Showing posts with label UMTS. Show all posts
Showing posts with label UMTS. Show all posts

Link Budget in WCDMA / UMTS

Link budget planning is part of the network planning process, which helps to dimension the required coverage, capacity and quality of service requirement in the network. UMTS WCDMA macro cell coverage is uplink limited, because mobiles power level is limited to (voice terminal 125mW). Downlink direction limits the available capacity of the cell, as BTS transmission power (typically 20-40W) has to be divided to all users. In a network environment both coverage and capacity are interlinked by interference. So by improving one side of the equation would decrease the other side. System is loosely balanced by design. The object of the link budget design is to calculate maximum cell size under given criteria:

Type of service (data type and speed)
Type of environment (terrain, building penetration)
Behavior and type of mobile (speed, max power level)
System configuration (BTS antennas, BTS power, cable losses, handover gain)
Required coverage probability

WCMDA Paging

Paging process in WCMDA or HSDPA system is called WCMDA Paging. The Paging Channel (PCH) is a downlink transport channel. The PCH is always transmitted over the entire cell. The transmission of the PCH is associated with the transmission of physical-layer generated Paging Indicators, to support efficient sleep-mode procedures.

Paging Channel selection
System information Block Type 5 (SIB 5) defines common channels to be employed in Idle mode. The UE may use Discontinuous Reception (DRX) in idle mode in order to reduce power consumption. When DRX is used the UE needs only to monitor one Page Indicator, PI, in one Paging Occasion per DRX cycle.
The Paging Indicator Channel (PICH) is a fixed rate (SF=256) physical channel used to carry the paging indicators.
Paging Procedure:

Basically two types of Paging Procedures in WCMDA Paging.

1) Idle Mode Paging
2) Dedicated Mode Paging
Idle mode paging is used when UE is in idle mode so we can say UE is in Cell PCH or URA PCH.PAGING TYPE 1 message on an appropriate paging occasion on the PCCH.

UE dedicated paging procedure is used to transmit dedicated paging information to one UE in connected mode in CELL_DCH or CELL_FACH state. PAGING TYPE 2 message on the DCCH using AM RLC.