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This paper proposes an efficient multiuser relaying scheme in OFDMA systems. In the proposed scheme, multiple terminals transmit packets simultaneously in the same subband and multiple relay stations retransmit their received signals in different subbands after subband conversion. The base station (BS) extracts each packet from multi-dimensional signals received at the different subbands. In advance...
This paper reformulates the multi-user OFDMA resource allocation problems in broadcast and multiple-access channels by defining an equivalent interference channel. The resulting problems are then solved by employing low-complexity algorithms for spectrum optimization in the interference channel. The re-formulation averts the high-complexity integer programming problem that otherwise results from an...
In high-mobility OFDM systems, Doppler distortions cause inter-carrier interference (ICI) that may degrade the system performance severely. Although thoroughly studied, hardly any approaches for ICI estimation and compensation exist that maintain the OFDM-specific subcarrier-wise signal processing and thus provide a solution with reasonable demands on complexity. For a multi-antenna receiver, this...
In 802.16e OFDMA systems, noise and co-channel interference on pilots degrade the accuracy of channel state information (CSI) obtained from channel estimation (CE) and system performance is deteriorated. To evaluate the system performance loss due to imperfect CSI, CE model should be used to incorporate noise and interference's impact on CSI into system level simulator (SLS). In this paper, a CE model,...
This paper proposes a sub-channel partitioning based on adaptive allocation of Variable Length Codes (VLCs) with Unequal Error Protection (UEP) scheme for Orthogonal Frequency Division Multiplexing (OFDM) system. In this scheme, video data is partitioned into high-priority (HP) and low-priority (LP) coefficients according to the importance of the data, then it is allocated to sub-channels for transmission...
Recently, the attentions of communication societies are paid to MIMO-OFDM systems. In this paper we propose a new beamforming method to the receive end of MIMO-OFDM systems. To make the method work with fewer known OFDM symbols, oversampling samples are employed and multistage decomposition based on orthogonality of sub-carriers of OFDM signal is used to formulate the beamforming weight vector for...
In an environment of shared radio spectrum, multiple systems may interfere with each other and cause significant impacts on system coexistence. In this paper we propose an adaptive subband selection technique based on orthogonal frequency division multiplexing (OFDM) to avoid interference for better system coexistence when multiple systems are operating in the same unlicensed industrial, scientific...
This paper discusses the problem of estimating the performance of an OFDMA receiver operating in a selective channel, prone to interference, wherein only a set of the OFDM sub-carriers is allocated to a user. Planning and deployment of an OFDMA system requires estimation of system performance in various signal to noise and interference (SINR) conditions. The problem is not trivial as both signal and...
Orthogonal frequency division multiplexing offset quadrature amplitude modulation (OFDM/OQAM) is a multi carrier modulation using staggered transmission on the I and Q axes. It uses as well an optimized non-rectangular pulse shaping. There are several advantages with respect to the conventional OFDM modulation, while the main drawback is the intrinsic intersymbol interference, hindering e.g. a proper...
Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H), which is required to operate under high mobility conditions resulting in significant Inter-carrier Interference (ICI). To mitigate ICI, several cancellation schemes have been proposed but they require reliable channel information at the receiver which is quite challenging...
Some communication applications, like multimedia, deliver data of different importance classes allowing unequal error protection (UEP) levels. In this paper, a multiple-input multiple-output (MIMO) system using orthogonal frequency division multiplexing (OFDM) is considered with a new UEP bit-loading algorithm based on the non-UEP algorithm by Chow, Cioffi, and Bingham. In the proposed bit-loading...
Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H) which is required to operate under high mobility conditions resulting in significant Inter-Carrier Interference (ICI). Under these conditions, the conventional one-tap per subcarrier channel estimation and equalization is suboptimal since it does not account for ICI...
This paper addresses adaptive channel estimation for time-varying mobile wireless channels with nonstationary statistics. We presents a reduced complexity adaptive channel estimator based on a set membership filtering approach known as the Optimal Bounding Ellipsoid (OBE) algorithm. To exploit time and frequency domain correlation properties of the channel in an efficient low-complexity way, we allow...
Ultra-wideband (UWB) systems possess several distinct features such as very high data rate, large multipath or frequency diversity and improved ranging precision while requiring low-power low-complexity transceivers. Among the different modulation schemes, differential PSK is an attractive option because it does not require channel estimation, and hence reduces implementation complexity. This paper...
The next generation of wireless networks (4G) will use OFDMA (Orthogonal Frequency Division Multiple Access) in the reverse link. In OFDMA, the reverse link resources assigned to a user are called tiles each of which consists of a subset of consecutive subcarriers. Since at most one user is assigned to each of these tiles then reverse link transmissions within a sector are orthogonal. However, the...
Effects of improved channel estimation are studied for a proposed IEEE 802.11n OFDM MIMO system. Three channel estimation methods are considered: maximum likelihood (ML), time-domain truncation (TDT) and model-based (MB). TDT and MB are particularly useful when the channel delay spread is short. For an MMSE receiver, MB shows a 1-2.5 dB improvement over ML on the packet error rate performance for...
In this paper we consider the coexistence issue between OFDM-based WLANs of the 802.11a family and time-hopping ultra wideband (TH-UWB) systems. A general analytical expression is provided for the bit error rate (BER) of the OFDM transceiver operating in the presence of UWB interference and the interferences caused by the multipath propagation phenomenon on the 802.11a OFDM signal, comprising intersymbol...
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