Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/22—TPC being performed according to specific parameters taking into account previous information or commands
  • H04W52/223—TPC being performed according to specific parameters taking into account previous information or commands predicting future states of the transmission
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/22—TPC being performed according to specific parameters taking into account previous information or commands

Definitions

• 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.
• wireless communication networks are playing an increasingly important role in our daily life, thanks to providing growingly rich and fast information service.
• wireless communication networks 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.
• 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.
• BS base station
• AP Access Point
• mobile terminals 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.
• 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.
• PAN Personal Area Network
• 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”.
• 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.
• CDMA-based Ad hoc wireless communication networks 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.
• 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).
• 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
• 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.
• 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.
• 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.
• the power control method in the present invention by exemplifying the Ad hoc wireless communication network in TDD mode as shown in Fig.1.
• 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.
• 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 ⁇ 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 signal sent by the transmitting node j.
• argc ' ,J is set by radio resource management layer and can be adjusted according to the quality of SIR r the communication link.
• BER Bit Error Rate
• the transmission power of the transmitting node j can be computed according to equation (2) and equation (3).
• 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.
• 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) .
• W(t) in equation (5) is a zero mean Gaussian white noise sequence, with
• the Kalman filter equations can be expressed as:
• ⁇ nter ( and T ⁇ nter (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.
• 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 ⁇ w 2 (t - ⁇ ) .
• the estimated ⁇ 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 ( .
• equation (11 ) yields ( in dBm.
• I mter (t) After 7 ⁇ nt ⁇ r ( 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.
• the unique burst and self-similarity of data traffic can help a receiving node to predict the inter-link interference power, or namely ⁇ mter (t) in the above equation (4).
• 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.
• 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 ⁇ nt ⁇ r ( (step SI O).
• 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 I ⁇ T&el ⁇ according to the following rule (step S20): _ , resort (' - 1) - ⁇ if BER est ⁇ BER req SIR>arse " j it) ⁇ [Sm ⁇ areel lJ (t - ⁇ ) + A if BER est > BER req where ⁇ 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):
• TSC Target SIR Control
• 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).
• 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 SIRlinger gel j (t - l) - A if TSC is "down” ⁇ / arger y C - S *, arge , , (' - l) + ⁇ if TSC is "up"
• 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 ta ⁇ get ⁇ (t) and predicted channel gain r ⁇ , and then adjusts its transmission power (step S90).
• the inter-link interference power l ⁇ nter (t) therein is predicted by using Kalman filter.
• 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.
• transmitting unit 40 in mobile terminal 10 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.
• the extracting unit 50 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.
• 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.
• 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.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

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• 2004
  • 2004-05-11 CN CNA2004100431102A patent/CN1697342A/zh active Pending
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  • 2005-04-28 EP EP05738335A patent/EP1751881A1/en not_active Withdrawn
  • 2005-04-28 WO PCT/IB2005/051387 patent/WO2005109673A1/en not_active Application Discontinuation
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