This presentation covers: What is a Radio Resource Unit ? Why do we need RRM ? Need of RRM in WCDMA ? RRM algorithms Objectives Different RRM functions : Handover, Power control, Admission Control, Code Management

1. Radio Resource Management in
WCDMA
Presentation by:
Naveen Jakhar, ITS
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2. Topics covered in this presentation:
 What is a Radio Resource Unit ?
 Why do we need RRM ?
 Need of RRM in WCDMA ?
 RRM algorithms Objectives
 Different RRM functions : Handover, Power control, Admission
Control, Code Management
 Conclusion
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3. Radio Resource Unit:
 A Radio Resource Unit (RRU) is the set of basic physical transmission
parameters necessary to support a signal waveform transporting end
user information
For example, in GSM, a radio resource unit is a 0.577 ms time slot
period every 4.615 ms on a 200 KHz carrier in the 900 MHz, 1800
MHz or 1900 MHz bands
 In CDMA, a radio resource unit is defined by a carrier frequency, a
code sequence and a power level
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4. Brief about UMTS and WCDMA:
 Universal Mobile Telecommunications System (UMTS) is a 3G cellular
telecommunication system, successor of GSM
 UMTS is designed to cope up with the growing demand of mobile
and internet applications with required quality of service parameters
 WCDMA is used for the radio interface of UMTS
Along with traditional telephony and data services offered by GSM,
UMTS will offer more high speed services to mobile equipment users
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5. Radio Resource Management:
 The delivery of multimedia services to the mobile user is one of the
goals of 3rd generation mobile communication system
 In a multiservice scenario, each service may require that a different
amount of radio resource units are supported. Services with higher
bit rates will, consequently, require more radio resource units
 The use of several different services at the same time raises the
demands for mechanisms to guarantee Quality of Service (QoS) for
each application
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6. Why do we need Radio Resource Management?
 The Cellular mobile communications are dynamic in nature
 Dynamism arises from multiple dimensions: propagation conditions,
traffic generation conditions, interference conditions
Thus, the dynamic network evolution calls for a dynamic
management of the radio resources, which is carried out by RRM
mechanisms
 Radio Resource and QoS management functionalities are very
important in the framework of WCDMA systems because the system
relies on them to guarantee a certain target QoS, maintain the
planned coverage area and offer a high capacity, objectives which
tend to be contradictory
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7. Why do we need Radio Resource Management?
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8. Why do we need RRM in WCDMA ?
 In WCDMA, users transmit at the same time and frequency by means
of different orthogonal spreading sequences
 The maximum available capacity in case of WCDMA is tightly
coupled to the amount of interference in the air interface
 Efficient management of radio resources may not involve an
important benefit for relatively low loads, but when the number of
users in the system increases to a critical number, good radio
resources management will be absolutely necessary
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9. Why do we need RRM in WCDMA ?
 The QoS parameters may be classified into two different levels:
network-level (such as blocking probability, dropping probability) and
connection-level (such as bit error rate, maximum transmission rate)
 One of the most important RRM tasks is to guarantee that every
single connection achieves the target Eb/No that ensures the BER
requirement
 The RRM functions need to adjust dynamically with : number of
simultaneous users, Bit Rate and Power Level
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10. 10

11. Why do we need RRM in WCDMA ?
 The number of users having a call in progress are defined as active
users – camping users and transmitting users
 Within a WCDMA cell, all users share the common bandwidth and
each new connection increases the interference level of other
connections, affecting their quality expressed in terms of a certain
Eb/No
 Capacity and coverage are closely related in WCDMA networks, and
therefore both must be considered simultaneously. The coverage
problem is directly related to the power availability, so the power
demands deriving from the system load level should be in accordance
with the planned coverage
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12. Different RRM functions in WCDMA:
 Open loop Power control
 Closed loop: Inner loop Power control
 Closed loop: Outer loop power control
 Admission control
 Code management
 Handover
 Congestion control and Cell breathing
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13. Admission Control:
 Admission control decides the admission or rejection of requests for
set-up and reconfiguration of radio bearers
 The request should be admitted provided that the QoS requirements
can be met and that the QoS requirements of the already accepted
connections are not affected by the new request acceptance
 Admission control is particularly relevant in WCDMA because there is
no hard limit on the maximum capacity
 Admission control algorithms are executed separately for uplink and
downlink because of the different issues impacting on both
communication directions
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14. Admission Control:
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15. Admission Control:
 WCDMA supports multimedia services, so admission control
algorithms must take into consideration that the amount of radio
resources needed for each connection request will vary
 Similarly, the QoS requirements in terms of real time or non real
time transmission should also be considered in an efficient admission
control algorithm
 In addition to the connection set-up request, admission control may
also be triggered by handover procedures, transport channel type
switching
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16. How does Admission Control take place?
 A transaction set-up request in UMTS is always triggered from the UE
side, either because it is the UE itself that is initiating an interaction
with the network or because the UE is answering a paging message
 Prior to the transaction set-up procedure, a signalling path from the
UE towards the CN needs to be established, which in the case of the
UTRAN is accomplished by means of an RRC connection and the
RANAP (Radio Access Network Application Part) protocol, which takes
care of the UTRAN-CN interactions
 With the help of the RRC and RANAP protocol, a transaction set-up
request message reaches the CN
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17. How does Admission Control take place?
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18. How does Admission Control take place?
 Therefore, it is always the CN that triggers a RAB establishment by
means of the RAB assignment message sent from the CN to the SRNC
 With the arrival of such a message, the Admission Control (AC)
algorithm is executed
 If the connection can be admitted, the SRNC establishes the
resources in the radio and Iub interfaces by means of the RRC radio
bearer establishment procedure
 Similarly, the required connections are established in the Iu
interface. If the establishment procedure succeeds, a positive
response is given in the message RAB assignment response and the
RAB is eventually set-up
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19. Power Control in WCDMA:
 The Transmitter adapts the output power according to Path Loss
 Mainly to solve the “Near-Far” problem
 Goal is that all users should experience the same SIR
Open Loop Power control (Initially, No signaling):
 UE uses PRACH (Pre-amble RACH) for access to NodeB, if receives
AICH – then no need for further open loop power control
 If No AICH (Acquisition Indication Channel) received – then UE
increases its power in the steps of 1 dB and waits for getting the AICH
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20. Power Control Implementation Open-loop: (Initially)
• UE measure received BS power & read
BS transmit power – calculate initial
transmit power.
• access acknowledged??
• Increase UE power by 1dB
Inner-loop (Fast) Power Control:
• NodeB compares received UE – power
& power target value (SIR)
•Increase/decrease UE power,
1dB, 1500 times/sec
Outer-loop (Slow) Power Control:
• FER measured by NodeB
• RNC increases/decreases
power target value of the
Inner-loop (SIR), 1 time/sec
RNC
Core
Network
During call
SIR – Symbol to interference Ratio
FER – Frame Error Rate

21. Closed loop Power Control in WCDMA:
Inner Loop Power Control also called Fast power control
 This control takes place between UE and NodeB (continuously: 1500
Hz or 1500 times/s, relative changes: 1 dB up or down)
 The transmitted power in order to reach the receiver with the
required Eb/No target
 Outer loop Power control also called slow power control
 It takes place between NodeB and RNC
 Outer loop power control is responsible for selecting a suitable
Eb/No target depending on the BLER (Block Error Rate) or BER (Bit
Error Rate) requirement
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22. Congestion Control / Load Control:
 Congestion control faces situations in which the QoS guarantees are
at risk due to the evolution of system dynamics (mobility aspects,
increase in interference, traffic variability, etc.)
 Congestion situations in the radio interface are caused by excessive
interference. Thus, congestion control algorithms need to monitor the
network status continuously in order to correct overload situations
when they are present
 The congestion control algorithm needs to exhibit a fast reactivity
under overload conditions in order to prevent degradation of the
quality of the connections
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23. Congestion Control / Load Control:
 Congestion control is closely supported by Admission Control and
Handover
 RT Load – Real Time load
 NRT – Non Real Time Load
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24. Congestion Control / Load Control:
The congestion or load control (LC) algorithm will reside in the
network side (RNC) and will be based on measurements acting as
algorithm inputs (e.g. uplink cell load factor, downlink transmitted
power, etc.)
 When a congestion situation is triggered, congestion resolution
actions are implemented with the aid of the RRC protocol
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25. Code Management:
 The Code management is devoted to managing the downlink OVSF
(Orthogonal Variable Spreading Factor) code tree used to allocate
physical channel orthogonality among different users
 The advantage of the OVSF codes used in the UTRAN downlink is
perfect orthogonality
 However, the drawback is the limited number of available codes.
Therefore, it is important to be able to allocate/reallocate the
channelization codes in the downlink with an efficient method, in
order to prevent ‘code blocking’
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26. Code Management:
‘Code blocking’ indicates the situation where a new call could be
accepted on the basis of interference analysis and also on the basis of
the ‘spare capacity’ of the code tree
but, due to an inefficient code
assignment, this spare capacity is
not available for the new call
that must, therefore, be blocked
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27. Code Allocation Preventing Code Blocking:
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28. Handover in WCDMA:
 In WCDMA more possibilities are open as long as the mobile
terminal can be connected to more than one cell simultaneously due
the presence of Rake receivers in UE and NodeB
 Handover involves three different steps: measurements, decision
and execution
 Measurements may be of different categories: intra-frequency (on
the same UTRAN carrier), inter-frequency (on a different UTRAN
carrier) or inter-RAT (on a radio access technology other than UTRAN)
 Handover decisions are taken as a result of relative comparisons on
CPICH measurements
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29. Types of Handover in CDMA:
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30. Handover Process in CDMA:
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31. Soft Handover - Changing active set in CDMA:
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32. Cell Breathing:
 As the number of users increases the maximum allowed path loss for
the reference user decreases
In some cases, the result is that the reference user’s path loss is
higher than the maximum tolerable one. In such cases, the reference
user would be in outage, so that it is not able to reach the cell site
with enough power to achieve the target Eb/No
 Therefore, it can be seen that the performance achieved depends on
the cell load level or, equivalently, on the air interface interference
level. This phenomenon is known as cell breathing, since it turns into
a variable cell coverage
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33. Conclusion:
 The various Radio Resource Management Functions which we have
discussed helps in maintaining the desired QoS for user satisfaction
 Radio Resource and QoS management functionalities are very
important in the framework of WCDMA systems because the system
relies on them to guarantee a certain target QoS, maintain the
planned coverage area and offer a high capacity
 The multimedia capabilities in the newer technologies like LTE and
4G are advancing day by day, so Radio Resource Management will
keep playing an important role in helping optimising the networks.
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34. References:
 3GPP 25.922 v6.0.1, ‘Radio resource management strategies (release
6)’
 3rd Generation Partnership Project; Technical Specification Group
Services and System Aspects General UMTS Architecture (3G TS
23.101 version 3.0.1). 2004
 H. Holma, A. Toskala, WCDMA for UMTS, John Wiley & Sons Ltd, 2nd
edition, 2000
http://www.rfwireless-world.com/
http://whytelecom.com/
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35. Thank You
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