Maximizing Throughput and Coverage for Wi Fi and Cellular

Transcription

1 Maximizing Throughput and Coverage for Wi Fi and Cellular A White Paper Prepared by Sebastian Rowson, Ph.D. Chief Scientist, Ethertronics, Inc. March 2012

2 Introduction Ask consumers and business users what improvements they would most like to see in wireless, and it s almost guaranteed that they ll say faster cellular or Wi Fi service, improved reliability or both. Delivering faster, more reliable wireless is an opportunity for vendors and service providers to differentiate themselves. But in both cellular and Wi Fi, that s easier said than done. For example, in access points (APs), smartphones, and tablets, designers and end users prefer highly compact form factors. This preference is at odds with the trend toward increasing the number of antennas to support Multiple Input, Multiple Output (MIMO) techniques and multiple frequency bands. Worse, in smartphones and tablets, the screen and battery take the majority of space in the device, with processors, antennas and other components left to make do with whatever space is available, frequently in less than optimal locations. Another challenge is rapid signal strength variations, which are present in every environment and sap throughput. Access points are frequently inside buildings. The walls and structures create a complex environment, decreasing throughput and connectivity. But it s even more of a problem for handheld devices simply because unlike Wi Fi access points, they re constantly on the move, so their conditions are always changing. This white paper provides an overview of a powerful, new solution to these challenges: Ethertronics Air InteRFace Processing System technology. The white paper will start with basic definitions of radiation patterns, multipath, diversity, etc. for a better understanding of antennas. The paper will then give an overview of the Air InteRFace Processing System technique and its benefits. To prove the technology, an implementation with an access point will be shown along with test results from measurements performed over more than 6 months. Results show that throughput can be increased almost 50% using the technique. Radiation Patterns, Multipath, and Diversity Explained The radiation pattern of an antenna is the variation in radiated or received power as a function of aspect angle. The radiation pattern of an antenna can be visualized as a 3 dimensional surface surrounding the antenna, where the shape of this 3D surface relates to the radiation intensity in the various directions. Typically the radiation pattern of an antenna is plotted on a logarithmic scale in units of db, where the radiation pattern is referenced to the maximum radiation intensity. A radiation pattern is "isotropic" if the pattern is the same in all directions. Antennas with isotropic radiation patterns don't exist in practice, but are sometimes discussed as a means of comparison Page 2 of 14

3 with real antennas. A theoretical isotropic antenna can be used as a reference for comparing an antenna s radiation performance, with the isotropic antenna having a 0 dbi (db referenced to isotropic) gain in all directions. Typically radiation patterns of antennas will have one or more nulls or regions of reduced radiation intensity. Figure 1 shows a typical radiation pattern from a passive antenna. Red areas indicated high gain, or a strong signal. Green areas indicated low gain or low signal strength. Typical Passive Antenna Fixed Radiation Pattern Figure 1: Typical passive antenna with a single, fixed radiation pattern. The polarization of an antenna is the polarization of the radiated fields produced by an antenna, evaluated in the far field. Polarization is the figure that the E field traces out while propagating. The co polarized component of the antenna s radiation pattern is the main or dominant linear polarization transmitted or received by the antenna. The cross polarization component of the antenna s radiation pattern defines the ability of the antenna to also transmit or receive the orthogonal linear polarization. Most antennas in wireless and mobile devices are linearly polarized, and have both co and cross polarized components. The cross polarized component comes in handy when the wireless device is operating in a multipath environment. Multipath is prevalent in wireless communications. Multipath, also termed multipath fading, is caused by reflections and scattering from objects in the path between the antennas on either end of a communication link: floors, ceilings, walls, buildings, vehicles, equipment, people, etc. The end result of multipath is that the signal level received at the antenna will fluctuate, with this fluctuation being caused by multiple reflected signals adding in and out of phase. This fluctuation in signal strength at the antenna can be quite large, and can at times result in the signal level dropping low enough to where the communication link is terminated. To mitigate the effects of multipath fading, antenna diversity schemes using multiple antennas have been developed. These antenna schemes can take many forms: radiation pattern diversity, spatial diversity, and polarization diversity. The basis of the technique is to use a second antenna to receive the incoming signal along with the first or main antenna. This second Page 3 of 14

4 antenna is located in a different position, has a different polarization, and/or has a different radiation pattern compared to the first antenna. When the signal at the first antenna drops due to multipath fading, the signal at the second antenna will often be a few, or several, db higher resulting in improved communication system performance. Implementing a standard antenna diversity technique requires a second antenna to be integrated into the wireless device. Figure 2 shows the receive signal strength as a device with two antennas moves through a multipath environment. Signal 1 and Signal 2 show the received signal strength at the two different antennas. The Combined Signal (in bold) is the signal obtained using switched diversity. In this case a simple algorithm is used to select the best antenna by switching antennas when the signal level falls below a pre defined threshold. The resulting signal has fewer weak spots than either of the individual signals and results in a high average receive signal strength. Figure 2: Signal strength of two antenna system in multipath environment. Page 4 of 14

5 Figure 3 shows the theoretical Bit Error Rate (BER) as a function of Signal to Noise Ratio (SNR) for different diversity antenna configurations. The same BER can be achieved with a lower SNR when a diversity system is used. To achieve a 1% BER with no diversity a 15 db SNR is required (black curve). In the case of two antenna receive diversity, the same BER is achieved with a 5 db SNR (brown curve). For a 1% BER the two antenna diversity provides the equivalent of a 10dB improvement in SNR. In the case of four antennas, the gain is about 15 db (blue curve). In practice the gains for a 10% BER are about 3 db with two antennas and 6 db with four antennas. Alamouti, IEEE JSAC, Oct 1998 Figure 3: Theoretical switched diversity gain for different antenna configurations. Page 5 of 14

6 Solution: Ethertronics Air InteRFace Processing System Technology Ethertronics Air InteRFace Processing System technology provides an alternate and improved method of providing diversity to a communication system. Air InteRFace Processing System solution combines the company s patented Isolated Magnetic Dipole (IMD) technology, Ethertronics active antenna systems approach and a patentpending algorithm combined to generate multiple radiation patterns from a single antenna structure. As a result, the Air InteRFace Processing System technique can dynamically respond to changing RF conditions fast enough to minimize multipath fading and in turn maximize both throughput and reliability. Using a sample and switch concept, multiple radiation patterns from the same antenna can be quickly surveyed to determine the best pattern to use for a specific multipath environment, resulting in faster data throughput. Ethertronics has demonstrated the ability to generate four unique radiation patterns from the same antenna when integrated into a cell phone, see Figure 4. Air InteRFace Processing System provides multiple radiation patterns from a single antenna structure. Ethertronics Air InteRFace Processing System Multiple Radiation Patterns Figure 4: Air InteRFace Processing System showing four modes. Air InteRFace Processing System technology takes advantage of the multipath environment to increase throughput and improve reliability in Wi Fi and cellular devices. Additionally, Ethertronics Air InteRFace Processing System technology is a smallvolume, power efficient solution, making it ideal for thin, handheld devices where space and battery life are always key concerns for systems designers and end users. Page 6 of 14

7 Testing Protocol to Prove Faster Throughput To prove the benefits of the technology, Ethertronics purchased two identical offthe shelf access points. The access points each contained two passive antennas. Ethertronics retrofitted one access point with two Ethertronics antennas one passive IMD and one active Air InteRFace Processing System (dual mode). While four modes, or radiation patterns, provide optimum performance, two modes are sufficient in an access point to demonstrate significant increases in throughput. Replacing one or more passive antennas in the access point with four mode Air InteRFace Processing Systems would yield even faster download speeds and improved reliability. Figure 5: Office layout Throughput testing was performed to compare the performance of the original off the shelf access point with the Ethertronics retrofit access point. Throughput measurements were carried out for the b/g band at Channel 1 (2412MHz). Testing was performed in an office space with cubicles, desks, walls, structural posts, etc. to simulate a typical multi path environment, see Figure 5 for an overview of the office space. A laptop was placed at 5 different distances from the access point: 10ft, 50ft, 75ft, 95ft, and 120ft. The client was kept stationary with the access point rotated in four different orientations: 0, 90, 180 and 270 degrees. The test locations included line of sight, as well as on the other side of cubicles and walls. Figure 6 illustrates the test set up including office layout and testing locations. Figure 6: Office floor plan Page 7 of 14

8 Performance Gains Include 46 Percent Faster Throughput This architecture can generate many radiation patterns. Ethertronics has determined the optimal number of radiation patterns to be four. This flexibility produces a significantly higher Signal to Interference plus Noise Ratio (SINR) than conventional passive antennas can yield. A high SINR ratio maximizes downlink speeds not merely incrementally, but instead to a degree that's noticeably faster to end users. The classic Dipole shaped radiation patterns are typically not realized in an actual product implementation due to the disturbance to the radiation pattern of the antenna from the internal structure of the wireless device. Nonetheless, the null locations, or regions of radiation pattern minima, can be altered using the Air InteRFace Processing System technique. Figure 7 shows 2 dimensional and 3 dimensional measured radiation patterns from a two mode Air InteRFace Processing System antenna configuration, where the Air InteRFace Processing System antenna was integrated into an access point. As can be seen from the 3 dimensional patterns, the null location rotates in the yz plane as the Air InteRFace Processing System antenna switches from Mode 0 to Mode 1. An additional benefit of the Air InteRFace Processing System architecture is a change in polarization properties of the antenna between Modes, as can be seen in the 2 Figure 7: Measured radiation for two mode system. dimensional radiation patterns. The color coded scale used in the 3D radiation patterns is in units of db. For the 2D radiation patterns, the blue and green traces show the linear components of the radiated field, with the red trace showing the total radiated pattern, which is a combination of the linear components. Page 8 of 14

9 For example, Table 1 shows how Ethertronics Air InteRFace Processing System solution significantly improved downlink speeds when it replaced the baseline passive antenna in an off the shelf access point. Throughput (MBPS) 10ft 50ft 75ft 95ft 120ft Off the Shelf Access Point Ethertronics Retrofit (Air InteRFace Processing System Download Speed Percentage Increase 2% 19% 46% 18% 11% Table 1: Measured throughput The off the shelf access point demo also shows how Ethertronics Air InteRFace Processing System solution maintains those throughput enhancements even over distances of 120 feet (Figure 8). Figure 8: Measured throughput graphically Page 9 of 14

10 Figure 9 illustrates the office environment used for the testing and the throughput increases for each testing location. The office, cubicle walls, and other physical obstructions create multipath signals, making for a challenging RF environment. Figure 9: Office layout including measured throughput increases. Figure 10 shows how Ethertronics Air InteRFace Processing System solution provided up to a 46 percent throughput improvement in the part of the office where multipath was highest. In this figure, data throughput improvement is shown for four distinct regions: 1. Line of Sight represents short range and high field strength regions. 2. Low Multipath Area represents intermediate distances with low multipath characteristics. 3. High Multipath Area where the distance between the access point and client is large and the multipath is high. Page 10 of 14

11 4. Low Level Signal where the distance is the greatest of the four regions and consequently the field strength is low. The multiple radiation patterns generated by the Air InteRFace Processing System antenna provide throughput benefits across all four regions, with the greatest benefit observed in the region where multipath is the highest. The reduced benefit in the line of sight region is due to the field strength being very large; in this region typical passive antennas provide adequate performance. Figure 10: Throughput as measured against distance from the access point. Key Benefits for Vendors, Mobile Operators, Telcos, Cable Operators and End Users The access point demo illustrates how Ethertronics Air InteRFace Processing System active antenna system solution provides several major benefits: Selects the best radiation pattern, from the multiple ones generated, to provide the best connection and fastest throughput. Provides interference suppression from unwanted signals, providing superior throughput and reliability. Changes radiation patterns dynamically to compensate for changes in the multipath environment. Even when the user is stationary, movement within the local environment will cause changes to the multipath, i.e. people walking by, doors opening and closing, vehicles passing by the building, etc. Page 11 of 14

12 The benefits listed above provide significant advantages for vendors, mobile operators, telcos, cable operators and end users. Telcos, mobile operators, cable operators, and other service providers that own Wi Fi networks can use Ethertronics equipped infrastructure to maximize performance and reliability. That helps them differentiate their wide area Wi Fi services and achieve their business goals. For example, a mobile operator could use a high performance Wi Fi network to encourage its 3G and 4G customers to switch to Wi Fi whenever possible. Over time, customers would realize that the Wi Fi network is as fast, if not faster, than 3G or 4G. This perception and usage enable the mobile operator to achieve its offload strategy. The high SINR ratio of Ethertronics Air InteRFace Processing System solution enables service providers to reduce the density of their access points, but not at the expense of coverage and throughput. Lower density also means fewer backhaul links, for additional OpEx savings. Or they could use conventional network architecture and use the high SINR ratio to provide higher speeds and greater capacity than rivals can. Enterprises could use Ethertronics equipped infrastructure to provide a superfast, highly reliable wireless LAN in their offices and other facilities. Speed and reliability would encourage employees to use the WLAN rather than more expensive technologies. For example, if employees are provided with VoIP softphone clients for their smartphones, they re more likely to make calls over Wi Fi, instead of cellular, when they know that the WLAN blankets their building, including traditional dead spots such as stairwells and elevators. Although this White Paper focuses on Wi Fi access points, the technology is applicable to a wide variety of other devices, bands, and air interfaces. For example, Original Equipment Manufacturers could use Ethertronics Air InteRFace Processing System solution to maximize the performance and reliability of their LTE smartphones, tablets or notebooks. Those benefits would apply across multiple bands, such as when an LTE Advanced (3GPP Release 10) device aggregates bandwidth across 700 MHz, 1900 MHz and 2.5 GHz to achieve throughput in the tens of megabits. Ethertronics Air InteRFace Processing System solution is particularly beneficial for cellular because of the use cases. In Wi Fi, user devices typically are stationary or moving at no more than pedestrian speeds. That sedentary usage makes for a far more stable RF environment, albeit one where multipath still is a major problem. In cellular, user devices typically are on the move, including at vehicular speeds. That makes for an even more variable RF environment, but one that Ethertronics algorithms still can easily handle. Page 12 of 14

13 A Cost Effective, Small Volume Design Ethertronics Air InteRFace Processing System solution also provides cellular vendors with a much needed solution to the problem of increasingly limited space inside smartphones and tablets. Space is particularly tight in 4G devices, which need antennas not only for LTE, but also for 3G fallback, Wi Fi, Bluetooth, and GPS. On top of everything, the number of LTE antennas is higher than their 3G counterparts simply because of MIMO requirements. Achieving the benefits of Ethertronics Air InteRFace Processing System architecture also requires Ethertronics' patent pending algorithm, which determines which radiation pattern provides the best performance for the RF environment at that particular moment. Ethertronics Air InteRFace Processing System solution is an innovative approach to diversity; providing superior performance in comparison to solutions simply using two passive antennas to mitigate multipath and maximize throughput. Those passive antenna solutions still have fixed radiation patterns, unlike Ethertronics Air InteRFace Processing System solution, which can generate many patterns to provide maximum flexibility. Another major drawback to passive solutions is volume and cost: They require multiple antennas, RF chains, and feed points, all of which take up precious board space inside the device and add to the cost. For many smartphone and tablet vendors, that s an unacceptable trade off. Conclusion: A Bold, New Way of Thinking about Antennas Ethertronics Air InteRFace Processing System solution is the latest example of how Ethertronics is innovating antennas to a new level. Historically device manufacturers, vendors and other ecosystem members have considered the antenna as a passive component with a single, fixed radiation pattern. Conventional thinking assumed that diversity schemes, with at least two antennas, were needed to offset multipath fading. Air InteRFace Processing System brings a new way of thinking about antennas by creating multiple radiation patterns from a single antenna structure. Thereby realizing the benefits of MIMO solutions without the additional volume and costs associated with multiple antennas. Ethertronics Air InteRFace Processing System solution represents a new way of thinking about active antenna system design and the role it plays in the user experience: as an integrated RF antenna system consisting of the antennas themselves and active components combined with advanced algorithms. This systems based strategy provides device designers with a fast, cost effective, and high performance alternative. Page 13 of 14

14 Air InteRFace Processing System is the next step in the evolution of antenna and RF systems solutions. Innovation will continue with more technologies and applications being introduced over the next year. Today, Ethertronics Air InteRFace Processing System solution provides a much needed alternative for Wi Fi Access Points. Ethertronics has also developed Air InteRFace Processing System solutions for a wide variety of other devices and air interfaces including smartphones, tablets, and notebooks for both 3G and 4G protocols. Future white papers will focus on implementation in other wireless devices including smartphones and tablets Ethertronics. All rights reserved. Ethertronics, the Ethertronics logo, Isolated Magnetic Dipole, Wireless InteRFace Processor, Air InteRFace Processing System are trademarks of Ethertronics. All other trademarks are the property of their respective owners. Page 14 of 14