The document discusses energy management issues in LTE networks, focusing on traffic patterns and power-saving techniques. It highlights the challenges posed by frequent transitions between connected and idle states, leading to excessive signaling and battery drain. Solutions such as adaptive DRX switching and user preferences for power savings are explored to balance power efficiency and performance in LTE networks.

1. Energy Management Issues in LTE
Prepared By : Gaurang Rathod
Research Scholar
Wireless Communication
India
rathodgaurang@hotmail.com

2. Agenda
 Introduction
 Energy Usage and Traffic Pattern of Traditional and
Emerging Internet Application
 Energy Management in LTE and DRX
 Power Saving Techniques
 Solutions in LTE Advanced Release 11
 Future Update Scope in LTE
 Conclusion
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3. Long Term Evolution
 LTE is a standard for wireless data communication and
evolution of the GSM/UMTS standards.
 Redesign and simplification of the network architecture
to an IP- based system with significantly high data rate
and reduced transfer latency.
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4. LTE Network Architecture
4[Source:Technical Overview of 3GPP Long Term Evolution (LTE) Hyung G. Myung
http://hgmyung.googlepages.com/3gppLTE.pdf ]

5. E-UTRAN Architecture
5[Source: E-UTRAN Architecture(3GPP TR 25.813 7.1.0)]

6. User Plane Protocol Stack
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 RLC and MAC sub layers perform the following functions
- Scheduling
- ARQ
- HARQ
 PDCP
- Ciphering
- Integrity Protection
- Header Compression
[Source: E-UTRAN Architecture(3GPP TR 25.813 7.1.0 )]

7. Control Plane Protocol Stack
7[Source: E-UTRAN Architecture(3GPP TR 25.813 7.1.0 )]

8. Continue…
 The various functions performed by RRC
- Broadcast and Paging
- RRC connection management
- Mobility functions
- UE measurement reporting and control
 NAS (Non Access Stratum)performs
- Authentication
- Idle mode mobility handling
- Paging origination
- Security control for the signaling between aGW and UE
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9. Traffic Pattern and Energy Usage
 The user equipment (UE) stays in RRC_Connected state
during active sessions and moves to RRC_Idle during
inactive sessions
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Figure: Traffic characteristics of traditional application

10. Continue…
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 UE often ends up moving between connected and idle
states frequently to send mostly short bursts of data
 Draining device battery and causing excessive signaling
overhead in LTE networks
Figure: Traffic characteristics of emerging internet application

11. Problems with Emerging Traffic Pattern
 Time spend in connected state is more compared to idle
state
 In connected state, UE listen to the network and
receive/transmit data. Thus consumes higher power (i.e.
about 1–1.5 W)
 Excessive signaling is required due to frequent transition
between connected and idle states
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12. RRC States and Tail Time
 Tail Time : Time defined by network during which no
packet activity in connected state is done then UE transit
to RRC_Idle state
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13. Inactivity Timer and Signaling Overhead
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 As inactivity timer time increases,
1. Signaling overhead is decrease
2. Duration of connected state is increase
Traffic
Type
Ratio of total data exchanged to total signaling
overhead for various inactivity timer values
1 s 5 s 10 s 15 s
Active
Session
1000 3000 5000 10000
Background
Session
40 100 180 270

14. Discontinuous Reception (DRX)
 DRX cycle optimized for power savings generally leads to
potentially increased delay, affecting the user experience
for delay-sensitive traffic.
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15. Power Saving Techniques
1. Always Connected with DRX
2. Fast Transition to Idle
3. Adaptive DRX Switching
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16. Always Connected with DRX
 UE stays in connected all the time
 Effectively eliminating the signaling overhead
 To save power, parameters for DRX mechanism is
chosen to be similar to when the UE is in idle state
 Example
A high value of long DRX cycle and smaller value of
inactivity timer
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17. Drawbacks of Always Connected with DRX
 If the UE moves between cells frequently while creating
little traffic activity, it will frequently be performing
handovers from one cell to another.
 A handover from one cell to another requires transfer of
all the UE’s configuration information from one eNB to
another and is very signaling-intensive.
 When in idle state, the UE does not have to perform
handovers.
 To maintain connectivity, UE has to perform various
operations periodically such as scanning and providing
periodic channel quality feedback measurements to the
eNB, all of which also consume power.
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18. Fast Transition to Idle
 UE indicates its desire to go to Idle state to the network
and network allow UE to switched to idle state without
waiting for inactivity timer expire.
 Tail time is reduced or eliminated entirely.
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19. Drawbacks of Fast Transition to Idle
 If the UE starts requesting connection releases very
frequently. Excessive transitions also increase the
battery power consumption.
 A prohibit timer can be used to define minimum wait
time between successive requests.
 The eNB may also impose an upper limit on the number
of requests in a predefined time window.
 If the UE crosses the limit, it will be prohibited from
sending further Fast Transition to Idle requests for the
remaining duration of the time window.
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20. Adaptive DRX Switching
 The DRX parameters are switched so as to adapt to
ongoing traffic activity to obtain the requisite balance
between power savings and performance.
 Power Saving : making the DRX long cycle longer (i.e.,
longer sleep in each cycle) and more frequent (i.e.,
shorter Inactivity Timer)
 Performance(Delay) : making the DRX long cycle shorter
and longer Inactivity Timer
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21. Continue…
 UE has the information on remaining battery power, the
number and type of applications running on the device.
 It is better for the UE to indicate to the network to which
DRX configuration to switch.
 This technique has a much better balance between low
power and low delay vs. using only a single DRX
configuration optimized for either power or performance.
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22. Solution Adopted in 3GPP Release 11
 UE assistance mechanism was adopted that enables UE
to send its preference to the network.
 Power Preference Indication Bit : UE can now send a
single bit to indicate its preference for power saving
Future Update Scope
 A single bit of PPI may not be sufficient to express UE’s
various power preferences
 Multiple bits of PPI may need to be incorporated in
future 3GPP releases so that UE can better inform the
network.
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23. Conclusion
 The traffic profile of emerging mobile Internet applications
differs from the traditional traffic profile as it consists of a
constant stream of random aperiodic traffic comprising very
small amounts of data during Inactive sessions, causing the UE
to frequently transition between Connected and Idle states.
Adaptive DRX is one of the main mechanisms envisioned as a
potential solution. It has been shown that DRX configuration
switching is desirable to adapt the requirements of running
applications and to maintain a trade-off between power saving
and latency requirements.
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24. References
1. M.Gupta, S. C. Jha, A. T. Koc, and R. Vannithamby,"Energy impact of
emerging mobile internet applications on LTE networks: issues and
solutions," Communications Magazine, IEEE , vol.51, no.2, pp.90,97,
February 2013.
2. C. Bontu and E. Illidge, “DRX Mechanism for Power Saving in LTE,”
IEEE Commun. Mag., vol. 47, no. 6, June 2009, pp. 48–55.
3. S. C. Jha, A. T. Koc, and R. Vannithamby, “Optimization of
Discontinuous Reception (DRX) for Mobile Internet Applications Over
LTE,” Proc. IEEE VTC-Fall ’12, Quebec, Canada, Apr. 2012.
4. “LTE RAN Enhancements for Diverse Data Applications,” 3GPP TR
36.822, V11.0.0, Sept. 2012.
5. www.tutorialspoint.com/lte/lte_quick_guide.htm
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