Small wireless-network cells are being deployed in growing numbers. For the most part, they are being used to provide capacity improvements in hot spots, where high subscriber densities overwhelm the macro cell. Compared to a macro cell, they provide lower output power in a lighter-weight, smaller form factor. In a recent study, NEC and Ubidyne partnered to investigate the benefits of three-dimensional (3D) -beamforming small cells with the use of active antenna technology. Titled “Enhanced Network Capacity and Coverage with 3D Beamforming Small Cells,” the resulting 15-page white paper benchmarks passive small cells with active-beamforming small cells.

Active-beamforming small cells are expected to be an integral part of future Long Term Evolution (LTE)/fourth-generation (4G) heterogeneous networks (HetNets). Yet small cells still face major obstacles, such as backhauling, site acquisition and maintenance, power supply, and inter-cell interference. In terms of backhauling, for example, the solution for every small cell must be decided on a case-by-case and site-by-site basis. Thus, backhauling is becoming more challenging for operators in terms of transport network complexity, the variety of backhauling options, and their ability to find the optimal solution. In dense urban areas, however, the biggest problem faced by operators is probably site acquisition and maintenance—a nearly impossible task when sites are limited.

Some of these challenges may be addressed with the array or 3D beamforming small cell. According to the firms’ study, 3D beamforming can lead to an average macro-cell load reduction (offloading) of 40%. An active 3D beamforming small cell comprises several antenna elements and transceivers, which are arranged in a matrix. Each antenna element has its own transceiver underneath it. In addition, a central controller and a baseband unit are located below the 4 x 4 transceiver matrix.

The antenna elements are spaced a fixed distance apart, relative to the wavelength of the transmitted and received signals. On the transmit side, signals from all transceiver elements superimpose to form a larger beam. That beam’s shape can be changed simply by varying the phase and amplitude transmitted by each transceiver. Receive beamforming is done in similar fashion. Thus, the matrix enables flexible vertical and horizontal beamforming—including independent beam shaping in the downlink (DL) and uplink (UL). Multiple simultaneous beams per cell with individual tilt optimization per beam also can be applied, as can multiple beams for multi-sector operation.

According to the firms’ investigations, 3D beamforming and individual tilt optimization for multi-beam, active small-cell antenna arrays outperforms existing passive small-cell solutions. In addition to providing about 4X higher offloading, beamforming can help to improve coverage, reduce the number of small cells and backhauling requirements, and reduce inter-cell interference. These advantages lower the cost of site acquisition and network-wide power consumption while improving network optimization.

Ubidyne GmbH, Magirusstr. 43, 89077 Ulm, Germany; +49 731 880071-0, www.ubidyne.com.

NEC Corp., 7-1, Shiba 5-chome, Minato-ku, Tokyo 108-8001, Japan, www.nec.com.