Last month, the GSA highlighted accelerating deployments of LTE networks, and predicted that there will be at least 103 LTE networks commercially launched by the end of 2012. While LTE itself is still a new wireless technology, the pace of further developments has not slackened. In my last post, I reported that Sprint Nextel and AT&T Mobility have announced their intentions to deploy LTE-Advanced in 2013. Some operators may have the opportunity to go straight to LTE-Advanced.
LTE-Advanced represents a further evolution of LTE, which is designed to be backward-compatible so that LTE handsets and devices will operate in LTE-Advanced networks. Vendors envisage that the first commercial deployments of LTE-Advanced will be in 2013. LTE-Advanced has been standardised by 3GPP in Release 10 and Release 11 and has been ratified by the International Telecommunication Union (ITU) as meeting its requirements for IMT-Advanced, which is regarded as true 4G. The ITU’s requirements were defined in 2008. Some of these requirements have been particularly challenging, such as:
- peak downlink data rates of 1Gbps for low mobility situations (and 500Mbps on the uplink)
- downlink peak spectral efficiency of 15 bits/s/Hz.
As well as meeting the ITU’s original requirements for 4G, LTE-Advanced also has to be able to support the massive continued growth expected in mobile traffic volumes.
LTE-Advanced will make use of a number of advanced techniques, which I will briefly discuss. These are:
- carrier aggregation
- enhanced Multiple-Input Multiple-Output (MIMO) antenna techniques
- Co-ordinated Multipoint (CoMP)
- Heterogeneous Networks (HetNets).
Carrier Aggregation. Achieving a peak downlink data rate of 1Gbps is simply not possible with the maximum bandwidth allocation (20MHz) of LTE. To meet its peak rate targets, LTE-Advanced must support a bandwidth of up to 100MHz – five times the maximum amount of spectrum with LTE. In recognition of the fact that it will be impossible for most mobile network operators to access a continuous 100MHz allocation of spectrum, LTE-Advance has been designed to aggregate spectrum resources scattered in multiple, non-contiguous frequency bands. LTE-Advanced can also aggregate spectrum where downlink bandwidth is different to the uplink bandwidth. LTE-Advanced terminals will be able to receive multiple component carriers simultaneously, whereas basic LTE terminals can only receive one component carrier. However, the system will provide backward compatibility with existing LTE devices.
Enhanced MIMO. MIMO is a radio antenna technology in which multiple spatially-separated antennas can be used at the transmitter and receiver to provide a variety of signal paths to carry the data. Complex digital signal processing of these signals provides enhanced data capacity. MIMO technology is already incorporated into LTE, on the downlink. The major enhancement with LTE-Advanced is that MIMO will be introduced on the uplink. In addition, there are further MIMO enhancements for the downlink, such as the use of a greater number of antennas (up to eight transmitting antennas with LTE-Advanced compared with a maximum of four with LTE).
Co-ordinated Multipoint (CoMP). Rather than having a single radio connection between a mobile device and a base station, CoMP is a range of techniques that utilise simultaneous connections to multiple base stations. By using these advanced methods, it is possible to combine received signals in such a way as to reduce interference and boost wanted signals. In LTE, high data rates are much easier to achieve closer to a base station than near the edge of its coverage area, where the received signal is generally much lower and interference levels are higher. CoMP will particularly help connections to mobile devices near the edge of a base station coverage area since it will be possible to combine signals received at the mobile device from adjacent base stations, and combine signals received at adjacent base stations from the mobile device.
Heterogeneous Networks (HetNets). While the enhancements described above will help to boost the spectrum efficiency (and therefore capacity) of LTE networks, they will, on their own, be unable to provide the capacity uplift needed to support the expected future growth in mobile traffic volumes. Greater densities of base stations will be necessary to achieve this. In addition, offloading to lower-power small-cell systems (e.g. WiFi, picocells and femtocells) will be essential, since it is likely that a large proportion of traffic will originate from indoor and hotspot locations. Heterogeneous Networks (HetNets) is a relatively new term that refers to the use of a combination of large and small cells (potentially using different radio technologies), working together to provide the optimal coverage and capacity. LTE-Advanced will provide enhanced capabilities for the collaboration of macro base stations and small-cell systems, particularly in terms of inter-operability and interference co-ordination and management.
It’s exciting to think that we will be seeing LTE-Advanced systems deployed as early as 2013. For operators currently deploying LTE networks, LTE-Advanced will help to ensure that they will be able to stay ahead of the predicted huge growth in mobile traffic volumes. For operators that are not planning to deploy LTE for some time (such as UK operators, for example, due to delays in the spectrum auction), they have the option of moving straight to LTE-Advanced.