Cellular networks must overcome many obstacles, including buildings, trees, signal fading, and multipath effects. One solution would involve simply increasing transmit power in the face of these obstacles, but the carefully crafted communications standards that govern cellular communications networks do not allow for such frivolous increases in transmit power. And approaches such as multiple-in, multiple-out (MIMO) methods can improve cellular network performance but require upgrades to the network's base stations and antennas. Fortunately, techniques such as the antenna-diversity technology developed by Magnolia Broadband (Bedminster, NJ) can enhance the performance of a code-division-multiple-access (CDMA) cellular network by making improvements to the handsets, rather than the base stations.

The company's mobile-transmitter-diversity (MTD) technology provides diversity gain by using the power control bit transmitted by a network's base station(s) and by using multiple transmit antennas within the mobile unit. Of course, the small size of modern mobile units limits the number of diversity antennas that can be practically employed in a handset, generally to two antennas. At the base station, of course, and depending on the installation, a greater number of diversity antennas are possible.

Magnolia Broadband's diversity technology exists in two forms: with equal-gain-diversity-combining (EGC) techniques and with maximum-ratio-diversity-combining (MRC) methods. In the former approach, MTD-EGC, only the phases of the signals transmitted from the mobile unit to the base station are adjusted to produce coherent combining at the base station's receiver. When the base station has only one receive antenna, and the MTD algorithm provides stable operation, this scheme is equivalent to two-level EGC approaches. In the latter method, both the phases and amplitudes of the signals transmitted from the mobile antennas are adjusted for coherent combining at the base-station's receiver. Using the same assumption that the base station has a single receive antenna, and assuming stability of the MTD algorithm, this method is equivalent to a two-level MRF technique.

Magnolia Broadband is a fabless semiconductor company that uses silicongermanium (SiGe) bipolar-complementary-metal-oxide-semiconductor (BiCMOS) technology for its ICs. The semiconductor process provides the performance needed for high-frequency wireless operation but with low power consumption.

Of course, application of Magnolia Broadband's MTD technology requires adoption by handset designers and suppliers. The technology, developed for use with a mobile unit's radio circuitry, is also applicable to baseband circuitry. It does add some cost to a handset, in terms of the additional integrated circuits (ICs) for implementing MTD in the handset and the licensing of the technology from Magnolia Broadband, but it provides significant enhancement in cellular network performance in terms of out-of-cell interference rejection.

In addition to reducing such cellular network quality-of-service (QoS) issues as dropped calls and sporadic reception, the company's DiversityPlus™ proprietary diversity algorithms and licensed ICs can enable communications carriers to improve coverage and boost data rates.

Originally developed for use with cdma2000 systems, the DiversityPlus™ technology is also being applied to UMTS, Wi-Fi, and WiMAX networks. In most systems, adding a single chip and pair of antennas to the handsets in a given network can improve network capacity by 40 percent and network coverage by 50 to 60 percent. The chip incorporates RF circuitry and an ARM 32-b reduced-instruction-set-computer (RISC) processor.

Magnolia Broadband, Inc., 550 Hills Dr., Bedminster, NJ 07921; (908) 234-0885, FAX: (908) 234-2552, Internet: www.magnoliabroadband.com