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In this paper, we propose a simple proportional fairness resource allocation technique for downlink OFDMA system, by re-arranging the set of users into four classes and setting different priority order. The classes are obtained according to buffers states and channels conditions. We offer priority to users having a delay sensitive traffic by considering those who have the fullest buffer and good channel...
In this paper we evaluate, by means of Extrinsic Information Transfer (EXIT) charts, an iterative receiver that has emerged as a promising candidate for non-coherent multi-user multi-antenna OFDM systems. The receiver performs parallel interference cancellation (followed by linear filtering) and channel estimation, using soft symbols obtained from a bank of single-user decoders. For the sake of conceptual...
This paper proposes a bit-interleaved coded transmission with multilevel modulation for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. In the proposed system, multiple layers are encoded and interleaved together, using one encoder and one interleaver, and then mapped by hierarchical symbol mapping. A corresponding receiver structure is presented, where...
The performance of a space-time block coded orthogonal frequency-division multiplexing (STBC-OFDM) system often relies on the assumption of quasi-static channels. For the time-varying multipath channel, co-channel interference (CCI) and inter-carrier interference (ICI) occur and performance degrades seriously. In this paper, we propose an iterative interference cancellation scheme to reduce both CCI...
In forward link multiuser space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) systems, the signal-to-noise power ratio (SNR) of each user's received signal is different from those of others. Thus, when subcarriers are not properly allocated to users, intensive bit errors occur in a specific user. This causes a burst error in such a user, and the number of correctable bits...
In this paper, we present a technique to enable accurate built-in measurement of EVM for OFDM transceivers. This measurement technique only relies on the decoded bit pattern, and does not require any additional test equipment. In order to accurately predict EVM without using analog signal analysis, we intentionally code more symbols into the bit pattern in test mode, which enables the decoding of...
The key requirement of 200 Mbps MB-OFDM UWB wireless system is that the OFDM block which is a 128 point FFT/IFFT processor has to operate at 528 MHz. The same way, a 64 state, rate-1/3 Viterbi decoder block is needed but this has to operate at 125 MHz. Novel schemes are essential for achieving these speeds on FPGAs. In this paper, novel schemes are proposed to meet the challenges of FPGA based OFDM...
A new soft-decode-and-forward (SDF) relay strategy for asynchronous wireless networks is presented in this paper. Unlike most previous works that assume simplified or idealized channel conditions, the new SDF relay strategy is designed to operate in practical asynchronous wireless networks with doubly-selective (both time-selective and frequency selective) fading. To combat the impairments caused...
In, we have proposed a novel cross-layer scheme based on resolution adaptive ADCs and fountain codes for the OFDM systems to lower the power consumption in ADCs. The simulation results show that it saves more than 70% power consumption in ADCs comparing to the current IEEE 802.11a system. In this paper, we investigate its performance in the realworld. Measurement results show that the FEC layer used...
We investigate the case of Block Turbo Codes (BTCs) combined with Orthogonal Frequency Division Multiplexing (OFDM) technique for Unmanned Aerial Vehicles (UAVs) highspeed data link. Considering the UAV channel with time-varying and multipath fast fading characteristics, a 3-path UAV channel model is developed, which can be readily implemented under simulation condition. Two typical communication...
We describe new concepts in broadband software define radio architectures optimized for very high bandwidth wireless communication protocols. This is important since a trend in wireless communication transceivers is the adoption of increasingly sophisticated radio link algorithms which maximize utility functions consisting of network capacity, data rate reliability, and throughput. Many prior efforts...
Orthogonal frequency division multiplexing (OFDM) systems may experience significant intercarrier interference (ICI) when used in doubly selective channels (time- and frequency-selective), particularly when large OFDM blocks are employed in order to achieve a high spectral efficiency. In this paper we recall a technique to mitigate ICI by splitting equalization at the receiver in two parts. A first...
In ultra wideband (UWB) system, multiband orthogonal frequency division multiplexing (MB-OFDM) has been proposed to provide high-speed transmission for short-range wireless links. In this paper, 2 dimensional (2D) single parity check product code (SPCPC) is investigated in MB-OFDM UWB communication for Rayleigh fading channel and additive white Gaussian noise (AWGN) channel in order to improve the...
The cooperative communication has recently gained momentum in the research community. This technique utilizes the notion of relay, as an intermediate node between the source and the destination, to enhance the overall system performance. In this paper we explored the benefits of adaptive cooperation, in which the relay adapts its relaying process in response to channel conditions and type of data...
If binary signaling is used in an n-channel OFDM link, the maximum possible bit rate is n bits per OFDM symbol duration. We show a simple scheme based on selective channel use that increases this capacity by nearly 60%. By using only k channels out of the n, we show how to use the choice of the k channels as an additional auxiliary channel. For proper choice of parameters, the information transferred...
The robustness to jamming signal is an important property for military communication systems. Some previous work has shown that the frequency domain code division multiplexing (CDM) efficiently rejects the interference. In general, however, the jamming signal has higher power than ordinary interference which leads to insufficient jamming rejection performance of these schemes. To mitigate this insufficiency,...
One of the main challenges of the 4th generation wireless systems is to provide high data rates in mobile environments. In these 4G products, WiMax (worldwide interoperability for microwave access) and LTE (long term evolution) will be the platform technologies. The rapid development of the Internet with new services and applications has created new challenges for the development of mobile communications...
In recent years the quadratic program (QP) is applied for the blind signal detection of the time-varying OFDM systems. The minimum solution of the QP could be obtained through the class of the sphere decoder (SD) algorithm, which is equivalent to the tree search approach. In this paper, we derive some formulas describing the probability information about the received signal. With these formulas, a...
Iterative technique at any communication receiver has been confirmed to exhibit some gains over its non-iterative counterpart. In this paper, we consider a turbo-coded OFDM system employing Iterative receiver that comprises of Turbo decoder and the Iterative decision directed channel estimation (DDCE) scheme that are working together in an iterative mode. The iterative DDCE scheme is based on the...
This paper proposes an optimal block differential space-frequency scheme for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. A rather general channel model is assumed, where the channel is frequency-selective and remains constant for only a single OFDM block. We achieve resilience against this fast fading environment by differentially encoding blocks...
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