The paper studies the capacity of the OFDM and the OFDMA relay networks. Two relay schemes, amplify-and-forward (AF) relay and decode-and-forward (DF) relay are analyzed and compared for both OFDM and OFDMA relay networks. A relay node selection algorithm is proposed for OFDMA relay network. Numerical results show that under small relay power transmission, AF outperforms DF while the opposite i...

Orthogonal Frequency Division Multiple Access (OFDMA) is today a part of many standard specifications. Despite its attractive features, it has two main drawbacks when employed in the uplink: The high peak-to-average power ratio inherited from Orthogonal Frequency Division Multiplexing (OFDM) and the inherent frequency diversity loss. The loss of frequency diversity can be alleviated by precodin...

This paper studies the error performances of two different 4G downlinks in a multi-cell environment. On the one hand, an orthogonal frequency division multiplexing (OFDM) based multiple access scheme (OFDMA), and on the other hand, a multi-carrier code division multiple access (MC-CDMA) scheme is proposed. Both transmission schemes are implemented in a cellular structure. The cellular environme...

This paper aims to The mobile WiMAX air interface adopts orthogonal frequency division multiple access (OFDMA) as multiple access technique for its uplink (UL) and downlink (DL) to improve the multipath performance. All OFDMA based networks, including mobile WiMAX experiences the problem of high peakto-average power ratio (PAPR). This thesis presents: Discrete-Cosine transform matrix (DCTM) pre...

It is well-known that mobile communication systems are usually limited in their performance and capacity by three major impairments, which are multi-path fading, delay spread and co-channel interference (CCI). OFDMA (OFDM-FDMA) system can cope with the multi-path fading and delay spread easily due to the beneficial properties of OFDM technology. Though OFDMA scheme avoids intra-cell interferenc...

The opportunistic beamforming (OB) technique in multicellular OFDMA networks is investigated in this paper. Three cross-layer radio resource management (RRM) algorithms for OFDMA operational scenarios are considered. These algorithms build upon typical network planning practices for OFDMA systems. The first two implement an OFDMA network with opportunistic rate adaptation while the third one ai...

We propose and demonstrate a novel optical orthogonal frequency-division multiple access (OFDMA)-based metro-access integrated network with dynamic resource allocation. It consists of a single fiber OFDMA ring and many single fiber OFDMA trees, which transparently integrates metropolitan area networks with optical access networks. The single fiber OFDMA ring connects the core network and the ce...

OFDMA is a new modulation method for the 2 generation of Broadband Wireless Access (BWA) systems that combines both upstream access and modulation together. OFDMA is based on modulating multiple orthogonal sub-carriers. Unlike traditional multi-carrier modulation schemes, several transmitters of the multiple access system modulate the sub-carriers simultaneously. OFDMA offers up to an 18dB gain...

The mobile Worldwide Interoperability for Microwave Access (Mobile WiMAX) air interface adopts orthogonal frequency division multiple access (OFDMA) as multiple access technique for its uplink (UL) and downlink (DL) to improve the multipath performance. All OFDMA based networks including mobile WiMAX experience the problem of high peak-toaverage power ratio (PAPR). The literature is replete wit...

For wireless local area networks based on OFDM we study the sum rate of time and frequency division multiple access (TDMA, OFDMA) as well as superimposed transmission (SUP). In the analysis traffic-imposed constraints on the maximum exploitable user rates apply. For a large number of subcarriers the effective sum rate is low with TDMA but much higher with OFDMA and SUP. The spatial properties o...