3GPP TSG RAN WG1 No. Time and place of meeting
Source: Beijing University of Posts and Telecommunications
Title: DL RS design based on compressed sensing for higher order MIMO Document for:Discussion and decision
LTE advanced (LTE-A) is expected to achieve higher DL peak and average cell throughput than LTE, and higher order MIMO in the DL of LTE-A is necessary. Higher order MIMO in the DL of LTE-A is up to 88
multi-antenna configuration to achieve the DL peak spectrum efficiency target . This means that the design of additional reference signal (RS) or novel method of channel estimation for LTE-A should be considered. The RS overhead with four antenna ports of LTE R8 is 14.28%. If the same density as for antenna port 2 and 3 in LTE is applied for new antenna port 4~7 in LTE-A, it would result in a very high RS overhead of 23.81%, which badly impacts the DL peak throughput and necessitates a new RS design with low overhead. Except requirement of low overhead above, some other key aspects for the RS design would be :
●Backward compatibility —LTE UEs shall be supported in LTE-A networks. Thus an
LTE UE should be able to operate within an LTE-A networks with almost the same performance as it was in LTE networks. The new RS can only be interpreted by LTE-A UEs.
This means any operation of LTE UEs should not be affected by the introduction of new RS;
in particular, implementations associated with RS-based estimation functions (channel estimation, CQI/PMI feedback determination, RSSI measurement, etc) should not be affected.
●Trade-off between gain and overhead — higher order MIMO shall provide substantial
gains over the existing MIMO schemes. Otherwise, introducing higher order MIMO is counter-productive. In this sense, we have to investigate trade-off between the gain from better channel estimation and the loss of peak and average cell throughput from the additional RS overhead. Therefore, we must consider the RS overhead when we design the new RS structure supporting up to 8 antenna ports. RS overhead should not be significantly increased.
●Simplicity — the introduction of the additional RS should not be unnecessary complex.