Beamforming in LTE FDD for Multiple Antenna Systems

Sammanfattning: High data rate is still the most crucial factor in cellular systems, and with 5g approaching new techniques are studied to achieve higher bit rates. Using MIMO technology, the spatial domain was exploited through beamforming and multiplexing multiple users’ data together assured more spectrum efficiency which resulted in higher bit rates. Reciprocity based beamforming is feasible in TDD systems due to channel reciprocity assumption between uplink and downlink, the same is not true for FDD systems, as a consequence of using different frequencies between uplink and downlink. Nonetheless, FDD systems are widely deployed because of the existing spectrum assignments and earlier technologies. In addition, FDD systems have advantages such as greater coverage, lower latency over TDD systems. The thesis objective is to study the feasibility of applying beamforming in FDD systems. We investigate for appropriate techniques based on uplink channel measurements and study its performance for various conditions like Doppler shift, number of users, and also compare those results with beamforming in TDD. Results are generated by implementing LTE physical layer and a practical channel model in MATLAB. Mainly three techniques are implemented, all of these used reciprocity in term of Angle of Arrival between uplink and downlink for an FDD channel. The obtained results showed that channel reciprocity based TDD systems perform much better than channel non reciprocity based FDD system in terms of the number of users which can be beamformed with an acceptable Bit Error Rate (BER). Also, the used beamforming techniques showed around 50% improvement in overall capacity for one cell, when compared to FDD system with no beamforming applied.