WO2006005220A1

WO2006005220A1 - Hierarchical softcell wireless network and access control method therefore

Info

Publication number: WO2006005220A1
Application number: PCT/CN2004/000772
Authority: WO
Inventors: Xiaodong Zhang; Zhiyong Bu; Xiaodong Wang; Jian Li; Fei Gong; Haoyu Xu; Miaomiao Zhang; Ping Zhou
Original assignee: Shanghai Research Centre For Wireless Technologies
Priority date: 2004-07-09
Filing date: 2004-07-09
Publication date: 2006-01-19
Also published as: CN101019452A; CN100505910C

Abstract

A hierarchical softcell wireless network and a access control method therefore are provided. The network comprises a signal covering plane, a softcell plane and a service requirement plane, wherein a control center controls wireless resource use and operate mode of distributed antennas to form multi-layer softcells overlapping geographically; service requirement plane centralizes services of different velocity scenes distributed geographically; the access control method of the hierarchical softcell network according to the present invention mapps a user terminal to a certain softcell in the softcells that is suitable for the terminal to service based on mapping relationship between velocity feature and softcell layer by estimating the velocity of the terminal. The hierarchical softcell wireless network considers network performance, practicability and complexity synthetically, and can reduce system interference, use wireless resource efficiently, equalize loads, control handover load level of the network and improve system capacity and service quality.

Description

Layered soft cell wireless network and access control method thereof

The present invention relates to wireless access networks and mobile communication systems, and more particularly to super three generation/fourth generation mobile communication systems. Background technique

Traditional cellular communication networks have many problems, such as: the near-far effect caused by the fluctuation of the signal power plane, and the difference in the quality of service between the central user and the edge user. The root cause of these problems is due to the cell coverage and base station in the traditional cellular communication network. The signal coverage of the antenna is tightly coupled, so that the network treats different service scenarios uniformly, thus losing the flexibility to distinguish the service requirements scenario.

Second- and third-generation mobile communication systems have made full use of radio resources such as frequency, time slot, and code channel, but their transmission rate and quality of service are still far from meeting future demands. As the number of mobile users continues to grow and the demand for mobile multimedia services increases, the bottleneck of wireless access networks will become more serious.

The frequency band used by the next-generation wireless communication system will be higher than that of the current system, and the attenuation of electromagnetic waves in the air becomes more serious. Under the same transmission power, the effective coverage of the antenna radiation signal will be smaller; According to the stricter mobile phone radiation standards that China is about to enforce, the SAR (Specific Absorption Rate) requirements are more stringent, that is, the electromagnetic wave radiated power is required to be lower, resulting in a further reduction of the cell radius. Therefore, the future mobile In the communication network, the cell radius becomes smaller, the base station density is larger, the base station is difficult to locate, and the network construction cost is higher.

Due to the above limitations, it is very difficult to achieve future high-rate, high-quality data transmission requirements and ubiquitous wide-area coverage requirements only by improving the transmission technology of existing cellular communication networks. Therefore, multi-antenna distributed access methods must be considered. Implement network diversity and convenient handoffs, thus greatly Improve system capacity and resource utilization. Summary of the invention

Aiming at the problems of low resource utilization and poor adaptability of service scenarios in the traditional cellular communication network, the present invention proposes a novel wireless access network, called a hierarchical soft cell (HSC, Hierarchical Soft).

Cell) Wireless network.

A layered soft cell wireless network according to the present invention includes:

Signal coverage plane 1-1, soft cell plane 1-2 and service requirement plane 1-3;

The service requirement plane 1-3 refers to a service requirement in various speed scenarios distributed geographically; the signal coverage plane 1-1 refers to a signal formed by the distributed antenna group 2-3 by transmitting and receiving wireless signals. Seamless signal coverage;

The users in the service demand planes 1-3 are divided into K user groups having different speed characteristics according to the terminal moving speed, where K^l;

Corresponding to the above K types of user groups having different speed characteristics, forming a soft cell plane 1-2 including a K layer soft cell;

The control center 2-1 and the distributed antenna group 2-3 perform signal transmission through the transmission medium 2-2; the one layered soft cell wireless network further includes:

The soft cell plane 1-2 is established on the basis of the signal coverage plane 1-1, and the control center 2-1 allocates radio resources to the soft cells of each layer according to the orthogonal allocation principle, thereby forming geographical overlapping and non-interference. K-layer soft cell;

Each of the soft cells in the K-layer soft cell is composed of n soft cells, where n^l; when K user groups with different speed characteristics are divided according to the terminal moving speed, uniform division can be performed;

When K user groups with different speed characteristics are divided according to the moving speed of the terminal, non-uniform division can be performed;

Projecting the services of the K user groups having different speed characteristics to a suitable soft cell layer, and Serving by the corresponding soft cell in the soft cell of the layer;

The user group of the different speed characteristics refers to a user group whose terminal moving speed is in different speed ranges;

The soft cell layer formed by the larger area soft cell serves the user group with higher terminal moving speed; the soft cell layer formed by the smaller area soft cell serves the user group with lower terminal moving speed; the control center 2 1 Completing the signal processing and control functions required for communication, and managing and scheduling the radio resources used by the distributed antenna group ₂ _ ₃ under its jurisdiction;

The control center 2-1 of the layered soft cell wireless network may manage the distributed antenna group 2-3 in a centralized control manner;

The control center 2-1 of the layered soft cell wireless network may manage the distributed antenna group 2-3 in a distributed control manner;

The control center 2-1 of the layered soft cell wireless network may manage the distributed antenna group 2-3 in a hierarchical control manner;

The transmission medium 2-2 may be a medium such as a wireless fiber, a millimeter wave, a free-space optical link, or a mixed medium that mixes the above various media;

The allocation method of the radio resource allocation has a fixed allocation, a dynamic allocation, and a hybrid allocation manner; the fixed allocation manner refers to a fixed allocation of all available radio resources to each layer of soft cells and each layer of soft cells in a pre-planning manner. Each soft cell;

The fixed allocation method includes two parts: allocation between soft cells in each layer and allocation in each layer of soft cells. First, all radio resources are divided into K parts according to the orthogonal allocation principle, and correspondingly allocated to the K layer soft cells. Then, the allocation in each layer of the soft cell is based on the resource allocation method of the traditional cellular network, and the available resources of the layer of the soft cell are allocated to the soft cells in the soft cell of the layer;

The fixed allocation mode is to divide the available spectrum resources into non-overlapping κ parts, correspondingly allocate to the κ layer soft cells, complete frequency division stratification, and then allocate to each soft cell according to the principle of frequency division multiple access. The spectrum resources of the layer are further allocated to each soft cell in its layer;

The fixed allocation method is to divide a certain time slice into non-overlapping κ segments, corresponding to each time period. The working time of a layer in the K-layer soft cell is completed, and the time division is completed. Then, according to the principle of the frequency division/time division combined multiple access method, the available spectrum resources and time of each soft cell layer are further allocated to the layer. Each soft cell; '

The dynamic allocation mode refers to uniformly managing all available radio resources in the control center 2-1, and implementing dynamic and on-demand radio resource allocation among soft cells of each layer;

The hybrid allocation method refers to firstly allocating a part of radio resources to each soft cell to adapt to basic service requirements, while retaining a part of radio resources used in the control center 2-1 for bursty service requirements, which is reserved. Dynamic allocation of resources, flexible scheduling between soft cells at each layer;

The orthogonal allocation includes: frequency division multiple access, time division multiple access, code division multiple access, orthogonal frequency division multiple access, and a combination manner of the foregoing manners;

The soft cell refers to a coverage area formed by using one or more geographically adjacent antenna elements to transmit using the same radio resource;

The radius of the soft cell coverage area and the shape of the coverage area may be determined according to the speed characteristics of the mobile terminal;

The radius of the coverage area of the soft cell is determined according to a speed characteristic of the mobile terminal supported by the soft cell;

The shape of the soft cell coverage area is determined by the moving speed of the mobile terminal in various directions.

The method for controlling access of a layered soft cell wireless network according to the present invention includes:

When a certain user terminal in the service requirement plane has a service demand, the control center 2-1 first obtains the moving speed estimation value of the terminal, and then, according to the mapping relationship between the terminal moving speed estimation value and the soft cell layer, the terminal is The service requirement is projected to the corresponding soft cell layer, and then the soft cell specifically connected in the corresponding soft cell layer is determined according to the terminal location, and finally the control center 2-1 allocates a certain channel resource in the access soft cell to the a user terminal that simultaneously controls multiple antennas of the soft cell to provide services for the terminal by using the channel;

The access control method further includes:

The estimated moving speed of the terminal may be measured by the control center 2-1, or may be End self measurement estimation;

During the process of the communication between the multiple antennas in the soft cell and the user terminal, all the antennas of the corresponding soft cell do not need to be in the active state at the same time, and the control center 2-1 can follow the principle of reducing interference according to the geographical location of the terminal. Certain antennas that selectively control the soft cell serve the user terminal.

In summary, for the soft cell according to the present invention, the soft cell coverage is determined by the speed characteristics of the terminal that needs to be served, and the soft cell coverage is implemented by multiple antenna combinations by the allocation of the radio resources. This removes the tight coupling relationship between single-antenna signal coverage and soft cell coverage, thereby enabling more efficient and flexible use of radio resources, improving the overall performance of the network, and soft cells formed according to the characteristics of the terminal moving speed can be better adapted. Business needs for various speed scenarios.

The implementation of signal coverage plane 1-1 allows for the construction of geographically overlapping multi-layer soft cells with the same set of distributed antenna groups 2-3. The users in the service demand plane are divided into user groups with different speed characteristics according to their speed characteristics, and the user groups with different speed characteristics are projected into the corresponding soft cell layers, which can effectively balance the load. The soft cell layer formed by the cooperation of the soft cells of the same layer ensures that the user group with a certain speed feature provides ubiquitous service; the seamless coverage of the signal coverage plane 1-1 ensures the full coverage of each layer of the soft cell in the region. Thereby achieving seamless access of the user terminal in any location and in any speed scenario. Compared with the traditional cellular communication system, the layered soft cell utilizes space resources more effectively, improves the system capacity, and also ensures the system's achievability and low processing complexity. DRAWINGS

1 is a schematic diagram of a logical function plane of a layered soft cell wireless network;

2 is a connection diagram of a physical structure of a layered soft cell wireless network;

3 is a schematic diagram of a method for forming a soft cell in a layered soft cell wireless network;

4 is an example 1 of a layered soft cell wireless network resource allocation manner;

FIG. 5 is a second example of a wireless network resource allocation manner of a layered soft cell;

6 is a flow chart of access control of a layered soft cell wireless network;

7 is a comparison of the capacity of a layered soft cell wireless network and a traditional cellular network; 8 is a comparison of carrier-to-interference ratio performance between soft cells of a layered soft cell and a traditional cellular network; FIG. 9 is a comparison of blocking rates of a layered soft cell wireless network and a conventional cellular network;

Figure 10 is a comparison of handover probabilities between a layered soft cell wireless network and a traditional cellular network.

11 is a comparison of dropped call rates between a layered soft cell wireless network and a traditional cellular network;

As shown in FIG. 1, the layered soft cell radio network of the present invention includes three logical function planes: a signal coverage plane 1-1, a soft cell plane 1-2, and a service requirement plane 1-3;

As shown in FIG. 2, the components of the physical structure of the layered soft cell wireless network according to the present invention include: a control center 2-1, a transmission medium 2-2, and a distributed antenna group 2-3. -3 includes a plurality of antenna elements distributed in geographically different regions; the transmission medium 2-2 may be a medium such as a wireless fiber, a millimeter wave, a free-space optical link, etc., which assumes the distributed antenna group 2-3 and control The task of connecting the center 2-1 includes collecting the radio frequency signals of the distributed antenna group 2-3 to the control center 2-1 and transmitting the radio frequency signals to be transmitted by the control center 2-1 to the distributed antenna group 2-3. Ensure that the information link between the distributed antenna group 2-3 and the control center 2-1 is clear; of course, it is also possible to complete the connection between the control center 2-1 and the distributed antenna group 2-3 according to the actual situation. The connection, for example, using a hybrid of millimeter wave and ROF, uses a millimeter wave for the distributed antenna unit near the center of the control center 2-1, and an ROF connection for the distributed antenna unit at the far end.

The service requirement planes 1-3 concentrate the service requirements in various speed scenarios distributed geographically. According to the speed characteristics of the user terminal, the mobile terminals in various scenarios are unified into the service demand planes 1-3, such as fixed access, nomadic access, medium-speed mobile, and high-speed mobile terminal access.

The signal coverage plane 1-1 refers to a seamless signal coverage formed by radiating electromagnetic waves from a large number of geographically widely distributed antenna elements. The geographically seamless coverage of signals is the basis for providing wide-area services for mobile terminals. Due to the loss of electromagnetic waves during the propagation process, the signals transmitted by one antenna unit cannot reach the entire geographical area, resulting in an antenna unit having only a certain effective coverage. The specific effective coverage is the radiation power of the antenna. Antenna pattern and propagation environment Set. In order to enable the signal to effectively cover all areas of the geographical area, seamless signal coverage of all geographically service areas can be achieved by geographically distributing a large number of antenna elements, thereby ensuring that there is no blind area in the service area.

The soft cell plane 1-2 is based on the signal coverage plane 1-1, which is composed of a plurality of soft cells. The soft cell refers to a coverage area formed by using one or more geographically adjacent antennas to transmit using the same radio resource according to a unified radio resource management policy of the control center 2-1, and the coverage area is the same. The radio resources are transmitted by multiple antenna elements each of which effectively covers the sum. As shown in Fig. 3, the small dotted hexagonal coverage 3-1 is the effective signal coverage of a single antenna, and the shadow coverage area 3-2 synthesized by the adjacent multiple antennas using the same radio resource is a soft cell.

According to the soft cell formation method, using the resource reuse concept in the traditional cellular network, the control center 2-1 controls the radio resources used by the distributed antenna group 2-3 to form a plurality of soft cells belonging to the same layer, in a seamless signal coverage plane. On the basis of 1-1, this layer of soft cells is geographically seamless;

The soft cell plane 1-2 may include a K (K 1 ) layer soft cell; the control center 2-1 allocates radio resources to each layer of soft cells according to an orthogonal radio resource allocation principle, thereby forming geographical overlaps and mutual Interfering K-layer soft cell. The purpose of tiering is to adapt to the speed scenarios of business needs and improve the overall performance of the system. For example, in order to obtain a high system capacity, a cell with a small area should be formed, so that the density of resource reuse is high, but at this time, a user group with a high moving speed inevitably causes an excessive handover load; The network load overhead caused by the network load is small, and a large-area cell should be formed to adapt to a user group with a high mobile speed. However, since the density of resource reuse is low at this time, the system capacity is small. In addition, the characteristics of terminal services in different speed scenarios are different. For example, the channel environment of stationary and low-speed mobile terminals is slowly changing, and more accurate channel estimation can be performed, thereby realizing high-rate data transmission; and the moving speed of the vehicle-mounted wireless terminal Fast, the channel changes faster, it is difficult to perform accurate channel estimation, and the transmission rate is generally low. In order to make full use of system resources and improve overall performance, it is necessary to form soft cells of different levels to serve mobile terminals with different speed characteristics. Different layers of soft cells are different in the size and shape of soft cells and different transmission technologies.

Each layer of soft cells includes at least one soft cell. As shown in Figure 1, the soft cell plane can be 1-2. Divided into layer 1 soft cell 1-4, layer 2 soft cell 1-5, layer K soft cell 1-6, wherein each layer of soft cell is composed of multiple soft cells belonging to the layer soft cell; As shown in FIG. 1, the first layer soft cell 1-4 is composed of n (n^l) soft cells 1-7 belonging to the first layer soft cell 1-4, and the kth layer soft cell 1-6 is belonged to the same. The m (m^l) soft cells 1-8 of the Kth soft cell 1-6 are composed of, of course, the other layer soft cells are also composed of j (j^l) soft cells of the same layer (not shown).

The layered soft cell wireless network divides all service requirements of the service demand plane into user groups with different speed characteristics according to the moving speed of the user terminal, and then projects the terminal services of different speed characteristics to the appropriate soft cell layer, that is, access To the soft cell layer adapted to the speed feature; and then determining the corresponding soft cell to serve according to the location of the terminal, which better balances the network load. In general, a soft cell with a larger area serves a user group with a higher mobile speed, and a soft cell with a smaller area serves a user group with a lower mobile speed. For example, as shown in FIG. 1, the area of the soft cells 1-8 constituting the Kth layer soft cell 1-6 is larger than the area of the soft cells 1-7 constituting the layer 1 soft cell 1-4, and the Kth layer soft cell 1-6 is generally used for a user group with a higher mobile terminal speed, and the first layer soft cell 1-4 is used for a user group with a lower mobile terminal speed.

Since the user groups of various speed characteristics can exist anywhere in the area, each layer of soft areas must achieve geographically seamless coverage. After the distributed antenna group 2-3 forms the seamless signal coverage plane 1-1 in the area, it is only necessary to control the radio resources used by the distributed antenna group 2-3 through the control center 2-1, so that multiple layers can be realized. Cover the covered soft area. It should be noted that the arrangement of the distributed antenna group 2-3 on which the signal coverage plane 1-1 is formed does not have to be uniformly arranged over the entire area, and the distributed antenna can be reasonably arranged according to the actual service demand situation and future development prediction. Group 2-3. A mandatory principle is that the antenna group must be arranged so that all antenna elements transmit at a certain power to achieve effective seamless coverage over the area.

Although multiple layers of overlapping soft cells are formed at a logical level, they rely on the same signal coverage plane 1-1 formed by the same distributed antenna group 2-3; this is layered with traditional cellular networks. The structure is different, where stratification is achieved by arranging base stations of different layers, that is, the macro cell layer is implemented by the macro cell base station, and the micro cell layer is implemented by the micro cell base station. After the concept of layered soft cell is introduced in the wireless network, since the cell is formed in a soft manner through the control center 2-1, wireless resources can be effectively used, the scalability and flexibility of the network are improved, and network planning and design are simplified. The complexity.

It should be noted here that in the description of the wireless network concept, configuration, working mode, etc. of the layered soft cell in this specification, unless otherwise specified, it is generally discussed for the downlink (control center to mobile terminal link). , that is, multiple antennas simultaneously transmit to the mobile terminal; uplink (mobile terminal to control center link), that is, multiple antenna units simultaneously receive the mobile terminal's transmit signal, for describing the concept of layered soft cell wireless network And the construction method is similar to the description of the downlink, so the description of the uplink is not specifically given.

The relationship between the soft cell plane layering mode, the radio resource allocation mode in each layer of the soft cell, and the correspondence between the user group and the soft cell layer will be described in detail below.

In order to realize communication between multiple users, many multiple access methods have been proposed, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDM A), and Code Division Multiple Access (CDMA). Code Division Multiple Access), Space Division Multiple Access (SDMA), Orthogonal Frequency Division Multiple Access (OFDM A), and the like. The layered soft cell wireless network also needs to use the above technology to realize communication between multiple users, but at this time, multiple layers of geographically overlapping soft cells are simultaneously formed on the same group of distributed antenna groups 2-3, so layered soft The radio resource allocation of the cell radio network includes two parts: inter-layer allocation and intra-layer allocation. Table 1 lists the wireless resource allocation modes between the soft cell layers and layers in the layered soft cell wireless network.

Table 1 The radio resource allocation modes in the layer and between layers given in Table 1 are all adopted in a single division manner. Of course, a combination of various multiple access technologies may also be adopted, such as using a frequency partition to divide different layers of soft cells, and some The combination of FDMA/TDMA can be adopted inside the soft cell of the layer. In addition, the multiple access modes of different layers may be different, for example, a layered soft cell wireless network divided into three layers of soft cells, which is divided into soft cells of each layer by frequency division, but for each layer, The radio resource allocation method is: FDMA is used in the first layer soft cell, TDMA is used in the second layer, and CDMA is used in the third layer. Since there are a variety of multiple access technologies, there are many combinations of wireless resource allocation methods, and those skilled in the art can easily think of alternative wireless resource allocation methods, which will not be described here.

A basic principle to be observed is: According to the orthogonal allocation principle, the radio resource allocation between the soft cell layers is ensured, and the radio resources between the layers are orthogonal and do not interfere with each other; the radio resources inside each layer of the soft cell The allocation can be completed in a conventional manner. According to the idea of resource reuse, under the condition that the interference level requirement is met, the limited resources allocated to the soft cell layer are reused to realize resource allocation in the soft cell layer, which is different from the traditional cellular network. A radio resource unit within a soft cell is used simultaneously in several antenna units.

The allocation and scheduling of radio resources in the wireless network of the layered soft cell is completed by the control center 2-1 in a centralized manner, so that an efficient and flexible allocation of radio resources can be realized, and a high resource utilization rate can be obtained. The allocation of wireless resources has a fixed allocation, dynamic allocation, and a mixture of the two.

The fixed allocation allocates all available radio resources to each soft cell and each soft cell in each layer of the soft cell in a pre-planned manner. The dynamic allocation mode refers to unified management of all available radio resources in the control center 2-1. Dynamic and on-demand wireless resource allocation is implemented between soft cells in each layer. At this time, the use efficiency of wireless resources is higher than that of fixed allocation, but the complexity of implementation is also improved. The hybrid allocation method refers to fixing a part of wireless resources. It is allocated to each soft cell to adapt to basic service requirements, while retaining a part of the radio resources used in the control center for bursty service requirements. This part of the reserved resources implements a dynamic allocation policy, which can be flexibly scheduled in each layer of soft cells, and mixed allocation. The method combines the advantages of fixed allocation and dynamic allocation, and compromises both wireless resource utilization and system processing complexity. It should be noted that only one control center 2-1 is depicted in FIG. 2, but the specific implementation needs to be based on the size of the actual network. For a small-scale networking, centralized management control can be adopted; for a network covering a large area, it is not feasible to introduce all antenna elements into one control center 2-1 for centralized processing. The following two methods can be used to solve this problem. One is to introduce the concept of distributed control, geographically distributed multiple control centers, which use high-speed fiber link connections for information exchange; and these control centers are logically They are unified, and the information they rely on in the process of network management and wireless resource allocation is the same, thus solving the problem of high processing complexity. The second is to introduce the idea of hierarchical management control. Similar to the structure adopted by the current telephone network, the first-level control center, the second-level control center, and the third-level control center are introduced. The first-level control center controls the network management in the small area. The level control center is connected to multiple control centers and many distributed antenna units under its jurisdiction, mainly to complete network management in a large coverage area, and so on.

To more clearly illustrate the concept of a layered soft cell wireless network, two examples of layered soft cell wireless networks formed in a fixed radio resource allocation manner are given below.

In the first example, the soft cell plane is layered by using the frequency division method, and the radio resource allocation is also performed by using the frequency division method in the same layer of the soft cell.

First, the terminal in the service demand plane is divided into user groups with different speed characteristics according to the moving speed, and the number of soft cell layers included in the soft cell plane is designed. For example, let the set of 1, 2, ... 4 be a division of the speed range [0] of the mobile terminal, that is, 0 _{≤ Vl} , _mffi; _≤ _V2 , _{mffi ≤} ... _≤ _v = ^, where ^ is the network capable For the maximum allowable terminal movement speed of effective service, the K-layer soft cell is designed, and the terminal moving speed characteristics adapted by each layer of soft cells are [0, _1⁄4ma J (H ] (v _2max , v _3max ], respectively).

A terminal with a moving speed of 0 indicates a fixed access mode. In order to conveniently represent the above speed division, the K speed characteristics are abbreviated as V ₂ corresponding to the above terminal speed characteristics.

The radius r of a single soft cell in each layer of the soft cell is proportional to the speed feature of the user group supported by the layer, and the specific scale factor of the two is determined by the processing capability of the layered soft cell wireless network. The purpose of this design is to control the network maintenance complexity introduced by the handover caused by the terminal movement, so that the whole The handover load of the networks is within a controllable level, and the layered soft-cell wireless network can serve both high-speed user terminals and high-speed transmission requirements of stationary and low-speed user terminals through layering, effectively Leverage wireless resources to fully exploit the potential of system capacity. Here, the concept of the soft cell radius is different from the concept of the radius in the circle, because the speed has a direction, so the soft cell radius is relative to the moving direction, and refers to the soft cell edge to the soft cell center in the moving direction. distance. For example, on a highway, the speed along the highway is fast, and the speed perpendicular to the highway is small, so the distance from the soft cell edge of the highway to the center of the soft cell is large, and the edge of the soft cell is perpendicular to the direction of the highway. The distance to the center of the soft cell is short, and the shape of the soft cell is similar to an ellipse.

Assuming that the speed of the terminal served by the entire network system ranges from 0 to 150 Km/h and divides it into three segments, the soft cell plane is divided into three layers of soft cells to accommodate user groups with different speed characteristics. The division of the speed characteristics of the user terminal can be uniformly divided and non-uniformly divided. For the convenience of implementation, uniform division can be adopted, the terminal with the moving speed of 0~50Km/h corresponds to the first layer soft cell, and the terminal with the moving speed of 50~100Km/h corresponds to the second layer soft cell, and the moving speed is 100~150Km/ The terminal of h corresponds to the third layer soft cell; in practice, the general low-speed user is more than the high-speed user. In order to effectively utilize the wireless resource, non-uniform division can be performed, such as the first layer, the second layer, and the third layer soft cell respectively. Corresponding to a user terminal with a moving speed of 0 to 30 Km/h, 30 to 75 Km/h, and 75 to 150 Km/h.

In this example, the entire soft cell plane is divided into three layers of soft cells, wherein the first layer of soft cells is used for the user group whose service terminal moves at a speed of 0 to 50 km/h, and the second layer of soft cells is used for service. The user group whose terminal moving speed is 50~100km/h, and the third layer soft cell is used for the user group whose service terminal moves speed is 100~150km/h, according to the different speed characteristics in the soft cell layer and the service demand plane. The mapping relationship between the user groups, when requested by the access terminal, is controlled by the control center 2-1 to access the corresponding soft cell layer for service according to the terminal speed information.

As shown in FIG. 4, it is assumed that the total available spectrum resource is ( ), and the frequency band 4-1 of the frequency range (F _{1 3} F ₂ ) is allocated to the first layer soft cell by using the frequency division layering method. ₂ , E ₃ ) The frequency band 4-2 is allocated to the second layer soft cell, and the frequency band 4-3 of the frequency range (F ₃ , ) is allocated to the third layer soft cell. Since the same antenna can simultaneously transmit signals of different frequencies, that is, the same antenna can simultaneously Transmitting (signals at different frequency points in the F, F frequency range, therefore, according to the above frequency division layering method, the same antenna can simultaneously transmit different frequencies belonging to the first layer, the second layer and the third layer soft cell For example, the same antenna can simultaneously transmit a signal with a frequency of ^ (^ is a certain frequency in the range of ( , F ₂ )), and the frequency is (F _b is a certain one in the range of ( F _{2 5 J} F ₃ ) a frequency of the signal S ₂ , the frequency is (^ is a certain frequency in the range of ( F ₃ , F ₄ )), because the signal of frequency F belongs to the first layer of soft cells, the frequency is E The signal S ₂ belongs to the second layer soft cell, and the signal of the frequency F belongs to the third layer soft cell, so that signals belonging to the three layer soft cells respectively exist in the same geographical position, and the two do not interfere with each other, and This is achieved by the same antenna unit.

In the above, it is discussed in the vertical direction that there is a possibility that a plurality of different layers of soft cell signals are transmitted by the same antenna unit at the same time, which also shows that the same group of distributed antenna groups can simultaneously form geographically overlapping mutual interferences. Layer soft cell. In the horizontal direction, that is, the problem involved in each layer of soft cells is mainly the determination of the size and shape of a single soft cell and the realization of seamless coverage of each layer in the region.

The soft cell design in the soft cell layer is based on the following two points: (1) According to the terminal characteristics of the user groups served by the soft cells of each layer, it is mainly designed according to the terminal speed characteristics; (2) Generally speaking A soft cell layer composed of a soft cell with a larger area serves a user group with a higher mobile terminal speed, and a soft cell layer composed of a soft cell with a smaller area serves a user group with a lower mobile terminal speed.

In order to adapt to the speed characteristics of the terminal, the soft cell radius r, ., r, is determined according to the terminal speed characteristics adapted by the soft cell of the layer, and the specific proportional coefficients of the two are determined by the processing capability of the network. Due to the loss of the signal in the propagation space, the signal transmitted by one antenna unit has a certain effective coverage. Assuming that the signal coverage of the antenna unit in the region is circular coverage and the radius is r _Q , a soft cell with a radius of ^ is formed. The number of antennas required can be based on h/r. l to get, where "represents the smallest integer greater than X, the specific number of antennas required is determined by the specific shape of the soft cell, the antenna arrangement, the overlap of adjacent antenna coverage, etc., so that it can be determined to adapt to the speed characteristics. How many antenna elements are included in a single soft cell of a subscriber group.

It is assumed that a soft cell that needs to be formed for a user group whose speed belongs to the range of 0 to 50 Km/h contains three days. The line, when serving a certain terminal of the speed characteristic user group, requires three adjacent antennas to simultaneously transmit a signal of a certain frequency within the frequency (F" F ₂ ). The total effective coverage of the signal S is the three of the transmitted signal S. The sum of the antenna units is effectively covered, and the coverage is the coverage of the corresponding soft cell. Similarly, if the soft cell needs to be formed for a user group whose speed belongs to the range of 50~100Km/h, there are nine antennas, that is, nine neighbors are required. The antennas simultaneously transmit signals of a certain frequency within ( , ) to the user terminal; for a user group whose speed belongs to the range of 100~150Km/h, the soft cell needs to form 27 antenna elements, then 27 adjacent antennas are needed. At the same time, a signal of a certain frequency within a range of ( , ₄ ) is transmitted to serve the user terminal.

The above describes the formation basis and implementation method of a single soft cell in each layer of the soft cell. On the basis of the signal coverage plane 1-1 formed by the distributed antenna group 2-3, as long as each antenna unit participates in the construction of any layer of soft cells, according to the method of forming the soft cell and the allocation of radio resources between layers By using the method, multiple layers of soft cells can be realized, and each layer of soft cells seamlessly covers the entire area. A limit case is that the control center 2-1 controls the coverage of each antenna unit to be a soft cell coverage, and the single antenna soft cell network formed at this time degenerates into a traditional cellular network; the difference is that the control center manages many soft A cell, unlike a base station in a traditional cellular network, controls a cell. The flexibility of the soft cell comes from the flexibility of its implementation method. The soft cell is realized by synthesizing the effective coverage of one or several antenna elements, and the synthesis is controlled by the control center 2-1 to control the allocation and use of the radio resources. of. It is required that, in the case where the antenna is not redundant, each antenna unit must be in a soft cell of a different layer at the same time to achieve seamless coverage of soft cells of each layer.

The shape of each layer of the soft cell, that is, how to select a plurality of antennas distributed in the region to implement the soft cell, such as selecting a square cell array, a circular array, or a rectangular array of antenna cells can form a soft cell of a corresponding shape. The design of the soft cell shape is related to the speed of the user groups supported by the soft cells of each layer in all directions, because the selection of the soft cell radius includes the moving direction information of the user terminal. Generally speaking, for the convenience of implementation, it can be uniformly designed with circular coverage, hexagonal coverage or square coverage; but for some special occasions, it can be treated differently in order to effectively utilize resources, such as street and highway coverage. It can be designed with ellipse or rectangle, so it needs to be considered comprehensively when planning the soft cell plane. The statistical characteristics of the population group to form soft cells of appropriate size and shape.

Note that users with the same speed characteristics may have different speeds in different directions in different regions, such as: For in-vehicle terminal users, the speed in all directions can be high in a wide area; but on the highway along the high speed The speed in the highway direction is very high, and the speed in the direction perpendicular to the highway is very low, so the soft cell layer adapted to serve the in-vehicle terminal can have different shapes in the soft area in the wide area and the soft cell in the highway. of.

A single layer of soft cells in a layered soft cell wireless network is equivalent to a traditional cellular communication network. Therefore, the wireless resource allocation mode in the soft cell plane layer can adopt a traditional multiple access technology, and the difference lies in the wireless resources allocated to the soft cell at this time. It is used simultaneously by one or several antenna elements to form soft cell coverage.

This example describes the use of FDMA multiple access mode in the layer, combined with the idea of resource reuse, to further allocate the frequency resources allocated to each layer of soft cells. Assume that the frequency reuse factor of the first layer soft cell is Ν _λ , the frequency reuse factor of the second layer soft cell is ₂ , and the frequency reuse factor of the third layer soft cell is N ₃ . N, N ₂ , and N ₃ can be determined according to the required carrier-to-interference ratio of the system. The analysis method is the same as that in the traditional cellular network. The difference is that multiple antennas exist in the same frequency soft cell at the same time. Radio resources work, which is different from the case where the same frequency cell in the traditional cellular network is only a single antenna.

As shown in FIG. 4, the spectrum resource 4-1 belonging to the first layer soft cell is divided into a series of channel units 4-5 according to the channel unit width required by the system. For convenience of presentation, it is assumed that the number of radio resources in the soft cells in a soft cell cluster is the same, that is, it is assumed that the total number of channels divided is one channel unit in each soft cell. According to the frequency reuse factor 该 of the layer soft cell, all channel elements 4-5 are divided into groups 4-4:, ₂ , ..., f- _N , and each group/ _w contains the entire channel unit group. L-5 channel units of 4-5; generally, the division of the group should comply with the principle that the adjacent channel is not arranged in the same soft cell, and at the same time not arranged in the adjacent soft cell, Figure 4 illustrates this principle. The channel unit group / _{w of the} first soft cell in one soft cell cluster of the first layer soft cell includes ΤΜ-Ρ / _W - ₂ , ..., channel 4-6, the channel unit group of the second soft cell in the cluster ₂ includes ₂ _,, ₂ _ ₂ , ..., J - _{2 →} channel 4-7, ..., the channel unit group of the Mth soft cell in the cluster / ^ includes ^, /^_ ₂ , ..., f _w Channel 4-8, , represents the carrier frequency of the jth channel in the i-th soft cell in a soft cell cluster of the first layer soft cell. After the frequency planning is completed, the first layer of soft cells are divided into soft cell clusters, and then, according to a regular manner, assigning, ₂ , ..., to the corresponding soft cells in each cluster completes the radio resources of the first layer of soft cells. distribution. Similarly, the spectrum resources 4-2 and 4-3 of the second and third layer soft cells are allocated according to the same principle.

In this way, a layered soft cell wireless network with three layers of soft cells is formed, and the three layers of soft cells are geographically overlapped, respectively adapted to user groups having different speed characteristics, and the wireless resources used by each layer of soft cells are Orthogonal, the layers do not interfere with each other. According to the above description, a layered soft cell wireless network having a K-layer soft cell can be conveniently constructed.

Example 2: The stratification of the soft cell plane is performed by using the time division method, and the FDMA/TDMA combined multiple access method is used for the radio resource allocation in the same layer of the soft cell.

According to the speed division similar to the first example, the user groups are divided into three categories. Correspondingly, a user group of three layers of soft cells serving the corresponding speed features needs to be constructed on the signal coverage plane. The soft cell construction method of the layered soft cell wireless network is the same, that is, the control center 2-1 controls one or several adjacent antenna units to transmit the composite soft cell coverage with the same radio resource. The difference between this example and the first example is that the radio resources used by the antennas in the soft cell are different. In the first example, the intra-layer resource allocation mode adopts FDMA, and the synthesis of adjacent antenna units working in the same channel constitutes a soft cell; The resource allocation method used in the middle layer is FDMA/TDMA, that is, one or several adjacent antenna units use the same channel and transmit signals in the same time slot, and the synthesized signal covers the coverage of the soft cell.

As shown in Figure 5, the layering of this example is implemented in a time division manner. The time slot segment TS1 indicated by 5-1 is allocated to the first layer soft cell, the time slot segment TS2 indicated by 5-2 is allocated to the second layer soft cell, and the time slot segment TS3 indicated by 5-3 is allocated to the third layer. The layer soft cell, the control center 2-1 controls the distributed antenna group 2-3 to transmit signals in the corresponding time slot segments, and the signals transmitted by different time slot segments serve the mobile terminals accessing the soft cells of different layers. The duplex mode can use TDD, FDD or FDD/TDD. When using TDD, each time slot segment needs to be further divided into two parts: uplink and downlink. If FDD is used, corresponding time slot division needs to be performed in the corresponding uplink frequency band. Only the downlink is considered here, and Figure 5 is only illustrative. The radio resource allocation of the downlink is similar for the uplink and will not be described here. The resource allocation mode in the layer adopts the FDMA/TDMA combination mode, and the frequency band allocation is first performed. Similar to the first example, the frequency reuse factor of each layer of the soft cell is determined according to the carrier-to-interference ratio requirements of the soft cells of each layer of the system. The time is divided into layers, so each layer of soft cells can use the entire spectrum resources of the system. For the first layer soft cell, the total spectrum resource is divided into a series of channel units 5-4 according to the bandwidth of the channel unit required by the system. For convenience of presentation, it is assumed that M soft cells in a soft cell cluster The number of internal radio resources is the same, that is, the total number of channels divided is ^><. Frequency reuse factor in the first layer of soft cells

, divide all channel units 5-4 into groups 5-5: /Μ, ₂ , ..., each group; _,. contains all channels of channel group 5-4; generally when grouping The principle that adjacent frequency channels are not arranged in the same soft cell and not arranged in adjacent soft cells should be observed. Figure 5 also illustrates this principle. A soft cell soft cell cluster in a first layer of a first group of soft channel cell / _w include _{_{_{1 →, / w _ 2,}}} ..., channels 5-6. The channel group / w of the second soft cell in the cluster includes / ^, ₂ _ ₂ , ..., H channel 5-7, ..., the channel group of the ^th soft cell in the cluster / ^ includes ₂ , ..., ^ channel 5 -8, , represents the carrier frequency of the jth channel in the i-th soft cell in a soft cell cluster of the first layer soft cell. The first layer of soft cells is divided into soft cell clusters, and then / _w , /;_ ₂ , ..., /^ are allocated to the corresponding soft cells in each cluster in a regular manner.

According to the principle of TDMA, further thinning of the time slot is performed for each channel. As shown in FIG. 5, based on the time slot segment TS1 allocated to the first layer soft cell, the time slot units TS1-1 and TS1 are further divided. -2, ..., TS1-M, so the smallest available channel unit is a certain time slot of a certain channel.

Assuming that a soft cell using a channel group in the first layer of the soft cell, the downlink transmission when serving a certain mobile terminal can be transmitted and transmitted in the time slot corresponding to TS1-j on the _w channel. It is performed simultaneously on the several antenna elements forming the soft cell. Since these antennas are controlled by the same control center, synchronization between the antenna transmission signals is very easy. The radio resource allocation and working mode of other layer soft cells are similar, not shown in FIG. 5, and will not be described here.

In the above examples, the effects of the wireless channel environment on the use of radio resources are not considered. In practice, it is necessary to introduce corresponding processing techniques to resist the influence of wireless fading time-varying channels, but the basic method of layered soft-cell wireless network construction has been described in the above examples.

Referring to FIG. 6, the access control procedure for the layered soft cell wireless network is further described in detail: In the initial network planning and design phase, detailed statistical analysis of the speed scene of the service requirement must be performed to determine the division mode of the terminal speed feature, and design The number of layers of the soft cell plane and the size, shape, and transmission technology of the corresponding soft cell, when the fixed radio resource allocation is used, the radio resource allocation needs to be completed; Step S6-1, one of the service demand planes has a service requirement ;

In step S6-2, the control center 2-1 performs speed estimation on the terminal, which may be measured by the network side control center 2-1, or may be reported to the control center 2-1 after the terminal itself performs speed estimation; Step S6- 3. Projecting the terminal service requirement to the corresponding soft cell layer according to the mapping relationship between the terminal moving speed and the soft cell layer.

Step S6-4: Determine, according to the location of the terminal, a soft cell that is specifically accessed in the corresponding soft cell layer. For example, in the layered soft cell wireless network in the first embodiment, if the service speed of the terminal A is 90 km/ h, then the control center 2-1 according to the corresponding relationship between the three-layer soft cell and the terminal moving speed: the first layer soft cell is used for the user group whose mobile terminal speed is 0~50km/h, and the second layer soft cell is used for The user group whose mobile terminal moves at a speed of 50~100km/h, and the third layer soft cell are used for the user group whose service terminal moves at a speed of 100~150km/h, then the terminal A is mapped to the second layer soft cell, because each layer The soft cell is seamlessly covered in the area, so the terminal A is necessarily in the coverage of a soft cell of the second layer soft cell, and the soft cell is the access soft cell of the terminal A;

Step S6-5, the control center 2-1 allocates a certain channel resource in the access soft cell to the terminal A, and controls multiple antennas of the soft cell to use the channel to provide service for the terminal A;

It should be noted that, in the process in which the terminal A communicates with multiple antennas in the corresponding soft cell, all the antennas of the corresponding soft cell do not need to be in the active state at the same time, and the control center 2-1 can reduce the interference according to the geographical location of the terminal. In principle, some antennas are selectively controlled to serve Terminal A, and the selected antennas have the same communication resources used for terminal services.

According to the concept of the layered soft cell wireless network and the access control method described above, the system capacity, The load-to-interference ratio, blocking rate, switching probability and call drop rate are simulated and analyzed, and compared with the corresponding performance of traditional cellular networks. It can be seen from the comparison that the layered soft cell wireless network achieves better performance than the traditional cellular network in the above five aspects.

The layered soft cell wireless network in the simulation uses frequency division layering, and the FDMA/TDMA multiple access mode is used in the layer.

(1) Capacity analysis

The simulation parameters used are as follows: the required coverage area is 20km ² , the coverage radius of a single antenna is 25m, and the circular coverage is, the coverage area of each antenna is A=1963.5m ² , assuming the coverage between individual antennas. If there is no overlap, it is required to arrange 20/0.0019635 «10186 antenna elements in the coverage area. The available bandwidth of the entire system is 5 MHz, the bandwidth of each channel is 200 KHz, and each channel includes 8 time slots. The multiplexing factor of each layer of soft cells in the layered soft cell network is 9 and is the number of layers.

Assuming that the ratio of the interlayer area in the wireless network of the layered soft cell, that is, the increase ratio of the upper layer of the adjacent soft cell layer to the lower layer is 2, the softness of each layer of the soft cell of the layered soft cell wireless network The coverage area of the cell is A, 2A, 4A, 8A, ..., 2 ^K A, and A is the coverage area of one antenna unit. Under a uniform and fixed channel allocation scheme, according to: c layered soft cell ⁼ 3⁄4ϋ

The total number of available channels in the total required coverage area is obtained.

Among them, the total required coverage area is 20km ^{2 in the} simulation _;

W. For the allocated bandwidth of the first layer soft cell, a fixed uniform allocation is adopted, that is, the available bandwidth in each layer is equal, and the total bandwidth is 5 MHz, and the available bandwidth of each layer of the soft cell is (5/iQMHz _;

β : is the bandwidth of one channel, set to 200 ΚΗζ.

N _r : the number of time slots for each channel, set to 8;

N . is the frequency reuse factor of the first layer soft cell. This analysis mainly reflects the capacity advantage of the layered soft cell wireless network. For the convenience of analysis, the multiplexing factor of the K-layer soft cell uniformly adopts the multiplexing factor under the single-antenna soft cell structure, which is the same as the traditional cellular network. Quality requirements required The reuse factor is the same. When the same multiplexing factor is used for the layered soft cells, the same-frequency interference will only be reduced, that is, the quality of service will be improved without being reduced. This can be seen from Figure 8, so the capacity comparison result here is conservative. , believable.

4: Soft cell area in the first soft cell in the layered soft cell wireless network.

The traditional cellular network adopts a single-layer cell configuration, which corresponds to the size of the soft cell in the layered soft-cell wireless network. The traditional cellular network analyzes the capacity of K different cell sizes, which are A, 2A, 4A, 8A, ··· , 2 ^ΚΛ Α, according to

r ₌ S WN± Obtain the number of available channels in the total coverage area of the traditional cellular network at the corresponding cell size.

Where the total requirements cover the area;

W : allocate bandwidth for the total;

B : The bandwidth of a channel.

Ν _τ : the number of time slots for each channel;

N: The multiplexing factor under the single-antenna cell structure is adopted, which is the multiplexing factor required by the traditional cellular network to achieve the signal quality requirement.

4: Area of the cell in a traditional cellular network.

Figure 7 depicts the capacity comparison of two network systems, the abscissa K represents the number of layers of the layered soft cell wireless network, 4 represents the area of the cell in the traditional cellular network; the ordinate is the available channel within the total coverage area of 20 km ² number. 7-1 shows the capacity change of the layered soft cell wireless network as the number of layers increases; 7-2 represents the capacity change of the traditional cellular network as the cell area increases.

Because the traditional cellular network is not suitable for medium and high speed mobile users, the cell area is too small, generally above 4A. Table 2 is the capacity improvement efficiency of the layered soft cell wireless network relative to the traditional cellular network, from Figure 7 and Table 2. It can be seen that the layered soft cell wireless network has a large capacity potential compared to the traditional cellular network. A 2A 2 ² A 2 ³ A 2 ⁴ A 2 ⁵ A 2 ⁶ A 2 ⁷ A 2 ⁸ A 2 ^y A

226354 113177 56588 28294 14147 7074 3537 1768 884 442

K

1 226354 0.00 1.00 3.00 7.00 15.00 31.00 63.00 127.00 255.00 511.00

2 169765 -0.25 : 0.50 2.00 5.00 11.00 23.00 47.00 95.00 191.00 383.00

3 132040 -0.42 0.17 1.33 3.67 8.33 17.67 36.33 73.67 148.33 297.67

4 106103 -0.53 -0.06 0.88 2.75 6.50 14.00 29.00 59.00 119.00 239.00

5 87712 -0,61 0.55 2.10 5.20 11.40 23.80 48.60 98.20 197.40

o

6 74272 -0.67 -0.34 o 0.31 1.63 4.25 9.50 20.00 41.00 83.00 167.00

7 64167 -0.72 0.43 0.13 1.27 3.54 8.07 17.14 35.29 71.57 144.14

8 56367 -0.75 -0.00 0.99 2.98 6.97 14.94 30.88 62.75 126.50

9 50203 -0.78 -0.56 -0.11 0.77 2.55 6.10 13.19 27.39 55.78 112.56

10 45227 -0,80:: -0:60 -0,20 0.60 2.20 5.39 11.79 24.58 50.15 101.30 Table 2

(2) Carrier to dry ratio analysis

Figure 8 illustrates the comparison of the carrier-to-interference ratio of the soft cells in different layers of the layered soft cell and the carrier-to-interference ratio in the traditional cellular network. The assumption here is that the higher the level, the larger the area of a single soft cell is, and the ratio of the increase is 2, that is, the increase ratio of the upper layer of the adjacent soft cell layer to the lower layer is 2. Because the soft cell formation in the layered soft cell wireless network is formed by multiple antennas together, under the condition that the transmission power of a single antenna unit is constant, the softer cell with larger area must be composed of more antennas, but Under the condition that the multiplexing factor is the same, this means that the distance of the same-frequency interference source increases, resulting in an increase in the carrier-to-interference ratio.

Figure 8 plots the carrier-to-interference ratio performance of different soft cell layers in a layered soft cell wireless network and the carrier-to-interference ratio of a traditional cellular network. 8-2, ..., 8-8 respectively represent the carrier-to-interference ratio performance of the first to eighth-layer soft cells in the layered soft cell wireless network; 8-9 represents the carrier-to-interference ratio performance of the conventional cellular network.

It can be seen from FIG. 8 that the higher the number of layers, the softer cell layer synthesized by the more antennas has better carrier-to-interference ratio performance when the multiplexing factor is the same, and the single antenna soft cell layer represented by K=l is equivalent. Single antenna base station cells in traditional cellular networks, so their carrier to interference ratios are equal.

It can be seen from Fig. 8 that the soft cell formed by multiple antennas obtains better carrier-to-interference ratio performance than the traditional cellular network under the same multiplexing factor, which means that the soft cell area is required under the same carrier-to-interference ratio performance requirement. The multiplexing factor of the large soft cell layer can be reduced, thereby increasing the capacity of the system. (3) Blockage rate analysis

Figure 9 illustrates a comparison of blocking rates between a layered soft cell wireless network and a conventional cellular network. The parameters used in the analysis are: The total required coverage area is 20km ² , the total available bandwidth is 5MHz, the bandwidth of each channel is 200KHz, and each channel includes 8 time slots. The multiplexing factor of each layer of soft cells is unified to 9. The coverage radius of a single antenna is 25m, which is set to a circular coverage. The coverage area of a single antenna is 1963.5m ² , and 10186 antenna elements need to be placed in the entire coverage area. Assuming that the distribution of user groups for various speed characteristics is uniform, the total traffic load per unit area is

Then the traffic load in each antenna unit coverage is 1.9365Erl, where Erl represents the Irish unit in the traffic theory.

In a layered soft cell radio network, assuming that the service payloads of the user groups with different speed characteristics adapted by each layer of soft cells are equal, the traffic load per unit area in the first layer of soft cells is λ = (λ/Κ). Erl/km ² , so the average blocking probability of a layered soft cell is:

The traditional cellular system adopts a single-layer fixed-cell structure, and the blocking probability is:

W · Ν where represents the Irish B formula. The corresponding symbol definition above is the same as defined in the capacity analysis.

Figure 9 plots the blocking ratios of the two networks. The abscissa K represents the number of layers of the layered soft cell wireless network, and 4 represents the cell area in the traditional cellular network. 9-1 indicates the trend of the blocking rate of the wireless network of the layered soft cell with the increase of the number of layers; 9-2 indicates the trend of the blocking rate of the traditional cellular network as the area of the cell increases.

It can be seen from Fig. 9 that the layered soft cell wireless network achieves better performance by simultaneously forming a soft cell layer adapted to a user group having different speed characteristics, compared to a conventional cellular network having a fixed cell size.

(4) Switching probability analysis

Figure 10 is a diagram showing the comparison of the switching performance between the layered soft cell wireless network and the traditional cellular network. The simulation parameters used are as follows: The cell of the traditional cellular network is circular, and the radius is fixed to 100 meters; The cell radio network arranges soft cells of different sizes for each user group of different speed characteristics, and the soft cells are assumed to be circular. In the simulation, the uniform speed division is used, and 0~50km/h is divided into 10 types of user groups, which are 0~5, 5~10, ..., 45~50km/h, respectively, which are judged to be suitable for different speed characteristic user groups. based soft cell radius is _{r ,. = [(1.7v ,. max} + v imin) /2.7] .t, characterized the terminal is required from the soft edge to the cell center 'time, with respect to the conventional cellular mobile network highest The user terminal with a speed of 50km/h takes about 7.2 seconds from the cell center to the cell edge, and the time is set to ^10 seconds for the layered soft cell wireless network, thereby determining the soft cell adapted to the different speed feature user groups. The soft cell radius within the layer. For each user group of speed characteristics, a large number of users are generated in the simulation, and each of the generated users is examined for 5 seconds under two networks to see whether or not to switch, thereby determining the switching probability.

Figure 10 depicts the comparison of handover probabilities in two networks, 10-1 represents the handover probability in different speed scenarios in a layered soft cell wireless network, and 10-2 represents the handover probability in different speed scenarios in a traditional cellular network. .

It can be seen from FIG. 10 that in a conventional cellular network, a fixed-size cell is used for a low-speed mobile terminal, but as the mobile terminal moves faster, the handover load exhibits a rapid growth trend; In the case of a wireless network, services of different speed characteristics are served by soft cell layer services adapted to different sizes thereof, so that the switching load of the entire network is always maintained within an acceptable level.

(5) Call drop rate analysis

Figure 11 shows a comparison of simulation results of a layered soft cell wireless network and a traditional cellular network drop rate. Assume that the user arrives at the Poisson distribution and randomly enters the respective networks according to the arrival rates (1⁄2 and ) of the two networks. After the user generates it, first assign it a random number uniformly distributed in the interval ^ , ^,.] ( = U, ..., 9, 10 ) as its rate, V _Li = (j - Y) X5bn/h, V _Hi = i 5bn/h, and generates a random number uniformly distributed in the interval [0, 2τ] as the moving direction of the mobile terminal. Then, a random number obeying the exponential distribution of the parameter // is generated as its talk time. In the simulation, it is assumed that the wireless resources of the network are sufficient, and the shadow fading model is used to calculate the received signal power of the mobile terminal.

For a traditional cellular network, each user communicates with only one base station. When the received power P _r {d)<P _r -thr shold is detected, the handover is performed, and if the handover process cannot be found, i - t / o base station, then the user is considered to be dropped; for the layered soft cell wireless network, each time the three antennas in the selected cell are served as one user, the received signal power from the three antennas is non-coherently combined, if When the combined received power _f < —^^1⁄2w, the antenna is switched. If the switching process is not found, _f ≥ P _f —

When the antenna is used, the user is considered to be dropped. At the end of the simulation, according to = ^N _N ^d ° ^p - ^h . " ^d ° ^ff gets the system call drop rate, where N _ _A. „ The number of users who have dropped calls, N _toto , is the total number of users in the system.

Figure 11 depicts the comparison of dropped calls in two networks. 11-1 shows the dropped call rate in different speed scenarios in a layered soft cell wireless network. 11-2 indicates the different speed scenarios in a traditional cellular network. Call drop rate. Table 3 shows the simulation parameters of the layered soft cell wireless network and the traditional cellular network dropped call rate;

table 3 As can be seen from the above description, the layered soft cell wireless network of the present invention is developed from the cellular networking theory, but it is different from the traditional cellular network. Cell coverage in traditional cellular networks is determined by single-antenna signal coverage. Single-antenna signal coverage is tightly coupled to cell coverage. For layered soft-cell wireless networks, single-antenna signal coverage is only a signal basis. The soft cell coverage is determined by the speed characteristics of the user terminal, and is formed by using one or more antennas to simultaneously use the same radio resource operation according to the allocation and use mode of the radio resources. The layered soft cell wireless network removes the tight coupling relationship between single antenna signal coverage and soft cell coverage, thereby enabling more efficient and flexible use of radio resources, improving the overall performance of the network, and forming softness according to the speed characteristics of the user terminal. The community is better adapted to the needs of the business.

The coverage of the soft cell is synthesized by the respective effective signal coverage of one or more adjacent antenna elements, and the total coverage of the signal transmitted by the antenna unit in one soft cell to the mobile user determines the soft cell coverage, and thus the user's movement It will be within the coverage of different antennas, but since each antenna uses the same radio resources, the small-range movement of the user terminal makes it within different antenna coverage, but this does not cause the radio resources used by the terminal. The traditional cellular network uses a single antenna cell. The signal coverage of a single antenna determines the cell coverage of the cellular network. When the mobile terminal is in different antenna coverage, the wireless resource must be switched. Compared with the single-antenna structure cell in the traditional cellular network, the layered soft cell wireless network has the advantages of flat signal power plane, low interference, and stable and controllable handover load.

In addition, the hierarchical structure of the layered soft cell wireless network is also different from the hierarchical structure in the traditional cellular network. Traditional cellular networks are tightly coupled with single-antenna signal coverage and cell coverage. To achieve different sizes of cells adapted to different service scenarios, different antennas must be used, so in traditional cellular networks, despite macro cells and The geographical coverage of the micro-cells is overlapping, but their coverage is achieved by the respective base station antennas, which leads to an increase in system hardware complexity and software complexity. For example, the information exchange between the macro cell base station and the micro cell base station is performed when the inter-layer handover is performed, and in the layered soft cell radio network, the inter-layer handover only needs to be processed in a centralized manner through the control center 2-1, which is convenient to implement. . Considering the current state of the art and the technological development in the next few years, the design of the layered soft cell wireless network adopts a fixed planning mode, that is, a single soft cell is geographically fixed, and the soft cells in each layer of the soft cell do not follow the user terminal location. The change dynamically changes. According to the pre-planning, when the terminal moves between different soft cells, a corresponding handover operation is required. Since the size of the soft cell is adapted to the speed characteristics of the mobile terminal at this time, the overhead of the handover can be controlled within a range that the system can withstand, which is achieved while using the layered soft cell network to obtain good performance. System achievability and processing complexity are low.

Claims

Rights request

A layered soft cell wireless network, characterized in that:

Signal coverage plane (1-1), soft cell plane (1-2), and service requirement plane (1-3);

The service requirement plane (1-3) refers to a service requirement in various speed scenarios distributed geographically; the signal coverage plane (1-1) refers to a distributed antenna group (2-3) Seamless signal coverage formed by transmitting and receiving wireless signals;

The users in the service demand plane (1-3) are divided into K user groups with different speed characteristics according to the terminal moving speed, where K^l;

Corresponding to the above K types of user groups having different speed characteristics, forming a soft cell plane (1-2) including a K layer soft cell;

The control center (2-1) and the distributed antenna group (2-3) transmit signals via the transmission medium (2-2).

2. The layered soft cell wireless network of claim 1 wherein:

The soft cell plane (1-2) is established on the basis of the signal coverage plane (1-1), and the control center (2-1) allocates radio resources to the soft cells of each layer according to the orthogonal allocation principle, thereby forming an area. Overlapping K-layer soft cells that do not interfere with each other.

3. The layered soft cell wireless network of claim 1 wherein:

Each of the soft cells in the K-layer soft cell is composed of n soft cells, where η 1 .

4. The layered soft cell wireless network of claim 1 wherein:

When K user groups with different speed characteristics are divided according to the terminal moving speed, they can be divided.

5. The layered soft cell wireless network according to claim 1, wherein - when K user groups having different speed characteristics are divided according to the terminal moving speed, non-uniform partitioning can be performed.

6. The layered soft cell wireless network of claim 1 wherein:

Traffic of the K user groups having different speed characteristics is projected to a suitable soft cell layer and served by a corresponding soft cell in the layer soft cell.

The layered soft cell wireless network according to claim 1, 4, 5 or 6, wherein: the user group of the different speed characteristics refers to a group of users whose terminal moving speed is in different speed ranges.

8. The layered soft cell wireless network of claim 6 wherein:

A soft cell layer composed of a large area soft cell serves a user group with a higher terminal moving speed.

9. The layered soft cell radio network according to claim 6, wherein the soft cell layer formed by the smaller area soft cell serves the user group whose terminal mobile speed is lower.

10. The layered soft cell wireless network of claim 1 wherein:

The control center (2-1) performs signal processing and control functions required for communication, and manages and uniformly schedules radio resources used by the distributed antenna group (2-3) under its jurisdiction.

11. The layered soft cell wireless network according to claim 1, wherein: the control center (2-1) of the layered soft cell wireless network can manage the distributed antenna group by using a centralized control mode (2) 3).

12. The layered soft cell wireless network of claim 1 wherein:

The control center (2-1) of the layered soft cell wireless network can manage the distributed antenna group (2-3) in a distributed control manner.

13. The layered soft cell wireless network of claim 1 wherein:

The control center (2-1) of the layered soft cell wireless network can manage the distributed antenna group (2-3) in a hierarchical control manner.

14. The layered soft cell wireless network of claim 1 wherein:

The transmission medium (2-2) may be a medium such as a wireless fiber, a millimeter wave, a free-space optical link, or a mixed medium in which the above various media are mixed.

15. The layered soft cell wireless network of claim 2, wherein - The allocation method of the radio resource allocation has a fixed allocation, a dynamic allocation, and a hybrid allocation manner.

The layered soft cell radio network according to claim 15, wherein: the fixed allocation mode refers to allocating all available radio resources to each layer of soft cells and each layer of soft cells in a pre-planning manner. Each soft cell.

The hierarchical soft cell radio network according to claim 15, wherein: the fixed allocation mode comprises two parts of allocation between soft cells of each layer and allocation in each layer of soft cells, first according to an orthogonal allocation principle. All the radio resources are divided into K parts, correspondingly allocated to the K layer soft cells, and then the allocation in each layer of the soft cells is according to the resource allocation method of the traditional cellular network, and the available resources of the layer soft cells are allocated to the Each soft cell in a layer soft cell.

The hierarchical soft cell radio network according to claim 15, wherein: the fixed allocation mode is that the available spectrum resources are divided into non-overlapping K parts, and correspondingly allocated to the K layer soft cells, and completed. The frequency division is layered, and then the spectrum resources allocated to each soft cell layer are further allocated to the respective soft cells in the layer according to the frequency division multiple access principle.

The hierarchical soft cell radio network according to claim 15, wherein: the fixed allocation mode is to divide a time slice into non-overlapping K segments, and each time period corresponds to the K layer soft cell. The working time of a certain layer is completed, and the time division is completed. Then, according to the principle of frequency division/time division combined multiple access mode, the available spectrum resources and time of each soft cell layer are further allocated to each soft cell in the layer.

20. The layered soft cell radio network according to claim 15, wherein: the dynamic allocation mode refers to uniformly managing all available radio resources in a control center (2-1), in each layer of soft cells. Dynamic, on-demand wireless resource allocation.

The hierarchical soft cell radio network according to claim 15, wherein: the hybrid allocation mode refers to firstly allocating a part of radio resources to each soft cell to adapt to basic service requirements while retaining A part of the radio resources are used in the control center (2-1) for the bursting of the service requirements. This part of the reserved resources is dynamically allocated and flexibly scheduled between the soft cells of each layer.

22. The layered soft cell wireless network of claim 2, wherein: The orthogonal allocation includes: frequency division multiple access, time division multiple access, code division multiple access, orthogonal frequency division multiple access, and a combination of the above manners.

23. The layered soft cell wireless network of claim 3, wherein:

The soft cell refers to a coverage area formed by one or more geographically adjacent antenna elements transmitting using the same radio resource.

24. The layered soft cell wireless network of claim 23, wherein: the radius of the soft cell coverage area and the shape of the coverage area are determined according to a speed characteristic of the mobile terminal.

The layered soft cell radio network according to claim 24, wherein: the radius of the soft cell coverage area is determined according to a speed characteristic of the mobile terminal supported by the soft cell.

26. The layered soft cell wireless network according to claim 24, wherein: the shape of the soft cell coverage area is determined by a moving speed of the mobile terminal in each direction.

27. The access control method for a layered soft cell wireless network according to claim 1, wherein:

When a certain user terminal in the service requirement plane has a service demand, the control center (2-1) first obtains an estimated moving speed of the terminal, and then according to the mapping relationship between the terminal moving speed estimation value and the soft cell layer, The terminal service requirement is projected to the corresponding soft cell layer, and then the soft cell specifically connected in the corresponding soft cell layer is determined according to the terminal location, and finally the control center (2-1) accesses a certain channel resource in the soft cell. And allocating to the user terminal, while controlling multiple antennas of the soft cell to provide services for the terminal by using the channel.

28. The access control method according to claim 27, wherein:

The estimated speed of movement of the terminal can be estimated by the control center (2-1), or can be measured by the terminal itself.

The access control method according to claim 27, wherein: in the process of communicating between the plurality of antennas in the soft cell and the user terminal, the corresponding soft cell All antennas need not be active simultaneously, a control center ^(2-1) may be reduced in accordance with the principles of interference, antenna selectively controlling certain soft cell for the user terminal according to the service location terminal is located.