KR19990011052A - Transceiver device for wideband code division multiple access wireless subscriber network base station system - Google Patents

Abstract

The transceiver circuit of the broadband-CDMA wireless subscriber network base station system according to the present invention comprises a modulator / demodulator circuit using a phase locked loop synthesizer as a local oscillator of a frequency conversion and modulation / demodulation circuit as a transceiver module. In order to save the number,

A transmitter for receiving an I / Q signal and performing modulation at an intermediate frequency and then outputting a high frequency signal; And a local oscillator configured to receive a high frequency signal, perform modulation to an intermediate frequency, and output the I / Q signal and a local oscillator to provide a carrier by an external reference clock to the transmitter and the receiver.

Description

Transceiver device for wideband code division multiple access wireless subscriber network base station system

The present invention relates to a transceiver device of a broadband code division multiple access (B-CDMA) wireless local loop (WLL) base station system, and more particularly, to a digital signal processor of a base station system. The present invention relates to a frequency conversion device having a frequency up-conversion function of a transmission signal and a frequency down conversion function of a reception signal for providing with a subscriber station.

Wireless subscriber network refers to the construction of a telephone line using a wireless system instead of a wired line from the telephone company to the subscriber.

This technology was first tried in the US Bell Labs in the early 70's as a way to reduce temporary equipment when making phone calls in sparsely populated areas such as farming and fishing areas, but it was not easy to secure radio frequencies and manufacture antennas and transceivers. And the installation cost was too high to reach the commercialization stage.

However, with the recent rapid development of electronic communication technology, various manufacturers have launched economic products in the market one after another, and service providers are showing great interest in commercializing this wireless subscriber network.

Currently, wireless subscriber network technology is popular among network operators around the world because of the advantages of wireless systems over copper or aluminum cables, which can reduce subscriber access costs in the province and provide faster access to service needs. Is selected as the transmission medium.

A few years ago, public wireless subscriber network access was included in the new telecommunications business, serving only in sparsely populated areas such as the Saudi Arabian desert, the Australian outback or the Texas plains.

In contrast to the threat of other transmission-based communication systems today, wireless subscriber networks are alive in extended mass media and sparsely populated areas.

For example, in markets such as Indonesia, the UK, South Africa and Brazil, wireless networks are expected to provide subscriber access at low cost.

The wireless subscriber network business, which was temporarily based in underdeveloped countries, is now being accepted as a progressive and permanently acceptable technology in the developed markets.

Table 1 shows a table comparing wireless subscriber network technologies with other transmission technologies.

The advantage of wireless subscriber networks is the use of fixed-to-fixed radio waves.

The loss of wired-to-wireless propagation in a wireless subscriber network is 20 dB / decade, but in the case of fixed-to-mobile propagation in a cellular mobile communication system, it is 40 dB / decade, which is a fairly high loss.

In addition, since the antenna is located in a high place of the building, the wireless subscriber network can eliminate the multipath phenomenon.

Carrier-to-Interference ratio (hereinafter referred to as C / I) in a 30KHz FM channel with no fading in wired to wired conditions requires 10dB. On the other hand, it requires about 18dB of C / I under mobile communication conditions.

This means that in a wireless subscriber network, a signal received under no fading can tolerate even more interference.

Another advantage is that the frequency reuse distance in the wireless subscriber network can be shorter because the wire-to-wired connection of the wireless subscriber network uses directional antennas at both ends to reduce the interference distance.

Decreasing the frequency reuse distance means increasing the communication capacity.

In the wireless subscriber network, handover does not occur due to the wired-to-wired connection. Wireless connections to each building and cell can be installed to reduce interference. This connection does not change after installation and the design is very simple.

However, the wireless subscriber network as described above is not the only advantage. The disadvantages of the wireless subscriber network can be summarized as follows.

First, it is difficult to directly compare the cost issues between wired and wireless systems because of changes in network distance, population distribution, and infrastructure utilization.

Secondly, current fixed wireless systems have less service area than copper wires. Therefore, most of them are limited to voice, facsimile and low speed data.

Third, there is no international standardization of wireless subscriber network technology. Therefore, there is no solution that satisfies the requirements of the wireless subscriber network and the wireless network.

The configuration of the wireless subscriber network system is as follows. In fact, cellular systems are suitable for wireless subscriber networks, and digital methods such as CDMA can provide 15 to 20 times the communication capacity of analog systems.

Moreover, when CDMA is applied to a wireless subscriber network system, it can have a communication capacity of two to three times higher than that used in a mobile communication system. Basic wireless subscriber network system is composed of subscriber equipment, wireless base station and OAM center.

A wireless base station consists of two parts, a wireless transceiver and a base station. The base station includes a digital radio processor. In the wireless subscriber network, there is no handover or power control function, which is a channel connection function between cells, so the base station is simply configured.

In general, cellular and personal communication service (PCS) networks can be used identically except for high frequency bands and are designed to minimize signal loss due to free space conditions.

There are two ways to configure a wireless subscriber network system. One is how the cell site is connected to the telephone central office, and the other is connected to the PBX when the private branch exchange (PBX) connected to the CO is the central station. That's how.

Wireless subscriber networks can also benefit from high-gain antenna and spread spectrum waveforms.

Since the C / I in the wireless subscriber network system is smaller than the mobile communication system, the capacity of the wireless subscriber network is higher than that of the mobile communication system. This is due to the difference that the wireless subscriber network is operated even under no fading conditions.

In wireless subscriber network-CDMA, each base station consists of nine sectors, and because of the frequency reuse factor of CDMA, all sectors can use the CDMA communication channel. This means that it is 9 times higher than the total cell capacity.

Since the wireless subscriber network operates under no fading conditions, the carrier can be applied with data compression technology without worrying about a burst error due to fading, and the data transmission cost is 100 times or more.

The 8kbps voice coder (vocoder) can also be easily used in wireless subscriber network system because it operates under non-fading condition.

Wireless subscriber networks are low-cost, high-capacity systems that can be used in any cellular system, such as a telephone company or a wireless communication device, and because of their inherent economics, can be a solution for operators.

Currently, CDMA is applied to obtain high communication capacity in wireless subscriber network system. CDMA is a system that is flexible in communication capacity without limiting the number of physical traffic channels.

Since the required E _b / I _o values vary depending on the application or service, one CDMA wireless channel (1.25 MHz) provides 20 to 45 traffic channels over a mobile communication network.

Power control is very important for CDMA systems. When a cell site receives a signal from a nearby transmitter, it must mask the signal from a distant transmitter, thus avoiding interference at a far and near distance.

It is important to match the transmit / power levels to each opposite channel. In order to expand the service to a large area, an extension range in a wireless subscriber network is important, and a repeater may be used to extend the range.

The repeater outputs multiple signal frequencies on the spectrum band, either microwave or optical, and then lowers them to CDMA signals in the remote cell area and connects them wirelessly to a wireless subscriber network terminal or building.

Therefore, economic problems may arise in establishing wireless subscriber networks in a wide range of areas.

Wireless subscriber networks are preferred because of the high cost of establishing telephone cables for some audiences, and CDMA wireless subscriber networks are needed to open high-capacity wireless telephony services in the third world, where telephone lines are not yet established. .

In addition, the characteristics of the use of the wireless subscriber network is that it can be easily applied to isolated areas or highlands of islands or coastal areas.

The wireless subscriber network system is composed of a fixed station, a cell area, a base station controller, and an OAM center, which is similar to the arrangement of a cellular mobile telephone system.

The difference is that the interface card of the wireless subscriber network is connected to the local exchange rather than to the switching office.

A wireless communication system such as a cellular system and a personal mobile communication system substantially constitutes a communication path with a mobile station and a mobile station, and controls a base station and a base station that communicate with each other. And a Mobile Switching Center.

The mobile terminal is composed of a mobile element (ME) and a SIM card. ME stands for telephone or data terminal. The SIM card has the function of a smart card configured for security function and memory function.

The base station performs a function of transmitting and receiving radio waves by contacting the mobile terminal through the air interface and performing specific signal processing on the air interface.

The base station performs speech coding and decoding in the case of speech, and synchronizes data in case of voice, and allocates an appropriate channel when the mobile terminal requests a channel.

The base station controller has a hierarchical structure for controlling a plurality of base stations.

The mobile switching center is a central controller for handling mobile terminal calls and performs several functions different from ordinary wired switching centers.

The mobile switching center provides a wired communication network with an interconnected interconnection, provides a switched connection between mobile terminals served by the mobile switching center, and manages the use of wireless channels. In addition, it provides control, handover, and roaming functions for the location processing of internal cells.

The present invention relates to a transceiver apparatus of a base station system having a function of converting a frequency in a channel between a mobile terminal and a base station in a wireless communication system having the above components.

In a wireless communication system, a multiple access scheme is used to accommodate a plurality of mobile terminals through a single communication channel and prevent collisions for data transmission between the mobile terminals and a base station.

In the multiple access method, a frequency division multiple access method (FDMA) in which the entire frequency band of one communication channel is divided and allocated to a subscriber, or the use time of the communication channel is divided not by dividing the channel into frequencies. Time division multiple access (TDMA), spread-spectrum modulation, and orthogonal code assigned to each subscriber There is a CDMA that can minimize mutual interference even when transmitting using the same frequency band.

In Korea, the above CDMA method is adopted.

In addition, different frequency bands are used by dividing a channel between the mobile station and the base station into an uplink transmitted from the terminal to the base station and a downlink transmitted from the base station to the terminal.

The transceiver of the base station system includes a frequency converter having an up- and down-conversion function of a transceiver signal and an automatic gain controller (AGC) having a function of adjusting a transmit / receive signal level to protect each component constituting the base station system. Must be used).

In the case of a transmitter, an intermediate frequency (IF) signal is received from a digital signal processor and converted into a secondary intermediate frequency signal using a frequency upconverting function through a mixer.

The second intermediate frequency signal is upconverted to a high frequency signal to be transmitted through a double balanced mixer, and this output signal becomes an input signal of a high power amplifier.

The receiver is composed of a double superheterodyne method, which amplifies a high frequency signal received from an antenna through a low noise amplifier and then down converts the frequency into a first intermediate frequency signal through a mixer. do.

The downconverted primary intermediate frequency signal is downconverted back to the secondary intermediate frequency via a mixer after gain adjustment is made in the automatic gain adjustment circuit.

In general, the structure of the receiver is complicated by the fact that the signal strength is not constant but continuously changes due to a fading phenomenon caused by the movement of a transmitter or receiver, a change in atmospheric conditions, and the like.

This change in intensity is a major cause of disturbing the normal operation of the receiving circuit. In other words, the user must have the ability to always adjust the gain of the amplifier in order to keep the strength of the received signal constant.

It is almost impossible to realize the design of the receiver when the signal change ranges from 20 dB to 30 dB. The solution to this problem is an automatic gain adjustment circuit.

The automatic gain adjustment circuit operates continuously to compensate for fluctuations in the strength of the received signal, reducing it to about 1 dB when a change in signal range between approximately 20 dB and 30 dB occurs.

In the conventional transceiver system of the broadband-CDMA wireless subscriber network base station, the transceiver circuit is complicated to perform the up- and down-conversion of the transmit / receive signal twice and transmit the intermediate frequency and the high frequency signal to the next stage. .

In addition, since the modulation / demodulation circuit is configured as a separate device there is a problem that there are many components of the base station system.

Therefore, the present invention to solve the above problems,

Transceiver circuit has been simplified by configuring the transceiver circuit in a single conversion method, and the modulation and demodulation circuit, which was composed of separate modules, can be configured together with the transceiver module to reduce the number of modules required by miniaturization and built-in modulation and demodulation circuit. An object of the present invention is to provide a transmitter of a wideband-CDMA wireless subscriber network base station system.

1 is a block diagram of a wideband code division multiple access wireless local loop base station transceiver according to the present invention;

* Explanation of symbols for main parts of the drawings

101. High frequency input signal 102. First order low noise amplifier

103. Bandpass filter 104. Second-order low noise amplifier

105. Bandpass Filters 106. Mixers

107. Intermediate frequency band filter 108. Intermediate frequency amplifier

109. SAW filter 110. Automatic gain adjustment circuit

111. I / Q Signal Demodulator 112. Lowpass Filter

113. External reference 10 MHz clock 114. Local oscillator 1

115. Local Oscillator 2 116. Local Oscillator 3

117. High Frequency Output Signals 118. High Frequency Amplifiers

119. High frequency filter 120. Output adjustment circuit

121. High frequency bandpass filter 122. Output adjustment circuit

123. Mixers 124. Intermediate frequency band filters

125. I / Q signal modulator 126. Low pass filter

The transmitter of the transceiver system according to the present invention, which was invented to achieve the above object,

Inputs 3.5, 5, 7, 10, 10.5, 14, and 15 MHz in-phase baseband signals and quadrature phase baseband signals (hereinafter referred to as I / Q signals) from the digital signal processor. A low pass filter (LPF) that receives and removes unwanted waves; A phase modulator (PM) for phase-modulating baseband I / Q signals by mixing with a local oscillator; A band pass filter (BPF) for removing unwanted waves of the intermediate frequency signal output from the modulator; A mixer for upconverting to a final transmit high frequency signal; An output adjustment circuit for adjusting a base station transmission output level; It consists of a high frequency band filter and a final output amplifier to remove unwanted waves from the mixer.

In addition, the receiver system according to the present invention, a low noise amplifier for low noise amplification of the high frequency input signal from the high frequency input terminal; A high frequency band pass filter for increasing selectivity of a received signal; A dual balanced mixer for down converting high frequency signals to intermediate frequencies; An intermediate frequency band pass filter for removing unwanted waves on the down-converted signal and simultaneously increasing selectivity of the receiver; It consists of an automatic gain adjustment circuit for adjusting the gain of the received signal level and a demodulator for demodulating the received signal into a baseband I / Q signal.

A phase locked loop (hereinafter referred to as a PLL) synthesizer is used as a local oscillator of the frequency conversion and modulation / demodulation circuit of the transceiver circuit configured as described above.

Hereinafter, a transmission and reception operation of a transceiver device of a broadband-CDMA wireless subscriber network base station system according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a transceiver device of a broadband-CDMA wireless subscriber network base station system according to the present invention.

As shown in the figure, a transmitter receives an I / Q signal, modulates it to an intermediate frequency, and outputs a high frequency signal; And a local oscillator for receiving a high frequency signal, performing a modulation at an intermediate frequency, and then outputting an I / Q signal, and providing a carrier by an external reference clock to the transmitter and the receiver.

The transmitter includes a low pass filter 126 for receiving an I / Q signal from a digital signal processor and removing unwanted waves, a phase modulator 125 for phase modulating the mixed I / Q signal through the mixer, and the phase. An intermediate frequency band pass filter 124 for removing unwanted waves from the modulator, and a mixer 123 for mixing the signals output from the filter 124 with signals generated from the local oscillator and upconverting the final transmitted high frequency signals. ), An output adjusting circuit 122 for adjusting the transmission output level, a high frequency band filter 121 for removing unwanted waves generated in the mixer, and a final output high frequency amplifier 118.

The receiver may further include a first low noise amplifier 102 for low noise amplifying the input high frequency input signal, a first high frequency band pass filter 103 for increasing selectivity of a received signal, and a second signal for amplifying the filtered signal. A second low noise amplifier 104, a second high frequency bandpass filter 105 for increasing the selectivity of the amplified signal, a double balanced mixer 106 for downconverting the filtered high frequency signal to an intermediate frequency, An intermediate frequency band pass filter 107 to increase selectivity, an intermediate frequency amplifier 108 for amplifying a frequency-converted signal, and a surface acoustic wave (SAW) filter that performs coding through the magnitude and phase of the amplified signal ( 109, automatic gain adjustment circuit 110 for constantly adjusting the gain of the received signal level, and I / Q signal demodulation circuit for demodulating the received signal into a baseband I / Q signal. and a low pass filter 112 for frequency selection of the final low frequency signal.

When the transmitter according to the present invention configured as described above receives an inphase baseband signal and a quadrature phase baseband signal independently from the digital signal processing unit and passes through the low pass filter 126, The unwanted wave component generated in the signal processor may be removed.

The I / Q signal and the signal generated by the local oscillator, which have been processed above, are multiplied by a mixer in the I / Q modulation circuit 125 to generate a signal corresponding to the sum and difference of the two signals, and the intermediate frequency generated here. Phase modulation is performed through the phase modulator using the signal.

The intermediate frequency signal subjected to the phase modulation is passed through the intermediate frequency band pass filter 124 to remove the unwanted components of the noise component and the harmonic wave component generated by the modulator 125.

The intermediate frequency signal passing through the intermediate frequency band pass filter 124 is multiplied by the signal of the local oscillator 114 by the double balance mixer 123 and up-converted to the final transmission frequency.

The high frequency signal, which is upconverted to the final transmitted high frequency signal, after the output level is adjusted by the output adjustment circuits 122 and 120 and the high frequency bandpass filters 121 and 119 remove the unwanted wave generated from the upconverting mixer. Finally, it is output through the output amplifier 118.

The operation of the receiver of the broadband-CDMA wireless subscriber network base station system according to the present invention will be described below.

The receiver amplifies the high frequency input signal input from the high frequency input at a low noise amplifier 102 having a high 1 dB compression point.

The first high frequency amplifier stage determines the noise figure (hereinafter referred to as NF) and gain of the receiver.

The most important points in designing a high frequency amplifier stage are sensitivity and noise figure.

Sensitivity is an index indicating how small a high-frequency stage can receive to obtain a satisfactory signal-to-noise ratio (hereinafter referred to as SNR).

In addition, NF is an exponent that expresses the ratio of the input signal and the noise ratio output signal to noise in decibel units.

After the first high frequency bandpass filter 103 is passed to increase the selectivity of the received signal, the second low noise amplifier 104 passes through the bandpass filter 105 after amplifying and then amplifying the signal level.

The high frequency signal passed through the band pass filter 105 is input to the dual balance mixer 106 which down-converts to the intermediate frequency, and multiplied by the signal generated by the local oscillator 114 to down-convert to the intermediate frequency signal corresponding to the difference.

Again, the intermediate frequency signal is amplified by the intermediate frequency amplifier 108 after passing through the intermediate frequency band pass filter 107 to remove the unwanted wave generated in the down-conversion mixer 106.

The intermediate frequency amplifier 108 is used at the front of the SAW filter 109 to eliminate the high insertion loss and the low NF effect generated in the SAW filter 109 used to increase the selectivity.

The intermediate frequency signal amplified through the above process is input to the SAW filter 109 to increase the selectivity.

The signal output from the SAW filter 109 is input to each I / Q demodulation circuit 111 after the received signal level is adjusted by the automatic gain adjustment circuit 110 to a certain level.

The I / Q demodulation circuit 111 finally transmits the demodulated signal input from the automatic gain adjustment circuit 110 to the low pass filter 112 and outputs the low frequency I / Q signal.

According to the above configuration, the present invention can simplify the transceiver by using the transceiver circuit of the broadband-CDMA wireless subscriber network base station system, and can reduce the number of modules required by the base station system through the built-in modulation / demodulation circuit. Have.

Claims (4)

A transmitter for receiving an I / Q signal and performing modulation at an intermediate frequency and then outputting a high frequency signal; A receiver which receives a high frequency signal and modulates it to an intermediate frequency and outputs it as an I / Q signal; And a local oscillator configured to provide a carrier by an external reference clock to the transmitter and the receiver. The method of claim 1, wherein the transmitter, A low pass filter for receiving an I / Q signal from the digital signal processor and removing unwanted waves; A phase modulator for phase modulating the I / Q signal filtered from the filter; An intermediate frequency band pass filter for removing unwanted waves from the phase modulator; A mixer for mixing the signal output from the filter with the signal generated from the local oscillator to upconvert it to a final transmit high frequency signal; An output adjustment circuit for adjusting a transmission output level of the mixed signal; And an output amplifier for finally amplifying the filtered signal, and a high frequency band filter for eliminating unwanted waves generated in the mixer. The method of claim 1, wherein the receiver, A low noise amplifier for low noise amplifying the input high frequency signal; A high frequency band pass filter for increasing selectivity of a received signal amplified by the amplifier; A dual balanced mixer for mixing down the high frequency signal filtered by the filter with the signal generated from the local oscillator and down converting it to an intermediate frequency; An intermediate frequency band pass filter for removing unwanted waves and increasing receiver selectivity with respect to the signal generated by the mixer; An automatic gain adjustment circuit for adjusting the gain of the level of the filtered received signal; A demodulator for demodulating the received signal output from the automatic gain adjustment circuit into a baseband I / Q signal; A transceiver device of a wideband code division multiple access wireless subscriber network base station system comprising a low pass filter for final low frequency selection. The method of claim 1, And said transceiver circuitry uses a phase locked loop synthesizer as a local oscillator of a frequency conversion and modulation and demodulation circuit.