FEATURE LTE ADVANCED
“We will have to see how quickly the market really picks up these latest trends,” he says. “But our experience with other mobile broadband technologies is that the demand is always for the operators to have the edge over their competitors. So I would be surprised if we needed to wait a long time before LTE Advanced comes. Our hardware is prepared for it and next year we will put out the first software releases covering LTE Advanced features.” Operators may want the edge in terms
of performance but they are driven by de- mand just as much as the vendors. And the disagreements over the likely timescales for deployment of LTE-A are fuelled by differ- ences of opinion over what shape that demand will take. The fundamental question here surrounds the future applications that will require throughput rates of up to 1Gbps. At the moment, in the earliest stages of the LTE life cycle, and before it is widely deployed, it
The sharpest tools in the box 1. Carrier Aggregation
Carrier aggregation will allow operators to combine as many as five Release-8 compatible carriers, thereby enhancing the data rates delivered to the end user without the need for contiguous frequency band allocations. So far this solution is limited to providing bandwidths with a maximum range of 100MHz, although this limit has only been imposed by foreseeable demand. Higher bandwidths could be easily supported, according to vendors. As with many network technologies, the benefits deliverable by carrier aggre-
gation are restrained by the number of users in a cell. With high numbers of users the benefits are likely to be marginal, but if the number of users is low, then a large amount of bandwidth can be allocated to each one. There are also limits to carrier aggregation in the uplink, as devices will lack the power necessary to enable multi-carrier transmission. Carrier aggregation is likely to be one of the earliest deployed technical ele-
ments of LTE-A.
2. Advanced MIMO schemes MIMO is supported by 3GPP Releases 8 and 9 for LTE, for up to four transmit and receiver antennas in the downlink but only single antenna transmission in the up- link. In Release 10 this has been expanded to eight in the downlink, with uplink MIMO introduced with support for four transmit and eight receiver antennas. As it stands there are question marks over how practical it will be to have four anten- nas in the handset, however. Furthermore, according to NSN, it needs to be borne in mind that the Release
10 network will also be supporting Release 8 and 9 devices. The capacity gain from Release 10 downlink MIMO enhancements could be negative since new reference symbols create overhead for all devices. These overheads could be decreased by reducing the Release 8 and 9 specific reference symbols, the firm says, but this would prevent non LTE-A devices from operating in MIMO mode, thereby lowering the data rates they could access.
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is difficult to conceive of a service or applica- tion that would require performance so far beyond the most advanced technology that reality has to offer. The industry and user base could see the benefits of video on mobile phones, delivered to the right place and in the right way before HSPA ever came along to make it possible, says Dan Warren. “It was only the fact that the technology wasn’t there to deliver it that stifled the growth of the service. Un- less LTE Advanced comes up with a really eye-watering application which is going to demand searingly fast speeds then where I really begin to struggle is in seeing what customers are going to want to do with it.” He adds a disclaimer, though: “But just be- cause we can’t see it, doesn’t mean it isn’t going to happen.” Arne Schälicke certainly thinks there will be a need for the technology, although he concedes that, for single users, the
absolute peak rates defined by the ITU will probably not be necessary. Instead he points to the German deployment of LTE at 800MHz, which is designed to roll out domestic broadband to homes beyond the reach of the fixed network. The devices in these deployments are LTE routers and he argues that such things deployed into SMEs would create the case for data rates that go significantly beyond what is currently available. Beyond this he talks in terms of volume
rather than applications. More and more users will have mobile broadband devices, he says, and will increasingly have them in multiples. Smartphones, laptops and tablets deployed in greater number will change the game. “The number of users who really embrace mobile broadband will grow,” he says, “and the us- age intensity per user will grow. Capacity is needed and LTE Advanced provides the most cost-efficient evolution path for that.” n
3. Coordinated multipoint transmission (CoMP)
Coordinated multipoint technology, based on Coordinated Scheduling/Coordinat- ed Beamforming, Joint Processing/Dynamic Cell Selection and Joint Processing/ Joint Transmission, was deemed insufficiently mature for inclusion in Release 10. Down the line it is seen as having the potential to improve cell edge performance and network capacity.
4. Relay Nodes Making use of the LTE-A air interface for self-backhaul, relay nodes allow for the deployment of small cells in locations where conventional backhaul technologies such as fixed line or microwave are unavailable or not viable. They are targeted at coverage limited environments, such as large macrocells, within the reach of which they would be used to boost coverage indoors or in urban canyons, for example. One particular benefit of relay nodes is that they are transparent to the user equipment, meaning there is no need for specialist technology within the device.
5. Heterogeneous and Self Organising Networks A network architecture rather than a specific technology, the ‘hetnet’ came to prominence at MWC 2011. The hetnet involves the widespread deployment of small cells among the wide area network and, in some anticipated scenarios, will function across a range of radio access technologies, with wifi taking the strain from the cellular network in certain places, for example. NSN says that “autono- mous or automated interference coordination and handover optimisation in such hierarchical network architectures are key aspects of heterogeneous networks”. Self organising networks will also play a role in the LTE-A environment. Some SON elements are already in existence, having first appeared in the femtocell space. But NSN says new developments to the concept are underway that will reduce cost of deployment and operation.
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