Performance Evaluation of Pilot-based Channel Estimation Techniques at Higher Modulation Order for LTE MIMO Downlink System
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Date
2016-02
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Addis Ababa University
Abstract
The number of smartphone users is increasing with increase in demand for high data rate. To fulfill this growing data rate demand, Long Term Evolution (LTE) is one technology option that is being widely deployed nowadays. LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink system as its modulation scheme and multiple-input multiple-output (MIMO) antenna to achieve the high data rate. OFDM has the advantage over the conventional single-carrier modulation schemes when the channel is frequency-selective fading and is widely used in current wireless networks.
There are different types of data detection methods used in the current wireless technology. However, detection without the knowledge of the channel state information (CSI) is challenging and if not impossible. This is because of the fact that the transmission channel between a transmitter and a receiver can vary be from a simple line-of-sight to a severely faded one by multipath fading; moreover, the channel is random and time varying in nature. Hence, channel estimation methods are required to acquire the CSI. LTE uses cell-specific reference signals (CRS) or known pilots to estimate the channel properties.
Different pilot-based channel estimation techniques are developed over the last few decades. These include Least Square (LS) and Linear Minimum Mean Square Error (LMMSE) algorithms. Previous work on channel estimation is limited to single-input single-output (SISO)-OFDM and MIMO-OFDM systems in combination with lower modulation schemes like binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). Further study is required to understand the performance of MIMO-OFDM technology in LTE and at higher order modulation schemes that include 16 quadrature amplitude modulation (QAM) and 64 QAM.
This thesis investigates the performance of higher-order modulation schemes for the downlink of LTE based on MIMO-OFDM. LS and LMMSE channel estimation algorithms are considered at the receiver. Moreover, international telecommunication union (ITU) channel models such as extended pedestrian A model (EPA), extended vehicular A model (EVA) and extended typical urban (ETU) are used to characterize the propagation environment. Simulation results show that,
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LMMSE has a higher gain than LS; however, the relative gain diminishes at higher SNR regions, specifically for SNR >30 dB. Similar results were reported in previous researches for the same system and channel model types but for lower order modulations.
Key words: - LTE, pilot-based channel estimation, MIMO, EPA, EVA, ETU
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Keywords
LTE, pilot-based channel estimation, MIMO, EPA, EVA, ETU