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Operators unhappy over Wi-Fi and unlicensed cellular coexistence plans

Controversy has raged for well over a year now over plans by some mobile network operators (MNOs) to extend their spectrum into unlicensed 5GHz bands currently occupied by Wi-Fi. The arguments have been both commercial and technical, centering on the rights of MNOs to compete with established Wi-Fi networks and at the same time the efficiency or fairness of mechanisms for coexistence between the two.

LTE-U enables 4G/LTE cellular services to be extended into the 5GHz unlicensed bands, which is obviously attractive for MNOs because it gives extra precious spectrum without having to pay for it while making it easier to support high bandwidth applications like premium live video streaming. But the initiative, initially proposed by Qualcomm and Ericsson, has gained some traction within the 3rd Generation Partnership Project (3GPP) primarily because many MNOs want to gain full control of heterogeneous networks combining licensed and unlicensed spectrum, so there is a major commercial force here.

MNOs have expressed frustration over Wi-Fi offload, which is necessary to avoid overload on their networks and give their subscribers the best quality experience, but means they have less control over end-to-end traffic. Not surprisingly though those Telcos with extensive Wi-Fi hot spot networks take a different line and are opposed to LTE-U. Therefore we find that operators like AT&T and BT with huge investment in Wi-Fi hotspots but smaller presence in cellular are opposed to LTE-U. On the other hand Telcos that have not bet so much on Wi-Fi but have major cellular operations now support LTE-U, including big hitters like Verizon, China Mobile, NTT DoCoMo, Deutsche Telekom and TeliaSonera.

Notably though some of the world’s biggest providers of mobile services are ambivalent about LTE-U, which some of them see as complicating rather than simplifying the drive towards heterogeneous services combining licensed and unlicensed spectrum. The view there is that Wi-Fi is best placed to occupy the unlicensed spectrum with a lot of momentum and investment behind it. The LTE-U camp counter that the technology can carry twice as much data as Wi-Fi in a given amount of 5 GHz spectrum through use of carrier aggregation via LTE-LAA. This was already defined in the LTE standards and enables multiple individual RF carrier frequencies, either in the same or different frequency bands, to be combined to provide a higher overall bit rate.

This may be true as far as it goes but is largely irrelevant for users wanting to access broadband services in their homes or public hot spots, according to the Wi-Fi community, a view shared by some MNOs as well. Birdstep, a leading Swedish based provider of smart mobile data products enabling heterogeneous services combining cellular and Wi-Fi, argues that the story is not just about the wireless domain itself but also the backhaul infrastructures behind it. Any spectral efficiency advantage offered by LTE-U would be more than cancelled out by inherent inefficiencies in the backhaul. By offering access to the world’s broadband infrastructures Wi-Fi offers greater overall scale and redundancy.

Another Wi-Fi specialist, Turkey based AirTies, contends that LTE-U is just a spectrum grabbing bid by MNOs and should be resisted. Air Ties has developed mesh and routing technologies designed to overcome the problems encountered by Wi-Fi in the real world and these are only going to get worse as unlicensed spectrum reaches even higher frequencies. The next generation of Wi-Fi based on the emerging IEEE 802.11ad standard will run in the much higher frequency band of 60 GHz, which will potentially yield a lot more capacity and performance but increase susceptibility to physical obstacles and interference. It will only work with further developments in the sort of intelligent beam forming, meshing and steering technologies that AirTies has invested in.

It is true that LTE-U proponents have worked hard to mitigate any impact of coexistence with LTE-U on Wi-Fi. In Europe and also Japan they were forced to do so anyway by regulations that required LTE-U to adhere to similar rules over fair access to spectrum as Wi-Fi. These rules insist on incorporation of LBT (Listen Before Talk) into LTE-U, a mechanism originally developed for fixed line Ethernet networks where there was a shared collision domain (it was called Carrier Sense Multiple Access or CSMA). Stakeholders that are not in favor of rapid LTE-U deployment point out that in the old Ethernet days before 10BaseT/switching, CSMA proved inefficient when there were to many devices trying to get onto the same collision domain. Total capacity could drop drastically and this issue could be reborn into the wireless world.

The European Union specified two options for LBT, one the scheme called DCF/EDCA already adopted for Wi-Fi standards and a newer scheme known as Load Base Equipment (LBE), differing in the procedure for backing off when detecting traffic in a given channel.

Naturally enough there has been an assumption in the LTE-U camp that any deployments will be safe if they do adhere to the EU’s LBE LBT standard. But this assumption has recently been challenged by CableLabs in a simulation modeling a million transmission attempts on sets of nodes following the EU LBE LBT rules. The EU LBE turned out to scale badly with increased numbers of devices, with growing numbers of collisions. This will only amplify concerns expressed by broadcasters such as Sky, as well as by some major vendors like Cisco with feet in both the Wi-Fi and LTE camps, that LTE-U poses a threat to quality of service for premium video especially.

There are no signs yet of the LTE-U camp giving up on their efforts to infiltrate the 5 GHz domain, arguing correctly that by definition unlicensed spectrum is free for all and cannot be owned by any one wireless technology. But there is a strong case for holding off from LTE-U deployments until further extensive tests and simulations have been carried out to assess the impact on capacity and QoS in real life situations.

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Wi-Fi offload can help mobile operators deliver network neutrality

Network neutrality has come back to the boil in 2014 following US carrier Verizon’s famous Federal court victory in January over the regulator FCC (Federal Communications Commission), allowing it to differentiate between services delivered to its broadband customers. This was followed in April by the European Union approving strict network neutrality with the message it would take a much tougher stance than the FCC in upholding the rules. Naturally this was widely interpreted as setting Europe apart from the US, but the reality is that both are taking a more nuanced approach than in the past. Even the EU proposals allow for provision of specialized services, providing they do not intrude into network capacity set aside for the general Internet. The tones may be different but the broader implication both in the US and Europe is that network neutrality can never be fully attained through legislation, any more than true equality of wealth can be achieved via measures such as progressive taxation – both are aspirations or focal points.

For mobile operators the aspiration of network neutrality has assumed a logistical and economic dimension with the great proliferation of data hitting their infrastructures. Many have opposed strict net neutrality for the simple reason that their core and backhaul networks have limited capacity and would be unable to cope without traffic engineering and the ability to differentiate between different service or application types.

But now Wi-Fi offload has entered to change the game, giving operators an option for relieving their overstretched backhaul networks and for that matter their radio access capacity as well, by taking advantage of broadband infrastructures. It was at the Mobile World Congress in 2013 that offload first seemed to have risen right up the agenda for mobile operators. Generally, particularly before deployment of 4G/LTE, broadband networks had greater capacity and crucially lower costs than the fixed backhaul networks serving radio base stations. For this reason those major Telcos with their own network of hot spots have been leading the march towards Wi-Fi offload. In the US AT&T has built large Wi-Fi hot zones in mostly urban areas with high levels of cellular traffic, specifically for offload to help relieve congestion on its core mobile network.

The implications of such offloading for network neutrality have not attracted much attention, but are likely to be profound nonetheless. The fundamental point is that by freeing up capacity on the mobile network, offloading can help mobile operators meet their net neutrality obligations as laid down by regulators in the region concerned, while still having scope to offer specialized services. An operator could say offer an OTT video service such as Netflix with guaranteed QoS over the cellular network, resorting to Wi-Fi offload for third party OTT services such as YouTube. Alternatively Wi-Fi could be used for specialized services, especially by operators like AT&T that have their own overlapping hot spots and cellular networks on a large scale.

We are already seeing this happen, with Sprint in the US now offering calling and messaging over Wi-Fi when within range of suitable hot spots. Sprint incidentally was one of the first major carriers in the world to make serious use of Wi-Fi offloading for data.

We are going to see plenty more such offerings over the coming years. It will be interesting to see the extent to which operators will align Wi-Fi and cellular within heterogeneous service offerings effectively to escape the shackles of net neutrality while obeying the basic rules as stipulated by regulators.