Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-03-03
2003-09-30
Nguyen, Duc (Department: 2682)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C455S436000, C455S439000, C455S442000
Reexamination Certificate
active
06628631
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a cellular mobile communication system and a radio communication apparatus, and more particularly to a handoff control method and apparatus in a mobile communication system which enable a mobile station to simultaneously use a plurality of radio channels to communicate with base stations.
In a CDMA (code division multiple access) mobile communication system, a handoff scheme called a “soft handoff” has been brought into practice. The soft handoff is described in U.S. Pat. No. 5,267,261.
The soft handoff is a handoff method which is characterized by uninterrupted communications and a cell diversity effect on the boundary between two cells. The soft handoff is implemented by utilizing a property of the CDMA scheme which permits simultaneous reception of a plurality of radio channels. More specifically, on uplink channels, a signal transmitted by a mobile station is received by a plurality of radio base stations, and the received signal is selected or combined in base station controller associated with the respective radio base stations to realize the above-mentioned property. On downlink channels, on the other hand, a plurality of radio base stations simultaneously transmit signals having the same information, which have been applied with different spreading, to a single mobile station, and the mobile station simultaneously receives the respective signals, despreads them to extract the same information, and then selects or combines the extracted information to realize the above-mentioned property.
However, during a soft handoff, since a plurality of radio base stations are each transmitting to a single mobile station an amount of information identical to that transmitted when no handoff is made, the single mobile station uses a number of downlink channels during a handoff several times larger as compared with that required when no handoff is made. In other words, when the soft handoff is applied, the number of downlink radio channels equal to the number of mobile stations involved in the soft handoff are used at minimum, thereby causing an increase in the amount of co-channel interference of down link channels and a decrease in the capacity of subscribers in the entire system. In addition, the soft handoff might cause each radio base station to run short of radio resources, hereby increasing the possibility of failure in setting new call.
As mentioned above, the conventional soft handoff implies a problem that the system capacity is reduced due to an increased amount of used radio resources in radio base stations and an increased transmission power. In particularly, an asymmetric high-speed circuit data communication, which is expected to experience a rapid increase in demands in near future, uses a large amount of radio resources in the downlink channels and transmission power, so that the high-speed circuit data communication, if the conventional soft handoff is applied thereto, would significantly affect the downlink channels of other users. However, if a hard handoff were applied to the channel switching high-speed data communication, this would introduce a problem of a large amount of dropped data due to interrupted communications.
SUMMARY OF THE INVENTION
The present invention has been made in view of the problem mentioned above, and its object is to provide handoff means which maintains a consistent amount of used radio resources in a radio base station regardless of whether a handoff is being made or not, while preserving the advantages of the conventional soft handoff, i.e., uninterrupted communications and cell diversity effect.
To achieve the above object, the present invention provides a handoff method, wherein a radio base station comprises means for performing error correction encoding and interleaving on transmission information, dividing the processed transmission information into a plurality of blocks, and transmitting each of the blocks through a plurality of downlink radio channels, a mobile station comprises means for simultaneously receiving the plurality of downlink radio channels transmitted from the plurality of radio base stations to the mobile station, and means for demodulating each of received signals and rearranging and decoding the demodulated signals to extract original information, wherein as the mobile station hands off from a first radio base station currently connected thereto to a second radio base station, a plurality of downlink radio channels are handed off in order at least on a one-by-one basis, and while the plurality of downlink radio channels are being handed off at least on a one-by-one basis, the remaining downlink radio channels continue communications.
In another aspect, the present invention provides a radio communication system having a mobile station and a plurality of radio base stations, wherein each of the radio base stations comprises an encoder for encoding transmission information directed to the mobile station, a divider for dividing the encoded transmission information into a plurality of partial channels, and a transmitter for transmitting the partial channels, the mobile station comprises a receiver for receiving the plurality of partial channels, a combiner for combining the plurality of received partial channels, and decoder for decoding the combined transmission information, and the mobile station hands off the plurality of partial channels at least on a one-by-one basis, when handing off from a first radio base station to a second radio base station.
In the radio base station, the encoder preferably encodes transmission information using a convolutional code.
When the plurality of partial channels are handed off to the second radio base station, the mobile station may continuously communicate a radio channel, which has not been handed off, through the first radio base station.
The radio base station preferably includes a switch for setting whether or not transmission is possible for each of the plurality of partial channels.
In a further aspect, the present invention provides a radio communication system having a mobile station and a plurality of radio base stations, wherein each of the radio base stations comprises an encoder for encoding transmission information directed to the mobile station, a divider for dividing the encoded transmission information into a plurality of partial channels, an orthogonal encoder for orthogonally encoding the plurality of partial channels respectively with orthogonal codes which are orthogonal to each other, a spreader for spreading the orthogonally encoded partial channels with the same spread code, and a transmitter for transmitting the spread partial channels, the mobile station comprises a receiver for receiving the plurality of partial channels, a despreader for despreading the plurality of received partial channels, a combiner for combining the despread partial channels, and decoder for decoding the combined transmission information, and the mobile station hands off the plurality of partial channels at least on a one-by-one basis, when handing off from a first radio base station to a second radio base station.
Also, when the plurality of partial channels are handed off to the second radio base station, the mobile station may continuously communicate a radio channel, which has not been handed off, through the first radio base station.
The radio base station preferably includes selecting means for setting whether or not transmission is possible for each of the plurality of partial channels. The selecting means may be a hardware switch or a software switch.
Further, in a radio communication system having a mobile station and a plurality of radio base stations, the radio base stations each comprises an encoder for convolutional encoding transmission information directed to the mobile station, a divider for dividing the convolutional encoded transmission information into a plurality of partial channels, and a transmitter for transmitting the partial channels, wherein the radio base station hands off the plural
Ishida Kazuhito
Mazawa Shiro
Antonelli,Terry,Stout & Kraus, LLP
Hitachi , Ltd.
Nguyen Duc
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