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This paper presents a cluster based resource allocation scheme for allocating physical resource blocks (PRBs) in downlink of OFDMA based cellular systems. The proposed scheme includes two phases of clustering and sum rate maximization. In the first phase users are clustered by using an interference graph in a way that users in each cluster are allocated the same PRB. This interference graph helps...
Cognitive Radio (CR) improves spectral efficiency by allowing unlicensed (secondary) users to concurrently operate with licensed (primary) users. The side-lobe interference from an OFDM-based secondary user (SU) causes unwanted interference to the primary user (PU) of the spectrum. While interference mitigation to the PU spectral band has received a lot of attention in recent literature, the novelty...
In this paper, we propose a distributed adaptive interference coordination algorithm for a practical orthogonal frequency division multiple access (OFDMA)-based mobile cellular systems. The designed algorithm can achieve an efficient frequency reuse for any user distribution and traffic load. Since no a priori frequency planning is required, the minimal coordination between base stations is also achieved...
This paper focuses on the coexistence problem of multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) systems and current radio systems such as IEEE802.11a. Aiming at improving the performance of MB-OFDM UWB, we attempt to avoid interferences from IEEE802.11a systems. The cognitive radio (CR) technology is introduced to detect the distribution of co-channel interferences...
This paper focuses on coordinated scheduling to combat uplink inter-cell interference for LTE/LTE-Advanced. In OFDM system, inter-cell interference is the dominant interference which limits system capacity, especially the performance of cell edge users. Meanwhile inter-cell interference in OFDM system has an inherent characteristic of interference fluctuation, which reduces the efficiency of channel...
Performance of next generation OFDM/OFDMA based Distributed Cellular Network (ODCN) where no cooperation based interference management schemes are used, is dependent on four major factors: 1) spectrum reuse factor, 2) number of sectors per site, 3) number of relay station per site and 4) modulation and coding efficiency achievable through link adaptation. The combined effect of these factors on the...
In current wireless standards like 3GPP LTE or IEEE 802.16 / WiMAX multiple access is based on orthogonal signalling using single-carrier frequency-division multiple access (SC-FDMA) or orthogonal frequency-division multiple access (OFDMA). Links between a base station and different terminals use mutually orthogonal radio resources. This paper studies potential gains in average cell throughput by...
In order to achieve high performances in data rate and spectral efficiency, Long Term Evolution(LTE) Radio Access Network(RAN) has employed Orthogonal Frequency Division Multiplexing(OFDM) on the physical layer. Due to the characteristics of OFDM, slight differences in frequency offset between an adjacent interferer and a LTE downlink signal leads to totally different impact of interference. This...
In this contribution we present the solution of the utility greedy discrete bit loading for interference limited multicell OFDM networks. Setting the utility as the sum of consumed power proportions, the algorithm follows greedy way to achieve the maximum throughput of the system. Simulation has shown that the proposed algorithm has better performance and lower complexity than the traditional optimal...
This paper investigates the problem of uplink subcarrier and power allocation in a Cognitive Radio (CR) network that operates opportunistically within vacant licensed Primary Users (PUs)spectrum. The resource allocation algorithm aims to maximize the CR network throughput under PUs interference constraints. In this paper, CR interference introduced into PUs sub-bands is modeled as a composite of two...
This paper considers the problem of subcarrier allocation in the downlink of multi-cell OFDMA networks. Firstly, a novel fractional frequency reuse architecture is proposed, where all available subcarriers are partitioned into two groups to which subcarriers are dynamically allocated. The first group is used in the center of each cell whereas the other which is partitioned into three sectors orthogonally...
The system characteristics of time division duplex-long term evolution (TDD-LTE) system and different inter-cell interference coordination (ICIC) algorithms are analyzed. Dynamic TDD-LTE system level simulator based on OPNET software is established to investigate the system performances with and without the interference coordination algorithms. Simulation results indicate that adopting the interference...
We consider the problem of sharing spectrum between different base stations in an OFDM network where some cells have a small radius. Such scenarios will become increasingly common in fourth generation networks where the need for ubiquitous high-speed coverage will lead to an increased use of small cells as well as indoor femtocells. Our aim is to devise autonomous algorithms for small cells and femtocells...
The downlink capacity of cellular networks is known to be strongly limited by inter-cell interference. In order to mitigate this interference, a number of frequency reuse schemes have recently been proposed. In this paper, we compare the potential capacity gains of these schemes accounting for the random nature of traffic.
Considering the new feature after introducing the relay nodes (RNs) into the conventional cellular networks and the existing interference coordination techniques, a novel method of interference coordination for cell-edge users in relay enhanced cells (RECs) is proposed in this paper. Firstly, all available frequency resource in each cell is divided into two parts. One part is allocated to users directly...
3GPP LTE is the evolution of UMTS which will make possible to deliver high quality multimedia services with an improved user experience. Since Radio Resource Management (RRM) has been recognized as a key point to successfully accomplish this target, the performance evaluation of a multi-cell resource allocation scheme applied to LTE downlink (DL) is presented in this paper. A semi-distributed RRM...
Interference aware user scheduling in fixed grid-of-beam (GoB) transmission is envisaged to significantly benefit from the receiver initiated busy burst (BB) protocol. Fixed GoB scheduling relies on the knowledge of the location of the intended users as well as the vulnerable users which effectively is provided by the BB protocol via exploitation of channel reciprocity. This paper studies the hybrid...
Spectrum sensing is a key enabling technology of cognitive radio. Reliable detection increases access opportunity to temporarily unused bands and prevents harmful interference to the licensed users. Due to the receiver noise, signal attenuation, and multi-path fading effect, however, it is usually not possible to determine the existence of primary signal with absolute certainty. Without the information...
Long Term Evolution (LTE) of UMTS Terrestrial Radio Access and Radio Access Network is a Fourth Generation (4G) wireless broadband technology which is capable of delivering high data transmission rates and low latency with reduced costs, among other promises. A key research topic is to design efficient and reliable Physical Downlink Control Channels (PDCCHs) that carry the downlink scheduling assignments...
In a frequency-division-duplex (FDD) system, uplink and downlink are allocated equal bandwidths. Due to the relative sparseness of uplink Internet traffic, the uplink spectrum is usually under-utilized. In this paper, we propose dynamic spectrum access algorithms allowing relay-assisted downlink to opportunistically transmit over the uplink spectrum, thereby maximizing its usage efficiency. Specifically,...
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