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We consider an Amplify-and-Forward relay selection for OFDM networks with fairness constraints where a source node communicates with a destination node with the help of one or more relays. The system model assumes all relays participate and considers the subcarrier pairing with fairness constraints on relays. Our subcarrier allocation algorithm is presented to maximize the system capacity based on...
In this study, orthogonal frequency division multiple access (OFDMA) based primary and secondary usage in a cognitive radio system is considered and conventional power spectral density (PSD) based technique is used to detect the opportunities in the spectrum. Primary user employs block-based or scattered subcarrier allocation scheme and the overlay system aims to utilize the spectral gaps. Comparison...
3GPP LTE specification is stable now in release 8. To meet much higher requirements than release 8, 3GPP has initiated the LTE-A (LTE-Advanced) study item. In LTE-A, CoMP (coordinated multiple point transmission and reception) and CA (carrier aggregation) are two new features. CoMP is used to improve coverage and to increase cell-edge throughput. It is considered as an effective approach for ICIC...
As the number of users increases, the amount of required feedback Channel State Information (CSI) at the base station becomes huge and prohibits the feasibility of conventional adaptive resource allocation algorithms in fairness-aware downlink OFDMA systems. Thus, this paper presents a novel mechanism making use of multi-user diversity to greatly reduce the feedback CSI while maintaining almost the...
Conflict-free power allocation for secondary user (SU) in cognitive networks is a challenging problem since the accessible spectrum of the SU is shared with the primary user (PU); the problem becomes to be especially difficult when it is wanted to achieve the maximum network capacity considering the mutual interference between PU and SU. In this paper, specifying the single SU case with multiple PUs,...
A cognitive OFDM-based relay network is considered in this paper. Communication between any node pair occurs on a spectrum pool of OFDM subcarriers where the subcarriers are not used by primary users. Therefore, the available spectrum for different transmitter-receiver pairs is distinct due to their location difference and so on. To satisfy different traffic demand and improve system performance,...
In this paper, we propose a block-based OFDM decode-and-forward relaying scheme for cooperative wireless networks. In the scheme, an OFDM symbol is divided into blocks and one relay is selected for each block. Theoretical outage performance is analyzed and evaluated, and a unified outage expression is developed for our scheme and the other two schemes. Monte Carlo simulations are carried out to validate...
Different to orthogonal frequency division multiplexing using cyclic prefix (CP-OFDM), time division synchronous OFDM (TDS-OFDM) employs pseudo noise (PN) sequence as the prefix. TDS-OFDM provides better power efficiency than CP-OFDM since the PN prefix can be used for channel estimation while CP-OFDM needs dedicated pilot symbols. However, when TDS-OFDM is considered with frequency domain multiple...
Resources allocation of OFDM system is a key factor that affects system performance. Parteek Bansal proposed a bit-power allocation algorithm under different bit error rate (BER). But the process of its bit allocation will cause high complexity and bad real-time to build a power-increment table. In this paper, a low-complexity multi-user subcarrier-bit-power allocation algorithm for wireless OFDMA...
In this paper, we study the resource allocation problem in the downlink of an OFDMA system. Taking into account the constraint that each user can be assigned only one modulation and coding scheme (MCS), our goal is to maximize the system utility, which can be either the sum rate of users or certain fairness metric. The joint subcarrier, rate, and power allocation problem is formulated, and a straightforward...
In this paper, a new resource allocation scheme is proposed for a two-way OFDM relay network. In the proposed scheme, two terminals exchange information with the help of multiple relays, and subcarriers and their power are successively allocated to the relays to maximize sum capacity. To achieve fairness for the relays, power constraint on each relay is imposed. Simulation results show that the proposed...
In OFDMA systems, reducing the inter-cell interference among adjacent cells is a very important issue especially for the cell-edge users. In this paper, we propose a distributed algorithm that maximizing the system total throughput considering proportional fairness. In our proposed algorithm, the frequency resources in each cell is divided into high and low power regions. The bandwidth allocations...
This paper proposes a novel semi-dynamic inter-cell interference coordination (ICIC) scheme for multi-cell OFDMA systems. The objective of the novel scheme is to strike a balance between ICI minimization and frequency reuse factor (FRF) maximization. Firstly, we divide cell-edge users into non-overlapping user groups based on users' geometry, and classify each group's available bandwidth, which includes...
The combination of multihop relay system and orthogonal frequency division multiplexing (OFDM) modulation is a promising way to increase capacity and extend coverage area. For OFDM two-hop relay system with separate power constraints, we consider joint subcarrier matching and power allocation problem to maximize the system capacity, where the relay strategy is decode-and-forward. We formulate the...
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...
An adaptive resource allocation scheme is proposed for regenerative relay-based orthogonal frequency division multiplexing access systems. This scheme allocates subchannels to guarantee fairness between users, and also saves energy by minimising the transmission power. The subchannel allocation for data rate fairness is considered between direct link users and relay stations in the first time subslot...
We propose a subchannel allocation by considering multiuser diversity to reduce self interference (SI) which arises due to the destrunction of orthogonality of spreading codes in orthogonal frequency division mutiple access - code division multiplexing (OFDMA-CDM) system. The conventional OFDMA-CDM does not effectively reduce SI, since it does not consider multiuser diversity. The proposed scheme...
This paper studies a new decentralized resource allocation strategy, named iterative spectrum shaping (ISS), for a multi-carrier-based spectrum sharing system, where two co-existing users independently and sequentially update transmit power allocation over parallel subcarriers to maximize their individual transmit rates. Unlike the conventional iterative water-filling (IWF) algorithm that applies...
We consider an OFDM (orthogonal frequency division multiplexing) point to point transmission scheme improved by a relay. For each carrier, symbols sent by the source may be retransmitted during a second time slot by the relay, which is assumed to be of the decode-and-forward (DF) type. For each relayed carrier the destination implements maximum ratio combining. Assuming perfect CSI (channel state...
It has been shown that adaptive power and rate allocation for multiuser orthogonal frequency multiplexing (OFDM) improves the system performance significantly. In this paper, the resource allocation that aims at minimizing the total transmission power under certain data transmission constraints is considered. First, the power variation for single-user water-filling while changing the subcarrier assignment...
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