(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) | ||||||||||
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(57)
Abstract |
METHOD
In wireless communication systems such as cellular telecommunication networks, the area covered by the network is divided into a number of cells 2, such as shown in Figure 5. Each cell 2 is served by a base transceiver station BTS which transmits signals and receives signals from terminals MS located in the associated cell. These terminals MS may be mobile stations and able to move between the cells 2. The mobile terminals MS will thus communicate with the base transceiver station BTS serving the cell in which the particular mobile station is located. When a mobile station MS moves from one cell 2 to another, handoff (also known as"handover") will occur. In other words, the mobile station MS will stop communicating with the base transceiver station BTS in the old cell and start communicating with the base transceiver station BTS in the new cell.
For the communication of data between mobile stations MS and base
transceiver stations BTS, packet data transmission techniques are
sometimes used. The data to be transmitted is divided into
packets which also include information such as the address of the
destination to which the packet is being sent and the identity
of the packet such as its number. In known systems, it has been
a problem that handoff can cause the loss of packets of data. For
example,
These untransmitted packets will then be lost.
It has therefore been propose to send the same data packets to
more than one base transceiver station. Thus, the same data
packets would be sent to the first and second base transceiver
stations. In this
It is also desired that the delay in receiving data packets should be minimised.
It is therefore an aim of embodiments of the present invention to remove or at least mitigate the problems of the known arrangements.
According to a first aspect of the present invention there is
provided a method of transmitting packets or data in a
communication network comprising
By identifying which data packets have been received by the second station and ensuring that the next data packet which is transmitted by the third station is the next required packet, it can be ensured that even during handoff, that the second station receives all of the data packets. The next required packet may be the packet subsequent to the identified last packet or may be a data packet which is being retransmitted, the first transmission of that packet being unsuccessful.
Preferably, at least some of the packets of data to be transmitted to the second station are provided both to the first and third stations. This has the advantage that when the first station stops transmitting packets and the third station starts transmitting packets, the third station will already have the necessary packets including the packet following the identified last packet. The wireless network may comprise a common node connected to the first and third stations, said common node being arranged to transmit data packets to the first and third stations. The method may include the step of acknowledging by the second station the correct receipt of the data packet.
According to a second aspect of the present invention, there is
provided a method of transmitting packets of data in a
communication network comprising at least first to third stations
and at least one common node, said second station arranged to be
in communication with at least one of said first and third
stations and said first and third stations being connected with
said common node, the method comprising the steps of indicating
to a common node that the second station is reachable via both
Preferably, in both aspects, the data packets are provided both to the first and third stations when the second station has a predefined parameter with respect to the first and third stations. That predefined parameter may be defined by the geographic position of the second station with respect to the first and third stations. Thus, the circumstances in which the first and third stations receive the same data packets can be defined with respect to the location of the second station with respect to the first and third stations. In a cellular network, the location may be predefined for each cell. It should be noted that the location is preferably a zone.
Alternatively, and more preferably, the at least one predefined parameter is defined by at least one parameter of signals received from at least one of the first and third stations satisfying a predetermined criteria. The signals may be the data packets received from the first and/or third stations or alternatively may be some other signals such as control signals, reference signals etc.
The parameter may be the received power level at the second
station from at least one of the first and third stations. For
example, when the power level of a signal received from the first
station falls below a predetermined threshold, the beginning of
the location may be defined. Likewise, the end of the location
may be defined by the power level of a signal received from the
third station exceeds a predetermined level. Alternatively, the
parameter may be the ratio of the power levels of signals
received at the second station from the first and third stations.
Yet another alternative is that the parameter may be the signal quality received at the second station from the first and/or third stations. Another alternative is for the parameter to be based on the quantity of traffic, the quality of service and/or quality of the signals.
Preferably, the parameter is averaged over time before it is determined if the criteria is satisfied. Thus, anomalous readings which could adversely effect the operation of the system can be ignored.
Preferably, said predefined location includes a handoff zone in which said first station hands off to said third station in that said second station stops receiving data packets from said first station and starts receiving data packets from said third station. Preferably, the handoff zone is surrounded on either side by a zone in which the second station receives data packets from a respective one of said first and third stations, and said first and third stations are both provided with the data packets.
This ensures that when handoff occurs, the third station has the next data packet to be transmitted to the second station.
When handoff takes place, said second station transmits a signal to the third station to advise the third station of which packet or packets were received from the first station and said third station transmits the data packet identified as being required after the last packet to said second station.
Preferably, the data packets are stored in the first and third stations when provided thereto. This is of advantage particularly if the data packet needs to be retransmitted due to an error.
Additionally, it ensures that when handoff occurs, the third station will have the next data packet to be transmitted. When handoff takes place, the data packets preceding the next data packet to be transmitted may be discarded in the third station.
Preferably, said and third stations are base transceiver
Preferably, the base stations and mobile stations are part of a cellular telecommunication network.
The common node may not be advised of the occurrence of handoff.
This may be unnecessary if, for example, the first and third stations are both provided with the data packets.
It is preferred that the common node has a higher hierarchy than the first and third stations in the wireless network. However, it is possible that one of the first and second stations could also provide the common node function.
Preferably, said data storage means is in said common node and/or at least one of said first and third stations. The acknowledgement may be sent to the common node. The data storage means may comprise buffer means. The common node may associate a unique number with each packet and the same data packets, each of which is associated with the unique number, are transmitted from said common node to both of the first and third stations.
The unique number may be in or associated with the packet. The common node may control the removal of said identified data packet from the or each data storage means.
The first station may be in communication with a first node and the third station may be in communication with a second node, said first and second nodes being in communication with said common node. The acknowledgement may be forwarded to the common node by one of said first and second nodes and the common node may advise the other of the first and second nodes that an acknowledgment has been received.
Alternatively, the first station is connected to a first node and
the third station is connected to a second node and one of the
first and second nodes is arranged to be the common node and said
acknowledgements are forwarded
Alternatively, the
Preferably, the acknowledgment of the receipt of a packet is sent by the second station to at least one of said first and third stations.
The data storage means may be provided in the first and third stations and the common node may be arranged to cause a transmitted packet to be removed from said data storage means of at least one of said first and third stations on receipt of an acknowledgement that said transmitted packet has been received by said second station.
The network is preferably a wireless network but may alternatively be a wired network.
The communication network may be a general packet radio system (GPRS) in which said first and third stations are base stations or base station controllers and said common node is a SGSN. The first and third stations may be in communication with different SGSNs, one of said SGSNs being designated as the common node, the other SGSN being arranged to forward acknowledgements to the common node.
Alternatively, said wireless communication network is a GPRS network and said first and second stations are SGSNs and said common node is a GGSN. In a further alternative, the first and third stations are base stations and said common node is a base station controller.
The communication network preferably has a plurality of cells
and/or areas and said second station is able co register with one
or more cells and/or one or more areas of said network at the
same time. The decision as whether or not che second station
registers with one or more cells or areas
According to a further aspect of the invention, there is provided
a system of transmitting packets of data in a communication
network
For a better understanding of the present invention and as to how the same may be carried into effect, reference will now be made by way of example to the accompanying figures in which : - Figure 1 illustrates the principles of embodiments of the present invention ; Figure 2 schematically shows the structure of a data packet ; Figure 3 shows the power levels of signals received at a mobile station from two adjacent base transceiver stations versus distance ; Figure 4 shows a schematic view of elements of a cellular telecommunications network ; Figure 5 shows a schematic view of a cellular telecommunications network ; Figure 6 shows an alternative embodiment of the present invention in a GPRS network ; and Figure 7 shows a modification to the embodiment shown in Figure 6.
One embodiment of the present invention will be described in the
context of a cellular telecommunications network which uses the
GSM (Global System for Mobile communications) standard.
Reference will first be made to Figure 1 which shows a first base
transceiver station BTS1 and a second base transceiver station
BTS2. A mobile station MS1 is currently in the cell 4 which is
associated with the first base transceiver station BTS1 and is
moving towards the cell 6 which is associated with the second
base transceiver station
Embodiments of the present invention are particularly applicable
to the transmission of packets of data from base transceiver
stations to a given mobile station. Figure 2 illustrates
schematically one possible structure for a data packet 10 to be
transmitted from a base transceiver station to a given mobile
station. The data packet may have a fixed length or,
alternatively may have any suitable length. The data packet
includes address information 12 which defines the mobile station
to which the data packet 10 is to be sent. The data packet 10
also includes information 14 relating to the identity of the
packet. For example, this identifying information 14 may comprise
the number of the packet. It should be appreciated that the
address information 12 and the identifying information 14 may be
of predetermined length and occupy predetermined locations in the
data packet. This is followed by the data
Reference will now be made to Figure 4 which schematically shows some of the elements of a cellular telecommunications network.
As can be seen, the first and second base transceiver stations BTS1 and BTS2 are connected to a base station controller BSC2.
As can be seen from Figure 4, a third base transceiver station BTS3 is also connected to the same base station controller BSC2 as the first and second base transceiver stations BTS1 and BTS2.
In practice, each base station controller 2 can be connected to any number of base transceiver stations.
As can be seen, three base station controllers
Each base transceiver station BTS1-3 is provided with a memory 20 in the form of a buffer which is able to store the packets of data received from the base station controller BSC2.
Referring back to Figure 1 and to Figure 3, an embodiment of the present invention will now be explained. Initially, the mobile station MS1 is in the cell 4 associated with the first base transceiver station BTS1. This corresponds to the part of the graph indicated by reference number 22 in Figure 3. As can be seen, the power of the signal received from the first base transceiver station BTS1 by the mobile station is very much greater than the power level of the signal received from the second base transceiver station BTS2. Accordingly, the data packets will be transmitted from the base station controller 2 only to the first base transceiver station 1. The data packets will then be transmitted by the first base transceiver station BTS1 to the mobile station MS 1.
An automatic retransmission protocol is also used so that if the mobile station MS1 does not correctly receive a data packet, the mobile station MS1 advises the first base transceiver station BTS1 of this. The first base transceiver station BTS1 will then retransmit the incorrectly received data packet.
The next data packet will only be transmitted once the first base
transceiver station BTS1 has received an acknowledgement from the
mobile station MS1 that the previous packet has been correctly
received. Of course, if the first base transceiver station BTS1
receives an indication from the mobile station MS1 that it has
not correctly received the data packet, then that data packet is
retransmitted. Accordingly, the data packet is retained the
buffer 20 until confirmation has been received that a
The mobile station MS1 now enters a zone 24 which is adjacent to
the handoff area 8. As can be seen from Figure 3, the difference
between the power level of the signal received from the first
base transceiver station BTS1 and the second base transceiver
station BTS2 at the mobile station MS1 is becoming smaller. As
soon as the mobile station enters this zone 24, the mobile
station sends a signal to the first base transceiver station BTS1
which causes that first base transceiver station BTS1 to send a
signal to the base station controller
In one alternative,
As the mobile station MS1 continues to move towards the second base transceiver station BTS2, the mobile station will enter the handoff zone 8. As shown in Figure 3, the power level of the signal received at the mobile station MS1 from the first and second base transceiver stations will be of a similar level.
Handoff will occur at some point as the mobile station MS1 travels through this zone. The base station controller BSC2 continues to transmit the data packets to both the first base transceiver station BTS1 and the second base transceiver station BTS2. However, the first base transceiver station BTS1 will stop transmitting data packets to the mobile station MS1 and the second base transceiver station BTS2 will start transmitting packets to the mobile station MS 1.
It should be noted that in terms of the data packet
communication, hard handoff will be operated. In other words, the
connection between the mobile station MS1 and the first base
transceiver station BTS1 will be terminated before the connection
is made between the mobile station MS1 and the second base
transceiver station BTS2. When the connection between the first
base transceiver station BTS1 and the mobile station MS1 is
terminated, the mobile station will know the identity of the last
correctly received packet from the first base transceiver
station. After the connection has been established with the
second base transceiver station BTS2, the mobile station MS1 will
send the identity of the last correctly received packet to the
second base transceiver station BTS2. The identity
The second base transceiver station BTS2 will then discard all
the packets in its buffer 20 up to and including the last
identified data packet. The second base transceiver station BTS2
will then start transmitting data packets
It should be noted that there is no need to advise the base station controller that handoff has occurred between the first and second base transceiver stations BTS1 and BTS2. This is because the base station controller BSC2 continues to send data packets to both the first and the second base transceiver stations BTS1 and BTS2.
Zone 26 is similar to zone 24 in that the data packets will be sent to both the first and the second base transceiver stations BTS1 and BTS2 and in that only one base transceiver station, in this case the second base transceiver station BTS2, transmits to the mobile station MS1. As can be seen from Figure 3, the level of the signal received at the mobile station MS1 from the second base transceiver station BTS2 is increasing relative to the received level of the signal from the first base transceiver station BTS1.
When the mobile station reaches the edge of zone 26 and moves
into region 28, the level of the signal received from the second
base transceiver station BTS2 will be very much higher than that
received from the first base transceiver station BTS1. This can
be seen from Figure 3. Accordingly, at this point the mobile
station MS1 will advise the second base transceiver station BTS2
that the edge of zone 26 has been reached. This information is
passed on to the base station controller BSC2 which stops sending
the data packets
The zone defined by regions 24,8 and 26 constitutes a multicast zone in which the data packets are transmitted to both the first and the second base transceiver stations BTS1 and BTS2.
There are a number of different ways in which the zones 24,8 and 26 can be defined. For example, these zones may be predefined.
In this embodiment, the location of the mobile station with respect to the first and second base transceiver stations BTS1 and BTS2 would be determined. For example, region 24 would occur when the mobile station is between x and y meters from the first base transceiver station and a and b meters from the second base transceiver station BTS2. In other words, the regions have fixed geographic locations with respect to the first and second base transceiver stations BTS1 and BTS2.
However, a more preferred method of defining these regions is to
rely on received level of the signals from the respective base
transceiver stations. Thus, the beginning of region 24 occurs
when the received power level of the signal from the first base
transceiver station BTS1 is less than the value
Likewise, the end of region 26 can be defined as occurring when the signal received from the first base transceiver station falls below level P2.
The beginning of the handoff region 8 can be defined as occurring
when the level of the signal received from the first base
transceiver station BTS1 falls below the power level P3, which
is between levels P1 and P2. Likewise, the end of the handoff
region 8 can be defined as when the signal received from the
In embodiments of the present invention, it is not necessary to use both the values of P1 and P2. Whilst these values have been shown as occurring at the same time for the received power levels of the signals from the different base transceiver stations, in practice this may not occur and accordingly, it is more preferably to use the value P1 which is indicative that the signal from the closer base transceiver station has exceeded a given value. In summary, the decision as to the location of the beginning and end of each zone may be defined only by the levels of the signals received from the first base station or the second station.
Alternatively the beginning and/or end of at least one zone may be defined only by the power level of the signals received from the first base transceiver station BTS1 whilst the beginning and/or end of at least one zone may be defined only by the power level of the signals received from the second base transceiver station. Additionally or alternatively both the received power level of signals from both the first and second base transceiver stations may be used to define the beginning and/or end of a zone.
In an alternative embodiment of the present invention, instead
of looking at the absolute power levels of the signal received
at the mobile station MS1 from the first and/or second base
transceiver station BTS1 and BTS2, the ratio between those
signals can be considered. For example, the beginning of the
region 24 may be defined as occurring when
It is of course possible to use other parameters in order to determine the location of the various regions. For example, instead of power level, signal quality or quantity may be used or the values may be based on the amount of traffic.
Alternatively, the location of the regions can be determined based on the quality of service required by a mobile station.
This may depend on the application required by the mobile station. For example speech has a lower requirement than data.
The regions may be therefore smaller for data than speech.
For those embodiments of the present invention which rely on measurements of conditions within the cellular network in order to define the location of the regions, it is preferred that decisions be made on the basis of average values rather than instantaneous values. For example, in the case where the power level of the signals received from the first and/or second base transceiver stations are used in order to determine the location of the region, the level of the signals used is based on an average. This is so as to avoid anomalous increases or decreases in the signal from providing false results. The level of the signal may be averaged over a predetermined number of frames.
It should be noted that the same protocol relating to the acknowledgement and retransmission of incorrectly received data packets also takes place in zones 24,8 and 26.
It should be noted that the transmission of the data packets may take place within allocated slots in frames. However, it is also possible that the timing of the sending of the data packets be independent of the time slot and frame structure.
The power level measurements may be based on the power level of
the data packets received from the base transceiver station or
alternatively may be based on other
It should be noted that in embodiments of the present invention, there is no reason why the regions 24 and 26 should be of the same size. One or other of those regions may be larger than the other. However, in practice it is likely that both of these regions will be of a similar size.
The base switching center BSC2 may be arranged to contain a routing table which stores the base transceiver stations to which the data packets are to be broadcast.
It should be appreciated that whilst the present invention has been described in the context of a GSM system, embodiments of the present invention are equally applicable to other access systems including other types of time division multiple access systems, frequency division multiple access systems, base division multiple access systems, spread spectrum multiple access systems such as code division multiple access and hybrids thereof. In one implementation of embodiments of the present invention in code division multiple access systems, whilst soft handoff may be used, the packets which are to be transmitted may or may not be transmitted to the mobile station by more than one base transceiver station at a time. Soft handoff is where the same signal is received by a mobile station from more than one base transceiver station.
The embodiment described hereinbefore shows the simultaneous
transmission of data packets to two base transceiver stations at
the same time. It is of course possible that more than two base
transceiver stations could receive the same data packets. It is
also possible that the first and second base transceiver stations
could receive the same data packets with the following data
packets being received by the second and a third base transceiver
Where the adjacent base transceiver stations are not controlled by a common base station controller, the same data packets would then be supplied to two different base station controllers which then, when appropriate, would supply che two adjacent base transceiver stations with the same data packets.
In one modification to the embodiment described hereinbefore, the buffer in the base transceiver stations could be omitted and instead included in the base station controller. In this modification, the acknowledgement which the base transceiver station receives from the mobile station would then be transmitted to the base station controller. If a packet needed to be retransmitted, the packet would be sent again to the base transceiver station. Thus, when handoff occurs, the base station controller would have the identity of the last acknowledged packet received by the mobile station. The base station controller would then be able to send to the new base transceiver station, the next data packet to be transmitted.
Reference will now be made to Figures 6 and 7 which show an
alternative implementation of the present invention in a general
packet radio service (GPRS) network. Referring first to Figure
6, a mobile station 100 is arranged to communicate with more than
one base station 102 and 104, for example when in soft handoff,
The two base stations 102 and 104 are connected to the same base
station controller 105 which is connected to a serving GPRS
support node (SGSN) 106. The SGSN 106 is connected to a gateway
GPRS support node 108 (GGSN). The SGSN 106 stores information
identifying the or each cell in which the mobile station 100 is
currently located. When the mobile station 100 is able to
communicate with more than one cell and has registered in more
than one cell, the mobile station is considered to be in more
than one cell by the SGSN. The description hereinafter will
consider the
Accordingly the SGSN 106 only sends the packet once to the base station controller 105 along with an indication that the packet has to be forwarded to both of the base stations 102 and 104. One or both base stations 102 and 104 will transmit the same packet to the mobile station 100. The packets received by the mobile station 100 may be acknowledged via the base station 102 or 104 from which the first received packet is transmitted.
Alternatively, the acknowledgement can be sent via either or both of the base stations, regardless of which base station transmitted the acknowledged packet. The base station 102 and/or 104 transmits the acknowledgement to the base station controller and/or SGSN 106. It should be noted that the acknowledgement confirms that the packet has been correctly received.
When the base station controller or the SGSN 106 receives the
acknowledgement from the respective base station 102 or 104, it
will know that the data packet has been correctly received. The
data packets may be buffered in the base stations 102 and 104,
the base station controller 105 or SGSN 106. In either case, the
receipt of an acknowledgement will cause the packet in question
to be removed from the buffering of the base station the base
station controller or the SGSN 108. Typically, in a time division
multiple access system (TDMA), a mobile station communicates with
one base station at a time whilst in a code division multiple
access system (CDMA), a mobile station can communicate with more
than one base station at the same time. In both access systems,
if uplink packets are correctly received by only one base
station, the base station controller or SGSN connected thereto
In the GPRS network, each data packet is provide with a unique identifier. The mobile station 100 can use this identifier to determine when duplicate packets are received. Each packet may include information identifying the base station from which the data packet has been received.
It is alternatively possible that a mobile station can pass the acknowledgement to any of the base stations with which it is registered or with which it is communicating and not just the base station from which it first received a given data packet.
For example, in a GPRS network, a mobile station might have acknowledged a packet from first base station and then move to the cell associated with a second base station. When this occurs, the mobile station may resend the acknowledgement to the second base station so that the second base station deletes the acknowledged packet from its buffer and then transmits the next packet to the mobile station.
Reference will now be made to Figure 7 which also shows a
possible arrangement in the GPRS network. In this arrangement,
the mobile station
In the first method of operation, the acknowledgement layer is
extended back to the GGSN 108'. In other words when the first
packet to be received by the mobile station 100', an
acknowledgement is sent by the mobile station
In the second method of operation, the acknowledgement mechanism
is extended between the GGSN
In the first way, the SGSN receiving the acknowledgment from the
mobile station (via a base station and base station controller)
sends an acknowledgement using the first identification number
to the GGSN 108'. The GGSN
Alternatively, the SGSN receiving the acknowledgement can advise the other SGSN directly that the data packet has been received.
This requires a connection between the
In one embodiment, one SGSN 106a or 106b is designated as the anchor SGSN. The anchor SGSN can also be referred to as a dominant node. The other SGSN is used only to route data. The anchor SGSN will have all the subscriber data and perform various GPRS functions such as SNDCP (subnetwork dependent convergence protocol) compression and LLC (logical link control) ciphering.
The data packets received by the anchor SGSN are thus suitably processed and forwarded to the base station connected thereto via the appropriate base station controller. The data packet is also forwarded to the other SGSN by the anchor SGSN which in turn forwards the packet to the other base station which is in communication with the mobile station, again via the appropriate base station controller. The other SGSN thus stores information so that it can identify the base station controller and the base station to which a given packet should be forwarded. The SGSN also stores information as to the anchor SGSN for each mobile station in a cell associated with that SGSN. All acknowledgements of the data are forwarded to the anchor SGSN either via the base station and base station controller connected thereto or from the other SGSN.
It should be appreciated that this method requires a mobile
station to designate one of the base stations to which it is
connected as the main base station. The main base station is the
base
In a modification to the embodiments described in relation to Figure 7, a network (eg ATM) is arranged between all of the SGSNs and all the base stations. With this modification, each base station just needs to know to which SGSN the mobile station is connected. Each base station which is connected to a mobile station will each transmit the same data packets to mobile station. Each base station which is connected to the same mobile station will forward acknowledgements from the mobile station to the associated SGSN. This method operates in a similar manner to that shown in Figure 6.
In the arrangements described in relation to Figure 7, data
packets will be buffered in the base stations
In the embodiments of Figures 6 and 7, data packets will be retransmitted if an acknowledgement is not received within a predetermined time. In both of the arrangements shown in. figures 6 and 7, a mobile station is arranged to register with a base station if that mobile station is in its cell. As will be apparent from the previous description, a mobile station can be in more than one cell at the same time. When a mobile station leaves a cell, the mobile station will deregister from that cell.
Depending on the implementation of the embodiments of the present
invention, the registration of the mobile station with a given
base station can be passed to one or more SGSNs and/or the GGSN
and/or the base station controllers. If the two base stations are
connected to two different SGSNs, the mobile station may be
registered with two different SGSNs. This information will be
It should be appreciated that in implementation of the present invention both of the arrangements of Figures 6 and 7 may be included in the same network. For convenience, in both of the arrangements shown in Figures 6 and 7, the mobile station is shown as communicating with two base stations at the same time.
Each mobile station can of course communicate with more than two base stations at the same time in certain circumstances.
In the embodiments described in relation to Figures 6 and 7, it is assumed that the mobile station might be registered in two cells or in a soft handoff situation. However, at other times, the mobile station will only be in a single cell. When the mobile station is on the border with a second cell, the mobile station will send a request to see if the mobile station can now additionally register with the base station associated with that other cell. The mobile station will then be advised as to whether or not a connection can be made to the base station of the second cell before the mobile station attempts any such connection.
If such a connection is permitted, any necessary connections and
exchange of information between SGSNs and the GSN as well as
between SGSNs themselves can be set up before the mobile station
makes any connection with the base station associated with the
second cell. Packets of data could thus be
In one possible implementation, the mobile station sends along
with update
It should be appreciated that the arrangement shown in relation to Figures 6 and 7 can be modifie to work in a hard handoff situation as well as or instead of in the soft handoff situation discussed hereinbefore, similar to that described in relation to Figures 1 to 5. In particular, in a CDMA system the base stations may be arranged so that only one base station at a time transmits data packets. However, more than one base station could receive the packets at the same time. The term base station controller is sometimes associated with the GSM standard. In other systems such as the CDMA system, a radio network controller provides a similar function to that described in relation to the base station controller hereinbefore. The term base station controller should in the context of this document be interpreted to include base station controllers as well as radio network controllers.
Aspects of the arrangements described in relation to the embodiments described in relation to Figure 1 to 5 may be incorporated in the arrangements described in relation to Figures 6 and 7 and vice versa.
In the context of this document, the term connection can be a wired connection or a wireless connection. Direct connections may be provided between base stations in some embodiments of the present invention.
Embodiments of the present invention
The embodiments described hereinbefore have been in the context of a wireless network. However embodiments of the invention may also be applicable to wired networks.
CLAIMS :
1. A method of transmitting packets of data in a communication
network comprising at least first to third stations, the method
comprising the
2. A method as claimed in claim 1, wherein said network comprises a common node connected to said first and third stations, said common node being arranged to transmit data packets to said first and third stations.
3. A method as claimed in any preceding claim including the step of acknowledging by the second station correct receipt of that data packet by the second station.
4. A method as claimed in any preceding claim, wherein the last packet correctly received by said second station from the first station is identified and the packet subsequent to the last correctly received packet is transmitted by the third station.
6. A method of transmitting packets of data in a communication
network comprising at least first to third stations and at least
one common node, said second station arranged to be in
communication with at least one of said first and third stations
7. A method as claimed in claim 5 or 6, wherein data packets are provided both to said first and third stations when the second station has at least one predefined parameter with respect to said first and third stations.
8. A method as claimed in claim 7, wherein said predefined parameter is defined by the geographic position of the second station with respect to the first and third stations.
9. A method as claimed in claim 7, wherein said at least one predefined parameter is defined by at least one parameter of signals received from at least one of said first and third stations satisfying a predetermined criteria.
10. A method as claimed in claim 9, wherein said signal parameter is the power level of a signal received at the second station from at least one of said first and third stations.
12. A method as claimed in claim 9,10 or
13.
14. A method as claimed in any of claims 7 to 13, wherein said predefined parameter is the quality of signals associated with at least one of said first and third stations.
15. A method as claimed in any of claims 7 to 14, wherein said parameter is averaged over time before it is determined if said criteria is satisfied.
16. A method as claimed in any of claims 7 to 15, wherein said predefined parameter defines a handoff zone in which said first station hands off to said third station in that second station stops receiving data packets from said first station and starts receiving data packets from said third station.
17. A method as claimed in claim 16, wherein said handoff zone is surrounded on either side by a zone in which the second station receives data packets from a respective one of said first and third stations and said first and third stations are provided with the same data packets.
18. A method as claimed in any preceding claim, wherein when handoff takes place, said second station transmits a signal to the third station to advise the third station of the which packet or packets were received from the first station and said third station transmits the data packet identified as being required after the last packet to said second station.
19. A method as claimed in any preceding claim, wherein if said
second station does not correctly receive a data packet, said
second station requests retransmission of said data packet.
21. A method as claimed in claim 20, wherein when handoff takes place, the data packets preceding said next data packet to be transmitted are discarded in said third station.
22. A method as claimed in claim 2 and 3 or claim 6 or any claim when appended thereto, wherein said acknowledgement is transferred to the common node.
23. A method as claimed in claim 2 or 6 or any claim appended thereto, wherein the common node associates a unique number for each packet and the same data packets, each of which is associated with the unique number are transmitted from said common node to both of the first and third stations.
24. A method as claimed in claim 2 or 6 or any claim appended thereto, wherein the common node controls the removal of said identified data packet from the or each data storage means.
26. A method as claimed in claim 25, wherein the acknowledgement is forwarded to the common node by one of said first and second nodes and the common node advises the other of the first and second nodes that an acknowledgment has been received.
27. A method as claimed n claim 2 or 6 or any of claims 3 to 5
or 7 to 24 when appended thereto, wherein the first station is
connected to a first node and the third station is connected to
a second node and one of the first and
28. A method as claimed in any of claims 25 to 27, wherein the first and second nodes and/or the first and third stations are connected together.
29. A method as claimed in claim 2 or 6 or any of claims 3 to 5 or 7 to 24 when appended thereto, wherein the first and third stations are connected to the common node via a network.
30. A method as claimed in claim 2 or 6 or any claim when appended thereto, wherein data storage means is provided in said common node.
31. A method as claimed in any preceding claim, wherein said network is a wireless network.
32. A method as claimed in any preceding claim, wherein said first and third stations are base stations.
33. A method as claimed in any of claims 1 to 31, wherein the first and third stations are base station controllers.
34. A method as claimed in claim 2 or 6 or any claim when appended thereto, wherein said communication network is a general packet radio system and said common node is a SGSN.
35. A method as claimed in claim 34, wherein the first and third stations are in communication with different SGSNs, one of said SGSNs being designated as the common node, the other SGSN being arranged to forward acknowledgements to the common node.
36. A method as claimed in any of claims 2 or 6 or any of claims
3 to
37. A method as claimed in any of claims 34 to
38. A method as claimed in claim 2 or 6 or any of claims 3 to 5 or 7 to 33, wherein said common node is a base station controller.
39. A method as claimed in claim 2 or claim 6 or claim appended thereto, wherein the common node is not advised of the occurrence of handoff.
40. A method as claimed in any preceding claim, wherein said second station is a mobile station.
41. A method as claimed in any one of the preceding claims, wherein said communication network has a plurality of cells or areas and said second station is able to register with one or more cells or areas of said network at the same time.
42. A method as claimed in any preceding claim, wherein packets of data are forwarded to at least one of said first and third stations before a connection is made with said second station.
43. A system of transmitting packets of data in a communication network comprising : - first, second and third stations,. wherein said first station is arranged to send a first number of the data packets to the second station, the second station is arranged to identify the which of the first number of packets it receives from the first station, and the third station is arranged to send a second number of data packets to the second station commencing with the data packet identified as being required after the last correctly received packet from the first station.
44. A system as claimed in claim 43, wherein said first and
third stations comprise storage means
45. A system as claimed in claim 44, wherein said storage means comprises a buffer.
46. A system as claimed in claim 43,44 or 45 wherein the second station is arranged to determine the last packet correctly received by the second station from the first station and the third station is arranged to transmit the packet subsequent to the last correctly received packet to the second station.
47. A system as claimed in any of claims 43 to 46, wherein the first and third stations are both provided with at least some of the same data packets for transmission to said second station.
48. A station for use in a communication network, said station being arranged to transmit packets of data to a second station, said second station being arranged first to receive a first number of packets from a further station, wherein said station is arranged, in use, to transmit a second number of data packets to the second station commencing with the data packet identified as being required after the last correctly received packet received by the second station from the further station.