Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-03-05
2001-08-07
Hunter, Daniel (Department: 2749)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S432300, C455S434000, C455S450000, C455S561000, C455S562100
Reexamination Certificate
active
06272335
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention claims priority from Japanese Patent Applications No. 9-050693 filed Mar. 5, 1997 and No. 9-060980 filed Mar. 14, 1997, which are incorporated herein by reference.
1. Field of the Invention
This invention is utilized in radio communications using time division multiple access (TDMA), and is suited for use in mobile communications and wireless LANs which make in-building use of portable radio terminals.
2. Description of Related Art
Demand for high-speed wireless access communications has recently been increasing, and TDMA is one of the principal access systems in this field. Sector antennas are utilized for high-speed wireless access communications in order to suppress multipath interference and obtain efficient frequency utilization. A sector antenna is an antenna which, by using a plurality of directional antennas, is capable of communicating with stations in all directions. In an access system which uses sector antennas, a radio base station successively switches among its sector antennas, thereby transmitting an access channel in all directions covered by the plurality of directional antennas. If TDMA is employed, the sector is switched over at every TDMA frame.
A problem here is that with a high-speed wireless access system, the optimum value for the number of sectors or the number of branches of a radio base station sector antenna differs according to the base station installation environment or radio wave propagation environment. However, if the number of sectors or branches is different at each radio base station, then when a radio terminal communicates with any of a plurality of radio base stations it will have to do so while referring to information on the relation between the method by which the radio base station selects the frequency and which antenna sector to use to transmit the access channel, and the number of sectors used for its transmission. However, when a high-speed wireless access system is implemented with a large number of installed radio base stations, it is difficult to ensure that a radio terminal holds separate information for all these base stations. Even if this is assumed to have been possible, it would still be more difficult to update this information each time the number of installed radio base stations is changed or their specifications are altered. There is therefore a need for a method capable of synchronizing flexibly against changes in the number of sectors used at a radio base station for transmission over the access channel, without holding any information at the radio terminal.
High-speed wireless access systems which involve dividing zones into pico-cells and installing a large number of radio base stations have been studied. However, an additional problem in this case is that access channels from a plurality of radio base stations are frequently received at one radio terminal. Namely, there are a plurality of radio carrier frequencies and the same radio carrier frequency is sometimes used by a plurality of radio base stations. Moreover, because a radio base station uses a sector antenna to transmit the access channels, a plurality of access channels which have been transmitted from one radio base station using different sectors will sometimes arrive at a radio terminal. That is, a radio terminal will sometimes receive the access channel from a plurality of base stations, at a plurality of frequencies or timings, or from a plurality of directions. It is then necessary for the radio terminal to switch among the radio carrier frequencies and sectors it receives, and to select from these the ones giving the best quality access channel. Hitherto, however, there has been no method for selecting the optimum access channel from among the plurality of access channels received by switching among the radio carrier frequencies and sectors the radio terminal receives, and for establishing synchronization on this basis.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a wireless access system capable of successfully addressing such tasks, and whereby a radio terminal can perform identical communication control in a variety of circumstances such as acquisition of synchronization and duration of communication, irrespective of the configuration of the radio base station antenna.
Namely, according to a first aspect of the present invention there is provided a radio channel control method which controls a plurality of antenna elements at a radio base station to transmit an access channel to and receive an access channel from a radio terminal in each frame. The method includes setting the antenna element ID s in a specific functional relation to the access channel ID a, wherein a radio terminal which communicates with a radio base station transmits and receives in accordance with the access channel ID a without knowing the antenna element ID s. Here, “an individual antenna element” signifies an individual sector of a sector antenna, or each of a plurality of antennas provided for diversity.
The access channel ID is an integer which cycles from “0” to “N−1”, and the number of antenna elements of a base station is preferably a divisor of N.
That is, although when using a sector antenna at a radio base station the number of sectors can be set freely, if the number of sectors is made a divisor of N, the base station can transmit and receive access channels uniformly in all directions.
It is also possible to give respective IDs to the uplink and downlink access channels and for these IDs to have the same functional relation to the antenna element ID, and for their cycling phase to differ. Namely, by ensuring that the cycling of the uplink access channels is out of phase with the cycling of the downlink access channels, a processing delay at a radio base station or a radio terminal can be absorbed by this offset in cycling phase. For example, a result of this is that after a radio terminal detects a downlink access channel it can transmit an uplink access channel with the minimum delay. Rapid connection and communication are therefore possible.
According to a second aspect of the present invention, there is provided a wireless access system having a radio base station and a radio terminal which can be connected to this radio base station by TDMA. The radio base station includes a plurality of antenna elements and means for transmitting and receiving an access channel in each frame and a means which, letting the access channel ID be a and the antenna element ID be s, sets:
s=f
(
a
)
(where f indicates a specific functional relation).
The radio terminal comprises a means for communicating with the radio base station in accordance with this access channel ID a.
A sector antenna can comprise a plurality of antenna elements, and a plurality of these sector antennas can be provided at a radio base station. A diversity means can also be provided for the plurality of sector antennas at the radio base station.
A radio terminal preferably comprises: a sector antenna having a transmitting and receiving azimuth which is switched among a plurality of azimuths at each frame and a means for switching the transmit and receive frequency every time the sectors of this sector antenna are switched through a complete cycle. The radio terminal further comprises an open aperture means which successively looks for a unique word in the received signal at all time, and synchronizing means which, when the unique word in question has been detected by the open aperture means, subsequently attempts to confirm synchronization a predetermined number of times. As a result, the channel with the best communication quality can be selected rapidly and reliably from among a plurality of access channels.
A radio terminal preferably also comprises a means for randomly switching the transmit and receive frequency until synchronization is established. This facilitates avoids the situation where, when a plurality of radio terminals are present, a large number of terminals establish synchronization at the same
Aikawa Satoru
Itoh Masahiko
Kurosaki Satoshi
Nakayama Yuji
Hunter Daniel
Nippon Telegraph and Telephone Corp.
Pillsbury & Winthrop LLP
Woldetatios Yemane
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