Radio communication system

Details Radio communication system Radio communication system

2000-05-23

2003-02-18

Vo, Nguyen T. (Department: 2682)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S069000, C342S383000

Reexamination Certificate

active

06522898

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-143466, filed May 24, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a radio communication system that is applied to, for example, indoor wireless radio LAN systems and adapted for data transmissions between a base station and a number of terminal stations.
Radio communications in indoor space are highly susceptible to fading due to multipath (multiple reflected waves). It is therefore effective to transmit and receive with directivity concentrated in the direction of maximum reception. For example, Japanese Unexamined Patent Publication No. 9-232848 discloses radio communications equipment that is constructed, as shown in
FIG. 15
, from an antenna array
1
, circulators
2
, receive modules
3
each comprising a low-noise amplifier and a down converter (D/C), analog-to-digital (A/D) converters
4
, quasi-coherent detectors
5
, local oscillators
6
and
7
, a digital beam former (DBF)
8
, a beam selector
9
, a maximum ratio combiner
10
, a demodulator
11
, an in-phase divider
12
, phase/amplitude correction units
13
, a weight separation calculation circuit
14
, a transmission weight calculation circuit
15
, quadrature modulators
16
, transmitting modules
17
each consisting of an up converter and a transmitting power amplifier, and transmitting local oscillators
18
and
19
.
Signals received by the elements of the antenna array
1
are amplified and converted into intermediate-frequency signals in the receive modules
3
and then converted into digital signals in the AID converters
4
. The digital signals are subjected to quasi-coherent detection in the quasi-coherent detectors
5
and then combined in the maximum ratio combination circuit
10
while varying their weight values so that S/N (signal to noise ratio) becomes maximum. At transmit time, the transmission weight calculation circuit
15
calculates transmitting weight values on the basis of the receiving weight values calculated by the weight separation/calculation circuit
14
. After transmit signals are weighted by the transmitting weight values, a transmitting main beam is formed and transmitted in the direction of maximum reception from the antenna array
1
via the quadrature modulators
16
and the transmitting modules
17
.
The conventional equipment needs to calculate the direction of arriving radiation in real time (namely, sequentially) and switch the directivity of the antenna in order to track the station with which the connection has been set up. As a result, the calculation processing is performed mainly by hardware rather than by software. Thus, the equipment has a problem of being complex in circuit arrangement and increasing in size.
To solve that problem, Japanese Unexamined Patent Publication No. 9-219615 discloses an adaptive array transmitter-receiver, which is provided, as shown in
FIG. 16
, with an array antenna
21
comprised of a plurality of antenna elements, weighting units
22
for weighting the amplitude and phase of each of signals which are to be transmitted from or are received by the antenna elements, a divider/combiner
23
for dividing transmit signals to the antenna elements or combining received signals from the antenna elements through the weighting units
22
, an interface (I/F)
25
, and an external operations unit
26
. The external operations unit
26
performs calculations for adaptive control of the antenna directivity in non-real time for each terminal to which transmission is to be performed and makes weight switching from terminal to terminal on a time-division basis with a time slot preallocated for each terminal. This allows the transmitter-receiver to be made simple in construction and reduced in size.
Each weighting unit
22
varies the phase and the amplitude in a signal supplied from the dividing/synthesis units
23
by predetermined amounts, or multiply the signal by a complex weight. Thus, the radio waves radiated from the antenna elements form a desired synthetic transmission directional pattern.
On the other hand, the phase and the amplitude of each of the signals received by the plural antenna elements are controlled by the weighting units
22
or the signal is multiplied by the complex weight. Then, the signals are combined by the dividing/synthesis unit
23
. The desired receiving directional pattern can be formed in this manner.
In the adaptive array transmitter-receiver disclosed in Japanese Unexamined Patent Publication No. 9-219615, in performing communications between the base station installed with the adaptive array antenna and each terminal, transmitting and receiving time slots are preallocated for each terminal. That is, with a system comprising a base station and N terminals, N transmitting time slots and N receiving time slots are preallocated. Each terminal is allowed to communicate with the base station only in time slots allocated to it.
With such a configuration, time slots allocated for each terminal are occupied by it regardless of whether it makes a request for communications. In the absence of a communication request, therefore, the allocated time slots result in waste of time. In addition, for terminals having a request for communications of large amounts of data, fixed time slots are not enough for such communication because of limited communication time. Data have therefore to be transmitted in a number of time slots, which results in reduced data communication efficiency.
In recent years, a wireless POS (point of sales) system has been installed in large-scale stores. In this wireless POS system, which consists of a host computer connected to the base station and a number of POS terminals connected with terminal station, inquiries about prices of goods and sales registration data are transmitted between the host computer and each POS terminal by radio. If, when the aforementioned adaptive array transmitter-receiver is used with the wireless POS system, communication requests for inquiries about prices of goods and sales registration data are intensively made by a certain POS terminal to the host computer, the length of the time slots allocated for that terminal may sometimes become insufficient. On the other hand, when another POS terminal makes no communication request, the time slots allocated for it result in waste of time. Therefore, the wireless POS system used with the conventional Adaptive array antenna is poor in efficiency.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a radio communications device for use in a base station which permits communications to be efficiently performed with a terminal station that makes a request for communications, does not spend any time on terminal stations that make no request for communications, and is simple in construction and a radio communication system which includes such a base station and a number of terminal stations.
In order to achieve the above object, according to the present invention, there is provided a radio communication system comprising a base station having a radio communications device that includes a receiving section which weights the amplitude and phase of each of received signals from a plurality of antenna elements, then combines the weighted signals into a composite signal and demodulates the resultant composite signal and a transmitting section which divides a modulated signal into a plurality of transmit signals, then weights the amplitude and phase of each of the transmit signals and radiates each of the weighted transmit signals from a corresponding respective one of the antenna elements, and a plurality of terminal stations each of which performs communications with the base station by radio, each of the terminal stations including transmitting means for, when a communication request occurs in it, transmitting a communication request signal in response to reception of a

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