Delivering 4x4 MIMO for LTE Mobile Devices
SkyCross Dual iMAT 4x4 MIMO Technology for LTE
March 2014
Introduction
With the rise of low-cost smartphones on the horizon, creating differentiation by leveraging the features mobile devices in a bundled mobile device/mobile service offerings is
increasingly hard to achieve. Larger screens, cameras, speakers, GPS for maps, and Bluetooth for device connectivity is flowing down from premium devices into mass market smartphone models. However, there is a new focus on the pipe itself and emerging data services are becoming more important than the device’s local capability. Tighter
integration between the network and the device will increasingly become differentiators for mobile operators. Speed of connection for high-speed data services, range extension and guaranteed data rates for quality of customer experience and reduced power consumption will increasingly become the central differentiators, much like the progression of other broadband platforms.
As such, how does the mobile industry continue forward with higher-speed service offerings and/or greater coverage/range? There has been progression through 2G, 3G, and 4G LTE. LTE-A is emerging. Dual-band carrier aggregation (CA) solutions, even three-band CA solutions are in discussion and roll out on some operators’ networks. As the demand for data continues to surge, pressure for higher speed will also continue. In addition to utilizing additional spectrum to achieve such higher rates, there are also techniques for improving spectral efficiency. Operators and device manufacturers have identified MIMO technology as one means to improve performance for LTE, starting with 2x2 solutions and moving to 4x4 MIMO in the future. However, unlike other wireless technologies that have moved to 4x4 MIMO, such as WiFi, a significant design challenge has limited LTE’s movement to 4x4 MIMO.
Opportunities for MIMO
Manufacturers and operators have long sought to increase mobile data speeds by adding MIMO (multiple input, multiple output) functionality to smartphone antennas. MIMO is a technology that utilizes multiple simultaneous signal transmission paths that are ideally
“uncorrelated.” Signal paths that are uncorrelated means that if one path experiences a deep fade the second path does not behave in the same way and essentially forms a secondary connection between the mobile device and the cellular tower (multi-path fading is especially common in high density areas and indoors but can occur anywhere for a
variety of reasons). Multi-path fading degrades signal integrity since more transmission errors occur creating the need for additional error correction overhead, this results in a decrease of data throughput. MIMO technology is an effective method to overcome the effects of multi-path fading and has successfully been applied in Wi-Fi networks. Cellular systems are now evolving to utilize MIMO and the specifications for LTE-Advanced, or LTE-A, can actually support up to 8x8 MIMO, meaning eight downlink and eight uplink simultaneous RF transmission paths. However, MIMO adoption for LTE has been constrained by the challenge of designing multiple antennas in a compact smartphone form factor that are not only sufficiently high gain but also have a low enough correlation factor between the different antenna combinations.
Most of today’s high-end handsets do not even incorporate 2x2 MIMO. Instead, they often rely on a single main antenna and a second diversity (receive only) antenna. The typical 4G LTE smartphone can support data rates in the 70-100 Mbps range using this 1x2 MIMO configuration. The two antennas are usually located as far as possible from one another to achieve sufficient spatial diversity to maximize isolation and minimize the correlation factor.
Given the challenges of designing high performing antennas for MIMO applications, smartphone manufacturers are trying to increase mobile data rates through use of an alternative approach using dual-band (or more) carrier aggregation. This technology allows multiple transceivers to operate simultaneously on different RF channels, and can
approximately double data rates (or higher depending on the number of aggregated channels). With one main and one diversity antenna, plus dual-band carrier aggregation, today’s smartphones can achieve throughput in the 140-200 Mbps range.
4x4 MIMO Design Challenges
Despite speed enhancements that can be realized through carrier aggregation, 4x4 MIMO continues to serve as a technology that can offer even higher data rates while utilizing precious spectrum more efficiently. As noted earlier, 4x4 MIMO requires four antennas of high efficiency that are gain balanced and independent of each other; i.e., exhibit low correlation. This is a major design challenge for a smartphone-sized device. Adding carrier aggregation introduces yet another level of complexity for the antenna designer, as it is very difficult to achieve high gain and low correlation across multiple bands.
Antenna co-location becomes harder to accomplish as more antennas are packed into one device. While many antenna designers can physically fit four MIMO antenna structures into a smartphone, the structures would likely be located so close to one another that the multiple transmission paths would be highly correlated, diminishing MIMO performance.
Further complicating matters, today’s smartphones also contain multiple other antennas to support WiFi, GPS, Bluetooth and NFC, which not only take up physical device space, but can also exacerbate signal interference. Integrating four antenna structures into a
smartphone-sized device is considered one of the biggest challenges for widespread 4x4 MIMO adoption.
As the only structure in a mobile device that communicates with the network, the antenna is vitally important. It’s also a logical component for ODMs and OEMs to consider when seeking increased data throughput. With consumers demanding faster and more reliable connections to support real-time applications, such as Video On Demand, the mobile industry is increasingly focusing on enhanced antenna technology to enhance data rates and improve network range and reliability.
Improved performance directly translates to new revenue generating and product/service differentiation opportunities for device manufacturers and operators.
TECHNOLOGY BREAKTHROUGH: SkyCross Dual iMAT 4x4 Technology SkyCross’ patented Isolated Mode Antenna
Technology (iMAT™) applies pattern diversity that enables designers to locate multiple antennas in close proximity while still achieving the high isolation/low correlation needed for MIMO
architectures. As such, iMAT antennas require less spatial separation than typical antennas, allowing more antennas to be integrated closer to one another and providing device makers more design flexibility.
This novel approach to antenna design may also include tuning, enabling the iMAT antenna to support multiple frequency bands while simultaneously achieving high radiated efficiency. iMAT technology enables antennas to deliver greater MIMO efficiency while minimizing the footprint needed compared to conventional designs.
SkyCross iMAT technology enables multiband 4G LTE MIMO to be designed onto a single (or multiple) antenna structure. Although the multiple antennas are closely co-located and operate on the same frequency at the same time, iMAT technology eliminates the performance issues associated with
mutual coupling and high pattern correlation coefficient from multiple nearby antennas.
OPERATOR TESTED: Deutsche Telekom Field Test, February 2014
Despite the challenges of implementing 4x4 MIMO for LTE, device manufacturers and mobile operators have continued to focus on MIMO to increase mobile data rates. In early 2014, Deutsche Telekom (DT) conducted field-testing of 4x4 MIMO using SkyCross Dual iMAT 4x4 technology in mobile device platforms. DT’s aim was to improve the user experience, increase network capacity, enhance coverage and boost peak data rates.
“SkyCross has developed a unique antenna solution for 4x4 MIMO that both solves the spatial issue of fitting numerous antennas into a small form factor with sufficient isolation, but also drastically improves data rates and overall performance.”
Bruno Jacobfeuerborn Chief Technology Officer Deutsche Telekom
Results released on February 20th, 2014, show that 4x4 MIMO can improve data rates, and provide cell range extension and system improvements in high-density urban areas where cell capacity is typically limited by interference. Initially, Deutsche Telekom
incorporated a 4x4 MIMO antenna array approximately the size of a typical cable television box – certainly too large to fit into a commercial
smartphone form factor. SkyCross designed the four antennas to operate across both Band 7 (2500 – 2690MHz) and Band 3 (1710– 1880MHz) to support dual-band carrier aggregation utilizing two 20MHz channels. By combining its iMAT 4x4 MIMO technology with dual band carrier aggregation, SkyCross technology enables mobile operators to integrate non-contiguous spectrum into a virtual single, 40MHz channel. Previously found to be impossible to deliver, Deutsche Telekom achieved a 4x4 MIMO solution in a traditional smartphone form factor. As noted by Deutsche Telekom’s CTO, Bruno Jacobfeuerborn, size and isolation have always been the industry’s chief challenge when considering 4x4 MIMO.
SkyCross has created the first-ever 4x4 MIMO plus carrier aggregation antenna solution for LTE, featuring
very significant testing results. Results demonstrated significant
performance gains for LTE, including a peak rate of 580 Mbps and improvement in cell edge performance as compared to 2x2 MIMO. Deutsche Telekom released its German market field test results and noted:
• Achieved 580 Mbps peak speed and ultimate cell edge performance with the new antenna technology on a live LTE network environment.
• Revealed the first commercially-viable 4X4 smartphone antenna from SkyCross, showcasing the antenna’s robustness in orientation, indoor/outdoor usage, line of sight or non-line of sight usage, or proximity to tower.
• Demonstrated the capability to combine LTE-A 4X4 MIMO and carrier
aggregation to deliver the best-in-class user experience in most spectrally efficient way.
SOLUTION: Dual iMAT 4X4 MIMO for LTE
For Deutsche Telekom, SkyCross implemented both Bands 3 and 7, however other LTE band combinations can be implemented as easily. Skycross designed the solution with consideration for other wireless technologies that are typically employed in smartphones, including WiFi, Bluetooth, GPS and NFC. SkyCross’ Dual iMAT technology delivers high isolation, low correlation, high gain (that is balanced), all in a very small form factor that
results in a high performance, cost effective MIMO solution.
Dual iMAT consists of a co-located pair of antenna structures – one at the top of the phone and one at the base – with both pairs supporting multiple bands. The benefits of this placement are threefold. First, placing the antennas at the top or bottom allows for a symmetrical design that results in balanced (or equal) gain. Second, the top and bottom locations provide supplemental spatial separation between the two pairs to achieve isolation. Another benefit of this arrangement is its ability to overcome head/hand effects from how users typically hold the device, since in most cases only one antenna pair may be covered at a given time.
Industry Implications
Successfully integrating four antenna structures into a smartphone has long been seen as the barrier to industry-wide adoption and commercialization of 4x4 MIMO. SkyCross’ Dual iMAT 4x4 antennas have now solved this problem. This opens the door to component, mobile device and infrastructure equipment makers to accelerate support for 4x4 MIMO.
The implications of such advancement suggest that 4x4 smartphone and tablet adoption of 4x4 MIMO could be significant in the coming years, with near term introductory
deployments as early as 2015. The benefits of 4x4 MIMO could result in as many as 300M additional 4x4 MIMO enabled mobile devices with complimentary infrastructure by 2018, according to preliminary analysis by Mobile Experts, a leading provider of mobile infrastructure and mobile device industry analysis.
4x4 MIMO Implications Resulting from SkyCross Dual iMAT Technology Breakthrough (Left Chart Provides Mobile Experts’ 2013 Forecast, Right Chart Provides Updated Preliminary Forecast)
Benefits
4x4 MIMO for LTE networks will soon deliver numerous benefits for mobile operators, handset manufacturers and consumers:
• Mobile operators will be able to introduce new services based on data rates of over 500 Mbps, and will also benefit from improved network capacity and fewer dropped calls. In short, they will be able to improve revenues while concurrently minimizing capital and operating expenses of their network infrastructure. With improved indoor coverage, a greater number of users will be able to rely on their smartphones, which will also serve to increase revenues for the service provider.
• Since device manufacturers will be able to fit advanced antennas into their existing smartphone form factors, device manufacturers will be able to create higher performing products without sacrificing the smartphone aesthetics and form factors preferred by consumers today.
• Consumers will enjoy five times faster data rates, increased performance, and the ability to, for example, stream HD video while operating other applications that require very high data rates. Dual iMAT also enables dramatically improved performance in cellular edge points, helping consumers avoid “dead zones.”
Further, for users located in high density urban areas and indoor environments, 4x4 MIMO will deliver a better experience.
Conclusion
Achieving 4x4 MIMO in a small smartphone form factor is no longer an unattainable goal, thanks to SkyCross’ unique Dual iMAT technology. Dual iMAT 4x4 MIMO plus carrier aggregation is the future of LTE. While Deutsche Telekom is the first carrier to explore this solution with SkyCross, it’s only a matter of time before this technology garners broader acceptance. As Joe Madden, principal analyst for Mobile Experts states, “This new approach by SkyCross takes antenna modeling and design to a new level. It’s not just bent metal anymore. With extremely advanced modeling, SkyCross appears to have a way to solve the multi-dimensional challenge of small size, multi-band MIMO antennas.”
“Field testing by Deutsche Telekom and SkyCross validates that 4x4 MIMO implementation is possible in a handset form factor, without sacrificing MIMO effectiveness. Until now, our forecast had been zero for 4x4 handsets, but this capability changes the game and opens up new possibilities for handset OEMs and for mobile operators.”
Joe Madden, Principal Analyst, Mobile Experts
Partnership & Cooperative Development
If you are interested in exploring partnership or development of reference designs with SkyCross on this breakthrough technology, please contact your local SkyCross
representative ([email protected]) or reach out to John Marshall, SkyCross’ Chief Marketing Officer and partnership program leader ([email protected]).
Development kits are available today for partners.
