1. ITU-T Workshop on Delivering Good Quality Telecommunication Service in a Safe Environment in Africa (Nairobi, Kenya, 26 July – 27 July 2010 )
FREQUENCY REUSE Mr. S. K. KIBE Director/Frequency Spectrum Management Communications Commission of Kenya
Nairobi, Kenya, 26 – 27 July 2010

2. SCOPE What is frequency reuse Examples of frequency reuse
Coverage versus capacity
Spectrum efficiency versus system performance
Strategies to improve frequency reuse
Nairobi, Kenya, 26 – 27 July 2010 2

3. What is frequency reuse
Ability to re-use frequencies to increase both coverage and capacity
Example of a frequency reuse plan for cluster size N = 3, with hexagonal cells
Reuse distance and cluster size indicates extent of frequency reuse
Nairobi, Kenya, 26 – 27 July 2010

4. Examples of frequency reuse
In UMTS Frequency reuse factor is 1, neighbouring cells can operate on the same frequency band
UMTS LTE uses fractional reuse. Users near base stations reuse the same frequencies (OFDM subcarriers), while users at the cell border are allocated to subcarriers in a coordinated manner between base stations in order to minimize interferences
Nairobi, Kenya, 26 – 27 July 2010

5. Coverage versus capacity
In an initial network, planners typically aim at maximum coverage
As subscribers increase, planners need to optimize the capacity of the network. Cell size should be as small as possible to accommodate additional capacity
Nairobi, Kenya, 26 – 27 July 2010 5

6. Spectrum efficiency
Spectrum efficiency SE in erlang/MHz/km2 can be defined as follows: Ac
SE =
BT N M Su
M is the number of channels per base station
BT is occupied bandwidth per channel
N is the cluster size
Ac is the carried traffic per cell in Erlangs
Su is the area of a cell
Nairobi, Kenya, 26 – 27 July 2010 6 6

7. Spectrum efficiency versus system performance
Spectrum efficiency decreases with increasing reuse distance and cluster size
System performance improves with increasing re-use distance and cluster size
Achieving high system performance and efficient use of the spectrum are conflicting objectives
Nairobi, Kenya, 26 – 27 July 2010

8. Strategies to improve frequency reuse
Use synthesised frequency hopping. Allows a greater number of radio channels to operate in each sector.
Use AMR adaptive Multi Rate to improve network resilience on interference. Defines multiple voice encoding rates each with its level of error control. Dynamically responds to radio conditions using the most effective mode of operation at each moment in time.
Nairobi, Kenya, 26 – 27 July 2010

9. Strategies to improve frequency reuse
Use dynamic frequency and channel allocation based on the current radio environment. Chooses a channel with most suitable C/I for new connections without increasing interferences on existing connections.
Implement hierarchical structure
Macro layer
Micro layer: Indoor micros for hot spots and tall indoor buildings, and street micros for high traffic spots
Nairobi, Kenya, 26 – 27 July 2010

10. Strategies to improve frequency reuse
Use dynamic power control. By using the minimum transmission power possible for the terminal and base station, interference in neighbouring cells can be minimised
Use discontinous transmission. Minimises transmission when a person is not talking. On average conversation, each user speaks less than 50% of the time.
Nairobi, Kenya, 26 – 27 July 2010

11. Strategies to improve frequency reuse
Use real measurements. Expensive but allows tighter frequency reuse
Uplink interference cancellation. Uplink interference is reduced allowing for tighter frequency reuse
Update geodata information, network planning data and calibration of propagation models
Build new sites
Nairobi, Kenya, 26 – 27 July 2010

12. Q&A Thank you
Nairobi, Kenya, 26 – 27 July 2010