JPH06244887A - Digital radio equipment - Google Patents

Abstract

PURPOSE: To provide a digital radio equipment using an inexpensive analog/ digital converter without any defect in signal limit or compression. CONSTITUTION: A digital radio equipment 2 for a mobile radio or a cordless telephone is provided with a signal compressing device for a base band signal and/or a strict limiting stage 6 in an RF and/or an IF stage 10. Thus, high integration is allowable under the configuration which is not so complicated compared with a known radio equipment, and costs can be saved. In this embodiment, a signal compressing device 12 is realized by a true logarithmic amplifier or compressing devices 13 and 14 having the transmission characteristics of a sine waveform. Digital signal expansion can be executed by using the sample of the base band signal as an address to an extended look-up table in a successive continuous signal processor 24 of the digital base band signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an analog receiver for receiving a phase-modulated or frequency-modulated radio frequency signal, said analog receiver being connected to a baseband converter. The conversion device includes an analog-to-digital conversion device for converting the plurality of radio frequency signals into at least one baseband signal and further sampling at least one baseband signal, and further including at least one baseband signal sample. The present invention relates to a digital wireless device including a digital processing device for processing.

[0002]

2. Description of the Related Art A digital radio device of this kind can be a transceiver when it also includes a transmission part and a switching device for switching between transmission and reception. This digital wireless device is, for example, a mobile wireless device,
Used in cordless telephone devices and paging devices.

A digital radio device of this kind is shown in DE-A-3925305. In this known digital radio device, compression and signal limiting are performed before the baseband conversion, and the baseband-converted radio frequency quadrature signal is sampled using an analog-to-digital converter. After this analog-to-digital conversion, the digital sample is further processed in known digital radio equipment. In this known wireless device, this wireless device is, for example, a so-called GSM device (Group Special Mo).
signal compression is performed to dynamically compress a radio frequency signal that is a 100 dB change at the antenna input side of the wireless device for use in a Cellular wireless device, such as a bile), pan-European mobile wireless device. To be done. The purpose of signal compression is to eliminate logarithmic interference and distortion in analog-digital conversion of orthogonal baseband signals. Without compression, to get the required number of significant bits at significantly lower signal strength,
A 20-bit A / D converter is needed. This type of A / D converter is extremely expensive. A disadvantage of this known signal limitation and compression is that the compressor, in the presence of interfering signals, forms intermodulation products that cannot be removed during subsequent processing of the baseband samples. Therefore, bandpass filtering is required before control and compression,
This is for example SAW (Surface Acoustic)
Wave) implemented by a separate device such as a filter.

[0004]

SUMMARY OF THE INVENTION It is an object of the invention to provide a digital radio device in which inexpensive analog-to-digital converters are used, which do not have the above-mentioned drawbacks of known digital radio devices.

[0005]

For this purpose, the digital radio apparatus according to the present invention is constructed as follows. That is, a digital radio device includes an equalizing non-linear device connected between a baseband converter and an analog-to-digital converter, the equalizing non-linear device converting a large signal at its input to a smaller signal. Compress more than. Due to signal equalization after baseband conversion, this equalizer consumes less power than logarithmic compression in known devices due to the lower frequency operating range. Limitations in RF and / or IF can be at least substantially avoided. Baseband equalization eliminates the need for a separate SAW filter. On the other hand, because baseband equalization is combined with other functions, the cost is reduced by constructing a simplified device. The dynamic range of analog-to-digital converters is proportional to cost, IC surface area, and power consumption. In other words, each additional bit doubles the complexity of the analog-to-digital converter.

In the construction of the digital audio device according to the invention, the equalizing nonlinear device is a logarithmic amplifier.
The logarithmic amplifier is a so-called real-time logarithmic amplifier that compresses the amplitude of the input signal while obtaining information about its polarity. By using this logarithmic amplifier, a signal having a significantly large amplitude range can be obtained.

In the configuration of the digital radio apparatus according to the present invention, the equalization nonlinear apparatus is an apparatus having a sinusoidal transmission characteristic. The sinusoidal transmission characteristic also causes the input signal with the larger amplitude to be compressed more than the smaller signal. On the other hand, tight restrictions on the baseband are avoided. The tight limitation of the baseband signal can cause phase errors, which can result in an unacceptable increase in the BER (bit error rate) of the demodulated digital signal.

In the arrangement of the digital radio device according to the invention, the digital radio device has at least one control device in the analog receiving part. Limitations at high signal levels do not cause significant performance degradation in baseband processing due to interference due to the presence of unwanted signals. Maximum signal control for analog-to-digital conversion is also achieved by adding some restrictions in the radio signal and / or in the intermediate frequency. The limits can be implemented with tight limits or with AGC (Automatic Gain Control). The fading signal can be accurately demodulated (by the equalizer) only when the amplitude information is secured. However, fading is expected only up to a certain field strength. Higher intensities occur when a person is in the vicinity of the transmitter and then one radio propagation from this transmitter to the receiver is likely to form, fading is not a problem. Under this condition of remarkably high signal strength,
Signal amplitude can be controlled without significantly affecting performance. Limiting is best done at radio frequencies or at intermediate frequencies, in order to avoid signal phase distortions that can occur with baseband limiting, and to reduce the dynamic range required later in the receiver.

In a digital radio arrangement according to the invention, the digital radio arrangement comprises at least one low-pass filter for filtering at least one baseband signal. It is achieved that unwanted signals are eliminated and that the demands placed on the bandpass filtering are reduced. The filtering at the lower frequency is also I
Facilitates integration of bandpass filter on C.

In the arrangement of the digital audio device according to the invention, the digital audio device comprises at least one bandpass filter at the input side of at least one signal limiting device. Bandpass filtering, which can be performed on the radio frequency signal and / or at the intermediate frequency, removes unwanted signals. In this way, the filtering action can be arranged over different frequency bands, ie at radio frequencies, at intermediate frequencies or at low frequencies. The low-pass filtering at the input of the logarithmic amplifier is chosen so that the signal of the adjacent channel is attenuated and the rest of the signal has a negligible effect on the dynamic compression.

In a digital radio arrangement according to the invention, a digital processing unit is provided for correcting at least one baseband signal sample. The purpose is to decompress the compression by the equalizing nonlinear device. Thus, where the quasi-linear result plays a greater role in noise, finer quantization is achieved for significantly smaller signals. On the other hand, where less accuracy is required, large quantization steps are used for stronger fading signals.

In a digital radio arrangement according to the invention, a processing unit is provided for correcting the sample by using the sample as an address for a correction look-up table which outputs an expanded sample value. There is. Use of a look-up table allows for rapid software correction of digitized baseband signals. Next, the present invention will be described with reference to the drawings using embodiments.

[0013]

1 shows a radio communication device with a radio device 2 in digital form according to the invention and at least one radio base station, of which at least one radio base station 3 is shown. The broadcasting station 3 communicates with the digital wireless device 2. This includes a receiver and a transmitter, for example using the TDMA communication method used in GSM.
It is pointed out in FIG. 1 that the signal transmitted and the signal received are notably defined using a solid line showing the direct path between the radio base station 3 and the digital radio apparatus 2 and a broken line showing the reflection path. Subject to multi-pulse propagation due to reflections, i.e. a delayed ghost image of the transmitted signal is received. In the case of more mobile digital radio equipment, the radio signal is subject to fading effects of 40 dB or more, which causes a signal strength that fluctuates very rapidly on the receiving side. Therefore, it is important that this digital receiver 2 can solve this kind of problem. The digital radio receiver 2 receives the phase-modulated or frequency-modulated signal from, for example, quadrature GMSK (Gaussian Minimum Shift Keying Gaussian Minimum S).
It includes an analog receiver 4 for receiving a signal that has been modulated by a shift key. The analog receiver 4 includes an RF input stage 5. This RF input stage can be connected to the signal limiting device 6 in the embodiment of the digital radio device according to the invention. The received and selectively limited signal is provided to an intermediate frequency mixing stage connected to the local oscillator 8. Although only one mixing stage 7 is shown, the frequency down conversion can be carried out via several mixing stages.
The mixing stage 7 is connected to an intermediate frequency stage 9. The intermediate frequency stage comprises a bandpass filter which can be connected to another limiting device 10. Unless the signal level is advantageously distributed over various intermediate frequencies and is not limited to more than -40 dBm, the performance of the digital radio device is BER (bits).
It is shown that the error rate, Bit Error Rate, is not substantially impaired. For example, GSM, GSM Recommendations 05.05, 3.5.0, Tra
ns mission and Reception,
1.39.89 defines a static channel condition for the RF signal level, -10d, for the purpose of BER measurement.
Assume between Bm and -40 dBm. RF signal is GS
Assuming to have a maximum signal level in the M device of -10 dBm, in an embodiment according to the invention the input RF signal is -40d in the RF and / or IF receiving stage.
Bm is tighter than Bm. Such tight restrictions are permissible. Tight restrictions should be avoided below the signal level of the strongest interfering wave. The down-converted received radio frequency signal is supplied to the baseband converter 11 for the purpose of obtaining a baseband signal. The baseband signal is fed to an equalizing nonlinear device for the purpose of implementing the baseband signal compression according to the invention. The equalizing non-linear unit 12 may include true logarithmic amplifiers 13 and 14 for compressing the respective quadrature baseband signals I and Q, namely the in-phase and quadrature signals. This kind of true logarithmic amplifier is based on SL531C (Plesse).
It could be a circuit in a y) type IC, or some other true logarithmic amplifier. Rather than the logarithmic amplifiers 13 and 14, the equalization nonlinear device 12 can include circuits with different transmission characteristics, for example sinusoidal transmission characteristics. Each of the baseband converters 11 includes a sine wave local oscillator 1
8 and a baseband conversion device 16, 17 connected to a cosine wave local oscillator 19. The baseband converter further includes respective reduction pass filters 20 and 21 for low pass filtering the quadrature signals I and Q. After signal compression, the baseband signal is, for example, A / D converters 22 and 2 in order to obtain the same sampling.
3 is supplied to an analog / digital converter.
The samples are provided to the digital processor 24 for baseband processing purposes. The processed signal, eg the call signal, is sent via the interface logic 25 to the PCM.
It is supplied to the (pulse code modulation) bus interface 26 and further to the handset, in which the conversion of digital signals into analog signals is carried out. In the case of call communication, an analog call signal is supplied to the speaker 28. In the bidirectional mode in the opposite direction, the analog call signal picked up by the microphone is supplied to the digital processing unit 24 via interfaces 26 and 25,
It is modulated in the transmission device 30 and converted into a radio frequency signal. The transmission device supplies the signal to the antenna 31 via the diplexer 30. The interface logic circuit is further connected to the device control unit 33. The control unit generates various control signals in a digital radio device such as a TDMA controller. Local oscillators 8, 18, 19 and analog-digital converter 2
Control signals C1 and C for controlling 2 and 23 respectively
2, C3, C4 and C5 are shown. For details of the known GSM receiver, see the article "Architektur eins".
Mobilfunkeretes fuel da
s Netz D ", P. Schoeffel et al., P.
hilps Innovation 1/1991,
pp. 132-139. Is shown in. FIG. 2 shows a signal compression device 1 used in the digital radio device 2.
3, 14 examples are shown. This compression device has a sinusoidal waveform transmission characteristic from -π / 2 to + π / 2. This transmission characteristic is indicated by the input / output ratio of the devices 13 and 14. This kind of sinusoidal transmission characteristic is realized and approximated by a number of cascaded amplifier stages with a non-linear transmission characteristic and / or by cascode amplifier stages. The composite transmission characteristic is an approximation of multiple terms of the sinusoidal transmission characteristic. When applying this type of sinusoidal characteristic, the lower level input signal is approximately linearly amplified, while the higher level input signal is compressed. This type of compression favors lower level noise signals with respect to quantization in A / D converters 22 and 23.

FIG. 3 shows the bit error rate BER and d under various propagation path conditions in the wireless device according to the present invention.
The simulation result with the signal level slev represented by Bm is shown. This simulation has an IF of -40
It was carried out in a receiver design where it was tightly limited above dBm, the baseband signal was compressed and A / D converted using a 6-bit A / D converter. Signal compression is -84
It was done in the signal range between dBm and -40 dBm. Characteristic masks M11 and M12 at -100 dBm
And M21 and M22 at higher signal levels are shown. For a test channel that behaves like a typical fading channel, the BER should not exceed M11 and M21, respectively, and for a test channel such as a static channel, the BER should be M21 and M22, respectively. Should not be exceeded. The simulation results show that in the case of a typical fading propagation path, the curves Simft1 and Si
mf2, and in the case of a static propagation path, Sims1 and Sims2. This simulation result shows that the specific receiver design has a BER characteristic M1.
1, M12 and M21, M22. Although signal compression increases BER, this increased BER still follows this property. The receiver design according to the invention enables a high level of cost-saving integration, i.e. starting from the limiting device 10 a plurality of circuits can be integrated in one integrated circuit. On the other hand, the signal limiting device 6, the mixing stage 7 and the local oscillator 8 can be integrated in another integrated circuit for more integration purposes.

The digital processing unit 24 is provided with a signal processor having a RAM and a ROM having software, for example, for decompressing a compressed signal, that is, for correcting baseband samples. In an embodiment, the software includes a look-up table addressed by baseband samples from A / D converters 22 and 23, and a look-up table that outputs decompressed sample values. Therefore, a quasi-linear result is obtained with a higher combined quantization level for lower level noise signals than for higher level signals.

[Brief description of drawings]

FIG. 1 is a block diagram of a wireless communication device having a digital wireless device according to the present invention.

FIG. 2 is a characteristic diagram of a signal compression device used in a digital wireless device.

FIG. 3 is a diagram of simulation results of a bit error rate and a signal level in a wireless device according to the present invention under various conditions.

[Explanation of symbols]

 1 Radio Communication Device 2 Digital Radio Device 3 Radio Base Station 4 Analog Receiver 5 RF Input Stage 6 Signal Limiting Device 7 Mixing Stage 8 Local Oscillator 9 Intermediate Frequency Stage 10 Limiting Device 11 Baseband Converter 12 Equalization Non-Linear Device 13, 14 Logarithmic amplifier 16,17 Baseband converter 18,19 Local oscillator 20,21 Low-pass filter 22,23 A / D converter 24 Digital processing device 25,26 Interface logic device 28 Speaker 30 Transmission device 31 Antenna 32 Diplexer 33 Controller unit

Claims (9)

[Claims] 1. An analog receiver (4) for receiving a phase modulated or frequency modulated radio frequency signal,
The analog receiving unit is connected to a baseband converter (11), which converts a plurality of radio frequency signals into at least one baseband signal, and further includes at least one baseband signal. A digital radio device (2) comprising an analog-to-digital converter (22, 23) for sampling a signal and further comprising a digital processor (24) for processing at least one sample of a baseband signal,
The digital radio device (2) includes a baseband converter (11) and an analog / digital converter (22, 2).
3) an equalizing non-linear device (12) connected between the equalizing non-linear device and the equalizing non-linear device compressing the larger signal at its input side more than the smaller signal. A digital wireless device. 2. Digital radio apparatus according to claim 1, wherein the equalizing non-linear unit (12) is a logarithmic amplifier. 3. The digital radio device according to claim 1, wherein the equalization non-linear device (12) is a device (13, 14) having sinusoidal transmission characteristics. 4. The digital radio apparatus according to claim 1, wherein the baseband signal is a quadrature signal. 5. Digital radio device according to any one of claims 1 to 4, characterized in that it comprises at least one signal limiting device (6, 10) in the analog receiving part (4). 6. At least one reduction pass filter (20, 2) for filtering at least one base signal.
The digital wireless device according to claim 5, including 1). 7. At least one bandpass filter (5, 9) comprising at least one signal limiting device (6, 1).
7. The digital radio receiver according to claim 5, which is provided on the input side of 0). 8. A digital processor (2) for correcting at least one baseband signal sample to decompress and expand by an equalizing non-linear unit (12).
4. A digital radio device according to any one of claims 1 to 7, characterized in that 4) is provided. 9. The processing device (24) for correcting a sample is provided, which processing device uses the sample as an address for a correction look-up table which outputs an expanded sample value. Digital wireless device.