Most Asian cellular carriers mulling over 3G have chalked out at least tentative transition paths towards that Holy Grail. If theyre GSM networks, its a safe bet EDGE (Enhanced Data for GSM Evolution) is being considered, to replace/augment GPRS for high speed data services. Because EDGE uses a new modulated scheme that is also used for UMTS/3G, EDGE becomes a sort of half-way house to 3G.

The cost to introduce 3G into an existing GSM network is enormous. A large portion of 3Gs non-license related costs pertain to new nodes patched into an existing GSM network to make it 3G compliant. And of course, these new nodes need to inter-operate with existing 2G and 2.5G nodes.

An alternative does exist, that until recently dare not speak its name. Marrying cellular and WiMax/WiFi clouds, is not just cheaper, but more in keeping with the times. Besides the cost benefits, such a union addresses two other big issues: bringing high speed data services with laser like precision to the urban users who need them and voice connectivity over cell phones to suburban residential homes with poor cellular reception.

Integrating selected WiFi Hot spots or WiMax Hot Zones into a cellular network requires an IP Network Controller (INC), an IP access network, a patch to allow the Wireless LAN (WLAN) access network to issue the relevant accounting information to the cellular clouds AAA (authentication, authorization, and accounting) server and an investment in IP roaming. Barring a few more widgets, thats essentially it.

Given the simplicity of such a solution, anyone who has seen engineers sweat over cell site deployment or attempted to work the math behind the cellular hex grid, has to wonder why the cell phone-wallahs have not already adopted WiFi/WiMax at their peripheries.

One however continues to sense discomfort in cellular circles over any open discussion on WiFi/WiMax. This may have something to do with the fact that the same user who demands everything be free on the Internet, is more than willing to pay a premium for his mobile service. The cellular carrier therefore, is understandably wary of encouraging bad habits in his paying customers.

Kineto, an equipment manufacturer, explains how such an eco-system would work.

- A subscriber with a WLAN, dual mode mobile phone moves within range of an access point to which the handset can connect.

- On attaching, the handset contacts the mobile operators INC over the IP access network, to be authenticated and authorized for mobile service access.

- If approved, the INC updates the subscribers location information in the network. From that point on, all mobile traffic is routed via the INC and over the IP access network. The subscriber is now on Voice over Broadband (VoB) and on a lower fixed line / VoB type tariff.

- When the subscriber moves outside the range of the serving access point, the INC facilitates roaming to the licensed outdoor network. The roaming process is completely transparent to the mobile subscriber.

- In addition, if a subscriber is on an active voice call or handset data session when they come within range (or out of range) of a service access point, the INC facilitates the handover of the active call between networks. The handover is completely transparent to the mobile subscriber.

- The WLAN access network issues the relevant accounting information to the cellular networks AAA server. This accounting information can then be incorporated into the operators specific CDRs enabling it to be assimilated into the operators existing legacy billing system, creating a single bill for Cellular and WLAN usage.

In divvying up responsibilities, the WLAN provider manages the network while the mobile operator looks after customer care and billing. The end-user pays his mobile operator for the usage of the WLAN. The charges for using a cell phone over a WLAN would be lower than cellular use but in most cases it would be incremental revenue that the cellular companies would otherwise lose to fixed-line or VoB networks.

The cellular-WiFi/WiMax eco system also ropes in homes and offices equipped with broadband. To connect, the home or office user goes to his mobile providers web portal and registers his WLAN into the IP Network Controller (INC). The subscribers cell phone is now patched into the WLAN and on a lower fixed line / Voice over Boradband (VoB) type tariff.

While there is growing competition in the VoB sector, only the cell phone operator decides whether the customer can get a combined cellular+VoB bill. A mobile providers Cellular-WLAN service shall therefore, stand head over shoulders over any Vonage type VoB service.

As we have seen, in a Cellular-WLAN eco system devices intelligently pick and choose from the wireless network offering the strongest signal or lowest price in a given area. It is a compelling picture that demands the cellular operators attention, more so in Asia.

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References & recommended reading

Books:
GPRS Demystified by Hoffman, John
GSM, GPRS and EDGE Performance : Evolution Towards 3G/UMTS
by Timo Halonen (Editor), Javier Romero (Editor), Juan Melero (Editor)
WLANs and WPANs towards 4G Wireless by Ramjee Prasad, Luis Munoz

White papers
Public Wireless LANs for Mobile Operators by Philippe Laine of Alcatel.
GSM to 3G, Evolution or revolution? by Hughes Software Systems & Adax
Europe Limited.
Handover between WCDMA and GSM by Gertie Alsenmyr,Joakim Bergstrom & others of Ericsson

Websites
http://www.gsmworld.com
http://www.cdg.org
http://www.kinetowireless.com
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