For LTE-Advanced, 3GPP Release 10 introduced several new features to augment the existing LTE standard, and these are aimed at raising the peak downlink data rate to 1 Gbps and beyond, as well as reducing latency and improving spectrum efficiency. Targets have also been set enabling the highest possible cell edge user throughput to be achieved.
If the high data rate targets are to be met, LTE-Advanced will require a channel bandwidth that is much wider than the 20 MHz currently specified for LTE. This will not be possible with just a single carrier in the limited spectrum bands available to most operators. Consequently, carrier aggregation—the ability to combine multiple carriers scattered around the spectrum—will be a key measure to achieve the wider effective bandwidth that will be required, typically up to 100 MHz. This means that multiple carriers comprised of either contiguous or non-contiguous spectrum need to be added together to allow these wider channel bandwidths—and thus faster data rates—to be achieved.
Implementing carrier aggregation in a network will mean that operators and infrastructure vendors will require a test mobile equipped with carrier aggregation, ahead of real mobile terminals becoming available.
Evolution to LTE-Advanced
The aim of the 3GPP program for LTE-Advanced is to meet or exceed the requirements of IMT-Advanced within the time frame laid down by the International Telecommunications Union Radiocommunication Sector (ITU-R).
The key targets of IMT-Advanced are: 100 MHz bandwidth, a data rate of 1 Gbps in the downlink and 500 Mbps in the uplink, with 8x8 MIMO and 4x4 MIMO, respectively, in the downlink and uplink. C-plane latency will be a maximum of 50 ms, while U-plane latency will be less than or equal to 5 ms. Table 1 compares these targets with the specification for LTE Release 8 and for LTE-Advanced.
Table 1: 3GPP LTE-Advanced specification compared with LTE Release 8 and IMT-Advanced targets
The evolved standard will offer a higher average spectrum efficiency and cell edge user throughput than Release 8 LTE, with greater spectrum flexibility due to newly allocated bands. Self-organizing networking and deployment will be an integral part of LTE-A, because the network complexity will make manual optimization unfeasible. It is envisaged that there will be a smooth and low cost transition from LTE (Release 8) to LTE-A over the intervening period.
Furthermore, LTE-A will need to coexist with LTE, with a progressive development in infrastructure and gradual upgrades to terminals. Functionality will also need to be scalable.