LTE CQI (Downlink)
NS-3 has been implemented based on FemtoForum Specifications. In
the FemtoForum specification document [FFSpec], we can find a
reference for the types of CQI format.According to[FFSpec], in
Section 4.3.2.4, there are 9 types of CQI format (P10, P11, P20,
P21, A12, A22, A20, A30, A31). Ok, now lets understand the meaning
of these types.Well, the 'P' and 'A' in the CQI types stand
forPeriodicandAperiodic. LTE standard defines these two types of
CQI report.The UE can be configured to send periodic CQI report to
eNodeB using the Physical Uplink Control CHannel (PUCCH). This
channel is exclusive for this kind of report.On the other hand, the
eNodeB can request a CQI report from the UE. In this case, we have
an aperiodic CQI that is sent through Physical Uplink Shared
CHannel (PUSCH). The CQI report is embedded into a resource
schudeled for uplink transmission[Sesia].There are also
differentgranularity for CQI reporting process. CQI reports can be
classified as: Widebandfeedback:The UE reports one wideband CQI
value for the whole systembandwidth. eNodeB-configured sub-band
feedback:The UE reports a wideband CQI value forthe whole system
bandwidth. In addition, the UE reports a CQI value for each
sub-band, calculated assuming transmission only in the relevant
sub-band. UE-selected sub-band feedback:The UE selects a set of
preferred sub-bandswithinthe whole system bandwidth. The UE reports
one wideband CQI value and one CQIvalue reflecting the average
quality of those selected sub-bands.The numbers in the CQI format
types (P10, P11, etc) are used to identify the modes of CQI
reporting [TS-36.213], concerning the granularity of the CQI report
and theuse of the Precoding Matrix Indicator (PMI), as can be seen
in the Table 1.Table 1: CQI feedback reporting modes
In the current release (ns3.16), NS-3 only has support
forP10andA30CQI reports.
NS-3 LTE CQI (Uplink)
In LTE networks, the eNodeB relies on CQI reporting to be aware
of the downlink channel quality. For the uplink direction we note
some differences.The firstmechanismof Channel State Information
(CSI) are the Sound Reference Signals (SRS). If the UE has received
a grant for uplink transmission, it sends the CSI data using the
SRS in the PUSCH.For the case when the UE has not received a grant
for uplink transmission, it uses the PUCCH to send the CQI
report.There is also one more case, when the UE does not have
access to a PUCCH. In this context, the UE must use the Physical
Random Access Channel (PRACH) to get access to a PUCCH.
