Record Details

Role of Channel State Information in Adaptation in Current and Next Generation Wireless Systems

Electronic Theses of Indian Institute of Science

View Archive Info
 
 
Field Value
 
Title Role of Channel State Information in Adaptation in Current and Next Generation Wireless Systems
 
Creator Kashyap, Salil
 
Subject Wireless Communication Systems
Orthogonal Frequency Division Multiple Access
Adaptation in Wireless Communication Systems
Channel State Information (CSI)
Transmit Power Adaptation
Transmit Antenna Selection
Cognitive Radio (CR)
Next Generation Wireless Systems
Current Wireless Systems
Antenna Selection
Cognitive Radios
OFDMA Systems
Long Term Evolution (LTE)
Communication Engineering
 
Description Motivated by the increasing demand for higher data rates, coverage, and spectral efficiency, current and next generation wireless systems adapt transmission parameters and even who is being transmitted to, based on the instantaneous channel states. For example, frequency-domain scheduling(FDS) is an instance of adaptation in orthogonal frequency division multiple access(OFDMA) systems in which the base station opportunistically assigns different subcarriers to their most appropriate user. Likewise ,transmit antenna selection(AS) is another form of adaptation in which the transmitter adapts which subset of antennas it transmits with. Cognitive radio(CR), which is a next generation technology, itself is a form of adaptation in which secondary users(SUs) adapt their transmissions to avoid interfering with the licensed primary users(PUs), who own the spectrum. However, adaptation requires channel state information(CSI), which might not be available apriori at the node or nodes that are adapting. Further, the CSI might not be perfect due to noise or feedback delays. This can result in suboptimal adaptation in OFDMA systems or excessive interference at the PUs due to transmissions by the SUs in CR.
In this thesis, we focus on adaptation techniques in current and next generation wireless systems and evaluate the impact of CSI –both perfect and imperfect –on it. We first develop a novel model and analysis for characterizing the performance of AS in frequency-selective OFDMA systems. Our model is unique and comprehensive in that it incorporates key LTE features such as imperfect channel estimation based on dense, narrow band demodulation reference signal and coarse, broad band sounding reference signal. It incorporates the frequency-domain scheduler, the hardware constraint that the same antenna must be used to transmit over all the subcarriers that are allocated to a user, and the scheduling constraint that the allocated subcarriers must all be contiguous. Our results show the effectiveness of combined AS and FDS in frequency-selective OFDMA systems even at lower sounding reference signal powers.
We then investigate power adaptation in underlay CR, in which the SU can transmit even when the primary is on but under stringent interference constraints. The nature of the interference constraint fundamentally decides how the SU adapts its transmit power. To this end, assuming perfect CSI, we propose optimal transmit power adaptation policies that minimize the symbol error probability of an SU when they are subject to different interference and transmit power constraints. We then study the robustness of these optimal policies to imperfections in CSI. An interesting observation that comes out of our study is that imperfect CSI can not only increase the interference at the PU but can also decrease it, and this depends on the choice of the system parameters, interference, and transmit power constraints. The regimes in which these occur are characterized.
 
Contributor Mehta, Neelesh B
 
Date 2017-11-24T17:55:58Z
2017-11-24T17:55:58Z
2017-11-24
2014
 
Type Thesis
 
Identifier http://hdl.handle.net/2005/2801
http://etd.ncsi.iisc.ernet.in/abstracts/3666/G26274-Abs.pdf
 
Language en_US
 
Relation G26274