EP1210806A1

EP1210806A1 - Demodulator which uses a delay detector

Info

Publication number: EP1210806A1
Application number: EP00956517A
Authority: EP
Inventors: André Neubauer
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 1999-09-08
Filing date: 2000-09-06
Publication date: 2002-06-05
Also published as: US20020111148A1; JP3601713B2; US6549588B2; CN1372745A; CN100399774C; JP2003509908A; WO2001019046A1; DE19942944A1

Abstract

Angle-modulated signals are transmitted in a communications system. Coding information is inserted into the data to be transmitted (dk) at regular intervals and phase-modulated together with said data to be transmitted (dk). This coding process is used for pulse shaping so that the receiver (27) can recover the digital data to be transmitted (dk) by processing the signal accordingly without the carrier phase being regulated and therefore, more simply.

Description

description

DEMODULATOR USING A DELAY DETECTOR

The present invention relates to a communication system according to the preamble of claim 1, in which wave-modulated signals, in particular MSK signals (minimum shift keymg), are transmitted, and a corresponding receiver.

In wireless communication systems, such as DECT systems (Digital European Cordless Telephone) or radio systems, which are operated in the so-called unlicensed ISM frequency bands (Industrial Scientific Medical), super heterodyne receivers are often used to receive and demodulate phase-modulated signals.

To achieve higher system integration and thus lower system costs, so-called low IF (intermediate frequency) or zero IF (ho odyn) receivers are also increasingly being used, which do not require external filters to suppress image frequencies. Low-IF receivers use a relatively low intermediate frequency, which can be, for example, approximately 1 MHz for input signal frequencies of approximately 2 GHz, while the intermediate frequency for zero-IF receivers is 0 MHz. With this type of receiver, the phase-modulated received signal is demodulated by means of suitable, often analog signal processing (e.g. with DECT receivers).

4 shows a simplified block diagram of such a low or zero IF (homodyne) receiver.

In phase modulation, the communication information to be transmitted is transmitted via the phase of a carrier signal, the phase of the carrier signal being changed as a function of the value of the communication information to be transmitted. The high-frequency signal x _RF (t) received via a receiving antenna 1 generally has the form X _RF (0 = "(0 cos (ύ> ₀ t + φ ₀ ) - v (t) s (ω ₀ t + <p ₀ ) = Re {[u (t) + jv (t)] exp (jω ₀ t + φ ₀ )}

Here ω ₀ denotes the carrier frequency, while φ _{0 represents} the zero phase. The signal components u (t) and v (t) contain the time-dependent phase information corresponding to the communication or night bits to be transmitted. By recovering this phase information, the values of the individual communication bits can be deduced in the receiver.

For this purpose, the reception signal x _RF (t) is first pre-filtered by means of a bandpass filter 14 and amplified by means of a linear amplifier 23 in m low-IF or zero-IF receivers. The received signal thus processed is then divided into two signal paths, namely an I and a Q signal path. In the I signal path, the received signal m in a mixer 15 is multiplied by the signal cos (ω ₀ t) of a local oscillator 17, while in the Q signal path the received signal in a mixer 16 is multiplied by the corresponding quadrature signal -sm (ω ₀ t) , which is obtained from the oscillator signal cos (ω ₀ t) with the aid of a corresponding phase shift unit 18. A low-pass filtering with the aid of appropriate anti-aliasing filters 19 and 20 and an A / D conversion with the aid of corresponding A / D converters 21 and 22 then take place in both signal paths. The output signals of the two signal paths are finally grounded evaluated by a (in the present case digital) signal processing unit in order to use the signals thus obtained to produce the generally complex useful signal [u (t) + jv (t)] ω ₀ t) with the desired phase information, from which in turn the values of the transmitted communication or message bits d _k can be derived.

It can be seen from the illustration in FIG. 4 that such a homodyne receiver generally has two real signal paths, each with a mixer 15 or 16, a filter 19 or 20 and an A / D converter 21 or 22 required. In addition, a component 18 is required to generate the quadrature signals of the local oscillator 17. The procedure described above is in principle suitable for all types of phase modulation. However, it does not take advantage of the properties of suitably defined modulation methods to reduce effort.

In the case of a phase- and frequency-rigid (ie coherent) reception, regulation of the carrier phase is also necessary in the receiver because of the unknown zero phase φ ₀ , which increases the implementation effort of the receiver accordingly.

The present invention is therefore based on the object of proposing a communication system for transmitting and receiving angle-modulated signals, in particular digital phase or frequency-modulated signals, and a corresponding receiver, the receiver being able to be implemented with significantly less effort.

This object is achieved according to the invention by a communication system with the features of claim 1 or a receiver with the features of claim 9. The subclaims each define preferred and advantageous embodiments of the present invention.

With the help of the present invention, a suitable definition of the digital modulation method for coding and pulse shaping is proposed, so that the receiver with respect to its analogue preliminary stage (front end) without carrier phase control and, based on the known homodyne receiver shown in FIG. 4, about half Circuit effort can be realized.

For this purpose, coding information or coding bits are inserted into the message bits to be transmitted, where in particular, for example, a coding bit with the fixed binary value "1" can be inserted between two successive message bits. The receiver is designed such that, by suitable signal processing of the angle-modulated signal based on the message and coding bits, the original message bits can be detected with only one real signal path, ie without a complex I / Q signal path. In contrast to the known homodyne receiver shown in FIG. 4, the destination of the receiver is therefore not the signal reconstruction, but the detection of the digital transmission data.

The proposed coding and pulse shaping make phase-incoherent demodulation of the angle-modulated received signal and detection of the digital transmit data independent of a possible phase shift between the high-frequency received signal of the receiver and the local oscillator signal, which is used in the receiver for mixing down the received signal into the baseband , enables. The carrier phase control required in the homodyne receiver shown in FIG. 4 can thus be omitted.

Furthermore, in contrast to FIG. 4, the mixer, filter and A / D converter only have to be provided once. Since no complex I / Q signal path is required, the

Quadrature signal generation for the local oscillator signal is eliminated, and there are no matching requirements to be observed between the I / Q signal paths.

The present invention is described below with reference to a preferred embodiment with reference to the drawing.

1 shows a simplified block diagram of a receiver according to the invention, FIG. 2 shows a possible implementation of a digital demodulator shown in FIG. 1,

3 shows a representation to explain the bit error rate that can be achieved when the present invention is applied, and

4 shows a simplified block diagram of a known homodyne receiver.

The present invention is explained below by way of example using MSK-modulated (minimum shift keying) signals for the noise-free case. However, the invention is not restricted to this type of modulation, but rather can be applied generally to all types of angle modulation, in particular to all CPFSK (continuous phase frequency shift keying) modulation methods, such as those used according to the DECT or GSM mobile radio standard ,

According to the MSK modulation, the phase of the carrier signal is rotated either by -π / 2 or by + π / 2 depending on the binary value d _k e {- 1,1) to be transmitted.

The high-frequency MSK signal x _RF (t) transmitted by a transmitter 25 shown in FIG. 1 via a transmitting antenna 26 and received by a receiver 27 via a receiving antenna 1 generally has the form:

'- RF (t) = cos (ω ₀ t + φ ₀ + Aφ + θ (t))

Here ω ₀ denotes the carrier frequency, φ ₀ the zero phase, Δφ the phase offset between the RF received signal and the signal from the local oscillator (not shown in FIG. 1) of the receiver 27 and θ (t) which are the result of the binary information to be transmitted adjusting phase change of the carrier signal. The transmitter 25 shown in Fig. 1 is designed such that not only the actual message bits d _k are transmitted phase-modulated, but also coding bits, which guide from the transmitter 25 at regular intervals before passing ^¬ be inserted, with the phase modulation in the Nachrichtenbitsequenz. In particular, it is proposed to code in such a way that a coding bit with the fixed binary value "1" is inserted between two successive message bits, so that the carrier phase is changed by + π / 2 during phase modulation by this coding bit.

The RF signal x _RF (t) thus generated by the transmitter 25 and received by the receiver 27 is first amplified with the aid of a linear amplifier 2 and fed to a mixer 3, where it is mixed with the signal 2cos (ω ₀ t + φ ₀ ). of the already mentioned local oscillator of the receiver 27 is multiplied so that the baseband signal y (t) = cos (Δφ + θ (t)) is generated by the mixer 3, which is low-pass filtered with the aid of an anti-aliasing filter 4 and scanned by means of an A / D converter 5 with the clock I / T and converted into a digital data sequence y _k = cos (Δφ + Θ _k ).

The following formula applies to the temporal course of the carrier phase change caused by the binary information transmitted in the signal x _RF (t):

θ _k = π / 2 - (f + / _t _, + ... + /, +

Because of the coding described above and carried out by the transmitter, in which every second bit to be transmitted has been set to the binary value "1", the following applies to the coefficients:

I _k = 1 for k = 2n, and

I _L = d _k for k = 2n + l (n = 0, 1, 2,...) This coding is a special case of Hadamard coding and is equivalent to a corresponding pulse shaping. As a result of the coding, the bit rate is 2 / T.

A digital demodulator 6 shown in FIG. 1 has the task of determining the transmitted message bits d _k by evaluating the individual sample values y. A possible implementation of the digital demodulator 6 is shown in FIG. 2 in the form of a simplified block diagram.

3, the digital demodulator 6 according to this exemplary embodiment comprises only three memory or delay elements 7-9, which form a shift register of the length 3, two multipliers 10 and 11 and an adder 12 and a sign. Detector 13. By interconnecting the multipliers 10 and 11 with the individual memory stages 7-9 of the shift register it is achieved that one of these two multipliers always multiplies two samples of the baseband signal sequence y _k , which go back to two successive message bits, while the other multiplier two Multiplied samples of the baseband signal sequence y _k , which are based on two successive coding bits. The multiplication results are added by the adder 12, so that the sign detector 13 can simply determine and output the values of the transmitted message bits d by evaluating the sign of the addition result.

The aforementioned coding not only implements pulse shaping, but in particular enables phase-incoherent demodulation and detection of the message bits d independently of a possible phase offset Δφ between the high-frequency received signal x _RF (t) and the local oscillator signal, so that none Carrier phase control is required. 3 shows the bit error rate (BER) that can be achieved using the present invention as a function of the bit signal-to-noise ratio E _b / N ₀ . The corresponding BER characteristics of other known demodulation methods (coherent and incoherent) are also shown for comparison. It can be seen from the illustration in FIG. 3 that the reduction in implementation effort that can be achieved with the aid of the present invention compared to incoherent FSK demodulation, as is implemented, for example, in DECT receivers with the aid of a complex I / Q signal path, at a bit error rate of 10 ^{"3 is} only bought with a reduced power efficiency of approx. 2dB.

To improve the performance efficiency, however, instead of the Hadamard coding described above, a higher-quality Hadamard coding can be used, in which the coding bits are inserted into the message bit sequence to be transmitted at greater intervals. In this case, the digital demodulator 6 shown in FIG. 2 must of course be adapted accordingly with regard to the length of the shift register and the connection of the two multipliers 10, 11 to the shift register.

Claims

claims

1. Communication system, wherein communication information (d) in the form of an angle-modulated signal (x _RF (t)) is transmitted between a transmitter (25) and a receiver (27), with the transmitter (25) for each communication information during the angular modulation ( d _k ) m the phase-modulated signal (x _RF (t)) is assigned a phase change of a carrier signal corresponding to the value of the communication information (d _k ), the receiver (27) comprising a mixer (3) to convert the angle-modulated signal (x _RF (t)) to be mixed with a signal having the carrier frequency (ω ₀ ) of the carrier signal and thus to generate a baseband signal (y (t)) which is freed from the carrier frequency (ω ₀ ) and a phase curve corresponding to the individual phase changes and wherein the receiver (27) comprises an analog / digital converter (5) in order to sample the phase curve of the baseband signal (y (t)) of the mixer (3) and convert it into a digital data sequence (y _k ), characterized in that the transmitter (25) is designed in such a way that it inserts m the communication information (d _k ) m regular information, coding modulated together with the communication information (d _k ) and m form the angle-modulated signal (x _RF (t)) to the receiver (27), and that the receiver (27) comprises a digital evaluation device (6) which on the one hand corresponds to successive communication information (d _k ) corresponding phase samples and on the other hand corresponding coding information corresponding phase samples of the digital data sequence (y) of the analog / digital converter (5) is initially processed separately, the processing results are combined with one another and the combination result is evaluated in order to retrieve the communication information (d _k ) as a function thereof.

2. Communication system according to claim 1, characterized in that the digital evaluation device (6) comprises: a shift register arrangement (7-9) for temporarily storing successive phase samples of the digital data sequence (y) of the analog / digital converter (5), a multiplier (10; 11) for multiplying the phase samples of the digital data sequence (y _k ) of the analog / digital converter (5) corresponding to the successive communication information (d _k ), a multiplier (11; 10) for multiplying the phase samples of the digital corresponding to the successive coding information Data sequence (y _k ) of the analog / digital converter (5), a combiner (12) for combining the multiplication results of the two multipliers (10, 11), and a detector device (13) for evaluating the combination result of the combiner ( 12) in order to retrieve the communication information (d _k ) depending on this.

3. Communication system according to claim 2, d a d u r c h g e k e n n z e i c h n e t that the combiner (12) is an adder.

4. Communication system according to one of the preceding claims, characterized in that the transmitter (25) is designed such that it inserts the coding information in each case between two successive communication information items (d _k ), and that the digital evaluation device (6) of the receiver (26) in each case two consecutive communication information (d _k ) corresponding phase samples and two consecutive coding information corresponding phase samples of the digital data sequence (y _k ) of the analog / digital converter (5) initially processed separately, the processing result combined with one another and evaluating the combination result in order to retrieve the communication information (d _k ) as a function thereof.

5. Communication system according to claim 4 and claim 2 or

3, characterized in that the shift register arrangement, to which the individual phase samples of the digital data sequence (y _k ) of the analog / digital converter (5) are supplied sequentially, comprises three delay elements (7-9) connected in series, that the one multiplier (10 ) multiplies the phase sample value currently supplied to the first delay element (7) from the analog / digital converter (5) and the phase sample value currently stored in the second delay element (8), and that the other multiplier (11) in each case multiplies the one in multiplied by the first delay element (7) and the phase sample currently stored in the third delay element (8).

6. Communication system according to claim 5, characterized in that the transmitter (25) is designed such that it modulates the to be transmitted to the receiver (27) sequence of binary communication information (d _k ) and coding information on the carrier signal such that in the angle-modulated Signal (x _RF (t)) is assigned a phase change in the carrier signal by + π / 2 to a first binary value to be transmitted and a phase change in the carrier signal by -π / 2 to a second binary V value to be transmitted, and that the detector device (13 ) detects the sign of the combination result of the combiner (12) in order to retrieve the binary value of each individual communication information (d _k ) as a function thereof.

7. Communication system according to one of the preceding claims, characterized in that the transmitter (25) is designed such that it inserts the same binary value as coding information into the communication information (d _k ) at regular intervals.

8. Communication system according to claim 6 and 7, so that the first binary value is selected as the value of the coding information, which results in a phase change of the carrier signal by + π / 2 in the angle modulation in the transmitter (25).

9. Communication system according to one of the preceding claims, characterized in that the receiver (27) is designed such that it receives the communication information (d _k ) by a phase-incoherent and single-channel signal processing of the angle-modulated signal (x _RF (t)) without I / Q- Distribution of the angle-modulated signal (x _RF (t)) is recovered.

10. Receiver for receiving angle-modulated signals for a communication system according to one of the preceding claims, wherein with an angle-modulated signal to be received (x _RF (t)) communication information (d) in the form of corresponding phase changes of a carrier signal are transmitted, the receiver ( 27) comprises a mixer (3) in order to mix the angle-modulated signal (x _RF (t)) with a signal having the carrier frequency (ω ₀ ) of the carrier signal and thus to generate a baseband signal (y (t)) which is freed from the carrier frequency (ω ₀ ) and has a phase curve corresponding to the individual phase changes, and wherein the receiver (27) comprises an analog / digital converter (5) to sample the phase curve of the baseband signal (y (t)) of the mixer (3) and convert it into a digital data sequence (yk), characterized in that in the received angle-modulated signal (x _RF (t)), the communication information (d _k ) together with coding information, which is inserted into the communication information at regular intervals, in the form of corresponding phase changes of the carrier signal, and that the receiver (27) has a digital evaluation device ( 6), which first processes phase communication values corresponding to successive communication information (d _k ) and, on the other hand, phase sampling values corresponding to successive coding information of the digital data sequence (yk) of the analog / digital converter (5) are initially processed separately, the processing results are combined with one another and the combination result is evaluated, to depend on it gig to regain the communication information (d _k ).

11. Receiver according to claim 10, that the receiver (27) is designed in accordance with one of claims 2-9.