CHANNEL ELEMENT (CE) DIMENSIONING
2G and 3G COMPARISON:
• in 2g systems, capacity of a sector is calculated by the number of available TCH timeslots.
… continuation: * in 3G systems, capacity of sector is calculated by the number of available CE. Utilization of CE varies for different traffic classes / bearers / services. Services PS: 8 kbps, 16 kbps CS: 12.2 kbps AMR PS: 32 kbps PS: 64kbps, 128 kbps (including ADCH) CS: 64 kbps PS: 256 kbps PS: 384 kbps (including ADCH) HSDPA scheduler reserved blocks for 5 codes (UL and DL) HSDPA UL SRB: 3.4 kbps Control Channels
CEs Required 1 2 4 8 16 32 1 16
DEFINITION:
• describes the SW licensed capacity resources required for a dedicated channel (DCH or E-DCH).
• the number of channel elements, NCE, required in a RBS is based on the traffic type, and is dependent on the radio bearers to be used, as well as on the number of simultaneous users for each specific radio bearer.
HARDWARE: • each time a dedicated channel is allocated, channel elements will be consumed in UL and DL. • the consumption can be described as a cost, and depends on the type of radio bearer for the dedicated channel. • if there is an insufficient amount of channel elements available, blocking might occur. To avoid blocking, a best effort user will be switched down to a lower rate to make channel elements available for the requested dedicated channel.
…continuation: • channel elements are asymmetrically allocated, which means that the CEs are allocated separately in uplink and downlink. Thus the CE requirements for the Node B must be computed separately for UL and DL using the individual service bit rates, and consider which among the UL and DL CE requirements is higher. • for HSDPA, aside from the 32 CEs reserved for HSDSCH downlink traffic, the corresponding A-DCH (Associated DCH) on uplink and SRB (Signaling Radio Bearer) on downlink must be considered.
… continuation:
* for UL A-DCH the channel elements needed is based on the bearer rate, while for DL SRB only one CE is used in each connection.
INPUTS REQUIRED:
• number of subscribers per Node B • traffic usage per subscriber per application: AMR, CS64, PS64, PS128, PS384, HSDPA or • traffic usage per application
ASSUMPTIONS:
* Soft Handover Overhead (SHO) = 30%
DIMENSIONING PROCESS:
• compute separately for UL and DL CE Requirements • determine the total traffic per application per Node B • compute the number of CEs required per application (R99 CE) • compute CEs needed by A-DCH based on HSDPA bearer rate for UL and 1 CE on each connection for DL • add the CEs required for R99 and HSDPA A-DCH
… continuation: • compute for the Soft Handover CE Requirement by multiplying the above result by SHO • add the CEs for HSDPA scheduler reserved block • add the CEs needed for control channels • sum up the CEs required for R99 and A-DCH, SHO, HSDPA scheduler and control channels to get the total required CEs for UL and DL • compare the DL and UL CE requirements; use the higher value to compute the number of modules required: eg. 1 module = 192 CEs
EXAMPLE: • Node B with 3 sectors • BH Traffic mix: 12 x AMR, 3 x CS64, 5 x 64/128 PS, 2 x 64/384 PS, 2 x 384/HSPDA • SHO = 30% • Max 16 HSDPA users per BTS Compute for the DL and UL CE Requirements
… continuation: Number of users
Services
UL CE Requirement
DL CE Requirement
12
12.2 kbps AMR
12*1 = 12
12*1 = 12
3
CS 64 kbps
3*4 = 12
3*4 = 12
5
PS 64/128 kbps
5*4 = 20
5*4 = 20
2
PS 64/384 kbps
2*4 = 8
2*16 = 32
2
384 A-DCH HSDPA
2*16 = 32
2*1 = 2
R99 and ADCH Reqt
84
78
SHO Requirements
84*0.3= 26
78*0.3 = 24
HSDPA scheduler
32
32
Control Channels
16
16
Total CEs Required
158
150
Module Required
=158/192 = 0.82 = 1 module
