JP3436480B2 - Diversity receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiver for performing diversity reception using a plurality of antennas. 2. Description of the Related Art Here, in a wireless communication system in which a plurality of terminal stations are accommodated in one base station, a case will be described in which a base station is provided with a plurality of antennas to perform diversity reception. FIG. 3 shows a configuration example of a conventional diversity receiving apparatus for performing selection diversity. In the figure, the receiving antennas are plural (here, three) sector antennas 1,
A signal transmitted from the terminal station is received by each antenna. The reception level of each antenna is measured by each of the level detectors 4-1 to 4-3. The level maximum value selection circuit 11 includes a level detector 4 corresponding to each antenna.
The reception levels measured in -1 to 4-3 are compared to select the antenna having the maximum reception level, and the high-frequency switch circuit 6 selects the reception signal of the antenna. The reception signal of the maximum reception level selected in this way is subjected to demodulation processing via the reception circuit 7, the demodulation circuit 8, and the baseband signal processing circuit 9. [0004] A system in which one base station temporally manages a plurality of terminal stations, and only a signal from one terminal station is received by a base station in a certain time slot. Thus, diversity reception that selects one antenna having the best reception level and communication quality is possible. That is, the reception by the selection diversity shown in FIG. 3 is possible. However, in a random access type wireless communication system in which a plurality of terminal stations randomly access a certain time slot, when diversity reception for selecting one antenna in accordance with a reception level or communication quality is performed, the following occurs. Problems arise. For example, when two terminal stations simultaneously access a certain time slot, the reception level of the antenna colliding with the signal from the two terminal stations is determined by combining the two signals. It may be higher than an antenna receiving only a signal from a station. At this time, if the antenna having the maximum reception level is selected by the configuration of the conventional selection diversity shown in FIG. 3, a signal whose quality has deteriorated due to signal collision is selected, and normal reception processing cannot be performed. On the other hand, a received signal for which a certain reception level can be secured without collision of signals is discarded. This means that the correlation between the reception level and the communication quality at the time of random access is not high, and the conventional selection diversity according to the reception level cannot be applied as it is. Further, when two terminal stations at different distances from the base station simultaneously access, even if a signal is received by each antenna without collision of signals, the maximum reception is achieved by the conventional selection diversity. Since the antenna of the level is selected, the signal of the terminal station close to the base station is always selected with priority. This poses a problem when a channel having the same frequency is spatially divided by using a sector antenna as an antenna, and the probability that signals from a plurality of terminal stations are separated and received by each sector antenna is high.
That is, even if the collision probability at the time of random access is reduced by using the sector antenna, in the conventional selection diversity according to the reception level, the access probability is imbalanced due to the distance. It is an object of the present invention to provide a diversity receiving apparatus capable of performing diversity reception without causing an imbalance in access probabilities of a plurality of terminal stations in a random access wireless communication system. [0009] A diversity receiving apparatus according to claim 1 receives signals randomly accessed from a plurality of terminal stations with a plurality of antennas for each time slot, and one of the signals is received. When selecting a reception signal of an antenna, one antenna is randomly selected from antennas whose reception level exceeds a predetermined threshold. FIG. 1 shows an embodiment of a diversity receiving apparatus according to the present invention. Here, a configuration example is shown in which a sector antenna is used as an antenna and selection diversity is performed using the reception level of each antenna as a selection criterion. In the figure, signals transmitted from a plurality of terminal stations in the same time slot are transmitted by sector antennas 1, 2, 2,
3 respectively. The level of the received signal of each antenna is measured by each of the level detectors 4-1 to 4-3. The antenna selection circuit 5 randomly selects one of the antennas whose reception level exceeds a predetermined threshold, and the high-frequency switch circuit 6 selects a reception signal from the antenna. The received signal is subjected to a demodulation process via a reception circuit 7, a demodulation circuit 8, and a baseband signal processing circuit 9. FIG. 2 shows an operation example of the antenna selection circuit 5. First, the remainder of the frame number K assigned to each base station and the number of sector antennas An is calculated as the initial value m (m = K mod An). Next, n = 1 is set as the sector number A to be selected first, and a value obtained by adding 1 to the remainder of m + n and An is calculated (A = (m + n mod An) +1).
If the reception level of the sector antenna of sector number A exceeds a predetermined threshold, the sector antenna is selected. If the reception level of the sector antenna of sector number A does not exceed the predetermined threshold, the next sector number A is calculated with n = n + 1, and the same operation is repeated until the number of sector antennas An is reached. As described above, a sector antenna having a predetermined reception level is randomly selected by the round robin method in which the initial sector numbers are sequentially switched. This operation example is one of the simplest methods of randomly selecting one antenna from the antennas whose reception level exceeds a predetermined threshold value, and is not limited to this. As described above, the diversity receiving apparatus according to the present embodiment does not always select the antenna having the highest reception level as in the related art, but randomly selects the antenna whose reception level exceeds a predetermined threshold. Therefore, it is possible to avoid a situation in which an antenna whose reception level is increased due to signal collision is always selected. Further, by using a sector antenna as an antenna, signals from a plurality of terminal stations are separated and received by each sector antenna as described above, and the collision probability at the time of random access can be reduced. In this case, as in the present embodiment, by randomly selecting one antenna from the antennas whose reception level exceeds a predetermined threshold, access from a plurality of terminal stations having different distances from the base station is performed. Can be equally processed. That is, it is possible to eliminate the imbalance in the access probability due to the distance. As described above, the diversity receiving apparatus according to the first aspect of the present invention randomly selects one antenna from the antennas whose reception level exceeds a predetermined threshold, thereby causing signal collision. As a result, the situation where the antenna having the higher reception level is always selected is avoided. Therefore, selection diversity can be performed even in a random access wireless communication system. In addition, since access from a plurality of terminal stations can be processed equally, selection diversity can be performed without causing an imbalance in the access probabilities of the plurality of terminal stations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a diversity receiver according to the present invention. FIG. 2 is a flowchart showing an operation example of an antenna selection circuit 5. FIG. 3 is a block diagram showing a configuration example of a conventional diversity receiving circuit (selection diversity). [Description of Signs] 1, 2, 3 Sector antenna 4 Level detection circuit 5 Antenna selection circuit 6 High frequency switch circuit 7 Receiving circuit 8 Demodulation circuit 9 Baseband signal processing circuit 11 Level maximum value selection circuit

Claims (1)

(57) [Claims 1] For each time slot, a signal randomly accessed from a plurality of terminal stations is received by a plurality of antennas, and a signal received by one of the antennas is selected. Means for detecting a reception level of each antenna for each time slot, and means for randomly selecting one antenna from antennas whose reception level exceeds a predetermined threshold for each time slot. A diversity receiving device comprising: