What does test equipment have to do with carrier aggregation?

& -June 25, 2013

Each technology has a time value, and the current availability of mobile bandwidth service may not seem compatible with the forecasted trend. LTE-Advanced seems like the next big thing in the mobile broadband industry, promising data rates of about 1 Gbps. Carrier aggregation is one of the most highly anticipated features of LTE-Advanced, which was developed to seek a balance of acceptance and feasibility. The carrier aggregation features of LTE-Advanced are sought after by service providers looking for ways to get more speed from their networks and use their spectrum more efficiently.

This article gives an insight into the growing importance of carrier aggregation in LTE-Advanced and the associated test equipment.

LTE-Advanced offers higher data rates than the initial rates of the LTE, which is possible to attain by extending transmission bandwidths (up to 100 MHz) by aggregating up to five LTE carriers. Carrier aggregation facilitates efficient use of the spectrum and can be applied for both frequency division duplexing (FDD) and time division duplexing (TDD). This technology allows the co-existence of Release 8/9 UEs and Release 10 UEs, indicating that each component carrier involved is completely backward-compatible. Carrier aggregation allows expansion of effective bandwidth delivered to a user terminal through concurrent use of radio resources across multiple carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth.

Primarily, there are three types of carrier aggregations:
1.    Intra-band contiguous carrier aggregation
2.    Intra-band non-contiguous carrier aggregation
3.    Inter-band non-contiguous carrier aggregation

The intra-band non-contiguous carrier is applicable when network sharing is applied, and the inter-band non-contiguous carrier will be used mainly for the fragmentation of bands.

To augment the current LTE standard, LTE-Advanced is packaged with several new features launched by 3GPP (release 10), most of which are aimed at:
•    Raising the peak downlink data rate to 1 Gbit/s and beyond
•    Reducing latency  
•    Improving spectrum efficiency

These features cannot be easily applicable until 20MHz can be extended to 100MHz. The possibility lays in obtaining wider transmission bandwidths by aggregating multiple contiguous carriers or non-contiguous carriers based on the availability of radio spectrum.

Carrier aggregation can tap the full potency of LTE-Advanced and solve the problems of spectrum availability. It is used to aggregate the newly deployed LTE networks and the evolving HSPA+ networks.  It allows transmission of data to one user simultaneously using both the HSPA and the LTE radio. It also enables fast load balancing across the carriers, improving the data rates of all end users.

With the lack of mobile broadband spectrum, the growth of backward-compatible carrier aggregation technology is inevitable, at least until the LTE networks take over completely. By 2017, we expect LTE to be deployed in all urban cities. The forecast for towns and rural areas suggests the reliability on legacy networks as major revenue generators. Fragmentation of mobile broadband networks will continue.

According to Frost & Sullivan, more than 70 percent of mobile users across North America and more than 50 percent of Asia Pacific mobile users are expected to subscribe to LTE. Hence, the presence of component carriers in smaller frequencies will help SPs across the globe provide low bandwidth services such as HSPA, HSPA+, GSM along with LTE-A services, driving the crucial need for carrier aggregation technology.
LTE-Advanced carrier aggregation is a complex and major technical advancement. The variations permitted in carrier aggregation increase the mobile device complexity. Receiving multiple frequencies with an overall increased bandwidth requires significant changes in the design of the receiver chain. End-user testing and base-station testing become extremely important.

According to Rohde & Schwarz, testing a mobile device that supports carrier aggregation will focus on the capability of the device to cope with the increased amount of data, which will be received with two receiving chains simultaneously. It will be necessary for testing to take place on the physical layer, protocol stack and E2E.

At the base station level, the major design challenge lies on the terminal side. Support of higher bandwidths and aggregating carriers in different frequency bands tremendously increases transceiver circuit complexity, including the design of components such as wideband power amplifiers, highly efficient switches and tunable antenna elements. This testing becomes significant because SPs use component carriers or elements from multiple operators that need to be compatible and with equivalent standards.

Developments in the test equipment markets have been very rapid since MWC 2013, when Anite PLC announced reaching peak data rates with commercial devices for LTE-Advanced carrier aggregation. Anite’s development toolset now provides support for carrier aggregation with 20+20 MHz bandwidth along with 4x2 MIMO antenna configurations that would help chipset manufacturers develop and test LTE-A products.

In addition, Anite worked with chipset manufacturers and achieved peak data rates of 3 Gbps with commercial devices for carrier aggregation.

Because of the overall complexity of LTE-A and frequency and bandwidth limitations, getting peak data rates on mobile networks represents the biggest challenge for operators.

Recently, Anritsu Company demonstrated the first single-box RF test ability for carrier aggregation  at CTIA 2013. The company exhibited a downlink rate of 300 Mb/s carrier aggregation test capability. This is a new option to its existing MT8820C one-box tester, which has been a success. The MT8820C RF tester is functional for 2G, 3G, 4G and LTE-Advanced, with the ability to calibrate wireless devices RF parametric testing and functional testing, including call processing or no-call-based testing. Efficient test solutions will also enable low-scale manufacturers to develop reliable LTE-A products in line with their milestones.

With the business cycle stepping out of the depression, fast connectivity is important to support the boom stage, highlighting the need for LTE-Advanced networks that will be able to provide high data rates within limited spectrum. The feasibility of this is highly dependent on the advancement and application of carrier aggregation. Thus, the demand for carrier aggregation test equipment is expected to rise.

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