JP4573462B2 - Base station receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a base station receiver, and more particularly to a base station receiver that performs reception in a TDMA communication system, detecting a reception level of a reception input from an output after filtering of a received signal by a filter, and inputting the filter A base that switches a control value used for performing automatic gain control so that the level becomes a set value to a control value that is held in advance according to the reception level difference of each mobile station every time a mobile station to be received is switched. It relates to the station receiver.
[0002]
[Prior art]
FIG. 2 is a block diagram showing the configuration of a conventional base station receiver in a TDMA communication system, and FIG. 3 is a diagram showing the frame configuration of a received signal received by the base station receiver of FIG. This base station receiver includes an antenna 31, a frequency converter 32, a gain controller 33, a filter 34, a demodulator 35, a reception level detector 36, a gain control value calculator 37, and a frame position detection. And a gain control switching timing generator 39. In this base station receiver, the received signal is taken in from the antenna 31 and frequency-converted by the frequency converter 32. The frequency-converted received signal is passed to the gain controller 33, and the gain controller 33 controls the reception level of the passed received signal. The signal whose reception level is controlled is input to the filter 34 and filtered. The filtered signal is demodulated into digital data by the demodulator 35.
[0003]
Here, AGC (automatic gain control) will be described. First, the following operation of AGC will be described. The reception level detector 36 receives the output of the filter 34 and detects the reception level. The detected reception level is passed to the gain control value calculator 37. The gain control value calculator calculates a gain control value from the received reception level, gives the calculated gain control value to the gain controller 33, and performs AGC. Next, the AGC switching operation will be described. The frame position detector 38 receives the frame-structured digital data output from the demodulator 35 and detects the unique word portion UW to detect the frame position. The detected frame position is passed to the gain control switching timing generator 39. The gain control switching timing generator 39 generates a timing for switching a gain control value with respect to a reception level difference between the currently receiving mobile station and the next receiving mobile station. This gain switching timing is notified to the gain control value calculator, and is switched to the gain control value of the next mobile station held in advance in accordance with the timing. The AGC follow-up operation is performed until the next gain control switching timing is notified.
[0004]
In the TDMA communication system described above, a plurality of mobile stations (four mobile stations M1 to M4 in FIG. 3) are connected through one channel of the base station. When these mobile stations M1 to M4 transmit at the same time, the transmission waves interfere with each other, so the base station adjusts the timing of each mobile station so that the transmission waves do not overlap or interfere with each other. . For example, as shown in FIG. 3 (a), the base station receiver, for example, performs burst transmission (intermittent) composed of frames transmitted from each of the mobile stations in a time-division manner with four timings (M1 to M4). Is being received. The transmission frame structure of each of the mobile stations M1 to M4 is, for example, shown as a burst signal of the individually assigned slot in FIG. 3B for the mobile station 2, and the ramp part R, the data parts DATA1, DATA2, and the unique word part. UW, guard part G and the like are included. The ramp part R is the rise time of the transmission output of the mobile station, the data parts DATA1 and DATA2 are the actual data transmission time in communication, and the unique word part UW is for the base station receiver to detect the frame position. The guard part G is a non-transmission time for preventing interference between mobile stations temporally adjacent to each other. In addition, as a standard for the output level of the burst signal described above, upper and lower limits as shown in FIG.
[0005]
Since the frame structure of transmission of the mobile station is defined in this way, in burst signal transmission by the mobile station, as shown in FIG. In the guard part G, the falling edge of the burst signal is terminated. On the other hand, after filtering the received signal, the base station receiver detects the reception level of the reception input and performs automatic gain control (AGC) so that the filter input level becomes a set value (Note that FIG. However, in practice, the transmission signal is configured in accordance with the standard as shown in FIG. 4).
As shown in FIG. 2, a conventional TDMA base station receiver performs filtering by a time-invariant filter and performs demodulation processing. However, there is a normal distance difference between each mobile station and the base station. In this case, a relative difference occurs in the reception level for each mobile station. Therefore, upon reception by the base station receiver, when the receiving mobile station is switched, the reception level is also switched at the same time.
[0006]
In the AGC when the mobile station received by the base station is switched, the control value held in advance is switched for the reception level difference of each mobile station, and then the follow-up control for the reception level is performed. Even when the mobile station is switched, the base station continuously receives signals, but a signal whose reception level fluctuates due to mobile station switching becomes a signal equivalent to a temporally discontinuous signal. When the filter of the base station receiver filters a temporally discontinuous signal, intersymbol interference occurs in signals before and after the temporally discontinuous signal, and erroneously determines when demodulated data is generated.
[0007]
Also, when filtering continuous signals, the longer the filter length, the smaller the intersymbol interference and the closer the band limit is to the ideal (censoring error). However, the shorter the filter length described above, the shorter the delay time (time until data input to the filter is output). The reception data used for calculating the control value in AGC can follow the fluctuation of the reception level faster as the delay time is smaller, and is ideal. In filter design using a time-invariant filter, it is necessary to consider this intersymbol interference and delay time.
[0008]
[Problems to be solved by the invention]
As described above, in a conventional TDMA base station receiver using a time-invariant filter, intersymbol interference occurs every time a connected mobile station is switched, and demodulation processing is performed while including degradation factors of demodulated data. There is a problem of going.
[0009]
The present invention has been made to solve the above problem, and provides a base station receiver that does not cause intersymbol interference when switching from a currently receiving mobile station to a next receiving mobile station. For the purpose.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention is a base station receiver that performs reception in a TDMA communication system, and after receiving signal filtering by a filter, detects the reception level of the reception input, A base that switches the control value used to perform automatic gain control so that the level becomes a set value to a control value that is held in advance for the reception level difference of each mobile station every time the mobile station to receive is switched. In the station receiver, the filter is configured by a plurality of different filters, and filter selection switching means is provided for performing the filtering by sequentially selecting a plurality of different filters during a period when the mobile station to be received is switched.
[0011]
According to such a configuration, the filter selection switching means sequentially selects a plurality of different filters to perform the filtering when moving from the currently receiving mobile station to the next receiving mobile station. Thus, it is possible to prevent the occurrence of interference between codes and avoid the deterioration of determination of demodulated data.
[0012]
Further, the present invention provides a plurality of frequency conversion means for frequency-converting a signal received from an antenna, gain control means for performing gain control on the frequency-converted signal, and a plurality of characteristics different from each other for filtering the gain-controlled signal. Filtering means, demodulating means for demodulating the filtered signal and converting it to digital data, frame position detecting means for detecting a frame position from the demodulated digital data, and reception level for detecting the reception level from the filtered signal Based on the frame position, a detection means, a gain control switching timing generating means for generating a gain control switching timing from the frame position, a gain control value calculating means for calculating a gain control value from the reception level and the gain control switching timing, Filter switching timing, A filter switching timing generating means for generating filter information changing Ri has a filter switching timing, and a filter information for switching, and a filtering switch means for selecting one of a plurality of filtering means sequentially.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a base station receiver in a TDMA communication system according to the present invention. This base station receiver includes an antenna 11, a frequency converter 12, a gain controller 13, filters 141, 142,..., 14n, a filter changeover switch 15, a demodulator 16, and a reception level detector 17. , A gain control value calculator 18, an output terminal 19, a frame position detector 20, a gain control switching timing generator 21, and a filter switching timing generator 22.
[0014]
First, the demodulation operation of the base station receiver of FIG. 1 will be described. The received signal (the signal frame follows that shown in FIG. 3) is taken from the antenna 11 and is frequency-converted by the frequency converter 12. The reception level of the frequency-converted signal is controlled by the gain controller 13. The signals whose reception levels are controlled are input to the filters 141, 142,. The filtered signals are sequentially selected and output by the filter changeover switch 15 (at the initial time, the output of the filter 141 is selected first). The outputs of the selected filters 141, 142,..., 14 n are demodulated into digital data by the demodulator 16 and output to the output terminal 19.
[0015]
Next, the following operation of AGC (automatic gain control) of the above-described base station receiver will be described. When the signal filtered by any one of the filters 141, 142,..., 14n is selected by the filter changeover switch 15, the reception level detector 17 inputs this and detects the reception level. The detected reception level is input to the gain control value calculator 18, and based on this, the gain control value calculator 18 calculates the gain control value. The calculated gain control value is input to the gain controller 13, and based on this, the gain controller 13 performs gain control on the output of the frequency converter 12, thereby executing AGC.
[0016]
Furthermore, the switching operation of AGC (automatic gain control) of the above-described base station receiver will be described. The frame position detector 20 receives the digital data output from the demodulator 16 and detects the frame position by detecting the unique word portion UW (see FIG. 3). The detected frame position is passed to the gain control switching timing generator 21 and the filter switching timing generator 22. The gain control switching timing generator 21 generates a gain control switching timing that is a timing for switching a gain control value with respect to a reception level difference between the currently received mobile station and the next receiving mobile station. . The generated gain control switching timing is notified to the gain control value calculator, and the control value of the next mobile station held in advance is switched at that timing. The AGC follow-up operation is performed until the next gain control switching timing is notified.
[0017]
Next, filter switching will be described. Based on the frame position detected by the frame position detector 20, the filter switch timing generator 22 notifies the filter switch 15 of the filter switching timing and the filter information to be switched next. When the filter changeover switch 15 receives the notification, the filter changeover switch 15 switches to the filter based on the filter information to be switched next notified at the same time.
The filter changeover switch 15 performs filtering using a filter based on the latest notification information unless a new filter changeover timing is notified. However, if the frame position cannot be detected, the initial filter 141 is used, and filtering is performed without switching the filter unless the frame position is detected.
[0018]
Further, the operation of the filter switching timing generator 22 will be described with reference to FIG. 3 and the following table. Here, in order to make the description easy to understand, three filters (n = 3) are assumed to have the following filter lengths.
[0019]
Filter type Filter length filter 141 3 symbol filter 142 2 symbol filter 143 1 symbol
As apparent from FIG. 3, the position of the symbol G [0] of the guard part G is 101 symbols after the last symbol position UW [9] of the detected unique word part pattern. When it is time to filter the symbol G [0] by the filter 141, the filters 141 to 142 prevent the intersymbol interference from occurring in the symbols DATA2 [98] and DATA2 [99], which are the previous two symbols. Information for switching to is notified to the filter changeover switch 15. When the filtering related to the symbol DATA2 [0 to 99] of the data part DATA2 is completed, the filter changeover switch 15 is notified of information for returning the selection to the filter 141.
[0021]
Here, the intersymbol interference caused by AGC switching and the mechanism by which the intersymbol interference can be removed by the filter switching operation described above will be described in detail.
First, intersymbol interference caused by AGC switching will be described. Switching the AGC control value is the same as changing the amplitude component of the received signal. A carrier wave is a modulated wave in which one or more of amplitude, phase, and frequency are changed based on a certain method, and AGC switching is performed in addition to the original modulation. It can be thought of as performing the same operation as applying modulation. Therefore, the reception data at the moment when AGC switching is performed causes intersymbol interference for the base station receiver.
[0022]
Next, the mechanism of intersymbol interference cancellation will be described. In order to perform filtering of a certain symbol, it is necessary to simultaneously use data for several symbols before and after that symbol (for the filter length). When the symbol to be filtered passes through the filter, the filter output when the symbol is in the middle of the filter is the filtering output of the symbol.
[0023]
As an example, if the filter length is 3 symbols and there is a symbol that causes intersymbol interference after 2 symbols, when filtering a certain symbol, if the filter length remains 3 symbols, Symbols that cause intersymbol interference after two symbols must be used, where intersymbol interference occurs. Therefore, by changing the filter length to 2 symbols, it is not necessary to use symbols that cause intersymbol interference when filtering, so that intersymbol interference does not occur. When the next symbol is filtered, it is not necessary to use a symbol causing intersymbol interference by changing the filter length to one symbol. Since the next is filtering of the symbol itself that causes intersymbol interference (the middle of the filter), the filter length remains 1 and is not changed. Similarly, if the filter length is increased while the symbol causing intersymbol interference passes through the middle of the filter, it causes intersymbol interference on symbols other than the symbols causing intersymbol interference. There is no.
[0024]
【The invention's effect】
Since the present invention is configured as described above, the filter selection switching means sequentially selects a plurality of different filters when moving from the currently receiving mobile station to the next receiving mobile station. Since the filtering is performed, it is possible to prevent the occurrence of interference between codes and avoid the determination deterioration of demodulated data, and improve the quality of burst reception at the time of filter switching.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a base station receiver in a TDMA communication system according to the present invention.
FIG. 2 is a block diagram showing a conventional example of a base station receiver in a TDMA communication system.
FIG. 3A is a diagram for explaining a frame structure of a received signal used in a base station receiver.
(B) is a figure which shows the content of the frame structure with respect to one mobile station.
(C) is a figure which shows the output change of a transmission / reception signal.
FIG. 4 is a diagram showing a frame structure of a received signal used in an actual system.
[Explanation of symbols]
11 antenna, 12 frequency converter, 13 gain controller, 141, 142,..., 14n filter, 15 filter changeover switch, 16 demodulator, 17 reception level detector, 18 gain control value calculator, 19 output end, 20 frame Position detector, 21 gain control switching timing generator, 22 filter switching timing generator.

Claims (2)

A base station receiver that performs reception in a TDMA communication system, detects a reception level of a reception input from an output after filtering of a reception signal by a filter, and performs automatic gain control so that the filter input level becomes a set value In the base station receiver that switches the control value used for performing each time the mobile station to be received switches to the control value held in advance according to the reception level difference of each mobile station,
The filter is composed of a plurality of different filters,
A base station receiver comprising filter selection switching means for sequentially selecting a plurality of different filters and performing the filtering during a period in which a mobile station to be received is switched. A frequency converting means for converting the frequency of the signal received from the antenna;
Gain control means for performing gain control on the frequency-converted signal;
A plurality of filtering means for filtering the gain-controlled signal, each having different characteristics;
Demodulation means for demodulating the filtered signal and converting it to digital data;
Frame position detecting means for detecting a frame position from the demodulated digital data;
Reception level detection means for detecting the reception level from the filtered signal;
Gain control switching timing generating means for generating gain control switching timing from the frame position;
A gain control value calculating means for calculating a gain control value from the reception level and the gain control switching timing;
Based on the frame position, filter switching timing, filter switching timing generating means for generating filter information to be switched,
A base station receiver comprising filtering switching means for sequentially selecting one of a plurality of filtering means from filter switching timing and filter information to be switched.

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