1. Field of the Invention
The present invention relates generally to a communication device and method for a CDMA mobile communication system, and in particular, to a device and method for gating transmission.
2. Description of the Related Art
A conventional CDMA (Code Division Multiple Access) mobile communication system primarily provides a voice service. However, the future CDMA mobile communication system will support the IMT-2000 standard, which can provide a high-speed data service as well as the voice service. More specifically, the IMT-2000 standard can provide high-quality voice service, moving picture service, Internet search service, etc.
In a mobile communication system, data communication service is typically characterized by transmissions of burst data alternates with long non-transmission periods. The bursts of data are referred to as “packets” of data. Data communication service in future mobile communication systems will employ a channel assignment method in which a dedicated channel is assigned only for the duration of the data transmission. That is, because of limited radio resources, base station capacity and power consumption of a mobile station, the mobile communication system connects a traffic channel and a control channel only for an actual data transmission duration and otherwise releases the dedicated channels (i.e., the traffic channel and the control channel) when there is no data transmitted for a predetermined amount of time. When the dedicated channels are released, subsequent communication is performed through a common channel, thus increasing utilization efficiency of the radio resources.
To accomplish this, the system supports various states based upon channel assignment circumstances and the existence or nonexistence of certain state information. FIG. 1 shows a state transition diagram for a data packet service in a mobile communication system.
Referring to FIG. 1, for packet service, there is an active state, a control hold state, a suspended state and a dormant state. In the control hold state, active state and suspended state, a data service option is connected, and in the other state, the service option is disconnected.
In the active state, data is transmitted between the mobile terminal and the base station using a dedicated traffic channel. The dedicated traffic channel becomes available when the data service transitions to the active state after connection of the service option. A base station and a mobile station perform initialization procedures of a radio link protocol (RLP) and a point-to-point protocol (PPP). When there is no data transmitted for a predetermined time T—Active in the active state, a transition occurs to the control hold state, whereupon the dedicated traffic channel is released. At this point, if it is judged that no data will be generated for a relatively long time (based on a prediction of the traffic to be generated thereafter), a direct transition to the suspended state or the dormant state takes place without passing through the control hold state.
If it is predicted that the traffic will be generated within a shorter time period, the control hold state is entered. In the control hold state, the service option, RLP-related information and PPP-related information are maintained in the base station and the mobile station, and a dedicated signaling channel (dsch) and a dedicated traffic channel (dtch) (the lower case representing that they are logical channels) are established in a dedicated control channel (DCCH), which is a physical channel. In this state, when data to be transmitted is generated within a predetermined time T—Hold, the data service establishes a dedicated traffic channel (DTCH, a supplement channel or fundamental channel, which are physical channels) and makes a transition back to the active state, in order to transmit the data. Otherwise, when no data is generated for the predetermined time T—Hold, the data service releases the dedicated control channel and then transitions to the suspended state. At this point, if it is judged that no data will be generated for a relatively long time based on a prediction of the traffic to be generated thereafter, a direct transition to the dormant state takes place without passing through the suspended state.
In the suspended state, the dedicated physical channels of the fundamental channel and the dedicated control channel, which were assigned to each mobile station, are released, thus the logical channels of the dedicated signaling channel (dsch), the dedicated traffic channel (dtch), and the dedicated medium access control channel (dmch) are all released. At this point, communication with the base station is performed using a common channel established in the physical channels of a paging channel and an access channel, which are commonly used by a plurality of mobile stations. However, in the suspended state, the information related to the service option, RLP-related information, and PPP-related information are still maintained in the base station and the mobile station. If data to be transmitted is generated within a predetermined time T—Suspended in the suspended state, the dedicated control channel and the dedicated traffic channel are both established to make a transition back to the active state. When no data is generated for transmission within the predetermined time T—Suspended, a transition to the dormant state happens.
In the dormant state, only the PPP is open for the data service and other call-related information is all discarded. When it is necessary to transmit data within a predetermined time T—Dormant in the dormant state, a dedicated signaling channel is assigned and then a transition to the active state occurs. Otherwise, when no data is generated for the predetermined time T—Dormant, even the PPP-related information is released and a transition to a packet null state occurs.
A conventional CDMA mobile communication system which mainly supports voice service, releases a traffic channel upon completion of data transmission and then reconnects the traffic channel when it is required to transmit data. However, the conventional channel assignment method is not suitable for a packet data service because of the time delay for reconnection of the channel. Therefore, to provide both packet data service and voice service, a new channel assignment method is required.
In general, during packet data service, data transmission occurs intermittently. Therefore, periods of packet data transmission alternate with periods of non-transmission. The mobile communication system either releases or maintains a channel in use for the periods of non-transmission. However, there are drawbacks associated with either maintaining or releasing a channel. Release of the channel causes an increase in service time due to a time delay for reconnection of the channel, and maintaining the channel causes a waste of the channel resources.
To solve these problems, there is proposed a method in which a dedicated control channel is provided between a base station and a mobile station to exchange traffic channel-related control signals over the dedicated control channel for the data transmission duration. The traffic channel is released and only the dedicated control channel is maintained for the non-transmission duration. In this manner, the mobile communication system can prevent a waste of the channel resources and rapidly reconnect the traffic channel when there is data to transmit. The operating state described above is called a control hold state.
The dedicated control channel, a physical channel, provides effective implementation of the control hold state. Unlike the fundamental channel used in existing systems, the dedicated control channel used in the control hold state is a physical channel. This provides a reduction in transmission power by not transmitting null traffic when there is no message or data to transmit.
In the control hold state, the dedicated control channel transmits no signal, when there is no signaling message to transmit. In future CDMA mobile communication systems, while the dedicated control channel is maintained, the mobile station transmits a reverse pilot channel to the base station over the dedicated control channel. The reverse pilot channel constantly transmits a signal, regardless of discontinuous transmission (DTX). Further, even a power control bit (PCB) is transmitted over the reverse pilot channel by multiplexing.
In the conventional method, to avoid a synch re-acquisition procedure in the base station while the dedicated control channel is not activated during the control hold state, the mobile station continuously transmits a reverse pilot channel signal in the control hold state. However, continuous transmission of the reverse pilot channel signal will increase interference between the reverse links, thereby causing a reduction in capacity of the reverse link. To solve this problem, there is a demand for a method of decreasing a period of a power control signal transmitted over a forward dedicated control channel, when there is no data to transmit over the dedicated control channel.
The present invention is based on Korean patent applications Nos. 98-28237, 98-29180 and 98-34146, all hereby incorporated by reference. These applications disclose a gating function, in which for the periods of non-transmission, the mobile station transmits an intermittent reverse pilot signal and the base station sends an intermittent power control signal to the mobile station over the dedicated control channel.
In addition, the present invention is based on Korean patent application Nos. 98-11381, 98-4498, 98-9389, 98-13958, 98-14878 and 98-36383, all hereby incorporated by reference. These applications disclose the IMT-2000 forward/reverse channel structure and the dedicated control channel.
In order to support the gating function between the mobile station and the base station, the following requirements should be satisfied. First, when the gating function is an optional function rather than a mandatory function supported in the mobile station and the base station, a control signal is required to make a negotiation for a supportable function between the mobile station and the base station. Second, a procedure for synchronizing the period of the power control signal is required to perform the gating function, between the mobile station and the base station. Third, since the gating function requires the procedure for synchronizing an operation between the base station and the mobile station, a control signal is required for synchronizing a gating-on time and a gating-off time between the base station and the mobile station. The invention discloses a method for meeting these requirements.