WO1996031970A1 - A demodulator for transmission systems and use of such a demodulator - Google Patents
A demodulator for transmission systems and use of such a demodulator Download PDFInfo
- Publication number
- WO1996031970A1 WO1996031970A1 PCT/DK1996/000162 DK9600162W WO9631970A1 WO 1996031970 A1 WO1996031970 A1 WO 1996031970A1 DK 9600162 W DK9600162 W DK 9600162W WO 9631970 A1 WO9631970 A1 WO 9631970A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- demodulator
- coherent
- receiver
- mode
- equalizer
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/22—Demodulator circuits; Receiver circuits
- H04L27/233—Demodulator circuits; Receiver circuits using non-coherent demodulation
- H04L27/2332—Demodulator circuits; Receiver circuits using non-coherent demodulation using a non-coherent carrier
Definitions
- the invention concerns a demodulator for use in a re ⁇ DCver for transmission systems and adapted to demodulate received signals according to a coherent principle in a first mode and to demodulate received signals according to a non-coherent principle in a second mode.
- Said channel equalization may be performed using a plu- rality of known equalization principles. These equaliza ⁇ tion or demodulation principles may be divided into co ⁇ herent and non-coherent ones.
- the refer ⁇ ence frequency of the receiver is so precise compared to the reference oscillator in the corresponding transmitter that it is possible to use a so-called coherent transmit- ter for equalizing the received signal.
- This receiver type requires that frequency and phase of the carrier wave of the received signal are known and constant for a given block of received data.
- the reference frequency In other transmission systems, such as e.g. DECT, how ⁇ ever, the reference frequency is not, or not always, so precise from the transmitter side that the receiver can use the coherent principle, it being therefore necessary to use a so-called non-coherent principle.
- the receiver does not know the exact frequency and phase of the re ⁇ ceived data block and moreover cannot expect that fre ⁇ quency and shape are constant through a whole data block.
- Receivers of the non-coherent type are usually not resis- tant to multipath propagation, which results in impaired quality of the data signals received.
- US Patent Specification 4 583 048 discloses a receiver wherein, in a coherent system, a training sequence is de ⁇ modulated non-coherently at the start of each block to enable adjustment of the phase, so that the rest cf the block may be demodulated coherently. However, this is merely done to ensure that the coherent demodulation can take place, and the receiver is not capable of demodulat ⁇ ing signals which can just be demodulated non-coherently.
- the invention provides a demodulator which, by means of the same hardware, is capable of receiving data informa ⁇ tion and demodulating these according to the coherent principle and the non-coherent principle, respectively.
- a demodulator which, by means of the same hardware, is capable of receiving data informa ⁇ tion and demodulating these according to the coherent principle and the non-coherent principle, respectively.
- it is a so-called multimode receiver which will be considerably cheaper to manufacture than a receiver con ⁇ taining two separate receiver circuits.
- the re ⁇ barrever will have a considerably higher quality in certain physical surroundings for the transmission systems which cannot (or not always) use coherent demodulation, and in these situations a longer range of the receiver is moreo ⁇ ver achieved.
- the demodulator comprises a differential detector, an equal ⁇ izer and a switch adapted to couple the received signals directly to the equalizer in the first mode of the de ⁇ modulator and to couple the received signals to the equalizer via the differential detector in the second mode of the demodulator.
- the receiver can receive data information by means of two different trans ⁇ mission systems, or that, in a system where the received signals are not always sufficiently good for demodulation to take place according to the coherent principle, the receiver can demodulate according to the coherent prin ⁇ ciple when this is possible and switch to the non-coher ⁇ ent principle when coherent demodulation is not possible.
- the demodulator is adapted to receive data which are transmitted in blocks of finite length, each said block containing a training sequence which is known be ⁇ forehand by the receiver, and the equalizer here com ⁇ prises a Viterbi equalizer.
- the demodulator is adapted to receive data signals from various transmission systems in each of the said modes, it is ensured, as mentioned, that the same receiver can serve as a receiver on two or more different transmission systems.
- An expedient embodiment of this receiver is adapted to receive data signals asso ⁇ ciated with transmission systems using modulation forms of MSK type, since this is a widely used modulation form.
- the demodulator may be adapted to receive data signals associated with a mobile telephone system of e.g. GSM or DCS/PCS type in the first mode, i.e. when the demodulator operates as a coherent demodulator.
- the demodula- tor may be adapted to receive data signals associated with e.g. a transmission system of DECT type in the sec- ond mode, i.e. when the demodulator operates as a non-co ⁇ herent demodulator. Owing to the extensive use of these transmission types a receiver capable of receiving sig ⁇ nals of these types will be extremely expedient.
- the de ⁇ modulator is arranged such that switching between coher- ent and non-coherent demodulation is controlled by sig ⁇ nals received from the transmitter side of the transmis ⁇ sion system, so that it is the received signal type which decides whether coherent or non-coherent demodulation takes place.
- switching between coherent and non-coherent demodulation is controlled by means of a detector capable of detecting whether the received sig ⁇ nals are suitable for coherent demodulation, it is en- sured that the receiver itself decides on the basis of the quality of the received signals whether to use coher ⁇ ent or non-coherent demodulation. This may be relevant either if the signal quality from the transmitter varies, or where transmitters having a sufficient quality for co- herent demodulation to be used in the receivers as well as transmitters which do not meet this requirement, are used within the same system.
- fig. 1 shows two transmitters of different type and a re- DCver in which the invention may be applied
- fig. 2 shows the structure of a data receiver
- fig. 3 shows an example of a differential detector
- fig. 4 shows an example of a time discrete channel model
- fig. 5 shows a setup for coherent Viterbi equalizer.
- fig. 6 shows a setup for a non-coherent Viterbi equal ⁇ izer
- fig. 7 shows an example of a multimode Viterbi equalizer.
- Fig. 1 shows a system having a receiver 11 capable of re ⁇ ceiving data information from two different transmission systems, and two transmitters 1, 2 representing the two different systems.
- the transmitter 1 may be a transmitter for a mobile telephone system of GSM or DCS 1800/DCS 1900 type.
- the transmitter 2 may be a transmitter for a DECT transmission system.
- Data are transmitted wirelessly in blocks from the two transmitters through a time-varying transmission channel to the receiver.
- the transmitted signal is subjected to noise as well as distortion. It is therefore necessary to perform a so-called channel equalization on the received signal in the receiver.
- This channel equalization is performed to equalize the distor ⁇ tion applied in the transmission channel and in the radio frequency receiver of the receivers.
- Data are transmitted in blocks of finite duration between the transmitters 1, 2 and the receiver 11.
- Each data block contains a se ⁇ quence, a so-called training sequence, which is known to the receiver, and which enables the receiver to estimate the pulse response of the transmission channel, i.e. from the modulator of the transmitter to the demodulator of the receivers.
- the transmitter 1 from a GSM or DCS system contains a bit source 3 which supplies the data to be transmitted, and a radio frequency modulator 4 which modulates the data sig ⁇ nal by means of an oscillator 5 for the reference fre ⁇ quency. The modulated data signal is then emitted from an antenna * 6.
- the transmitter 2 from a DECT system similarly contains a bit source 7, a radio frequency modulator 8, a reference frequency oscillator 9 and an antenna 10.
- the receiver 11 receives data signals on the antenna 12, following which they are first processed in a radio fre- quency part 13 capable of receiving signals of GSM/DCS as well as DECT type.
- the radio frequency part 13 contains the reference frequency oscillator 14 of the receiver and a phase shift 15 ensuring that the data signals appear in a complex form on the output of the radio frequency part. This is shown in the figure by the two signals I, Q. Suitable amplification, filtering and mixing are per ⁇ formed in the radio frequency part to ensure sufficient selectivity and signal/noise ratios until the further processing of the data signals is performed.
- the data signals are passed from the radio frequency part 13 to the data receiver 16 in which the channel equalization and the detection proper take place.
- the radio frequency part 13 and the data receiver 16 are controlled by a con ⁇ trol circuit 17.
- Fig. 2 shows the structure of the data receiver 16.
- the complex signals I, Q are fed to a differential detector 18, a switch 19 and a channel estimator 20.
- the signals may be fed via the switch 19 either di ⁇ rectly or via the differential detector 18 to an equal- izer 21, which may e.g. be a Viterbi equalizer or another equalizer of MLSE type (Maximum Likelihood Sequence Esti ⁇ mator) .
- the channel estimator 20 finds the instantaneous transmission channel pulse response, which is then used by the equal- izer 21 to perform equalization, thereby allowing the re ⁇ ceived data information to be estimated.
- the reference frequency of the re- ceivers is so precise compared to the reference oscilla ⁇ tor in the corresponding transmitter that it will be pos ⁇ sible to use a so-called coherent receiver for equalizing the signal received.
- This receiver type requires that frequency and phase of the carrier wave of the received signal are known and constant for a block of received data.
- a so-called Viterbi equal ⁇ izer may be used, it being understood that the receiver has full knowledge of the frequency and phase of the re ⁇ ceived carrier wave.
- the channel pulse response is first estimated in the channel estimator 20 on the basis of the known sequence of the signal which is received. This estimate of the channel distortion is then used in the unit 21, which performs equalization and estimation of the bits which are received.
- the coherent version of the data receiver does not use the differential detector, as mentioned, and the complex baseband signal is therefore just bypassed, as shown.
- the reference frequency is not so precise as to enable the receiver to employ the coherent principle. Therefore, a so-called non-coherent principle is used.
- the reason is that the reference oscillator in the DECT transmitter 2 according to the DECT specification has very lenient frequency stability requirements, so that it cannot be expected that it is appropriate to implement a coherent receiver solution.
- the basis of the non-coherent principle is that the receiver does not know the exact frequency and phase of the received block, and that fre ⁇ quency and phase are not necessarily constant through a whole block.
- Fig. 3 shows an example of how the differential detector 18 may be constructed.
- the detector contains a time delay element 22 and an ele ⁇ ment 23 which performs complex conjugation of the sig ⁇ nals, which are still in a complex form (I, Q) .
- the re ⁇ sulting signal is then mixed with the original signal in the mixing stage 24.
- various dif- ferential detectors are available, and the detector shown in fig. 3 is merely an example of such a differential de ⁇ tector.
- the received signal is fed via the switch 19 to the equalizer 21, which is capable of performing so-called differential Viterbi equalization of the received signal by means of the estimated channel pulse response.
- This type of equalization is basically the same as the differential one, but with a few modifications because of the inclu ⁇ sion of the differential detector in the receiver chain.
- the pulse response of the channel is esti ⁇ mated in this type of transmission systems by means of a special bit sequence in the transmitted blocks. This makes it possible to generate a so-called time discrete channel model in the receiver which describes the influ- ence of the channel on the transmitted signal.
- This fig ⁇ ures shows an example of an estimated channel pulse re ⁇ sponse with L+l taps, called ho, ..., h L -
- the values 1 ⁇ are the symbols transmitted from the transmitter, which may generally take on complex values. It is assumed that I k can take on a total of M different values.
- This de ⁇ scription of the channel model means that it can be de ⁇ scribed as a state machine, in which the states can take on the values I k - 2 , •••, J k- L ) • This results in a state machine having a total of M states described by various combinations of the symbols I in the state de ⁇ scription Sj ⁇ -
- Fig. 5 shows the setup of input signal to the coherent Viterbi equalizer
- fig. 6 correspondingly shows the setup for input signal to the non-coherent Viterbi equal ⁇ izer.
- I k ( h 0 'I k +h l 'I k-l) ' ( h 0- I k-l +h I k-2)*
- the coherent and non-coherent Viterbi equalizations may be implemented such that just a single block must be capable of making calculations correspond ⁇ ing to either the coherent or the non-coherent receiver solution, while all the other blocks are common to the two solutions.
- the block "generation of reference received signal" must be capable of handling both the coherent setup and the non-coherent setup shown in figs. 5 and 6. All other blocks are the same for the two receiver types.
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU53324/96A AU5332496A (en) | 1995-04-05 | 1996-04-03 | A demodulator for transmission systems and use of such a demodulator |
EP96909985A EP0819348A1 (en) | 1995-04-05 | 1996-04-03 | A demodulator for transmission systems and use of such a demodulator |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DK0391/95 | 1995-04-05 | ||
DK39195A DK39195A (en) | 1995-04-05 | 1995-04-05 | Data receiver for transmission systems and use of such data receiver |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1996031970A1 true WO1996031970A1 (en) | 1996-10-10 |
Family
ID=8092982
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/DK1996/000162 WO1996031970A1 (en) | 1995-04-05 | 1996-04-03 | A demodulator for transmission systems and use of such a demodulator |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0819348A1 (en) |
AU (1) | AU5332496A (en) |
DK (1) | DK39195A (en) |
WO (1) | WO1996031970A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1102448A2 (en) * | 1999-11-15 | 2001-05-23 | Ericsson Inc. | Adaptive phase demodulation |
US6580930B1 (en) | 1999-04-15 | 2003-06-17 | Ericsson, Inc. | Signal detector selector and method for selecting a detector |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4583048A (en) * | 1985-02-26 | 1986-04-15 | Rca Corporation | MSK digital demodulator for burst communications |
US5117441A (en) * | 1991-02-25 | 1992-05-26 | Motorola, Inc. | Method and apparatus for real-time demodulation of a GMSK signal by a non-coherent receiver |
US5375143A (en) * | 1990-11-14 | 1994-12-20 | Motorola, Inc. | Method for channel adaptive detecting/equalizing |
WO1995013677A1 (en) * | 1993-11-09 | 1995-05-18 | Pacific Communication Sciences, Inc. | Method and apparatus for dual demodulation of mobile channel signals |
-
1995
- 1995-04-05 DK DK39195A patent/DK39195A/en unknown
-
1996
- 1996-04-03 AU AU53324/96A patent/AU5332496A/en not_active Abandoned
- 1996-04-03 WO PCT/DK1996/000162 patent/WO1996031970A1/en not_active Application Discontinuation
- 1996-04-03 EP EP96909985A patent/EP0819348A1/en not_active Withdrawn
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4583048A (en) * | 1985-02-26 | 1986-04-15 | Rca Corporation | MSK digital demodulator for burst communications |
US5375143A (en) * | 1990-11-14 | 1994-12-20 | Motorola, Inc. | Method for channel adaptive detecting/equalizing |
US5117441A (en) * | 1991-02-25 | 1992-05-26 | Motorola, Inc. | Method and apparatus for real-time demodulation of a GMSK signal by a non-coherent receiver |
WO1995013677A1 (en) * | 1993-11-09 | 1995-05-18 | Pacific Communication Sciences, Inc. | Method and apparatus for dual demodulation of mobile channel signals |
Non-Patent Citations (2)
Title |
---|
IEEE TRANSACTIONS ON COMMUNICATIONS, Volume 42, No. 7, July 1994, UPAMANYU MADHOW et al., "Universal Receivers with Side Information from the Demodulators: An Example for Nonselective Rician Fading Channels", pages 2395-2405. * |
IEEE TRANSACTIONS ON INFORMATION THEORY, Volume 37, No. 2, March 1991, UPAMANYU MADHOW et al., "A Parallel Systems Approach to Universal Receivers", pages 291-306. * |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6580930B1 (en) | 1999-04-15 | 2003-06-17 | Ericsson, Inc. | Signal detector selector and method for selecting a detector |
EP1102448A2 (en) * | 1999-11-15 | 2001-05-23 | Ericsson Inc. | Adaptive phase demodulation |
EP1102448A3 (en) * | 1999-11-15 | 2003-12-10 | Ericsson Inc. | Adaptive phase demodulation |
Also Published As
Publication number | Publication date |
---|---|
DK39195A (en) | 1996-10-06 |
AU5332496A (en) | 1996-10-23 |
EP0819348A1 (en) | 1998-01-21 |
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