Information rate that can be transferred over a given bandwidth is limited by the information theory. Capacity depends on
many factors such as the signal to noise ratio (SNR), channel state information (CSI) and the spatial correlation in the
propagation environment. It is very important to increase spectral efficiency in order to meet the growing demand for
wireless services. Thus, Multiple input multiple output (MIMO) technology has been developed and applied in most of
the wireless standards and it has been very successful in increasing capacity and reliability. As the demand is still
increasing, attention now is shifting towards large scale multiple input multiple output (MIMO) which has a potential of
bringing orders of magnitude of improvement in spectral and energy efficiency. It has been shown that users channels
decorrelate after increasing the number of antennas. As a result, inter-user interference can be avoided since energy can
be focused on precise directions. This paper investigates the limits of channel capacity for large scale MIMO. We study
the relation between spectral efficiency and the number of antenna N. We use time division duplex (TDD) system in order
to obtain CSI using training sequence in the uplink. The same CSI is used for the downlink because the channel is
reciprocal. Spectral efficiency is measured for channel model that account for small scale fading while ignoring the effect
of large scale fading. It is shown the spectral efficiency can be improved significantly when compared to single antenna
systems in ideal circumstances.
The high demand on the wireless networks and the need for higher data rates are the motivation to develop new
technologies. Recently, the idea of using large-scale MIMO systems has grabbed great attention from the researchers
due to its high spectral and energy efficiency. In this paper, we analyze the UL channel estimation error using large
number of antennas in the base station where the UL channel is based on predefined pilot signal. By making a
comparison between the identified UL pilot signal and the received UL signal we can get the realization of the channel.
We choose to deal with one cell scenario where the effect of inter-cell interference is eliminated for the sake of
studying simple approach. While the number of antennas is very large in the base station side, we choose to have one
antennal in the user terminal side. We choose to have two models to generate the channel covariance matrix includes
one-ring model and exponential correlation model. Figures of channel estimation error are generated where the
performance of the mean square error MSE per antenna is presented as a function signal to noise ratio SNR. The
simulation results show that the higher the SNR the better the performance. Furthermore, the affect of the pilot length
on the channel estimation error is studied where two different covariance models are used to see the impact of the two
cases. In the two cases, the increase of the pilot length has improved the estimation accuracy.
Recently, the single-carrier and multi-carrier transmissions have grabbed the attention of industrial systems.
Theoretically, OFDM as a Multicarrier has more advantages over the Single-Carrier especially for high data rate. In this
paper we will show which one of the two techniques outperforms the other. We will study and compare the performance of BER for both techniques for a given channel. As a function of signal to noise ratio SNR, the BER will be measure and studied. Also, Peak-to-Average Power Ratio (PAPR) is going to be examined and presented as a drawback of using OFDM. To make a reasonable comparison between the both techniques, we will use additive white Gaussian noise (AWGN) as a communication channel.
Proc. SPIE. 8498, Optics and Photonics for Information Processing VI
KEYWORDS: Signal to noise ratio, Transmitters, Modulation, Doppler effect, Receivers, Telecommunications, Wireless communications, Data communications, Orthogonal frequency division multiplexing, Mobile communications
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier technique that is being used more and more in
recent wideband digital communications. It is known for its ability to handle severe channel conditions, the efficiency of spectral usage and the high data rate. Therefore, It has been used in many wired and wireless communication systems such as DSL, wireless networks and 4G mobile communications. Data streams are modulated and sent over multiple subcarriers using either M-QAM or M-PSK. OFDM has lower inter simple interference (ISI) levels because of the of the low data rates of carriers resulting in long symbol periods. In this paper, BER performance of OFDM with respect to signal to noise ratio (SNR) is evaluated. BPSK Modulation is used in s Simulation based system in order to get the BER over different wireless channels. These channels include additive white Gaussian Noise (AWGN) and fading channels that are based on Doppler spread and Delay spread. Plots of the results are compared with each other after varying some of the key parameters of the system such as the IFFT, number of carriers, SNR. The results of the simulation give visualization of what kind of BER to expect when the signal goes through those channels.