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When fast and accurate channel state information (CSI) at the transmitter is available, opportunistic power control (OPC) is an attractive alternative to signal-to-interference-and-noise ratio (SINR) target following approaches, because it maximizes throughput by taking advantage of fast channel variations. On the other hand, in multiple-input multiple-output (MIMO) systems, open loop schemes such...
One of the phenomena that degrades the performance of multicarrier modulation (MCM) systems is the spectral nulls that multipath channel may have. As a result, the affected subcarrier signals may be severely degraded resulting in a loss of symbols. In this paper we have studied how to overcome this problem by taking advantage of spatial diversity along with the knowledge of channel state information...
This paper presents a low-complexity multiuser MIMO detection algorithm. The MIMO receiver exploits Radial space-Division Multiple Access (RDMA) principle, by paring and scheduling the MIMO multiusers with distinguishable radial space-divisions to the receiver. By exploiting the Channel State Information (CSI) and eigenvalue analysis, the MIMO receiver can selectively deploy the Linear Minimum Mean...
In this paper we focus on the subcarrier allocation for the uplink OFDMA based cooperative relay networks. Multiple cells were considered, each composed of a single base station (destination), multiple amplify and forward (AF) relay stations and multiple subscriber stations (sources). The effects of inter-cell interference (ICI) have been considered to optimize the subcarrier allocation with low complexity...
In this paper we present a new adaptive fractional frequency reuse scheme (AFFR) for multi-cell OFDMA based IEEE 802.16e network. The adaptive fractional frequency reuse (AFFR) scheme is managed by the access service network gateway (ASN-GW) which coordinate a set of BSs (one cluster). To make better usage of radio resources; we assume that the cell area is virtually divided into two different zones:...
While cyclic prefix (CP) is no larger than the delay span of wireless channels in an orthogonal frequency division multiplexing (OFDM) system, inter-block interference (IBI) and inter-carrier interference (ICI) will occur and the performance of the system will be deteriorated. If OFDM is designed with long enough CP, the efficiency of OFDM modulation is significantly reduced. To effectively mitigate...
In this paper, we propose a radio resource allocation (RRA) scheme for multiuser multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing access (OFDMA) systems in order to achieve the optimal system throughput. The proposed RRA algorithm adaptively schedules 3-dimension (3-D) (space, frequency and time) slots to different users according to various channel state information...
This paper considers the dynamic resource allocation in a multiuser context taking into account the quality of service (QoS) requirements for the high-rate ultra-wideband (UWB) systems. The aim of this paper is twofold. First, we exploit the effective SINR method in the multi-band WiMedia solution proposed for UWB systems. This method is based on the exploitation of the characteristics of multiple...
IMT-advanced systems of the future will be based on OFDMA and frequency divicion duplex will be widely used. Multihop techniques, e.g. the use of fixed relays, are also considered a key technology. The OFDMA resources have the dimensions time, frequency and space. In all these dimensions a radio channel is variable due to fading. On the other hand a complete utilization of the channel capacity close...
In this paper, we propose a robust soft decision method based on channel state information (CSI) for coded orthogonal frequency division multiplexing (COFDM) systems. In the presence of co-channel interference (CCI), conventional soft decision decoding is performed by a simple erasing method for frequency selective CCI. But the conventional method cannot obtain sufficient performance gain because...
In this paper, challenges regarding the provision of channel state information (CSI) on a multi-user (MU) MIMO-OFDM downlink are addressed. Reference symbols (pilots) support coherent detection at the receiver and enable link adaptation at the transmitter, but add overhead and consume transmit power. As spatial transmit processing combined with multiple access essentially requires the provision of...
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,...
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