Communications system and corresponding receiver unit

Details Communications system and corresponding receiver unit Communications system and corresponding receiver unit

2002-03-08

2003-04-15

Trost, William (Department: 2683)

Pulse or digital communications

Receivers

Angle modulation

C455S313000, C455S316000, C455S318000, C455S116000, C455S071000, C455S130000, C375S279000, C375S280000, C375S329000, C329S304000

Reexamination Certificate

active

06549588

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a communications system in which angle-modulated signals, in particular MSK signals (Minimum Shift Keying) are transmitted, and to a corresponding receiver.
Superheterodyne receivers are frequently used for receiving and demodulating phase-modulated signals in wire-free communications systems, such as DECT systems (Digital European Cordless Telephone) or radio systems that are operated in the so-called unlicensed ISM frequency bands (Industrial Scientific Medical). In order to achieve greater system integration and thus reduced system costs, so-called low-IF (Intermediate Frequency) or zero-IF (homodyne) receivers are also increasingly being used, which do not require any external filters to suppress mirror frequencies. Low-IF receivers use a relatively low intermediate frequency which may be, for example, about 1 MHz for input signal frequencies of about 2 GHz, while the intermediate frequency in zero-IF receivers is 0 MHz. In receivers of this type, the phase-modulated received signal is demodulated using suitable signal processing, which is frequently analog (for example in DECT receivers).
FIG. 4
shows a simplified block diagram of such a low-IF or zero-IF (homodyne) receiver.
In the case of phase modulation, the communication information that will be transmitted is transmitted via the phase of a carrier signal, with the phase of the carrier signal being varied as a function of the value of the communication information to be transmitted. The radio-frequency signal X
RF
(t) received via a receiving antenna
1
in general has the form:
X
RF
(
t
)
=u
(
t)cos(&ohgr;
0
t+&phgr;
0
)
−v
(
t
)sin(&ohgr;
0
t+&phgr;
0
)
=Re{[u
(
t
)
+jv
(
t
)]exp[(
j&ohgr;
0
t+&phgr;
0
)}
In this case, &ohgr;
0
denotes the carrier frequency, with &phgr;
0
representing the zero phase. The signal components u(t) and v(t) contain the time-dependent phase information, which corresponds to the communication or message bits that will be transmitted. The values of the individual communication bits can be deduced in the receiver by recovering this phase information.
For this purpose, in low-IF or zero-IF receivers, the received signal X
RF
(t) is initially filtered using a bandpass filter
14
, and is amplified using a linear amplifier
23
. The received signal that has been processed in this way is then split between two signal paths, namely an I signal path and a Q signal path. In the I signal path, the received signal is multiplied in a mixer
15
by the signal cos(&ohgr;
0
t) from a local oscillator
17
, while in the Q signal path, the received signal is multiplied in a mixer
16
by the corresponding quadrature signal −sin(&ohgr;
0
t), which is obtained from the oscillator signal cos(&ohgr;
0
t) by using an appropriate phase shifting unit
18
. Low-pass filtering, using appropriate respective anti-aliasing filters
19
and
20
, and A/D conversion, using respective appropriate A/D converters
21
and
22
, are then carried out in both signal paths. The output signals from the two signal paths are finally evaluated by a signal processing unit (which, in the present case, is digital) to obtain, from the signals recovered in this way, the generally complex useful signal [u(t)+jv(t)]−exp(&ohgr;
0
t) with the desired phase information, from which the values of the transmitted communication or message bits d
k
can in turn be derived.
It can be seen from
FIG. 4
that such a homodyne receiver generally requires two real signal paths having a respective mixer
15
or
16
, a respective filter
19
or
20
, and a respective A/D converter
21
or
22
. Furthermore, a component
18
is required, in order to produce the quadrature signals from the local oscillator
17
. The procedure described above is, admittedly, in principle suitable for all types of phase modulation. However, it does not exploit the characteristics of suitably defined modulation methods in order to reduce the complexity.
In the case of phase-locked and frequency-locked (that is to say coherent) reception, it is also necessary to control the carrier phase in the receiver, since the zero phase &phgr;
0
is unknown, which increases the implementation complexity in the receiver in a corresponding manner.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a communications system for transmitting and receiving angle-modulated signals which overcomes the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to provide a communications system for transmitting and receiving angle-modulated signals, specifically digital phase-modulated or frequency-modulated signals, and a corresponding receiver, in which case the receiver can be implemented with considerably less complexity as compared with prior art receivers.
With the foregoing and other objects in view there is provided, in accordance with the invention, a communications system that includes a transmitter for transmitting an angle-modulated signal having communication information and coding information that have been modulated onto a carrier signal at a carrier frequency. The transmitter inserts the coding information into the communication information at regular intervals. The transmitter constructs the angle modulated signal by performing an angle modulation process in which, for each item of the communication information and for each item of coding information, a corresponding phase change in the carrier signal is obtained. The communications system includes a receiver for receiving the angle-modulated signal. The receiver has a mixer for mixing the angle-modulated signal with a signal having the carrier frequency of the carrier signal such that a baseband signal is obtained in which the carrier frequency has been removed. The baseband signal has a phase profile corresponding to the phase change for each item of the communication information and to the phase change for each item of coding information. The receiver has an analog/digital converter for sampling the phase profile of the baseband signal from the mixer and for converting the baseband signal to a digital data sequence having phase sample values. The receiver has a digital evaluation device that receives the digital data sequence from the analog/digital converter. The digital evaluation device initially separately, obtains first processing results by processing ones of the phase sample values corresponding to successive items of the communication information and obtains second processing results by processing ones of the phase sample values corresponding to successive items of the coding information. The digital evaluation device combines the first processing results with the second processing results to obtain a combination result. The digital evaluation device evaluates the combination result to recover the communication information as a function of the combination result.
In accordance with an added feature of the invention, the digital evaluation device includes: a shift register configuration for buffer-storing successive ones of the phase sample values of the digital data sequence from the analog/digital converter; a multiplier for obtaining a first result by multiplying together the ones of the phase sample values that correspond to the successive items of the communication information; a multiplier for obtaining a second result by multiplying together the ones of the phase sample values that correspond to the successive items of the coding information; a combiner for obtaining a combination result by combining the first result and the second result; and a detector device for evaluating the combination result from the combiner to recover the communication information as a function of the combination result.
In accordance with an additional feature of the invention, the combiner is an adder.
In accordance with another feature of the invent

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