If there’s one certainty in wireless, it’s multipath. Also known as multipath fading, it occurs when objects such as floors, ceilings, walls, buildings, vehicles, equipment, and people in the path between the antennas on either end of a communication link cause signal scattering and reflection. The signal level received at the antenna will fluctuate due to the multiple reflected signals adding in and out of phase. If the fluctuation causes the signal level to drop low enough, the link will be lost, ending the call or data session.

Multipath is a major problem in cellular and Wi-Fi because it undermines a provider’s ability to deliver the quality of service and high speeds that users increasingly demand. Most handheld devices are mobile, which compounds the problem because their multipath environment is constantly changing.

Previous solutions have focused on antenna diversity schemes, using multiple antennas in a single device. Typically, two antennas (MIMO) are used, with the second antenna located in a different position to provide a different polarization and/or radiation pattern. When the signal level of the first antenna drops due to multipath fading, the signal level of the second antenna is often a few or several dB higher, resulting in improved performance.

This solution is problematic given the limited space available inside wireless devices, often in less than optimal locations. Adding a second antenna requires additional volume and cost. Multiple antennas, RF chains, and feed points are needed, taking up valuable board space and adding to the cost. This is an unacceptable tradeoff for many smart-phone and tablet vendors.

New active antenna systems with an advanced antenna structure plus active components such as tunable capacitors and/or switches can be used to provide innovative capabilities not possible with traditional passive antennas. For example, the Ethertronics Air InteRFace Processing System uses multipath to maximize throughput and performance without requiring additional space in the device and higher component costs.

Handset, tablet, laptop and other device OEMs gain a powerful new option in the process for differentiating their products in the eyes of mobile operators and their customers. This technology also can be applied to Wi-Fi access points.

The Air InteRFace Processing System combines an active antenna system with an algorithm that together generates a theoretically infinite number of radiation patterns from a single antenna by changing the antenna mode (Fig. 1). As a result, the active antenna system now can dynamically respond to changing RF conditions quickly enough to minimize multipath-related problems and in turn maximize both throughput and reliability.

46% Higher Throughput

While an infinite number of radiation patterns is possible, the optimal number is four patterns. Using a sample and switch concept, the algorithm can quickly survey multiple radiation patterns from the same antenna to determine the best pattern to use for the given RF environment, at that particular moment, in that particular place. The algorithm automatically makes another selection as the device moves into a new environment. The active antenna system then can dynamically respond to changing RF conditions quickly enough to minimize multipath fading, providing significantly faster data throughput speeds and improved reliability.

This flexibility produces a significantly higher signal-to-interference plus noise ratio (SINR) than conventional passive antennas can yield. A high SINR maximizes uplink and downlink speeds—not merely incrementally, but instead to a degree that’s noticeably faster to end users.

The table illustrates how this active antenna system significantly improved downlink speeds when it replaced one of the two baseline antennas in an off-the-shelf access point. (A vendor could choose to replace only one or all of the antennas to provide additional performance and reliability.) Figure 2 shows how this active antenna system maintains throughput enhancements over distances of 120 feet.

Figure 3 illustrates the office environment used in the demo. The cubicle walls and other physical obstructions created multipath signals, making for a challenging RF environment. Yet the active antenna system improved throughout by up to 46% in the part of the office where multipath was highest.

One Solution For Multiple Applications

This access point demo is just one example of this technology’s potential applications. In handheld devices such as smart phones and tablets, this active antenna system also is ideal for mitigating the detuning effects due to the position of the user’s head, hand, or both as there are multiple radiation patterns to choose from. As a result, it provides a noticeably better user experience with fewer dropped calls and consistently higher data throughput.

The key word is “noticeably.” Device OEMs and service providers benefit when performance is so superior to the competition that their customers and reviewers notice. For example, they gain a market differentiator that enables them to compete less on price. At the very least, consistently great performance avoids the swings that drive up customer support inquires and complaints. 

In Wi-Fi applications, the active antenna system enables a lower density of access points with no performance tradeoffs. It could be attractive to enterprises because it lowers the capital and operational expenditures of their office wireless local-area networks (WLANs).

Changing Conventional Wisdom

Historically, antennas have been considered passive structures with a single, fixed radiation pattern. Conventional thinking was to offset multipath fading by using diversity schemes with at least two antennas. This solution is at odds with the trend of bigger screens, bigger batteries, “thin” devices, and an ever-shrinking amount of space for components, including antennas.

Innovative, new active antenna system technologies are changing this thinking by creating multiple radiation patterns from a single antenna structure, providing MIMO’s benefits without the additional volume and costs incurred with traditional diversity schemes. Active antenna system technology is changing the way antennas are perceived in the user experience: as an integrated RF antenna system consisting of the antennas and active components combined with advanced algorithms. This systems-based strategy gives device designers a fast, cost-effective, and high-performance alternative to differentiate their products in a very competitive landscape.