SoftRAN : Software Defined RAN Aditya Gudipati†, Daniel Perry†, Li Erran Li*, Sachin Katti † Stanford University†, Bell Labs*

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

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

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

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

Coupled Radio Resource Management: Mobility BS2 BS1 Client1 Client1 Dense deployments Higher frequency of handovers More candidate base stations Coordinating handovers critical

In dense deployments, Radio Resource Management needs to be tightly coordinated

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

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

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

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

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

SoftRAN: SDN Approach to RAN Efficient use of wireless resources Global view on interference and load Simplified network management Plug-and-play control algorithms

Challenges: Backhaul Latency controller time radio element frequency

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

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

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