LTE Advanced – Key features and differentiators

As a wireless technology, LTE is still in early stages of deployment in various countries outside US. But that has not prevented the wireless operators from talking about its next version, LTE Advanced (LTE-A). Technology Inflation has become the nature of wireless industry. The next big thing is always around the corner. In their attempt to lure customers away from their competitors, many service providers love to declare their adoption of the latest and fastest wireless standard. As long as this latest technology presents a substantial data rate improvement over the previous version, it is labeled as a new generation. This is also what is happening with LTE Advanced. A superior form of the already velocious LTE, some call it the actual 4G. For others it could be 4.5G. Without getting into the generation debate, I will keep referring to this technology as LTE Advanced throughout this article. According to the 3GPP group, LTE-A networks should support a downlink data speed of 3 Gbps and uplink speed of 1.5 Gbps. Let us understand the primary features of LTE Advanced that would propel LTE towards achieving those speeds. Most of these were formalized as part of 3GPP Release 10 –

• Carrier Aggregation – One of the most popular aspects of LTE-A is that it allows a combination of up to five component carriers of varying bandwidth to aggregate and form a cumulative bandwidth of maximum 100 MHz. In comparison, contemporary LTE networks support only a single channel with a maximum bandwidth of 20 MHz. Carrier aggregation can be achieved within the same band using contiguous or non-contiguous stream of channels or between channels from two different bands. It offers an ideal solution to operators who do not own a contiguous chunk of 100 MHz spectrum. The technique can be applied to both FDD and TDD versions of LTE. Carrier aggregation will perhaps be the first attribute of LTE Advanced that goes into live action. For more details on carrier aggregation, refer to an earlier article on this blog here.
• Higher order MIMO – Multiple Input Multiple Output (MIMO) increases the bitrate by using multiple transmission and receiver antennas. While LTE can support 4×4 MIMO configuration with 2×2 being the most common, LTE-A will have the capability to run 8×8 configurations in downlink and 4×4 in the uplink. Higher order MIMO directly improves spectral efficiency and throughput. Theoretically, 8 spatial streams can achieve speeds which are about 8x faster than a single input single output system.
• Relay nodes and Heterogeneous networks – Relay nodes are deployed to provide better coverage and capacity at cell edges. Such nodes are low power base stations that act as repeaters to enhance the signal quality and rebroadcast the signal. They connect with eNodeB via wireless interface and offer substantial cost savings as compared to a new eNodeB installation. The concept of relay nodes directly ties into the idea of a heterogeneous network (HetNet). As I discussed here, HetNets enable wireless networks of varying cell sizes, output power and radio access technologies to work together towards the goal of boosting network coverage and capacity. With many wireless operators believing that small cells would be an essential part of their future strategy, there is a big industry push towards HetNets. LTE Advanced will further drive the deployment and adoption of heterogeneous networks.
• Enhanced Inter-Cell Interference Coordination – eICIC will be the primary interference management and mitigation procedure adopted in the LTE-A network. It is typically used in a heterogeneous network where both macro and pico cells transmit and receive data at the same time. The weaker signal from the smaller cell can be easily overpowered by the stronger signal from the larger cell. In eICIC, certain subframes are transmitted by the macro cell without any data. These almost blank subframes (ABS) are low power control channels. The users in the pico cell area then communicate with their base station during such blank subframes. This minimizes the interference between the macro and pico cell on both traffic and control channels. Advanced interference mitigation schemes have been used in LTE networks, but with the increasingly high density of wireless network cells, more sophisticated schemes like eICIC are required.
• Coordinated Multipoint (CoMP) Transmission – Formalized in 3GPP Release 11, CoMP would be another key characteristic of a true LTE Advanced network. In a Coordinated multipoint transmission and reception scenario, multiple eNodeBs work with each other dynamically to avoid interference with other transmission signals. This leads to a better utilization of system resources and an enhancement of both network coverage and quality for cell edge users.

Above five functionalities are generally considered to be the vital differentiating factors which will separate LTE-A from its predecessors. There are plenty of other evolutionary technology proposals which have been suggested for LTE-A. Here are some of them –

• Enhanced Self-Organizing Networks – SONs are self-configuring, optimizing and healing mobile networks. As the name suggests, self-configuration applies to newly deployed eNodeBs, self-optimization is performed by active base stations to regulate parameters in synchronization with the overall network situation and self-healing features automatic detection and compensation of network outages. The concept of SONs will be implemented in LTE Advanced networks.
• Further Evolved Multimedia Broadcast Multicast Control – eMBMS ensures an economical mechanism for the operator to deliver broadcast and multicast services. First defined for LTE, eMBMS has been further refined and enhanced for LTE Advanced. It offers more carrier configuration flexibility, higher video resolution services because of higher LTE bit rates and a dynamic reservation/release of network resources.
• Cognitive Radio – Cognitive radios are designed to understand their environment and modify their own parameters like frequency, power, and modulation in such a way so as to utilize the unused spectrum dynamically in order to maximize spectral efficiency and minimize interference. While not explicitly defined within the LTE-A proposals, cognitive radios have been a prime area of interest for such networks because they can solve the spectrum scarcity problem.

One has to take into account that a real LTE-A network could have many more cutting-edge attributes and not every LTE Advanced network will sport all the above features. LTE-A is actually a collection of technologies. Consequently, we have to be careful about the marketing strategies that the network operators will follow. They could implement just one or two of above technologies and called their network LTE Advanced as long as it doubles or triples the current data rates. Few operators already claim that they are on the path to LTE Advanced. Last fall, Russian service provider Yota announced the world’s first LTE-A in Moscow with speeds up to 300 Mbps on consumer devices. Of course there are no LTE-A capable devices available yet. Korea’s SK Telecom has recently advertised its plans to launch LTE Advanced network by September of this year. They claim to have applied carrier aggregation, CoMP, femtocells and self-organizing network capability to their network. In US, T-Mobile has been happily declaring that since they were last to the LTE party and thus have the latest hardware, their transition to LTE-A would be faster and smoother. AT&T, Verizon and Sprint have been deploying small cells and advanced MIMO as part of their future LTE Advanced strategy. China Mobile and Vodafone New Zealand have tested the technology while achieving peak downlink speeds of 300 Mbps. Australia’s Telstra is also using carrier aggregation to launch LTE-A services later this year. Hardware manufacturers are not far behind. Qualcomm, Broadcom, Agilent, Ericsson and many others are already out with their LTE Advanced capable chipsets and network equipment.

Again, all above claims must be taken with a grain of salt. Wireless service providers are in a tightly competitive market and it is their business to tout the deployment of state of the art technologies. But it is for the consumers to decide that how much speed is good enough for them. Industry analysts like us can help them in separating truth from hype. Yes, LTE Advanced, whenever it gets here would be very awesome, but will not arrive in its true form before 2015.