Ericsson Counter: Drops on SDCCH

 CNDROP : The total number of dropped SDCCH channels in a cell.

CNRELCONG :  Number of released connection on SDCCH due to TCH— and transcoder congestion in underlaid and overlaid subcell. The subset for overlaid subcells is CNRELCONGSUB. The two counters are located in CLSDCCH and CLSDCCHO respectively. CNDROP is stepped at the same time.

CDISTA : Dropped SDCCH connection at excessive Timing Advance (TA).

CDISSS :  Dropped SDCCH connection at low signal strength on down— or uplink in underlaid subcell i.e. belowLOWSSDL and/or LOWSSUL. There is also a counter for overlaid subcell, CDISSSSUB.

CDISQA : Dropped SDCCH connection at bad quality down— or uplink per cell in underlaid subcell i.e. worse than BADQDL and/or BADQUL. There is also a counter for overlaid subcell, CDISQASUB.

Read Also other topis : Ericsson Counter: Call Attempts, Paging, Congestion, Dropped Calls, Handover, Speech Quality, Intra-Cell Handover, OL/UL Subcell

Ericsson Counter: Call Attempts

CCALLS : Channel allocation attempt counter (on SDCCH).

CMSESTAB : Successful MS channel establishments on SDCCH.

CCONGS : Congestion counter for underlaid subcell. Stepped per congested allocation attempt. The counter for overlaid subcell is CCONGSSUB.

CESTCHACTIV :  Number of SDDCH establishment failure that occurs under channel allocation and channel activation. Note that this counter is stepped also in case of SDCCH congestion.

CESTIMMASS : Number of SDCCH establishment failure due to timeout after sending Immediate Assignment, timer T3101 expired.

TFCASSALL : Number of assignment complete messages for all MS power classes in underlaid subcell, full-rate. There is also an identical counter for overlaid subcells, TFCASSALLSUB. There are corresponding counters for half-rate.

TASSATT : Number of first assignment attempts on TCH for all MS power classes. Both successful and unsuccessful attempts are counted in the target cell.

TASSALL : Number of first assignment attempts on TCH for all MS power classes. Successful attempts are counted in the target cell and failed attempts are counted in the serving cell. The serving cell is the cell where the mobile station was tuned to an SDCCH or TCH for signalling.

TCASSALL : Number of assignment complete messages on TCH for all MS power classes.

Read Also other topis : Ericsson Counter: Paging, Drops on SDCCH, Congestion, Dropped Calls, Handover, Speech Quality, Intra-Cell Handover, OL/UL Subcell

Ericsson Counter : Paging

PAGPCHCONG :  Number of paging messages discarded due to full cell paging queue.

PAGETOOOLD  : Number of paging messages discarded due to being too long in the paging queue. At the point when a page is taken from the paging queue, its age is calculated and compared to the BTS parameter AGE-OF-PAGING (the parameter is set to 5 seconds in Ericsson BSS). If it is too old, it is discarded and PAGETOOLD is incremented.

TOTPAG :  Number of paging messages received from the MSC.

TOTCONGPAG : Number of paging messages discarded due to lack of capacity in the BSC or due to congestion in the BSC paging queues or due to no Data Link Individual is available for a paging request taken from the paging queue.

NLAPAG1LOTOT : Number of first page attempts to an LA.

NLAPAG2LOTOT : Number of repeated page attempts to an LA.

NLAPAG1RESUCC :  Number of page responses to first page to an LA.

NLAPAG2RESUCC :  Number of page responses to repeated page to an LA.

NLALOCTOT : Total number of LU attempts in the LA.

NLALOCSUCC :  Number of successful LUs in the LA. 

Read Also other topis : Ericsson Counter: Call Attempts, Drops on SDCCH, Congestion, Dropped Calls, Handover, Speech Quality, Intra-Cell Handover, OL/UL Subcell

Bit Error Rate (BER)

The environmental effects on the received signal produce interference and impairments in the form of Bit Error Rate (BER). BER is defined as the ratio of the number of incorrect bits received versus the total number of bits. BER is estimated by the RBS on the reverse-link and by the MS on the forward-link. IS-136 does not state explicitly how the BER should be estimated but does specify the recommended accuracy for BER estimations. BER measures the effects of radio environment-introduced impairments which are discussed in the Speech Quality and Link Budget documents in this RF module.

Bit error rates are reported in Classes as shown in Table

The BER is estimated by comparing the detected bits (after deinterleaving) with the decoded bits that have been encoded. The BER Classes represent the BER before any forward error correction takes place.

INTERFERENCE in GSM

In GSM   systems, there can be interference to cells from their neighbor cells that use the same frequency or adjacent frequencies or both. There can even be interference from cells in other systems. Interference can be classified as Co-Channel Interference (CCI) and Adjacent Channel Interference (ACI) from the same system (intrasystem interference) or between different systems (intersystem interference).

Co-channel Interference

Because of frequency reuse in GSM  systems, the reused frequencies in other cells can interfere with the serving cell. CCI depends on the reuse plan. For example, the 7/21 reuse plan has a CCI greater than the 9/27 reuse and less than the 4/12 reuse plan. Therefore, to reduce the CCI it is recommended to increase the reuse pattern or, equivalently, increase the reuse distance between cells of the same frequency groups. The impact of increased CCI is a degradation in voice quality. The CCI is measured in terms of Carrier-to-Interference Ratio ( C/I) . For analog systems, C/I of 17 dB is considered appropriate for good voice quality.The BER for a digital system with and without diversity for different C/I levels.

Relationship between C/I and BER

Adjacent Channel Interference

The avoidance of using adjacent channels in neighbor cells is a good practice and is possible in a theoretical 7/21 reuse pattern. In practical systems, adjacent channel assignments in neighbor cells can occur quite often. When the carrier power is increased in a cell, it can cause interference to an adjacent channel in the neighbor cell. The IS-136 standard specifies acceptable levels for Carrier-to-Adjacent Interference Ratio (C/A) that produces acceptable voice quality in terms of BER for uplink interference as shown in figure

Overlay and Underlay Cells

In the overlay/underlay cell design, two cells (micro or macro) are defined at the same Radio Base Station (RBS) to transmit in the same direction, omnidirectional or sectored. The overlay cell has a lower output power, smaller coverage and provides service to Mobile Stations (MSs) close to the RBS. The underlay cell has higher power, wider coverage and provides service to an MS farther away from the RBS.

The underlay cell contains voice channels (analog or digital), control channels and a locating device. The overlay cell contains only a group of voice channels (digital or analog) and depends on the underlay cell to set up calls and perform handover. The reverse-link RSS during call origination or page response determines whether the overlay or the underlay cell is used.

Relationship between an overlay and underlay cell.

The main advantage of using overlay cells is to increase the traffic handling capacity without building new sites. Overlay cells can be used to reduce problems in the transition areas between small and large radius cells.

One of the disadvantages of the overlay cell is based on the assumption that its originating traffic is very close to the RBS. When the traffic is far away from the RBS, the overlay cell will not be used.

The ideal places to position overlay cells are on RBS sites, either in the center of or very close to major roads and highways, especially where the traffic is forced to move slowly during busy periods. They are most suitable at the edge of a suburban area. The overlay can handle the suburban traffic and the underlay can be used primarily for the rural area.

PDCH: Packet Data Channel in GPRS

PDCHs may also be used by TBFs in Dual Transfer Mode (DTM). The DTM TBFs may either use PDCHs already allocated for normal GPRS/EGPRS traffic or trigger allocation of additional PDCHs that then can be used for normal GPRS/EGPRS traffic too. Some PDCHs can later be returned to the CSD when they are no longer needed, or when CS traffic or Abis demand requires it.

There are different types of PDCHs; dedicated PDCHs, semi-dedicated PDCHs and on-demand PDCHs.

Dedicated PDCHs:

The number of dedicated PDCHs in a cell is set by the operator. These PDCHs are allocated at configuration from the CSD to the PSD for GPRS/EGPRS traffic and can then not be pre-empted by CS traffic. A GSL resource and an Abis resource is allocated at the time of allocation. The number of dedicated PDCHs can only be decreased by the operator.

Semi-dedicated PDCHs:

The number of semi-dedicated PDCHs in a cell is also set by the operator. These PDCHs are allocated at configuration from the CSD to the PSD for GPRS/EGPRS traffic and cannot be pre-empted by CS traffic. The number of semi-dedicated PDCHs can only be decreased by the operator. Semi-dedicated PDCHs will be activated first when there is need for more PDCHs for PS traffic, that is the GSL resource is not allocated until needed. The Abis resource is not allocated until needed either if the channel has a flexible Abis resource, When there is no longer any traffic need for a semi-dedicated PDCH (no TBF is reserved on it), it will be put in the PSD idle list (PIL). Eventually the GSL resource and the Abis resource (if a TCH with flexible Abis is used) will be returned to the respective pool.

On-demand PDCHs:

On-demand PDCHs are allocated from the CSD only when there is need for more PDCHs for PS traffic. At on-demand PDCH allocation also the GSL resource is allocated. The Abis resource is also allocated if the channel has a flexible Abis resource,  When there is no longer any traffic need for an on-demand PDCH (no TBF is reserved on it), it will be put in the PIL. Eventually the GSL resource and the Abis resource (if a TCH with flexible Abis is used) will be returned to the respective pool and the PDCH will be deallocated from the PSD and returned to the CSD. On-demand PDCHs can also be pre-empted by CS traffic.