Interview: How MIMO tech is advancing high-speed LTE data services

The rise of low-cost smartphones is happening: larger screens, more powerful cameras, speakers, GPS and Bluetooth connectivity are just some of the features flowing down from premium devices into mass-market smartphone models.

Furthermore, speed of connection for high-speed data services, range extension and guaranteed data rates for quality of customer experience and reduced power consumption are allowing device makers to differentiate.

SkyCross, a global designer and manufacturer of advanced antenna and RF solutions, has introduced a new antenna technology that combines its iMAT higher-order MIMO technology with dual band carrier aggregation. This provides faster data rates and can benefit customers, mobile operators and device manufacturers. We spoke to John Marshall, CMO at SkyCross, to find out more.

TechRadar Pro: What advancements are being made in the LTE industry to advance data speeds?

John Marshall: While there has been much progression through 2G, 3G, and 4G LTE, LTE-Advanced is finally 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 higher-order MIMO in the future.

TRP: How about antennas specifically? What advancements are underway?

JM: For antennas specifically, SkyCross has designed the four antennas in one antenna structure 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 higher-order 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.

TRP: 4x4 MIMO is popular in Wi-Fi – why has this technology not been employed in LTE devices?

JM: Manufacturers and operators have long sought to increase mobile data speeds by adding MIMO functionality to smart phone antennas. MIMO is a technology that utilizes multiple simultaneous signal transmission paths that are ideally "uncorrelated."

Uncorrelated means that 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 facing 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, which results in decreased 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.

TRP: What are some of the challenges facing LTE antenna designers?

JM: LTE antenna designers face significant challenges, as higher-order 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.

Furthermore, 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 Wi-Fi, 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 higher-order MIMO adoption.

TRP: But SkyCross has successfully implemented higher-order MIMO for LTE. How does SkyCross' dual iMAT technology enable this breakthrough?

JM: 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, SkyCross' patented Isolated Mode Antenna Technology (iMAT™) eliminates the performance issues associated with mutual coupling and high pattern correlation coefficient from multiple nearby antennas.

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.

TRP: What are the benefits of SkyCross' dual iMAT antennas?

JM: Higher-order 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. This will allow for improved 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."

TRP: What does higher-order MIMO technology mean for the future of the mobile / telecommunications industry, and for consumers?

JM: Successfully integrating four antenna structures into a smartphone has long been seen as the barrier to industry-wide adoption and commercialization of higher-order 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 higher-order MIMO.

The implications of such advancement suggest that 4x4 smartphone and tablet adoption of higher-order MIMO could be significant in the coming years, with near term introductory deployments as early as 2015. The benefits of higher-order MIMO could result in as many as 300M additional higher-order 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.

TRP: What are SkyCross' plans for the future?

JC: Thanks to SkyCross' unique technology, Dual iMAT higher-order MIMO plus carrier aggregation very well may be the future of LTE. 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."

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