JP4009232B2 - Base station for subscriber radio access system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio communication performed using a TDMA / TDD (Time Division Multiple Access / Time Division Duplex, time division multiple access / time division duplex) method in a FWA (Fixed Wireless Access) system. The present invention relates to a point-to-multipoint (PMP / base station-to-multiple station connection) wireless communication apparatus.
[0002]
[Prior art]
When radio is used in the communication system, it is not necessary to lay a track, so that the introduction cost of the entire system can be reduced.
[0003]
A subscriber radio access system is a typical example, and a plurality of subscriber stations are arranged relatively close to a base station, and a radio transmission path using microwaves or millimeter waves is provided between the base station and each subscriber station. Connecting.
[0004]
FIG. 11A shows a conceptual diagram of the PMP communication system as such a subscriber radio access system. Here, four subscriber stations 2-1 to 2-4 are connected to the base station 1. FIG. ing. In the following description, the transmission direction from the base station 1 to each of the subscriber stations 2-1 to 2-4 is “downlink”, and the transmission direction from each of the subscriber stations 2-1 to 2-4 to the base station 1 is This is referred to as “up”.
[0005]
There are several systems for this subscriber radio access system. One of them is a time-division bidirectional communication system (Time) that uses a single frequency channel for both downlink burst and uplink burst transmission in a time division manner. (Division Duplex: TDD).
[0006]
FIG. 11B is a schematic diagram showing a time series of bursts by this time division bidirectional communication method, and the horizontal axis is the time axis.
[0007]
First, the downlink burst 3 is transmitted from the base station 1 to each of the subscriber stations 2-1 to 2-4. In the downstream burst 3, timing and data amount for transmitting the upstream bursts 4-1 to 4-4 from the subscriber stations 2-1 to 2-4 to the base station 1 are designated.
[0008]
Each of the subscriber stations 2-1 to 2-4 transmits uplink bursts 4-1 to 4-4 to the base station 1 according to the designated timing. Note that a plurality of uplink bursts 4-1 to 4-4 may be transmitted from the same subscriber station (for example, subscriber station 2-1) within one burst period.
[0009]
Thereby, it is possible to transmit the upstream burst 3 and the downstream bursts 4-1 to 4-4 on the single frequency channel without colliding.
[0010]
FIG. 10 is a block circuit diagram showing a configuration around the demodulation unit of the base station 1 or the subscriber stations 2-1 to 2-4 in the subscriber radio access system. That is, the base station 1 and the subscriber stations 2-1 to 2-4 have basically the same configuration.
[0011]
In the receiving system of the base station 1 or the subscriber stations 2-1 to 2-4, a received RF signal received from an antenna (not shown) is amplified by a low noise amplifier (LNA) and then down-converted to an intermediate frequency (IF) The received IF signal passes through the variable gain amplifier 11 and is demultiplexed into an I signal (in-phase component) and a Q signal (quadrature component) by the quadrature detector 12.
[0012]
The demultiplexed I and Q signals are converted into digital signals by the A / D converter 13 and further demodulated by the demodulator 14 to obtain a demodulated signal. In addition, the I signal and the Q signal converted into digital signals are output to the burst detection circuit 15 and the reception level measurement circuit 17.
[0013]
The burst detection circuit 15 executes a demodulation process in the demodulator 14 based on the I signal and the Q signal output from the A / D converter 13 based on the detection result. In FIG. 10, the thick arrow means that the I signal and the Q signal are transmitted in parallel.
[0014]
For example, as shown in FIG. 9, burst detection in the burst detection circuit 15 is performed on a preamble block set before a communication data block (communication data block) as transmission target information in a burst signal of one frame. Done.
[0015]
The burst detection circuit 15 continues to detect the head of the burst signal based on the burst detection window opening / closing signal output from the demodulator 14 while the burst detection window is open.
[0016]
In the subscriber stations 2-1 to 2-4, since the downlink burst 3 is transmitted from the base station 1 at a constant period, once the burst detection signal is output, this timing is the burst for the next burst signal. The detection window is opened.
[0017]
The AGC 16 controls the reception signal input to the demodulator 14 to be constant as a correction for fluctuations in the reception level of the burst signal due to the state of the transmission line (for example, weather change). Updated.
[0018]
Specifically, immediately before the burst signal is received, the gain value obtained with the burst signal received before the burst signal to be received is set, and the burst received thereafter by the burst detection signal The reception level of the burst signal is measured at the head of the signal (preamble CR), and the gain of the variable gain amplifier 11 is adjusted by the AGC 16 so that the input value to the demodulator 14 is optimized from the measured value. It is.
[0019]
For example, when the subscriber stations 2-1 to 2-3 are in a transmission relationship with the base station 1, when the initial connection is started such as when the power of the subscriber station 2-4 is newly started, the base station The gain of the AGC 16 on the 1 side is fixed to an indefinite value or a predetermined value because the optimum gain value cannot be found because the reception level is not measured.
[0020]
[Problems to be solved by the invention]
By the way, in FWA, on the assumption that the level fluctuation between burst signals is gradual and there is no big fluctuation, the maximum fluctuation width of the gain update is set small.
[0021]
Under these circumstances, during normal communication shown in FIG. 8A, when a subscriber station (for example, subscriber station 2-4) cannot receive a downlink burst at a certain time for some reason, FIG. As shown in (B), subsequent uplink bursts are not transmitted.
[0022]
The base station 1 waits for the burst signal from the subscriber station 2-4, but cannot receive the burst signal from the subscriber station 2-4 because no uplink burst is transmitted.
[0023]
At this time, the base station 1 cannot receive because the reception level has suddenly decreased due to some cause (for example, rainfall) and cannot be received, or because there was no transmission from the subscriber station in the first place. Since it is not possible to determine whether or not it has occurred, it is necessary to update the AGC 16.
[0024]
That is, as shown in FIG. 7A, when the uplink burst of the subscriber station 2-4 happens to transmit a plurality of bursts within this burst period, the uplink burst is not transmitted. Regardless, the AGC 16 may operate, and as a result, the gain may be maximized.
[0025]
Thereafter, as shown in FIG. 7 (B), an uplink burst is received from the subscriber station 2-4 in the next burst cycle. However, since the gain is set to be large, the received signal is saturated and is normally It cannot be demodulated.
[0026]
Further, as shown in FIG. 7C, the burst signal received until the AGC 16 updates the gain and the normal reception can be performed is discarded without being normally received.
[0027]
On the other hand, as shown in FIG. 6 (A), if the reception level suddenly decreases due to rain or the like, and it is erroneously determined that there is no signal despite being actually received, FIG. As shown in B), it is expected that the AGC 16 does not move and the subsequent burst signal cannot be received. Note that, as shown in FIG. 6C, if the reception level is restored, the gain update does not deviate greatly, so it is assumed that the normal level is restored immediately.
[0028]
In order to solve the above problem, an object of the present invention is to provide a base station for a subscriber radio access system that can make gain adjustment by AGC appropriate even in an unforeseen situation.
[0029]
[Means for Solving the Problems]
The present invention is a base station for a subscriber radio access system that transmits and receives burst signals to and from a plurality of subscriber stations by transmitting and receiving burst signals at different timings with different subscriber stations. A request signal transmitting means for periodically transmitting a request signal for requesting the subscriber station to transmit a burst signal for measurement for measuring a propagation delay time with the subscriber station; A variable gain amplifier that adjusts the level of a burst signal received from an antenna; an A / D converter that converts an output signal from the variable gain amplifier into a digital signal via a quadrature detector and outputs the signal as a received burst signal; A gain acquisition unit that obtains the gain of the variable gain amplifier based on the level of the received burst signal, and compares the level of the received burst signal with a predetermined no-signal threshold Includes a signal determining portion, when the level of the received burst signal is greater than or equal to the no-signal threshold, the variable gain amplifier, the level of the burst signal to which the received burst signal is received after being received, the adjusted based on the gain obtained based on the received burst signal, the level of the received burst signal is less than the no-signal threshold, and the received burst signal has been sent in response to pairs to the request signal When it is not a measurement burst signal, the variable gain amplifier determines the level of the burst signal received after the reception burst signal is received based on the burst signal received before the reception burst signal is received. adjusted based on the determined gain, the level of the received burst signal is less than the no-signal threshold, and the receiving server Strike signal, when a measurement burst signal transmitted as a response against the request signal, the variable gain amplifier, the level of the burst signal to which the received burst signal is received after being received, the reception The adjustment is based on the gain obtained based on the burst signal .
[0030]
Also, in the subscriber base station for a wireless access system according to the present invention, a downlink signal indicating a condition of transmitting a burst signal the non measurement burst signal includes a downlink signal transmission unit that transmits to the subscriber station Preferably, the subscriber station transmits a burst signal that is not the measurement burst signal based on a condition indicated by the downlink signal.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the wireless communication apparatus of the present invention will be described with reference to the drawings.
[0032]
FIG. 1 is a block circuit diagram of the main part of the wireless communication apparatus of the present invention, FIG. 2 is an explanatory diagram of burst signals used in the present invention, FIG. 3 is an operation flow diagram of the wireless communication apparatus of the present invention, and FIG. FIG. 5 is a one-cycle burst configuration diagram showing the AGC operation in signal sequence in time series, and FIG. 5 is a one-cycle burst configuration diagram showing the AGC operation in time sequence in low level signals.
[0033]
In FIG. 1, in the receiving system of the base station 1 or the subscriber stations 2-1 to 2-4, a received RF signal received from an antenna (not shown) is amplified by a low noise amplifier (LNA), and then an intermediate frequency (IF The received IF signal down-converted to) is demultiplexed into an I signal (in-phase component) and a Q signal (orthogonal component) in the quadrature detector 22 through the variable gain amplifier 21.
[0034]
The demultiplexed I and Q signals are converted into digital signals by the A / D converter 23 and further demodulated by the demodulator 24 to obtain a demodulated signal. The I signal and Q signal converted into digital signals are output to the burst detection circuit 25 and the reception level measurement circuit 26.
[0035]
The reception level measurement circuit 26 outputs a reception level measurement value to an AGC (Automatic Gain Control) 27 and a no-signal determination circuit 28.
[0036]
Further, as shown in FIG. 2, the burst signal used in the present invention starts with a carrier recovery (CR) signal mainly for reception level measurement, and uses bit timing recovery (for extracting symbol timing of data). (BTR) signal and a unique word for determining whether the burst signal is a signal of a master station (base station 1) or a slave station (subscriber stations 2-1 to 2-4) and determining the head of data UW) signal, and after these preamble blocks, there are data symbols (data blocks).
[0037]
Thereby, when there is an interference station (for example, subscriber station 2-2) on the extension line of the base station 1 with respect to a new entry station (for example, subscriber station 2-4), The station 1 and the interference station can be easily distinguished.
[0038]
By the way, in order to specify the timing of the uplink burst accurately as described above, a measurement burst signal (hereinafter referred to as “DMF”) for measuring the delay time of each of the subscriber stations 2-1 to 2-4 in a part of the uplink burst. ").
[0039]
The DMF is received at the base station 1 side and the timing range is known, but the timing itself is undecided, so demodulation starts at the burst detection timing of the burst detection circuit 25.
[0040]
At the beginning of the connection of the subscriber stations 2-1 to 2-4 with the base station 1, DMF transmission requests are periodically sent to the subscriber stations 2-1 to 2-4 registered in the base station 1. Keep sending.
[0041]
In response to the DMF transmission request, the subscriber station (for example, the subscriber station 2-4) that has started up the power supply transmits the DMF to the base station 1 at a predetermined transmission timing of one burst period.
[0042]
The base station 1 receives the DMF, calculates the delay time of the subscriber station 2-4 whose power is turned on from the timing, determines the transmission timing of the upstream burst other than the DMF (time alignment), and thereafter Data communication is performed using.
[0043]
The burst detection circuit 25 opens the burst detection window based on the burst detection window open / close signal output from the demodulator 24 and outputs a burst detection signal to the demodulator 24 based on the detection result.
[0044]
The no-signal determination circuit 28 compares the measurement value (RxL) with a preset no-signal threshold (ThL) based on the reception level measurement (step 1) from the reception level measurement circuit 26 (step 2). If the no-signal threshold value is larger than the measured value, the process is terminated. If the measured value is larger than the no-signal threshold value, the gain of the variable gain amplifier 21 is updated by the AGC 27.
[0045]
As a result, as shown in FIG. 4 (A), even though the uplink burst of the subscriber station (for example, the subscriber station 2-4) happens to transmit a plurality of bursts within this burst period, When the uplink burst is not transmitted due to the fact that the subscriber station 2-4 cannot receive the downlink burst, the gain of the variable gain amplifier 21 is not updated. As shown in FIG. 4B, even if an uplink burst is transmitted from the subscriber station 2-4 in the next period, the level of the uplink burst and the gain that has not been updated are not greatly disrupted, so normal demodulation is performed immediately. be able to.
[0046]
Further, as shown in FIG. 5A, in the case where reception is actually performed due to a sudden drop in the reception level with respect to the upstream burst due to rain or the like, The gain update of the AGC 27 is not performed for the corresponding uplink burst (determined as pseudo-no signal), and the gain update by the AGC 27 is performed only for the DMF regardless of the reception level.
[0047]
As a result, as shown in FIG. 5B, even if an uplink burst is transmitted from the subscriber station 2-4 in the next period or the like, the level of the uplink burst and the gain that has not been updated are not significantly disrupted. Immediately, normal demodulation can be performed.
[0048]
At this time, since the gain of the AGC 27 is updated even when there is no signal in the DMF, it is considered that the gain of the no signal is also updated. However, the gain update range by the AGC 27 when the DMF is determined as no signal is updated normally. It can be relaxed by making it narrower than the range.
[0049]
【The invention's effect】
The subscriber radio access system base station of the present invention is configured as described above, so that gain adjustment by AGC can be made appropriate even in unexpected situations.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram of a main part of a wireless communication apparatus of the present invention.
FIG. 2 is a configuration diagram of a burst signal used in the present invention.
FIG. 3 is an operation flowchart of a no-signal determination process according to the present invention.
4A and 4B are one-cycle burst configuration diagrams showing AGC operations in a time series when there is no signal.
FIGS. 5A and 5B are one-cycle burst configuration diagrams showing AGC operations in time series when a low level signal is used.
FIGS. 6A to 6C are one-cycle burst configuration diagrams showing the operation of a conventional AGC in a time series at the time of a low-level signal.
FIGS. 7A to 7C are one-cycle burst configuration diagrams showing, in time series, the operation of a conventional AGC when there is no signal. FIGS.
FIGS. 8A and 8B are burst configuration diagrams of one cycle showing in time series when a normal reception state is changed to a no-signal state.
FIG. 9 is a schematic diagram of a configuration of a burst signal.
FIG. 10 is a block circuit diagram of a main part of a conventional wireless communication device.
11A is a conceptual diagram of a PMP communication system as a subscriber radio access system, and FIG. 11B is a schematic diagram showing a burst time series by a time-division bidirectional communication system.
[Explanation of symbols]
21 variable gain amplifier, 22 quadrature detector, 23 A / D converter, 24 demodulator, 25 burst detection circuit, 26 reception level measurement circuit, 27 AGC, 28 no signal determination circuit.

Claims (2)

A base station for a subscriber radio access system that transmits and receives burst signals to and from a plurality of subscriber stations by transmitting and receiving burst signals at different timings with different subscriber stations,
A request signal transmitting means for periodically transmitting a request signal for requesting the subscriber station to transmit a burst signal for measurement for measuring a propagation delay time with the subscriber station;
A variable gain amplifier that adjusts the level of the burst signal received from the antenna;
An A / D converter that converts the output signal from the variable gain amplifier into a digital signal via a quadrature detector and outputs it as a received burst signal;
A gain acquisition unit for obtaining a gain of the variable gain amplifier based on a level of the received burst signal;
A no-signal determination unit that compares the level of the received burst signal with a predetermined no-signal threshold;
With
When the level of the received burst signal is equal to or higher than the no-signal threshold, the variable gain amplifier obtains the level of the burst signal received after the received burst signal is received based on the received burst signal. Adjust based on the gain
Wherein less than the received burst signal level is the no-signal threshold, and, when the received burst signal is not the measurement burst signal transmitted as a response against the request signal, the variable gain amplifier, the received the level of the burst signal burst signal is received after being received, adjusted based on the gain obtained based on the burst signal received before the received burst signal is received,
Wherein less than the received burst signal level is the no-signal threshold, and, when the received burst signal is a measurement burst signal transmitted as a response against the request signal, the variable gain amplifier, the A base station for a subscriber radio access system, wherein a level of a burst signal received after a received burst signal is received is adjusted based on a gain obtained based on the received burst signal . A base station for a subscriber radio access system according to claim 1 ,
A downlink signal transmitting means for transmitting a downlink signal indicating a condition for transmitting a burst signal that is not the measurement burst signal to the subscriber station;
The subscriber station
A base station for a subscriber radio access system, wherein a burst signal that is not the measurement burst signal is transmitted based on a condition indicated by the downlink signal.

Images