the idea is to extend battery life by using the minimum possible power while maintaining reliable communications. From the point of any cellular network, proper power control helps in keeping interference at a manageable level while improving capacity and the overall service to the mobile subscriber. UMTS, unlike SM, has a greater need to combat the near!far problem. " U# close to the $ode!% transmitting at the same power as another at the cell edge, will potentially block out the latter. To To maintain reliable links to all U#s, the received power at the $ode!% should be about the same. This means that propagation path loss between theU# and the $ode!% should be taken into account. &n an ideal environment, this alone is sufficient. %ut real environments are rarely ideal. 'hannel conditions vary,, in the short term and in the long term. (ecogni)ing all these, we can relate easily to the three vary main power control mechanism in UMTS* +.
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5.
pen loop power control* control * this relates directly to the path loss. "s the name suggests, this control has no feedback. &t simply sets the initial power at which the U# should transmit. This initial settings happens via ((' signalling. This control is in the U# and the ($'. Outer loop power control* control * this relates to long term variations of the channel. " target S&( is specified. &f the received S&( is less than this target, transmit power needs to be increased. -therwise, it needs to be decreased. &n practice, / target 0uality is in terms of transport channel block error ratio ratio 1%/#(2. The %/#( can be related to a target S&(. &f the received S&( is less than the target, %/#( is likely to be not met. "lternatively "lternatively,, if the %/#( is more than the target, transmit power has to be increased. This control is in the U# and the ($'. This is also known as slow closed loop power control. &t happens at the rate of +3!+33 4). Inner loop power control* control * this is also known as fast closed loop power control. &t happens at a rate of +633 4) to combat fast fading. This control is with the U# and the $ode!%. 7hile outer loop control is set at ((' level and executed at /ayer +, fast power control happens at /ayer + in order to meet the %/#( target set by outer loop control. The effect of this control is that even in a fading channel, the received power is maintained constant so as to achieve the %/#( target. This is represented in Figure + 89. Figure 1: UMTS Fast Power Control Combating Fast Fading
Fast power control is important in keeping interference to a minimum and improving capacity. 7ithout 7ithout it, transmit power would have higher to meet 0uality targets. The gain from this control is as much as 6.: d% at the receiver for pedestrian pedestrian speeds for :kbps speech with +3ms interleaving and antenna diversity.. The gain is less at the transmitter and for higher speeds 89. diversity The problem with fast power control are the spikes in power when deep fades are encountered. This may be necessary for the connection but it also introduces interference to neighbouring cells where the U#s may not necessarily be experiencing adverse channel conditions. (ecogni)ing this fact, the rate of fast power control can be ad;usted to suit the need. For example, for non!real time services, a higher %/#( can be tolerated. "s a result, i t is permissible to be in a fade and lose packets, leaving it to (/' to retransmit. So although +633 4) is the maximum rate, both U/ and / allow for lower rates by which it is meant that T<' bits do not change from slot to slot. For / power control, <'=M-# <'=M-# controls this behaviour enabling the use of same T<' for 5 slots. For U/ power control, >
that ad;ust the transmit power. power. These gain factors are set independent of fast power control. For <("'4, the preamble and the message parts can operate at different power levels. &f #!'4 is used, the power levels of #!<''4 and #!<'4 can be different and are in relation to <''4 and <'4 powers. &n the /, <''4 and <'4 are time multiplexed and each can operate at a different power. &n addition, different fields of / <''4 can operate at different power levels. ifferent / channels can operate at different power levels. &f compressed mode is enabled, f urther dynamics are involved. The step si)es 1in d%2 for power ad;ustment can also be varied at the same rate as outer loop power control. Specific rules apply for F!<'4.
Why Power Control? •
All UMTS users occupy the same frequency spectrum at the same time! Frequency and time are not used as discriminators
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UMTS operates y usin" codes to d iscriminate etween users
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UMTS interference comes mainly from neary users
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#ach user is a small $oice in a roarin" crowd %% ut with a uniquely reco$erale code
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To achie$e acceptale ser$ice quality& the the transmit power of all users must e ti"htly controlled so that their si"nals reach the ase station with the same si"nal stren"th and the asolute minimum power le$el demanded to a$oid the 'ear%Far #ffect
'ear%Far #ffect
#('o ) Power Control
Fast Power Control
Purpose of Power Control
Cate"ory of Power control
Open Loop Measure the channel interference condition and adj ust the initial transmitted power Close Loop Inner Loop Measure the S*+ ,Si"nalin" to *nterference +atio-& compare with the tar"et S*+ $alue& and then send power control instruction to U# The frequency of WC.MA inner loop power control is /01123 *f measured S*+4tar"et S*+& decrease the U# transmitted power *f measured S*+ Close Loop Outer Loop Measure the 56#+ ,5loc7 #rror +ate-& and ad8ust the tar"et S*+ The frequency of WC.MA outer loop power control is /19/1123 *f measured 56#+4tar"et 56#+& decrease the tar"et S*+ $alue *f measured 56#+
:pen 6oop Power Control Unalanced for U6(.6 si"nal& not accurate& only used in initial sta"e
:pen loop power control
Close 6oop ; *nner 6oop Power Control
Close 6oop ; :uter 6oop Power Control
Closed 6oop Power Control
R99 Power Control
Physical +andom Access Channel
Uplin7 open loop power control of P+AC2 •
Preamle<*nitial
power ; CP*C2<+SCP U6 interference Constant @alue Primary CP*C2 .6 T> power is the transmit power of the main pilot channel
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,S*50(- o
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U6 interference is the uplin7 interference& which is measured and otained y 'ode5 and updated in real time in S*5B Constant @alue is a $alue related with the cell en$ironment *t is a $alue depends on the ser$ice rate and quality carried y P+AC2 *f the $alue of Preamle<*nitial
Transmit power of P+AC2 messa"e part •
Power +amp Step is the power offset etween two continuous preamles
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Pp
Uplin7 .edicated Physical Channel
Uplin7 open loop power control of dedicated channel •
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.PCC2<*nitial
#('o is the quality factor of the .PCC2 P*6:T domain
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'T*T is the uplin7 interference& which is otained y 'ode5 throu"h measurement and updated in real time in S*5B
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PD is the spectrum spread "ain& E0
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CP*C2
.PCC2 ) .P.C2 power "ain factor
.ownlin7 common channel initial power The transmit power of P%CP*C2 depends on the proportion of maimum transmit power of a
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cell The $alues of P%CCPC2& P%SC2& S%SC2& A*C2& and P*C2 depend on the offset to P%
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CP*C2 •
The transmit power of the data domain of S%CCPC2 depends on the PC2 transmit power and the maimum $alue of the maimum transmit power of FAC2 The transmit power of the TFC* domain and Pilot domain of S%CCPC2 are indicated respecti$ely y the offsets ,P:/ and P:- as opposed to the transmit power of the d ata domain
.ownlin7 .edicated Physical Channel
.ownlin7 open loop power control of dedicated channel
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PD is the ser$ice processin" "ain
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Pt&CP*C2 is transmission power of the CP*C2 ,d5m-
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#c%cpich('o is CP*C2 #c('1,d5- reported y the U#
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Gmin is the lower limit of the downlin7 ortho"onal factor
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Gma is the upper limit of the downlin7 ortho"onal factor
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7 is the coefficient factor *ts fied $alue is 11/
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6 represents path loss 6 is otained from the measurement result reported y the U# *f 6 cannot e otained& its $alue is /1d5
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7/ and 7E are scenario parameters
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Pt&total is the total transmit power of a cell efore a suscrier accesses the cell
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H=/1I,,#('1-(/1-& where #('o is the #('o of the su%ser$ice confi"ured correspondin" to the current rate of the access ser$ice Power:ffset is different for different situation
.ownlin7 open loop power control of dedicated channel
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:n the .PC2& the its of TFC*& TPC and P*6:T are also multipleed esides the data its ecause the information carried y these its is important Therefore& the needed power is also a little hi"her than that of the data domain The power $alue depends on the offset as opposed to the power of the data domain and is indicated with P:/& P:E and P: respecti$ely
Uplin7 inner loop power control •
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At the recei$in" end& the S*+ measurement ,S*+=#('o- is done for each recei$ed radio lin7 The measurement result is compared with the tar"et S*+ ,S*+tar"et- required y the ser$ice *f S*+ J S*+tar"et& control information is returned to the sender with a transmit power command whose it $alue is 1 *f S*+ K S*+tar"et& a TPC command whose it $alue ein" / is returned throu"h the downlin7 control channel to the sender The sender 8ud"es whether to increase or decrease the transmit power dependin" on the recei$ed TPC command and specified power control al"orithm
Uplin7 inner loop power control al"orithms •
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Al"orithm /L the transmit power of sender can e ad8usted in e$ery timeslot #ach timeslot& the recei$er 8ud"es& whether to increase or d ecrease the transmit power of the sender dependin" on the recei$ed TPC command Suppose the TPCs of all radio lin7 sets are /& then TPC
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Transmit power is not ad8usted in the first four timeslots ,TPC
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Al"orithm / is to perform inner loop power control at each timeslot& while al"orithm E is to perform inner loop power control only once e$ery fi$e timeslots That is& the frequency is hi"her to perform inner loop power control in al"orithm /& When the en$ironment of moile communication is quite unfa$ourale and the channel fades $ery quic7ly& al"orithm / helps the transmit power to con$er"e fast to meet the ser$ice quality requirement With al"orithm E& the inner l oop power control is performed e$ery fi$e timeslots& that is& the frequency is lower to perform inner loop power control in al"orithm E So al"orithm E is applicale when the en$ironment of moile en$ironment is quite fa$ourale and the channel fades slowly or hardly fade
.ownlin7 *nner 6oop Power Control •
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Al"orithm /L U# sends a TPC command at each timeslot The UT+A' ad8usts the transmit power at each timeslot accordin" to the TPC command Al"orithm EL U# sends a TPC command for three timeslots The UT+A' ad8usts the transmit power once e$ery three timeslots accordin" to the TPC command Al"orithm / is for fast channel fadin" and Al"orithm E for slow channel fadin"
Uplin7 :uter 6oop Power Control •
The initial S*+Tar"et $alue is determined upon ser$ice access& and produce the decision command y the quality information that is otained from the measurement report *f ad8ustment is necessary& S*+Tar"et is ad8usted slowly and is used to notify 'ode5 'ode5 compares the S*+ in the dedicated measurement report with the latest S*+Tar"et and ma7es the sin"le lin7 S*+ approach to S*+Tar"et throu"h inner loop power control *n this way& the ser$ice quality will not fluctuate drastically in a chan"in" radio en$ironment
Uplin7 :uter 6oop Power Control al"orithms
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Principle for increaseL When the tolerance 56#+ period ,56#+AccpPeriod- has not epired yet& ut the numer error loc7s has alr eady eceeded the error transport loc7 numer threshold ,#rrorThresh-& now increase S*+Tar"et Principle for decreaseL When the error l oc7 tolerance counter is no less than the tolerance 56#+ period ,56#+AccpPeriod- .ecrease S*+Tar"et if now the recei$ed numer of error loc7s is less than the error transport loc7 numer threshold ,#rrorThresh- eep the S*+Tar"et same if now the recei$ed numer of error loc7s equals to the error transport loc7 numer threshold ,#rrorThresh-
.ownlin7 :uter 6oop Power Control The downlin7 outer loop power control is reali3ed in the U# +'C pro$ides 56#+tar"et to U#
Control Part Dain Factor
HSDPA Power Control
Total Power Allocation of 2S.PA
Static allocation y +'C •
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Count eforehand the a$era"e data throu"hput in a related area& and estimate the numer of 2S%P.SC2s to e confi"ured and needed power Confi"ure the percenta"e of power occupied y 2S.PAL 2spaPwr+atio in :MC+ *f the resource has to e reallocated due to chan"es in the a$era"e data throu"hput in this area& ma7e the confi"uration in :MC+ a"ain and notify 'ode 5
.ynamic allocation y +'C •
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*nitial 2S%P.SC2 and 2S%SCC2 total power ,2spaPwr+atio- are confi"ured in :MC+ accordin" to the numer of physical 2S%P.SC22S%SCC2 channels confi"ured for the cell 2spaPwr+atio is ad8usted dynamically alon" with the power occupation ratio y non%2S.PA and 2S%.SC2 users
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2spaPwr+atio is dynamically ad8usted when the 2S.PA resource con"estion occurs
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The o$erload control module tri""ers 2spaPwr+atio to decrease in the e$ent of o$erload
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When there is no 2S%.SC2 user& 2spaPwr+atio can only e decreased alon " with the power chan"e of non%2S
.ynamic Power Ad8ustment for 2S.PA and .PC2
Free allocation of 'ode 5 Free power allocation is determined y al"orithm of 'ode 5 ased o n a$ailale power& ser$ice priority and NoS +'C should ha$e the allowed a$ailale power of 2S.PA confi"ured as /11O
2S%.PCC2 AC Power :ffset for Sin"le +adio 6in7 or *ntra%'ode 5 2ando$er
2S%.PCC2 'AC Power :ffset for Sin"le +adio 6in7 or *ntra%'ode 5 2ando$er
2S%.PCC2 CN* Power :ffset for Sin"le +adio 6in7 or *ntra%'ode 5 2ando$er
2S%.PCC2 AC Power :ffset for *nter%'ode 5 2ando$er
2S%.PCC2 'AC Power :ffset for *nter%'ode 5 2ando$er
2S%.PCC2 CN* Power :ffset for *nter%'ode 5 2ando$er
Pendin" Times Threshold for Power 5alance 5etween .PC2 and 2S.PA
2SPA Total .ownlin7 Power Allocation Method
2SPA Total .ownlin7 Power
Minimum 2SPA Total .ownlin7 Power
Maimum 2SPA Total .ownlin7 Power
There are total 3 types of power control in WCDMA: * Open Loop * Inner Loop * Outer Loop Open Loop Power Control: The open-loop power control technique requires that the transittin! entity easures the channel interference an" a"#usts its transission power accor"in!ly$ This can %e "one quic&ly' %ut the pro%le is that the interference estiation is "one on the recei(e" si!nal' an" the transitte" si!nal pro%a%ly uses a "i)erent frequency' which "i)ers fro the recei(e" frequency %y the systes "uple+ o)set$ As uplin& an" "ownlin& fast fa"in! ,on "i)erent frequency carriers "o not correlate' this etho" !i(es the ri!ht power (alues only on a(era!e$ Inner Loop:In this etho" the recei(e" si!nal-to interference ratio ,.I/ is easure" o(er a 001- icrosecon" perio" ,i$e$' one tie slot' an" %ase" on that (alue' a "ecision is a"e a%out whether to increase or "ecrease the transission power in the other en" of the connection$ 2ote that the "elay inherent in this close"-loop etho" is copensate" for %y a&in! the easureents o(er a (ery short perio" of tie$ The transit power control ,TC %its are sent in e(ery tie slot within the uplin& an" the "ownlin&$ There is not a neutral si!nal4 all power control si!nals contain either an increase or "ecrease coan"$ Outer Loop : The outer loop power control functions within the %ase station syste' an" a"#usts the require" .I/ (alue ,.I/tar!et' which is then use" in the inner loop control$ Di)erent channel types' which can %e characteri5e" %y' for e+aple' "i)erent co"in! an" interlea(in! etho"s' constitute a channels paraeters$ Di)erent channel paraeters ay require "i)erent .I/tar!et
