Abstract—Compared to conventional time-domain equalization, frequency-domain equalization (FDE) presents a computationally ef�cient alternative for the reception of single carrier (SC) transmissions. In this paper, we consider iterative FDE (IFDE) with explicit frequency-domain channel estimation (FDCE) for non-cyclic-pre�xed SC systems. First, an improved IFDE algorithm is presented based on soft iterative interferencecancellation. Second, a new adaptive FDCE (AFDCE) algorithm based on per-tone Kalman �ltering is proposed to track and predict the frequency-domain channel coef�cients. The AFDCE algorithm employs across-tone noise reduction, exploits temporal correlation between successive blocks, and adaptively updates the auto-regressive model coef�cients, bypassing the need for prior knowledge of channel statistics. Finally, block-overlapping is used to facilitate the joint operation of IFDE and AFDCE. Simulation results show that, compared to related IFDE and adaptive channel estimation schemes, the proposed schemes offer lower mean-square error (MSE) in channel prediction, lower bit error rate (BER) after decoding, and robustness to non-stationary channels. Index Terms—Iterative frequency-domain equalization, frequency-domain channel estimation, Kalman �lter, MMSE, single carrier, time-varying frequency-selective channels.

In this paper novel equalization algorithms for continuous phase modulations (CPMs) are illustrated. Both conventional (linear and decision- feedback) and turbo equaliza-tion techniques are devised. All of them operate in the frequency domain, process two samples per channel symbol and their derivation is based on the Laurent decomposition of CPM signals. Numerical results evidence that the proposed equalization strategies enable the use of CPMs over severely frequency selective wireless channels.

Abstract—In this paper, two analytical methods are presented to investigate the soft information evolution characteristics of a soft-input soft-output (SISO) linear equalizer and its application to the design of turbo equalization systems without the reliance on extensive simulation. Given the channel and a SISO equalization algorithm, one method explored is to analytically compute the bit-error rate (BER) of the SISO equalizer in two extreme cases (no and perfect a priori information) from which a BER transfer characteristic is estimated. The second approach is to compute the mutual information [a key parameter of the extrinsic information transfer (EXIT) chart] at the two end points of the EXIT function. Then, by modeling the SISO equalizer BER transfer and EXIT functions as linear, some of the behavior of linear turbo equalization, such as how the BER performance can be improved as iterations proceed, can be predicted. Further, soft information evolution characteristics of different linear SISO equalizers can be compared and the usefulness of iterative methods such as linear turbo equalization for a given channel can be determined. Compared with existing methods for generating EXIT functions, these predictive methods provide insight into the iterative behavior of linear turbo equalizers with substantial reduction in numerical complexity. Index Terms—Bit-error rate (BER) analysis, extrinsic information transfer (EXIT) chart, iterative decoding, linear equalizer, soft-input soft-output (SISO) equalizer, turbo equalizer. I.

We propose a soft noncoherent equalizer for coded transmissions over unknown time- and frequency-selective, or doubly selective, channels. Such a soft equalizer can be used in conjunction with a soft decoder as part of a turbo reception scheme. Like a number of existing designs, ours is motivated by the use of the expectation maximization (EM) algorithm to estimate the unknown channel parameters, and manifests as an iteration between soft channel estimation and soft coherent equalization. As a departure from the existing designs, which assume a Gauss-Markov (i.e., autoregressive) channel and employ a trellis whose number-of-states grows exponentially in the channel length, we use a basis expansion (BE) model for the channel and a soft tree-search in place of the trellis, leveraging recent ideas from the MIMO literature. The complexity of our schemes grows only linearly in the block length and quadratically in the number of BE coefficients. Numerical experiments show performance that is close to genie-aided bounds and robust to mismatch in channel-fading rate. 1.

Wireless communication systems targeting at broadband and mobile data trans-missions commonly face the challenge of fading channels which are both time and frequency selective. Therefore, the design of effective equalization and estimation algorithms for such channels becomes a fundamental problem of communication sys-tems. On one hand, multi-carrier transmission systems demonstrate prominent po-tential to combat the doubly selective fading, however, several factors may retard their applications, such as: high peak-to-average power ratio, sensitivity to phase noise, etc. On the other hand, single carrier transmission is a conventional approach and has important applications, such as HDTV broadcasting systems, underwater acoustic communication systems. In this dissertation, we focus on receiver design for effective and efficient reception of single-carrier transmissions through doubly se-lective channels. Our target is to design and develop a group of channel estimation and equalization algorithms in the frequency-domain, which enable high performance reception of single-carrier transmission with low computational complexity. Motivated by