Downlink Shared Channel Evaluation of LTE System Master of Science Thesis in Communication Engineering

Long term evolution (LTE) of universal mobile telecommunications system (UMTS) is one of the most developed wireless broadband systems worldwide. Based on orthogonal frequency-division multiple access (OFDMA), it provides high-speed data packets access for various deployment scenarios. Link adaptation is a technique used in the LTE system in order to exploit the benefits of the frequency selectivity of the wireless channels. With link adaptation, the spectral efficiency can be further improved. But to perform link adaptation, certain quality information of the channel is required at the transmitter side. In the frequency-division duplex (FDD) LTE system, the channel quality information is fed back from the user equipment (UE) to the base station (eNB). For the purpose of minimizing the overhead, the channel quality information is quantized and the UE only feeds back the corresponding channel quality index (CQI) to the eNB. Various ways of calculating the CQI at the UE side has been proposed and one of the most accepted ways is the exponential effective SINR mapping (EESM) that is utilized in this thesis. In order to minimize the control signal overhead, in the LTE standard, only one modulation and coding scheme (MCS) can be used for each UE in the downlink, though UE may feed back different CQI values for its preferred sub-band. 15 different CQIs and their corresponding MCSs have been defined as the uplink feedback values. In this thesis work, we implement multiuser schedulers that allocate the available recourse blocks (RBs) and assign a proper MCS to different users within single input single output (SISO) transmission scheme in physical layer and investigate their performance.