Multi Carrier Network Configuration
FIELD OFTHE INVENTION
The present invention relates to a method of acknowledging receipt of a control
message instructing a change in carrier configuration in a multi-carrier wireless
telecommunications network, a network node, base station, and user equipment
operable to carry out that method, and a computer program product.
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.
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 can be within the same frequency band, or
region of radio spectrum, or distributed over two frequency bands provided in the radio
spectrum.
4C-HSDPA is an extension to Dual Cell High Speed Downlink Packet Access (DCHSDPA).
It should be understood that 4C-HSDPAcan potentially double and quadruple
the downlink throughput of DC-HSDPA and single cell HSDPA respectively. 4C-HSDPA
may also be referred to as MC-HSDPA (Mul†i Carrier HSDPA) or 3C-HSDPA when a base
station transmits (or a user equipment receives) simultaneous transmissions from four or
more or three cells respectively.
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 by messages in the uplink.
In a multi-carrier system, there will typically be provided one "primary" 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.
One or more of the secondary carriers can, however, be deactivated without loss of
functionality. A base station may choose to deactivate a carrier if it is experiencing
particularly poor radio condition. Downlink carriers may be deactivated or activated
by a base station using a High Speed Shared Control Channel (HS-SCCH) Order. User
equipment acts to return feedback that the order has been received. That feedback is
sent by user equipment using a High Speed Dedicated Physical Control Channel (HSDPCCH),
a feedback channel provided on the primary uplink carrier.
The HS-DPCCH channel is also used to send information regarding the downlink carrier
radio conditions experienced by the user equipment. That information is included in a
single message which also includes feedback relating to a n HS-SCCH order, if received.
In particular, the message sent by User Equipment on that channel relating to radio
conditions being experienced includes information relating to the channel quality, also
known as the Channel Quality Indicator (CQI) (for which 1= bad; 30=best) and a Pre-
Coding Control Indication (PCI), if appropriate.
If a base station fails to receive feedback or incorrectly interprets feedback that user
equipment has received a n order to deactivate (or reactivate) one or more secondary
downlink carriers when the order has not been received by user equipment, it
reconfigures downlink carrier transmission. As a result, information sent relating to
downlink carrier radio condition on an HS-DPCCH channel from the user equipment to
a base station subsequent to any reconfiguration may be misinterpreted by a base
station, thus leading to inefficiency and reduced functionality in the wireless
communications network.
Accordingly, it is desired to improve the resilience of the reconfiguration process in a
multi-carrier wireless telecommunication network.
SUMMARY
Accordingly, a first aspect provides a method of acknowledging receipt of a control
message instructing a change in 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 method comprising the steps of:
receiving the control message,
encoding a n acknowledgement of safe receipt of the control message,
transmitting the acknowledgement of safe receipt, and a predetermined period after
the transmission of the acknowledgement of safe receipt, re-transmitting the
acknowledgement of safe receipt.
Multi-carrier high speed downlink packet access networks typically consist of one
primary carrier and a number of secondary carriers. Secondary carriers are indexed as
secondary carrier 1, secondary carrier 2, and so forth. A primary downlink carrier
contains essential control channels and cannot be deactivated. Secondary downlink
carriers may be deactivated by a base station. As explained above, in order to
deactivate one or more secondary carriers, a base station uses a High Speed Shared
Control Channel (HS-SCCH) Order. User equipment acknowledges receipt of such a n
order using a feedback channel, known as a High Speed Dedicated Physical Control
Channel (HS-DPCCH). That channel is also used by user equipment to send feedback
information regarding the downlink radio conditions being experienced by that user
equipment on each carrier. That information includes the CQI and PCI for each
channel.
In a single carrier system, the HS-DPCCH typically uses a spreading factor of 256. In a
multi-carrier network, for example a 4C-HSDPA the HS-DPCCH may use a spreading
factor of 128. Such a spreading factor operates to take the number of symbols or bits in
the original signal and increase it by a factor of 28, thereby increasing the coding gain
of the signal. That is to say, the signal is 128 times stronger, or requires 128 less signal to
noise ratio to be correctly received.
The size of the feedback message, including feedback regarding whether a
reconfiguration order has been received and radio condition being experienced by
carriers, remains constant, irrespective of how many carriers are activated in the multicarrier
wireless telecommunications network. In other words, when only one carrier is
activated, the entire message may be dedicated to feeding back information
regarding that single carrier. If feedback information is required for two carriers, half of
the message may be allocated to feeding back information relating to each of those
carriers. As the number of carriers in a multi-carrier system increases, it will be
understood that the portion of message allocated to each carrier is restricted.
Furthermore, it will be understood that as the number of active carriers increases, the
difference between messages indicating various statuses of radio condition and
feedback diminishes. That is to say, the Hamming distance between different states or
codewords reduces. If the protection offered to the feedback information is less, the
likelihood of misinterpretation of that message increases. That is to say, the feedback
message consists of acknowledgements (ACK/NACK/DTX) and CQI/PCI. 10 bits are
used for the acknowledgements and a bit pattern (codeword) is used to represent a
status. More possible statuses results in more codewords, and the differences between
two codewords e number of bits that are different) becomes smaller, ie Hamming
distance shrinks. This may lead to it being prone to error. The other portion of the
feedback message, such as the CQI and PCI, typically uses additional bits for coding
gain. In the case of CQI and PCI, the final product is typically 20 bits, so if a CQI is
longer (to code the extra carrier) less padding is used. For example, in single carrier,
CQI is, say, 5 bits, 15 bits may be used for padding. For two carriers, CQI is 0 bits, and
10 bits may be used for padding.
It will be appreciated that if a base station changes downlink carrier configuration and
instructs that configuration change, it will modify its expectation regarding the format of
the message which will be transmitted by user equipment encoding feedback
information regarding the state of the various carriers. In particular, if a base station is
operating using two downlink carriers, then activates two further carriers, the messages
expected after the reconfiguration ought to relate to four carriers, not two. It will
therefore be understood that if the user equipment does not receive the
reconfiguration order, or receives the reconfiguration order yet does not successfully
acknowledge receipt of that order to a base station, or that a message is interpreted
as a n acknowledgement when no reconfiguration order was received by user
equipment, there is significant scope for a base station to misinterpret the feedback
information being sent by user equipment.
The first aspect recognises that by sending an acknowledgement message to a base
station, then waiting a predetermined period of time before automatically re
transmitting that acknowledgement can increase the chance that the
acknowledgement message is successfully received and correctly interpreted by the
base station.
By repeating the message, rather than increasing power, the likelihood of interference
is minimized. Although a repetition may take time which otherwise may be used for
user data, if a n acknowledgement of a reconfiguration order is successfully received,
that short-term inefficiency is compensated for by improved overall network
performance. A base station may be configured to expect the repetition of
transmission.
In one embodiment, the method comprises the step of more than one retransmission.
Accordingly, further repeating transmission of the acknowledgement may further
increase the likelihood of successful receipt by a base station. The number of
repetitions may be configured and agreed between user equipment and a base
station in response to field testing in order to balance potential disruption to user data
being sent by retransmitting the acknowledgement message with improved overall
network performance.
In one embodiment, the method further comprises the steps of reconfiguring hardware
in response to the instructed change in carrier configuration. Accordingly, the
reconfiguration may be carried out directly in response to receipt of a reconfiguration
order. Reconfiguration of hardware may, however, be delayed until after the
retransmission of the acknowledgement occurs.
In one embodiment, the step of transmitting the acknowledgement of safe receipt
occurs prior to the step of reconfiguring hardware and the step of re-transmitting said
acknowledgement of safe receipt occurs after the step of reconfiguring hardware.
In one embodiment, the step of transmitting the acknowledgement of safe receipt,
occurs prior to the step of reconfiguring hardware and the step of re-transmitting the
acknowledgement of safe receipt occurs during the step of reconfiguring hardware.
Accordingly, it will be understood that typically user equipment allows a reception
reconfiguration period of, for example, 12 time slots. During this reconfiguration of
reception apparatus, the user equipment may still retain full uplink (transmission)
functionality. Depending on configuration, it will thus be understood that user
equipment may send the retransmission of acknowledgement of safe receipt one or
more times during hardware reconfiguration.
In one embodiment, the step of encoding an acknowledgement of safe receipt of the
control message comprises encoding an acknowledgement of safe receipt comprising
additional coding operable to reduce misinterpretation of the acknowledgement.
Accordingly, rather than sending a message which includes a large proportion of
information relating to the status of radio carriers, and in which the feedback
confirming safe receipt of the reconfiguration order may be only a very small portion, a
greater portion of message may be allocated to an acknowledgement of safe receipt
of a reconfiguration order. It will be appreciated that in such an arrangement a base
station may not receive radio condition feedback for all carriers, as might usually be
expected in a feedback message of which the acknowledgement of safe receipt
forms part. However, CQI information is not required for deactivated carriers after user
equipment reconfiguration. A base station may stop sending data packets on
deactivated carriers after a reconfiguration order is sent, and hence no longer needs
CQI information in respect of those carriers.
In one embodiment, the additional coding comprises additional redundancy.
Accordingly, the proportion of a feedback message allocated to the
acknowledgement of safe receipt message may be increased. The larger message
includes tolerance such that the message can be successfully decoded, even with a
degree of corruption or errors.
In one embodiment, the additional coding comprises a check sum, or a cyclic
redundancy check. A check sum may allow errors in an acknowledgement of safe
receipt message to be detected. Accordingly, if an error is detected, a base station
may await a repetition of that acknowledgement message.
In one embodiment, the acknowledgement of safe receipt comprises a message of
predetermined length.
The message may comprise a predetermined (unique) codeword acting asa special
acknowledgement that acknowledges ONLYreceipt of a reconfiguration. In this
respect, the message only acknowledges the order (one acknowledgement) thereby
giving opportunity for more coding gain.
In one embodiment, the control message comprises an instruction to activate or
deactivate one or more carriers in a multi-carrier wireless telecommunications network.
In one embodiment, the control message comprises an order to activate or deactivate
reception of downlink carriers in a multi-carrier wireless telecommunications network. In
one embodiment, the control message comprises an order to activate or deactivate
transmission of uplink carriers in a multi-carrier wireless telecommunications network.
Although primarily discussed in relation to downlink carrier activation and deactivation,
it will be appreciated that the method disclosed herein has analogous application in
an uplink carrier scenario.
In one embodiment, the acknowledgement of safe receipt is transmitted on an existing
control channel associated with a carrier. In one embodiment, the encoding step
comprises selection of a known codeword in response to receipt of the control
message. Accordingly, the acknowledgement comprising additional coding may
comprise a newly defined codeword in, for example, an HS-DPCCH, or a new physical
channel. It may, however, be possible, in order to avoid having to redesign a new
codeword or physical channel, to re-use existing codewords for the HS-DPCCH in an
atypical context, such that they have a high likelihood of safe and accurate receipt at
a base station.
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 acknowledge receipt of a control
message instructing a change in 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:
reception logic operable to receive the control message,
encoding logic operable to encode an acknowledgement of safe receipt of
the control message, and
transmission logic operable to transmit the acknowledgement of safe receipt,
and a predetermined period after the transmission of the acknowledgement of safe
receipt, re-transmit the acknowledgement of safe receipt.
In one embodiment, said network node comprises user equipment. In one
embodiment, said network node comprises a base station.
In one embodiment, said transmission logic is further operable to perform more than
one repetition.
In one embodiment, the network node further comprises reconfiguration logic
operable to reconfigure hardware in response to the instructed change in carrier
configuration.
In one embodiment, the transmission logic is operable to perform the step of
transmitting acknowledgement of safe receipt prior to said step of reconfiguring
hardware and perform the step of re-transmitting said acknowledgement of safe
receipt after the step of reconfiguring hardware.
In one embodiment the transmission logic is operable to perform the step of
transmitting said acknowledgement of safe receipt prior to the step of reconfiguring
hardware and perform the step of re-transmitting the acknowledgement of safe
receipt occurs during the step of reconfiguring hardware.
In one embodiment the encoding logic is operable to encode an acknowledgement
of safe receipt comprising additional coding operable to reduce misinterpretation of
the acknowledgement.
In one embodiment the additional coding comprises additional redundancy.
In one embodiment, the additional coding comprises a check sum.
In one embodiment the acknowledgement of safe receipt comprises a message of
predetermined length.
In one embodiment, the control message comprises an instruction to activate or
deactivate one or more carriers in a multi-carrier wireless telecommunications network.
In one embodiment the control message comprises an order to activate or deactivate
reception of downlink carriers in a multi-carrier wireless telecommunications network.
In one embodiment the transmission logic is operable to transmit the
acknowledgement of safe receipt on an existing control channel associated with a
carrier.
In one embodiment the encoding logic is operable to select a known codeword in
response to receipt of the control message.
A fourth aspect provides a method of acknowledging receipt of a control message
instructing a change in 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 method comprising the steps of:
receiving the control message.
encoding an acknowledgement of safe receipt of the control message
comprising additional coding operable to reduce misinterpretation of the
acknowledgement; and
transmitting the encoded acknowledgement of safe receipt.
Accordingly, rather than sending a message which includes a large proportion of
information relating to the status of radio carriers, and in which the feedback
confirming safe receipt of the reconfiguration order may be only a very small portion, a
greater portion of message may be allocated to an acknowledgement of safe receipt
of a reconfiguration order. It will be appreciated that in such an arrangement a base
station may not receive radio condition feedback for all carriers, as might usually be
expected in a feedback message of which the acknowledgement of safe receipt
forms part. However, CQI information is not required for deactivated carriers after user
equipment reconfiguration. A base station may stop sending data packets on
deactivated carriers after a reconfiguration order is sent, and hence no longer needs
CQI information in respect of those carriers. It will be appreciated that the advantages
offered by additional coding may reduce the requirement to repeat transmission of the
acknowledgement of safe receipt.
In one embodiment, the additional coding comprises additional redundancy.
Accordingly, the proportion of a feedback message allocated to the
acknowledgement of safe receipt message may be increased. The larger message
includes tolerance such that the message can be successfully decoded, even with a
degree of corruption or errors.
In one embodiment, the additional coding comprises a check sum, or a cyclic
redundancy check. A check sum may allow errors in an acknowledgement of safe
receipt message to be detected. Accordingly, if an error is detected, a base station
may await a repetition of that acknowledgement message.
In one embodiment, the acknowledgement of safe receipt comprises a message of
predetermined length.
In one embodiment, the method further comprises the step of transmitting the
acknowledgement of safe receipt, and a predetermined period after the transmission
of the acknowledgement of safe receipt, re-transmitting the acknowledgement of safe
receipt.
In one embodiment, the method comprises the step of more than one repetition.
Accordingly, further repeating transmission of the acknowledgement may further
increase the likelihood of successful receipt by a base station. The number of
repetitions may be configured and agreed between user equipment and a base
station in response to field testing in order to balance potential disruption to user data
being sent by retransmitting the acknowledgement message with improved overall
network performance.
In one embodiment, the method further comprises the steps of reconfiguring hardware
in response to the instructed change in carrier configuration. Accordingly, the
reconfiguration may be carried out directly in response to receipt of a reconfiguration
order. Reconfiguration of hardware may, however, be delayed until after the
retransmission of the acknowledgement occurs.
In one embodiment, the step of transmitting the acknowledgement of safe receipt
occurs prior to the step of reconfiguring hardware and the step of re-transmitting said
acknowledgement of safe receipt occurs after the step of reconfiguring hardware.
In one embodiment, the step of transmitting the acknowledgement of safe receipt,
occurs prior to the step of reconfiguring hardware and the step of re-transmitting the
acknowledgement of safe receipt occurs during the step of reconfiguring hardware.
Accordingly, it will be understood that typically user equipment allows a reception
reconfiguration period of, for example, 12 time slots. During this reconfiguration of
reception apparatus, the user equipment may still retain full uplink (transmission)
functionality. Depending on configuration, it will thus be understood that user
equipment may send the retransmission of acknowledgement of safe receipt one or
more times during hardware reconfiguration.
In one embodiment, the control message comprises an order to activate or deactivate
reception of downlink carriers in a multi-carrier wireless telecommunications network. In
one embodiment, the control message comprises a n order to activate or deactivate
transmission of uplink carriers in a multi-carrier wireless telecommunications network.
Although primarily discussed in relation to downlink carrier activation and deactivation,
it will be appreciated that the method disclosed herein has analogous application in
an uplink carrier scenario.
In one embodiment, the acknowledgement of safe receipt is transmitted on a n existing
control channel associated with a carrier. In one embodiment, the encoding step
comprises selection of a known codeword in response to receipt of the control
message. Accordingly, the acknowledgement comprising additional coding may
comprise a newly defined codeword in, for example, an HS-DPCCH, or a new physical
channel. It may, however, be possible, in order to avoid having to redesign a new
codeword or physical channel, to re-use existing codewords for the HS-DPCCH in an
atypical context, such that they have a high likelihood of safe and accurate receipt at
a base station.
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 acknowledge receipt of a control
message instructing a change in 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:
reception logic operable to receive the control message,
encoding logic operable to encode an acknowledgement of safe receipt of
the control message comprising additional coding operable to reduce
misinterpretation of the acknowledgement; and
transmission logic operable to transmit the acknowledgement of safe receipt.
In one embodiment, the network node comprises a base station. IN one embodiment,
the network node comprises user equipment.
In one embodiment, the additional coding comprises additional redundancy.
In one embodiment, the additional coding comprises a check sum.
In one embodiment, the acknowledgement of safe receipt comprises a message of
predetermined length.
In one embodiment, the transmission logic is further operable to transmit the
acknowledgement of safe receipt, and a predetermined period after the transmission
of the acknowledgement of safe receipt, re-transmitting the acknowledgement of safe
receipt.
In one embodiment the transmission logic is operable to perform the step of more than
one repetition.
In one embodiment the network node further comprises reconfiguration logic
operable to reconfigure hardware in response to the instructed change in carrier
configuration.
In one embodiment the transmission logic is operable to perform the step of
transmitting acknowledgement of safe receipt prior to said step of reconfiguring
hardware and perform the step of re-transmitting said acknowledgement of safe
receipt after the step of reconfiguring hardware.
In one embodiment the transmission logic is operable to perform the step of
transmitting said acknowledgement of safe receipt prior to the step of reconfiguring
hardware and perform the step of re-transmitting the acknowledgement of safe
receipt occurs during the step of reconfiguring hardware.
In one embodiment the control message comprises an instruction to activate or
deactivate one or more carriers in a multi-carrier wireless telecommunications network.
In one embodiment the control message comprises an order to activate or deactivate
reception of downlink carriers in a multi-carrier wireless telecommunications network.
In one embodiment the transmission logic is operable to transmit the
acknowledgement of safe receipt on an existing control channel associated with a
carrier.
In one embodiment the encoding logic is operable to select a known codeword in
response to receipt of the control message.
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 2a is a schematic illustration of a method of carrier reconfiguration of a multicarrier
network;
Figure 2b is a schematic illustration of a possible issue whilst the reconfiguring a multicarrier
network;
Figure 2c is a schematic illustration of a further possible issue when reconfiguring a multicarrier
network;
Figure 3 illustrates schematically one embodiment of channel reconfiguration
according to one embodiment;
Figure 4 illustrates schematically a possible special acknowledgement format for use in
one embodiment;
Figure 5 illustrates schematically a possible alternative special acknowledgement for
use in one embodiment;
Figure 6 illustrates schematically a reconfiguration method according to one
embodiment utilising a special acknowledgement; and
Figure 7 illustrates schematically a reconfiguration method according to a further
embodiment utilising a special acknowledgement.
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 RNC
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-HSDPA consists 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 carriers 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.
A base station is operable to deactivate or reactivate any one or more of the
secondary downlink carriers using a High Speed Shared Control Channel (HS-SCCH)
order. If sent, and successfully received, user equipment acknowledges receipt of a n
HS-SCCH order by using a feedback message which is sent to the base station on a
High Speed Dedicated Physical Control Channel (HS-DPCCH) provided on a n uplink
carrier. That channel operates, in such a context, as a feedback channel.
The acknowledgement is sent as part of a message which also includes information
regarding the downlink radio conditions being experienced by that user equipment for
each currently activated carrier. The message includes information regarding Channel
Quality Indicator (CQI) and Pre-coding Control Indication (PCI), and is typically of a
fixed size, irrespective of how many downlink channels are in operation.
The message is sent from user equipment to a base station using a spreading factor of
128. Each symbol in the signal is multiplied by a code of length 128 symbols. The total
number of symbols in the original signal is therefore increased by 128. Such coding
practice increases the gain of the signal by a factor of 128. That is to say, the signal is
128 times "stronger" or requires 128 times less signal to noise ratio to be safely received.
Figure 2a is a schematic illustration of a method of reconfiguring downlink carriers in a
multi-carrier network. In particular, base station 20 is operating to communicate with
user equipment 50. In this particular embodiment, a 4C-HSDPA network is schematically
illustrated. That is to say, base station 20 provides for downlink carriers CI, C2, C3, C4
on which it communicates with user equipment 50. A time axis in Figure 2a runs
vertically down the page.
In Figure 2a the base station and user equipment are initially operating using all four
downlink carriers. Whilst operating normally, the user equipment sends feedback
information 100 for each carrier 100A, 100B, lOOC, 100D using a n HS-DPCCH physical
channel, using a spreading factor of 128. That feedback information 100 is sent (as
indicated by arrow 10 ) to base station 20
In order to reconfigure downlink carrier configuration for user equipment 50, base
station 20 sends (as indicated by arrow 121) an SC-SCCH order 120 to user equipment
50 instructing reconfiguration of the downlink carriers. In the example shown in Figure
2a, base station 20 decides to deactivate carriers C2 and C3 and sends HS-SCCH
orders to that effect.
In the scenario shown in Figure 2a user equipment 50 acknowledges safe receipt of the
HS-SCCH order by means of a n acknowledgement sent as part of the information
relating to carrier 1 (CI), ie the acknowledgement of receipt of the reconfiguration
order is sent to base station 20 within information 100a.
User equipment 50, having successfully received the instruction to reconfigure,
proceeds to reconfigure itself (indicated by arrow 131) to operate one of the two
carriers, namely CI and C4, as requested by base station 20.
In this particular example, since only two carriers remain active, in reporting future
feedback information regarding those carriers - that is to say, information regarding the
downlink radio conditions on carriers 1 and 4, including CQI and PCI - the user
equipment may repeat that feedback information 100a, 100c relating to CI and C4
within the feedback information message 100.
Since the base station has received an acknowledgement from the user equipment
and knows that the user equipment has successfully been able to reconfigure, it will
also know that the new feedback information transmitted by the user equipment
includes repetition and can operate to combines the feedback information 100a, 100c
from the repetitions in message 100 to obtain processing gain.
Figure 2b is a schematic illustration of a possible issue when reconfiguring a multi carrier
network. The scenario illustrated is directly analogous to that illustrated in Figure 2a, in
that the network comprises a 4C-HSDPA network in which the base station is initially
using all four carriers and then decides to deactivate carrier 2 and carrier 3.
Corresponding reference numerals have been re-used where appropriate.
In this case, although the user equipment successfully receives the order to reconfigure
and reconfigures to operate only with CI and C4, the acknowledgement sent by user
equipment 50 to base station 20 is not successfully received by the base station.
The user equipment 50 proceeds to reconfigure 131 to operate the two carriers and
acts to repeat the information 100a, 100c for the two active carriers when sending
feedback information after reconfiguration. In this situation (where information is
repeated within feedback message 100) the transmit power for HS-DPCCH transmissions
is typically reduced by a factor of 2, ie reduced by 3 decibels, since the base station 20
can, if aware of the new format of the message, utilise coding gain to correctly
interpret the messages from the repetition.
In the scenario illustrated in Figure 2b, the user equipment repeats the feedback
information for the two remaining active carriers and sends it to the base station with 3
decibels less power. Since no acknowledgement is received by the base station, the
base station assumes that the user equipment did not receive the order and that the
information being sent by the user equipment relates to four carriers. The base station
in this case fails to decode that the carriers which were deactivated by the user
equipment (namely carrier 2 and carrier 3) are no longer being used by the user
equipment. Although some of the feedback information 100a, 100c for carrier 1 and
carrier 4 arrives in the same location within feedback message 100 as before carrier
deactivation, it is possible that the base station may also fail to decode those feedback
information messages, since they are now sent with 3 decibels less power and the base
station cannot take advantage of the processing gain offered by repetition.
Figure 2c is a schematic illustration of a further possible issue when reconfiguring a multi
carrier network. The scenario illustrated is directly analogous to that illustrated in Figures
2a and 2b, in that the network comprises a 4C-HSDPAnetwork in which the base station
is initially using all four carriers and then decides to deactivate carrier 2 and carrier 3.
Corresponding reference numerals have been re-used where appropriate.
In the scenario shown in Figure 2c, the user equipment fails to receive the HS-SCCH
order to deactivate carrier 2 and carrier 3. The base station, in the scenario illustrated,
then wrongly misinterprets a n HS-DPCCH message containing only usual feedback
information from the user equipment as an acknowledgement of its previous order to
reconfigure carrier configuration.
The user equipment continues to send feedback information relating to four carriers
without any transmit power reduction. As shown schematically in Figure 2c, the base
station 20 in this scenario is expecting the feedback to be a repetition of the two
carriers which it believes to be activated. The base station therefore wrongly assumes
feedback information 100b is actually 100c, and that feedback information 100c is a
repetition of 100a. Although the feedback information is sent without a power
reduction, the base station may try to combine that feedback information assuming a
feedback message format repetition has been employed, thereby failing to decode
any of the feedback information successfully.
It is desired to ensure that the process of sending feedback information (HS-DPCCH) in
response to a n HS-SCCH reconfiguration order is robust enough to minimise errors such
asthose illustrated schematically in Figures 2b and 2c.
It is possible, since the feedback information message 100 sent on the HS-DPCCH has
no error check, to mitigate the chances of error 1 and error 2 by increasing the
reliability of the feedback message sent on the HS-DPCCH being received at the base
station 20.
One way of achieving increased reliability may be to program user equipment 50 such
that if it does receive a reconfiguration order it automatically increases its transmission
power on the HS-DPCCH. The increase in transmit power may be continued after
receipt of an HS-SCCH order for several transmissions, or a predetermined period of
time. Such a n increase in power improves the probability that a base station will
receive a n acknowledgement sent in the HS-DPCCh feedback message 100, and
thereby reduces the probability of the type of error shown in Figure 2b. However, such
an increase in HS-DPCCH transmit power (or any transmit power) increases uplink
interference which degrades uplink throughput. Such interference would be
particularly significant if a base station decides to activate or deactivate secondary
carriers for more than one user equipment, for example if it wishes to switch off one of its
transmitters it may send such a reconfiguration order to deactivate a secondary carrier
for all user equipment currently attached to that base station. Furthermore, for those
user equipment operating at maximum transmit power, for example at a cell edge, if
additional power is provided to the HS-DPCCH it will need to scale or reduce its power
allocation for its primary data channel. That is to say, the channel responsible for uplink
of user data. Reduction in power for its uplink data channel will degrade its uplink
throughput.
Increasing transmit power for the feedback message 100 does not reduce the
likelihood of the scenario set out in Figure 2c, in which the user equipment fails to
receive the configuration change order in the first place.
It has been recognised that it may be possible to mitigate some of the errors shown in
Figure 2b and 2c by utilising repetition steps spaced in time and/or by use of a special
acknowledgement message.
Figure 3 illustrates schematically one embodiment of channel reconfiguration
according to one embodiment. The embodiment shown in Figure 3 utilises both
repetition and a special form of acknowledgement message, but it will be appreciated
that either repetition or a special form of acknowledgement message may equally be
utilised an offer improvements and mitigation of the errors shown in Figures 2b and 2c
without use of the other.
The scenario illustrated in Figure 3 is directly analogous to that illustrated in Figures 2a,
2b and 2c, in that the network comprises a 4C-HSDPA network in which the base station
is initially using all four carriers and then decides to deactivate carrier 2 and carrier 3.
Corresponding reference numerals have been re-used where appropriate.
According to the embodiment shown in Figure 3, when user equipment 50 receives a
carrier reconfiguration order 20 (HS-SCCH order) to deactivate or activate some of the
secondary carriers it will, as with the scenarios shown in Figures 2a-c, initially respond
with a standard acknowledgement forming part of the feedback channel (HS-DPCCH).
Assuming it has safely received the reconfiguration order, user equipment 50 then takes
2 slots to perform the reconfiguration 131 .
During those 12 slots there are typically no HS-DPA packets sent from the base station to
the user equipment. In the particular embodiment shown in Figure 3, the user
equipment 50 operates, having received an HS-SCCH order (120) to sending a repeat
of the reconfiguration order acknowledgement by using a special acknowledgement
message 200. The special acknowledgement message can be sent after the usual
feedback information on the usual feedback channel (HS-DPCCH). It will be
appreciated that in some embodiments it can be sent instead of the usual feedback
information.
The special acknowledgement 200 is typically chosen and can be better selected with
high coding gain or to incorporate a check sum, thereby increasing the chance that
the base station 20 will successfully recognise that an acknowledgement has been
sent. Furthermore, a special acknowledgement can be sent again after user
equipment reconfiguration, thereby further increasing the reliability of the
reconfiguration request acknowledgement. That repeated transmission of the special
acknowledgement message is represented as message 201 in Figure 3.
If the special acknowledgement is sent after usual feedback information, as shown in
Figure 3, the base station gets two confirmations: once from usual feedback
information and another from the special acknowledgement. Such an arrangement
may delay user equipment reconfiguration, since two messages are sent from user
equipment 50 before the reconfiguration process can commence. However, that
delay is typically of the order of one sub-frame (three time slots) and may not be
significant.
If a special acknowledgement is sent instead of the usual feedback information, the
base station does not get the acknowledgement for data packets sent on other,
secondary, carriers which are not used to send the reconfiguration order (ie does not
receive feedback information 100a, 100b, 100c and lOOd). The base station then also
misses out on CQI and PCI information for each of carriers CI to C4, but this is of less
relevance since that data is not needed after user equipment reconfiguration for those
carriers which are being deactivated. In that respect, a base station can stop sending
data packets on secondary carriers when it sends the reconfiguration order 120 and
hence, would not need acknowledgement and CQI and PCI information in respect of
those deactivated secondary carriers.
I† will be appreciated that it may be possible, depending on user equipment
implementation, that the special acknowledgement may be sent within the 12 slot time
period 131 usually allowed for reconfiguration. This is possible since, during carrier
reconfiguration, the user equipment typically needs only to reconfigure its downlink
reception configuration (the uplink transmission configuration may still be fully active).
In such a n arrangement, the special acknowledgement 200, or the usual feedback
information 100, may be sent several times to increase the probability of the
acknowledgement reaching a base station. In such a scenario, the base station may
be programmed to expect the special acknowledgement, or repetitions of the usual
feedback information, from user equipment during the reconfiguration period.
The special acknowledgement 200 may comprise a newly defined codeword for HSDPCCH,
or may comprise a new physical channel. It will be appreciated that to avoid
having to redesign a new codeword or physical channel, existing codewords for HSDPCCH
may be used. For example, it may be possible to re-use an existing codeword
that would typically be used in a single carrier scenario or network since the special
acknowledgement is performing only the task of acknowledging safe receipt of a
carrier reconfiguration order from the base station.
In such a scenario, it will be appreciated that whilst the codeword is configured to
include CQI and PCI information for a single carrier, the actual information is not
important since it is a special acknowledgement, performing the task of
acknowledging safe receipt of a reconfiguration order. As a result, the codeword may
be chosen to have a CQI of 0 . In such a scenario, since a spreading factor of 128 is
Typically used in a multi carrier arrangement, the single carrier codeword may be
repeated twice to match the usual length of message used in a single carrier system,
which uses a spreading factor of 256.
The format of one possible special acknowledgement is shown schematically in Figure
4. It will be appreciated that a base station expects such a format of message in
response to a reconfiguration order when a n embodiment of the present invention has
been implemented. Furthermore, the base station does not expect any other form of
acknowledgement, and a n absence of such a special acknowledgement indicates
that user equipment has failed to receive the carrier reconfiguration order.
The codeword illustrated schematically in Figure 4 represents a valid feedback
message 100 format when the user equipment has only one active downlink carrier.
That is to say, when it is not operating in multiple input multiple output mode and utilises
only the primary downlink carrier. Although such a codeword can be used in all
situations, to avoid conflicting the codeword shown in Figure 4 with a valid codeword
for one active carrier without multiple input multiple output, a codeword designed for
more than two streams can be used. In such a scenario a base station would not
expect user equipment with one active carrier to send feedback for two or more active
carriers, and modifying the codeword thereby makes the codeword distinct. In such a
scenario any of the feedback channel codewords for multiple carriers may be used -
for example, it may be possible to use a release 8 HS-DPCCH codeword for carriers
operating without MIMO. In such a scenario, a double acknowledgement may be
used, followed by a CQI = 0 and a CQI = 30. Two extreme ends of CQI are used, since
it is unlikely that one carrier is invalid whilst the other has the best possible radio
condition. Since the codeword utilises only two carriers, it is repeated to fill available
message length. Such a n arrangement is shown schematically in Figure 5. It will be
appreciated that any format of special acknowledgement may be used, but it must be
consistent and known by both user equipment and base station for it to operate
efficiently.
It will be appreciated that a special acknowledgement 200 works best if the message is
coded such that it utilises a high coding gain or utilises a check sum, for example.
Either method employs additional coding, and ensures that the acknowledgement
message is received more reliably by a base station.
Figure 6 illustrates schematically a reconfiguration method according to one
embodiment utilising a special acknowledgement. Such an arrangement illustrates
how one embodiment may enable recovery from the type of error illustrated
schematically in Figure 2b. Reference numerals have been re-used as appropriate.
In the scenario shown in Figure 6, the base station 20 initially operates with three active
downlink carriers CI, C2, C3. The base station 20 decides to deactivate two secondary
carriers (C2 and C3) and sends a reconfiguration order 120 which is received
successfully by user equipment 50. The user equipment sends a n acknowledgement to
the base station 20 using the usual feedback mechanism 100. The base station,
however, fails to receive that usual feedback information.
The user equipment 50 is configured such that when it receives a reconfiguration order
from base station 20 it automatically sends a special acknowledgement. In particular,
it is programmed to send two special acknowledgements 200 using a codeword such
a s that shown in Figure 4 . The base station 20 expects a normal feedback but that
message is not received. The base station also expects and receives two special
acknowledgements and realises that the user equipment has, in fact, successfully
received the reconfiguration order. In the scenario shown in Figure 6, the user
equipment is operable to send special acknowledgements during the 12 slot
reconfiguration period. After reconfiguration, the user equipment sends feedback
information for one carrier, since the two secondary carriers C2 and C3 have been
deactivated. The base station will thus be able to correctly decode the feedback
information sent post-reconfiguration, since it has received two special
acknowledgements 200 and knows that the user equipment has successfully received
the reconfiguration order.
Figure 7 illustrates schematically a reconfiguration method according to a further
embodiment utilising a special acknowledgement. In the scenario shown in Figure 7, it
can be seen how recovery from the type of error described in relation to Figure 2c may
be enabled. In the scenario illustrated in Figure 7, the base station 20 initially operates
using only one active carrier CI . The base station 20 decides to activate three
secondary carriers (C2, C3 and C4). The base station sends a reconfiguration order 120
to user equipment 50. However, the user equipment 50 fails to receive the order 120
and continues sending the usual feedbacks 100 relating to only the one active carrier
of which it is aware (CI), to the base station 50. In the scenario shown in Figure 2c the
base station could misunderstand the feedback sent by user equipment as an
acknowledgement to the reconfiguration order. In this case, the base station expects
two or more special acknowledgements but instead continues to receive normal
feedback messages 100 from the user equipment. As a result, the base station 20
realises that the user equipment 50 has not received the reconfiguration order 120 and
continues to decode the feedback being sent by user equipment using the previous
format (having one active carrier). Furthermore, having realised that the user
equipment 50 has not received the reconfiguration order 120, the base station 20 may
re-send the reconfiguration order 120 to activate C2, C3 and C4 (step not shown in
Figure 7).
It will be appreciated that embodiments of the present invention revolve around
increasing the probability of successfully receiving feedback information and, in
particular, an acknowledgement of the reconfiguration order. In particular, in each
case it is possible to resend the feedback with higher protection, for example by
specially coding the acknowledgement, or to increase the likelihood that a feedback
message is successfully received, that message may be repeated a number of times.
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 acknowledging receipt of a control message instructing a change
in carrier configuration in a multi-carrier wireless telecommunication network, said multicarrier
wireless telecommunications network comprising a plurality of network nodes
operable to substantially simultaneously transmit and receive signals on more than one
radio frequency carrier within a sector of said telecommunications network,
said method comprising the steps of:
receiving said control message,
encoding an acknowledgement of safe receipt of said control message,
transmitting said acknowledgement of safe receipt, and a predetermined period after
said transmission of said acknowledgement of safe receipt, re-transmitting said
acknowledgement of safe receipt.
2. A method according to claim 1, further comprising the step of more than one
retransmission.
3. A method according to claim 1or claim 2, further comprising the steps of
reconfiguring hardware in response to the instructed change in carrier configuration.
4 . A method according to claim 3, wherein said step of transmitting said
acknowledgement of safe receipt, occurs prior to said step of reconfiguring hardware
and said step of re-transmitting said acknowledgement of safe receipt occurs after said
step of reconfiguring hardware.
5. A method according to claim 3, wherein said step of transmitting said
acknowledgement of safe receipt, occurs prior to said step of reconfiguring hardware
and said step of re-transmitting said acknowledgement of safe receipt occurs during
said step of reconfiguring hardware.
6 . A method according to any preceding claim, wherein said step of encoding an
acknowledgement of safe receipt of said control message comprises encoding an
acknowledgement of safe receipt comprising additional coding operable to reduce
misinterpretation of said acknowledgement.
7. A method according to claim 6, wherein said additional coding comprises
additional redundancy.
8. A method according to claim 6 or claim 7, wherein said additional coding
comprises a check sum.
9. A method according to any preceding claim wherein said acknowledgement
of safe receipt comprises a message of predetermined length.
10. A method according to any preceding claim, wherein said control message
comprises an instruction to activate or deactivate one or more carriers in a multi-carrier
wireless telecommunications network.
1. A method according to claim 10, wherein said control message comprises an
order to activate or deactivate reception of downlink carriers in a multi-carrier wireless
telecommunications network.
12. A method according to any preceding claim, wherein said acknowledgement
of safe receipt is transmitted on an existing control channel associated with a carrier.
13. A method according to any preceding claim, wherein said encoding step
comprises selection of a known codeword in response to receipt of said control
message.
14. A computer program product operable, when executed on a computer, to
perform the method of any one of claims 1to 13 .
15. A network node operable to acknowledge receipt of a control message
instructing a change in 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 radio frequency carrier within a sector of said
telecommunications network,
said network node comprising:
reception logic operable to receive said control message,
encoding logic operable to encode an acknowledgement of safe receipt of
said control message, and
transmission logic operable to transmit said acknowledgement of safe receipt,
and a predetermined period after said transmission of said acknowledgement of safe
receipt, re-transmit said acknowledgement of safe receipt.