U.S. patent application number 13/726991 was filed with the patent office on 2014-06-26 for umts reselection performance in small cell systems.
This patent application is currently assigned to SpiderCloud Wireless, Inc.. The applicant listed for this patent is SpiderCloud Wireless, Inc.. Invention is credited to Amit Butala, Hithesh Nama, Pete Worters.
Application Number | 20140179323 13/726991 |
Document ID | / |
Family ID | 50896866 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140179323 |
Kind Code |
A1 |
Butala; Amit ; et
al. |
June 26, 2014 |
UMTS RESELECTION PERFORMANCE IN SMALL CELL SYSTEMS
Abstract
A beacon cell adapted for use in a small cell RAN includes dual
identities--a beacon identity and a regular or "live" identity--in
which the identities are individually configured to address
differing performance requirements in the small cell RAN. The
beacon identity in the cell is specially configured to meet the
performance requirements for mobile user equipment (UE) to be able
to quickly and easily move from a macrocell base station in a
mobile operator's network to the small cell RAN using a process
called "reselection." The live identity is configured to meet all
requirements for service to be provided to the UE within the small
cell RAN. Once captured by the beacon identity of the beacon cell,
the UE can then immediately reselect to the live identity of the
cell which operates in a conventional manner.
Inventors: |
Butala; Amit; (Sunnyvale,
CA) ; Nama; Hithesh; (San Jose, CA) ; Worters;
Pete; (San Carlos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SpiderCloud Wireless, Inc. |
San Jose |
CA |
US |
|
|
Assignee: |
SpiderCloud Wireless, Inc.
San Jose
CA
|
Family ID: |
50896866 |
Appl. No.: |
13/726991 |
Filed: |
December 26, 2012 |
Current U.S.
Class: |
455/437 |
Current CPC
Class: |
H04W 36/0005 20130101;
H04W 36/04 20130101; H04W 48/12 20130101; H04W 36/0061
20130101 |
Class at
Publication: |
455/437 |
International
Class: |
H04W 36/04 20060101
H04W036/04 |
Claims
1. A method of operating a radio node in a small cell network, the
method comprising the steps of: configuring the radio node with
dual identities, a first identity of the dual identities being a
beacon identity and the second identity of the dual identities
being a live identity; instantiating a magic PSC (primary
scrambling code) in the radio node to identify the beacon identity
to UE (user equipment) during cell discovery, a magic PSC being a
PSC that is included in a neighbor list broadcast by a macrocell to
facilitate selection; instantiating a non-magic PSC in the radio
node to identify the live identity to the UE; operating the beacon
identity so that the radio node transmits at a minimum signal
quality level needed for reselection of the radio node by the UE
from a neighboring macrocell; capturing the UE into the small cell
network via reselection from the macrocell to the beacon cell using
the magic PSC; enabling the UE to reselect to the live identity
from the beacon identity after capture of the UE; and operating the
live identity in a conventional manner for a small cell.
2. The method of claim 1 in which the beacon identity is operated
at a reduced power level compared to the live identity, or at a
substantially similar power level to the live identity.
3. The method of claim 2 in which the power level of the beacon
identity is approximately 5 dB lower than the live identity power
level.
4. The method of claim 1 including a further step of deploying a
plurality of beacon cells in the small cell network, each of the
beacon cells among the plurality sharing a common magic PSC.
5. The method of claim 4 including a further step of operatively
coupling one or more beacon cells in the small cell network to a
services node, the services node providing connectivity to a core
network of a mobile operator.
6. The method of claim 4 including a further step of deploying
small cells identified using magic PSCs other than the commonly
shared magic PSC.
7. The method of claim 1 in which the step of operating comprises
reconfiguring one or more channels in a downlink to the UE.
8. The method of claim 7 in which the reconfiguring comprises
operating the one or more channels at levels that are cumulatively
no greater than approximately 20% of a normal power level for a
small cell, the one or more channels comprising PSCH (Primary
Synchronization Channel), SSCH (Secondary Synchronization Channel),
CPICH (Common Pilot Channel), and PCCPCH (Primary Common Control
Physical Channel).
9. The method of claim 7 in which the reconfiguring comprises
optimizing a BCH (Broadcast Channel) by implementing one or more
modifications to an SIB (System Information Block), the
modifications selected from SIB3 containing a dummy cell Id, low
values for intrafrequency searching, short timers, or low
reselection hysteresis, SIB5 containing a very low value for RACH
(Random Access Channel) maximum transmit power, a large backoff for
RACH retransmits, fewer RACH reattempts, or a dummy configuration
for SCCPCH (Secondary Common Control Physical Channel), SIB11
containing only a PSC of a live cell in a neighbor list with large,
negative offsets, compressing SIB 11 into a single segment,
dropping SIB2, or fitting one or more SIBs into a repetition cycle
of 16.
10. The method of claim 1 including a further step of scheduling a
fixed or deliberate timing offset between the beacon identity and
the live identity to improve UE reselection behavior.
11. The method of claim 1 in which the small network, macrocell,
and UE are operational in accordance with UMTS (Universal Mobile
Telecommunications System) under 3GPP (Third Generation Partnership
Project).
12. The method of claim 1 in which a power level of the beacon
identity is configured to be one of static, variable, a function of
a duty cycle, based on residual power of the live identity of the
small cell, or based on throughput requirements of users attached
to the live identity of the small cell.
13. The method of claim 1 including a further step of deploying a
plurality of beacon cells in the small network, each of the beacon
cells among the plurality using multiple magic PSCs.
14. The method of claim 8 including a further step of enabling an
AICH (Acquisition Indicator Channel) channel.
15. The method of claim 14 including a further step of sending
NACKs (non-acknowledgements) on the AICH channel to prevent UEs
from attempting to PRACH (physical random access channel) on the
beacon identity.
16. The method of claim 15 including a further step of enabling an
SCCPCH (Secondary Common Control Physical Channel) and using RRC
(Radio Resource Control) reject messages to influence UE
behavior.
17. One or more computer-readable media containing instructions
which, when executed by one or more processors disposed in an
electronic device, implement the method of claim 1.
18. One or more computer-readable media containing instructions
which, when executed by one or more processors disposed in an
electronic device, implement a method for facilitating reselection
of user equipment (UE) from a macrocell to a small cell in a small
cell network, the method comprising the steps of: manipulating
channels transmitted over a downlink between the small cell and a
UE to create a selectively operable beacon identity for the small
cell, the beacon identity being configured to enable the UE to
discover the beacon identity at a minimum signal quality level for
the transmitted channels, the beacon identity being identified by a
magic PSC to enable reselection to the small cell when the beacon
identity is operated; and selectively operating the beacon identity
so that the small cell is switched from functioning as a beacon
cell to enable reselection to functioning as a conventional small
cell, the conventional small cell being identified by a non-magic
PSC to enable handover of the UE to neighboring small cells in the
small cell network.
19. The one or more computer-readable media of claim 18 in which
the method further comprises linking the selective operation of the
beacon identity to a control object, the control object being
cognizant of conditions on the small cell network or implementing a
duty cycle for the beacon identity.
20. The one or more computer-readable media of claim 19 in which
the conditions comprise UE loading on the small cell network.
21. The one or more computer-readable media of claim 19 in which
the control object is either instantiated locally in the small cell
or is instantiated remotely from the services node.
22. A method of deploying small cells in a small cell network in an
indoor enterprise space, the method comprising the steps of:
locating a plurality of beacon cells within the indoor enterprise
space, the locations providing substantially contiguous radio
coverage within selected portions of the space, each of the beacon
cells among the plurality being configured with dual identities, a
first identity of the dual identities being a beacon identity
having a magic PSC (primary scrambling code) that is commonly
shared among the beacon cells, the commonly shared magic PSC
identifying the beacon identity to UE (user equipment) for
reselection, and the second identity of the dual identities being a
live identity having a non-magic PSC for identifying the live
identity to UE for handover; manually locating one or more magic
PSC cells within the indoor enterprise space, each magic PSC cell
using a unique magic PSC that is not the commonly shared magic PSC;
operating the beacon cells and magic PSC cells to facilitate
capture of the UE via reselection from a macrocell to either a
magic PSC cell or to a beacon identity of a beacon cell; and
handing over the UE to a neighboring small cell as the UE moves
within the indoor enterprise space.
23. The method of claim 22 in which the beacon identity is created
by operating the beacon cell so that broadcast channels are
transmitted at minimum requirements for reselection of the beacon
cell by the UE.
24. The method of claim 23 in which the broadcast channels of the
beacon identity include a nominal timing offset compared to
broadcast channels of the live identity.
25. The method of claim 22 including a further step of switching
the beacon cell between the beacon identity and the live identity
so that the beacon cell has only one identity at time.
26. The method of claim 22 in which the beacon identity and live
identity are operated substantially simultaneously.
27. A method for configuring a small cell in a small cell radio
access network (RAN), the method comprising the steps of:
configuring a first identity in the small cell for accommodating
conventional user equipment (UE) behavior, the conventional UE
behavior including reselection in to the small cell network from a
cell on another RAN, the other RAN not being managed by the small
cell RAN; configuring a second identity in the small cell for
providing a RAN service, the RAN service facilitating service to
the UE within the small cell RAN; and optimally re-associating the
UE between the first and second identities of the small cell.
28. The method of claim 27 in which the RAN service is implemented
using reselection.
29. The method of claim 27 in which the RAN service is implemented
using handover.
30. The method of claim 27 in which the first identity is a beacon
identity and including a further step of dynamically managing a
power level of the beacon identity.
31. The method of claim 30 in which the dynamic management is
implemented, at least in part, via a coupling to a control system
or sub-system, the control system or sub-system being incorporated
into small cell or being external to the small cell.
32. The method of claim 27 in which the first identity is a beacon
identity and the second identity is a live identity and including a
further step of operating the beacon identity and live identity to
have substantially similar power levels.
33. The method of claim 27 including a further step of broadcasting
a magic PSC in a small cell's neighbor list in SIB11 (System
Information Block 11) with a relatively large hysteresis.
Description
BACKGROUND
[0001] Operators of mobile systems such as Universal Mobile
Telecommunications Systems (UMTS) are increasingly relying on
wireless small cell radio access networks (RANs) in order to deploy
indoor voice and data services to enterprises and other customers.
Such small cell RANs typically utilize multiple-access technologies
capable of supporting communications with multiple users using
radio frequency (RF) signals and sharing available system resources
such as bandwidth and transmit power. While such small cell RANs
operate satisfactorily in many applications, there exists a need
for further improvements in small cell RAN technologies.
[0002] This Background is provided to introduce a brief context for
the Summary and Detailed Description that follow. This Background
is not intended to be an aid in determining the scope of the
claimed subject matter nor be viewed as limiting the claimed
subject matter to implementations that solve any or all of the
disadvantages or problems presented above.
SUMMARY
[0003] A beacon cell adapted for use in a small cell RAN includes
dual identities--a beacon identity and a regular or "live"
identity--in which the identities are individually configured to
address differing requirements in the small cell RAN. The beacon
identity in the cell is specially configured to meet the
requirements for mobile user equipment (UE) such as mobile phones,
smartphones, tablets, etc., to be able to quickly and easily move
from a macrocell base station in a mobile operator's network to the
small cell RAN using a process called "reselection." Reselection
can be utilized, for example, when the equipment user moves from an
outdoor area within the radio coverage of the macrocell into a
building serviced by the small cell RAN. Once the UE is associated
with the small cell RAN, the beacon identity is no longer used to
control the UE. Instead, the beacon cell internally switches the UE
from the beacon identity to the live identity. The live identity is
configured to meet all requirements for service to be provided to
the UE within the small cell RAN. Thus, the present beacon cell
advantageously enables rapid reselection of a UE from the macrocell
to the small cell RAN and then provides the same level of RAN
service to the UE in the small cell RAN as would a conventional
small cell.
[0004] Due to the predetermined configuration of macrocells,
reselection requires a reserved primary scrambling code (PSC) for
cell identification, termed a "magic PSC" in the description that
follows. There are usually very few, for example six, magic PSCs
available in typical applications. However, since reselection does
not rely on cell disambiguation (as needed for other RAN services)
a PSC in a beacon identity can be reused without any risk of
disambiguation failure. In addition, the beacon identity can be
broadcast with reduced power and lower signal quality so long as
the broadcast channels remain decodable over an acceptable fraction
of the coverage area of the beacon cell. By contrast, the live
identities of all cells in the small cell RAN cannot typically be
satisfactorily configured using just the magic PSCs and thus they
require other (i.e., non-magic) PSCs. The live identities thus use
a relatively large set of PSCs and can operate at normal power and
signal quality levels to facilitate satisfactory quality-of-service
and cell disambiguation for RAN service. The reduced power level of
the beacon identity reduces the opportunity for RF interference
with the live identity but still enables rapid reselection to the
small cell RAN from the macrocell. Once captured by the beacon
identity of the beacon cell, the UE can then immediately reselect
to the live identity of the cell which operates in a conventional
manner including, for example, handover to neighboring cells in the
small cell RAN as the UE moves through the service area.
[0005] In various illustrative examples, each deployed beacon cell
is configured to reuse (i.e., commonly share) the same magic PSCs.
As the number of magic PSCs that are reserved for reselection is
strictly limited, the present beacon cell advantageously broadens
the footprint of cells in the small cell RAN that are equipped to
capture UEs from the macrocell via reselection because many or all
of the cells in a given deployment can be beacon cells.
[0006] The beacon identity will typically broadcast only to the
minimum requirements for reselection by reconfiguring several
physical and transport channels in the downlink to the UE Timing
and power utilization of the beacon cell are also manipulated to
further optimize reselection performance. The beacon identity may
also be adapted for selective and/or dynamically configurable
operation using a duty cycle, for example, or be operated in
response to conditions on the small cell RAN such as UE
loading.
[0007] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows an illustrative mobile telecommunications
environment in which the present small cell reselection performance
improvement may be practiced;
[0009] FIG. 2 shows how a primary scrambling code (PSC) is utilized
to uniquely identify cells to user equipment (UE) where cells can
include a serving cell and neighboring cells;
[0010] FIGS. 3 and 4 respectively show two different ways in which
a serving cell may be changed;
[0011] FIG. 5 shows illustrative features and characteristics which
are incorporated into a beacon cell which may be utilized to
implement the present small cell reselection performance
improvement;
[0012] FIG. 6 is an illustrative taxonomy of modifications that may
be utilized to implement aspects of beacon cell functionality;
[0013] FIG. 7 is a flowchart of an illustrative method for improved
reselection performance using a beacon cell;
[0014] FIG. 8 illustratively shows how a small cell RAN (Radio
Access Network) may include a mix of cell types;
[0015] FIG. 9 shows an illustrative radio interface protocol
architecture (3GPP TS 25.301); and
[0016] FIG. 10 shows a simplified functional block diagram of
illustrative hardware infrastructure for a radio node that may be
utilized to implement the present beacon cell.
[0017] Like reference numerals indicate like elements in the
drawings. Elements are not drawn to scale unless otherwise
indicated.
DETAILED DESCRIPTION
[0018] FIG. 1 shows an illustrative mobile telecommunications
environment 100 in which the present small cell reselection
performance improvement may be practiced. The mobile
telecommunications environment 100, in this illustrative example,
is arranged as a Universal Mobile Telecommunications System (UMTS)
as described by the Third Generation Partnership Project (3GPP),
although it is emphasized that the present principles described
herein may also be applicable to other network types and protocols.
The environment 100 includes an enterprise 105 in which a small
cell RAN 110 is implemented. The small cell RAN 110 includes a
plurality of radio nodes 115.sub.1 . . . N. Each radio node 115 has
a radio coverage area (graphically depicted in the drawings as a
hexagonal shape) that is commonly termed a small cell. Thus, the
small cell RAN 110 may be viewed as a small cell network, i.e., a
portion of a UMTS Terrestrial Radio Access Network (UTRAN) under
3GPP. A small cell may also be referred to as a femtocell, or using
terminology defined by 3GPP as a Home NodeB. In the description
that follows, the term "cell" typically means the combination of a
radio node and its radio coverage area unless otherwise indicated.
A representative cell is indicated by reference numeral 120 in FIG.
1.
[0019] The size of the enterprise 105 and the number of cells
deployed in the small cell RAN 110 may vary. In typical
implementations, the enterprise 105 can be from 50,000 to 500,000
square feet and encompass multiple floors and the small cell RAN
110 may support hundreds to thousands of users using mobile
communication platforms such as mobile phones, smartphones, tablet
computing devices, and the like (referred to as "user equipment"
(UE) and indicated by reference numerals 125.sub.1-N in FIG. 1).
However, the foregoing is intended to be illustrative and the small
cell reselection performance improvement can be typically expected
to be readily scalable either upwards or downwards as the needs of
a particular usage scenario demand.
[0020] In this particular illustrative example, the small cell RAN
110 includes one or more services nodes (represented as a single
services node 130 in FIG. 1) that manage and control the radio
nodes 115. In alternative implementations, the management and
control functionality may be incorporated into a radio node,
distributed among nodes, or implemented remotely (i.e., using
infrastructure external to the small cell RAN 110). The radio nodes
115 are coupled to the services node 130 over a direct or local
area network (LAN) connection (not shown in FIG. 1) typically using
secure IPsec tunnels. The services node 130 aggregates voice and
data traffic from the radio nodes 115 and provides connectivity
over an IPsec tunnel to a gateway 135 in a core network 140 of a
mobile operator. The core network 140 is typically configured to
communicate with a public switched telephone network (PSTN) 145 to
carry circuit-switched traffic, as well as for communicating with a
packet-switched network such as the Internet 150.
[0021] The environment 100 also generally includes UTMS Node B base
stations, or "macrocells", as part of the UTRAN as representatively
indicated by reference numeral 155 in FIG. 1. The radio coverage
area of the macrocell 155 is typically much larger than that of a
small cell where the extent of coverage often depends on the base
station configuration and surrounding geography. Thus, a given UE
125 may achieve UTRAN connectivity through either a macrocell or
small cell in environment 100.
[0022] A UE 125 connected to the UMTS network environment 100 will
actively or passively monitor a UTRAN cell. As shown in FIG. 2,
such a cell is termed the "serving cell" 205 and as the UE 125
moves throughout the environment 100, it will continually evaluate
the quality of the serving cell as compared with that of
neighboring cells 210. As shown, both small cells and macrocells
can identify themselves to the UE 125 using a unique primary
scrambling code (PSC) 215 that is transmitted over a downlink to a
UE as representatively indicated by reference numeral 220. By using
different PSCs, neighboring cells 210 may thus be disambiguated
from the serving cell 205.
[0023] There are two different ways in the UMTS network environment
100 (FIG. 1) in which the serving cell may be changed. For a UE in
active communications, called the Cell_DCH state using 3GPP
terminology, the serving cell changes are controlled by the network
using a process termed "handover." As shown in FIG. 3, handover
between small cells 120 in the small cell RAN 110 is supported in a
UMTS network to provide RAN service to the UE (RAN service may also
utilize reselection in some cases). However, handover between a
macrocell and a small cell is typically unsupported in many UMTS
deployments. Instead, for UEs 125 that are inactive or passively
communicating with the network, the UEs autonomously select a new
serving cell, through a process called "reselection." While the
reselection process is autonomous, it is steered based on
parameters broadcast by the current serving cell. These parameters
are signaled on the BCH (broadcast channel under 3GPP) channel and
indicate the neighboring cell PSCs and signal quality at which
reselection is permitted.
[0024] Accordingly, reselection is typically the only path over
which UEs 125 can detect the small cell RAN 110 and switch over
from the macrocell 155 to a small cell 120, as shown in FIG. 4.
There are several usage scenarios in which a user would need to
reselect to the small cell RAN 110. These include, for example:
[0025] 1. Ingress: This is a dominant scenario in which a user in
the exterior of the small cell RAN moves into the small cell RAN.
[0026] 2. Redirect: In the case of overload, the small cell RAN
redirects users to the macrocell. This affects UEs not just when
establishing voice traffic, but also UEs handling background
packet-switched traffic. Typically, it can be expected that the
macrocell coverage would be marginal, but once on the macrocell,
the UE will not return to the small cell RAN except through the
reselection procedure. A given small cell RAN may also have
adequate capacity for voice, but if under-dimensioned for
packet-switched traffic, may still bleed users to the macrocell,
and those users would continue to remain on the macrocell when
establishing voice calls. [0027] 3. Coverage holes: The coverage
from the small cell RAN may not be consistent. For example,
laboratories, elevators, atriums, and other locations in the
enterprise may have localized coverage issues that result in loss
of users to the macrocell. [0028] 4. System issues: Radio system
reboots, loss of core network connectivity, etc., could result in
affected users reselecting to the macrocell.
[0029] If reselection performance is not satisfactory, the small
cell RAN will see lower than desired utilization, resulting in
continued overload on the macrocell network and poorer user
experience in-building.
[0030] Typically, the macrocells in the UMTS network usually
reserve a small set of PSCs for permitting reselection by UEs 125
to the small cell RAN 110 (FIG. 1). The PSCs are colloquially known
as "magic PSCs" because they have special properties--the UE 125
will reselect to a cell 120 in the small cell RAN 110 identified by
a magic PSC even at low "quality" levels, for example, very low
RSCP (received signal code power) and SNR (signal-to-noise ratio)
levels, thereby accelerating the reselection of the UE to cells
using these magic PSCs. A representative magic PSC 405 is shown in
FIG. 4.
[0031] Conversely, while some cells 120 in the small cell RAN 110
can use regular (i.e., non-magic PSCs), a UE 125 on the macrocell
155 will never reselect to a small cell RAN cell 120 that uses a
non-magic PSC, regardless of the quality of the non-magic PSC.
However, once on the small cell RAN 110, the UEs 125 may handover
or reselect to a cell having any PSC, including non-magic PSC.
Since it is typically desirable to redirect users to the small cell
RAN as soon as they enter the coverage area of the small cell RAN
for the reasons discussed above, small cells identified by a magic
PSC are often located at points within the enterprise 105 where
such cells can influence the reselection from the macrocell 155 for
the largest fraction of users.
[0032] In typical current implementations of small cell networks
(i.e., those not utilizing the present small cell reselection
performance improvement), the configuration of cells having magic
PSCs within the small cell RAN often needs to be carefully
implemented because the quality of magic PSC assignments determines
the reselection-in performance for the small cell RAN. The
configuration process typically entails two steps. The first step
comprises manual configuration of those cells using magic PSCs by
setting an appropriate parameter in the radio node. As noted above,
cells at the ingress routes to the small cell RAN (e.g., entrances
to the enterprise) and cells in common areas (lobbies, atriums,
cafeterias, etc.) are recommended as prime candidates to improve
the overall system reselection performance. The second step
comprises a REM (radio environment measurement) scan and PSC
assignment. This is an automated process that generally determines
the best PSC to be used by a cell based on RF and topology
considerations.
[0033] While the configuration steps discussed above can provide
satisfactory results in many network implementations, the manual
configuration can often increase the complexity of the installation
since it requires knowledge of the building floor plans, adds
additional installation and configuration steps, and may be prone
to errors. More particularly, insufficient allocation of magic PSCs
can result in UEs remaining on the macrocell which has degraded
even though they are in the coverage area of the small cell RAN. In
addition, a dense allocation of magic PSCs can result in
disambiguation failures, which, while improving reselection
behavior, would degrade handover performance.
[0034] Such issues may be addressed by a beacon cell that is
arranged to improve reselection performance in small cell systems
such as the small cell RAN 110 shown in FIG. 1 and described in the
accompanying text. As shown in FIG. 5, a beacon cell 505 includes a
radio node 510 that is specially configured to have two distinct
identities. One identity is a beacon identity in which the beacon
cell 505 can function and behave as a beacon that is specifically
intended to capture UEs from the macrocell via reselection using a
magic PSC. The other identity is the standard or "live" identity in
which the beacon cell 505 can function and behave conventionally as
a regular small cell to provide RAN service to a UE once it is
associated with the small cell RAN. In some usage scenarios, the
beacon cell 505 supports both identities simultaneously, while in
other scenarios the beacon identity is utilized on a selective
basis, as described in more detail below. Beacon cells may be used
to supplement cells that are identified with magic PSCs in a given
small cell RAN deployment, or replace such magic PSC cells in their
entirety in some cases. Similarly, beacon cells can be used to
supplement regular cells in a given small cell RAN deployment, or
replace such cells in some cases.
[0035] The configuration of the beacon cell 505 with dual
identities results, at least in part, from the recognition that RAN
service and reselection from a macrocell have differing performance
requirements. Reselection from a macrocell requires a magic PSC but
does not rely on cell disambiguation. Additionally, as long as the
broadcast channels are decodable, the overall quality of the cell
is not important. By contrast, after the UE becomes associated with
the small cell RAN via the beacon identity, the provision of RAN
service does not require a magic PSC, but does require cell
disambiguation.
[0036] Accordingly, in view of the foregoing recognition, the
beacon identity 520 may include a number of features and
characteristics, as shown in FIG. 5. The beacon identity 520
utilizes one or more magic PSCs (as indicated by reference numeral
525). In some cases, the same particular magic PSC (e.g., one of
six reserved PSCs in one illustrative implementation scenario) is
reused by each of the beacon cells 505 in a small cell RAN, while
in other cases, two, three, or up to all six of the magic PSCs are
utilized in the beacon cells with varying degrees of reuse (530).
For example, three magic PSCs may be reused across multiple beacon
cells, while two magic PSCs are utilized in single instances, and
the sixth magic PSC is not utilized in a beacon cell and reserved
for other uses. Note, however, that it may be desirable in some
implementations to maintain backwards compatibility by reusing a
single magic PSC for beacon cells while reserving the remaining
five magic PSCs for conventional usage. In the event that handover
from a macrocell to a small cell RAN is supported in the future,
some live identities can be configured with magic PSCs that are not
used by any beacon identities in order to also provide a path of
handover from macrocells to the small cell RAN. In most typical
small cell RAN implementations, once a magic PSC is selected for
beacon cell use it should not be configured for use by any other
non-beacon cells.
[0037] The live identity 515, by comparison to the beacon identity
520, uses regular, non-magic PSCs (as indicated by reference
numeral 535). Each live identity in a beacon cell uses a spatially
unique PSC and PSC reuse is carefully managed (540). For example,
in some implementations, it may be desirable to reuse PSCs for the
live identities as infrequently as possible.
[0038] In order to reduce interference between the beacon and live
identities when both identities are simultaneously utilized,
channel powers can typically become critically important.
Accordingly, the beacon identity 520, in comparison to the live
identity 515 which broadcasts conventionally, uses a modified
broadcast (550) where such modifications can be described in terms
of differences in the SIBs (System Information Blocks) between the
beacon identity and live identity. FIG. 6 shows an illustrative
taxonomy 600 of modifications (as indicated by reference numeral
602) that may be made to several physical and transport channels in
the downlink between the beacon cell and a UE to enable such
broadcast to minimum requirements for reselection. Such enablement
entails configuring certain physical channels to cumulatively
utilize no greater than approximately 20% of regular live cell
power (604). The reconfigured physical channels include PSCH
(Primary Synchronization Channel), SSCH (Secondary Synchronization
Channel), CPICH (Common Pilot Channel), and PCCPCH (Primary Common
Control Physical Channel), as respectively indicated by reference
numerals 606, 608, 610, and 612.
[0039] The BCH (Broadcast Channel) may also be configured to aid
rapid reselection and prevent a UE from transmitting to the beacon
cell at high power (614). In particular, certain SIBs can be
modified: SIB3 (616) may be modified to contain a dummy cell ID
(618). It may be possible to reuse the same dummy cell ID for all
beacon identities across cells in a given small cell RAN
deployment. SIB3 may be further configured to contain low values
for intrafrequency searching, short timers, and low reselection
hysteresis (620).
[0040] SIB5 (622) may be configured to contain a relatively low
value for RACH (Random Access Channel) maximum transmit power
(624), a relatively large backoff for RACH retransmits (626), and
fewer RACH reattempts (628). SIB5 may be optionally configured, in
some implementations, to contain a dummy configuration for SCCPCH
(Secondary Common Control Physical Channel) (630).
[0041] SIB11 (632) may be configured to contain only one
neighboring cell via the PSC of a live cell in the neighbor list
having large (negative) offsets (634). SIB2 (638) may be dropped as
non-essential (640). Each of the SIBs (642) may be optionally
configured to fit into a repetition cycle of 16 (i.e., 160 ms) to
further expedite the reselection process by reducing the time
required for SIB inspection (644).
[0042] Returning again to FIG. 5, as noted above, the beacon
identity 520 can present interference with the live identity 515
which can limit the total power available to the cell's normal
operation and thus potentially have some nominal impact on cell
capacity in some cases. Typically, the BCH can be decoded by a UE
as low as -17 dB chip SNR. Accordingly, the beacon identity 520 can
be configured about 5 dB lower than the live identity 515 and thus
the power utilization of the beacon identity can be lowered to
approximately 6% of the total cell power (as indicated by reference
numeral 555). Various control schemes may also be implemented to
allow for dynamic power management of the beacon identity 520, for
example, using a new control or by a tie-in (560) to an existing
control system or sub-system incorporated in the radio node or
external to the node, for example, the downlink power manager or
HSDPA (High-Speed Downlink Packet Access) power harvesting module.
Under such control, the beacon identity may be powered up and down
in an opportunistic manner.
[0043] In another illustrative example, in a completely unloaded
small cell RAN the CPICH of the beacon identity can have
substantially the same power level as the live identity CPICH so as
to have the same footprint for both reselection and normal RAN
service operation. In this case, when a UE moves within the small
cell RAN, there will be a possibility of it reselecting briefly to
the beacon identity of an adjoining beacon cell, which should be
avoided when possible. To this end, all beacon cells in a small
cell RAN may advertise a magic PSC in their neighbor list in SIB 11
with a relatively large hysteresis. This can be expected to prevent
such a reselection to the adjoining beacon identity once the UE is
within the small cell RAN in many scenarios. It is also possible
that the reselection to the adjoining beacon identity may even be
prevented in cases when the UE goes into a coverage hole and
returns back to the small cell RAN after going to the macrocell or
through a full scan of all PSCs.
[0044] A nominal timing offset of a few chips between the beacon
and live identities may also be utilized to compensate for the
observation that some UEs may have difficulty detecting the lower
power beacon signal having the same timing as a stronger signal
from the live identity (565).
[0045] The beacon identity 520 may further be optionally configured
to be selectively operated (570). That is, the beacon cell 505 can
have both the beacon and live identities operating simultaneously,
or the beacon identity can be selectively switched off so that the
beacon cell 505 essentially defaults to conventional live cell
behavior with no support for reselection in from the macrocell.
Such selective operation could be implemented, for example, using a
duty cycle methodology or via coupling to a control that has
awareness of external conditions such as UE loading on the small
cell RAN, or throughput requirements of users attached to the live
identity of the small cell.
[0046] Other optional configurations may include enabling an AICH
(Acquisition Indicator Channel) and sending NACKs
(non-acknowledgements) on the AICH to prevent UEs from attempting
to PRACH (physical random access channel) on the beacon identity,
and enabling an SCCPCH (Secondary Common Control Physical Channel)
and using RRC (Radio Resource Control) reject messages to influence
UE behavior.
[0047] FIG. 7 is a flowchart of an illustrative method 700 for
improved reselection performance using multiple instances of the
beacon cell 505 shown in FIG. 5 and described in the accompanying
text when deployed in a small cell RAN. It should be understood
that the specific order or hierarchy of the steps in the method
disclosed is an illustration of exemplary approaches. Based upon
design preferences, it is understood that the specific order or
hierarchy of steps in the method may be rearranged. The
accompanying method claims present elements of the various steps in
a sample order, and are not meant to be limited to the specific
order or hierarchy presented. The method starts at block 705. A UE
is in an inactive state on a macrocell at block 710. At block 715,
the UE reads SIBs from the macrocell to get the PSCs of the
neighboring cells for reselection. As discussed above, magic PSCs
are utilized by cells that support reselection. When the UE moves
into small cell RAN coverage, at block 720, it will discover a
beacon cell, at block 725.
[0048] If the UE can decode the beacon identity SIBs at decision
block 730, then control passes to block 735 and the UE will
reselect the live identity virtually immediately. If the UE cannot
decode the beacon cell SIBs for any reason, the UE will continue to
stay on the macrocell and control passes back to block 725 and the
UE will discover another beacon cell and the above steps are
repeated until a live identity in a beacon cell is successfully
reselected. Because utilization of beacon cells typically enables a
reselection beacon to be broadcast over a relatively large area
from many or all of the cells in the small cell RAN, capture of UEs
from the macrocell to the small cell RAN is significantly enhanced.
And any UEs that leak out to the macrocell can typically be
expected to be quickly re-acquired by the beacon cell-equipped
small cell RAN.
[0049] When a live identity is successfully reselected, then the UE
will camp on that beacon cell and the small cell RAN will behave
and operate as normal, as shown at block 740. For example, the UE
will move from a serving cell to a neighboring cell in the small
cell RAN using normal handover. In some cases, even when the UE is
in the coverage area of the small cell RAN, it may still not be
associated with the small cell RAN and additional occurrences of
reselection from the macrocell to the small cell RAN may need to
occur. For example, as discussed above, reselection may be needed
subsequent to a UE being directed to a macrocell due to a coverage
hole, overload, system error/reboot, or the like. In such cases,
control is returned from decision block 745 back to block 725, and
the method shown in blocks 725-745 is repeated.
[0050] FIG. 8 illustratively shows how a small cell RAN 800 may
include cells selected from different cell types. The cell types
include: (1) beacon cells 505; (2) non-beacon cells which are
identified using a magic PSC, termed "magic PSC cells" here and
indicated by reference numeral 805 in FIG. 8, (3) regular,
non-beacon cells which are identified using regular PSCs (i.e.,
non-magic PSCs), termed "regular cells" here and indicated by
reference numeral 810, and (4) a small cell that has a beacon
identity only and no live identity, as indicated by reference
numeral 815. It is noted that all cell types could be designed and
constructed, in some implementations, to share a single common
physical platform but differ in beacon functionality according to
variable configuration settings. In some cases, such settings may
be selectable via executable software on the cell or remote control
(e.g., from the services node 130 shown in FIG. 1, or at a location
that is remote from the small cell RAN), or selected via firmware
and/or hardware, or various combinations of software, firmware, and
hardware.
[0051] In one illustrative deployment scenario using mixed cell
types, the beacon cells 505 are arranged to commonly share a single
magic PSC thus enabling the maximum number of discrete magic PSC
cells 805 to also be utilized in the small cell RAN 800. In this
scenario, the magic PSC cells are configured and deployed using
conventional manual techniques. No regular cells 810 are utilized
as all of the cells in the small cell RAN 800, other than the magic
PSC cells, are configured as beacon cells 505.
[0052] In a second illustrative deployment scenario using mixed
cell types, beacon cells 505 and magic PSC cells 805 are configured
and deployed in a small cell RAN in a similar manner as in the
first scenario. Regular cells 810 are also utilized in certain
locations in the enterprise where reselection to the small cell RAN
from the macrocell may be undesired (for example, when a cell
bleeds out beyond its desired coverage area over a pedestrian
walkway).
[0053] In a third illustrative deployment scenario using mixed cell
types, the cell 815with beacon identity only can be used to overlay
an existing small cell RAN deployment of regular cells 810 and
magic PSC cells 505.The foregoing deployment scenarios are intended
to be illustrative and deployment scenarios using other
combinations of cell types and configurations are envisioned as
required to meet the needs of a given implementation.
[0054] FIG. 9 shows an illustrative radio interface protocol
architecture 900 that is arranged in accordance with 3GPP TS 25.201
and which may be used to facilitate implementation of various
aspects of the present beacon cell (e.g., beacon cell 505 in FIG.
5). The architecture 900 is arranged in three protocol layers: the
physical layer (L1) as indicated by reference numeral 905; the data
link layer (L2) 910; and the network layer (L3) 915. The L2 layer
910 above the L1 layer 905 is responsible for the link between the
UEs and beacon cells over the L1 layer. In the user plane 920, the
L2 layer 910 includes a media access control (MAC) sublayer 925, a
radio link control (RLC) sublayer 930, and a packet data
convergence protocol (PDCP) sublayer 935, which are terminated at
the beacon cell on the network side.
[0055] The PDCP sublayer 935 provides header compression for upper
layer data packets to reduce radio transmission overhead and
handover support for UEs between small cells. The RLC sublayer 930
provides segmentation and reassembly of upper layer data packets,
retransmission of lost data packets, and reordering of data packets
to compensate for out-of-order reception due to hybrid automatic
repeat request (HARQ). The MAC sublayer 925 provides multiplexing
between logical and transport channels. The MAC sublayer 925 is
also responsible for allocating the various radio resources (e.g.,
resource blocks) in one cell among the UEs. The MAC sublayer 925 is
also responsible for HARQ operations.
[0056] In the control plane 940, the radio interface protocol
architecture 900 is substantially the same for the physical layer
905 and the L2 layer 910 with the exception that there is no header
compression function for the control plane. The control plane also
includes a radio resource control (RRC) sublayer 945 in the L3
layer 915. The RRC sublayer 945 is responsible for obtaining radio
resources (i.e., radio bearers) and for configuring the lower
layers using RRC signaling between the beacon cell and the UE.
[0057] FIG. 10 shows a simplified functional block diagram of
illustrative hardware infrastructure for a radio node (e.g., radio
node 510 in FIG. 5) that may be utilized to implement the present
beacon cell 505. It is emphasized at the outset that the various
discrete elements shown are intended to be illustrative, and that
functionalities provided by a given element may be combined with
those provided by another element, for example, as a matter of
design preference. In addition, some elements are not shown in FIG.
10 for sake of clarity in exposition such as buses and various
circuits such as timing sources, peripherals, analog-to-digital and
digital-to-analog converters, voltage regulators, and power
management circuits, and the like which are well known in the art,
and therefore, will not be described any further.
[0058] A controller/processor 1005 implements the functionality of
the L2 layer 910 shown in FIG. 9 and described in the accompanying
text. The controller/processor 1005 may include one or more
sub-processors 1010 or cores that are configured to handle specific
tasks or functions. The controller/processor 1005 typically
provides header compression, ciphering, packet segmentation and
reordering, multiplexing between logical and transport channels,
and radio resource allocations to the UE based on various priority
metrics. The controller/processor 1005 is also responsible for HARQ
operations, retransmission of lost packets, and signaling to the
UE.
[0059] An RF processor 1015 implements various signal processing
functions for the downlink including the L1 layer 905 (i.e.,
physical layer) shown in FIG. 9 and described in the accompanying
text. The RF processor 1015 may include one or more sub-processors
1020 or cores that are configured to handle specific tasks or
functions. Exemplary signal processing functions include coding and
interleaving to facilitate forward error correction (FEC) at the UE
and mapping to signal constellations based on various modulation
schemes (e.g., binary phase-shift keying (BPSK), quadrature
phase-shift keying (QPSK), M-phase-shift keying (M-PSK), and
M-quadrature amplitude modulation (M-QAM)). The coded and modulated
symbols are then split into parallel streams. Each stream is then
mapped to an OFDM (orthogonal frequency-division multiplexing)
subcarrier, multiplexed with a reference signal (e.g., pilot) in
the time and/or frequency domain, and then combined together using
an Inverse Fast Fourier Transform (IFFT) to produce a physical
channel carrying a time domain OFDM symbol stream. The OFDM stream
is spatially pre-coded to produce multiple spatial streams. Channel
estimates from a channel estimator (not shown) may be used to
determine the coding and modulation scheme, as well as for spatial
processing. The channel estimate may be derived from a reference
signal and/or channel condition feedback transmitted by the UE.
Each spatial stream is then provided to an antenna via a
transmitter that modulates an RF carrier with a respective spatial
stream for transmission.
[0060] A memory 1025 stores computer-readable code 1030 that is
executable by one or more processors in the beacon cell 505
including the controller/processor 1005 and/or the RF processor
1015. The memory 1025 may also include various data sources and
data sinks (collectively represented by element 1035) that may
provide additional functionalities. For example, a data sink may be
used to facilitate L3 layer processing to the extent that such
upper layer processing is implemented on the beacon cell.
[0061] The code 1030 in typical deployments is arranged to be
executed by the one or more processors to implement the beacon
identity features shown in FIG. 5, including power utilization,
timing offsets, and selective operations, as well as the
modifications to the transport and physical channels shown in FIG.
6 via control of the L1 and/or L2 layers (elements 905 and 910
respectively in FIG. 9). The code 1030 additionally enables
implementation of both the beacon cell identity and live identity
using the same hardware infrastructure in a given beacon cell when
executed.
[0062] The hardware infrastructure may also include various
interfaces (I/Fs) including a communication I/F 1040 which may be
used, for example, to implement a link to the services node 130
(FIG. 1), LAN, or to an external processor, control, or data
source. In some cases, a user I/F 1045 may be utilized to provide
various indications such as power status or to enable some local
control of features or settings.
[0063] Several aspects of telecommunication systems will now be
presented with reference to various apparatus and methods described
in the foregoing detailed description and illustrated in the
accompanying drawing by various blocks, modules, components,
circuits, steps, processes, algorithms, etc. (collectively referred
to as "elements"). These elements may be implemented using
electronic hardware, computer software, or any combination thereof
Whether such elements are implemented as hardware or software
depends upon the particular application and design constraints
imposed on the overall system. By way of example, an element, or
any portion of an element, or any combination of elements may be
implemented with a "processing system" that includes one or more
processors. Examples of processors include microprocessors,
microcontrollers, digital signal processors (DSPs), field
programmable gate arrays (FPGAs), programmable logic devices
(PLDs), state machines, gated logic, discrete hardware circuits,
and other suitable hardware configured to perform the various
functionalities described throughout this disclosure. One or more
processors in the processing system may execute software. Software
shall be construed broadly to mean instructions, instruction sets,
code, code segments, program code, programs, subprograms, software
modules, applications, software applications, software packages,
routines, subroutines, objects, executables, threads of execution,
procedures, functions, etc., whether referred to as software,
firmware, middleware, microcode, hardware description language, or
otherwise. The software may reside on a computer-readable media.
Computer-readable media may include, by way of example, a magnetic
storage device (e.g., hard disk, floppy disk, magnetic strip), an
optical disk (e.g., compact disk (CD), digital versatile disk
(DVD)), a smart card, a flash memory device (e.g., card, stick, key
drive), random access memory (RAM), read only memory (ROM),
programmable ROM (PROM), erasable PROM (EPROM), electrically
erasable PROM (EEPROM), a register, a removable disk, and any other
suitable media for storing or transmitting software. The
computer-readable media may be resident in the processing system,
external to the processing system, or distributed across multiple
entities including the processing system. Computer-readable media
may be embodied in a computer-program product. By way of example, a
computer-program product may include one or more computer-readable
media in packaging materials. Those skilled in the art will
recognize how best to implement the described functionality
presented throughout this disclosure depending on the particular
application and the overall design constraints imposed on the
overall system.
[0064] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the
claims.
* * * * *