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Various techniques have been proposed to address the problem of resource allocation in multi-carrier communications. These techniques, for the most part, arise from information-theoretic measures or otherwise associated with the channel behavior, which does not necessarily model the coding being employed. In this paper, an optimization technique is tailored for low density parity-check (LDPC) coded orthogonal frequency-division multiplexing (OFDM) systems, by employing the so-called general stability condition introduced by Richardson et al. The latter formulates a necessary condition for the belief-propagation decoder to perfectly decode a received vector with no errors. The general condition is re-formulated so as to model practical multi-carrier systems, such as OFDM. Consequently, a general resource-allocation framework is laid down for optimizing the transmitted power based on the characteristics of the LDPC code in use. The proposed optimization technique is utilized for power allocation in orthogonal frequency-division multiple access systems; and the transmitted power is minimized while guaranteeing reliable decoding. To validate the proposed approach, it is compared to information-theoretic-based methods that aim at optimizing the mutual information between the transmitter and the receiver. Both approaches are shown to provide almost identical performance for the scenarios addressed in this paper. [ABSTRACT FROM AUTHOR]

Elimination of rogue Access Points (APs) is a challenging security goal of growing interest and practical importance. However, even when network administrators suspect that such devices are indeed present to attack their organization, physically locating their whereabout is an intricate task. In this work a method is suggested for implementing autonomous Direction Finding (DF), i.e., an apparatus for passively identifying the Angle-of-Arrival (AoA) of a received Wi-Fi signal, using a standard off-the-shelf Wi-Fi receiver. Modern wireless communication standards, such as Wi-Fi (e.g. IEEE 802.11n), are based on Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) technologies. The key contribution of the current work is an approach of employing the multiple receiving antennas jointly with OFDM Channel State Information (CSI) as the basis for implementing an interferometry DF tool. This approach is theoretically investigated via numeric analysis, and practically validated by a working prototype. The performance of the prototype was evaluated both in the laboratory, in a sterile environment, as well as in field trials. In realistic indoor setting the prototype was able to acquire the AoA with a median error of 8–15 degrees. [ABSTRACT FROM AUTHOR]

Adaptive bit loading algorithms are proposed for multi-channel systems in general, and orthogonal frequency division multiplexing in particular. A discrete coding-modulation adaptation is considered. Constant power allocation is assumed for all subchannels, while the bit error rate on different subchannels is unconstrained. The proposed algorithms are computationally efficient and require limited amount of feedback resources. Their performance compare favorably with other practical schemes known in the art. [ABSTRACT FROM AUTHOR]

Single Carrier FDMA (SC-FDMA) plays an important role in modern wireless communications as an alternative to OFDM mainly since it exhibits low peak-to-average power ratio. Accordingly, SC-FDMA is employed as the uplink scheme for the 3GPP long term evolution (LTE). In the presence of multipath, the SC-FDMA signal may arrive at the receiver perturbed by inter-symbol-interference, which renders the single-tap frequency-domain equalization suboptimal. Optimum maximum likelihood detection for SC-FDMA is often prohibitively complex, and hence useful mostly as a performance bound for suboptimal detection schemes. In this work, the optimum-detector performance is analyzed in detail; the analysis can be easily applied to any SC frequency-domain equalization scheme. Closed form bounds on the achievable bit error rate are provided for low and high SNR regimes in correlated and uncorrelated Rayleigh fading channels. The bounds reveal that the diversity order at high SNR is significantly smaller than in the low SNR regime. Moreover, error rate flaring behavior is demonstrated under optimum detection of SC-FDMA. The analytical results are verified by simulations. [ABSTRACT FROM AUTHOR]