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In this paper, a point-to-point orthogonal-frequency- division multiplexing (OFDM) system with a decode-and- forward (DF) relay is considered. The transmission consists of two hops. The source transmits in the first hop, and the relay transmits in the second hop. Each hop occupies one time slot. The relay is half-duplex, and capable of decoding the message on a particular subcarrier in one time slot,...
We propose two encoding strategies for a two user cooperative Orthogonal Frequency Division Multiple Access (OFDMA) system, based on block Markov superposition encoding. We obtain the expressions for the resulting achievable rate regions for both encoding strategies, and evaluate them through simulations. We show that, by allowing for re-partitioning and re-encoding of the cooperative messages across...
In this paper, we consider an OFDM-based cooperative diversity system where a source communicates with a destination with the help of a relay in Amplify-and-Forward relaying or Decode-and-Forward relaying. First, we propose a scheme to selecting the "best" relay to assist the transmission. And then, we present two power allocation schemes to minimize system outage probability, based on statistical...
This paper considers a two-hop orthogonal frequency division multiple (OFDM) wireless communication systems with a source, a decode-and-forward (DF) relay and a destination. We develop a low complexity rate adaptive power allocation strategy at the source and the relay, with respect to individual transmit power constraints, if the channel state information at the transmitter is given. To further enhance...
In this paper, we investigate distributed relay selection in OFDM-based cooperative wireless networks. A selective Decode-and-Forward relaying strategy is adopted, in which one relay is selected to forward the entire OFDM symbol. Theoretical outage performance is analyzed and evaluated first. Then six relay selection schemes based on different selection criteria are given. The outage performance of...
In this paper, we aim to maximize the weighted sum rate of Orthogonal Frequency Division Multiplexing (OFDM) relaying systems. In the considered system we jointly optimize subcarrier pairing in two consecutive time slots and power allocation on each subcarrier in each time slot. In addition, the destination combines the signals from the source and the relay pertaining to the same message in each two...
We consider a multi-source mesh network of static access points wherein sources use decode-and-forward to cooperate with each other. All transmissions use orthogonal frequency division multiplexing (OFDM). Our objective is to maximize the minimum achievable rate across all flows. We find a tight upper bound on the performance of the subcarrier-based cooperation and show that selecting a single relay...
We1 consider transmission over a set of parallel MARCs (multiple-access relay channel) based on the OFDM (Orthogonal Frequency Division Multiplexing) modulation. Two users communicate to a common destination (D) with the help of a relay (R) over a set of parallel channels. The relay operates in decode and forward (repetition coding type) and half duplex modes. The problem considered is the maximization...
The ever-increasing demand for precious radio spectrum along with the inefficient usage of licensed band has led to the advent of the cognitive radio (CR) technology, which aims to provide opportunistic spectrum usage to unlicensed users and thus lead to the co-existence and interference control problem among heterogeneous systems. In this paper, an interference minimization and subcarrier power allocation...
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 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...
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...
In this paper, an effective joint allocation of power and subcarriers is proposed under the total power constraint, aiming to maximize the capacity of OFDMA relaying network. In DF (decode and forward) scheme, an equivalent transmit rate formulation is developed, optimal power allocation is obtained by linear optimization and Lagrange multiplier method. By using this optimal power allocation, an efficient...
In this paper, with the purpose to exploit the space and the frequency diversity, we propose an amplify-and-forward (AAF) cooperative system using orthogonal frequency division multiplexing (OFDM) with space-frequency codes (SFC). The signal processing algorithm of this presented system is introduced in detail and we also provide the system optimal power allocation strategy. Simulation results prove...
Low power consumption is one of the key elements to make UWB technology be the solution for future short-range and high-speed indoor wireless communications. To face the power limitation drawback, while still maintaining significant error correction capabilities, employing cooperation into UWB communications can bring a great performance. In this paper, symbol-error-rate (SER) performance is analyzed...
This paper considers a novel approach to multicarrier orthogonal frequency division multiplexing-based interleave-division multiple-access (OFDM-IDMA) that facilitates both channel estimation and multi-user detection. Specifically, users employ interleavers based upon their channel state information (CSI) to optimize pilot symbol locations, instead of random interleavers as in conventional IDMA. Two...
In this paper, a new criterion for reordering of low-density parity-check (LDPC) coded orthogonal frequency division multiplexing (OFDM) subframes is proposed for type I hybrid automatic repeat request (H-ARQ) systems. It is verified from numerical analysis that a subframe reordering pattern having larger channel capacity shows better bit error rate (BER). Also, it is shown that the subframe reordering...
Joint power allocation, relay selection, and sub-carrier assignment are critical and challenging for achieving full benefits of OFDM based cooperative relay networks. In this paper, we study such a problem in a dual-hop multi-relay OFDM system with an objective of maximizing the spectral efficiency under a total power constraint. The system consists of a pair of source and destination and multiple...
We consider an OFDM (orthogonal frequency division multiplexing) point to point transmission scheme improved by means of multiple relays. For each carrier, symbols sent by the source during a first time slot, may be retransmitted during a second time slot by the relays, which are assumed to be of the decode-and-forward (DF) type. For each relayed carrier the destination implements maximum ratio combining...
The challenge of our work is to enhance the effectiveness of packet retransmission in multi-user OFDMA based communication systems. Based on information theory, we propose a retransmission scheduler (re-scheduler) that recomputes the allocation of chunks for negatively acknowledged packets only when correct packet decoding is impossible or it requires a too large number of retransmissions. Our proposal...
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