WO2005109673A1

WO2005109673A1 - Power control method and apparatus with inter-link interference prediction for use in cdma wireless communication networks

Info

Publication number: WO2005109673A1
Application number: PCT/IB2005/051387
Authority: WO
Inventors: Shu Zhang; Mengtian Rong; Li Sun
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-05-11
Filing date: 2005-04-28
Publication date: 2005-11-17
Also published as: CN1697342A; EP1751881A1; CN1951030A; 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 WITH INTER-LINK INTERFERENCE PREDICTION FOR USE IN CDMA WIRELESS COMMUNICATION NETWORKS

Field of the Invention The present invention relates generally to a power control method and apparatus for use in wireless communication networks, and more particularly, to a power control method and apparatus for use in CDMA wireless communication networks.

Background Art of the Invention In current society, wireless communication networks are playing an increasingly important role in our daily life, thanks to providing growingly rich and fast information service. Presently, there are two kinds of wireless communication networks: one is based on fixed infrastructure, such as cellular phone networks; the other has no fixed infrastructure, such as Ad hoc networks. In an infrastructure-based network, the size of the cell is to be decided by the transmission range of the BS (base station) or AP (Access Point), and mobile terminals in the cell can communicate directly with the BS or AP. But in an Ad hoc network, mobile terminals are self-organizing, so two mobile terminals can establish direct communication between them, or establish mutual communication through the forwarding (multi-hop) of other mobile terminals between them. With this nature, Ad hoc networks have found applications in many fields, such as PAN (Personal Area Network), military environment and search & rescue operations, and are embracing a broad and bright future of the application. During the past few years, researchers across the world have conducted various researches on CDMA-based Ad hoc wireless communication networks, including "Fleetnet-lnternet on the Road" in Europe, and Chinese 863 high-tech project "Self-organizing wireless network based on 3G techniques". With researches going in further depth, CDMA-based Ad hoc wireless communication network has encountered more challenging problems, such as the system architecture, information routing, power control, system synchronization, access control, radio resource allocation and so on. Due to the near-far effect, CDMA systems are self-interfering or interference-limited. Therefore, among the above issues, power control has become a major factor affecting the performance of CDMA-based Ad hoc wireless communication networks. At present, in the ongoing researches conducted on CDMA-based Ad hoc wireless communication networks, the method similar to the open-loop power control or closed-loop power control mechanism used in cellular wireless communication networks is employed, that is, the transmission power of the transmitting node is adjusted with reference to history information (e.g. the BER of several previous radio frames). The conventional power control methods are described in detail in "Topology control of multi-hop wireless networks using transmit power adjustment", published in IEEE INFOCOM, vol.2, by R. Ramanathan and R. Rosales-Hain, "A Power Control MAC Protocol for Ad Hoc Networks", published in ACM

International Conference on Mobile Computing and Networking (MobiCom), September 2002, by Eun-Sun Jung, and Nitin H. Vaidya, and "Clustering with power control", published in IEEE MILCOM, vol. 2, by T.J. Kwon and M. Gerla. However, due to the dynamic topology of Ad Hoc networks and mobility of nodes in Ad Hoc wireless communication networks, the inter-link interference at a given receiving node caused by other communicating links, may fluctuate dramatically. If measurements on the SIR and interference are based on history information at the receiving node and the derived power control message is fed back to the corresponding transmitting node, the power control information cannot reflect accurately the influence of potential interferences in current network. Consequently, if the transmitting node adjusts its transmit power periodically based on the power control message which is fed back from the receiving node, the convergence rate of the power control method is very slow, thus degrade the energy efficiency, increase network interference and deteriorate the performance of the Ad hoc wireless communication network. To solve the above problem of system performance degradation, a new power control method is needed. Summary of the Invention An object of the present invention is to provide a new power control method and apparatus, with which, all nodes in the Ad hoc wireless communication network can share the network resources equally, thus effectively enhance the energy efficiency, reduce the network interference and optimize the network performance. A power control method for use in wireless communication networks in accordance with the present invention, executed by a receiving node, comprising: receiving the radio signal from a transmitting node; predicting the inter-link interference power upon the receiving node according to the received radio signal; sending a power control message to the transmitting node, such that the transmitting node can adjust its transmission power according to the predicted inter-link interference power included in the power control message. A power control method for use in wireless communication networks in accordance with the present invention, executed by a transmitting node, comprising: receiving a power control message from a receiving node; extracting the predicted inter-link interference power upon the receiving node from the power control message; adjusting the transmission power of the transmitting node according to the predicted the inter-link interference power. Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

Brief Description of the Drawings For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings, and in which: Fig.1 is a schematic diagram illustrating the typical Ad hoc wireless communication network; Fig.2 depicts the flowchart of the power control method in the present invention; Fig.3 illustrates the architecture of the mobile terminal for executing the power control method in accordance with an embodiment of the present invention. The same reference numeral refers to the like or the corresponding feature and function in all of the accompanying drawing.

Detailed Description of the Invention According to the power control method provided in the present invention: at a given receiving node in the wireless communication network, predict the inter-link interference power upon the receiving node caused by other communicating links, based on the particular burst and self-similarity of the traffic such as voice, image, IP data and etc; feed the predicted interference power back to the transmitting node, such that the transmitting node can adjust its power for transmitting radio signal based on the feedback information. Detailed description will be given below to the power control method in the present invention, by exemplifying the Ad hoc wireless communication network in TDD mode as shown in Fig.1. As Fig.1 shows, in the Ad hoc network constructed by multiple mobile terminals (nodes), when a node communicates with a neighbor node, a link connection between them will be maintained. For nodes allocated in different timeslots, the communication links between them won't produce signal interference; but for a pair of transmitting node and receiving node that are allocated in the same timeslot but use different spreading codes for radio signal transmission and reception, an inter-link interference will occur. It is assumed that there is a receiving node i in the network and it receives radio signal sent from a transmitting node j. To meet the SIR (Signal Interference Ratio) requirement at receiving node i, the transmission power of the transmitting node j should satisfy the following equation (1 ):

where, G is processing gain; t is timeslot number, which is set to zero at the beginning of a frame;

^Pj^' is the transmission power of the transmitting node j in mW; ^r,j^' is the channel gain from the transmitting node j to the receiving node i; .mer( _j j_{n rn} \j_ι j_s t_ne total sum of the interference power produced by the transmit power of other communicating nodes except said transmitting node j upon the receiving node i, or namely, the inter-link interference produced by other communicating links upon the receiving node i. The propagation channels used by said other nodes are within the same timeslot, but use different spreading codes. ^bk is the background noise in mW. '^arge' ^{» J} is the target SIR at the receiving node i, for extracting the

SIR (t signal sent by the transmitting node j. Usually, '^argc' ^,J is set by radio resource management layer and can be adjusted according to the quality of SIR r the communication link. For example, ^,arge' " ' can be adjusted according to a computed BER (Bit Error Rate): when the BER is high,

^slR< ι^e, ,^j (0 should be increased; when the BER is low, ^SIR'^«β« « ^ should be decreased. The above equation (1) can also be written as: SIR_{IMSel lJ} ( r_v ( - G where E = I_mter(t) ₊ N_bk ( 3 ) The transmission power of the transmitting node j can be computed according to equation (2) and equation (3). However, l_mer(t) is the inter-link interference upon the receiving node i, which is a real-time stochastic process, and the inter-link interference i_mler(t) fluctuates dramatically from time to time due to the variability of the Ad hoc network, thus it's unlikely to predict the accurate information of l_{m r}(t) . From the above equations (2) and (3), it can be seen that a key factor for the transmitting node j to adjust its transmission power timely and accurately is to acquire the current information of l_mler(t) . In the current and future wireless communication networks, voice, image and IP data are still the main traffics delivered in the network. For these traffics, burst and self-similarity are the most important statistical characteristics, which means that the inter-link interference upon the receiving node i is correlated from one timeslot to the next. According to the time correlation of l_mler(t) , Kalman filter can be used to detect the received radio signal at the receiving node i, so as to predict the value of i_mter(t) .

When the predicted l_mter(t) is acquired, the above equation (3) can be modified as:

E = I_Mer( + N_hk (4 ) where l _er(t) is the predicted value of l_mter(t) . If l_mler(t) is defined as: _{ιn r}( = l01g[/_ιnler( ] (dBm ) The dynamic process of the inter-link interference power (in dBm) can be represented by first-order Markov process as: i_mtr(t-l) = cfi_mtr(t-2) + W(t -l) (5) where a is a weighting factor, 0 <αr < l , and a can be defined as: -₍c -+Δ) a = e ^η ( 6 ) where v is the velocity of the receiving node i, η is the power control rate, c and Δ are constant coefficient and constant offset, respectively, which are defined by high layer. W(t) in equation (5) is a zero mean Gaussian white noise sequence, with variance as σ (t . The variance of _ιnter( can be written as:

\- Let Y(t) be the measured interference power at timeslot t: Y(t-l) = i_mler(t-\) + U(t-l) (8) where U(t) is measurement noise, which is also a zero mean Gaussian white noise sequence, with variance asσ . Because _mter(/) is independent of U(t), we get a variance of Y(t) as: σ_r ²(t-l) = σ_M ² _tr(t-l) + σl ⁽9) When Kalman filter is adopted to process the interference signal upon the receiving node i, the Kalman filter equations can be expressed as:

P( = ²-p(t-\) + ά_w ²(t-\) ⁽13) p(t-l) = [\-K(t-l)]-p(t-l) (14) where _ιnter( and T_ιnter(t) denote the posteriori and priori estimate of ( _> respectively, that is, the detected value and the predicted value of CO! K(t) ^{is the} Kalman gain; P(t) and ^p(t) are the priori and posteriori estimated error variance. It's assumed that a measurement accuracy of ±4dB for measured ( is required in normal condition. If assume that

according to equation (7) and equation (9), we yield: σ² _v(t-\) = (\-a²)-[σ²(t-l)-σ_u ²] (15) Based on the interference measurement of the last L timeslots, we can obtain the estimation ά_w ²(t) of σ_w ²(t) according to equations (16) to (18): m_γ(t-\) = - ∑Y(j) (16)

The receiving node i measures the interference for each timeslot, and these interference measurements are used as input of equations (16) to (18) to estimate σ_w ² (t - \) . The estimated σ_w ² (t - \) and the current interference measurements are used as input of the Kalman filter equations (10) to (14) to predict the interference power ^_nter( . In fact, equation (11 ) yields ( in dBm. We obtain 7_ιnter( in mW as: I_mter(t) =

After 7_ιntβr( is computed, it will be used as the predicted interference power in equations (4) and (2), for calculating the transmission power p_; of the transmitting node j. From the above description, it can be seen that the unique burst and self-similarity of data traffic can help a receiving node to predict the inter-link interference power, or namely ι_mter(t) in the above equation (4). After the receiving node feeds the predicted the inter-link interference power back to the transmitting node in the network, the transmitting node can adjust its transmission power according to the feedback information. The following description will be given to the transmission power control method to be executed between transmitting node j and the corresponding receiving node i in an Ad hoc network, in conjunction with Fig.2. First, as Fig.2 illustrates, after receiving the radio signal from transmitting node j, receiving node i detects the background noise of the radio signal, and uses the Kalman filter herein to predict the inter-link interference power 7_ιntβr( (step SI O). Second, receiving node i estimates the Bit Error Rate (BER_est) of the receiving channel in conventional way according to the received signal, and adjusts SlR_{IΛT&el υ} according to the following rule (step S20): _ , „ (' - 1) - Δ if BER_est < BER_req ^SIR>arse"^{j it) ~} [Sm_{ιareel lJ} (t - \) + A if BER_est > BER_req where Δ is a fixed power control step and BER_req is the required BER for satisfying the QoS. Then, receiving node i generates a TSC (Target SIR Control) command in conventional way, and sends it to the corresponding transmitting node j according to the following rule (step S30):

P' down " if BER_est < BER_req TSC command = \ ^q 1 "up " if BER_est > BER_req Next, receiving node i calculates E according to equation (4) (step S40). Afterward, receiving node i broadcasts a power control message including the calculated E to its neighbor nodes via the control channel (step S50). The corresponding transmitting node j can adjust its transmission power according to the power control message and other neighbor nodes can also use this broadcast message for channel estimation, to get the access information and route information. After receiving the power control message from receiving node i , transmitting node j extracts the information of E from the power control message (step S60). Then, transmitting node j adjusts SiR_{lttitl v} (t) according to the TSC command from receiving node i and with reference to the following rule (step ^SIR„ _{gel j} (t - l) - A if TSC is "down" ^_/arger y C - S *,_arge, , (' - l) + Δ if TSC is "up"

S70): Next, transmitting node j predicts channel gain _v in conventional way (step S80). Transmitting node j calculates transmit power p_t with equation (2), according to the extracted E, adjusted SlR_{taτget υ} (t) and predicted channel gain r_υ , and then adjusts its transmission power (step S90). As can be seen from the above description in conjunction with Fig.2, when receiving node i calculates E with equation (2), the inter-link interference power l_ιnter(t) therein is predicted by using Kalman filter. Hence,

when transmitting node j extracts E from the received power control message and with it to adjust the transmit power according to power p_} calculated from equation (2), transmitting node j uses the current prediction information of the interference power at the receiving node, rather than adjusts transmit power based on history information in conventional mode. The above power control method for use in CDMA wireless communication systems in the present invention, can be implemented in computer software, or computer software, or in combination of both. Fig.3 illustrates the hardware architecture of the mobile terminal for implementing power control in CDMA wireless communication system in accordance with an embodiment of the present invention, wherein the components same as those in conventional mobile terminals are not shown herein. As shown in Fig.3, when transmitting unit 40 in mobile terminal 10, as the above transmitting node j, sends a radio signal to another mobile terminal 10 which acts as the above receiving node i, after receiving unit 20 in said another mobile terminal 10 as receiving node i receives the radio signal, predicting unit 30 herein processes the radio signal by using the above Kalman filter, to predict the inter-link interference power upon receiving node i. Afterwards, transmitting unit 40 in receiving node i sends a power control message to transmitting node j, so that the transmitting node j can adjust its transmission power according to the predicted inter-link interference power included in the power control message. When receiving node 20 in transmitting node j receives the power control message from receiving node i, the extracting unit 50 herein extracts the predicted inter-link interference power upon receiving node i, and provides the background noise included in the power control message to adjusting unit 60, so that adjusting unit 60 can adjust the transmission power of transmitting unit 40 in transmitting node j with the above equation (2) according to the predicted inter-link power and background noise.

Beneficial Results of the Invention

As stated above, with regard to the power control method and apparatus provided in the present invention, a receiving node can use Kalman filter to predict and calculate the inter-link interference power according to the unique burst and self-similarity of the data traffic, and feed the predicted value back to the transmitting node, so that all nodes in the CDMA-based Ad hoc network can equally share the network resources. Thus, the corresponding transmitting node adjusts its transmission power by using the current prediction information of the interference power at the receiving node, rather than based on history information in conventional way. Therefore, the power control method in the present invention can enable the whole network with higher energy efficiency, lower interference and better system performance, compared with conventional ones. Although the present invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the power control method and apparatus for use in CDMA wireless communication networks disclosed in the present invention can be made various changes without departing from the spirit and the scope of the invention. Therefore, the range of the present invention should be defined by the attached claims.

Claims

What is claimed is:

1. A power control method for use in wireless communication networks, executed by a receiving node, comprising: (a) receiving a radio signal from a transmitting node;

(b) predicting an inter-link interference power upon the receiving node according to the received radio signal;

(c) sending a power control message to the transmitting node such that the transmitting node can adjust its transmission power according to the predicted inter-link interference power included in the power control message.

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

3. The power control method according to claim 2, wherein said power control message further includes background noise.

4. The power control method according to claim 1 , 2 or 3, wherein the predicted inter-link interference power can be obtained through processing said radio signal by using Kalman filter.

5. The power control method according to claim 4, wherein said power control message is broadcasted over a control channel.

6. The power control method according to claim 5, further comprising: generating a TSC command according to the received radio signal; sending the TSC command to said transmitting node.

7. A power control method for use in wireless communication networks, executed by a transmitting node, comprising:

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

(b) extracting a predicted inter-link interference power upon the receiving node from the power control message;

(c) adjusting the transmission power of the transmitting node according to the predicted inter-link interference power.

8. The power control method according to claim 7, wherein said inter-link interference power is a total sum of the interference power produced by the transmission power of other communicating nodes except said transmitting node upon said receiving node.

9. The power control method according to claim 8, wherein said power control message further includes background noise and the method further includes: adjusting the transmission power of said transmitting node according to the background noise.

10. The power control method according to claim 7, 8 or 9, wherein said predicted inter-link interference power is obtained by said receiving node processing said radio signal through Kalman filter.

11. The power control method according to claim 10, wherein said transmitting node receives said power control message via the control channel.

12. The power control method according to claim 11 , further comprising: receiving a TSC command from said receiving node; adjusting the transmission power of said transmitting node according to the TSC command.

13. The power control method according to claim 12, further comprising: measuring the channel gain between said transmitting node and said receiving node; adjusting the transmission power of said transmitting node according to the channel gain.

14. A mobile terminal, comprising: a receiving unit, for receiving a radio signal sent from another mobile terminal; a predicting unit, for predicting an inter-link interference power upon the mobile terminal according to the received radio signal; a transmitting unit, for sending a power control message to said another mobile terminal such that said another mobile terminal can adjust its transmit power according to the predicted inter-link interference power included in the power control message.

15. The mobile terminal according to claim 14, wherein the inter-link interference power is a total sum of the interference power produced by the transmit power of other communicating mobile terminals except said another mobile terminal upon said mobile terminal.

16. The mobile terminal according to claim 15, wherein said predicting unit processes said radio signal with Kalman filter to get the predicted inter-link interference power.

17. A mobile terminal, comprising: a receiving unit, for receiving a power control message from another mobile terminal; an extracting unit, for extracting a predicted inter-link interference power upon said another mobile terminal from the power control message; adjusting the transmission power of the mobile terminal according to the predicted inter-link interference power.

18. The mobile terminal according to claim 17, wherein the inter-link interference power is a total sum of the interference power produced by the transmit power of other communicating mobile terminals except said mobile terminal upon said another mobile terminal.