Co-ordinated Multi point transmission and reception- 3GPP Rel 11

The main reason to introduce CoMP is to improve network performance at cell edges. In CoMP a number of TX (transmit) points provide coordinated transmission in the DL, and a number of RX (receive) points provide coordinated reception in the UL. 


TX/RX-point
A TX/RX-point constitutes of a set of co-located TX/RX antennas providing coverage in the same sector. 

The set of TX/RX-points used in CoMP can either be at different locations, or co-sited but providing coverage in different sectors, they can also belong to the same or different eNBs. CoMP can be done in a number of ways, and the coordination can be done for both homogenous networks as well as heterogeneous networks.  In figure 8 two simplified examples for DL CoMP is shown. In both these cases DL data is available for transmission from two TX-points. 

Joint Transmission
When two, or more, TX-points, transmit on the same frequency in the same subframe it is called Joint Transmission.


Dynamic Point Selection
When data is available for transmission at two or more TX-points but only scheduled from one TX-point in each subframe it is called Dynamic Point Selection. 

Joint Reception
For UL CoMP there is for example Joint Reception, a number of RX-points receive the UL data from one UE, and the received data is combined to improve the quality. 

When the TX/RX-points are controlled by different eNBs extra delay might be added, since the eNBs must communicate, for example in order to make scheduling decisions. When CoMP is used additional radio resources for signaling is required e.g. to provide UE scheduling information for the different DL/UL resources.


                           
Figure . DL CoMP  a) Joint Transmission;  two TX-points transmit to one UE in the same radio resource,
b) Dynamic Point Selection; two TX points are ready to transmit, but only one will be scheduled in each subframe.

Reference:
1. 3GPP TR 36.814: Further Advancements for E-UTRA Physical Layer Aspects
2. Coordinated Multipoint Trials in the Downlink - Fraunhofer Heinrich Hertz Institute
3. Berlin Field Trial in October 2009-Youtube-Video

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