Small cell tmo54097 w pdf

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Hi there, welcome to the course about "9360 Small Cell Solution Features". I’d like to provide you
with an overview of all the basic Small Cell Solution features.
I hope you enjoy the course.

After you finish this course, you will be able to:
 Describe the Small Cell access control feature,
 Explain the principles of Small Cell location design,
 Explain Auto-Configuration and self-optimization,
 Explain the principles of Small Cell Solution mobility,
 Describe additional features such as UE-based A-GPS and Cell Broadcast Services in support of
CMAS.
At the end you will need to pass the end-of-course assessment or L2A to successfully complete
this course. You will need to achieve a score of 80% or better to pass the test and receive credit
for the course.
Please click Next to continue.

This course consists of 5 lessons.
In lesson 1, we are going to have a look at the access restriction procedures. We shall learn that
both open access as well as closed access is supported and how the closed access mode is
realized.
Lesson 2 provides the principles of the location design needed when deploying Small Cells.
Lesson 3 explains how Auto-Configuration and self-optimization principally works.
In lesson 4, you’ll learn how Small Cell mobility is implemented.
In lesson 5, I will describe additional features such as UE-based Assisted GPS and Cell Broadcast
Service in Support of CMAS.
Select the lesson you are interested in or select the lessons in the given order to follow the
recommended learning path.

Lesson 1 – Small Cell access restrictions.
In this lesson, you will learn how to explain the access restriction methods in case of ―closed
access‖.

To avoid core network overload that can be caused by numerous attempts to camp on the Small
Cell, the Small Cell takes the appropriate action to restrict or authorize access.
The Small Cell can operate in open and in closed access control mode. In the closed access
control mode, only registered users are allowed to camp on the cell and establish a call. The
authorized users are kept in a so-called Access Control List (ACL) stored in the Small Cell, which
can have up to 256 entries. The owner or operator can update the Access Control List.
Access control is performed during the Location Area Update, the Routing Area Update or GPRS
Attach procedure when attempting to move from the Macro cell to the Small Cell. The Location
Area Update is initiated because the Small Cells have a different Location Area Code from the
Macro cells. The UE identification is made using the IMSI. If the IMSI is not available, it is fetched
by the Small Cell from the UE.
The Location Area Update procedure initiated by a UE is intercepted by the Small Cell and is
transmitted to the 3G-MSC only if the UE is authorized, that is, part of the ACL, on this particular
Small Cell. If the UE is not part of the ACL, the Small Cell rejects the call. An equivalent process
occurs for the Routing Area Update.
For prioritized open access in a corporate Small Cell Solution the ACL is used to prioritize owners
or guests over public users.
Priority is taken into account at call admission and can potentially lead to pre-emption, redirection
or downgrading of calls from public users before impacting the private users.

The following use cases are possible when a user tries to 'camp on' a closed access Small Cell:
Private and invited users who are in the Access Control List (ACL) shall be accepted.
Public Small Cell Users are users who are not in the ACL of the current Small Cell, but in the ACL
of another Small Cell in the same Location Area of the Small Cell Solution. These users should not
be able to 'camp on' the Small Cell. However, they should not be permanently barred from the
Location Area Identifier, so that they can still attach to their own Cell. The BSG stores all the ACLs
of the Solution.
Public users who are not in any ACL of the Solution. They should be rejected and permanently
barred from the Location Area.
An emergency call has to be authorized in any Small Cell.

Let's start with the message flow for the private and invited user that is registered in the Access
Control List of the current Small Cell.
When the User Equipment (UE) informs that it is in the coverage area of the Small Cell, it
establishes the RRC Connection to the Small Cell in order to update its location.
The UE sends a Location Area Update Request or a Routing Area Update Request.
If the IMSI is not available, the Small Cell fetches the IMSI from the UE by sending a non-access
stratum identity request to the User Equipment.
The Small Cell checks whether the IMSI is stored in the Access Control List (ACL).
If the User Equipment is allowed to access this cell, the Location Area update is forwarded to the
MSC for the allowed users.
The MSC is performing a Location Update and sends a Location Update Accept message back to
the UE.
At the end, the signaling connection is released.

In the case of a public user who is not in any Access Control List of the Solution, the beginning of
the message flow is the same as in the former case.
When the Small Cell does not have the IMSI stored in its own ACL it sends a request to the BSG
to learn if this IMSI is stored in any other ACL of the Solution.
Here a negative response arrives from the BSG, therefore the Location Area update is rejected
using the cause ―No Suitable Cells In Location Area‖.
As a consequence, the UE shall store the Location Area Identifier in the list of "forbidden location
areas for roaming" and it shall search for a suitable cell in another location area in the same
PLMN. Now the signaling connection is released.

In the case of a public Small Cell user who is not in the Access Control List of the current Small
Cell, but in the ACL of another Small Cell in the same Location Area of the Small Cell Solution and
who uses a UMTS Subscriber Identity Module or USIM the beginning of the message flow is the
same as in the former case.
The Small Cell queries the BSG to check, if this UE belongs to any other Small Cell Access Control
List associated to this Location Area. This time a positive response arrives from the BSG.
Now the Small Cell uses the authentication request to cause an authentication failure. The Small
Cell authenticates the UE but does not include the Authentication Token Information Element in
the User Equipment request. Since the network therefore does not authenticate itself, the UE
responds with an Authentication Failure with the cause ―GSM authentication unacceptable‖.
The Small Cell repeats the authentication failure another 2 times. After 3 consecutive failed
authentications, the UE enters idle mode and the Small Cell is barred until the timer T3360
expires. The maximum value for T3360 is 1280 seconds. This corresponds to 21 minutes.
The Small Cell releases the radio resources locally with a delay of 2 seconds after transmission of
the last authentication request.

A ―non-Small Cell‖ User Equipment will not be allowed to 'camp on' a Small Cell, because it will be
denied access by the UE Access Restriction procedure.
This will result in the USIM being updated with the Small Cell Location Area as ―forbidden‖.
The non-Small Cell UE will search again for a suitable cell to 'camp on', using the cell selection
procedure.
If the Macro cell is available, then the User Equipment can obtain service from the Macro cell.
If no coverage is available, then the User Equipment goes into ―Emergency Calls only‖ mode and
searches for any suitable cell to 'camp on', including the Small Cell (this time ignoring forbidden
Location Areas).
In this case the Security and Authentication procedures are not performed. The Emergency call is
identified thanks to the ―Establishment cause‖ Information Element of the RRC connection request
set to ―emergency call‖ or via an optional Information Element in the Initial Direct Transfer
message; this is a UMTS Release 6 feature.

Once identified, the Small Cell provides the following functionalities.
The Small Cell will allow public access for emergency call establishment as described before.
The Small Cell supports prioritized handling for Mobile Originated Emergency Circuit Switched
voice calls.
The Small Cell provides geographical information for its location on request for an emergency call,
via RANAP location report procedure. Possible formats for localization are: Geographical
coordinates and Service Area Identifier, including Cell ID, Location Area Code and Routing Area
Code.
The Small Cell also provides a Pre-emption process for emergency calls.

The Small Cell Management supports a set of web-based Application Programming Interfaces or
API to exchange provisioning data related to the Small Cell specific Access Control List or White
List. The home subscriber is limited in the number of UEs that may be registered as authorized to
use the home cell. The registered UEs are kept in an Access Control List within the Small Cell and
are used to allow only authorized UEs to 'camp on' the cell and establish a call. The ACL can be
updated by the Small Cell owner or operator.
The subscribers can update their Access Control Lists by accessing a customer system via a well
known URL. Using web access to the customer system, the subscriber is able to modify the
Access Control List for his Small Cell, in order to allow different IMSIs access to his Small Cell. The
customer system has a profile for each subscriber with a predefined username and password,
which is needed for the login. Up to 32 IMSIs can be added to the ACL for a Small Cell.
The customer system converts the MSISDNs into IMSIs and exports the updated list to the web
based Application Programming Interface of the HDM. The web based API, which is part of the
HDM, offers a well-known URL, including all needed parameters, to be used by the external
customer system. The Access Control List of the subscriber is kept on the customer system.
The HDM updates the user Tag of the subscriber information. This is to allow the ACL to persist
even in the event of a factory reset of the Small Cell. The HDM updates the Small Cell with the
latest modified ACL using the command ―Set Parameter Value‖.
The Small Cell informs the HDM about the update of the access mode.
The BSG receives the ACL from the Small Cell Management, stores it and verifies the list upon
registration of the Small Cell.

Lesson 2 – Small Cell location design.
As we have learnt in the previous lesson, access restriction is based on the Location Area Update
procedure. Therefore each Small Cell in closed access mode should have a Location Area Code
that is different from the Macro network. To avoid barring conditions of neighbor Small Cells as
shown in the previous lesson and to avoid a paging overload situation of the BSG, a range of
Location Area Codes should be reserved for the Small Cell network. This has impact on the macro
network.
From release 3.0 onwards, Small Cells in open access are allowed to use the same Location Area
and Routing Area as the Macro network. This has been implemented to support large
deployments of Metro cells in public places. With a new paging interface and internal performance
optimizations on both the BSR Gateway and the Small Cell, the additional paging load is reduced.
In this lesson you will learn the basic principles for a location design when implementing a Small
Cell Solution.

A Small Cell Solution network supports a high number of end users. The pre-requisites for the
design of such a network are mainly:
 the number of Small Cells in the network that are planned to be deployed,
 the number of Small Cell Solutions and to which core Network Elements they shall be
connected,
 the network growth plan and
 adaptation of the Macro network per Small Cell Solution.

Here in our example, the whole country could be served by two Small Cell Solutions at the
beginning that can be increased to 9 Solutions later on. Solutions 1 through 5 will be connected to
core network A and Solutions 6 through 9 connected to core network B. Then we have to assign
the area codes: Location Area IDs and Service Area IDs.

There are typically some constraints on the number of area codes that are supported in the Core
Network Elements. For example, the Alcatel-Lucent SoftSwitch only supports 32.000 Service Area
ID values. This means that the full range of Service Area IDs cannot be used.
Examples of other constraints are:
Location Area Code (LAC) ranges cannot be shared between MSCs in order to be able to uniquely
identify the right VLR to go to.
LAC allocation schemes between 2G and 3G have been optimized according to network planning
rules which limit the available number of free codes for the Small Cell network. If for example the
2nd digit of the LAC is odd or even it means that the Location Area is 2G or 3G.
In some cases, the IT system cannot see all the fields in the area code for example a LAC
contained in the Service Area Identity (SAI) may or may not be visible. This would limit the
number of Small Cells in the PLMN.
In some cases, the SAI is made the same as the Cell Global Identity (CGI) by setting the Service
Area Code (SAC) to the Cell ID field. This cannot be done with the Small Cell Network since more
than 64.000 Small Cells are envisioned.

Let's now look at the area code assignment guidelines.
If the network operator does not want to provide or does not have the possibility to provide the
location information (meaning longitude and latitude) for each Small Cell, random location area
code assignment will be used.
Thereby the Small Cell Adaptation Layer assigns the Location Area Code randomly from a list of
allowed LACs per Solution, defined in the parameter ―allowedLACset‖.
For the incident that neighbor Small Cells share the same LAC, an alarm will be raised to the
Small Cell Management . This feature is called ―Detection of collapsing Location Area Identifier
(LAI)‖.
In this case the Small Cells are not going into service and need manual re-provisioning.
When location information is available the mobile operator can apply special billing, for example a
home zone tariff, and assigns separate Location Area Codes manually to each group of users
(owner, guest, emergency call).
If the network operator does not want to provide special billing, he has to pre-define location
objects which can be combined to map Macro core network areas and assign the Location Area
Code range given in the child objects. This way of auto LAC assignment is described in more
detail in the following slides.

TMO54075W
Page 19
Before a network rollout can take place, ―Locations‖ need to be defined in case of auto LAC
assignment.
A Location object is defined through top left and bottom right coordinates and has the Location
Area Code, Routing Area Code, Service Area Code range as child objects, which are needed by
the Small Cell Adaptation Layer to assign a Location Area Code to the Small Cell.
The following rules apply:
Locations may not overlap.
Locations are needed on a per Small Cell basis.
There is no ―real‖ limit on the number of locations per Small Cell Solution, that is an MSC or RNC
area can be designed out of a number of location rectangles.
“Locations” define 3GPP areas: LAC, RAC and SAC.
For one range of LACs per location, neighboring Small Cells should not share the same LAC since
location update triggers the access restriction procedure.

Using the defined location with the corresponding Location Area Code range can be used by the
Small Cell Adaptation Layer within the WMS to automatically assign LACs to the Small Cells.
LACs are allocated to Small Cells such that:
Small Cells do not use the same codes as the ones used by other neighboring Small Cells within
range.
Small Cells choose the code that is being used as far away as possible.
No changes to the codes are made once allocated to minimize disruptions.
The Small Cell Adaptation Layer algorithm needs the following inputs:
Location information of the deployed Small Cell from the positioning software (latitude and
longitude, z-coordinate), the number of codes available for use and the deployment area and grid
size for calculation partitioning to reduce computational requirements.

Here we see an example of the Location Area Code assignment algorithm. We have defined four
non-overlapping locations or LAC zones given their top-left and bottom-right latitude and
longitude.
Each of these locations gets a set of Location Area Codes that can be allocated to the Small Cells
deployed, for example LAC1, 2, 3, 4 and 5. Remember, for Small Cells in closed access these LACs
must not be in use by the Macro network, while Small Cells in open access are allowed to use the
same LACs.
When a new Small Cell is pre-provisioned, its position is derived from the user’s address and
stored in the database at the Small Cell Management. The Small Cell Management extracts the
positions and codes of its neighboring Small Cells, and inputs them into the algorithm.
If not all codes have been used up (i.e. the number of Small Cells deployed is less than the
number of codes available), then the new Small Cell is assigned a code that has not been used.
Otherwise, the distance of the new Small Cell with all other deployed Small Cells is calculated
using the usual techniques. The code that is re-used furthest away is chosen and assigned to the
new Small Cell.

Here another example is given for a large network.
First we have to define a planning approach, which is aligning Solution borders to MSC or RNC
areas of a country. This means we can actually create many locations with the same set of LACs,
RACs and SACs. Then we match longitude and latitude squares to the Macro Layer MSC or RNC
area.
The Small Cell Adaptation Layer assigns the LAC according to distance, ignoring square. This
means if we would have two Small Cells close to borders in different locations the Small Cell
Adaptation Layer would still work correctly.

A Small Cell Group targets various customers' needs, mainly to cover some private or public
areas, like enterprise, hotels or airports, where the individual Small Cell capacity or coverage is
not sufficient.
The coverage can be provided by a group of Small Cells, located close together, instead of only
one Small Cell. Additionally, non co-located Small Cells may also be part of a group, for example
for a company having multiple offices or stores.
Small Cells belonging to the same group have a common set of parameters.
They operate in the same access control mode, open or closed access, and they share a common
Access Control List.
To support large Enterprise deployments, the Access Control List can be extended to a maximum
of 10.000 members from release 3.0 onward.
To avoid unnecessary Location and Routing Area Updates, all Small Cells belonging to the same
group have a common Location Area Code and Routing Area code definition.
This common set of parameters also simplifies network operations.
One Small Cell can belong to only one Group and all Small Cells of one group must belong to the
same Small Cell Solution.
Between Small Cells belonging to the same Small Cell Group, inter-Small Cell handover is
supported for all combinations of circuit switched and packet switched calls.
Small Cell to Small Cell handover is not supported across Small Cell Groups.

Lesson 3 – Small Cell auto-configuration.
The Small Cell incorporates configuration and self-optimization functions that do not need
intervention by the end user or operator.
In this lesson you will learn how Auto-Configuration and self-optimization are carried out.

Product identification such as the bar code and the Small Cell identification are programmed and
labeled in the factory.
For security purposes, Small Cell products are provisioned with digital certificates that will be used
for authentication during the IPSec tunnel establishment.
The user subscribes to the service in a shop or on the web. He selects the Customer Premises
Equipment type and services, and then fills in his personal details.
The End user receives confirmation of the subscription and login information as well as the Small
Cell if not already handed over in the operator's shop.
The Subscriber switches on the Small Cell and connects the LAN cable to the DSL Router. The
Auto-Configuration procedure starts automatically, going through the following steps:
 First, there is the Initialization, to contact the Small Cell Gateways
 Then Authentication,
 Auto-configuration of initial parameters and
 Verification of the Small Cell location.
 Finally, the authorized User Equipment is registrered.
Once the Auto-Configuration procedure has been completed, the Small Cell starts to work and the
Subscriber receives a confirmation call or SMS on his mobile phone.

Auto-Configuration is performed for the initial start-up of the Small Cell and involves two
phases.
The first phase takes place in the Small Cell Management. Here the LAC, SAC and RAC are
determined and a list of the most probable 2G and 3G Macro neighbor cells is assigned. Certificate
chains generated by the Certificate Authorities are uploaded to the Small Cell Management.
When the Small Cell connects for the first time, it will retrieve its certificate chain from the Small
Cell Management and will store it. The installed certificates will be used by the Small Cell to set
up IPSec tunnels.

The second phase takes place in the Small Cell itself. Probable 2G and 3G Macro neighbor cells
from a prioritized subset, are ranked to select THE ONE cell for handover, should a given quality
threshold be crossed. The scrambling code is also determined.

Self-optimization is performed by the Small Cell during its life time that is network listening to
update whatever elected Macro 2G and 3G cell and the primary scrambling code.

Therefore, we can summarize that the key points of the configuration are the most appropriate
scrambling code, the optimum maximum power, the neighboring list, the Target Cell ID for
handover and the digital certificates.

Let's now take a look at the Auto-Configuration message flow!
After connecting the Small Cell to the power supply and to the DSL Router the 1st LED is on. The Small Cell
receives an Ethernet MAC address from initial contact information and sends an IP Request to the DHCP
server to request - a local IP address, a local netmask, a default gateway that is the DSL Router and a DNS
IP address. The DHCP server will provide among others the IP address of the DNS.
With the IP address of the DNS, the Small Cell is able to request the IP address of the Security Gateway of
the Small Cell Solution from the ISP DNS. This phase is indicated by the blinking of the 2nd and 3rd LEDs.
Now the Small Cell can reach the Security Gateway that will be the Tunnel Endpoint for the secure IP
connection. In this example, we assume that shared secrets are used for Small Cell authentication. So upon
receiving a message from the Small Cell, the Security Gateway forwards the message to the AAA server via
the ALSMS for authentication.
When the AAA server authenticates the Small Cell the Security Gateway, the Brick, is finishing the IPSec
tunnel setup and provides the following information to the Small Cell: the inner IP address and netmask as
well as the Mobile Operator's DNS IP address. Note that the IP addresses given here, are just examples.
If the Small Cell does not have any software loaded, which is the case when you connect the Small cell for
the very first time, it contacts the internal DNS to receive the IP address of the File Server. Static data
updates are delivered to the Small Cell Management Solution and saved to a special file directory.
The Small Cell now establishes a secure connection, a so-called Transport Layer Security or TLS, downloads
the current software and performs a reboot to activate it.
Upon successful activation the Small Cell again goes through the previously explained steps: DHCP request
to receive an IP address, DNS query to resolve the Security Gateway's IP address and the authentication

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procedure connected with an IPSec tunnel establishment.
30

The Small Cell now requests the Home Device Manager's IP address from the internal DNS.
Upon receiving the HDM's IP address the Small Cell is able to send a Register Request in an inform message
to the HDM.
The HDM puts a message (a Registration Notification) into the Java Message Service or JMS queue. The
Wireless Management System or WMS is subscribed to the Java Message Service and looks regularly into the
HDM JMS queue. Upon receiving registration notification; using its internal Data Base, the WMS updates the
static data URL and creates a bulkCM file containing all parameters for the Small Cell, sends it to the File
Server and informs the HDM about the location the URL of the bulkCM file. The HDM forwards the URL in a
connection request message to the Small Cell. With the URL of the bulkCM file, the Small Cell is able to
download the bulkCM file, get the static data file URL and then download the static data file.
Upon completion of the download the Small Cell performs a soft reset and re-establishes the IPSec tunnel to
the assigned Security Gateway and again contacts the HDM. At this point a check is performed indicating
whether the SW and data signatures are correct.
The Small Cell now enters the RF Auto-configuration mode as already explained to determine the scrambling
code, transmit power and GSM and W-CDMA neighbor cells. During this phase the 3rd LED is off.
After this RF Auto-configuration period the Small Cell sends a Register Request to the BSG to setup up a
signaling connection.
After receiving the positive response from the BSG the 2nd LED on the Small Cell is turned on. During
normal operation the Small Cell and BSG exchange heartbeat messages. The Small Cell is now in service. In
case of a mobile originated service request from a User Equipment the user plane to the BVG or BPG has to
be established. Once the user plane to the BVG or BPG is established the 3rd LED on the Small Cell is on.

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Please note the meaning of the LEDs depends on the Small Cell product and the version.
31

Upon completion of the auto-configuration, the self-optimization feature ensures optimal radio
setting of the Small Cell.
There are two methods of detecting whether the Small Cell Common Pilot Channel (CPICH)
transmit power needs to increase or decrease.
First, when mobiles have active calls established, the coverage is maintained based on the
mobiles measurements of the serving Small Cell's Common Pilot Channel quality.
The CPICH transmit power is increased if the serving Small Cell’s CPICH quality is lower than the
pre-defined threshold or lower than a neighbor cell CPICH quality.
The Common Pilot Channel quality is given as Chip Energy of Noise level or Ec/No.
The CPICH transmit power is decreased if the serving Small Cell's CPICH quality is higher than the
pre-defined threshold.

Second, when there is no mobile in connected mode, coverage is optimized based on the overall
Received Signal Strength Indicator measurements that is the same method as for auto-
configuration. A copy of the configuration file for the Small Cell is uploaded and stored in the
Small Cell Management.

This feature allows controlling the uplink interference a Small Cell User Equipment creates on the
receiver of neighboring Macro cells or Small Cells.
The interference occurs when a Small Cell UE comes close to the border of the neighboring cell,
and there is also a UE on the border of the neighboring cell with high user density and both UEs
have high uplink data rates.
The Small Cell User Equipment raises the noise floor of the neighboring Macro cell or Small Cell. It
also shrinks the uplink coverage of the neighbors and may suffer degradation of the uplink
throughput.
To overcome this situation, the Small Cell obtains a pathloss estimate from the User Equipment to
the neighbor cell through measurements. The maximum interference created by the UE to the
neighbor is calculated from the UE's maximum transmit power minus the pathloss. If this
maximum interference level is greater than an operator defined threshold, the Small Cell
reconfigures the UE's maximum power.
So the UE's maximum transmit power is dynamically adjusted to the level required, most of the
time, the UE will not be restricted. User Equipments which are not interfering with the neighbor
cell are allowed to transmit with higher uplink power and will achieve the maximum potential data
rate.

The continuous coverage self-optimization feature allows the Small Cell to adapt its coverage so
that public users are not attracted to it.
This is applicable to the residential deployment where the Small Cell has an Access Control List. If
the Small Cell has been placed in a non optimum position such as near a window overlooking the
street, the Small Cell may attract numbers of public users who are rejected during the location
update procedure as they are not in the Access Control List. This will have two impacts.
First, if Small Cell and Macro networks share a carrier, the Small Cell may interfere with the Macro
coverage. This may result in Macro coverage holes.
Second, there may be increased signaling load on the core network. The magnitude of this
depends on the UE behavior on returning to the Macro network after a Location Area Update
procedure with the Small Cell.
The Small Cell coverage optimization attempts to limit these effects on the Macro network. In
order to assess the impact on the Macro network, the Small Cell monitors registration and mobility
events. It uses these statistics to adjust the Small Cell coverage by increasing or decreasing its
Common Pilot Channel's transmit power. If necessary the power may be reduced below the
existing auto-configured minimum.
The Small Cell will provide user indication via LEDs whilst the Small Cell transmit power is reduced
below the value set by auto-configuration. The purpose of this is to indicate to the end user that,
if possible, it may be advantageous to relocate the Small Cell to a central position in the user's
property and away from public areas.

From release 4.1, the self-optimization capabilities of Small Cells are improved by allowing a
dynamic adaptation of the Small Cell coverage. The purpose of this coverage adaptation is to
reach 2 main objectives. The first one concerns load balancing over cells. If a cell is overloaded,
its coverage can be reduced by decreasing its transmit power. Here the aim is to transfer some
load to less-loaded neighbor cells that will increase their transmit power and consequently their
coverage. These power changes are applied in real time in order to punctually reduce a Small Cell
or a grouped Small Cell overload.

The second objective is inherent to load balancing as it concerns coverage. Indeed, the overlap
between the Small Cells must be sufficient to provide continuous coverage and good conditions
for mobility. For that, it is important to configure the minimum transmit power so that the Small
Cell transmit power always stays above this pre-defined threshold.

This improvement applies to 2 types of deployment: standalone Small Cells and grouped Small
Cells. In case of overload, a standalone Small Cell will try to transfer users into the Macro network
instead of transferring them into another Small Cell. If a grouped Small Cell is overloaded, it will
try to transfer users to less-loaded neighbor Small Cells or to the Macro network.

There are several conditions to dynamic coverage adaptation. The Small Cells must be neighbors.
Moreover, Small Cell to Small Cell handover must be possible. Finally, there must be good radio
conditions for all the neighbor Small Cells and the macro neighborhood to perform the handover.
Note that the handover is possible with all the neighbors.

Also, I want to draw your attention to the fact that power changes will impact all the neighbors
even if they are not geographically close to the overloaded Small Cell.

Let’s illustrate that with the most basic scenario. Let’s take the example of Small Cells A and B
with a coverage area of the same size. Let’s assume that their transmit power is identical. There
are many users in the coverage area of Small Cell A that captures all the traffic. Small Cell B is
much less loaded. To adjust their coverage areas, Small Cell A will decrease its transmit power
while Small Cell B will increase its own. This way, the traffic load will be balanced between both
Small Cells. As you can see, the overlap between A and B is maintained in order to provide
continuous coverage and mobility.

We have seen that self-optimization is triggered independently by each Small Cell. Within a group
of Small Cells, if more than one Small Cell simultaneously initiate a periodic sniffing, the Small
Cells of the group will not be able to detect each other. This may result in mobility limitations,
thereby degrading KPI.

To prevent two Small Cells of a same group from performing self-optimization at the same time,
sniffing is coordinated and scheduled for each Small Cell in a group. Self-optimization is triggered
by the operator via an HDM command and in some particular cases, can be switched off the same
way in some particular cases. When the feature is disabled, a Small Cell within a group can trigger
self-optimization on-demand. But this can only be done during a quiet period. The Small Cell then
reports real-time notification for status information of self-optimization when it was triggered by
the Small Cell Management Solution. The Small Cell keeps track of the last triggered auto-
configuration cycle and will not trigger another due to any valid reasons within a pre-configured
time interval. This feature requires that all the Small Cells of a same group be configured with the
same site ID.

Lesson 4 – Small Cell Solution mobility.
In this lesson, you will learn the principles of Small Cell Solution mobility in idle mode (called cell-
reselection) and in connected mode (called handover).

The Small Cells support co-deployment in UMTS, LTE and/or GSM Macro networks.
Remember that Small Cells are of a very small size compared to the 2G or 3G Macro cells, as the
name implies and that a Macro cell may cover many of the Small Cells.
Re-selection is supported from Small Cell to Macro cell and vice versa, and from 3G Small Cell to
LTE Cell.
To achieve this, each Small Cell should be configured with Macro cell information (for example,
the primary scrambling codes for GSM, LTE frequencies).

Cell reselection is supported from UMTS and GSM Macro cells to Small Cells.
For cell reselection to the Small Cell, the Macro cells must broadcast the frequency and primary
scrambling code of the Small Cells with associated cell selection and reselection parameters.

Cell reselection is also supported from Small Cells to LTE, UMTS and GSM Macro cells.
Small Cells may be introduced on the same or different UMTS frequency as the UMTS Macro
network, so cell reselection to and from UMTS Macro cells on the same or different UMTS
frequencies is possible.

For cell reselection from the Small Cell to UMTS and GSM Macro cells, each Small Cell keeps an
internal list of candidate neighbor cells up-to-date. This list is a combination of manually
configured neighbor cells, informed neighbor cells (that is to say direct neighbor cells detected
through inter Small Cell signaling) and cells detected using UE measurements and reports on
radio conditions from connected UEs. Small Cells are also provided with mechanisms to update
their list of neighbor cells (either automatically or under supervision) based on information derived
from the earlier phase implementations. The Small Cell will automatically fine-tune its macro
neighbor list by prioritizing and selecting a subset of the best neighbor cells signaled around the
UE.

The Small Cell adjusts the prioritization of cells that are selected for inclusion using a re-worked
prioritization mechanism from the earlier phase and broadcasts the list of neighbor cells to the UE
in SIB11. This list is limited to a maximum of 32 intra-frequency neighbor cells, a maximum of 32
inter-frequency neighbor cells and a maximum of 32 GSM neighbor cells, all with their associated
cell selection and reselection parameters.
Auto-Configuration, self-configuration and self-optimization procedures determine the neighbor
cells.

For cell reselection from the Small Cell to LTE Macro cells, SIB19 is used. SIB19 contains the
priority setting for the UTRA Serving Cell, and information about neighboring E-UTRA carriers,
together with the corresponding priority settings for reselection.

The main reselection criterion is the Small Cell quality.
The UE shall camp on a Small Cell as soon as Small Cell coverage is provided.
The UE shall even camp on the Small Cell when the Macro cell quality is strong or better than the
Small Cell quality (for example when a Macro base station is nearby).
The UE shall move to Macro layer when the Small Cell coverage becomes weak.

Let’s take a look at the principles of Small Cell mobility in connected mode.
Handover from Small Cells to 3G and 2G Macro cells is supported for all combinations of circuit-
switched and packet-switched calls.
Incoming handover from 3G Macro cells to Small Cells is supported for all combinations of circuit-
Incoming handover from 2G Macro cells to Small Cells is supported for circuit-switched calls.
Between neighboring Small Cells within a Small Cell Group handover can be done for all
combinations of circuit-switched and packet-switched calls.
Incoming handover from LTE to 3G Small Cells is supported for all combinations of circuit-
The Small Cell handover functionality consists of the following UTRAN functions:
First the need for handover must be determined; this means that a handover trigger must be
present.
Here a quality based algorithm has been implemented. The Small Cell monitors the cell quality
and level using UE measurements and reports, and information derived from the earlier phase
implementations. If the measured quality is below a pre-defined level, the handover is initiated.
In the second step, the target cell must be determined. The Small Cell internally maintains a list
of candidate neighbor cells. The Small Cell automatically optimizes its neighbor list by prioritizing
and selecting a subset of the best neighbor cells signaled towards the UE. This list is a
combination of manually configured neighbor cells, informed neighbor cells and cells detected
through UE measurements, within a limit of 32 neighbor cells per type. The Small Cell notifies the
UE of the selected best neighbor cells in a measurement control message.
The last step is the execution of the handover procedure.

The inter-Small Cell handover algorithm is based on UE measurements of the serving Small Cell
and the neighboring Small Cells. The handover is triggered, when the quality of a neighboring
Small Cell is better than the current serving Small Cell.
The inter-Small Cell handover is performed locally within the Small Cell Solution; it does not
impact the SGSN. The control plane and the user plane are switched in the BSR Gateway from the
source to the target Small Cell.
Source and target Small Cells must belong to the same Small Cell Solution, they must be
connected to the same BSR Gateway and they must belong to the same Small Cell Group.

The handover procedure between the Macro network and the Small Cell Solution is fully 3GPP
compliant. Upon a handover trigger, the Macro network initiates the standard relocation
procedure; no special measures are required in the Macro network for the Small Cell handover.
The core network selects the target RNC based on addressing information received in the
"Handover Required" message from the Macro network. The core network initiates the relocation
procedure with the Small Cell Solution, which appears to be an RNC for the core network.

Handover between the Small Cell and the Macro network is performed using the standard RNS
relocation procedure.
Two methods exist to select the target cell – blind handover and UE or mobile assisted handover.
For blind handover, the target Macro cell is determined from auto-configuration and self-
optimization. This handover is very fast, because it is initiated as soon as the triggering condition
is fulfilled and no neighbor cell measurements are required between the triggering condition and
the handover procedure.
For mobile assisted handover, the best target Macro cell is determined just before the handover
and it is based on UE measurements for the current UE location.

The operator can configure preferences for the target cell selection, like independent handover
trigger thresholds for circuit switched calls and packet switched calls and the preferred 3G
frequencies. He can also independently configured if W-CDMA or GSM is the preferred technology
for circuit switched calls, packet switched calls and combinations to deploy service based layering.

When a multi-mode UMTS & LTE-capable UE is camping on LTE, the UE stays connected to LTE
as long as possible. In case of a mobile terminated or mobile originated circuit-switched voice call,
the UE is handed over to a 3G Small Cell in case Circuit Switched FallBack is enabled.

Once the CS call is terminated (either due to a normal completion or call drop), the UE is sent
back to LTE at the earliest possible moment, provided that there are LTE neighboring frequencies
defined in the serving cell. The dual-mode UE then quickly returns to the LTE network as soon as
this CS call is ended, without having to wait for a transition to the idle mode followed by a
reselection to LTE. It is assumed that LTE is the preferred radio access technology for PS services
whereas 3G Small Cells are used to cover CS voice calls.

Lesson 6 – Small Cell Solution additional features.
In this lesson, you will learn the principles of Small Cell Solution GPS location, through the use of
assistance data and the principles of cell broadcast services in support of CMAS.

The GPS-based location functionality of the UE makes use of a Global Positioning System (or GPS)
receiver. When GPS signals are weak, which can be the case in indoor locations, an autonomous
GPS receiver will fail to get a location fix with the required accuracy. In some cases, the GPS may
never be able to determine a GPS location fix. As far as emergency calls are concerned, it may be
necessary to precisely locate a UE in all locations.

One way to improve the accuracy is to provide the UE with GPS assistance data. GPS assistance
data is sent by the Small Cell to the UE. Assistance data is obtained by the A-GPS server
connected to a GPS Reference Network (or GRN) through the Small Cell Gateway.
The Assisted GPS positioning method provides high accuracy. Compared with stand-alone GPS, A-
GPS reduces the GPS start-up and acquisition times, increases the UE GPS sensitivity and enables
to UE to consume much less power.
Note that UE-based assisted GPS feature is only supported by Metro Cells.

The Cell Broadcast Service (or CBS) supports the US Commercial Mobile Alert System (CMAS).
The purpose of CMAS is to broadcast emergency warning messages. These broadcast messages
are issued by Federal Agencies. They can be presidential alerts, imminent threats or child
abduction emergency, also called AMBER alerts. AMBER stands for America’s Missing: Broadcast
Emergency Response.
Typical AMBER alerts are broadcasted over a 24h period with a repetition period of 1 minute.
National alerts are broadcasted by every cell in the network. County alerts are only broadcasted by
cells within a county area.
Starting in 2014, some operators want to broadcast 2 alerts at a 1 minute interval – 1 in English
and 1 in Spanish, each message being limited to 90 characters.

The CBS service is low frequency and best effort. Warning messages are not acknowledged by the UEs.
To be able to receive warning messages from the Federal Agencies, the UEs must support a specific
application. This application provides a common look and feel for all UEs in terms of ring cadence, display or
vibration. This is transparent for the UTRAN, which means that there is no way for the UTRAN to know if the
messages have been received.
Level 2 DRX is an inband technique that is applied on Dynamic Common Traffic Channel (CTCH) content.
Level 1 DRX schedules on FACH. Level 2 DRX is referred to as “inband scheduling message”. Inband
scheduling message is sent on the CTCH together with the actual CB message.
UEs must receive CB message in DRX mode. A schedule message allows UEs to enter the DRX mode. The
schedule message contains information about the interest and location of a CB message.
Operators can configure the schedule period and CB capacity reservation.
So, to be able to receive CB messages, the UEs must support Level 1 and Level 2 CBS DRX.
With the Level 2 DRX method, cells can send alerts more frequently, daily for example. Daily tolerant alerts
are broadcasted with scheduled 1st transmit. Cells with alerts broadcast for many hours at short repetition
intervals are large cells with low mobility. The UE must read every CTCH Tx at cell reselection until the
schedule message has been successfully decoded.
Note that this feature is not supported on residential deployments as the traffic load would strongly impact
the Small Cell gateway performance.

How are warning messages broadcast? Let’s suppose that the Federal Agencies want to warn all
the mobile users in a given geographical area that a hurricane approaches the country. So the
message will be sent from the Federal Alert Gateways and will pass through the operator network
via the Commercial Mobile Service Provider (or CMSP) Gateway. In the operator network, the
message will be managed by the Cell Broadcast Center (or CBC) that will distribute the warning
message to the RNC of the Macro network and to the Small Cell gateway in the Small Cell
network. The CBC uses the Service Access Broadcast Protocol (or SABP) to send the message to
the Small Cell gateway over a TCP connection. In the end, all the UEs located in the targeted area
will receive the warning message from the Small Cells using the Broadcast/Multicast message (or
BMC) protocol.

This completes the course "9360 Small Cell Solution Features".

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