WIMAX AND LTE - Either or both?
The battle is on to deliver the next generation of very high speed data services to consumers in
both fixed and mobile locations. Nigel Wright looks at the relative strengths and weaknesses of the two leading technologies, WiMAX and LTE
WiMAX and 3GPP Long-Term Evolution (LTE) are two different (but not necessarily competing) technologies that will eventually be used to achieve data speeds of up to 100 Mbps. Speeds that are fast enough to potentially replace wired broadband connections with wireless, and enable services such as HDTV on mobiles and TVs without the need for a fixed-line or dish in the home, as well as a host of other exciting services currently seen as too bandwidth-hungry to be delivered using existing mobile technologies.
WiMAX and LTE are both in different stages of development. WiMAX is widely recognised as being the first that will be brought to market. The world's first large scale mobile WiMAX deployment is due in the US in spring 2008 under the Xohm brand by Sprint Nextel. However, although LTE may on paper be some years off, it will bring with it many advantages, not least the fact that operators will be able to evolve their existing infrastructure and base station real estate to deliver it.
Realistic expectations
There is much expected of WiMAX and it's probably fair to say that some of this can be classified as ‘hype' yet there is much to be excited about, provided we set realistic expectations with early stage deployments. It's also important to remember that WiMAX comes in two distinctly different flavours - mobile WiMAX (referred to under standard 802.16e) and fixed (802.16d). There are significant differences between the two, not least the fact that it's technically much easier to deliver the high bandwidth speeds to a stationary external antenna associated with fixed WiMAX than it is to one on a mobile device in someone's pocket or handbag.
This means that whilst symmetrical speeds of 10 Mbps may be technically possible at a range of 10km today, in practice this is likely to be achieved only using fixed WiMAX and is reliant on other variables for its success, such as a high quality external antenna with line-of-sight to the base station. Given this situation is far from common and that buildings get in the way and degrade WiMAX signals, it will be more likely that mobile WiMAX users will only see half that data rate at much shorter distances from the base station - at least until techniques such as MIMO (multiple input multiple output) and beamforming are perfected to counter, and even take advantage of the multipath effects from physical obstructions.
The spectrum issue
One of the biggest obstacles to widespread WiMAX deployments is the lack of available high quality spectrum. In the US, Sprint benefits greatly from its 2.5 GHz spectrum holdings. This relatively low-frequency band allows greater coverage per base station since signals travel much further than at higher frequencies. This results in fewer base stations needed, making WiMAX cheaper to deploy in the US than in other markets that don't have access to the same spectrum. Even given the availability of 2.5 GHz spectrum, for Sprint's network to provide nationwide coverage it will require more than 60,000 base stations across the US.
In Europe, bandwidth below 2.5GHz is scarce and mostly occupied by analogue TV and current GSM mobile signals. Therefore, until now most European WiMAX trials and licences have been limited to the 3.5 GHz or even 5 GHz bands with often disappointing results, which is why we haven't seen anywhere near as much WiMAX traction in Europe as the US. It may not be until after analogue broadcast signals are switched off across Europe (with the UK scheduled for 2012) that sub 2.5 GHz spectrum becomes available and we start to see large-scale European WiMAX deployments.
An open door for LTE?
An alternative high speed mobile technology that could be used instead of, or to run alongside, WiMAX is LTE. The crucial difference is that, unlike WiMAX, which requires a new network to be built, LTE runs on an evolution of the existing UMTS infrastructure already used by over 80 per cent of mobile subscribers globally. This means that even though development and deployment of the LTE standard may lag Mobile WiMAX, it has a crucial incumbent advantage.
There is also no doubt that the advent of WiMAX has injected a new sense of urgency to the LTE standardisation effort. This may help provide operators keen to control investment with the confidence to wait for LTE technology to reach maturity before upgrading their existing infrastructure, rather than invest in a brand new WiMAX network.
Even prior to the arrival of LTE, speeds of up to 7.2 Mbps are currently being reached by existing HSPA technology, which is being used by more than five million subscribers worldwide. And speeds are getting faster - within the next two years it is expected that downlink speeds will reach up to 14 Mbps, which will in turn provide high quality TV and other bandwidth-hungry applications. Although HSPDA is designed for high-speed data in the downlink only, HSUPA is also beginning to arrive in some markets now, increasing uplink rates to a maximum of 5.8 Mbps. This will enable additional services that benefit from symmetrical data rates, such as online gaming and videoconferencing.
At these speeds, HSDPA becomes a realistic candidate to replace wired Internet access with wireless in some cases. It is therefore possible that even with WiMAX and LTE developments, HSDPA will be enough to satisfy the needs of many users or will be a satisfactory interim solution prior to LTE's arrival.
A combination of the two?
So which technology will ultimately prevail? It is arguable that LTE is more ‘risk-free' than WiMAX because it will run on an evolution of existing mobile infrastructure. Also, mobile operators will be able to use their experience from current 3G and HSDPA networks to carry out the incremental fine-tuning necessary to ensure that the rollout of LTE will deliver on user expectations. Also in Europe it has the advantage of being unaffected by the lack of available spectrum.
However, the recognition of WiMAX as an IMT-2000 technology by the ITU in October 2007 is a significant step, that in the future may help WiMAX to gain a foothold in today's UMTS spectrum and so close the spectrum availability gap, but the full impact of this move has yet to unfold.
Nevertheless, LTE is still perhaps three to four years from being ready whereas mobile WiMAX equipment is entering the final testing phase now. Some operators far from seeing LTE as being less of a risk may take the view that by missing an early mover advantage into ultra high speed mobile broadband and waiting for LTE would have an impact in terms of potential subscribers perhaps attainable by moving to WiMAX now.
Also LTE will start to come to the forefront at the same time as analogue TV signals are switched off in Europe, making the spectrum debate largely irrelevant to the WiMAX versus LTE argument. This is of course provided national governments release spectrum for WiMAX and it's available at a price that operators deem worth paying.
Interestingly many operators have already stated their interest in both camps. In August of this year, Vodafone, a key advocate of LTE, declared itself ‘technology neutral' and joined the WiMAX Forum. This pragmatic approach is perhaps a sign that for now many operators will adopt a ‘wait and see' approach and learn from the experiences of early pioneers such as Sprint Nextel before deciding whether to choose WiMAX or LTE.
Ultimately the decision may be to use both. As Spirent Nextel is showing in the US, the real estate occupied by an operator's current base stations can also be used to site new WiMAX base stations. Then the strategy could be that LTE is used to support mobile broadband users and WiMAX to support fixed or lower-mobility broadband users. Alternatively, they could well use LTE for macro cellular coverage and WiMAX for micro cell coverage.
In all likelihood many devices of the future will ship with both LTE and WiMAX capability, meaning full compatibility across both technologies. Consumers will probably not even know which particular technology is delivering high speed data to them and they're hardly likely to care, so long as it works to their satisfaction, and the content provided is engaging and available at the right price.
Nigel Wright is Vice President of Product Marketing, Spirent Communications
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