Key challenges with automatic Wi-Fi / Cellular handover

Recently in a conference I mentioned that the 3GPP standards are working on standards that will allow automatic and seamless handovers between Cellular and Wi-Fi. At the same time operators may want to have a control where they can automatically switch on a users Wi-Fi radio (if switched off) and offload to Wi-Fi whenever possible. It upset quite a few people who were reasoning against the problems this could cause and the issues that need to be solved.

I have been meaning to list the possible issues which could be present in this scenario of automatically handing over between Wi-Fi and cellular, luckily I found that they have been listed very well in the recent 4G Americas whitepaper. The whitepaper is embedded below but here are the issues I had been wanting to discuss:

In particular, many of the challenges facing Wi-Fi/Cellular integration have to do with realizing a complete intelligent network selection solution that allows operators to steer traffic in a manner that maximizes user experience and addresses some of the challenges at the boundaries between RATs (2G, 3G, LTE and Wi-Fi).
Figure 1 (see above) below illustrates four of the key challenges at the Wi-Fi/Cellular boundary.
1) Premature Wi-Fi Selection: As devices with Wi-Fi enabled move into Wi-Fi coverage, they reselect to Wi-Fi without comparative evaluation of existing cellular and incoming Wi-Fi capabilities. This can result in degradation of end user experience due to premature reselection to Wi-Fi. Real time throughput based traffic steering can be used to mitigate this.
2) Unhealthy choices: In a mixed wireless network of LTE, HSPA and Wi-Fi, reselection may occur to a strong Wi-Fi network, which is under heavy load. The resulting ‘unhealthy’ choice results in a degradation of end user experience as performance on the cell edge of a lightly loaded cellular network may be superior to performance close to a heavily loaded Wi-Fi AP. Real time load based traffic steering can be used to mitigate this.
3) Lower capabilities: In some cases, reselection to a strong Wi-Fi AP may result in reduced performance (e.g. if the Wi-Fi AP is served by lower bandwidth in the backhaul than the cellular base station presently serving the device). Evaluation of criteria beyond wireless capabilities prior to access selection can be used to mitigate this.
4) Ping-Pong: This is an example of reduced end user experience due to ping-ponging between Wi-Fi and cellular accesses. This could be a result of premature Wi-Fi selection and mobility in a cellular environment with signal strengths very similar in both access types. Hysteresis concepts used in access selection similar to cellular IRAT, applied between Wi-Fi and cellular accesses can be used to mitigate this.

Here is the paper:

Integration of Cellular and Wi-Fi Networks from Zahid Ghadialy

ANDSF: Evolution and Roaming with Hotspot 2.0

Access Network Discovery and Selection Function (ANDSF) is still evolving and with the introduction of Hotspot 2.0 (HS 2), there is a good possibility to provide seamless roaming from Cellular to Wi-Fi, Wi-Fi to Wi-Fi and Wi-Fi to Cellular.

There is a good paper (not very recent) by Alcatel-Lucent and BT that explains these roaming scenarios and other ANDSF policies related information very well. Its embedded below:

What's next with 802.11!

From another brilliant presentation by R&S from their LTE Summit 2013. Last year I had a similar overview from Agilent here. This one is much more detailed on what's coming next for WiFi.

802.11: a jet plane window’s view from Zahid Ghadialy

802.11u, Passpoint and Hotspot 2.0 (HS 2.0)

Came across this interesting Video on Youtube explaining 802.11u that is embedded below.




A bit more detailed presentation on the same topic by Ruckus is also embedded below:


Related posts:

• Wi-Fi & Packet Core (EPC) Integration
• Hotspot 2.0, Next Generation Hotspot (NGH), etc.
• Cellular-Wi-Fi Integration - technology and standardization roadmap

Wi-Fi & Packet Core (EPC) Integration

Yesterday I wrote a blog post on whether Wi-Fi is the third RAN in the Metrocells blog. Today I am posting this excellent presentation that details how this Wi-Fi integration with EPC will be done.

Wi-Fi & packet core integration from Zahid Ghadialy

Ten things Wi-Fi had in common with public toilets!

Interesting perspective from a presentation by Agilent in Cambridge Wireless Small Cells SIG.

Energy-efficient femtocell implementation

In an earlier post, we saw an idea on how to have energy efficient Femtocell. Here is a practical implementation from ALU on energy efficient Femtocell.

Energy-efficient femtocell: Practical implementation from Zahid Ghadialy

Small Cells 'Terminology' and 'Comparison'

Here is AT&T's attempt in comparing the small cells. The above comparison is probably based on the assumption that LTE Small cells are not yet widely available. Once they are, then LTE can be put in for most columns in the Technology part.

See also:

• Small Cells: Comparison and Deployment Scenarios - NSN

Four Options for Traffic Offloading

Hotspot 2.0, Next Generation Hotspot (NGH), etc.

From ZDNET:


Hotspot 2.0 is about certifying the hotspot itself, providing authentication using SIMs or certificates and the 802.11i standard, and using the recent 802.11u standard to provide performance and other information about the hotspots visible to a device. This will allow you to roam onto a hotspot with good connectivity that you have the right account to use, doing away with the need to select the network or enter your details into a web page, as you do today.

The Wi-Fi Alliance deals with the Wi-Fi hardware and the authentication specification under the name Passpoint, but this certification doesn't cover everything. The Wireless Broadband Alliance is a group of mobile and Wi-Fi operators that takes the Passpoint certification and ensures interoperability with other parts of the network — including authenticating to carriers' remote access RADIUS (Remote Authentication Dial-In User Service) servers, as well as roaming and billing.

"Next Generation Hotspot is the implementation of Hotspot 2.0 into a real, live network", explains Nigel Bird, the NGH Standardisation Manager at Orange Group.

From Next Generation Hotspot whitepaper:


A new program called Next Generation Hotspot (NGH) - using the latest HotSpot 2.0 specification1 - allows a mobile subscriber to connect automatically and securely to Hotspots using his service provider credentials while maintaining roaming visibility for the operator. NGH enables operators to continuously monitor and manage “cellular-like” service over Wi-Fi domestically and internationally so as to enhance performance and meet the demand for mobile data services over heterogeneous RANs - cellular and Wi-Fi. This enables mobile operators to simultaneously optimize backhaul throughput, offload specific traffic rapidly (e.g. video) and achieve better economics than traditional, cellular-only solutions.

The Wireless Broadband Appliance (WBA) and Small Cells Forum recently announced collaboration on this topic, see here.

More details are available in this presentation embedded below:

Cellular-Wi-Fi Integration - technology and standardization roadmap

Interdigital: Cellular-Wi-Fi Integration from Zahid Ghadialy

Cellular or WiFi: Which is the preferred network access?

I was going through this report by Cisco on "What do Consumers want from WiFi" and came across this interesting picture. 

With the ease and availability of easy WiFi, it would be the preferred access technology whenever possible. Cellular access would be generally reserved for mobility scenarios or where there is no wifi network to allow access.

Another interesting observation from above is that the survey puts WiFi and Cellular security to the same level. Though the cellular is more secure in case of an open public WiFi scenario where an eavesdropper may be able to get hold of login/password information it is generally at the same level of security to a secured WiFi. On the other hand with cellular, lawful interception may be much more easy as compared to using secure WiFi.

I am sure that the content of last paragraph are debatable and am happy to hear your viewpoints.

A slidecast of the Cisco whitepaper mentioned above is embedded as follows:

Seamless offloading between Cellular Network and WLAN (CNW)

Last month I wrote a post about the 'Virtual Femtocell' concept. Apparently there is a company already doing this. The following is from GigaOm:

SR-Mobile, a Korean company that also has offices in Plano, Texas, is looking to help cellular carriers make seamless handoffs with Wi-Fi networks, enabling them to easily offload traffic from their cellular networks. The company, which is demonstrating its technology later this month at the Mobile Asia Expo, allows a carrier to switch a call or data traffic seamlessly between Wi-Fi, 3G and 4G. It does this with the help of a virtual radio agent mobile application on a mobile device that automatically switches between cellular and Wi-Fi modems. The VRA app works with a smart radio mobile controller that can access the network server and transfers the network traffic to the network core.


The benefit of this approach is that it allows a Wi-Fi hotspot to act as a virtual base station, which can be easily added and managed by an operator. If there’s capacity on the Wi-Fi network, it can seamlessly handle calls and data but if it gets overcrowded, it can switch back to the cellular network. SR’s approach also means that a carrier can expand their network capacity without a lot of investment, by relying on their existing Wi-Fi network or their user’s private Wi-Fi network. SR, which was founded by James Lee, a former senior staffer at Samsung Telecom America, is working on a trial with Korean operator KT, which will test SR’s technology on select LG phones.

More details about their solution in their presentation below:

Seamless offloading between Cellular Network and WLAN (CNW) from Zahid Ghadialy

Real Life Pictures of Small Cells Deployments in London

Visitors of this blog seemed to like the last set of deployment pictures I put up. As a result here is another set of pictures from the same Telefonica presentation by Robert Joyce. See also my earlier post on the same topic here.

Femtocells vs. Wi-Fi - Conflict or Complement?

How Wi-Fi and Femtocells complement one another to optimise coverage and capacity

View more presentations from Zahid Ghadialy

A presentation from the LTE World Summit 2012.

LTE - Service Opportunities; threats and challenges for the Rail Industry

Interesting presentation:

LTE - Service Opportunities; threats and challenges for the Rail Industry

View more documents from Zahid Ghadialy

See Also:

• Wi-Fi in Public Transport over LTE

Three Phases of WiFi Integration

From a presentation by Ericsson in the LTE World Summit 2012. Presentation available here.

Operator WiFi is becoming an important proposition and there are advantages and disadvantages of both of them. The above picture summarises the phases in which it may take place.

See also:

• Integration of Wi-Fi with Cellular Networks - WBA
• Operators strategy for supporting the ‘Mobile Data Explosion’ 

The 'Virtual' Femtocell and a competition for OTT Apps

Over the last few months we have been thinking of so many ideas around small cells and this is something that we thought. It looks very simple and straightforward and having talked to a few small cells experts, off the record, none of them seem to be able to see anything wrong with this concept. With the 'Small Cells World Summit' just round the corner I am sure this could be something worth a discussion.

I am explaining the concept using an HSPA+ setup but there is no reason why this would not work in an LTE Setup. This is a typical connection for HSPA+ Femtocell setup with the gateway acting as a concentrator for all Iuh connections and having a single Iu connection towards the core. I have not shown CS/PS connection separately for simplicity. 

We propose a 'Virtual' or 'Invisible' Femtocell concept where we think that the Femtocell is redundant but the concept can be used to avoid the coverage and capacity problems faced by the operators and at the same time avoid the 'Signalling storm', atleast on the access network side. Now most smartphones have WiFi stack inbuilt. For this concept to work, WiFi in the phone is a must. Instead of having a Femtocell in between, a modified stack could be embedded in the phone itself. The output of the phone over WiFi are the Iuh messages that can terminate at the gateway and no difference would be needed from the core network side. This is illustrated in the picture below.

The phones would also need to have an enhanced UI to be able to allow a user to select only this option when roaming. You don't want a situation where the user thinks that he is camped on the 'Virtual' femtocell and making/receiving calls while he is not and run up a huge bill.

Advantages of this approach:

• The Femtocells are no longer really needed and the end customer does not require to buy a separate equipment, which is different for different operators.
• The phones can be working whenever a reliable WiFi connection is available, even if they are abroad without incurring costly roaming charges.
• Some operators that do not have a lot of spectrum available avoid using Femtocells as they can cause interference and black holes in the coverage. 
• There is no worry of a femtocell being used abroad illegally thereby causing interference with spectrum in another country.
• Some security issues can be totally avoided and it would be worth for the operators that the keys being used cannot be seen by others.
• A lot of people use OTT apps like Skype, Viber, Whatsapp when abroad, being camped on WiFi to avoid costly roaming charges. This approach would mean that the normal Voice and Messaging becomes similar to OTT and can help operator avoid losing out to the OTT apps. 

Disadvantages of this approach:

• WiFi spectrum is already congested and does not always give reliable coverage.
• Security issues would have to be looked in detail to make sure this would be secure enough. Since this concept is similar to creating a VPN between the phone and the gateway, I wouldnt think there would be any issues though.
• Roaming revenues are a big cash cow for the operators, most of them would be unwilling to lose this if the phones are using this approach.

I think this concept is more suitable for the Residential Femtocells rather than the other Small Cells (enterprise, metro, pico, etc.) and there will always be a need for them. The main reason being that on a large scale, WiFi is extremely unreliable, prone to interference and not future proofed. A new device may cause interference that may take forever to resolve. Operating a small cell in the licensed spectrum would always make sense and the reliability would be much higher.

If you think this makes sense please click the 'Useful' checkbox so that I know.

As a company we are always looking to engage with other companies to discuss similar ideas. If you are a company dealing with Small Cells and are open to discussing similar ideas, please let us know.

Integration of Wi-Fi with Cellular Networks

Integration of Wi-Fi with Cellular Networks

View more presentations from Zahid Ghadialy

Presented by Tiago Rodrigues in the ITM Optimisation event in Prague on 18th April 2012.

There is another paper by NSN on the same topic that is available here. 

WiFi: Standards, Spectrum and Deployment

Yesterday, IEEE published its fourth revision to 802.11. The updates include faster throughput, improved cellular hand-offs, and better communication between vehicles in addition to other improvements.The following from IEEE website:

The new IEEE 802.11-2012 revision¹ has been expanded significantly by supporting devices and networks that are faster, more secure, while offering improved Quality of Service and, improved cellular network hand-off. IEEE 802.11 standards, often referred to as “Wi-Fi®,” already underpin wireless networking applications around the world, such as wireless access to the Internet from offices, homes, airports, hotels, restaurants, trains and aircraft around the world. The standard’s relevance continues to expand with the emergence of new applications, such as the smart grid, which augments the facility for electricity generation, distribution, delivery and consumption with a two-way, end-to-end network for communications and control.

IEEE 802.11 defines one MAC and several PHY specifications for wireless connectivity for fixed, portable and mobile stations. IEEE 802.11-2012 is the fourth revision of the standard to be released since its initial publication in 1997. In addition to incorporating various technical updates and enhancements, IEEE 802.11-2012 consolidates 10 amendments to the base standard that were approved since IEEE 802.11’s last full revision, in 2007. IEEE 802.11n™, for example, defined MAC and PHY modifications to enable much higher throughputs, with a maximum of 600Mb/s; other amendments that have been incorporated into IEEE 802.11-2012 addressed direct-link setup, “fast roam,” radio resource measurement, operation in the 3650-3700MHz band, vehicular environments, mesh networking, security, broadcast/multicast and unicast data delivery, interworking with external networks and network management.

“The new IEEE 802.11 release is the product of an evolutionary process that has played out over five years and drawn on the expertise and efforts of hundreds of participants worldwide. More than 300 voters from a sweeping cross-section of global industry contributed to the new standard, which has roughly doubled in size since its last published revision,” said Bruce Kraemer, chair of the IEEE 802.11 working group. “Every day, about two million products that contain IEEE 802.11-based technology for wireless communications are shipped around the world. Continuous enhancement of the standard has helped drive technical innovation and global market growth. And work on the next generation of IEEE 802.11 already has commenced with a variety of project goals including extensions that will increase the data rate by a factor of 10, improve audio/video delivery, increase range and decrease power consumption.”

¹ IEEE 802.11™-2012 “Standard for Information technology--Telecommunications and information exchange between systems Local and metropolitan area networks--Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”

The following is from a presentation by Agilent in LTE World Summit last year. It summarises the 802.11 standards, the Spectrum available and deployment use cases.