This paper presents a new subband allocation scheme for multiuser OFDMA systems. Adaptive OFDMA systems have focused on adapting the allocation of subcarriers and power to the instantaneous channel conditions of all users. Using frequency hopping pattern in OFDMA system allow users to minimize intercell and intracell interference, and perform frequency diversity. In contrast to conventional FH-...

The performance of Orthogonal Frequency Division Multiple Access (OFDMA) system degrades significantly in doubly dispersive channels. This is due to the fact that exponential sub-carriers do not match the singular functions of this type of channels. To solve this problem, we develop a system whose sub-carriers are chirp functions. This is equivalent to exploiting Fractional Fourier Transform (F...

Frequency-hopping (FH) methods in the Orthogonal frequency division multiplexing access(OFDMA) system,which are to assign user-specific subcarrier to the active users, have been paid much attention to in the broadband wireless communication system. In this paper, we present a novel multiple access scheme, referred to as CDM-FH-OFDMA, which is the extension of FH-OFDMA with code division multipl...

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...