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Choice of channel assignment strategy impacts the performance of the system, particularly as to how calls are managed when a mobile user is handed off from one cell to another.
Channel assignment strategies
Channel Assignment Strategies AJAL.A.J Assistant Professor –Dept of ECE,Federal Institute of Science And Technology (FISAT) TM MAIL: firstname.lastname@example.org
Introduction Related Work Channel Assignment Strategy Results Conclusions02/07/13 2
Channel Assignment Strategies For efficient spectrum utilization, frequency reuse scheme should be consistent with objectives ► Increasing system capacity ► Minimizing interference Strategies can be classified as Fixed and Dynamic 3
Related WorkA Channel Assignment Strategy using Four Partially Overlapping Channels in Mid-scale Wireless Mesh Networks
Fixed Channel Assignment Strategy In Fixed Channel Assignment Strategy, ► Each cell is allocated a predetermined set of voice channels. ► A call attempt can only be served if unused channel in that particular cell is available ► If all channels are occupied then the call is blocked. Several variation exist like borrowing strategy • A cell is allowed to borrow a channel from neighboring cell if all of its channels are occupied • A mobile switching center (MSC) supervises such procedures and ensures that borrowing of channel does not disrupt the or interfere with any of the calls in progress in the donor cell 5
Dynamic Channel Assignment Strategy Dynamic Channel Assignment Strategy ► Voice channels are not allocated to cells permanently ► On each call request, the BS requests a channel from MSC. ► MSC allocates a channel by taking into account • the likelihood of future blocking within the cell • The frequency of use of the candidate channel, reuse distance 6
► Hence, MSC only allocates a channel if that is not presently in use in the cell which falls within minimum restricted distance of frequency reuse.► It reduces the likelihood of the call blocking, increasing the trunking capacity of the system.► It requires MSC to collect real-time data on channel occupancy, traffic distribution and RSSI of all channels • This increases storage and computational load on the system • But provides increased channel utilization and decreased call blocking 7
Channel Assignment Strategies• Frequency reuse scheme – increases capacity – minimize interference• Channel assignment strategy – fixed channel assignment – dynamic channel assignment• Fixed channel assignment – each cell is allocated a predetermined set of voice channel – any new call attempt can only be served by the unused channels – the call will be blo c ke d if all channels in that cell are occupied• Dynamic channel assignment – channels are not allocated to cells permanently. – allocate channels based on request. – reduce the likelihood of blocking, increase capacity.
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. interference A variety of channel assignment strategies has been developed: fixed or dynamic. 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.
Dynamic channel assignment Dynamic channel assignment strategies require the RNC to collect real-time data on channel occupancy, traffic distribution, and radio distribution 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). assignment
Dynamic channel assignment Advantage: reduces call blocking (that is to say, it increases the trunking capacity), and increases voice quality Disadvantage: increases storage & computational load @ MSC requires real-time data from entire network related to: channel occupancy traffic distribution Radio Signal Strength Indications (RSSIs) from all channels 11
Rules for channel assignment Do not assign co-channels or adjacent channels at the same cell site (not applicable for CDMA). Do not assign co-channels in adjacent cell sites (not applicable for CDMA). Do not mix and match channel groups in a cell or sector. Avoid adjacent channel assignment in adjacent cell sites (not applicable for CDMA). Maintain proper channel separation for any channel assignment for a sector or site. Maximize the distance between reusing cell sites.
FPOC Channel Assignment Strategy a 17 b 26 19 c d 39 29 e 19 16 28 f 38 g 23 27 h 29 i Node order of assignment : MAPe assigned linkeb: 39 radio11 radio radio22 radio assigned linkeh: 38 linkeb: 39 linkeh: 38 assigned link : 29 linkef: 28 linked: 29 ba assigned link : 28 ef16 02/07/13
FPOC Channel Assignment Strategy a LinkSet3 17 b 26 LinkSet5 39 19 c d LinkSet1 29 e 19 16 LinkSet2 LinkSet6 28 f 38 g 23 27 h LinkSet4 29 i Link Link set1 set2 Link Link set3 set6 Link Link set5 set417 02/07/13 Conflict Graph
FPOC Channel Assignment Strategy a LinkSet3 17 b 26 19 LinkSet5 39 c d LinkSet1 19 29 e 16 LinkSet2 LinkSet6 28 f 38 g 23 27 h LinkSet4 29 i Traffic Conflict-free Channels LinkSet1 67 null Channel 1 LinkSet2 67 null Channel 4 LinkSet4 56 LinkSet3 Channel 8 LinkSet5 42 LinkSet6 Channel 11 LinkSet6 42 LinkSet5 Channel 11 LinkSet3 36 LinkSet4 Channel 818 02/07/13
a b c d e f g h i j Transmission Range k l m n o Interference Range p q r s t u v w x y02/07/13 19
Reserved Channel Scheme (RCS) The reserved channel scheme (RCS) is similar to NPS except that a number of channels or transceivers in each BS are reserved for handoffs. In other words, the channels are divided into two groups: the normal channels, which serve both new calls and handoff calls, the reserved channels, which only serve handoff calls.