Channel Element (CE) Resource

CE resources are a type of NodeB hardware resource. The number of CEs supported by single NodeB indicates the channel demodulation capabilities resource of the NodeB. The more CEs a NodeB supports, the more powerful the channel demodulation and service processing capabilities for serving the customers. Services at different rates require different numbers of CEs to ensure proper channel demodulation.

In a RAN, CE resources are managed by both the RNC and NodeB. The NodeB reports its CE capacity to the RNC. The RNC determines whether to admit a new service based on the number of CEs that need to be consumed and controls CE resources during CE congestion.

This ensures the proper use of CE resources. The NodeB dynamically manages CE resources and rapidly adjusts the number of CEs that can be consumed based on the actual service rate. This increases CE resource usage.

A proper use of CE resources increases the number of UEs that can be admitted and improves the service quality of the admitted UEs.

Basic Channel Element Concepts

CE is a basic unit that measures the channel demodulation capabilities of a NodeB. CEs are classified into uplink (UL) CEs and downlink (DL) CEs.

• One UL CE needs to be consumed by a UL 12.2 kbit/s voice service (SF = 64) plus 3.4 kbit/s signaling.
• One DL CE needs to be consumed by a DL 12.2 kbit/s voice service (SF = 128) plus 3.4 kbit/s signaling.

If only 3.4 kbit/s signaling traffic is carried on a DCH or HSPA channel, one CE still needs to be consumed. The number of CEs that need to be consumed by services of other types can be calculated by analogy.

The number of UL and DL CEs supported by a NodeB is determined by the NodeB hardware capabilities and the licensed CE capacity. The number of UL and DL CEs supported by the NodeB hardware is called the physical CE capacity. The licensed CE capacity may differ from the physical CE capacity. The smaller determines the number of CEs that can be used by an operator.

CE is a concept of the NodeB side. On the RNC side, it is called NodeB credit. The RNC performs admission and congestion control based on the NodeB credit. In the UL, the number of Node credit resources is twice that of CEs. In the DL, the number of NodeB credit resources equals that of CEs.

CE Sharing in a Resource Group

To facilitate baseband resource management, NodeB baseband resources fall into UL and DL resource groups. The UL and DL resource groups are independent with each other.

• UL Resource Group 

UL resource group is a UL resource pool shared on a per-channel basis, more than one cell can be setup in one UL resource group, One UL resource group can have multiple baseband boards, but one board can belong to only one UL resource group. CE resources in one UL resource group can be shared by baseband boards. This means that UEs in a cell in a UL resource group can set up services on any board in the group. The physical CE capacity of a UL resource group is the total CE capacity of baseband boards in the group.

• DL Resource Group

Different from a UL resource group, a DL resource group is shared on a per-cell basis. Resources in a DL resource group are allocated to each baseband board based on cells; one board can be configured to multiple DL resource groups. DL CE resources for UEs in the same cell can be provided by any baseband board in the DL resource group. CE resources in one DL resource group can be shared only within a baseband board.

NodeB CE Capacity Specifications

Typically different baseband boards of a NodeB have their own CE capacity specifications. For exampled, the detailed CE capacity specifications supported by each type of baseband board, see the BBU3900 Hardware Description product by Huawei

CE capacity here refers to the number of CEs that can be consumed by UL and DL R99 services and HSUPA services. It does not include CE resources reserved by the NodeB for common and HSDPA channels.

Rules for Calculating CE Consumption

The RNC determines the number of CEs required for a service based on the SF that matches the service rate. When an RAB connection is set up or released for a service, CE resources must be allocated or taken back and the number of CEs must be deducted or added accordingly. Different rules for calculating CE resource consumption apply to channels or services of different types.

• CE resources reserved by the NodeB for common and HSDPA channels are shown in gray. 
• CE resources that need to be consumed by R99 and HSUPA services are shown in pink.

Common Channels CE Consumption

CE resources required on the UL and DL common channels are reserved by the NodeB. Therefore, they do not occupy the licensed CE capacity. These CEs do not need to be considered in the calculation of CE consumption.

HSDPA Channels CE Consumption

Similarly, the NodeB reserves CE resources for the high-speed downlink shared channel (HS-DSCH) and the related control channels if HSDPA is used. These CEs also do not need to be considered in the calculation of CE consumption.

Note that the signaling of an HSDPA UE that is not performing an R99 service occupies one DCH and needs to consume one DL CE. If the SRB over HSDPA function is enabled, the signaling of an HSDPA service does not consume additional CE resources. For an HSDPA UE that is performing an R99 service, its signaling and the R99 service occupy the same DCH. Therefore, only the CEs consumed on R99 traffic channels need to be calculated.

R99 Service CE Consumption

For an R99 service, the RNC determines the number of CEs and NodeB credit resources that need to be consumed based on the SF that matches the maximum bit rate (MBR) of the service.

Direction	Rate (kbit/s)	SF	Number of CEs Consumed	Corresponding Credits Consumed
UL	3.4	256	1	2
	13.6	64	1	2
	8	64	1	2
	16	64	1	2
	32	32	1.5	3
	64	16	3	6
	128	8	5	10
	144	8	5	10
	256	4	10	20
	384	4	10	20
DL	3.4	256	1	1
	13.6	128	1	1
	8	128	1	1
	16	128	1	1
	32	64	1	1
	64	32	2	2
	128	16	4	4
	144	16	4	4
	256	8	8	8
	384	8	8	8

HSUPA Service CE Consumption

For an HSUPA service, the RNC determines the number of CEs and NodeB credit resources that need to be consumed based on the SF that matches the service rate. The RNC determines the SF based on a certain rate in the following ways:

• If the UL enhanced L2 function is disabled and the NodeB indicates in a private information element (IE) that dynamic CE resource management has been enabled in the cell, the RNC calculates the SF based on the larger of the bit rate of one RLC PDU and the guaranteed bit rate (GBR).
• If the UL enhanced L2 function is disabled, the RLC PDU size is fixed. The bit rate of one RLC PDU is determined by the RLC PDU size and transmission time interval (TTI).
• If the UL enhanced L2 function is enabled and the NodeB indicates in a private IE that dynamic CE resource management has been enabled in the cell, the RNC calculates the SF based on the larger of the bit rate of the smallest RLC PDU and the GBR.
• If the UL enhanced L2 function is enabled, the RLC PDU size is flexible. The bit rate of the smallest RLC PDU is determined by the minimum RLC PDU size and the TTI. The minimum RLC PDU size can be specified by the RlcPduMaxSizeForUlL2Enhance parameter.
• If the NodeB reports that dynamic CE resource management has been disabled, the RNC calculates the SF based on the MBR.
• If the NodeB does not report whether dynamic CE resource management has been enabled, the RNC calculates the SF based on the value of the HsupaCeConsumeSelection parameter and whether the UL enhanced L2 function is enabled.
• If HsupaCeConsumeSelection is set to MBR, the RNC calculates the SF based on the MBR.
• If HsupaCeConsumeSelection is set to GBR:
• If the UL enhanced L2 function is disabled, the RNC calculates the SF based on the larger of the bit rate of one RLC PDU and the GBR.
• If the UL enhanced L2 function is enabled, the RNC calculates the SF based on the larger of the bit rate of the smallest RLC PDU and the GBR.

After determining the SF, the RNC searches the CE consumption mapping listed below

Direction	Rate (kbit/s)	SF	Number of CEs Consumed	Corresponding Credits Consumed
UL	8	64	1	2
	16	64	1	2
	32	32	1	2
	64	32	1	2
	128	16	2	4
	144	16	2	4
	256	8	4	8
	384	4	8	16
	608	4	8	16
	1450	2SF4	16	32
	2048	2SF2	32	64
	2890	2SF2	32	64
	5760	2SF2+2SF4	48	96

CE Consumption of 4-Way Receive Diversity

The use of 4-way receive diversity does not affect DL CE consumption but doubles UL CE consumption. The use of 4-way receive diversity can be configured by resource group. UL CE consumption of a resource group doubles if the resource group is configured with 4-way receive diversity. CE consumption of a common resource group remains unchanged.

examples of CE Consumption

• UE A, which performs a UL 64 kbit/s and DL 384 kbit/s service on the DCH, consumes three UL CEs and eight DL CEs.
• UE B, which performs a UL 64 kbit/s and DL 1024 kbit/s service on the DCH and HS-DSCH respectively, consumes three UL CEs and one DL CE if the DL signaling radio bearer (SRB) is carried on the DCH.
• UE C, which performs a UL 608 kbit/s and DL 1024 kbit/s service on the E-DCH and HS-DSCH respectively and at the same time performs an AMR speech service, consumes nine UL CEs and one DL CE.

Source: http://www.ajusady.com/