Several technical options compete with femtocells. Some are complementary and we can expect to find devices or users where different technologies are used in different situations.
a) WiFi vs Femtocells
Data only solutions within the home are popular, and use WiFi and a standard broadband link to allow multiple laptops and other WiFi enabled devices to share high speed internet, usually at a fixed monthly rate.
Additionally, this can be complemented by WiFi access from a range of public locations, such as railway stations, pubs, motorway services, airports and hotels. The growing collaboration for interoperability between hotspot operators allows a single subscription to operate in many places. However, this can never be as ubiquitous as the wide area mobile coverage.
WiFi hotspot service has been built on by several internet voice operators, including Skype, which enables access from any WiFi hotspot with a commercial agreement through The Cloud.
A more sophisticated solution developed by TruPhone combines the low cost use of WiFi where available reverting to mobile coverage where its not. Calls and text messages are sent using IP to a separate TruPhone number, which forwards it using the cheapest technology available at the time. This service uses a lot of data and is arguably less efficient on radio spectrum than traditional cellular voice call. Therefore users would typically require to pay for an additional data package from their mobile operator as well as any TruPhone costs. Some operators don’t allow VoIP applications of this type, and others charge a premium to permit this.
b) WiMax vs Femtocells
WiMax has been touted as a very low cost, higher speed alternative to 3G. Claims of a range of up to 70km and data rates of up to 70Mbit/s at prices similar to WiFi. The technology is based on 802.11 (WiFi), but addresses many of the known problems such as contention between different users, and power efficiency. The radio modulation is OFDM which handles multipath well.
However, the reality is that a range of 4 miles is more realistic when used with an indoor modem, such as one integrated into a laptop. Data rates above 10MBit/s are also likely to require very favourable conditions. Therefore, in order to compete effectively with 3G mobile operators, a similar large number of cellsites would be required with all the associated issues of site ownership, power, backhaul and network management.
The technology is likely to find favour in delivering broadband DSL comparable services in countries without significant copper wires in the ground, and connecting remote rural areas where fixed point-to-multipoint outdoor antennae can be used to achieve the longer distances required.
The mass production of 3G chipsets in both devices and cellsites continues to drive costs down through high volumes. Intel has invested heavily to incorporate WiMax functionality into their chipsets. Spectrum costs for WiMax may be lower than for 3G, however less valuable (ie higher) frequencies have been allocated in many countries.
c) LTE (Long Term Evolution) vs Femtocells
LTE is the next radio transmission technology within the GSM standards family. It follows on from 2G GSM, 3G UMTS and 3.5G HSPA radio systems already in service, and uses a quite different radio technique (OFDM) to achieve extremely high data throughput.
The 3GPP standards body has already released a specification for the interface, which will likely be revised and improved as was the case for previous technologies. The system can use both (or either) the FDD spectrum assigned for 3G and the TDD spectrum which is typically issued but unused. [WiMax is currently limited to the TDD spectrum only, although it is rumoured there may be an FDD version in the future.]
Operators are expecting to start deployment of LTE and be able to offer commercial service by 2010, leaving a short window for femtocells to gain supremacy/adoption.
Several vendors have already demonstrated high performance implementations - Ericsson have already announced speeds achieved of over 100Mbit/s in 20Mhz of TDD spectrum at 2.6GHz. Bear in mind that these rates are unlikely to be achieved in poor radio conditions.
With capacity of this magnitude deployed at existing 3G cellsites, relatively high data capacity and speeds could be offered without the need for individual femtocells or homezones to be deployed. Combine this with lower cost high capacity backhaul links to the cellsites, and the economics of such as offer for mainstream users who want straightforward, simple services "that just work", and this could limit the overall takeup of dedicated femtocells especially where fixed network broadband is not available.
However, note that the power consumption of wide area high speed data services is much greater than that needed for femtocells due to the longer range and thus higher power of the radio transmission.