Browsing by Author "Esteves, Nelson"
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- A class of iterative FDE techniques for reduced-CP SC-based block transmissionPublication . Gusmão, António; Torres, Paulo; Dinis, Rui; Esteves, NelsonFor conventional CP-assisted (Cyclic Prefix) block transmission systems, the CP length is selected according to the expected maximum delay spread. In this paper, an SDDC-aided (Soft Decision Directed Correction), iterative FDE (Frequency Domain Equalization) technique is presented for reduced-CP, SC-based (Single Carrier) block transmission systems using conventional frame structures. A more sophisticated Turbo SDDC-FDE technique is then proposed for improved performances in such systems, through a moderately increased complexity. The relations with some already known iterative FOE techniques are established, and a set of performance results is used to show the advantages of the SDDC-aided approach, namely the following: the fact that it can operate in an acceptable way even when, for the sake of implementation simplicity, no decoding operations are used to improve the iterative FDE process; the possibility of achieving the maximum power efficiency gain that a strong CP reduction allows.
- Code-assisted SC/FDE block transmission with reduced cyclic prefix overheadPublication . Gusmão, António; Torres, Paulo; Dinis, Rui; Esteves, NelsonFor conventional CP-assisted (Cyclic Prefix) SC/FDE implementations (Single- Carrier/Frequency Domain Equalisation), as well as for OFDM implementations (Orthogonal Frequency Division Multiplexing), the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimise the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long FFT block for FDE purposes and keeping good performances through a moderate increase of the FDE receiver complexity. Firstly, we present an algorithm for a Decision-Directed Correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. Next, we present and evaluate a novel class of reduced CP SC/FDE schemes, which takes advantage of the DDC algorithm for replacing ”useless” CP redundancy by fully useful channel coding redundancy. A very efficient block transmission, especially for both strongly time-dispersive and time-varying channel conditions, is then achieved.
- On SC/FDE block transmission with reduced cyclic prefix assistancePublication . Gusmão, António; Torres, Paulo; Dinis, Rui; Esteves, NelsonFor conventional CP-assisted (Cyclic Prefix) SC/FDE implementations (Single- Carrier/Frequency-Domain Equalisation), as well as for OFDM implementations (Orthogonal Frequency Division Multiplexing), the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimise the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long FFT block for FDE purposes and keeping good performances through a moderate increase of the FDE receiver complexity. Firstly, we present an algorithm for a Decision-Directed Correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. The resulting FDE performance is then evaluated in worst-case (CP-free) conditions, and the impact of previous decisions which are not error-free is shown to be rather small. In the following, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of the DDC algorithm for replacing "seless" CP redundancy by fully useful channel coding redundancy: highly power/bandwidth efficient block transmission schemes, especially recommendable for both strongly time-dispersive and time-varying channel conditions, are then achieved.
- A reduced-CP approach to SC/FDE block transmission for broadband wireless communicationsPublication . Gusmão, António; Torres, Paulo; Dinis, Rui; Esteves, NelsonFor conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations.
- A turbo FDE technique for reduced-CP SC-based block transmission systemsPublication . Gusmão, António; Torres, Paulo; Dinis, Rui; Esteves, NelsonFor conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP is recommendable, since it allows good performances through the use of simple frequency-domain equalization (FDE) techniques. In this letter, a soft-decision-directed correction (SDDC)-aided turbo FDE technique is presented for reduced-CP SC-based block transmission systems using conventional frame structures. The relations with some already known iterative FDE techniques are established, and a set of performance results is reported and discussed. The advantages of the proposed approach are emphasized, namely, the possibility of approximately achieving (besides the obvious bandwidth efficiency gain) the maximum power efficiency gain that a strong CP reduction allows.