EP1362450A1

EP1362450A1 - Network with adaptation of the modulation method

Info

Publication number: EP1362450A1
Application number: EP02710264A
Authority: EP
Inventors: Joerg Habetha
Original assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips Electronics NV
Current assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips NV
Priority date: 2001-02-16
Filing date: 2002-02-13
Publication date: 2003-11-19
Also published as: WO2002067492A1; US20030125066A1; US7171169B2; CN1328870C; KR20030029524A; CN1461541A; JP2009027737A; KR100913932B1; DE10107850A1; JP2004519894A

Abstract

In a first step, a transmitting terminal selects a modulation method at the beginning of data transmission in a network consisting of several terminals. The selection is based on the estimated user receive signal/noise power ratio (C/)I, wherein a maximum admissible packet error rate (PER) is not exceeded. In a second step, the transmitting terminal determines the transmitting power required for the desired packet error rate for the modulation method selected in the first step..

Description

Network with an adjustment of the modulation process

The invention relates to a network with several terminals that exchange messages via a wireless medium. Such a network can be an ad hoc network that is self-organizing and can consist of several subnetworks, for example.

From the document “J. Habetha, A. Hettich, J. Peetz, Y. Du: Central Controller Handover Procedure for ETSI-BRAN HIPERLAN / 2 Ad Hoc Networks and Clustering with Quality of Service Gurantees, l ^st IEEE Annual Workshop on Mobile Ad Hoc Networking & Computing,, Aug. 11, 2000 "an ad hoc network with several terminals is known. At least one terminal is provided as a controller for controlling the ad hoc network. With such a network it is desirable that the energy consumption of the terminals is as low as possible.

The object of the invention is therefore to create a network in which the energy consumption of the terminals is reduced.

The task is solved by a network of the type mentioned at the beginning by the following measures:

The network contains several terminals, each as a sending terminal at the start of a data transfer

- In a first step, a modulation method is provided, in which the maximum packet error rate for an estimated received signal-to-noise power ratio is not reached or the maximum packet delay is not reached or the maximum data throughput is achieved, and - in a second step to determine the transmission power are provided which result for a desired packet error rate or packet delay for the modulation method selected in the first step.

The invention can be used in various mobile radio systems, such as UMTS (Universal Mobile Telecommunications System), HIPERL AN / 2, Bluetooth etc. become. The invention is particularly suitable for ad hoc networks in which communication can take place over several radio sections. The ad hoc networks can either be completely decentralized or divided into sub-networks. Not only are the terminals mobile within the sub-networks, but also a terminal working as a central controller (function of a base station). As a result, when a terminal is set up, a modulation method is selected in a first step, in which the maximum packet error rate is undercut for an estimated useful reception signal-to-noise power ratio, and then in a second step the transmission power is determined which is suitable for a desired packet error rate results in a quasi-optimum for the transmission power for the modulation method selected in the first step. The maximum permitted packet error rate (minimum packet error rate) is chosen so that secure data transmission is guaranteed under the most unfavorable conditions. In contrast, the desired packet error rate (target packet error rate) depends on the type of data to be transmitted (voice, file download, Internet data, etc.). In this way, quasi-optimized energy consumption for the terminal can be achieved. The desired packet error rate can be smaller or larger than the maximum allowed packet error rate.

The desired packet error rate also depends on the service requirements for tolerable transmission delay. This is due to the fact that, when using an automatic repeat request (ARQ) error protection protocol, a higher packet error rate results in more frequent retransmissions and thus a longer packet transmission time or delay. Therefore, instead of the packet error rate, the packet delay can also be a criterion. It is also possible to use data throughput as a criterion.

A sending terminal is provided to determine the estimated received signal-to-noise ratio as the maximum transmit power minus estimated path losses between a sending terminal and a receiving terminal and a parameter. The determination of the path losses specifies claim 3 and the initial value of the parameter claim 4.

In order to determine the transmission power in the second step, curve values for a packet error rate as a function of the useful signal-to-noise power ratio are stored in a terminal for various modulation methods. Claim 6 specifies the measures which have to be carried out in the case of changed reception conditions. Claim 7 describes how adaptively the parameter and the desired packet error rate are adjusted.

The invention also relates to a terminal in such a network.

Exemplary embodiments of the invention are explained in more detail below with reference to the figures. Show it:

1 shows an ad hoc network with three sub-networks, each of which contains terminals provided for radio transmission,

2 shows a terminal of the local network according to FIG. 1,

3 shows a radio device of the terminal according to FIG. 2, FIG. 4 shows an embodiment of a bridge terminal provided for connecting two sub-networks,

Fig. 5 MAC frame of two sub-networks and the MAC frame structure of a bridge terminal and

6 shows a diagram with various curve profiles associated with specific modulation methods, which represent a packet error rate as a function of the useful received signal-to-noise power ratio.

The exemplary embodiment shown below relates to ad hoc networks which, in contrast to traditional networks, are self-organizing. Each terminal in such an ad hoc network can provide access to a fixed network and can be used immediately. An ad hoc network is characterized by the fact that the structure and the number of participants are not specified within the specified limit values. For example, a participant's communication device can be removed from the network or integrated. In contrast to traditional mobile radio networks, an ad hoc network does not depend on a permanently installed infrastructure.

The area of the ad hoc network is usually much larger than the transmission area of a terminal. Communication between two Terminals may therefore require additional terminals to be switched on so that they can transmit messages or data between the two communicating terminals. Such ad hoc networks, in which a forwarding of messages and data via a terminal is necessary, are referred to as multihop ad hoc networks. A possible organization of an ad hoc network is to regularly form sub-networks or clusters. A sub-network of the ad hoc network can be formed, for example, by terminals connected via radio links by participants sitting around a table. Such terminals can be, for example, communication devices for the wireless exchange of documents, images, etc.

Two types of ad hoc networks can be specified. These are decentralized and centralized ad hoc networks. In a decentralized ad hoc network, the communication between the terminals is decentralized, ie each terminal can communicate directly with any other terminal, provided that the terminals are in the transmission range of the other terminal. The advantage of a decentralized ad hoc network is its simplicity and robustness against errors. In a centralized ad hoc network, certain functions, such as the multiple access function of a terminal to the radio transmission medium (Medium Access Control = MAC) are controlled by a specific terminal per sub-network. This terminal is referred to as a central terminal or central controller (CC). These functions do not always have to be carried out by the same terminal, but can be transferred from one terminal working as a central controller to another terminal then acting as a central controller. The advantage of a central ad hoc network is that an agreement on the quality of service (QoS) is possible in a simple way. An example of a centralized ad hoc network is a network that is organized according to the HIPERLAN / 2 Home Environment Extension (HEE) (see J. Habetha, A. Hettich, J. Peetz, Y. Du, “Central Controller Handover Procedure for ETSI BRAN HIPERLAN / 2 Ad Hoc networks and clustering with Quality of service gurantees "l ^st Annual IEEE workshop on Mobile Ad Hoc Networking & computing, Aug. 11, 2000).

1 shows an exemplary embodiment of an ad hoc network with three subnetworks 1 to 3, each of which contains a plurality of terminals 4 to 16. The terminals 4 to 9 are part of the sub-network 1, the terminals 4 and 9 of the sub-network 2 10 to 12 and the sub-network 3, the terminals 5 and 13 to 16. In a sub-network, the terminals belonging to a sub-network exchange data via radio links. The ellipses shown in FIG. 1 indicate the radio range of a sub-network (1 to 3), in which largely problem-free radio transmission is possible between the terminals belonging to the sub-network.

Terminals 4 and 5 are called bridge terminals because they enable data exchange between two sub-networks 1 and 2 or 1 and 3. The bridge terminal 4 is responsible for the data traffic between the subnetworks 1 and 2 and the bridge terminal 5 for the data traffic between the subnetworks 1 and 3.

A terminal 4 to 16 of the local network according to FIG. 1 can be a mobile or fixed communication device and contains, for example, at least one station 17, a connection control device 18 and a radio device 19 with antenna 20, as shown in FIG. 2. A station 17 can be, for example, a portable computer, telephone, etc.

A radio device 19 of the terminals 6 to 16, as shown in FIG. 3, contains, in addition to the antenna 20, a radio-frequency circuit 21, a modem 22 and a protocol device 23. The protocol device 23 forms from that of the

Connection control device 18 received data stream packet units. A packet unit contains parts of the data stream and additional control information formed by the protocol device 23. The protocol device uses protocols for the LLC layer (LLC = Logical Link Control) and the MAC layer (MAC = Medium Access Control). The MAC layer controls the multiple access of a terminal

Radio transmission medium and the LLC layer perform flow and error control.

As mentioned above, in a sub-network 1 to 3 of a centralized ad hoc network, a specific terminal is responsible for the control and management functions and is referred to as a central controller. The controller also works as a normal terminal in the associated sub-network. The controller is used, for example, for registering terminals that start operating in the sub-network, for establishing a connection between at least two terminals in the radio transmission medium, for resource management and for access control in the radio transmission medium responsible. For example, a terminal of a sub-network is assigned transmission capacity for data (packet units) by the controller after registration and after registration of a transmission request.

In the ad hoc network, the data can be exchanged between the terminals using a TDMA, FDMA or CDMA method (TDMA = Time Division Multiplex Access, FDMA = Frequency Division Multiplex Access, CDMA = Code Division Multiplex Access). The methods can also be combined. Each sub-network 1 to 3 of the local network is assigned a number of specific channels, which are referred to as channel bundles. A channel is determined by a frequency range, a time range and, for example, in the CDMA method by a spreading code. For example, each sub-network 1 to 3 can have a specific, different frequency range with a carrier frequency fj available for data exchange. In such a frequency range, for example, data can be transmitted using the TDMA method. The sub-network 1 can be assigned the carrier frequency f _ls the sub-network 2 the carrier frequency f ₂ and the sub-network 3 the carrier frequency f ₃ . The bridge terminal 4 works on the one hand in order to be able to carry out a data exchange with the other terminals of the sub-network 1, with the carrier frequency fi and on the other hand in order to be able to carry out a data exchange with the other terminals of the sub-network 2, with the carrier frequency f ₂ . The second bridge terminal 5 contained in the local network, which transmits data between the subnetworks 1 and 3, works with the carrier frequencies ft and f ₃ .

As stated above, the central controller has, for example, the function of access control. That means that the central controller for the formation of

Frame of the MAC layer (MAC frame) is responsible. The TDMA method is used here. Such a MAC frame has different channels for control information and user data.

A block diagram of an exemplary embodiment of a bridge terminal is shown in FIG. 4. The radio switching device of this bridge terminal each contains a protocol device 24, a modem 25 and a radio-frequency circuit 26 with an antenna 27. A radio switching device 28 is connected to the protocol device 24, which is further connected to a connection control device 29 and a buffer memory device. direction 30 is connected. In this embodiment, the intermediate storage device 30 contains a storage element and serves for intermediate storage of data and is implemented as a FIFO module (First In First Out), ie the data are read from the intermediate storage device 30 in the order in which they were written. The terminal shown in Fig. 4 can also operate as a normal terminal. Stations connected to the connection control device 29, which are not shown in FIG. 4, then supply data to the radio switching device 28 via the connection control device 29.

The bridge terminal according to FIG. 4 is alternately synchronized with a first and a second sub-network. Synchronization means the entire process of integrating a terminal in the sub-network up to the exchange of data. If the bridge terminal is synchronized with the first sub-network, it can exchange data with all terminals and with the controller of this first sub-network. If data is supplied from the connection control device 29 to the radio switching device 28, the destination of which is a terminal or the controller of the first subnetwork or a terminal or controller of another subnetwork which can be reached via the first subnetwork, the switching device forwards this data directly to the protocol device 24. The data are temporarily stored in the protocol device 24 until the time period determined by the controller for the transmission has been reached. If the data output from the connection control device 29 is to be sent to a terminal or the controller of the second subnetwork or to another subnetwork to be reached via the second subnetwork, the radio transmission must be delayed until the period in which the bridge terminal is synchronized with the second sub-network. Therefore, the radio switching device forwards the data whose destination is in the second sub-network or whose destination can be reached via the second sub-network to the buffer device 30, which temporarily stores the data until the bridge terminal with the second sub-network is synchronized.

If data from a terminal or the controller of the first subnetwork is received by the bridge terminal and its destination is a terminal or the controller of the second subnetwork or a terminal or controller of another subnetwork to be reached via the second subnetwork, become this data is also stored in the buffer device 30 until synchronization with the second sub-network. Data, the destination of which is a station of the bridge terminal, are passed directly via the radio switching device 28 to the connection control device 29, which then routes the received data to the desired station. Data whose destination is neither a station of the bridge terminal nor a terminal or controller of the second sub-network is sent to another bridge terminal, for example.

After the synchronization change of the bridge terminal from the first to the second sub-network, those located in the intermediate storage device 30 become

Read data from the buffer device 30 again in the write order. Subsequently, during the duration of the synchronization of the bridge terminal with the second sub-network, all data whose destination is a terminal or the controller of the second sub-network or another sub-network to be reached via the second sub-network can be immediately removed from passed to the radio switching device 28 to the protocol device 24 and only the data, the destination of which is a terminal or the controller of the first subnetwork or another subnetwork to be reached via the first subnetwork, is stored in the buffer device 30.

The MAC frames of two sub-networks SN1 and SN2 are usually not synchronized. A bridge terminal BT is therefore not connected to a sub-network SN1 or SN2 not only during a switchover time Ts but also during a waiting time Tw. This can be seen from FIG. 5, which shows a sequence of MAC frames of the sub-networks SN1 and SN2 and the MAC frame structure of the bridge terminal BT. The switchover time Ts is the time required for the bridge terminal to synchronize with a sub-network. The waiting time Tw indicates the time between the end of synchronization with the subnetwork and the start of a new MAC frame for this subnetwork.

Assuming that the bridge terminal BT is only connected to a sub-network SN1 or SN2 for the duration of a MAC frame, the bridge terminal BT only has a channel capacity of 1/4 of the available channel capacity of a sub-network on. In the other extreme case, the BT bridge terminal for one is connected to a sub-network for a long time, the channel capacity is half the available channel capacity of a sub-network.

As described above, each sub-network contains a central controller for controlling the assigned sub-network. When commissioning a subnetwork, it must be ensured that only one terminal takes over the function of the central controller. It is assumed that not every terminal can take over the function of the central controller. To determine a central controller, for example, the procedure is such that each terminal that can assume a controller function checks whether there is another terminal in its reception area that can perform the controller function. If this is the case, the detecting terminal determines that it will not become a controller. If all other terminals also carry out these checks, a terminal remains at the end that does not detect any other terminal with a controller function and thus takes over the controller function. The signals to be transmitted in the network via radio links are previously modulated using a specific digital modulation method. Possible modulation methods are, for example, BPSK (binary phase sampling), QPSK (quaternary phase sampling), 16 QAM (16 quadrature amplitude modulation) and 64 QAM. The signals to be modulated are coded before the modulation, for example using a punctured convolutional code. Here, e.g. Code rates of 3/4 or 9/16 can be used.

When a connection is established between a sending terminal and one or more receiving terminals, a suitable modulation method and a suitable transmission power are determined adaptively according to the method described below, depending on the reception conditions.

At the beginning of a transmission (step 1), a modulation method is first defined or selected by a sending terminal. This is done by using stored curve values in a table (or memory) in the sending terminal (see FIG. 6), which shows the packet error rate (PER = packet error rate) as a function of the received signal-to-noise ratio (C / I). represent for different modulation methods, the modulation method is selected, which falls below a minimum packet error rate (maximum allowed packet error rate) of, for example, 0.01 at an estimated useful reception signal-to-noise power ratio C / I _es t. The useful The received signal-to-noise ratio C / I _est is previously estimated as the maximum transmission power T _x minus the estimated path losses L _p between a transmitting terminal and a receiving terminal and an adaptive parameter AMM (Adaptive Modulation Margin):

C / I _est = T _x - L _p - AMM

For the AMM parameter, an initial value to be determined (e.g. 0 dB) is assumed when establishing a connection. The path losses L _p are determined by the exchange of power control messages between the sending terminal and the receiving terminal (during the connection establishment). In this case, a modulation method known to both the sending and the receiving terminal and a specific channel intended for this are used. The power control messages are broadcast at maximum transmission power, which means that the path losses from the receiving terminal can be estimated on the basis of the received power.

For example, if the estimated useful reception signal-to-noise power ratio C / I _es t = 26.5 dB, then in the first step according to FIG. 6, which shows various exemplary curve values for selected modulation methods, the modulation method 16 QAM with a coding rate of 3/4 selected.

The necessary or optimal transmission power is then determined in a second step. Here, an initial value for a target packet error rate (desired packet error rate) PERo is first defined (cf. FIG. 6). In contrast to the fixed minimum packet error rate (or maximum allowed packet error rate), which is chosen so that secure data transmission is guaranteed under the most unfavorable conditions, the target packet error rate (or desired packet error rate) depends on the type of data to be transmitted (language, Download of a file, internet data etc.) dependent. Since the modulation method has already been defined in the previous step, the useful reception signal-to-noise power ratio C / I _re q required for the target packet error rate PERo is then read out on the basis of the curve values stored for this modulation method (see FIG. 6). The transmission power, which corresponds to this useful received signal-to-noise power ratio C / I _req at the target packet error rate PERo, is in the _hereinafter referred to as PPE _RO . The target packet error rate P _P ER _O results from the useful received signal-to-noise power ratio C / I _req using the relationship

PPER _O = C / I _req + L _p + AMM

The path losses L _{p were} estimated in the first step on the basis of the exchanged power control messages. The transmission of the data is now started with the transmission power P = min (P _ma , PPE _RÖ ). P _{max represents} the maximum permissible transmission power that is permitted by the authorities, for example.

In the example for the first step, the modulation _method 16 QAM with a coding rate of 3/4 was selected for the estimated useful received signal-to-noise power ratio C / I _eSt ⁼ 26.5 dB. The intersection of the curve of the modulation method 16 QAM with a coding rate of 3/4 with the target packet error rate PERo is at the useful reception signal-to-power ratio C / I _req = 23.5 dB. A transmission power reduction of 3 dB has thus been achieved in the second step compared to the first step.

During the ongoing connection, changes in path conditions or reception performance may occur due to changes in the reception conditions (obstacles, weather, other statistical influences, mobility of the terminals, etc.). In this case, the first and second steps are carried out again in a third step, the two parameters AMM and PERO not being reinitialized, but the previous values being retained. Alternatively, the third step can be used periodically.

The two parameters AMM and PER ₀ can also be changed adaptively in a further, fourth step. For this purpose, the parameters AMM and PERo are periodically adjusted on the basis of performance parameters of system operation. The following parameters can alternatively or in combination be used as performance parameters: "percentage of successful connection attempts", "reciprocal of the average packet error rate in the network", "reciprocal of the average packet delay in the network", "throughput of the overall system", "reciprocal of the number of connection drops ". This adjustment can be in the same or larger time intervals as the adjustment after the third step. The following regulation is used to change the two parameters AMM and PERo, where LKi denotes the value of a performance parameter in a specific time period (or period) tj with i = 0, 1, 2, ...:

The AMM parameter is first adjusted:

IF LKi> LKi-1 AND was increased at the end of tu AMM, THEN AMM is increased by 1 dB;

IF LKi> LKi-1 AND was lowered at the end of tu AMM,

THEN AMM is lowered by 1 dB;

IF LKi <LKi-1 AND was increased at the end of tu AMM,

THEN AMM is lowered by 1 dB; IF LKi <LKi- 1 AND was increased at the end of tu AMM,

THEN AMM is increased by 1 dB.

The parameter PER _{0 is} then adjusted (based on the performance parameter "average packet error rate in the overall network" PER _av, for example):

IF PER _av , i <PER _aVj i-ι,

THEN PER ₀ is divided by 0.9;

IF PER _av , i> PERav,! -!

Then PER _{0 is} multiplied by 0.9.

Instead of the simple regulation described, it is also possible to use regulations of a higher order or regulation techniques, such as Kaiman filters or fuzzy regulators.

In the example above, the regulation is carried out in such a way that both parameters are reset independently of one another. However, dependent regulations are also conceivable. This means that the AMM parameter and then the PERo parameter are not set first, but rather that the AMM parameter and then the PERo parameter are increased together. As an alternative to the packet error rate PER, the stored curve values can also represent the dependence of the average packet delay or the throughput on the useful signal-to-noise ratio (C / I). The use of packet delay is described first, followed by the use of throughput.

When using the average packet delay, the modulation method is selected as a function of the useful received signal-to-noise ratio (C / I) for various modulation methods, which is less than a fixed minimum delay for an estimated useful received signal-to-noise ratio C / I _est . The estimated useful reception signal-to-noise power ratio C / I _est is determined as described above, the AMM parameter also being used.

Then, in a second step, the necessary or optimal

Transmission power determined. Here, an initial value for an average target delay (desired packet delay) To is first determined, which depends on the type of data to be transmitted (language, downloading a file, Internet data, etc.). Since the modulation method was already defined in the previous step, the useful received signal-to-power ratio C / r _req required for the target delay To is then read out on the basis of the curve values stored for this modulation method.

The two parameters AMM and T ₀ are optimized based on performance parameters during network operation, as when using the packet error rate PER. The adaptation of the AMM parameter is identical to the procedure described above. The parameter T _{0 is} then adjusted (based on the performance parameter “average packet delay in the overall network” T _av, for example):

IF T _{aV; i} <Tav.i-1,

THEN T ₀ is divided by 0.9;

THEN T _{0 is} multiplied by 0.9. Any performance parameters can be used for this process (for example, the average packet error rate in the overall network can be selected for the adjustment of the To parameter as before for the adjustment of the PERo parameter).

When using the throughput instead of the packet error rate, the modulation method is selected as a function of the useful received signal-to-noise power ratio (C / I) for different modulation methods, which delivers the maximum throughput at an estimated useful received signal-to-noise power ratio C / I _es t. The estimated useful reception signal-to-noise power ratio C / I _es t is determined as described above, the parameter AMM also being used.

The necessary or optimal transmission power is then determined in a second step. The optimal transmission power with a fixed modulation method is determined using one of the two methods described above either on the basis of the packet error rate (and the PERo parameter) or on the basis of the average packet delay (and the To parameter).

As previously described, the parameters AMM and PERo or To are optimized during operation of the network on the basis of performance parameters.

Claims

CLAIMS:

1. Network with multiple terminals, each as a sending terminal

Start of a data transfer

are provided in a first step for the selection of a modulation method in which, for an estimated useful reception signal-to-power ratio, the maximum packet error rate is not reached or the packet delay is less than the maximum allowable packet delay or the maximum data throughput is achieved, and

are provided in a second step for determining the transmission power which results for a desired packet error rate or packet delay for the modulation method selected in the first step.

2. Network according to claim 1, characterized in that a transmitting terminal for determining the estimated useful signal-to-noise ratio is provided as the maximum transmission power minus estimated path losses between a transmitting terminal and a receiving terminal and a parameter.

3. Network according to claim 2, characterized in that a sending terminal is provided for exchanging power control messages with a receiving terminal and for determining the path losses on the basis of the power control messages returned by the receiving terminal.

4. Network according to claim 2, characterized in that a terminal sets the parameter to zero when establishing a connection.

5. Network according to claim 1, characterized in that a terminal contains stored curve values for different modulation methods for a packet error rate, a packet delay or a data throughput depending on the useful signal-to-noise ratio.

6. Network according to claim 1, characterized in that a transmitting terminal is provided either due to changed reception conditions or periodically again to perform the first and second steps to determine a modulation method and a transmission power.

7. Network according to claim 2, characterized in that a transmitting terminal for adapting the parameter and the desired packet error rate or packet delay is provided on the basis of performance variables at certain intervals.

8. Terminal in a network with several other terminals that act as a sending terminal at the start of a data transfer

are provided in a first step for the selection of a modulation method in which, for an estimated useful received signal-to-noise power ratio, the maximum packet error rate is not reached or the packet delay is less than the maximum allowable packet delay or the maximum data throughput is achieved, and