Q&A on Long Term HSPA Evolution with Nokia Siemens Networks

Karri Kuoppamaki, Head of Technology; Karri Ranta-aho, Senior Specialist, 3GPP Standardization; and Ajit Kahaduwe, Head of Industry Environments.


Converge! -- What is the significance of Long Term HSPA Evolution for the industry?


NSN -- This is a pretty significant milestone. We as a company are firm believers in HSPA and that is why we are part of this initiative for driving further enhancements of 3GPP standards and taking HSPA beyond its current capabilities. The target we have in mind is to achieve peak data rates in excess of 650 Mbps in the downlink -- a significant improvement from where we are today.


Converge! -- How will you achieve this performance?


NSN We are looking at techniques that have already been discussed for LTE, such as using multiple antennas, carrier aggregation, and multiple transmission. We are not really reinventing the wheel here so much as taking existing building blocks and applying them in the context of HSPA. We are using proven technologies to enhance HSPA.


The existing 3GPP Release 10 already extends the carrier bandwidth beyond dual-carrier (already implemented in some networks today) to allow for 4 carriers. What we are now proposing for 3GPP Release 11 is to extend that to 8 carriers. This would cover 40 MHz of spectrum in one direction.


Converge! -- Is there a possibility of going beyond 8 carriers? What is the physical limit?


NSN Technically, the sky is the limit, but realistically it is a question of how much bandwidth an operator has at its disposal. Even if the technology would allow you to do more, there is only so much a network operator can actually posses and use for ordinary communication. So these 8 carriers would correspond to 40 MHz, which is already pushing the limit for many operators.


Converge! -- Do you need new silicon in the devices to enable 8 carriers?


NSN - That is correct. We will need a new round of devices, but as we introduce the new enhancements, we are not obsolescing the old devices. They will continue to coexist in the same bands.


Converge! -- Do you need changes in the base stations?


NSN - NSN's Flexi base station was developed to be modular and cater to future needs. Of course there will be some spectrum specifics that need to be looked at, for example on which bands this is deployed. But, in principle, we are evolving our base station for this.


Converge! -- Is Long Term HSPA Evolution an efficient use of spectrum as compared to LTE?


NSN It is an efficient use of spectrum and having a wider carrier is also going to bring benefits. You have more spectrum to schedule at your disposal which is going to improve the efficiency. There are benefits to going beyond 2-carriers from an efficiency standpoint. Some efficiency gains come from being able to choose which carrier to schedule at any given instant, so having more carrier to choose from is a benefit.


When we compare this to LTE, we are now talking about a comparable number of bits per hertz in efficiency.


Converge! -- Are there notable trade-offs for Long Term HSPA Evolution in terms of the number of simultaneous users, range or building penetration?


NSN We don't think there are any such trade-offs. In fact, some of the additional items being looked at for the next 3GPP Release will improve factors such as coverage. For instance, beam forming will improve data coverage beyond what it is today. In terms of the number of simultaneous users, these technologies do not effect that either. Generally, whenever we add bandwidth to a system, that automatically increases the number of simultaneous users that can be supported.


Converge! -- What are the implications for power efficiency for devices and for base stations?


NSN When we are talking of higher bandwidth and greater data flows, that means more processing is required and this puts more stress on the device's battery while the transmission is ongoing. On the other hand, the higher bandwidth means the transmission time will be reduced, so we may end up saving battery power.


Regarding the base station, it's no different from other transmissions. It comes down mainly to the power of the amplifier. For the actual baseband operation, the more users that we can support with a single processing element, the more energy efficient it will become. It is also good to remember that the existing HSPA standards are introducing a number of capabilities -- such as continuous packet connectivity -- that reduce power consumption and improve battery life. These are also applicable to Long Term HSPA Evolution.


Converge! -- Will Long Term HSPA Evolution be more suitable for the large, macro base stations or is it suitable for pico cells as well?


NSN From a technology perspective, there is no difference. It will come down to economics and the available bandwidth of the operators. The antenna placement may make this more applicable to smaller base stations, but cases may vary.


Converge! -- Which operators will be more interested in Long Term HSPA Evolution compared to LTE?


NSN These are not mutually exclusive. We at NSN believe in both LTE and HSPA Evolution. As LTE evolved, so too must HSPA. There are currently more than 350 commercial WCDMA networks which could benefit from this technology. One of the items that is being looked at in conjunction with this HSPA Evolution is HSPA + LTE Carrier Aggregation, which would be applicable for operators with both technologies. Carrier Aggregation, which is being considered for standardization, allows for load balancing between HSPA and LTE connections. A user could have simultaneous reception of HSPA and LTE. Basically, LTE already allows for aggregating carriers together; HSPA Evolution will do the same; and this technique would do this as well.


Converge! -- What are the next steps?


NSN We need to roll up our sleeves in the standards delegations and starting working on these new items that were opened last week. Then we must bring next wave of features to 3GPP for assessment.
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