Abstract
Orthogonal frequency division multiplexing (OFDM) has emerged as a modulation scheme that can achieve high data rates over frequency selective fading channel by efficiently handling multipath effects. This paper proposes receiver design for space-time block coded MIMO OFDM transmission over frequency selective time-variant channels. Joint channel and data recovery are performed at the receiver by utilizing the expectation-maximization (EM) algorithm. It makes collective use of the data constraints (pilots, cyclic prefix, the finite alphabet constraint, and space-time block coding) and channel constraints (finite delay spread, frequency and time correlation, and transmit and receive correlation) to implement an effective receiver. The channel estimation part of the receiver boils down to an EM-based forward-backward Kalman filter. A forward-only Kalman filter is also proposed to avoid the latency involved in estimation. Simulation results show that the proposed receiver outperforms other least-squares-based iterative receivers.
Highlights
Orthogonal frequency division multiplexing (OFDM) is a technique that enables high speed transmission over frequency selective channels with simple equalizers
For frequency flat fading channels, space-time codes provide diversity and coding gain benefits compared with singleinput single-output (SISO) systems improving the BER performance of the system [1]
Given the similarity between the two approaches and the fact that the abbreviation STBC is more familiar, we continue to use this abbreviation to refer to our frequency-space codes.) When multiple antennas (MIMO) are combined with OFDM, space-time codes can be used per tone, providing the benefit of multiple antennas with simple channel equalization
Summary
Orthogonal frequency division multiplexing (OFDM) is a technique that enables high speed transmission over frequency selective channels with simple equalizers. Given the similarity between the two approaches and the fact that the abbreviation STBC is more familiar, we continue to use this abbreviation to refer to our frequency-space codes.) When multiple antennas (MIMO) are combined with OFDM, space-time codes can be used per tone, providing the benefit of multiple antennas with simple channel equalization. Techniques for channel estimation fall into 3 distinct classes: (1) training/pilot-based, (2) semiblind, and (3) blind methods. Semiblind methods make use of both pilots and additional channel/input data constraints to perform channel identification and equalization. These methods use pilots to obtain an initial channel estimate and improve the estimate by using a variety of a priori information. The channel estimate can be improved iteratively in a data-aided fashion [12], or more rigourously by the expectation maximization (EM) approach [16,17,18,19,20,21]
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