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Cognitive radio networks are receiving a lot of research attention lately. Most user equipment in state-of-the-art wireless communication systems are equipped with two antennas. In this paper, we take advantage of the two transmit antennas in an underlay cognitive radio network scenario. Secondary users use the two transmit antennas in order to insert a null in the direction of the primary base station,...
The multicast/broadcast service (MBS) has emerged as a key technology for delivering multimedia contents in wireless networks.The development of orthogonal frequency division multiplexing access (OFDMA) and multiple-input multiple-output (MIMO) communications have provided a high-throughput air interface for delivering the multimedia contents in MBSs. To further improve the spectral efficiency for...
DVB-H (Digital Video Broadcasting, Handheld) is based on the terrestrial version of DVB, i.e. DVB-T, and it has been designed especially for the moving environment. The performance of the system takes into account the variations of the power levels and bursty interferences of the radio path. DVBH is adequate especially for the small handsets as the typical terminal screen size requires only a fraction...
System-level simulations of packet-based orthogonal frequency-division multiple access (OFDMA) cellular networks require a proper consideration of the channel-dependent fast fading/scheduling in order to produce meaningful results. However, generating the time and frequency selective fast fading channels and performing detailed channel-adaptive scheduling for each user in a multi-cellular system is...
We study the performance of a two-hop full-duplex OFDM relay link, where the relay, or in-band repeater, amplifies and forwards its input signal on the same channel as the main transmitter. We derive new closed-form expressions for the end-to-end signal-to-interference and noise ratio (SINR) when the multipath channels are modeled with clustered exponential power-delay profiles. Our system model incorporates...
Fractional frequency reuse (FFR) has been actively studied in order to reduce inter-cell interference, especially for cell edge users in current orthogonal frequency division multiple access systems. However, the best resource block (RB) allocation to the edge users is limited by conventional FFR, which has subbands consisting of contiguous RBs. In this paper, we propose a band-distributed FFR scheme...
This paper introduces a new method for distributed interference mitigation in full spectral-reuse OFDMA cellular networks. This considers the use of pre-defined frequency-domain power profiles helping make the interference more predictable across the subcarriers. We propose a method for computing the power profiles so as to maximize the capacity of the system in case of maximum throughput scheduling,...
This paper addresses the subcarrier and power allocation problem in the uplink of an OFDMA system under the cognitive radio environment. The objective is to maximize the sum-rate of secondary users, without causing adverse interference to the primary users. We formulate the optimization problem subject to the individual power constraints and the interference constraints. Since the problem cannot be...
We propose to maximize achievable rate in OFDM systems via the adaptation of the cyclic prefix (CP) length jointly with tone and bit loading. We show that significant gains are obtained compared to the case of using a fixed CP with duration equal to the channel. Several metrics for the CP design are described. They tradeoff between performance and complexity. Both single user and multiuser OFDM are...
In OFDMA cellular system, the inter-cell interference is the main interference of the system, which greatly degrades the system performance. In order to enhance cell average throughput and the cell-edge user's peak bit rate, a hybrid inter-cell interference mitigation scheme is proposed. The hybrid scheme combines the fractional frequency reuse scheme and the frequency hopping scheme, in which cell-edge...
Hop adaptive MAC-PDU (Protocol Data Unit) size optimization is proposed for Orthogonal Frequency Division Multiple Access (OFDMA) based wireless relay networks. Such optimization improves the end-to- end goodput via MAC-PDU size optimization. We provide design and evaluation for two hop cellular networks with fixed relays where the Base Station (BS) to Relay Station (RS) links are potentially robust...
While intercell interference coordination (ICIC) for the downlink of multi-cell systems in general and orthogonal frequency division multiple access (OFDMA) networks in particular has been extensively studied, the uplink has received less attention. For the uplink, the impact of ICIC on the overall system throughput ("the ICIC gain") must be analyzed in a system model that captures specific...
In this paper, we derived closed-form expressions for the SINR distributions in OFDMA cellular system using fixed relays. First of all, the intercell interference at the BS and the RS are characterized and it is found that the intercell interference power is successfully modeled as the average of it. From the interference power modeling, the pdfs of SINRs for the four uplink cases are analyzed. The...
We consider a realistic albeit simplified scenario for wireless cellular systems of the next generation (4G and beyond), where MIMO-OFDM, opportunistic scheduling, channel state information at the transmitter and limited base-station cooperation are envisaged. We propose two strategies with limited base-station cooperation that can be easily implemented with today's technology and achieve an approximate...
WiMAX (IEEE 802.16) is a broadband wireless access technology that enables convergence of mobile and fixed broadband networks through scalable OFDMA (orthogonal frequency division multiple access) technology. This paper presents the modeling of WiMAX propagation channel statistically. WiMAX channel performance of different frequency bands applied in Asia Pacific region are investigated and evaluated...
In this paper we report the first real-time measurements of a 3GPP-LTE multiple antenna system in typical indoor and outdoor scenarios. In a single cell, single user scenario we demonstrate throughput exceeding 100 Mbit/s with a 2times2 MIMO configuration. This throughput gain is significant as compared to existing single antenna systems. We describe the basic LTE system design and prototype ingredients...
Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H), which is required to operate under high mobility conditions resulting in significant Inter-carrier Interference (ICI). To mitigate ICI, several cancellation schemes have been proposed but they require reliable channel information at the receiver which is quite challenging...
Some communication applications, like multimedia, deliver data of different importance classes allowing unequal error protection (UEP) levels. In this paper, a multiple-input multiple-output (MIMO) system using orthogonal frequency division multiplexing (OFDM) is considered with a new UEP bit-loading algorithm based on the non-UEP algorithm by Chow, Cioffi, and Bingham. In the proposed bit-loading...
This paper addresses adaptive channel estimation for time-varying mobile wireless channels with nonstationary statistics. We presents a reduced complexity adaptive channel estimator based on a set membership filtering approach known as the Optimal Bounding Ellipsoid (OBE) algorithm. To exploit time and frequency domain correlation properties of the channel in an efficient low-complexity way, we allow...
Ultra-wideband (UWB) systems possess several distinct features such as very high data rate, large multipath or frequency diversity and improved ranging precision while requiring low-power low-complexity transceivers. Among the different modulation schemes, differential PSK is an attractive option because it does not require channel estimation, and hence reduces implementation complexity. This paper...
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