AGL Magazine - AGLM - June 2017

The Advantages Of Wireless Backhaul For Small Cells

Don Bishop 2017-06-01 07:45:00

Nitin Madan, product line manager at Broadcom.

Using a combination of unlicensed frequencies, phased antenna arrays for beam steering and semiconductor chips initially designed for consumer products makes the difference in providing affordable backhaul for small cells. The cost and difficulty of providing backhaul to small cells can make the difference in whether carriers would construct the access points. In the early days of cellular network construction, carriers were reluctant to share antenna space on their towers with competing carriers. Similar reluctance to share small cell installations with other carriers either provides a competitive advantage or hampers network densification, depending on one’s point of view. Randall Schwartz, a senior analyst and consultant with Wireless 20/20, led a session about small cell connectivity at the Tower & Small Cell Summit in September 2016. He said when connecting the small cell to the wireless network costs more than the small cell itself, it drives Wireless 20/20 crazy as it develops business plans for small cell deployment. “If you can buy a small cell for $3,000, but a broadband connection with wireless is $5,000, that's an immediate red flag for us,” he said. Schwartz questioned whether wireless carriers should view small cells as dedicated resources (one carrier per small cell) versus shared resources, the way carriers share antenna space on towers. A panelist in the session, Nitin Madan, product line manager at semiconductor manufacturer Broadcom, is responsible for his company’s 60-GHz products and some of its Wi-Fi combination products for mobile phones. He said that mobile network operators pursue deployment of access points such as small cells primarily to increase capacity, sometimes referred to as network densification, and extending coverage is not a high priority for them. Nitin Madan, product line manager at Broadcom. Photo by Don Bishop “The only way we can provide gigabit speed to the next billion people on a mobile platform is with network densification,” Madan said. “Although that’s well understood, many underestimate the logistics. Each of these small infrastructure nodes has to be supplied with power and fiber or some other high-bandwidth backhaul. This is more expensive than what we imagine it could be if installers have to dig up the streets. The permitting process of going municipality by municipality, community by community, blows up any business case.” Three Elements Broadcom’s effort to make the process of connecting the small cells with a fiber hub over multiple hubs wirelessly as inexpensive as possible rests on three elements: its use of radio-frequency (RF) spectrum; phased antennas; and high-volume, consumer-grade silicon devices (semiconductors). First, Broadcom tries to use unlicensed frequencies in the band from 57 Ghz to 71 Ghz. “There’s plenty of spectrum out there, with no upfront cost to obtaining permission to use the frequencies,” Madan said. Second, the company tries to use phased antenna arrays for electronic beam-steering. “Using beam-steering allows you to be pretty sloppy in your deployment,” Madan said. “You do not need two dish antennas precisely pointing at each other anymore, because of electronic beam-forming. Each node can find the next node or backup node in case the first node is blocked for some reason.” Third, as much as possible, Broadcom uses high-volume consumer silicon that goes into the mobile cell phones so that, at the outset, the components the company uses have a certain base volume that subsidized much of the research and development. “This is important, and it’s also not traditional in the infrastructure industry,” Madan said. “Because we use consumer silicon, each wireless link is not fivenines reliable. But you can do mesh networking to make sure that the network, as a whole, is robust.” (Five-nines reliability refers to making the connection 99. 999 percent reliable, which represents a maximum of about five hours of outage in a year’s time.) "The RF side offers Broadcom flexibility, because it can arbitrarily increase the number of antennas the RF module has to support." High Frequencies In the semiconductor business, cost is a function of volume, and Madan said Broadcom uses derivatives of technologies architected for consumer electronics to control the cost. He said the architected solutions tend to be modular. Path loss at 60 Ghz is extremely high. “It’s a hostile frequency because of oxygen absorption and other effects that reduce range,” Madan said. Engineers can increase the range by increasing the amount of power that the antenna panel can output, which Broadcom does by increasing the number of antennas. Madan said the use of 60-GHz frequencies makes it simple to increase the number of antennas because they are so small. “With the form factor of an iPhone, you can have units that can communicate 300 meters line-of-site with a good margin of signal strength at multigigabit-per second speeds,” he said. To serve the 4G small cell market, Broadcom makes use of the technology it developed for Wi-Fi, including the intellectual property of the semiconductor chips themselves. The company also uses software it developed for Wi-Fi test infrastructure so its customers won’t have so steep a learning curve — because they're familiar with products the company already makes. Moreover, Madan said the company views the market as too new for accurate product forecasts. “I cannot tell you today what RF range the market needs to connect a small cell site to the closest fiber over wireless,” he said. “That’s why we’ve tried to make our system as flexible as possible, so that as people learn and discover the optimum configuration, it does not demand us to tape out and design new chips for each iteration.” The RF side offers Broadcom flexibility, because it can arbitrarily increase the number of antennas the RF module has to support. Meanwhile, on the baseband processing side, most of the timing’s sense of logic is in software that the company can change with a firmware upgrade. “But the real flexibility comes in the way we architected the RF front end,” Madan said. “We’re optimistic about it because, with the use of phased antenna arrays, you’re not broadcasting energy in every direction. We focus a narrow beam of energy toward the receiver. This allows us to use the spectrum more wisely.” Broadcom wants to replace the fiber that comes to the small cell site. “We want to make wireless fiber on the backend.” Madan said. “How the user accesses that network, I’m completely agnostic to — it could be 5G; it could be Wi-Fi. At Broadcom, we like Wi-Fi. We have a strong feeling that 80 percent of all wireless data goes over Wi-Fi, and we don’t see that changing.” Especially for deployments that call for non-line-of-sight wireless connections, Madan said he is bullish on the Citizens Broadband Radio Service, which allows access to frequencies in the 3.5-GHz band. “Indoors, CBRS could be a big advance coupled with our technological innovations such as massive multiple-input, multiple-output communications. With line-of-sight wireless connections, millimeter-wave frequencies still have some advantages.” The CBRS and millimeter-wave frequencies would complement each other well, Madan said. He said the days in which the telecom industry operated on a cost-plus model may be behind us. “We need to find ways to cut the cost, because I don’t think we can pass on the cost as price increases to the end customers anymore,” he said.

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