail and other services. This supports active call handoff between Wi-Fi and the cellular network.
There are several commercial live networks using UMA, such as T-Mobile USA (HotSpot@Home) and France Telecom/Orange (Unique). France Telecom report good takeup of the service, which may be partly due to the heavy penetration of WiFi/DSL modems already sold, and the much larger geographic coverage (and thus potential poor coverage areas) of the country.
The system requires customers to use a special dual-mode GSM/WiFi phone which restricts the choice of phones significantly. The Wi-Fi mode can be used both at home and at any T-Mobile or France Telecom hotspot when out and about. Calls can be handed over between the hotspot and the macrocellular network. T-Mobile allow access from any WiFi hotspot, even abroad, while France Telecom restrict access to their own hotspots (including domestic ones).
However UMA is much less suitable for data than voice, with smartphone users simply choosing to directly access the internet via Wi-Fi. This restricts the relevance of the solution to areas with poor voice coverage, and so the solution is not expected to grow further.
Wi-Fi Calling (VoWi-FI)
Functionally similar to UMA, Wi-Fi calling uses the same IMS voice switching core network as Voice over LTE. It can use any IP connection to setup and manage voice and video calls. It was given a major boost by being incorpoated into the iPhone 6 release in September 2014. Early adopters include T-Mobile USA, and announcements followed by other major US carriers. Operators would typically have to have launched VoLTE before being ready to offer VoWi-Fi because it relies on the same core network services.
There are cautions about not supporting seamless handover when leaving the serving Wi-Fi hotspot, and quality would be restricted in congested areas, but it may be useful feature when at home.
Improved microcellular coverage and capacity
If the service provided by the operator is adequate to meet customers needs, then they may not feel it necessary to install different technologies with associated cost and risk. However, to meet the forecast demand for data growth it is difficult to find an operator who does not have small cells somewhere in their roadmap.
3G technology has a roadmap with continuous improvements, including HSPA+ that are being deployed today to increase capacity. New handsets and devices are be required to take full advantage of the improvements. While this may provide a capacity increase of several times, it will not meet forecast demand on its own.
3G at lower frequencies such as 850Mhz or 900Mhz
Part of the reason that 3G does not operate well indoors is that the global frequency allocated is around 2100MHz. Some countries, notably Australia, have deployed 3G systems at 850MHz (which is close to the 900MHz 2G GSM frequency commonly used). As a result, much longer distances can be reached in rural areas (claimed broadband service of 2Mbit/s at a distance of 120km using an ourdoor antenna), whilst inbuilding penetration is much improved in urban areas.
European operators have been reallocating their existing 2G GSM spectrum at 900MHz for use by 3G. This so-called spectrum refarming is approved by regulators. Most smartphones are already capable of operating at these frequencies, and so the changeover can be quite rapid. The increased range and spectral efficiency of the 3G technology provides increased capacity and performance compared to 2G.
DAS (Distributed Antenna Systems)
Coverage of large buildings, shopping complexes, stadiums and similar large public areas can justify a Distributed Antenna System. These transmit the RF signal to multiple antennas throughout the building or complex. The advantage is that the same DAS installation can be shared across multiple network operators and can concurrently handle 2G/3G/LTE and even Wi-Fi. The initial cost of such systems can be quite significant and involve specialist RF planning and engineering.
Next, who are the manufacturers of small cells?