U.S. patent application number 17/229209 was filed with the patent office on 2021-07-29 for hand-in with topology hiding.
The applicant listed for this patent is Parallel Wireless, Inc.. Invention is credited to Kaitki Agarwal, Rahul Atri, Yang Cao, Zeev Lubenski, Prashanth Rao.
Application Number | 20210235343 17/229209 |
Document ID | / |
Family ID | 1000005512173 |
Filed Date | 2021-07-29 |
United States Patent
Application |
20210235343 |
Kind Code |
A1 |
Cao; Yang ; et al. |
July 29, 2021 |
Hand-In with Topology Hiding
Abstract
Systems and methods for performing handover coordination between
base stations are disclosed. In a first embodiment, a method is
disclosed, comprising: receiving, at a base station, a first
serving cell signal measurement and a first neighbor cell signal
measurement from a particular user equipment (UE); sending an
adjustment message, from the base station to the UE, containing a
cell-specific offset of the serving cell and a cell-specific offset
of the neighbor cell in a reporting threshold based on at least one
handover adjustment factor received from a coordinating node;
receiving, at the base station and subsequent to adjusting the
cell-specific offsets, a second serving cell signal measurement and
a second neighbor cell signal measurement; and deciding whether to
trigger a handover event based on the first and the second serving
cell signal measurement and the first and the second neighbor cell
signal measurement and the cell-specific offsets.
Inventors: |
Cao; Yang; (Westford,
MA) ; Lubenski; Zeev; (North Andover, MA) ;
Agarwal; Kaitki; (Westford, MA) ; Rao; Prashanth;
(Wilmington, MA) ; Atri; Rahul; (Pune,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Parallel Wireless, Inc. |
Nashua |
NH |
US |
|
|
Family ID: |
1000005512173 |
Appl. No.: |
17/229209 |
Filed: |
April 13, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16028069 |
Jul 5, 2018 |
10979946 |
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17229209 |
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15810003 |
Nov 10, 2017 |
10979948 |
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16028069 |
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62420099 |
Nov 10, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 84/045 20130101;
H04W 36/14 20130101; H04W 36/0085 20180801; H04W 88/16 20130101;
H04W 36/0058 20180801; H04W 36/0011 20130101; H04W 36/0055
20130101; H04W 36/00837 20180801 |
International
Class: |
H04W 36/00 20060101
H04W036/00; H04W 36/14 20060101 H04W036/14 |
Claims
1. A method for performing handover coordination between base
stations, comprising: receiving, at a base station, a first serving
cell signal measurement and a first neighbor cell signal
measurement from a particular user equipment (UE); sending an
adjustment message, from the base station to the UE, containing a
cell-specific offset of the serving cell and a cell-specific offset
of the neighbor cell in a reporting threshold based on at least one
handover adjustment factor received from a coordinating node;
receiving, at the base station and subsequent to adjusting the
cell-specific offsets, a second serving cell signal measurement and
a second neighbor cell signal measurement; deciding whether to
trigger a handover event based on the first and the second serving
cell signal measurement and the first and the second neighbor cell
signal measurement and the cell-specific offsets; enabling, at a
coordinating node, receipt of measurement reports from the UE;
resolving, at the coordinating node, an E-UTRAN cell global
identifier (ECGI) of the neighbor cell based on information
received from the UE; and updating, at the coordinating node, an
automatic neighbor relations (ANR) table based on the information
received from the UE, thereby enabling handout of the UE from the
base station managed by the coordinating node to the neighbor cell
not managed by the coordinating node.
2. The method of claim 1, further comprising receiving the second
serving cell signal measurement and the second neighbor cell signal
measurement from the particular user equipment, and, handing over
the particular user equipment to a neighboring base station.
3. The method of claim 1, wherein the base station is an in-vehicle
base station, and the in-vehicle base station is configured to
allow user equipments to connect to the in-vehicle base station
while the in-vehicle base station is stationary, in motion, or as
configured by an operator.
4. The method of claim 26, further comprising allocating, at a
coordinating node, a unique PCI to the in-vehicle base station when
the in-vehicle base station is stopped, and associating the unique
PCI with a GPS location.
5. The method of claim 1, further comprising requesting, from the
base station to the UE, ECGI of the neighbor cell, and resolving,
at the base station, ECGI of the neighbor cell based on the
received ECGI information from the UE.
6. The method of claim 1, further comprising translating, at the
coordinating node, a first handover message from a first protocol
to a second protocol and a second handover message from the second
protocol to the first protocol.
7. The method of claim 1, wherein the handover adjustment factor is
calculated based on a prior user equipment handover.
8. The method of claim 1, wherein the coordinating node is a
gateway situated between the small cell and a cellular operator
core network node.
9. The method of claim 1, wherein the base station is a macro cell,
and wherein the cell-specific offsets are adjusted to decrease
handovers away from the macro cell, thereby causing user equipments
to tend to remain attached to the macro cell instead of being
handed over to a small cell and being handed back to the macro
cell.
10. The method of claim 1, wherein the base station is a macro
cell, and wherein the cell-specific offsets are adjusted to
increase handovers away from the macro cell and toward the small
cell.
11. The method of claim 1, wherein the base station is a small
cell, and wherein the cell-specific offsets are adjusted to
decrease handovers away from the small cell and toward the macro
cell.
12. The method of claim 1, wherein the base station is a small
cell, and wherein the cell-specific offsets are adjusted to
increase handovers away from the small cell and toward the macro
cell.
13. The method of claim 1, further comprising adjusting the
cell-specific offset of the serving cell and the cell-specific
offset of the neighbor cell subsequent to a prior handover and
based on the at least one handover adjustment factor.
14. The method of claim 1, the handover adjustment factors further
comprising inter-layer adjustment factors.
15. The method of claim 1, the handover adjustment factors further
comprising inter-radio access technology (inter-RAT) handover
adjustment factors, for handing over from LTE to 3G or to another
RAT.
16. The method of claim 1, further comprising reporting of load and
topology to the coordinating node.
17. The method of claim 1, further comprising reporting of load and
topology within a cluster of small cells to each small cell in the
cluster, and from at least one cell in the cluster to the
coordinating node.
18. The method of claim 1, further comprising using an X2 overload
indicator to communicate load.
19. The method of claim 1, further comprising performing
coordination between macro and small cells for sharing topology
information and load distribution information between the macro and
small cells.
20. The method of claim 1, further comprising centralizing radio
resource management (RRM) functionality at a macro cell layer to
coordinate inter-layer mobility and determine a target cell for
handover using UE measurement reports.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/028,069, filed Jul. 5, 2018, which is a continuation-in-part
of, and claims priority under 35 U.S.C. .sctn. 120 to, U.S. patent
application Ser. No. 15/810,003, entitled "Hand-In With Topology
Hiding" and filed Nov. 10, 2017, which itself is a non-provisional
conversion of, and claims priority under 35 U.S.C. .sctn. 119(e)
to, U.S. Provisional App. No. 62/420,099, filed Nov. 10, 2016, each
of which is also hereby incorporated by reference in its entirety.
The present application hereby incorporates by reference U.S. Pat.
App. Pub. Nos. US20110044285, US20140241316; WO Pat. App. Pub. No.
WO2013145592A1; EP Pat. App. Pub. No. EP2773151A1; U.S. Pat. No.
8,879,416, "Heterogeneous Mesh Network and Multi-RAT Node Used
Therein," filed May 8, 2013; U.S. Pat. No. 8,867,418, "Methods of
Incorporating an Ad Hoc Cellular Network Into a Fixed Cellular
Network," filed Feb. 18, 2014; U.S. patent application Ser. No.
14/777,246, "Methods of Enabling Base Station Functionality in a
User Equipment," filed Sep. 15, 2016; U.S. patent application Ser.
No. 14/289,821, "Method of Connecting Security Gateway to Mesh
Network," filed May 29, 2014; U.S. patent application Ser. No.
14/642,544, "Federated X2 Gateway," filed Mar. 9, 2015; U.S. patent
application Ser. No. 14/711,293, "Multi-Egress Backhaul," filed May
13, 2015; U.S. Pat. App. No. 62/375,341, "S2 Proxy for
Multi-Architecture Virtualization," filed Aug. 15, 2016; U.S.
patent application Ser. No. 15/132,229, "MaxMesh: Mesh Backhaul
Routing," filed Apr. 18, 2016, each in its entirety for all
purposes, having attorney docket numbers PWS-71700US01, 71710US01,
71717US01, 71721US01, 71756US01, 71762US01, 71819US00, and
71820US01, respectively. This application also hereby incorporates
by reference in their entirety each of the following U.S. Pat.
applications or Pat. App. Publications: US20150098387A1
(PWS-71731US01); US20170055186A1 (PWS-71815US01); US20170273134A1
(PWS-71850US01); US20170272330A1 (PWS-71850US02); and Ser. No.
15/713,584 (PWS-71850US03).
BACKGROUND
[0002] Small cell base stations are base stations that have less
transmit power and range than a macro base station, which typically
provides approximately 40 watts of transmit power or more. Small
cells are typically part of a heterogeneous network (HetNet). It is
understood that the embodiments described below pertain to Long
Term Evolution (LTE) networks and technologies, but not to the
exclusion of 3G, UMTS and/or other networks and technologies.
SUMMARY
[0003] Systems and methods for performing handover coordination
between base stations are disclosed. In a first embodiment, a
method is disclosed, comprising: receiving, at a base station, a
first serving cell signal measurement and a first neighbor cell
signal measurement from a particular user equipment (UE); sending
an adjustment message, from the base station to the UE, containing
a cell-specific offset of the serving cell and a cell-specific
offset of the neighbor cell in a reporting threshold based on at
least one handover adjustment factor received from a coordinating
node; receiving, at the base station and subsequent to adjusting
the cell-specific offsets, a second serving cell signal measurement
and a second neighbor cell signal measurement; and deciding whether
to trigger a handover event based on the first and the second
serving cell signal measurement and the first and the second
neighbor cell signal measurement and the cell-specific offsets.
[0004] The method may further comprise receiving the second serving
cell signal measurement and the second neighbor cell signal
measurement from the particular user equipment, and, handing over
the particular user equipment to a neighboring base station. The
base station may be a small cell, and the method may further
comprise coordinating with a macro cell. The handover adjustment
factor may be calculated based on a prior user equipment handover.
The coordinating node may be a macro cell. The coordinating node
may be a gateway situated between the small cell and a cellular
operator core network node.
[0005] The method may further comprise receiving the at least one
handover adjustment factor as a value from a coordinating node. The
method may further comprise using cached measurement report data
and not requesting updated measurement reports from user
equipments.
[0006] The base station may be a macro cell, and the cell-specific
offsets may be adjusted to decrease handovers away from the macro
cell, thereby causing user equipments to tend to remain attached to
the macro cell instead of being handed over to a small cell and
being handed back to the macro cell. The base station may be a
macro cell, and the cell-specific offsets may be adjusted to
increase handovers away from the macro cell and toward the small
cell. The base station may be a small cell, and the cell-specific
offsets may be adjusted to decrease handovers away from the small
cell and toward the macro cell. The base station may be a small
cell, and the cell-specific offsets may be adjusted to increase
handovers away from the small cell and toward the macro cell.
[0007] The method may further comprise adjusting the cell-specific
offset of the serving cell and the cell-specific offset of the
neighbor cell subsequent to a prior handover and based on the at
least one handover adjustment factor. The method may further
comprise adjusting the cell-specific offset of the serving cell and
the cell-specific offset of the neighbor cell on a per-UE basis
based on a velocity of the particular UE.
[0008] The handover adjustment factors may further comprise an
overload condition of a macro overlay layer, overload condition of
one or more small cells, location of the particular UE, and type of
data usage by the particular UE. The handover adjustment factors
may further comprise available modulations and in-use modulations
at the serving cell and the neighbor cell, and available power
levels at the serving cell and the neighbor cell, and the handover
adjustment factors may further comprise inter-layer adjustment
factors. The handover adjustment factors may further comprise load
and scheduling status of frequencies at the serving cell and at the
neighbor cell. The handover adjustment factors may further comprise
inter-radio access technology (inter-RAT) handover adjustment
factors, for handing over from LTE to 3G or to another RAT.
[0009] The method may further comprise reporting of load and
topology to the coordinating node. The method may further comprise
reporting of load and topology within a cluster of small cells to
each small cell in the cluster, and from at least one cell in the
cluster to the coordinating node. The coordinating node may be the
macro cell. Load may be calculated based on one or more of user
count, data throughput, processor load, memory load, and radio
resource utilization.
[0010] The method may further comprise using an X2 overload
indicator to communicate load. The method may further comprise
performing coordination between macro and small cells for sharing
topology information and load distribution information between the
macro and small cells. The method may further comprise centralizing
radio resource management (RRM) functionality at a macro cell layer
to coordinate inter-layer mobility and determine a target cell for
handover using UE measurement reports.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram showing a macro and small cell
deployment scenario with handover, in accordance with some
embodiments.
[0012] FIG. 2 is a signal quality diagram of a handover scenario
from a serving cell to a neighbor cell, in accordance with some
embodiments.
[0013] FIG. 3 is a signal quality diagram of a second handover
scenario from a serving cell to a neighbor cell, in accordance with
some embodiments.
[0014] FIG. 4 is a call flow showing a first intra-frequency
multi-layer handover procedure, in accordance with some
embodiments.
[0015] FIG. 5 is a call flow showing a second intra-frequency
multi-layer handover procedure, in accordance with some
embodiments.
[0016] FIG. 6 is a call flow showing a first handover procedure
using reported load conditions, in accordance with some
embodiments.
[0017] FIG. 7 is a call flow showing a second handover procedure
using reported load conditions, in accordance with some
embodiments.
[0018] FIG. 8 is a call flow showing a network overload policy
being applied to a user equipment, in accordance with some
embodiments.
[0019] FIG. 9 is a schematic diagram showing distance calculation
with power management, in accordance with some embodiments.
[0020] FIG. 10 is a schematic diagram showing load balancing, in
accordance with some embodiments.
[0021] FIG. 11 is a flowchart showing dynamic handover adjustment,
in accordance with some embodiments.
[0022] FIG. 12 is a schematic diagram showing PCI allocation, in
accordance with some embodiments.
[0023] FIG. 13 is a schematic diagram of a virtualization server in
a Long Term Evolution (LTE) architecture, in accordance with some
embodiments.
[0024] FIG. 14 is a schematic diagram of a mesh network base
station, in accordance with some embodiments.
DETAILED DESCRIPTION
[0025] Small cells may be deployed in conjunction with macro cells.
Such a deployment may be referred to as a multi-layer deployment,
with the macro cell understood to be laid over the micro cell.
Various deployment scenarios exist, as shown in the attached FIG.
1. For example, multiple small cells may be overlapping within the
coverage area of a single macro (overlapping underlay), or multiple
small cells may not be overlapping within the coverage area of a
single macro (non-overlapping underlay), or multiple
non-overlapping macros may be deployed in conjunction with
overlapping micro cells (coverage augmentation with overlapping
underlay), or multiple overlapping macros may be deployed in
conjunction with overlapping micro cells (overlapping overlay with
overlapping underlay). Other deployment scenarios exist. It is
understood that the systems and methods described herein may be for
one deployment, or for more than one deployment, or may be extended
to work with more than one deployment.
[0026] In a first embodiment, a small cell and/or a core network
are enabled to have a policy for user equipments (UEs) camping on
base stations, otherwise known as a camping policy. Camping may
involve cell selection or re-selection, and may involve idle
mobility or connected mobility (for handovers and redirections).
Management of mobility may be based on one or more of: network
overload conditions/thresholds; current/typical traffic patterns or
services used of the UE; UE speed, location, or movement pattern;
UE measurements; and UE capability and access restrictions.
[0027] In some cases, the UE shall be caused to remain camped on
the macro cell instead of handing over to a micro cell or small
cell. For example, this may be useful in a macro coverage/small
cell underlay situation. This has the advantages that a number of
handovers will be reduced, as the macro has greater footprint area,
better signal quality, and handovers shall only occur in cases that
the micro or small cell has better coverage and quality (SINR).
However, the disadvantages include the difficulty of cell ID reuse,
and the difficulty of causing a UE to hand over to a micro or small
cell with potentially worse signal. As well, this may not provide
good coverage if the UE is moving quickly.
[0028] In some cases, the UE shall be caused to camp on the micro
or small cell, which lacks the disadvantages of the prior approach,
but will involve a higher number of potential overload conditions
and hence a higher number of handovers.
[0029] Why Camping strategy is important: Handovers in connected
mode shall be avoided as much as possible; Potential call/session
drop; Increases signaling and data traffic due to the big number of
small cells; and Increase backhaul usage. Camping allows to predict
and minimize potential layer overload conditions. At least two
clear camping strategies exist: Camping on Micro and Camping on
Macro.
[0030] Camping on Macro: Pros--Minimized number of handovers (once
UE in connected mode) Handovers performed only in case of the
potential overload conditions Handovers performed based on the
measurements in case of the coverage problems Cons--In case of
handover, handover will be performed from Macro to Micro Potential
problem with Cell Ids. Due to the big number of the small cells
sell id will be reused and this would require "non" standard
handover method (see handover section) Normal handover measurement
mechanisms will not work a s Macro may have stronger signal. Would
require some "non" standard handover method (see handover section)
UE speed shall be taken into account.
[0031] Camping on Micro: Cons--High number of handovers (once UE in
connected mode) Potential Overload Conditions will be reached fast
and hence number of handovers will be high Pros--Standard handover
mechanism. Measurement based handover is not required--blind
handover potentially will have very high success rate No UE speed
shall be taken into account.
[0032] In some cases camping shall be assigned based on the
following strategies, as shown in Table 1, below.
TABLE-US-00001 TABLE 1 Overload Overload UE Camp Camp Of Macro of
Micro Speed on Macro on Micro X High X Mobility X Medium X Mobility
X Low X Mobility X High X Mobility X Medium X Mobility X Low X
Mobility
[0033] In cases of network overload, once UE in idle mode gets
close to a small cell and can receive SIB messages, the UE may be
forced to select a small cell using measurements (thresholds sent
with SIB1) and cell reselection (using priority information
provided in SIB3). If the small cell becomes overloaded
subsequently, an SIB1 with a Cell Barred indication may be
sent.
[0034] Regarding UE speed, if a UE is moving at a speed higher than
a threshold X, which may be calculated based on coverage areas, it
may be prohibited from selecting or reselecting micro cells. A
reselection time T{reselection} may be set that may be combined
with the High, Medium, and Low mobility factors defined in 3GPP TS
36.304. T{reselection} may be long enough for a UE to not be able
to select the small cell when the UE transits the small cell at
high speed. The parameter may be sent to the UE using an SIB3
message. Under normal conditions high speed and medium speed users
shall not enter any small cell in a small cell layer, but in a
configuration where coverage augmentation with overlapping underlay
is provided, small cell selection may be required. In such cases
the small cells may have knowledge of their macro neighbor
coverage. Measurement reports from the UEs camping on each small
cell can be used to estimate macro Coverage and overlapping zone.
As an alternative, exchange of such information may be enabled
using proprietary extensions over the X2 protocol.
[0035] UE speed policy for camping. In some embodiments, UE moving
with the speed >X (X shall be automatically calculated based on
the small cell coverage radios) shall not select or reselect Micro
Cells. 3GPP TS 36.304 defines High, Medium and Low Mobility states.
3GPP TS 36.331 defines TreselectionEUTRA parameter which shall be
combined with the High, Medium and Low mobility factor.
TreselectionEUTRA shall be long enough for the UE moving with the
high speed, passing through the Micro Cell coverage not be able to
select the Micro Cell. This parameter is transmitted with SIB3
message. Under normal conditions high speed and medium speed users
shall not enter the Micro Layer, but in configuration "Coverage
augmentation with overlapping underlay" presented on slide one
Micro Selection may be required. To have fully automated Camping
policy based on Speed, Micro eNodeBs shall have a knowledge of the
Macro neighbor coverage. Measurement report from the UEs camping on
Micro can be used to estimate the Macro Coverage. As alternative
exchange of the proprietary extensions over the X2 shall be
implemented.
[0036] In a second embodiment, a handover policy appropriate for
small cells is described. Connected mobility may require
coordination between the macro and micro layers, based on various
factors. For example, factors such as overload conditions of macro
and micro layers, the location of a UE to be used for hand-ins, the
type of application and/or data being used may be assessed in the
course of providing connected mobility. More specifically, when a
neighbor cell becomes better than a serving cell, as determined on
the basis of RSRQ/RSRP, a time delay may be in place around the
time at which the trend is identified and the time at which the
trigger is activated to cause the handover. The time delay may be
biased based on various factors, such as layer overload conditions,
UE speed, type of data being transferred, and/or other factors, and
the Ocn, Ocs, and hysteresis parameters may be made changeable to
allow this time delay to be changed dynamically. More specifically,
a micro cell may detect an internal overload, may send an
RRCConnectionReconfiguration request to the UE to hand the UE over
to the macro cell, and in the same message cause the Ocn, Ocs,
and/or hysteresis parameters to be changed on the UE. The same
overload-driven dynamic parameter-biased handover could take place
between a macro cell and a micro cell.
[0037] In some embodiments, a macro layer may have an algorithm
that performs a look-ahead handover. Specifically, the macro may
perform a handover based on topology and load distribution
knowledge of the micro layer. In some embodiments the macro may
cause a handover using these criteria and/or processing performed
at a cloud coordination server. The cloud coordination server may
be located between the collection of micro cells and the macro
layer, in some embodiments. The cloud coordination server may
interact with both the macro and the micro layers to leverage SON,
MRO, ANR, and ICIC features in both macro and micro layers. The
coordination server may coordinate inter-layer mobility.
[0038] In some embodiments, a trigger may be used. A small cell
base station, Cell A, may have a region within a first region
centered around the center of Cell A, within which its transmit
signal is received at -90 dBm. A trigger A2 may be set at -90 dBm,
demarcating a first trigger region. If a UE reports poor coverage
but is within this trigger region, transmit power can be increased
to make a UE stay within the cell. Alternately, this trigger A2/A4
may be used for load sharing, such that when UEs are predicted to
have bad coverage and greater than threshold coverage from
neighbor, UEs that are within this trigger region can be offloaded
forcefully to neighbor cells.
[0039] A second trigger region may be set at -100 to -108 dBm,
trigger A3, to enable normal handover based on UE speed and
clutter. A third trigger region may be set at -110 dBm, drag
further, when the target is already, we can keep UEs on their
source cells for a longer time to delay handover and the resultant
increased load on the target cell. Trigger release may also be
performed with re-direct to the second best RF/IRAT/Inter Frequency
neighbor in case of highly loaded primary neighbor neighbors or
dragging for Ping-Pong oscillating UEs.
[0040] In some embodiments, potential PCI confusion is alleviated.
Due to the typical cell size of Micro eNodeBs being much smaller
than macro cells, there can be multiple eNodeBs within the coverage
of the Macro eNodeB that have the same PCI. This may lead to PCI
confusion, wherein the source eNodeB is unable to determine the
correct target cell for handover from the PCI included in the
measurement reports from the UE. In some cases, a measurement
report may be requested from the UE to clarify the PCI, by, for
example, causing the UE to report an ECGI.
[0041] For an UE located away from or not camped on micro cells,
there is no need to perform measurements and no need to receive SIB
messages. In the case that the micro network is overloaded, there
is no need for the UE to perform measurements or acquire system
information of the micro cells. In the case that multiple
destination micro eNodeBs may have more or less the same signal
quality, the handover decision may be made based on overload
conditions and additional matrix (for example number of number of
UEs with specific data traffic).
[0042] In some embodiments, a smart handover algorithm may be
provided that determines whether handover should be performed based
either on (1) load or (2) coverage trigger. For load-based
handover, the handover source cell may assess what cell has better
resources, may distinguish based on type of traffic/application,
and may incorporate historical peak hour patterns into a
determination of which cell the handover should target. Different
parameter profiles may be created for different traffic patterns,
and the profiles may be tuned. For example, a profile for a cell
covering a highway should be tuned to cause users to be handed over
immediately, to cause A3 to be less so that the trigger will
trigger more quickly, reducing hysteresis and offset, reducing
number of minimum reports, reducing time to trigger, etc.
[0043] A distance and/or a location of the UE may be deduced from
timing advances and SRS. The location of the UE may also be
determined by adjusting transmit power, identifying which UEs are
near the cell edge, and providing that information back to a SON
module to further adjust coverage and/or transmit power. Dynamic
transmit power may also be used to offload traffic by changing cell
footprint. Idle users may also be offloaded forcibly to less-loaded
cells by changing offsets.
[0044] For coverage-triggered handovers, in addition to the radio
frequency environment (e.g., clutter) and UE speed, one significant
problem is ping-pong, or oscillating, handovers. This problem
occurs when a UE is handed over back and forth between the same two
cells. When performing a handover, to reduce ping-pong situations,
the target base station may consider the last handover time and the
last served PCI for the incoming UE, and if the handover from the
same PCI was less than a given number of seconds prior (e.g., 2
seconds), and/or a number of handovers from the same PCI has
exceeded a threshold, the target base station may change the cell
individual offset parameter, delay handover reporting, may delay
execution of handover for this UE by a given number of
milliseconds, or perform other steps to reduce the likelihood that
the handover will successfully complete.
[0045] In a third embodiment, a method for allocating physical cell
identifiers (PCIs) is described. A centralized entity or
coordinating node, which may be a Parallel Wireless LTE access
controller (LAC), may prepare an active set of neighbor sites. The
active set may have all neighboring PCIs, including indoor, macro,
neighbor of macro, small cell base stations, including those under
and not under the management of the centralized entity, CSGs, etc.
Based on the active set, PCIs may be allocated, either at the
centralized entity or elsewhere. In some embodiments, the active
set may include, or allocation of PCIs may incorporate, multiple
inputs, such as GPS coordinates, neighbor lists of some or all
transmitters around a base station, UE measurements, handover
statistics (weighting, rate of success, etc.), and overshooting
cells or cells that may be visible to more than one small cell/base
station. Overshooting cells, also called boomer cells, may cause
PCI allocation confusion as they are visible from more than one
base station. Timing advance commands and GPS coordinates may be
used to perform PCI allocation to avoid the re-use of a PCI used by
a boomer cell.
[0046] As another example of the third embodiment, given a dense
environment in which only a small number of PCIs are available for
allocation, and a single frequency band of 2.3 GHz is intended for
use for a dense heterogeneous network of 5.times.5 kilometers
square, supporting several thousand small cells, some indoor and
some outdoor, with interference among the cells, the PCI allocation
environment is complex. To help allocate PCIs effectively, clusters
may be identified based on handover patterns (weightage/attempts),
UE measurements such as indoor leakage, distance from the small
cells to the macro cell (or from each other), GPS coordinates,
closed subscriber group, X2 neighbor communications, and
outdoor/indoor characteristics. Each cluster may be assigned
individual PCIs and neighbor lists, which can be an active set or a
cluster's neighbor list. All cells in a configurable radius may
have all the PCIs as dummy neighbors, to ensure that the same PCI
is not allocated. For cells further away than distance D, or
(number of allocable PCIs) mod 3/6/30, whichever is greater, PCI
duplication may occur. In some embodiments, boomer cells may be
identified by timing advance counters and/or excluded.
[0047] In a fourth embodiment, systems and methods for a sniffing
mode base station are described. In some embodiments, a base
station may remain in a sleep mode instead of a broadcasting mode.
When a given number of UEs approach the small cell base station
(HO/MOS), the base station may become active. When the macro cell
or when a neighboring base station becomes loaded, the base station
may also become active. Transmit power may also be adjusted such
that the base station's transmit power is low instead of or during
sleep mode.
[0048] In a fifth embodiment, systems and methods for small cell
discovery are described. If small cells is under overlay of a macro
cell, due to signal imbalance, even if radio conditions are good
for connecting to the small cell, due to the macro cell the SINR is
degraded. To solve this issue, higher search thresholds may be
configured for the macro cell, specifically, QRexmin level, to
cause a UE to remain with the small cell even if the UE also has
macro coverage.
[0049] In a sixth embodiment, systems and methods for paging load
optimization are described. In some embodiments, it may not be a
good idea for a small cell to handle paging when overlaid by a
macro due to its lesser processing power, capabilities and backhaul
capacity. In order to limit the paging area of a small cell to a
geographical area covered by one macro cell, all small cells can
use the cell identity of their strongest neighboring macro cell to
decide on their initial paging area code. Idle UEs may be offloaded
to macro cells by adjusting reselection parameters. Configuration
of tracking area codes of small cells to be the same as tracking
area codes of neighboring cells to avoid multiple tracking area
updates (TAUs) may also be performed.
[0050] In a seventh embodiment, systems and methods for a dynamic
neighbor list based on search zones suitable for a mobile vehicle
are described. One-way neighbor addition may also be enabled. In
some embodiments, a base station, such as an eNodeB, may be fitted
in a moving bus. As the bus moves along the route, it moves closer
to and further from other base stations, which may be macro base
stations. To provide service to users on the bus. Reference
transmit power may be dynamically controlled so that cell area is
confined to the bus only and does not include area outside the bus,
so as not to cause service disruptions for users outside the bus,
such as people standing outside the bus or people within another
nearby bus located at a bus depot.
[0051] As the bus moves, the base station may be configured with a
neighbor table at geographic intervals of approximately 100 to 300
meters, or another distance, as appropriate. The bus location and
distance may be determined by GPS or another means. The neighbor
table may be created on the bus or at a centralized node, such as
in a self-organizing network (SON) module, in some embodiments. The
base station installed in the bus may report neighbor cells, their
PCIs, neighbor cells' RSRPs reported by UEs, and neighbor cells'
RSRQs reported by UEs, and may report this information to a
centralized node, in some embodiments.
[0052] In some embodiments, LTE UEs may be solicited to collect, or
may be passively subject to collection from, serving cell RSRP,
and/or tracking area, pathless, cell center and cell edge status.
In some embodiments, LTE UEs may also be subject to collection of
information regarding handovers, including information about the
location of handovers, and PCIs of handover target cells.
[0053] In some embodiments, the SON module in the centralized node
may maintain a history of several days' worth, such that SON will
attempt to determine the appropriate PCI given any PCI request
situation, including PCI conflict or PCI confusion situations. The
SON may continue to refine its results based on GPS measurements.
UE GPS measurements and/or base station GPS measurements may also
be tracked by the SON module, in some embodiments. The method thus
described could be used as appropriate on any other type of moving
vehicle, such as a car, plane, boat, train, airship, balloon, or
other conveyance.
[0054] In an eighth embodiment, automatic neighbor relations
methods and procedures are described. One or more of Retainability
issues, high drop rate, and handover failure may be used as
triggers. A method may be performed that involves: storing a
current neighbor list for reverting at a later time; scanning a
neighbor list; adding potential neighbors; scanning neighbors at a
particular distance, the search ring radius for Omni antennas and
search sector area for directional antenna can be function of
number of inputs: can be user defined or based on an RF planning
propagation model (via manual or RF tools) or input can be farthest
neighbor distance (with Handover success rate greater than
threshold e.g. 95%) added to user defined, clutter based search
criteria (additional distance), removing overshooting neighbors
and, in some embodiments, blacklisting them for the next 24 hours
or another configurable time period; removing neighbors with less
than Y % handover success rate and, in some embodiments,
blacklisting them for the next 24 hours or another configurable
time period; creating a neighbor table using the remaining
neighbors. If one or more measured key performance indicators does
not improve, the configuration may be reverted to the prior
neighbor list.
[0055] In a ninth embodiment, the use of various key performance
indicators (KPIs) is described for improvement of performance of a
network. KPIs are obtained, and stored over time. The KPIs may be
stored over a configurable period of time, which may be 24 hours. A
user or machine process may look back into the KPIs for trends.
Once trends are identified, the parameters may be adjusted and
changes may be made in the network. The changes may be requested,
in some embodiments, with an acceptance step provided subsequently,
in some embodiments. The changes may be performed for a subset of
the network, in some embodiments. If the changes are identified to
provide improved performance, the changes may be accepted. If the
changes are identified to degrade performance, the changes may be
reverted and/or rejected, and/or the initial configuration may be
restored. In some embodiments, restoration to an initial
configuration may be performed automatically after a time period
for certain applications, such as congestion control and load
sharing, and/or other applications which change over time but are
desired to be reset.
[0056] Systems and methods are disclosed for providing enhanced
performance for networks incorporating "small cell" base stations.
Small cell base stations are base stations that have less transmit
power and range than a macro base station, which typically provides
approximately 40 watts of transmit power or more. Small cells are
typically part of a heterogeneous network (HetNet). It is
understood that the embodiments described below pertain to Long
Term Evolution (LTE) networks and technologies, but not to the
exclusion of 3G, UMTS and/or other networks and technologies.
[0057] Small cells may be deployed in conjunction with macro cells.
Such a deployment may be referred to as a multi-layer deployment,
with the macro cell understood to be laid over the micro cell.
Various deployment scenarios exist, as shown in the attached FIG.
1. For example, multiple small cells may be overlapping within the
coverage area of a single macro (overlapping underlay), or multiple
small cells may not be overlapping within the coverage area of a
single macro (non-overlapping underlay), or multiple
non-overlapping macros may be deployed in conjunction with
overlapping micro cells (coverage augmentation with overlapping
underlay), or multiple overlapping macros may be deployed in
conjunction with overlapping micro cells (overlapping overlay with
overlapping underlay). Other deployment scenarios exist. It is
understood that the systems and methods described herein may be for
one deployment, or for more than one deployment, or may be extended
to work with more than one deployment.
[0058] In some embodiments, due to the typical cell size of Micro
eNodeBs being much smaller than macro cells, there can be multiple
eNodeBs within the coverage of the Macro eNodeB that have the same
PCI. This may lead to PCI confusion, wherein the source eNodeB is
unable to determine the correct target cell for handover from the
PCI included in the measurement reports from the UE. In some cases,
a measurement report may be requested from the UE to clarify the
PCI, by, for example, causing the UE to report an ECGI.
[0059] In some embodiments, when a PCI conflict is detected, a
handover request may be forked. Specifically, the handover request
may be sent from the source cell to all cells known to the source
cell that have that PCI. Two or more handover requests, then, may
be created. However, only one handover request will ultimately be
met/satisfied, because the receiving cell will determine either
that the cell does contain the UE identified in the request and
return a handover acknowledgement message, or that the cell does
not contain the UE identified in the request and will fail and/or
not return a handover acknowledgement message. The handover request
may be sent either via X2 or S1, in some embodiments.
[0060] The challenges include extensive coordination between macro
and micro layers. Coordination could be using X2 messages or other
messages, in some embodiments. The coordination could involve
handover adjustment factors, such as: overload conditions of cells;
location, position, velocity, direction of a UE (especially
important for handling hand-ins to the micro cell layer); type of
data and application usage; and other factors. Scheduler data could
also be exchanged, and ideally knowledge and interlayer influence
could be exerted on the adopted modulation and power control
parameters.
[0061] A "Look ahead handover" method is disclosed, which may be
situated at a macro cell layer. This method could use one or more
of the following information: partial or full topology and load
distribution knowledge of the Micro Layer by Macro; partial or full
Micro Layer topology and load distribution of the Micro Layer by
each Micro in a Micro Cluster, etc. In some cases, Micro/Macro RRM
could be centralized (or at least the subset of the RRM
functionality) in order to be able to coordinate inter layer
mobility, either at the macro or at another location. The macro and
micro layers could interact with SON, MRO, ANR, ICIC
communications, and with the "Look ahead handover" algorithm as
well, as follows.
[0062] Handover from Macro Layer to Micro Layer is different from
normal handover procedure in two aspects: Firstly, potential PCI
confusion. Due to the typical cell size of Micro eNodeBs being much
smaller than macro cells, there can be multiple eNodeBs within the
coverage of the Macro eNodeB that have the same PCI. This may lead
to PCI confusion, wherein the source eNodeB is unable to determine
the correct target cell for handover from the PCI included in the
measurement reports from the UE. Secondly, battery life of UEs is a
concern. Measurements performed by UE drain the battery. For UE
been away from the Micro Cells, there is no need to perform
measurements and no need to receive SIB messages. In case of the
Micro network overloaded, there is no need for UE to perform
measurements or acquire system information of the Micro Cell
eNodeBs. Multiple Destination Micro eNodeBs may more or less same
signal quality. The handover decision shall be made based on the
overload conditions and additional matrix (for example number of
number of UE with specific data traffic, etc.).
[0063] In a smart handover, the handover selection algorithm could
be activated or triggered based on load.
[0064] Issues could include: a need to choose the cell with better
resources. The algorithm could distinguish between types of
traffic, application, peak hour patterns. The solution may be one
or more of the following: creating Different parameters profiles
for different traffic patterns; optimizing parameters such that
Handover is smooth, or dynamically changing TX power to offload
traffic by changing cell foot print. Idle users can be forcefully
offloaded to less loaded cells by changing offsets.
[0065] The handover selection algorithm could also be activated by
coverage information. Issues that could arise include Ping Pongs
(Oscillations), frequent HOs, Clutter type Highway etc., UE speeds.
The solutions could be as described hereinbelow. Alternately, one
more possibility could be A2 prior to A3 reporting.
[0066] FIG. 1 is a schematic diagram showing a macro and small cell
deployment scenario with handover, in accordance with some
embodiments. User equipment (UE) 101 is passing through a region
where there are many base stations providing wireless access,
perhaps using a Long Term Evolution (LTE) radio access technology
(RAT). A macro base station provides umbrella coverage to a large
geographic area, shown here as macro layer 102. Small cells 103,
104, 105, 106, 107 each provide coverage over a smaller geographic
area. Small cells 104, 106 are overloaded. In operation, UE 101
would ideally remain within cellular coverage; in order to do so it
could remain attached to macro 102, or it could be handed over from
macro 102 to small cell 103, and then to small cell 104 and so on
in sequence. However, as shown, since small cell 104 is overloaded,
UE 101 cannot effectively be handed over from small cell 103 to
small cell 104, shown as handover path 112, and typically the UE
would be handed over back to macro 102, shown as handover path
111.
[0067] However, in accordance with some embodiments of the present
disclosure, it is possible to adjust handover characteristics of
one or more base stations in the path of the UE to effective
provide "look ahead handover," that is, using information about
potential future handovers to improve handover characteristics. In
the present exemplary scenario, UE 101 should not be handed over
from macro layer 102 to small cell 103 at all. This is accomplished
as follows.
[0068] In operation, macro base station 102, which is the serving
base station, is made aware of the likelihood that UE 101 will soon
be handed over to small cell 103, in some cases using the direction
and velocity of UE 101. Logic at macro 102 is programmed to be
aware that a UE showing the characteristics of UE 101 will quickly
be handed over to small cell 104. Macro 102 is also aware that
small cell 104 is in an overload state, such as by receiving an X2
message from small cell 104, or such as receiving a message from a
coordinating gateway of small cell 104 (not shown) regarding the
status of small cell 104. Macro 102 thus performs an adjustment to
delay or reduce the likelihood of a handover to small cell 103,
thus preventing handover to small cells 103 and 104. The adjustment
will be described in connection with FIGS. 2 and 3.
[0069] FIG. 2 is a signal quality diagram of a handover scenario
from a serving cell to a neighbor cell, in accordance with some
embodiments. FIG. 2 depicts a modified version of Event A3
(neighbor becomes better than serving cell by an offset) as
described in 3GPP TS 36.331, hereby incorporated by reference in
its entirety, specifically with reference to Rel. 10, version 19,
section 5.5.4.4. The UE uses the two inequalities 3-1 and 3-2 to
determine when to send measurement reports, which result in the
base station directing handover, as follows.
Mn+Ofn+Ocn-Hys>Mp+Ofp+Ocp+Off Inequality A3-1 (Entering
condition):
Mn+Ofn+Ocn+Hys<Mp+Ofp+Ocp+Off Inequality A3-2 (Leaving
condition):
[0070] where Mn is a signal measurement result of the new
neighboring cell, Ofn is a frequency-specific offset for the
neighbor cell, Ocn is a cell-specific offset of the neighboring
cell, Ofp and Ocp are corresponding frequency-specific and
cell-specific offsets for the serving cell (Primary Cell), Hys is a
hysteresis value, and Off is an offset value, as described in 3GPP
TS 36.331.
[0071] When Inequality A3-1 is crossed, the UE enters a temporary
state; this state is exited when Inequality A3-2 is crossed or when
Inequality A3-1 no longer holds true. In the prior art, this is
when the neighbor cell is significantly better by the sum of the
three offsets than the primary cell. However, the serving base
station is able to send these offsets to an attached UE. The
serving base station may thus calculate separate offsets on a
per-cell, per-UE basis, and can send these offsets to the UE to
dynamically adjust handovers.
[0072] A plot is shown of signal quality (labeled RSRQ/RSRP but
which could be any equivalent signal quality measure) versus time.
Line 201 is the signal measurement of the serving station. Line 211
is the signal of the neighbor node. Signal 202 is the serving cell
signal combined with the prior art offset value, and signal 203 is
the signal combined with the adjusted offset value, in accordance
with some embodiments. Signal 212 is the neighbor signal combined
with the prior art offset value, and signal 213 is the signal
combined with the adjusted offset value, in accordance with some
embodiments. The offsets depicted here have caused a greater time
to trigger Event A3 222 to be used rather than the ordinary time to
trigger 221, resulting in the base station being more "sticky," and
hanging on for longer to an attached UE. As all the offsets can be
adjusted by the serving base station in conjunction with one or
more coordinating nodes, it is possible that the serving base
station can be more or less likely to hand over, and this may also
be dependent on each individual UE and target cell.
[0073] FIG. 3 is a signal quality diagram of a second handover
scenario from a serving cell to a neighbor cell, in accordance with
some embodiments. Similar to FIG. 2, various measurement reporting
thresholds (A2, serving becomes worse than threshold, and A4,
neighbor becomes better than threshold) are shown. The equations
for A2 and A4 are:
Ms+Hys<Thresh Inequality A2-1 (entering condition):
Ms-Hys>Thresh Inequality A2-2 (leaving condition):
Mn+Ofn+Ocn-Hys>Thresh Inequality A4-1 (entering condition):
Mn+Ofn+Ocn+Hys<Thresh Inequality A4-2 (leaving condition):
[0074] Signal 301 is a signal of the serving cell, and signal 302
is a prior art signal plus hysteresis, and signal 303 is an
enhanced signal plus hysteresis. Signal 311 is a neighbor signal,
and 312 is a prior art signal plus offsets, and 313 is an enhanced
signal plus offsets. Time to trigger 321 (event A2) and 322 (event
A4) are shown according to the prior art. Although the times to
trigger using the enhanced signals are not shown, they would result
in the base station becoming more "sticky" here as in FIG. 2 (by
retarding the time when the events A2 and A4 are triggered). In
some embodiments, one or more of these thresholds and offsets may
be configured according to a need to either increase or decrease
handover likelihood in a particular case.
[0075] FIG. 4 is a call flow showing a first intra-frequency
multi-layer handover procedure, in accordance with some
embodiments. Macro cell A 401 is in a network with micro cell C
402, micro cell B 403, and micro cell A 404. A UE 428 is also
shown. At step 410, the current location of the UE is known based
on initial camping at cell A. At steps 411, 412, and 413, X2 load
conditions are reported, showing that load conditions are normal at
macro cell A and overload is detected at cells B and C, as well as
internal overload being present at cell A in step 414.
[0076] At this stage, a desirable handover is determined at micro
cell A to constitute a handover to macro 401, based on load, and
offsets Ocn and Ocs are calculated accordingly to bias the handover
to hand over to the macro. At step 415, an
RRCConnectionReconfiguration is performed as a prelude to handover,
sending the Ocn and Ocs to the UE, resulting in measurement report
416. At step 417, the handover is requested by cell A, and at step
418, the UE acknowledges the handover, resulting in the UE being
located at the macro at step 421.
[0077] At a later time, the load conditions may improve at cells A,
B, and C. When macro cell A receives normal X2 load condition
reports 419, 420, 423, and when macro cell A detects internal
overload at step 422, the macro can calculate a new set of offsets
and send the offsets to the UE via RRCConnectionReconfiguration
message 424, which is acknowledged 425. The macro cell A sends a
handover request 426, which may be via X2 or S1, which is
acknowledged 427 and the UE is handed over.
[0078] FIG. 5 is a call flow showing a second intra-frequency
multi-layer handover procedure, in accordance with some
embodiments. Macro cell A 501, micro cells A 504, B 504, and C 502,
and UE 529 are shown. In FIG. 5, an overload is detected at micro
cells A, B, and C, and a handover is caused from micro cell A to
macro cell A as in FIG. 4, but in an alternate embodiment the
timeToTrigger parameter in message 515 is changed to bias the
handover. A handover is performed 517 and acknowledged 518 as a
result to macro cell A.
[0079] At a later time, when the micro cells are not overloaded,
macro cell 501 sends an RRConnectionReconfiguration message with a
biased timeToTrigger value and a mobility scaling factor, resulting
in a handover 526 to micro cell A and response 527. The macro cell
A is also able to determine, at step 528 before sending the
handover request, whether the handover should be requested based on
one or more coordination factors. Here, the factors of load, UE
mobility (UE speed), data type, UE distance from macro cell are all
considered before sending the message to hand over.
[0080] FIG. 6 is a call flow showing a first handover procedure
using reported load conditions, in accordance with some
embodiments. In some cases multiple micro cells may share the same
PCI, particularly when they are not visible to each other. Macro
cell A 601, micro cell A 604, micro cell B 603, and micro cell C
602 are shown, together with UE 623, which is presently located at
(attached to) macro cell A at step 610. The micro eNodeBs could be
grouped into the CSG with 27-bit standard identities, in some
embodiments. The destination handover decision at micro cell A is
based on the X2 load conditions and additional matrices retrieved
from micro cells A, B, and C at 612, 613, 614. The handover
decision is performed at step 716. When the UE is queried for a
measurement report at step 717, 718, a PCI conflict is detected at
step 719 at the macro based on the response from the UE. An
additional measurement 620 is requested and at 621 is received,
identifying the CGI or other identifier of the target cell, so that
the handover 622 can be appropriately directed.
[0081] FIG. 7 is a call flow showing a second handover procedure
using reported load conditions, in accordance with some
embodiments. FIG. 7 is similar to FIG. 6 except that instead of
causing the UE to obtain an ECGI identifier to uniquely identify
the target cell, handover forking is used. This results in a single
handover request being sent both to micro cell 802 and 803, which
share the same PCI. Only one of the requests is successful.
[0082] FIG. 8 is a call flow showing a network overload policy
being applied to a user equipment in idle mode, in accordance with
some embodiments. Load balancing in a network can be enabled by
causing a coordinating node, in this instance macro cell A 801, to
receive X2 load indications from micro cells 802, 803, 804 and also
for a UE to receive Cell Barred messages directly from these macro
cells. Once UE in idle mode gets close to Micros and can receive
SIB messages it shall be forced to select Micros using measurements
(thresholds sent with SIB1) and cell resection using priorities
(information provided in SIB3). If Micros become overloaded SIB1
with CellBarred indication shall be sent. Load Balancing can be
achieved from dynamic TX power and RET from Macro.
[0083] FIG. 9 is a schematic diagram showing distance calculation
with power management, in accordance with some embodiments. UE
location for smart algorithm can be deduced from Timing advance and
SRS, in some embodiments. Cells 901, 902 share a coverage region.
Cell 901 has a max cell distance 901a and a coverage region 901b.
Cell 902 also has a max cell distance 902a and a coverage region
902b. However, these cells overlap in such a way that cell 902
should be configured to cover more of the cell edge. Based on UE
measurement reports, and based on tracking signal strength at the
UEs at the cell edge, transmit power SON optimization is performed.
This results in cell 903 and 904, where cell 903 has a smaller cell
area 903b, but stronger signal to all users, including to users in
the cell edge, as cell 904 now has increased its coverage area 904b
to cover the cell edge. Distance can be based on: average of X
numbers of TA values; PHR reports; improved QOS for cell edge
users. Additionally, when distance is available, mobile load
balancing, congestion control may be performed.
[0084] In some embodiments, parameter profiles could be made and
applied to certain handsets. For example, Handover Optimized
Parameters for Highway sites would be such Handover takes place
asap; A3 to be less to triggered quickly; Hysteresis and offset
also to support fast Handover; Less number of Min reporting
required; Time to trigger to be reduced; and H/W sites to have
multiple common PLMNS/TACs.
[0085] FIG. 10 is a schematic diagram showing load balancing, in
accordance with some embodiments. A less loaded neighbor 1001 and a
loaded cell 1002 are shown. When the loaded cell is known to be
loaded, it can coordinate using SON to a coordinating node or to
each other via X2 to cause the transmit power of cell 1003 to go up
and cell 1004 to go down, causing cell edge users to be moved from
the loaded to less loaded cell.
[0086] FIG. 11 is a flowchart showing dynamic handover adjustment,
in accordance with some embodiments. At step 1101, the coordinating
node, which may be a separate gateway RAN node or may be the macro
cell, may consider the last handover time and last served PCI for a
UE. This may be at attach time for the UE, or at a subsequent time
such as prior to a handover request. At step 1102, various
parameters may be checked to determine whether handover is
appropriate. For example, as shown here, if the handover of that UE
(or in some embodiments another UE or all UEs) from the same PCI
was within a short time before, here shown as 2 seconds, and/or if
a large number of handovers has been performed from that cell for
the same UE, then the cell individual offset, delay handover
reporting parameters, etc. may be changed for this UE to avoid
unnecessary handovers. This change can take effect immediately and
may last for a period of time, such as X milliseconds as shown.
[0087] FIG. 12 is a schematic diagram showing PCI allocation, in
accordance with some embodiments. Cluster 1 1210, comprising macro
cells 1211, 1212, 1213, 1214, 1216, 1217 and small cell base
stations 1215, 1218, is shown. Cluster 1 has indoor leakage at
location 1212, from an indoor access point or enterprise access
point. Cluster 2 1220 is also shown, comprising indoor base station
1221, macro cells 1223, 1224, 1229, and small cell base stations
1225, 1226, 1227, 1228. Macro 1219 is in the cell edge between both
base stations. Based on the active set list (cluster 1 neighbor
list), macro 1229 is assigned the PCI value of 1 from a pool of
values, since the other base station with PCI 1 is base station
1211, which is far away. In some embodiments the radius can be
configurable. In some embodiments assignment may happen
automatically; in other embodiments it may occur with
preplanning.
[0088] FIG. 13 is a schematic diagram of a virtualization server in
a Long Term Evolution (LTE) architecture, in accordance with some
embodiments. Virtualization server 1301 provides services to, and
is coupled to, eNodeB 1 1302 and eNodeB 5 1303, on a RAN side of a
network (i.e., inside of the gateway). Virtualization server 1301
provides services to, and is coupled to, MME 1304, macro eNodeB
1305, and macro eNodeB 1306, on a core network side of the network
(outside of the gateway).
[0089] Within virtualization server 1301 are self-organizing
network (SON) module 1311, containing neighbor relation table (NRT)
1312 and UE measurement report processing module 1313; evolved
packet core (EPC) module 1321, containing EPC finite state machine
module 1322 and macro eNodeB table 1323; radio access network (RAN)
module 1331, containing eNodeB finite state machine module 1332 and
tracking area module 1334; and user equipment (UE) module 1341,
containing UE finite state machine module 1342, S1/X2 handover
mapping table 1343, and paging module 1344. Each of modules 1311,
1321, 1331, and 1341 are coupled to each other within
virtualization server 1301, and may execute on one or more shared
processors (not shown) coupled with memory (not shown).
[0090] In some embodiments, SON module 1311 may perform NRT
maintenance, load information processing and fractional frequency
reuse (FFR) processing; RAN module 1331 may perform X2 association
management with eNodeBs 1302, 1303; EPC module 1321 may perform X2
association management with macro eNodeBs 1305, 1306; and UE module
may perform X2 handover and S1/X2 translation between eNodeBs 1302,
1303 and macro eNodeBs 1305, 1306. All the above managers/modules
interact with each other to accomplish the assigned
functionality.
[0091] In any given call flow or message exchange, each module
1322, 1332, 1342 may independently track the state of the core
network/macro eNodeB, the internal eNodeB, and the UE, in some
embodiments, such that the state of each of the components is fully
known by one of the modules.
[0092] In some embodiments, EPC module 1321 may contain EPC finite
state machine module 1322 and macro eNodeB table 1323. EPC finite
state machine module 1322 may track the state of any messages or
call flows being sent or received with a macro eNodeB, such as
macro eNodeBs 1305, 1306. EPC FSM module 1322 may, for example,
determine whether a handover has been initiated by macro eNodeB
1305, 1306, as well as other functions. EPC FSM module 1322 may
also track which eNodeBs within the network are involved in
communicating with the macro eNodeBs, and may perform network
address translation by mapping incoming requests and messages from
an eNodeB address external to the gateway 1301 to an address
internal to the gateway 1301, using eNodeB table 1323. In some
embodiments the tracking and network address translation functions
may be performed at the RAN module or in another module. Macro
eNodeB table 1323 may track all macro eNodeBs and any connections,
bearers, tunnels, or calls open between an eNodeB internal to the
gateway, such as eNodeBs 1302 and 1303.
[0093] In some embodiments, RAN module 1331 may contain RAN finite
state machine module 1332 and eNodeB table 1334. RAN module 1331 is
the counterpart to EPC module 1321 on the side of the network
inside the gateway. RAN FSM module 1332 may track and receive
messages and requests, and may track the state of the RAN node in
any message exchange. An eNodeB table may include a mapping to from
an eNodeB ID or cell ID to the ECGI ID used outside of the private
network. In some embodiments, RAN module 1331 may perform network
address translation, if applicable, on messages received by RAN
module from eNodeBs 1302, 1303, so that the messages can be sent
upstream to the EPC and/or core network. In some embodiments,
network address translation is used at both RAN module 1331 and EPC
module 1321, for connections initiated at the RAN and at the EPC,
respectively.
[0094] The tracking area module 1334 maintains a list of all
eNodeBs that are in each particular tracking area. For some
virtualization servers, a single tracking area may include all
eNodeBs coupled to server 1301. For others, multiple tracking areas
may be tracked, with some subset of the eNodeBs served by
virtualization server 1301 being part of each of the multiple
tracking areas. When a paging request is sent for a UE, in some
cases the list of base stations that are part of the single
tracking area may be considered as part of the information used for
identifying a set of base stations to perform paging.
[0095] As RAN module 1331 is in the data path for all S1
communications to the core network, including communications to MME
1304, RAN module 1331 may perform proxying and network address
translation for the S1 connection, in addition to supporting the X2
connection, in some embodiments. RAN module 1331 may also pass
along any UE measurement reports received from UEs to either or
both of UE module 1341 and SON module 1311.
[0096] In some embodiments, UE module 1341 may contain UE finite
state machine module 1342 and handover mapping table 1343. UE
finite state machine module 1342 may track states for call flows
that are in process between a UE connected to one or more eNodeBs
and either a core network node or a target eNodeB. For example, UE
FSFM 1342 may track when an X2 handover request message has not
been responded to and should expire. UE FSFM 1342 may also track
X2/S1 handovers, in conjunction with handover mapping table 1343.
When an X2 handover request is received, UE FSFM 1342 may, in some
embodiments, determine whether a handover should be translated from
S1 to X2, or vice versa, before the handover should continue. UE
module 1341 handles UE-related requests from both the RAN module
1331 (from nodes internal to gateway 1301) and from EPC module 1321
(from nodes external to gateway 1301).
[0097] Paging module 1344 records information about each UE that
comes in contact with virtualization server 1301, through eNodeBs
1302, 1303, or other eNodeBs or base stations. Information such as
physical location, historical location, handovers and handover
preferences, as described elsewhere herein, is collected in the
paging module. When a downlink data notification is received at the
virtualization server, the EPC module 1321 requests that the paging
module 1344 assist in locating the UE. Paging module 1344, in some
embodiments, may come up with a precise eNodeB, or may come up with
a set of eNodeBs or multiple sets of eNodeBs to be paged to locate
the UE, based on the stored location information. This list of
eNodeBs is then sent to the RAN module 1331 to initiate paging
requests thereto.
[0098] FIG. 14 is a schematic diagram of a mesh network base
station, in accordance with some embodiments. Mesh network base
station 1400 may include processor 1402, processor memory 1404 in
communication with the processor, baseband processor 1406, and
baseband processor memory 1408 in communication with the baseband
processor. Base station 1400 may also include first radio
transceiver 1410 and second radio transceiver 1412, internal
universal serial bus (USB) port 1416, and subscriber information
module card (SIM card) 1418 coupled to USB port 1414. In some
embodiments, the second radio transceiver 1412 itself may be
coupled to USB port 1416, and communications from the baseband
processor may be passed through USB port 1416.
[0099] A tracking area state module 1430 may maintain the tracking
area code for base station 1400, as well as the PLMN for the base
station's network, enabling the base station to report its tracking
area code and tracking area identity. Tracking area state module
may also pass through requests from a core network module to send a
new tracking area list to a UE. Tracking area state module may be
in communication with a core network, as shown. Additionally, local
EPC 1420 may be used for authenticating users and performing other
core network-dependent functions when no backhaul link is
available. Local EPC 1420 may include local HSS 1422, local MME
1424, local SGW 1426, and local PGW 1428, as well as other modules.
Local EPC 1420 may incorporate these modules as software modules,
processes, or containers. Local EPC 1420 may alternatively
incorporate these modules as a small number of monolithic software
processes. Virtualization layer 1430 and local EPC 1420 may each
run on processor 1402 or on another processor, or may be located
within another device.
[0100] Processor 1402 and baseband processor 1406 are in
communication with one another. Processor 1402 may perform routing
functions, and may determine if/when a switch in network
configuration is needed. Baseband processor 1406 may generate and
receive radio signals for both radio transceivers 1410 and 1412,
based on instructions from processor 1402. In some embodiments,
processors 1402 and 1406 may be on the same physical logic board.
In other embodiments, they may be on separate logic boards.
[0101] The first radio transceiver 1410 may be a radio transceiver
capable of providing LTE eNodeB functionality, and may be capable
of higher power and multi-channel OFDMA. The second radio
transceiver 1412 may be a radio transceiver capable of providing
LTE UE functionality. Both transceivers 1410 and 1412 are capable
of receiving and transmitting on one or more LTE bands. In some
embodiments, either or both of transceivers 1410 and 1412 may be
capable of providing both LTE eNodeB and LTE UE functionality.
Transceiver 1410 may be coupled to processor 1402 via a Peripheral
Component Interconnect-Express (PCI-E) bus, and/or via a
daughtercard. As transceiver 1412 is for providing LTE UE
functionality, in effect emulating a user equipment, it may be
connected via the same or different PCI-E bus, or by a USB bus, and
may also be coupled to SIM card 1418.
[0102] SIM card 1418 may provide information required for
authenticating the simulated UE to the evolved packet core (EPC).
When no access to an operator EPC is available, local EPC 1420 may
be used, or another local EPC on the network may be used. This
information may be stored within the SIM card, and may include one
or more of an international mobile equipment identity (IMEI),
international mobile subscriber identity (IMSI), or other parameter
needed to identify a UE. Special parameters may also be stored in
the SIM card or provided by the processor during processing to
identify to a target eNodeB that device 1400 is not an ordinary UE
but instead is a special UE for providing backhaul to device
1400.
[0103] Wired backhaul or wireless backhaul may be used. Wired
backhaul may be an Ethernet-based backhaul (including Gigabit
Ethernet), or a fiber-optic backhaul connection, or a cable-based
backhaul connection, in some embodiments. Additionally, wireless
backhaul may be provided in addition to wireless transceivers 1410
and 1412, which may be Wi-Fi 802.11a/b/g/n/ac/ad/ah, Bluetooth,
ZigBee, microwave (including line-of-sight microwave), or another
wireless backhaul connection. Any of the wired and wireless
connections may be used for either access or backhaul, according to
identified network conditions and needs, and may be under the
control of processor 1402 for reconfiguration.
[0104] Other elements and/or modules may also be included, such as
a home eNodeB, a local gateway (LGW), a self-organizing network
(SON) module, or another module. Additional radio amplifiers, radio
transceivers and/or wired network connections may also be
included.
[0105] Processor 1402 may identify the appropriate network
configuration, and may perform routing of packets from one network
interface to another accordingly. Processor 1402 may use memory
1404, in particular to store a routing table to be used for routing
packets. Baseband processor 1406 may perform operations to generate
the radio frequency signals for transmission or retransmission by
both transceivers 1410 and 1412. Baseband processor 1406 may also
perform operations to decode signals received by transceivers 1410
and 1412. Baseband processor 1406 may use memory 1408 to perform
these tasks.
[0106] In some embodiments, the radio transceivers described herein
may be base stations compatible with a Long Term Evolution (LTE)
radio transmission protocol or air interface. The LTE-compatible
base stations may be eNodeBs. In addition to supporting the LTE
protocol, the base stations may also support other air interfaces,
such as UMTS/HSPA, CDMA/CDMA2000, GSM/EDGE, GPRS, EVDO, other
3G/2G, 5G, legacy TDD, or other air interfaces used for mobile
telephony. In some embodiments, the base stations may be multi-RAT
base stations and may support any combination of the RATs described
herein. In some embodiments, the base stations described herein may
support Wi-Fi air interfaces, which may include one or more of IEEE
802.11a/b/g/n/ac/af/p/h. In some embodiments, the base stations
described herein may support IEEE 802.16 (WiMAX), to LTE
transmissions in unlicensed frequency bands (e.g., LTE-U, Licensed
Access or LA-LTE), to LTE transmissions using dynamic spectrum
access (DSA), to radio transceivers for ZigBee, Bluetooth, or other
radio frequency protocols, or other air interfaces.
[0107] In some embodiments, the base stations that are described
herein may be mobile base stations, configured to transmit while
stationary, while in motion, or in some configurable combination
thereof. Advantages would be understood by one having skill in the
art for using features of the present invention with a mobile or
moving cell. For example, a coordinating node performing dynamic
PCI allocation to a moving cell reduces the chance of PCI confusion
observed by a UE. Additionally, since there are moving cells, a
macro base station can advantageously resolve the ECGI of the
neighbor cell by getting information from a UE, as described
herein, and not depending on the internal mapping of PCI-ECGI that
is typically used for static layout. A moving base station is
described at least at U.S. Pat. No. 8,867,418, "Methods of
Incorporating an Ad Hoc Cellular Network Into a Fixed Cellular
Network," filed Feb. 18, 2014, which is incorporated by reference
earlier in this document.
[0108] In some embodiments, anywhere that hand-in is described in
this document, one of ordinary skill in the art would understand
that a hand-out would also be able to be performed using
appropriate modifications well-understood in the art. For example,
an X2 connection towards the coordinating node (where the
coordinating node is a node as described herein, and may be a
Parallel Wireless LTE Access Controller [TM], or Parallel Wireless
HetNet Gateway [TM]) can be available for handover, including
handin and handout. The coordinating node routes the incoming
handover to the correct moving cell, and may perform X2-S1 handover
conversion if required.
[0109] In some embodiments, for handouts from the area of control
of the coordinating node to a base station not under coordination,
the coordinating node may: enable measurement reporting by the EU;
resolve ECGI (cell identity) of neighbors by asking the UE and
update the ANR table using this information, as described elsewhere
herein; build/update a single X2 connection towards the macro on
behalf of a set of moving cells by virtualizing them; perform
handover decision making based on various criteria; and perform
handover conversion as required between S1 and X2, as described at
least within U.S. patent application Ser. No. 14/642,544,
"Federated X2 Gateway," filed Mar. 9, 2015, previously incorporated
by reference.
[0110] In some embodiments, PCI allocation and automatic neighbor
relations (ANR) buildup for moving cells is described. A unique PCI
can be allocated every time a cell stops moving and wants to
broadcast. The coordinating node builds up knowledge (for example,
a mapping and list) over time of the complete area, using the
methods described herein, e.g., network scan results provided by
the cell; GPS/location tagging; X2 based exchanges with peer
macros; and UE based measurement reporting of neighbors. This
enables PCIs to be allocated while avoiding PCI conflicts and
confusion.
[0111] In some embodiments, the base stations described herein may
use programmable frequency filters. In some embodiments, the base
stations described herein may provide access to land mobile radio
(LMR)-associated radio frequency bands. In some embodiments, the
base stations described herein may also support more than one of
the above radio frequency protocols, and may also support transmit
power adjustments for some or all of the radio frequency protocols
supported. The embodiments disclosed herein can be used with a
variety of protocols so long as there are contiguous frequency
bands/channels. Although the method described assumes a single-in,
single-output (SISO) system, the techniques described can also be
extended to multiple-in, multiple-out (MIMO) systems.
[0112] The foregoing discussion discloses and describes merely
exemplary embodiments of the present invention. In some
embodiments, software that, when executed, causes a device to
perform the methods described herein may be stored on a
computer-readable medium such as a computer memory storage device,
a hard disk, a flash drive, an optical disc, or the like. As will
be understood by those skilled in the art, the present invention
may be embodied in other specific forms without departing from the
spirit or essential characteristics thereof. For example, wireless
network topology can also apply to wired networks, optical
networks, and the like. The methods may apply to LTE-compatible
networks, to UMTS-compatible networks, to Wi-Fi networks, or to
networks for additional protocols that utilize radio frequency data
transmission. Various components in the devices described herein
may be added, removed, or substituted with those having the same or
similar functionality. Various steps as described in the figures
and specification may be added or removed from the processes
described herein, and the steps described may be performed in an
alternative order, consistent with the spirit of the invention.
Features of one embodiment may be used in another embodiment.
Accordingly, the disclosure of the present invention is intended to
be illustrative of, but not limiting of, the scope of the
invention, which is specified in the following claims.
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