Transmission time adjusting apparatus and method between RNC and UE in a CDMA communication system

A method of adjusting the transmission time of data in a CDMA communication system. A UE (User Equipment) measures the time difference between the received time of a downlink DPCH (Dedicated Physical Channel) and the transmitted time of an uplink DPCH and reports it to an RNC (Radio Network Controller). The RNC transmits transmission time adjustment information to a node B and the UE if the time difference is out of a predetermined range. The node B then adjusts the transmission time of the downlink DPCH according to the transmission time adjustment information and transmits the downlink DPCH at the adjusted time. The UE receives the downlink DPCH by adjusting a search time for the downlink DPCH according to the transmission time adjustment information.

PRIORITY

This application claims priority to an application entitled “Transmission Time Adjusting Apparatus and Method between RNC and UE in a CDMA Communication System” filed in the Korean Industrial Property Office on Jun. 30, 2001 and assigned Serial No. 2001-39177 and to an application entitled “Transmission Time Adjusting Apparatus and Method between RNC and UE in a CDMA Communication System” filed in the Korean Industrial Property Office on Jul. 4, 2001 and assigned Serial No. 2001-41407, the contents of both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method of transmitting DPCH (Dedicated Physical Channel) frames between an RNC (Radio Network Controller) and a UE (User Equipment) in a CDMA (Code Division Multiple Access) communication system, and in particular, to an ATTA (Adaptive Transmission Time Adjustment) method for adaptively adjusting transmission time between an RNC and a UE.

2. Description of the Related Art

In general, an RNC adjusts transmission time for data communication with a UE via a node B in a CDMA communication system. For the transmission time adjustment, the UE transmits an uplink DPCH frame T0chips (1024 chips) after receiving a downlink DPCCH (Dedicated Physical Control Channel)/DPDCH (Dedicated Physical Data Channel). The DPCCH and the DPDCH are collectively called the DPCH. In real implementation, however, a propagation time delay is involved according to the distance between the node B and the UE. In this case, a serving RNC (SRNC) requests the UE to report the time difference between the received time of the downlink DPCH (DL DPCH) frame and the transmitted time of the uplink DPCH (UL DPCH) frame (hereinafter, referred to as UE Rx−Tx time difference). The SRNC adjusts a DPCH frame offset IE (Information Element) in an RRC (Radio Resource Control) Reconfiguration message based on the UE Rx−Tx time difference in order to inform the UE about the transmission time adjustment. The SRNC only transmits the transmission time adjustment information to the UE but cannot adjust the transmission time of the UE.

Specifically, an RNSAP (Radio Network Subsystem Application Part)/NBAP (Node B Application Part) message has no IE related with downlink transmission time adjustment and thus does not support the downlink DPCH transmission time adjustment of the SRNC.

The UE usually transmits an uplink DPCH frame To chips after receiving a downlink DPCH frame. Here, an initial adjustment error must be limited within ±1.5 chips. The UE then adjusts its transmission time within a ¼ chip duration every time period of 200 ms from the downlink DPCH frame.

When the UE enters a handover region, it receives downlink DPCH data from a plurality of cells. Since each DPCH data has a different propagation delay, the UE cannot adjust its uplink DPCH transmission time. The UE performs a tracking process while implementing a handover from a source node B to a target node B. Also in the case, the UE receives signals with different propagation delays from the source node B and the target node B and thus cannot adjust its transmission time.

When the UE moves out of the handover region, the variance a of the time difference between the received time of the downlink DPCH frame and the transmitted time of the uplink DPCH frame may exceed an allowable value of 128 chips. Therefore the UE cannot adjust its transmission time.

FIG. 1illustrates a time relationship between downlink DPCH data and uplink DPCH data in a handover region on the assumption that the UE moves from cell1to cell2. The UE adjusts its transmission time according to the transmission time of cell1, at every predetermined time during handover, and then according to the transmission time of cell2, after the handover is complete.

According to the first method, the UE transmits an uplink DPCH103time T0after receiving a downlink DPCH101from cell1. In the second method, that is, when the UE enters the handover region, it receives downlink DPCHs101,105,107,110,111and113with different propagation delays from cell1and cell2. Thus, the UE transmits uplink DPCHs103,109and112in every predetermined time period without adjusting its transmission time. Then, when the UE moves out of the handover region and enters the coverage area of cell2, the time difference of the received time of a downlink DPCH115and the transmitted time of an uplink DPCH117becomes T0+α. The UE performs a tracking process within a ¼ chip duration in the unit of 200 ms and thus the UE cannot adjust the transmission time of the uplink DPCH.

As described above, the conventional CDMA communication system has no path in which a control signal for robust transmission time adjustment between a downlink DPCH and an uplink DPCH is transmitted. Therefore, when the UE enters a handover region, it cannot adjust the transmission time of the uplink DPCH. Moreover, the tracking on the basis of the ¼ chip duration is insufficient to ensure the DPCH transmission time adjustment.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a method of transmitting a control signal for adaptive transmission time adjustment of downlink and uplink DPCHs between an RNC and a UE.

It is another object of the present invention to provide a method of adjusting the transmission time of downlink and uplink DPCHs using control signals for adaptive transmission time adjustment between an RNC and a UE.

It is a further object of the present invention to provide a method of maintaining the time difference between the transmitted time of a downlink DPDCH from a node B and the transmitted time of an uplink DPDCH from a UE to be a predetermined value by changing the transmission time of the downlink or uplink DPDCH.

It is still another object of the present invention to provide an ATTA method between a plurality of nodes B and a UE in a handover region.

To achieve the above and other objects, there is provided a method of adjusting the transmission time of data in a CDMA communication system. A UE measures the time difference between the received time of a downlink DPCH and the transmitted time of an uplink DPCH and reports it to an RNC. The RNC transmits transmission time adjustment information to a node B and the UE if the time difference is out of a predetermined range. The node B then adjusts the transmission time of the downlink DPCH according to the transmission time adjustment information and transmits the downlink DPCH at the adjusted time. The UE receives the downlink DPCH by adjusting a search time for the downlink DPCH according to the transmission time adjustment information.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides control signals for downlink DPCH-uplink DPCH transmission time adjustment between a UTRAN (UMTS Terrestrial Radio Access Network) and a UE. Especially, the present invention enables transmission time adjustment in such a non-time adjustment situation as a handover region illustrated inFIG. 1.

In accordance with the present invention, an RNC in the UTRAN requests the UE to measure the UE Rx−Tx time difference and report it. Based on the UE Rx−Tx time difference, the RNC decides whether to transmit the downlink DPCH or the uplink DPCH later than the previous time.

Referring toFIG. 2, upon request from the RNC, the UE measures the UE Rx−Tx time difference (α), which is defined as the time difference between the received time of the downlink DPCH and the transmitted time of the uplink DPCH, and reports it to the RNC in step201. In step202, the RNC compares the UE Rx−Tx time difference α with an allowed time difference T0+Δ. If Rx−Tx time difference(α) is equal to or greater than T0+Δ, the RNC determines whether α+SU×UCF is less than another allowed time difference Δ in step203. If the condition of step202is satisfied, the RNC determines to delay the downlink DPCH frame, and if the condition of step203is satisfied, the RNC determines to delay the uplink DPCH frame. In the former case, the RNC sets an NCF (Node B Control Factor) that makes α equal to or less than Δ after time alignment in step204. In the latter case, the RNC sets a UCF (UE Control Factor) that makes α equal to or less than Δ after time alignment in step205.

How the NCF and the UCF are determined will be described in more detail. Upon receipt of the UE Rx−Tx time difference from the UE, the RNC determines how long the downlink DPCH or uplink DPCH is to be delayed. That is, the RNC compares T0+α with T0+Δ. Here, Δ is a threshold by which it is determines whether the node B and the UE is to adjust their transmission time. While Δ is variable, it is usually 128 chips, or 147 chips with an empirical stabilizing value added.

If T0+α is greater than T0+Δ, the RNC decides to change the transmission time of the downlink DPCH from the node B. Then, in order to reset T0+α to be T0, the RNC delays the transmission time of the node B by a multiple of 256 chips. This time delay value is the NCF. On the other hand, if T0+α is less than T0+Δ, the RNC decides to delay the transmission time of the UE. The time delay may be set on a chip basis or on the basis of a multiple of 256chips. This decision is implementation-dependent. The uplink time delay value is the UCF. Finally, if T0+α is equal to T0+Δ, the RNC maintains the transmission time of the downlink and uplink DPCHs.

With regard to determination of delayed transmission of the downlink DPCH, the RNC determines whether the UE Rx−Tx time difference satisfies the condition expressed as
α<256×NCF+Δ(1)

If Eq. (1) is satisfied, the RNC sets the NCF and transmits it to the node B by a Radio Link Reconfiguration Prepare message and to the UE by a Physical Channel Reconfiguration message. The NCF may be set to 1, 2 or 3 and as stated before, Δ is 128 chips, or 147 chips with an empirical stabilizing value added. The RNC sets a two-bit NCF to an appropriate value indicating the multiple of 256 chips in a reserved area, or additionally uses one bit to indicate the UCF or NCF in the Radio Link Reconfiguration Prepare message. The Physical Channel Reconfiguration message can be constructed in the same manner as the Radio Link Reconfiguration Prepare message. However, if the UCF is set on a chip basis, the number of chips to be shifted must be indicated in the messages.

FIG. 3illustrates a time relationship between the downlink and uplink DPCHs on a CFN/SFN axis in the UE. Referring toFIG. 3, the time difference between the starting received time301of the downlink DPCH and the starting transmitted time302of the uplink DPCH is T0+α. T0is statically determined, 1024 chips and α is an accumulation of propagation delay for a predetermined time due to the movement of the UE.

FIG. 4is a flowchart illustrating a robust transmission time adjustment method in the CDMA communication system according to an embodiment of the present invention. Generation and transmission of the NCF will be described below with reference toFIG. 4.

Referring toFIG. 4, upon request from the RNC, the UE measures the UE Rx−Tx time difference using the received time of the downlink DPCH and the transmitted time of the uplink DPCH and reports it to the RNC via the node B in step401. The RNC determines whether the UE Rx−Tx time difference satisfies Eq. (1) in step402and sets the NCF that makes α equal to or less than a threshold Δ if Eq. (1) is satisfied in step403. The RNC transmits the NCF to the node B by the Radio Link Reconfiguration Prepare message in step404and to the UE by the Physical Channel Reconfiguration message in step406. Upon receipt of the Radio Link Reconfiguration Prepare message, the node B detects the NCF from the message and delays the transmission time of the downlink DPCH frame according to the NCF in step405. For example, if the NCF is 1, 2 or 3, the node B delays the downlink DPCH frame by 256 chips for NCF=1, by 256×2 chips for NCF=2, or by 256×3 chips for NCF=3. Upon receipt of the Physical Channel Reconfiguration message, the UE detects the NCF from the message and delays a searching time for the downlink DPCH frame according to the NCF in step407.

FIG. 5illustrates alignment of the downlink DPCH frame with the uplink DPCH by delaying the downlink DPCH frame according to the NCF in the node B of the CDMA communication system according to the embodiment of the present invention.

Referring toFIG. 5, the node B aligns the downlink DPCH frame with the uplink DPCH frame by delaying the downlink DPCH frame according to NCF(k) to make the UE Rx−Tx time difference 128 chips or less. Specifically, reference numeral501denotes the starting received time of the downlink DPCH frame before alignment, reference numeral502denotes the starting received time of the downlink DPCH frame after alignment, and reference numeral503denotes the time delay of the node B by which the node B determines the NCF. The NCF is set to a multiple of 256 chips.

With regard to determination of delaying the uplink DPCH, the RNC determines whether the UE Rx−Tx time difference satisfies the condition expressed as
α+SU×UCF<Δ(2)

If Eq. (2) is satisfied, the RNC transmits the UCF to the node B and the UE by the Radio Link Reconfiguration prepare message and the Physical Channel Reconfiguration message, respectively. The SU (Shifting Unit) is set to 1, 4, 8, 16, 64, 128, or 256 chips. The SU is usually 128 chips, or 147 chips with a stabilizing value added.

FIG. 6illustrates measuring the UE Rx−Tx time difference in the UE upon request from the RNC in the CDMA communication system according to another embodiment of the present invention. Here, the UE Rx−Tx time difference is less than T0−Δ. Since delaying the downlink DPCH frame causes information loss due to data frame overlap in the first embodiment of the present invention, the uplink DPCH frame is delayed for time adjustment. Referring toFIG. 6, reference numeral601denotes the received time of the downlink DPCH frame and reference numeral602denotes the starting transmitted time of the uplink DPCH frame.

FIG. 7is a flowchart illustrating a robust transmission time adjustment method in the CDMA communication system according to the second embodiment of the present invention. The UCF is first determined using the UE Rx−Tx time difference and transmitted to the node B by the Radio Link Reconfiguration Prepare message and the Physical Channel Reconfiguration message, respectively.

Referring toFIG. 7, upon request from the RNC, the UE measures the UE Rx−Tx time difference and reports it to the RNC in step701. The RNC determines whether the UE Rx−Tx time difference satisfies Eq. (2) in step702and sets the UCF that makes α equal to or less than the threshold Δ if Eq. (2) is satisfied in step703. The RNC transmits the UCF to the node B by the Radio Link Reconfiguration Prepare message in step704and to the UE by the Physical Channel Reconfiguration message in step706. Upon receipt of the Radio Link Reconfiguration Prepare message, the node B detects the UCF from the message and delays a searching time for the uplink DPCH frame according to the UCF in step705. Upon receipt of the Physical Channel Reconfiguration message, the UE detects the UCF from the message and delays the transmission time of the uplink DPCH frame according to the UCF in step707. If the SU is 256 chips, the UCF is 1, 2 or 3. The UE delays the uplink DPCH frame by 256 chips for UCF=1, by 256×2 chips for UCF=2, or by 256×3 chips for UCF=3.

FIG. 8illustrates alignment of the uplink DPCH frame with the downlink DPCH by delaying the uplink DPCH frame according to the UCF in the UE of the CDMA communication system according to the second embodiment of the present invention.

Referring toFIG. 8, the UE aligns the uplink DPCH frame with the downlink DPCH frame by delaying the uplink DPCH frame according to UCF(v). Reference numeral803denotes the time delay of the UE by the UCF. The UCF is set to 1, 4, 8, 16, 128, or 256 chips.

Transmission time adjustment in the case of two nodes B in a handover region will be described below. Obviously, the same transmission time adjustment method is applied when three nodes B exist in the handover region.

In the handover region, the UE receives downlink DPCH frames from the two nodes B. The UE measures different UE Rx−Tx time differences between the uplink DPCH frame and the downlink DPCH frames that have arrived at the UE at different times and reports them to the RNC. The RNC determines an NCF or UCF according to Eq. (1) and Eq. (2) using the two UE Rx−Tx time differences.

If the RNC determines two NCFs, it delays each downlink DPCH frame according to a corresponding NCF. The node B delays the transmission time of the downlink DPCH frame by 256 chips for NCF=1, by 256×2 chips for NCF=2, and 256×3 chips for NCF=3.

FIG. 9illustrates the received times of downlink DPCH frames905and906and the transmitted time of an uplink DPCH frame907on the CFN (SFN) axis in the UE in the case where the RNC determines a UCF for cell1and an NCF for cell2.

Referring toFIG. 9, reference numerals901and902denote the received times of the downlink DPCH frame905and the downlink DPCH frame906, respectively. Reference numeral903denotes the starting transmitted time of the uplink DPCH frame907. In the handover region, the time difference between the uplink DPCH frame907and the downlink DPCH frame905is different from hat between the uplink DPCH frame907and the downlink DPCH frame906.

FIG. 10illustrates alignment of the uplink DPCH frame with the downlink DPCH frame from cell1by delaying the uplink DPCH frame according to a received value UCF(v) in the UE.

Referring toFIG. 10, reference numeral1001denotes the transmission times of the uplink DPCH frame907ofFIG. 9before time alignment and reference numeral1002denotes the transmission times of an uplink DPCH frame1007after time alignment. Reference numeral1003denotes the received time of a downlink DPCH frame1009from cell2before time alignment. For alignment of the uplink DPCH frame1007with the downlink DPCH frame1009from cell2, the RNC should determines an NCF that satisfies Eq. (3).
α+SU×UCF<256×NCF+Δ(3)
where the UCF is a time delay for time alignment already calculated by Eq. (2).

Reference numeral1004denotes the received time of a downlink DPCH frame from cell2after time alignment by Eq. (3). Control signals for the transmission time adjustment are transmitted by the Radio Link Reconfiguration Prepare message and the Physical Channel Reconfiguration message, with a CFN-related field added for simultaneous transmission time adjustment for cell1and cell2.

FIG. 11is a flowchart illustrating a transmission time adjustment method using a UCF and an NCF calculated by UR Rx−Tx time differences in a handover region according to a third embodiment of the present invention. The UCF and NCF are transmitted to the nodes B and the UE, respectively by the Radio Link Reconfiguration Prepare message and the Physical Channel Reconfiguration message.

Referring toFIG. 11, upon request from the RNC, the UE measures UE Rx−Tx time differences α1and α2for the radio links of cell1and cell2and reports them to the RNC in step1001. The RNC determines whether the UE Rx−Tx time difference for cell1satisfies Eq. (2) in step1102. If it does not, the RNC awaits the next UE Rx−Tx time difference for cell1(not shown). On the other hand, if Eq. (2) is satisfied, the RNC determines a UCF that makes α1equal to or less than the threshold Δ for the radio link of cell1in step1103. Then the RNC transmits the UCF to the node B of cell1by the Radio Link Reconfiguration Prepare message in step11031and to the UE by the Physical Channel Reconfiguration message in step11033. Upon receipt of the Radio Link Reconfiguration Prepare message, the node B of cell1detects the UCF from the message and delays a search time for the uplink DPCH frame according to the UCF in step11032. In step11034, upon receipt of the Physical Channel Reconfiguration message, the UE detects the UCF from the message and delays the transmission time of the uplink DPCH frame according to the UCF. If the SU is 256, the UCF is 1, 2 or 3. The UE delays the uplink DPCH frame by 256 chips for UCF=1, by 256×2 chips for UCF=2, and by 256×3 chips for UCF=3.

Concurrently, in steps1104and1105, the RNC determines an NCF that satisfies Eq. (3) using the UE Rx−Tx time difference α2for the radio link of cell2that has reflected the time alignment for cell1. That is, the RNC sets an NCF that makes α2equal to or less than the threshold Δ for the radio link of cell2. Then the RNC transmits the NCF to the node B of cell2by the Radio Link Reconfiguration Prepare message in step11051and to the UE by the Physical Channel Reconfiguration message in step11053. Upon receipt of the Radio Link Reconfiguration Prepare message, the node B of cell2detects the NCF from the message and delays the transmission time of its downlink DPCH frame according to the NCF in step11052. Here, the NCF is 1, 2 or 3. In step11054, upon receipt of the Physical Channel Reconfiguration message, the UE detects the NCF from the message and delays a search time for the downlink DPCH frame from cell2according to the NCF.

While it has been described that the downlink DPCH from cell2is determined to be delayed with respect to the downlink DPCH from cell1, if a certain amount of DPCH frame loss is accepted, the downlink DPCH from cell2can be transmitted earlier than before to be aligned with the uplink DPCH. Also in this case, signaling is performed using the Radio Link Reconfiguration Prepare message and the Physical Channel Reconfiguration message.

In accordance with the present invention as described above, the RNC transmits transmission time adjustment control information to the node B and the UE so that time alignment is stably and adaptively made between the downlink DPCH frame and the uplink DPCH frame during a handover.