Frequency Reuse for Improved Coverage and Capacity in Telecommunication Services

1. FREQUENCY REUSE Mr. S. K. KIBEDirector/Frequency Spectrum ManagementCommunications Commission of Kenya ITU-T Workshop on Delivering Good Quality Telecommunication Service in a Safe Environment in Africa (Nairobi, Kenya, 26 July – 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

3. What is frequency reuse Ability to re-use frequencies to increase both coverage and capacity Example of a frequency reuse plan forcluster size N = 3, with hexagonal cells Reuse distance and cluster size indicates extent of frequency reuse

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

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

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 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

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.

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

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.

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

12. Q&AThank you