Method and apparatus for improving RRC connection procedure

The present invention provides a method for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system. The method includes steps of performing an RRC Connection procedure, and resetting or re-establishing a lower layer protocol entity for Signalling Radio Bearers (SRBs) when a cell reselection occurs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for improving a Radio Resource Control (RRC) Connection procedure, and more particularly, to a method and apparatus for improving the RRC Connection procedure by correctly resetting or re-establishing a lower layer protocol entity.

2. Description of the Prior Art

Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple. Besides, one NB is responsible for controlling one or more cells, and thus a user equipment (UE) establishing connection with the network means the UE establishing connection with one cell of NB.

In LTE system, Radio Resource Control (RRC) layer of the UE merely includes two RRC states, i.e. RRC_IDLE and RRC_CONNECTED; and Radio Bearers for transmitting RRC signals, generally called Signaling Radio Bearers (SRBs), are divided into the following three types:

1. SRB0 is for exchanging RRC messages over a Common Control Channel (CCCH). Uplink (UL) and Downlink (DL) both use a Transparent Mode (TM) RLC entity,

2. SRB1 is for exchanging RRC messages and upper layer Non-Access Stratum (NAS) messages over a Dedicated Control Channel (DCCH). The UL and DL both use an Acknowledged Mode (AM) RLC entity.

3. SRB2 is for exchanging upper layer NAS messages over DCCH. The UL and DL both use the AM RLC entity.

Through use of the SRBs, the RRC layers of the UE and the network can exchange RRC messages, as a basis for radio resource settings, for completing various RRC control procedures. For example, the UE in RRC_IDLE state can establish RRC connection with the network through a RRC Connection Establishment procedure, while the UE in RRC_CONNECTED state can re-establish RRC connection with the network through a RRC Connection Re-establishment procedure.

For the above two RRC connection procedures, the RRC layer of the UE shall generate a Connection Request message (or a Connection Re-establishment Request message), and the UE shall initiate a Random Access procedure in lower layer, i.e. MAC layer, for transmitting the Connection Request message (or the Connection Re-establishment Request message) to the network over CCCH. Meanwhile, the UE can perform radio measurement for neighboring cells, and reselect to another cell when measuring results reach to cell reselection criteria, i.e. a cell re-selection occurs. Detailed operation of the above RRC connection procedures is referable in related specification and not narrated herein.

According to the current specification, when the cell reselection occurs during an ongoing RRC Connection procedure, the RRC layer of the UE would then generate a new Connection Request message (or a new Connection Re-establishment Request message) to the lower layer for transmission to a new selected cell. However, since the MAC layer is not reset and the RLC layer mapping to the SRB is not re-established as well, the Random Access procedure for an original cell is still executed, causing the Random Access procedure for the new cell cannot be correctly performed. In addition, if the Connection Request message (or the Connection Re-establishment Request message) for the original cell cannot be sent out before the cell reselection occurs, there would be two or more Connection Request messages (or Connection Re-establishment Request messages) in a transmission buffer of the RLC layer. As a result, the follow-up RRC Connection procedure cannot be completed correctly, and may cause errors, such as sending a redundant Connection Request message (or Connection Re-establishment Request message) to the new cell.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide a method and apparatus for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communications system.

According to the present invention, a method for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system is disclosed. The method includes steps of performing an RRC Connection procedure; and resetting or re-establishing a lower layer protocol entity for a Signalling Radio Bearer (SRB) when a cell reselection occurs.

According to the present invention, a communications device for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system is disclosed. The communications device includes a processor for executing a program code, and a memory, coupled to the processor, for storing the program code. The program code includes steps of performing an RRC Connection procedure; and resetting or re-establishing a lower layer protocol entity for a Signalling Radio Bearer (SRB) when a cell reselection occurs.

DETAILED DESCRIPTION

Please refer toFIG. 1, which illustrates a schematic diagram of a wireless communications system1000. The wireless communications system1000can be a 3G mobile telecommunications system, an LTE (long-term evolution) system or other mobile communications systems, and is briefly composed of a network and a plurality of user equipments (UEs). InFIG. 1, the network and the UEs are simply utilized for illustrating the structure of the wireless communications system1000. Practically, the network may comprise a plurality of base stations (Node Bs), radio network controllers and so on according to actual demands, and the UEs can be devices such as mobile phones, computer systems, etc.

Please refer toFIG. 2, which is a functional block diagram of a communications device100in a wireless communications system. The communications device100can be utilized for realizing the UEs inFIG. 1, and the wireless communications system is preferably the LTE system. For the sake of brevity,FIG. 2only shows an input device102, an output device104, a control circuit106, a central processing unit (CPU)108, a memory110, a program code112, and a transceiver114of the communications device100. In the communications device100, the control circuit106executes the program code112in the memory110through the CPU108, thereby controlling an operation of the communications device100. The communications device100can receive signals input by a user through the input device102, such as a keyboard, and can output images and sounds through the output device104, such as a monitor or speakers. The transceiver114is used to receive and transmit wireless signals, delivering received signals to the control circuit106, and outputting signals generated by the control circuit106wirelessly. From a perspective of a communications protocol framework, the transceiver114can be seen as a portion of Layer 1, and the control circuit106can be utilized to realize functions of Layer 2 and Layer 3.

Please continue to refer toFIG. 3.FIG. 3is a diagram of the program code112shown inFIG. 2. The program code112includes an application layer200, a Layer 3202, and a Layer 2206, and is coupled to a Layer 1218. The Layer 3202comprises a Radio Resource Control (RRC) layer, and performs radio resource control. The Layer 2206comprises a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer, and performs link control. The Layer 1218performs physical connections. Besides, the Layer 3202can exchange RRC messages with the network through Signalling Radio Bearers (SRBs) so as to complete various RRC procedures.

In the LTE system, when an RRC Connection procedure is performed, the Layer 3202shall generate a Connection Request message (or a Connection Re-establishment Request message) and a Random Access procedure in the MAC layer shall be initiated for transmitting the Connection Request message (or the Connection Re-establishment Request message) to the network over CCCH. At this time, if a cell reselection occurs, the Layer 3202would then generate a new Connection Request message (or a new Connection Re-establishment Request message) to the lower layer for transmission to a new cell. In such a situation, the embodiment of the present invention provides an RRC Connection improving program code220for accurately resetting or re-establishing a lower layer protocol entity to complete the follow-up RRC Connection procedure.

Please refer toFIG. 4, which illustrates a schematic diagram of a process40. The process40is utilized for improving an RRC Connection procedure in a UE of the wireless communications system1000, and comprises the following steps:

Step402: Perform an RRC Connection procedure.

Step404: Reset or re-establish a lower layer protocol entity for an SRB when a cell reselection occurs.

According to the process40, if the cell reselection occurs during the RRC Connection procedure performed by the UE, the lower layer protocol entity for the SRB would be reset or re-established in the embodiment of the present invention. Moreover, the step of resetting or re-establishing the lower layer protocol entity for the SRB further includes re-establishing a Transparent Mode (TM) RLC entity and resetting a Medium Access Control (MAC) entity.

Thus, when cell reselection occurs during the RRC Connection Procedure, the UE would reset or re-establish the lower layer protocol entity for the SRB so as to discard a previous RRC Connection Request message (or a RRC Connection Re-establishment Request message) and to stop an ongoing Random Access procedure. As a result, the follow-up RRC Connection procedure can be correctly completed, so as to prevent the previous Connection Request messages (or the Connection Re-establishment Request messages) from being transmitted to the new cell or prevent the Random Access procedure being performed inaccurately.

Preferably, the above RRC Connection procedure can be an RRC Connection establishment procedure or an RRC Connection Re-establishment procedure. Besides, in the embodiment of the present invention, re-establishing the TM RLC entity further includes flushing a transmission buffer of the RLC entity, so that all un-transmitted RLC Service Data Units (SDUs) in the transmission buffer can be discarded.

In summary, when the cell reselection occurs during the RRC Connection Procedure, the embodiment of the present invention resets or re-establishes the lower layer protocol entity for the SRB, so as to correctly complete the follow-up RRC Connection procedure and avoid errors.