Wireless Radio Technologies

1. WiFi and WiFi Mesh

Wireless Fidelity (WiFi) is a wireless technology based on a family of standards
developed by IEEE and denoted as 802.11. The 802.11 family contains a large number
of standards that regulate the mode of operation and possible improved features.
WiFi can be successfully used for VoIP services, but it has many limitations that range from the number of simultaneous users, problems with mobility, quality of service, etc.
However, additional standards from the 802.11 family can improve performance for
VoIP. Such features include e.g., quality of service, support for faster mobility handoffs, increased coverage and capacity, etc. However, most of these features are not backwards compatible and are available only to more specialized equipment. This
means that both the access point and the WIFi mobile devices need to support them.

If we attempt to consider all the variables and features available in WiFi that affect VoIP, it is very complicated to make a generalization that can be considered as a baseline for the technology. Therefore, in general, the performance and cost of using VoIP over WiFi is more easily characterized based on its deployment case.

 WiFi mesh networks are a special case of WiFi network that is deployed to provide
connectivity to city-wide hotspots. Several networks have already been deployed and
many cities in the US, and quite a few outside, are either committing to, or studying the possibility of deploying a city-wide WiFi coverage using wireless mesh networks.
Several cities are in the planning stages, while smaller cities have already deployed
networks which attempt to provide broadband wireless access ubiquitously. The goals in setting up these wireless mesh networks are multiple, and include providing broadband access to underserved communities or supporting emergency services. However, one of the main reasons is to reduce the cost per bit of wireless access to support applications which reduce the expenditures of a city.
The hope is that a lower cost per bit would provide the incentive to use applications on the go, thereby increasing the productivity of city employees. Alternatively, if the network is operated by a provider, the lower cost per bit would provide the margin to compete for mobile applications with cellular operators. Metropolitan WiFi mesh networks are seen by some investors as a potential disruptive technology for legacy cellular operators. A WiFi mesh network combined with a VoIP handheld device could become an alternative to the cellular handset.

2 WCDMA and HSDPA
The third generation of wireless telecommunication systems is an evolution of previous wireless systems that enables high bit rate data services. Wideband Code Division Multiple Access (WCDMA) is the main third generation air interface in the world and is most commonly deployed in the 2GHz band. However, in some other countries such as US and parts of Europe, it can also be deployed around 800-900MHz. The standardization efforts are carried out within the 3rd Generation Partnership Project(3GPP). As of 2007, the number of WCDMA subscribers had exceeded 130 million
globally in over 150 commercial networks. The next phase of WCDMA, i.e. High-
Speed Downlink Packet Access (HSDPA) is currently being intensively deployed
worldwide to provide wireless broadband connectivity. When introducing HSDPA in
3G networks the end user experience and system capacity with VoIP applications will
improve considerably. When later on also adding high-speed uplink (HSUPA), the
system capacity and end user experience will improve even further. HSDPA and
HSUPA correspond to 3GPP Releases 5 and 6 respectively. Further HSPA evolution is
specified in Release 7 and is known as HSPA+. In addition 3GPP specified a new radiosystem called Long Term Evolution (LTE) in Release 8, which was completed in 2009.

3G cellular systems are also evolving towards a flat all IP architecture. The evolution is developed step by step based on 3GPP releases (see Figure 9). For this reason, VoIP performance in particular is very important because it brings a significant improvement in cellular networks in regard to the capacity of voice users. Therefore, it is envisioned that VoIP will replace circuit switched calls completely in the long term.

3 FLASH-OFDM
FLASH-OFDM (Fast Low-latency Access with Seamless Handoff Orthogonal
Frequency Division Multiplexing) is a proprietary system developed by Flarion. Later
the technology was purchased by Qualcomm. FLASH-OFDM technology generated a
lot of interest as a packet switched bearer which could compete with 3G cellular
systems. FLASH-OFDM has been available for several years and at the time of its
completion it outperformed 3G networks both in terms of bandwidth, latency and
mobility support for data communications. However, despite the early development of
the technology, to date there are only a limited number of networks available.
FLASH-OFDM is a wireless broadband technology that can provide nearly ADSL
performance. This means that FLASH-OFDM can be a technological rival for ADSL,
and in some cases may be the only feasible option to provide broadband access.
FLASH-OFDM also operates on a licensed spectrum, but usually at lower frequencies
than HSDPA (e.g., 450MHz). Due to the low frequency, a large coverage area can be
achieved with a single base station. Thus, it is a particularly interesting option for emerging markets, and especially for rural areas that may lack other
telecommunications infrastructure. However, in the 450MHz spectrum there is
significantly less bandwidth than at higher frequencies. In Finland, only two 1.25MHz
blocks are available for FLASH-ODFM. Therefore, while FLASH-OFDM operating at
low frequencies can be feasible for rural and not very densely populated areas, it lacks sufficient capacity for big cities.

4 Interworking Technologies
VoIP can be used on different wireless broadband access technologies. These networks
are different and are usually independent of each other as well. Hence, they do not
provide interoperability. However, there are techniques that can be useful in providing VoIP continuity and interworking across different networks. The most relevant ones are Unlicensed Mobile Access (UMA), also known as Generic Access Network (GAN), Mobile IP (MIP) and Voice Call Continuity (VCC). Whilst MIP focuses on packet data only, VCC provide means for interoperability between circuit switched voice networks and packet switched voice, and UMA supports both packet data interoperability and circuit switched voice to VoIP interworking. In this work we focus on MIP and UMA as VCC was not fully compliant or supported at the time of this thesis. VCC is part of 3GPP Release 7 specifications and is seen as a potential interworking solution for future networks such as LTE.