Implementation Challenges

Though active antenna techniques offer significant performance advantages to network operators in terms of coverage, capacity, and terminal battery life, these schemes haven’t been deployed widely due to a number of practical implementation considerations and economic limitations with traditional analog RF network equipment.

Significant additional equipment and installation costs are required to deploy most of these systems. As discussed above, RET and advanced adaptive tilt systems require electromechanical subsystems for the control and activation of the vertical tilt functions. MIMO, beam forming, and advanced diversity systems require the addition of multiple RF components (such as transceivers, power amplifiers, and masthead amplifiers), multicolumn passive antenna arrays, coax cables/feeders, and associated mounting hardware.

In addition to the purchase cost of these components, these elements add to the cost and complexity of the installation, with site license fees to install new equipment and increased installation costs to contractors due to the additional weight and wind load. In some cases, costly rooftop or tower re-enforcement may be required to support the additional network elements.

Increasingly, OPEX costs are becoming the dominant factor impacting their total cost of ownership. Unfortunately, with traditional analog RF systems, the OPEX costs typically scale directly with the added complexity of the active antenna approach taken. Additional active components like masthead amplifiers, power amplifiers, and advanced tilt systems consume more power.

Monthly site leasing costs are also increased based on the weight or wind load of these added elements, which can be a significant potential problem for MIMO antennas. These added costs are particularly acute in rural areas in emerging markets where sites are powered by costly trucked-in diesel fuel and in areas where site real estate/leasing costs are at a premium due to local community restrictions against “unsightly” masthead or rooftop equipment.

In general, “cost of quality” tends to scale with an increasing number of RF components within complex systems. This has led to significant concern by many operators that employing advanced antenna systems may degrade network reliability and increase repair and maintenance costs. Furthermore, electromechanical RET and advanced tilt systems add further complexity and are subject to higher potential failure rates than solid-state system elements.

And, the obvious concern with traditional active antenna systems is the added carbon footprint from both the manufacturing of added network elements and the fuel consumed to power them. In addition, an increasingly challenging problem for operators is related to the visual impact of adding new equipment to existing cellular sites.

For example, a local operator in Scottsdale, Ariz., was unable to get approval to install a traditional cabinet-mounted basestation on the ground below an existing antenna tower. So, the operator had to commit to dig a chamber underground and bury the new equipment to hide it from view—a very expensive solution!

Changing the Radio Architecture

So how can the performance benefits of advanced antenna solutions be achieved without the penalties of higher costs, reduced reliability, and negative environmental impact? One solution is the antenna embedded radio (AER), a fundamentally different radio architecture for mobile communications.

This new network radio architecture implements a novel signal-processing chain inside the AER (Fig. 3). A central basestation radio server exchanges data with the server over a fiber-optic link according to standards established by the Common Public Radio Interface/Open Base Station Architecture Initiative (CPRI/OBSAI). A central processing unit (C-hub) inside the AER controls all RF micro-radio (m-radio) units individually, each serving one antenna element.

This fully digital processing chain allows for the individual adjustments of amplitude and phase of each antenna element as well as the grouping of several elements into logical antennas with independently fading signals. The AER system is highly scalable and easily reconfigurable, permitting the groupings to be dynamically changed online through the radio sever.

Figure 4 shows an example of the scalable configuration realizing up to four independent logical antennas. As indicated, with no change in hardware, the AER system can be configured to replicate the performance of traditional remote radio head + passive antenna systems (when configured for one Tx and two Rx signal paths). The AER has built-in Tx diversity and can be configured to support 2x2 or 4x4 MIMO signal paths, providing a “future proof” solution as the network software from basestation OEMs evolves to exploit these capabilities.

Figure 5 illustrates the simplicity of deploying the AER system. Because of the high level of integration, the AER can be mounted up the tower or on a rooftop as if it were a traditional passive antenna. Then, operation only requires the CPRI or OBSAI fiber-optic cable and power supply to be connected the input of the AER.