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Monday, January 20, 2014

Tracing Multicarrier Evolution in today’s networks:

The most straightforward way of increasing the data rates is to use more bandwidth. Dual cell (dual carrier) HSDPA (DC-HSDPA) in Release 8 uses two adjacent carriers in downlink to push the data rates up twofold. DC-HSDPA networks were widely launched during 2011. The bandwidth can be further increased to 20 MHz in Release 10 by using four carriers and even to 40MHz in Release 11 with eight carriers. The uplink dual cell was included in Release 9 specifications. The multicarrier evolution is illustrated in Figure below;

Operators have deployed multiple carriers in their networks almost from the very beginning of WCDMA for capacity reasons. Harnessing the already-deployed multicarrier infrastructure to delivering data to one user is a cost-efficient way for increasing the system peak data rates. The spectrum utilization is also significantly improved because it is possible to efficiently balance the loading between carriers and reduce the probability that some carriers don’t see any loading while some other carriers are fully utilized due to a momentary high-data rate download. Multicarrier links also enable frequency domain scheduling,  providing system gains even if all carriers in the system are fully utilized. Notably the system benefits of improved spectrum utilization, more dynamic load balancing and frequency domain scheduling gains are available even if only a fraction of the devices in the system are multicarrier capable.

Release 9 also brought the possibility to allocate the two carriers from two different frequency bands to a DC-HSDPA device, and this was further extended in Release 10 so that the four carriers can be split between two frequency bands. The figure below illustrates the standard supported band combinations that can be aggregated to a multicarrier capable device. As a multiband capable device is anyway built with the RF hardware capable of receiving HSDPA on different frequency bands, it is attractive to aim at using that same RF hardware also simultaneously for improved data rates and better spectrum utilization.

Release 11 work is ongoing for aggregation of a block of non-adjacent carriers to a fourcarrier HSDPA device. The bands for which the support is worked on are Band I (2100 MHz) and Band IV (2100/1700MHz). The practical side of this is that the supporting device is expected to require two independently tuneable receiver chains capable of receiving on the same frequency band. A possible implementation option could be to use the two receivers as receiver diversity in case it is configured to receive a set of carriers adjacent to each other and it houses two antennas, and in the case it is configured to receive a set of carriers not adjacent to each other it could allocate one receiver chain to receive one frequency block and the other receiver chain to receive the other frequency block.

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