05. Frequency Management and Channel Assignment.pdf
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This document discusses frequency management and channel assignment in cellular networks. It covers: - Frequency management which includes designating setup and voice channels, numbering channels, and grouping voice channels into subsets. - Channel assignment which allocates specific channels to cell sites on a long-term basis and mobile units on a short-term basis during calls. - The original 666 channels were divided into blocks A and B, with setup channels in specific ranges and voice channels assigned to each block. Additional spectrum has since been added up to channel 1023.
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05. Frequency Management and Channel Assignment.pdf
- 1. Frequency Management and Channel Assignment
- 2. After completing this chapter a student will be able to: ➢Frequency Management ➢ Frequency Spectrum Utilization ➢ Set-up Channels ➢ Channel Assignment
- 3. Frequency Management • Frequency management – Designating set-up channels and voice channels (done by the FCC), – Numbering the channels (done by the FCC), and – Grouping the voice channels into subsets (done by each system according to its preference).
- 4. Channel Assignment • Means the allocation of specific channels to cell sites and mobile units. • A fixed channel set – Cell site- long-term basis • During a call- Mobile unit - short-term basis (handled by MTSO).
- 5. Channel Assignment • Ideally channel assignment should be based on causing the least interference in the system.
- 6. Numbering the Channels • The total number of channels (January 1988) is 832. • But most mobile units and systems are still operating on 666 channels. • A channel consists of two frequency channel bandwidths, – one in the low band – one in the high band
- 7. Numbering the Channels • Two frequencies in channel 1 are – 825.030 MHz (mobile transmit) and – 870.030 MHz (cell-site transmit) • The two frequencies in channel 666 are – 844.98 MHz (mobile transmit) and – 889.98 MHz (cell-site transmit)
- 8. Numbering the Channels • The 666 channels are divided into two groups: – block A system – block B system
- 10. Numbering the Channels • Each block has 333 channels • The 42 set-up channels are assigned as follows. – Channels 313 - 333 block A – Channels 334 - 354 block B • The voice channels are assigned as follows. – Channels 1 - 312 (312 voice channels) block A – Channels 355 - 666 (312 voice channels) block B
- 11. Numbering the Channels- Additional Spectrum Allocation • New additional spectrum allocation - 10 MHz - additional 166 channels are assigned • a 1 MHz is assigned below 825 MHz (or 870 MHz) • additional channels will be numbered up to 849 MHz (or 894 MHz) and will then circle back • The last channel number is 1023 (=210) • There are no channels between channels 799 and 991.
- 12. New Additional Spectrum Allocation
- 13. Full Spectrum Frequency Management
- 14. Full Spectrum Frequency Management
- 15. Grouping into Subsets • Voice channels for each system is 312 • We can group these into any number of subsets 21 set-up channels for each system • it is logical to group the 312 channels into 21 subsets • Each subset then consists of 16 channels • In each set, the closest adjacent channel is 21 channels away
- 16. Grouping into Subsets • The 16 channels in each subset - connected to a channel combiner • Wide separation between adjacent channels - requirement of minimum isolation • Each 16-channel subset is idealized for each 16-channel combiner
- 17. Grouping into Subsets • In a seven-cell pattern system each cell contains three subsets, iA + iB + iC where i is an integer from 1 to 7 • The total number of voice channels in a cell is about 45 • The minimum separation between three subsets is 7 channels (21/3)
- 18. Grouping into Subsets • If six subsets are equipped in an omnicell site, • Minimum separation between two adjacent channels can be only three (21/6 > 3) physical channel bandwidths • For Example
- 19. Techniques for increasing frequency spectrum • Increasing the number of radio channels using narrow banding, spread spectrum, or time division • Improving spatial frequency-spectrum reuse • Frequency management and channel assignment • Reducing the load of invalid calls – Voice storage service for No-Answer calls – Call forwarding – Call waiting for Busy-Call situations – Queuing
- 20. Set-up Channels • Set-up channels, also called control channels, • Channels designated to set up calls • A system can be operated without set-up channels • Set-up channels can be classified by usage into two types – access channels – paging channels
- 21. Access channels - Operational functions • Power of a forward set-up channel [or forward control channel (FOCC)] • The set-up channel received level (Threshold)-RECC • Change power at the mobile unit(Messages) – Mobile station control message – System parameter overhead message – Control-filler message • Direct call - retry
- 22. Channel Assignment to the Cell Sites-Fixed Channel Assignment • Set-up channels & Voice channels • long-term basis
- 23. Fixed Channel Assignment • N = 4, 7, 12 Setup-channels – 21 channels – cell reuse patterns – Omni-directional antennas – One channel per cell – Unused set-up channels – Avoid interference between block A and B
- 24. Fixed Channel Assignment • Voice Channels – 21 subsets – Min. cochannel & Adjacent channel interference • 3 SAT Tones
- 25. Channel Assignment to Travelling Mobile Units • Underlay-overlay • Frequency Assignment • Tilted Antenna
- 26. Channel Assignment to Travelling Mobile Units Underlaid-overlaid cell arrangements (a) Undelay-overlay in omnicell (b) underlay-overlay in sectorized cells (c) two-level handoff scheme
- 28. Fixed Channel Assignment • Adjacent-Channel Assignment • Channel Sharing and Borrowing • Sectorization
- 29. Adjacent-Channel Assignment Adjacent channel assignment. (a) Omnidirectional-antenna cells (b) directional-antenna cells
- 30. Channel Sharing and Borrowing • Channel Sharing Algorithm
- 31. Sectorization • The 120o sector cell for both transmitting and receiving • The 60o sector sell for both transmitting and receiving • 120o or 60o sector cell for receiving sectorization only , and transmitting antenna is omni-directional
- 32. Non-Fixed Channel Assignment Algorithms • Dynamic Channel Assignment • Hybrid channel Assignment • Borrowing channel Assignment • Forcible-borrowing channel Assignment
- 33. Simulation Process and Results Cellular system. Vehicle and radio- channel distribution in the busy rush hour
- 34. Simulation Process and Results • Average Blocking • Handoff Blocking