nokia siemens networks white paper efficient resource utilization improves the customer experience

8/12/2019 Nokia Siemens Networks White Paper Efficient resource utilization improves the customer experience

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White paper

Efcient resource utilizationimproves the customer experience

Multiow, aggregation and multi band load

balancing for Long Term HSPA Evolution


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Contents

2. Executive summary

3. Resource utilization in

current networks

5. Features enhancing

network utilization

5. Multi Band Load

Balancing

7. Multi Carrier HSDPA

9. Multiflow

12. HSPA LTE Carrier

Aggregation

13. Further considerations

14. Summary

15. Abbreviations

2 Efficient resource utilization improves the customer experience

The first of these features is Multi Band

Load Balancing (MBLB), which spreads

traffic over the different layers, such that

more resources are made available for

each user and performance is therefore

improved.

Another feature is Multi Carrier HSDPA,

which is extended in Rel 11 to eight

carriers. This improves utilization by

allowing free resources in the other

carriers to be used flexibly.

Multiflow is a 3GPP Rel 11 feature

candidate, designed to improve cell edge

data rates by enabling the transmission of

data from multiple cells instead of via a

single cell as in HSDPA today. This leads

to a doubling of the power available for

the wanted signal, increasing the overall

user throughput

HSPA-LTE carrier aggregation, a feature

candidate for future 3GPP releases,

enhances traffic steering by enabling fast

load balancing between the two radios,

ensuring efficient spectrum utilization

even when traffic is very bursty. The gain

is similar to that of multi carrier HSPA: if

the load is low, large efficiency gains can

be expected, whereas when loads are

high, the gain decreases.

These features bring a major

improvement to HSPA by using network

resources more efficiently, giving larger

throughputs for end users and allowing

faster response times.

Executive summary

With the growing popularity of

smartphones and the increasing use of

applications designed to make use of

their capabilities, traffic is rising

dramatically. As well as application

related traffic, with frequent updates to

and from applications such as social

networking sites and health monitoring

functions, smartphones are giving rise

to significant signaling loads.

Much of this traffic is bursty in nature,

leading to imbalances in network

utilization. Resource requirements vary

greatly over time and between cells

and frequency layers. At any one time,

many parts of the network have

significant free resources, while other

parts need to deliver high data speeds.

Underused resources are common in a

typical network. This is inefficient for

network operators, as well as

potentially degrading the user

experience, it also means

communications service providers

(CSPs) may not be making efficient

use of network investments.

An answer to this is provided by

features that form part of the latest

3GPP standardization release of Long

Term HSPA Evolution, the 3GPP Rel

11, as well as related features from

earlier HSPA standardization releases.

These features take advantage of

under-used resources to enhance

performance for the user.

Figure 1. Long Term HSPA Evolution components.

3GPP Release

11+ Long Term

HSPA Evolution

FuturePresent New features

Carrier aggregation

Multipoint systems

Further enhancements

to CELL_FACH

HSPA+LTE

aggregation+

MIMO

4x

MIMO

2x


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HSPA is the leading cellular data

service currently in use around

the world. Traffic on HSPA

networks continues to grow and

evolve as users develop new

ways of interacting with one

another and the information

around them, and CSPs seek

to differentiate and maximize

their revenue.

The smartphone segment of the

market has experienced very

rapid growth within a short time,

leading to a wide user base and

a rich diversity of applications.

Smartphone traffic may be driven

by a number of processes that

Resource utilization incurrent networks

3Efficient resource utilization improves the customer experience

expect always on, landline-like

connectivity and which may operate

even while the user is not interacting

with the phone. Social networking,

news, healthcare monitoring, push

e-mail and other autonomous apps

may give rise to small amounts of

update data in both directions. Another

factor is interactive usage, which may

range from web browsing, for which

short, high burst speeds are critical to

the user experience, to voice and

video, where steady QoS is key. It also

covers file down/uploading, in which

average burst speeds affect the user

experience. Apart from application

data, smartphones generate signaling

load that must be dealt with effectively

by the network.

In many markets, tablets and PC

dongles have seen significant uptake,

generating large amounts of data when

users are active. Traffic patterns may

involve web browsing, video streaming

and file up/download, with

requirements similar to smartphones

The coming years are also expected to

witness a significant expansion in the

amount of machine-to-machine (M2M)

communications within networks,

which will bring new types of traffic

profile and QoS requirements.

A key characteristic of the traffic growth

is that traffic has become bursty, with

periods of activity in which high burst

speeds are critical to user experience,

interspersed with periods of inactivity.

Radio resource requirements vary

greatly over time and between cells

and frequency layers. At any one time,

many parts of the network have

significant unused resources, while

other parts need to deliver high

data speeds.

An example of this can be seen in

Figures 2 and 3, where the average

Transmission Time Interval (TTI) usage

over all cells in a Radio Network

Controller (RNC) area of a mature 3G

network is shown, both against the

hours in a 48 hour period and as a

cumulative distribution function (cdf)

over the different cells. The TTI usage

is a measure of the network load in

a cell.

From the figures, the following can

be seen:

The average load over 48 hours

is 12.2%.

During the busiest hour of the day,

20% of the cell capacity is used on

average, or 6.8% of the overall

daily traffic.

19% of the cells have a load of

less than 1%, where the median

TTI load over the different cells

is 9%. 5% of the cells have an average

load during busy hour of more

than 77%.

Figure 2. Average TTI usage over all cells in an RNC area versus the hours in a 48 hour period.

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

05 10 15 20

Hours for two days

AverageTTIusageove

rallcells

25 30 35 40 45

Average usage

12.2% over

48 hour period

Figure 3. Cumulative distribution of average TTI usage during busy hour per cell.

0

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0.2

0.3

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1

00.1 0.2 0.3 0.4

TTI usage

Cumulativedistribution

0.5 0.6 0.7 0.8 0.9 1


4/164 Efficient resource utilization improves the customer experience

Figure 4. Cumulative distribution of the number of connected users and number of users with data in the buffers over a 24 hour period in a mature 3G network.

0.01 0.1

Number of users

1 10 100

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0.2

0.3

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0.8

0.9

1

0


Number of

active users

Number of

active users

with data

Due to the bursty nature of the data

traffic and delays in state transfers

between idle and connected modes,

the number of users connected to a

cell is much larger than the number of

users with actual data reception or

transmission. An example of this can

be seen in Figure 4. Sampled over a

24 hour period and across all cells in

one RNC area, it compares the

cumulative distribution of the average

number of connected users per hour

with the average number of

connected users with data in the

buffers. The median for the number of

connected users is around 3.6, while

only in 5% of the time and cells is

there more than one user with

data present.

With packet traffic, two key aspects of

performance are user equipment

(UE) burst throughput and packet call

capacity. Packet call capacity is the

maximum packet call load that, when

offered to a cell, can be served to the

users. Packet call capacity is typically

restricted by the slowest burst

throughputs, so improving these not

only makes it fairer for users but also

improves packet call capacity.

In recent years, research and

standardization has focused on

maximizing link spectral efficiency

through features such as Higher order

Modulations, MIMO, Continuous

Packet Connectivity (which also aims

to improve user equipment battery life)

and on managing or mitigating

interference via technologies such as

interference cancelling receivers in the

downlink and uplink interference

cancellation. Progress on these

features has enabled good link

efficiency and interference

management. However, improving the

ability of the network to focus

resources instantly where they are

needed by using a more liquid capacity

has great potential for enabling

improved user experiences and higher

packet call capacities. The rest of this

paper focuses on these features.

Resource utilization incurrent networks


5/165Efficient resource utilization improves the customer experience

Maximum coverage

from low frequency band

900 900 900

Balance the network load Avoid frequent handovers

Match UE and

network capability

Only far away calls

go to low band

Direct load to least loaded

layers, ensuring that micro

layer also gets traffic

High speed UE goes to

umbrella layer, avoid macros

Direct UEs according

to service or HSPA

capability (DC, MIMO)

2100 2100

Micro Micro

2100 2100 2100 2100 2100

Figure 5. Example of Multi Band Load Balancing features and the improvements they bring.

Features enhancingnetwork utilization

As we saw in the previous section,

underused resources are common in a

typical network. In this section, we

introduce four features that use these

free resources to enhance

performance for the user.

Multi Band Load Balancing

Multi Band Load Balancing (MBLB) is

applicable when separate bands are

used for HSPA, such as the 900 and

2100 MHz band. The feature spreadsthe traffic over the different layers, such

that more resources are made

available for each user and

performance is improved. This is

relevant for todays mature HSPA

networks today, since, as shown in the

previous section, traffic is distributed

quite unequally over the different cells

(see Figure 2). There are several

benefits, as illustrated in Figure 5.

Maximize coverage from the low

frequency layer.

Balance the network load, i.e.

maximize the user throughputs.

Avoid frequent handovers by, for

instance using different settings for

fast moving mobiles.

Matching device and network

capability, such as MIMO, Dual

Carrier (DC), and operating band

capability.

Matching services to network

capability, such as speech service.

The MBLB feature uses several

mechanisms to manage the load and

customer experience in multi-layer and

multi-band HSPA networks. A user can

be redirected to another layer under

different circumstances:

During the setup of a call

When there is no active data

transmission and reception

During transition to the

Cell_DCH state

When entering a new cell with

different preferred layer priorities

Several criteria are taken into account

in the layer selection decision,

including capabilities and speed, the

service used, the load and channel

quality in the source and target cells

and the signal strength of the target

cell. The actual change of layer can

then be applied via handover, radio

bearer re-configuration, or redirection.



As an example, Figure 6 shows the

performance in terms of user

throughput of the redirection scheme at

the transition to Cell_DCH. The layer

selection in this example takes into

account information on channel quality

and load in the serving and target cells:

at the transition to Cell_DCH, a UE

(Rel 6 or later) can report the best

intra/inter-frequency cells (target cells).

The RNC may then enforce a redirect

to a target cell if it has sufficient

channel quality and whose load is

lower than the serving cell, thus

optimizing the customer experience.

The performance plot shows that the

redirection mechanism offers no

significant benefit in terms of UE

throughput when the mobility settings

for idle and connected mode are

optimized. However, redirects provide

a large gain when non-optimal mobility

settings are adopted. The optimum

settings are challenging to identify in

real networks with inconsistent load,

cell size, antenna orientations and

tilting. Therefore, the redirect scheme

could be a simple way to boost

network performance.

Figure 6. Average UE throughput with and without MBLB redirection (redirect).

200

400

600

800

1000

1200

0

Optimal settings Suboptimal settings Suboptimal settings

with MBLB redirection

Userthroughput(Mbps)

Average user throughput



Multi Carrier HSDPA

Dual Carrier (DC) HSDPA is a 3GPP

release 8 feature commercially

deployed in a large number of markets.

However, the disadvantage of the

feature is that it limits the aggregation

to two 5 MHz radio carriers within the

same band. This is changed in Rel 9,

which introduces DC for carriers in

different bands. Rel 10 extends the

functionality to aggregation over four

carriers, with Rel 11 extending it still

further to eight carriers. This leads to a

peak data rate of 672 Mbps when

combined with 4x4 MIMO.

The benefits of aggregating multiple

carriers are significant for the end user,

since a diversity gain can be achieved

from scheduling on the best carrier(s)

and especially due to the fact that free

resources in the other carriers can be

used flexibly. As described in the first

section, free resources are often

available. The gains can be seen in

Figures 7 and 8. These show the

cumulative distribution of the average

user throughput and the mean packet

call delay for the macro cells scenario,

with an average cell load of 1 Mbps

consisting of bursty traffic.

Figure 7. Cumulative distribution of the average data throughput (Mbps) for 1, 4 and 8 carriers at low

offered load (1 Mbps).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

010 20 30 40

User data throughput (Mbps)

Cumulativepr

obability

50 60 70 80 90 100

1 carrier available from 8 carrier bandwidth

4 carriers available from 8 carrier bandwidth

All carriers available in 8 carrier bandwidth



Figure 8. Mean data connection delay (s) for 1, 4 and 8 carriers at low offered load (1 Mbps) with data

connections of 1 Mbit.

Figure 9. Mean normalized cell throughput (Mbps) for 1, 4 and 8 carriers as a function of the offered load.

The gains depend significantly on the

load in the system. If the load is high,

then there will be fewer free resources

on the other carriers, which results in

lower gains. Multi carrier HSPA also

gives a capacity gain, which can be

seen in Figure 9, which shows the

mean cell throughput per carrier as a

function of the offered load per carrier.

It can be seen that with an offered load

per carrier of around 2 Mbps, the

system with a single carrier starts to

become saturated, whereas with a

larger number of carriers, the offered

load can still be served. Using

multicarrier aggregation increases the

total packet call capacity of the

network, in addition to the gains in

individual user throughput.

0.02

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0

Scheme

Meandataconnectiondelay(s)

1 carrier available from 8 carrier bandwidth

4 carriers available from 8 carrier bandwidth

All carriers available in 8 carrier bandwidth

10

20

30

40

50

60

00 1 2 3 4 5

Offered load per carrier (Mbps)

Meanpacketcallthroughput(Mbps)

Single carrier

Quad carrier

Oct carrier



Multiflow

Another feature enabling a better use

of resources in cellular systems is

Multiflow. This is a 3GPP Rel 11

feature candidate, designed to improve

cell edge data rates by enabling the

transmission of data from multiple cells

to a UE at the common cell edge,

instead of transmitting the data via a

single cell as in HSDPA today. This is

illustrated in Figure 10 for dual cell

operation.

Each of the data flows in Multiflow can

be scheduled independently. This

leads to a doubling of the power

available for the desired signal at the

UE, which is used to increase the

overall user throughput. For Rel 11,

Multiflow is considered for up to four

different flows over two different

frequencies, one can send data from

up to four different cells to a UE.

Multiflow can be done among cells of

the same site (intra-site Multiflow) orbetween sites (inter-site Multiflow). In

the latter case, the data is split in the

RNC and directed to each of the

different base stations, taking the

throughput and load from that cell into

account. In the intra-site case, the data

is split in the MAC layer and the base

station can perform joint scheduling in

order to further optimize resource

usage (similar to DC HSDPA). Both of

these cases are illustrated in Figure 11.

Scheduling of the Multiflow streamscan be done in different ways. A

common requirement for the scheduler

is to minimize the effect on the non

Multiflow terminals. This can be done

by differentiating scheduling for the

serving cell and the cell that is assisting

in Multiflow transmission. More

precisely, the traffic in each cell is

prioritized in such a way that traffic

belonging to UEs that use the cell as a

serving cell is prioritized over the UEs

that use it as an assisting cell. This

means the benefit from Multiflow willonly be seen when the neighboring cell

has unused resources. As outlined

previously, in current networks there is

a large Multiflow potential, as typically,

many TTIs are available where there is

no user scheduled.

Interference Signal Signal Signal

Current HSDPA HSDPA Multi Point

Data stream 1 Data stream 1Data stream 2

Inter-site multi flow

Inter-site multi flow

Base station

Base station

RNC

Base station

RNC

Figure 10. Multiflow transmission and conventional HSDPA.

Figure 11. Intra-site and inter-site Multiflow.



Other scheduling methods are also

possible, based, for example, on the

UE throughput, load, service type, or

QoS.

Multiflowdoes not require coordination

of the packet schedulers taking part in

the Multiflow transmission, thus

simplifying the concept and enabling

inter-site deployment. Uncoordinated

transmission, however, may lead to

situations where a UE receives two

flows simultaneously from two base

stations. To spatially separate and

successfully decode the flows, the

terminal must have a minimum of two

receive antennas and interference-

aware receiver chains.

Figure 12 shows the cumulative

distribution of the throughput

experienced by the user with and

without Multiflow (including both intra-

site and inter-site Multiflow UEs). At the

low values of the cumulative

distribution, users at the cell edge gain

particular benefit from Multiflow, since

they are the most likely to receive

transmissions from multiple cells with

adequate signal quality.

Figure 12. Cumulative distribution of throughputs experienced by users with and without inter-site multiflow. Total offered load is 400 kbps/cell.

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0.9

1.0

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0 2 4 6 8 10 12 14 18 20

User experienced throughput (Mbps)


Reference all UEs

Multiflow all UEs

16



The Multiflow gain depends on the

offered load, see Figure 13. At lowload, the gains are considerable,

whereas they disappear at high load.

This is because at high load, the

assisting cells do not have free

resources and thus will never

schedule to the Multiflow user.

Several variations of Multiflow are

considered in 3GPP, depending on

the number of carriers in use in the

network and on the amount of

simultaneous RX chains that the UE

can handle. In a network in which onlyone carrier frequency is used, the UE

will be required to receive up to two

links simultaneously. Hence this

variant is called Single Frequency

Dual Cell (SF-DC) aggregation. In a

dual carrier network, the UE can best

take advantage of a neighboring cells

carriers if it has a receiver with four

RX chains; hence this variant is

labeled Multiflow Dual Frequency

Quad Cell (DF-4C) aggregation.

The combination of Multiflow andmultiple beams can be used to further

Figure 13. Mean user throughput versus offered load per cell.

0

1

2

3

4

5

6

7

8

9

10

11

00.5 1 1.5

Offered load (Mbps)

Userexperiencedthroughput(Mbps)

2 2.5 3 3.5

All UEs refAll UEs mflow5-% tile ref

5-% tile mflow

Figure 14. Combination of vertical sectorization and multipoint.

Potential Multiflow areas

optimize the system. As an example,

Figure 14 shows the case where

vertical sectorization is used in

combination with Multiflow. This way,

during high load, one can utilize the

capacity increase due to vertical

sectorization, whereas during low

load, users at the cell edges benefitfrom Multiflow.



Figure 15. HSPA + LTE aggregation.

HSPA LTE Carrier

Aggregation

HSPA-LTE carrier aggregation is a

feature under consideration in 3GPP

for future releases beyond 3GPP Rel

11. The idea is that one UE can

simultaneously use resources from

both LTE and HSPA, thus increasing

the peak data rate and cell edge data

rates of both systems. Even before Rel

11, it is possible to aggregate over

several carriers in both LTE and HSPA,

with traffic being steered between the

two systems by inter-system

handovers, as illustrated in Figure 15.

HSPA-LTE carrier aggregation

enhances traffic steering by enabling

fast load balancing between the two

radios, ensuring efficient spectrum

utilization even under the most bursty

traffic conditions. The gain

mechanisms are very similar to that of

multi-carrier HSPA: if the load is low,

large gains can be expected, whereas

when loads are high, the gain

decreases.

Simultaneous

reception ofHSPA and LTE

Handover

between HSPAand LTE

Multi carrier

reception of

HSPA

Multi carrier

reception of LTE

HSPA + LTE

aggregation

HSPA carrier

aggregation

LTE carrier

aggregationLTE

HSPA



Further considerations

The previous section described

different features which help boost the

customer experience by improving

radio utilization. These features focus

primarily on the downlink but also lead

to uplink improvements:

Multi Band Load Balancing

improves the uplink performance,

since, when directing the UE to

another layer, both downlink and

uplink are considered in cell and

layer selection. Benefits are similar

to those in the downlink.

Multiple carrier HSPA is also

supported for the uplink from Rel 9,

however the number of carriers is

limited to two. A different number of

carriers is supported in the

downlink and uplink because

downlink traffic volumes exceed

uplink volumes, and because the

UE will often become limited by

transmit power as the number of

carriers increases.

Multiflow is a pure downlink feature.

The uplink signal will typically be in

soft or softer handover when

multipoint is being used in the

downlink.

In addition to the features mentioned in

the previous section, Long Term HSPA

Evolution brings further improvements:

Further enhancements to Cell_

FACH, while maintaining the good

performance of Cell_PCH and

Cell_DCH. This is mainly focused

on traffic from smartphones.

Uplink Closed Loop Transmit

Diversity, enhancing the uplink to

support TX diversity. At a later

phase, uplink MIMO may be added

to the specification, enhancing the

uplink peak data rate.

Downlink 4x4 MIMO, enhancing

spectral efficiency and peak data

rate in the downlink.



Summary

Figure 16. Feature overview.

Multi band load

balancing (MBLB)

- Improves the user performance

- Utilizes free downlink and uplink resources in other bands/carriers

- Operates on a per second level

- Supported for all UEs

Multi carrier HSPA

- Improves peak rates and user throughput

- Utilizes free downlink and uplink resources in other co-located carriers/cells- Operates on a per TTI level

- Supported for Rel 8+ UEs (2 carriers for Rel 8 up to 8 carriers for 3GPP Rel 11)

Multiflow

- Improves cell edge user throughputs

- Utilizes free downlink resources in other cells (intra- and intersite)

- OPrates on a per TTI level

- Candidate for 3GPP Rel 11

- Requires UE support

HSPA - LTE

aggregation

- Improves the user performance

- Utilizes free downlink and uplink resources in other systems

- Requires UE support

Traffic in todays networks is bursty,

alternating between periods of activity

in which high burst speeds are critical

to user experience, and periods of

inactivity. This results in a significant

amount of free resources in todays

mature HSPA networks. A number of

features are being introduced to

improve the customer experience by

increasing the utilization of these

network resources. An overview of the

different features and their benefits is

given in Figure 16.

These features bring a major

improvement to HSPA by simply using

network resources more efficiently

leading to the end user seeing larger

throughputs and faster response times.

The benefits of these features are hard

to quantify because they are often

inter-dependent and also vary

according to the actual network

scenario. However, some possible

benefits include:

MBLB: Optimum performance can

be achieved with a minimal amount

of tuning needed, leading to lower

operational costs

Multi carrier HSPA: With eight

carriers, an increase in user

throughput of up eight times that of

a single carrier could be expected

Multiflow can lead to a gain at

the cell edge of up to 50%

HSPA-LTE carrier aggregation

can achieve significant peak

data rate gains although the

amount depends on spectrum

allocations and load.

As well as the features dealt with in

this white paper, other features

beyond its scope are being

developed and will be introduced

simultaneously, maintaining the

rapid evolution of HSPA.



Abbreviations

3GPP Third Generation Partnership Project

Cell_DCH Cell Dedicated Channel

Cell_FACH Cell Forward Access Channel

Cell_PCH Cell Paging Channel

CSP Communications service provider

DC Dual Carrier

DF-4C Dual Frequency Quad Cell

HSDPA High Speed Downlink Packet Access

HSPA High Speed Packet Access

LTE Long Term Evolution

M2M Machine-to-machine

MBLB Multi Band Load BalancingMIMO Multiple-Input Multiple-Output

QoS Quality of Service

RNC Radio Network Controller

SF-DC Single Frequency Dual Cell

TTI Transmission Time Interval

UE User Equipment


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