CN102413093A - A method for estimating OFDM network capacity - Google Patents

Abstract

The invention discloses an OFDM network capacity estimation method, which comprises the following steps: step 101, selecting a specific network scheme and related parameters; step 102. define SINR transform to SINR_trans(ii) a 103, obtaining a channel activity linear function a through the slope D and the intercept coefficient G_i(ii) a 104, from the channel activity linear function a_iCalculating the channel activity a of a single user; step 105, determining the total up/down channel activity; step 106, checking whether the total up/down channel activity is less than 1; step 107, if the total up/down channel activity is greater than 1, the network capacity is overloaded, the relevant parameters are removed, and then the step 101 is re-entered; step 108, if the total up/down channel activity is less than 1, the network capacity can be used for service, the relevant parameters are saved, and then step 101 is re-entered.

Description

A sort of OFDM Network Capacity Estimation Method

technical field

The invention relates to the technical field of data communication, in particular to a capacity calculation method for a wireless network using adaptive modulation and coding and orthogonal frequency division multiplexing technology, in particular to an OFDM network capacity estimation method.

Background technique

In order to estimate the existing network or plan the network structure of the wireless network, it is necessary to determine the capacity and coverage of the entire network or a part of the network and the expected load of the network. Such a calculation is highly desirable for setting antenna parameters, modifying and matching network elements, and building a completely new wireless network. Capacity describes the potential data throughput in a communication network and the number of users that can be served by that network. Typically, a wireless communication network consists of a number of base stations or antenna stations, each covering a fixed area. When wireless network users are located in these coverage areas, they will be connected to the network through at least one serving antenna. Therefore, the station's location and antenna parameter settings have a great influence on the capacity of the network and the efficiency of the entire network. In order to optimize these network parameters, various issues such as the number and location of users, type of service provided, user requirements, interference and noise between network devices and many more issues have to be considered.

For data transmission, the signal of the wireless link is modulated onto a carrier signal. This can be done by changing the phase, frequency or amplitude of the carrier. For example, digital modulation techniques include phase shift keying (PSK), frequency shift keying (FSK), and amplitude keying (ASK). In phase shift keying, the transmitted signal is modulated by changing the phase of the reference signal. Each of the defined number of phases corresponds to a unique bit pattern, forming a symbol that defines the bits that a digital signal is allowed to transmit. The demodulator at the receiving end can extract the original signal through phase detection or phase transformation. There are also many phases available for phase modulation, such as binary phase shift keying with two phases and quadrature phase shift keying with four phases. In a similar way, FSK data transmission is achieved by changing the output frequency of the carrier signal, eg, between two BFSK or more discrete frequencies. Amplitude keying keeps the frequency and phase unchanged and changes the amplitude to transmit signals, for example, using two different levels of amplitude to represent binary 0 and 1. More well-known modulation methods such as Quadrature Amplitude Modulation (QAM) employ two carrier waves with different phases for amplitude modulation. The term "quadrature" means that these carriers are switched at 90° phase. Further techniques and combinations can be envisioned. In addition, various coding techniques make the signal more suitable for transmission, which will include improving the quality and accuracy of transmission, modifying the frequency spectrum of the signal, increasing the amount of information, providing error detection and correction, and data security. Many coding schemes are relatively mature and widely used in technologies such as forward error correction.

Each modulation and coding method has its own advantages such as bandwidth realization, as well as fault tolerance and interference immunity. Modulation and coding schemes therefore have a significant impact on the data transmission rate of a wireless communication network. Adaptive modulation and coding (AMC, also called link adaptation) takes full advantage of this technical feature. Through the AMC, the modulation and coding scheme of the subsequent data transmission in the communication link is determined according to the currently obtained signal quality and the current channel condition. This can be obtained by feeding back to the transmitter the transmitted signal quality, or by assuming that the received signal approximates the transmitted signal. Some encoding schemes support high transmission rates or data throughput, while others increase noise immunity and reduce bit error rates at the expense of bit rate. The system can select the appropriate modulation and coding scheme in real time to optimize the signal-to-interference-plus-noise ratio (SINR), the signal quality of the wireless link. When the SINR drops below a predefined threshold, the modulation method should be changed in order to obtain a better SINR. Some other parameters related to the communication link or protocol also change with the modulation and coding scheme.

OFDM, another modulation method for data transmission, is not limited to wireless communication networks. OFDM is a modulation method based on multiple orthogonal subcarriers. Each subcarrier is modulated at a low symbol rate by the modulation method introduced above, such as QAM or PSK. Orthogonality prevents crosstalk between subcarriers even though the frequency bands of the subcarriers are very close together.

The concept of OFDM can also be used in the access scheme, namely OFDMA (Orthogonal Frequency Division Multiple Access). The basic method is to assign different OFDM subcarriers to different users. However, OFDM can also be combined with other access schemes such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Code Division Multiple Access (CDMA).

Typical networks using OFDM/OFDMA include: LTE (Long Term Evolution), which is the mainstream technology for post-3G mobile communications; WiMAX (Worldwide Interconnection for Microwave Access), which aims to provide long-distance wireless data transmission; and Flash-OFDM ( Fast low-latency seamless switching OFDM access), a mobile communication network based on packet data switching. This article does not discuss in detail the basic principles of these communication networks and related technical standards.

The AMC introduced above is suitable for OFDM systems, and each orthogonal subcarrier adopts adaptive modulation and coding, which will further improve the stability of the link. Of course, AMC can also be applied to all or some subcarriers simultaneously.

In an OFDM-based network, the number of users served by one antenna largely depends on the interference of adjacent antennas. When the interference is relatively large, the obtained signal-to-noise ratio is small, so AMC will choose a modulation scheme with low throughput but high noise stability. Conversely, interference from other antennas in the network depends on their location, setup, and loading. The loading of an antenna in turn depends on the number of users served by that antenna and the interference from other antennas. Therefore, the transmission and user capacity of each antenna cannot be considered separately, but a coupling equation should be used to take all antenna and user factors into consideration. The presence of user locations in the corresponding equations complicates the solution of the coupled equations, since the number of users and the number of user locations greatly exceeds the number of possible antenna locations. As an example, consider a network containing 100 to 10,000 antenna locations, while as many as 10 million user locations are considered. This makes the performance estimation of the communication network become a lengthy process of solving numerical equations.

In UMTS (Universal Mobile Telecommunications System) wireless networks, the basic situation is similar. However, we know that the adaptive power control adopted in UMTS network can be linearized. In this way, only the average influence of the user's location is considered, so that the user's location can be removed from the coupled equations, which greatly simplifies the equations. Usually there are only about 100 to 10,000 equations left, which can be easily solved by numerical iterative algorithm, so as to obtain a simple and fast method for UMTS network capacity estimation.

Since the OFDM network does not have an adaptive power control mechanism and all signals use a constant transmission power, the method adopted in the above UMTS system cannot be used in the OFDM network. Therefore, only complex and time-consuming simulation techniques are used to calculate the capacity of OFDM networks.

Contents of the invention

The object of the present invention is to provide a kind of OFDM network capacity estimation method, has adopted following technical scheme to realize:

A kind of OFDM network capacity estimation method is characterized in that, comprises the following steps:

Step 101. Select a specific network solution and related parameters;

Step 102. Define the transform of SINR as SINR _trans ;

Step 103. Obtain the channel activity linear function a _i through the slope D and the intercept coefficient G;

Step 104. Calculate the channel activity a of a single user from the active linear function a _i ;

Step 105. Determine total up/down channel activity;

Step 106. Check whether the total up/down channel activity is less than 1;

Step 107. If the total up/down channel activity is greater than 1, then the network capacity is overloaded, remove relevant parameters, and then re-enter step 101;

Step 108. If the total up/down channel activity is less than 1, then the network capacity can be used for service, save relevant parameters, and then re-enter step 101.

。 Further, in step 102,

.

。 Further, in step 103, the channel activity linear function

.

Further, in step 105, the calculation formulas of the total uplink/downlink channel activity are respectively,

和

and

，其中，

,in,

，

,

，

,

，

,

，

,

，

,

，

,

，own是当前信道容量确定的天线的相关参数，other是无线网络中其他天线的相关因子，

是控制信道的信道活性，

是天线c的接收噪声功率，

是用户i接收设备的噪声功率，

是相对于天线c用户设备i 的下行接收功率，

是上行接收功率。

, own is the relevant parameter of the antenna determined by the current channel capacity, other is the relevant factor of other antennas in the wireless network,

is the channel activity of the control channel,

is the received noise power of antenna c,

is the noise power of user i receiving equipment,

is the downlink received power of user equipment i relative to antenna c,

is the uplink received power.

The above description is only an overview of the technical solutions of the present invention. In order to understand the technical means of the present invention more clearly and implement them according to the contents of the description, the preferred embodiments of the present invention and accompanying drawings are described in detail below. The specific embodiment of the present invention is given in detail by the following examples and accompanying drawings.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the present invention and constitute a part of the application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention. In the attached picture:

Figure 1 shows a schematic diagram of the structure of a standard wireless network of the present invention.

Figure 2 is an example of modulation and coding scheme, SINR and data throughput.

Figure 3 plots channel activity and SINR against the corresponding linear approximation.

Fig. 4 shows the specific steps of the OFDM network capacity estimation method of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

Figure 1 shows a standard structure of a wireless communication network with several antennas c. The locations of the antennas in this example are chosen arbitrarily, and the inventive method optimizes the antenna locations by calculating the antenna locations of the potential diversity and the capacity of the settings. The figure only shows _c1 to _c4 antennas, and the number n of antennas is not limited in the actual application of the invention. The area around each antenna is divided into individual pixels for analysis, with each pixel being an area element. Each pixel may have different parameters such as type of territory (urban, rural, ...). At each pixel, several users u _i (or user terminals) request the services of the wireless network. User u _i may be stationary or mobile within the location. The network will provide one or more services, and each service has different parameter standards, such as bit error rate, traffic requirements, and so on. Services may include data services, voice services, and more. The demand for the number of users and the type of service is derived from the usage of the existing network, or is estimated based on previous usage and average user behavior. The area covered by an antenna c _n is defined as a cell, such as the circle around the antenna in Figure 1 . In this example, only one possible state or snapshot of the network is given, and all potential user locations must be considered in network performance evaluation.

After the above parameters are given, a channel load or channel activity can be determined. Channel activity is defined as the ratio of necessary throughput to available throughput. The channel activity of uplink/downlink is defined separately, or defined for each user individually according to the user's demand for data transmission rate. The uplink refers to from the mobile terminal or user equipment to the antenna, while the downlink is the opposite, from the antenna to the user terminal. The achievable or provable throughput depends on the signal-to-interference-noise ratio, SINR, which in turn depends dynamically on the modulation and coding scheme provided. The larger the SINR value, the higher the current bit transmission rate. In addition, the user's movement speed also has a certain impact on the AMC mechanism. Under the same SINR, the greater the bandwidth, the faster the user's movement speed can be. In addition, SINR is also related to the relative positions of users and antennas or base stations. Users close to the antenna generally obtain higher SINR than users on the border. Figure 2 shows example values of AMC modulation scheme, data throughput and SINR and their interrelationships.

Therefore, according to specific embodiments of the present invention, a mapping relationship between SINR values and channel activity can be defined. The mapping relationship can be obtained from known (or measured) SINR values and data throughput obtained based on different coding and modulation schemes. The present invention introduces a transformation of SINR, which is defined as the (-SINR/10) power of 10 or

（1）

(1)

The unit of SINR is dB.

When mapping SINR _trans to channel activity at a given user rate v, an approximately linear relationship between channel activity and SINR _trans can be derived. Figure 3 shows several data points and the linear relationship between them. From the above mapping relationship, two coefficients D and G related to the user rate can be obtained. These two coefficients define the linear function of the average channel activity a _i of a single user i :

a _i = D _i + G _i ∙ SINR _trans = D _i + G _i /10 ^SINRi/10 (2)

D and G are constants related to the user rate, D defines the y-axis intercept of the linear channel activity function, G gives the slope; a _i is the channel activity of each user, and SINR _i is the signal-to-interference-noise ratio of a single user .

In some embodiments D and G are obtained by linear fitting to the measured values of channel activity and SINR, as shown in FIG. 2 . Figure 3 shows a linear mapping relationship from the channel activity value to the SINR transformation value. The straight line fitted to the data points in Figure 3 shows that this linear approximation does not have much error. In other embodiments, the coefficient of the linear function can also be calculated from the ratio of bit energy to noise density (ie, E _b /N ₀ ) and the transmission activity factor. In many digital communication systems the E _b /N ₀ value is used to specify the minimum power required for channel transmission. The transmission activity factor represents the ratio of the transmission time of the signal in the channel to the specified time interval, so the value is in the range of 0 to 1.

The coefficients D and G (and thus the calculated channel activity) depend not only on the user rate, but also on the type of traffic and whether the user is located indoors or outdoors. The coefficients of the uplink/downlink channels are also different, so an average channel activity a _i ^dl and correlation coefficients ^Ddl and ^Gdl are defined for the downlink channel, and the same is true for the uplink.

For two antennas c and d, the total up/downlink channel activity is determined by the sum of the channel activities of all users served by that antenna. The result is the following equation:

（3）

(3)

（4）

(4)

(单位mW)为在天线c处的干扰功率，其定义为 in,

(unit mW) is the interference power at antenna c, which is defined as

（5）

(5)

是控制信道的信道活性，

是天线c覆盖区内的接收噪声功率。通过解这些线性方程就可以估算出一个网络的容量。通过少量的迭代可快速得到线性方程组的数值解，这里对迭代方法不做详细讨论。 Equations (3) and (4) determine the total downlink channel activity and uplink channel activity of antenna c. The coefficients U and V are discussed and defined in more detail below; in any case own refers to the relevant parameters of the antenna serving the current channel, while other describes the relevant parameters of other antennas in the wireless network.

is the channel activity of the control channel,

is the received noise power in the coverage area of antenna c. The capacity of a network can be estimated by solving these linear equations. Numerical solutions of linear equations can be quickly obtained through a small number of iterations, and the iterative method will not be discussed in detail here.

When the a _c value of the uplink or downlink channel is greater than 1 ( _ac > 1), it means that the corresponding cell c is overloaded, and the antenna will not be able to provide services for all users in the coverage area. Therefore, the _ac values of the uplink and downlink channels must satisfy the condition of being less than 1 at the same time. This helps to plan a high-performance network, provide necessary services for enough users, and meet the user's requirements for quality of service. It is also possible to adjust network parameters to avoid overloading of certain cells.

From equations (3) to (5), it can be seen that in the downlink channel, the influence of other antenna d is included in the total channel activity of antenna c through the coefficients V _d ^other and a _d ; in the uplink channel, this influence is considered in the interference Power I _c inside. In equations (3) and (5), the summation considers all antennas in the network except antenna c.

The parameters used in the equation are defined as follows:

（6）

(6)

（7）

(7)

（8）

(8)

（9）

(9)

（10）

(10)

（11）

(11)

The summation of equations (6) to (11) is done over all user sets Sc served by a given antenna _c . h _i is the noise power of user i's receiving device, P _c ^dl is the downlink received power received by user i from antenna c, and P _c ^ul is the uplink received power in mW.

The above is just one example of these correlation coefficients. In other embodiments, if a directional antenna is used, there will be no interference in areas other than the radiation direction of the antenna, so these coefficients can be set to 0.

The above-described linear approximation of channel activity and the introduction of the SINR transformation value greatly simplify the calculation of channel activity/load of a wireless network. A large number of interdependent, nonlinear complex equations are replaced by only a small number of linear equations. This allows for a simple and fast calculation of coverage and efficiency for a certain network setup.

The above discussion assumes that the antenna positions and some location information of the users are pre-defined. The above method can also be applied to any combination of antennas when there are multiple possible antenna positions to be calculated. By comparing all the calculation results (based on the given demand situation), an optimal solution is obtained.

Fig. 4 shows the specific steps of the OFDM network capacity estimation method of the present invention. Generally speaking, it is necessary to consider various possible wireless network networking schemes, and determine the best scheme according to its quality of service (QoS) and the number of users served. The adjustable parameters of the networking scheme include the antenna position when planning a new network, and other parameters, such as transmission power, services provided, service specifications, carrier frequency, and so on.

A specific network scheme and related parameters are first selected in step 101 . The parameters used for planning and optimization may be the parameters of the existing network, or calculated on the basis of other networks. In step 102, the SINR transform defined in equation (1) above is determined. Through this SINR transformation, a linear approximation of the channel activity is obtained in step 103 by determining the slope and intercept coefficients. As mentioned above, this coefficient can be obtained from a linear fit of the mapping of channel activity to SINR transformed values, and the resulting linear function describes the channel activity. In step 104 the channel activity of an individual user is determined. Considering all antennas in the network and all users served by each antenna in different ways, the total uplink/downlink channel activity is determined through equations (3) and (4) in step 105 . For planning and optimization purposes, it will be checked in step 106 whether the total up/down channel activity is less than one. A value greater than 1 indicates that the cell will be overloaded, and a value less than 1 indicates that all users can be served under given parameter conditions. Therefore, if the selected network scheme shows overload, the relevant parameters will be removed in step 107, and new parameters will be selected to rerun the above calculation method. When the network scenario shows acceptable capacity values, the relevant parameters are stored in step 108 . Afterwards, compare all stored acceptable network solutions in terms of quality, cost, and efficiency, and select the best network solution from them.

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present invention, and its purpose is to enable those of ordinary skill in the art to understand the content of the present invention and implement it accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the essence of the present invention shall fall within the protection scope of the present invention.

Claims (4)

1. An OFDM network capacity estimation method, characterized by comprising the steps of:

step 101, selecting a specific network scheme and related parameters;

step 102. define SINR transform to SINR_trans；

103, obtaining a channel activity linear function a through the slope D and the intercept coefficient G_i；

104, from the channel activity linear function a_iCalculating the channel activity a of a single user;

step 105, determining the total up/down channel activity;

step 106, checking whether the total up/down channel activity is less than 1;

step 107, if the total up/down channel activity is greater than 1, the network capacity is overloaded, the relevant parameters are removed, and then the step 101 is re-entered;

step 108, if the total up/down channel activity is less than 1, the network capacity can be used for service, the relevant parameters are saved, and then step 101 is re-entered.

2. The OFDM network capacity estimation method of claim 1, wherein: in a step 102, the process is executed,。

3. the OFDM network capacity estimation method of claim 1, wherein: in step 103, a channel activity linear function。

4. The OFDM network capacity estimation method of claim 1, wherein: in step 105, the calculation formulas of the total uplink/downlink channel activity are respectively,

and

wherein

，

，

，

，

，

，

own is the relevant parameter of the antenna determined by the current channel capacity, other is the relevant factor of other antennas in the wireless network,is the channel activity of the control channel and,

is the received noise power of the antenna c,

is the noise power of the user i receiving device,is the downlink received power of user equipment i relative to antenna c,

is the uplink received power.

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