2.11 – COMP (COORDINATE MULTIPOINT) – CAPACITY & COVERAGE ENHANCEMENT IN 4G LTE


In cellular communication Inter-Cell interference
has always been a major concern. In Second generation communication the operators
divided the allocated bandwidth and cells in the vicinity used different frequency to
operate. The technique is popularly known as frequency
reuse. But with the evolution of communication the
users became data hungry and Operators had to allocate more resources to the Users or
provide them with more bandwidth. To overcome this, a frequency reuse factor
of 1 is used in 4G i.e all cells uses same frequency . As a result at the cell edge users
may face Inter cell interference. So what did the Operators came up with to
mitigate this issue? Hello Everyone! Welcome back to the Fundamentals of LTE. Today we will see how using Multipoint Co-ordination
the user experience at the cell-edge is improved by exchanging cell information among different
base stations. The prime motivation of Coordinated multipoint
as described by 3GPP are To improve the coverage
To improve the cell edge throughput and To increase the overall system throughput. There are primarily 2 types of CoMP. 1. Intrasite CoMP – Where Multiple sectors of
One eNB co-operates. The Advantage of Intra-site CoMP is that significant
amount of information can be exchanged since the communication is within the cells of same
eNodeB and doesn’t involve the backhaul. 2. Intersite CoMP. This involves coordination of multiple eNodeBs. It puts additional burden on the backhaul
as lot of information is exchanged. Now there are Two ways by which Coordinated
multipoint operates. The first method is called JOINT PROCESSING.
In this method for downlink transmission, data is transmitted to the UE simultaneously
from a number of different eNBs. The aim is to improve the received signal
quality and strength. In Uplink the PUSCH is received at multiple
cells. The basic concept behind this format is to
utilise antennas at different sites. By coordinating between the different eNBs
a virtual antenna array is formed. The signals received by the eNBs are then
combined and processed to produce the final signal. This technique allows for signals that are
very low in strength, or masked by interference to be received with few errors. In both UL and DL the Joint Processing method
places a high demand onto the backhaul network. A lot of data needs to be exchanged between
the co-ordinated eNodeBs. Depending upon the number of eNodeBs involved
this data may double or triple. The Second Method is called Co-ordinated scheduling
or Beamforming In this case data to a single UE is transmitted
from one eNB. For Downlink, transmit beamforming weights
are generated. Based on it the scheduling decisions as well
as any beams are coordinated to reduce the unnecessary interference from other cells. As a result, the cell edge user throughput
can be improved due to the increase in received SINR In Uplink the UE transmits the Physical Uplink
Shared Channel using a Resource Block to a Single cell. The scheduling decision is based on the coordination
among the cells. This format provides a much reduced load in
the backhaul network because only the scheduling data needs to be transferred between the different
eNBs that are coordinating with each other. The major challenges faced in Co-ordinated
Multipoint Transmission reception are – Efficient feedback compression,
Reduced feedback delay, Efficient channel prediction at the precoder,
Flexible formation of cooperation clusters, Handling of outer interference within the
cluster, Efficient multi-user selection,
Flexible networking behind Coordinated Multipoint, Integration of Coordinated Multipoint into
higher layers and Reduce cost of base station synchronization
and low-phase noise transmitters. Now, One of the key requirements for LTE is
that it should be able to provide a very low level of latency. The additional processing required for multiple
site reception and transmission could add significantly to any delays. This could result from the need for the additional
processing as well as the communication between the different sites. To overcome this, it is anticipated that the
different sites may be connected together in a form of centralized RAN, or C-RAN. So friends, We have seen here that Coordinated
multipoint enhances the overall system performance through dynamic coordination among multiple
geographically separated eNBs or cells from same eNBs for transmission and reception. In our next video we will see how throughput
is calculated. You can post your doubts in the comment section. Happy Learning.

12 comments

thanks for the video. Will you make videos about the core Network, EPC? And how packets from UE to internet flow?

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