Pulse or digital communications – Transceivers
Reexamination Certificate
1998-03-10
2001-03-20
Chin, Stephen (Department: 2734)
Pulse or digital communications
Transceivers
C375S232000, C375S284000, C375S285000, C375S346000
Reexamination Certificate
active
06205170
ABSTRACT:
OBJECT OF THE INVENTION
The present invention refers to a data transmission reception unit to exchange data with a remote unit by means of a channel using non-linear modulation/demodulation treatment means, for example frequency modulation/demodulation.
STATE OF THE ART
The use of frequency modulation methods, like that used in the European standard for wireless communication DECT, of the GFSK type, makes the use of frequency demodulators, for example by means of discriminators, recommendable; in this way, the recovery of data is possible by means of a simple threshold detector to decide between the two logic values “1” or “0”.
In some fields of application of these methods, this type of receiver is sufficient due to the fact that the maximum temporary dispersion of the signal in the receiver is rather less than a symbol and, hence, the interference between symbols due to the radio channel is hardly detectable.
However, in other applications where radio coverage is greater and induces multiple trajectories of the waves, the effects of attenuation and reflection in the propagation thereof have to be taken into account. Therefore, the use of equalizers is recommendable, which rectify this effect that degrades the signal quality, considerably enhancing the probability of error of the recovered symbols. For this reason, some kind of equalizer is used, as shown in the article “Adaptive equalization for DECT systems operating in low time-dispersive channels” by J. Fuhl and G. Schultes, published in the magazine “Electronics Letters”, Nov. 25, 1993, vol. 29, N 24, pages 2076-2077. In this article, an adaptive equalizer of the well-known DFE (decision feedback equalizer) type is used and where 16 bits of burst synchronization defined in the DECT are used as a training sequence. The training sequence is stored in a ROM memory and is applied to the equalizer when the signal corresponding to the training sequence received appears in the input thereof. This avoids that the possible errors that are produced in the detector when the coefficients of the filters are still unsuitable are fed back to the equalizer and permits that the convergence is produced faster.
When the type of modulation/demodulation is non-linear, even under ideal propagation conditions the demodulated signal may be considerably distorted due to the mentioned non-linear effect. Under these conditions, the convergence of the equalizer may be inadequately produced, since the non-linear process to which the received signal is submitted is not being duly taken into account. For example, the frequency modulator and the frequency discriminator introduce non-linear distortions given that the voltage-frequency conversion characteristic on the one hand, and the frequency-voltage on the other, are not a constant as in the ideal case.
More specifically, the invention refers to a transmission/reception unit, including a bidirectional correction device for the inter-symbolic interference acting through both directions of the radio channel. The device permits the correction of interferences in both directions of the data route, including an equalizer in the reception chain and a predistorter in the transmission chain. The objective of incorporating the bidirectional correction function of the inter-symbolic interference in the same transmission/reception unit is to reduce the cost of the other unit(s) that exchange data with said unit.
A device of this type, including an equalizer and a predistorter, is known from the document “Adaptive channel preceding for personal communications” by W. ZHUANG et al., published in the magazine “Electronics Letters”, Sep. 15, 1994, vol. 30, N 19, pages 1570-1571. In this document, a solution to the problem of linear modulation/demodulation is proposed, this being phase modulation.
This limitation is the result of the superposition of the non-linear effects and the inter-symbolic interference effects due to the multiple trajectories of the waves, which hinders a “bidirectional equalization” in only one transmission/reception unit. If the non-linear effects do not permit the effective correction of the inter-symbolic interference in the received signal, an imperfect predistortion results, which may be worse than not using this predistortion. Furthermore, the requirements for updating the equalizer coefficients and the predistorter coefficients for each transmission/reception period using a short signal sequence to assess the channel status have to be taken into account.
CHARACTERIZATION OF THE INVENTION
One objective of the present invention is to propose a transmission/reception unit for a communications system operating in a non-linear mode, that includes a bidirectional correction device for the inter-symbolic interference. The invention is applied to the DECT system, but not exclusively.
As a result, a data transmission/reception unit that exchanges data with a remote unit by means of a channel using distributed modulation/demodulation treatment means distributed between said data transmission/reception unit and said remote unit, said transmission/reception unit including equalization means to equalize a first signal received from said remote unit and predistortion means to predistort a second signal transmitted to said remote unit, is characterized according to the invention in that (a)—the modulation/demodulation treatment means work according to a non-linear mode and (b)—the unit includes
(b1) means to store information which is representative of a non-linear distortion of said modulation/demodulation treatment means and which defines a non-linear reference and
(b2) means to adjust equalization means coefficients according to the signal received from the remote unit and said representative information, the mentioned adjusted coefficients being transmitted to said predistortion means.
Therefore, both in the equalizer and in the predistorter, the correction of the inter-symbolic interference is carried out independently from the non-linear distortion resulting from modulation/demodulation.
According to a first embodiment, the transmission/reception unit is characterized in that the adjustment means are calculation means minimizing an error signal in the equalization means, on the one hand according to said signal received from the remote unit and, on the other, to the mentioned representative information.
According to a second embodiment, the adjustment means include:
means to sample said first signal received from the remote unit to a frequency which is higher than a frequency of logic symbols associated to the received signals and to define sets of samples, each one defined by a sample phase,
means to correlate said representative information with each one of the sample sets of the signal received from the remote unit, in order to determine an a priori optimum sample set,
means to select a sample set between said a priori optimum sample set and some of said sample sets defined by respective sample phases near to the sample phase of said a priori optimum sample set, the selected set being the one that produces the smallest equalization error signal with respect to a sequence of logic symbols, and
calculation means to minimize an error signal in the equalization means according, on the one hand, to said signal received from the remote unit when it is sampled with the sample phase of the selected sample set, and on the other hand, to said logic symbol sequence.
REFERENCES:
patent: 4995057 (1991-02-01), Chung
patent: 5574990 (1996-11-01), Flanagan
patent: 5732333 (1998-03-01), Cox et al.
patent: 5748678 (1998-05-01), Valentine et al.
patent: 5778029 (1998-07-01), Kaufmann
patent: 5987069 (1999-11-01), Furukawa et al.
patent: 0 202 596 A2 (1986-11-01), None
patent: 0 405 743 A2 (1991-01-01), None
patent: 0 655 849 A1 (1995-05-01), None
patent: 07058679 (1995-03-01), None
Burriel Lluna Rafael
Casajús Quirós Javier
Fernández Durań Alfonso
Nunez Leon De Santos Gregorio
Paez Borrallo José Manuel
Alcatel
Chin Stephen
Ha Dac V.
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Transmission/reception unit with bidirectional equalization does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transmission/reception unit with bidirectional equalization, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transmission/reception unit with bidirectional equalization will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2548033