Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
1998-08-04
2001-07-24
Urban, Edward F. (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S307000, C455S337000, C375S340000, C375S350000
Reexamination Certificate
active
06266521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a receiver for radio communications and to a method for demodulating reception signals, and more particularly, to a receiver suitable for a radio communications system wherein the transmission speed and modulation method are variable.
2. Description of the Related Art
Of currently used radio telephone methods and radio paging systems, there are known systems wherein the transmission speed and modulation method can be varied. For example, in the FLEX (registered trademark) system, which is a radio paging system, there are three transmission speeds (1600/3200/6400 bps) and two modulation methods (2FSK (Frequency Shift Keying)/ 4FSK), and two symbol rates are set (1600/3200 sps). In a radio paging system of this kind, in order to minimize noise bandwidth, desirably, the pass bandwidth of an LPF (Low Pass Filter) located in the signal path after quadrature detection is changed in accordance with the symbol rate.
However, in conventional receivers, if the aforementioned LPF is formed by an analogue circuit, for example, then the LPF is designed to be compatible with a symbol rate of 3200 sps. Therefore, if the symbol rate is 1600 sps, problems arise, such as increased susceptibility to noise and deterioration of the bit error rate (BER).
In order to resolve problems of this kind, the output signal from the aforementioned LPF is converted to binary form, and BER degradation is reduced by passing the signal again through a moving average-type digital LPF which changes bandwidth according to the symbol rate.
However, the moving average-type filter comprises numerous stages of shift registers. Therefore, the circuit becomes relatively large in size, and power consumption also increases. In particular, in radio telephones and pagers of recent years, it has been sought to reduce power consumption and to increase call time and standby time, but if a moving average-type filter is used as described above, then it is difficult to achieve increases in call time and standby time, due to the scale of the circuit involved.
SUMMARY OF THE INVENTION
With a view to resolving the foregoing problems, it is an object of the present invention to provide a receiver, whereby the bit error rate can be reduced by means of a simple circuit composition, whilst reducing power consumption.
The object of the present invention is achieved by means of a receiver comprising: a detector circuit which receives an intermediate frequency signal and converts it to a base band signal; a binary converting circuit which is connected to said detector circuit and converts said base band signal to binary form; a filter circuit which receives output signal from said binary converting circuit and passes frequency components of said output signal, which are odd factors of the fundamental frequency of said output signal; and a decoding circuit which is connected to said filter circuit and decodes output signal in accordance with a clock recovered from the output signal from said filter circuit.
According to the present invention, a signal converted to binary form by the binary converting circuit and having an approximately square waveform is filtered by a filter circuit which transmits frequency components that are odd factors of the fundamental frequency of the signal. Consequently, noise components are adequately removed, thereby allowing the bit error rate to be reduced.
The object of the present invention is also achieved by means of a pager comprising: a quadrature detector which receives an intermediate frequency signal and performs quadrature detection; a first filter which is connected to said quadrature detector and passes low-frequency in the output of said quadrature detector; a comparator which is connected to said first filter and converts the output of said first filter to binary form using a prescribed threshold value; a second filter which is connected to said comparator and extracts a prescribed signal from the output of said comparator; a clock recovery circuit which is connected to said second filter and recoveries a clock by acquiring and tracking synchronization with respect to the output of the second filter; a sampler which is connected to said second filter and samples the output of the second filter on the basis of the clock output by said clock recovery circuit; and a second comparator which is connected to said sampler and converts the signal sampled by said sampler to binary form; wherein said second filter transmits frequency components which are odd factors of the fundamental frequency of the output signal of said comparator.
The object of the present invention is achieved by method for demodulating reception signals comprising the steps of: converting an intermediate frequency signal to a base band signal; converting said base band signal to binary form; transmitting frequency components which are odd factors of the fundamental frequency of the signal by filtering said binary signal; and decoding filtered signal in accordance with a clock recoveried from the basis of the filtered signal.
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Hattori Tadayuki
Seki Kazuhiko
McDermott & Will & Emery
Uniden Corporation
Urban Edward F.
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