Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
  • H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing

Definitions

• the present invention relates to a method and to a homodyne receiver for demodulating a signal modulated to a carrier frequency.
• the invention relates in particular to the reduction of the DC offset that arises in principle in a homodyne receiver.
• the signal 1 to be received is fed to a mixer 3 via an amplifier 2.
• the signal is a
• Local oscillator 4 is given to the mixer via a desired path 6 and, since the local oscillator 4 is operated at the frequency of the signal 1 to be received (FIG. 2), mixed with it into the baseband. Other frequencies naturally occur during the mixing process, but these are not of interest here and can be suppressed, for example, by suitable filters. A DC voltage signal thus arises which is demodulated in the demodulator 9.
• the local oscillator 4 has only finite isolation from its surroundings, so that the signal of the Local oscillator 4 is coupled via an undesired path 7 in the receiving branch of the receiver. This undesired coupling occurs due to capacitances with a phase shift ⁇ .
• the phase-shifted signal of the local oscillator 4 is now also passed to the mixer 3 and also mixed to zero with the original signal of the local oscillator 4 coupled in via the desired path 6. This creates an additional DC voltage signal, the so-called DC offset. overlaps with the desired signal.
• a homodyne receiver which has a mixer to which the signal to be demodulated and a further signal from a local oscillator are supplied.
• the homodyne receiver also has a modulator for spreading the local oscillator signal by means of a spreading code and a demodulator for spreading the output signal of the mixer.
• the invention further relates to a mobile radio receiver, such as. B. a base station or a mobile station of a wireless communication system having such a homodyne receiver.
• a method for demodulating a signal modulated to a carrier frequency in which the modulated signal is mixed with a signal from a local oscillator and the output signal resulting therefrom is demodulated again, modulating the signal of the local oscillator with a spreading code and despreading of the output signal resulting from the mixing takes place.
• the spreading code advantageously has a periodic rectangular course.
• Figure 1 shows schematically as a solution according to the invention a homodyne receiver with spread
• Figure 2 shows schematically a homodyne receiver according to the prior art with the undesired coupling mechanism.
• FIG. 1 shows in simplified form the branch of a homodyne receiver relevant to the invention.
• the signal of the local oscillator 4 is now spread by means of a modulator with a spreading code and passed on a desired path 6 on a mixer 3.
• This spread now causes two things: Firstly the modulated signal 1 to be received, which is fed to the mixer 3 via an amplifier 2, is mixed with the signal of the local oscillator 4 to zero, but is also spread by it.
• the spreading of the modulated signal is not intended and must therefore be reversed by a despreader 5 before demodulation. This is easily possible since the spreading code is known and was generated in the receiver itself. This happens after sampling the signal in the baseband.
• the undesired coupling mechanism described in the prior art leads to the spread signal of the local oscillator 4 being coupled into the receiving branch. As described above, it undergoes a phase shift ⁇ with respect to the desired path 6.
• both spread but phase-shifted signals of the local oscillator are mixed.
• the result of this mixing is a noise signal, which can also be shown mathematically: two spread signals that are not exactly in phase mix to form an uncorrelated signal, i.e. to a noise signal. This noise can be eliminated by using suitable filters.
• the signal of the local oscillator 4 which is coupled in via the undesired coupling path 7 is thus converted into noise and does not lead to a DC offset, as in the case of non-spread local oscillator signals.
• the phase-shifted, spread, coupled-in signal of the local oscillator 4 thus has little or no influence on the signal to be received.
• the suppression of the phase-shifted signal of the local oscillator 4 depends on the spreading factor with which the signal of the local oscillator 4 is spread and the size of the phase shift ⁇ , since this is a measure of the decorrelation.
• the spreading code can, for example, have a periodic rectangular course or any other suitable shape.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Superheterodyne Receivers (AREA)
• Noise Elimination (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Applications Claiming Priority (1)

Publications (1)

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• 2000
  • 2000-09-12 JP JP2002527042A patent/JP2004509496A/ja not_active Withdrawn
  • 2000-09-12 CN CN00819885.3A patent/CN1454408A/zh active Pending
  • 2000-09-12 WO PCT/DE2000/003174 patent/WO2002023712A1/de not_active Application Discontinuation
  • 2000-09-12 EP EP00963981A patent/EP1329018A1/de not_active Withdrawn

Non-Patent Citations (1)

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