Base Station Operation and User
Association Mechanisms For EnergyDelay Tradeoffs in Green Cellular
Networks
by Kyuho Son, Hongseok Kim, Yung Yi, Bhaskar
Krishnamachari
Haluk Celebi/ hc2489
Outline
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Motivation
Problems to be solved
System model
Solution approaches and algorithms
Main Motivation
• BSs are large underutilized: Traffic is below
10% of peak 45% of the time.
• UMTS BS consumes 800-1500W, and radio 3040W. Thus, not only turning off the
transceivers, we need to turn off BS
completely.
Problems to be solved
1. User association: When the set of active BS
changes, MT needs to be associated with a
new BS
2. Energy efficient BS operation: finding optimal
set of active BS
- Paper gives a distributed algorithm to solve 1st
problem optimally. For 2nd problem, it offers
several greedy algorithms.
System Model and Problem
Formulation
•  ( x)
arrival rate
Traffic load density
Set of active BS
Transmission rate of user i
located at x
Fraction of time required
to deliver
traffic load from BS i to
location x
Feasible solution to the problem: utilizations of BSs
Note that in optimal case p(x) is either 1 or 0
Cost function
•n is the parameter that determines between the flow level
performance and the energy level consumption
Flow level performance
is a parameter specifying the degree of load balancing
Each MT prefers a BS that gives
the highest rate
Minimizing number of flows,
thus delay in M/M/1 queue
Thus as α increases, cost function places more importance on
traffic load instead of transmission rate
Cost function of Energy
Portion of fixed power consumption.
Energy that is spend only depends on the radio.
In other case, when q =1, regardless of the
utilization amount of energy spend is Pi. That`s where turning
BS off becomes more important
We assume femto cells are more energy proportional (smaller q values)
macro cells.
Solution approach to the problem
•Solving two cost functions together is hard.
•We assume that flow arrival, and departure process is
much faster than the period of determining active and
passive BSs
•Decompose problem into two sub-problems
•Solve user association problem. For given active BS
set find which BS each MT should connect to
•BS operation problem
Connection policy
It`s proved in the paper that with this policy, each MT is able to choose optimal BS
Energy Efficient BS operation