JPS63200635A - Transmultiplexer - Google Patents

Abstract

PURPOSE:To attain a digital transmultiplexer TMUX whose frequency is not limited depending on the frequency interval and flat by receiving an output of N-set of inserted digital subfilters and applying high speed Fourier transformation at the speed of the inserted clock. CONSTITUTION:Delay circuits 12-1-12-N are connected to the output of a time/space division converting switch 11 and N-set of complex base band signals having a coincident timing are generated by applying a delay proportional to the arrival sequence of the corresponding signal. Further, the interpolation digital subfilters 17-1-17-N are connected to the delay circuits 12-1-12-N to apply prescribed filtering based on the timing by the channel clock and the interpolated clock and a filter output is generated at the sampling speed of the interpolated clock. Then the output of the digital subfilters 17-1-17-N is received to apply high speed Fourier transformation at the speed of the interpolated clock. Thus, a flat filter characteristic at each channel band is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital transform multiplexer (hereinafter abbreviated as TMUX) that is widely used in communication networks.

[Conventional technology]

TMUX is widely used for FDM/TDM conversion in communication networks.

The configuration of a conventional TMUX is shown in FIG. 1 is a local oscillator, 2 is a π/2 transfer device, and 3 and 4 are mixers.

5 and 6 are LPFs, 7 and 8 are A/D converters, 9 is a multiplexed clock oscillator (frequency NΔf), 10 is an N frequency divider, 11 is a switch circuit, 12-1 to 12-N are delay devices,
13-1 to 13-N are digital sub-filters.

14 is an N-point FFT.

[Problem that the invention seeks to solve]

A diagram of the operating principle of T■■ is shown in Figure 6. 31 is a BPF tuned to a frequency corresponding to ω, and 32 is a multiplier.

33 is a carrier phase generator, 34 is an N frequency divider, and 35 is a sunshield.

FIGS. 7(a) and 7(b) show a basic diagram of an FIR type digital filter and its division into subfilters. 41
is a shift register, 42-1.42-2. ...42
-L is a coefficient, ), hl+"·hL 1 weighting circuit, and 43.44 is an adder.

Figure 8 shows N=4. O showing the relationship between the impulse responses of the digital filter and the sub-filter when L=24 The principle of TMUX will be explained with reference to the above drawings FIGS. 5 to 8. The characteristics of the basic LPF are shown in Figure 7 (,).

Then, the N sub-filter divisions are:

becomes. however.

t=.

z=8jofr=8jω/(NΔf) (4
). Δf is the channel frequency spacing.

is the period of the multiplexing clock. It has the frequency characteristics of formula (1) or (2).

ω=toΔω=k(2πΔf) (6)
The transfer function of a digital BPF whose center frequency is (k=o, ±1.±2...., ±100-1) is.

, 2πk z → ej(ω−ωk)T=6 3 ,
-z (7) Through variable transformation.

becomes.

On the other hand, the output of the φ converter 7.8 in FIG.

R(z) =ΣrnZ” (9)
shall be. However, γ is a complex sequence consisting of a pair of real and imaginary part signals.

The received signal is also divided into sub-signals in the same way as the filter.

It can be expressed as however.

R1 (ZN) = ΣγnN tent (ZN)”
It is α.

Therefore, the output when input signal R(z) is passed through BPF H(z;k) is.

It can be expressed as

Here, the output of BPF k is changed to ω → 0 (rad/s
To convert the frequency to ee).

z Yo6j (ω+ωk)T=ej? ni-z (11
By variable transformation.

, 2π H(z;k)R(z) l z−+zej N k totoru. However, Hα=0 (α<0.α>N). 2α→
The term zn means interpolation between signal sequences of NT=1/Δf at a period of T. That is, Hn-4(ZN)
・Rt (zN) time minc 0, N, 2 N
, -..., the interpolation output timing based on zn is as shown in FIG.

In the conventional TMUX, only n=N-1 is selected in FIG. 9. That is, the BPF-frequency conversion output is sampled at a channel clock frequency of Δf. By selecting only n=N-1, the TMUX output is.

In other words, the circuit configuration of this device is shown in FIG.

TMUX has the excellent advantage that it is common to all channels and can realize a filter group with accurate frequency characteristics using a digital circuit.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional method, an output signal is obtained as a signal sequence sampled at a channel spacing frequency of 9 essentially Δf. Therefore, it is impossible to realize filter characteristics having a frequency band wider than Δf.

By the way, Figure 4 (,) shows the basic frequency characteristics of the filter, and (b) shows the TMLJX when a wideband signal is input.
shows the frequency characteristics of the output signal. When the bandwidth of the basic filter is limited to within Δf, as shown by the solid line □ in the figure, the frequency spectrum is correctly output as shown in FIG. 4(b). However, as shown by the broken line, if a filter with a frequency characteristic wider than Δf is used, the output signals overlap in frequency due to aliasing, making it impossible to separate the signals correctly. For this reason, it is not impossible to achieve filter characteristics that are flat within the band, but in order to achieve filter characteristics that are as flat as possible within the band, it is necessary to design a filter with steep frequency characteristics. occurs, and the scale of the two circuits increases.

The present invention aims to overcome the above-mentioned drawbacks of the conventional T■■ and provide a TMUX whose two-frequency characteristics are not limited to Δf and are flat.

[Means for solving problems]

The transmultisolexor according to the invention has two frequency intervals Δ
Two mixers that convert the frequency of the N-channel input IF multiplexed signal FDM multiplexed at f into a baseband complex signal, and two mixers that sample the output of the two mixers, convert it to a digital numerical signal, and output it. A/D converter, and the two A/D converters
a frequency dividing circuit that divides the NΔf multiplexed clock supplied to the /D converter to generate a channel clock divided by N and an interpolation clock divided by N/m; and the two A/D converters. a time/space division conversion switch that receives a device output and separates and outputs an input time series into N separate outputs every N samples based on the timing by the multiplexing clock and the channel clock; and the time/space division conversion switch. a delay circuit connected to the output of the delay circuit for generating N complex baseband signals at a speed Δf with coincident timing by adding a delay proportional to the order of arrival of the corresponding signals; N interpolation-type digital subfilters that perform predetermined filtering based on timing by a channel clock and an interpolation clock, and generate a filter output at the sample rate of the interpolation clock; and an N-point FTT circuit that receives the output and performs fast Fourier transform at the speed of the interpolation clock.

〔Example〕

The TMUX of the present invention is shown in FIG. The same parts as in FIG. 5 are given the same numbers and their explanation will be omitted. 15 is an N/m frequency divider,
16 is an m frequency divider. The case where m = 2 will be mainly described below. 17-1 to 17-N are interpolation type digital sub-filters used in the present invention.

Figure 2 shows an interpolation type digital subfilter HN of the present invention.
1′-n(ZN) configuration is shown. Figure 2(a) shows o<,
In the case of t4-I, Fig. 2(b) shows 2 t (N i
The case is shown below. 21, 22, 23 are digital subfilters, 24 is an N/2 sample advancer, 25
is an N/2 sample delayer, and 26 is an adder.

FIG. 3 shows the input/output timing relationship of the interpolation type digital sub-filter used in the present invention.

FIGS. 4(c) and 4(d) show the relationship between the basic filter characteristics of T■■ according to the present invention and the actual filter characteristics.

The essence of the present invention is to sample the basic BPF-frequency conversion output of 2α→ not at Δf but at an integral multiple thereof, that is, at a frequency of m·Δf. For example, in the case of 9m-2, only n=N-1 at 2α→ (, n-N
/2-1 and 3N/2-1 are also selected and output. That is, TMUX of the present invention is used as an output signal.

Remaining days below This is what you get. The above formula is further

It can be written as

however.

+HN-1-z(ZN). That is, the interpolation type digital sub-filter of the present invention uses two digital sub-filters as shown in FIG. As shown in the figure, the filter results are interpolated and output at twice the input signal speed.

Similarly, when m = 4, four digital subfilters are combined to output four interpolated outputs for each input sample. Usually m = 2 is sufficient.

The filter characteristics of the TMUX of the present invention are shown in Fig. 4(c).
Shown in (d). As can be seen from FIG. 4(d), the T of the present invention
Since the sampling frequency of the output signal is 2Δf (m=2), M'UX must be Δf if the frequency band does not exceed 2Δf.
TM based on a basic filter with wider frequency characteristics than
UX can be realized.

Therefore, as shown in Fig. 4(c) and (d), Δf
Not only is it possible to realize a TMUX having a completely flat transfer characteristic over the range, but also no aliasing occurs even if a filter characteristic with a gentle slope is used as shown by the broken line. Therefore, the scale of the digital filter can be small, or large out-of-band attenuation can be easily achieved. In addition, since the TMLJX of the present invention has a sampling frequency higher than the signal bandwidth of the output signal, signal processing is easy, such as easily realizing an analog LPF for returning to a continuous signal.

〔Effect of the invention〕

The present invention provides the following effects.

(1) Since it is possible to realize TMUX with completely flat filter characteristics in the band of each channel, F of any modulation method can be achieved.
Do not cause spectrum deformation for DM signals (TM
Can perform UX operations.

(2) Since a filter having gentle frequency characteristics can be used even outside the channel band, large attenuation outside the filter band can be easily achieved.

(3) The output signal is twice the channel spacing frequency (m-
2) Because it can be obtained from a speed sample value series.

Subsequent signal processing such as interpolation is easy.

(4) The TMUX of the present invention having the above characteristics can be expected to be widely used in terrestrial or satellite communication networks in which one type of modulation method is used.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of the TM[JX of the present invention, FIG. 2 shows the configuration of the interpolation type digital sub-filter of the present invention in two cases, and FIG. 3 shows the input and output signals of the interpolation type digital filter. Figure 4 shows the timing relationship, and Figure 4 shows the conventional (Figure a)
, b) and the filter characteristics of the TMUX of the present invention (Fig. C2d), FIG. 5 shows the configuration of the conventional TMUX, and FIG.
The figure is a diagram for explaining the operating principle of a conventional TMUX, and Figure 7 shows the basic configuration of a conventional digital filter (Figure a).
FIG. 8 is a diagram showing a conventional digital filter (FIG. a) and the impulse response of the sub-filter, and FIG. 9 is a diagram for explaining output timing. In the figure, 11 is a switch circuit, 12-1 to 12-N are delay devices, 14 is an N-point FFT, and 15 is an N/m frequency divider. 16 is an m frequency divider, and 17-1 to 17-N are digital sub-filters.

Claims (1)

[Claims] 1. Two mixers that convert the frequency of N-channel input IF signals FDM multiplexed with a frequency interval Δf into baseband complex signals, and sample the outputs of the two mixers and convert them into digital numerical signals. Two output A/D converters and a multiplexed clock of NΔf supplied to the two A/D converters are divided into N-divided channel clocks and N
a frequency dividing circuit that generates an interpolated clock divided by /m;
a time/space division conversion switch that receives the outputs of the A/D converters and separates and outputs the input time series into N separate outputs every N samples based on the timing by the multiplexed clock and the channel clock; a delay circuit connected to the output of the time/space division conversion switch for generating N complex baseband signals of a time-matched speed Δf by adding a delay proportional to the arrival order of the corresponding signals; N interpolation type digital sub-filters connected to a circuit and performing predetermined filtering based on timing by the channel clock and the interpolation clock, and generating a filter output at the sampling rate of the interpolation clock; and an N-point FFT circuit that receives the output of the digital sub-filter and performs fast Fourier transform at the speed of the interpolation clock.