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In OFDM systems, the inter-symbol interference and inter-block interference are eliminated by using null-tones (NT) and cyclic prefix (CP) redundancy of length higher than the channel size. To preserve a high bit rate, channel shortening method is required to reduce the redundancy. Recently, channel shortening technique with differential encoded OFDM systems without the NT was introduced. This technique...
We consider a heterogeneous multiuser OFDM wireless network serving both QoS constrained high-priority users and best-effort users. We investigate resource allocation to maximize the total network utility by specifying two different utility functions for the two user classes. Our strategy is to first maximize the number of satisfied high-priority users before allocating the remaining resource among...
Filter bank based multicarrier systems (FBMC) offer a number of benefits over conventional orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP). One benefit is the improved spectral efficiency by not using a redundant CP and by having much better control of out-of-band emission. Another advantage is the ease of accommodating multiple users in an FDMA fashion especially in the...
This paper proposes a new semi-blind data-selective affine-projection algorithm for channel equalization considering that the transmitted symbols belong to an M-QAM constellation. The main novelties of this algorithm are the combination of the affine-projection (AP) and set-membership (SM) concepts with the formulation of an error measure that is related to a square region (in the complex plane) centered...
This paper introduces a constrained version of a recently proposed generalized data windowing scheme applied to the conjugate gradient algorithm. This scheme combines two types of data windowing, the finite-data sliding window and the exponentially weighted data window, in an attempt to attain the best of both methods in a linearly constrained scenario. The proposed algorithm was tested in a simple...
In this paper we propose a blind adaptive channel estimator for multicarrier CDMA systems. The proposed algorithm is derived from the stochastic gradient solution for the linearly constrained minimum variance detector and it is shown to present lower computational complexity when compared to a well-known solution. It is shown through computer simulations that both the channel estimation and receiver...
Recent results show that an adaptive transversal least-mean-square (LMS) equalizer in a narrowband-interference dominated environment operates at a mean weight vector that is different from that of the Wiener equalizer of the same structure. In addition, the time-varying component of the LMS weight vector results in a steady-state mean square error (MSE) that can be substantially lower than that for...
This paper presents a study about q-ary product turbo codes applied to FFH-CDMA systems. A method to implement the q-ary soft decoding is proposed. First, an adaptation of Chase decoding algorithm to satisfy q-ary symbols requirements is developed. The adaptation does not significantly increase decoding complexity when compared to the binary algorithm. Second, a modification of iterative (turbo) decoding...
This paper presents an enhanced permeable layer mechanism useful for reliable packetized multimedia transmission. Packet header recovery at various protocol layers using MAP estimation is the cornerstone of the proposed solution. The available intra-layer and inter-layer header correlation is used to define a reduced set of header configurations for further processing. The best candidate is then obtained...
This work presents a new version, with reduced computational complexity, of the covariance-based direction-of-arrival (CB-DoA) algorithm. The new algorithm incorporates the concept of beamspace projection before performing the DoA estimation. Such modification reduces the dimensions of the matrices employed by the elements pace CB-DoA, simplifying the resulting computations while preserving the detectability...
In this work we study joint multiuser detection using factor graphs for an N frequency T user noisy multiple access channel. This channel may model a frequency hopped code division multiple access system. The system is separated in two parts: multiuser detector and a code. We present a factor graph for the multiuser detector and obtain from it extrinsic information transfer (EXIT) curves. Paired with...
In this paper we investigate the decoding of parallel turbo codes over the binary erasure channel suited for upper-layer error correction. The proposed algorithm performs ldquoon-the-flyrdquo decoding, i.e. it starts decoding as soon as the first symbols are received. This algorithm compares with the iterative decoding of codes defined on graphs [1], in that it propagates in the trellises of the turbo...
We address the problem of resource allocation on an OFDMA downlink under fairness constraints with limited channel state information (CSI). Target QoS corresponds to a minimum user data rate, a target bit-error rate and a maximum outage probability. The only available CSI is the channel average gain of each user. This partial CSI can be viewed as a shadowed pathloss that yields a modified user distribution...
Receive diversity with multiple antennas is a very well-known technique to improve receiver performance in fading environments. The concept is particularly simple in OFDM systems, where the channel effect on each subcarrier amounts to a complex multiplication of the transmitted symbol. It is also well known that, provided the antenna noise covariance matrix is known by the receiver, interference rejection...
In this work we present efficient channel estimation algorithms for wideband amplify-and-forward (AF) based relay networks which utilize a recently proposed transmission model. It is shown that all channels in the network from the source through the relays to the destination/receiver node can be blindly estimated up to a phase ambiguities vector which contains the phases of the direct source to destination...
In this paper, source and relay precoders are derived which optimize upper and lower bounds on the Gaussian MIMO relay channel capacity. First, the prior art on the cut-set upper-bound on capacity is extended by showing that the optimization of the source and relay codebooks can be formulated as a convex problem without having to introduce a scalar parameter that captures their cross-correlation....
Hybrid MIMO communication systems combine spatial multiplexing with diversity gain to achieve both high spectral efficiency and link reliability. We present a novel generalized hybrid scheme that allows the use of any number of spatial multiplexing layers (V-BLAST) and any number of quasi-orthogonal layers (ABBA).We also present a low-complexity, ordered, successive interference cancellation receiver...
Wireless communication systems must be designed to mitigate fading to guarantee a reliable communication. In future technologies, a successful method to improve reliable communication over a wireless link is to use multiple antennas. Recently, a lot of effort has been put into designing closed-loop STBCs schemes with a full rate, full diversity and some array gain for four transmit antennas with one...
In this paper, we present a joint algorithm to estimate the fine symbol timing and carrier frequency offsets of wireless orthogonal frequency division multiplexing (OFDM) signals. To jointly estimate synchronization parameters using the maximum likelihood (ML) criterion, we propose to transmit a special pilot symbol. By using a periodic training sequence, we convert the problem of obtaining the ML...
Hybrid automatic repeat request (HARQ) improves the throughput performance of ARQ by combining retransmission of packets with forward error correction coding. In MIMO systems employing HARQ and equalization, optimal performance at the receiver is obtained when the signals corresponding to each transmission are combined before the equalizer. Performance can be exchanged for reduced receiver memory...
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