JP2002076958A - Base station receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sensitivity and interference suppression performance of a base station receiver used for CDMA system mobile radio communication in the wide frequency band of the 3rd generation. SOLUTION: A bandwidth of a front-end RF band-pass filter 1 is set as the bandwidth for allowing transmission of only one channel among assigned three to four channels. A low noise amplifier assures a high gain to realize high sensitivity and interference suppression characteristic. As a result, the circuits after the mixer in the next stage have been freed from restriction of noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a W-CDMA (Wideband or Wideband Code Division Multiple Access) mobile communication system which is being put to practical use as a radio access system for a third generation (next generation) mobile communication system. The present invention relates to a base station receiving device in a communication system.

[0002]

2. Description of the Related Art Narrowband digital modulation / demodulation TDMA in a currently used second generation mobile communication system.
The radio access system uses a narrow band modulation / demodulation technique, and is provided at a receiving intermediate frequency stage for selectively receiving one of the multi-frequency channels constituting the system in the base station receiver. A configuration in which a desired wave is selectively amplified and demodulated by a narrow band filter is widely used, and excellent reception performance is exhibited.

However, after converting a narrow-band multi-frequency channel to an intermediate frequency (hereinafter, referred to as IF), one of them is converted to an intermediate frequency.
When a channel is selectively received, an RF signal is converted into an IF by a frequency converter (hereinafter, referred to as a mixer).
To the input terminal of the mixer, signals of adjacent and next adjacent channels which become interference waves and various unnecessary interference waves passing through the RF band-pass filter of the high frequency stage may be simultaneously input.

For this reason, the mixer has a distortion characteristic, in particular,
Since the operating point is set by the third-order intercept characteristic for the third-order intermodulation distortion, the dynamic range is limited. To avoid this, the design of the RF front end requires the interference suppression characteristic that is in the opposite condition to the reception sensitivity. It is necessary to consider a trade-off with the above, and in particular, in the base station receiving apparatus, expansion of hardware including power consumption is inevitable.

At present, the radio characteristic specification of the transmitting / receiving section of the base station device arranged in each cell of the wideband CDMA system for which a system experiment is being conducted as a third generation mobile communication system is, for example, 20 MHz at a transmitting / receiving frequency of 2 GHz band. A maximum of 3 to 4 RF channels are arranged in a band, and the minimum frequency interval of each channel is 5 MHz. The pass bandwidth (B) for each RF channel is approximately 4 MHz, and the occupied frequency bandwidth (A) is slightly narrower.

At the time of actual operation, the number of RF channels of the transmitting / receiving unit mounted on the base station apparatus is expected to be 3 to 4 channels for a large-scale base station and 1 to 2 channels for a small-scale base station. In a micro base station, a pair of RF
It is expected that channels will be implemented in many cases.

FIG. 4 is a diagram showing an example of the configuration of a conventional base station receiving apparatus, which is an example of the configuration of a general linear receiving apparatus that selects and receives a multi-frequency channel of a multi-access system that is currently widely used. In FIG. 4, reference numeral 11 denotes a broadband low-loss RF filter that passes all RF channels of the system frequency, and is, for example, a low-loss coaxial or semi-coaxial resonator. Reference numeral 12 denotes a high-intercept low-noise amplifier (hereinafter referred to as LNA) having a general gain. Here, the high intercept means that the second and third order intercept points are high, the linear capability is high, and the amplification degree has a margin.

Reference numeral 13 denotes a wide band RF filter that allows all RF channels to pass, and is, for example, a small SAW (surface acoustic wave) filter. 14 is 50 to 100 mW in order to satisfy the high intermodulation suppression characteristics of the base station receiver, for example, to maintain the high second and third order intercept characteristics.
A high intercept frequency converter (eg, a DBM (Double Balanced Mixer)) that requires a class of local injected power.

Reference numeral 4 denotes a general linear receiver for demodulating a digital signal. That is, 41 is an intermediate frequency filter,
A filter that removes interference waves in the bands of adjacent and next adjacent channels at the IF stage of a normal receiver.
It is a W filter. Therefore, the conventional receiving apparatus has interference-free reception performance in which the adjacent and next adjacent interference waves are completely cut off and prevented in cooperation with the RF bandpass filter 1. 4
Reference numeral 2 denotes a variable gain amplifier for maintaining the characteristics of the linear receiver and supplying a constant level to the next-stage demodulator. 4
Reference numeral 3 denotes a demodulator for detecting an IF signal to obtain a baseband signal.

[0010]

As described above, the RF filter 11 and the mixer 14 currently used in the base station receiver of the narrow-band digital cellular system have the frequency assigned 2
To selectively receive multi-frequency channels in the 0 MHz band,
A wide-band filter covering the entire service frequency band of the system, for example, having a pass band width of 25 MHz.

However, in the selective reception of the multi-frequency system, since all frequencies other than the desired wave are interference waves, the LNA 12 and the mixer 14 constituting the reception unit front end are
It is necessary to have interference immunity that satisfies the tolerance of the system in consideration of these interference waves. For example, there is a problem that it is necessary to provide an LNA or a mixer having an extremely high third-order intercept point.

In addition, since the base station receiver is required to have high reception sensitivity in order to maintain high system service quality, it is necessary to provide a low-noise front end in consideration of total reception noise. There's a problem.

As is well known, the noise power converted to the reception input end is represented by a noise figure as an index thereof,
Ideally, a low-noise and high-gain amplifier is arranged as a front-end LNA to amplify a desired wave to a level where the noise power at the subsequent stage can be ignored.

However, if the gain is simply increased, the desired wave and the interfering wave are also amplified to a high level and input to the mixer 14, and even if a mixer having a high third-order intercept point is provided, the reception intermodulation characteristics and the sensitivity suppression can be suppressed. Since the characteristics are remarkably degraded, the only option is to set the optimum gain to an extent commensurate with the trade-off between low noise characteristics and interference immunity.

An object of the present invention is to provide a base station receiving apparatus capable of demodulating a wideband digitally modulated CDMA wave with high sensitivity and high interference suppression performance.

[0016]

According to the present invention, there is provided a base station receiving apparatus comprising an RF band-pass filter provided at an input terminal of a receiving apparatus with only one desired wave among three or four frequencies allocated to W-CDMA. 1, the LNA 2 arranged at the reception front end is set to a high gain, and the subsequent stages of the LNA 2 and thereafter, the normal mixer 3 and the IF configuring the linear receiver 4
The filter 41, the variable gain amplifier 42, the demodulator 43 and the like are connected in cascade so as not to be restricted by noise. That is, the RF band-pass filter 1 has a low-loss pass characteristic with respect to a desired wave, and approximately 15 to
A digitally modulated desired wave having an effective attenuation of 20 dB is band-limited to pass and output 99% or more of energy, and adjacent and next adjacent channels in the vicinity of the desired wave and various types of signals that degrade reception performance In which interference waves are removed.

As a result, an interfering wave other than the desired wave f _R , for example, an interfering wave related to the reception intermodulation characteristic defined in the specification of the W-CDMA system, that is, f _R ± 10
MHz and f _R ± 20.1 MHz signal, 30
Since an attenuation of ４０40 dB or more is provided, it is possible to obtain characteristics similar to those of an ideal receiver that performs demodulation by passing only a desired wave with zero insertion loss.

For example, if the attenuation of the RF bandpass filter 1 against the interfering wave is 30 dB, the gain of the conventional LNA can be increased by 30 dB, so that the subsequent stage is configured to completely ignore the noise level. be able to.

As a result, as for the front-end device constituting the LNA 2, it is sufficient to simply set a low-noise device, and it is possible to reduce the overall noise figure of the reception to the limit of the device and to obtain a high sensitivity. Reception performance can be easily obtained.

As described above, the receiving apparatus according to the present invention employs W-
A high-sensitivity, high-interference canceller, characterized in that an RF band-pass filter for passing only one of three to four frequencies assigned in the CDMA system in a radio frequency band and removing an interfering wave is provided at an input end of a receiver. High performance receiver.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic configuration of a base station receiving apparatus according to the present invention is based on three to three allocated to services of the W-CDMA system.
A low-loss RF bandpass filter that passes a predetermined one of the four frequencies, and a low-noise, high-gain L that amplifies its output.
It has an NA, and is provided with a generally used mixer and a linear receiver for demodulating a digital signal at the subsequent stage.

FIG. 1 is a block diagram showing a basic configuration of a base station receiving apparatus for receiving one predetermined frequency according to the present invention. In the figure, 1 is an RF bandpass filter that passes only one predetermined frequency (RF channel), 2 is a high-gain low-noise amplifier, 3 is a general frequency converter widely used for base stations, for example, a double balanced Mixer.

Reference numeral 4 denotes a general linear receiver for demodulating a digital signal. Reference numeral 41 denotes an intermediate frequency filter used in an IF stage of a normal receiver, which is a filter for removing an interference wave inputted to an adjacent or next adjacent channel, for example, an IF band SAW filter. Accordingly, it is possible to obtain interference-free reception performance in which the adjacent and next adjacent interference waves are completely cut off and prevented in cooperation with the RF bandpass filter 1. Reference numeral 42 denotes a variable gain amplifier for maintaining the characteristics of the linear receiver and supplying a constant level to the next-stage demodulator. Reference numeral 43 denotes a demodulator for detecting an IF signal to obtain a baseband signal.

FIG. 2 shows an example of a single characteristic of the RF bandpass filter 1 of the present invention. B is the pass bandwidth, and A is the occupied frequency bandwidth of the desired wave to be passed. It has an attenuation of approximately 15 to 20 dB at the edge of the pass band B of the adjacent channel which becomes an interference wave, and approximately 40 to 50 at the center frequency of the adjacent channel.
The amount of attenuation in dB is shown. By this characteristic, for example, a desired reception wave is passed without losing its energy, and an interference wave in the band of the adjacent or next adjacent channel is attenuated to a desired value to block the interference wave. It is possible to do.

If the transmitting side of the system limits the root Nyquist band, the characteristics of the above-mentioned RF bandpass filter 1 may have transmission characteristics similar to root Nyquist waveform shaping matched thereto.

FIG. 3 shows a reception bandpass filter (F ₁ ) of the present invention.
The general characteristics of a filter as an antenna duplexer composed of a transmission band filter (F3) and a transmission band filter (F3) will be described. B is the pass bandwidth,
A is the occupied frequency bandwidth. In this example, the transmission / reception frequency interval is shown as (2 × ΔF). Transmission band filter has the same filter characteristics and the reception band filter, which represents attenuation of schematic 15~20dB the edge of the passband width B of the adjacent channel (F _2). Due to this characteristic, the adjacent and next adjacent channel leakage power of the own station transmitter is reduced, and unnecessary wave mixing into the own station receiver is suppressed.

[0027]

As described in detail above, by implementing the present invention, it is possible to reduce the noise of the base station receiver in the third generation mobile communication system using the W-CDMA system, that is, to increase the sensitivity, and In addition, interference waves corresponding to adjacent and next adjacent channels and other interference interference waves can be attenuated and removed at the reception input end, so that the interference immunity is 100 to 1000.
The gain can be increased by a factor of two or more (two to three digits) or more, and the gain of the front end can be increased, which has been troublesome under the contradictory conditions. That became easier.

In particular, since it is expected that the number of RF channels is often one or two in a small base station, it is possible to provide a high quality system service in the small base station by applying the present invention. Yes, its practical effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of filter characteristics according to the present invention.

FIG. 3 is a diagram illustrating an example of filter characteristics of the antenna duplexer according to the present invention.

FIG. 4 is a block diagram showing an embodiment according to a conventional configuration.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 1 RF channel pass type RF bandpass filter 2 High gain / low noise amplifier 3 Frequency converter 4 Linear receiver 41 Intermediate frequency filter 42 Variable gain amplifier 43 Digital signal demodulator 11 Wideband low loss RF bandpass filter 12 High intercept low noise Amplifier 13 Broadband RF bandpass filter 14 High intercept frequency converter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hidekatsu Ueno 43rd Tsurumumadai, Tenno-cho, Tennocho, Minamiakita-gun, Akita Prefecture Within 224 Kokusai Denki Engineering Co., Ltd. 43-224 224 Kokusai Electric Engineering Co., Ltd. (72) Inventor Hiroshi Hoshigami 3--14-20 Higashinakano, Nakano-ku, Tokyo Kokusai Electric Co., Ltd. (72) Mitsufumi Nagano 3-14-20 Higashinakano, Nakano-ku, Tokyo No. Kokusai Denki Co., Ltd. F-term (reference) 5K022 EE01 EE35 5K052 AA02 BB02 DD04 EE04 EE21 5K067 AA03 AA24 CC10 EE10 GG11 JJ11 KK00

Claims (3)

[Claims] 1. A base station receiving apparatus provided in a base station in a broadband CDMA mobile communication system, for selecting a received signal of a desired channel from a plurality of radio channels allocated at predetermined frequency intervals and digitally demodulating the selected signal. An apparatus, comprising: an RF bandpass filter that passes only one of the plurality of wireless channels; a low-noise amplifier that amplifies its output with high gain; and a frequency converter that converts the output to an intermediate frequency. A linear receiver that selectively amplifies and demodulates an intermediate frequency signal output from the frequency converter and outputs a baseband demodulated signal, wherein the RF bandpass filter and the low noise amplifier are adjacent to each other by a high frequency stage. Cascade connection by attenuating and removing interfering signals such as the next adjacent channel signal and amplifying with high gain The base station receiver and wherein the function of said frequency converter and said linear receiver is so not constrained by noise is. 2. The RF band-pass filter has an effective attenuation of 15 to 20 dB at an end of a pass band of an adjacent channel, limits a band of a digitally modulated desired reception wave, and passes 99% or more of energy. The base station receiving apparatus according to claim 1, wherein the base station receiving apparatus is configured to output the received signal. 3. The RF band-pass filter according to claim 1, wherein the RF band-pass filter has transmission characteristics similar to root Nyquist waveform shaping under matching conditions with a transmission wave subjected to a system-defined root Nyquist band limitation. 2. The base station receiver according to 1.