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In this paper, we investigate different HARQ strategies with unreliable feedback channel. In classical approaches, retransmitted packets are different versions of the same user data. In order to improve HARQ performance, we propose to construct redundancy packets by jointly encoding several data packets. This strategy is referred to as HARQ Multiple Packet Incremental Redundancy (MP-IR). It can eliminate...
This paper presents indoor experimental results on an implemented real-time downlink multiuser multiple-input multiple-output (DL-MU-MIMO) transceiver for next generation wireless LAN systems. In the transceiver, channel state information (CSI) is estimated at each station (STA) and fed back to an access point (AP) on a real-time basis. At the AP, transmit beamforming weight for DL-MU-MIMO transmission...
Cognitive radio (CR) can successfully deal with the growing demand and the scarcity of the wireless spectrum. To increase the spectrum usage, CR technology allows secondary users to access licensed spectrum bands. Since licensed users have priorities to use the bands, the secondary users need to continuously monitor the activities of the licensed users to avoid interference and collisions. In this...
In this paper, we consider the resource allocation problem in the uplink transmission of an orthogonal frequency-division multiple access (OFDMA) based cognitive radio (CR) network. The resource allocation aims to maximize the uplink throughput of secondary users (SUs) in CR network under the constraints of the primary user (PU) interference and the transmit power limits of SUs. In general, the optimal...
Deliberate clipping is a simple solution to high Peak-to-Average Power Ratio problem of OFDM signal. In Amplify-and-Forward OFDM relay networks, due to the limited resource, deliberate clipping is also suggested. However, clipping is a nonlinear process and may cause significant performance degradation. Based on Bussgang Linearization Theory, we provide a linear system model for Amplify-and-Forward...
In a multi-cell wireless network, an efficient interference mitigation technique is an inevitable part of the current state-of-the-art wireless system. As opposed to conventional interference mitigation techniques which treat the interference as noise, a multi-layer rate splitting scheme can be considered to improve the performance by decoding part of the interference. In this paper, we adapt the...
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...
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...
In this paper, we present two optimal resource allocation schemes that maximize throughput and symbol correct rate (SCR). The throughput and SCR are derived. The derived throughput and SCR are optimized with respect to the sensing time, the source transmission power and the relay transmission power. Numerical results show that the optimal sensing time is dependent on the primary user's signal-to-noise-ratio...
This paper investigates the resource allocation problem in a relay-aided cognitive radio (CR) system under the orthogonal frequency division multiplexing (OFDM) transmission. Different from the conventional CR resource allocation problem, the relay node here is capable of performing subcarrier permutation over two hops such that the signal received over a particular subcarrier is forwarded on a different...
We consider a time-slotted primary system where both the primary channel and primary activity are modeled as two independent two-state Markov chains. The primary transmitter can be idle or busy, whereas the channel can be in erasure or not. Moreover, the sensing channel between the primary transmitter and secondary transmitter is modeled as a two-state Markov chain to represent two levels of sensing...
In this work we compare full-duplex (FD) and half-duplex (HD) relaying in terms of outage probability and throughput. We consider a practical FD relay model where the loop interference between transmitted and received signals is taken into account. We analyze two modes for FD transmission, block Markov encoding and multi-hop transmission without interference cancellation, and two different modes for...
We consider a random access primary network. At the beginning of each time slot, a number of secondary users sense the channel and make an access decision based on the spectrum sensing outcome and the channel state information (CSI). Specifically, the channel is accessed by a secondary transmitter with a probability that depends on both the sensing metric and the gain or signal-to-noise-ratio (SNR)...
In this paper, we propose a high throughput and hardware efficient Fast Fourier Transform (FFT) architecture for Long Term Evolution (LTE) application. The proposed enhancement delay element matrix (EDEM) which contains the mixed radix unit supports 25, 16, 9, 8, 5, 4, 3 and 2-point FFTs. The reuse technology is also applied into EDEM to reduce the hardware resource. The EDEM reduces the computation...
The exponential increase in data traffic demand has focused attention on two layer network deployment strategies where low-power pico base-stations are placed within a macro cell coverage area targeting specific capacity demands. Two aspects of such a network are different from a macro-only deployment and are studied in this paper — (i) the choice of antenna geometry and polarization for a non-sectorized...
In the two-user MISO interference channel using transmit zero-forcing (ZF) strategy, if transmit antenna selection based on direct link channel gain is applied to select no less than two transmit antennas, we find that under limited feedback using more transmit antennas will actually induce more interference to the other users. In the high SNR region, the upper bounds of the throughput and the relative...
Two-tier femtocell networks, which comprise macro-cells underlaid with short range femtocells, are under intensive study due to their improved indoor coverage and data rate advantages as compared to conventional single-tier macrocellular networks. Nevertheless, the implementation of two-tier networks with universal frequency reuse causes severe cross-tier interference from the femtocells to the macrocellular...
Cognitive radio (CR), as the novel approach to improve the utilization of the available radio spectrum is introduced under the constraint that the current authorized users are sufficiently protected against any harmful interferences. However, there are many challenges associated with detection of the primary users (PUs) which need to be addressed carefully. One of the most important challenges in...
Given the growing concern over energy consumption and associated global warming, green communication is becoming more and more important. Lots of efforts have been put into investigating energy efficiency based design in wireless systems. Unfortunately, the maximum energy efficiency of a point-to-point link is normally achieved when the transmit power approaches zero, which, however, is not desirable...
Cooperated multi-point technique in HSPA+ system has not been paid attention until the Single Frequency Dual Cell (SF-DC) mode, where one user equipment (UE) may be served by dual NodeBs simultaneously in the single carrier frequency network, is proposed recently. In the previous research, the system-level performance with SF-DC operation had not been studied comprehensively. The main contribution...
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