Bad EcNo with good RSCP can be caused by 2 things (barring any equipment issues as experts have pointed out)

1. DL interference such as SC clash or pilot pollution (lack of dominant server), check your SC plan or reduce the number of interfering servers by down tilting some unnecessary sectors. you can confirm this if EcNo is poor, RSCP is good and UE Tx power is low

2. Too high cell cell loading/ high noise or interference floor (check if RTWP and TCP mean values are high as last poster mentioned) you can confirm this if EcNo is poor, RSCP is good and UE Tx power is high, try to balance traffic between F1 and F2, check if any carrier is carrying traffic from afar (overshooting) and reduce its coverage, reduce set value for mobile access power on node b.

Why CQI? Some Questions answered

Why CQISeveral times we’ve asked ourselves these questions:Q: Why do we get poor Ec/No when conducting HSDPA Drive Test?Q: What is the calculations behind Ec/No going low when HSDPA session is initiated?Q: Why do we consider CQI as a Quality Metric when conducting HSDPA Drive Test instead of Ec/No?Take a look at the following slides 

Why CQINote the CQI value is 27 (good) while EcNo is about to explode (-12db)

Lets start by establishing some basics:Ec/No for most of you is a Quality & Capacity measuring Metric. It generally gives us the idea how good or bad the link Quality is. However, by definition, its quite confusing – CPICH Ec/No = Pilot channel quality energy per chip over total received power spectral density ORRSCP = RSSI + Ec/NoEcNo = RSCP - RSSILet’s go back to developing BasicsWHAT?!?!?Ok…..

So, we establish that, The CPICH Ec/No measurements collected during HSDPA Transmission could mask the true radio conditionsTo avoid this, we have to monitor the Ec/No in IDLE mode only, which is a true reflection of Interference and coverage problems HSDPA session adds to the overall load of the cell which is taken into consideration during computing Ec/No. As calculations above proved that this does not, necessarily, depict the TRUE radio Conditions.So, what is the ALTERNATIVE to Ec/No in HS session? Its called Channel Quality IndicationCQI

Why CQI

What is CQIHSDPA utilizes link adaptation techniques to substitute power-control and variable spreading factorThe HS-DSCH link-adaptation algorithm at the Node-B is very dynamic, and adjusts the transmit bit rate on the HS-DSCH every 2-ms TTI.The UE periodically sends a CQI to the serving HS-DSCH cell on the uplink high-speed dedicated physical control channel (HS-DPCCH)The CQI tells the NodeB scheduler, the data rate the UE expects to be able to receive at a given point in time.

NOTE: The HSDPA system defines a different CQI mapping table for different categories of UEs. The category is determined according to the capability of UEIn addition to CQI, UE also sends HARQ on HS-DPCCH

Below figure shows the steps how CQI helps in determining the initial throughput that a UE terminal demands from the systemSTEPSSINRis used to evaluate the channel quality as observed by the receiver, where a standard single antenna Rake is used because it is the most common in the SISO HSDPA terminals.CQI value for a given SINR is done via a linear mapping, as shown in figure

HSDPA – CQI involvement

HSDPA – CQI involvementSTEPSThe CQI values are used by the link adaptation algorithm at the Node-B. Every CQI value reported corresponds to the Transport Block Size (TBS) that can be granted on a particular Modulation type and Number of codesExample of a UE category 10 CQI values from 0 to 30 are shown in the figure. Other UE categories are shown in the following slideThe CQI is further defined as the TBS that can be supported with a BLER no greater than 10% -

STEPSWhile CQI is sending UE’s requirement to the system in UL, there is BLER calculation going on and UL HARQ (Hybrid Auto Repeat Request) mechanism is helping in maintaining the BLER to below 10%. So the system (NodeB) is essentially calculating the Data Rate to be scheduled to the user based on CQI reports and BLER which it receives from the UESo DATA RATE (bps) = TBS (bits)/ TTI (sec) * (1-BLER)HSDPA – CQI involvement

HSDPA – UE Categories 1-12

STEPSWhile CQI is sending UE’s requirement to the system in UL, there is BLER calculation going on and UL HARQ (Hybrid Auto Repeat Request) mechanism is helping in maintaining the BLER to below 10%. So the system (NodeB) is essentially calculating the Data Rate to be scheduled to the user based on CQI reports and BLER which it receives from the UESo DATA RATE (bps) = TBS (bits)/ TTI (sec) * (1-BLER)HSDPA – CQI involvement

HSDPA – UE Categories 1-12