Current Issue : July - September Volume : 2012 Issue Number : 3 Articles : 6 Articles
In this paper an overview of Long Term Evolution (LTE) and Long Term Evolution-Advanced (LTE-A) is presented. It will offers superior experience to user and simplified technology for next generation mobile broadband. It provides ubiquitous coverage and roaming with existing 2G and 3G networks. Now day, mobile data traffic is expected to overtake voice traffic, which will place high requirements on mobile networks today and in the future.LTE, meets Next Generation Mobile Network’s (NGMN) requirements. Third Generation Partnership Project Long Term Evolution (3GPP LTE) aim to provide high performance services for mobile voice, video and data services at low cost deployments. LTE and LTE-Advanced technologies are candidates for the fourth generation (4G) mobile communication networks....
Orthogonal frequency division multiplexing (OFDM) is an effective technique for high-speed digital transmission over timedispersive\r\nchannels. However, for coherent detection, a reliable channel estimation (CE) is required. OFDM is characterized by\r\nits high peak-to-average power ratio (PAPR), which makes it very sensitive to nonlinear distortions that may affect the channel\r\nestimation accuracy leading to a bit error rate (BER) performance degradation. In this paper, we present closed-form BER\r\nexpression for OFDM with a pilot-assisted CE in a nonlinear and frequency-selective fading channel. We discuss how, and to\r\nwhat extent, the nonlinear degradation affects the BER performance with the CE based on a time/frequency division-multiplexed\r\n(TDM/FDM) pilot. The analysis is based on a Gaussian approximation of the nonlinear noise due to both HPA amplitude\r\nlimitation and quantization. We also evaluate the estimator�s mean square error (MSE) with both TDM and FDM pilots. Our\r\nresults show that pilot-assisted CE using FDMpilot is more sensitive to nonlinear distortions than the CE using a TDMpilot, since\r\nits pilot subcarriers are affected by nonlinear noise due to both the HPA and the quantization....
This article draws a general retrospective view on the first 10 years of cognitive radio (CR). More specifically, we\r\nexplore in this article decision making and learning for CR from an equipment perspective. Thus, this article depicts\r\nthe main decision making problems addressed by the community as general dynamic configuration adaptation\r\n(DCA) problems and discuss the suggested solution proposed in the literature to tackle them. Within this\r\nframework dynamic spectrum management is briefly introduced as a specific instantiation of DCA problems. We\r\nidentified, in our analysis study, three dimensions of constrains: the environmentââ?¬â?¢s, the equipmentââ?¬â?¢s and the userââ?¬â?¢s\r\nrelated constrains. Moreover, we define and use the notion of a priori knowledge, to show that the tackled\r\nchallenges by the radio community during first 10 years of CR to solve decision making problems have often the\r\nsame design space, however they differ by the a priori knowledge they assume available. Consequently, we\r\nsuggest in this article, the ââ?¬Å?a priori knowledgeââ?¬Â as a classification criteria to discriminate the main proposed\r\ntechniques in the literature to solve configuration adaptation decision making problems. We finally discuss the\r\nimpact of sensing errors on the decision making process as a prospective analysis....
Interference-aware multiple access is an enabler to cost-efficient and reliable high data-rate local area wireless access. In this paper,\r\nwe propose an interference-aware radio resource management scheme where receivers informabout their throughput, interference,\r\nand signal levels by means of broadcast messages tied to data reception. In the proposed scheme, the conventional scheduler is\r\nextended to interference-aware operation where individual scheduling decisions are based on estimated change in system-level\r\nperformance. The performance of the proposed scheme is evaluated in system simulations where it is compared to a conventional\r\nscheduler and a centralized scheduler (global optimum). The convergence of the proposed scheduler is analyzed and signaling\r\noverhead of an example implementation is characterized. The results demonstrate that the proposed scheme enables fair and\r\nefficient wireless access in challenging interference scenarios, for example, multiple networks deployed in the same geographical\r\narea and sharing a common band....
This paper considers the reliable transmission for wireless multicast networks where multiple sources want to distribute\r\ninformation to a set of destinations with assistance of a relay. Basically, the reliability of a communication link is assured via\r\nautomatic repeat request (ARQ) protocols. In the context of multisource multicast networks, the challenge is how to retransmit\r\nthe lost or erroneous packets efficiently. In traditional approaches, the retransmission of lost packets from a single source is\r\ntreated separately, and thus it may cause a considerable delay. To solve this problem, we propose the relay detects, combines,\r\nand forwards the packets which are lost at destinations using network coding. In the proposed ARQ protocol, the relay detects\r\npackets from different sources and combines the lost packets using NC. In particular, two packet-combination algorithms are\r\ndeveloped to guarantee that all lost packets are retransmitted with the smallest number of retransmissions. Furthermore, we\r\nanalyze the transmission bandwidth and provide the numerical results to demonstrate the superior performance of the proposed\r\nARQ protocol over some existing schemes....
The average channel capacity and the SINR distribution for multiuser multiple input multiple output (MIMO) systems in\r\ncombination with the base station based packet scheduler are analyzed in this paper. The packet scheduler is used to exploit\r\nthe available multiuser diversity in all the three physical domains (i.e., space, time and frequency). The analysis model is based on\r\nthe generalized 3GPP LTE downlink transmission for which two spatial division multiplexing (SDM) multiuser MIMO schemes\r\nare investigated: single user (SU) and multiuser (MU) MIMO schemes. The main contribution of this paper is the establishment\r\nof a mathematical model for the SINR distribution and the average channel capacity for multiuser SDM MIMO systems with\r\nfrequency domain packet scheduler, which provides a theoretical reference for the future version of the LTE standard and a useful\r\nsource of information for the practical implementation of the LTE systems....
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