Orthogonal frequency division multiplexing (OFDM) is a very popular modulation scheme because it requires a very simple receiver in transforming a frequency-selective channel into multiple flat-fading channels. Furthe...
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ISBN:
(纸本)9781424493326
Orthogonal frequency division multiplexing (OFDM) is a very popular modulation scheme because it requires a very simple receiver in transforming a frequency-selective channel into multiple flat-fading channels. Furthermore, multiple-input-multiple-output (MIMO) OFDM systems employing transmit diversity techniques, such as space-time (ST) and space-frequency (SF) coding, increase robustness and reliability over wireless fading channels. However, time-variation of the channel due to mobility disrupts orthogonality among subcarriers and yields intercarrier interference (ICI), limiting the performance of OFDM. In this paper we first recall a reduced-complexity technique to mitigate ICI in single-input-single-output (SISO) OFDM systems denoted per sub-block equalization (PSE) which operates on sub-blocks of the received OFDM symbol. Next we propose an extension of PSE to MIMO SF-OFDM systems. In particular, the Alamouti scheme is used in conjunction with PSE to combat ICI. Performance of the proposed scheme is evaluated for mobile digital video broadcasting DVB-T2 2 x 1 and 2 x 2 MIMO scenarios that suit with a possible extension to handheld devices in a next generation DVB-H. Numerical results show that the new receiver provides a gain from 21% to 33% with respect to the conventional OFDM receiver in terms of vehicular speed at which a target bit error rate can be maintained.
Baseband adaptive array processing is a traditional approach to mitigating interference at a digital receiver. In the presence of sufficiently strong interference, this mitigation fails if receiver (RX) front-end comp...
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ISBN:
(数字)9781665482431
ISBN:
(纸本)9781665482431
Baseband adaptive array processing is a traditional approach to mitigating interference at a digital receiver. In the presence of sufficiently strong interference, this mitigation fails if receiver (RX) front-end components, such as amplifiers and ADCs, are driven into non-linear operation or if the RX responds by decreasing its gain and losing sensitivity to the signal. Instead of requiring costly RX components with high dynamic-range, we explore a novel Multiple-Input Multiple-Output (MIMO) scheme that uses hybrid analog-digital beamforming to mitigate a strong interferer in wideband line-of-sight (LOS) channels. This scheme uses true-time delay analog beamforming within antenna subarrays to mitigate most of the interference ahead of the RX front-end and then linear spatial equalization to mitigate residual interference at baseband. Alamouti space-frequency coding at the transmitter and MIMO receive processing are used to exploit the frequency-selective channel imposed by the analog beamforming stage. We show that this architecture can outperform traditional Single-Input Multiple-Output (SIMO) schemes under strong interference using low complexity processing in a relatively low-complexity hardware implementation. The specific case of intervehicular (V2V) LOS channels is considered in detail.
This paper introduces a computationally efficient pilot aided channel estimation method for space-frequency block coding (SFBC) Orthogonal frequency Division Multiplexing (OFDM) systems under frequency selective chann...
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ISBN:
(纸本)9781424495375
This paper introduces a computationally efficient pilot aided channel estimation method for space-frequency block coding (SFBC) Orthogonal frequency Division Multiplexing (OFDM) systems under frequency selective channels. The proposed method, simulated under WiMax requirements, is based on the use of eight pilots defined in the standard to estimate the channel parameters at constant interval. The pilots are also coded in the same SFBC format to simplify the estimation computations, but can be modulated by different modulation scheme to reduce the estimation error. The method offers tradeoff between accurate channel estimation and efficient bandwidth usage as more pilots would allow the algorithm to perform a more accurate estimation but at the cost of less transmitted data. Performances are evaluated for high mobility applications and with pilots modulated using different modulation schemes. Simulation results are presented for different number of antenna at the receiver, different values of Doppler shifts and different modulations for pilot and data subcarriers.
This paper introduces a method to design spacefrequency trellis codes for a system that combines space-time coding with orthogonal frequency division multiplexing (OFDM) to realize broad-band wireless communications. ...
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ISBN:
(纸本)9781467355797
This paper introduces a method to design spacefrequency trellis codes for a system that combines space-time coding with orthogonal frequency division multiplexing (OFDM) to realize broad-band wireless communications. It has been pointed out in the literature that the frequency-selective fading, which usually occurs in such combined system, turns out to produce a beneficial effect on the error rate performance by providing the frequency diversity in addition to the spatial diversity. This enables space-frequency codes to exploit greater diversity than the space-time codes. However, exhaustive search for space-frequency trellis codes is impractical. The only existing heuristic design method has a drawback in the spectral efficiency, and in turn degrades the coding gain (energy efficiency,) which is also the primary purpose of space-frequency coding. We propose a practical method to design the space-frequency codes that exploit full diversity while maximizes the coding gain at a desired spectral efficiency. The simulation results show the superior error rate performance of the codes designed by the proposed method.
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