KR20050099900A - Apparatus of demultiplexing channel in multicarrier system - Google Patents

Abstract

The present invention provides an apparatus for separating each channel of a signal having a multiplexed channel in a multicarrier system using a demultiplexing scheme of a multi-stage multiphase filterbank. In accordance with an aspect of the present invention, an apparatus for separating a multiplexed channel into a desired channel signal includes: a polyphase filter bank for separating the multiplexed one or more input channel signals into channel signals having one or more different bands. ) Is configured in multiple stages, and the input signal channel is separated into the desired channel signal through the multiphase filter bank configured in the multiple stages.

Description

Channel Separator in Multicarrier System {APPARATUS OF DEMULTIPLEXING CHANNEL IN MULTICARRIER SYSTEM}

The present invention relates to a channel separating apparatus in a multicarrier system, and more particularly, to an apparatus for separating each channel using a demultiplexing method of a multi-stage multiphase filterbank for a signal having a multiplexed channel in a multicarrier system.

In general, the demultiplexing method is classified into a per channel method, a polyphase method, a multistage method, and the like. In this case, the Per Channel method is composed of a bandpass filter bank and performs demultiplexing. The selection of each input signal and conversion to a lower frequency band are performed by a combination of digital filtering and decimation. This Per Channel approach is generally very flexible and simple to control, but the hardware is complex because of the high computational complexity that requires as many channels of filtering and decimation as possible. The Per Channel method is flexible because it is suitable when the transmission rate and the number of channels to be processed are changed, and can be handled only by changing the filter coefficient and decimation factor by the required number of channels. Referring to Fig. 1, a structural diagram of demultiplexing having N channels is shown. Referring to one channel as shown in FIG. 2, it is a system element and a basic parameter for the k-th channel of the K channel filter banks.

2, the input signal silver Modulated by, filter Lowpass filtering is performed. Since, channel signal Reduce the sampling rate by the factor M to make Filter in this system Is called an analysis filter because it determines the frequency response and bandwidth of each channel. Where the center frequency of the channel Is defined as in Equation 1 below.

The complex modulation function The channel signal is expressed as Equation 2 below.

In addition, the polyphase method uses a digital processor called a polyphase network and a block processor of a fast Fourier transform type that processes an output signal from the digital filter to perform demultiplexing. The multiphase filter bank method is more efficient than the Per Channel method, and the multiphase structure for implementing the DFT filter bank is to apply a multiphase decimator structure.

This is easily implemented when the decimation rate M and the number of channels K are the same, and the demultiplexer uses a clockwise commutator polyphase structure to facilitate the construction of a multiphase filter bank. Bandpass Filter Sample response to a polyphase branch of Is as shown in Equation 3 below.

In this case, the branch input signal is expressed by Equation 4 below.

here Of the multiphase structure Th branch and k means k th channel of the filter bank. The overbar notation refers to a clockwise commutator model of multiphase structure.

Is as shown in Equation 5 below.

Equation 5 above Substituting into the above Equation 2 is as shown in Equation 6.

Where the lowpass analysis filter The first polyphase branch may be defined as in Equation 7 below.

And a bandpass polyphase filter Can be separated by product. Like this May be defined as in Equation 8 below.

First term of Equation 8 above Is a function of sample time m and the second term Silver multiphase branch Is a function of and channel k.

If the above definition is applied to the filter bank structure of Equation 2 or Equation 1, Equation 9 may be derived.

In addition, by changing the variable of Equation (9), it can be defined as shown in Equation (10).

Also, n And r and If summed, Equation 11 is obtained.

In addition, Equation 12 is a DFT form of a convolution output of a polyphase branch.

Here, "*" represents convolution, and this equation may represent the structure of FIG. 3 (a) for a single filter bank channel k.

The output signal is independent of the filter channel number k by Equation (12) above. Therefore, it is clear from Equation 12 or FIG. 3A described above that an operation including a polyphase filter can be shared in all filter bank channels reducing the elements of M in the total operation.

In addition, in Equation 12, the DFT may be performed at an efficiency of M log ₂ M using the FFT.

Finally, the multistage method is also called a tree structure, and the input signal is successively divided into smaller frequency bands in the tree of each step and processed using multistage decimation. This structure is not limited to a constant filter bank, providing greater flexibility in the choice of filter bank design.

4 is a diagram illustrating an example of a two-stage integer band tree structure for a general band. 4A is an example of a four-channel two-stage tree structure. The input signal x (n) is filtered at the first stage of the tree by a lowpass filter and a highpass filter, which are divided into two equal parts as in FIG. 4 (b). These signals are respectively reduced to the sampling rate of factor 2 and filtered by the low pass filter and the high pass filter of the second stage.

As a result, the signal is once again reduced in sampling rate by factor 2 and generates a constant filter bank arrangement of four bands as shown in FIG. Since the process of highpass filtering and reducing the sampling rate by 2 produces an inverted spectrum, the roles of the lowpass filter and the highpass filter above step 2 are interchanged to compensate for this inversion.

As described above, the Per Channel method is generally high in flexibility and simple in control circuits, but the hardware is complicated because the computational complexity is high because it requires filtering and decimation operations as many as the number of channels. In addition, the multiphase filter bank method is relatively simple, but is useful when the number of FFT points and the decimation ratio are the same. In addition, the multi-step method has a high complexity of hardware.

Accordingly, an object of the present invention is to provide an apparatus and method for configuring hardware by reducing computational complexity when multiplexing channels.

Another object of the present invention is to provide an apparatus and method for separating each channel from a signal having multiplexed channels in a multicarrier system using a demultiplexing scheme of a multi-stage multiphase filterbank.

In order to achieve the above object, the present invention provides a device for separating a multiplexed channel into a desired channel signal, the multiphase filter bank for separating the multiplexed one or more input channel signal into a channel signal having one or more different bands (Polyphase Filter Bank) is configured in a multi-stage (Multistage), characterized in that the input signal channel is configured to be separated into the desired channel signal through the multi-phase filter bank composed of the multi-stage.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same elements in the figures are represented by the same numerals wherever possible. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

5A is a diagram illustrating a configuration of a multistage multiphase filter bank according to an exemplary embodiment of the present invention, and FIG. 5B is a diagram illustrating a configuration of a multiphase filter bank of each stage according to an exemplary embodiment of the present invention.

5A and 5B, each of the polyphase filter banks, that is, the polyphase filter banks configured as shown in FIG. 5B, is configured as shown in FIG. 5A in N number of stages. In addition, in order to separate each channel, as shown in FIG. 5A, a plurality of multiphase filter banks may be provided and configured flexibly.

Referring to FIG. 5B, the multi-stage multiphase filter bank method of the present invention divides the multiplexed N input signals into M signals using the first-phase polyphase filter bank 500 and each separated signal is second. Used as input of a stage. In addition, each of the M separated signals is separated into K signals using a second-phase polyphase filter bank 502, which is used as an input to each of the third-phase polyphase filter banks. In this way, each polyphase filter of the multi-level (N) is used to separate the channel to obtain the desired channel signal. As above, the channel is separated to separate the desired channel signal.

FIG. 6 is a diagram illustrating a change of a sample rate at each polyphase filter bank stage according to an exemplary embodiment of the present invention. Next, a process of separating the multiplexed channel according to the present invention will be described with reference to FIG. 6.

The multiplexed signal x (n), at which the sample rate is input to Fs at the first stage, is reduced to a sample rate of Fs / M at the output of the polyphase filter bank 600. In addition, the sample rate of the output signal of the multiphase filter bank of each stage is decreased while passing through the multiphase filter bank stages 600,. Therefore, the sample rate is reduced over several stages, so it is easy to implement hardware, and the computational complexity is significantly reduced by using a multiphase filter structure.

In the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the equivalent of claims and claims.

As described above, the present invention reduces the computational complexity by using a multiphase structure and implements it in multiple stages by using a multi-stage method, so that signals of channels having different bands can be separated from each other. There is a possible advantage. In addition, many systems can be adjusted according to the implementation, which allows for a flexible design.

1 is a structural diagram showing a structure of a general channel separator;

2 is a diagram illustrating a channel separator using a general single channel filter;

3A is a diagram illustrating a polyphase structure for a k-th channel of a typical DFT filter bank channel separator;

3B is a diagram illustrating a general multiphase structure DFT filter bank structure;

4A to 4B show an example of a two-stage integer band tree structure for a general band,

5A is a diagram illustrating a configuration of a multistage multiphase filter bank according to an embodiment of the present invention;

5B is a diagram illustrating a multiphase filter bank configuration of each stage according to an embodiment of the present invention;

FIG. 6 illustrates a change in sample rate at each polyphase filter bank stage in accordance with an embodiment of the present invention. FIG.

Claims (2)

An apparatus for separating a multiplexed channel into a desired channel signal, A polyphase filter bank for separating the multiplexed one or more input channel signals into channel signals having one or more different bands is configured in multiple stages, and the input signal channel is configured in the multiple stages. And separate the desired channel signal through a phase filter bank. The multiplexed input channel signal of claim 1, wherein the sample rate is input at Fs, is reduced to a sample rate of Fs / M at the output of the polyphase filter bank, and passes through the multiphase filter bank configured in the multi-stage. Wherein the sample rate of the output signal of the multiphase filter bank of each stage is reduced.