# Sectoring Use a directional antenna to control the interference and [frequency reuse](frequency%20reuse.md) of [channels](../RF%20Chip%20Design/channels.md). Reduce the number of interferences ([SIR](signal%20to%20interference%20ratio.md) is inversely proportional to number of interferers). ## Principle - Use directional antenna to divide cells into sectors - Divide [channels](../RF%20Chip%20Design/channels.md) in one cell evenly among the M sectors (2,3,6,...) - K (number of nearest interferes) is 2 for 120° directional antenna and 6 for 60° ones  Note that there are **two options for 120° sectors!**   There are only 2 interferes for this mobile user! (as opposed to 6 with no sectoring) ## Advantages 1. Increase [SIR](signal%20to%20interference%20ratio.md) by reducing co-channel interference by decreasing the number of closes frequency reuse neighbour 1. K becomes 2 with 120°, corresponding to a factor of 3 2. If SIR is fixed, we can decrease N which increases system capacity (more users!) ## Drawbacks 1. Lose [trunking efficiency](trunking%20efficiency.md) since we separate the channel 2. Increase the number of antennas at each BS 3. Static setting - decide on the sectoring at the beginning. 4. Number of handoffs increases when the mobile moves from one sector to another.  ## Engineering Tradeoffs Reduce co-channel interference $\rightarrow$ allow small N (more frequency frequency reuse) $\rightarrow$ increase capacity BUT lose trunking efficiency. **Most of the time the increase in capacity is more than the loss in trunking efficiency (in experience - calculations needed).** ## Other details Separate signals using hardware (not signal processing). Not the smartest way to implement [SDMA](Spatial%20division%20multiple%20access.md) - SDMA all antennas use the same frequency, here the antennas use different frequencies. [^1] # References [^1]: [TELE4652-lecture-00](../../03%20-%20University/TELE4652/Lectures/TELE4652-lecture-01.pdf)