Base station apparatus and radio communication method

Details Base station apparatus and radio communication method Base station apparatus and radio communication method

1999-11-05

2004-04-13

Bocure, Tesfaldet (Department: 2631)

Pulse or digital communications

Systems using alternating or pulsating current

Plural channels for transmission of a single pulse train

C375S347000, C375S299000, C455S132000, C455S101000

Reexamination Certificate

active

06721367

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a base station apparatus and radio communication method used in a digital radio communication system.
2. Description of the Related Art
A propagation model in a radio communication is explained with reference to FIG.
1
. By way of example, suppose the number of antennas of the radio communication apparatus (base station apparatus) is 3. In
FIG. 1
, two paths A and B indicate downlink (transmission from a base station to terminal) propagation paths. A signal transmitted from base station apparatus
1
is reflected by building
2
and arrives at an antenna of terminal apparatus
3
. Such a propagation path is called a “multi-path propagation path” and communication quality generally deteriorates if this multi-path propagation cannot be compensated. In this example, suppose the signal from building
2
is received by the receiving side with a delay within the range of its time resolution. Transmission directivity in this case is shown in FIG.
2
.
Thus, if this signal contains a great delay, this delay may be a major factor of deterioration of the communication quality. To suppress multi-path propagation, it is desirable to transmit signals to either path A or path B. Furthermore, a communication system such as a CDMA transmission system in which a same band and time are shared can suppress interference with other stations by narrowing the range of transmission directivity, providing an effective way of achieving high frequency utilization efficiency. Therefore, it is extremely important to detect a direction of an optimal communication quality and perform transmissions focusing on that direction.
FIG. 3A
to
FIG. 3C
are delay profiles showing the propagation path characteristics of path A and path B in FIG.
1
. In
FIG. 3
, the horizontal axis represents the time and the vertical axis-represents the propagation loss. That is, t
0
and t
1
on the receiving side represent timings of path A and path B, respectively and the height difference represents a difference in the reception level (difference in propagation loss). The fact that the reception timing differs between path A and path B means that path A and path B differ in the propagation distance.
A delay profile generally changes as a terminal moves. That is, the communication quality of each of path A and path B changes.
FIG. 3A
shows that the communication quality of path A is better, while
FIG. 3B
shows that both paths have equivalent levels of communication quality and
FIG. 3C
shows that the communication quality of path B is better.
A conventional base station apparatus is explained below.
FIG. 4
is a block diagram showing a configuration of a base station apparatus that carries out conventional adaptive array transmission. By way of example, suppose the number of antennas is 3.
The transmitting side of this terminal modulates a transmission signal by modulation circuit
11
. A plurality of reception weighting factors calculated by weighting factor calculation circuit
12
based on an advance information signal are output to selection circuit
13
where an optimal weighting factor is selected, and processing circuit
14
performs a multiplication (generally complex multiplication) using this weighting factor. Naturally, it is also possible to perform a multiplication after calculating only an optimal weighting factor. Then, radio transmission circuit
15
carries out frequency conversion and amplification on the transmission signal and transmits it from antennas.
In a propagation environment as shown in the delay profiles in
FIG. 3
, the base station apparatus above performs transmission by forming directivity in the direction of path A when the communication quality of path A is better as shown in FIG.
3
A. The base station apparatus also performs transmission by forming directivity in the direction of path B when the communication quality of path B is better as shown in FIG.
3
C. On the other hand, if path A and path B have equivalent levels of communication quality as shown in
FIG. 3B
, the base station apparatus performs transmission by forming directivity in either direction.
Therefore, if the other end of communication is a moving terminal, the delay profiles change with time, and therefore, the base station apparatus shown in
FIG. 4
can always perform transmission with array antennas of an optimal communication quality by making its weighting factor selection circuit switch a weighting factor according to a change in the delay profiles.
Here, transmission timing is generally not changed in accordance with directivity switching. This is because in the case of continuous transmission, changing transmission timing will cause problems such as discontinuation or overlap of a transmission signal and collapse of orthogonality (code orthogonality in the case of CDMA, and time orthogonality in the case of TDMA) with other channels with which the transmission signal is multiplexed. etc.
The calculation of the receiving side at the other end of communication (terminal) is explained using FIG.
5
. On the terminal side, a reception signal received by an antenna is output to radio reception circuit
22
via antenna duplexer
21
. Radio reception circuit
22
carries out amplification, frequency conversion and A/D conversion on the reception signal and extracts a baseband signal or IF signal.
In a CDMA system using a spread spectrum (SS) communication system, a reception signal is output to correlator (or matched filter)
23
and despread by the same spreading code as that used for spreading processing on the transmitting side. The despread signal is output to timing detection circuit
24
. Timing detection circuit
24
calculates the power of the correlator output and detects time to when the power is large. This timing to is output to sampling circuit
25
. Sampling circuit sends the reception signal with timing t
0
to demodulation circuit
26
. Demodulation circuit
26
demodulates and outputs the reception signal.
On the other hand, a non-CDMA communication system generally sends the extracted baseband signal or IF signal to timing detection circuit
24
. Timing detection circuit
24
calculates an optimal reception timing. The optimal reception timing is calculated, for example, by the transmitter side embedding a pattern known to both the transmitter and receiver in a frame and transmitting this signal. The receiver side performs A/D conversion with several to over ten times the one-symbol time and performs a correlation calculation with the known symbol. Then, the receiver side detects timing to when the power resulting from the correlation calculation is large. This timing to is output to sampling circuit
25
. Sampling circuit
25
sends the reception signal of timing t
0
to demodulation circuit
26
. Demodulation circuit
26
demodulates and outputs the reception signal.
On the other hand, the transmission signal is modulated by modulation circuit
27
, that is, in the CDMA transmission system, the transmission signal is spread using a predetermined spreading code. The modulated signal is frequency-converted and amplified by radio transmission circuit
28
and transmitted from an antenna via duplexer
21
.
Then, the following is an explanation of the calculation of a base station in a radio communication system when adaptive array reception and adaptive array transmission based on information thereof are applied. The calculations of the conventional base station in FIG.
6
and the terminal in
FIG. 5
are explained. By way of example, suppose the number of antennas of the apparatus is 3.
First, the uplink is explained. The terminal on its transmitting side modulates a transmission signal by modulation circuit
27
. This modulated signal is frequency-converted and amplified by radio transmission circuit
28
and transmitted from the antennas via antenna duplexer
21
.
The base station sends signals received from its antennas to radio reception circuit
32
via respective antenna duplexers
31
. Radio reception

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