Cqi writting

Cqi writting

• 1.
  CQI CQI stands forChannel Quality Indicator. As the name implies, it is an indicator carrying the information on how good/bad the communication channel quality is. This CQI is for HSDPA. (LTE also has CQI for its own purpose).CQI is the information that UE sends to the network and practically it implies the following two i) Current Communication Channel Quality is this-and-that. ii) I (UE) want to get the data with this-and-that transport block size, which in turn can be directly converted into throughput In HSDPA, the CQI value ranges from 0 ~ 30. 30 indicate the best channel quality and 0, 1 indicates the poorest channel quality. Depending which value UE reports, network transmit data with different transport block size. If network gets high CQI value from UE, it transmits the data with larger transport block size and vice versa. What if network sends a large transport block even though UE reports low CQI, it is highly probable that UE failed to decode it (cause CRC error on UE side) and UE send NACK to network and the network have to retransmit it which in turn cause waste of radio resources. What if UE report high CQI even when the real channel quality is poor? In this case, network would send a large transport block size according to the CQI value and it would become highly probable that UE failed to decode it (cause CRC error on UE side) and UE send NACK to network and the network have to retransmit it which in turn cause waste of radio resources. How UE can measure CQI? This is the most unclear topic to me. As far as I know, there is no explicit description in any standard on the mechanism by which the CQI is calculated, but it is pretty obvious that the following factors play important roles to CQI measurement.  signal-to-nose ratio (SNR)  signal-to-interference plus noise ratio(SINR)  signal-to-noise plus distortion ration (SIDR) It is unclear how these factors are used and weather there is any other factors being involved. Speech Quality Indicator (CQI)  Signaled to node-b in UL each 2ms on HS-DPCCH  Integer number from 0 to 30 corresponds to to a transport resource combination (TFRC)given by  Modulation  Number of channelization codes  Transport block size  For a given condition the BLER for this TFRC shall not exceed 10%.
• 2.
  CQI Coding mappingtable. RSCP (Received Signal Code Power) - denotes the power measured by a receiver on a particular physical communication channel or power level of pilot channel of a cell. It is used as an indication of signal strength, as a handover criterion, in downlink power control, and to calculate path loss. RSSI (Received Signal Strength) Signal power over the complete 5 MHz carrier which includes all Components received, including the signals from the current and neighboring cells on the same frequency. In an isolated cell having only CPICH power to transmit and with none of the other channels utilized, the effective RSSI can be seen by the UE would be (Fraction of) PCPICH power. However RSSI changes when the 5MHz carrier will carry power for other dedicated or control channels. In that case, the effective power perceived By the UE would be the transmitted power of the serving cell + the power transmitted by neighbor cells over the same carrier frequency.
• 3.
  EcNo Received energyper chip (Ec) of the pilot channel divided by the total noise power density (No). In other words the EcNo is the RSCP divided by the RSSI. And again in other words: The better this value the better can a signal of a cell be distinguished from the overall noise. The EcNo is usually expressed in dB as it is a relative value. The value is negative as the RSCP is smaller than the total received power. As the RSCP this Value can be used to compare different cells on the same carrier and handover or cell reselection decisions can be taken Ec/No= RSCP-RSSI