JPH0758940B2 - Multipath fading simulator - Google Patents

Description

Description: [Object of the Invention] (Industrial field of application) The present invention relates to a multipath fading simulator that artificially generates indoors the multipath fading that occurs in a transmission path of a mobile signal. .

(Prior Art) Conventionally, when signal transmission is performed in mobile radio communication, the level of the received wave fluctuates greatly due to multipath propagation, and the transmission characteristics deteriorate significantly. A fading simulator is used to efficiently study the transmission characteristics indoors.

Fading simulator input wave s (t) _{is, s (t) = s 1} cos (ω c t) -s 2 sin (ω c t) When represented as ..., the output wave r (t ) is converted _{r (t) = a 1 (} t) s 1 cos (ω c t) -a 2 (t) s 2 sin (ω c t) as ....... However, s ₁ and s ₂ are the amplitudes of the in-phase component and the quadrature component of the signal, and the ω _c carrier frequency.
Also, a ₁ (t) and a ₂ (t) are the real and imaginary parts of the fading complex envelope signal ₂ (t), where a ₁ (t) and a
₂ (t) normally has a Gaussian distribution with an average value of 0.
A signal with such a Gaussian distribution is a low-pass filter whose bandwidth is sufficiently smaller than the clock frequency of the PN signal for the output PN signal of the PN (pink noise) signal generator with a very long cycle. It is obtained by band limiting. That is, two PN signal generation circuits generate two series of PN signals, regard these PN signals as white noise, perform spectrum shaping with a low-pass filter, and generate a fading complex envelope a ₁ (t) and a ₂ ( t) is generated.

By the way, when the delay time due to multipath propagation becomes longer than the symbol interval of the signal, not only the level fluctuation of the received wave as described above but also the frequency characteristic of the propagation path becomes a problem in the actual propagation path. Such a propagation path cannot be approximated by the above fading simulator. FIG. 2 shows the configuration of a multipath fading simulator that simulates a propagation path having frequency characteristics.

In this multipath fading simulator, the modulated signal is supplied to the power distribution circuit 31 via the input terminal 30, and is divided into five waves by the power distribution circuit 31. Of the five waves, one wave is directly supplied to the quadrature modulator 32, and the remaining four waves are supplied to the quadrature modulator 32 after passing through delay circuits 33 having different delay times. The signal divided into five waves is modulated by the quadrature modulator 32 with the signals generated by the five independent two-dimensional Gaussian noise generating circuits 34, and the synthesizing circuit 35
Are combined and output from the output terminal 36. In this example,
It is possible to generate five waves with different delay times, that is, five paths.

FIG. 3 shows the configuration of a fading simulator for diversity reception. This example simulates a two-branch diversity, and the signals divided into two by the power distribution circuit 40 are input to two fading simulators 41 and 42, respectively. The configurations of the two fading simulators 41 and 42 are the same as the configurations of the multipath fading simulator in FIG. 2, and therefore the same components are designated by the same reference numerals as those in FIG. 2 and their description is omitted. In general, in a multi-path fading simulator with a plurality of branches, the delay times of the corresponding paths are assumed to be the same.

(Problems to be Solved by the Invention) However, in the conventional multipath fading simulator shown in FIG. 2, a SAW (surface acoustic wave) filter is generally used as the delay circuit 33. It has the characteristic that the pass band of the signal becomes narrower as the value gets larger. Therefore, the conventional multipath fading simulator using the SAW filter as the delay element has a drawback that the range of the carrier frequency of the input modulated wave cannot be made sufficiently large.

Further, in the conventional multipath fading simulator for diversity shown in FIG. 3, two branches (fading simulators 41, 42) set to the same delay time are used.
There is a drawback that the two-dimensional Gaussian noise in between cannot be correlated.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art. An object of the present invention is to limit the correlation between branches only to a path having the same delay time, which is necessary when simulating diversity reception. Therefore, it is to provide a multipath fading simulator that can be realized with a very simple circuit configuration.

[Structure of Invention]

(Means for Solving the Problem) A multipath fading simulator according to the present invention that achieves the above object is configured such that a multipath fading generation circuit of a plurality of branches and delay profiles of the multipath fading generation circuits are set to be the same. And a multipath control circuit for inserting a correlation determined only between fading complex envelope signals in a delay time path.

(Operation) According to the multipath fading simulator of the present invention, the delay profile of each circuit of the multipath fading generation circuit of a plurality of branches is set to be the same, and only between fading complex envelope signals in a path of the same delay time. A defined correlation is entered.

(Embodiment) Hereinafter, the present invention will be described in detail with reference to the drawings by embodiments.

An embodiment of the present invention is shown in FIG. 1, which shows the configuration of a fading simulator for diversity reception. This example is for simulating a two-branch diversity, in which a signal divided by the power distribution circuit 40 is divided into two fading simulators 41, 4.
Entering 2 respectively. The configuration of the two fading simulators 41, 42 is the same as the configuration of the multipath fading simulator of FIG. 2 except for the configuration of the two-dimensional Gaussian noise generation circuit 34, and therefore the same components have the same reference numerals as in FIG. Is attached and its description is omitted. In this embodiment, in the corresponding quadrature modulator 32 of the two fading simulators 41 and 42, an independent two-dimensional Gaussian noise generating circuit 22 is generated via a correlation adding circuit 21 provided outside the fading simulators 41 and 42. Is modulated with the signal.

Generally, in a multi-path fading simulator with a plurality of branches, the corresponding paths have the same delay time, and therefore the paths having the same delay time in the delay profile are selected. Here, it is assumed that the M-th path P _1M of the branch ₁ and the N-th path P _2N of the branch 2 have the same delay time. P _1M and P
_{The 2N} fading complex envelopes Z _1M and Z _2N can be generated by forming a circuit represented by the following equation.

However, X _1M and X _2N are mutually independent complex Gaussian signals obtained by connecting a PN signal generator and a low-pass filter. At this time, if <| X _1M | ² > = <| X _2N | ² > = σ ² , then <| Z _1M | ² > = <| Z _2N | ² > = σ ² <Z _1M Z ^* _2N > = ρ σ ² , and a signal having a ρ correlation between the complex Gaussian signals Z _1M and Z _2N is obtained.

In this way, by inserting correlations only in the paths having the same delay time, it is possible to obtain correlated signals, and it is possible to make the device size much smaller than in the case where all correlations are added.

〔The invention's effect〕

According to the present invention, there is an effect that it is possible to realize with a very simple circuit configuration by limiting the correlation between branches only to the paths having the same delay time, which is necessary when performing the simulation of diversity reception.

[Brief description of drawings]

FIG. 1 is a block diagram of a two-branch multipath fading simulator that can add correlation between branches according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional multipath fading simulator, and FIG. It is a block diagram of a two-branch multipath fading simulator. 11 …… input terminal 12 …… mixer, 13 …… bandpass filter, 14 …… frequency conversion circuit, 15 …… multipath fading simulator, 16 …… mixer, 17 …… output terminal, 18 …… variable frequency oscillator, 19 …… control circuit, 20 …… display circuit, 21 …… correlation adding circuit, 22,34 …… two-dimensional Gaussian noise generation circuit, 31,40 …… power distribution circuit, 32 …… quadrature modulator, 33 …… Delay circuit, 35 ... Synthesis circuit.

Claims (1)

[Claims] 1. A multi-path fading generation circuit of a plurality of branches and a correlation determined only between fading complex envelope signals in paths having the same delay profile of each multi-path fading generation circuit and having the same delay time. And a multipath control circuit for inserting the multipath fading simulator.