Small cell challenges include PIM, site acquisition

Operators are deploying small cells in larger numbers, but testing solutions company Anritsu contends passive intermodulation (PIM) could be present problems for some of these rollouts.

The company notes that PIM is not a huge problem with indoor installations because operators can move their antennas within a 1-meter diameter to reduce PIM generated by a nearby PIM source. But outdoor deployments of small cells mounted on poles and buildings are another matter indeed. "Moving the telephone pole [by 1 meter] is not a practical option," said Anritsu on its PIM Source educational blog.

The company proposed a solution, which involves using an antenna with a "clover leaf" azimuth pattern rather than a true omni-directional pattern to enable an operator to "steer" one of the azimuth nulls in the direction of a nearby PIM source. This can be accomplished by rotating the antenna on the mount.

In testing this approach, Anritsu recorded a significant reduction in PIM when the null in the azimuth pattern faced the PIM source. "We achieved as much as 30 dB reduction in PIM by simply rotating the antenna," the company said.

"Quasi-omni antennas look like a good option for small cell deployments, especially for sites where PIM sources are unavoidable," Anritsu added, noting this approach was suggested by Nicolas Cordaro of Verizon Wireless (NYSE:VZ).

Verizon has grown increasingly active in the small cell arena. In May, the operator said it would deploy LTE small cell products from Alcatel-Lucent (NASDAQ: ALU) and Ericsson (NASDAQ:ERIC) starting in the second half of this year to enhance localized capacity and coverage. Verizon had previously said it would deploy 200 LTE small cells this year.

Yet even if technical hurdles can be surmounted, operators are finding that outdoor site acquisition for small cells remains "challenging," according to a recent service provider survey conducted by Infonetics Research. The research firm is predicting that small cells will outnumber macro cell sites, but not by massive amounts because small cells will only be applied to targeted locales.

According to Infonetics' new survey, 83 percent of respondent operators have deployed small cells, which is up 11 percent from the 2012 survey. Further, 78 percent of respondents rated "multimode" and "seamless integration with macrocellular networks" as very important small cell features.

Infonetics also said alternatives to small cells such as Ericsson's Radio Dot System can reduce the need for distributed antenna systems (DAS) in locations such as medium to large enterprises. But operators expect small cells will complement DAS rather than replace them.

For more:
- see this Anritsu blog entry
- see this Infonetics release

Related articles:
ABI: LTE small cells driving backhaul growth
Verizon's rumored demands may help explain small cell slowdown
Small cell, DAS deployments could speed up under new FCC rules
Ericsson goes after enterprise, DAS market with Dot
Verizon taps Alcatel-Lucent, Ericsson for LTE small cells