Method and apparatus for transmitting channel quality indicator information

188071/2 γηυ ηο'ϊή Ίΐορ,τ3,Ν,ι jnna ιιτη nn,1nef,i ιρηηι nony

Method and apparatus for transmitting channel quality indicatorinformation

InterDigital Technology Corporation C.180127 01801273\ 120-01 WO 2007/024780 PCT/US2006/032604

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[0001] [0002] [0003]

Express Mail Label No. EV680508590US

METHOD AND APPARATUS FOR ADJUSTINGCHANNEL QUALITY INDICATOR FEEDBACKPERIOD TO INCREASE UPLINK CAPACITY

FIELD OF INVENTION

The present invention is related to a wireless communication system. More particularly, the present invention is related to a method andapparatus for adjusting a channel quality indicator (CQI) feedback period toincrease uplink capacity in a wireless cnmmnniratinn system.

[0004]

BACKGROUND

[0005] In a wireless communication system, such as universal mobiletelecommunication services (UMTS) terrestrial radio access (UTRA), a wirelesstransmit/receive unit (WTRU) sends a channel quality indicator (CQI), (orchannel quality estimates), to a base station. The CQI is used for adaptivemodulation and coding (AMC), channel sensitive scheduling, or the like. Thebase station determines an optimal modulation scheme and coding rate for theWTRUs based on the reported CQIs. The base station also uses the reportedCQIs when determining which WTRUs should be allowed for transmission.[0006] The frequency of generation and transmission of the CQIs iscontrolled by parameters specified by a radio network controller (RNC). Theparameters are given to the WTRU through radio resource control (RRC)signaling at call setup or upon reconfiguration.

[0007] The transmission of CQIs by the WTRUs, although beneficial foroptimizing the capacity on the downlink, generates interference on the uplink.This interference may decrease the uplink capacity of the wirelesscommunication system when the number of WTRUs that are required to transmit,a CQI is large. Furthermore, it is often the case that the transmission of CQIs bycertain WTRUs is superfluous. Such a situation arises when a WTRU has nopending transmission on the downlink due to a period of inactivity at theapplication level. -1- 188071/2 [0008] The interference caused by the transmission of CQIs from non-active WTRUs may be reduced by updating the CQI parameters so that the CQIs are generated by thoseWTRUs less frequently. However, this approach does not work well in practice because theCQI parameter update is performed through the RRC signaling, which is slow. By the timethe CQI parameter update is communicated to the WTRU, the user of the WTRU may haveresumed activity, and performance would suffer until a new update is sent to restore theoriginal frequency of CQI generation.

[0009] In addition, in some circumstances it is desirable to reduce the interference from CQI transmissions during a limited period of time in order to increase the capacityavailable on the uplink when there is a temporary need for more capacity, (e.g., when one userhas a large amount of data to upload, such as a picture).

[0010] Therefore, it is desirable to provide a method to adjust the CQI feedback period more quickly and efficiently to increase uplink capacity.

[0011] US 20051005589 entitled “Apparatus and method for selective power control for an OFDM mobile communication system” discloses a method for controlling downlinkpower transmitted from a base station to subscriber stations in a mobile communicationsystem employing an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, inwhich data is carried from the base station to the subscriber stations by subchannels to each ofwhich a plurality of subcarriers are assigned. The method includes the steps of receiving fromthe subscriber stations channel condition information of each of the subchannels togetherwith information related to a subcarrier having a channel condition below a threshold fromamong at least one subcarrier included in each of the subchannels; calculating transmissionpower for each of the subchannels based on the received information; and transmitting each ofthe subchannels with the calculated transmission power, excluding the subcarrier having achannel condition below the threshold.

[0012] US2004110473A entitled “Reliability detection of channel quality indicator (CQI) and application to outer loop power “ discloses a method for improving the reliability ofa channel quality indicator (CQI) message in a wireless communications network whichbegins with receipt of the CQI message. The CQI message is then decoded, and a decisionmetric value for each symbol in the CQI message is computed. A largest decision metric valueand a second largest decision metric value for the CQI message are determined. The reliabilityof the CQI message can be determined by comparing the two largest decision metric values.This method may be applicable to high-speed downlink packet access in time division duplex,frequency division duplex, or other modes of transmi ssion. 2 188071/1

[0°12aJ SUMMARY

[0012b] jn accordance with an aspect of the presently disclosed subject matter, thereis provided a wireless transmit/receive unit (WTRU) comprising: means for receiving aradio resource control (RRC) message including channel quality indicator (CQI)configuration information, wherein the CQI configuration information indicates a numberof transmission time intervals (TTIs) between CQI transmissions; means for transmitting CQI information in TTIs in response to the configurationinformation; means for monitoring a physical layer downlink control channel; andmeans, in response to the physical layer downlink control channel indicating a CQIcommand and including a cyclic redundancy check (CRC) masked with a WTRU identityassociated with the WTRU, for transmitting CQI information in a TTI in response to theCQI command instead of the received RRC message.

[0012c] In accordance with an embodiment of the presently disclosed subjectmatter, there is further provided a WTRU wherein information on the physical layerdownlink control channel includes a single bit indicating the CQI command.

[0012d] In accordance with an aspect of the presently disclosed subject matter, there is yet further provided a method for use by a wireless transmit/receive unit (WTRU)comprising: receiving a radio resource control (RRC) message including channel qualityindicator (CQI) configuration information, wherein the CQI configuration informationindicates a number of transmission time intervals (TTIs) between CQI transmissions;transmitting CQI information in TTIs in response to the configuration information;monitoring a physical layer downlink control channel; and in response to the physical layerdownlink control channel indicating a CQI command and including a cyclic redundancycheck (CRC) masked with a WTRU identity associated with the WTRU, transmitting CQIinformation in a TTI in response to the CQI command instead of the received RRCmessage.

[0012e] In accordance with an embodiment of the presently disclosed subjectmatter, there is yet further provided a method wherein information on the physical layerdownlink control channel includes a single bit indicating the CQI command. 2a 188071/1 [0012f] In accordance with an aspect of the presently disclosed subject matter, thereis yet further provided a base station comprising: means for transmitting a signal with aradio resource control (RRC) message including channel quality indicator (CQI)configuration information to a wireless transmit/receive unit (WTRU), wherein the CQIconfiguration information indicates a number of transmission time intervals (TTIs)between CQI transmissions; means for receiving CQI information from the WTRU in TTIsin response to the configuration information; means for transmitting a physical layerdownlink control channel to the WTRU, wherein the physical layer downlink controlchannel indicates a CQI command and includes a cyclic redundancy check (CRC) maskedwith a WTRU identity associated with the WTRU; and means for receiving CQIinformation from the WTRU in a TTI in response to the CQI command instead of the RRCmessage.

[0012g] In accordance with an embodiment of the presently disclosed subjectmatter, there is further provided a base station wherein information on the physical layerdownlink control channel includes a single bit indicating the CQI command.

[0012h] The present invention is related to a method and apparatus for adjusting a CQI feedback period to increase uplink capacity in a wireless communication system. The uplinkcapacity is increased by reducing the uplink interference caused by CQI transmissions. Inaccordance with a first embodiment of the present invention, a WTRU monitors a status ofdownlink transmissions to the WTRU and sets the CQI feedback period based on the status ofthe downlink transmissions to the WTRU. In accordance with a second embodiment of thepresent invention, a base station monitors uplink and downlink transmission needs. The basestation determines the CQI feedback period of at least one WTRU based on the uplink anddownlink transmission needs and sends a command to the WTRU to change the CQI feedbackperiod of the WTRU. 2b PCT/US2006/032604 WO 2007/024780

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[00 Ϊ4] Figure 1 is a flow diagram of a process for adjusting a CQI feedbackperiod in accordance with a first embodiment of the present invention.

[0015] Figure 2 is a flow diagram of a process for adjusting a CQI feedback period in accordance with a second embodiment of the present invention.

[0016] Figure 3 is a block diagram of a WTRU which implements theprocess of Figure 1.

[0017] Figure 4 is a block diagram of a base station which implements the process of Figure 2.

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS[0019] When referred to hereafter, the terminology "WTRU" includes but is not limited to a user equipment, a mobile station (STA), a fixed or mobilesubscriber unit, a pager, or any other type of device capable of operating in awireless environment. When referred to hereafter, the terminology "base station"includes but is not limited to a Node-B, a site controller, an access point (AP) orany other type of interfacing device in a wireless environment.

[0020] The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude ofinterconnecting components.

[0021] Figure 1 is a flow diagram of a process 100 for adjusting a CQIfeedback period in accordance with a first embodiment of the present invention.In accordance with the first embodiment, a WTRU autonomously adjusts the CQIfeedback period based on downlink transmission status. The WTRU is initiallyconfigured with a normal CQI feedback period, and the WTRU reports a CQI to abase station via an uplink channel every CQI feedback period.

[0022] The WTRU monitors the status of downlink transmissions to theWTRU (step 102). In monitoring the downlink transmission status, the WTRUmay maintain a counter for counting the number of consecutive transmissiontime intervals (TTIs) that do not include a transmission for the WTRU. Forexample, in high speed downlink packet access (HSDPA), the number of TTIs -3- WO 2007/024780 PCT/US2006/032604 that do not include a transmission for the WTRU may be determined by detectinga valid cyclic redundancy check (CRC) on downlink transmissions on a high speedshared control channel (HS-SCCH). The counter is reset when a valid downlinktransmission to the WTRU is detected, (e.g., in HSDPA, a valid CRC is detectedon the HS-SCCH).

[0023] The WTRU then adjusts the CQI feedback period based on thestatus of the downlink transmissions (step 104). A piece-wise function or a look-up table (LUT) may be used to select a new CQI feedback period based on thecounter value, such that the CQI feedback period is increased as the countervalue increases, and the CQI feedback period is decreased as the counter valuedecreases. An exemplary mapping scheme for mapping the counter value to theCQI feedback period is shown in Table I. As shown in Table 1, the increased CQIfeedback periods may be a factor of the normal CQI feedback period. The basestation may monitor and detect CQIs from the WTRU every normal CQI feedbackperiod regardless of the CQI feedback period setting in the WTRU. With thisscheme, it is avoidable to miss CQIs due to inconsistent CQI feedback periodsettings in the WTRU and the base station. The parameters in Table 1 areconfigurable via a higher layer signaling, which is preferably performed at callsetup.

The number of TTIs without atransmission for the WTRU CQI feedback period 0-31 normal feedback period, P 32-63 2P 64-127 3P 128-511 4P 512 or higher 5P Table [0024] Alternatively, the WTRU may be given multiple CQI feedback periods, (for example, two (2) CQI feedback periods: an active CQI feedback period and an inactive CQI feedback period), via RRC signaling, and may switch between the CQI feedback periods in accordance with the counter value, (i.e., the number of TTIs without a transmission for the WTRU). For example, when the-4- WO 2007/024780 PCT/US2006/032604 counter value is below a threshold, the active CQI feedback period is selected,and when the counter value is equal to or above the threshold, the inactive CQIfeedback period is selected.

[0025] After the WTRU adjusts the CQI feedback period based on thestatus of the downlink transmissions, the process 100 returns to step 102 tofurther monitor the downlink transmission status.

[0026] Figure 2 is a flow diagram of a process 200 for adjusting a CQIfeedback period in accordance with a second embodiment of the presentinvention. In accordance with the second embodiment, a base station sends acommand to increase or decrease the CQI feedback period of the WTRUs based onuplink and downlink transmission needs. The base station increases the CQIfeedback period, (which means less frequent CQI feedbacks), when the uplinktransmission needs increase, while the downlink transmission needs can still besupported with the less frequent CQI feedbacks. As frequent CQI feedbacks arebeneficial to downlink performance, the base station trades downlink capacity foruplink capacity on a short term basis.

[0027] The base station monitors uplink transmission needs and downlink transmission needs (step 202). The uplink and downlink transmission needs aredetermined based on an amount of data buffered in each of the WTRUs for uplinktransmissions and an amount of data buffered in a base station for downlinktransmissions to each of the WTRUs, respectively. The amount of data bufferedin the WTRU for uplink transmission is indicated by the WTRU. For example,such indication may be given by a scheduling request, a happy bit or trafficvolume measurement as in UTRA Release 6.

[0028] Alternatively, the base station may estimate the time required totransmit the data currently in the buffer of each WTRU and the time required totransmit the data buffered in the base station for each WTRU based on averagedownlink and uplink throughput to and from each of the WTRUs.

[0029] The base station determines whether it is desirable to change theCQI feedback period of at least one WTRU based on the uplink transmissionneeds and the downlink transmission needs (step 204). The base station may -5- WO 2007/024780 PCT/US2006/032604 increase the CQI feedback period when the uplink transmission needs are highand the downlink transmission needs are low, and may decrease the CQIfeedback period, (or restore the original CQI feedback period), when the uplinktransmission needs are low or the downlink transmission needs are high.

[0030] For example, if, for at least one WTRU, the estimated time required to transmit data in a buffer of the WTRU exceeds a pre-determined threshold,(i.e., the uplink transmission needs are high), it is desirable to reduce theinterference caused by CQI transmissions by increasing the CQI feedback period.Therefore, the base station determines if some or all of the downlinktransmissions could afford less frequent CQI feedbacks. In order to determinethis, the base station may determine if the estimated time required to transmitthe data in the buffer of the base station on the downlink is within a pre-determined threshold. If it is determined that some or all of the downlinktransmissions may afford less frequent CQI transmissions, (e.g., the estimatedtime required to transmit the data in the buffer of the base station is within thepredetermined threshold), the base station determines to increase the CQIfeedback period.

[0031] If it is determined at step 204 that it is not desirable to change the CQI feedback period, the process returns to step 202 to further monitor theuplink and downlink transmission needs. If it is determined at step 204 that it isdesirable to change the CQI feedback period, the base station then sends acommand to at least one WTRU to change the CQI feedback period of the WTRU(step 206). After sending the command, the process 200 returns to step 202 tomonitor the uplink and downlink transmission needs.

[0032] If the base station subsequently determines that restoring theoriginal CQI feedback period is desirable for some or all of the WTRUs, (i.e., if thebase station determines that the estimated time required to transmit the data inthe buffer of the base station on the downlink exceeds the pre-determinedthreshold, or if the base station determines that the estimated time required totransmit the data in the buffer of each of the WTRUs on the uplink is below the -6- WO 2007/024780 PCT/US2006/032604 pre-determined threshold), the base station sends a command to some or allWTRUs to restore the original CQI feedback period of their CQI transmissions.[0033] The command must be transmitted quickly, (e.g., within a few tensof milliseconds), to the concerned WTRUs or all WTRUs after a decision is madeby the base station. The command may be transmitted by any suitable means.For example, in UTRA Release 6, the command may be sent via an HS-SCCH.During each 2ms TTI, the HS-SCCH includes information necessary for eachWTRU to determine if any data will be transmitted to the WTRU in the next TTI.The HS-SCCH includes bits for indicating a channelization code set combinationfor the WTRU. Currently, there are eight (8) unused bit combinations for thechannelization code set combinations. One of the 8 unused bit combinations maybe used for the purpose of sending the command to change the CQI feedbackperiod. For example, one of the unused bit combinations may be used to signalan increase of the CQI feedback period and another to signal a restoration of theoriginal CQI feedback period.

[0034] The amount of change of the CQI feedback period in response to the command from the base station may be pre-determined, (e.g., by a factor of 2).Increase of the CQI feedback period by a factor of 2 means that every other CQIthat would normally be transmitted with the original configuration is now nottransmitted. Alternatively, the amount of change of the CQI feedback period inresponse to the command may be signaled upon call setup or reconfiguration.For example, two sets of CQI feedback periods may be given to the WTRU, andswitched in accordance with the command.

[0035] The information contained in a specific TTI in an HS-SCCH isnormally only used by one specific WTRU, which is identified through bit-masking of the CRC field with a WTRU-specific sequence, (WTRU identity (ID)).In order to provide a significant interference reduction on the uplink within ashort amount of time, it is desirable that all WTRUs monitoring a given HS-SCCH be commanded a change of the CQI feedback period at the same time.Therefore, a special WTRU ID for all WTRUs may be used to transmit thecommand via the HS-SCCH. -7- 188071/2 [0036] Figure 3 is a block diagram of a WTRU 300 which implements theprocess 100 of Figure 1. The WTRU 300 includes a downlink status monitor 302, a CQIfeedback controller 304 and an LUT 306 (optional). The downlink status monitor 302monitors a status of downlink transmissions to the WTRU. The downlink status 5 monitor 302 may include a counter 308 to count the number of consecutive TTIs that donot include transmissions to the WTRU. The CQI feedback controller 304 sets the CQIfeedback period based on the status of the downlink transmissions to the WTRU asstated hereinabove.

[0037] Figure 4 is a block diagram of a base station 400 which implements the 10 process 200 of Figure 2. The base station 400 includes a monitor 402 and a CQIfeedback controller 404. The monitor 402 monitors uplink transmission needs anddownlink transmission needs. The CQI feedback controller 404 determines the CQIfeedback period of at least one WTRU based on the uplink transmission needs and thedownlink transmission needs and sends a command to at least one of the WTRUs to 15 change the CQI feedback period. 01801273\93-01 -8- , crnxan rwzn ατα pnow pnszn irn πτ “|»oa,ρνιη ηχΰπ naoana ma™ na^maa np’ioz .zruwan rwaa mpnan pmib oxnm□ιηπη Pi?

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