SoftRAN : Software Defined RAN
Aditya Gudipati†, Daniel Perry†,
Li Erran Li*, Sachin Katti †
Stanford University†, Bell Labs*
2
LTE - Radio Access Network
S-Gateway 1
Client1
BS1
Client2
Client3
P-Gateway
BS2
BS3
I
N
T
E
R
N
E
T
S-Gateway 2
Client4
Core Network
Radio Access Network
High Capacity, Uniform Coverage Wide-Area Wireless Network
3
RAN Actions: Radio Resource
Management
1. Assign each client to a base station
Flow 1 Flow 2
dB
time
time
dB
dB
dB
dB
frequency
2. Assign resource blocks (timefrequency slots) to each flow
frequency
3. Assign transmit powers to be
used for each resource block
4
RAN Challenges
• Increasing demand on wireless resources
– Dense deployments of small cells
Radio Resource Management
gets coupled across base stations
5
Coupled Radio Resource Management:
Interference
BS2
BS1
Client1
Client2
• Power used by BS1 affects interference at Client 2
• Interference at Client 2 affects power reqd. at BS2
6
Coupled Radio Resource Management:
Mobility
BS2
BS1
Client1
Client1
• Dense deployments
– Higher frequency of handovers
– More candidate base stations
– Coordinating handovers critical
7
In dense deployments,
Radio Resource Management
needs to be tightly coordinated
8
LTE-RAN: Current Architecture
• Distributed control plane
• Tight coordination becomes infeasible with density
– Huge demands on the backhaul network
• Inefficient radio resource management
• Hard to manage in a dense network
9
SoftRAN: Big Base Station Abstraction
Big Base Station
Radio Element 1
time
controller
frequency
Radio Element 2
time
time
Radio Element 3
frequency
time
frequency
10
SoftRAN Architecture
CONTROLLER
RAN Information Base
Periodic Updates
Controller
API
•
•
•
RADIO ELEMENTS
Interference
Map
Bytes
Rate
Queue
Size
Flow
Records
Network
Operator
Inputs
QoS
Constraints
Radio
Element
API
Radio Element
3D Resource Grid
POWER
FLOW
Frequency
Radio Resource
Management
Algorithm
11
SoftRAN: SDN Approach to RAN
Coordination :
X2 Interface
Control Algo
Control Algo
OS
OS
Packet Tx/Rx
Control Algo
Packet Tx/Rx
OS
Packet Tx/Rx
BS1
Control Algo
BS3
Control Algo
OS
OS
Packet Tx/Rx
Packet Tx/Rx
BS2
BS4
BS5
12
SoftRAN: SDN Approach to RAN
Control Algorithm
Operator Inputs
Network OS
Packet Tx/Rx
Packet Tx/Rx
Packet Tx/Rx
BS1
BS3
BS5
Packet Tx/Rx
BS2
Packet Tx/Rx
BS4
13
SoftRAN: SDN Approach to RAN
• Efficient use of wireless resources
– Global view on interference and load
• Simplified network management
– Plug-and-play control algorithms
14
Challenges: Backhaul Latency
time
controller
15
Challenges: Backhaul Latency
• Refactor control plane based on latency
- Low latency ( < 1 ms) => No refactoring
• Principles for refactoring:
- Controller manages global network state
- Radio Elements leverage frequently varying local
network state
16
Implementation
• Incrementally deployable on current
infrastructure
– No modification to Base Station – client interface
– New API definitions for Base Station
• Femto API: Standardized interface between scheduler
and L1 *
*http://www.smallcellforum.org/resources-technical-papers
17
Future Vision
• Expand SoftRAN to include 3G and Wifi
networks
• Coordinated management of all available
radio resources
THANKS !