research s-umts white paper original

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Qualcomm Technologies, Inc.

Not to be used, copied, reproduced, or modified in whole or in part, nor its contents revealed in any manner to others

without the express written permission of Qualcomm Technologies, Inc.

Qualcomm is a trademark of QUALCOMM Incorporated, registered in the United States and other countries. All

QUALCOMM Incorporated trademarks are used with permission. Other product and brand names may betrademarks or registered trademarks of their respective owners.

Qualcomm Technologies, Inc.

5775 Morehouse Drive

San Diego, CA 92121

U.S.A.

2013 Qualcomm Technologies, Inc.

All rights reserved.

Scalab le UMTS (S-UMTS)

Solut ion for Fragmented GSM Spectrum Refarm ing

February 2013


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Scalable UMTS (S-UMTS)

2013 Qualcomm Technologies, Inc 2

1 Introduction

UMTS supports a Frequency Division Duplex (FDD) mode of operation which employs a nominal 5MHz carrier spacing. A contiguous block of at least 5 MHz spectrum is needed to deploy aUMTS/HSPA+ carrier. There are, however, many scenarios where an operator cannot accommodate acomplete 5 MHz carrier. For example, refarming of spectrum from legacy wireless systems may result infragmented spectrum, and local regulators might have allocated small blocks of spectrum to the operators.

The inability of existing UMTS/HSPA+ to make use of fragmented spectrum results in suboptimalresource utilization.

The goal of Scalable UMTS (S-UMTS) is to enable the support of UMTS/HSPA+ in half or a quarter of

full UMTS/HSPA+ carrier bandwidth, while maintaining coverage and spectral efficiency. S-UMTS has a

number of key use cases, including phased refarming of GSM spectrums and maximized utilization ofUMTS/HSPA+ spectrum. This paper discusses S-UMTS and its use cases.

2 GSM Refarming Challenges

One of the key challenges to GSM refarming is the fragmented 2G spectrum allocation. For example,

GSM has a carrier bandwidth of 200 kHz, it is not necessary to allocate a large contiguous block ofspectrum for the operators to deploy a GSM network. Figure 1 illustrates representative examples of 900MHz spectrum allocation in several countries:

In Czech Republic, the operators are allocated multiple blocks of spectrum in the 900 MHz band,

each with less than 5 MHz bandwidth. Some operators have more than 5 MHz of total spectrum

in the band, but it is not contiguous spectrum.

In China, the bandwidth of the allocated 900 MHz spectrum is not a multiple of 5 MHz. For

example, China Unicom has 6 MHz of GSM spectrum in the 900 MHz band.

In Brazil, there exist spectrum blocks with bandwidth less than 5 MHz. For example 2.5 and 1.5

MHz carriers in the 900 MHz band.

In India, there exist many types of fragmented spectrum in different regions. For example, 4.1

and 2 MHz in the 900 MHz band.


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Figure 1: Representative Examples of 900 MHz Spectrum Allocation

Existing UMTS/HSPA+ does not support spectrum with less than 5 MHz bandwidth, making itchallenging to deploy UMTS/HSPA+ using fragmented spectrum from GSM refarming. Even if morethan 5 MHz of contiguous spectrum is available, it cannot be fully utilized if the available bandwidth is

not a multiple of 5 MHz.

Another challenge of GSM refarming is the difficulty in clearing 25 contiguous GSM carriers to deploy

UMTS/HSPA+ due to existing GSM capacity requirements. In some cases, operators have obligations tomaintain GSM networks to support services such as machine-to-machine communications. They must

provide certain level of GSM capacity for the long term and cannot make available the entire GSMspectrum for UMTS/HSPA+. A solution that enables phased migration from GSM to UMTS/HSPA+,

starting with less than 5 MHz of refarmed spectrum, is therefore desirable.

3 Scalable UMTS

S-UMTS enables the support of UMTS/HSPA+ in less than 5 MHz spectrum. Specifically it makespossible for UMTS/HSPA+ to operate in and of the full UMTS/HSPA+ carrier bandwidth. Figure 2

illustrates this capability of S-UMTS. The full UMTS/HSPA+ carrier is allocated a nominal 5 MHz ofspectrum including the guard bands, while most of the carriers energy typically occupies 4.2 MHz

bandwidth. The and bandwidth S-UMTS carriers occupy 2.1 MHz and 1.05 MHz bandwidth,respectively, excluding any required guard bands.


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Figure 2: Scalable UMTS

S-UMTS achieves bandwidth reduction by a technique referred to as time dilation, which scales the chip

rate of the S-UMTS carrier relative to that of the full UMTS/HSPA+ carrier. Figure 3 shows time dilationwith a scaling ratio N=2, where the chip duration is doubled, and the occupied bandwidth is reduced tohalf, compared to a full UMTS carrier. Figure 3 also shows that the energy per chip is maintained and thetotal transmit power of S-UMTS is 1/N of full UMTS.

Figure 3: Time Dilation

Table 1 illustrates that a full UMTS/HSPA+ carrier with 3.84 Mcps chip rate typically occupies 4.2 MHz

bandwidth excluding guard bands. A bandwidth carrier with 1.92 Mcps chip rate and 2.1 MHzoccupied bandwidth can be generated by using a scaling ratio N=2. Similarly, a bandwidth carrier that


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has a 1.05 MHz occupied bandwidth can be generated by using a scaling ratio N=4. Note that as the chiprate and therefore bandwidth is scaled down, the Transmission Time Interval (TTI) is increased. The

HSDPA TTI for the full, and carriers are 2ms, 4ms, and 8ms, respectively.

Table 1: Scalable UMTS Waveforms

S-UMTS

Carrier

Type

Scaling

Ratio (N)

Chip Rate

(Mcps)

Bandwidth*

(MHz)

HSDPA

TTI

(ms)

Full carrier 1 3.84 4.2 2

carrier 2 1.92 2.1 4

carrier 4 0.96 1.05 8

*Excluding guard bands

S-UMTS makes the deployment of UMTS/HSPA+ possible in fragmented spectrum with less than 5 MHzbandwidth. In addition, it provides a number of advantages:

Offers similar spectral efficiency as UMTS/HSPA+

Maintains the same link budget as full bandwidth UMTS/HSPA+ and preserves network plans

Maintains similar overhead ratio as full bandwidth UMTS/HSPA+

Supports both WCDMA voice and HSPA+ data services

Maintains voice quality as full bandwidth UMTS

Simple system design leverages existing system assets

Applicable to all 3GPP bands

4 S-UMTS Enables Refarming of All GSM

Spectrum

As discussed in Section 2 , operators working on refarming GSM spectrum for UMTS/HSPA+ face twomajor problems:


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1. The mismatch between the bandwidth of spectrum available from GSM refarming and the

minimum UMTS/HSPA+ bandwidth requirement. Spectrum blocks smaller than 5 MHz cannot

be utilized by UMTS/HSPA+, which results in under utilization of valuable resource.

2. The lack of a phased approach to migrate from GSM to UMTS/HSPA+. An entire 5 MHz block

of GSM carriers must be cleared to deploy one UMTS/HSPA+ carrier, which limits the available

GSM capacity after refarming. Furthermore, the inability to match GSM spectrum to capacity

requirements means that operators need to maintain more GSM capacity than necessary, thus

resulting inefficient spectrum utilization.

S-UMTS addresses the above two problems by enabling operators to refarm all of the required GSMspectrum in a phased manner. Figure 4 illustrates the ability of S-UMTS to support UMTS/HSPA+ in less

than 5 MHz spectrum. Figure 4(a) shows that S-UMTS can make use of isolated fragments of spectrumfrom GSM refarming to deploy standalone UMTS/HSPA+ carriers. Figure 4(b) shows that these spectrum

fragments can further be aggregated with a full UMTS carrier through HSPA+ multi-carrier aggregation.The aggregated carrier has higher combined data rate compared to the single full carrier, thus achievinghigher trunking efficiency and better user experience.

(a) (b) .

Figure 4: GSM Refarming Using S-UMTS

Figure 5 illustrates that S-UMTS enables phased UMTS/HSPA+ migration. An operator that has 5 MHzGSM spectrum can start refarming with a or bandwidth S-UMTS carrier. In this way, the operatorcan introduce UMTS/HSPA+ service gradually while continuing to support GSM traffic. Eventually,when GSM service is not needed, it can be completely phased out to support a full UMTS carrier.


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Figure 5: S-UMTS Enables Phased GSM to UMTS/HSPA+ Migration

5 S-UMTS Maximizes UMTS/HSPA+Spectrum Utilization

UMTS/HSPA+ generally allocates 5 MHz of spectrum per carrier. In reality, for co-located carriers, acarrier separation of less then 5 MHz is sufficient to maintain low inter-carrier interference. For operatorswith 10 or 15 MHz of contiguous spectrum, there is an opportunity to introduce an additional S-UMTS

carrier in the available spectrum. This can potentially maximize the utilization of available spectrum.

Figure 6 illustrates that additional S-UMTS carriers can be added to 10 MHz and 15 MHz blocks of

contiguous UMTS/HSPA+ spectrum. A 10 MHz spectrum block can be used to support twoUMTS/HSPA+ carriers, which typically occupy 4.2 MHz each, and one bandwidth S-UMTS carrier.Similarly, a 15 MHz spectrum block can be used to support three UMTS/HSPA+ carriers and one

bandwidth S-UMTS carrier.


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Figure 6: S-UMTS Enables the Support of Additional Carriers in UMTS/HSAP+ Spectrum

6 Conclusions

S-UMTS supports the deployment of UMTS/HSPA+ in and of the full UMTS/HSPA+ carrierbandwidth. It enables UMTS/HSPA+ to effectively make use of fragmented and leftover spectrum, and

resolves two key problems associated with GSM refarming:

1. Insufficient spectrum to deploy UMTS/HSPA+, and

2. Inability to free up 25 contiguous GSM carriers due to existing GSM capacity requirements

In addition, S-UMTS enables the deployment of additional carriers in existing UMTS/HSPA+ spectrum.

Thus maximizing resource utilization and improving network capacity.

Another key advantage of S-UMTS is its limited impact to UMTS/HSPA+ system design. S-UMTS aims

at maintaining the link budget as 5 MHz UMTS/HSPA+ and delivering similar spectral efficiency in all3GPP bands. It maintains service capabilities of existing UMTS/HSPA+, including circuit-switched

voice, SMS, and packet data . S-UMTS is currently a 3GPP Release 12 candidate feature.

research s-umts white paper original

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