CN105722148A - Method for avoiding ineffective load balance in heterogeneous network of LTE-A system - Google Patents
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Abstract
The invention relates to a method for avoiding ineffective load balance in heterogeneous network of LTE-A system, and all the micro base stations start the RE expanding capability in the heterogeneous network. The method comprises steps of obtaining a temporary service district index on the basis of the sum of the micro base station RSTP and the RE expansion offset value and the RSRP between the user device and the macro base station, if the obtained temporary service district index is the index of the macro base station or the index of the base station which generates the maximum RSRP at the user device, determining the index as a service base station, otherwise, determining the base station according to the estimated signal to the relation between interference plus noise power ratio level and the preset threshold, wherein if the signal to the relation between interference plus noise power ratio level is greater than or equal to the preset threshold, the base station with the temporary service district index is determined as a service station, and, if the signal to the relation between interference plus noise power ratio level is smaller than or equal to the preset threshold, determining whether all base stations comprise a micro base station, if yes, determining the micro base station as service base station according to the magnitude of the RSRP between the micro base station and each base station, if not, eliminating the temporary district index and afresh executing the steps of the method. By using the method, the current eICIC technology is no longer used.
Description
Technical Field
The invention relates to a wireless communication technology, in particular to a method for avoiding ineffective load balancing in a heterogeneous network of an LTE-A system.
Background
To meet additional demands in terms of service capacity and/or coverage in cellular, LTE-a networks, low power small cells (e.g., microcells) can be deployed among macrocells. The network formed is often referred to as a heterogeneous network (HetNet). Specifically, when a plurality of open access micro cells (also referred to as micro base stations PeNB) are deployed in the coverage area of a macro cell (also referred to as macro base station MeNB), some User Equipments (UEs) can be served by the plurality of micro cells, thereby achieving the benefit of load balancing.
In LTE-a systems, when base stations transmit reference symbols (orthogonal to each other for different base stations), each user equipment measures the power of the reference symbols received from its surrounding base stations (including its serving base station). And, any user equipment will measure its reference symbolThe received power (RSRP) is reported to its serving base station. For any user equipment UEjBy usingA set of cell indices representing its surrounding base stations. And, using RSRPijRepresenting a UEjMeasured power of reference symbols received from base station i, then the conventional cell association criterion based on measured reference symbol received power may be expressed as follows:
whereas in case of a macro-micro cell co-channel deployment, if the cell association criterion is still given as equation (1), more user equipments will be associated to the macro cell than to the micro cell, since the transmission power of the micro cell is much smaller than the transmission power of the macro cell. In this case, the available resources of the microcell are not fully utilized, and in the macrocell, competition for the available resources is severe. To more efficiently utilize the potential load balancing functionality provided by the micro cells, the UE is adapted to any one user equipmentjIn particular, the following cell association criteria (2) will be proposed for heterogeneous networks for macrocell co-channel deployments:
Cell_IDserving＝argmax{i}{RSRPij+·biasi}(2)
wherein,and 0 when i is a macro cell index and 1 when i belongs to a micro cell index.
In the above equation (2), when i belongs to the microcell index, the offset value biasiA non-negative value so that more user equipments can be served by the micro cell. Since the use of offset values amounts to giving the micro cell the ability to extend the range associated with the user equipment, this procedure is called coverage extension (RE) of the micro cell, which is also called coverage extension offset value.
Currently, in LTE release-10 (Rel-10), it is recommended to set the coverage extension bias value in a cell-specific (cell-specific) manner. Also, in view of simplicity of implementation, in LTERel-10, it is recommended to set the same coverage extension bias value for all the micro cells, as shown in the following equation (3):
Cell_IDserving＝argmax{i}{RSRRPij+·bias}(3)，
wherein,and 0 when i is a macro cell index and 1 when i belongs to a micro cell index.
Based on the extensive evaluation reports made by 3GPP in the relevant standardization work, the following conclusions can be drawn:
(1) for the case that the coverage extension is not performed by the micro cell, for the downlink control channel, the inter-cell interference problem does not exist, and for the downlink data channel, the inter-cell interference cancellation (ICIC) technology in LTE release-8 or 9(Rel-8/9) is reused to well solve the inter-cell interference problem.
(2) However, for the case of using the coverage extension bias scheme currently proposed by 3GPP, it is observed that although increasing the coverage extension bias value enables more user equipments to be served by the corresponding micro cell, the interference between the macro cell and the corresponding micro cell may cause the user equipment associated to the corresponding micro cell to experience a lower signal-to-interference-and-noise ratio (especially for the user equipment at the edge of the corresponding micro cell), so that the probability of the downlink control channel transmission failure of the user equipment associated to the corresponding micro cell is increased. In addition, when the coverage extension bias value is large, the problem of the downlink control channel caused by inter-cell interference is very serious, and the ICIC technique in lte rel-8/9 cannot effectively solve the problem of the inter-cell interference of the downlink control channel. In addition, since good control channel performance is a prerequisite for successful transmission of the data channel, if the inter-cell interference problem of the downlink control channel cannot be solved well, the performance of the data channel will be seriously affected.
In other words, using the coverage extension biasing scheme currently recommended by 3GPP, the corresponding load balancing caused by the microcell coverage extension may become ineffective due to the intercell interference present on the downlink control channel. Specifically, if the coverage extension bias value set by the micro cell is larger, the proportion of the ineffective load balancing caused by the coverage extension of the micro cell is higher.
In order to solve the above-mentioned problem of inter-cell interference of the downlink control channel, various "enhanced inter-cell interference cancellation (elcic)" technical schemes have been proposed. These eICIC solutions can be broadly divided into two categories, namely, resource orthogonalization partitioning and power scaling schemes.
The basic idea of the resource orthogonalization division scheme is to orthogonally allocate radio resources for a downlink control channel between a macro base station and a micro base station, so as to reduce mutual interference as much as possible. Including both time division multiplexing and frequency division multiplexing techniques.
Since the signals transmitted on the downlink control channel are transmitted over the entire frequency band, the frequency division multiplexing solution is not suitable for solving the above-mentioned inter-cell interference problem of the downlink control channel.
The technical scheme of time division multiplexing mainly comprises an Almost Blank Subframe (ABS) technology and a time domain shifting (timing) technology.
In the ABS technical solution proposed by 3GPP standardization, a macro base station serving as an interference source transmits only basic signals such as Cell-specific reference signals (CRS) without performing data transmission on a Physical Downlink Control Channel (PDCCH) in some subframes configured as ABS. Obviously, in the subframe configured as the ABS, no data transmission is performed on the Physical Downlink Shared Channel (PDSCH), i.e., no data transmission is performed on the data channel. In addition, in the implementation of ABS technology, interference packets in the time domain must be exchanged between neighboring cells via some kind of communication link between base stations, for example, a backhaul link based on an X2 interface. However, ABS techniques still suffer from the problem of "CRS on control signal" interference, since the macrocell base station still needs to transmit CRS even in almost blank subframes. More importantly, the inherent drawback of such time-division multiplexing ICIC techniques is the reduction of the time domain resources available in the macro cell, resulting in a reduction of the throughput performance of the user equipment in the macro cell; this problem is particularly acute if there are multiple micro cells that require the macro base station to use ABS on the control channel for them to cancel inter-cell interference. Furthermore, when the time division multiplexing technique of ABS is applied to a Frequency Division Duplex (FDD) system, the strict requirement for time synchronization is not reduced at all, which will cause difficulty in implementation.
In addition, the time domain shifting (timing) technology also has many disadvantages that the inter-cell interference cannot be completely eliminated.
The power regulation scheme includes: the method comprises the steps of reducing the transmission power of a downlink control channel at a macro base station serving as an interference source, and enhancing the transmission power of the downlink control channel at a interfered micro base station for user equipment positioned at the edge of a corresponding micro cell. However, the former may reduce the effective coverage area of the macro cell and may cause coverage dead angles, while the latter may consume too much power resources and may reduce the user scheduling gain of the corresponding micro cell, so that it is not suggested to be adopted in practical commercial network deployment.
In view of the foregoing, we need to consider designing an enhanced coverage extension biasing scheme for avoiding inefficient coverage extension-induced load balancing while not suffering from the disadvantages of existing eICIC solutions.
Disclosure of Invention
According to the understanding of the background technology and the existing technical problems, the invention provides a method for avoiding invalid load balancing in a heterogeneous network of an LTE-A system, which does not aim at optimizing the existing eICIC technical scheme, but optimizes a coverage extension bias technical scheme when establishing an incidence relation between user equipment and a cell so as to realize ingenious avoidance of interference between cells and further optimize the performance of the whole system.
The method for avoiding invalid load balancing in the user equipment of the heterogeneous network of the LTE-A system according to the present invention, wherein the heterogeneous network comprises at least one macro base station, at least one micro base station and at least one user equipment, and the at least one micro base station is to turn on the coverage extension capability, the method comprises the following steps:
A. the UE obtains a temporary serving cell index of the UE based on the sum of the measured reference symbol received power between the UE and the at least one micro base station and a coverage extension offset value set by the corresponding micro base station and the measured reference symbol received power between the UE and the at least one macro base station;
B. determining a first base station having a temporary serving cell index as a serving base station of the user equipment if the temporary serving cell index is an index of one of the at least one macro base station or an index of a base station that generates a maximum reference symbol received power at the user equipment among all macro base stations and micro base stations;
C. otherwise, the base station with the temporary serving cell index is definitely a micro base station and the association relationship between the temporary cell and the ue is also definitely caused by coverage extension of the corresponding micro cell, at this time, the serving base station of the ue is determined according to a relationship between a signal to interference and noise ratio level of the ue determined by the temporary serving cell index and a predetermined threshold, wherein the step (C) further includes:
c1: determining the first base station with the temporary serving cell index as a serving base station of the user equipment if the signal to interference plus noise ratio level is greater than or equal to the predetermined threshold;
c2: if the signal-to-interference-and-noise ratio level is less than the preset threshold value, judging whether all the base stations only comprise one micro base station;
-if only one micro base station is included in all base stations, the user equipment determining its serving base station directly from the size of the reference symbol received power between the user equipment and said each base station;
-if more than or equal to two micro base stations are comprised in said all base stations, removing said temporary serving cell index from the set of cell indices of said all base stations and then re-executing the steps of the method.
In one embodiment according to the present invention, different offset values or the same offset value is set for the at least one micro base station. Those skilled in the art will appreciate that the scheme based on the coverage extension can set the same or different bias values, which are determined case by case.
In one embodiment according to the present invention, when the same offset value is set for the at least one micro base station, the step (C2) of the method is simplified as follows:
if the SINR level is less than the predetermined threshold, the UE determines its serving base station directly from the magnitude of the reference symbol received power between the UE and each base station.
In one embodiment according to the present invention, the load balancing is achieved due to coverage extension of the micro cell, and the ineffective load balancing is that the downlink control channel of the user equipment has an unacceptable signal to interference plus noise ratio level as a result of the coverage extension of the micro cell causing the user equipment to be served by the first micro base station.
In an embodiment according to the present invention, the predetermined threshold is a target signal to interference plus noise ratio of a downlink control channel, or a larger one of the target signal to interference plus noise ratio of the downlink control channel and the target signal to interference plus noise ratio of a downlink data channel, wherein the target signal to interference plus noise ratio of the downlink data channel is a minimum value of the target signal to interference plus noise ratios of the downlink data channels corresponding to all the levels of alternative modulation and coding schemes that can be used by the downlink data channel.
In an embodiment according to the present invention, when said ue is in connected mode and currently served by a macro base station, and when said ue considers to switch from the macro base station currently serving said ue to another base station, if the method according to the present invention is terminated after step (C1) is performed, the estimated sir level used in step (C1) is called a first sir level, and the target base station for the handover is necessarily a micro base station.
In an embodiment of the present invention, the first signal to interference plus noise ratio level can be included in a handover request message sent by the macro base station currently serving the ue to the micro base station serving as the handover target base station, so that the micro base station serving as the handover target base station can assist the macro base station to make a decision on whether to accept the handover request according to the first signal to interference plus noise ratio level and assist the micro base station to make a plan for air interface resources to be used by the ue to be handed over after deciding to accept the handover request. This is not mandatory but optional. That is, the first signal to interference and noise ratio level may be included in a handover request message transmitted from the macro base station currently serving the user equipment to the micro base station as the handover target base station, or may not be included in a handover request message transmitted from the macro base station currently serving the user equipment to the micro base station as the handover target base station. Even if the first sir-nr level is not included in the handover request message sent by the macro base station currently serving the ue to the micro base station as the handover target base station, the micro base station as the handover target base station can make a decision as to whether to accept the handover request and plan air interface resources to be used by the ue to be handed over after deciding to accept the handover request. However, when the first sir-nr level is included in the handover request message sent by the macro base station currently serving the ue to the micro base station as the handover target base station, the micro base station as the handover target base station can make a more reasonable decision on whether to accept the handover request according to the first sir-nr level, and make a more reasonable plan for air interface resources to be used by the ue to be handed over after deciding to accept the handover request.
If the coverage extension bias scheme currently proposed by the 3GPP is used, it must be used together with an existing elcic (evolved nodeb) technical scheme (such as ABS technical scheme proposed by the 3 GPP) to solve the inter-cell interference problem of the downlink control channel to some extent, and also the system performance is adversely affected by the disadvantages of the existing elcic technical scheme, such as the reduction of the utilization rate of time domain communication resources and the interference of the CRS to the control channel.
However, if the enhanced coverage extension biasing scheme proposed by the present invention is used, there is no need to use any existing elcic solution, because the inter-cell interference of the downlink control channel is already skillfully avoided in the enhanced coverage extension biasing scheme proposed by the present invention (i.e. when the association relationship between the user equipment and the cell is established). Specifically, in the method according to the present invention, the association between the ue and the corresponding micro cell caused by the coverage extension of the micro cell is implemented only when a certain signal to interference plus noise ratio (sinr) requirement is met, and the conventional Reference Symbol Received Power (RSRP) -based cell association is implemented when the above mentioned sinr requirement is not met, thereby effectively solving the above mentioned inter-cell interference problem of the downlink control channel.
In addition, when setting the bias value of the coverage extension of the micro cell, since the bias value cannot be too large (too large causes too serious interference) or too small (too small does not achieve the purpose of load balancing through the coverage extension), in the current standardization work of 3GPP, experimental simulation is usually used to determine the appropriate bias value based on experience. However, such bias values determined by experimental simulation are closely related to the network environment on which the experimental simulation is based, and the network environments are various in actual network deployment, so that it is difficult to ensure that the bias values determined by experimental simulation based on a specific network environment can be applied to various network environments; at the same time, the experimental simulation is performed for each typical network environment, and the workload is huge (even unrealistic).
If the enhanced coverage extension biasing scheme proposed by the present invention is used, it is not necessary to perform any experimental simulation, but it is only necessary to simply set the bias value to a larger value (here, the bias value is set to be larger rather than smaller because the purpose of coverage extension for the micro cell is to achieve load balancing, which is contrary to the purpose if the bias value is set to be smaller). Because the inter-cell interference of the downlink control channel is skillfully avoided in the scheme proposed by the invention (namely, when the association relationship between the user equipment and the cell is established), the worry about the existence of ineffective load balance caused by the coverage range expansion of the micro cell is not needed. Even if the bias value is set to be too large for some specific network environments, so that most of load balancing which would otherwise be caused by the coverage extension of the micro cell does not happen finally (because the bias value would be invalid and therefore avoided by the scheme of the invention), the base station can timely decide to adjust the magnitude of the bias value through evaluating the load balancing effect.
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Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments thereof, which proceeds with reference to the accompanying drawings.
Fig. 1 shows a flow chart 100 of a method according to the invention.
In the drawings, like or similar reference numbers indicate like or similar devices (modules) or steps throughout the different views.
Detailed Description
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof. The accompanying drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments according to the invention. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
Fig. 1 shows a flow chart 100 of a method according to the invention. As can be seen from the figure: the method 100 for avoiding invalid load balancing in a heterogeneous network of an LTE-a system according to the present invention includes at least one macro base station, at least one micro base station, and at least one user equipment, where the at least one micro base station will turn on a coverage extension capability, and includes the following steps:
first, in step 110, the ue obtains a temporary serving cell index of the ue based on a sum of a measured reference symbol received power between the ue and at least one micro base station plus a coverage extension offset value set by the corresponding micro base station and the measured reference symbol received power between the ue and at least one macro base station;
specifically, for example, the index of the macro cell is identified as {0}, and the cell index set of the micro cell is identified as {1, 2, 3, 4,. and. K } (assuming that there are K micro base stations around the user equipment). The received power of the reference symbol generated by the corresponding base station with the cell index k at any user equipment with the user index j is recorded as XkjIn watts, where K belongs to any one of {0, 1, 2, 3, 4, · K }. In one embodiment according to the present invention, different offset values or the same offset value is set for the at least one micro base station. Those skilled in the art will appreciate that the scheme based on the coverage extension can set the same or different bias values, which are determined case by case.
Specifically, in step 110, when different coverage extension bias values are set for different micro cells, the temporary serving cell index of the user equipment j is determined by the following equation:
wherein omegacurrSet of temporary serving cell indices as alternatives, whose initial value is set to Ωcurr0, 1, 2, 3, 4. In the above equation (4), when k is the macro cell index, it is equal to 0 (i.e., coverage extension is not performed for the macro cell), and when k belongs to the micro cell index, it is equal to 1.
Next, in step 120, if the temporary serving cell index is an index of one of the at least one macro base station or an index of a base station that generates the largest reference symbol received power at the user equipment among all macro base stations and micro base stations, the first base station having the temporary serving cell index is determined as the serving base station of the user equipment.
Specifically, if Cell _ IDscrving，tmp0 or Cell _ IDserving，tmp＝argmax{k＝0，1，...，K}{XkjGet the Cell index as Cell _ IDserving，tmpThe first base station of (a) is determined to be the serving base station of user equipment j, at which point the method ends.
Otherwise, in the next step 130, the base station with the temporary serving cell index is definitely a micro base station, and the temporary "association relationship between cell and user equipment" is also definitely caused by coverage extension of the corresponding micro cell, at this time, the serving base station of the user equipment is determined according to the relationship between the signal to interference plus noise ratio level of the user equipment determined by the temporary serving cell index and the predetermined threshold.
In particular, for the receiving end of the downlink, i.e. the user equipment, P is usednoiseThe average power of Additive White Gaussian Noise (AWGN) is expressed in watts. PnoiseCan be calculated using the following equation: pnoise＝PnoiseperHz× workgbandwidth × noisedirection, wherein PnoiseperHz＝10-174[dBm]/10×10-3(in watts), workgbandwidth denotes the operating bandwidth, which is a given system parameter, and noise denotes the noise figure, which is 10 for the ITU channel model or the 3gpp sccm channel model, respectively7[dB]/10Or 109[dB]/10. For simplicity, the average power of additive white gaussian noise at different user equipments is uniformly scaled by the parameter PnoiseAnd performing identification. By SINRCCHtarget[dB]Represents a target signal-to-interference-and-noise ratio for a downlink control channel to achieve successful transmission in an LTE-a system, which is a system parameter with a given value.
Step 130 further comprises the steps of:
in summary, in sub-step 132, if the signal to interference plus noise ratio level of the user equipment determined by the temporary serving cell index is greater than or equal to a predetermined threshold, the first base station with the temporary serving cell index is determined as the serving base station for the user equipment;
specifically, if Cell _ IDserving，tmpNot equal to 0 and Cell _ IDscrving，tmp≠argmax{k＝0，1，...，K}{Xkj}, the Cell index is Cell _ IDscrving，tmpMust be a micro base station, and the temporary index is Cell _ IDscrving，tmpThe association relationship between the Cell and the user equipment j is also defined as Cell _ D by the Cell indexserving，tmpIs caused by coverage extension, when a predetermined threshold value of the signal-to-interference-and-noise ratio level is setIs SINRCCHtargetThen, it is determined whether the following equation (5) holds:
wherein i is Cell _ IDserving，tmp。
At this time, if equation (5) holds, the Cell index is Cell _ Dserving，tmpThe first base station of (a) is determined to be the serving base station of user equipment j, at which point the method ends.
Conversely, if equation (5) above does not hold, that is, in sub-step 134, if the signal to interference and noise ratio level of the user equipment determined by the temporary serving cell index is less than a predetermined threshold, it is determined whether only one micro base station is included among all base stations;
-if only one micro base station is included in all base stations, the user equipment determining its serving base station directly from the size of the reference symbol received power between the user equipment and each base station. Specifically, the cell index is argmax{k＝0，1，...，K}{XkjThe base station of { is determined to be the serving base station of the user equipment j, at this time, the method is ended;
-if more than or equal to two micro base stations are included in all base stations, removing the temporary serving cell index from the set of cell indices of all base stations and then re-performing the steps of the method. Specifically, Ω is updatedcurrIs omegacurr＝Ωcurr-Cell_IDsecring，tmPAnd then returns to step 110 to re-execute the steps of the method.
In an embodiment according to the present invention, when the same coverage extension offset value is set for the at least one micro base station, step 134 of the method is simplified as follows:
if determined by the temporary serving cell indexAnd if the signal-to-interference-and-noise ratio level of the user equipment is less than the preset threshold value, the user equipment directly determines the service base station thereof according to the size of the reference symbol receiving power between the user equipment and each base station. Specifically, the cell index is argmax{k＝0，1，...，K}{XkjThe base station of { circumflex over } determines to be the serving base station of user equipment j, at which point the method ends.
In an embodiment according to the present invention, the predetermined threshold of the signal-to-interference-and-noise ratio level may be set as a target signal-to-interference-and-noise ratio (SINR) of the downlink control channelCCHtarget) I.e. as shown in equation (5) above. Meanwhile, further, the predetermined threshold may also be set as the larger one of the target signal-to-interference-and-noise ratio of the downlink control channel and the target signal-to-interference-and-noise ratio of the downlink data channel, wherein the target signal-to-interference-and-noise ratio of the downlink data channel is the minimum value of the target signal-to-interference-and-noise ratios of the downlink data channels corresponding to all the alternative modulation and coding scheme levels that can be adopted by the downlink data channel.
In particular, the target signal-to-interference-and-noise ratio of the downlink data channel is recorded asIn this case, the equation (5) used in the step 130 is rewritten into the following equation:
wherein i is Cell _ IDserving，tmp。
In an embodiment according to the present invention, when the ue is in connected mode and currently served by a macro base station, and when the ue considers to switch from the macro base station currently serving the ue to another base station, if the method according to the present invention is terminated after performing step 132, the estimated sir level used in step 132 is referred to as a first sir level, and the target base station for the handover is necessarily a micro base station.
In particular, byRepresents the first signal to interference and noise ratio level, which may be determined by the following equation:
in one embodiment according to the invention, the first signal to interference plus noise ratio levelCan be included in a handover request message sent by the macro base station currently serving the user equipment j to the micro base station as the handover target base station. This is not mandatory but optional. That is, the first SINR levelIt may not be included in the handover request message transmitted from the macro base station currently serving the user equipment j to the micro base station serving as the handover target base station. If it isThe micro base station serving as the handover target base station is not included in the handover request message sent by the macro base station currently serving the user equipment j to the micro base station serving as the handover target base station, and the micro base station serving as the handover target base station can decide whether to accept the handover request and plan air interface resources for the user equipment j to be handed over after deciding to accept the handover request. However, whenContained in a macro currently serving user equipment jWhen the base station transmits a handover request message to the micro base station as the handover target base station, the micro base station as the handover target base station can be based onTo make a more reasonable decision on whether to accept the handover request and to make a more reasonable plan for the air interface resources to be used by the user equipment j to be handed over after deciding to accept the handover request.
According to the method of the present invention, there is no need to use any existing elcic solution, because the inter-cell interference of the downlink control channel is already skillfully avoided in the enhanced coverage extension biasing scheme proposed by the present invention (i.e. when establishing the association between the ue and the cell). Specifically, in the method according to the present invention, the association between the ue and the corresponding micro cell caused by the coverage extension of the micro cell is implemented only when a certain signal to interference plus noise ratio (sinr) requirement is met, and the conventional Reference Symbol Received Power (RSRP) -based cell association is implemented when the above mentioned sinr requirement is not met, thereby effectively solving the above mentioned inter-cell interference problem of the downlink control channel.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Furthermore, it will be obvious that the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. Several elements recited in the apparatus claims may also be implemented by one element. The terms first, second, etc. are used to denote names, but not any particular order.
Claims (7)
1. A method for avoiding inefficient load balancing in user equipment of a heterogeneous network of an LTE-a system, wherein the heterogeneous network comprises at least one macro base station, at least one micro base station and at least one of the user equipment, and the at least one micro base station is to turn on a coverage extension capability, the method comprising the steps of:
A. the UE obtains a temporary serving cell index of the UE based on the sum of the measured reference symbol received power between the UE and the at least one micro base station and a coverage extension offset value set by the corresponding micro base station and the measured reference symbol received power between the UE and the at least one macro base station;
B. determining a first base station having a temporary serving cell index as a serving base station of the user equipment if the temporary serving cell index is an index of one of the at least one macro base station or an index of a base station that generates a maximum reference symbol received power at the user equipment among all macro base stations and micro base stations;
C. otherwise, the base station with the temporary serving cell index is definitely a micro base station and the association relationship between the temporary cell and the ue is also definitely caused by coverage extension of the corresponding micro cell, at this time, the serving base station of the ue is determined according to a relationship between a signal to interference and noise ratio level of the ue determined by the temporary serving cell index and a predetermined threshold, wherein the step (C) further includes:
c1: determining the first base station with the temporary serving cell index as a serving base station of the user equipment if the signal to interference plus noise ratio level is greater than or equal to the predetermined threshold;
c2: if the signal-to-interference-and-noise ratio level is less than the preset threshold value, judging whether all the base stations only comprise one micro base station;
-if only one micro base station is included in all base stations, the user equipment determining its serving base station directly from the size of the reference symbol received power between the user equipment and said each base station;
-if more than or equal to two micro base stations are comprised in said all base stations, removing said temporary serving cell index from the set of cell indices of said all base stations and then re-executing the steps of the method.
2. The method of claim 1, wherein different offset values or the same offset value is set for the at least one micro base station.
3. The method of claim 2, wherein when the same offset value is set for the at least one micro base station, the step (C2) of the method is simplified to:
if the SINR level is less than the predetermined threshold, the UE determines its serving base station directly from the magnitude of the reference symbol received power between the UE and each base station.
4. The method of claim 1, wherein the load balancing is achieved due to coverage extension of a micro cell, and the inefficient load balancing is such that a downlink control channel of the user equipment may have an unacceptable signal-to-interference-and-noise ratio level as a result of having the user equipment served by a first micro base station due to coverage extension of a micro cell.
5. The method of claim 1, wherein the predetermined threshold is a target signal-to-interference-and-noise ratio of a downlink control channel or a larger one of the target signal-to-interference-and-noise ratio of the downlink control channel and the target signal-to-interference-and-noise ratio of a downlink data channel, and wherein the target signal-to-interference-and-noise ratio of the downlink data channel is a minimum value of target signal-to-interference-and-noise ratios of the downlink data channel corresponding to all levels of alternative modulation and coding schemes that can be used for the downlink data channel.
6. The method of claim 1, wherein when said user equipment is in connected mode and currently being served by a macro base station, and when said user equipment considers switching from a macro base station currently serving said user equipment to being served by another base station, if the method of claim 1 is to be terminated after performing step (C1), the estimated signal to interference and noise ratio level used in step (C1) is referred to as the first signal to interference and noise ratio level.
7. The method of claim 6, wherein the first SINR level is included in a handover request message sent by the macro base station currently serving the UE to the micro base station serving the UE, so that the micro base station serving the UE can assist the micro base station to decide whether to accept the handover request according to the first SINR level and plan air interface resources to be used by the UE to be handed over after deciding to accept the handover request.
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