8/11/2019 Why Power Control is Not Used in HSDPA

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Why Power control is not used in HSDPA?Let us begin with HSDPA for which power control is significantly differentfrom R99 channels. HSDPA does not have fast power control as in R99 DLDP H. However! power control is "ust as important for HSDPA. #nner looppower control happens implicitly in HSDPA based on Adaptive $odulationand oding %A$ &. 'his can be understood by ac(nowledging that ) D$A isan interference limited system. Although reducing power! results in reducedinterference this does not have significant impact for users close to the*ode+,. Such users do not benefit much by decreasing power nor doessystem capacity increase. #t is (nown that power control dynamics is only -d, in DL and / d, in 0L. ,eyond the - d, limit! new techni1ues such asA$ are more beneficial.

'hus! when users close to the *ode+, e2perience e2cellent channel

conditions! modulation could be changed from 3PS4 to 56 3A$ with anadditional increase in coding rate %less redundancy&. 'his increasesbandwidth for a given user. )ithin the cell7sector! fast scheduling %anothernew feature in HSDPA& enables 1uic( decisions so that one user may begiven7denied more resources for relatively short time periods to ma(e thebest use of channel conditions at that moment in time. 'his increases overallsystem capacity towards what is optimal. Such benefits were not possiblewith only R99 fast power control.

)e can infer that power control is done implicitly because when modulationand coding are changed based on 3# feedbac( received from the 08 on 0LHS+DP H! *ode+, will also ad"ust its transmission power. 8very 3# isassociated with a reference power offset that is used by the 08 when itcalculates the 3# to send to the *ode+,. 'his calculation is also dependenton the 08 category.

f course! open loop power control e2ists. 'he *ode+, is commanded by theR* with specific power offsets. 'here is a power offset for HS+S H that:srelative to DL DP H power. ;or HS+PDS H! where multiple codes are used!all codes will be transmitted with the same power <'S -=.-5>! =.-.55?. 'hetransmission that the *ode+, can use for HS+PDS H is indicated as a

percentage of the total power available to the *ode+,. 'his is indicated forevery priority class with weights for every 08. 'hus! differentiation in termsof priority and 08 is partly implemented with these power weights. #t is thenleft to the *ode+, to manage these power profiles efficiently. 'his is animplementation issue and has been the sub"ect of many patents.

8/11/2019 Why Power Control is Not Used in HSDPA

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How Power Control is implemented in HSDPA?

Initial Power is set in the same way as open Loop Power control of DCH & there is no further power control on HSDPA Shared Channel HS-DSCH. The Channel ate is controlled !yadapti"e modulation & codin# formats.The principles and functionality of the power control for the HSDPA associated dedicatedchannels are the same as for the DPCH power control.HS-DPCCH power is an ofset relative to DPCCH depending upon whether the UE isin so t handof or not.

The Power or HS-SCCH is xed.