RU2427089C1 - Base station for wireless broadband access network - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: base station of a wireless broadband access network, having an access point (1), an antenna (5), a channel busy signal generating unit (16), an additional transmitting antenna (17), also includes a first switch (3), a second switch (4), a first buffer amplifier (6), a first mixer (7), a power divider (10), a first heterodyne (9), a strobed preamplifier (11), a first sideband filter (12), a second mixer (8), a first key (14), a first high frequency band-pass filter (13), a second buffer amplifier (15) and a detector (2).

EFFECT: high throughput of the base station of a wireless broadband access network, as well as the number of client stations simultaneously working with the network and wider coverage area.

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Description

The invention relates to communication technology and can be used to create wireless broadband access networks.

The base station of the wireless broadband access network is known (see Golyshko A. Part 4. BWA in the struggle for mass. - Communication World. Connect! No. 10, 2002), which contains an access point and an antenna whose input-output is connected to the point's input-output access.

However, this device has the disadvantage that the performance of the base station, due to the features of the CSMA / CA access protocol (Carrier Sense Multiple Access With Collision Avoidance, “multiple access with carrier control and conflict prevention”) is sharply reduced due to the known effect “ Hidden Node (hidden node), when the client stations are out of the radio hearing zone of each other. This effect is exacerbated with an increase in the number of client stations. The RTS / CTS (Request To Send / Clear To Send, Request to Send / Ready to Send) collision avoidance mechanism implemented in the IEEE 802.11 standard is not able to effectively solve the problem (see http: //www.nnn.tstu. com / twn / hidden_node / index_k.html).

In addition, there is a known base station of a wireless broadband access network (see US patent No. 7545827 B2 dated 06/09/2009), which is a prototype of the invention, comprising an access point, an antenna, the input-output of which is connected to the input-output of the access point, a signal conditioning unit channel busy channel (IBTG, Intelligent Busy Tone Generator), built into the access point, an additional transmitting antenna, the input of which is connected to the output of the channel busy signal generating unit. In this device, the solution to the “hidden node” problem is assumed due to the fact that the channel busy signal generation unit generates a signal similar in structure to the signal used in the preamble of information packets. Such a signal is emitted by an additional transmitting antenna while the base station is receiving an information packet from some client station, while other client stations receive it and, in accordance with the CSMA / CA protocol, considering the medium busy, postpone their own transmission, thereby avoiding collisions.

However, this device has the following disadvantages. The channel busy signal generated by the device, which does not contain information about the transmitted packet and has only the physical component, is not able to coordinate the work of client stations. For normal operation, as laid down in the CSMA / CA protocol, all client stations must receive not only preambles, but also headers of information packets that contain information about the duration of the packet, otherwise the network loses its connectivity and there are known problems. The behavior of the network when client stations receive only a modulated carrier (as in the preamble of the packet) becomes completely unpredictable; moreover, the channel busy signal can block client stations during heavy traffic. This happens as follows. Let there be a client station that started transmission first (let's call it 1), and any other client station (let's call it N). Client station N will receive a channel busy signal. Having detected the preamble (carrier), for example, within about 15 μs for an IEEE 802.11b device, client station N will try to receive the packet header within 192 μs (see IEEE Std 802.11b-1999, p.24-25). In this case, even if the carrier signal disappears immediately after 15 μs, the CCA mechanism (clear channel assessment, channel occupancy estimation) (see IEEE Std 802.11b-1999, p.24-25) will indicate that the channel is busy before the reception time expires SFD (start frame delimiter, initial frame determinant), and only after that the CCA signal will be reset, and client station N will go to the standard CSMA / CA procedure, which also takes some time (the real time the client station is in such a “blind” »State, let’s call it Ts, depends on the implementation features, so, for client stations made on the basis of the Prism II chipset, the applicant observed a time of about 200 μs, and for those made on the Agere chipset (Orinoco brand) about 300 μs). Thus, the reception of the channel busy signal does not occur continuously, but with “pieces” that are multiples of Ts. In this regard, client station N can be in a practically inoperative state (it can neither receive nor transmit packets) during the time from 0 to Ts after the end of the packet from station 1. Since the CSMA / CA mechanism assumes competitive access to the environment, the appearance of an additional delay time for client station N exceeding the DIFS (Distributed Inter Frame Space, inter-frame gap of the distributed coordination function) will cause it to constantly “lose the fight” for access to the client’s environment Station 1, and under intensive traffic from the client station 1 will be locked. It is clear that with the simultaneous operation of several client stations, each of them will experience similar problems, reducing the overall throughput of the base station. This will be aggravated with an increase in the number of simultaneously working client stations, limiting their potential number.

In addition, this device has a limited range, as it can completely block the client station if it is located at a considerable distance from the base station. This is due to the echo effect. The client station transmitting the packet will receive a busy channel signal with a delay of 1 μs per 150 m of distance from the base station. As noted above, if this delay is about 15 μs, the client station will be blocked for the time Ts, but at this time (within 10 μs after the end of the packet reception) the base station should send an ACK packet to the client station (abbreviation from Acknowledge, confirmation ) If the client station does not receive it, it will try to repeat its packet. But the result will be the same, and as a result, the packet will be lost.

The objective of the invention is to increase the throughput of a base station of a wireless broadband access network, the number of client stations working simultaneously with it, and increase its radius of action.

The problem is achieved by the fact that the first switch, the input-output of which is connected, is introduced into the base station of the wireless broadband access network containing an access point, an antenna, a channel busy signal generating unit, an additional transmitting antenna, the input of which is connected to the output of the channel busy signal generating unit to the input-output of the access point, the second switch, the input of which is connected to the output of the first switch, the input-output of the second switch is connected to the input-output of the antenna, the first bu A black amplifier whose input is connected to the output of the second switch, a first mixer, the signal input of which is connected to the output of the first buffer amplifier, a power divider, one output of which is connected to the heterodyne input of the first mixer, the first local oscillator, whose output is connected to the input of the power divider, a gated preamplifier the input of which is connected to the output of the first mixer, the first sideband filter, the input of which is connected to the output of the gated preamplifier, the second mixer, the signal input of which о is connected to the output of the first sideband filter, and the heterodyne input of the second mixer is connected to another output of the power divider, the first key, the input of which is connected to the output of the first sideband filter, and the output is connected to the input of the channel busy signal generation unit, the first high-pass filter the input of which is connected to the output of the second mixer, the second buffer amplifier, the input of which is connected to the output of the first high-pass bandpass filter, and the output is connected to the input of the first switch, p, the input of which is connected to the input-output of the access point, and the output is connected to the control inputs of the first and second switches, the control input of the first key and the control input of the gated preamplifier; the channel busy signal generation unit is made in the form of a series-connected preamplifier, a second sideband filter, a second key, an amplifier with automatic gain control, a third mixer, a second high-pass filter, a power amplifier, and a second local oscillator, the output of which is connected to the corresponding input of the third a mixer, a broadband signal detector, the input of which is connected to the output of the preamplifier, a single-shot, whose input is connected to the output of the detector broadband of the signal, and an output connected to the control input of the second switch, wherein the input of the preamplifier is input unit for generating a channel busy signal, and the power amplifier output is the output of the block forming a channel busy signal.

In Fig.1 shows a structural diagram of the proposed device, Fig.2 is a structural diagram of a block for generating a channel busy signal, Fig.3 is an amplitude-frequency characteristic of a sideband filter, Fig.4 is a signal spectrum at the antenna output, Fig. 5 - spectrum of the signal at the input-output of the access point; FIG. 6 - spectrum of the signal at the output of the channel busy signal generation unit. All spectra are shown relative to the center frequency of the received signal.

The proposed device (Fig. 1) contains an access point 1, for example, of IEEE 802-11a / b / g standard, a detector 2 made on a microcircuit, first 3 and second 4 switches made on pin diodes, an antenna 5, for example, collinear, the first buffer amplifier 6, which is a low-noise amplifier with a gain of 10 dB, made on a transistor, the first 7 and second 8 mixers made on Schottky diodes according to a balanced circuit, the first local oscillator 9, which is a controlled oscillator on a transistor, made using microstrip techno phase stabilized frequency reference oscillator 5 MHz by the PLL, a power divider 10, made on a microstrip line, a gated preamplifier 11, made on a chip having a gain of 40 dB and containing LC filters of intermediate frequency, the first sideband filter 12, which is a high-quality bandpass a filter based on surface acoustic waves, the first high-pass bandpass filter 13, made by microstrip technology, the first key 14, made on pin diodes, the second buffer amplifier 15, connected to the transistor and having a gain of 10 dB, the unit for generating a busy signal of channel 16, the structural diagram of which is shown in Fig. 2, an additional transmitting antenna 17, similar to antenna 5.

The channel 16 employment signal generating unit (Fig. 2) contains a preamplifier 18 made on a microcircuit and having a gain of 40 dB, a second sideband filter 19, which is a high-quality bandpass filter on surface acoustic waves, similar to 12, the second key 20, made on pin diodes, an amplifier with automatic gain control 21, which is a microcircuit with a gain of 40 dB and a dynamic range of input signals of 45 dB, the second local oscillator 22, which is a controlled oscillator on a transistor, is flaxen using microstrip technology, stabilized by the frequency of the reference oscillator 5 MHz by the PLL method, the third mixer 23, made on the Schottky diodes according to the balanced circuit, the second high-pass filter 24, made on the microstrip technology, the power amplifier 25, which is a linear amplifier with microchips with a gain of 50 dB and an output power of 30 dBm (at a compression level of 1 dB), a broadband signal detector 26, made on a chip, a single vibrator 27.

The device operates as follows. In transmission mode, an RF signal (with a level of about 20 dBm) appears at the output of access point 1, which is detected by detector 2. As a result, a control voltage appears at the output of detector 2, which switches the input-output of switch 3 to its output, and the input-output of the switch 4 at his entrance. Thus, the access point is connected to the antenna 5. Also, the control voltage from the detector 2 opens the contacts of the first key 14, disconnecting the input of the employment signal generating unit of channel 16 from the output of the first band-pass filter 13, and blocks the gated preamplifier 11, thereby preventing part of the RF power the signal of access point 1, leaked from the input of switch 4 to its output due to imperfect isolation between them, to the input of the channel signal occupation signal generating unit 16. Base operation stations of a wireless broadband access network in this mode does not differ from the work of analogs and occurs in a standard manner for the IEEE 802.11 standard.

In the mode of receiving an information packet from a client station, an antenna 5 output has a signal (with a level from -80 dBm to -35 dBm for this device implementation) with a central frequency Fs, the spectrum of which is shown in Fig. 4 (we consider the operation in the DSSS reception mode ( Direct Sequence Spread Spectrum, expanding the spectrum using the direct sequence method) of a signal, basically working in the OFDM reception mode (orthogonal frequency-division multiplexing, orthogonal frequency division multiplexing) of a signal is no different). The signal from the output of the antenna 5 enters the input-output of the second switch 4 and then through its output to the input of the first buffer amplifier 6, there it is amplified and then fed to the signal input of the first mixer 7. A signal is received at the heterodyne input of the first mixer 7 through a power divider 10 the first local oscillator 9 with a frequency of Fg1. At the output of the first mixer 7, a differential frequency signal Fr is generated, which, after amplification by a gated preamplifier 11, is fed to the input of the first filter of the side band 12. Between frequencies Fs and Fg1, a ratio must be satisfied so that the difference frequency Fr is on the slope of the amplitude-frequency characteristic (for example, right) of the first sideband filter 12 at a point where the attenuation is about 45 dB, with Fs being greater than Fg1. As a result, at the output of the sideband filter 12, a single-band intermediate frequency signal is generated, the carrier and the second (in this case, the upper, sideband of which is suppressed by 45 dB or more. Next, this single-band signal is fed to the signal input of the second mixer 8 and through the closed first key 14 to the input of the signal occupancy signal generating unit of channel 16. The signal of the first local oscillator 9 is fed to the heterodyne input of the second mixer 8 through a power divider 10. At the output of the second mixer 8, signals of difference and total h the frequencies that go to the input of the first band-pass filter 13. The first band-pass filter 13 selects a signal of the total frequency, which, after amplification in the second buffer amplifier 15, through the first switch 3 is fed to the input-output of access point 1. Thus, the input-output of access point 1 it turns out that the signal (Fig. 5) is a single-band copy of the original signal at the output of the antenna 5. It has been experimentally verified that such a signal (both DSSS and OFDM) is processed without any degradation in the receivers of access points and client their stations (which is important for further consideration) of the IEEE 802.11a / b / g standard, made on various chipsets.

Let us further consider what happens with a single-band intermediate frequency signal received at the input of the channel 16 busy signal generating unit. It is amplified by the preamplifier 18 and is fed to the input of the second sideband filter 19, which has the characteristic shown in Fig. 3. At the same time, a control voltage appears at the output of the broadband signal detector 26, triggering the one-shot 27. A pulse is generated at the output of the one-shot 27, the duration of which is chosen equal to the sum of the preamble times and the information packet header (for DSSS, for example, 192 μs). This pulse is supplied to the control input of the second key 20 and closes it. In this case, a single-band intermediate frequency signal from the output of the second sideband filter 19 passes to the input of the amplifier with automatic gain control 21, the output of which is then fed to the signal input of the third mixer 23. The signal from the output of the second local oscillator 22 is received at the heterodyne input of the third mixer 23. this frequency Fg2 of the second local oscillator 22 is selected from the relation Fg2 = 2Fs-Fg1. At the output of the third mixer 23, differential and total frequency signals are generated, which are fed to the input of the second band-pass filter 24. The second band-pass filter 24 emits a signal of the total frequency, which, after amplification in the power amplifier 25, goes to the input of an additional transmitting antenna 17. The level of this signal is about 20 dBm for given values of the receiving signal and the specified parameters of the elements of the device. This signal is a signal of channel occupancy in the proposed device and is transmitted to the air. The signal spectrum at the input of the additional transmitting antenna 17 has the form shown in Fig.6. It is a single-band signal, a mirror signal coming to the input-output of access point 1. In order for the signal emitted by the additional transmitting antenna 17 to not interfere with reception, the necessary isolation must be provided between it and antenna 5. The experiments show that with the selected frequency response of the filters 12 and 19 (Fig. 3), a decoupling of 60 dB is sufficient. For example, in the case of collinear antennas in the 2.4 GHz band, this can be achieved by spacing them along the axis by a distance of about 1.5 m. If necessary, the required isolation can be reduced by using filters with a large out-of-band attenuation value or by using cascaded filters.

A single-band signal emitted by an additional transmitting antenna 17 is received by all client stations (we remember that one client station is transmitting at this time). As already noted, such a signal can be processed at their receiver. Since this signal contains both the preamble and the header of the information packet of the transmitting client station, other client stations, having received it, will receive complete information about the duration of the packet and will be able to coordinate their work in accordance with the protocol, in the same way as if they themselves "heard" the transmitting client station. Thus, in comparison with the base station of the wireless broadband access network adopted as a prototype, the channel busy signal in the proposed base station of the wireless broadband access network does not block client stations, the proposed base station of the wireless broadband access network really solves the "hidden node" problem due to which an increase in its throughput and the number of client stations simultaneously working with it is achieved.

Consider how the above-mentioned echo effect manifests itself in the operation of the proposed base station of a wireless broadband access network. In the general case, it will take place when the following relation holds: Tb-Tack + Td> Tg, where Tb is the duration of the channel busy signal. Tack is the duration of the ACK packet transmitted by the client station, Tb is the doubled propagation delay time of the signal from the base station to the client station, Tg is the time required for the carrier to detect the signal by the receiving device. In the base station of the wireless broadband access network adopted for the prototype, Tb = Tack, while in the proposed base station of the wireless broadband access network Td is limited to the sum of the preamble and header times (specified in single-shot 27). Thus, it is easy to see that the range of the proposed base station of the wireless broadband access network is larger by (* in meters) 150 * (Tack-Tb), with times expressed in microseconds. For example, at operating speeds of 2 Mbps this value will be 8400 m.

Claims (1)

A base station of a wireless broadband access network containing an access point, an antenna, a channel busy signal generating unit, an additional transmitting antenna, the input of which is connected to an output of a channel busy signal generating unit, characterized in that a first switch is inserted into it, the input-output of which is connected to access point I / O, the second switch, the input of which is connected to the output of the first switch, the input / output of the second switch is connected to the input / output of the antenna, the first buffer amplifier the input of which is connected to the output of the second switch, the first mixer, the signal input of which is connected to the output of the first buffer amplifier, a power divider, one output of which is connected to the heterodyne input of the first mixer, the first local oscillator, the output of which is connected to the input of the power divider, gated preamplifier, input which is connected to the output of the first mixer, the first sideband filter, the input of which is connected to the output of the gated preamplifier, the second mixer, the signal input of which is connected to the first sideband filter, and the heterodyne input of the second mixer is connected to another output of the power divider, the first key, the input of which is connected to the output of the first sideband filter, and the output is connected to the input of the channel busy signal generation unit, the first high-pass filter, whose input connected to the output of the second mixer, the second buffer amplifier, the input of which is connected to the output of the first bandpass high-pass filter, and the output is connected to the input of the first switch, the detector, the input of which connected to the input-output of the access point, and the output is connected to the control inputs of the first and second switches, the control input of the first key and the control input of the gated preamplifier; the channel busy signal generation unit is made in the form of a series-connected preamplifier, a second sideband filter, a second key, an amplifier with automatic gain control, a third mixer, a second high-pass filter, a power amplifier, and a second local oscillator, the output of which is connected to the corresponding input of the third a mixer, a broadband signal detector, the input of which is connected to the output of the preamplifier, a single-shot, whose input is connected to the output of the detector broadband of the signal, and an output connected to the control input of the second switch, wherein the input of the preamplifier is input unit for generating a channel busy signal, and the power amplifier output is the output of the block forming a channel busy signal.

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