WO2005096562A1

WO2005096562A1 - Method for transmitting signals in a radio communications system

Info

Publication number: WO2005096562A1
Application number: PCT/EP2005/050959
Authority: WO
Inventors: Rüdiger Halfmann; Matthias Lott; Michael Meincke; Maria Dolores PÉREZ GUIRAO; Egon Schulz
Original assignee: Siemens Aktiengesellschaft
Priority date: 2004-03-23
Filing date: 2005-03-03
Publication date: 2005-10-13
Also published as: DE102004014191A1

Abstract

The invention relates to a method for transmitting signals in a radio communications system comprising at least one first and one second frequency channel (1,2,3). According to the invention, a station uses at least the first and/or the second frequency channel (1,2,3), in accordance with a temporal model, to transmit and/or receive signals.

Description

description

METHOD FOR TRANSMITTING SIGNALS IN A RADIO COMMUNICATION SYSTEM

The invention relates to a method for signal transmission in a radio communication system, in particular in a decentralized radio communication system.

Future radio systems will support very high data rates, for example to be able to serve multimedia applications with the required quality of service. A further increasing number of participants is also to be expected, so that further frequency bands have to be developed for use by radio systems. To use these frequency bands efficiently, however, radio systems must operate over a wide frequency range.

Various methods for resource allocation and multiplexing are used in radio systems. In addition to multiplexing in the time domain (Time Division Multiplex, TDM) and code area (Code Division Multiplex, CDM), various frequency channels are implemented using the FDM method (Frequency Division Multiplex). In the FDM method, a broad frequency spectrum is divided into many frequency channels separated in the frequency range, each with a narrow bandwidth, which results in a frequency channel grid defined by the spacing of the carrier frequencies. This advantageously allows several participants to be served simultaneously on different frequency channels and the resources to be better adapted to the individual needs of the participants. A sufficient distance between the frequency channels ensures

that interference between channels can be reduced and controlled.

Furthermore, by separating into several frequency channels, services with different quality of service requirements (QoS - Quality of Service) can be offered. In this case, higher-priority services are not in competition with lower-priority services, as a result of which quality of service requirements can advantageously be guaranteed by resource allocation in frequency ranges.

In order to use narrow-band frequency channels by means of an appropriate access method called FDMÄ (Frequency Division Multiple Access), the transmitter and receiver must each coordinate and select a corresponding carrier frequency. Before using the corresponding resource, ie the radio channel, it must be checked whether the selected resource is not already being used by other stations. The resource is then reserved and the reservation may be communicated to other potential stations, so that these stations do not subsequently access the resource simultaneously and cause collisions. The challenge here is to make the use of these frequencies as efficient as possible with little effort and, if possible, only one transmitter and receiver (transceiver) per station. In addition, there may be the boundary condition that all stations have equal rights, ie no station takes over control functions over several stations for the allocation of the frequency channels. Particularly in self-organizing networks and networks without infrastructure, so-called ad hoc networks, there are often stations with equal rights that carry out the same algorithms and protocols. A well known

An example of such networks is the wireless local area network (Wireless 1AN) according to the IEEE 802.11 standard.

If the stations in such networks are not informed about the use of the frequency channels of other stations, since corresponding information is not collected and distributed by a central station, a station cannot decide which frequency channel they propose or select for communication with another station should. In addition, a station does not know when another station is ready to receive what frequency. A station could therefore generally not establish a connection to another station if the frequency channels were chosen arbitrarily by both. In addition, a distribution service (broadcast) on one frequency would only reach a part of the stations that happen to be on this frequency.

It is therefore necessary to coordinate the use of these orthogonal resources. If a specific frequency is to be used for this purpose at fixed times, ie all stations are ready to receive at this frequency, then the frequencies available in parallel cannot be used. These resources would then be unused and not available for these stations. ^{■ •}

In existing cellular mobile radio systems, the frequencies are assigned by a central station, the base station (BS base station), to the mobile stations (MS mobile station) located in a radio cell of the base station. In the GSM (Global System for Mobile Communication), for example, a central frequency channel per radio cell is used to transmit general information, which is used by the mobile stations to create a frequency channel for the Learn to register and request resources. If a mobile station wishes to transmit data, it requests this from the base station on the frequency channel known to it. The base station then informs the mobile station of the corresponding carrier frequency on which it can communicate with the base station. The allocation and management of the available resources is controlled centrally in a base station controller (BSC - Base Station Controller) and signaled by the base station. The same applies to third generation systems

UMTS (Universal Mobile Telecommunications System), which also signal the allocation of frequencies according to the central approach with the help of a base station. Due to the central control, this approach cannot be used in a decentralized system without a central authority.

Other systems, such as WLAN systems (Wireless Local Area Network) according to the HIPERLAN Type 2 standard, for example from the document ETSI / BRAN "Broadband Radio Access Networks (BRAN); HIPERLAN Type 2 Functional Specification Data Link Control (DLC) Layer ; Part 4 - Ξxtension for Home Environments., Draft DTR / BRAN-0020004-4, ETSI, Sophia Antipolis, France, April 2000, known, '- ^' or according to the IEEE 802.11 standard use only one carrier frequency for communication to another frequency serves to avoid interference due to, for example, an already existing use of the selected frequency by other stations.If a new, usable carrier frequency is found, all stations send and receive on this frequency, in HIPERLAN / 2 this method is known as Dynamic Frequency Selection (DFS) is known: simultaneous, demand-dependent use of multiple frequencies by any number However, stations for increasing the possible total capacity of the system or an individual connection are not provided. The maximum data rate is therefore limited to one frequency channel.

Similar to the DFS method according to the HIPERLAN / 2 standard, the document R. Sakata, K. Naka, H. Murata, S. Yoshida, Performance Evaluation of Autonomous Decentralized Vehicle-grouping Protocol for Vehicle-to-vehicle Communications, in Prov , IEEE VTC, Boston, MA, Sep. 24-28, 2000, pp.153-157, proposed a system in which vehicles form groups that use different frequencies. Adjacent vehicles share the same carrier requirement. By measuring the active frequency channels, it is possible to participate in several groups and switch groups at the same time in order to take into account the changing network topologies. It is assumed that generally only one frequency is used for the data exchange, while the other frequencies are only received in order to prepare the assignment and a possible frequency change. In order to be able to receive on other frequencies at the same time, it is proposed to use two transceivers, one for data exchange and the second for measuring other potential frequencies. However, the use of several available frequencies for communication with neighboring stations for data exchange is not described here either.

The cordless telephone standard DECT (Digital Enhanced Cordless Telephone) specifies flexible use of resources, including various frequency channels. The procedure for using the resources is called Dynamic Channel Selection (DCS). Although in the system in the so-called "basic mode", a base station exclusively allocates resources controls, the forwarding of data packets is supported. For this purpose, the availability of resources is checked and documented in a similar way to a distributed, decentralized system.

Due to the special role of the base station, the mechanisms of the DECT system are not applicable to decentralized systems. In addition, DECT does not provide for direct communication between the stations or to set up several parallel connections on different frequency channels. Rather, a station searches for a frequency channel to decrease or increase the data rate by selecting a number of time slots.

The object of the invention is therefore to enable the most efficient use of several available frequency channels in a decentrally organized system. This object is achieved by the features of the independent claims. Further developments of the invention can be found in each dependent patent claim.

Advantageously, the method according to the invention advantageously enables the use of several frequency channels with only one transceiver in an asynchronous system without a central instance. Furthermore, it is ensured that class - specific, for example, highly prioritized data or. Signals are received by receivable stations within a certain time interval, and a more efficient use of the transmission resources is guaranteed.

The invention is explained in more detail with reference to games from exemplary embodiments. It show

1 shows an exemplary random access of a radio station to three frequency channels, and FIG. 2 shows first exemplary transmission / reception accesses to three frequency channels with different priorities, FIG. 3 shows an exemplary station-specific access pattern to the three frequency channels, FIG. 4 shows second exemplary transmission / reception accesses only one prioritized frequency channel, and FIG 5 frequency channel assignments in a DSRC system.

In the scope of the invention, the term station is understood to mean a mobile or stationary partial subscriber terminal capable of radio communication, or else a radio station assigned, for example, to a machine. The following examples are based on the following boundary conditions, but are not limited to them. Thus, only one transmitter / receiver unit (transceiver) is required in each station to carry out the method according to the invention, which advantageously reduces costs. Furthermore, there is access to transmission media, i.e. Frequency channels, according to an optional access protocol known as random access. There is also no central instance for central control of resource use, and access by multiple stations is asynchronous, i.e. the stations are not synchronized with each other.

1 shows an example of how a station for transmitting and receiving accesses three frequency channels 1 to 3 separated in frequency. After a random access on frequency channel 1, the station sends one or more data packets, for example. After transmission, the station performs a frequency change and receives one or more data packets on frequency channel 2 another station. After this reception, the station in turn accesses frequency channel 3 by means of random access and sends one or more data packets. The access is therefore optional, and due to the boundary condition of the only one transceiver, the station can either transmit or receive on the frequency channels. The frequency change and switching between sending and receiving are generally associated with a certain time delay.

2 shows a first example of a time use of three frequency channels 1 to 3 by a station. In addition to the example in FIG. 1, in this example the frequency channels are provided with a respective priority Z, frequency channel 1 having a highest priority, frequency channel 2 having a next lower priority and frequency channel 3 having a lowest priority. The priority relates, for example, to the meaning of the data or signals transmitted on the respective frequency channels, i.e. Data with a high priority or meaning for a large number of further stations is sent by one station on frequency channel 1, while data or signals of less importance, such as a data exchange between two stations, are transmitted on frequency channel 3.

The time component t of the frequency channels 1 to 3 is divided into N first time intervals with a respective length of X ms in FIG. An exemplary choice of N = 8 results in a considered second time interval Y = N * X ms.

Highly prioritized data or signals are periodically transmitted repeatedly by the station over a number of first time intervals, in the example of FIG. 2 over all N first time intervals. This advantageously ensures that the data or signals for all active further stations located in the radio coverage area of the station can be received within the second time interval Y, even if the respective transmitter / receiver device only during the first time interval X on the first fre - Quenzkanal 1 is aligned.

In order to send data or signals on frequency channel 1 with the highest priority, the station will therefore switch to frequency channel 1 for at least the duration of the second time interval Y and send the data or signals with a period X ms. So that another station can receive this data or signals from the station, shown in FIG. 2 by the dash delimited by two points - receive foreign broadcasts - it must switch to frequency channel 1 within the second time interval Y for at least a first time interval X. , It is irrelevant when this occurs within the second time interval Y.

In the example in FIG. 2, in addition to frequency channel 1 with the highest priority, frequency channel 2 with a next lower priority is used in order to ensure secure reception of priority data or signals. In this case, the station sends data or signals repeatedly during four (Y / 2) first time intervals X within the second time interval Y.

In order to ensure that the data or signals are received by further stations in this case, another changes Station every Y / 2 ms for the period of at least one first time interval X on frequency channel 2. Here, too, it is irrelevant when this change takes place within the second time interval Y.

The described approach ensures that data or signals with a highest priority can be received by a further station by simply changing to frequency channel 1 and receiving on this channel during only a first time interval X within the second time interval Y. This advantageously allows only very little effort for the further station and thus an increase in the probability of reception. In the case of data or signals of the next lower priority, on the other hand, the maximum delay is Y / 2 ms due to a two-time switch for frequency interval 2 for a first time interval X, the further station possibly being outside the transmission period of Y / 2 ms during a first access ,

The pattern according to the invention for time-controlled access to a plurality of frequency channels thus has the advantage that the reception of periodically transmitted signals is guaranteed on at least one frequency channel with a higher priority, although it is used asynchronously by stations with only one transmitting / receiving device each.

3 shows a structure of a switchover pattern between the sending and receiving of a further station which follows from the example in FIG. This further station can use the frequency channel 3 for sending and / or receiving data or signals from / to other stations during the first five time intervals X in the second time interval Y. Only during fixed The time period, in this case the second, sixth and seventh first time interval X, the further station must change to frequency channels 1 and 2 in accordance with the above description in order to receive data or signals with higher priority.

If a virtual frame, as well as transmission and reception time intervals, corresponding to the second time interval Y in the above example, are defined for each station, the position of these intervals can differ between the stations, i.e. lie asynchronously. Asynchronous intervals do not influence the functioning of the system, since the maximum intervals between the transmission of prioritized data or signals and the reception time intervals defined individually for each station ensure that these data or signals are received. Due to the free choice of the first time intervals for receiving data or signals with higher priority, the occurrence of periods in which, for example, frequency channel 3 is not used, is advantageously prevented and the system capacity is thus increased.

The pattern thus specifies for a station when and how often the station must receive within the virtual frame on frequency channels with higher priority data or signals, and when and how long it has to transmit correspondingly prioritized data or signals. The time intervals between sending and receiving are predetermined, for example, throughout the system, but they can vary relative to one another.

4 shows a simplified example, in which data or signals with higher priority are only sent on frequency channel 1, meanwhile on frequency channels 2 and 3 optional transmission can take place. Furthermore, the second time interval Y is chosen to be shorter in time and now corresponds to four first time intervals X. Reception of prioritized data or signals on frequency channel 1 by another station is thus already ensured by four repeated transmissions from the station.

The method according to the invention can advantageously be implemented in the DSRC system (Dedicated Short Range Communication) currently in the standardization process. The DSRC system is designed to enable digital communication between vehicles and the edge of the road, as well as between vehicles. It is used for both safety-related purposes, such as forwarding hazard reports, and private or public applications such as toll collection, Internet access in the vehicle, etc.

The basis for the radio access of the DSRC system is the IEEE standard 802.11, which, however, is part of the standardization to a so-called road access standard

802.11aR / A is to be expanded. As shown in FIG. 5, the system provides seven frequency channels in the frequency spectrum from 5850 to 5925 MHz. One of the frequency channels is defined as a control channel, which is to be used primarily for the transmission of safety-related messages such as hazard reports. The further frequency channels serve as service channels for the transmission of further data, for example for traffic flow control, inter — vehicle communication or toll collection. The control channel should also be used to announce the time, type and scope of these messages. A characteristic of security-relevant messages is periodic

repeated transmission to ensure their reception by the vehicles.

Access to the medium, i.e. the so-called medium access control (MAC) within the channels is randomly controlled according to the well-known CSMA / CA procedure (Carrier Sense Multiple Access / Collision Avoidance) of the IEEE 802.11 standard. This means that access is asynchronous and decentralized without control by a central authority.

The method according to the invention can be implemented in a DSRC system, for example in accordance with the preceding exemplary embodiments. The frequency channel with the highest priority (frequency channel 1) would accordingly be the control channel of the DSRC system, and the frequency channel with the next lower priority (frequency channel 2) would be the channel for public safety applications. All other channels are not prioritized and thus correspond to frequency channel 3 in the above examples.

Claims

claims

1. Method for signal transmission in a radio communication system with at least a first and a second frequency channel (1, 2, 3), in which a station according to a temporal pattern aα f at least the first and / or the second of the frequency channels (1 , 2,3) accesses for sending and / or receiving signals.

2. The method of claim 1, wherein the frequency channels (1,2,3) are structured in time into a number of first time intervals (X) in a periodically repeating second time interval (Y).

3. The method of claim 1 or 2, wherein the station sends signals on the first (1) and / or the second (2) of the at least two frequency channels (1,2,3) with a predetermined number of repetitions.

4. The method according to the preceding claim, wherein the number of repetitions for transmitting the signals is selected depending on a priority assigned to the respective frequency channel (1, 2).

5. The method according to any preceding claim, in which the at least two frequency channels (1, 2, 3) are assigned different priorities.

6. The method as claimed in one of claims 2 to 5, in which signals from the station on the first (1) and / or the second from at least one further station during at least one of the first time intervals (X) within a second time interval (Y) Frequency channel (2) can be received.

7. The method according to claim 6, wherein the station and the at least one further station are not synchronized.

8. The method of claim 1, wherein the station accesses the first (1) or the second frequency channel (2) for transmitting signals depending on a priority of the signals.

9. The method according to any preceding claim, in which the station and the at least one further station use individual station time patterns to access the frequency channels (1, 2, .3).

10. The method according to any preceding claim, wherein the radio communication system is a decentrally organized system.

11. Station of a radio communication system, with a transceiver which is designed to access at least a first and / or second frequency channel (1, 2, 3) for transmitting and / or receiving signals according to a temporal pattern.