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In this paper, a novel cell architecture in relay-enhanced Orthogonal Frequency-Division Multiple Access (OFDMA) cellular networks is proposed. By spatially reusing the spectrum in the same cell, the frequency efficiency is enhanced, while the co-channel interference is reduced by dividing the coverage of both the base stations (BSs) and the relays into sectors, thus the MSs at the cell edge can attain...
This paper deals with the designing of low complexity scheduling for multiuser MIMO-OFDM systems with limited CSI (channel state information). By using quantization technology, we can get semi-orthogonal region sets. Thus, the transmitter can carry out user scheduling by using the feedback CSI, which including channel direction information (CDI) and channel quality information (CQI) and the quantized...
We study a dynamic inter-cell interference coordination scheme formulated using a novel binary integer linear programming optimization technique. The scheme aims to maximize utility, where different utility measures have been defined to model varying levels of user fairness. The formulated problem is decomposed into a number of smaller sub-problems and solved iteratively to ease the computational...
DVB-H (Digital Video Broadcasting, Handheld) is based on the terrestrial version of DVB, i.e. DVB-T, and it has been designed especially for the moving environment. The performance of the system takes into account the variations of the power levels and bursty interferences of the radio path. DVBH is adequate especially for the small handsets as the typical terminal screen size requires only a fraction...
The next generation 3GPP long-term evolution (LTE) mobile system will use orthogonal frequency division multiplexing access (OFDMA) as the key technology to improve the spectrum efficiency and flexible user resource allocation. One of the challenges of OFDMA systems is the interference at the cell edge where users are likely to get high interference from neighbouring cells. In a network with non-uniform...
We present field experiment results on multiple input multiple output (MIMO) precoding using orthogonal frequency division multiple access (OFDMA) in the E-UTRA downlink. We measured the throughput performance of 4??4 MIMO precoding with 1- to 4-stream transmission. Time variation characteristics of throughput, SINR, and antenna correlations are compared to evaluate the selection criteria for the...
Reference symbols (pilots) support coherent detection, but add overhead and consume transmit power. A sophisticated pilot design needs to trade-off the attainable channel estimation accuracy with the induced losses in bandwidth & power efficiency. MIMO transmission, transmit beamforming, and spatial multiplexing further complicate pilot design. In this paper a unified analytical framework is developed...
This paper considers a transmit beamforming and subcarrier power allocation method for orthogonal frequency division multiple access (OFDMA) systems. As the beamforming vector control criterion, we employ the maximization of so-called signal-to-leakage-plus-noise ratio (SLNR) at each base station, which enable us to obtain closed form beamforming vector by using only locally available information...
This paper focuses on emulation of the link-level processing for efficient system-level simulations of MIMO-OFDM based mobile communication systems. While the downlink of 3GPP's long term evolution (LTE) and the various MIMO transmission modes used therein stand in the focus of our considerations, the proposed techniques can be applied to other MIMO-OFDM based communication systems such as WiMAX....
In this paper, we present a new tone reservation (TR) scheme that facilitates peak-to-average power ratio (PAPR) reduction in orthogonal frequency-division multiplexing systems employing antenna selection on a per-subcarrier basis. In contrast to conventional TR schemes, the proposed technique does not lead to a reduction in the data rate, although it does introduce a controllable level of interference...
The advanced MIMO (multiple-input multiple-output) system can provide higher capacity gain or higher diversity gain in modern wireless networks. The capacity gain is achieved by interference cancellation technique to fully utilize the spatial degree of freedom. In a multiuser wireless system, the increased degrees of freedom provide the chance to select multiple wireless stations (STAs) to maximize...
An orthogonal frequency division multiplexing (OFDM) system suffers performance degradation when the length of the cyclic prefix (CP) is less than the channel impulse response. The root cause of this degradation is the inter-carrier interference (ICI) and inter-symbol interference (ISI) introduced by the excessive multipath delay. Generally, MIMO beamforming is helpful in mitigating such interference...
This paper evaluates the ultra low complexity non-eigen decomposition (NED) algorithm for adaptive interference mitigation. Current blind beamforming algorithms require computational complexity too high for many target applications. NED does not rely on the eignenvalues and eigenvectors used by conventional algorithms and requires significantly less computations, with a total computational load of...
We propose a random beamforming technique in multiuser multi-antenna orthogonal frequency division multiplexing (OFDM) systems for a large system capacity and fairness among users. In the proposed technique, we allocate several beams on each subcarrier to users based on signal-to-interference plus noise ratio (SINR) and all the remaining beams on each subcarrier by the proportional fairness (PF) algorithm...
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...
This paper addresses multiuser linear precoding using multiple cooperating base stations (BSs). All BSs, and potentially the users, are equipped with multiple antennas. Prior work in multiuser precoding with a single BS extensively uses a downlink/uplink duality that significantly reduces the computation load. Here we show that the presence of asynchronous interference, unfortunately always present...
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...
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...
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