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Radio Resource Management - Radio Admission Control and Bearer Control Radio Resource Management (RRM) is an E-UTRAN Node B (eNodeB) application level function that ensures the efficient use of available radio resources. RRM manages the assignment, re-assignment and release of radio resources, taking into account single and multi-cell aspects. Radio Admission Control (RAC) is a sub-function of RRM. The task of RAC is to admit or reject the establishment requests for new radio bearers. The establishment of a bearer is based on the outcome of the RAC Algorithms. Radio Bearer Control (RBC) is also another sub-function of RRM. The establishment, maintenance and release of Radio Bearers involve the configuration of radio resources associated with them. It is based on the outcome of RBC Algorithm. This paper primarily focuses on the admission, establishment and maintenance of radio bearers. We We discuss a strategy for RAC and RBC, including Quality of Service (QoS) requirements, priority levels and provided QoS of in-progress sessions and QoS requirements of the new radio bearer request.
About the Author Pundalik Kandolcar
Pundalik Kandolcar has been an Assistant Consultant with Tata Consultancy Services (TCS) in the Telecom group for the past six years. He has used his experience and understanding of Access and Bearer Control (ABC) to write this paper. Mukesh Kumar Das Mukesh Kumar Das has been an IT Analyst with Tata Consultancy Services (TCS) in the Telecom Next-Gen R&D group for the last one year. He is involved in Initiatives and Proof of Concept (PoC) for LTE technology. He has used his experience and understanding of RAC and RBC to write this paper. Saugata Mukherjee The late Saugata Mukherjee worked as a Consultant with TCS in a large R&D telecom account and with the Telecom Next-Gen R&D group. He had significant experience in wireless access and core technologies.
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Table of Contents 1
Introduction
5
2
Radio Admission control Algorithm
7
3
Radio Bearer Control Algorithm
9
4
Conclusion
11
5
Acknowledgement
12
6
References
12
3
Abbreviations Abbreviation/ Acronym
Expansion
RRM
Radio Resource Manager
eNB
eNodeB or E-UTRAN Node B
RAC
Radio Admission Control
RBC
Radio Bearer Control
QoS
Quality of Service
ABC
Access and Bearer Control
LTE
Long Term Evolution
GSM
Groupe Spécial Mobile or Global System for Mobile Communications
RLC
Radio Link Control
MAC
Medium Access Control
RRC
Radio Resource Control
PDCP
Packet Data Convergence Protocol
CMC
Connection Mobility Control
UE DRA PS ICIC LB
User Equipment Dynamic Resource Allocation Packet Scheduling Inter-Cell Interference Coordination Load Balancing
GBR
Guaranteed Bit Rate
AC
Admission Control
RAN
Radio Access Network
ARP
Allocation and Retention Priority
ERAB
E-UTRAN Radio Access Bearer
QCI
Quality Class Identifier
BW
Bandwidth
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Introduction This paper provides an insight into the admission and management of bearers for the efficient use of radio resources. Admission deals with establishment of a new bearer depending on the feasibility and availability of resources. Management of bearer is taken care of by bearer control, which deals with the modification or deletion of bearers. This paper will be useful for design approach and prototype development from developer prospect . eNodeB Architecture eNodeB (eNB) is the hardware, which connects to a mobile phone network that communicates directly with mobile handsets (User Equipment). It is similar to a base transceiver station (BTS) in Groupe Spécial Mobile/Global System for Mobile Communications (GSM) networks. Radio link specific protocols, including the Radio Link Control (RLC) and Medium Access Control (MAC) protocols terminate at the eNodeB. The Packet Data Convergence Protocol (PDCP), which is responsible for header compression and ciphering, is located in the eNB. In the control plane, the eNB uses the Radio Resource Control (RRC) protocol for application level RRC. Figure 1 depicts the eNodeB (eNB) architecture.
Radio Admission Control Radio Bearer Control Connection Mobility Control Inter-Cell RRM eNodeB Measurement Configuration & Provision Dynamic Resource Allocation RRC MME PDCP RLC MAC
S1
S-GW
P-GW
PHY
EPC
eNodeB Figure 1: eNB Architecture
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Radio Resource Management (RRM) Overview Radio Resource Management (RRM) is an eNB application level function that ensures the efficient use of available radio resources. RRM manages the assignment, re-assignment and release of radio resources considering single and multi-cell aspects. The primary goal of RRM is to control the use of radio resources in the system while also ensuring that the Quality of Service (QoS) requirements of the individual radio bearers are met and the overall usage of radio resources on the system level is minimized. The objective of RRM is to satisfy the service requirements at the smallest possible cost to the system, ensuring optimized use of spectrum. Long Term Evolution (LTE) RRM includes a variety of algorithms that provide services, such as power control, resource allocation, mobility control, and QoS management to ensure the best use of available radio resources. RRM has various functions. Selected key functions are described in the following sections. Radio Admission Control (RAC) Radio Admission Control (RAC) admits or rejects establishment requests for new radio bearers. The goal of RAC is to ensure high radio resource utilization by accepting radio bearer requests if radio resources are available. This simultaneously ensures proper QoS for in-progress sessions by rejecting radio bearer requests when they cannot be accommodated. Radio Bearer Control (RBC) Radio Bearer Control (RBC) involves the establishment, maintenance and release of radio bearers. RBC is also concerned with the maintenance of radio bearers of in-progress sessions at the change of the radio resource situation due to mobility and so on. RBC is involved in the release of radio resources associated with radio bearers including at-session termination and handover. Connection Mobility Control (CMC) Connection Mobility Control (CMC) oversees the management of radio resources related to idle or connected mode mobility. Handover decisions may be based on UE and eNB measurements. In addition, handover decisions can use other inputs, including neighbor cell load, traffic distribution, transport and hardware resources and operator defined policies for the account. Dynamic Allocation of resources to UE’s in both uplink and downlink (DRA) Dynamic Resource Allocation (DRA) or Packet Scheduling (PS) allocates and de -allocates resources including buffering and processing resources and resource blocks to user and control plane packets.
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Inter-Cell Interference co-ordination (ICIC) Inter-Cell Interference Coordination (ICIC) manages radio resource blocks to keep inter-cell interference under control, based on the feedback from multiple cells. Load Balancing (LB) Load balancing (LB) handles uneven distribution of the traff ic load over multiple cells. The purpose of LB is to influence the load distribution in such a manner that radio resources remain highly utilized and the QoS of in-progress sessions are maintained, and call dropping probabilities are kept to a minimum. Application RRM as a service function on the eNB can be considered in the following logical realization form.
RRM Adaptation
s t u p n I e n a l P l o r t n o C , s t n e m e r u s a e M B R
s t u p n I c i m a n y D
Application RRM Service
s t u p n I n o i t a r u g i f n o C
Manages & Updates Shared Data
Notifics
(Access, Qos, Mobility)
E-UTRAN
UEs
s t n e m e r u s a e M
S1 Interfaces
NW
c t s t e u g p i n n I d e n n e a P l , P s a e t u a e D u Q
XP Interfaces (Mobility)
Uu Interface (Access, Profiles, Qos)
eNB System Level Inputs
Radio Stack (RRC, MAC, S1, X2 takes appropriate Procedural action
Figure 2: Application RRM Logical View
Radio Admission Control Algorithm Radio Admission Control (RAC) admits or rejects establishment requests for new radio bearers. One of the approach has been described below which is based on Priority Guaranteed Bit Rate (GBR). Priority GBR Based It is important to realize that Admission Control (AC) is not standardized shlould be, different realizations of LTE Radio Access Network (RANs ) will run different admission control algorithms.
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Start
Get Available BW UL/DL?
GBR?
No
Allocate configured min non-GBR BW
YES
Allocate Min BW to all ERABs
YES
Min BW Configured? No Sort the ERAB list first on priority, next on GBR basis
End of ERAB list?
YES
END
No
Is a variable BW UL/DL
Update available BW UL/DL
YES Allocate SRB to ERABs
Reject Request
Can trigger RBC?
No
YES Trigger RBC to allocate on ARP basis?
Figure 3: Prioritized GBR based RAC Algorithm
The figure above depicts an approach according to which GBR is granted based on priority and GBR requested. The algorithm in contention situation triggers RBC in which case the allocation happens based on allocation and retention priority (ARP) parameters.
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Pros and Cons Pros: n
n
High priority GBR requests are granted first. In contention situation, higher priority E-utran Radio Access Bearer (ERABs) can pre-empt lower priority ones.
Cons: Pre-emption would lead to release of lower priority ERABs. Recommendations for operator use Operators can set Quality Class Identifier (QCI) (QoS profiles) and priority levels for different customer base, (privileged and others) and allocation would be done on priority and GBR basis. In contention situation a higher privilege customer gets priority over lower ones and can pre-empt lower ones.
Radio Bearer Control Algorithm Radio Bearer Control (RBC) involves the establishment, maintenance and release of radio bearers. One of the approach has been described below based on Fair-share. Prioritized/Weighted Max-Min Fair Share While the RAC is concerned with the allocation of initial bandwidth or GBR, RBC algorithm is responsible for allocating the remaining maximum bandwidth demand. For this, the algorithm considers the overall resource situation in the E-UTRAN, the QoS requirements of in-progress sessions and QoS requirement for the new service Prioritized/weighted max-min fairshare bandwidth allocation technique tries to maximize the minimum share for non-satisfied flows. Priority/weight is considered during allocation so higher priority gets a higher share than lower ones.
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The Figure on the previous page explains the Algorithm. Start
For all active Uses get the ERAB list. Also get available BW UL/DL
Create ERAB list
Initialize Total Weight = 0
End of ERAB list?
Yes
Total Weight+= Weight No Calculate Weight Weight = (15-QoS Priority Level)
Calculate Weighted Demand Weighted Demand = (MAX BW-GBR)/Weight
All ERABs allocated?
Yes
No Calculate FairShare FairShare=Avail BW/Total Weights
Update available BW UL/DL
For all ERABs whose Weighted Demand< FairShare, allocate BW
Re-calculate Total Weights = Weights (Allocated)
Yes
Atleast one Demand Fully Satisfied?
No
End Calculate Fairshare Fairshare-(Avail EW/Total Weights)
Figure 4: Prioritized/Weighted Max-Min Fairshare RBC Algorithm 10
Pros and cons Pros: The pros of prioritized/weighted max-min fairshare bandwidth allocation technique are as follows: n
n
n
n
n
Normalize demands with corresponding weights. Allocate resources in order of increasing demands, normalized by weight. Satisfy users with relatively small demands. Ensure that users do not get a resource share larger than their demand. Ensure that users with un-satisfied demands get an equal share of unused resources proportional to their weights.
Cons: The cons of the technique are as follows: Max-min fairness in communication networks assumes that resources (capacities of communication links) are allocated to flows in advance, as opposed to best-effort networks. Recommendations for operator use Different flows might have different QoS requirements, such as: n
n
Voice and video flows require different bandwidth (BW) levels. Customers of video service are willing to pay more to get required BW.
This algorithm helps to categorize user’s priority and allocate higher BW share to privileged users.
Conclusion RAC and RBC are vital for eNB operation, session establishment, session continuity and session closure and network performance optimization while users are on the move or not. Several studies have shown that users need customized services according to their use and specific requirements. Users utilizing high BW applications such as online gaming or streaming can have a faster and an enhanced experience with these algorithms. Users with high privileges in terms of services and QoS will always get GBR at any point of time. We consider an optimized access and management approach that can be adapted to engineering parameters, because accommodating field results is necessary to ensure that system resources are effectively utilized.
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Acknowledgement We (Pundalik Kandolcar and Mukesh Kumar Das) would like to express our gratitude to all those who made it possible to complete this white paper. We would also like to thank our colleagues from the Next-Gen R&D Group for all their help and support during the writing of this paper.
References [1] 3GPP TS 36.101 UE Radio Transmission and Reception http://www.3gpp.org . [2] 3GPP TS 36.331 RRC Protocol Specification http://www.3gpp.org . [3] 3GPP TS 36.300 http://www.3gpp.org [4] 3GPP TS 36.322. E-UTRA radio link control (RLC) protocol specification. ftp://ftp.3gpp.org/Specs/archive/36_series/36.322/ [5] 3GPP TS 36.321. E-UTRA medium access control (MAC) protocol specification. ftp://ftp.3gpp.org/Specs/archive/36_series/36.321/ [6] 3GPP TS 25.913. Requirements for evolved UTRA (E-UTRA) and evolved UTRAN (E-UTRAN). ftp://ftp.3gpp.org/Specs/archive/25_series/25.913/ [7] http://lte-epc.blogspot.in/2012/03/rrm-functions.html
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