METHOD AND DEVICE FOR REDUCING INTERFERENCE AMONG
FEMTOCELLS IN AN ACCESS DEVICE OF A FEMTOCELL
FIELD OF THE INVENTION
The present invention relates to a scheme for reducing interference among cells,
especially to a method and a device for reducing interference among Femtocells in an
access device of a Femtocell.
BACKGROUND OF THE INVENTION
Nowadays, Femtocell has been paid more and more attention to by network operators
and their vendors since it can increase system capacity and enlarge indoor coverage.
In Femtocell techniques, end users use access points (APs) as access devices at home
or office. These access devices are accessed to core network via for example digital
user line (DSL). Because most of traffic is delivered via backhaul, the spectrum
resources at the air interface between access devices and user terminals are spared and
can be used for real mobile services. On the other hand, because the access devices in
Femtocell are often close to the user terminals, effective coverage of wireless signal
can be realized with very limited power.
Due to the above various advantages of Femtocell techniques, corresponding
extension of related standards is already underway. For example, IEEE 802.16m has
been defined WiMAX Femto AP (WFAP), and 3GPP also defines home
eNodeB (HeNB). HeNB communicates with user terminals based on LTE or LTE-A
standard so that it is not necessary for user terminals to have multi-mode function and
the cost is effectively controlled.
However, there are still some problems to solve in Femtocell techniques, for example:
1) As the access device such as an AP is installed by end users individually, the cell
planning is impossible. Thus, this characterization of Femtocell makes it difficult to
reduce interference by means of Femtocell planning.
2) Mutual interference among adjacent access devices is difficult to be avoided,
because the original introduction of Femtocell access device is mainly for the purpose
of solving the problem of indoor signal coverage.
The existing technology provides some solutions for avoiding inference among
Femtocells. According to an existing solution, after a user buys a Femtocell access
device, the network address such as IP address or MAC address used by the access
device will be registered in network. Thereafter, these network addresses are
forwarded to a Femtocell proxy server, and a variety of parameters including wireless
transmit power etc. will be configured by the proxy server according to the address
information provided by all end users. This solution has obvious drawbacks. Firstly,
the network address used by the access device is possible to change, for example due
to a relocation installation caused by the end user's movement. In this case, the end
user has to re-register the new network address of the access device at the proxy
server at network side, resulting in less flexibility and worse user experiences.
Secondly, because the Femtocell proxy server configures the parameters almost
without knowing the particular network condition of the access device, the finally
configured parameters are often highly conservative. Taking the discussed access
device as an example, the proxy server assigns it less wireless transmit power so as to
avoid interfering Femtocells served by other access devices, even if no other access
device around this access device is in operation. This is obviously disadvantageous to
resource optimization. Moreover, even if the wireless transmit power of the access
device is controlled, the interference among Femtocells is not necessarily solved
effectively.
According to another existing solution, in order to reduce interference among
Femtocells, a dynamic power control (DPC) mechanism is defined in both uplink and
downlink at air interface between access device and user terminals, in which the
access device limits its own transmit power below a threshold, and once its actual
transmit power exceeds this threshold, this access device will believe that it is
interfering other Femtocells around it and will adjust its transmit power below this
threshold. Especially under a dense deployment of Femtocell network, such power
control way is helpful to reducing interference among Femtocells, but it is at the cost
of reduced quality of service (QoS) and throughput.
SUMMARY OF THE INVENTION
The disclosure of the present invention is based on the recognization of the following
technical problems:
Firstly, in all kinds of solutions in the prior art, the scheme for reducing interference
among Femtocells does not depend on a sensing performed by the access device for
the network environment where it locates, which results in aimless control of
performance and parameters of access device in all aspects. Due to such aimlessness,
conservative control way has been widely used such that the system performance
degrades to a great extent. A return therefore is a reduction of the interference which
may not exist. In other words, the discussion about reducing interference should be
under the assumption that there exists at least one interfered object. Therefore,
preferably, an interference source makes some actions purposefully and effectively
according to indications from the interfered part. This will be descried in detail in the
following.
According to an embodiment of the present invention, there is provided a method for
reducing interference among Femtocells in a first access device of a first Femtocell,
comprising the following steps: a receiving step, wherein, said first access device
receives a first wireless signal which is periodically transmitted by a second access
device of a second Femtocell, and said first wireless signal comprises characteristic
information of said second access device; a judging step, wherein, said first access
device judges whether the level of said first wireless signal exceeds a first
pre-determined threshold and interferes at least one user terminal in said first
Femtocell; a first executing step, wherein, if the level of said first wireless signal
exceeds said pre-determined threshold and interferes said at least one user terminal in
said first Femtocell, said first access device creates a cooperative working mode
between said first access device and said second access device by interacting with said
second access device so as to reduce interference between said first Femtocell and
said second Femtocell.
According to another embodiment of the present invention, there is provided a first
apparatus for reducing interference among Femtocells in a first access device of a first
Femtocell, comprising: a receiver, for receiving a first wireless signal which is
periodically transmitted by a second access device of a second Femtocell, wherein
said first wireless signal comprises characteristic information of said second access
device; a first unit, forjudging whether the level of said first wireless signal exceeds a
first pre-determined threshold and interferes at least one user terminal of said first
Femtocell; a second unit, for creating a cooperative working mode between said first
access device and said second access device by interacting with said the second access
device so as to reduce interference between said first Femtocell and said second
Femtocell, if the level of said first wireless signal exceeds said pre-determined
threshold and interferes said at least one user terminal of said first Femtocell.
By using the above-mentioned method and first apparatus, the Femtocell access
device can sense the condition and change of the surrounding wireless environment in
time so as to dynamically adjust its wireless parameters to optimize system
performance. In addition, when serious interference appears, the access device can
reduce the interference by creating the cooperative working mode, and the
interference can be transformed into useful signal with the help of an advantageous
cooperative mode.
BRIEF DESCRIPTION OF THE DRAWINGS
By reading the detailed description of the non-limiting embodiments with reference to
the following drawings, other objects, features and advantages of the present
invention will become apparent.
Fig. 1 shows a typical application scenario of the present invention;
Fig. 2 shows a flow diagram of a method for reducing interference among Femtocells
in an access device according to an embodiment of the present invention;
Fig. 3 shows a flow diagram of a system method for reducing interference among
Femtocells according to an embodiment of the present invention;
Fig. 4 shows a structural block diagram of an apparatus for reducing interference
among Femtocells according to an embodiment of the present invention.
The same or similar reference signs refer to the same or procedure features or
apparatus/module.
DETAILED DESCRIPTION OF EMBODIMENTS
Here at least one embodiment of the method and apparatus of the present invention as
shown in the drawings will be mentioned. It should be understood that these
embodiments are illustrated by explaining each aspect of the present invention, but
should not be understood as limits to the present invention. For example, features
shown or illustrated as a part of one embodiment may be used in another embodiment
so as to get another embodiment. The present invention covers these embodiments as
well as all kinds of varieties which fall into the scope and spirit of the present
invention.
Fig. 1 shows a typical scenario of the method and apparatus provided by the present
invention, showing a part of a residential building, wherein, unit 1 locating at the
upper floor of unit 2 is installed with Femtocell access device 3 and unit 2 is installed
with Femtocell access device 4. Access device 3, 4 are installed somewhere at home
by users according to their actual requirements and the positions can be adjusted as
required. In the figure, they are shown as being in the similar positions in units 1 and
2 only for the clarity of the drawing.
The concept of Femtocell is firstly explained previous to discussing the problem of
interference among Femtocells in detail. According to the existing theory in the field,
a Femtocell is an area covered and managed by an access device and is similar to a
cell covered and managed by a base station in the traditional wireless communication
network. The Femtocell is much smaller in terms of range of the coverage than the
traditional cell. Only for the purpose of describing the particular embodiment more
vividly, it is considered that the installation of the access devices such as access
device 3 is mainly for meeting the use requirement in unit 1 and its original intention
does not include serving user terminals outside unit 1. Therefore, the same reference
signs are used for the Femtocells and the units in the example shown in Fig. 1. As a
result, the Femtocell managed by access device 3 is also called Femtocell 1, and
similarly, the Femtocell managed by access device 4 is called Femtocell 2.
In Fig. 1, there is user device 5 such as a notebook, also called computer 5, in
Femtocell 1, and the wireless link between it and access device 3 is referred to as the
combination of their reference signs, namely 35. There is user device 6 in unit 2 such
as a mobile phone, also called mobile 6, and the wireless link between it and access
device 4 is referred to as the combination of their reference signs, namely 46.
According to the traditional Femtocell techniques, link 35 and 46 are desired or
contributive links, but link 36 and 45 are the links which are undesired or not
contributive or even causes interference. To be specific, when access device 3 sends a
signal to computer 5, and if access device 4 sends a signal to mobile 6 at this moment
as well, the signal in link 36 represented by a dotted line constitutes the interference to
the signal in useful link 46 due to the frequency reuse among Femtocells, and
correspondingly, the signal in link 45 constitutes the interference to the signal in
useful link 35. Certainly, some interference is strong and some is weak, which will be
discussed in the following.
Referring to Fig. 2 showing a flow diagram of a method for reducing interference
among Femtocells in an access device according to an embodiment of the present
invention and describing access device 3 shown in Fig. 1, the skilled in the art knows
that the same features and procedures are applicable to access device 4 as well. Due to
the symmetry between access devices, when an access device is discussed, this access
device is a first access device which is called and the Femtocell managed by it is a
first Femtocell, while each of its adjacent access devices can be regarded as a second
access device in a second Femtocell, and vice versa. In addition, a wireless signal
which is transmitted by the first access device and can be used to sense the first access
device and obtain the level of the signal is called a second ratio signal, the wireless
signal received by the first access device for sensing the second access device and
obtaining the level of the signal is called a first wireless signal. The relationship and
difference of these concepts will become clearer in the following.
As mentioned above, each access device needs to transmit some signals to be sensed
by transmitters in order to make adjacent access devices know its existence and be
able to determine interference level. According to different embodiments of the
present invention, such kind of signals may be downlink signals transmitted to user
terminals as well as signaling signal to be dedicatedly provided to other access device.
In particular, in step 26, access device 3 periodically transmits the second wireless
signal comprising characteristic information of access device 3, for example MAC
address, hardware number, IP address or other identifying information.
Executing of step S26 is mainly for realizing, for example, sensing the first access
device namely access device 3 and detecting signal level by other access devices such
as access device 4. Similarly, other access devices also transmit such wireless signal,
wherein the first wireless signal transmitted by the second access device such as
access device 4 comprises characteristic information of access device 4.
Because downlink signal transmitted by a access device to user terminals normally
does not carry characteristic information of the access device, access device 4 adds its
own characteristic information in a pre-determined position of downlink signal at
regular intervals, for example 10 frames, in order to use this kind of downlink signal
to realize sensing among devices, By pre-configurations, access device 3 can
"overhear" downlink signal from access device 4 and at least obtain the part of signal
carrying characteristic information of access device 4. For example, the "overhearing"
is carried out every 10 frames. When the first wireless signal is not normal downlink
signal but a signal dedicatedly used for mutual sensing among access devices, the
problem might become simpler. Based on pre-configurations for each access device,
the second access device such as access device 4 will transmit the first wireless signal
in a dedicated channel and add its own characteristic information into the first
wireless signal. Likewise, based on pre-configuration, the first access device such as
access device 3 can receive this signal and obtain the characteristic information of
access device 4 from it so as to determine who has transmitted this first wireless
signal.
According to an embodiment of the present invention, taking access device 3 as an
example, it may use its inherent antenna/antennas to transmit the second wireless
signal and receive the first wireless signal. Alternatively, access device 3 is equipped
with dedicated antenna/antennas to receive and transmit the above-mentioned signals.
The above-mentioned first and second wireless signal are received and transmitted via
air interface of access devices. However, considering that this air interface is mainly
used for communication between access devices and user terminals, other
communication process among access devices will be all realized via backhaul
according to an embodiment of the present invention in order to reduce the occupation
of the valuable wireless resources. In particular, in step S22, a connection based on IP
protocol is established between access device 3 and 4 with the help of characteristic
information of access device 4. If the characteristic information of access device 4
included in the first wireless signal is not IP address but MAC address or hardware
number, access device 3 will access an auxiliary address device, for example a route,
in which a map between MAC address or hardware number and IP address of each
access device is pre-stored, and establish the above-mentioned connection after
finding the IP address of access device 4.
Step S22 will particularly happen at the time when access device 3 or 4 is just
switched on and being initialized, because they do not sense the existence of the other
part, and thus, the connection over backhaul will be established after they sense the
existing of the other part. Because the first and second wireless signal are transmitted
periodically, in the case that the connection over backhaul has been established,
access device 3 need not re-establish the backhaul connection with access device 4 but
only keep this connection active after access device 3 has received the first wireless
signal.
The established connection between access device 3 and 4 is not always active. For
example, the user in unit 2 switches off access device 4 when leaving for work, and
thus, access device 3 certainly will not receive any first wireless signal transmitted by
access device 4 until access device 4 is switched on again. When access device 3 does
not receive the first wireless signal from access device 4 during a certain time interval,
it will remove the connection previously established and consider access device 4 as
not existing .
Further, step S22 may be related to the level of the first wireless signal. In particular, a
second pre-determined threshold is pre-set in access device 3 and corresponds to the
level of the first wireless signal. As a result, after having received the first wireless
signal, access device 3 determines the level of the received signal represented, for
example, by received signal strength indicator (RSSI), and then compares it with the
second pre-determined threshold. If the level of the first wireless signal is relatively
strong and exceeds the second pre-determined threshold, it means that it is very
possible for access device 4 to cause high interference to Femtocell 1. On the contrary,
if the level of the first wireless signal is common and does not exceed the second
pre-determined threshold, it means that it is perhaps of low possibility that access
device 4 causes interference to Femtocell l.As a result, especially when the number of
the connections over backhaul is limited, access device 3 preferably establishes
connections over backhaul only with those access devices which transmit the first
wireless signal whose level exceeds the second pre-determined threshold. Certainly,
an access device previously determined as not being a potential strong interference
source may be determined as a potential strong interference source later, because the
transmit power at air interface of each access device may change over time. For
example, the transmit power is increased to guarantee quality of service (QoS), and
vice versa.
It should be understood that step S22 may be omitted, because it is a preparation,
namely that it establishes an active connection with an interference source over
backhaul which is not sensitive to signaling overhead before unaffordable interference
does not actually happen yet such that in the following working process, once a strong
interference source is detected, it immediately interacts with the interference source
via the established connection without occupying any resource of air interface. As a
simple alternative way, the first wireless signal is transmitted periodically, and thus,
when access device 3 detects that the existence of access device 4 at its power-on, it
does not in a hurry to establish a connection between the two, but will establish the
connection over backhaul to interact only after extracting characteristic information of
the interference source, namely access device 4, from the interference signal when
access device 4 actually interferences a certain user terminal in Femtocell 1 later. This
and other alternative ways will be described in more detail in the following.
Next, step S23 is discussed. In particular, at least one parameter of access device 3 at
air interface may also be determined with reference to the level of the first wireless
signal. When the first wireless signal is dedicated to the sensing among access devices
and signal detection, the transmit power of this signal may be fixed, e.g. Px, and as a
result, access device 3 knows what the actual level of the signal transmitted with such
transmit power Px is when it arrives at access device 3. Based on the assumption that
the channel between access device 3 and 4 is symmetrical or substantially
symmetrical, access device 3 can approximately estimate what the interference level
applied to Femtocell 2 by the signal transmitted by access device 3 is if the access
device 3 takes Px as its transmit power. As a relatively conservative way, if the
received level of the first wireless signal is strong, obvious interference is caused
when there are user terminals occupying the same time-frequency resources in
Femtocell 1 and 2, and access device 3 will determine initial transmit power lower
than Px. As a result, when a user terminal such as computer 5 requests access later,
access device 3 will transmit wireless downlink signal to computer 5 with transmit
power lower than Px. Certainly, because access device 3 does not know whether there
is user terminal which uses the same time-frequency resources with computer 5 in
Femtocell 2, it can thus be seen that the way in which access device 3 enforces itself
to use lower initial transmit power is conservative. To the contrary, if the signal level
has been attenuated to a relatively low or negligible level when the first wireless
signal transmitted with transmit power Px arrives at access device 3, access device 3
may roughly determine that when access device 3 transmits downlink signal with
transmit power Px, it will not cause interference with considerable level to Femtocell
2 even if there are user terminals which occupy the same time-frequency resources in
Femtocell 1, 2, respectively, Therefore, after computer 5 requests access, the transmit
power with which access device 3 transmits wireless downlink signal to computer 5
may be equal to or slightly greater than Px.
Step S24 and step S25 are more inclined to the case that two access devices provide
access for user terminals managed by them, respectively. Likewise, steps S24 and S25
are also based on the measurement of the level of the first wireless signal which is
transmitted periodically. In particular, in step S24, access device 3 judges whether the
level of the first wireless signal exceeds a first pre-determined threshold and will
interference at least one user terminal in Femtocells. There are several ways to
implement this judgment, which are introduced as below, respectively:
24.1) In theory, interference is created under the assumption of the reuse of
transmission resource such as time-frequency resource blocks among Femtocells.
Therefore, access device 3 not only considers the level of the first wireless signal but
also judges whether this first wireless signal really causes interference to at least one
user terminal in Femtocell 1. In this case, the first wireless signal is normally
downlink signal transmitted from access device 4 to a certain user terminal such as
mobile 6 in Femtocell 2, but carries the characteristic information of access device 4
therein. As a result, if the level of the first wireless signal exceeds the first
pre-determined threshold and mobile 6 to which the first wireless signal directed
actually uses the same time-frequency resource blocks with at least one user device
served by access device 3, for example computer 5. Therefore, the first wireless signal
is an interference signal which has to be considered.
Certainly, the above interference among Femtocells is created as access device 3, 4
simultaneously transmit downlink signals to computer 5 and mobile 6 managed by
them, respectively. Therefore, access device 3 may be equipped with two sets of
antennas in order to receive the above-mentioned first wireless signal while
transmitting downlink signal to computer 5.
24.2) As an easy implementing way of step S24, access device 3 only considers the
level of the first wireless signal, and obtains the judgment result in step S24 according
to the relationship between the level of the first wireless signal and the first
pre-determined threshold.
If the judgment result in step S24 is negative, the method will go back before step S21,
namely waiting for receiving the next first wireless signal, which is not repeated .
To the contrary, if the judgment result in step S24 is positive, the method will go into
step S25 which is to be described in detail hereinafter.
In view of the problem that Femtocell 2 is applying strong interference to Femtocell 1,
step S25 can be realized in different ways according to different embodiments of the
present invention, as below:
Embodiment 1: access device 4 uses beamforming scheme to reduce interference to
computer 5.
According to Embodiment 1, access device 4 is required to be equipped with multiple
transmit antennas and generates a beam with directivity by means of these antennas to
concentrate the energy in the direction pointing to mobile 6, to enhance signal quality
and to reduce the interference to computer 5. Considering the characterization of
beamforming, the beamforming technique is not the best choice when computer 5 and
mobile 6 roughly locate in the same direction with respect to access device 4.
Information such as channel status information required by access device 4 to make
beamforming may be provided by access device 3 via an IP connection previously
established over backhaul. If no IP connection between the two is established
previously, access device 3 may eventually establish such connection according to the
characteristic information of access device 4 in the first wireless signal. It should be
understood that the advantage of using backhaul to make more information
interactions among access devices, it is not excluded that the interactions among
access devices are made in a wireless manner.
Embodiment 2: access devices 3, 4 perform downlink transmission for computer 5
and mobile 6 by means of multi-base station (Multi-BS) pre-coding.
According to Embodiment 2, access devices 3, 4 perform joint pre-coding, wherein
access devices 3 may collect the status information of channel 35, 45, 36, 46, generate
pre-coding matrix, and provide access device 4 with corresponding vector/vectors.
Such Multi-BS pre-coding technique may enable access devices 3, 4 to each serve
computer 5 and mobile 6 simultaneously, or may enable access device 3 to serve
computer 5, access device 4 to serve computer 6 while reducing the interference to
computer 5 by, for example, generating a null in the direction of computer 5 by means
of pre-coding.
Embodiment 3: access devices 3 re-schedules computer 5 so that computer 5 avoids
interference from access device 4.
According to Embodiment 3, there is more than one downlink resource block which
access devices 3 can allocate. For example, computer 5 is originally scheduled on
time-frequency resource block T1F1, and now, because this resource block has been
used in adjacent Femtocell and the signal level is relatively strong, the interference is
avoided by scheduling computer 5 on T2F1 or T2F1 or T2F2 etc. to separate
computer 5 and mobile 6 in at least one of time domain and frequency domain. This
scheme reduces the interference at the cost of more resource utilization.
Embodiment 4: access devices 4 re-schedules mobile 6 to avoid causing interference
to computer 5
Embodiment 4 shares the same concept with Embodiment 3, but now it is access
device 4's turn to re-schedule user terminals, for example from T1F1 to T2F1. In
practice, different access devices or different Femtocells may have different priorities.
In the case that step S25 needs to be executed, such re-scheduling is always performed
by the access device with lower priority. Without loss of generality, the access device
having the largest amount of allocatable resources may be assigned with relatively
low priority. For example, an access device has 200M allocatable downlink
bandwidth while another access device has only 10M, and the former is preferably
selected to perform re-scheduling.
Alternatively, the access device having more remaining resource to allocate may be
assigned with relatively low priority.
Embodiment 5: access device 4 reduces the transmit power when transmitting
downlink signal to mobile 6, so as to reduce the reference to computer 5.
Optionally, after access devices 3 judges that the level of the first wireless signal
exceeds the first pre-determined threshold, it may inform access device 4 about this
information in an IP link, and accordingly, access device 4 reduces the power
allocation on the time-frequency resource block such as T1F1 corresponding to the
first wireless signal, so as to avoid the interference to computer 5.
In practice, it may happen that The QoS in link 46 degrades rapidly after access
device 4 reduces the transmit power when transmitting downlink signal to mobile 6,
and if hybrid automatic repeat request (HARQ) technique is used at air interface of
access device 4, mobile 6 will frequently request access device 4 to retransmit
downlink data. In view of the overall system, this guarantees that Femtocell 1 is not
interfered, but the cost is the influence on the traffic of mobile 6. For this reason, after
being aware of the above-mentioned status of the QoS of link 46, access device 4
interacts with access device 3 again and changes the cooperative way between them,
for example into any way in Embodiments 1-3. Certainly, if access device 4 is
changed into the way in Embodiment 4, it performs re-scheduling without interacting
with access device 3.
Step S27 in Fig.2 is a subsequent step after the second wireless signal transmitted by
access device 3 is determined by other devices such as access device 4 as possibly
causing interference. Here, access device 3 plays the same role as access device 4 in
all the above embodiments while access device 4 plays the same role as access device
3 in all the above embodiments, which is not repeated.
In the existing Femtocell techniques, access devices widely use closed subscriber
group (CSG) as an admission mode. The combination of the present invention and
CSG will be described in the following with reference to a particular example.
There are only two adjacent Femtocells in the examples discussed above, but the
skilled in the art can apply the present invention to the case that there are multiple
adjacent Femtocells by reading the content of this application without any creative
effort. Moreover, the case of multiple adjacent Femtocells is also covered by the
present invention.
Next, the embodiments of the present invention is described in view of system by
referring to Fig.3 and combining Fig.l, wherein the role of access device 4 is
equivalent to a first access device, and access device 3 is a second access device with
respect to access device 4.
Step S301: access device 4 is switched on, receives a first wireless signal from access
device 3 for the first time after the power-on and thus detects the existing of adjacent
access device 3, namely establishing an IP connection with access device 3 over
backhaul.
Step S302: mobile 6 requests to access to access device 4 to receive downlink data.
Step S303: access device 4 judges whether mobile 6 is in a pre-stored CSG list.
Step S304: if mobile 6 is in the pre-stored CSG list of access device 4, access device 4
will accept this access request.
Step S305: subsequently, access device 4 still monitors the level of the first wireless
signal transmitted by access device 3 and compares it with a first pre-determined
threshold.
Step S306: if the level of the first wireless signal exceeds the first pre-determined
threshold, it is necessary for access device 4 to create a cooperative working mode
with access device 3. Therefore, access device 4 firstly requests a bond from access
device 3. After receiving the bonding request from access device 4, access device 3
determines that the downlink transmission of Femtocell 1 has influenced Femtocell 2,
and then accepts this bonding request.
Steps S307-S308: in order to meet the authorization requirements of CSG, access
device 3, 4 exchange CSG information of mobile 6 and computer 5.
Step S309: access device 4 adds the received information of computer 5 into the local
CSG list so that computer 5 becomes one of the user terminals which can be
temporarily allowed to access to access device 4.
Step S310: access device 3 adds the received information of mobile 6 into the local
CSG list so that mobile 6 becomes one of the user terminals which can be temporarily
allowed to access to access device 3.
Steps S311-S312: subsequently, computer 5 initiates an access request to access
device 4, and mobile 6 initiates an access request to access device 3.
Steps S313-S314: based on the updated CSG list, access devices 3, 4 accept the access
requests from access from mobile 6 and computer 5 respectively.
Steps S315-S316: subsequently, access devices 3, 4 may process the downlink
transmission to mobile 6 and computer 5 based on various schemes for serving
multiple user devices by multiple network devices such as base stations that now exist
or are developed in the future such as Multi-BS pre-coding technique, thereby solving
the problem of mutual interference between Femtocell 1 and 2.
After all embodiments of the method provided by the present invention are introduced,
the first apparatus provided by the present invention will be briefly described with
reference to the above description for the embodiments of the method as follows.
Refer to Fig.4 showing a block diagram of the first apparatus 4 1 for reducing
interference among Femtocells in a first access device of a first Femtocell, which
comprises:
Receiver 411, for receiving a first wireless signal which is periodically transmitted by
a second access device of a second Femtocell, wherein said first wireless signal
comprises characteristic information of said second access device. It corresponds to
the above step S21.
First unit 412, forjudging whether the level of said first wireless signal exceeds a first
pre-determined threshold and interferes at least one user terminal of said first
Femtocell. It corresponds to the above step S24.
Second unit 413, for creating a cooperative working mode between said first access
device and said second access device by interacting with said the second access
device, so as to reduce the interference between said first Femtocell and said second
Femtocell, if the level of said first wireless signal exceeds said pre-determined
threshold and interferes said at least one user terminal of said first Femtocell. It
corresponds to the above step S25.
Further, first apparatus 4 1 also comprises third unit 414 for establishing a connection
between said first and second access device over backhaul according to the
characteristic information of the second access device in the first wireless signal. It
corresponds to the above step S22.
Said second unit 413 is further used for creating a cooperative working mode between
said first access device and said second access device by interacting with said the
second access device, so as to reduce interference between said first Femtocell and
said second Femtocell, if the level of said first wireless signal exceeds said
pre-determined threshold and interferes said at least one user terminal of said first
Femtocell. It corresponds to the above step S25.
Further, the above-mentioned cooperative working mode comprises at least one of the
following: said second access device uses a beamforming scheme to reduce the
interference to said at least one user terminal; said first access device, said second
access device, said at least one user terminal and other user terminals of said second
Femtocell which occupy the same transmission resources as said at least one user
terminals perform downlink transmission using Multi-BS MIMO (Multi-input
Multi-output); said first access device re-schedules said at least one user terminal so
as to avoid the interference from said second access device; said second access device
re-schedules said other user terminals so as to avoid interfering said at least one user
terminals; said second access device reduces transmission power when transmitting
signals to said other user terminals so as to reduce interference to said at least one user
terminal.
Further, the first access device uses closed subscribe group to control the access at its
air interface. Second unit 413 comprises: first element 4131 for obtaining
characteristic information of each user terminal in said second Femtocell, which
corresponds to the above step S307 when taking access device 3 in Fig.l as an
example; second element 4132 for adding said characteristic information of each user
terminal of said second Femtocell into the closed subscribe group controlled by said
first access device, which corresponds to the above step S310.
Further, the second access device uses closed subscribe group to control the access at
its air interface. Second unit 413 comprises: first transmitter 4133, for transmitting
characteristic information of each user terminal in said first Femtocell to the second
access device so that said second access device updates the closed subscribe group
used by said second access device accordingly, which corresponds to the above step
S308 when taking access device 3 in Fig.l as an example.
Further, first apparatus 4 1 further comprises: second transmitter 415 for periodically
transmitting a second wireless signal which comprises characteristic information of
said first access device, which corresponds to the above step S26.
Further, first apparatus 4 1 further comprises: fourth unit 416 for creating a
cooperative working mode between said first access device and said second access
device based on an interaction initiated by said second access device, so as to reduce
the interference between said first Femtocell and said second Femtocell, which
corresponds to the above step S27.
For the skilled in the art, it is obvious that the present invention is not limited to the
details of the above exemplary embodiments, and the present invention can be
realized in other specific forms without departing from the spirit or basic features of
the present invention. Therefore, in all aspects, the embodiments should be regarded
as illustrative and non-limiting. The scope of the present invention is defined by the
appended claims rather than the above description and the invention is intended to
embrace all modifications fairly falling within the meaning and scope of the claims
under the doctrine of equivalents. Any reference signs in the claims should not be
regarded as limiting the involved claims. Further, it is obvious that the term
"comprise" does not exclude other units, singular does not exclude plural. The terms
such as "first", "second" are used to represent the name rather than any specific order.
CLAIMS
1. A method for reducing interference among Femtocells in a first access device of
a first Femtocell, comprising the following steps:
a receiving step, wherein said first access device receives a first wireless signal
periodically transmitted by a second access device of a second Femtocell, and said
first wireless signal comprises characteristic information of said second access device;
a judging step, wherein said first access device judges whether the level of said
first wireless signal exceeds a first pre-determined threshold and interferes at least one
user terminal in said first Femtocell;
a first executing step, wherein, if the level of said first wireless signal exceeds said
pre-determined threshold and interferes said at least one user terminal in said first
Femtocell, said first access device creates a cooperative working mode between said
first access device and said second access device by interacting with said second
access device, so as to reduce interference between said first Femtocell and said
second Femtocell.
2. The method according to claim 1, wherein, after said receiving step, the method
further comprises:
determining at least one parameter at air interface of said first access device
according to the level of said first wireless signal.
3. The method according to claim 1, wherein, after said first receiving step, the
method further comprises:
a connection establishing step, wherein said first access device establishes a
connection between said first access device and said second access device over
backhaul according to the characteristic information of said second access device in
said first wireless signal;
said first executing step further comprises:
if the level of said first wireless signal exceeds said first pre-determined threshold
and interferes said at least one user terminal of said first Femtocell, said first access
device interacts with said second access device via said connection established over
backhaul so as to create said cooperative working mode between said first access
device and said second access device.
4. The method according to claim 1, wherein, said cooperative working mode
comprises at least one of the following:
said second access device uses a beamforming scheme to reduce interference to
said at least one user terminal;
said first access device, said second access device, said at least one user terminal
and other user terminals of said second Femtocell which occupy the same
transmission resources with said at least one user terminals perform downlink
transmission using Multi-BS MIMO;
said first access device re-schedules said at least one user terminal so as to avoid
interference from said second access device;
said second access device re-schedules said other user terminals so as to avoid
interfering said at least one user terminals;
said second access device reduces transmission power when transmitting signals
to said other user terminals so as to reduce interference to said at least one user
terminal.
5. The method according to claim 1, wherein said first access device uses closed
subscriber group to control the access at its air interface, and said first executing step
further comprises:
obtaining characteristic information of each user terminal in said second
Femtocell;
adding said characteristic information of each user terminal in said second
Femtocell into the closed subscriber group controlled by said first access device.
6. The method according to claim 1, wherein said second access device uses
closed subscriber group to control the access at its air interface, and said first
executing step further comprises:
transmitting characteristic information of each user terminal in said first Femtocell
to said second access device so that said second access device updates the closed
subscribe group used by said second access device accordingly.
7. The method according to claim 1, wherein, the method further comprises:
a transmitting step, wherein said first access device periodically transmits a
second wireless signal which comprises characteristic information of said first access
device.
8. The method according to claim 7, further comprising:
a second executing step, wherein said first access device creates a cooperative
working mode between said first access device and said second access device based
on an interaction initiated by said second access device, so as to reduce the
interference between said first Femtocell and said second Femtocell.
9. A first apparatus in a first access device of a first Femtocell for reducing
interference among Femtocells, comprising:
a receiver, for receiving a first wireless signal periodically transmitted by a second
access device of a second Femtocell, wherein said first wireless signal comprises
characteristic information of said second access device;
a first unit, for judging whether the level of said first wireless signal exceeds a
first pre-determined threshold and interferes at least one user terminal of said first
Femtocell;
a second unit, for creating a cooperative working mode between said first access
device and said second access device by interacting with said the second access
device, so as to reduce interference between said first Femtocell and said second
Femtocell, if the level of said first wireless signal exceeds said pre-determined
threshold and interferes said at least one user terminal of said first Femtocell.
10. The first apparatus according to claim 9, further comprising:
a third unit, for establishing a connection between said first access device and said
second access device over backhaul according to the characteristic information of said
second access device in said first wireless signal;
said second unit is further used for:
if the level of the first wireless signal exceeds said first pre-determined threshold
and interferes said at least one user terminal of said first Femtocell, said first access
device interacts with said second access device via the connection established over
backhaul so as to create said cooperative working mode between said first access
device and said second access device.
11. The first apparatus according to claim 9, wherein, said cooperative working
mode comprises at least one of the following:
said the second access device uses a beamforming scheme to reduce interference
to said at least one user terminal;
said first access device, said second access device, said at least one user terminal
and other user terminals of said second Femtocell which occupy the same
transmission resources as said at least one user terminal perform downlink
transmission using Multi-BS MIMO;
said first access device re-schedules said at least one user terminal so as to avoid
interference from said second access device;
said second access device re-schedules said other user terminals so as to avoid
interfering said at least one user terminal;
said second access device reduces transmission power when transmitting signals
to said other user terminals, so as to reduce interference to said at least one user
terminals.
12. The first apparatus according to claim 9, wherein said first access device uses
closed subscribe group to control the access at its air interface, and said second unit
comprises:
a first element, for obtaining characteristic information of each user terminal in
said second Femtocell;
a second element, for adding said characteristic information of each user terminal
in said second Femtocell into the closed subscribe group controlled by said first
access device.
13. The first apparatus according to claim 9, wherein said second access device
uses closed subscribe group to control the access at its air interface, and said second
unit further comprises:
a first transmitter, for transmitting characteristic information of each user terminal
of said first Femtocell to said second access device so that said second access device
updates the closed subscribe group used by said second access device accordingly.
14. The first apparatus according to claim 9, wherein, further comprising:
a second transmitter, for periodically transmitting a second wireless signal which
comprises characteristic information of said first access device.
15. The first apparatus according to claim 14, further comprises:
a fourth unit, for creating a cooperative working mode between said first access
device and said second access device based on an interaction initiated by said second
access device, so as to reduce the interference said first Femtocell and said second
Femtocell.