Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Patent
1996-06-07
1998-08-04
Ton, Dang
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
H04J 100
Patent
active
057905550
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FILED
The present invention relates to a signal multiplexer which combines the power of multiple, modulated and different frequency-band signals (hereinafter referred to simply as modulated signals). The signal multiplexer is applied to, for example, a multi-carrier transmission system used in mobile communications, satellite communications or radio paging systems.
BACKGROUND ART
FIG. 1 illustrates a conventional signal multiplexer. Input signals from input port 11.sub.1 to 11.sub.n are converted by frequency converting means 12.sub.1 to 12.sub.n into signals of different frequency bands, respectively. In each frequency converting means 12.sub.i (i=1, 2, . . . , n), the frequency of the input signal from the input port 11.sub.i is mixed by a multiplier 14.sub.i with the frequency f.sub.i of a local signal from a local oscillator 13.sub.i and a desired frequency band f.sub.i ' is filtered by a band-pass filter 15.sub.i from the mixed output as the output of the frequency converting means 12.sub.i. Here, the input signal from the input port 11.sub.i is, for example, a baseband signal which is BPSK modulated, QPSK modulated, QAM modulated or an intermediate frequency signal which is modulated by a certain type of modulation scheme. The output signals from the frequency converting means 12.sub.1 to 12.sub.n are linearly combined by power combining means 16, which provides the combined output to an output port 17. The power combining means 16 linearly combines multiple, modulated and different frequency-band signals that are provided from n input channels and is constructed by a transformer circuit or hybrid circuit. In this way, the n-channel input signals are multiplexed in the frequency space. The multiplexed signal is output from output port 17 as a multi-carrier signal, which is composed of different frequency-band signals and has equally spaced carrier components. In some cases, the band-pass filters 15.sub.1 to 15.sub.n are omitted and instead a band-pass filter is provided at the output side of the power combining means 16.
FIG. 2 shows the basic principle of a conventional m-ary FSK signal multiplexer for m=2. For m>2, the configuration of the multiplexer is the same as in the case where m=2, except that m local oscillators are used. This conventional multiplexer comprises n (n.gtoreq.2) m-ary FSK modulators 5.sub.i (i=1, 2, . . . , n) corresponding to n channels and a power combining means 6. Each m-ary FSK modulator 5.sub.i is composed of input ports 1.sub.i, m (m=2 in this example) local oscillators 2.sub.i and 3.sub.i which oscillate at different frequencies, and signal switching means 4.sub.i which selects and outputs either one of the outputs from the oscillators 2.sub.i and 3.sub.i in accordance with the code of the input signal to the input port 1.sub.i. The output signals from the m-ary FSK modulators 5.sub.i are different in frequency band and are linearly combined by the power combining means 6 constructed by a transformer circuit or hybrid circuit, and an FSK signal multiplexed in the frequency space is provided at an output port 7.
The local oscillators 2.sub.i and 3.sub.i are all shown to operate independently of each other. However, in some cases, reference frequency oscillating means is provided and its output is split into all the oscillators 2.sub.i and 3.sub.i in order to improve the frequency accuracy of all the local oscillators 2.sub.i and 3.sub.i.
As shown in FIG. 3, the m-ary FSK modulator 5.sub.i may sometimes be constructed by one oscillating means (usually a PLL synthesizer) which is able to change the frequency of the output signal in accordance with the signal at the input port 1.sub.i. The circuit configuration in FIG. 3 is identical with that in FIG. 2 except for the provision of reference frequency oscillating means 8 and the configuration of the m-ary FSK modulator 5.sub.i. The m-ary FSK modulator (PLL frequency synthesizer) 5.sub.i in FIG. 3 is made up of low-pass filter means 9.sub.i, amplifying means 10.sub.i, a voltage-controlled oscillator (VCO) 41
REFERENCES:
patent: 5278548 (1994-01-01), Haber
patent: 5519702 (1996-05-01), Takahashi
Kumagai Ken
Narahashi Shoichi
Nojima Toshio
Tarusawa Yoshiaki
NTT Mobile Communications Network Inc.
Ton Dang
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