POWER SAVING
FIELD OFTHE INVENTION
The present invention relates to a method of controlling a power saving mode of user
equipment in a multi-carrier wireless telecommunications network, and a computer
program product and user equipment operable to carry out that method.
BACKGROUND
Single carrier wireless telecommunications systems are known. In those systems, radio
coverage is provided to user equipment, for example, mobile telephones, by
geographical area. A base station is located in each geographical area to provide
required radio coverage. User equipment in a n area served by a base station receives
information and data from a base station and transmits information and data to a base
station.
Information and data transmitted by a base station to user equipment occurs on
channels of radio carriers known as "downlink carriers". Information and data
transmitted by user equipment to a base station occurs on uplink data channels of
radio carriers known as "uplink carriers".
An area served by a base station typically comprises several sectors which together
define a coverage area for that base station. Typically, a base station serves three
sectors. Those sectors are typically served by separate antenna arrays provided on a
base station.
It is possible to allow base stations and user equipment to each transmit simultaneously
on more than one carrier. Furthermore, it is possible to allow user equipment and base
stations to receive simultaneously on more than one carrier frequency. Such multicarrier
networks allow for a n increase in data throughput across the network when the
network is busy. However, those same networks typically require provision of a n
increase in hardware and increased power consumption to provide full functionality,
which may not be energy efficient when data traffic across the network is low.
It is desired to provide a multi-carrier network having improved power consumption
characteristics.
SUMMARY
Accordingly, a first aspect provides a method of controlling a carrier configuration of a
network node in a multi-carrier wireless telecommunication network, the multi-carrier
wireless telecommunications network comprising a plurality of network nodes operable
to simultaneously transmit and receive signals on more than one radio frequency carrier
within a sector of the telecommunications network, the method comprising the steps
of:
monitoring an indication data traffic received over a predetermined time
period on each carrier to determine whether the data traffic received over the time
period meets a predetermined set of conditions,
transmitting a request to deactivate each carrier determined to meet the
conditions;
monitoring for receipt of a positive response to the request and implementing
deactivation for each carrier for which a positive response is received.
It is possible to allow base stations and user equipment to each transmit simultaneously
on more than one carrier. Furthermore, it is possible to allow user equipment and base
stations to receive simultaneously on more than one carrier frequency.
In such a scenario, each carrier, both uplink and downlink, is individually and
independently power controlled.
Dual Cell High Speed Uplink Packet Access (DC-HSUPA) will allow user equipment to
transmit (uplink) data on two adjacent frequency carriers. This allows for a n increase in
data throughput from user equipment relative to a single carrier arrangement. In 4
Carrier High Speed Downlink Packet Access (4C-HSDPA) user equipment can receive
(and a base station can transmit on) up to four simultaneous downlink carriers from a
base station.
In 4C-HSDPA, a sector is defined as the geographical coverage area of a base station
(also known as a Node B). A sector can consist of several cells, where each cell aims to
cover the same geographical coverage as the sector and uses a separate frequency
carrier for its transmission.
Each carrier in a multi-carrier network can be within the same frequency band, or
region of radio spectrum, or distributed over two or more frequency bands provided in
the radio spectrum.
Multi-carrier systems allow for an increase in data throughput from user equipment and
from a base station. The term "multi carrier network" used herein is envisaged to cover
both DC-HSDPA, 3C-HSDPA, 4C-HSDPAand MC-HSDPAnetworks.
In a typical multi-carrier wireless telecommunications network, one of the downlink
carriers provided will typically be known as an "anchor" or "primary" carrier. The
anchor carrier has a particular functional purpose and whilst user equipment and base
stations may be able to receive and transmit on one or more carrier simultaneously, the
anchor uplink and downlink carriers are the carriers upon which a base station monitors,
controls and instructs various functional aspects of a relationship between user
equipment and a base station including, for example, mobility events. That is to say, an
anchor carrier provides essential control channels for downlink and uplink operation
and mobility events are managed based upon measurements made by user
equipment and reported on an anchor carrier uplink.
In a multi-carrier system, there will typically be provided one "primary" or "anchor"
carrier and one or more "secondary" carriers. The secondary carriers are indexed as:
secondary carrier 1, secondary carrier 2, secondary carrier 3, etc. Since the primary
carrier contains essential control channels, it cannot be deactivated without affecting
operation of the wireless telecommunication network and, in particular, operation of
the user equipment. The primary carrier is therefore typically not deactivated.
Autonomous user equipment deactivation of a downlink carrier which is being received
may save some power at user equipment, but may disrupt base station scheduling
since the base station may expect all downlink carriers to be active. A base station
scheduler allocates downlink resources and also transmits packets to user equipment.
Hence, if a base station schedules transmissions on a secondary carrier, it expects that
this secondary carrier is "activated" (able to be received) at the user equipment. If a
base station scheduler is unaware that reception of a secondary carrier has been
deactivated by user equipment, it may continue to retransmit packets to the user
equipment. That retransmission can cause unnecessary interference in cell,
detrimentally affecting the operation of the network.
In the downlink it is beneficial that a base station knows when reception of downlink
secondary carriers has been deactivated. The first aspect recognizes that a possible
solution is to allow user equipment to request, secondary carrier deactivation.
One such a request has been received by a base station, it may decide, based on a
set of predetermined criteria, whether to deactivate the requested secondary carriers.
If accepted, a base station may instruct deactivation of secondary downlink carriers,
and send an instruction to user equipment.
In accordance with the first aspect, user equipment takes no action to deactivate
reception of a carrier until a positive response is received. In such a scenario it will be
appreciated that a base station remains in control of deactivation of downlink
secondary carriers and this will not disrupt the base station scheduler.
In one embodiment, the predetermined set of conditions comprise an indication that
substantially no data is being received on a carrier. Accordingly, it will be understood
that a request for deactivation will only be sent when user equipment determines that
activity on that carrier is sufficiently low, thereby minimising potential disruption to
operation of the user equipment.
In one embodiment, the wireless telecommunications network is operable to
simultaneously transmit and receive signals on more than one radio frequency carrier,
the radio frequency carriers comprising a primary carrier and at least one secondary
carrier, the carriers being spread over two predetermined frequency bands, the
primary carrier being provided in a primary frequency band and at least one of the
secondary carriers being provided in a secondary frequency band.
Carriers in a multi-carrier network may be provided in one predetermined frequency
band, or may be provided across two or more predetermined frequency bands. Those
bands are provided in the radio spectrum. If all carriers in a multi-carrier network are
provided in a single frequency band, that band is known as the primary band. If the
carriers are spread over two predetermined frequency bands, the frequency band that
contains the primary carrier is known as the primary band and the frequency band that
contains only secondary carriers is referred to as the secondary band.
User equipment which is capable of receiving multi-carrier downlink carriers configured
over a primary and secondary band may require two receiver chains, one for each
frequency band. An energy saving may be achieved if, in periods of appropriate
network activity, user equipment is able to deactivate the receiver chain for the
secondary band.
Accordingly, once a request has been received by a base station, it may decide,
based on a set of predetermined criteria, whether to deactivate the requested
secondary carriers.
Since energy saving can be best achieved by shutting off a n entire receiver chain, it
will be appreciated that it offers greatest power savings to request to deactivate a
group of secondary carriers attached to a receiver chain, for example, the set of
secondary carriers located within the secondary band. Or for a base station to
recognize that all carriers meeting the predetermined criteria are in the secondary
band, and send a n appropriate response to the requests.
In one embodiment, the monitoring step further comprises the step of monitoring each
carrier provided in the secondary band to determine whether the data traffic received
over the time period meets the predetermined set of conditions. Accordingly, user
equipment may itself be operable to determine all carriers in the secondary band are
sufficiently inactive for a secondary band receiver chain to request to be turned off.
In one embodiment, the transmitting step further comprises the step of transmitting a
secondary band deactivation request when all carriers provided in the secondary
band are determined to meet the predetermined set of conditions. Accordingly, rather
than send a n independent request for each carrier, user equipment may be operable
to recognise that the carriers in the secondary band meet inactivity criteria and
transmit a single request, representing a request to deactivate a secondary band
receiver chain.
In one embodiment, the method further comprises the step of deactivating secondary
band reception on receipt of a positive response for all of the carriers provided in said
secondary band. Accordingly, no reduction in functionality is implemented until
approval and permission is received from a base station, thus minimising disruption to
the network.
In one embodiment, the deactivation request comprises a layer 1 signalling message.
In one embodiment, the deactivation request comprises a layer 2 signalling message.
It will be appreciated that such low level signalling ensures that the request and
response can be implemented rapidly. User equipment may be operable to send a
deactivation request to a base station in a number of ways, including, for example, at
Layer 1 using a reserved E-TFCI (E-DCH Transport Format Combination Indicator) in EDPCCH
(E-DCH Dedicated Physical Control Channel); at Layer 1 using a reserved
Channel Quality Indication (CQI) codeword (e.g. CQI value of 31); A new Layer 1
message; at Layer 2 adding 3 bits or 1 bit to MAC message, such additional bits may
only be sent when a deactivation request is needed; or a new Layer 2 message.
In one embodiment, the method further comprises the step of transmitting a
cancellation request when it is determined a carrier no longer meets the
predetermined conditions. Accordingly, it is recognised that, after user equipment
sends an deactivation request which has not been actioned by a base station, the
conditions being experienced by user equipment may change. For example, user
equipment may receive data traffic on all carriers mode and no longer wish to
deactivate any secondary carriers. In such a case, user equipment may operate to
send another request to the base station, which cancels the deactivation request sent
previously. The cancellation request may be sent using similar or analogous signalling to
that used for the initial deactivation request.
In one embodiment, the method steps are performed whilst the wireless
telecommunication network node is operating in discontinuous transmission or
reception mode.
User equipment may be operable to operate in a "discontinuous reception" (D x)or
"discontinuous transmission" (DTx) mode. Such modes allow user equipment to save
battery power when the UE is in an inactive period (for example, when user equipment
is in an idle state). During discontinuous reception user equipment shuts down its
reception antenna and periodically wakes up to receive possible data traffic and
information, for example, paging messages, from wireless telecommunications network
via data sent on downlink channels to user equipment from a base station. If the
messages received by user equipment in the wake-up periods are deemed to exceed
a threshold, or indicate that base station wishes to send more information to user
equipment, user equipment is operable to exit from the discontinuous reception mode.
Similarly, a discontinuous transmission (DTx) mode may be implemented by user
equipment. In such a case, when in a substantially idle mode, user equipment shuts
down its transmitter and only wakes up periodically to transmit packets of data to the
network via uplink channels to the base station. Implementing carrier deactivation
whilst in discontinuous mode allows greater power savings to be made. It will be
understood that if already operating in discontinuous mode data traffic is already likely
to be low.
A second aspect provides a computer program product, operable when executed on
a computer, to perform the method of the first aspect.
A third aspect provides a network node operable to control a carrier configuration in a
multi-carrier wireless telecommunication network, the multi-carrier wireless
telecommunications network comprising a plurality of network nodes operable to
simultaneously transmit and receive signals on more than one radio frequency carrier
within a sector of the telecommunications network, the network node comprising:
monitoring logic operable to monitor an indication data traffic received over a
predetermined time period on each carrier to determine whether the data traffic
received over the time period meets a predetermined set of conditions,
transmission logic operable to transmit a request to deactivate each carrier
determined to meet the conditions;
response logic operable to monitor for receipt of a positive response to the
request and implement deactivation for each carrier for which a positive response is
received.
In one embodiment, the predetermined set of conditions comprise an indication that
substantially no data is being received on a carrier.
In one embodiment, the wireless telecommunications network is operable to
simultaneously transmit and receive signals on more than one radio frequency carrier,
the radio frequency carriers comprising a primary carrier and at least one secondary
carrier, the carriers being spread over two predetermined frequency bands, the
primary carrier being provided in a primary frequency band and at least one of the
secondary carriers being provided in a secondary frequency band.
In one embodiment, the monitoring logic is further operable to perform the step of
monitoring each carrier provided in the secondary band to determine whether the
data traffic received over the time period meets the predetermined set of conditions.
In one embodiment, the transmission logic is further operable to transmit a secondary
band deactivation request when all carriers provided in the secondary band are
determined to meet the predetermined set of conditions.
In one embodiment, the network node comprises deactivation logic operable to
deactivate secondary band reception on receipt of the positive response for all of the
carriers provided in said secondary band. That deactivation step may comprise
deactivation of a reception chain associated with a secondary band.
In one embodiment the transmission logic is further operable to transmit a cancellation
request when it is determined a carrier no longer meets the predetermined conditions.
In one embodiment, the method steps are performed whilst the wireless
telecommunication network node is operating in discontinuous transmission or
reception mode.
In one embodiment, the network node comprises user equipment. In one
embodiment, the network node comprises a base station.
A fourth aspect provides a method of controlling a carrier configuration of a network
node in a multi-carrier wireless telecommunication network, the multi-carrier wireless
telecommunications network comprising a plurality of network nodes operable to
simultaneously transmit and receive signals on more than one radio frequency carrier
within a sector of the telecommunications network, the method comprising the steps
of:
monitoring for a request to deactivate each carrier, the request being
indicative that, over a predetermined time period, data traffic on that carrier has been
determined to meet a predetermined set of conditions
determining, in response to the request to deactivate each carrier, whether a
set of carrier deactivation conditions have been met, and
transmitting a positive response to the request if the carrier deactivation
conditions have been met.
Accordingly, it will be understood that the fourth aspect provides a method to be
implemented by a network node in response to receipt of a request issued in
accordance with the first aspect.
In one embodiment, the method further comprises the steps of:
storing an indication of receipt of the request and
periodically repeating the step of determining.
Accordingly, if conditions at a base station are not initially suitable to instruct
deactivation of a carrier determined to meet predetermined conditions (for example, if
there are data packets to be sent), but those conditions are later met, a positive
response may still be sent.
In one embodiment the carrier deactivation conditions comprise an indication that a
carrier is not scheduled to be used for transmission for a predetermined time period.
Accordingly, it will be understood that a positive response may only be sent when a
base station scheduler indicates that it is sensible to do so in view of network conditions.
A fifth aspect provides a computer program product, operable when executed on a
computer, to perform the method of the fourth aspect.
A sixth aspect provides a network node operable to control carrier configuration in a
multi-carrier wireless telecommunication network, the multi-carrier wireless
telecommunications network comprising a plurality of network nodes operable to
simultaneously transmit and receive signals on more than one radio frequency carrier
within a sector of the telecommunications network, the network node comprising:
request monitoring logic operable to monitor for a request to deactivate each
carrier, the request being indicative that over a predetermined time period, data
traffic on that carrier has been determined to meet a predetermined set of conditions;
determination logic, operable to determine, in response to the request to
deactivate each carrier, whether a set of carrier deactivation conditions have been
met, and
response transmission logic operable to transmit a positive response to the
request if said carrier deactivation conditions have been met.
In one embodiment, the network node further comprises:
Indication logic operable to store an indication of receipt of said request and
repetition logic operable to periodically repeat said step of determining.
In one embodiment the set of carrier deactivation conditions comprise an indication
that a carrier is not scheduled to be used for transmission for a predetermined time
period.
Further particular and preferred aspects of the present invention are set out in the
accompanying independent and dependent claims. Features of the dependent
claims may be combined with features of the independent claims as appropriate, and
in combinations other than those explicitly set out in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described further, with reference to
the accompanying drawings in which:
Figure 1 illustrates the main components of a telecommunications network according
to one embodiment;
Figure 2 illustrates schematically various configurations of primary and secondary
downlink carriers across a primary and secondary band for a four and three carrier
multi-carrier network;
Figure 3 illustrates schematically a method of deactivating secondary downlink carriers
in response to user equipment request according to one embodiment; and
Figure 4 illustrates schematically a method of deactivating secondary downlink carriers
in response to user equipment request according to a further embodiment.
DESCRIPTION OFTHE EMBODIMENTS
Figure 1 illustrates a wireless telecommunications system 10 according to one
embodiment. User equipment 50 roam through the wireless telecommunications
system. Base stations 20 are provided which support areas of radio coverage 30. A
number of such base stations 20 are provided and are distributed geographically in
order to provide a wide area of coverage to user equipment 50. When user equipment
is within a n area served by a base station 30, communications may be established
between the user equipment and the base station over associated radio links. Each
base station typically supports a number of sectors within the geographical area of
service 30.
Typically, a different antenna within a base station supports each associated sector.
Accordingly, each base station 20 has multiple antennae and signals sent through the
different antennae, are electronically weighted to provide a sectorized approach. Of
course it will be appreciated that Figure 1 illustrates a small subset of the total number
of user equipment and base stations that may be present in a typical communication
system.
The wireless communications system is managed by a Radio Network Controller (RNC)
40. The RNC 40 controls operation of the wireless communications system by
communicating with a plurality of base stations over a backhaul communications link
60. The network controller also communicates with user equipment 50 via each base
station and thus effectively manages the entire wireless communications system.
In a multi carrier system each sector served by a base station can have several carrier
frequencies or "carriers" associated therewith. A carrier or cell supported by a carrier
covers the same geographical region as a sector. Each cell is served by a different
carrier frequency. It will therefore be understood that in a single carrier system the cell
is equivalent to a sector since a sector has only one cell or carrier frequency.
Nonetheless, in a multi carrier network each sector may comprise several cells, each
cell being served simultaneously by a different carrier frequency.
User equipment 50 typically transmits information and data to a base station 20 so that
it can be re-routed within a wireless telecommunications network. User equipment
may, for example, need to transmit data to the base station in order to relay text
messages, voice information when a user is using the equipment to make a telephone
call, or other data. The base station 20, in combination with parameters set by the NC
40, allocate a resource to user equipment in a manner that aims to optimise operation
of the wireless telecommunications network 10. User equipment 50 can send data to a
base station on one or more carriers known as "uplink carriers".
A base station in a multi-carrier system is operable to communicate and send data and
information to user equipment on a set of down link carriers. In a multi carrier system,
having either multi carrier uplink or multi carrier downlink, each carrier will have
substantially independent downlink radio links from a base station to user equipment
and vice versa. The downlink radio links are managed independently, since each
carrier will likely have different radio publication paths to user equipment.
In a multi carrier system it has been agreed that one of the carriers will act as a socalled
anchor or primary carrier. The anchor carrier functionally operates such that it is
used as a basis upon which mobility events, handover, and other control
In one embodiment of a multi carrier system, known as 4 Carrier High Speed Downlink
Packet Access Network (4C-HSDPA), a sector is defined as the geographical coverage
area of a base station. The sector consists of several cells, in which each cell aims to
cover the same geographical area as the sector. Each cell uses a separate frequency
carrier for transmission. Each frequency carrier can be provided within the same
frequency band or distributed over two frequency bands. 4C-HSDPA offers the
possibility of user equipment being able to receive up to four simultaneous downlink
transmissions from four different cells, from one base station. It can therefore be
understood that 4C-HSDPA can potentially quadruple the downlink throughput of a
single carrier network.
4C-HSDPAconsists of one primary (or anchor) carrier and up to three secondary
carriers. The secondary carriers are indexed as secondary carrier 1, secondary carrier 2,
and secondary carrier 3. The primary carrier contains essential control channels and
cannot be deactivated without causing disruption to communication between a user
equipment and the base station. It will be understood that any one or more of the
secondary downlink carriers can be deactivated by a base station without substantially
disrupting communication and control between user equipment and a base station,
and that as long as a primary uplink carrier remains in operation, one or more
secondary uplink carriers, if provided, may be deactivated without disrupting
communication between user equipment and a base station.
Carriers in a multi-carrier network may be provided in one predetermined frequency
band, or may be provided across two or more predetermined frequency bands. Those
bands are provided in the radio spectrum. If all carriers in a multi-carrier network are
provided in a single frequency band, that band is known as the primary band. If the
carriers are spread over two predetermined frequency bands, the frequency band that
contains the primary carrier is known as the primary band and the frequency band that
contains only secondary carriers is referred to a sthe secondary band.
Figure 2 illustrates schematically various configurations of primary and secondary
downlink carriers across a primary and secondary band for a four and three carrier
multi-carrier network. Throughout the Primary band is denoted as 100, the secondary
band as 200. A primary carrier PI is provided in primary band 100. That primary band
may also contain one or more secondary carriers SI , S2, S3. The secondary band 200
contains only one or more secondary carriers SI, S2, S3.
User equipment 50 which is capable of receiving multi-carrier downlink carriers
configured over a primary and secondary band may require two receiver chains, one
for each frequency band. An energy saving may be achieved if, in periods of
appropriate network activity, user equipment 50 is able to deactivate the receiver
chain for the secondary band.
Autonomous user equipment deactivation of a receiver chain may, however, disrupt
base station scheduling since the base station may expect the downlink carriers in the
secondary band to be active. This may particularly be true if a base station and user
equipment are operating according to a discontinuous transmission and/or reception
mode in order to save energy.
User equipment 50 may operate in a "discontinuous reception" (DRx)or "discontinuous
transmission" (DTx) mode. Such modes allow user equipment 50 to save battery power
when the UE is in a n inactive period (for example, when user equipment is in a n idle
state).
During discontinuous reception user equipment 50 shuts down its reception antenna
and periodically wakes up to receive possible data traffic and information, for
example, paging messages, from wireless telecommunications network 0 via data sent
on downlink channels to user equipment 50 from base station 20. If the messages
received by user equipment 50 in the wake-up periods are deemed to exceed a
threshold, or indicate that base station 20 wishes to send more information to user
equipment 50, user equipment is operable to exit from the discontinuous reception
mode.
Similarly, a discontinuous transmission (DTx) mode may be implemented by user
equipment. In such a case, when in a substantially idle mode, user equipment shuts
down its transmitter and only wakes up periodically to transmit packets of data to the
network 10 via uplink channels to the base station 20.
In UMTS, the UE can be in a n idle (i.e. not connected) or a Connected mode. A UE in
idle mode does not have a Radio Resource Control (RRC) connection. If a UE is RRC
connected, it can be in one of five different RRC states, namely, CelLDCH, CelLFACH,
Enhanced CelLFACH, CelLPCH and URA_PCH states. A UE usually moves into
CelLDCH state when its traffic is high. In CelLDCH the DRx/DTx cycle is a function of
the Connection Frame Number (CFN), which has a size of 256 giving a maximum
DRx/DTx cycle of 0.256 seconds. The DRx/DTx cycle is expected to be short in CelLDCH
given the high traffic at the UE.
CelLDCH state is one of RRC states where the UE is capable of high download (and
upload) throughputs using HSDPAtransport channels. In CelLDCH, the network can
allow the UE to operate in Discontinuous Transmission (DTx) and/or Discontinuous
Reception (DRx) if the UE detects a pre-determined period of inactivity (uplink or
downlink). In DTx the UE shuts off its transmitter and turns it on periodically to transmit
the uplink pilot or when it needs to send essential control information (e.g. Scheduling
Information). Similarly in DRx, the UE shuts its receiver and only turns it on to periodically
turns on to receive data or when it needs to receive essential control information. This is
to conserve energy and extend the UE battery life.
If autonomously deactivating a secondary band receiver chain, UE 50 may
continuously transmit a NULL CQI (Channel Quality Index) on the primary uplink carrier
in relation to secondary carriers in the deactivated secondary band, thereby implicitly
indicating to a base station 20 that those carriers have been deactivated.
Such a method leaves a base station 20 essentially unaware that the UE 50 has
deactivated the secondary band receiver chain, since a NULL CQI is still interpreted as
the carrier being active but in a poor radio condition.
A base station may eventually deactivate such a downlink carrier but that deactivation
is based on implementation at the base station. If the UE re-activates a secondary
band reception chain and associated carriers, those reactivated carriers begin to
report valid CQI but the base station 20 may, depending on implementation criteria,
not instantly schedule high resources to that UE on those reactivated carriers since it has
been in poor radio condition for a period of time.
It is possible to implement secondary carrier deactivation such that a wireless
communications network 1 provides a configurable timer to each secondary carrier to
user equipment 50. On entry to a DTx/DRx mode user equipment 50 may start these
timers for each of their carriers and if there is no traffic activity when the timer expired,
the UE may automatically deactivate the secondary carrier whose timer has expired.
Use of such timers give a base station some time to prepare the scheduling for
secondary carrier deactivation by user equipment. However, since user equipment
may autonomously move into DTx/DRx mode, a base station will need to estimate
when a UE has entered DTx/DRx mode and hence a base station will not typically be
aware of when the timers have started. A base station can only estimate the start and
end of the timer which leads to uncertainty of the UE downlink secondary carrier
activation status. In the case where a base station is aware of the timer, it may lose
synchronization with the timer since it is possible that the timer may be restarted if the
user equipment receives data. For example, a base station sends a packet to user
equipment, but user equipment fails to receive it. User equipment may sent a DTx, to
indicate no packet has been received but the base station may misinterpret it as an
acknowledgement and wrongly assume a timer has been reset. Meanwhile, the timer
at UE times out and the UE deactivates a carrier, leaving a base station unaware of
that deactivation.
I† is possible for a network †o give permission †o a UE to allow autonomous secondary
carrier deactivation but restrict this to secondary carriers provided in a secondary
band. Reactivation of carriers that are autonomously deactivated may then only be
performed by a base station. Such a method still faces the problem that a base station
may be unaware that a secondary carrier has been deactivated by a UE. If a base
station is unaware that a carrier is deactivated, it will not act to activate it and thus UE
may lose operability and data throughput offered by a secondary downlink carrier
leading to lower than possible throughput performance.
A base station scheduler allocates downlink resources and also transmits packets to the
UE. Hence, if a base station schedules transmissions on a secondary carrier, it expects
that this secondary carrier is "activated" (able to be received) at the UE. If a base
station scheduler is unaware that reception of a secondary carrier has been
deactivated by user equipment 50 it may continue to retransmit packets to the UE.
That retransmission can cause unnecessary interference in cell 30.
In the downlink it is beneficial that a base station knows when reception of downlink
secondary carriers has been deactivated. A solution is to allow user equipment to
request, secondary carrier deactivation via layer 1or layer 2 signalling.
One such a request has been received by a base station, it may decide, based on a
set of predetermined criteria, whether to deactivate the requested secondary carriers.
Since energy saving can be best achieved by shutting off a receiver chain, it will be
appreciated that it offers greatest power savings to UE to request to deactivate a
group of secondary carriers attached to a receiver chain, for example, the set of
secondary carriers located within the secondary band.
Requesting individual deactivation of secondary carriers in a four carrier system may
require 3 bits in the request, where each bit represents the deactivation request for a
secondary carrier (e.g. 1 = request to deactivate, 0 = no change). Alternatively, if UE is
allowed to only request to turn off all secondary carriers in the secondary band, only 1
bit is required.
Upon receiving a request, a base station can decide to accept (or ignore) the UE
request from user equipment. If accepted, a base station may instruct deactivation of
secondary downlink carriers by using the existing carrier reconfiguration orders (HSSCCH)
orders to deactivate the requested downlink secondary carriers. In such a
scenario i† will be appreciated that a base station remains in control of deactivation of
downlink secondary carriers and this will not disrupt the base station scheduler.
It is possible that, after user equipment 50 sends a deactivation request which has not
been actioned by a base station, the conditions being experienced by user equipment
may change. For example, user equipment may exit DTx/DRx mode and no longer
wish to deactivate any secondary carriers. In such a case, UE sends another request to
the base station, which cancels the deactivation request sent previously. The
cancellation request may be sent using the same 3 bits used for the initial deactivation
request, for example, the UE can send "000" indicating a cancel (or no change to
secondary carrier activation status). In the case where UE has usedl bit to request for
deactivation of all carriers in the Secondary Band, the UE can send a "0" indicating
cancellation of previous request.
If the base station has failed to receive the previous deactivation request from user
equipment and then receives a cancellation request, a base station can be
configured to ignore the cancellation since it cannot have performed any
deactivation/activation to the UE secondary carriers based on the initial deactivation
request.
User equipment 50 may be operable to send a deactivation request to a base station
in a number of ways, including, for example:
• At Layer 1 using a reserved E-TFCI (E-DCH Transport Format Combination
Indicator) in E-DPCCH (E-DCH Dedicated Physical Control Channel).
• At Layer 1 using a reserved Channel Quality Indication (CQI) codeword (e.g.
CQI value of 31).
• A new Layer 1 message
• At Layer 2 adding 3 bits or 1 bit to MAC message. These additional bits may
only be sent when a deactivation request is needed.
• A new Layer 2 message
Figure 3 illustrates schematically a method of deactivating secondary downlink carriers
in response to user equipment request according to one embodiment. In the example
shown in Figure 3, a four downlink carrier multi-carrier network is provided, having four
carriers: a primary carrier PI, and three secondary carriers SI, S2, S3. PI and SI are
provided in primary band 100. S2 and S3 are provided in secondary band 200.
As illustrated schematically in Figure 3, UE is operating in DRx mode, and receivers
"wake up" at time slots indicated asT .
If the user equipment detects no activity on the downlink carriers for a predetermined
period of time, it may be configured to decide that the receiver chain corresponding
to the Secondary Band can be switched off to save energy, in the example
illustrated, a 3 bit request is used by the UE to indicate which secondary carrier it wishes
to deactivate. Here 1 = deactivate and 0 = no change and 1t bit = Secondary Carrier
1, 2nd bit = Secondary Carrier 2 and 3rd bit = Secondary Carrier 3.
In this example, to deactivate the Secondary Band, the UE would send "Oi l " to the NB.
The deactivation request is sent at 12.
The base station receiving the request evaluates its scheduler and, if conditions are
met, for example, there are no packets scheduled to be sent on the secondary carriers
in the immediate futures, can decide to grant the UE request. If the request is granted,
the base station sends a carrier reconfiguration order (HS-SCCH order) to the user
equipment to deactivate Secondary Carrier 2 and Secondary Carrier 3.
When the carriers in the Secondary Band are deactivated, the UE can turn off this
receiver chain. This deactivation is shown as period 300 in Figure 3.
Figure 4 illustrates schematically a method of deactivating secondary downlink carriers
in response to user equipment request according to a further embodiment.
The carrier configuration is initially analogous to that shown in Figure 3 and reference
numerals and letters have been reused as appropriate.
The UE is in DRx and detects no activity for a predetermined amount of time and
decides to request that the receiver chain corresponding to the Secondary Band be
be switched off to save energy. A 3 bit request is sent at T2 by the UE to indicate which
secondary carriers it wishes to deactivate. In this case, 1= deactivate and 0 = no
change and 1 bit = Secondary Carrier 1, 2nd bit = Secondary Carrier 2 and 3 d bit =
Secondary Carrier 3. To deactivate the Secondary Band, the UE would send 0 11" to
the NB.
In the scenario shown in Figure 4, the base station either fails to receive the request or
decides to execute this request at a later time and no carrier reconfiguration order is
sent to the user equipment.
Since the UE does not receive any HS-SCCH order to deactivate any secondary
carriers, it continues to operate with all the downlink secondary carriers in the
secondary band active.
At time T3, the UE exit the DTx/DRx mode, for example, because a user wishes to make
a call. Since the user equipment is not aware whether the base station is still processing
the previous deactivation request, it sends a cancellation with bit pattern "000". On
receiving the cancellation request, the base station may choose to ignore it it failed
to receive the initial request) or it will cancel the UE previous request to deactivate
downlink carriers in the Secondary Band.
Whilst the examples of Figure 3 and Figure 4 relate to use of a deactivation method in
which user equipment is in discontinuous transmission and reception mode, it will be
appreciated that the method may be used whilst the user equipment is not operating
in such discontinuous modes.
The method described allows user equipment to request to turn off one ore more
secondary carriers, thereby saving energy and battery life. By using a request system,
to which a base station may respond, the base station scheduler is not disrupted and
the base station remains in control of the downlink secondary carrier deactivation
process.
The base station may, of course, deactivate secondary carriers using appropriate
reconfiguration orders, even if no request has been received from user equipment, in
order to save energy. The method does, however, allow user equipment to have some
level of control, and is now wholly slave to the base station, since it can request
deactivation.
A person of skill in the art would readily recognize that steps of various above-described
methods can be performed by programmed computers. Herein, some embodiments
are also intended to cover program storage devices, e.g., digital data storage media,
which are machine or computer readable and encode machine-executable or
computer-executable programs of instructions, wherein said instructions perform some
or all of the steps of said above-described methods. The program storage devices may
be, e.g., digital memories, magnetic storage media such as a magnetic disks and
magnetic tapes, hard drives, or optically readable digital data storage media. The
embodiments are also intended to cover computers programmed to perform said
steps of the above-described methods.
The functions of the various elements shown in the Figures, including any functional
blocks labelled as "processors" or "logic", may be provided through the use of
dedicated hardware as well as hardware capable of executing software in association
with appropriate software. When provided by a processor, the functions may be
provided by a single dedicated processor, by a single shared processor, or by a
plurality of individual processors, some of which may be shared. Moreover, explicit use
of the term "processor" or "controller" or "logic" should not be construed to refer
exclusively to hardware capable of executing software, and may implicitly include,
without limitation, digital signal processor (DSP) hardware, network processor,
application specific integrated circuit (ASIC), field programmable gate array (FPGA),
read only memory (ROM) for storing software, random access memory (RAM), and non
volatile storage. Other hardware, conventional and/or custom, may also be included.
Similarly, any switches shown in the Figures are conceptual only. Their function may be
carried out through the operation of program logic, through dedicated logic, through
the interaction of program control and dedicated logic, or even manually, the
particular technique being selectable by the implementer as more specifically
understood from the context.
It should be appreciated by those skilled in the art that any block diagrams herein
represent conceptual views of illustrative circuitry embodying the principles of the
invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state
transition diagrams, pseudo code, and the like represent various processes which may
be substantially represented in computer readable medium and so executed by a
computer or processor, whether or not such computer or processor is explicitly shown.
The description and drawings merely illustrate the principles of the invention. It will thus
be appreciated that those skilled in the art will be able to devise various arrangements
that, although not explicitly described or shown herein, embody the principles of the
invention and are included within its spirit and scope. Furthermore, all examples recited
herein are principally intended expressly to be only for pedagogical purposes to aid the
reader in understanding the principles of the invention and the concepts contributed
by the inven†or(s) to furthering the art, and are to be construed as being without
limitation to such specifically recited examples and conditions. Moreover, all statements
herein reciting principles, aspects, and embodiments of the invention, as well as
specific examples thereof, are intended to encompass equivalents thereof.
CLAIMS
1. A method of controlling a carrier configuration of a network node in a multicarrier
wireless telecommunication network, said multi-carrier wireless
telecommunications network comprising a plurality of network nodes operable to
substantially simultaneously transmit and receive signals on more than one active radio
frequency carrier within a sector of said telecommunications network, said method
comprising the steps of:
monitoring an indication of data traffic received on at least one carrier to
determine whether said data traffic received over said time period meets a
predetermined set of conditions,
transmitting a request to deactivate said at least one carrier determined to
meet said conditions;
monitoring for receipt of a positive response to said request and implementing
deactivation for said at least one carrier for which a positive response is received.
2. A method according to claim 1, wherein said predetermined set of conditions
comprise an indication that substantially no data is being received on said at least one
carrier.
3. A method according to claim 1 or claim 2, wherein said wireless
telecommunications network is operable to simultaneously transmit and receive signals
on more than one radio frequency carrier, said radio frequency carriers comprising a
primary carrier and at least one secondary carrier, said carriers being spread over two
predetermined frequency bands, said primary carrier being provided in a primary
frequency band and at least one of said secondary carriers being provided in a
secondary frequency band.
4. A method according to claim 3, wherein said monitoring step further comprises
the step of monitoring at least one carrier provided in said secondary band to
determine whether said data traffic received over said time period meets said
predetermined set of conditions.
5. A method according to claim 3 or claim 4, wherein said transmitting step further
comprises the step of transmitting a secondary band deactivation request when all
carriers provided in said secondary band are determined to meet said predetermined
set of conditions.
6 . A method according to any one of claims 3 to 5, further comprising the step of
deactivating secondary band reception on receipt of said positive response for all of
said carriers provided in said secondary band.
7 . A method according to any preceding claim, wherein said method further
comprises the step of transmitting a cancellation request when it is determined a carrier
no longer meets said predetermined conditions.
8. A method according to any preceding claim, wherein said method steps are
performed whilst said wireless telecommunication network node is operating in
discontinuous transmission or reception mode.
9. A computer program product, operable when executed on a computer, to
perform the method of any one of claims 1to 8.
10. A network node operable to control a carrier configuration in a multi-carrier
wireless telecommunication network, said multi-carrier wireless telecommunications
network comprising a plurality of network nodes operable to substantially
simultaneously transmit and receive signals on more than one active radio frequency
carrier within a sector of said telecommunications network, said network node
comprising:
monitoring logic operable to monitor an indication of data traffic received over
a predetermined time period on at least one carrier to determine whether said data
traffic received meets a predetermined set of conditions,
transmission logic operable to transmit a request to deactivate said at least one
carrier determined to meet said conditions;
response logic operable to monitor for receipt of a positive response to said
request and implement deactivation for said at least one carrier for which a positive
response is received.
11. A method of controlling a carrier configuration of a network node in a multicarrier
wireless telecommunication network, said multi-carrier wireless
telecommunications network comprising a plurality of network nodes operable to
substantially simultaneously transmit and receive signals on more than one active radio
frequency carrier within a sector of said telecommunications network, said method
comprising the steps of:
monitoring for a request to deactivate at least one carrier said request being
indicative that data traffic on said at least one carrier has been determined to meet a
predetermined set of conditions
determining, in response to said request to deactivate said at least one carrier,
whether a set of carrier deactivation conditions have been met, and
transmitting a positive response to said request if said carrier deactivation
conditions have been met.
12. A method according to claim 11, further comprising the steps of:
storing an indication of receipt of said request and
periodically repeating said step of determining.
13. A method according to claim 1 or claim 12, wherein said set of carrier
deactivation conditions comprise an indication that a carrier is not scheduled to be
used for transmission for a predetermined time period.
14. A computer program product, operable when executed on a computer, to
perform the method of any one of claims 11to 13.
15. A network node operable to control carrier configuration in a multi-carrier
wireless telecommunication network, said multi-carrier wireless telecommunications
network comprising a plurality of network nodes operable to substantially
simultaneously transmit and receive signals on more than one active radio frequency
carrier within a sector of said telecommunications network, said network node
comprising:
request monitoring logic operable to monitor for a request to deactivate at
least one carrier said request being indicative that, over a predetermined time period,
data traffic on said at least one carrier has been determined to meet a predetermined
set of conditions;
determination logic, operable to determine, in response to said request to
deactivate said at least one carrier, whether a set of carrier deactivation conditions
have been met, and
response transmission logic operable to transmit a positive response to said
request if said carrier deactivation conditions have been met.