CN1951030A

CN1951030A - Power control method and apparatus with inter-link interference prediction for use in cdma wireless communication networks

Info

Publication number: CN1951030A
Application number: CNA2005800147645A
Authority: CN
Inventors: 张树; 戎蒙恬; 孙礼
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2004-05-11
Filing date: 2005-04-28
Publication date: 2007-04-18
Also published as: CN1697342A; EP1751881A1; WO2005109673A1; KR20070020032A; JP2007537643A

Abstract

A power control method for use in wireless communication networks: after a receiving node receives radio signal from a transmitting node, the receiving node predicts an inter-link interference power upon itself according to the received radio signal, and sends a power control message to the transmitting node; after the transmitting node receives a power control message from a receiving node, it extracts the inter-link interference power predicted by the receiving node, and adjusts its transmit power according to the predicted inter-link interference power.

Description

Power control method and apparatus employing inter-link interference prediction for use in CDMA wireless communication networks

Technical Field

The present invention relates to a power control method and apparatus in a wireless communication network, and more particularly, to a power control method and apparatus for use in a CDMA wireless communication network.

Technical Field

In the present society, wireless communication networks are playing an increasingly important role in people's lives by virtue of their increasingly rich and fast information services.

Currently, there are two types of wireless communication networks: one is a fixed infrastructure based wireless communication network, such as a cellular telephone network; another is a wireless communication network without fixed facilities, such as an Ad hoc (Ad hoc) wireless communication network.

In fixed infrastructure based networks, the transmission range of a base station or access point determines the size of the cell with which mobile terminals within the cell communicate directly. However, in an Ad hoc wireless communication network, mobile terminals are self-organizing, and two mobile terminals establish communication with each other either directly or through forwarding (multihop) by other mobile terminals between the two mobile terminals. Due to this inherent characteristic of Ad hoc wireless communication networks, they have a wide application prospect in many fields, such as Personal Area Networks (PANs), military environments, and search and rescue operations.

In the past few years, researchers at home and abroad have conducted various studies on Ad hoc wireless communication networks based on CDMA technology, including: the european "fleet network-Internet on the road (Fleetnet-Internet)", and the chinese 863 high-tech project "3G technology-based ad hoc wireless network". As research progresses further, ad hoc wireless communication networks based on CDMA technology also present more challenging problems, such as: organization of the system, information routing, power control, system synchronization, access control, and radio resource allocation. Since the near-far effect causes the CDMA system to have a self-interference or interference-limited characteristic, the power control becomes an important factor affecting the performance of the Adhoc wireless communication network based on the CDMA technology in the above problem.

Currently, in the research of Ad hoc wireless communication networks based on CDMA technology, an open-loop power control method or a closed-loop power control method similar to that used in cellular wireless communication networks is adopted, that is: the transmitting power of the transmitting node is adjusted based on historical information, such as the error rate of previous radio frames. This conventional Power Control method is described in "Topology Control using transmit Power adjustment for multi-hop wireless networks" (published by r.ramatahan and r.rosales-Hain in IEEE INFOCOM, vol.2), "Power Control Protocol for multi-hop networks (a Power Control MAC Protocol for hoc networks Ad)" published by sub-joint and Nitin h.vaidya in ACM International Conference mobile computing and Networking (mobile), 2002 month 9, and "cluster using Power Control" (published by t.j.kwon and m.gerla in IEEE miom, vol.2.

However, in an Ad hoc wireless communication network, due to the dynamic topology of a multihop network and the mobility of nodes, the interference (inter-link interference) between links generated by other communicating links suffered by one receiving node in the network fluctuates greatly. If SIR (signal to interference ratio) and interference measurements are made at the receiving node based on historical information and the resulting power control information is fed back to the corresponding transmitting node, it is not possible for the power control information to accurately reflect the effects of potential interference in the current network. Therefore, if the transmitting node periodically adjusts its transmit power according to the power control information fed back by the receiving node, the power control method will have a slow convergence rate, and further reduce energy efficiency, increase network interference, and affect the performance of the Ad hoc wireless communication network.

In order to solve the above-mentioned problem of system performance degradation, a new power control method is required.

Disclosure of Invention

One of the objects of the present invention is to provide a new power control method and apparatus, by which each node in an Ad hoc wireless communication network can equally share network resources, thereby effectively improving energy efficiency, reducing network interference, and optimizing network performance.

A power control method in a wireless communication network according to the present invention, the method performed by a receiving node, comprising the steps of: receiving a wireless signal from a transmitting node; predicting an interference power value between links received by the receiving node according to the received wireless signal; sending a power control message to the sending node to enable the sending node to adjust its transmit power according to the predicted inter-link interference power value included in the power control message.

A power control method in a wireless communication network according to the present invention, the method performed by a transmitting node, comprises the steps of: receiving a power control message from a receiving node; extracting the interference power value between the links received by the receiving node through prediction from the power control message; and adjusting the transmitting power of the transmitting node according to the predicted interference power value between the links.

Other objects and results of the present invention will become more apparent and more readily appreciated as the same becomes better understood by reference to the following description and appended claims, taken in conjunction with the accompanying drawings.

Drawings

The invention will be described in detail below with reference to the following figures and specific embodiments, wherein:

FIG. 1 is a schematic diagram of a typical Ad hoc wireless communication network;

FIG. 2 is a flow chart of a power control method according to the present invention;

fig. 3 is a composition diagram of a mobile terminal for performing a power control method according to an embodiment of the present invention.

The same reference numbers in all figures indicate similar or corresponding features or functions.

Detailed Description

The power control method provided by the invention comprises the following steps: at a receiving node in a wireless communication network, an interference power value between links to which the receiving node is subjected by other communicating links is predicted based on a burst (burst) and a self-similarity (self-similarity) specific to a traffic (traffic) such as voice, video, and IP data, and the predicted interference power value is fed back to a transmitting node, so that the transmitting node can adjust its power for transmitting a wireless signal based on the feedback information.

Hereinafter, the power control method of the present invention will be described in detail by taking an Ad hoc wireless communication network operating in TDD (time division duplex) mode as an example shown in fig. 1.

As shown in fig. 1, in the Ad hoc network composed of a plurality of mobile terminals (nodes), when each node communicates with its neighboring (neighbor) node, a link connection is maintained between the node and its neighboring node. Nodes distributed in different time slots, wherein signal interference cannot be generated by communication links among the nodes; interference between links occurs between pairs of transmitting and receiving nodes (pairs) assigned to receive and transmit radio signals using different spreading codes in the same time slot.

Assume that there is a receiving node i in the network that receives a wireless signal transmitted from a transmitting node j. In order to satisfy the requirement of signal to interference ratio sir (signaling ratio) of the signal received at the receiving node i, the power of the signal transmitted by the transmitting node j should satisfy the following formula (1):

wherein,

g: is the processing gain;

t: is the number of the time slot, and the value is set to 0 at the beginning of a frame;

p_j(t): the transmitting power of the transmitting node j is mW;

r_ij(t): is the channel gain from the transmitting node j to the receiving node i;

I_inter(t): in mW, which is the other node than the transmitting node-j that is simultaneously communicating with each otherThe sum of the interference power formed at the receiving node-i, i.e.: the receiving node i is subject to interference between its resulting links by other communicating links. The transmission channels used by these other nodes are also in the same time slot but use different spreading codes.

N_bk: background noise in mW;

SIR_{target ij}(t): is the target SIR at the receiving node i for extracting the signal transmitted by the transmitting node j. SIR in general_{target ij}(t) is set by the radio resource management layer and its value can be adjusted according to the quality of the communication channel. For example, the SIR may be corrected based on the calculated bit error rate BER (BitError Rate)_{target ij}(t) adjusting SIR when BER is high_{target ij}(t) should be increased, SIR when BER is low_{target ij}(t) should be decreased.

The above formula (1) can be rewritten as follows:

wherein,

E＝I_{int er}(t)+N_bk (3)

the transmit power of the transmitting node j can be calculated according to equations (2) and (3).

However, it is not limited toDue to I_{int er}(t) is the interference between links received by the receiving node I, which is a real-time random process, and the variability of the Ad hoc network causes the interference between the links to fluctuate greatly with time, so that it is impossible to know I in advance_{int er}(t) accurate information.

It can be seen from the above equations (2) and (3) how to make the sending node j know about I_{int er}The current information of (t) becomes an important factor for the sending node j to accurately adjust its transmitting power in time.

In present and future wireless communication networks, voice, video, and IP data remain the primary services communicated in the network. For such traffic burstiness and self-similarity are the most important statistical properties, which means that the interference between links experienced by the receiving node I is correlated from one time slot to the next, and thus according to I_{int er}(t) in the receiving node I, the received wireless signal may be detected using a Kalman filter to predict I_{int er}(t) is a numerical value. When employing predicted I_{int er}(t) in the case of numerical values, the above formula (3) is modified as follows:

E = {\tilde{I}}_{int er} (t) + N_{bk} - - - (4)

wherein,

is I_{int er}(t) the predicted value.

If will i_{int er}(t) is defined as:

i_{int er}(t)＝10lg[I_{int er}(t)](dBm)

the dynamic process of representing the interference power value (in dBm) between the links using a first order Markov (Markov) process is:

i_{int er}(t-1)＝α·i_{int er}(t-2)+W(t-1) (5)

where α is a weighting coefficient, 0 < α < 1, and α can be defined as:

where v is the velocity of the receiving node i, η is the power control rate, and c and Δ are constant coefficients and constant offsets, respectively, defined by higher layers.

W (t) in equation (6) is a zero-mean Gaussian white noise sequence with variance σ_w ²(t)。

i_{int er}The variance of (t) can be expressed as:

assuming that y (t) is the interference power measured in the tth slot, then:

Y(t-1)＝i_{int er}(t-1)+U(t-1) (8)

where U (t) is the measurement noise, which is also a zero mean white Gaussian noise sequence with variance σ_U ²。

Due to i_{int er}(t) is independent of U (t), and therefore the variance of Y (t) can be found to be:

when the kalman filter is used to process the interference signal received by the receiving node i, the formula of the kalman filter can be expressed as:

wherein,

andrespectively represent i_{int er}(t) posterior (posteriori) and prior (priori) estimates, namely: detected i_{int er}(t) value and predicted i_{int er}(t) a value, K (t) is a Kalman gain,

and

are a posteriori and a priori estimates of the error variance.

Suppose that under normal conditions, for i measured_{int er}(t) for + -4 dB measurement accuracy, if sigma is assumed_U3dB, i.e.:

from equations (7) and (9), it can be derived:

σ can be obtained by the following equations (16) to (18) from the measurement of the interference for the latest L slots_w ²(t) estimated value

The receiving node i measures the interference experienced in each reception time slot, and these interference measurements are used as input values for equations (16) to (18) for the evaluationDerived from the estimation

The interference value obtained by the current measurement is used as the input value of the above Kalman filter formulas (10) to (14) to calculate the predicted interference power

In fact, obtained from formula (11)In dBm. If mW is taken as a unit, thenShould be expressed as:

{\tilde{I}}_{int er} (t) = 10^{(\frac{{\tilde{i}}_{int er} (t)}{10})} (mW)

is obtained through the calculationThen, will

The numerical value of (c) is substituted into the formulas (4) and (2), and the transmitting power p of the transmitting node j can be calculated_j。

As can be derived from the above formula, the burstiness and self-similarity specific to data services in a receiving node can make it possible to predict the inter-link interference power value experienced by the receiving node in the receiving node, that is: in the above formula (4)

The receiving node only needs to feed back the predicted interference power value between the links to the sending node in the network, and then the sending node can adjust the power of sending wireless signals according to the feedback information.

In the following, a transmission power control method performed in a transmitting node j and a corresponding receiving node i according to the present invention in an Ad hoc network will be described with reference to fig. 2.

As shown in fig. 2, first, after receiving a wireless signal from a transmitting node j, a receiving node i detects background noise of the wireless signal, and obtains an interference power value between links by using kalman filter prediction therein

(step S10).

Secondly, the receiving node i estimates the BER of the received channel from the received signal in a conventional manner_estAnd adjusting SIR according to the following criteria_{target ij}Value of (d) (step S20):

where Δ is a fixed power control step size; BER_reqIs the BER required to meet the quality of service.

Then, the receiving node i generates a TSC (target SIR control) command in a conventional manner and transmits the command to the corresponding transmitting node j according to the following criteria (step S30):

next, the receiving node i calculates the value of E according to formula (4) (step S40).

Thereafter, the receiving node i broadcasts a power control message including the calculated E value to neighboring nodes via a control channel (step S50). The corresponding transmitting node j can adjust the power of its transmitted signal according to the power control message, and other neighboring nodes can also use the broadcast message to perform channel estimation to obtain access information and routing information.

Upon receiving the power control message from the receiving node i, the transmitting node j first extracts information of E from the power control message (step S60).

Then, the transmitting node j adjusts the SIR according to the following rule based on the received TSC command from the receiving node i_{target ij}Numerical value of (t) (step S70):

the transmitting node j then predicts the channel gain r in the conventional manner_ij(step S80).

According to the extracted E value and the adjusted SIR_{target ij}(t) value and predicted channel gain r_ijThe transmitting node j can recalculate the transmit power p according to equation (2)_jAnd adjusts the power of its transmitted wireless signal according to the result of the calculation (step S90).

As can be seen from the above description with reference to fig. 2, when the receiving node i calculates the value E by using equation (2), the interference power value between the links is the same

Is predicted by using a kalman filter, so that when the transmitting node j extracts an E value from the received power control information, and calculates the power p obtained according to the formula (2) by using the E value_jWhen adjusting the power of its transmitted signal, the transmitting node j uses the predicted interference power information to which the current receiving node is subjected, instead of adjusting the power of the transmitted signal based on the history information as in the conventional mode.

The power control method for the CDMA wireless communication system of the present invention may be implemented by computer software, or implemented by computer hardware, or implemented by a combination of computer software and computer hardware.

The hardware composition of a mobile terminal for a CDMA wireless communication system implementing power control according to an embodiment of the present invention is shown in fig. 3, in which the same components as those of a conventional mobile terminal are not shown in fig. 3.

As shown in fig. 3, when the transmitting unit 40 in the mobile terminal 10 as the transmitting node j transmits a wireless signal to the other mobile terminal 10 as the receiving node i, the receiving unit 20 in the other mobile terminal 10 as the receiving node i receives the wireless signal, and the predicting unit 30 therein processes the wireless signal by using the kalman filter to predict the inter-link interference power value received by the receiving node i; then, the sending unit 40 in the receiving node i sends a power control message to the sending node j, so that the sending node j can adjust its transmission power according to the predicted inter-link interference power value included in the power control message.

When the receiving unit 20 in the sending node j receives the power control message from the receiving node i, the extracting unit 50 therein extracts the interference power value between the links which the receiving node i receives through prediction from the power control message, and provides the background noise also included in the power control message to the adjusting unit 60, so that the adjusting unit 60 can adjust the transmitting power of the sending unit 40 in the sending node j according to the predicted interference power value between the links and the background noise by using the above formula (2).

Advantageous effects

In summary, in the power control method and apparatus provided by the present invention, at a receiving node, according to the burstiness and self-similarity specific to the data service, the kalman filter is used to predict and calculate the interference power value between the links received by the receiving node, and the predicted value is fed back to the transmitting node, so that each node in the Adhoc network based on the CDMA technology can equally share the network resources, therefore, in the corresponding transmitting node, the interference power prediction information received by the current receiving node can be used instead of adjusting the power of the transmitted signal based on the history information as in the conventional mode, so that the present invention can make the whole network have higher energy efficiency, lower interference and better system performance compared with the conventional power control algorithm.

It will be appreciated by those skilled in the art that the power control method and apparatus for a CDMA wireless communication system disclosed in the present invention can be modified in various ways without departing from the scope of the invention. Therefore, the scope of the present invention should be determined by the contents of the appended claims.

Claims

1. A method of power control in a wireless communication network, the method performed by a receiving node, comprising the steps of:

(a) receiving a wireless signal from a transmitting node;

(b) predicting an inter-link interference (inter-link interference) power value of a link to which the receiving node is subjected according to the received wireless signal;

(c) sending a power control message to the sending node to enable the sending node to adjust its transmit power according to the predicted inter-link interference power value included in the power control message.

2. The power control method according to claim 1, wherein the inter-link interference power value is a sum of interference powers of the transmission power of other nodes communicating except the transmitting node to the receiving node.

3. The power control method of claim 2, wherein the power control message further includes background noise.

4. A method of power control according to claim 1 or 2 or 3, wherein the radio signal is processed by a Kalman filter to obtain the predicted inter-link interference power value.

5. The power control method of claim 4, wherein the power control message is broadcast via a control channel.

6. The power control method as claimed in claim 5, further comprising the steps of:

generating a TSC (target Signal to interference ratio control) command according to the received wireless signal;

the TSC instruction is sent to the sending node.

7. A power control method in a wireless communication network, the method performed by a transmitting node, comprising the steps of:

(a) receiving a power control message from a receiving node;

(b) extracting the interference power value between the links received by the receiving node through prediction from the power control message;

(c) and adjusting the transmitting power of the transmitting node according to the predicted interference power value between the links.

8. The power control method according to claim 7, wherein the inter-link interference power value is a sum of interference powers of the transmission powers of other nodes, except the transmitting node, which are performing communication, to the receiving node.

9. The power control method of claim 8, wherein the power control message further includes background noise, and the method further comprises the steps of:

and adjusting the transmitting power of the transmitting node according to the background noise.

10. The power control method according to claim 7, 8 or 9, wherein the predicted inter-link interference power value is obtained by the receiving node processing the wireless signal through a Kalman filter (Kalman filter).

11. The power control method of claim 10, wherein the transmitting node receives the power control message via a control channel.

12. The power control method as claimed in claim 11, further comprising the steps of:

receiving a TSC (target signal to interference ratio control) command from the receiving node;

and adjusting the transmitting power of the transmitting node according to the TSC instruction.

13. The power control method as claimed in claim 12, further comprising the steps of:

measuring a channel gain between the transmitting node and the receiving node;

and adjusting the transmitting power of the transmitting node according to the channel gain.

14. A mobile terminal, comprising:

a receiving unit for receiving a wireless signal transmitted from another mobile terminal;

a prediction unit, configured to predict an inter-link interference (inter-link interference) power value received by the mobile terminal according to the received wireless signal;

a sending unit, configured to send a power control message to the other mobile terminal, so that the other mobile terminal can adjust its transmit power according to the predicted inter-link interference power value included in the power control message.

15. The mobile terminal of claim 14, wherein the inter-link interference power value is a sum of interference powers formed on the mobile terminal by transmission powers of other communicating mobile terminals except the other mobile terminal.

16. The mobile terminal of claim 15, wherein the prediction unit processes the wireless signal using a Kalman filter (Kalman filter) to obtain the predicted inter-link interference power value.

17. A mobile terminal, comprising:

a receiving unit for receiving a power control message from another mobile terminal;

an extracting unit, configured to extract, from the power control message, an interference power value between links to which the other mobile terminal is subjected through prediction;

and an adjusting unit, configured to adjust the transmission power of the mobile terminal according to the predicted inter-link interference power value.

18. The mobile terminal of claim 17, wherein the inter-link interference power value is a sum of interference powers formed by transmission powers of other mobile terminals, except the mobile terminal, which are performing communication, to the other mobile terminal.