LTE (Long Term Evolution, also known as 4G) is entering the hype-cycle, and being rapidly pushed up to the ‘peak of inflated expectations’, just like IMS (IP Multimedia Subsystem), PTT (Push To Talk), FMC (Fixed Mobile Convergence), and far too many other technologies to name here. So to cut through the hype and hopefully present a pragmatic view on the technology I thought it timely to make a few points, as I find I’m often repeating myself on this topic (I hope its not old age.)
A few pointers on what the technology can do:
- LTE will not greatly improve spectral efficiency compared with HSPA+ (High Speed Packet Access). Within a 5MHz slot you could achieve perhaps 80 Mbit/s with HSPA+ (using MIMO (Multiple In Multiple Out) technology), compared to 100 Mbit/s with LTE. A 20% increase is unlikely to have customers demanding LTE. The only tangible difference will be a slightly lower round-trip delay for LTE perhaps down to 10-20ms compared to perhaps 30-35ms with HSPA+, though with a flat IP core (moving RNC (Radio Network Controller) and SGSN (Serving GPRS Support Node) out of the data path) that could drop to about 20ms for HSPA+.
- LTE enables a higher peak data rates by using more bandwidth, scaling from 1.25 MHz (useful for the CDMA operators, hence Verizon’s decision to adopt LTE) to 20 MHz and beyond. LTE uses OFDM (Orthogonal Frequency Division Multiplexing), the same technology used in DSL (Digital Subscriber Loop), that is lots of little carriers, rather that one big one carrier as in HSPA, which gives LTE its flexibility.
- LTE can use FDD (Frequency Division Duplex) and unpaired TDD (Time Division Duplex) bands bought during the heady days of 3G spectrum auctions, where HSPA and GSM cannot operate in those bands
- LTE is a global standard, with a global frequency plan, hence can leverage global volumes, another reason behind Verizon’s decision to adopt LTE, rather than pay an average $15 premium for its (CDMA) devices. This is also the fundamental reason why the total cost of ownership of WiMAX networks will remain more expensive than LTE.
- HSPA has some funny technologies hidden away in it such as macro cell diversity, i.e. a terminal may use 2 or 3 cells at the same time. LTE does away with these complexities so does not need RNC nodes. LTE also has built in operational and maintenance capabilities, such as self-tuning to help control operational costs.
- By 2010 most GSM base stations in Western Europe will be over 20 years old. Most were put in during the “cheap-energy days.” Today, finally, green credentials matter to companies so LTE will enable the power consumption of mobile operators RANs (Radio Access Network) in the long run to be reduced by up to 50%.
A few pointers on the market’s development:
- DoCoMo and Verizon are in unique positions that force a move to LTE faster than the rest of the market, so by 2010 they will likely be deploying LTE, and will be the first movers.
- Most in the GSM community will be working through HSPA+, which will significantly delay their need to move to LTE.
- The Flat IP core I referred to previously is a way of leapfrogging to the SAE (System Architecture Evolution), which can be thought of as the 4G Core, while LTE is the 4G RAN. With the core upgraded, and a relatively fast RAN in HSPA+, most operators are only going to deploy LTE based upon operation needs. Hence you’ll likely see LTE being deployed more broadly in the market around 2013.
- And of course the good old chestnut of handset availability. This is actually likely to be less of an issue compared to say 3G as most of the customers using LTE will be using a laptop with a USB fob. Just remember to bring a spare laptop battery when you use LTE!