WO2000070835A1 - Procede pour evaluer des parametres de canal a l'aveugle - Google Patents

Procede pour evaluer des parametres de canal a l'aveugle Download PDF

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Publication number
WO2000070835A1
WO2000070835A1 PCT/DE2000/001482 DE0001482W WO0070835A1 WO 2000070835 A1 WO2000070835 A1 WO 2000070835A1 DE 0001482 W DE0001482 W DE 0001482W WO 0070835 A1 WO0070835 A1 WO 0070835A1
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Prior art keywords
channel
data symbols
data
subscriber
data signal
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PCT/DE2000/001482
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German (de)
English (en)
Inventor
Markus Doetsch
Peter Jung
Jörg PLECHINGER
Peter Schmidt
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Infineon Technologies Ag
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Publication of WO2000070835A1 publication Critical patent/WO2000070835A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H04L25/023—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols
    • H04L25/0236—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols using estimation of the other symbols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/713—Spread spectrum techniques using frequency hopping

Definitions

  • the invention relates to a method for estimating channel parameters of a radio channel of a mobile radio system used for the transmission of a message according to the preamble of claim 1.
  • the constant change in the transmission properties of the mobile radio channel makes it necessary for a receiver (in addition to receiving the transmitted data signals) to continuously determine the current transmission properties of the mobile radio channel in order to enable detection of the received data signals. This applies both to the transmission link from a mobile station to a base station (uplink) and to the transmission link from a base station to a mobile station (downlink).
  • the transmission properties of the mobile radio channel are determined using a channel estimator present in the receiver.
  • TDMA Time Division Multiple Access: time division multiplex
  • FDMA Frequency Division Multiple Access: frequency division multiplex
  • Frequency sub-bands have been referenced in recent years CDMA (Code Division Multiple Access: Code Division Multiplex) driving gained significantly in importance.
  • CDMA Code Division Multiple Access: Code Division Multiplex
  • a subscriber-specific code is embossed on each data symbol to be transmitted, which code makes the transmitted data symbol distinguishable (and thus detectable) from transmitted data symbols of other participants, as it were, in the manner of a fingerprint.
  • a first known method for channel estimation in CDMA transmission systems is in the book "Analysis and Design of Digital Mobile Radio Systems” by P. Jung, Stuttgart, B.G. Teubner, 1997 in chapter 6.3 and there described in particular on pages 253 (upward stretch) and 261 (downward stretch).
  • the channel estimation is based on so-called learning or training sequences, which are integrated in the CDMA radio data block in addition to the message-carrying sequences as middle messages (i.e. in the middle of a data block).
  • the symbol sequence of the training sequence is known to the channel estimator provided on the receiver side.
  • the channel estimator determines the channel parameters in the form of the channel impulse responses on the basis of a comparison with the transmitted ("undisturbed") training sequence known to it.
  • the determined channel impulse responses are then used to detect message-carrying data symbols adjacent to the training sequence.
  • a CDMA radio data block executes an alternating sequence of a channel measurement step and a message data detection step (based on the result of the channel measurement step).
  • a disadvantage of both known methods is that the use of training sequences or pilot signals reduces the maximum transmission rate of information (hereinafter referred to as the information rate) that can be achieved with CDMA data transmission.
  • information to be transmitted means all data symbols that are not specifically provided for the purpose of channel estimation in the transmitted signal. Accordingly, the information to be transmitted also includes in particular the message to be transmitted.
  • the invention has for its object to provide a method for estimating channel parameters of a radio channel, which enables a high information rate in CDMA multiple access systems.
  • An essential advantage of the method according to the invention is that by using data symbols of the data signal to be transmitted that are unknown a priori for the channel estimation, the amount of special data symbols that must be inserted into the data signal to be transmitted specifically for the purpose of channel estimation is used ( training sequences, pilot signal), can be reduced or that no such special data is required at all. be done. The transmission capacity thus freed up can be used to increase the information rate.
  • the estimated channel parameters can be determined solely from the data symbols of the data signal to be transmitted that are unknown a priori to the receiver. Another possibility is to continue to use special data symbols (training sequences, pilot signal) provided for this purpose for the estimation of the channel parameters.
  • special data symbols training sequences, pilot signal
  • an optimal compromise can be made between the inexpensive but inexpensive (conventional) channel estimation by means of special data symbols, and the channel estimation based on the invention, which is unknown to the receiver and may be more complex but allows a higher information rate Data symbols can be found.
  • a “hybrid" channel estimation according to the invention can be implemented in such a way that first a rough estimation of the channel parameters takes place in a conventional manner (using training sequences or a pilot signal) and the channel parameters are subsequently re-estimated to achieve higher accuracy using the channel estimation according to the invention.
  • a first embodiment of the method according to the invention is characterized in that the data symbols of the data signal to be transmitted which are unknown a priori to the receiver are data symbols carrying control information.
  • data symbols carrying control information are data symbols, the coding information (for example the code rate used in the channel coding for the channel coding or the spreading factor used in the spread coding), information relating to the cellular structure of the mobile radio network (for example the frequency ranges of the neighboring base stations), general Information about the available services or similar information intended to control or monitor the mobile radio system contain.
  • This control information is a priori unknown to the recipient (which is why it is communicated to him), but is usually constant (at least over a longer period of time) and is emitted in constant repetition, so that it is known to the recipient after an initial detection . They can then be used according to the usual procedure for a channel estimation, ie the channel estimator determines the estimated channel parameters by correlating these data symbols carrying the control information of the received, subscriber-specific, separated data signal with the data symbols of the receiver to be transmitted which have become known to the receiver Data signal.
  • a second embodiment of the method according to the invention is characterized in that the data symbols of the data signal to be transmitted which are unknown a priori to the receiver are data symbols carrying messages.
  • Sequences of message-bearing data symbols usually have no special regularities or repetitions.
  • a preferred procedure for channel estimation using message-bearing data symbols is characterized in that the channel estimator determines the estimated channel parameters by correlating message-bearing data symbols of the received, subscriber-specific, separated data signal with hypotheses of the corresponding message-bearing data symbols of the data signal to be transmitted, ascertained by data detection. In this embodiment, no knowledge of the data symbols to be transmitted is required on the receiver side.
  • the channel parameters can be estimated in an iterative manner by using channel parameters which were determined when the channel was estimated earlier in order to determine the hypotheses of the message-carrying data symbols of the data signal to be transmitted.
  • the channel estimation according to the invention takes place on the basis of subscriber-specific (ie CDMA) coded data symbols, the CDMA code used has a considerable influence on the effort required and the quality of the channel estimation.
  • a Frank Fadoff-Chu sequence a Frank sequence or a polyphase sequence is preferably used as the CDMA code sequence.
  • These sequences have an ideal pulse-shaped periodic autocorrelation function (PAKF) (and are therefore also referred to below as sequences with "perfect" PAKF).
  • Kasami sequences are characterized by a PAKF and PKKF (periodic cross-correlation function) with good (but not perfect) correlation properties.
  • the algorithm of the signal-matched filtering is preferably used for the channel estimation.
  • the MF channel estimation is extremely cost-effective and has the advantage that it has a maximum signal-to-noise ratio at its output. However, it is only free from systematic estimation errors if the sequences on which the estimation is based of message-carrying (CDMA-decoded) data symbols of the received data signal have ideal correlation properties. Since the above-mentioned complex CDMA code sequences have a perfect PAKF, they are particularly suitable for MF channel estimation.
  • a mean channel parameter can expediently be calculated from a plurality of (N) channel parameters. This is particularly favorable when the transmission properties of the mobile radio channel change only comparatively slowly, which is the case, for example, with a stationary mobile station in an obstacle-free (rural) radio wave propagation area.
  • interpolated M interpolated channel parameters are determined between two successive channel estimates.
  • the determination of interpolated channel parameters can be advantageous, for example, in the case of a rapidly moving mobile station in areas which are unfavorable for wave propagation (e.g. cities), since under these conditions the transmission properties of the mobile radio channel change quickly and additional channel parameter values are required which are cost-effective due to interpolation (without implementation) a channel estimate) can be generated.
  • Figure 1 is a schematic representation of the air interface of a mobile radio system.
  • FIG. 2 shows a block diagram of a transmission device
  • 3 shows a block diagram of a CDMA spreading code encoder and an example of a spread-coded data symbol generated therewith; 4 shows a schematic representation of the structure of a CDMA message data block;
  • Fig. 5 is a block diagram of a receiver device
  • FIG. 6 shows a structural representation of the channel estimator shown in FIG. 5.
  • FIG. 1 shows a schematic representation of the air interface of a cellular mobile radio system.
  • Bidirectional communication connections can be set up between three mobile stations MSI, MS2, MS3 assigned to individual subscribers and a common base station BS.
  • the respective transmission behavior of the air interface is described by the three radio channels K1, K2, K3.
  • the communication connections between the base station BS (connected to a long-distance communication network) and the mobile stations MSI, MS2, MS3 are subject to a multipath propagation, which is caused by reflections, for example, on buildings or
  • MS3 or BS overlap the signal components of the different propagation paths of a subscriber signal as a function of time. As a result, the transmission properties of the radio channels K1, K2, K3 change continuously.
  • the subscriber separation carried out in the receiver devices of the mobile stations MSI, MS2, MS3 or the base station BS is carried out by one of the known CDMA
  • FH Frequency Hopping: Frequency jump-
  • MC- multicarrier code: multi-carrier-
  • DS- direct sequencing-
  • the transmission device BSS contains control means SES with a storage device PLC, modulation means MOD and a high-frequency transmission stage HFS.
  • the modulation means MOD are supplied with data symbols x which are intended for a specific mobile station MSI or MS2 or MS3 of a specific subscriber.
  • the message-carrying data symbols x contain the voice message to be transmitted.
  • a first (optional) data processing device DATS of the modulation means MOD the message-carrying data symbols x are brought into a data structure suitable for radio transmission.
  • This step includes, for example, error protection by channel coding (i.e. adding redundancy) and interleaving (i.e. deliberately changing the data symbol sequence) of the message-carrying data symbols x.
  • data symbols s carrying control information can be generated and added to the data symbols carrying messages.
  • the data symbols x which may be channel-coded and interleaved are referred to as d below.
  • a data block is subsequently formed in a block former BS of the modulation means MOD.
  • Different types of data blocks are usually used.
  • the sequence of data symbols d is first divided into sequences with because NS divides data symbols d.
  • the number NS is communicated to the block builder BS by the control means SES.
  • a training sequence of data symbols z known a priori by the receiver and optionally further data symbols are added to the sequences of data symbols d carrying messages.
  • the resulting block structure will be explained later in connection with FIG. 4.
  • control information For the transmission of control information, other data blocks, possibly constructed in a similar manner, can be formed which contain the data symbols s carrying control information.
  • Data symbols d, s which carry messages and carry control information can also be present together in one data block.
  • At least the message-carrying data symbols d (usually also the control information-carrying data symbols s and other data symbols such as z) are subjected to a subscriber-specific spreading coding in a spreading code encoder SPRZCOD of the modulation means MOD.
  • the spreading code sequence C used for this purpose is also stored in the memory device SPS and is communicated by this to the spreading code encoder SPRZCOD.
  • FIG. 3 shows a block diagram of the CDMA spreading code encoder SPRZCOD, as can be used in the modulation means MOD in the case of DS-CDMA coding.
  • the elements c (i) are also referred to below as chips c (i) of the code sequence C and L is referred to as the length of the code sequence C. It is assumed that the duration of a chip c (i) is shorter than the duration of a data symbol d (or s or z).
  • the number Q of chips c (i) per data symbol d is 8.
  • the CDMA-coded message-carrying data symbol d c (i) is also referred to in the following in simplified form as d c .
  • s c or z c denotes a spread-coded data symbol carrying control information or a spread-coded data symbol of the training sequence.
  • the spread-coded data symbols available at the output of the modulation means MOD are fed to the high-frequency transmission stage HFS, where they are converted into an analog signal, modulated onto a carrier and emitted as a radio wave.
  • a message data block used in the method according to the invention can, but need not, be different from CDMA message data blocks, as are already used in conventional methods for channel estimation.
  • the structure of the message data block shown here as an example is practically identical to that of a conventional CDMA transmission used data block, ie it consists of a first sequence SI of NS message-carrying data symbols d c , a training sequence TR from the receiver known a priori data symbols z c , a second sequence S2 of NS message-carrying data symbols d c and one ending the data block Protection sequence GP.
  • the method according to the invention is based on the fact that the message-carrying data symbols d c of the sequences SI, S2 are at least partially used for the channel estimation on the receiver side.
  • message data blocks with a significantly smaller number of data symbols z c specially provided for the channel estimation can be used in the training sequence TR than in the case of conventionally used message data blocks.
  • the training sequence TR (or a pilot signal or the like) can even be dispensed with entirely.
  • the number 2NS of message-carrying data symbols d c can be increased and a comparatively high information rate can thus be achieved.
  • the total time period of a data block can be approximately 0.5 ms.
  • a data block can contain a total of approximately 150 data symbols, for example.
  • the receiver device MSE contains control means SEE with a storage device SPE, demodulation means DMOD with a spreading code decoder SPRZDECOD, a channel estimator KS, a data detector DD and a data processing device DATE as well as a high frequency reception stage HFE.
  • the high-frequency receiving stage HFE receives the radio wave emitted by the transmitting device BSS via an antenna and converts it into an analog received signal in the usual way by down-watching.
  • the analog received signal is digitized in a manner not shown by an analog / digital converter with a sufficiently high sampling rate, at least corresponding to the chip rate, and bandwidth-limited by means of a downstream digital filter.
  • the digital, spread-coded received signal obtained in this way is supplied to the spread-code decoder SPRZDECOD of the demodulator means DMOD.
  • the spreading code decoder SPRZDECOD separates the subscriber signals, which requires knowledge of the spreading code sequence C used on the transmitter side as well as synchronization with the spreading code encoder SPRZCOD on the transmitter side.
  • the spreading code sequence C used by the transmitter i.e. the subscriber-specific CDMA code
  • the spreading code sequence C used by the transmitter is stored in the storage device SPE on the receiving side. It is either predefined or is negotiated every time the call is started between the base station BS and the mobile station MSI, MS2, MS3, i.e. selected from a plurality of code sequences C stored in the storage device SPE.
  • the spreading code decoder SPRZDECOD can be identical to this in the case of the spreading code encoder SPRZCOD shown in FIG. it can also consist of a multiplier that multiplies the incoming digital, spread-coded received signal by the associated spread code sequence C.
  • the spread code sequence C used for the spread coding / decoding is discussed below.
  • Particularly suitable code sequences C have good correlation properties.
  • a subscriber-separated digital reception signal is available at the output of the spreading code decoder SPRZDECOD. This contains, among other things, the disturbed versions d, s and z of the data symbols d carrying messages, data symbols s carrying control information and data symbols z of the training sequence TR.
  • the subscriber-separated digital reception signal is fed to a data detector DD.
  • a data detector DD In the case of a channel estimation using message-carrying data symbols, at least some of the data symbols d are supplied, and in the case of a channel estimation using data symbols carrying control information, at least some of the data symbols s are supplied to the channel estimator KS. If available, the data symbols z of the training sequence TR, which are provided specifically for a channel estimation, are also supplied to the channel estimator KS.
  • the channel estimator KS accepts the data symbols d and / or s and, where appropriate, z provided for the channel estimation.
  • the channel estimator KS has a knowledge of the supplied part of the (“disturbed”) data symbols d and / or s and possibly z nis ready via the associated (“undisturbed") data symbols d, s, z.
  • the channel estimator uses a computing algorithm to calculate current channel parameters h1, h2, ... of the mobile radio channel K1 or K2 or K3. With each channel estimation, the determined current channel parameters h1, h2, ... are output at an output A of the channel estimator KS.
  • the knowledge at the input K about the data symbols d, s, z to be transmitted is of a different nature.
  • data symbols carrying control information s are to contribute to the channel estimation, they are initially not known to the channel estimator KS (ie a priori), but can be determined quickly (also due to a frequently small supply of values) and are then until they change sent out repeatedly, known at least for a while. Precise knowledge is therefore available after a short time with regard to the data symbols s. This is thus made up of the received data signal and possibly additional
  • the channel estimator KS is provided with hypothetical knowledge H (d) of the message-carrying data symbols d to be transmitted, which is essentially generated solely from the received data signal.
  • H (d) can be generated by an iterative channel estimation and data detection process.
  • hl previously estimated in the channel estimator KS, h2
  • ... is calculated by means of the data detector DD with regard to data symbols d that are currently running ⁇ and hypotheses of the data symbols d to be transmitted that are the basis of the data symbols d that are currently arriving, and then these hypotheses of d the channel estimator KS as (hypothetical)
  • the channel estimator KS can optionally have a priori knowledge, for example, of known properties E (h) of the channel impulse response h or of known properties E (n) of the interference n occurring in the mobile radio channel for the estimation of the channel parameters hl, h2,. .. to provide.
  • the received data signal for estimating the channel parameters according to the invention is subjected to a double correlation (once with the code sequence C for subscriber separation and once with the knowledge regarding d and / or s and possibly z).
  • the algorithms described in the book by P. Jung mentioned in chapter 5.2.3 on pages 201-206 can be used to estimate the channel parameters hl, h2, ... (ie the channel impulse response h). These algorithms are the subject of the present application by reference. These are the algorithms for signal-adapted filtering, the Gaussian estimate, the ML estimate and the MAP estimate.
  • the estimated channel parameters h1, h2, ... (channel impulse response h) are fed to the data detector DD. This determines by folding the received disturbed versions d (possibly s, z) with the current channel impulse response h (parameterized by the channel parameters hl, h2, ...)
  • Estimated data symbols d (possibly s, z) for the data symbols d to be transmitted (possibly s, z).
  • the block structure (see FIG. 4) must also be taken into account, i.e. A distinction must be made as to which of the estimated data symbols d relate to data symbols d carrying messages and which of the estimated data symbols relate to other information.
  • corresponding data about the block structure used (including the sequence length NS) are stored in the storage means SPE and are communicated to the demodulator DMOD.
  • the estimated data symbols d for the message-carrying data symbols d are fed to the (optional) data processing device DATE.
  • the processing steps carried out in the transmitting data processing device DATS are essentially reversed, i.e. deinterleaving and channel decoding take place.
  • the data symbols which have been deinterleaved and decoded in DATE are designated by x and are the estimates of the data symbols x in Fig. 2 (i.e. the detection result of the receiving device MSE).
  • the channel estimation can be carried out continuously (ie without a break) or at discrete times.
  • the time period between two successive channel estimates and also the time period of the individual channel estimates can be adapted to the current circumstances.
  • a comparatively long period of time (approximately 3 ms) can be set between two successive channel estimates, while in the case of a fast one variable mobile radio channel a short period of time (about 0.3 ms) between two successive channel estimates can be set.
  • the duration of a single channel estimate can be, for example, 50 to 80 times a chip duration (it does not have to be a multiple of the symbol duration).
  • the channel parameters hl, h2, ... can be calculated in each case.
  • the latter can be advantageous, for example, if instead of a long-lasting channel estimate with high accuracy, many short-term channel estimates are carried out with a correspondingly lower accuracy, then by choosing a suitable number of channel estimates for the averaging (for example 2 to 5), channel-optimized optimization is always carried out between the accuracy of the estimation result (ie the result of the averaging) and the repetition rate of the averaging can be realized.

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

Abstract

L'invention concerne un procédé permettant d'évaluer des paramètres d'un canal de téléphonie mobile, selon lequel un code et spécifique de l'abonné est imprimé à un signal de données à transmettre. Le signal de données ainsi codé de manière spécifique de l'abonné est émis par le biais du canal téléphonique et est reçu par un récepteur. Ledit récepteur, sur la base du code, obtient un signal de données séparé de l'abonné et l'achemine jusqu'à un estimateur de canal. Ce dernier détermine les paramètres du canal téléphonique et utilise à cet effet des symboles de données dont il ne connaît pas les symboles de données correspondants émis.
PCT/DE2000/001482 1999-05-12 2000-05-11 Procede pour evaluer des parametres de canal a l'aveugle WO2000070835A1 (fr)

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DE1999122184 DE19922184A1 (de) 1999-05-12 1999-05-12 Verfahren zur Schätzung von Kanalparametern
DE19922184.7 1999-05-12

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DE10122689C2 (de) * 2001-05-10 2003-04-30 Siemens Ag Verfahren zur Kanalschätzung eines Mobilfunkkanals und Mobilfunk-Empfangsgerät
DE102008007113A1 (de) 2008-01-31 2009-08-06 Universität Paderborn Verfahren und Vorrichtung zur Schätzung von Kanalparametern

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