HK1089611B - Wireless communication method and apparatus coordinating node-b's and supporting enhanced uplink transmissions during handover - Google Patents

Description

Wireless communication method and apparatus for coordinating node-bs and supporting eu transmissions during handover

Technical Field

The present invention relates to wireless communication systems. More particularly, the present invention relates to a method and apparatus for coordinating node-bs and supporting Enhanced Uplink (EU) transmissions during handover.

Background

Many schemes have been proposed to improve coverage, throughput and transmission delay of eu transmissions in the third generation partnership project (3 GPP). One of the developments is to move the function of scheduling and allocating Uplink (UL) physical channel resources from the Radio Network Controller (RNC) to the node-B. The node-B may make more efficient decisions and manage uplink radio resources on a short-term basis than the rnc. Similar approaches have been adopted in downlink High Speed Data Packet Access (HSDPA) in Universal Mobile Telecommunications System (UMTS) Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes.

It is also known that performance can be greatly increased using Medium Access Control (MAC) level automatic repeat request (ARQ) and hybrid automatic repeat request (HARQ). Applying these techniques during soft handover may provide additional significant benefits.

Figure 1 shows a conventional wireless multi-cell communication system 100 including a wireless transmit/receive unit (WTRU)105, a node-B110, a Radio Network Controller (RNC)115 and at least two cells 120A, 120B. Each cell 120A, 120B is provided by the node B110. The node-B110 is controlled by a radio network controller 115. The handover process is initiated when a cell change providing the best radio conditions is determined between cells 120A and 120B.

As shown in fig. 1, an "intra-node B handover" occurs when a wtru is changed from one cell to another by the same node-B control. An "inter-node-B handover" occurs when a wtru is controlled by a different node-B to change from one cell to another. In the latter case, the node-B that controls the cell before the handover is referred to as the source node-B, and the node-B that controls the cell after the handover is referred to as the target node-B.

During soft handover, the WTRU establishes a plurality of connections with a plurality of node-Bs in the active set. In this case, scheduling and hybrid automatic repeat request operations may create problems. The wtru may receive a conflicting eu transmission schedule from more than one node-B. The WTRU also has difficulty receiving, decoding and processing hybrid automatic repeat request positive and negative acknowledgments (ACK/NACKs) generated by the plurality of node-Bs. Soft buffering for hybrid automatic repeat request processing in the node B may deteriorate during soft handover.

One approach to support h-arq across multiple node-bs when the wtru is in soft handover is to place ack/nack generation functionality in the rnc that can drive single ack/nack based on the results of the multiple node-bs. However, this approach significantly delays the ack/nack process, which is a highly undesirable performance factor.

When a wtru performs an inter-node-B hard handover, the source node-B that was the node-B before the completion of the hard handover may not be able to successfully receive eu transmissions of data packets that were nacked before the hard handover activation time. Other wtrus competing for uplink resources may not be provided with sufficient actual resources in the source cell. If data blocks that were nacked prior to the handover are sent to the source node-B before the handover activation timer expires, these data blocks may be combined with the previous data blocks for h-arq decoding. In this method, decoding is transmitted using the data blocks in the source cell despite the failure. If the data block that was nacked before the handover is not transmitted to the source node-B before the handover activation timer expires, it is again transmitted in the target cell as a new data block. In this case, the previous transmissions of these data blocks in the source cell are not used.

Disclosure of Invention

The present invention relates to wireless communication methods and apparatus for coordinating node-bs for enhanced uplink transmissions during handover. The apparatus may be a wireless communication system, a radio network controller, a node-B, and/or an Integrated Circuit (IC).

In one embodiment, a wireless multi-cell communication system includes a radio network controller, a plurality of node-bs, and a plurality of wtrus. Each node-B provides at least one cell and schedules eu transmissions from wtrus. Once the rnc is aware of the need for soft handover, the wtru establishes a connection to the node-B in the active set. One of the node bs in the active set is designated as a primary node B and all other node bs are designated as non-primary node bs. The radio network controller or wtru selects a primary node-B and informs the primary node-B to other node-bs. During soft handover, the primary node-B may schedule eu transmissions and perform ack/nack.

In various embodiments, the rnc initiates a hard handover for a wtru connected to a source node-B. When the wtru is connected to the source node-B by stopping transmission and reception, the rnc notifies the source node-B. The rnc may send an activation timer to the source node-B to set the handover time. The handover is completed when the activation timer expires.

The source node-B may determine whether there are any previously transmitted data packets that were nacked by the source node-B. To receive as many previously nacked data packets as possible before the activation timer expires, the source node-B may adjust the priority and/or adjust the Modulation and Coding Scheme (MCS) used for the transmission of the data packets transmitted by the wtru.

Drawings

The invention will be understood in more detail from the following description and the accompanying drawings.

Fig. 1 shows a conventional wireless communication system;

FIG. 2 shows a system using an uplink scheduler placed in a primary node-B for enhanced uplink during soft handover in accordance with the present invention;

FIG. 3 shows a system for using an ACK/NACK generation function placed in a primary node-B for EU during soft handover in accordance with the present invention;

FIG. 4 is a process flow diagram of method steps involved in coordinating node-Bs during soft handover in accordance with one embodiment of the invention; and

figure 5 is a flowchart of a process including method steps for prioritizing transmission of nacked data in a source node-B prior to hard handover in accordance with various embodiments of the present invention.

Detailed Description

The present invention will be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout.

Hereinafter, the term "wtru" may include, but is not limited to, a User Equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment.

The term "node-B" as used herein may include, but is not limited to, a base station, site controller, access point or other interconnecting component in a wireless environment.

The present invention may be implemented in, for example, GSM-FDD, TDD, TDSCDMA, CDMA2000 (CDMA2000) (EV-D0 and EV-DV), or any type of wireless communication system.

The features of the present invention may be incorporated into an integrated circuit or be configured in a circuit comprising a plurality of interconnected components.

Figure 2 illustrates a wireless multi-cell communication system 200 that employs an uplink scheduler disposed in a primary node-B in accordance with the present invention. The wireless multi-cell communication system 200 includes a wtru 205, a plurality of node-bs 210 (i.e., 210A, 210B), a radio network controller 215, and a plurality of cells 260 (i.e., 260A, 260B, 260C). Cells 260A and 260C are provided by node B210A. The cell 260B is provided by the node B210B. All node bs 210 are controlled by a radio network controller 215.

During soft handover, the wtru 205 establishes a plurality of connections with the node-bs 210 included in the active set. Each transmission from the wtru 205 is processed independently at each node-B210. One of the node bs 210 in the active set is designated as a primary node B210A and the other node B is designated as a non-primary node B210B.

As shown in fig. 2, the primary node-B210A includes a medium access control entity 250A that includes an uplink scheduler 255. Each non-master node 210B also includes a medium access control entity 250B. Each mac entity 250A, 250B handles eu transmissions. The uplink scheduler 255 in the mac entity 250A is responsible for scheduling the eu transmission.

According to an embodiment of the present invention, the uplink scheduler 255 is implemented only in the primary node-B210A during soft handover. The wtru 205 receives only the ul transmission schedule from the primary node-B210A in the primary cell 260A. However, the primary node-B210A cannot transmit the scheduling information to the non-primary node-B210B every Transmission Time Interval (TTI). In order for the primary node-B210A to allocate resources of the wtru 205 for transmission in cells controlled by the non-primary node-B210B, resources scheduled by the primary node-B250A in the plurality of cells 260B controlled by the non-primary node-B210B cannot be allocated by the non-primary node-B210B. Thus, some of the actual resources shared by all cells in the active enhanced uplink subset should be allocated and reserved by the particular node-B for wtru 205 during soft handover, so these resources are only available to primary node-B210A.

The ul scheduler 255 located in the primary node-B210A considers that the interference level caused by eu transmission at any cell 260A, 260B, 260C in the active eu subset is below a predetermined maximum allowed interference level. Thus, the primary node-B250A limits the transmission power level of the wtru 205 so that the interference level is also within the maximum allowed interference level in the other cells 260B, 260C. To do this, the rnc 215 must send the necessary information, such as the transmission power level and interference level, of the cell 260B controlled by the non-primary node-B210B to the primary node-B210A, which then uses the information to schedule ul transmissions.

Eu scheduling information is transmitted to the wtru 205 via the primary cell 260A only by the primary node-B210A. During soft handover, the wtru 205 receives only the eu scheduling information in the primary cell 260A, although the eu scheduling information in all other cells 260B, 260C is valid.

In one embodiment, the primary node-B250A is selected by the rnc 215 or the wtru 205. The rnc 215 may select the node-B having the highest percentage of correctly received data blocks during the predetermined time window as the primary node-B.

In another embodiment, the rnc 215 may generate node-B statistics, such as Bit Error Rate (BER) or Frame Error Rate (FER), or the like, for a predetermined time interval. The radio network controller 215 may then select the node B with the best performance as the primary node B210A. The rnc 215 may then inform the primary node-B210A to the wtru 205 and all other node-bs via Radio Resource Control (RRC) and Iub signaling, respectively.

In another embodiment, the wtru 102 may select the node-B210 with the best downlink preamble power (i.e., the best downlink path loss or highest coding power) as the primary node-B210A. The wtru 205 may measure the power of the preamble received from all of the node-bs 210 and select the node-B210 with the highest preamble power as the primary node-B210A. The wtru 205 then informs all other node-bs of the primary node-B210A via fast physical layer signaling.

The wtru 205 may report the downlink preamble power of all cells 260 to the rnc 215. The rnc 215 then selects a node-B210 as the primary node-B210 a based on the combined uplink and downlink quality. During the predetermined time window, the uplink quality of the cell 260 is based on the percentage of correctly received data blocks (or bit error rate, frame error rate, or the like), while the downlink quality of the cell 260 is based on the wtru's received downlink preamble power. The rnc 215 then informs the primary node-B210A to the wtru 205 and all other node-bs 210 via rrc notification and Iub signaling, respectively.

The present invention is superior to prior art systems. With the present invention, the WTRU does not receive a conflicting schedule of an EU transmission from the node-B during soft handover. In addition, eu transmissions are scheduled in consideration of the interference level and radio resources in cells controlled by non-primary node-bs. The signaling delay from the primary node-B210A to the wtru 205 is much lower than the signaling delay from the rnc 215 to the wtru 205.

In various embodiments, fig. 3 shows a wireless multi-cell communication system 300 similar to the system 200 shown in fig. 2. As shown in fig. 3, the primary node-B210A includes a mac entity 250A having an ack/nack generator 305. Only the primary node-B210A has the ack/nack generator 305. The primary node-B210A may perform a hybrid automatic repeat request with incremental redundancy or may simply fail to implement an automatic repeat request with incremental redundancy.

Still referring to FIG. 3, the primary node-B210A may receive at least one data packet from the WTRU 205 via the primary cell 260A and perform error checking on the data packet. Any error checking method such as a periodic redundancy check (CRC) can be used. If the primary node-B210A correctly decodes the data packet, such as by crc, the primary node-B210A sends an ack to the wtru 205 and also transmits the correctly decoded packet data to the rnc 215. If the primary node-B210A cannot correctly decode the packet data, the primary node-B210A sends a negative acknowledgement to the wtru 205.

The non-primary node-B210B also performs error checking on the data packet. However, the non-primary node-bs 210B do not send acknowledgments or negatives to the wtru 205. Conversely, the non-primary node-B210B transmits the successfully decoded packet data to the rnc 215. During soft handover, only the primary node-B210A generates hybrid automatic repeat request (or arq), ack and nack, and control retransmissions.

The mac layer identified by the non-primary node-B210B receiving wtru may be used to transmit successfully received transmissions in the universal mobile telecommunications system terrestrial radio access network (UTRAN). Since the non-primary node-B210B is unaware of how wtrus have been scheduled for eu transmission by the primary node-B210A, the non-primary node-B210B may send correctly received transmissions to the correct rnc radio link depending on in-band mac layer signaling of wtru identities. The same method may be implemented by the primary node-B210A even though the primary node-B210A may perceive which wtrus are scheduled.

Preferably, the primary node-B210A can process transmissions using soft combining, while the non-primary node-B210B does not need soft combining to process transmissions. If the primary node-B sends a negative acknowledgement to the wtru 205, the nacked data packets are stored in the buffer of the primary node-B210A and the nacked data packets are combined with the retransmitted data packets. In contrast, the non-primary node-B210B does not store the nacked data packets. This eliminates soft buffer degradation problems between node bs 210 and compounds multiple independent acks and/or nacks.

When the add-on combining process is implemented, measures should be taken to avoid soft buffer corruption. The queue information or new data pointer is needed to cause the node B210 to detect that the wtru 205 is no longer processing duplicate data for a particular wtru harq process, but rather transmits new data. This is particularly required because the node B210 has no other way of knowing that a new transmission has been activated. Alternatively, the non-primary node-B210B may perform a simple automatic repeat request without using an add combining process. This eliminates the soft buffer corruption problem.

In the case where the non-primary node-bs 210B perform simple arq without using an add-on combination, the wtru 205 must transmit a self-decodable data packet to ensure that all node-bs 210 can decode the transmission regardless of the earlier transmission. Preferably, the hybrid automatic repeat request functionality is terminated at the node B210. Each node-B210 transmits a successfully decoded data packet with an explicit transmission identification, such as a transmission queue number (TSN), to the rnc 215. The rnc 215 may optionally use data packets directed from the non-primary node-bs 210B. The mac entity 310, which is located in the rnc 215, is used to perform in-queue delivery processing to deliver data to higher layers on all packets received from the node B210. After the rnc mac entity 310 completes its reordering, it sends data to Radio Link Control (RLC) (not shown). The missing packets are identified to the rnc 215 and the wtru 205 is notified via rlc signaling.

Alternatively, eu transmissions may identify wtru identity, hybrid automatic repeat request processing, transmission queuing, and/or New Data Indicator (NDI) to facilitate soft combining in the non-primary node-B210B. If this method is used to facilitate soft combining in non-primary node-bs 210B, the primary node-B210A may not have to rely on scheduling and h-arq ack/nack decisions to determine when combining should be performed.

There are two options for ack/nack message transmission. The first option is synchronous transmission. The ack/nack messages are transmitted after a unique time delay for the corresponding uplink transmission or eu channel configuration message. The second option is asynchronous transmission. There is no unique delay between the transmission of the ack/nack message and the corresponding uplink transmission or eu channel allocation message. Explicit information in the ack/nack message identifies the corresponding uplink transmission so that the wtru 205 can make the correct correlation between the ack/nack message and the transmission. This correlation is achieved by identifying h-arq process numbers and/or unique queue numbers, such as tx queue numbers, by each ack/nack feedback message to the wtru 205.

Preferably implemented in embodiments with asynchronous ack/nack feedback, the non-primary node-B210B may provide a hybrid automatic repeat request ack/nack result to the primary node-B210A to avoid unnecessary retransmissions of transmissions that were erroneously received by the primary node-B210A but correctly received by the non-primary node-B210B. The non-primary node-bs 210B do not send ack or nack messages directly to the wtru 205. The non-primary node-B210B sends ack/nack or crc check results to the rnc 215. The rnc 215 then sends the ack or crc result to the primary node-B210A.

To expedite h-arq processing, the first ack message received by the rnc from any non-primary node-bs 210B is preferably forwarded to the primary node-B210A immediately. The primary node-B210A also immediately generates an acknowledgment message if the transmission was correctly received at the primary node-B210A without waiting for feedback from the non-primary node-bs 210B. The primary node-B210A generates an ack message immediately upon receiving the ack message forwarded from the rnc, even though other ack messages may be forwarded. Since the acknowledgment is generated if either path is successful, the acknowledgment can be generated once the first successful transmission is found.

Alternatively, to simplify the design of ack/nack generator 205, only a subset of the generating nodes may be used. For example, the acknowledgement may only be generated at the rnc, or the rnc and the primary node-B210A.

When the wtru 205 transmits an uplink transmission, the wtru 205 waits for the minimum time required for the primary node-B210A to transmit ack/nack feedback for each h-arq. For each h-arq, if an ack is received by the wtru 205, the wtru 205 may send new data in the next available or allocated opportunity.

The negative message may only be generated in the rnc 215 because it is the only node with all the necessary information in soft handover to determine that any node-B210 has not successfully received. If the rnc 215 does not receive any acknowledgment from the node-B210 within a predetermined time interval. The rnc 215 forwards the negative message to the wtru 205 via the primary node-B210A.

This procedure can be performed without explicitly negating the instruction. In this example, the lack of acknowledgment reception within a particular time interval is treated as an explicit negative command at the primary node-B210A and/or the wtru 205.

Figure 4 is a process flow diagram 400 including method steps in a coordinating node-B during soft handover in accordance with one embodiment of the present invention. In step 405, the rnc 215 makes a decision to activate an inter-node-B soft handover. In step 410, the wtru 205 establishes connections with at least two node-bs in the active set. In step 415, one of the node bs 210 in the active set is designated as a primary node B210A, while the remaining one or more node bs 210 in the active set are designated as non-primary node bs 210B. In step 420, the primary node-B210A may control uplink transmissions during soft handover by performing eu scheduling and h-arq operations.

Figure 5 is a flowchart 500 of a process including method steps for prioritizing the transmission of nacked data in a source node-B before a hard handover is completed, in accordance with various embodiments of the present invention. In step 505, the rnc 215 makes a hard handover decision to activate the wtru 205 connected to the source node-B210. In step 510, the rnc 215 sends an activation timer to the source node-B210 to set the handover time.

Still referring to fig. 5, if the source node-B210 determines that there is a previously nacked data packet, the previously nacked data packet should be retransmitted as much as possible before the handover activation timer expires. Otherwise, the system may lose the benefit of incrementally combining previous transmissions and retransmissions. Therefore, the source node-B scheduler 255 takes into account the handover activation time when scheduling the nacked data packets. If the source node-B210 does not have enough radio resources to schedule the transmission of all the nacked data packets in time, the source node-B210 should try to schedule the nacked data packets as much as possible.

Still referring to fig. 5, to attempt to transmit the nacked data packet before the handover activation timer expires, the source node-B210 adjusts the priority of the transmission (step 525), and in step 530, the source node-B210 adjusts the modulation and coding scheme of the transmission (step 530). The better priority of scheduling is given to data packets that have been nacked. If the radio resources are sufficient, a more sophisticated modulation and coding scheme may be used to increase the likelihood of successful transmissions from the wtru 205 to the source node-B210. In step 535, the handover is completed when the activation timer expires.

In order for the wtru 205 to know that the scheduled uplink transmission is intended for a data packet with a previous transmission failure, the uplink scheduler 255 of the source node-B210 may specify that the scheduled uplink transmission is intended for a previously nacked data packet. This may be accomplished by including h-arq processes to identify ul scheduling information transmitted from the source node-B210 to the wtru 205. By receiving the scheduling information from the source node-B210, the wtru 205 knows that the scheduled transmission is for hybrid automatic repeat request process identification generation related specific data that is transmitted with the scheduling information.

While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention described above.

Claims (7)

1. In a multi-cell wireless communication system including a radio network controller, a plurality of node-bs and at least one wireless transmit/receive unit (wtru), a method of coordinating node-bs during handover, the method comprising:

the rnc activating an inter-node-B soft handover;

the wtru establishing communication connections with at least two of the plurality of node-bs;

designating and informing a particular node B of the plurality of node Bs as a primary node B and another node B of the plurality of node Bs as a non-primary node B;

wherein the primary node-B transmits eu scheduling information to the wtru and the non-primary node-bs do not transmit the eu scheduling information; and

the rnc is informed to the wtru that the particular node-B is the primary node-B.

2. The method of claim 1 wherein the primary node-B is selected based on uplink performance statistics at each node-B.

3. The method of claim 2 wherein the primary node-B is selected based on reports generated by the wtru regarding a combination of uplink and downlink quality.

4. The method of claim 3 wherein the downlink quality is downlink pilot power.

5. An integrated circuit for coordinating node-bs during handover in multi-cell wireless communications including a radio network controller, a plurality of node-bs and at least one wireless transmit/receive unit, the integrated circuit comprising:

circuitry configured to designate and notify a particular node B of the plurality of node Bs as a primary node B and one or more other node Bs as non-primary node Bs;

wherein the primary node-B transmits eu scheduling information to the wtru and the non-primary node-bs do not transmit the eu scheduling information; and

circuitry configured to notify the WTRU that the particular node-B is the primary node-B.

6. A radio network controller in a multi-cell wireless communication system including a plurality of node-bs, the radio network controller comprising:

circuitry configured to control a plurality of node-bs;

circuitry configured to initiate a soft handover between node-bs;

circuitry configured to designate and notify a particular node B of the plurality of node Bs as a primary node B and one or more other node Bs as non-primary node Bs;

wherein the primary node-B transmits eu scheduling information to a wireless transmit/receive unit and the non-primary node-bs do not transmit the eu scheduling information; and

circuitry configured to notify the WTRU that the particular node-B is the primary node-B.

7. An integrated circuit, the integrated circuit comprising:

circuitry configured to control a plurality of node-bs;

circuitry configured to initiate a soft handover between node-bs;

circuitry configured to designate and notify a particular node B of the plurality of node Bs as a primary node B and one or more other node Bs as non-primary node Bs;

wherein the primary node-B transmits eu scheduling information to a wireless transmit/receive unit and the non-primary node-bs do not transmit the eu scheduling information; and

configured to inform the wtru that the particular node-B is the primary node-B.