DE10147951A1 - Signalisation method for adaptive coding and modulation in data network uses calibration phase for determination of bit-loading table for adaption of initial modulation - Google Patents

Abstract

The signalisation method uses a limited duration calibration phase effected simultaneous with transmission using an initial modulation, for determination of a bit-loading table at the receiver, with transmission of the bit-loading table to the transmitter at the end of the calibration phase and use of the bit-loading table for coding and modulation of the useful data to be transmitted via a second modulation mode.

Description

The invention relates to a signaling method for a adaptive modulation in a data network according to claim 1.

When using adaptive modulation on a multi Carrier communication system in a data network, especially a computer network, both modulation and also the coding per subcarrier and thus the Data transfer rate per subcarrier depending on the quality of the channel used for transmission. This is it required that a transmitter either be aware of the Quality of the transmission channel or alternatively knowledge of the pro Subcarrier to be transmitted data volume / data rate. This is usually done by having a receiver use the channel missed and the measurement result to the transmitter in the form of notifies possible data transfer rate or usable data rate. This measurement result is also called a bit loading pattern designated. The transmitter can then do that per subcarrier encode and modulate the amount of data transferred accordingly.

In the receiver for radio signals there is a bit loading pattern especially when evaluating the reception field strength (RSSI: Radio Signal Strength Indication), the signal-to-noise ratio a received radio signal and the interference ratio of the radio signal. The calculation result is then transmitted to the transmitter of the radio signals. In TDD Transmission systems (Time Division Duplex) and in FDD Transmission systems (Frequency Division Duplex) is the Transmission channel as stationary for a certain period of time considered (so-called Wide Sense Stationary Channel), so that the determined bit loading pattern for this period as can be validly accepted.

Such a TDD transmission system is, for example wireless LAN standard HIPERLAN / 2 (hereinafter referred to as H / 2 by the ETSI as part of the BRAN project has been standardized. H / 2 enables construction faster wireless LANs with a typical data rate of 27 Mbit / s. In an H / 2 network, a distinction is made between Mobile stations (MTs for short: Mobile Terminals) and access points (APs for short: Access Points).

• 1. Beim Centralised Mode (cm) sind die APs an ein Festnetz, beispielsweise ein Ethernet, angeschlossen. MTs melden sich bei einem AP an und kommunizieren über diesen AP, d. h. alle von oder zu dem MT übertragenen Nutzdaten laufen über den AP. In der Regel kommunizieren MTs nicht direkt miteinander, außer ein MT agiert als AP.
• 2. Dagegen können im optionalen Direct Link Mode (DiL) MTs auch direkt miteinander kommunizieren, also Nutzdaten miteinander austauschen. Ein Central Controller (CC) überwacht und verwaltet den Datenaustausch zwischen MTs. Sowohl CC als auch MT können an das Festnetz angeschlossen sein.

H / 2 enables two different operating modes:

• 1. In centralized mode (cm), the APs are connected to a fixed network, for example an Ethernet. MTs register with an AP and communicate via this AP, ie all user data transmitted from or to the MT run via the AP. Typically, MTs do not communicate directly with each other unless an MT acts as an AP.
• 2. On the other hand, in the optional Direct Link Mode (DiL) MTs can also communicate directly with one another, i.e. exchange user data with one another. A central controller (CC) monitors and manages the data exchange between MTs. Both CC and MT can be connected to the fixed network.

At H / 2 the physical transmission channel is in frames divided the same amount of time. These frames are called MAC Frames (Medium Access Control) referred to as the division in the MAC sublayer of the H / 2 service model. The MAC sublayer is a functional unit of the Data link control (DLC) data link layer. It provides functions Access control to the physical transmission medium Available. The MAC sublayer protocol is a master-slave protocol since an AP has an MT capacity assigns the MT for the transmission of user and control data can use.

H / 2 uses Orthogonal Frequency to transmit the data Division Multiplexing (OFDM). This takes place in the Physical layer of the H / 2 service model, called the PHY layer referred to as. OFDM is a multi-carrier process and uses different frequency carriers simultaneously - in the following also called subcarrier - for data transmission that different can be modulated. This results in depending on the modulation method used different Data rates. Currently there are modulation methods in the H / 2 standard BPSK (Binary Phase Shift Keying), QPSK (Quaternary Phase Shift Keying), 16 QAM (16 point quadrature Amplitude Modulation) and 64 QAM (64 point QAM).

The maximum possible data rate of a transmission channel to be able to use with the help of adaptive modulation Establishing a connection between a transmitter and a receiver in a multi-carrier based wireless LAN Network performed a calibration. During the phase the calibration, the transmission channel is measured and a Bit loading pattern calculated by the receiver, which to the Transmitter is transmitted. The transmitter then selects based on the bit Loading patterns of one of the above Modulation method. However, during the calibration phase no user data are currently being transmitted. This leads to the Data transmission at a delay in the time when data transfer can begin. With an H / 2 network where with the help of adaptive modulation an optimal Exploitation of the transmission channel would be achieved the resulting delay at least the duration of a MAC frame.

The object of the present invention is a Signaling method for adaptive modulation in a multi Propose carrier-based data network, in which essentially no delay in data transmission when Establishing a connection between a transmitter and a receiver occurs.

This task is accomplished through a signaling process for an adaptive modulation in a data network with the Features solved according to claim 1. Preferred embodiments of the Procedures result from the dependent claims.

The idea underlying the invention is that during a calibration phase to adjust the Modulation and coding per subcarrier already includes user data with one predetermined coding and modulation coded and modulated and transmitted over the channel to be measured. According to the first data transmission and the Calibration takes place essentially simultaneously, so hardly Data transmission delays when establishing a connection occur. In this way, for example, in an H / 2- Network faster access to network data enables, such as packet data such as the Internet Protocol.

• - Nutzdaten zwischen einem Sender und einem Empfänger des Datennetzwerks mit einem ersten vorgegebenen Codierungs- und Modulationsverfahren codiert und moduliert und über einen Übertragungskanal zwischen Sender und Empfänger übertragen werden, wobei
• - etwa gleichzeitig zur Übertragung eine zeitlich begrenzte Kalibrierungsphase durchgeführt wird, in welcher eine Bit- Loading-Tabelle, und damit implizit auch die Datenübertragungsrate pro Subträger, vom Empfänger ermittelt wird, und
• - nach Abschluss der Kalibrierungsphase die ermittelte Bit- Loading-Tabelle an den Sender übertragen wird, der entsprechend der ermittelten Bit-Loading-Tabelle zu übertragende Nutzdaten mit einem zweiten, adaptiven Codierungs- und Modulationsverfahren codiert und moduliert.

Specifically, the invention relates to a signaling method for adaptive modulation and coding in a data network, in which

• - User data between a transmitter and a receiver of the data network are encoded and modulated with a first predetermined coding and modulation method and transmitted over a transmission channel between the transmitter and receiver, wherein
• - A time-limited calibration phase is carried out approximately simultaneously with the transmission, in which a bit loading table, and thus implicitly also the data transmission rate per subcarrier, is determined by the receiver, and
• - After completion of the calibration phase, the determined bit loading table is transmitted to the transmitter, which codes and modulates the user data to be transmitted in accordance with the determined bit loading table using a second, adaptive coding and modulation method.

The calibration phase can take place when establishing a connection between sender and receiver or continuously during a Connection between transmitter and receiver can be carried out.

A modulation method is preferably used Multi-carrier method, in particular OFDM, used.

In addition, the user data are preferably packet-oriented transmit the transmission channel.

In a currently preferred embodiment of the method the bit determined during the calibration phase Loading table via a signaling channel from the receiver transmitted to the transmitter.

The inventive method is preferably in one wireless LAN used, in particular on the HIPERLAN / 2 standard based. Because HIPERLAN / 2 data networks Using OFDM as a modulation method can here Invention can be applied particularly advantageously. Furthermore the same procedure is also based on an FDD Multi-carrier system advantageously applicable.

When used in a HIPERLAN / 2 data network preferably in a first MAC frame the calibration phase and the transmission of the determined bit loading table from Receiver to transmitter instead; in second, subsequent MAC The user data with the adaptive coding and Modulation method coded and modulated. The Calibration phase can mainly be periodically specified in fixed Distances according to a predetermined number of MAC frames be repeated.

Furthermore, the bit loading table can be in at least one short Transport channel of a MAC frame are transmitted.

To get the information about the bit loading table or the adaptive coding and modulation in a short transport The 48th OFDM carrier frequencies with HIPERLAN / 2 to 16 clusters, each with three different carrier frequencies are combined; Per The adaptive modulation is then clustered using 3 bits coded. This results in a total of 48 bits for the information to be transmitted via the Data transfer rate, more precisely the modulation to be used for the carrier frequencies.

The method according to the invention is described below using the example of H / 2, especially for different operating modes of H / 2 explained in connection with the drawings. The painting show in

FIG. 1A, the basic signaling at a H / 2 in the DiL mode;

FIG. 1B, the division of a MAC frame in the DiL mode;

Fig. 1C the timing of the signaling in the DIP mode according to Fig. 1A,

Fig. 2A shows the basic signaling at a H / 2 in CM mode;

FIG. 2B is the division of a MAC frame in CM mode;

Fig. 2C shows the timing of the signaling in cm- mode of FIG. 2A,

Figure 3 shows a sequence of three MAC frames in CM mode with an inventive signaling channel LCCH AM for AM.

Figure 4 shows a sequence of three MAC frames in DiL mode with an inventive signaling channel LCCH AM for AM.

Figure 5 illustrates the signaling according to the invention for adaptive modulation in the continuous operation m example of a MAC frame.

Fig. 6 is a table of possible bit combinations for the SCH field; and

Fig. 7 is a table showing the contents of the bit-loading information for AM in a forward and reverse SCH;

It is particularly noteworthy that this Invention not only on centrally controlled access methods such as z. B. applied the master-slave based access method can also be organized on a decentralized basis Access procedures such as B. the CSMA / CA / CD (Carrier Sense Multiple Access / Collision Avoidance / Collision Detection) Access method.

The abbreviations used below preferably in connection with H / 2 are explained in a list of abbreviations at the end of the description. In the introduction, the mapping of logical channels in H / 2 to the transport channels is briefly explained (logical links on the right, transport channels on the right):
1. Downlink direction:
BCCH - BCH
FCCH - FCH
RFCH - ACH
LCCH - SCH
RBCH - SCH, LCH
DCCH - SCH, LCH
UDCH - LCH
UBCH - LCH
UMCH - LCH
2. Uplink direction:
UDCH - LCH
DCCH - SCH, RCH
LCCH - SCH, RCH
ASCH - RCH
3.DIL mode:
UDCH - LCH
UBCH - LCH
UMCH - LCH
DCCH - LCH, SCH
RBCH - LCH, SCH
LCCH - SCH

The transport channels BCH, FCH, ACH, LCH, SCH and RCH are the basic construction elements of PDU sequences.

FIG. 1A shows the signaling sequence based on the channels used for PDUs of a MAC frame transmitted in an H / 2 data network which is operated in DiL mode. Two mobile stations MT1 and MT2, for example computers with wireless LAN adapters, communicate under the "supervision" of a central computer which acts as a CC and is also designated.

The signaling process when setting the adaptive Coding and modulation is briefly explained below: The Mobile station MT1 calls in the uplink direction Central computer CC with an RR message via the channel DCCH Transmission capacity. The central computer CC then shares the Mobile stations MT1 and MT2 via the channel FCCH using a RG message corresponding transmission capacity. The mobile station MT1 then begins in DiL mode via the Channel UDCH with a first, predetermined modulation with the Mobile station MT2 to communicate. Both mobile stations MT1 and MT2 swap in DiL mode via the LCCH channel Information from if necessary. Finally, the Mobile station MT2 for adaptive coding and modulation, more specifically, channel AM provided for signaling it LCCH the mobile station MT1 the coding to be used and Modulation using a bit loading table so that the in the user data contained in the following MAC frames can be encoded and modulated.

Fig. 1B shows the division of a MAC frame in DiL mode with the channel AM LCCH for setting the adaptive coding and modulation.

FIG. 1C shows the time sequence of a connection establishment of the direct link mode according to FIG. 1A initiated by MT1 in detail.

The main signaling sequences are for the DIL and CM mode the same as with reference to FIG. 2A and FIG. 2C can be reproduced. Here, FIG 2B. The structure of a MAC frame. The receiver starts with an RR message to the central computer, which works either as an AP in CM mode or as a CC in DiL mode. The central computer usually replies with an RG message via the FCCH channel. This message also receives the second mobile station MT2 operating as a transmitter in DiL mode. In both modes, the signaling sequence for setting the adaptive coding and modulation is almost the same. The receiver first sends the first sequence of LCH PDUs with a predetermined, fixed coding and modulation, which corresponds, for example, to the average data rate to be transmitted. On the basis of the reception quality of the first sequence of LCH PDUs, the receiver, that is to say the central computer CC or the receiving mobile station, calculates the bit loading table and sends the corresponding data transmission rate in the AM LCCH channel to the transmitter in the next MAC frame.

It should be separately noted that in the direct link mode according 1C MT1 the transmitter and MT2 of the receiver, while in the cm fashion shown in Fig. 2A, Fig. 2B and Fig. 1A, Fig. 1B and Fig.. 2C MT2 the transmitter and MT1 / CC the receiver are in accordance with the language used above.

At this point it should be noted that sender and receiver can either be a mobile station MT or an AP / CC. In the terminology used here is the recipient Establishment that the desired bit loading pattern or desired data transfer rate calculated and the calculated Transmits the result to the sender. Accordingly, the Transmitter the device which the the calculated bit Loading pattern or the one calculated per subcarrier Data transfer rate used for subsequent transfers. Among the subsequent transfers will be a period of consecutive understood the following MAC frames, for which the calculated Bit loading pattern or the calculated data transfer rate is the same if no other bit loading pattern or none different data transfer rate to the transmitter from the receiver is signaled.

Fig. 3, the signaling method is to adjust the adaptive modulation for the CM-mode wherein MT1 in the downlink of the first MAC frame yet no valid bit loading pattern has available and thus used for the transmission to be transmitted user data determined modulation. In the structure of three successive MAC frames 1, 2 and 3 shown, the channel AM LCCH is transmitted first in the UL direction. Consequently, the calculated bit loading pattern or the calculated data transmission rate is received with the sequence of LCH PDUs. Depending on the computing power available for calculating the bit loading pattern or the data transmission rate, the first channel AM LCCH can be sent in the first or second MAC frame. Both are possible, however the channel AM LCCH should be sent in the UL and DL direction with the second MAC frame.

Based on a slightly different connection setup in DiL mode according to FIG. 4, the first MAC frame is also used here for the transmission of user data via the channel UDCH. More specifically, a first sequence of LCH-PDUs with a given QAM is transmitted on all carrier frequencies. On the basis of the reception of this sequence of LCH PDUs, the receiver is able to calculate the bit loading pattern or the data transfer rate per subcarrier and to transmit it or it to the transmitter in the same or following MAC frame.

The dashed lines in FIGS. 3 and 4 indicate that the bit loading pattern or the data transmission rate can sometimes still be transmitted in the same MAC frame when the AM LCCH message is received. For example, this is the case if the shortest maximum calculation delay in the devices used is approximately 40 μs. However, this is not recommended in cases where the computing power of the facilities reaches its limits. It should also be noted that there is no UL and DL direction in the AM LCCH channel in DiL mode; the same AM LCCH messages in the FL and RL directions are used for this.

H / 2 uses 48 carriers (frequencies) to transmit Payload. Each carrier can use eight different ones Modulation method, each consisting of a coding and a Modulation. A total of 48 would be Carrier and 8 possible modulation methods 144 bits each required to signal the adaptive modulation. With a cluster size of 3, however, the 144 bits can 48 bits can be reduced. These 48 bits can be a SCH over which 52 bits can be transmitted.

In Fig. 5 it is shown that a transmitted bit-loading pattern for all other p MAC frames from the n-th MAC frame are valid. User data is sent in the nth MAC frame, for example with the first sequence of LCHs including a UDCH with a first, predetermined modulation. This first, predetermined modulation can have a low data transmission rate in order to be insensitive to channel interference. In a second step, the desired bit rate per subcarrier for data transmission or data transmission rate for AM is communicated via an LCCH (UL / DL / DiL) specially provided for AM. This is still done in the nth MAC frame. The bit rate communicated via the AM LCCH or the corresponding coding and modulation table is used in the subsequent MAC frame n + 1.

The bit combinations for the SCH field are shown in the table shown in FIG . In particular with the new bit combination 1010 in the penultimate table line, the possibility of adaptive coding and modulation according to the invention is introduced. In addition, the reserved bit combinations 1011-1111 can be used in the sense of the invention, for example for further refinements when setting the adaptive modulation. In CM mode, the terms forward link correspond to the downlink and reverse link to the uplink. In DiL mode, the mobile station initiating the connection should send the AM bit load SCH in forward link and receive the AM bit load SCH in reverse link.

So that the signaling according to the invention can be easily implemented in the currently available H / 2 standard, at least one channel SCH should be sufficient for the transmission of the information about the adaptive modulation to be used during the calibration phase. The information fits into exactly one SCH channel if the 48 carrier frequencies are divided into 16 clusters, for example. Each cluster then contains three different carrier frequencies. For the adaptive coding and modulation, the modulation to be used is now coded using 3 bits per cluster. This results in a total of 48 bits for the modulation of all clusters. A SCH channel comprises 52 bits and can therefore carry the information of 48 bits. In addition, there is only minimal overhead compared to the current H / 2 standard. Fig. 7 shows a table with the contents of the at least information to be transmitted in a Forward / downlink and a reverse / uplink SCH channel. Abbreviations ACH Access Feedback Channel
AM Adaptive Modulation
AP access point
ASCH Association Control Channel
BCCH Broadcast Control Channel
BCH broadcast channel
BPSK Binary Phase Shift Keying
BRAN Broadband Radio Access Network
CA / CD Collision Avoidance / Collision Detection
CC Central Controller
cm Centralized Mode
CSMA Carrier Sense Multiple Access
DCCH Dedicated Control Channel
DiL Direct Link Mode
DL downlink
DLC Data Link Control
FL forward link
ETSI European Telecommunications Standard Institute
FCCH Frame Control Channel
FCH Frame Channel
FDD Frequency Division Duplex
H / 2 High Performance Radio Local Area Network 2
LAN Local Area Network
LCCH Link Control Channel
LCH Long Transport Channel
MAC Medium Access Control
MT Mobile Terminal
OFDM Orthogonal Frequency Division Multiplexing
PDU Protocol Data Unit
PHY physical layer
QAM Quadrature Amplitude Modulation
QPSK Quaternary Phase Shift Keying
RACH Random Access Feedback Channel
RBCH RLC broadcast channel
RCH Random Channel
RFCH Random Access Feedback Channel
RG Resource Grant
RL reverse link
RLC Radio Link Control
RR Resource Request
RSSI Radio Signal Strength Indication
SCH Short Transport Channel
TDD Time Division Duplex
UBCH User Broadcast Channel
UDCH User Data Channel
UL uplink
UMCH User Multicast Channel

Claims (13)

1. Signaling method for adaptive coding and modulation in a data network, in which
User data between a transmitter and a receiver of the data network are coded and modulated with a first, predetermined modulation method, consisting of coding and modulation, and are transmitted via a transmission channel between the transmitter and receiver, wherein
a time-limited calibration phase is carried out approximately simultaneously with the transmission, in which a bit loading table is determined by the receiver, and
after completion of the calibration phase, the determined bit loading table is transmitted to the transmitter, which, in accordance with the determined bit loading table, codes and modulates the useful data to be transmitted using a second, adaptive modulation method, consisting of coding and modulation, before transmission. 2. Signaling method according to claim 1, characterized characterized that the calibration phase at Establishing a connection between transmitter and receiver is carried out. 3. Signaling method according to claim 1, characterized characterized that the calibration phase continuously during a connection between transmitter and receiver is carried out. 4. Signaling method according to one of claims 1-3, characterized in that the Modulation method on a multi-carrier system, in particular OFDM, is applied. 5. Signaling method according to one of the preceding Claims, characterized in that the Packet-oriented user data via the transmission channel be transmitted. 6. Signaling method according to one of the preceding Claims, characterized in that the Data transfer rate determined during the calibration phase via a signaling channel from the receiver to the transmitter is transmitted. 7. Signaling method according to one of the preceding Claims, characterized in that it is in a wireless LAN that is used in particular on the HIPERLAN / 2 and / or the IEEE802.11a and / or the IEEE802.11b standard based. 8. Signaling method according to claim 7, characterized characterized in that in a first MAC frame Calibration phase and the transmission of the determined bit Loading table from receiver to sender takes place and in second, subsequent MAC frames the user data with the adaptive coding and modulation coded and modulated become. 9. Signaling method according to claim 8, characterized characterized that the calibration phase periodically at predetermined intervals according to a predetermined Number of MAC frames is repeated. 10. Signaling method according to one of claims 7-9, characterized in that the Data transfer rate in at least one short transport channel MAC frames is transmitted. 11. Signaling method according to claim 10, characterized marked that for the user data transmission used OFDM carrier frequencies to clusters with the same many carrier frequencies are combined and per cluster the same adaptive coding and modulation applied becomes. 12. Signaling method according to one of the preceding Claims characterized in that they are based on a frequency Division duplex and / or a time division duplex system be applied. 13. Signaling method according to one of the preceding Claims characterized in that they are either based on centrally coordinated access procedures, especially master Slave-based access procedures, or on a decentralized basis organized access procedures, especially CSMA based Access method, or applied to a combination become.