CN101207892B - A Subchannel Planning Method for Orthogonal Frequency Division Multiplexing System - Google Patents

Abstract

The invention discloses a subchannel planning method for an OFDM system, comprising: (a) determining the number N of base stations in a cluster, and each base station is divided into S sectors; (b) determining each sector in the cluster Multiplexed N subchannel groups, and determine the priority of the above subchannel groups in the corresponding sectors, and the priorities of the same subchannel groups in different sectors of the same base station are different; (c) according to the actual business of each sector The available sub-channel groups are allocated according to the order of priority. The method proposed by the invention can carry out sub-channel planning according to the dynamic changes of capacity and coverage, realize the dynamic planning of sub-channels, and the realization method is simple, and the network does not need to be reconfigured when the service and capacity change.

Description

A Subchannel Planning Method for Orthogonal Frequency Division Multiplexing System

technical field

The invention relates to a sub-channel planning method for an Orthogonal Fre-quency Division Multiplexing (OFDM) system, which belongs to the technical field of communication.

Background technique

OFDM technology was proposed in the 1960s as a high-speed transmission technology for wireless communication systems. In recent years, with the rapid development of digital signal processing technology and integrated circuit technology, this system has been applied in various communication standards, such as IEEE802.16 series standards, 3GPP Long-Term Evolution (Long-Term Evolution, LTE), etc.

Orthogonal Frequency Division Multiple Access (OFDMA) system is a multiple access communication system based on OFDM technology. In an OFDMA system, a wireless carrier is divided into multiple mutually orthogonal subcarriers, and all available subcarriers are divided into subchannels. According to different division methods, a subchannel can contain one or more subcarriers. The above-mentioned subchannel is a unit of resource allocation and scheduling, and different subchannels can be allocated to different users at the same time.

Like other cellular communication systems, the OFDMA system also needs to determine the frequency reuse mode and perform frequency planning during network planning, among which:

Frequency reuse is realized based on the characteristics of radio wave propagation path loss, and its unit is carrier. When the distance between two base stations is far enough, the carrier frequency used for one base station can be reused by the carrier frequency of another base station, thereby improving spectrum efficiency. The area covered by each base station is called a cell, and cells that use the same frequency are called co-frequency cells. The distance D between these same-frequency cells is called the frequency reuse distance. In the design, the frequency reuse distance D must be far enough to make the co-subchannel interference level low enough to ensure the coverage quality.

The basic unit of frequency planning is a cell cluster, and frequency reuse is performed within the coverage area with the cluster as a unit. A cluster is a collection of N cells. These N cells use all the available spectrum resources, but the operating frequency of each cell is different. The distribution mode and frequency allocation scheme of each cell in the cluster determine the frequency reuse mode.

In an OFDMA system, a single carrier channel is composed of multiple mutually orthogonal subcarriers, and subcarriers are grouped to form subchannels. Based on sub-channel scheduling and inter-cell interference control, the OFDMA system realizes frequency reuse with a distance of 1. In this way, the number N of cells in each cluster is 1.

The OFDMA system can be networked with a single carrier. At this time, the OFDMA system needs to manage and schedule subcarriers and subchannels reasonably. At present, which subcarrier or group of subchannels to use is mostly determined by the carrier-to-interference ratio C/I of subcarriers or subchannels in the cell. The scheduling and management of subcarriers and subchannels in the entire network are very complicated, which also makes network subcarriers , The management and scheduling effects of sub-channels are greatly affected.

For the OFDMA system, the requirements for coverage and capacity change in different stages of network construction, in different regions, and in different time periods. In the initial stage of network construction, users are different and capacity requirements are not large, and network planning needs to focus on coverage quality; with the increase of users, network capacity requirements gradually increase, and network planning needs to formulate capacity improvement measures at this time; Areas, network planning needs to focus on capacity. In areas with high traffic volume, high capacity needs to be guaranteed in planning; when network traffic volume is not high, coverage quality needs to be considered; when network traffic volume is large, network capacity needs to be guaranteed; obviously the above Changes in network capacity and coverage requirements have put forward higher requirements for the planning of OFDMA systems.

At present, OFDMA system single-carrier networking has not effectively dealt with dynamic changes in network capacity and coverage, and its main shortcomings are as follows:

(1) There is a lack of overall planning, and the scheduling and management of subcarriers and subchannels is highly complex;

(2) The adaptability to the dynamic changes of coverage and capacity is weak, and there is no corresponding dynamic planning measure.

Contents of the invention

The technical problem to be solved by the present invention is to propose a sub-channel planning method for an OFDMA system, so that the OFDMA system frequency planning is adaptable to dynamic changes in coverage and capacity.

The present invention is achieved through the following technical solutions:

A subchannel planning method for an OFDM system, comprising:

(a) determine the number N of base stations in the cluster, and each base station is divided into S sectors;

(b) Determine the N subchannel groups multiplexed by each sector in the cluster, and determine the priority of the above subchannel groups in the corresponding sector, and the priorities of the same subchannel groups in different sectors of the same base station are different;

(c) According to the actual traffic volume of each sector, assign available sub-channel groups in order of priority.

Further, the sub-channel groups are divided as follows:

When in the OFDM system, the total number of sub-channels is M, the M sub-channels are equally divided into N×S sub-channel groups, and the number L of sub-channels in each sub-channel group is:

Further, in the step (b), it is determined that the N subchannel groups multiplexed by each sector in the cluster are implemented in this way:

When the number of allocated subchannel groups in each sector in the cluster is 0, the allocation is performed as follows:

Allocate a group of different sub-channel groups for each sector in the cluster;

When the number of allocated subchannel groups in each sector in the cluster is less than N, the allocation is performed as follows:

Each sector in the i-th base station (1≤i≤N) respectively multiplexes the same Numbered sector to which subchannel groups have been allocated.

Further, the priority of the sub-channel groups in the corresponding sector in the step (b) is determined according to the sequence of the sub-channel groups allocated to the sectors.

Further, described step (c) further comprises:

The subchannels in the same subchannel group are used in a random order or according to a predetermined subchannel numbering sequence.

Further, after step (c), it further includes:

(d) When a sector sub-channel group is not enough to provide data transmission capacity, and there are sub-channel groups with the same lowest priority as the above-mentioned used sub-channel group that are idle in other sectors, call the above-mentioned idle sub-channel group, the priority of the called sub-channel group remains unchanged, but it is set to be used after the sub-channel group of the same priority in the sector.

Further, after step (d), it further includes:

(e) According to the distance from the base station, each sector is divided into multiple coverage areas with the same number of sub-channel groups actually in use in this sector, and the sub-channel groups in use in each sector are divided according to the priority Sort by high and low, and assign coverage areas sequentially from outside to inside.

Furthermore, for the coverage of the sub-channels in the same sub-channel group, such a method is adopted: each sub-channel covers the same area.

Furthermore, the following method is used for the subchannel coverage in the same subchannel group:

In the coverage area, sub-areas are further divided according to the size of the traffic and the distance from the base station, and the sub-areas are allocated according to the priority of actual use.

Further, according to the different requirements of different components in the OFDM system frame, separate sub-channel planning is performed on these components.

Compared with the prior art, the method proposed in the present invention can carry out sub-channel planning according to the dynamic changes of capacity and coverage, realize the dynamic planning of sub-channels, and the implementation method is simple, and the network does not need to be reconfigured when the service and capacity change. configuration.

Description of drawings

Fig. 1 is the frequency reuse mode figure of OFDMA system (N=4, S=3) in the embodiment of the present invention;

Fig. 2 is a schematic diagram of allocating one group of sub-channel groups per sector in the system shown in Fig. 1;

FIG. 3 is a schematic diagram of assigning two groups of subchannel groups per sector in an embodiment of the present invention;

FIG. 4 is a schematic diagram of allocating 4 subchannel groups per sector in an embodiment of the present invention;

FIG. 5 is a schematic diagram of subchannel groups actually allocated to each sector in an embodiment of the present invention;

Fig. 6 is a schematic diagram of temporarily borrowing a set of sub-channel groups from an adjacent low-traffic sector by a high-traffic sector of the same base station in an embodiment of the present invention;

Fig. 7 is a schematic diagram of temporarily borrowing a set of sub-channel groups from two adjacent low-traffic sectors in the high-traffic sector of the same base station in the embodiment of the present invention;

FIG. 8 is a schematic diagram of allocation of sub-channel group coverage when each sector of the base station uses a set of sub-channel groups in an embodiment of the present invention;

FIG. 9 is a schematic diagram of allocation of sub-channel group coverage when each sector of the base station uses two sub-channel groups in an embodiment of the present invention;

FIG. 10 is a schematic diagram of distribution of sub-channel group coverage when each sector of the base station uses three groups of sub-channel groups in an embodiment of the present invention;

FIG. 11 is a schematic diagram of allocation of sub-channel group coverage when each sector of the base station uses four sub-channel groups in an embodiment of the present invention.

Detailed ways

The present invention will be further introduced below in conjunction with the accompanying drawings and specific embodiments, but not as a limitation of the present invention.

As shown in Figure 1, it is a frequency reuse mode diagram of an OFDMA system. There are 4 clusters in the figure, which are respectively marked as A, B, C, and D; 4 base stations are arranged in each cluster, that is, N=4, respectively Denoted as B ₁ , B ₂ , B ₃ , B ₄ , there are 3 sectors in each base station, that is, S=3, denoted as S _i,1 , S _i,2 , S _i,3 (1≤i ≤4); the frequency planning method of the system is as follows:

1. Allocate the first group of subchannel groups to each sector of the base station in the cluster, and set its priority.

To allocate the first group of sub-channels to each sector, the above-mentioned available spectrum resources need to be divided into N×S=12 sub-channel groups and numbered as 1, 2, . . . , 12 respectively. The above sub-channel groups are allocated according to the numbers, and the results are shown in Table 1:

Table 1 Group 1 Sub-channel Group Allocation Table

It can be found from Table 1 that this is a traditional multiplexing mode (4 base stations × 3 sectors), each sector is assigned a group of sub-channel groups, and sub-channel groups among all sectors are not repeated. The subchannel group numbers between sectors of the same base station differ by 4. Set the priority level of each group of sub-channel groups allocated this time as the highest level, which is recorded as level 1. At this time, a schematic diagram of allocation of sub-channel groups is shown in FIG. 2 .

2. Allocation of the second sub-channel group in the cell, and setting its priority.

The second group of sub-channels is allocated to each sector, and the allocation method is as follows:

Because the second group of sub-channel groups is the secondary multiplexing of the first group of sub-channel groups in the cluster, the multiplexing distance is lower than that of the first group, and the use priority is ranked after the first group. The multiplexing mode of two subchannel groups per sector is shown in Table 2. The subchannel groups in the sector are sorted by priority and separated by "/". The schematic diagram of subchannel allocation this time is shown in Figure 3.

Table 2 Allocation table of 2 groups of sub-channel groups per sector

3. Allocation of the 3rd and 4th sub-channel groups in the cell, and setting their priority.

For each sector, the 3rd and 4th sub-channel groups are allocated, and the allocation method is as follows:

Since the 3rd and 4th sub-channel groups are the re-multiplexing of the 1st and 2nd sub-channel groups in this cluster, the multiplexing distance is lower than that of the 1st and 2nd groups, and the use priority is ranked after the 1st and 2nd groups , group 4 has a lower priority than group 3. Table 3 shows the allocation results of the sub-channel groups this time. After the multiplexing is completed, each sector has 4 groups of available sub-channels. The schematic diagram of sub-channel group allocation in each sector is shown in Figure 4. The carriers in the sectors are sorted by priority and separated by "/":

Table 3 3 and 4 sub-channel group allocation table for each sector

It can be seen from Table 3 that the 4 groups of sub-channels allocated by the same sector number of each base station are the same, but the order of use priority is different. If the sub-channel groups in the same sector have no order of use and are used completely randomly, serious overlap of sub-channel groups will occur, increasing the degree of interference. However, due to the introduction of priority in the above-mentioned allocation method, it is possible to realize that the degree of multiplexing changes with the dynamic change of the capacity, and the degree of interference is reduced.

4. According to the needs of the business volume of each sector, the sub-channel groups are allocated step by step according to the priority order of the sub-channel groups.

One point to explain: In this step, the sub-channels in the same sub-channel group can be used in the following two ways: (1) random use; (2) according to the number of sub-channels from large to small or from small to large Use sequentially. The order of use above is preset.

From the above description, it can be known that in the frequency planning method of the OFDMA system, since the allocation of subchannel groups is carried out according to the order of priority, the priorities of the same subchannel group numbers in different sectors are different, so different sectors The probability of the same carrier frequency used by the base stations in the network is greatly reduced, which can effectively reduce the degree of co-channel interference, which not only meets the needs of traffic changes, but also ensures the coverage quality.

In the above-mentioned embodiment, it is the frequency planning method for the OFDMA system with the number of base stations in the cluster N=4 and the number of sectors S=3. This method can be extended and applied to any cluster where the number of base stations is N and the number of sectors is S. OFDMA system frequency planning. It should be noted that the allocation of subchannel groups between the sectors of the base station in the cluster needs to be repeated many times until the number of subchannel groups allocated in each sector is N, and the newly allocated subchannels in the sector The group is determined in this way: when the number of allocated sub-channel groups in each sector of each base station is 0, each sector of each base station is allocated a group of sub-channel groups that are different from each other; when each base station When the number of allocated sub-channel groups in each sector of is less than N, it is allocated according to the following method: Each sector in the i-th base station (1≤i≤N) multiplexes the h-th base station (1≤h≤N, h≠i, and the h-th base station sub-channel group has never been multiplexed to the i-th base station) The sub-channel group allocated by the sector with the same number. The priority order among the newly multiplexed sub-channel groups remains unchanged, but the priority is arranged after those sub-channel groups that have been allocated. When sub-channel group allocation is performed, if a newly allocated sub-channel group is duplicated with an already allocated sub-channel group, the sub-channel group will not be added to the sub-channel group allocated to the sector this time.

表示不大于x的最大整数，按照1、2、...、N×S进行子信道组编号，子信道组i＝{SC_(i-1)×L+1，SC_(i-1)×L+2，...，SC_i×L}，(1≤i≤N×S)。由此，还有M-L×N×S个子信道没有被分配到子信道组中，这些子信道可以用于高业务量基站扩容、室内覆盖或其它用途。One more point: in other embodiments, if in an OFDMA system in which the number of base stations in any cluster is N and the number of sectors is S, the number of sub-channels is M, denoted as SC ₁ , SC ₂ , ..., SC _M , Divide M sub-channels into N×S groups on average, then the number of sub-channels L in each sub-channel group is

Indicates the largest integer not greater than x, the number of sub-channel groups is carried out according to 1, 2, ..., N×S, sub-channel group i={SC _(i-1)×L+1 , SC _{(i-1)× L+2} , . . . , SC _i×L }, (1≤i≤N×S). Therefore, there are still ML×N×S subchannels not allocated to the subchannel group, and these subchannels can be used for capacity expansion of the base station with high traffic volume, indoor coverage or other purposes.

In the above frequency planning method, other auxiliary methods may be further added, so that the frequency planning method has a wider application range and better effect.

(1) Temporary borrowing of sub-channel groups among sectors of the same base station

As shown in Figure 5, when the traffic volume of sector 1 of a certain base station is large, sector 1 uses two sets of sub-channel groups, and the number of sub-channel groups is: 1/2. At this time, the traffic of sector 2 and sector 3 The amount is small, and only one set of sub-channel groups is used, of which sector 2 uses the sub-channel group numbered 5, and sector 3 uses the sub-channel group numbered 9.

When the traffic of sector 1 gradually increases and the third sub-channel group needs to be added, if the traffic of the other two sectors does not change significantly, the third priority sub-channel group 3 should be enabled according to the above frequency planning method. However, since the sub-channel groups 6 and 10 of the second priority in sectors 2 and 3 are not used, the interference caused by using the sub-channel group of the second priority is lower than that of using the sub-channel group of the third priority. channel group. Therefore, sector 1 may temporarily borrow the second priority idle subchannel group 6 from sector 2 at this time, and the subchannel group allocation diagram of the base station at this time is shown in FIG. 6 .

When the traffic volume of sector 1 continues to increase and the fourth sub-channel group needs to be added, if the traffic volume of the other two sectors still does not change significantly, then sector 1 can temporarily borrow the second priority from sector 3 The idle sub-channel group 10, at this time, the sub-channel group allocation schematic diagram of the base station is shown in FIG. 7 .

According to the above description of the implementation method, it can be known that the introduction of the sub-channel group priority realizes the dynamic change of the multiplexing degree with the capacity, adapting to the dynamic change of the network capacity, and the temporary borrowing method of the sub-channel group enhances the security of different sectors in the base station. The ability to adapt to uneven capacity distribution in the interval and the ability to adapt to drastic changes in sector services.

(2) Dynamic allocation of subchannel group coverage

Since subchannel groups with different priorities in each sector have different degrees of reuse and degrees of interference. Therefore, in order to increase the multiplexing distance of the sub-channel group with low priority, it is also possible to dynamically allocate the coverage of the sub-channel group.

According to the number n of sub-channel groups in use in this sector and the distance from the base station, this sector can be divided into n band-shaped areas with the same number of sub-channel groups actually in use in this sector, and the priority Sort from high to low, and allocate coverage areas from outside to inside, high-priority sub-channel groups cover the outer circle area of the sector, and low-priority sub-channel groups cover the sector inner circle area. The multiplexing distance of the low-priority sub-channel group is small, and the short-distance coverage area is allocated, which reduces the working power, reduces the degree of interference, and improves the coverage quality.

There are two methods for setting the sub-channel coverage in the same sub-channel group: (1) the same coverage method, that is, each sub-channel covers the same area; (2) the different coverage method, that is, within the coverage area by distance The base station further divides the sub-areas by far and near, and allocates sub-areas according to the priority of actual use.

When the traffic volume changes and the number of sub-channel groups used needs to be adjusted, the coverage area of the sub-channel group is adjusted accordingly.

The following uses base station 1 in the system with N=4 and S=3 as an example to further illustrate how the coverage is dynamically adjusted:

As shown in Figure 8, according to the traffic requirements, each sector of the base station uses a set of sub-channel groups, and the coverage is the entire sector at this time;

As shown in FIG. 9 , according to traffic requirements, each sector of the base station needs to use two sets of subchannel groups, and each sector is also divided into inner and outer areas. High-priority sub-channel groups 1, 5, and 9 cover the outer areas of their respective sectors, and low-priority sub-channel groups 2, 6, and 10 cover the outer areas of their respective sectors;

As shown in FIG. 10 , according to traffic requirements, each sector of the base station needs to use three groups of sub-channel groups, and each sector is correspondingly divided into inner, middle and outer areas. High-priority sub-channel groups 1, 5, and 9 cover the outer areas of their respective sectors, second-priority sub-channel groups 2, 6, and 10 cover the middle areas of their respective sectors, and third-priority sub-channel groups 3, 7, and 11 cover the internal areas of the respective sectors;

As shown in Figure 11, each sector uses four groups of sub-channel groups according to the needs of traffic volume, and each sector is divided into four parts according to the distance from the base station, and correspondingly allocated to sub-channel groups of different priorities.

It should be pointed out that the embodiment of the present invention is described by taking OFDMA as an example, but the method of the present invention is also applicable to other OFDM systems.

It can be seen from the above-mentioned embodiments that the OFDMA system planning method provided by the present invention supports the dynamic change of subchannel group multiplexing degree with the system capacity, the same-channel interference is small, and the implementation is simple. For the entire network, the frequency Planning can be realized in one step, and it is highly adaptable to dynamic changes in coverage and capacity, and does not need to reconfigure the network when the service and capacity of the network change.

One point that needs to be explained for the present invention is that OFDMA frames are divided into uplink frames and downlink frames, frames in each direction can be divided into user data symbols and system overhead symbols, and system overhead symbols can be further subdivided. For example, IEEE 802.16e OFDMA downlink frame consists of long preamble Preamble, FCH, DL-MAP, UL-MAP, and downlink burst DL Burst, in which downlink burst DL Burst is used to send user data, and other parts belong to system overhead; IEEE The 802.16e OFDMA uplink frame consists of Ranging sub-channels, uplink burst DL Burst and other parts, in which the downlink burst DL Burst is used to send user data, and other parts belong to the system overhead.

In the OFDMA system, the uplink user data symbols and downlink user data symbols of subchannels can adopt the same or different subchannel planning methods, and each part of the system overhead can also adopt different subchannel planning methods according to the usage, that is to say, according to OFDMA For the different requirements of different components in the system frame, separate sub-channel planning can be carried out for these components according to the method proposed by the present invention.

Claims (8)

1. A method for planning sub-channels of an orthogonal frequency division multiplexing system comprises the following steps:

(a) determining the number N of base stations in a cluster, wherein each base station is divided into S sectors;

(b) determining N sub-channel groups multiplexed by each sector in a cluster, and determining the priority of the sub-channel groups in the corresponding sectors, wherein the priority of the same sub-channel group in different sectors of the same base station is different;

(c) distributing usable sub-channel groups according to the actual traffic of each sector and the priority order; wherein,

the step (b) of determining the N subchannel groups multiplexed by each sector in the cluster is implemented as follows:

when the number of the sub-channel groups already allocated in each sector in the cluster is 0, the allocation is performed according to the following method:

respectively allocating a group of different sub-channel groups for each sector in the cluster;

when the number of the sub-channel groups which are already distributed in each sector in the cluster is less than N, the distribution is carried out according to the following method:

each sector in the ith base station respectively multiplexes the sub-channel groups which are already distributed by the sectors with the same number of the h base station; wherein i is more than or equal to 1 and less than or equal to N, h is not equal to i, and the sub-channel group of the h base station is never multiplexed to the i base station;

and (c) determining the priority of the sub-channel group in the corresponding sector according to the sequence of the sub-channel groups distributed to the sector.

2. The method of claim 1, wherein the group of subchannels is partitioned by:

when the total number of sub-channels in the ofdm system is M, the M sub-channels are averagely divided into nxs groups of sub-channel groups, where the number L of sub-channels in each sub-channel group is:

3. the method of claim 1, wherein step (c) further comprises:

the order of use for the subchannels within the same subchannel group is either random use or in a predetermined subchannel numbering order.

4. The method of claim 1, further comprising, after step (c):

(d) when one sector subchannel set is not enough to provide data transmission capacity, and other sectors still have a subchannel set which is free and has the same priority as the lowest priority in the used subchannel set, the free subchannel set is called, and the priority of the called subchannel set is not changed, but is set to be used after the subchannel set with the same priority in the sector.

5. The method of claim 4, further comprising, after step (d):

(e) according to the distance from the base station, each sector is divided into a plurality of coverage areas with the same number of sub-channel groups as the number of the sub-channel groups actually used by the sector, and the sub-channel groups in use in each sector are sequentially distributed from outside to inside according to the priority ranking.

6. The method of claim 5, wherein the method is employed for subchannel coverage within the same subchannel group: each subchannel covers the same area.

7. The method of claim 5, wherein the method is employed for subchannel coverage within the same subchannel group:

and further dividing sub-areas in a coverage area according to the size of the traffic and the distance from the base station, and dividing the sub-areas according to the actually used priority.

8. The method of claim 1, wherein the portions are separately sub-channel planned according to different requirements of different components in an ofdm frame.

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