Method for managing the state of micro base stations by following the
variations of traffic requirements, and associated controller device.
FIELD OF THE INVENTION
The invention relates generally to telecommunication systems and in
particular to a method for energy saving at the level of base station, and
associated controller device. Specifically, in case of cellular networks, it is
proposed to switch on/off selected cells to follow the variations in traffic load.
BACKGROUND OF THE INVENTION
A mobile communication network comprises portable devices, such
as cell phone, in radio communication with fixed base stations. These base
stations comprise in particular antennas having a more or less large coverage.
The coverage areas depend amongst other things on the emission power. The
macro cell covers a broad area and may communicate with a large number of
portable devices, whereas the micro cell cover a small cover and can manage a
small number of portable devices. The radio network is thus arranged
hierarchically: the macro cell ensures the coverage of a large area and the
micro cell ensures a high capacity of communication with the cell phones.
According to the characteristics of the area and in particular of the population
density and it is advantageous to increase the number of micro cells in order to
offer a better capacity in this area.
The radio coverage of each micro cell is managed by a device called
"eNodeB" in the Long Term Evolution (LTE) technology. This device consumes
energy. In certain cases, the eNodeB is switched on but does not manage any
communication with portable device, for example during the night in residential
zone, when the activity of the portables is very limited. Most of time and power
of the eNodeB are thus consumed for nothing.
To save energy during low load period, it seems relevant to switch
off cells - for example one or multiple micro cells are switched-off while the
macro cells remain intact in order to avoid any coverage holes. In dense
deployments, the number of unused micro cells being high, such solutions can
lead to substantial energy savings. This will introduce a decrease of available
network capacity. An important issue is to decide which micro cells to switch off
such that coverage areas with mobile subscribers do not suffer from an undue
reduction of capacity. Inversely, when the need for capacity increases, we need
also to decide which micro cell to switch on to provide required capacity.
A solution consists in the macro cell managing all the portable
devices when the traffic is low. However, the capacity of the macro cell can
very quickly become insufficient when the portable devices in Idle mode
become active, i.e. when they enter into communication.
Another solution consists in switching on uniformly one micro cell out
of two, one out of three etc. , proportionally to the actual traffic load. But this
empirical method may cause call drops and low quality of service in the radio
communication network. The problem when choosing the cell to switch off
using actual traffic load generated by the "active users" is that the reduced
capacity may be not enough to serve portable devices in Idle mode already
attached to this cell that when such UEs become active.
When the portable device is in Idle mode, it is difficult to locate it
because it does not emit signal. It is easy to count the number of cell phones in
active mode, but it is difficult to determine the number of portable device in Idle
mode per base station... In fact, the idle mode procedure implemented in the
LTE standard does not permit to know how many terminals in idle mode are
under the coverage of a given eNodeB. In fact the portable device is registered
to the MME and the eNodeB has no context information. The only geographical
information we have on the terminal is at the granularity of the Tracking Area,
as the portable device performs Tracking Area updates when moving and also
periodically when not moving. The radio network cannot decide optimum
number of switched on micro cell in order to offer a sufficient capacity for the
active portable devices and the portable devices in Idle mode which could
wake-up
This granularity of the Tracking Areas doesn't give enough
information of the number of UEs in idle mode under the coverage of an
eNodeB.
The present invention allows among others advantages of estimating
the number of portable devices within a zone and of determining the number of
switched on micro cells to ensure the potential requests for traffic
SUMMARY OF THE INVENTION
An aspect of the invention relates to a method to manage the state
of a plurality of micro base stations inside a mobile communication network is
provided. The network comprises at least a macro cell containing at least one
Tracking Area covering a plurality of micro cells associated with a micro base
station. The method includes the steps of:
- switching on of all the micro base stations contained in said
Tracking Area of the macro cell,
- counting of the messages of paging to determine the number of
portable devices in Idle mode inside said Tracking Area,
- switching off at least one micro base station in the Tracking Area
when the number of portable devices in Idle mode in the said Tracking Area is
lower than a first determined value.
With this manner, the number of micro base stations in active mode
is optimized, and thus the global power consumption of all micro base stations
inside a macro cell is decreased and the time of use of micro base station is
limited. The method allows taking switch on/off decisions of micro cells based
o n potential needs for traffic information, Typically, the number of user
terminals in idle mode in a given geographical area permits to evaluate what
would be the potential needs for traffic. The present invention uses location
area update and paging activity information to predict cell by cell traffic
requirements. Hence, information of location and number of idle mode
terminals becomes useful to simply anticipate needs for traffic.
According to another aspect of the present invention, the switching
on of all the micro base stations contained in said Tracking Area of the macro
cell is triggered when the current load of the macro cell exceeds a second
determined value. It happens when the macro is detecting an increase of traffic,
e.g. high number of connection requests, typically when lot of terminals are
attached to the macro if most of micros are switched off.
According to another aspect of the present invention, the switching
off of at least one micro base station is performed when the estimated number
of portable devices in Idle mode managed by this micro base station is lower
than a third determined value. This way, only micro cells with less probable
traffic will be switched off for energy reasons. Then, even if the capacity is
reduced, it will not impact the service quality. Similarly, this information on
paging activity can also used to switch on a cell expected to have a large
number of terminal in Idle modes, which could "potentially" wake up and need
for traffic.
According to another aspect of the present invention, the number of
portable devices managed by this micro base station takes into account the
information of localization provided by applicative servers in communication
with the portable devices located in the micro cell. With this manner, the
portable devices are better located and the number of portable devices in Idle
mode in each micro cell is better estimated.
According to another aspect of the present invention, the macro cell
contains only one Tracking Area. With this manner, the processing for
determining the number of portable device per micro base station is only based
on estimation at the micro base station level.
According to a variant of the present invention, the macro cell
contains several Tracking Areas; the step of switching on all the micro base
stations contained in the Tracking Areas is successively performed for each
Tracking Area. With this manner, the processing for determining the number of
portable device has a better granularity.
According to a variant of the present invention, the switching on of
all the micro base stations contained in said Tracking Area is periodically
performed, spaced by a regular time interval. With this manner, it is possible to
periodically update the number of switched-on micro base station.
The present invention also relates to a controller of mobile
communication network controlling the traffic inside a macro cell comprising
means of communication with a plurality of micro base stations associated with
a micro cell, the macro cell containing at least one Tracking Area covering a
plurality of micro cell, characterized in that said controller comprises:
- means of emission of a first signal to switch on all micro base
stations in said Tracking Area,
- a counter of messages of paging to determine the number of
portable devices in Idle mode inside said Tracking Area of the macro cell,
- means of emission of a second signal to switch off at least one
micro base station of said Tracking Area when the number of portable devices
in Idle mode inside said Tracking Area is lower than a first determined value.
The present invention also relates to a computer program product
comprising instructions for performing the steps of the method as claimed when
the program is executed on a network controller.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the
detailed description given herein below and the accompanying drawings,
wherein like elements are represented by like reference numerals, which are
given by way of illustration only and thus are not lim iting of the present
invention and wherein:
FIG. 1 illustrates a set of three zones of Paging, called "Tracking
Area" or TA in LTE technology.
FIG. 2 illustrates the structure of the communication network to
control the activity of each micro cell within a given macro cell.
FIG. 3 is a flowchart illustrating example operation of steps to
optimize the number of switched-on eNodeBs in a communication network.
FIG.4 illustrates a first structure of a macro cell comprising a plurality
of Tracking Area
FIG. 5 illustrates a second structure of a macro cell comprising only
one Tracking Area
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Figure 1 - 5 and the following description depict specific exemplary
embodiments of the invention to teach those skilled in the art how to make and
use the invention. For the purpose of teaching inventive principles, some
conventional aspects of the invention have been simplified or omitted. Those
skilled in the art will appreciate variations from these embodiments that fall
within the scope of the invention. Those skilled in the art will appreciate that the
features described below can be combined in various ways to form multiple
variations of the invention. As a result, the invention is not limited to the
specific embodiments described below, but only by the claims and their
equivalents.
In particular, the invention is applicable to several radio access
technologies such as: GSM, WCDMA, LTE. According to each technology, a
radio base station (or radio access node), such as a Base Transceiver Station
(BTS) for the Global System Mobility (GSM) standard, or a NodeB for Universal
Mobile Telephone System (UMTS) standard, or an eNodeB for Long Term
Evolution (LTE) standard, communicates with portable devices, such as mobile
phones, PDAs or laptops equipped with radio module. The portable device
communicates with a macro base station located within a range of a few
kilometers; the area covered by such a base station is referred to as a macro
cell. In a macro cell, the micro base stations associated with the micro cells
ensures a high capacity of communication with the portable devices. After this
paragraph, we detail this invention by using the LTE technology.
Figure 1 illustrates a set of three zones of Paging, called "Tracking
Area" or TA in LTE technology. The Tracking Area comprises a plurality of
micro cells 1. Three micro cells by Tracking Area are represented in the figure
1, this number may be variable per Tracking Area. A network element called
Mobile Management Entity 2 (or MME) communicates with each micro cell and
manages in its memory the identity of the portable device present in each
Tracking Area, among other information.
Standard LTE paging procedure gives only information at the
granularity of the Tracking Area. To have information at the micro base station
level (i.e. at an eNodeB level in LTE technology), we use Random Access
messages sent by the terminals that exit idle mode when having been paged
for an incoming call, or when performing a Tracking Area Update during
mobility in idle mode. These messages are sent toward a given eNodeB and
thus can be used as more accurate location information than the classical
paging messages, i.e. at the eNodeB granularity instead of Tracking Area
granularity
When a portable device leaves or enters in a given Tracking Area
(TA), a communication arises with the micro cell and the portable device can be
located at this time. LTE specification well defines "Random Access messages"
sent by the portable devices in Idle mode when they become active because of
incoming call or when they change Tracking Area. The LTE random access
procedure is used when there is a trans iti o n from RRC_I DLE t o
RRC_CONNECTED, to achieve UL time synchronization for a UE.
MME centralizes all the communications informing that a portable
device changes Tracking Area. In this way, MME can at all times determine the
estimated number of portable devices in Idle mode, called "TA_Counter", within
each Tracking Area. For updating the value TA_counter, the MME updates the
number of portable devices in Idle mode under this Tracking Area taking into
account the number of Tracking Area.
Figure 2 illustrates the structure of the various elements making it
possible to control the activity of each micro cell 1 within a given macro cell 3 .
This activity depends in particular on the presence of portable devices 4 within
each micro cell. A controller 5 is able to enter in communication with each
eNodeB. This controller 5 may send a message of wake-up to a switched-off
eNodeB, and a message of switch off. Controller 5 is also connected to the
MME 2 and thus receives the number of portable devices in Idle mode present
in each Tracking Area the controller 5 may be for example a part of Radio
Controller Network (RNC) or Serving GPRS Support Node (SGSN) or Home
NodeB Gateway (HNB-GW) for WCDMA technology, or a part of MME or Home
enhanced NodeB Gateway (HeNB-GW) for LTE technology.
Controller 5 is also connected to one or more applicative databases
6 . These databases are hosted in one or more servers making it possible to
deliver a service to users. These services are mainly local, for example:
delivering of a ticket of transport within a station, indicating of the road traffic at
a certain location, supplying of product within a store, use of the Global
Positioning System (GPS) function, etc. These services proposed to the owner
of the portable device are related to a determined location, so that when the
service is required or delivered by the portable device, it is located with
precision. This permits to have location information for both active and portable
devices.
The controller 5 receives from MME information about the total
number of portable devices in Idle mode within each Tracking Area, but the
MME doesn't provide the number of portable devices in Idle mode within a
micro cell. The estimation of number of portable devices in Idle mode sent by
the eNodeB and the information provided by applicative databases 6 improve
the reliability of this number at the level of each micro cell (eNodeB_counter).
When a portable device 4 moves, it need to ensure the continuity of
its management so that it can constantly receive incoming calls and that it can
possibly send some. So, the portable device in idle mode has to respect criteria
of "cell reselection" to be attached to a new Tracking Area. When a cell
reselection toward a micro cell has been decided, the portable device transmits
a message of "location update" towards the micro cell. At the time of this
message, the portable device performs a random request for access (UL
random access attempt) towards the micro cell. Each micro cell counts the
number of portable device having required to be relocated towards the
Tracking Area comprising this micro cell and sends this number to controller 5 .
To improve the estimate of the number of portable devices in Idle mode by
micro cell, the network may use an applicative server of geolocalisation which
counts the number of portable devices in Active and Idle mode according to
given areas. This number is transmitted to the controller 5 to update the
counter (eNodeB_counter) of portables devices in idle mode for each micro
cell.
Thus, by using the number of portable devices in Idle mode in the
Tracking Area provided by MME, the estimation of number of portable devices
in Idle mode and information from the applicative databases, controller 5 is able
to roughly determine the number of portable devices in Idle mode in each micro
cell. The system described above according to a preferred embodiment will
now be discussed in terms of function. A method making it possible to optimize
the number of switched-on eNodeBs is illustrated by the flowchart of figure 3 .
Initially (step 3 .1) , the activity at the level of a macro cell is
estimated. This estimation is performed by comparing the load of current traffic
of the macro cell with a determined value THRESHOLD 1. If this threshold is
exceeded, then it needs to wake-up more micro cells to carry out the traffic.
At step 3.2, all the micro cells which were switched off in each
Tracking Area are switched on. According to a variant, the method is performed
one tracking Area after the other, and at each loop, all the micro cells of a
determ ined Tracking Area are switched on. This switching on is
advantageously triggered by a message broadcast to all the micro cells of the
macro cell, those which are switched on does not change state. At the
switching on, the eNodeB emits a radio signal called "Beacons signal". The
portable devices detect the emission of new Beacon signal and determine this
one getting the best level of quality. During step 3.3, so by receiving the
Beacon signals, if the conditions of cell reselection are met, then the portable
devices in Idle mode perform a "location update" towards new Tracking Area by
carrying out a random access towards the micro cell. The procedures of cell
reselection are well described by specifications "LTE Random Access
procedure" and it is useless to explain them more. Other devices remain on the
same Tracking Area because the conditions of cell reselection are not met.
At step 3.4, the controller determines for each micro cell the
estimated number of portable devices in Idle mode : value eNodeB_counter.
After the switching-on, the eNodeB counts the number of portable devices
which request to be managed by it. The controller 5 also takes into account the
information provided by the applicative database 6 for determining the number
of portable devices in Idle mode in each micro cell. The MME updates
TA_counter counting the number of portable devices which have selected each
TA. The values eNodeB_Counter and TA_counter are transmitted to the
controller 5 .
Here how is calculated the eNodeB_counter value:
According to the statistical analysis of the network, one can
determine a > 1, such as the number of portable devices in Idle mode by micro
cell is equal to: a x (number of UL RACH attempts),
and according to the use of the application; one can determine a
second number b < 1 such as number of portable devices in Idle mode by micro
ce l l = b x (number of portable devices either in active or in Idle mode
determined by the application). At the end, the value eNodeB_counter is equal
t o t h e ave ra g e of t h e n umb e r s ( a x nb_UL_RACH_attempt, b x
nb_users_application).
Then, the controller 5 of network compares the number of portable
devices 4 in Idle mode in each Tracking Area (TA_counter) with a threshold
value THRESHOLD 2 (step 3.5). If this number is higher than the threshold, it
is necessary to maintain switched-on all the eNodeB of corresponding Tracking
Area so that all micro cells remain in an active state. In this case, the method
does not optimize the number of wake-up eNodeBs because the current traffic
requires leaving the eNodeB switching-on. At the step 3.6, all the eNodeBs in
the corresponding Tracking Area remain switched-on.
On the other hand, if the value THRESHOLD 2 is not exceeded, it is
possible to shutdown some eNodeBs. At step 3.7, for each micro cell of the
Tracking Area, the estimation of number of portable devices in Idle mode
(eNodeB_counter) is compared with a threshold value THRESHOLD 3 . If the
value THRESHOLD 3 is not exceeded, then the eNodeB can be shutdown
because the potential need for traffic is not sufficient. If portable devices are in
communication mode in the micro cell, then they perform a handover towards
the macro cell which ensures the coverage for the hierarchical network.
At step 3.8, at least one eNodeB is switched-off. The corresponding
Beacons Signal is not emitted more, then the few portables which were
managed by it will search another Beacons signal and another corresponding
micro cell or they will directly manage by the macro cell. At the end of these
steps, the numbers of micro cells in active and inactive state are adapted to the
current needs for traffic.
This situation lasts only a time and it is necessary to update this
state at the end of a certain duration to periodically follow the evolutions of the
requests for traffic. The method comprises a temporization step (step 3.9) at
the end of which all the steps previously described (3 . 1 to 3.8) are re-run.
According to a first variant of embodiment illustrated by figure 4 , the
macro cell contains a plurality of Tracking Area (TA). MME manages the
information of the number of portable devices 4 in Idle mode in each TA.
According to another variant of embodiment, illustrated by figure 5 , all micro
cells of the macro cell belong to the same Tracking Area. Then, MME contains
only one number of portable devices in Idle mode for this macro.
Where a component is referred to above, unless otherwise
indicated, reference to that component (including a reference to a "means")
should be interpreted as a reference to any component which performs the
function of the described component (i.e. is functionally equivalent to the
described component), including components which are not structurally
equivalent to the disclosed structure which performs the function in the
illustrated exemplary embodiments of the invention.
Where a step in a method is referred to above, unless otherwise
indicated, reference to that step should be interpreted as a reference to any
step which achieves the same result as the step (i.e. is functionally equivalent
to the described step), including steps which achieve a stated result in different
ways from those disclosed in the illustrated exemplary embodiments of the
invention. As will be apparent to those skilled in the art in the light of the
foregoing disclosure, many alterations and modifications are possible in the
practice of this invention
CLAIMS
1. Method to manage the energy mode of a plurality of micro base
station inside a mobile communication network, the network comprising at least
one macro cell (3) containing at least one Tracking Area (TA) covering a
plurality of micro cells ( 1 ) each one associated with a micro base station, the
method being characterized in that it comprises the steps:
- switching on of all the micro base stations contained in said
Tracking Area (TA) of the macro cell,
- counting of the messages of paging to determine the number of
portable devices (4) in Idle mode inside said Tracking Area,
- switching off at least one micro base station in the Tracking Area
when the number of portable devices (4) in Idle mode in the said Tracking Area
is lower than a first determined value (THRESHOLD 2).
2 . The method according to claim 1 characterized in that the
switching on of all the micro base station contained in said Tracking Area (TA)
of the macro cell is triggered when the current load of the macro cell exceeds a
second determined value (THRESHOLD 1) .
3 . The method according to claim 1 or 2 characterized in that the
switching off of at least one eNodeB is performed when the number of portable
devices (4) managed by this micro base station is lower than a third determined
value (THRESHOLD 3).
4 . The method according to claim 3 characterized in that the number
of idle and active portable devices (4) managed by this micro base station
takes into account the information of localization provided by applicative
servers in communication with the portable devices (4) located in the micro cell.
5 . The method according to any one of claims 1 to 4 characterized in
that the macro cell contains only one Tracking Area.
6 . The method according to any one of claims 1 to 4 characterized in
that the macro cell contains several Tracking Areas, the step of switching on of
all the micro base stations contained in the Tracking Areas is successively
performed for each Tracking Area.
7 . The method according to any one of claims 1 to 6 characterized in
that the switching on of all the micro base stations contained in said Tracking
Area is periodically performed, spaced by a regular time interval.
8 . Controller (5) of mobile communication network controlling the
traffic inside a macro cell (3) comprising means of communication with a
plurality of micro base stations associated with a micro cell ( 1) , the macro cell
containing at least a Tracking Area (TA) covering a plurality of micro cell,
characterized in that said controller (5) comprises
- means of emission of a first signal to switch on of all micro base
stations in said Tracking Area,
- a counter of messages of paging to determine the number of
portable devices (4) in Idle mode inside said Tracking Area of the macro cell,
- means of emission of a second signal to switch off at least one
micro base station of said Tracking Area when the number of portable devices
in Idle mode inside said Tracking Area is lower than a first determined value
(THRESHOLD 2).
9 . Controller (5) of network according to claim 8 comprising a means
of comparison between the current load of the macro cell and a second
determined value (THRESHOLD 1) , to trigger the emission of the first signal
when the current load of the macro cell exceeds the second determined value.
10 . Controller (5) of network according to claim 8 or 9 characterized
in that it comprises a means of comparison between the number of portable
devices managed by said micro base station and a third determined value
(THRESHOLD 3), to trigger the emission of the second signal to switch off said
micro base station when the number of portable devices managed by this micro
base station is lower than the third determined value.
11. Controller (5) of network according to claim 10 , characterized in
that it comprises means of communication towards applicative servers adapted
to locate portable devices (4) in each micro cell, the number of idle and active
portable devices managed in a given micro base station taken into account the
information of locating provided by said applicative servers.
12. Controller (5) of network according to any one of claims 8 to 11,
characterized in that the macro cell managed by the controller contains only
one Tracking Area (Tai).
13 . Controller (5) of network according to any one of claims 8 to 11,
characterized in that the macro cell managed by the controller contains several
Tracking Area, means of emission of a first signal to switch on all micro base
stations of a Tracking Area being successively triggered for each Tracking
Area.
14. Controller (5) of network according to any one of claims 8 to 13 ,
characterized in that the means of emission of the first signal sends periodically
said first signal, spaced by a regular time interval.
15 . computer program comprising computer-executable instructions
for performing a method when the program is run on a network controller, the
method comprising the steps according to the claims 1 to 7 .