Hetnets are Coming But More Spectrum Said Still Needed for Mobile Broadband

Mobile operators should take a three-step approach to creating heterogeneous networks (hetnets) to boost coverage and capacity to meet user demand for data-hungry services, said Ericsson Mobile Broadband Director Hanna Maurer Sibley in an interview. The first is to “improve” existing macro cells with more spectrum, advanced antennas and advanced radio base stations, she said. Operators should then “densify” the macro network with a small number of strategic cells to improve capacity, she said.

Most operators have already completed these stages and are now moving to the “add” phase and testing microcells, picocells and Wi-Fi, Maurer Sibley said. Giving end-users a better experience requires “intelligent off-load” that’s monitored from handsets, radio access networks and core networks, Small Cell Forum Vice President-Americas Andy Germano told us. Both said hetnets face several challenges and won’t do away with the need for more spectrum to be allocated to mobile services.

How operators add small cells is “crucial” to their success, Maurer Sibley said. They must carefully analyze where to add the cells and coordinate signals to be coherent with their macro deployment, she said. This is the most technically advanced way to coordinate, in order to derive the most benefits from the macro and small-cell layers, she said.

"Coordination” is a key word in Ericsson’s heterogeneous network strategy, Maurer Sibley said. For coordination to work best, the vendor for the macro and pico cells must be the same, she said. The pico and macro layers need to share information quickly, which is easier if they both have the same vendor, she said. Operators are trialing a variety of “add” approaches now, but there are no large deployments yet, she said.

Ericsson launched a new dialogue with operators on “app coverage” in a June mobility report (http://xrl.us/bppjeq), said Maurer Sibley. It wants the discussion to move to whether, for example, a user can access YouTube or Netflix on the bus, she said. The apps that people want are becoming more important to end-user satisfaction, so operators are talking to Ericsson about how to provide apps at various locations on their networks, she said. Heterogeneous networks are a way to solve app coverage problems, she said.

Hetnets are a “buzzword” in the industry now, Small Cell Forum’s Germano said in an interview. He defined them as a combination of the macrocellular architecture of towers and mobile networks; dual-mode technology that enables different signaling technologies (2G, 3G, 4G) in the same box, Wi-Fi, distributed antenna systems, and cloud radio access networks. Hetnets are more than just small cells and Wi-Fi, he said. Operators around the world are leveraging all of these technologies for delivering services and connecting back to the core network, he said.

Small cells can also be femtocells deployed at home, Germano said. Around 60 operators have committed to deploying small cells in the U.S., Europe and Asia, he said. The U.S. likely has deployed the most femtocells because Sprint, Verizon and AT&T are shipping high volumes of them, he said. The U.S. is the first place where all three major operators decided to offer femtocells, and the same is happening in Japan, he said. In the U.K., Vodafone, which was the first operator to announce the launch of femtocells (in July 2009), has shipped them to at least six countries around the world, he said. Small cells for better coverage appears to be a customer-retention tool, he said. At the next power level are picocells, followed by microcells and “metrocells,” which are deployed on buildings, light poles and other places where network operators need frequency coordination with the macro network, Germano said.

Hetnets face several challenges, said Germano and Maurer Sibley. Because regulations on radio base stations are national, cell sites in Russia, for example, had to be approved by the military, said Germano. Many rules in Japan, Brazil, Turkey and elsewhere had to be revamped to support small cells and hetnets, he said.

The forum has also seen concerns on the radio side, Germano said. Some operators originally worried about interference to macro cells from femtocells, he said. The original benefit of small cells was increased coverage, but indoor usage raises no interference issues with macros, he said. Now, however, with pico and micro cells being used more outdoors, operators are starting to pay attention to interference, he said.

Capacity is a huge issue with mobile networks because of smart devices, and operators are embracing small cells as a way to off-load capacity, Germano said. He sees “heavy migration” to capacity value propositions such as off-loading data from the macro to smaller cells, and the use of Wi-Fi to relieve the capacity crunch.

Another benefit of small cells is more efficient spectrum use, Germano said. Smaller cells mean fewer people sharing the same spectrum, and re-use of the spectrum, he said. Allocating more spectrum is important for adding capacity but it’s also expensive and takes years, he said. In addition, devices are needed to support new spectrum, he said.

With Wi-Fi, spectrum is free, but because anyone can use it, mobile providers can’t guarantee quality of service, Germano said. But given the data tsunami, operators are doing whatever they can to off-load capacity. The forum predicts offloading will require Wi-Fi and small cells together to provide the best user experience, he said. Intelligent off-load through monitoring from handsets, the radio access network and core networks will create more efficiency and give users a better mobile experience, he said.

Spectrum frequencies used in North America and Europe for mobile broadband are generally the same, with exceptions such as the 700 MHz band used in the U.S. for 4G and the 2.6 GHz band available in Europe but not North America, said Maurer Sibley. The bigger issue is how much spectrum will be needed for wireless services in the future, she said. Ericsson believes much more spectrum will be necessary if operators want to keep customer happy, she said.