1. Basics of Cellular Communications Grade of Service, Interference, & Capacity

2. The Cellular Concept Early Mobile Communications The Cellular Concept
Single, high powered transmitter with an antenna mounted on a tall tower
The Cellular Concept
Replace a single high power transmitter (large cell) with many low power transmitters (small cells) each providing coverage to only a small portion of the service area

3. Frequency Reuse
Cluster
Cluster
Each base station is allocated a group radio channels to be used within a small geographic area
Base station in adjacent cells are assigned channel groups which contain completely different channels than neighboring cells E D F A G B C
Cluster
Total Number of Channels in the System:
C=MkN=MS
M: Number of clusters within the system
K: Number of channels per cell
N: Cluster Size
S: Number of available physical channels
A Cluster: A Group of N cells that which collectively use the complete set of available frequencies

4. Locating Co-channel Cells
Number of Cells per Cluster N = i2+ij+j2, i, j are non-negative integers
To find nearest co-channel neighbor of a given cell
Move i cells along any chain of hexagons
Turn 600 counter clockwise and move j cells
i=3, j=2, N=19

5. Grade of Service and Capacity (i.e., Blocking Probability)

6. Trunking & Grade of Service
Trunked Radio System:
Each user is allocated a channel on per call basis, and upon termination of the call, the previously occupied channel is immediately returned to the pool of available channels.
Grade of Service:
A measure of the ability of a user to access the trunked system
GOS measures in cellular networks
Probability that a call is blocked
Probability a call experiences a delay greater than a certain queuing time

7. Traffic Intensity Traffic intensity generated by each user: Au Erlangs
Au = H
H : average duration of the call
λ : average number of call requests per unit time
For a system containing U users and unspecified number of channels, Total offered traffic intensity: A Erlangs
A = UAu
In C channel trunked system, if the traffic is equally distributed among the channels, Traffic intensity per channel : Ac Erlangs
Ac = UAu/C

8. Types of Trunked Systems
Calls Blocked Cleared Trunking System
No queuing provided for call requests and calls are blocked if no available channels
Calls Blocked Delayed Trunking System
Queuing is provided to hold call requests. Calls are blocked if no available channels for a certain delay
Assumptions:
Calls arrive as determined by Poisson distribution
Infinite number of users
Memoryless arrivals of requests : all users can request channel at any time
Probability of user occupying a channel is exponentially distributed
Finite number of channels available in the trunking pool

9. Erlang B Formula M/M/C/C Queuing System
Queue Size
C Servers and Exponential Service Times
Inter-arrival time distribution
Service time distribution
Number of Servers
Exponential Interarrival Time
(Poisson Arrival Process)

10. Erlang B Curves

11. Erlang C Formula

12. Erlang C Curves
Pr[delay>0]