Selami Sahin

Full rate full diversity space-time block code selection for more than two transmit antennas

In this paper, we propose a full rate space-time block code selection technique, which achieves full diversity when more than two transmit antennas are used for transmission. Only one or few feedback bits are needed at the transmitter, representing relative state information of the channels. Moreover, the proposed scheme allows separate decoding of transmitted symbols at the receiver. It is shown by computer simulations that, the new approach provides SNR improvement, especially when feedback errors occur, compared to the transmit antenna selection technique associated with Alamoutis scheme, for the same number of feedback bits

Increasing Diversity with Feedback: Balanced Space-Time Block Coding

We propose a novel coding scheme, which guarantees full diversity for any number of transmit antennas, provided that few bits of feedback from the receiver to the transmitter are available. This coding scheme is arranged as an extension of orthogonal space-time block coding and preserves its linear decoding complexity. Moreover, it is full rate when the underlying coding method is the Alamoutis scheme. It is shown by computer simulations that the new approach provides SNR improvement, and it is more resilient to feedback errors compared to the antenna selection technique on the basis of same number of feedback bits.

Physical-layer network coding with limited feedback in two-way relay channels

In this study, the authors introduce the limited feedback technique into the physical-layer network coding which is the most spectrally efficient protocol for two-way relay channels, consisting of one relay and two end (source) nodes. In amplify-and-forward strategy, each source node obtains full channel state information (CSI) of the channel between relay and itself from training sequences and partial CSI of the channel between relay and the other node by means of a limited number of feedback bits provided by the relay. In the decode-and-forward strategy, the authors completely remove training sequences and the source nodes provide the partial CSI of the link between relay and themselves from limited feedback bits, the CSI of the other link being useless for this strategy. Tight upper bounds on the bit error probability depending on the number of feedback bits are derived for binary phase shift keying (PSK) and quadrature-PSK modulations for both strategies. It is shown via computer simulations that the bit-error-rate performance of the system with full CSI at all nodes is achieved for both strategies by using a few number of feedback bits. Moreover, the computation complexity is reduced for the proposed scheme with a single antenna at all nodes.

Improvement of required SNR for satellite-to-ground optical communication via aperture diversity by using PPM

In this paper, in order to achieve sufficient bit error rate (BER) as a function of the zenith angle between satellite and ground station, SNR requirement is investigated utilizing pulse position modulation (PPM). In order to realize explicit results, many parameters included zenith angle have been considered. Results indicate that, to achieve desired BER, SNR values are in wide range while zenith angle changes from small to large values. It is shown that, instead of to establish the link with predetermined intervals of the zenith angle, aperture diversity at the receiver is utilized to communicate even large zenith angles with reasonable values of the SNR.

On the performance of satellite-to-ground optical communication over atmospheric turbulence channels with pointing errors

We investigate the effect of atmosphere and device parameters on the performance of satellite-to-ground optical links. The parameters that we take into account are link distance, Rytov variance, wavelength, Fried parameter, zenith angle, aperture diameter, beam waist and jitter variance. We consider two modulation schemes, pulse position modulation (PPM) and binary polarization shift keying (BPOLSK), and evaluate the performance for both uncoded and coded systems considering single and multiple aperture receivers. The results show that especially for large zenith angles the performance loss can be compensated with diversity and coding and thus communication time that the satellite and ground station stay connected can be extended.

Amplify-and-forward strategy with limited feedback in two-way relay channels

In physical-layer network coding (PLNC) for two-way relay channels (TWRC), consisted of one relay and two end nodes, implementation of amplify-and-forward (AF) strategy is difficult due to the need for full channel state information (CSI) about the two links at all nodes, which cause extra protocol complexity. In this paper, we introduce the limited feedback technique into the PLNC protocol utilizing AF strategy and propose a practical scheme in which the partial CSI is fed back to the end nodes from relay using limited number of feedback bits to inform about the other link. Upper bounds on the bit error probability depending on the number of feedback bits are derived for binary phase shift keying (BPSK) and quadrature-PSK (QPSK) modulations. It is shown via computer simulations that the error performance of the system with full CSI at all nodes are achieved by using a few number of feedback bits. Moreover, the computation complexity is reduced for the proposed scheme with single antenna at all nodes.

Physical-layer network coding with limited feedback based on decoding at relay

In two-way relay channels (TWRC), consisted of one relay and two end nodes, it is generally assumed that all nodes have full channel state information (CSI) about the two links. However, one end node can not obtain the CSI of the link between relay and the other end node, without extra protocol complexity. Therefore, it is difficult to implement the strategies such as partial-decode-and-forward (PDF) in physical-layer network coding (PLNC) which is the most spectrally efficient protocol for TWRC. In this paper, we introduce the limited feedback technique into the PDF and decode-and-forward (DF) strategies of PLNC protocol and propose a practical scheme in which the partial CSI is fed back to the end nodes from relay using a limited number of feedback bits. In PDF strategy, each source node obtains full CSI of the channel between relay and itself from training sequences and partial CSI of the channel between relay and the other node by means of a limited number of feedback bits provided by the relay. In DF strategy, we remove training sequences and the source nodes provide the partial CSI of the link between relay and themselves from limited feedback bits, the CSI of the other link being useless for this strategy. For binary phase shift keying (BPSK) and quadrature-PSK (QPSK) modulations, tight upper bounds on the bit error probability (BEP) depending on the number of feedback bits are derived for all strategies. It is shown via computer simulations that the bit-error-rate (BER) performance of the system with full CSI at all nodes are achieved for both strategies by using a few number of feedback bits. Moreover, the computation complexity is reduced for the proposed scheme with single antenna at all nodes.

Required SNR improvement for downlink optical communication via channel coding and aperture diversity by utilising PPM

In this study, it is aimed to investigate the required signal-to-noise ratio (SNR) that provides a sufficient bit error rate (BER) according to the zenith angle between the ground station and satellite when pulse position modulation is utilised. Many parameters such as scintillation index, link distance, wavelength, Rytov variance, Frieds parameter, aperture diameter of the receiver and zenith angle have been considered to achieve realistic results. Due to the restrictions on the system, some parameters are specified as deterministic; the obtained results suggest that the required SNR value changes in a wide range from small to large values of the zenith angle to achieve sufficient BER. Therefore, either SNR adjustment as a function of the zenith angle is provided or the interval of the zenith angles to establish the link is determined previously in order to avoid the high link margin. It is shown that, instead of the second choice, aperture diversity is utilised at the receiver to establish communication even for large zenith angles with a reasonable value of the SNR. Besides aperture diversity, channel coding with error correction codes further improves the performance.

On the performance of downlink optical communication via relaying in the presence of pointing errors

We investigate the error performance of a satellite-to-ground optical link between a low-earth orbit (LEO) satellite and an optical ground station (OGS) in which a geostationary orbit (GEO) satellite is used as a relay. We perform a bit-error probability (BEP) analysis by taking the atmospheric turbulence effects and pointing errors into account. We use pulse position modulation (PPM) and consider both decode-and-forward (DF) and amplify-and-forward (AF) relaying schemes. Results show that for small pointing errors DF scheme outperforms AF scheme in terms of bit error rate (BER) performance. We also demonstrate that error control coding can significantly improve error performances especially for high pointing errors.

Partial-decode-and-forward strategy with limited feedback for two way relay channels

In two-way relay channels (TWRC), consisted of one relay and two end nodes, it is generally assumed that all nodes have full channel state information (CSI) about the two links. However, one end node can not obtain the CSI of the link between relay and the other end node, without extra protocol complexity. Therefore, it is difficult to implement the strategies such as partial-decode-and-forward (PDF) in physical-layer network coding (PLNC) which is the most spectrally efficient protocol for TWRC. In this paper, we introduce the limited feedback technique into the PDF strategy in PLNC protocol and propose a practical scheme in which the differential phase information between two channels is fed back to the end nodes from relay using a limited number of feedback bits. For binary phase shift keying (BPSK) modulation, tight upper bounds on the bit error probability (BEP) depending on the number of feedback bits are derived. It is shown via computer simulations that the bit-error-rate performance of the system with full CSI at all nodes is achieved using a few number of feedback bits.