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Scalable UMTS (S-UMTS)

UMTS FDD only supports a nominal 5 MHz channel bandwidth. However, in many scenarios such as spectrum fragmentation due to re-farming from legacy systems, operators cannot accommodate a complete 5 MHz carrier. This results in suboptimal spectrum usage.

The goal of Scalable UMTS (S-UMTS) is to enable UMTS support in a fraction of full UMTS carrier bandwidth without significant impact to spectral efficiency, link budget, device complexity or system design.

S-UMTS achieves bandwidth reduction by applying flexible UMTS waveform, with decreased chip rate and "dilated" time relative to full UMTS. The figure below illustrates the application of the time dilation concept to generate 1/2-bandwidth S-UMTS, where the chip duration is doubled compared to a full UMTS waveform.

S-UMTS is expected to find a number of applications, for example:

1. Re-farming GSM spectrum for UMTS

It might not be feasible for the operators to re-farm 5 MHz of GSM carriers at once due to GSM capacity requirements and other constraints. Gradual migration from GSM to UTMS is therefore preferred. The following figure illustrates scenarios where a S-UMTS carrier can be deployed with as little as 1.05 MHz of re-farmed spectrum.

2. Additional UMTS carriers

When the available spectrum is less than 5 MHz or it is not a multiple of 5MHz, S-UMTS enables operators to maintain optimal spectrum usage by deploying carriers in less than 5 MHz bandwidth. The following figure illustrates the deployment of a full UMTS carrier and an additional S-UMTS carrier in 6 MHz and 7 MHz spectrum.

3. HSPA Supplemental Downlink

S-UMTS enables the aggregation of less than 5 MHz S-UMTS carriers with a full UMTS Anchor Carrier. This provides additional downlink capacity, while limiting the overhead carried by the S-UMTS carrier. The following figure illustrates a Multi-Carrier HSDPA scenario.