Method and arrangement in a radio communication system

Details Method and arrangement in a radio communication system Method and arrangement in a radio communication system

1998-04-28

2000-08-01

Ngo, Ricky

Multiplex communications

Communication over free space

Combining or distributing information via time channels

370443, H04B 7212

Patent

active

060977175

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL BACKGROUND

The present invention concerns a process for a radio communication system which is arranged for packet data transmission according to a message-synchronized ALOHA protocol with reservation. The invention concerns a process for requesting access in a momentarily overloaded mobile radio system wherein an access request received in a ase station from each station in a first group of mobile stations cannot be responded to by channel reservation for the first group of mobile stations.
The invention also concerns a base station and a mobile station in a radio communication system for packet data transmission.


PRIOR ART

In the case of mobile radio communication systems for packet data transmission a base station can communicate with a plurality of mobile stations via one or a plurality of time-divided channels between the base station and the mobile stations. A time-divided channel is divided into time slots. A data burst with a number of information bits can be transmitted in each time slot. The mobile stations do not communicate continuously with the base station and a plurality of mobile stations can therefore compete for the same time-divided channel. Channels are allocated dynamically, separately from the channel requirement of the mobile stations and channel allocation is controlled by the base station.
A mobile station announces a channel requirement by sending an access request to the base station. This access request is sent in a reservation phase in the time-divided channel for transmission from the mob ie stations to the base station. Different types of protocol can be used in order to control the access request and channel allocation. A conventional protocol in the case of dynamic allocation of time-divided radio channels is a message-synchronized ALOHA protocol with reservation. In the case of this protocol, each packet transmission is preceded by a reservation. A short message with a request for channel reservation is sent at random from a mobile station to a base station. According to the ALOHA reservation protocol, the result of this access request is fed back by the base station giving the mobile station access to at least part of the time-divided channel.
Since many mobile stations may have a need of packet data transmission, collisions can occur as a result of a number of mobile stations sending access requests simultaneously. This means that, of the messages sent simultaneously, in the best case the base station can accept one message (by using the so-called "capture" effect). In the case of a collision, the sending mobile stations which do not receive channel reservation have to repeat their access requests. In order to reduce the risk of a further collision, the repeated transmission occurs after a given time interval which varies for each mobile station. It is well known that this time interval can vary randomly for each mobile station.
When all the free channel capacity in a radio communication system has been reserved for communication, overloading occurs if a further mobile station sends an access request to the base station. The latter receives the access request in itself from the mobile station but cannot comply with this request within a given predetermined time interval since there is no free channel capacity. The mobile station is then forced to repeat the access request in the same way as in the case of a collision, when the predetermined time interval has elapsed. This naturally leads to unnecessary extra channel loading, unnecessary delays in the mobile system and the risk of collisions occurring when transmissions are repeated.
U.S. Pat. No. 5,166,929, for example, earlier disclosed a multiple-access protocol, in the case of which feedback concerning the status of an access channel is provided from the base station to the mobile stations. The mobile stations can thereby receive information concerning the result of an access request, for example, that a collision has occurred, and whether the next time slot is open for the sending of new access requests.

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patent: 5790535 (1998-08-01), Kou
"Medium Access Priority," Motorola, Edinburgh, Mar. 1995, pp. 1-3.

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