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Orthogonal frequency division multiplexing (OFDM) systems may confront significant intercarrier interference (ICI) when applied in doubly selective channels. Furthermore, the insufficient cyclic prefix (CP) leads to interblock interference (IBI) which again results in ICI. These interferences cause an early error floor in conventional receivers. In this paper, we characterize the doubly selective...
The combined use of orthogonal frequency-division multiplexing (OFDM) and wireless multiple-input multiple-output (MIMO) links is becoming common. For many applications, such as ad hoc wireless networks, interference is a significant issue. MIMO links allow for the spatial mitigation of interference; however, spatial interference mitigation when using OFDM modulation performs somewhat poorly because...
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...
Channel adaptive transmission in multi-user MIMO systems is seen as a promising concept to achieve high spectral efficiencies in future radio networks: Based on feedback on actual channel conditions, the base station allocates transmission resources to the user terminals where they can support high data rates. However, due to the delay between evaluation of the channels at the terminals and application...
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...
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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