Saini, Naveen Kumar and Kuchi, Kiran
(2018)
Optimize Power Allocation Scheme to Maximize
Sum Rate in CoMP with Limited Channel State
Information.
Masters thesis, Indian Institute of Technology Hyderabad.
Abstract
Extensive use of mobile applications throws many challenges in cellular systems like cell edge
throughput, inter cell interference and spectral e�ciency. Many of these challenges have been
resolved using Coordinated Multi-Point (CoMP), developed in the Third Generation Partnership
Project for LTE-Advanced) to a great extent. CoMP cooperatively process signals from base sta-
tions that are connected to various multiple terminals (user equipment (UEs)) at transmission and
reception. This CoMP improves throughput, reduces or even removes inter-cell interference and
increases spectral e�ciency in the downlink of multi-antenna coordinated multipoint systems.
Many researchers addressed these issues assuming that BSs have the knowledge of the common
control channels dedicated to all UEs and also about the full or partial channel state information
(CSI) of all the links. From the CSI available at the BSs, multiuser interference can be managed
at the BSs. To make this feasible, UEs are responsible for collecting downlink CSI. But, CSI
measurement (instantaneous and/or statistical) is imperfect in nature because of the randomly
varying nature of the channels at random times. These incorrect CSI values available at the BSs
may, in turn, create multi-user interference. There are many techniques to suppress the multi-user
interference, among which the feedback scheme is the one which is gaining a lot of attention. In
feedback schemes, CSI information needs to be fed back to the base station from UEs in the uplink.
It is obvious, the question arises on the type and amount of feedback need to be used. Research
has been progressing in this front and some feedback techniques have been proposed. Three basic
CoMP Feedback schemes are available. Explicit or statistical channel information feedback scheme
in which channel information like channels's covariance matrix of the channel are shared between the
transmitter and receiver. Next, implicit or statistical channel information feedback which contains
information such as Channel quality indication or Precoding matrix indicator or Rank indicator. 1st
applied to TDD LTE type structure and 2nd of feedback scheme can be applied in the FDD system.
Finally, we have UE which tranmit the sounding reference signal (CSI). This type of feedback scheme
is applied to exploit channel reciprocity and to reduce channel intercell interference and this can be
applied in the TDD system. We have analyzed the scenario of LTE TDD based system. After this,
optimization of power is also required because users at the cell edge required more attention than
the user locating at the center of the cell. In my work, it shows estimated power gives exponential
divercity for high SNR as low SNR too.
In this method, a compression feedback method is analyzed to provide multi-cell spatial channel
information. It improves the feedback e�ciency and throughput. The rows and columns of the
channel matrix are compressed using Eigenmode of the user and codebook based scheme speci�ed
in LTE speci�cation. The main drawback of this scheme is that spectral e�ciency is achieved with
the cost of increased overheads for feedback and evolved NodeB (eNB). Other factor is complexity
of eNodeB which is to be addressed in future work.
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