1. 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
P-Gateway
BS2
Client2
Client3
BS3
S-Gateway 2
Core Network
Client4
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
frequency
2. Assign resource blocks (time-frequency slots) to each flow
3. Assign transmit powers to be
used for each resource block

4. Radio Resource Management gets coupled across base stations
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
Radio Element 1
time
controller
frequency
Radio Element 2
Radio Element 3
time
time
time
radio element
frequency
frequency
frequency

10. SoftRAN Architecture CONTROLLER RAN Information Base RADIO ELEMENTS
Periodic Updates
Controller
API
Bytes
Rate
Queue
Size
Network
Operator
Inputs
RADIO ELEMENTS
Interference
Map
Flow
Records
QoS
Constraints
3D Resource Grid
Radio Resource
Management
Algorithm
Radio
Element API
Time
Radio Element
POWER
FLOW
Frequency

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
BS3
Control Algo
Control Algo
BS5 OS OS
Packet Tx/Rx
Packet Tx/Rx
BS2
BS4

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
Packet Tx/Rx
BS2
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
controller
time
radio element
frequency

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 * *

17. Future Vision THANKS ! Expand SoftRAN to include 3G and Wifi networks
Coordinated management of all available radio resources
THANKS !