Multi Band Cells ( MBC ) in GSM

Multi Band Cells (MBC)

A multi band network consists of cells from different frequency bands for example: 900/1800 MHz
−By combining these frequencies in the same cell with 1 common BCCH, the radio performance and traffic capacity are improved where the no. of cells and




-Using MBC concept with only 1 BCCH, this will reduce the no. of defined neighbors to 50% leading to better accuracy for the measurement reports coz there will be more time available for measurements for each neighbor.


-The Dynamic OL/UL subcells (Concentric cells) is a prerequisite feature for the Multi Band Cells.
−Mostly the frequency band with “Better coverage” (i.e. lower frequency band) is configured as the Underlaid subcell while the other frequency band with “Worse coverage” (i.e. higher frequency band) is configured as the Overlaid Subcell.
−Ex: 900MHz frequency band UL, while 1800MHz frequency band OL

−It is recommended to select the BCCH frequency to lie in the “Better Coverage” i.e. UL subcell.
−for the previous example then BCCH frequency will belong to the 900MHz band

−A parameter CSYSTYPE defines the band of the used BCCH frequency in a multi band cell.
−A parameter BAND defines the band of the Channel Group, where the channel group consists of no. of frequencies as will be seen later.
−As mentioned before, the path loss/Distance to cell border/time advance criteria will define the coverage limit of the frequency band used in the OL subcell vs. UL subcell, (In this case the OL&UL will belong to two different bands)
−Also the traffic load can be maintained between the two subcells (that belong to two different bands) using the subcell load distribution feature where the SCLDSC parameter will define which subcell is preferred first.







Overlaid Underlaid Subcells in GSM


−Traffic Capacity of a cellular network can be increased by either adding more frequencies or reducing the frequency reuse distance.
−One approach is to apply a second frequency re-use pattern with a tighter frequency reuse (Overlay) on the existing pattern.
−These cells should be restricted in size, so shorter reuse distance can be accomplished without causing Co-channel/Adjacent channel interference.
−They are termed Overlaid (OL) Subcells, whereas the original cells will be called Underlaid (UL) Subcells.
−Now by having more frequencies per cell, then Network capacity is increased
-The fundamental idea behind the OL/UL subcells is to let the traffic close to the site to be moved to the OL subcell, while traffic close to the cell border to be moved to the UL subcell.
−In that way of treading the traffic, the frequencies in the OL subcell can have tighter frequency reuse.
-Using the OL/UL concept we can solve the case as follows:






-f4 will be used in the OL subcell and it will be restricted to serve in a small area only near to the site so interference from the neighbor cell will be minimized and a good C/I can be enjoyed.
To maintain the service area of the OL subcell restricted to a certain region we have three thresholds we can play with:
A.Path Loss Threshold
B.Timing Advance Threshold
C.Distance to Cell Border Threshold
−With the ordinary OL/UL subcells, the MS near the cell will camp on the overlaid subcell but even if the OL subcell got high utilized there is no way to push traffic to the UL subcell.
−Using Subcell Load Distribution (SCLD) Concept, we can configure the cell to use the OL as the preferred subcell initially and when traffic on the OL increased beyond certain load, any extra traffic will be offloaded to the UL subcell.





Monitor the Incoming Paging in GSM



Paging Groups
−The MS will monitor the incoming paging in only specific times, and the rest of the time it will remain in sleeping mode.
−In this way we save the MS battery and we decrease the UL interference on the system.
−The MS will monitor the incoming paging when the “Paging Group” assigned for this MS is transmitted only.
−The CCCH block can be used by either PCH or AGCH.
−When the CCCH block is used for paging it will be called “Paging Block”
−The Paging Block consists of 4 consecutive Time slots lie in 4 consecutive frames.
−The Paging Block can be used to page 4/3/2 users according to IMSI or TMSI is used when paging the MS ( Length IMSI = 2 TS, Length TMSI = 1 TS)

−The group of users belong to the same paging block will be called “Paging Group” 

IMSI, MSISDN


MCC  MNC  MSIN
( 3Digits) ( 2Digits) ( 10Digits)

IMSI : International Mobile Subscriber Identity IMSI = MCC + MNC + MSINMCC= Mobile Country Code (3 digits)MNC= Mobile Network Code (2 digit )MSIN= Mobile Subscriber Identification Number (10 digits)Ex: IMSI = MCC-MNC-MSIN = 404-22-1234567890 where,602 -  India Country Code22  -   Bharti Airtel  Network Code1234567890 -  Mobile Subscriber Identification Number
MSISDN : Mobile Station Integrated Services Digital NetworkMSISDN = CC + NDC + SNCC= Country Code (2-3 digits)NDC= Network Destination Code (2-3 digit )SN= Subscriber Number ( max 10 digits)

Duplexer


The duplexer incorporates the receiver multicoupler system and the transmitter combiner system to a common antenna. Duplexers are especially useful in a microcell application where space is limited, costs are kept to a minimum, and the building owner or manager places limits on the number of antennas allowed in the building.

The types of duplexing that can be used in a wireless system are:

· Separate TX antenna, or no duplexing
· Single, or one antenna
· Double, or two antenna

When no duplexing is used, three separate antennas are connected, on for transmit and two for receiver. This configuration results in lower output power.

In single duplexing, one antenna is used for transmit and receive. A second receive antenna could be connected for receiver diversity. This configuration allows a single antenna to be used but also results in lower output power.


In double duplexing, two antennas are used for both TX and RX and results in the maximum possible output power.

Common Channel Configuration in LTE

Common Channel Configuration
Uplink resource blocks are required to be allocated for uplink control signaling (PUCCH). The number of RBs will be dependent on bandwidth and loading.

Downlink resources are also allocated for downlink control signaling on the PDCCH channel. This is specified as the number of OFDM symbols (Control Format Indicator).

PDCCH and PUCCH allocations will have an impact on peak data throughputs and system capacity. The PDCCH power boost feature makes it possible to adjust the power of the PDCCH to match the actual number of needed Control Channel Element (CCE) resources. Use cases include beam forming coverage extension, range extensions for small cells and general increase of the PDCCH capacity, which is useful for e.g. VoLTE applications. The maximum power increase is 6 dB.

The feature can be used in conjunction with the Enhanced PDCCH Link Adaptation feature which can provide significantly increased PDCCH capacity, as the RBS better determines the number of CCEs to utilize for UEs, independently from PDSCH.

The Enhanced PDCCH Link Adaptation feature introduces a dedicated link adaptation capability for PDCCH. This allows the eNB to control the number of CCEs to be used in PDCCH allocations to be optimized for a specific PDCCH BLER target, rather than using a fixed offset from the PDSCH link adaptation. It is expected that this will significantly increase the number of UEs that can be scheduled per TTI, as it relates to PDCCH usage. 

Cell Reference Symbol Power Configuration

The Adjustable Cell Reference Symbol (CRS) Power feature (FAJ 121 3049) was introduced in L14A. This feature enables flexible setting of the CRS power (Pa) and also enables flexible setting of the type-B resource element power (PDSCH).
The feature improved flexibility for tuning and optimization of downlink resource element power allocation and can lead to improved DL throughput, such as in high dense networks.




The feature controls two factors:
• CRS Power Boost setting (Pa) in the range +3dB to -3dB, previously this value had been fixed by system constant to +3dB.
• Type-B resource element boosting (Pb/Pa) in the range {5/4, 1, 3/4, 1/2}, previously this value had been fixed by a system constant to 1.