CN106686658B - Interval relay load balancing method applied to downlink OFDMA cellular network - Google Patents
Interval relay load balancing method applied to downlink OFDMA cellular network Download PDFInfo
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- H04W28/08—Load balancing or load distribution
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Abstract
The invention discloses an inter-cell relay load balancing method applied to a downlink OFDMA cellular network, which is characterized in that an overload cellular cell, a shared relay station and six adjacent cells around the shared relay station form a resource distribution and communication transmission system structure, the shared relay station and a cellular base station coordinate the transfer of users at the edge of the overload cellular cell according to the calculated subcarrier demand, and users in different areas use subcarriers of different carrier sets and a frequency reuse mode of 1 × 6 according to the division of carrier resources and time slots. The invention can effectively reduce the inter-cell interference of the cellular cell system, improve the frequency spectrum utilization rate, save the carrier resources and improve the user data transmission rate. Because the relay station shared among the cells is adopted, the method has the advantages of simple structure, stable transmission and higher throughput, and the load among the cell systems is better balanced.
Description
Technical Field
The invention discloses an interval relay load balancing method applied to a downlink OFDMA cellular network. The method is mainly used for solving the problems of low resource utilization rate of an adjacent cell and low user data transmission rate due to resource shortage of an overloaded cell, and belongs to the technical field of cellular network communication.
Background
OFDMA is a multiple access scheme adopted to allocate subcarriers to different users based on Orthogonal Frequency Division multiple access (OFDM) technology. In recent years, the wireless communication device has been widely used in wireless communication. Because the OFDMA technique employs the OFDM modulation technique in the cell, the subcarriers are orthogonal to each other, so that Inter Symbol Interference (ISI) is effectively eliminated, that is, intra-cell Interference can be avoided. However, since the frequency reuse factor is 1 in the OFDMA wireless cellular communication system, that is, different cells use the same frequency spectrum resource, serious Inter-Cell Interference (ICI) is generated. In some urban business center segments, because of the high density of user traffic, communication hot spot areas tend to form, causing shortage of spectrum resources and high blocking rate. However, the neighboring cell segment will typically still have sufficient remaining resources, resulting in wasted resources with respect to the overloaded area. Load Balancing (LB) has been developed to fully and efficiently utilize system resources.
The load balancing technical scheme of the OFDMA cellular network can effectively balance cell systems with larger resource utilization rate difference, relieve the resource shortage of overloaded cells, reduce the blocking rate, improve the resource utilization rate of light-load cells and improve the user data transmission rate.
Disclosure of Invention
The invention aims to provide an interval relay load balancing method applied to a downlink OFDMA cellular network, which can solve the problems of low resource utilization rate of an overload cell and low user data transmission rate of an adjacent cell due to resource shortage of the overload cell when a hot spot cell is overloaded and congested.
In order to achieve the above object, the technical solution provided by the present invention is an inter-cell relay load balancing method applied to a downlink OFDMA cellular network, comprising the steps of:
1) when a certain time slot is initial, the cellular base station layer is responsible for calculating the total number of subcarriers required by all users in the current cell, carrying out carrier pre-allocation, judging whether the number exceeds a threshold value, if so, executing the step 2, otherwise, executing the step 4;
2) based on a spectrum division strategy of a time division slot and a carrier set, carrying out load transfer on edge users of different partitions in an overloaded cell to a corresponding light-load adjacent cell through a shared relay station, wherein the transferred users and the nearest partition of the corresponding adjacent cell share one set of carrier set;
3) in the state after the edge user is transferred, the cellular base station and the shared relay station redistribute the subcarriers according to the recalculated subcarrier requirements of the user;
4) and after the load balancing execution is finished, the cellular base station layer updates the load information and returns to the step 1.
Preferably, the threshold value in step 1 is 90% of the maximum number of subcarriers.
Further, the frequency spectrum division scheme of the time division slot and the carrier set in step 2 specifically comprises:
1) in the frame transmission of the system, each frame is divided into two time slots, the transmission conditions of different cells in different time slots are different, for adjacent cells, the transmission from a Base Station (BS) to an inter-cell Relay (RS) or the direct-connection transmission from the BS to a user Mobile Station (MS) is carried out in the first time slot, and the indirect transmission from the inter-cell RS to the MS is carried out in the second time slot; for the target cell, in the first time slot, the transmission from the BS to the MS is performed, in the second time slot, the transmission from the BS to the MS is still performed, when the target cell is overloaded, the transmission range of the BS in the target cell is reduced, and 6 RSs relay users to 6 neighboring cells around respectively;
2) the method comprises the steps of adopting a carrier allocation scheme with a frequency reuse mode of 1 × 6, dividing a total carrier N into 6 different subcarrier sets which are respectively numbered as N1, N2, N3, N4, N5 and N6, dividing each cell into 6 sectors, adopting a set of subcarrier sets for each sector, adopting the same subcarrier set for sectors at the same position in each cell, and adopting the subcarrier set in a relay region from the nearest sector of the corresponding adjacent cell.
The invention has the beneficial effects that:
the invention adopts the relay station shared among the cells, has the advantages of simple structure, stable transmission and larger throughput, and ensures that the load among the cell systems is well balanced.
The novel resource allocation scheme of the time division slot carrier set and the frequency reuse mode of 1 × 6 can effectively reduce the inter-cell interference of a cellular cell system, improve the frequency spectrum utilization rate, save carrier resources and improve the user data transmission rate.
Drawings
Figure 1 is a schematic diagram of a cellular architecture model of the method of the present invention.
Fig. 2 is a schematic diagram of a spectrum partitioning policy model of a carrier set according to the method of the present invention.
Fig. 3 is a schematic diagram of the time slot partitioning strategy of the architecture of the method of the present invention.
Fig. 4 is a flowchart of an interval relay load balancing method of a downlink OFDMA cellular network of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Aiming at the problem that the traditional load balancing method based on inter-cell switching is low in efficiency, the method realizes a load balancing mechanism of user switching and a novel resource allocation scheme based on inter-cell relay so as to reduce system interference and improve the utilization rate of frequency spectrum; and combining the subcarrier redistribution scheme to improve the system throughput rate and the user data rate. A shared relay station is arranged between adjacent cells to realize user switching, and a novel resource allocation scheme of a time-division slot carrier set is combined to carry out load balancing. The adopted shared relay station and the cellular base station can coordinate the transfer of the users at the edge of the overloaded cell according to the calculated subcarrier demand. The time-division and carrier-set frequency spectrum division scheme divides each transmission frame into two time slots, and adopts a frequency reuse mode of 1 × 6. The scheme can effectively reduce the inter-cell interference of the cellular system, thereby saving carrier resources and improving the service quality of users.
The invention relates to a resource allocation and communication transmission system structure which is formed by an overloaded cell, a shared relay station and six adjacent cells around the overloaded cell. The shared relay station and the cellular base station coordinate the transfer of users at the edge of the overloaded cellular cell according to the calculated subcarrier demand, and according to the division of carrier resources and time slots, users in different areas use subcarriers of different carrier sets and a frequency reuse mode of 1 x 6, so that the inter-cell interference of a cellular cell system can be effectively reduced, the frequency spectrum utilization rate is improved, the carrier resources are saved, and the data transmission rate of the users is improved.
In the whole design method, the method is mainly divided into two parts: the method comprises the steps of firstly, forming a resource allocation and communication transmission system structure by the overloaded cell, the shared relay station and six adjacent cells around the overloaded cell, and secondly, setting a set of frequency spectrum division strategies of time slots and carrier sets. The main process steps, as shown in fig. 4:
step 1) when a certain time slot is initial, the cellular base station layer is responsible for calculating the total subcarrier number required by all users in the current cell to perform carrier pre-allocation, and judging whether the threshold value is exceeded or not, wherein the threshold value is 90% of the maximum subcarrier number. If the threshold value is exceeded, executing the step 2, otherwise, executing the step 4.
And 2) carrying out load transfer on edge users of different partitions in the overloaded cell to a corresponding light-load adjacent cell through a shared relay station based on a spectrum division strategy of a time division slot and a carrier set, wherein the transferred users and the nearest partition of the corresponding adjacent cell share a set of carrier set, and executing the step 3.
And step 3) in the state after the edge user is transferred, the cellular base station and the shared relay station redistribute the sub-carriers according to the recalculated user sub-carrier requirements.
And step 4) updating the load information by the cellular base station layer after the load balancing execution is finished, and executing the step 1.
In the above method, the scheme for dividing the time slot and the carrier set spectrum specifically includes:
1) in the frame transmission of this system, each frame is divided into two slots. Different cells in different time slots have different transmission conditions. For the adjacent cells, in the first time slot, the transmission from the Base Station (BS) to the Relay (RS) between the cells or the direct transmission from the BS to the user (MS) is performed, and in the second time slot, the indirect transmission from the RS between the cells to the MS is performed. For the target cell, in the first time slot, the BS-to-MS transmission is performed, and in the second time slot, the BS-to-MS transmission is still performed, and when the target cell is overloaded, the transmission range of the BS in the target cell is reduced, and 6 RSs relay users to 6 neighboring cells around respectively.
2) And a frequency reuse mode is adopted to allocate the 1 × 6 carriers. Dividing the total carrier N into 6 different subcarrier sets, which are respectively numbered as N1, N2, N.. and N6, dividing each cell into 6 sectors, wherein each sector respectively adopts a set of subcarrier sets, and sectors at the same position in each cell adopt the same subcarrier set. The subcarrier sets employed within the relay zone are from the nearest sector of the corresponding neighboring cell.
The main variables and their definitions:
meaning of variable name:
RBS: coverage radius of cell BS
dR: coverage radius of relay RS
Beta: pathloss exponent for links in cellular systems
K: total number of subcarriers in cell
r: distance of target user MS to its service base station
ri: distance between target user MS and ith adjacent cell base station BS
W: sub-carrier bandwidth
Rreq: minimum data rate required by user
PBS: transmission power of cell BS
sloti: indicates the ith time slot
First, a shared relay station is set in the neighborhood between cells, as shown in fig. 1. For ease of calculation, we assume a coverage radius R for each cellBSIs 100 m. The number of users in the target cell is 74, the number of users in each neighboring cell is 20, and each cell is uniformly distributed. The total subcarrier number K of the cell is 512, the subcarrier bandwidth W is 30KHZ, and the path loss exponent beta is 2. Data rate per user requirement RreqIs 256 Kbps. When the relay covers radius dRAt 20 m.
Secondly, the overloaded cell, the shared relay station and six adjacent cells around the overloaded cell form a resource allocation and communication transmission system structure. After setting the new resource allocation strategy for the time slot and the carrier set as shown in fig. 2 and fig. 3, the following steps are performed:
step 1) when the first time slot of the call request is initial, the cellular base station layer calculates that each call meets the requirement of the lowest rate R according to the formulas (1) and (2)reqThe number of sub-carriers and the corresponding range are integrated to obtain the current cellAnd (3) carrying out carrier pre-allocation on the total number of the subcarriers required by all users, and judging whether the number of the subcarriers exceeds a threshold value, wherein the threshold value is 90% of the maximum number of the subcarriers. Calculated to have exceeded the threshold, step 2 is performed.
Calculating the minimum rate requirement R met by each call link in different time slotsreqNumber of subcarriers of (a):
calculating the signal-to-interference ratio of the link in the ith time slot of the time slot:
and step 2) edge users of different partitions in the overloaded cell transfer load to a corresponding light-load adjacent cell through a shared relay station, and the transferred users and the nearest partition of the corresponding adjacent cell share a set of carrier wave set, as shown in fig. 2. Step 3 is performed.
And 3) in the state after the edge user is transferred, the cellular base station and the shared relay station integrate the corresponding range according to the formulas (1) and (2), recalculate the subcarrier requirements of the user and redistribute the subcarriers. In a new state, the average throughput rate of the target cell is improved by 231Kbps, and idle carriers of adjacent cells are fully utilized.
And step 4) updating the load information by the cellular base station layer after the load balancing execution is finished, and returning to the step 1.
Claims (2)
1. An interval relay load balancing method applied to a downlink OFDMA cellular network is characterized by comprising the following steps:
1) when a certain time slot is initial, the cellular base station layer is responsible for calculating the total number of subcarriers required by all users in the current cell, carrying out carrier pre-allocation, judging whether the number exceeds a threshold value, if so, executing the step 2, otherwise, executing the step 4;
2) based on a spectrum division strategy of a time division slot and a carrier set, carrying out load transfer on edge users of different partitions in an overloaded cell to a corresponding light-load adjacent cell through a shared relay station, wherein the transferred users and the nearest partition of the corresponding adjacent cell share one set of carrier set, and the time division slot and carrier set spectrum division scheme specifically comprises the following steps 2-1) and 2-2):
2-1) in the frame transmission of the system, each frame is divided into two time slots, the transmission conditions of different cells in different time slots are different, for adjacent cells, in the first time slot, the transmission from a Base Station (BS) to an inter-cell Relay (RS) or the direct transmission from the BS to a user (MS) is performed, in the second time slot, the indirect transmission from the RS to the MS in the cell is performed, for a target cell, in the first time slot, the transmission from the BS to the MS is performed, in the second time slot, the transmission from the BS to the MS is still performed, when the target cell is overloaded, the transmission range of the BS in the target cell is reduced, and 6 RSs relay users to 6 adjacent cells around respectively;
2-2) adopting a frequency reuse mode of 1 × 6 carrier allocation scheme, dividing a total carrier N into 6 different subcarrier sets, which are respectively numbered as N1, N2,. and N6, dividing each cell into 6 sectors, wherein each sector respectively adopts a set of subcarrier sets, the same subcarrier set is adopted by the sectors at the same position in each cell, and the subcarrier set adopted in a relay region is from the nearest sector of the corresponding adjacent cell;
3) in the state after the edge user is transferred, the cellular base station and the shared relay station redistribute the subcarriers according to the recalculated subcarrier requirements of the user;
meaning of variable name:
RBS: coverage radius of cell BS;
beta: path loss exponent of a link in a cellular system;
k: total number of subcarriers in a cell;
r: the distance from the target user MS to its serving base station;
ri: the distance from the target user MS to the ith adjacent cell base station BS;
Rreq: the minimum data rate required by the user;
PBS: of cell BSA transmission power;
sloti: represents the ith time slot;
step 1) when the first time slot of the call request is initial, the cellular base station layer calculates that each call meets the requirement of the lowest rate R according to the formulas (1) and (2)reqIntegrating the corresponding range to obtain the total subcarrier number required by all users in the current cell, then performing carrier pre-allocation, judging whether the threshold value is exceeded or not, wherein the threshold value is 90% of the maximum subcarrier number, and if the threshold value is exceeded by calculation, executing the step 2;
calculating the minimum rate requirement R met by each call link in different time slotsreqNumber of subcarriers of (a):
wherein w represents a subcarrier bandwidth;
calculating the signal-to-interference ratio of the link in the ith time slot of the time slot:
4) and after the load balancing execution is finished, the cellular base station layer updates the load information and returns to the step 1.
2. The method for interval relay load balancing in downlink OFDMA cellular networks according to claim 1, wherein the threshold in step 1 is 90% of the maximum number of subcarriers.
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