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WO1999026423A2 - Prediction de signaux dans des communications mobiles et systemes utilisant ces predictions pour la reception et le decodage de signaux - Google Patents

Prediction de signaux dans des communications mobiles et systemes utilisant ces predictions pour la reception et le decodage de signaux Download PDF

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Publication number
WO1999026423A2
WO1999026423A2 PCT/NZ1998/000165 NZ9800165W WO9926423A2 WO 1999026423 A2 WO1999026423 A2 WO 1999026423A2 NZ 9800165 W NZ9800165 W NZ 9800165W WO 9926423 A2 WO9926423 A2 WO 9926423A2
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WO
WIPO (PCT)
Prior art keywords
channel
signal
received
antenna
behaviour
Prior art date
Application number
PCT/NZ1998/000165
Other languages
English (en)
Other versions
WO1999026423A3 (fr
Inventor
Rodney Grant Vaughan
Joergen Bach Anderson
Original Assignee
Industrial Research Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Industrial Research Limited filed Critical Industrial Research Limited
Priority to NZ504379A priority Critical patent/NZ504379A/xx
Priority to AU12653/99A priority patent/AU1265399A/en
Publication of WO1999026423A2 publication Critical patent/WO1999026423A2/fr
Publication of WO1999026423A3 publication Critical patent/WO1999026423A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H04B7/0842—Weighted combining
    • H04B7/0845—Weighted combining per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/005—Control of transmission; Equalising

Definitions

  • the invention comprises a method for predicting future channel behaviour for a multipath time-varying channel, for example in a mobile communications system, and communications systems and receivers.
  • the radio channel imposes a fading signal envelope and randomly changing phase on the received signal.
  • the cause is changing multipath radiowave propagation.
  • the signals borne by the multiple waves from different directions and with different delays are combined in a receiving antenna.
  • the interference between the received signals causing the fading envelope with an associated changing phase.
  • the resultant (received by the antenna) signal has fading which depends on both the frequency of operation and on time.
  • the fading and other related distortion caused by the mobile radio channel degrades the quality of the channel, resulting in a degraded spectral efficiency.
  • Signal processing techniques such as equalisation, rake combination, and diversity antennas using signal combination can help mitigate the effects of the multipath-induced degradation.
  • the control of these processes is adaptive in order to follow the time-varying nature of the channel.
  • the signal processing solutions for maximising capacity in this case include reception (following the changing phase and amplitude of the interferers) and cancelling the unwanted signals (interferers).
  • the cancellation occurs during controlled combination of those signals which originate from: different diversity antennas; different time delay bins in the signal from a single antenna; different frequencies from a single antenna; or a combination of these.
  • a central problem in mobile communications is the short-term (several signal fades) unpredictability of the received signals ie, the short-term unpredictability of the mobile channel.
  • a method for predicting the future channel behaviour for a multipath time-varying channel in a communications receiver including an antenna, comprising:
  • the invention comprises a communications receiver including an antenna, including:
  • (b) means arranged to process the past samples to characterise the multipath components, or an equivalent set thereof, of the received signal
  • (c) means arranged to estimate the future channel behaviour from the estimated multipath signal characteristics
  • (d) means arranged to apply the channel behaviour prediction information in the processing of signal subsequently received to improve the channel quality.
  • Either the receiving terminal may be mobile or the transmitter may be mobile and the receiving terminal fixed.
  • Time-dependent fading can be viewed in two ways: the incoming waves are changing in their direction (relative to the receiving antenna), phase and perhaps amplitude; or the receiver is moving relative to the incoming waves. In general, both the incoming waves are changing their characteristics and the terminal is moving relative to them. Often, however, most of the scatterers from which the waves reradiate (including ground and other landscape features, buildings (walls, ceilings), furniture, cars, poles, wires, people, etc) are effectively static. For a static transmitter (eg a fixed base station), the dominant cause of the time variation in the radio channel is the motion of the receiver.
  • a static transmitter eg a fixed base station
  • the radio channel can be predicted, if the contributing multipath rays combined in the receiving antenna can be characterised by estimating the direction, amplitude, and phase of the principal multiple signals received by the antenna.
  • Figure 1 illustrates indicative scatterers in an outdoor multipath environment
  • Figure 2 illustrates the effective scatterers with a "past” trajectory over which the scatterers are characterised and a “future” trajectory over which the channel can be predicted from the channel model
  • Figure 3 shows a configuration for applying the method of the invention to diversity channel (antenna diversity) combination
  • Figure 4 shows a configuration for applying the signal prediction method of the invention to equaliser control and/ or rake control
  • Figure 5 shows a configuration for applying the signal prediction method of the invention to signal detection and/ or decoding
  • Figures 6(a) and 6(b) are plots of predicted channel amplitude and phase referred to further in the example below.
  • samples of the channel behaviour are obtained from samples of the signal originally received by the antenna. It may be necessary to avoid "corruption” of the samples of the radio channel by compensation or correction of any "unwanted” changes in the transmitted signal (through amplitude or phase modulation). Such changes may in turn corrupt the prediction process.
  • the avoidance can be achieved by known techniques such as using an appropriate signal modulation, or adding a component to the transmitted information signal for "sounding" the channel, such as a pilot carrier or a signature signal in a repeating time slot of the transmission.
  • the past samples are then processed to characterise the multipath components, or an equivalent set thereof, of the signal received by the antenna. This requires computation typically by a digital signal processor. In a changing radio channel, the past samples are continually updated, resulting in the estimate of the future behaviour being continually updated.
  • the estimated multipath signal characteristics are then used to estimate the future behaviour of the radio channel, based on the assumption that the future mobile trajectory is known.
  • the calculation is again typically interpreted in a digital signal processor.
  • the future trajectory of the mobile is assumed to be following the same trajectory, as when the prior samples of the channel were taken, although the patent is not restricted to this.
  • the knowledge of the future radio channel behaviour is then applied to process signals, or to control or to help control a process, in order to improve the channel quality.
  • Diversity signals from diversity antenna branches, or from diverse frequency channels, or from other diversity channels such as rake channels, can be combined.
  • the effect of the changing phase and/or amplitude of the received signals can be effectively corrected before and during the signal detection stage.
  • the knowledge of the future radio channel can be used to control antenna diversity, equalisers and rake processors, or other processors to mitigate multipath effects.
  • the model for the short-term channel behaviour feature the Rayleigh-like fading of the envelope comprises a set of effective scatterers whose discrete contributions are summed.
  • the model is written in terms of the baseband equivalent transfer function which depends on position z and baseband frequency ⁇
  • N complex amplitudes
  • ai their directions given by the spatial Doppler frequencies
  • Ti Ti.
  • kc is the wavenumber of the carrier frequency.
  • the size of the neighbourhood in space and frequency over which the effective scatterers are constant is not known from a snapshot receiver signal, but if the physical scatterers are in the far-field of a lineal locus of the mobile then for narrow relative bandwidths, the effective scatterers will be constant for at least a few wavelengths at microwave frequencies. In dealing with effective scatterers, recall the effect of the antenna is included.
  • the scattering model gives the possibility of knowing the channel transfer function (in the neighbourhood) before the mobile has reached that position. How this can be done is demonstrated by addressing only the narrowband (ie flat-fading) channel, ie:
  • the re-inclusion of frequency does not alter the prediction concept.
  • the invention also includes the prediction of frequency-behaviour in an analogous way to distance behaviour.
  • the frequency prediction is useful in wideband systems such as the IMT-2000 type mobile communications systems.
  • the scatterers must be characterised. Then scatterers can be tracked, in principle, since they are slowly changing with respect to the mobile position.
  • the concept is illustrated in Figures 2(a) and (b).
  • the prediction covers the interpolation of the channel behaviour between the sampled positions (or sampled frequencies, or both).
  • the samples are uncorrelated, but the samples will normally have nonzero correlations, and any solution algorithm should be sufficiently robust to handle this.
  • a large number (cf., N in equation 1) of parameters (cf., the complex a; and the m) are found which characterise the channel.
  • the parameters are found using the above simultaneous equations approach or found (estimated in some optimal sense) via known signal processing techniques such as the many methods established for spectral analysis [see for example, S.M.Kay and S.L.Marple, "Spectrum Analysis, a Modern Perspective", Proceedings of the IEEE, Volume 69, pp. 1380- 1419, November 1981; and Kay: Modern Spectrum Estimation, Prentice-Hall, 1987].
  • the advantage of solving for many parameters is that the interpolation and extrapolation can be very accurate and the extrapolation can extend to cover many fades.
  • the disadvantage is that this takes considerable computing power and time which is a problem for power efficient terminals such as personal communications devices.
  • N may be as low as 2 to 5. This has the advantage of offering feasible implementation using low power processing such as available in small personal terminals. The feasibility is based on the fact that relatively low processing power (processing capability) and quick estimation can be achieved for low battery power consumption.
  • the invention includes the case where h is multidimensional, and in particular the two-dimensional case where h is a function of z and frequency ⁇ .
  • the variation in h(z,&) over a frequency band is then sampled ⁇ 1 ⁇ in both z and ⁇ and the solution process (2) gives a( ⁇ , u), where ⁇ is the set of relative time delays of each contribution ⁇ ; is the direction u
  • Samples of the magnitude only of ⁇ (u, ⁇ ) are sufficient, in principle; since it is known that, in principle, the complex h(u, ⁇ ) can be calculated from the magnitude of a( ⁇ , u). This means, in particular,, that constant envelope modulation can be used, and the complex channel can be derived without the need for a pilot type signal.
  • the application of the invention may be in current and in particular in future communications systems where the rate of change of the channel is relatively fast.
  • An example of such a system is an IMT-2000 - type mobile communications system which must be able to operate with fast fading channels when the mobile terminal is moving quickly (up to 500 k /hr) and microwave frequencies (1.8/ 1.9 GHz) are employed.
  • Figure 3 shows a configuration for applying the method of the invention to diversity channel (antenna diversity) combination.
  • Figure 4 shows a configuration for applying the signal prediction method of the invention to equaliser control and/ or rake control.
  • Figure 5 shows a configuration for applying the signal prediction method of the invention to signal detection and/ or decoding.
  • the signal processing is standard, but using "feed-forward" setting of the weights.
  • FIG. 6(a) shows the phase of the channel.
  • the solid line depicts a linear interpolation of the channel measurement samples.
  • the circles are the extrapolated (predicted) channel samples.
  • the predicted samples show that the phase was predicted accurately over a distance of about 20 samples and that the samples follow the phase "jump" at sample 12.
  • the prediction in this example begins to become less accurate at sample 25.
  • Figure 6(b) shows the amplitude for the same example. The amplitude of the first two "future" maxima are well defined and accurate to about 1 dB for the first one and about 5 dB for the second one.

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

Abstract

L'invention concerne un procédé de prédiction du comportement futur relatif au canal pour un canal par trajets multiples à variation temporelle, par exemple dans un récepteur de communication mobile. Ce procédé consiste à collecter dans le signal reçu des échantillons du comportement passé relatif au canal, à traiter ces échantillons passés afin de caractériser les composantes de propagation par trajets multiples, à faire une estimation du futur relatif au canal à partir des caractéristiques de signal par trajets multiples estimées (et à assumer que la trajectoire mobile future est connue dans le cas d'un récepteur mobile), puis à appliquer cette prédiction du comportement de canal au traitement du signal reçu ultérieurement afin d'améliorer la qualité de canal.
PCT/NZ1998/000165 1997-11-13 1998-11-13 Prediction de signaux dans des communications mobiles et systemes utilisant ces predictions pour la reception et le decodage de signaux WO1999026423A2 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
NZ504379A NZ504379A (en) 1997-11-13 1998-11-13 Prediction of signals in mobile communications and systems that use the prediction for signal reception and decoding
AU12653/99A AU1265399A (en) 1997-11-13 1998-11-13 Prediction of signals in mobile communications and systems that use the prediction for signal reception and decoding

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NZ32917397 1997-11-13
NZ329173 1997-11-13

Publications (2)

Publication Number Publication Date
WO1999026423A2 true WO1999026423A2 (fr) 1999-05-27
WO1999026423A3 WO1999026423A3 (fr) 1999-07-15

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AU (1) AU1265399A (fr)
WO (1) WO1999026423A2 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1156597A1 (fr) * 2000-05-18 2001-11-21 Nec Corporation Terminal mobile dans un système AMRC avec transmission en diversité
WO2004036931A2 (fr) * 2002-10-11 2004-04-29 Fg Microtec Gmbh Procede pour commander une transmission de donnees dans des reseaux radios
GB2399987A (en) * 2003-03-27 2004-09-29 Ubinetics Ltd Method of predicting the state of a channel
US6879969B2 (en) * 2001-01-21 2005-04-12 Volvo Technological Development Corporation System and method for real-time recognition of driving patterns

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI881007A0 (fi) * 1988-03-04 1988-03-04 Teuvo Kohonen Foerfarande foer adaptiv avlaesning av kvantiserade signaler.
US5844952A (en) * 1993-05-19 1998-12-01 Ntt Mobile Communications Network Inc. Time diversity receiver

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1156597A1 (fr) * 2000-05-18 2001-11-21 Nec Corporation Terminal mobile dans un système AMRC avec transmission en diversité
US6792279B2 (en) 2000-05-18 2004-09-14 Nec Corporation Mobile terminal for transmission diversity CDMA communication system
US6879969B2 (en) * 2001-01-21 2005-04-12 Volvo Technological Development Corporation System and method for real-time recognition of driving patterns
WO2004036931A2 (fr) * 2002-10-11 2004-04-29 Fg Microtec Gmbh Procede pour commander une transmission de donnees dans des reseaux radios
WO2004036931A3 (fr) * 2002-10-11 2005-02-03 Thomas Kelz Procede pour commander une transmission de donnees dans des reseaux radios
GB2399987A (en) * 2003-03-27 2004-09-29 Ubinetics Ltd Method of predicting the state of a channel
GB2399987B (en) * 2003-03-27 2006-10-11 Ubinetics Ltd Wireless communications system

Also Published As

Publication number Publication date
WO1999026423A3 (fr) 1999-07-15
AU1265399A (en) 1999-06-07

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