Base Station Location and Service Assignment in W-CDMA Networks Joakim Kalvenes 1 Jeffery Kennington 2 Eli Olinick 2 Southern Methodist University 1 Edwin L. Cox School of Business 2 School of Engineering

2 Wireless Network Design: Inputs Potential locations for radio towers (cells) “Hot spots”: concentration points of users/subscribers (demand) Potential locations for mobile telephone switching offices (MTSO) Locations of access point(s) to Public Switched Telephone Network (PSTN) Costs for linking towers to MTSOs, and MTSOs to PSTN

3 Wireless Network Design: Problem Determine which radio towers to build (base station location) Determine how to assign subscribers to towers (service assignment) Determine which MTSOs to use Maximize profit: revenue per subscriber served minus infrastructure costs

4 Wireless Network Design Tool

5 Code Division Multiple Access (CDMA) Technology The basis for 3G cellular systems Channel (frequency) allocation is not an explicit issue since the full spectrum is available in each cell –New calls cause incremental noise (interference) –New calls admitted as long as the signal-to-noise ratio stays with in system limit –Power transmitted by handset depends on distance to assigned radio tower –Tower location and assignment of customer locations to towers must be determined simultaneously

6 Power Control Example Subscriber at Location 1 Assigned to Tower 3 Tower 3 Received signal strength must be at least the target value P tar Signal is attenuated by a factor of g 13

7 Signal-to-Interference Ratio (SIR) Tower 3 Tower 4 Subscriber at Location 1 assigned to Tower 3 Two subscribers at Location 2 assigned to Tower 4

8 Constants and Sets Used in the Model L is the set of candidate tower locations. M is the set of subscriber locations. g mℓ is the attenuation factor from location m to tower ℓ. is the set of tower locations that can service customers in location. is the set of customer locations that can be serviced by tower ℓ.

9 More Constants and Sets Used in the Model d m is the demand (channel equivalents) in location r is the annual revenue generated per channel. is the FCC mandated minimum service requirement. is the cost of building and operating a tower at location. SIR min is the minimum allowable signal-to- interference ratio. s = 1 + 1/SIR min.

10 Decision Variables Used in the Model y ℓ =1 if a tower is constructed at location ℓ; and zero, otherwise. The integer variable x mℓ denotes the number of customers (channel equivalents) at that are served by the tower at location The indicator variable q m =1 if and only if location m can be served by at least one of the selected towers.

11 Integer Programming Model The objective of the model is to maximize profit: subject to the following constraints:

12 Integer Programming Model

13 Quality of Service (QoS) Constraints For known attenuation factors, g ml, the total received power at tower location ℓ, P ℓ TOT, is given by For a session assigned to tower ℓ –the signal strength is P target –the interference is given by P ℓ TOT – P target QoS constraint on minimum signal-to-interference ratio for each session (channel) assigned to tower ℓ:

14 Quality of Service (QoS) Constraints