FREQUENCY MANAGEMENT AND CHANNEL ASSIGNMENT

1. FREQUENCY MANAGEMENT AND CHANNEL ASSIGNMENT BY HARPINDER KANG KHATTRA

2. Frequency –Spectrum Utilization • 1. Increasing the number of radio channel using narrow banding, spread spectrum, or time • division. • 2. Improving spatial frequency-spectrum reuse. • 3. Frequency management and channel assignment. • 4. Improving spectrum efficiency in time

3. 5. Reducing the load of invalid calls a. Off-air call setup—reducing the load of setup channels b. Voice storage service for No-Answer calls c. Call forwarding d. Reducing the customers’ Keep-Dialing cases e. Call waiting for Busy-Call situations f. Queuing

4. Frequency management Frequency management refers to • designating setup channels and voice channels • numbering the channels • grouping the voice channels into subsets

5. Channel assignment • Channel assignment refers to the allocation of specific channels to cell sites and mobile units • Ideally channel assignment should be based on causing the least interference in the system..

6. Channel assignment strategies • For efficient utilization of the radio spectrum, a frequency reuse scheme is consistent with the objectives of increasing capacity and minimizing interference. • A variety of channel assignment strategies has been developed: fixed or dynamic. • The choice impacts the performance of the system, particularly as to how calls are managed when a mobile is handed off from one cell to another.

7. Fixed and Dynamic assignment • Fixed frequency assignment: permanent • certain frequencies are assigned to a certain cell • problem: different traffic load in different cells • Dynamic frequency assignment: temporary • base station chooses frequencies depending on the frequencies already used in neighbor cells • more capacity in cells with more traffic • assignment can also be based on interference measurements

8. Fixed channel assignment • Each cell is allocated a predetermined set of channels. • Any call attempt within the cell can only be served by the unused channel. • If all the channels in that cell are occupied, the call is blocked and the subscriber does not receive service. • Several variations of the fixed assignment strategy exists.

9. Dynamic channel assignment • Channels are not allocated to different cells permanently. • Instead, each time a call request is made, the serving BS requests a channel from the RNC. • The RNC then allocates a channel to the requested cell following an algorithm that takes into account the likelihood of future blocking within the cell, the frequency of use of the candidate channel, the reuse distance of the channel, and other cost functions. • Accordingly, the RNC only allocates a given frequency if that frequency is not presently in use in the cell or any other cell which falls within the minimum restricted distance of frequency reuse to avoid co-channel interference.

10. Dynamic channel assignment [continue] • Dynamic channel assignment strategies require the RNC to collect real-time data on channel occupancy, traffic distribution, and radio signal strength indications (RSSI) of all channels on a continuous basis. • This increases the storage and computational load on the system but provides the advantage on increased channel utilization and decreased probability of blocked call. • There are also hybrid strategies (Flexible channel assignment).

11. Rules for channel assignment • Do not assign co-channels or adjacent channels at the same cell site . • Do not assign co-channels in adjacent cell sites . • Do not mix and match channel groups in a cell or sector. • Avoid adjacent channel assignment in adjacent cell sites . • Maintain proper channel separation for any channel assignment for a sector or site. • Maximize the distance between reusing cell sites.

12. FIXED CHANNEL ASSIGNMENT SCHEMES • Adjacent-Channel Assignment • Channel Sharing and Borrowing • Sectorization • Underlay-Overlay Arrangement

13. Adjacent-Channel Assignment Adjacent channel assignment. (a) Omnidirectional-antenna cells; (b) directional-antenna cells.

14. Channel Sharing and Borrowing Channel-sharing algorithm

15. Sectorization • Comparison of Omnicells (Nonsectorized Cells) and Sectorized Cells Omnicells:- If a K = 7 frequency-reuse pattern is used, the frequency sets assigned in each cell can be followed by the frequency-management chart. However, terrain is seldom flat; therefore, K = 12 is sometimes needed for reducing co-channel interference. For K = 12, the channel-reuse distance is D = 6R, or the co-channel reduction factor q = 6. Sectorized Cell:- There are three basic types. The 120◦-sector cell The 60◦-sector cell The 120◦- or 60◦-sector cell

16. Underlay-Overlay Arrangement • Overlaid Cells. Underlaid-overlaid cell arrangements. (a) Underlay-overlay in omnicell; (b) underlay-overlay in sectorized cells

17. Implementation. (c) two-level handoff scheme.

18. Reuse Partition 1. The K range is 3 to 9; the operational call quality can be adjusted and more reuse patterns are available if needed. 2. Each channel set of old K = 9 systems is the subset of new K = 3 systems. Therefore, the amount of radio retuning in each cell in this arrangement is minimal. 3. When cell splitting is implemented, all present channel assignments can be retained.

19. NONFIXED CHANNEL ASSIGNMENTALGORITHMS • Fixed Channel Algorithm • Dynamic Channel Assignment • Hybrid Channel Assignment • Borrowing Channel Assignment • Forcible-Borrowing Channel Assignment