CN105722148A - Method for avoiding ineffective load balance in heterogeneous network of LTE-A system - Google Patents

Abstract

The present invention relates to a method for avoiding invalid load balancing in user equipment of a heterogeneous network of an LTE-A system, and all micro base stations in the heterogeneous network will enable RE expansion capabilities. The method includes: obtaining a temporary serving cell index based on the sum of the RSRP of the user equipment and the micro base station plus the RE extension offset value and the RSRP between the user equipment and the macro base station; The index of the base station is determined as the serving base station; otherwise, the serving base station is determined according to the relationship between the estimated SINR level and the predetermined threshold, wherein, if the former is greater than or equal to the latter, the base station is determined as the serving base station base station; if it is less than the latter, then judge whether only one micro base station is included; if so, determine its serving base station according to the size of RSRP between it and each base station; otherwise remove the temporary serving cell index and then re-execute the steps of the method . According to the method of the present invention, the existing eICIC technology can no longer be used.

Description

Method for avoiding invalid load balancing in heterogeneous network of LTE-A system

technical field

The present invention relates to wireless communication technology, in particular, to a method for avoiding invalid load balancing in a heterogeneous network of an LTE-A system.

Background technique

In order to meet additional demands on service capacity and/or coverage in cellular networks and LTE-A networks, low-power small cells (such as micro cells) can be deployed in macro cells. The formed network is generally called a heterogeneous network (HetNet: heterogeneous network). Specifically, when multiple open-access micro cells (also called micro base stations PeNB) are deployed in the coverage area of macro cells (also called macro base stations MeNB), some user equipments (UEs) can be connected by multiple micro cells To serve, so as to achieve the benefits of load balancing.

In the LTE-A system, when base stations transmit reference symbols (which are mutually orthogonal to different base stations), each UE measures the power of reference symbols received from surrounding base stations (including its serving base station). And, any user equipment will report its measured reference symbol received power (RSRP: reference symbol received power) to its serving base station. For any user equipment UE _j , use Indicates the set of cell indexes of its surrounding base stations. And, if RSRP _ij is used to represent the power of the reference symbols received from base station i measured by UE _j , then the conventional cell association criterion based on the measured reference symbol received power can be expressed as follows:

$\mathrm{<span\; class="notranslate">\; Cell</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; I</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; serving</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arg</span>}\mathrm{<span\; class="notranslate">\; ma</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; RSRP</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; surr</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the case of co-channel deployment of macro and micro cells, if the cell association criterion is still given by Equation (1), then more user equipments will be associated to the macro cell than to the micro cell, because The transmission power of a micro cell is much smaller than that of a macro cell. In this case, the available resources of the micro cell are not fully utilized, while in the macro cell, the competition for the available resources will be very intense. In order to make more effective use of the potential load balancing function provided by micro cells, for any user equipment UE _j , the following cell association criteria (2) will be suggested for heterogeneous networks with co-channel deployment of macro and micro cells :

Cell_ID _serving = argmax _{i} {RSRP _ij +ε·bias _i }(2)

in, And ε=0 when i is a macro cell index, and ε=1 when i belongs to a micro cell index.

In the above formula (2), when i belongs to the micro cell index, the bias value bias _i is a non-negative value, so that more user equipments can be served by the micro cell. Since the use of the offset value is equivalent to giving the micro cell the ability to extend the range associated with the user equipment, this process is called the coverage extension of the micro cell (RE: rangeextension), and the above offset value is also called the coverage extension offset value.

Currently, in LTE Release-10 (Rel-10), it is recommended to set the coverage extension offset value in a cell-specific manner. And, considering the simplicity of implementation, in LTErel-10, it is recommended to set the same coverage extension bias value for all micro cells, as shown in the following formula (3):

Cell_ID _serving = argmax _{i} {RSRRP _ij + ε bias} (3),

in, And ε=0 when i is a macro cell index, and ε=1 when i belongs to a micro cell index.

Based on a large number of evaluation reports made by 3GPP in related standardization work, the following conclusions can be drawn:

(1) For the case where the coverage of the micro cell is not expanded, there is no inter-cell interference problem for the downlink control channel, and for the downlink data channel, the inter-cell interference in LTE Release-8 or 9 (Rel-8/9) is reused Interference cancellation (ICIC) technology can well solve the problem of inter-cell interference.

(2) However, for the case of using the coverage extension offset scheme currently recommended by 3GPP, it is observed that although increasing the coverage extension offset value can allow more UEs to be served by the corresponding microcell, but at this time The interference between the macro cell and the corresponding micro cell will cause the user equipment associated to the corresponding micro cell to experience a lower SINR (especially for the user equipment at the edge of the corresponding micro cell), so that the associated to The probability that the user equipment of the corresponding micro cell fails to transmit the downlink control channel is increased. In addition, when the coverage expansion offset value is large, the problem of the downlink control channel caused by inter-cell interference will be very serious, and the ICIC technology in LTE Rel-8/9 cannot effectively solve the downlink control channel The inter-cell interference problem of the channel. In addition, since good control channel performance is a prerequisite for successful data channel transmission, if the inter-cell interference problem of the downlink control channel cannot be well resolved, then 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 microcell coverage extension may become ineffective due to the inter-cell interference existing on the downlink control channel. Specifically, if the coverage expansion offset value set by the micro cell is larger, the proportion of invalid load balancing caused by the coverage expansion of the micro cell will be higher.

In order to solve the above-mentioned inter-cell interference problem of the downlink control channel, many "enhanced inter-cell interference cancellation (eICIC: enhancedICIC)" technical solutions have been proposed. These eICIC technical solutions can be roughly divided into two types, namely, a resource orthogonal division solution and a power adjustment solution.

The basic idea of the resource orthogonal division scheme is to allocate the wireless resources used for the downlink control channel orthogonally between the macro base station and the micro base station, so as to reduce mutual interference as much as possible. These include time-division multiplexing and frequency-division multiplexing.

Since the signal transmitted on the downlink control channel will be transmitted on the entire frequency band, the technical solution of frequency division multiplexing is not suitable for solving the above-mentioned inter-cell interference problem of the downlink control channel.

The technical solution of time division multiplexing mainly includes almost blank subframe (ABS: Almost Blank Subframe) technology and time domain shifting (timeshifting) technology.

In the ABS technical solution recommended by 3GPP standardization, the macro base station as the source of interference does not transmit data on the physical downlink control channel (PDCCH) in some subframes configured as ABS, but only transmits cell-specific reference signals ( CRS: Cell-specificReferenceSignal) and other basic signals. Obviously, in the subframe configured as an ABS, no data transmission is performed on the physical downlink shared channel (PDSCH), that is, no data transmission is performed on the data channel. In addition, during the implementation of the ABS technology, the interference packets in the time domain must be exchanged between adjacent cells via some kind of communication link between base stations, such as a backhaul link based on the X2 interface. However, ABS technology still suffers from the "CRS to control signal" interference problem, because even in almost blank subframes, macro cell base stations still need to transmit CRS. More importantly, the inherent defect of this time-division multiplexing ICIC technology is that it reduces the available time-domain resources in the macro cell, resulting in a decrease in the throughput performance of the user equipment in the macro cell; if there are multiple micro cells, the macro base station is required to provide It uses ABS on the control channel to eliminate inter-cell interference, which will be extremely problematic. In addition, when the time-division multiplexing technology of ABS is applied to a frequency-division duplex (FDD) system, its strict requirements on time synchronization will not be reduced in the slightest, which will bring considerable difficulty in implementation.

In addition, the time-domain shifting (timeshifting) technology also has many shortcomings such as being unable to completely eliminate inter-cell interference.

The power adjustment scheme includes: reducing the transmission power of the downlink control channel at the macro base station as the interference source, and increasing the transmission power of the downlink control channel at the interfered micro base station for user equipment located at the edge of the corresponding micro cell. However, since the former will reduce the effective coverage of the macro cell and may cause coverage dead spots, while the latter may consume too much power resources and reduce the user scheduling gain of the corresponding micro cell, it is not recommended in actual commercial network deployment Adopted.

To sum up, we need to consider designing an enhanced coverage extension biasing scheme to avoid invalid load balancing caused by coverage extension, and at the same time, this scheme will not have the disadvantages of the existing eICIC technical scheme.

Contents of the invention

Based on the above understanding of the background technology and existing technical problems, the present invention proposes a method for avoiding invalid load balancing in the heterogeneous network of the LTE-A system. This method is not intended to optimize the existing eICIC technical solution , but to optimize the coverage expansion offset technical scheme when establishing the association relationship between the user equipment and the cell, so as to achieve clever avoidance of inter-cell interference and further optimize the performance of the entire system.

According to the method for avoiding invalid load balancing in a user equipment of a heterogeneous network of an LTE-A system according to the present invention, the heterogeneous network includes at least one macro base station, at least one micro base station, and at least one For the user equipment, the at least one micro base station will enable the coverage extension capability, and the method includes the following steps:

A. The user equipment is based on the sum of the calculated reference symbol received power between the user equipment and the at least one micro base station plus the coverage extension offset value set by the corresponding micro base station and the calculated Acquiring the temporary serving cell index of the user equipment by referring to the received power of symbols between the user equipment and the at least one macro base station;

B. If the temporary serving cell index is the index of a macro base station in the at least one macro base station or the index of the base station that generates the largest reference symbol received power at the user equipment among all macro base stations and micro base stations, then determining a first base station having the temporary serving cell index as a serving base station of the user equipment;

C. Otherwise, the base station with the temporary serving cell index must be a micro base station and the association relationship between the temporary cell and the user equipment must also be caused by the coverage expansion of the corresponding micro cell. At this time, according to the The relationship between the signal-to-interference and noise ratio level of the user equipment determined by the temporary serving cell index and a predetermined threshold is used to determine the serving base station of the user equipment, wherein the step (C) further includes:

C1: If the SINR level is greater than or equal to the predetermined threshold, determine the first base station with the temporary serving cell index as the serving base station of the user equipment;

C2: If the signal-to-interference-noise ratio level is less than the predetermined threshold, judge whether all base stations include only one micro base station;

- If only one micro base station is included in all base stations, the user equipment determines its serving base station directly according to the received power of reference symbols between the user equipment and each base station;

- If all the base stations include more than or equal to two micro base stations, remove the temporary serving cell index from the set of cell indexes of all the base stations, and then re-execute the steps of the method.

In an embodiment according to the present invention, different offset values or the same offset value are set for the at least one micro base station. Those skilled in the art should understand that the same or different offset values can be set for the solution based on coverage extension, and the offset value is determined according to specific conditions.

In an 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:

If the SINR level is smaller than the predetermined threshold, the user equipment determines its serving base station directly according to the received power of reference symbols between the user equipment and each base station.

In one embodiment of the present invention, the load balancing is achieved due to the coverage expansion of the micro cell, and the invalid load balancing refers to the user's As a result of the equipment being served by the first micro base station, the downlink control channel of the user equipment has an unacceptable level of SINR.

In an embodiment according to the present invention, the predetermined threshold is the target SINR of the downlink control channel, or the target SINR of the downlink control channel and the SINR of the downlink data channel The larger one of the target SINR, wherein the target SINR of the downlink data channel is the downlink data corresponding to all the alternative modulation and coding scheme levels that can be adopted by the downlink data channel The minimum value of the channel target SINR.

In an embodiment according to the present invention, when the user equipment is in connected mode and is currently being served by a macro base station, when the user equipment considers switching from the macro base station currently serving the user equipment to being served by the If another base station serves, if the method according to the present invention will be terminated after performing step (C1), the estimated SINR level used in step (C1) at this time is called the first signal The interference-to-noise ratio level, and the target base station of the handover at this time must be a micro base station.

In an embodiment according to the present invention, the first SINR level can be included in the message sent by the macro base station currently serving the user equipment to the micro base station serving as the handover target base station In the handover request message, so that the micro base station as the handover target base station can assist it to make a decision on whether to accept the handover request according to the first signal-to-interference-noise ratio level, and assist it in deciding to accept the handover request Then make a plan for the air interface resources that will be used by the user equipment that is about to be handed over. This point is not mandatory, but optional. That is to say, the first SINR level may be included in the handover request message sent by the macro base station currently serving the user equipment to the micro base station serving as the handover target base station, or may not Included in a handover request message sent by the macro base station currently serving the user equipment to the micro base station serving as the handover target base station. Even if the first SINR level is not included in the handover request message sent by the macro base station currently serving the user equipment to the micro base station serving as the handover target base station, as the handover target base station The femto base station can also make a decision on whether to accept the handover request and make a plan for the air interface resources that will be used by the user equipment that is about to be handed over after deciding to accept the handover request. However, when the first SINR level is included in the handover request message sent by the macro base station currently serving the user equipment to the micro base station serving as the handover target base station, the micro base station serving as the handover target base station The base station can make a more reasonable decision on whether to accept the handover request according to the first signal-to-interference-noise ratio level, and after deciding to accept the handover request, make a decision on the air interface resources that will be used by the user equipment to be handed over. More rational planning.

If the coverage extension offset scheme currently recommended by 3GPP is used, it must be used together with an existing eICIC technical scheme (such as the ABS technical scheme recommended by 3GPP) to solve the problem of the downlink control channel to a certain extent. The problem of inter-interference interference, and the system performance will be adversely affected by the shortcomings of the existing eICIC technical solutions, such as the reduction of the utilization of time-domain communication resources caused by the use of ABS technical solutions and the interference of CRS on the control channel, etc. .

However, if the enhanced coverage extension offset scheme proposed by the present invention is used, any existing eICIC technical solution does not need to be used, because the inter-cell interference of the downlink control channel is already within the enhanced coverage proposed by the present invention. In the extended offset scheme (that is, when the association relationship between the user equipment and the cell is established), it is cleverly avoided. Specifically, in the method according to the present invention, the association between the user equipment and the corresponding micro cell caused by the coverage extension of the micro cell is realized only when a certain signal-to-interference-noise ratio (SINR) requirement is met; When the dry-to-noise ratio is low, the traditional reference symbol received power (RSRP)-based cell association is implemented, thereby effectively solving the above-mentioned inter-cell interference problem of the downlink control channel.

In addition, when setting the offset value of the coverage extension of the micro cell, the offset value should neither be too large (too large will cause too serious interference) nor too small (too small will not achieve coverage expansion). To achieve the purpose of load balancing), in the current standardization work of 3GPP, the experimental simulation is usually used to determine the appropriate bias value based on empiricism. However, such bias values determined by experimental simulation are closely related to the network environment on which the experimental simulation is based. However, in actual network deployment, the network environment is diverse, and it is difficult to ensure The offset value determined by the experimental simulation of the network environment can be applied to a variety of network environments; at the same time, the workload will be huge (even unrealistic) to carry out experimental simulation for each typical network environment of).

If the enhanced coverage extension bias scheme proposed by the present invention is used, no experimental simulations need to be carried out, and the bias value only needs to be set to a larger value (here, it is set to be larger than It is not smaller because the purpose of extending the coverage of the micro cell is to achieve load balancing, if it is set to a smaller value, it will be contrary to the purpose). Because the inter-cell interference of the downlink control channel has been cleverly avoided in the scheme proposed by the present invention (that is, when the association relationship between the user equipment and the cell is established), there is no need to worry about invalid micro-cell coverage. Load balancing due to scaling. Even for some specific network environments, the set bias value is too large, so that most of the load balancing that would have been brought about by the expansion of the coverage of the micro cell will not occur in the end (because it will be invalid will be circumvented by the solution of the present invention), the base station can decide to adjust the size of the offset value in a timely manner by evaluating the effect of load balancing.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

FIG. 1 shows a flowchart 100 of the method according to the invention.

In the drawings, the same or similar reference numerals denote the same or similar means (modules) or steps throughout different views.

detailed description

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof. The accompanying drawings show, by way of example, specific embodiments in which the invention can be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments in accordance with 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. Accordingly, the following detailed description is not limiting, and the scope of the invention is defined by the appended claims.

FIG. 1 shows a flowchart 100 of the method according to the invention. It can be seen from the figure that according to the method 100 for avoiding invalid load balancing in a heterogeneous network of an LTE-A system according to the present invention, the heterogeneous network includes at least one macro base station, at least one micro base station, and At least one user equipment and at least one micro base station will enable the coverage extension capability, and the method includes the following steps:

First, in step 110, the user equipment is based on the sum of the calculated reference symbol received power between the user equipment and at least one micro base station plus the coverage extension offset value set by the corresponding micro base station and the calculated user equipment Obtaining the temporary serving cell index of the user equipment by referring to received power of symbols between the equipment 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, ..., K} (assuming that there are K micro cells around the user equipment) base station). The received power of the reference symbol generated by the corresponding base station with cell index k at any user equipment with user index j is denoted as X _kj , and the unit is watts, where k belongs to {0, 1, 2, 3, 4, .. ., K} in any one. In an embodiment according to the present invention, different offset values or the same offset value are set for the at least one micro base station. Those skilled in the art should understand that the same or different offset values can be set for the solution based on coverage extension, and the offset value is determined according to specific conditions.

Specifically, in step 110, when different coverage extension offset values are set for different micro cells, the temporary serving cell index of user equipment j is determined by the following formula:

$\mathrm{<span\; class="notranslate">\; Cell</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; I</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; serving</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; tmp</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arg</span>}\mathrm{<span\; class="notranslate">\; ma</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}_{\mathrm{<span\; class="notranslate">\; curr</span>}}}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; kj</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; bias</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \}</span>$

Wherein, Ω _curr is a set of candidate temporary serving cell indexes, and its initial value is set as Ω _curr ={0, 1, 2, 3, 4, . . . , K}. In the above formula (4), when k is a macro cell index, ε=0 (that is, no coverage extension will be performed for the macro cell), and when k belongs to a micro cell index, ε=1.

Next, in step 120, if the temporary serving cell index is the index of one of the at least one macro base station or generates the largest reference symbol received power at the user equipment among all macro base stations and micro base stations the index of the base station, then determine the first base station with the index of the temporary serving cell as the serving base station of the user equipment.

Specifically, if Cell_ID _{scrving, tmp} = 0 or Cell_ID _{serving, tmp} = argmax _{{k = 0, 1, ..., K}} {X _kj }, then determine the first base station whose cell index is Cell_ID _{serving, tmp} as The serving base station of user equipment j, at this point the method ends.

Otherwise, in the next step 130, the base station with the temporary serving cell index must be a micro base station, and the temporary "association relationship between the cell and the user equipment" must also be extended by the corresponding micro cell Therefore, at this time, the serving base station of the user equipment is determined according to the relationship between the SINR level of the user equipment determined by the temporary serving cell index and a predetermined threshold.

Specifically, for the receiving end of the downlink, that is, the user equipment, P _noise represents the average power of additive white Gaussian noise (AWGN), and the unit is watt. P _noise can be calculated using the following formula: P _noise = P _noiseperHz × workingbandwidth × noisefigure, wherein, P _noiseper Hz = 10 ^-174[dBm]/10 × 10 ^-3 (unit is watt), workingbandwidth represents the working bandwidth, which is a given system parameter, and noisefigure represents the noise figure, which is 10 ^{7 [dB]/10} or 10 ^{9 [dB]/10} for the ITU channel model or the 3GP PSCM channel model, respectively. For simplicity, the average power of the additive white Gaussian noise at different user equipments is uniformly identified by the parameter P _noise . SINR _CCHtarget [dB] represents the target signal-to-interference-noise ratio for successful transmission of the downlink control channel in the LTE-A system, which is a system parameter with a given value.

Step 130 further includes the following steps:

In general, in sub-step 132, if the signal-to-interference and 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 to be a serving base station of the user equipment;

Specifically, if Cell_ID _{serving, tmp} ≠ 0 and Cell_ID _{scrving, tmp} ≠ argmax _{{k=0, 1, ..., K}} {X _kj }, then the base station whose cell index is Cell_ID _{scrving, tmp} must be a micro base station, And the temporary "relationship between the cell whose index is Cell_ID _{scrving, tmp} and user equipment j" must also be caused by the coverage expansion of the micro cell whose cell index is Cell_D _{serving, tmp} . The predetermined threshold of the ratio level is set as SINR _CCHtarget , and then it is judged whether the following formula (5) is established:

where i=Cell_ID _{serving, tmp} .

At this time, if formula (5) holds true, the first base station whose cell index is Cell_D _{serving, tmp} is determined as the serving base station of user equipment j, and the method ends at this point.

On the contrary, if the above formula (5) is not established, 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 judged that all Whether only one micro base station is included in the base station;

- If only one micro base station is included in all base stations, the user equipment determines its serving base station directly according to the received power of reference symbols between the user equipment and each base station. Specifically, the base station whose cell index is argmax _{{k=0, 1, ..., K}} {X _kj } is determined as the serving base station of user equipment j, and the method ends at this point;

- If all base stations include more than or equal to two micro base stations, remove the temporary serving cell index from the set of cell indexes of all base stations, and then re-execute the steps of the method. Specifically, Ω _curr is updated to Ω _curr =Ω _curr -Cell_ID _{secring,tmP ,} and 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 expansion offset value is set for the at least one micro base station, step 134 of the method is simplified as:

If the signal-to-interference-noise ratio level of the user equipment determined by the temporary serving cell index is smaller than the predetermined threshold, the user equipment directly receives power based on reference symbols between the user equipment and each base station. Size to determine its serving base station. Specifically, the base station whose cell index is argmax _{{k=0, 1, . . . , K}} {X _kj } is determined as the serving base station of user equipment j, and the method ends at this point.

In an embodiment according to the present invention, the predetermined threshold of the SINR level can be set as the target SINR of the downlink control channel (ie SINR _CCHtarget ), that is, as in the above formula (5) shown in . At the same time, further, the predetermined threshold may also be set to the larger one of the target SINR of the downlink control channel and the target SINR of the downlink data channel, wherein the downlink data The target signal-to-interference-noise ratio of the channel is the minimum value among the target signal-to-interference-noise ratios of the downlink data channel corresponding to all alternative modulation and coding scheme levels that can be adopted by the downlink data channel.

Specifically, the target SINR of the downlink data channel is recorded as At this point, the formula (5) that will be used in the above step 130 will be rewritten as the following formula:

Wherein, i=Cell_ID _{serving, tmp} .

In an embodiment according to the present invention, when the user equipment is in connected mode and is currently being served by a macro base station, when the user equipment considers switching from the macro base station currently serving the user equipment to being served by the If another base station serves, if the method according to the present invention will be terminated after performing step 132, the estimated SINR level used in step 132 at this time is called the first SINR level , and the handover target base station must be a micro base station at this time.

Specifically, with Represents the first SINR level, which can be determined by the following formula:

In one embodiment of the present invention, the first SINR level It can be 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. This point is not mandatory, but optional. That is to say, the first SINR level It may also not be 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. like Not included in the handover request message sent by the macro base station currently serving user equipment j to the micro base station as the handover target base station, the micro base station as the handover target base station can decide whether to accept the handover request and can decide to accept Air interface resources are planned for the user equipment j to be switched over after the handover request. However, when When included in the handover request message sent by the macro base station currently serving user equipment j to the micro base station as the handover target base station, the micro base station as the handover target base station can according to To make a more reasonable decision on whether to accept the handover request, and make a more reasonable plan for the air interface resources that will 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 eICIC technical scheme, because the inter-cell interference of the downlink control channel has already been included in the enhanced coverage extension offset scheme proposed by the present invention (that is, in establishing The association relationship between the user equipment and the cell) is cleverly circumvented. Specifically, in the method according to the present invention, the association between the user equipment and the corresponding micro cell caused by the coverage extension of the micro cell is realized only when a certain signal-to-interference-noise ratio (SINR) requirement is met; When the dry-to-noise ratio is low, the traditional reference symbol received power (RSRP)-based cell association is implemented, thereby effectively solving the above-mentioned inter-cell interference problem of the downlink control channel.

It will be apparent to those skilled in the art that the invention is not limited to the details of the above-described exemplary embodiments, but that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Accordingly, the embodiments should be regarded in all respects as exemplary and not restrictive. Furthermore, it is obvious that the word "comprising" does not exclude other elements and steps, and the word "a" does not exclude the plural. A plurality of elements recited in device claims may also be embodied by one element. The words first, second, etc. are used to denote names and do not imply 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.