Method and apparatus for sending feedback for downlink shared traffic transmitted to multiple wireless transmit/receive unitsTechnical Field
The present invention relates to wireless communications.
Background
Introduction of downlink shared services (i.e., broadcast or multicast transmissions) on a high speed physical downlink shared channel (HS-PDSCH) has been discussed in several contexts, including enhanced Multimedia Broadcast Multicast Services (MBMS) and transmissions to wireless transmit/receive units (WTRUs) in a Radio Resource Control (RRC) CELL _ FACH state. For downlink shared services, the same data flow is intended for multiple WTRUs known or thought to be in a cell, and the network may allow other WTRUs to view the data. It is important to guarantee delivery of data to a part or most of the WTRUs and mechanisms to provide such guarantees should be supported.
The use of HS-PDSCH or similar channels for delivery of downlink shared traffic provides several advantages. The HS-PDSCH is a shared physical channel well suited for delivering traffic over a wide range of quality of service (QoS) classes. The HS-PDSCH is also optimized for packet services that are likely to be most shared services (e.g., Forward Access Channel (FACH) data and MBMS data are likely to be packetized). The HS-PDSCH also supports hybrid automatic repeat request (HARQ), which can be used to guarantee or greatly improve packet delivery if HARQ is combined with a suitable feedback mechanism.
In order to utilize the HARQ mechanism of the HS-PDSCH, a feedback mechanism is needed that allows the WTRU to send positive Acknowledgement (ACK) or Negative Acknowledgement (NACK) feedback to the node B. In High Speed Downlink Packet Access (HSDPA), ACK or NACK messages are delivered to the node B via a dedicated uplink channel, i.e. a high speed dedicated physical control channel (HS-DPCCH). This not only guarantees the availability of channel resources for delivering ACK or NACK messages, but also allows the node B to identify from which WTRU a particular ACK or NACK message originated.
In addition, the performance of HSDPA is greatly enhanced by feedback of Channel Quality Indicator (CQI) availability from the WTRU. Conventionally, the CQI is also sent via HS-DPCCH and the node B can identify the source of the CQI.
While the above approach is practical when the HS-PDSCH is used primarily to carry dedicated data in the CELL _ DCH state, it is no longer practical to deliver shared or dedicated data when the WTRU is operating in the CELL _ FACH state. Any other existing mechanism for delivering ACK/NACK and CQI feedback is not satisfactory for state operation outside the CELL _ DCH state (i.e., when dedicated resources are not available). There may be a very large number of WTRUs listening to a particular shared service in a cell. Dedicating resources to these WTRUs and requiring ACK/NACK feedback from each of these WTRUs would have a very adverse impact on the uplink capacity of the communication system. Also, a WTRU that is not registered in a cell may not be able to access resources.
Since no dedicated resources are allocated in the CELL _ FACH state, the only existing alternative for delivering the ACK or NACK message and CQI is via the Random Access Channel (RACH). Delivering ACK or NACK messages and CQI via RACH can have a severe impact on uplink capacity and is not practical. If ACK or NACK messages and CQIs are delivered from all WTRUs, conventional RACH operation may require a large number of retransmissions of nearly all data, assuming that the downlink data is shared among a large number of WTRUs. Therefore, feedback delivery via RACH is impractical.
It would be desirable to provide a mechanism for feedback from a WTRU for downlink shared traffic with minimal impact on uplink and downlink capacity.
Disclosure of Invention
A method and apparatus for providing feedback for downlink shared traffic transmitted to multiple WTRUs is disclosed. The WTRU receives a downlink transmission from the node-B and decodes the downlink transmission. If the decoding is unsuccessful, the WTRU sends a predefined burst indicating a NACK to the node-B via a contention-based shared feedback channel. The predefined burst may be sent only once without requiring an acknowledgement from the node B. The node B calibrates the downlink transmit power on the downlink shared channel in order to transmit downlink transmissions to the WTRU with a high probability of successful reception. The node B increases the transmit power for downlink transmissions based on a predetermined function when it receives a NACK and decreases the transmit power when it does not receive any NACK.
The node-B may send a downlink transmission including at least two data streams with different Modulation and Coding Schemes (MCSs) such that WTRUs with high signal quality decode all data streams and WTRUs with low signal quality decode less than all data streams. The node-B also sends at least one Channel Quality Indicator (CQI) threshold to the WTRUs such that each WTRU measures CQI on a received downlink transmission and determines which data stream each WTRU should provide feedback for based on the CQI threshold and the measured CQI.
Drawings
The invention will be understood in more detail from the following description of preferred embodiments, given by way of example and made apparent in conjunction with the accompanying drawings, in which
Figure 1 is a block diagram of an example WTRU in accordance with one embodiment;
FIG. 2 is a block diagram of an example node B in accordance with one embodiment;
fig. 3 is a flow diagram of a method of providing feedback for downlink shared services via a downlink shared channel, according to one embodiment;
figure 4 shows one possible power variation scheme for the HS-PDSCH; and
fig. 5 is a flow diagram of a method of providing feedback for downlink shared traffic transmitted to multiple WTRUs via HSDPA according to another embodiment.
Detailed Description
A "WTRU" as referred to hereinafter includes, but is not limited to, a User Equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a Personal Digital Assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. Reference hereinafter to a "node B" includes, but is not limited to, a base station, a site controller, an Access Point (AP), or any other type of interfacing device capable of operating in a wireless environment.
Fig. 1 is a block diagram of an example WTRU100 in accordance with one embodiment. The WTRU100 includes a transmitter 102, a receiver 104, a decoder 106, and a CQI measurement unit 108 (optional). The receiver 104 receives a signal from a node B. The decoder 106 decodes the signal received from the node B. The decoder 106 may decode a high speed shared control channel (HS-SCCH) signal when the WTRU100 is in the Cell _ FACH state. The decoder 106 may decode downlink transmissions on the high speed physical downlink shared channel (HS-PDSCH) if the WTRU100 successfully decodes a WTRU Identity (ID) on a signal on the HS-SCCH. The transmitter 102 sends feedback (i.e., decoded CQI or acknowledgement based on downlink transmissions) to the node bs via a contention-based shared feedback channel, which will be described in detail below. The CQI measurement unit 108 outputs CQI, which will be described in detail below.
Fig. 2 is a block diagram of an exemplary node B200 in accordance with the present invention. Node B200 includes an encoder 202, a transmitter 204, a receiver 206, and a transmit power and MCS control unit 208. Encoder 202 encodes the data stream(s) for transmission. The transmitter 204 sends a downlink transmission including data stream(s) for downlink shared traffic coding to the plurality of WTRUs via a downlink shared channel. The transmit power and MCS control unit 208 controls the downlink transmit power and/or MCS on the downlink shared channel so that downlink transmissions are transmitted to WTRUs with a high probability of successful reception. The receiver 206 receives feedback from the WTRUs via a contention-based shared feedback channel.
Fig. 3 is a flow diagram of a method 300 of providing feedback for a downlink shared service via a downlink shared channel, according to one embodiment. The WTRU100 receives a downlink transmission via a downlink shared channel for downlink shared traffic, which is provided to a plurality of WTRUs from the node-B200 (step 302). The WTRU100 decodes the downlink transmission (step 304). If the decoding is not successful, the WTRU100 sends a predefined burst representing a Negative Acknowledgement (NACK) to the node-B200 via the contention-based shared feedback channel (step 306). The predefined burst may be sent only once without requiring an acknowledgement from the node B200. If the decoding is successful, the WTRU100 does not send feedback (i.e., ACK is implicit).
A new uplink shared feedback channel, physical random access feedback channel (P-RAFCH), is introduced for sending feedback from the WTRU100 to the node-B200. The P-RAFCH is a contention-based random access channel. At least one P-RAFCH may be associated with each HS-SCCH in the downlink. If several downlink shared traffic are supported on the HS-PDSCH(s), a set of P-RAFCHs are provided for the downlink shared traffic and each P-RAFCH may be dedicated to a specific downlink shared traffic.
The configuration of the shared feedback channel (i.e., P-RAFCH) may be communicated via System Information Blocks (SIBs) and may vary between cells. Alternatively, the shared feedback channel configuration may be signaled to WTRUs connected to a Radio Access Network (RAN) through dedicated RRC signaling (e.g., the WTRUs operating in CELL _ FACH state). The node B200 broadcasts the available scrambling codes and time slots for accessing the shared feedback channel. The access slot duration may be the same as for the conventional RACH and may be matched (i.e., derived) to the Transmission Time Interval (TTI) of the downlink shared traffic. When the WTRU100 needs to provide feedback, the WTRU100 randomly selects a code and an access slot associated with a particular TTI on a particular downlink shared service and sends their feedback.
In feedback transmission (i.e., predefined bursts), no transmit power ramping mechanism is used as compared to the conventional RACH. The WTRU100 may send each feedback only once and does not need its acknowledgement of reception from the node-B200. The transmit power for feedback may be determined based on the received power measured on a reference channel (e.g., common pilot channel (CPICH), HS-PDSCH, etc.) and a network-provided offset. The offset value may be included in the SIB. Alternatively, the network may instruct the WTRU100 to use absolute power and provide rules when the WTRU100 is allowed to provide feedback. For example, the WTRU100 may be allowed to send feedback only if the received reference channel power exceeds a predefined value.
If the WTRU100 has selected a node B from several synchronized node Bs transmitting the same downlink transmission, the WTRU100 transmits a NACK to only that selected node B. If the WTRU100 performs soft combining of signals from multiple node Bs in the active set, the WTRU100 sends a NACK to the strongest node B in the active set.
The WTRU100 may send a NACK whenever the WTRU100 fails to decode the downlink transmission. Alternatively, the WTRU100 may send a NACK after two or more consecutive downlink transmission failures. For example, the WTRU100 may send a NACK only if m out of n consecutive transmissions have failed. The number of m and n may be determined by the network. For the purpose of counting m of n, the original transmission, the retransmission, both, or a related combination of both, may be counted. The ability to actually send a NACK may depend on some random number with a probability set by the network. The network may instruct that the desired NACK transmission be made on a cell other than the one in which the downlink shared service (e.g., MBMS) was received. The cell is indicated by the network.
In one embodiment, the feedback may be anonymous. If the feedback is passed, the node-B200 knows that a portion of the WTRUs in the cell are unable to decode the downlink transmission in a particular TTI. Alternatively, the WTRU ID may be signaled. According to one embodiment, the downlink shared traffic may be a signature code mapped to WTRU-specific payload transmissions that will be P-RAFCH. According to another embodiment, the WTRU connection ID may be signaled along with the feedback. According to yet another embodiment, the opportunity to access the contention-based shared feedback channel may be to map to downlink shared traffic so that the wtru id may be verified based on a predefined mapping. The mapping may be transmitted by the network.
The node B200 calibrates the transmit power and/or adjusts the MCS of the downlink shared channel carrying the shared downlink traffic so that it covers the desired coverage area (i.e., cell or portion of a cell) with a high probability. By adjustment of the transmit power and/or MCS, the probability that the WTRU100 will not receive downlink data in a TTI may be set to a desired operating point that is preferably close to zero. Since the WTRU100 sending the NACK is almost certainly at the edge of the cell or a portion thereof, the downlink power calculation should be done under this assumption. Because the node B200 knows the size of the cell or a portion thereof, the node B200 may configure the downlink transmit power and/or MCS so that it does not significantly interfere with other signals. Thus, only very individual WTRUs may need to send a NACK in any single TTI. A rule may be set to prohibit the WTRU from sending feedback in this way where the feedback power is fixed.
Since the WTRU100 sending the NACK is almost certainly at the edge of the cell or a portion thereof, the uplink transmit power on the shared feedback channel (e.g., P-RAFCH) may be determined under this assumption. Because the node B200 knows the size of the cell or a portion thereof, the node B200 configures the uplink transmit power so that it does not significantly interfere with other signals at the node B200.
Under the above assumptions (NACK is hardly expected per TTI), node B200 may allocate enough shared feedback channel resources to keep the NACK collision probability low and node B200 can receive a large number of NACKs without seriously affecting the uplink capacity.
If node B200 receives at least one NACK, node B200 schedules a retransmission for which a NACK is received. In this way, the HS-PDSCH operates as it conventionally would under normal HSDPA operation. Packet delivery is guaranteed to the same extent as it is under current HARQ (i.e. subject to the maximum limit for retransmissions and errors in NACK feedback).
The node B may maintain a threshold and retransmit the downlink transmission only if the number of NACKs from the WTRU exceeds the threshold. When data delivery is not guaranteed, it is guaranteed that only a few WTRUs are affected. This limits the impact on downlink shared traffic throughput for a small number of WTRUs. Alternatively, node B200 may ignore the NACK. The node B200 may not allocate resources to the shared feedback channel to achieve the same result.
Node B200 may aggregate NACKs (i.e., keep track of the data that needs to be retransmitted) and retransmit the multiple downlink transmissions later as a single packet. In this case, the sequence number and buffering may need to be extended.
The node B200 may perform the following downlink power control mechanism for the HS-PDSCH. Let PnIs the HS-PDSCH power reference (i.e., power per bit) in TTI n. If a NACK is received, node B200 may set the transmit power reference for TTI (n +1) as follows:
Pn+1＝Pn+ f (number of NACKs) ΔNACK(ii) a Or equation (1)
Pn+1＝PMAX. Equation (2)
If node B200 does not receive a NACK, node B200 may set the transmit power reference for TTI (n +1) as follows:
Pn+1＝Pn-ΔACKequation (3)
Here, ΔACK，ΔNACK> 0, f () is a positive non-decreasing function (but may be a constant value) of its argument. If the node B200 does not receive any NACKs, the node B200 may decrease the transmit power reference by a predefined decrement. Once a NACK is received, the transmit power reference may be increased by a predefined increment. The predefined increment and decrement may or may not be the same. The increase may depend on the number of NACKs received (but may be a constant value). Incremental increments f (number of NACKs) ΔNACKPreferably much larger than the reduced decrement ΔACK. Fig. 4 shows one possible power variation scheme for the HS-PDSCH.
The actual transmit power in TTI n depends on P as is conventionalnAnd the data format selected for the data. In addition, the maximum and minimum power may be set to limit the actual transmit power.
In addition to or as an alternative to transmit power control, node B200 may adjust the MCS of the downlink shared traffic in a similar manner. The node B200 may increase the order of MCS when no NACK is received and may decrease the order of MCS when at least one NACK is received.
For both power control and MCS control, the node B200 considers resources allocated to other services in determining the possible transmit power ranges and MCSs. For example, if the load generated by other traffic is low, the node-B200 may increase its transmit power for downlink shared traffic and/or decrease the MCS, which allows more WTRUs to decode the traffic.
When the node-B200 needs to know how many WTRUs are listening to the downlink shared traffic, the node-B200 may temporarily (e.g., one (1) TTI) request that all WTRUs send a NACK. To this end, the node B200 may transmit a specific burst or data sequence with CRC check for intentional errors. This will force all WTRUs to respond with a NACK. The node B200 counts the number of received NACKs and makes an allowance for loss due to fading and collisions. This not only provides a count that should be roughly correct, but also obtains a distribution of uplink channel quality if the NACK power is "absolute" (as opposed to relative received power).
Fig. 5 is a flow diagram of a method 500 for providing feedback for downlink shared traffic transmitted to multiple WTRUs via HSDPA, in accordance with another embodiment. When the WTRU is in the Cell _ FACH state, WTRU100 receives signaling on the HS-SCCH from node B200 (step 502). If the WTRU100 successfully decodes the identity of the WTRU100 on signaling on the HS-SCCH, the decoder 106 may decode the downlink transmission on the HS-PDSCH (step 504). The WTRU100 sends an acknowledgement to the node-B200 via the contention-based shared feedback channel and based on decoding of the downlink transmission (step 506). The transmission on the shared feedback channel and the signaling on the HS-SCCH have a fixed timing relationship.
One shared feedback channel includes one scrambling code and one channelization code in the uplink. At least one shared feedback channel is associated with each HS-SCCH in the downlink. The shared feedback channel is shared among all WTRUs that are requested to monitor the associated HS-SCCH in CELL _ FACH.
Transmissions by different WTRUs on the shared feedback channel are time division multiplexed and follow timing restrictions with respect to signaling on the HS-SCCH. More specifically, after having successfully decoded its WTRU ID (i.e., high speed radio network temporary identity (H-RNTI) on HS-SCCH, the WTRU100 transmits ACK or NACK messages over the associated shared feedback channel at fixed time intervals, the duration of the time interval should be set so that the time is long enough for the WTRU100 to receive and decode data on the HS-PDSCH and estimate whether there is error (i.e., Cyclic Redundancy Check (CRC) verification), the transmissions on the shared feedback channel must last no more than one (1) TTI length to avoid collisions between WTRUs transmitting feedback, and a sufficient guard period should be defined to avoid collisions between WTRUs having different time offsets (e.g., near-far problem) when transmitting on the shared feedback channel.
The information and parameters related to the shared feedback channel may be signaled to the WTRU100 at the same time that the HS-SCCH related information is signaled, either through SIBs on the Broadcast Control Channel (BCCH)/Broadcast Channel (BCH) or through dedicated RRC signaling (e.g., a new Information Element (IE) in the RRC connection setup message).
The transmission power at which the WTRU100 sends feedback may be set based on the received power measured on the reference channel (e.g., CPICH, HS-PDSCH, etc.) and a network provided offset value. The offset value may be part of a SIB. Alternatively, the network may instruct the WTRU100 to use absolute power, but provide rules when the WTRU100 is allowed to provide feedback. For example, the WTRU100 is allowed to send feedback when the received reference channel power is below a predefined value. Alternatively, the conventional HS-SCCH may be modified to include power control information related to feedback transmission on the shared feedback channel. Power offset or relative power command (e.g., increase or decrease) bits may be introduced into the HS-SCCH to adjust the WTRU transmission power on the shared feedback channel. Optionally, the WTRU100 may include channel quality information in the feedback.
Hereinafter, a scheme for transmitting CQI via P-RAFCH is disclosed. The CQI is also transmitted via the P-RAFCH. When CQI feedback can be scheduled or triggered, the node B must distinguish between NACK-only feedback, CQI-only feedback, and CQI feedback triggered by NACK (i.e., NACK + CQI). The P-RAFCH burst includes a data type indicator for indicating NACK only, CQI only, or NACK + CQI, a data field for carrying CQI bits when needed, and a reference field for carrying modulation phase and power reference when needed.
These fields may be mapped to bursts (i.e., each data is transmitted in its own time segment) by Time Division Multiplexing (TDM). Alternatively, the fields may be mapped to bursts by Code Division Multiplexing (CDM) (e.g., based on the signature of the structure in the PRACH preamble). Alternatively, the fields may be mapped to bursts by Frequency Division Multiplexing (FDM). FDM is particularly suitable for systems such as Long Term Evolution (LTE), where a large number of subcarriers may be used. The basic physical channel resources used to carry these fields may be, but are not necessarily, orthogonal at least at the WTRU.
The data field, if present, may use any multi-dimensional modulation scheme, with each physical channel resource (time slot, signature, carrier, etc.) providing a dimension in the modulation vector space. Some examples of possible modulation schemes are as follows:
(1) multidimensional m-Phase Shift Keying (PSK) (including Binary Phase Shift Keying (BPSK) (m ═ 2), Quadrature Phase Shift Keying (QPSK) (m ═ 4)), m is an integer power of 2. The amount of physical channel resources required is M/log2m and requires an auxiliary phase and power reference.
(2) Multidimensional m-Quadrature Amplitude Modulation (QAM) (including BPSK (m-2), QPSK (m-4)), m is an integer power of 2. The amount of physical channel resources required is M/log2m and requires an auxiliary phase and power reference.
(3) And (5) m-element orthogonal modulation. The number of physical channel resources required is M (i.e., M-M) and no additional phase and power references are required.
(4) m-ary biorthogonal modulation. The number of physical channel resources required is M/2 (i.e., M-M/2) and additional phase and power references are required.
(5) Multidimensional on-off keying, (i.e., M/2 carriers with or without power). The amount of physical channel resources required is M/2 (i.e., M-M/2) and no additional phase and power references are required.
The modulation scheme to be used should be signaled to the WTRU. Certain modulation schemes may require the use of phase and power references, while other modulation schemes do not. The reference may be sent with a data type indicator if needed. The data type indicator and the reference field may be transmitted on separate physical resources. Alternatively, only the data type indicator is sent and the reference field is derived therefrom using decision feedback (i.e. the data type indicator is assumed to be correctly demodulated, which allows it to be reused as a reference signal).
In addition, to avoid explicit transmission of the data type indicator, the CQI may always be triggered due to the need to transmit a NACK (i.e., NACK and CQI are always sent together). Alternatively, if a NACK is sent and a CQI does not need to be sent, a data field corresponding to the highest CQI value may be used. These types of transmissions are referred to as implicit data type formats. The use of this format should be signaled to the WTRU.
The node B detects the presence of power on the completed burst. If power is detected in the burst space and a data type indicator is used, the node B reads the data type indicator. If a CQI is present, the CQI is demodulated according to the modulation scheme used. The presence of power indicates NACK and CQI transmission if an implicit data type format is used.
The node B may collect CQIs over some time period due to the multicast nature of the transmission and the need to serve most or all WTRUs. The node B selects the minimum CQI over this time period and schedules the data rate according to the minimum CQI. In this manner, all WTRUs may be served with a high probability.
However, this scheme has the disadvantage that WTRUs with poor channel conditions may significantly reduce the throughput of the overall system. The node B cannot directly recognize that such a WTRU is present because all feedback from multiple WTRUs is anonymous. To address this problem, the node B may collect statistics on CQI transmissions and may ignore any CQI that is statistically far from most CQIs. Then, the node B may select a minimum CQI from the remaining CQIs and use it as a reference.
Alternatively, the node B may select a particular small subset of CQIs (e.g., 20% or less or 10% or less) after removing the outliers. The node B may then use the average (e.g., actual average, median, etc.) of these. The highest CQI is unlikely to have any impact on system operation due to multicast characteristics. Thus, the WTRU may not send the highest possible CQI value.
Another embodiment operating on the basis of layer 2/3(L2/3) is disclosed below. The WTRU100 listens for network signaling that informs the WTRU100 when, how often, and to whom to report feedback of the downlink shared traffic. The WTRU100 decodes the signal on the allocated TTI for the shared downlink traffic. The WTRU100 then collects statistics of decoding success rate or failure rate and compares the decoding statistics to predefined thresholds provided by the network. If the decoding statistics are worse than a predefined threshold, the WTRU100 sends feedback.
If the WTRU100 has selected a node B from several synchronized node bs transmitting the same data, the WTRU100 transmits feedback only to that selected node B. If the WTRU100 performs soft combining of signals from multiple node bs in the active set, the WTRU100 sends feedback to the strongest node B in the active set.
The network may instruct that the desired NACK transmission be made on a cell other than the one in which the downlink shared service (e.g., MBMS) was received. The cell is indicated by the network.
The downlink shared traffic may be mapped to a code to be transmitted with NACK. Alternatively, the WTRU connection ID may be signaled. Alternatively, if PRACH is used for feedback, the physical channel access opportunities may be mapped to downlink shared traffic. The mapping may be indicated by the network. The CQI information may be transmitted with the NACK or in the location of the NACK, if desired. Since the signaling is at L2/3, a large number of bits are supported in a straightforward manner.
Some downlink shared traffic (e.g., video) may use a layered QoS mechanism where a particular user obtains higher throughput and quality than other users. In a wireless system, an important factor in determining user QoS is the throughput that can be achieved given the user's location in the system. The maximum throughput achievable at the cell edge is generally less than the throughput achievable around the cell center. Layered QoS can be supported without feedback from dedicated physical channels.
One conventional layered QoS mechanism, such as Digital Video Broadcasting (DVB), is based on hierarchical modulation. In hierarchical modulation, multiple data streams (typically high and low priority) are modulated into one single signal that is received by all users. Users with good signal quality can decode both data streams, while users with low signal quality can only decode the high priority data stream. For example, the data stream may be encoded as a 16 quadrature amplitude modulation (16QAM) signal. The quadrant in which the signal is located represents two high priority bits, while the signal position within the quadrant represents two low priority bits. Users with good signal quality can decode the signal as 16QAM, while users with low signal quality can only decode the signal as Quadrature Phase Shift Keying (QPSK) and can only extract high priority bits.
According to the present teachings, some new signaling is provided. From a network perspective, all WTRUs reporting their ACK or NACK feedback based on the decoding of the high priority data stream alone may not be satisfactory because it would lack information regarding the performance of the location-favorable WTRU. On the other hand, it is also not satisfactory to have all WTRUs provide feedback based on the decoding of all data streams, since a WTRU with a bad location will overload the P-RAFCH with NACKs.
The network sets at least one CQI threshold to decide which data stream each WTRU should provide feedback on. The CQI threshold(s) are signaled from the network (e.g., on the BCCH, Dedicated Control Channel (DCCH), or MBMS Control Channel (MCCH) for broadcast, multicast or unicast).
The WTRU100 measures its own CQI (or average CQI). The WTRU100 compares the measured CQI to the CQI threshold(s) and determines a minimum CQI threshold that is higher than the measured CQI. This CQI threshold corresponds to a particular subset of the data stream(s) for which the WTRU100 needs to report feedback. The WTRU100 reports ACK or NACK feedback on a subset decoding of the data stream(s) determined based on the CQI comparison. It is possible to further constrain a subset of data flows to report feedback based on the WTRU's subscription to high quality traffic.
The specific CQI threshold may be set below a value at which the WTRU100 is not allowed to provide feedback. For example, in the case where there are only two data streams (high priority data stream and low priority data stream) and two CQI thresholds (high CQI threshold and low CQI threshold) are set, the WTRU100 may report feedback on both the high priority and low priority data streams if the measured CQI exceeds the high CQI threshold. The WTRU100 may report feedback only on high priority data streams if the measured CQI is below the high CQI threshold but above the low CQI threshold. The WTRU100 may not provide feedback at all if the measured CQI is below the low CQI threshold.
Node B200 may sometimes change the CQI threshold(s) based on the loading condition. For example, in case the load of the node B200 is low due to other traffic, the node B200 may allocate more resources to the downlink shared traffic and encode the data streams with less active MCS, which allows more WTRUs to enjoy high QoS. In the case of high contention between downlink shared traffic and other traffic, the node B200 may use more active MCSs to transmit data streams to reduce the amount of resources used for downlink shared traffic.
Alternatively, the multiple data streams may be transmitted separately at different times or with different codes. For example, high priority data streams may be transmitted with less aggressive MCS while low priority data streams may be transmitted with more aggressive MCS. This allows more flexibility in the selection of MCS and CQI thresholds for decoding the data streams. The disadvantage is that the efficiency is low since the data streams are not combined in the same signal.
Examples
1. A method for sending feedback for downlink shared traffic transmitted to multiple WTRUs.
2. The method of embodiment 1, comprising: the WTRU receives a downlink transmission from the node-B via a downlink shared channel.
3. The method of embodiment 2, comprising: the WTRU sends a predefined burst indicating at least one of NACK and CQI to the node-B via a contention-based shared feedback channel.
4. The method according to embodiment 3, wherein the predefined burst is sent only once without requiring an acknowledgement from the node B.
5. The method as in any one of embodiments 3-4, wherein the transmit power for the predefined burst is determined based on a received power of a reference channel from the node B.
6. The method as in any embodiments 3-5 wherein the WTRU receives an absolute transmit power for a predefined burst from the node-B and the WTRU transmits the predefined burst only if the received power on a reference channel from the node-B is below a predefined value.
7. The method as in any one of embodiments 3-6 wherein the WTRU selects a particular node-B among a plurality of node-Bs that send the same downlink transmission, and the WTRU sends a predefined burst to only the selected node-B.
8. A method as in any of embodiments 3-7 wherein a WTRU performs soft combining of downlink transmissions received from a plurality of node Bs in an active set and transmits a predefined burst to a node B having the strongest signal among the node Bs in the active set.
9. The method as in any embodiments 3-8 wherein the WTRU sends the predefined burst only if m out of n consecutive transmissions fail.
10. The method according to any of embodiments 3-9, wherein the predefined burst comprises at least one of a data type indicator indicating one of NACK only, CQI only, and NACK + CQI, a data field for carrying CQI bits, and a reference field for carrying a modulation phase and a power reference.
11. The method of embodiment 10 wherein the data type indicator, the data field, and the reference field are mapped to the predefined burst by one of TDM, CDM, and FDM.
12. The method as in any one of embodiments 10-11, wherein if only a NACK is sent, the data field carries a highest CQI value.
13. A method for sending feedback for downlink shared traffic transmitted to multiple WTRUs via HSDPA.
14. The method of embodiment 13, comprising: when the WTRU is in RRC Cell _ FACH state, the WTRU receives signaling on HS-SCCH from the node B.
15. The method of embodiment 14, comprising: if the WTRU successfully decodes the identity of the WTRU on signaling on the HS-SCCH, the WTRU decodes the downlink transmission on the HS-PDSCH.
16. The method of embodiment 15, comprising: the WTRU sends an acknowledgement to the node B via a contention-based shared feedback channel based on decoding of the downlink transmission, the transmission on the shared feedback channel and the signaling on the HS-SCCH having a fixed timing relationship.
17. The method of embodiment 16 wherein the transmit power for the acknowledgement on the shared feedback channel is determined based on the received power of a reference channel from the node B.
18. A method as in any of embodiments 16-17 wherein a WTRU receives an absolute transmit power for an acknowledgement on a shared feedback channel from a node B and the WTRU transmits an acknowledgement only if the received power on a reference channel from the node B is below a predefined value.
19. A method as in any of the embodiments 16-18 wherein the HS-SCCH carries power control information for acknowledgement.
20. A method for supporting transmission of feedback for a downlink shared service transmitted to a plurality of WTRUs via a downlink shared channel.
21. The method of embodiment 20, comprising: the node B sends downlink transmissions to the plurality of WTRUs via a downlink shared channel, and the node B calibrates downlink transmit power on the downlink shared channel so that the downlink transmissions are transmitted to the WTRUs with a high likelihood of being successfully received.
22. The method of embodiment 21, comprising: the node-B receives a predefined burst as feedback from the WTRU via a contention-based shared feedback channel, the feedback indicating at least one of a NACK and a CQI.
23. The method of embodiment 22 wherein the predefined burst is sent only once without requiring an acknowledgement from the node B.
24. A method as in any of embodiments 22-23 wherein when a node B receives a NACK, the node B increases the transmit power of the downlink transmission based on a predetermined function, and when the node B does not receive any NACK, the node B decreases the transmit power.
25. The method as in any one of embodiments 22-24 wherein the transmit power is reduced based on the number of NACKs.
26. A method as in any of embodiments 22-25 wherein a node-B adjusts the MCS based on feedback from the WTRU.
27. The method according to any of embodiments 22-26, further comprising: the node B transmits a specific downlink transmission including an error to the WTRU.
28. The method of embodiment 27, comprising: the node B counts the number of WTRUs based on feedback sent in response to a particular downlink transmission.
29. A method as in any of embodiments 21-28 wherein a node B retransmits a downlink transmission only if the number of NACKs from the node B exceeds a predetermined threshold.
30. A method as in any of embodiments 21-29 wherein a node B collects CQIs from WTRUs during a time period, selects a minimum CQI during the time period, and schedules a data rate based on the minimum CQI.
31. The method of embodiment 30 wherein the node B ignores the statistically exceptionally low CQI when selecting the minimum CQI.
32. A method as in any of embodiments 21-29 wherein a node B collects CQIs from WTRUs over a certain time period, selects a subset of CQIs, calculates an average of the CQIs in the subset, and schedules a data rate based on the average.
33. The method of embodiment 20, comprising: the node-B sends a downlink transmission for a downlink shared service to a plurality of WTRUs via a downlink shared channel, the downlink transmission comprising at least two data streams, each data stream being processed with a different MCS such that a WTRU with high signal quality is able to decode all data streams and a WTRU with low signal quality is able to decode less than all data streams.
34. The method of embodiment 33, comprising: the node-B sends at least one CQI threshold to the WTRUs, wherein each WTRU measures CQI on a received downlink transmission and determines which data stream each WTRU should provide feedback for based on the CQI threshold and the measured CQI.
35. The method of embodiment 1, comprising: a WTRU receives a downlink transmission for a downlink shared service from a node-B via a downlink shared channel, the downlink transmission including at least two data streams, each data stream being processed with a different MCS such that WTRUs with high signal quality are able to decode all the data streams and WTRUs with low signal quality are able to decode less than all the data streams.
36. The method of embodiment 35, comprising: the WTRU receives a CQI threshold from the node B.
37. The method of embodiment 36, comprising: the WTRU measures CQI on the received downlink transmission.
38. The method of embodiment 37, comprising: the WTRU determines which data stream the WTRU should provide feedback to the node B by comparing the measured CQI to a CQI threshold.
39. The method of embodiment 38, comprising: the WTRU sends feedback to the node B for the determined data flow.
40. A WTRU for providing feedback for downlink shared traffic transmitted via a downlink shared channel.
41. The WTRU of embodiment 40, comprising: a receiver that receives a downlink transmission for a downlink shared service from a node B via a downlink shared channel.
42. The WTRU of embodiment 41, comprising: a decoder for decoding the downlink transmission.
43. The WTRU of embodiment 42, comprising: a transmitter for transmitting a predefined burst indicating at least one of a NACK and a CQI to a node B via a contention-based shared feedback channel.
44. The WTRU of embodiment 43 wherein the transmitter sends the predefined burst only once without requiring an acknowledgement from the node-B.
45. A WTRU according to any of embodiments 43-44, wherein a transmit power for a predefined burst is determined based on a received power of a reference channel from a node B.
46. A WTRU according to any of embodiments 43-45, wherein a predefined burst is sent with an absolute transmit power indicated by a node B only if a received power on a reference channel from the node B at the time is below a predefined value.
47. A WTRU according to any of embodiments 43-46, wherein if a particular node B has been selected from a plurality of node Bs that sent the same downlink transmission, the transmitter sends a predefined burst only to the selected node B.
48. A WTRU according to any of embodiments 43-47, wherein a decoder soft combines downlink transmissions received from a plurality of node Bs in an active set, and a transmitter transmits a predefined burst to a node B having a strongest signal among the node Bs in the active set.
49. A WTRU according to any of embodiments 43-48, wherein a transmitter sends a predefined burst only if m out of n consecutive transmissions fail.
50. A WTRU according to any of embodiments 43-49, wherein the predefined burst includes a data type indicator indicating one of NACK only, CQI only, and NACK + CQI.
51. A WTRU according to any of embodiments 43-50, wherein the predefined burst includes a data field for carrying CQI bits and a reference field for carrying a modulation phase and a power reference.
52. The WTRU of embodiment 51 wherein the data type indicator, the data field and the reference field are mapped to the predefined burst by one of TDM, CDM and FDM.
53. A WTRU according to any of embodiments 51-52, wherein if only a NACK is sent, the data field carries the highest CQI value.
54. A WTRU for providing feedback for downlink shared traffic transmitted to multiple WTRUs via HSDPA.
55. The WTRU of embodiment 54 comprising a receiver for receiving a signal.
56. The WTRU of embodiment 55 comprising a decoder for decoding a signal on the HS-SCCH when the WTRU is in the RRC Cell _ FACH state and for decoding a downlink transmission on the HS-PDSCH if the WTRU successfully decodes a WTRU identity on the signal on the HS-SCCH.
57. The WTRU of embodiment 56 comprising a receiver configured to send an acknowledgement to the node B via a contention-based shared feedback channel based on decoding of the downlink transmission, the transmission on the shared feedback channel and the signaling on the HS-SCCH having a fixed time relationship.
58. The WTRU of embodiment 57 wherein the transmit power for the acknowledgement on the shared feedback channel is determined based on the received power of a reference channel from the node-B.
59. A WTRU according to any of embodiments 57-58, wherein the transmitter sends feedback at an absolute transmit power indicated by a node B only if a received power on a reference channel from the node B is below a predefined value.
60. A WTRU according to any of embodiments 57-59, wherein the HS-SCCH carries power control information for acknowledgement.
61. A node-B for supporting transmission of feedback for a downlink shared service transmitted to a plurality of WTRUs via a downlink shared channel.
62. The node-B of embodiment 61 comprising a transmitter to send downlink transmissions for downlink shared traffic to a plurality of WTRUs via a downlink shared channel.
63. The node-B of embodiment 62 comprising a transmit power and MCS control unit to control at least one of a downlink transmit power and an MCS on a downlink shared channel such that a downlink transmission is transmitted to the WTRU with a high likelihood of being successfully received.
64. The node-B of embodiment 63 comprising a receiver for receiving a predefined burst as feedback from the WTRU via the contention-based shared feedback channel, the feedback indicating at least one of NACK and CQI.
65. The node B of embodiment 64 wherein the predefined burst is sent only once without requiring an acknowledgement from the node B.
66. The node-B of any of embodiments 64-65 wherein the transmitter increases the transmit power for downlink transmissions based on a predetermined function when a NACK is received and decreases the transmit power when a NACK is not received.
67. The node-B of any of embodiments 64-66 wherein the transmit power is reduced based on the number of NACKs.
68. A node-B as in any of embodiments 64-67 where the transmitter adjusts the MCS based on feedback from the WTRU.
69. The node-B of any of embodiments 63-68 wherein the transmitter is configured to transmit a downlink transmission including an error and the receiver is configured to count the number of WTRUs based on feedback sent in response to the downlink transmission including an error.
70. A node-B as in any of embodiments 64-69 wherein the transmitter is configured to retransmit the downlink transmission only if the number of NACKs from the WTRU exceeds a predetermined threshold.
71. The node-B of embodiment 61 comprising a transmitter configured to send a downlink transmission for a downlink shared service to a plurality of WTRUs via a downlink shared channel, the downlink transmission comprising at least two data streams, the transmitter further configured to send a CQI threshold to the WTRUs.
72. The node-B of embodiment 71 comprising an encoder adapted to encode data streams, each data stream processed with a different MCS, such that WTRUs with high signal quality decode all data streams and WTRUs with low signal quality decode less than all data streams.
73. The node-B of embodiment 72 comprising a receiver for receiving feedback from the WTRUs, wherein each WTRU measures CQI on a received downlink transmission and determines which data stream each WTRU should provide feedback for based on a CQI threshold.
74. The WTRU of embodiment 40 comprising a receiver configured to receive a downlink transmission and a CQI threshold for a downlink shared service from a node B, the downlink transmission comprising at least two data streams, each data stream processed with a different MCS.
75. The WTRU of embodiment 74 comprising a decoder for decoding downlink transmissions such that a WTRU with high signal quality is able to decode all data streams and a WTRU with low signal quality is able to decode less than all data streams.
76. The WTRU of embodiment 75 comprising a CQI measurement unit for generating CQI on a received downlink transmission.
77. The WTRU of embodiment 76 comprising a transmitter configured to determine which data stream the WTRU should provide feedback to the node B for by comparing the measured CQI to a CQI threshold and to send feedback to the node B for the determined data stream.
Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. The methods or flow charts provided in the present invention may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of the computer-readable storage medium include read-only memory (ROM), random-access memory (RAM), registers, buffer memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM discs and Digital Versatile Discs (DVDs).
For example, suitable processors include: a general-purpose processor, a special-purpose processor, a conventional processor, a Digital Signal Processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) circuit, any Integrated Circuit (IC), and/or a state machine.
A processor in association with software may be used to implement a radio frequency transceiver for use in a Wireless Transmit Receive Unit (WTRU), User Equipment (UE), terminal, base station, Radio Network Controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a video phone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, and BluetoothA module, a Frequency Modulation (FM) radio unit, a Liquid Crystal Display (LCD) display unit, an Organic Light Emitting Diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any Wireless Local Area Network (WLAN) module.