The document discusses power control in 3G networks. It describes the need for power control to address the near-far effect in cellular systems and reduce interference. There are two main types of power control: inner loop power control, which operates fast to compensate for fading and distance, and outer loop power control, which operates slower to maintain signal quality. Inner loop power control can be open-loop, where the transmitting device adjusts its power, or closed-loop, where the receiving device provides feedback to adjust transmission power.

1. Power Control
in
3G
Presented By:
 Manish Srivastava

2. Contents

Introduction to 3G

Need for Power Control

Near-Far Effect

Interference in CDMA Cellular Systems

Types of Power Control

Conclusion

3. Some Key Terms…
•Coherence Bandwidth: Measurement of the range of
frequencies over which the channel can be considered “flat”
or in other words, the approximate maximum bandwidth or
frequency over which two frequencies of the signal are likely
to experience comparable or correlated amplitude fading.
•Multipath Fading: Multipath propagation is the
phenomenon that results in radio signals reaching the
receiving antenna by two or more paths. The effects include
construction and destructive interference and phase shifting
of the signal. Destructive interference causes fading. It causes
jitter and ghosting effect in television transmissions and
deceives the radar receiver.
•Shadowing: Signal fading caused due to obstacles.
•MS: Mobile Station
•BS: Base Station

4. Introduction to 3G
3G, short for 3rd Generation, is a term used to represent
the 3rd generation of mobile telecommunications
technology. This is a set of standards used for mobile
devices and mobile telecommunication services and
networks that comply with the International Mobile
Telecommunications-2000 (IMT-2000) specifications by
the International Telecommunication Union.
3G finds application in wireless voice telephony, mobile
Internet access, Fixed Wireless Internet access, video calls
and mobile TV.

5. Need of Power Control

Low signal reception is due to improper power control.
(Near Far Effect)

Efficient power control is very important for CDMA
network performance.

It is needed to minimize the interference in the system.

Reducing the interference results in direct increase in
system capacity.

6. Near – Far Effect
In the uplink direction, all signals should arrive
at the base station’s receiver with the same
signal power. The mobile station cannot transmit
using fixed power levels because the cells would
be dominated by users closest to the base station
and faraway users cannot get their signals heard
in the base station. The phenomenon is called
the near-far effect.
In order to solve this problem we require uplink
power control.

7. The downlink signals transmitted by one base station are
orthogonal (Signals which do not interfere with each
other). However, it is impossible to achieve full
orthogonality in typical usage environments. Signal
reflections cause non-orthogonal interference even if
only one base station is considered. Moreover, signals
sent from other base stations are of course non-
orthogonal, thus they increase the interference level.
The signals should be transmitted with the lowest
possible power level, so that it maintains the required
signal quality.

8. fig. Near–Far Effect in the Uplink Direction
(MS: Mobile Station)
Without Power Control:
Tx level MS a = Tx level MS b = Tx level MS c
Rx level MS a < Rx level MS b < Rx level MS c
With Power Control:
Tx level MS a > Tx level MS b > Tx level MS c
Rx level MS a = Rx level MS b = Rx level MS c

9. Interference Problem
•In CDMA cellular systems, reducing the interference results
in direct increase in system capacity.
•Interference can be reduced by: Sectorisation, voice activity
monitoring, beam forming techniques, diversity techniques
(SSTD), power control.
•Power control is needed in both 3G and near-far problem.

10. TYPES OF POWER CONTROL
Power
Control
Inner Loop Outer Loop
(Open & Closed)

11. INNER LOOP POWER CONTROL SYSTEM

Power control compensates for: distance,
shadowing and multipath fading.

Distance and Shadowing affects: On both FW(BS to
MS) and Rev.(MS to BS) Links.

Mobile measure signal on the FW link and adjusts its
power accordingly.

12. 
Multipath fading:
Frequency separation between FW and Rev. links >>
coherence BW of the channel.
Hence, both links fade independently. Base station
has to tell the mobile how to adjust its power.

The rate of change in the channel is function of:
mobile speed, number of fading resolvable paths,
carrier frequency, etc.

13. OPEN LOOP POWER CONTROL SYSTEM
•
The open loop power control technique requires that
the transmitting entity measures the channel
interference and adjusts its transmission power
accordingly.
•
In this process, the MS estimates the transmission
signal strength by measuring the received power level
of the pilot signal from the BS in the downlink, and
adjusts its transmission power level in a way that is
inversely proportional to the pilot signal power level.
•
Consequently, the stronger the received pilot signal, the
lower the MS transmitted power.

14. CLOSED LOOP POWER CONTROL
•
In the closed-loop power control technique, the quality
measurements are done on the other end of the
connection in the base station and the results are then
sent back to mobiles transmitter so that it can adjust its
transmitted power.
•
This method gives much better results that the open
loop method but it cannot react to quick changes in the
channel conditions.

15. FAST CLOSED-LOOP POWER CONTROL TECHNIQUE
•In this method, the received SIR is measured over a 667
microseconds (one Time period), and based on that value, a
decision is made about whether to increase or decrease the
transmission power in the other end of the connection.
•The transmit power control (TPC) bits are sent in every time slot
within uplink and downlink. All power control signals contain
either an increase or decrease command.
•In uplink, When BS receives the UE signal it compares the
signal strength with the pre-defined threshold value at the BS. If
the UE transmission power exceeds the threshold value, the BS
sends a Transmission Power Command to the UE to decrease its
signal power. If received signal is lower than the threshold target
the BS sends a command to UE to increase its transmission
power.
•In downlink, the roles of UE and BS are interchanged.

16. TWO SPECIAL CASES FOR FAST CLOSED
LOOP POWER CONTROL

Soft Handover: How to react to multiple power
control commands from several sources. At the
mobile, a “power down” command has higher
priority over “power up” command.

Compressed Mode: Large step size is used after a
compressed frame to allow the power level to
converge more quickly to the correct value after
the break.

17. Fig. Uplink Closed Loop Power Control
Fig. Downlink Closed Loop Power Control

18. Thank You!!!