Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1997-11-10
2001-05-01
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S464000, C455S062000
Reexamination Certificate
active
06226520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radio communication systems and, more specifically, to a method for setting up a stable call in a radio communication system using dynamic channel allocation.
2. Description of the Related Art
Conventionally, as depicted in
FIG. 3A
, upon cell set-up between a radio terminal and a radio communication system, a base station performs the call set-up while checking whether or not a call request exists from a subscriber terminal. Initially, the base station checks all available traffic channels under service for a traffic channel having more than a predetermined RSSI (received signal strength indicator) level. In the radio communication system having the above dynamic channel allocation, the traffic channel is dynamically allocated in the base station and the subscriber terminal when an outgoing call request from the subscriber radio terminals
100
a,
100
b,
and
100
c
is made, as shown in FIG.
1
. Namely, when the radio subscriber requests the outgoing call at his position through the radio terminal
100
a,
the radio terminal
100
a
selects the channel having little interference and transmits the call request message to the base station
110
a.
The call set-up in the radio communication system is achieved by exchanging the channel information of the base station and the subscriber radio terminal by using only the corresponding traffic channel between the base station and the subscriber radio terminal in determining the radio traffic channel used by the new call set-up. Therefore, since the radio communication system using the fixed channel allocation re-uses the radio channels, it is understood that the limited radio channels provide service to a large amount of traffic. However, the allocations of channels requires careful engineering analyses of radio propagation conditions and traffic patterns within and between the cells. Fixed allocation cellular radio systems are engineered so that harmful levels of interference from signals used in neighboring cells are unlikely to be encountered.
Micro-cellular radio systems tend to use dynamic, rather than fixed, channel allocation. With dynamic channel allocation (DCA), each cell can potentially use any traffic channel for a given call of those allocated to the entire service. The decision as to which channel to use is made dynamically, i.e., based on channel usage conditions experienced at the time of call set-up. The decision is also made in a decentralized manner, i.e., by the base station or subscriber terminal in question, without any centralized coordination with other cells. This has an advantage in that no detailed engineering analyses are required for each cell site, cell sites can be easily added or moved, and more traffic can be handled than with fixed allocation because unused channels in neighboring cells can be borrowed.
In present systems incorporating DCA, the determination as to which channel is to be used for a call set-up is made according to channel information from either the base station or the subscriber terminal. The disadvantage with this approach is that appreciable interference may be present on that channel from the viewpoint of the other end of the link. For example, a traffic channel may have little appreciable interference, as monitored by the base station. However, the same traffic channel may have unacceptable interference at the subscriber terminal.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for maintaining a stable radio connection by minimizing interference caused by the traffic channel used in the radio communication system.
In order to achieve the above object, the present invention provides a call processing method for exchanging channel information between a radio terminal and a base station by using a traffic channel. The method comprises the steps of: selecting a traffic channel having interference below a given level by the radio terminal, the selection being made in response to an outgoing call request by using the radio terminal by a radio subscriber; making a proposed list of available traffic channels: selecting a traffic channel having the least interference from the proposed list; requesting the call to the base station; investigating all of the available traffic channels by the base station; making a proposed list of traffic channels having interference below a given level; storing the list; determining whether or not a traffic channel selected at the terminal is a channel included in the proposed list of the base station. The method further includes the steps of returning to a RSSI (received signal strength indicator) scan mode when a call request was not received from the radio terminal by the base station; and continuously investigating the RSSI of available traffic channels. A call request response is forwarded to the radio terminal when there is a corresponding traffic channel in the proposed traffic channel list of the base station. The radio terminal then checks whether or not a call request response message at the traffic channel selected by the radio terminal is received from the base station. The call processing is continued which fixes a traffic channel and transmits hand shake information to the base station when the call request response message was received from the base station.
When the traffic channel presented by the radio terminal is not found in the base station's proposed list, the interference level of traffic channels in the base station's proposed list is compared with the interference level of traffic channels sent from the terminal's proposed list and a different traffic channel having the least interference is selected. The selected traffic channel being included in two lists of the base station and radio terminal.
Once another traffic channel is selected, the base station forwards a traffic channel changing request message to the radio terminal, requesting a change of the channel to the traffic channel re-selected by the base station. A determination is made by the radio terminal whether or not a changing request message to the selected channel is received from the base station. When the changing request message to the selected channel is made and received by the radio terminal from the base station, the call request is forwarded again to the base station after the radio terminal changes the channel into the base station's selected traffic channel. The base station then determines whether or not the radio terminal's subsequent call request message is received at the changed traffic channel after the base station has changed the channel into the traffic channel it selected previously.
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Chow C.
Dilworth & Barrese LLP
Hunter Daniel
Samsung Electronics Co,. Ltd.
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