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Two techniques for channel estimation and co-channel interference rejection are presented for the multiple-input, multiple-output (MIMO) uplink in the Long Term Evolution-Advanced (LTE-Advanced) system. The first technique consists of estimating the desired users' channels in the frequency domain (FD) before estimating interference covariance matrices for interference rejection. In the second technique,...
This paper addresses the distributed power adaptation (DPA) problem on the downlink for wireless cellular networks. As a consequence of uncoordinated local scheduling decisions in classical networks, the base stations produce mutual uncontrolled interference on their co-channel users. This interference is of a variable nature, and is hardly predictable, which leads to suboptimal scheduling and power...
Error performance and power allocation for multi-hop decode-and-forward (DF) systems are addressed. The different channels treated are Rayleigh, Rician, Nakagami-m, and Nakagami-q, and these are collectively referred to as generalized fading. The modulation can be any linear scheme. The asymptotic (high SNR) error rate expression is derivedwhich can incorporate independent and non-identically distributed...
Hybrid automatic repeat request (HARQ) is a well-known technique for improving system throughput and link performance of wireless communication systems, including cooperative communication systems. In this paper, we exploit the limited feedback applied to the two-source turbo coded cooperation scheme to define a particular cooperative HARQ protocol, called two-level HARQ, where the decision on retransmission...
This paper proposes a dynamic symbol adaptation scheme for downlink and point-to-point multiple input multiple output (MIMO) systems aiming at the minimization of the overall system bit error rate. The proposed scheme adaptively changes the order or the values of the symbols to be transmitted within a sub-frame of symbols with the objective to enhance the received symbols' power. The adaptation is...
This paper considers opportunistic spectrum access for secondary users (SUs) from an adaptive learning perspective. A SU dynamically hops over multiple idle frequency-slots of a licensed frequency band, each with an adaptive activity factor. Aiming to determine the optimal activity factors of SUs, an algorithm is developed, in which each SU independently adjusts its activity factors by learning other...
In this work, a robust joint signal and interference alignment is designed for cognitive multiple-input multiple-output (MIMO) interference channel in which single primary link coexists with multiple secondary links. Considering channel imperfections and finite signal-to-noise ratio (SNR) in practice, we propose a worst-case joint design to not only minimize the leakage of interference signals but...
We deal with interference channels with (i) delayed channel state information at the transmitter (CSIT), and (ii) delayed output feedback at the receiver and no CSIT. We extend the algorithm by Maleki et al. [8] for M = 3 users to any M ≥ 3 under the constraint that all the transmitter/receiver pairs are active simultaneously. We propose a retrospective interference alignment algorithm achieving M...
Interference alignment is proposed for achieving the maximum degrees of freedom in interference channels. In the present paper, a scenario consisting of several pairs of multiple antenna nodes and a single MIMO relay helping the interference alignment is considered. The interference alignment is performed in two subsequent transmission phases assuming a time-invariant channel during the two transmission...
In this work, we investigate the impact of placing a half-duplex relay in the X channel in the presence of limited channel state information (CSI). Specifically, we consider the scenarios when the sources have no CSI, while the relay either has perfect CSI or delayed CSI. We develop transmission strategies for each scenario to facilitate interference alignment with the help of the relay. We show that...
This paper is concerned with the maximization of the weighted sum-rate in the multicell MIMO multiple access channel (MAC). Considered is the multicell network operating on the same frequency channel with multiple mobile stations (MS) per cell. Assuming the interference coordination mode in the multicell network, each base-station (BS) only decodes the signals for the MSs within its cell. However,...
We obtain the jointly optimal power allocation and partner selection policies, that maximize the sum rate of a cooperative OFDMA system with mutually cooperating pairs of users. We show that the power allocation and partner selection steps can be performed sequentially, and the latter step can be formulated as a maximum weighted matching problem on an undirected graph, which can be solved in polynomial...
We present a practical link adaptation algorithm for MIMO-OFDM systems. The proposed solution is based on sounding the channel periodically and choosing the optimal mode that will maximize the throughput or energy efficiency while satisfying the application's quality of service (QoS) requirements. In addition, we address practical problems such as computational complexity of the algorithm and determination...
This paper considers the resource allocation problem for a Multiple Access Relay Channel (MARC). A transmission scheme with OFDMA and Amplify-and-Forward (AF) relaying is assumed. To maximise the sum rate a joint allocation of transmit power and subcarriers has to be done. This problem is known to be NP-hard and can only be solved by an exhaustive search which is not feasible for practical problem...
Incorporating wireless transceivers with numerous antennas (such as Massive-MIMO) is a prospective way to increase the link capacity or enhance the energy efficiency of future communication systems. However, the benefits of such approach can be realized only when proper channel information is available at the transmitter. Since the amount of the channel information required by the transmitter is large...
We considers the beamforming assisted multiple-antenna receiver for space-division multiple-access based multiuser systems that employ high-throughput quadrature amplitude modulation (QAM) signalling. The bit error ratio (BER) expression as the function of the beamformer's weight vector is derived, and the minimum BER (MBER) beamforming receiver is then obtained as the solution of the resulting optimisation...
In this paper, we investigate efficient beamforming schemes for downlink broadcast channels of MIMO systems. Optimal solution to this problem is known to be infeasible due to the prohibitive complexity and recent research focuses on suboptimal approaches with reduced complexity. We first present a progressive beamforming method that maximizes the net gain in sum throughput for newly added users and...
We consider an overlay mode of an orthogonal frequency division multiple access (OFDMA) based cellular system using orthogonal beamforming to provide broadband wireless access for rural users. In overlay mode, since the signals transmitted to rural users should not interfere with mobile users of higher priority in the OFDMA-based cellular system, the beamforming vectors to rural users have to be orthogonal...
In this paper we consider secure transmission for the multiple-input, multiple-output, single-antenna-eavesdropper systems with perfect information of the main channel and only the statistics of the eavesdropper's channel state information known at the transmitter. We adopt the celebrated artificial-noise (AN) assisted beamforming, which was studied by Goel and Negi with the limitation that the AN...
This paper proposes means to exploit the additional degrees of freedom that can be achieved by using beam-tilting antennas for the purposes of multiuser communication without substantially increasing investment in system resources. Specifically, by using such beam-tilting antennas the wireless channel can be used as a means to spread the users in space rather than in frequency as is currently the...
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