The recent increase of mobile data usage and emergence of new applications such as MMOG (Multimedia Online Gaming), mobile TV, Web 2.0, streaming contents motivated the 3rd Generation Partnership Project (3GPP) to work on the Long-Term Evolution (LTE). LTE is the latest standard in the mobile network technology tree that previously realized the GSM/EDGE and UMTS/HSxPA network which is designed to increase the capacity and speed of mobile telephone networks. The main objectives of LTE are to increase spectrum efficiency and reduce latency, allow flexible spectrum deployment in existing or new frequency spectrum and to enable co-existence with other 3GPP Radio Access Technologies (RATs).
But what about WiMAX- another 4G technology designed to move data rather than voice also based on OFDM air interface technology? Are these two technologies rivals such as GSM and CDMA or more like siblings? And here’s the crux. Sibling rivalry does exist. Mobile operators with FDD spectrum would pick LTE, but vertical markets such as transportation, healthcare, utilities, and public safety would also naturally gravitate towards WiMAX.
As a technology, LTE is considered to be indistinguishable from WiMAX. The evolution steps for both the technologies are not in sync, which means that at any time the latest version of one of the two technologies may be a bit ahead, but the endless comparisons have failed to conclusively show that which one is better than the other.
The million dollar question of the two 4G technologies being converged remains unanswered. The chances of LTE and WiMAX being merged even in the future are very slim. Technically, even though there are many similarities between the two standards (OFDM, MIMO, all-IP oriented, etc.), the details, especially at the Physical Layer-level, are pretty divergent. LTE has set aggressive performance requirements that rely on physical layer technologies, such as, Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) systems, Smart Antennas to achieve these targets. A harmonization may happen in the network level for seamless handover between the two networks but it’s pretty much a dual mode type of service just done in a more efficient way. From this perspective, in order for a complete harmonization to happen, one camp very much has to ditch their previous developments, which seems unlikely. From a political/market perspective, almost all major players in LTE are not active participants of WiMAX (Samsung is an exception), so there is usually some resistance towards WiMAX from the LTE camp.
Certainly not to forget comes the latest TD-LTE. LTE becomes much more intriguing almost disruptive with TD-LTE. There are two versions of LTE. FDD-LTE uses the FDD paired spectrum with two separated channels, one for the uplink and one for the downlink, which is the type of spectrum most mobile operators have. TD-LTE uses TDD unpaired spectrum channels that combine uplink and downlink, and split resources on the basis of real-time demand. Voice is inherently symmetric in the uplink and downlink so it is well suited for FDD spectrum allocations. Data traffic benefits from TDD spectrum, as it is typically asymmetric but the degree of uplink/downlink asymmetry is not fixed. The development of TD-LTE was initially pushed by China Mobile and regarded as a mainly Chinese standard, similarly to TD-SCDMA.
And an obvious question, ‘Why sudden interest in TD-LTE?’ The main drivers of support for TD-LTE are firstly, the FDD LTE and TD-LTE versions of the 3GPP standard are very similar. As a result, devices can support both the FDD and TDD interfaces through a single chipset–i.e., without any additional cost. Thus, TD-LTE will benefit from the wide availability of FDD LTE devices that will be able to support TD-LTE as well. Unlike WiMAX, TD-LTE does not need to prove to have a substantial market share to convince vendors to develop devices as they simply need to add TD-LTE support to the existing ones. Additionally, in effect, this ability to roam between FDD LTE and TD-LTE means operators can use TD-LTE networks to augment their FDD LTE network for more capacity or other applications such as video broadcasting, while operators choosing to use TD-LTE as their “main” network can still offer their subscribers the ability to roam to other operators’ FDD LTE networks in different countries. Secondly, there is a lot of TDD spectrum available, and in most cases it is cheaper and under-utilized. 3G licenses frequently have TDD allocations and upcoming 2.5 GHz auction in most cases contemplate TDD bands.
WiMAX operators are increasingly keen on requiring vendors to be able to support both a transition to WiMAX 16m and to TD-LTE as smooth as possible. WiMAX has been successfully in making regulators more comfortable with TDD spectrum allocations and, as a result, with increases in the availability of spectrum that can be used for TDD interfaces and that is technology neutral. Mobile operators have traditionally shown little interest in TDD spectrum and tried to stop additional TDD allocations to prevent WiMAX players to enter in their markets. With TD-LTE, however, they may finally have a way to use TDD spectrum and benefit from it. So is WiMax losing the battle, but winning the war at the same time?
Filed Under: Infrastructure