CN101835254A

CN101835254A - Orthogonal frequency division multiplexing access system and power control method thereof

Info

Publication number: CN101835254A
Application number: CN200910127006A
Authority: CN
Inventors: 王军虎; 龚园园
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2009-03-10
Filing date: 2009-03-10
Publication date: 2010-09-15
Anticipated expiration: 2029-03-10
Also published as: CN101835254B; WO2010102482A1

Abstract

The invention relates to a power control method of an orthogonal frequency division multiplexing access system, comprising the following steps of: acquiring cell interference parameters, a maximum path loss difference threshold value and a minimum path loss difference threshold value sent by a service base station by a mobile terminal; determining a target signal interference noise ratio value of the mobile terminal according to the acquired cell interference parameters, the maximum path loss difference threshold value, the minimum path loss difference threshold value and base station signal path loss acquired by measurement by the mobile terminal; and selecting a modulation encoding manner by the mobile terminal according to the confirmed target signal interference noise ratio value and regulating the transmitting power thereof so as to carry out signal transmission. By applying the power control method, the problem that the current power control method can not cover all selective modulation encoding manners is solved, the power control efficiency can be improved under the condition of lesser expenses and the performance and the frequency spectrum utilization ratio of the system are further enhanced.

Description

Orthogonal frequency division multiplexing access system and power control method thereof

Technical Field

The present invention relates to the field of communications, and in particular, to an Orthogonal Frequency Division Multiplexing Access (OFDMA) system and a power control method thereof.

Background

In a wireless communication system, power control is an important transmission quality control means, and aims to overcome the problem of communication performance degradation caused by wireless channel fading and interference. With the change of wireless channel fading or shading, the base station or the mobile terminal adjusts the transmission power to compensate the influence of the channel change on the quality of the received signal, so that the power control is also a link adaptation technology. In B3G/4G systems using OFDM (Orthogonal Frequency Division Multiplexing) as a core technology, such as LTE (Long term evolution) and WiMAX (worldwide interoperability for Microwave Access) systems, OFDMA (Orthogonal Frequency Division Multiplexing Access) has been adopted as an important Access method. In the OFDMA technology, the problem of co-channel interference between users in a cell is overcome due to the strict orthogonality between subcarriers. However, in the same-frequency networking mode, i.e. when the frequency reuse factor is 1, the interference between cells is still a factor for suppressing the system capacity. The interference between different cells or sectors is called co-channel interference (co-channel interference). In a cell, when a mobile terminal uses a large transmission power to transmit a signal, it may cause interference effect to neighboring cells, especially generate strong interference to communications of users at the edge of the neighboring cells, resulting in reduced coverage and capacity at the edge of the neighboring cells.

In the prior art, a power control algorithm is also called a differential path loss power compensation algorithm, which measures a pilot power ratio of a Signal of a serving base station and a Signal of an interfering base station to determine a target SINR (Signal to interference and noise ratio) of a user, and then performs power control. As shown in fig. 1, the serving base Station of the Mobile terminal (MS) is BS1, and the interfering (neighbor cell) base Station is BS 2. The differential path loss power compensation algorithm is used for carrying out power control on the basis of the arrival power difference of the service base station and the interference base station.

In the differential path loss power compensation algorithm, a target SINR value is determined according to the difference delta PL between the path loss of the strongest adjacent base station interference signal and the path loss of the service base station signal. When the Δ PL is smaller, that is, the path loss difference between the strongest interference signal and the serving base station is smaller, it indicates that the path losses of the signals from the interfering base station and the serving base station to the mobile terminal are equivalent, and the strength of the uplink signal transmitted by the mobile terminal to the interfering base station and the serving base station is also equivalent, that is, the degree of interference influence generated by the mobile terminal is larger, and at this time, the set target SINR should be smaller, and a low-order modulation coding mode is selected, which is favorable for reducing interference; conversely, the larger Δ PL, the larger the target SINR is set, which is advantageous in improving the system throughput.

In practical application, the target SINR value is compared with the entry threshold values of various modulation coding modes to determine the data sent by the userThe modulation and coding scheme of (1). It should be noted that the value of α (α is the path loss correction factor, and 0 < α < 1) and Δ PL are key factors that affect the target SINR value of each user, and the value of α is determined by the system according to the network interference level and the cell throughput performance, and is fixed in a cell. When α is constant, Δ PL and the target SINR value form a simple linear relationship. The fluctuation of the delta PL influences the selection of the modulation coding mode of the user, and the dynamic range of the delta PL necessarily influences the selection range of the modulation coding mode. The parameter α is a factor for enlarging or reducing the correspondence between the dynamic range of Δ PL and the modulation coding scheme selection range. Therefore, the value of α determines whether Δ PL is reasonably associated with the modulation and coding scheme. Let T be_(dB)(T_(dB)A target SINR value at a cell edge, that is, a target SINR value when Δ PL is 0) corresponds to an entry threshold value of the lowest order modulation coding scheme,

(

a predetermined maximum target SINR value) corresponding to the entry threshold value of the highest order modulation coding scheme, the relationship between the target SINR value and the path loss difference Δ PL is shown in fig. 2 and 3. The slope of line M1 in fig. 2 and 3 is 1-alpha. In fig. 2, the slope of the straight line M1 is small, i.e., α is large, i.e., the degree of path loss compensation is low, so even when Δ PL reaches the maximum, the target SINR does not reach the SINR required by the highest MCS (modulation and coding scheme), and the cell user cannot select the highest-order one-segment modulation and coding scheme. Although M1 in fig. 3 can cover the target SINR values corresponding to all MCSs, the slope is not reasonable. In fig. 3, M1 has a larger slope, that is, α has a smaller value, and the path loss compensation degree is high, and when Δ PL is lower, target SINR values corresponding to all MCSs are traversed, so that the probability of using a higher-order MCS by a cell user is increased, and the level of generating interference is increased. Therefore, it can be seen that when the value of α is not reasonable, the spectrum efficiency of the cell and the degree of interference generated at the edge of the cell are unbalanced, which limits the systemThe potential capacity is exploited, limiting the overall performance of the system.

In summary, how to solve the problem that the spectrum efficiency of a cell and the degree of generated cell edge interference are unbalanced because all selectable modulation and coding schemes cannot be covered due to the limitation of the value of α in the current power control method becomes a problem to be solved urgently.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a power control method and apparatus for an orthogonal frequency division multiplexing access system, which solves the problem that the current power control method cannot cover all selectable modulation and coding modes.

In order to solve the above problems, the present invention provides a power control method of an orthogonal frequency division multiplexing access system, comprising,

the mobile terminal obtains a cell interference parameter, a maximum path loss difference threshold value and a minimum path loss difference threshold value which are sent by a service base station;

the mobile terminal determines a target signal interference noise ratio of the mobile terminal according to the obtained cell interference parameters, the maximum path loss difference threshold value and the minimum path loss difference threshold value and the measured base station signal path loss;

and the mobile terminal selects a modulation coding mode according to the determined target signal interference noise ratio value and adjusts the transmitting power of the modulation coding mode to transmit signals.

The invention also provides an orthogonal frequency division multiplexing access system, which comprises a base station and a mobile terminal,

the base station is a service base station of the mobile terminal and comprises a parameter notification module used for sending a cell interference parameter, a maximum path loss difference threshold value and a minimum path loss difference threshold value to the mobile terminal;

the mobile terminal comprises a computing module and a signal transmitting module, wherein,

the calculation module is configured to receive the cell interference parameter, the maximum path loss difference threshold value, the minimum path loss difference threshold value, and the measured base station signal path loss sent by the base station, determine a target signal interference noise ratio of the mobile terminal, and send the target signal interference noise ratio to the signal transmission module;

and the signal transmitting module is used for selecting a modulation coding mode according to the received target signal interference noise ratio value sent by the calculating module and adjusting the transmitting power to transmit signals.

Compared with the prior art, the invention can solve the problem that the current power control method can not cover all selectable modulation coding modes, can improve the efficiency of power control under the condition of smaller overhead, and further improves the performance and the spectrum utilization rate of the system.

Drawings

Fig. 1 is a diagram illustrating signals and interference received by a mobile terminal in the prior art;

fig. 2 is a diagram 1 illustrating a relationship between a target SINR value and a path loss difference in the prior art;

fig. 3 is a diagram 2 illustrating a relationship between a target SINR value and a path loss difference in the prior art;

FIG. 4 is a flow chart of a prior art differential path loss compensation based power control;

fig. 5 is a flowchart of a power control method of an orthogonal frequency division multiplexing access system of the present invention;

fig. 6 is a schematic diagram of an orthogonal frequency division multiplexing access system of the present invention;

FIG. 7 is a schematic diagram of a simulated cell family;

FIG. 8 is a graph illustrating a comparison of system interference levels under different alpha conditions according to the prior art;

fig. 9 is a schematic illustration of interference levels according to an example of the invention.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

In the current differential path loss power compensation algorithm-based power control method, as shown in fig. 4, the method comprises the following steps,

step 401, the mobile terminal obtains the path loss difference by continuously measuring the serving base station signal and the strongest interference signal and calculating according to formula (1);

<math><mrow><msub><mi>ΔPL</mi><mrow><mo>(</mo><mi>dB</mi><mo>)</mo></mrow></msub><mo>=</mo><msubsup><mi>P</mi><mrow><mo>(</mo><mi>dBm</mi><mo>)</mo></mrow><mrow><mi>rx</mi><mo>,</mo><mi>serving</mi></mrow></msubsup><mo>-</mo><msubsup><mi>P</mi><mrow><mo>(</mo><mi>dBm</mi><mo>)</mo></mrow><mrow><mi>rx</mi><mo>,</mo><mi>strongest</mi><mo>_</mo><mi>neighbor</mi></mrow></msubsup><mo>+</mo><msubsup><mi>P</mi><mrow><mo>(</mo><mi>dBm</mi><mo>)</mo></mrow><mrow><mi>tx</mi><mo>,</mo><mi>strongest</mi><mo>_</mo><mi>neighbor</mi></mrow></msubsup><mo>-</mo><msubsup><mi>P</mi><mrow><mo>(</mo><mi>dBm</mi><mo>)</mo></mrow><mrow><mi>tx</mi><mo>,</mo><mi>serving</mi></mrow></msubsup></mrow></math>

formula (1)

Wherein,

is the received signal power of the serving base station;

the signal power of the strongest interfering base station is received;

the transmit signal power of the interfering base station that is strongest;

is the transmit signal power of the serving base station.

Step 402, the mobile terminal calculates a target SINR value by using a formula (2) according to the target SINR value, the path loss correction factor and the maximum target SINR value of the cell edge given by the service base station;

formula (2)

Wherein, T_(dB)A target SINR value for a cell edge, i.e., when Δ PL is 0; Δ PL is the difference between the signal path loss of the largest neighbor base station that reaches the mobile terminal and the signal path loss of the serving base station, the measurement of the path loss of the base station signal being obtained by preliminary measurement of the handover procedure of the mobile terminal with the base station; alpha is a path loss correction factor, and alpha is more than 0 and less than 1;

is the specified maximum target SINR value.

And step 403, the mobile terminal selects a proper modulation coding mode according to the obtained target SINR value, calculates the transmitted power according to the formula (3), and transmits the signal.

{TxPSD}_{(dBm)} = \min ({SINR}_{0} + I + PL, {TxPSD}_{(dBm)}^{\max})

Formula (3)

Wherein, TxPSD is the emission power density; SINR₀Obtaining a target SINR value; i is the channel interference level in a cell or sector; PL is measured path loss;

is the maximum power density allowed for mobile terminals to transmit within the cell.

The current power control method based on the differential path loss power compensation algorithm is just because when the value of alpha is unreasonable, all selectable modulation coding modes cannot be covered, so that the cell spectrum efficiency and the generated cell edge interference degree are unbalanced, the discovery of the potential capacity of the system is limited, and the overall performance of the system is limited.

In order to solve the problem, the improved power control method of the orthogonal frequency division multiplexing access system of the invention comprises that the mobile terminal determines a target SINR value of the mobile terminal (namely the SINR in the formula (4)) according to the cell interference parameter, the maximum path loss difference threshold value and the minimum path loss difference threshold value notified by the base station and the measured base station signal path loss₀) (ii) a And selecting a proper modulation coding mode according to the determined target SINR value of the mobile terminal, further obtaining the transmitting power, and transmitting the signal.

The mobile terminal obtains cell interference parameters sent by a service base station, wherein the cell interference parameters comprise a cell edge target signal interference noise ratio and a maximum target signal interference noise ratio.

The base station signal path loss obtained by the mobile terminal measurement comprises the signal path loss of the service base station of the mobile terminal and the signal path loss of the largest adjacent base station.

Formula (4)

Wherein, T_(dB)A target SINR value for a cell edge, i.e., when Δ PL is 0; Δ PL is the difference between the signal path loss of the largest neighbor base station that reaches the mobile terminal, the measurement of which is obtained by preliminary measurement of the handover procedure, and the signal path loss of the serving base station; c1 and C2 are the lower and upper limits of the path loss difference;

is the specified maximum target SINR value.

When delta PL is larger than C2, the highest order modulation coding mode is used; when the delta PL is smaller than C1, using the modulation coding mode with the lowest order; therefore, the users (users with larger delta PL) at the center of the cell use a high-order modulation coding mode, and the users (users with smaller delta PL) at the edge of the cell use a low-order modulation coding mode; wherein, the modulation coding mode of the highest order and the modulation coding mode of the lowest order are both selected from the selectable set of modulation coding modes specified by the system.

And obtaining the minimum value of the sum of the target SINR, the cell interference level and the path loss of the service base station and the maximum transmission power threshold of the transmission power spectrum density of the mobile station through the determined target SINR value of the mobile terminal.

{TxPSD}_{(dBm)} = \min ({SINR}_{0} + I + PL, {TxPSD}_{(dBm)}^{ma})

Wherein, TxPSD is the emission power density; SINR₀Is the target SINR value of the mobile terminal; i is the channel interference level in a cell or sector; PL is measured path loss;

As shown in fig. 5, the power control method of the ofdm access system of the present invention specifically includes the following steps:

step 501, the mobile terminal obtains a path loss value through continuous measurement of a service base station signal and a strongest interference signal and through a difference between a received signal power and a transmitted signal power, and further obtains a path loss difference value;

step 502, the mobile terminal calculates a target SINR value according to a target SINR value of a cell edge, a maximum path loss difference threshold value, a minimum path loss difference threshold value, a maximum target SINR value, and an obtained path loss difference value sent by the serving base station;

step 503, the mobile terminal selects a suitable modulation coding mode according to the obtained target SINR value, and calculates the transmitted power according to the following formula to transmit the signal.

{TxPSD}_{(dBm)} = \min ({SINR}_{0} + I + PL, {TxPSD}_{(dBm)}^{\max})

As shown in fig. 6, the ofdm access system of the present invention includes a base station and a mobile terminal, wherein,

the base station is a service base station of the mobile terminal and comprises a parameter notification module used for sending a cell interference parameter, a maximum path loss difference threshold value and a minimum path loss difference threshold value to the mobile terminal; the cell interference parameters comprise a cell edge target SINR value and a maximum target SINR value;

the mobile terminal comprises a power measuring module, a calculating module and a signal transmitting module, wherein,

the power measurement module is used for measuring and obtaining the path loss of the base station signal of the mobile terminal and sending the path loss to the calculation module; wherein the base station signal path loss comprises the signal path loss of the serving base station of the mobile terminal and the signal path loss of the largest adjacent base station;

the power measurement module obtains the signal path loss of the adjacent base station of the mobile terminal through the preliminary measurement of the switching process.

The calculating module is configured to receive the cell interference parameter, the maximum path loss difference threshold value, the minimum path loss difference threshold value, and the measured base station signal path loss sent by the base station, determine a target signal interference noise ratio of the mobile terminal through calculation, obtain a transmitting power according to the determined target signal interference noise ratio, and send the obtained target signal interference noise ratio and the transmitting power of the mobile terminal to the signal transmitting module;

the signal transmitting module is used for receiving the target signal interference noise ratio value and the transmitting power sent by the calculating module, selecting a modulation coding mode according to the target signal interference noise ratio value, and adjusting the transmitting power according to the obtained transmitting power to transmit signals.

The present invention is further illustrated by the following specific examples.

In the example, a static system simulation platform is used to simulate the differential path loss compensation algorithm and the improved differential path loss compensation algorithm of the invention. The system composition comprises 7 cell clusters, each cell cluster is composed of 19 regular hexagonal cells, and each cell is divided into three sectors. The cell cluster composition is shown in fig. 7. The frequency reuse factor is 1, that is, all sectors use the same frequency point resource. The simulation provides that 10 users are scattered per sector, and the users are scattered evenly in the network. The mobile terminal determines the sector with the strongest received signal as the serving cell by measuring the received signal strength of 57 sectors.

After a channel is allocated to each mobile terminal, the received signal strength and the interference strength are calculated to obtain a target SINR value of each user, so that modulation coding selection and power control are performed. The system simulation parameters are shown in table 1; the OFDMA parameters used for the simulation are shown in table 2; the transmission model is shown in table 3; the threshold values shown in table 4 are used for the selection of the modulation and coding scheme.

Table 1: simulation parameters

Table 2: OFDMA system parameters

Table 3: transmission model

Table 4: error code of 10^-3Entry threshold corresponding to time modulation coding mode

The power control simulation results for different alpha values in the differential path loss power compensation algorithm are shown in table 5 and fig. 8. Fig. 8 is an IoT probability distribution curve for a system user. In the simulated configuration, Δ PL has a maximum of 20dB, and when α is 0.575, SINR₀And Δ PL is a completely linear relationship; when α is greater than 0.575 (e.g., α ═ 0.6), the highest order modulation coding scheme loses the opportunity to be used; when α is smaller than 0.575 (for example, α ═ 0.4), the probability that the highest order modulation coding scheme is used increases. As can be seen from the simulation results, the decrease of α (i.e., the increase of the slope) improves the throughput of the system, but the interference level of the whole system increases and the coverage probability of the whole system decreases; the increase of alpha can reduce the interference level of the system and improve the coverage probabilityBut the system throughput is reduced. In fig. 8, the horizontal axis iot (interference over thermal) is an interference-over-thermal ratio, which is a parameter reflecting the inter-cell interference level.

Table 5: comparison of System Performance at different alpha

Simulations of the improved differential path loss power compensation algorithm of the present invention are shown in table 6 and fig. 9. Table 6 shows the performance simulation of the system under different values of C1 and C2. In fig. 9, the closer the curve is to the upper left, the lower the interference level corresponding to the curve is, and it can be seen that the values of C1 and C2 are different, which results in different interference levels of the system. C1 increases, which decreases the throughput of the system and increases the coverage of the system; c2 increases, which increases the throughput of the system and decreases the coverage of the system. The best state of system performance can be obtained by selecting proper C1 and C2, for example, when C1 is 8dB, and C2 is 15dB, the throughput can be 1.86, and the coverage is 98.48%. In the differential path loss power compensation method, it is difficult to use one parameter α to coordinate the best compromise between coverage probability and throughput, for example, α is 0.4, when coverage is good, throughput is low, and α is 0.6, when throughput is high, coverage is reduced.

Table 6: comparison of System Performance at different C1 and C2

From the above, it is clear from the simulation results in the examples that the present invention enables the power control algorithm to achieve the best compromise between system throughput and system coverage by adjusting the parameters C1 and C2. Meanwhile, the adjustment of C1 and C2 has the advantages of being more intuitive, simple and flexible compared with the adjustment of the path loss correction factor alpha.

The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention disclosed herein are intended to be covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A power control method of an orthogonal frequency division multiplexing access system, comprising,

2. The power control method of claim 1,

the mobile terminal obtains cell interference parameters sent by a service base station, wherein the cell interference parameters comprise a cell edge target signal interference noise ratio and a maximum target signal interference noise ratio;

3. The power control method of claim 1,

the mobile terminal selects a modulation coding mode, and further comprises,

when the delta PL is larger than the maximum path loss difference threshold value, the mobile terminal selects the modulation coding mode of the highest order;

when the delta PL is smaller than the minimum path loss difference threshold value, the mobile terminal selects a modulation coding mode of the lowest order;

where Δ PL is a difference between a signal path loss of a largest neighboring base station that reaches the mobile terminal and a signal path loss of a serving base station.

4. The power control method of claim 1,

the step of the mobile terminal transmitting signals comprises,

and the mobile terminal obtains the transmitting power according to the determined target signal interference noise ratio, adjusts the transmitting power according to the obtained transmitting power and transmits signals.

5. The power control method of claim 2,

the measurement of the signal path loss of the neighboring base station of the mobile terminal is obtained by a preliminary measurement of a handover procedure.

6. An orthogonal frequency division multiplexing access system comprising a base station and a mobile terminal, characterized in that,

7. The orthogonal frequency division multiplexing access system of claim 6,

the cell interference parameters sent to the mobile terminal by the parameter notification module further include a cell edge target signal interference noise ratio and a maximum target signal interference noise ratio.

8. The orthogonal frequency division multiplexing access system of claim 6,

the mobile terminal also comprises a power measurement module which is used for measuring and obtaining the path loss of the base station signal of the mobile terminal and sending the path loss to the calculation module; wherein, the base station signal path loss includes the signal path loss of the serving base station of the mobile terminal and the signal path loss of the largest adjacent base station.

9. The orthogonal frequency division multiplexing access system of claim 6,

the calculation module is further configured to obtain a transmission power according to the determined target signal to interference noise ratio of the mobile terminal and send the transmission power to the signal transmission module.

10. The orthogonal frequency division multiplexing access system of claim 9,

and the signal transmitting module selects a modulation coding mode according to the target signal interference noise ratio, adjusts the transmitting power according to the obtained transmitting power and transmits signals.