Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
1999-11-04
2001-05-29
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
Frequency hopping
C375S373000, C327S129000
Reexamination Certificate
active
06240127
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for reducing interfering signals from an output signal of a digital synthesizer arrangement, the frequency of the output signal being determined by a signal which is supplied to the arrangement and to which signal is added a signal which breaks the periodicity of the signal.
BACKGROUND OF THE INVENTION
In radio systems, various frequency synthesis methods are used which employ, for instance, a reference signal source or a control signal by means of which one or more frequencies are generated. In a digital frequency synthesis, commonly used methods include DDS (Direct Digital Synthesis) and NCO (Numerically Controlled Oscillator) methods. Particularly in a radio system using frequency hopping, the synthesizer which performs the synthesis must be capable of becoming tuned quickly in small frequency steps over the entire frequency band. Synthesis methods are used together with various modulation methods.
Converting digital frequency information into analog in a DA converter is one of the drawbacks of the frequency synthesis. The conversion of a signal into analog has contributed to the generation of interfering signals in the output of the synthesis arrangement. Interfering signals have also been generated in an AD-converted signal. The interfering signals have caused interference peaks in the spectrum of the output signal of the synthesizer arrangement. If the interfering signals have exceeded the limits for interfering signals mentioned in the recommendations, the operation of some parts of the radio system has been impaired or possibly hindered altogether.
In frequency synthesis arrangements, various methods are used for reducing interfering signals in the output signal. A known method employs a digital frequency word by which the frequency of a signal obtained from the output of the arrangement is determined. In the method, the periodicity of the signal is broken, which results in fewer potential interfering signals in the output signal. The signal is broken at every clock cycle. The value of a breaking signal varies in such a manner that at every other clock cycle the value is a logical zero, and at every other clock cycle the value is a logical one.
The problem of the method described above is that the signal breakage has not been sufficiently efficient. Consequently, the output signal includes interfering signals even after the breakage.
BRIEF DESCRIPTION OF THE INVENTION
An object of the invention is thus to provide a method and a synthesizer arrangement so as to solve the above-mentioned problems. This can be achieved by a method of the type described in the introduction, the method being characterized by forming a signal which comprises the information on the phase of an output signal of the arrangement, forming a pseudo-random signal, adding the signal which comprises the phase information to the signal used in determining the frequency and to the pseudo-random signal in order to form a sum signal, feeding back part of the signal which comprises the phase information on the output signal to form a next sum signal.
The invention further relates to a synthesizer arrangement which is used for reducing interfering signals from an output signal of a digital synthesizer and which comprises a reception means which receives a signal determining the frequency of the output signal, a signal which breaks the periodicity of the signal being added to the received signal.
The synthesizer arrangement is characterized in that the arrangement comprises a means which forms, on the basis of the received signal, a signal which comprises the information on the phase used in the output signal, a generator means which forms a pseudo-random signal, a summing means which forms a sum signal by adding the signal which comprises the phase information to the signal used in determining the frequency and to the pseudo-random signal, and in which summing means part of the signal formed by the means is added to a next sum signal.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea that a pseudo-random signal is added to a frequency word, and after the addition, the signal comprising the pseudo-random signal is forwarded and added to next pseudo-random signals.
Several advantages can be achieved by the method and arrangement of the invention. In the method, the periodicity of the signal is effectively broken, whereby the generation of interfering signals in the spectrum of an output signal of the arrangement is prevented. The efficiency of breaking the periodicity is based on the fact that a pseudo-random signal is added to a sum signal for the formation of which the pseudo-random signal has already been used.
Furthermore, the method enables the frequency of the output signal to be changed in small frequency steps over an entire frequency band. The arrangement is relatively easy to implement for instance by discrete components. The arrangement can be implemented relatively easily on DDS or NCO systems already in use. A wider dither-free range can be achieved by means of the arrangement than by the known methods, and the arrangement can thus be implemented using fewer bits.
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patent: 5426392 (1995-06-01), Kornfeld
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patent: 858170 (1998-08-01), None
patent: 9808315 (1998-02-01), None
Altera Law Group LLC
Nokia Telecommunications Oy
Pham Chi
Phu Phuong
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