1. CDMA dynamic reverse link power control with variable quality of service
Sunjeev Kumar gupta, Ranjit kumar karma
Department Of Electronics and Computer
Kathmandu Engineering College, Kathmandu, Nepal
ABSTRACT
For wireless communication systems, In this paper, we propose new dynamically
iterative power control algorithms have been power control with QOS for different substreams
proposed to minimize the [2]. For this, we study first the embedded trellis
transmitter power while maintaining reliable coded modulation for UEP on which punctured
communication between mobiles and base convolutional codes have been applied for reliability
stations. A digital cellular radio code- of a substreams increased through migration from
division multiple-access (CDMA) system can only high rate to low rate code. But we found difficulties
support a finite number of users before the to provide trellis equivalent of variable rate
interference plus noise power density, I0, received at convolution code by varying constellation size so
the cellular base station causes an unacceptable proper solution is to perform UEP by using a fixed
frame-error rate. Once the maximum interference rate trellis code & varying power. This makes
level is reached, new arrivals should be blocked. In beneficial to transmit the minimum power necessary
a power-controlled CDMA system, the base station to support the given QOS for a substream as this
can direct mobiles to reduce their power and data creates least interference to other users.
rate to reduce interference and allow more users on
the system. In current IS-95 systems, forward link 2. NECESSITY OF POWER CONTROL
power control is far less powerful than reverse link
power control. Thus, this paper presents an All users in CDMA share the same RF band
algorithm to focus on the current IS-95 reverse link through the use of PN codes, each user looks like
power control but in a more general sense, it random noise to other users. So power of each
presents a systematic approach to the designing of a individual user therefore must be carefully
power control unit. In this paper, we present a controlled so that no one user is unnecessarily
power control algorithm, which simultaneously interfering with others who are sharing the same
minimizes interference & also provides variable band. Under no power control the MS nearer to the
QOS contracts for different traffic types in a CDMA BS transmits higher power than the MS far from the
system by assigning different power levels to each BS transmits lower power. This makes greater
traffic type. enjoyment to the MS nearer to the BS than others.
This is the classic near-far problem in SSMA
1. INTRODUCTION system.
Power control is implemented to overcome
A substream of the individual user (concept near-far problem & to maximize capacity by the
similar to internet protocol defines flow headers to action of controlled transmitted power from each
support variable QOS across different applications) user such that received power of each user is equal
consist of one media type (audio or video).The to one other.
substream abstraction enhances network efficiency
by only the appropriating more resources.
Substrems are variable rate & multiplexed into one
aggregate stream for each user. Sum of substream
bit rates for any user don‟t exceed total bit rate of
that user‟s stream [1]. Each stream then undergoes
channel coding, modulation & power control before
being assigned a spreading code & transmitted.
Different substream consists of audio, video & data
all have different unequal error protection so that
higher efficiency is made for protecting must
significant bits than to least significant bits.
Fig.1 Power Controlled System

2. One problem that has to be immediately identical to reverse path loss. So better Closed Loop
solved in power control is initial mobile transmit Power Control (CLPC) is forwarded to compensate
power which can‟t be controlled by the BS.So the for power fluctuation due to fast reyleigh fading
best solution is the MS to attempt to transmit a involving both BS & MS. CLPC continues measures
series of access probe i.e. a series of transmissions the link quality along with OLPC & its contribution
of progressively higher power. This process is in reverse link (uplink) is as follow:
continued until the BS acknowledgment & step size  BS continuously monitors Eb/No on
for the access probe correction is specified by reverse link.
system parameter PWR_Step.  If Eb/No is too high (exceeding certain
Knowing received power & ERP of BS, threshold) then BS commands MS to
MS would know how much it needs to transmit decrease it‟s transmit power & vice versa.
power to compensate path loss [3]. But in reality,  The power control commands are in the
MS neither know ERP of BS nor received power form of power control bits & amount of
contributed by the neighboring BS, So generic power up & down per PCB is normally
assumptions of initial power transmission of MS in +1dB or -1dB.
decibels:
Ptinitial=-Pr – 73 + NOM_ PWR + INIT_PWR. Since, CLPC is combated Rayleigh fading, MS
Where NOM_PWR & INIT_PWR are the response to these PC commands must be very fast
adjustments factors. These adjustment factors are .So Power Control Bits (PCBS) are directly sent
broadcasted by MS in access parameter message. over traffic channel by robbing some bits from
traffic channel.
Fig.3 PCBS are multiplexed directly onto
baseband system at 19.2 Kbps
The PCBS are integrated into traffic
channel by robbing selected bits from baseband
Fig 2 Initial transmit power stream. The stream of PCBS at 800 bps is Power
Control Sub channel (PCS). Since the rate of PCB
2.1. POWER CONTROL PROCESS transmission is 800 bps, a PCB is sent once every
(1/800) second or 1.25 ms. Since PCB is sent every
After initial power transmission, two methods 1.25 ms, each traffic channel frame is divided into
open loop & closed loop power control in (20 ms/1.25 ms) or 16 segments called Power
proceeded. After a call is established & as MS Control Groups (PCGS). Since each PCG is 1.25 ms
moves around within cell, path loss between MS & in duration & baseband is at a rate of 19.2 Kbps then
BS will continue to change, so received power at each PCG contains (19.2 *1000)*(1.25*1000) OR
MS will change & open loop power control will 24 bits.
continue to monitor MS received power Pr & adjust In a closed loop section, for example BS
MS transmit power. measures Eb/No in PCG7, decide in PCG8 for
Pr= -Pr -73 + NOM_PWR + INIT_PWR + (sum inserting 0 or 1 & transmit decided 0 or 1 during
of all access probe correction). PCG9 on forward traffic channel. This process is
Open Loop Power Control (OLPC) is used to repeated for every power control group in the frame
compensate for slow-varying & log-normal [4]. The PCG can be inserted in any one of 1 st 16
shadowing effects but inadequate to compensate fast positions. The exact location of PCB in PCG is
Rayleigh fading coz of frequency dependency & determined by decibel value of four most significant
works under assumption of forward path loss is bits of decimator output.

3. Fig 4 Closed loop power control using PCBS
Closed loop power control has inner loop & outer
loop.
Fig 5 Schematic CLPC
Inner loop decides the power up & down decision
by threshold decision. Outer loop makes
dynamically adjusted to maintain an acceptance
FER. This CLPC is also assisted by the soft handoff
process.
3. PROPOSED CONTROL SYSTEM Fig 6 Reverse link PC functions carried out by BS.
The reverse link power control with the On the MS side, it receives forward link
multiple co-ordinations of substreams leading the signal. It recovers PCB & based on PCB, makes a
variable quality of service scheme is shown a below. decision (closed loop decision) to power up/down
The fig. 6 shows high level schematic of the system by (1 dB).This correction is combined with open
considered. The subsystems for each user are loop terms & combined result is fed to transmitter
statically multiplexed into one stream (How this is so that it can transmit at the power (proper) level.
done in accordance with the substreams‟ different
delay bounds will not be described in this
paper).The stream then undergoes channel coding,
modulation & power control before being assigned a
code & transmitted. BS demodulates & estimate
FER of reverse link, this information on reverse link
frame quality is fed into threshold which adjusts
(Eb/No) based on received frame quality. The PCB
are multiplied onto forward traffic channel &
transmitted to MS [5].

4. - If feasible, how do we allocate power to each
substream?
- Hoe do we decide if we can admit a new stream
without violating the reliability guarantees for
streams in progress?
In this paper we don‟t consider the reliability
requirement of a substream by its desired E/I
(remains for future work)
Let
K= No of substreams.
(Eb/No)= E/I required by substream I, i= 1,
2……K.
βi = 1, if substream I is transmitting during the
current time slot
0, otherwise
xi = Power assigned to substream I given that it
is transmitting during current time slot
P = Total Power
N = Spreading Code Processing Gain
σi2 = Intercell interference experienced by
stream i.
The E/I experienced by substream „i‟ is
given by the expression
Nxi
E/I= ………Eq. (1)
( i     k xk )
k i
We wish to minimize total power subject to
constraints that E/N for every substream is satisfied
i.e. minimize
k
P    k xk ……….Eq. (2)
k 1
such that
Nxi
( i    k xk )

≥ E N 
b
oi
..........Eq. (3)
k i
For i=1....k
xi ≥0 and (Eb ) >0 ............Eq. (4)
N
The Eq. (4) can be expressed in the form of linear
program matrix as
Fig.7 Reverse link Power Control functions carried 

1
N
- Eb 
No 1 2
   - Eb  N 
o1 k


out by MS.


A=  - Eb 
No 2 1
 1
N
 - E
b
N

o2 k 

4. POWER CONTROL ALGORITHM      
Before PC, each of the substrams has its 

 Eb
-
No k 1

 - Eb No  2
k
   1
N



own desired reliability requirement, we wise to .........Eq. (5)
address three issues [6]:
- How to determine if the set of requirement is
feasible or not?

5.  xi 
 
  1 Eb

2
No 1 
   [2]K.S. Gilhousen et al, “On the capacity of a
cellular CDMA system,”IEEE Trans. Vehicular
X=    , b=   , Technology, vol. 40, no. 2, pp. 303-312,
x 
 k
 2 Eb
1
 No k 

   May1991.
[3]Theodore S. Rapport,” Wireless Communication,
Principles & Practice,”2nd Edition, Published in
c = 1   k .........Eq. (6) New Delhi, 2005.
The above equations are modified as: [4]Samuel C. Yang,” CDMA RF Signal
Minimize cx such that Engineering,” London, ISBN 0-89006-991-
Ax ≥ b, x ≥ 0 .......Eq. (7) 3.1998.
The Eq. (7) is solved optimally for finding closed [5]Qualcomm Inc., “Compatibility Standard for
form optimal solution to the system. Dual-Mode Wideband Spread Spectrum Cellular
A feasible solution to the system Ax=b, x ≥ 0 is System,” TIA/EIA/IS- 95, July 1993.
obtained by considering following assumptions: [6]Google search as www.power control algorithm
xi = i i  i2  P  ......Eq. (8)
class based power control algorithm in cdma.html.
Where
α=
E N  , i=1....k
b
N  E 
o
i ......Eq. (9)
b
N oi
And total transmitted power
k
  k k k2
P= k 1 ......Eq. (10)
k
1    k k
k 1
From Eq. (10), 0≤ P≤ ∞ if and only if
k
  k k < 1 ......Eq. (11)
k 1
If Eq.(11) holds true, then x ≥ 0 and Eq. (8) & (9)
represent a finite.
Now from Eq.(1) & (11), under comparison , βk is
constant integer so, x<<1≈ 0 provides unique
solution to the system [Ax ≈ 0].
5. CONCLUSION
Dynamically PC algorithm performs the
task of closed loop power control as well as QOS
improvement Substream concept enhances network
efficiency as well as combating of both near far
problem & self -jamming/anti-jamming problem. It
reduces the MS transmission power & the capacity
of the system enhances but system becomes more
complex in the case of substream division.
6. REFERENCES
[1]Research documents from University of
California at Berkeley, Berkeley, CA94720
published by Louis C. Yun and David G.
Messerschmitt.