Operators are increasingly facing the need to deliver higher data rates. In this regard, LTE Release 10 facilitates carrier aggregation, allowing for the parallel transmission of multiple LTE carriers to and from a single terminal. This enables an increased overall bandwidth and corresponding data rates. Up to five 20 MHz carriers can be aggregated, resulting in an overall bandwidth of up to 100 MHz for both downlink and uplink.

In addition to the aggregation of contiguous carriers within a single frequency band, LTE also supports aggregation of carriers in different frequency bands. Such out-of-band carrier aggregation or spectrum aggregation allows operators with fragmented spectra to provide wider bandwidths, enabling higher data rates and more efficient utilisation of available spectrum.

Extended multi-antenna transmission 

LTE Release 10 improves LTE downlink multi-antenna transmission capabilities to support spatial multiplexing with up to eight antennas and eight corresponding transmission layers. Together with the bandwidth extension of up to 100 MHz enabled by carrier aggregation, this enables peak data rates of 3 Gbps or 30 bps per Hz.

LTE Release 10 also supports uplink multi-antenna transmission, with up to four antennas and four corresponding transmission layers. This facilitates uplink peak data rates of up to 1.5 Gbps in 100 MHz or 15 bps per Hz.

Relaying functionality 

LTE Release 10 supports the relaying functionality, allowing mobile terminals to communicate with the network through a relay node wirelessly connected to a donor-eNodeB using LTE radio access technology and LTE spectrum. The relaying functionality may provide a fast and cost-efficient way to increase the coverage of an LTE network. This includes coverage area extensions as well as an increase in data rates.

Enhanced support for heterogeneous network deployments 

Densification of radio access networks can help in meeting future traffic and data rate demand. This includes complementing a macro-cell layer with additional low-power pico cells that can extend traffic and data rate capabilities as per requirement.

Such heterogeneous network (HetNet) deployments are possible in current mobile communication networks, including the first release of LTE. However, LTE Release 10 has features that can further mitigate interference among the cell layers, thereby increasing the scope for HetNet deployments.

Spectrum convergence 

A key benefit of all LTE releases is that they provide convergence in terms of radio access for paired and unpaired spectrum, allowing for more efficient spectrum utilisation.

There are two duplex alternatives for mobile communication – FDD for paired spectrum and TDD for unpaired spectrum. These duplex schemes have been supported by different 3GPP radio access technologies so far – GSM and WCDMA/HSPA for FDD and TD-SCDMA for TDD. Although FDD has historically been the dominant duplex scheme for mobile communication, interest in TDD is growing. One of the reasons for this is the availability of unpaired spectrum, the efficient use of which requires a highly capable and globally accepted TDD technology.

By supporting both FDD and TDD through the same radio access technology, LTE provides convergence of radio access for paired and unpaired spectrum into a single globally accepted technology. This is especially beneficial for TDD and utilisation of unpaired spectrum, which have so far suffered from limited terminal availability and market momentum.

Relation of LTE to HSPA 

HSPA’s performance matches that of LTE in many areas and for many applications. HSPA also has the advantage of being a proven technology with a large footprint. Compared to LTE, data rates provided by HSPA are limited by narrower bandwidths and multi-antenna capabilities defined by the specifications.

However, it is likely that some of these limitations will be relaxed in the future. 3GPP has already initiated work on improving HSPA bandwidth capabilities to meet the IMT-Advanced requirement of 40 MHz.

Today, 3GPP provides two highly capable radio access technologies for mobile broadband – 3G evolution based on HSPA and 4G LTE. 3G evolution based on HSPA will coexist with LTE, going forward.

Current market 

The first commercial LTE network was launched by TeliaSonera in Sweden in December 2009 and currently covers almost 30 cities, delivering data rates of close to 100 Mbps.

Several other operators are currently deploying commercial mobile broadband networks based on LTE. These include AT&T, Verizon and MetroPCS in North America, T-Mobile in Europe, and NTT DOCOMO and KDDI in Japan. LTE has become the main migration path not only for network operators using 3GPP-based technologies, but also for many operators using 3GPP2-based CDMA2000/1x-EV-DO radio access technology.

In fact, 3GPP2-based operators such as MetroPCS, Verizon and KDDI are among the first to commercially deploy LTE on a large scale.

A number of Wi-Max operators are also moving towards LTE. These include Russian operator Yota and North America-based Clearwire.

A further indication that LTE is a preferred long-term solution for mobile broadband is the decision of the Next Generation Mobile Networks Alliance to select LTE as the radio access technology for next-generation mobile broadband.

Conclusion 

LTE networks are now in commercial operation alongside HSPA networks. The evolution of LTE provides bandwidth extension and spectrum aggregation, extended multi-antenna transmission, relaying capability and enhanced support for HetNet deployments. 

The performance and capabilities of LTE meet, and in many cases exceed, the requirements of IMT-Advanced as defined by the ITU. Therefore, LTE is a 4G technology that is positioned to meet the ever-growing requirements of not only today’s mobile broadband networks, but also those of the future.