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Femtocells are a promising solution for the provision of high indoor coverage and capacity. Furthermore, OFDMA-based femtocells have proven to be highly versatile when dealing with cross-layer co-channel interference; however, concerns still exist related to the impact of the different access methods to femtocells in an overlaid network. Femtocells based on a Closed Subscribers group, where only device...
In this paper, a new feedback scheme is proposed for downlink OFDMA system with frequency domain packet scheduling to achieve multiuser diversity. Recent work showed that the multiuser diversity can be gained by using the so-called average best-M feedback scheme where bit-mask indicating the identification of best M subcarriers together with the average channel quality indicator of those subcarriers...
In this paper, we present a novel approach to evaluate the downlink Erlang capacity of a cellular Orthogonal Frequency Division Multiple Access (OFDMA) system with 1:1 frequency reuse. Erlang capacity analysis of traditional cellular systems like Global System for Mobile communications (GSM) cannot be applied to cellular OFDMA because in the latter, each incoming call requires a random number of subcarriers...
Frequency-domain scheduling and rate adaptation have helped next generation orthogonal frequency division multiple access (OFDMA) based wireless cellular systems such as Long Term Evolution (LTE) achieve significantly higher spectral efficiencies. To overcome the severe uplink feedback bandwidth constraints, LTE uses several techniques to reduce the feedback required by a frequency-domain scheduler...
As the demand for mobile broadband services are growing, cellular networks are heading towards their fourth generation (4G). Long Term Evolution - Advanced (LTE-A) is emerging as a major candidate for 4G cellular networks. MIMO technology combined with OFDMA is a major technological change in 4G compared to their 3G counterparts. However various MIMO configurations and modulation/coding schemes(MCS)...
This paper presents the analysis of the throughput enhancements using threshold-based PUSC in WiMAX OFDMA system. We consider a point-to-multipoint (PMP) WiMAX network where base station (BS) schedules downlink packets for simultaneous transmissions to multiple users. Using the OFDMA option in the WiMAX standard, users are assigned different subchannels for reception of their data using the same OFDM...
In modern Orthogonal Frequency Division Multiple Access (OFDMA) systems Multi-User Multiple-Input Multiple-Output (MU-MIMO) techniques are employed to increase the cell and user throughput without additional bandwidth or transmit power requirements. The increased throughput in the downlink is achieved by simultaneous transmission to multiple mobile stations (MSs) over the same time-frequency resources...
In this paper, we present a new power allocation algorithm called distributed inter-cell power allocation (DIPA) that improves the throughput-fairness trade-off without inter-BS coordination for multi-cell OFDMA systems in fast time-varying environment. In order to preclude the affection of instantaneous channel variation, the DIPA is designed to operate in large time scale (or super-frame) based...
In this paper, we present new feedback reduction schemes that reduce the feedback load needed for opportunistic scheduling in the multicast OFDMA system. Considering the characteristics of the multicast system that the feedback of the user with the poorest channel condition dictates the transmission rate, we designed the proposed schemes such that it can reduce the total feedback load by sacrificing...
The latest generation of wireless networks use OFDMA (Orthogonal Frequency Division Multiple Access) transmission technology in the downlink (e.g, WiMAX and LTE). The downlink is divided into bandwidth units and UEs (User Equipments) are each allocated a subset of these. Since at most one UE is assigned to each of these units, downlink transmissions within a sector are orthogonal. However, the transmission...
In this paper, multiple-input multiple-output (MIMO) layer shifting with cubic metric (CM) preserving precoder and downlink control signal sharing is proposed as a uplink transmission scheme for 3GPP Long Term Evolution (LTE). The design criteria for CM preserving precoder are presented and uplink precoder is designed accordingly. By sharing MCS (modulation and coding scheme) and/or HARQ (hybrid automatic...
The LOS components of the base station (BS) can provide a high SNR to mobile stations (MSs), but they cannot achieve a high spatial multiplexing gain in the MIMO-OFDMA system. The spatial multiplexing gain is obtained by degrees of freedom between MIMO antenna arrays. MIMO channels should be uncorrelated to achieve the maximum degrees of freedom, and it depends on rich scattering environments which...
In this paper, a new channel estimation method is proposed for channel estimation in the 3GPP LTE downlink. The channel estimation is first implemented in the time-domain before selecting the dominant channel taps to improve the signal to noise ratio (SNR) by ignoring the taps corresponding to the lower powers. In the frequency-domain, the transformed channel data corresponding to the pilot positions...
This paper analyzes the problem of allocating power and subchannels in the downlink of a multi-cell, full-reuse OFDMA cellular system. We propose a distributed iterative algorithm, in which the allocation is performed independently in each cell, by maximizing the cell rate subject to a power constraint. The algorithm restricts the set of users that can be allocated on each subchannel, in order to...
In this paper we consider the Downlink Beamforming (DLBF) and resource allocation problem in MIMO-OFDMA systems. We consider the sum-power minimization or margin adaptive problem. This is a variable Signal to Interference and Noise Ratio (SINR), non-convex optimization problem and many aspects of this problem are not well understood. By using uplink downlink duality we first obtain the expression...
This paper focuses on the problem of maximizing the system utility for real-time services in OFDMA cellular systems. We evaluate the upper bound for the global maximum of the system utility, whose actual value is very difficult to obtain when the utility functions are not concave. A linear programming based resource allocation algorithm is proposed to approach the bound, and a priority-based resource...
This paper presents a framework based on self-organization to jointly self-optimize the spectrum assignment and the transmission power in the context of downlink OFDMA femtocell deployments. It is a distributed framework where each femtocell acts as an autonomous entity. Femtocells perform spectrum and transmission power assignment based on users' reported measurements, which are employed to sense...
Weighted ergodic sum-rate maximization in OFDMA uplink is investigated. A finite set of achievable rates is assumed. The problem is formulated as a convex optimization problem. An analytical solution is derived using the Lagrangian dual decomposition. Numerical results show that the weights can be adjusted to increase the fairness in the system or to increase the priority of certain users.
The downlink of the Long Term Evolution (LTE) would be OFDMA based and combination of Hybrid ARQ at the data link layer with adaptive modulation and coding (AMC) at the physical layer might be employed. Constellation rearrangement (CR) technique is used in HARQ to enhance MQAM performance. An improved mapping method is used in full IR to enhance system performance. An improved SNR estimation algorithm...
The problem of resource allocation for the downlink of wireless systems operating over a frequency-selective channel is investigated. It is assumed that both the Base Station (BS) and each user are equipped with a single antenna (Single Input Single Output - SISO case) and Orthogonal Frequency Division Multiple Access (OFDMA) is used as a multiple access scheme. A suboptimal, but efficient scheme...
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