A low-complexity design of multi-antenna relay processing is proposed for two-way relay networks with asymmetric data flows. The proposed scheme adopts three-phase (3P) analog network coding (ANC) which allows orthogonal transmission of two communicating nodes to overcome some disadvantages of two-phase (2P) ANC protocols. For the 3P ANC, we propose antenna selection at the relay to exploit the diversity without channel estimation and rate-aware relay power allocation (RPA) to improve the outage performance under the asymmetric rate requirements. The results show that the proposed scheme without or with RPA outperforms the conventional two-phase ANC significantly in various relay locations. It is also shown that the suboptimal RPA proposed for practical implementation provides a performance close to that of the optimal RPA.

A class of low-complexity multi-antenna relaying schemes is proposed for orthogonal frequency division multiplexing based one-way and two-way relay networks. In the proposed schemes, two single-antenna terminal nodes complete the data transfer in two time phases via a multi-antenna amplify-and-forward relay without channel state information, discrete Fourier transform (DFT), and inverse DFT. The relay signal processing consists of receive combining, power scaling, and transmit diversity, where instantaneous time domain power scaling is proposed for power scaling and power-based selection combining and cyclic delay combining are proposed for receive combining, to leverage the performance only with time domain operations. An approximation to the outage probability is also derived to predict the coded performance behavior under practical channel models. It is shown by evaluating the outage probability and coded bit error rate that the proposed schemes outperform the conventional schemes of comparable complexity.

We consider two-way relay (TWR) networks consisting of two communicating nodes and multiple relays built upon orthogonal frequency-division multiplexing signaling. For low-cost implementation of relays, two pragmatic TWR protocols are proposed based on analog network coding (ANC). The proposed two-phase (2P)- and three-phase (3P)-ANC schemes employ time-domain instantaneous power scaling and relay selection to improve the outage performance without equipping discrete Fourier transform (DFT) and inverse DFT functions at the relay. In particular, we devise a relay power allocation factor and a resultant relay selection metric for the proposed 3P-ANC scheme, which can be implemented at low complexity. For the proposed schemes, the outage probability and achievable diversity order are also analyzed, which reveals a larger diversity order of the 3P-ANC scheme than the 2P-ANC scheme. The results from analysis and simulation show that the proposed schemes outperform the conventional 2P-ANC schemes employing time-domain average power scaling and distributed space-time block coding or frequency-domain power scaling and relay selection.

This paper considers a relay system using two-layer superposition coding to minimize the expected distortion of a Gaussian source at the destination node. For the system, we propose two types of layer- selective relaying based on the local decoding result at the relay and the decoding result at the destination node fed back to the relay. One type of the proposed scheme uses decode-and-forward (DF) in the design of the relay signals, while the other type uses both DF and amplify-and-forward (AF). For the proposed scheme, we analyze the outage probabilities and evaluate the expected distortion according to the relay location. The results reveal that the proposed scheme improves the finite SNR performance, in particular when the relay node is closer to the source node than it is to the destination node.

We consider a relay network that delivers a Gaussian source by employing successive refinement source coding and superposition coding of layers at the source node and successive decoding at the relay and destination nodes. For the network, making use of the decoding results at the relay and destination nodes of the first transmission, an efficient relaying strategy of layers is proposed to minimize the expected distortion (ED) when only the average channel state information is available at the source node. Three types of the proposed scheme, defined as Prop-DF, using decode-and-forward signals, Prop-AF, using amplify-and-forward signals, and Prop-MF, using mixed-forward signals, are addressed and analyzed in terms of the outage probability and distortion exponent. Unlike other studies, we have also taken the relay location into account in deriving the distortion exponent showing the high SNR behavior of the ED. The results show that the proposed scheme increases the distortion exponent up to twice that of the conventional relaying schemes when the relay is close to the source node, and that Prop-MF provides the best performance for most relay locations.

This paper analyzes a two-way relaying (TWR) system where two sources with multiple antennas exchange data via an amplify-and-forward relay with a single antenna. In the system considered herein, the link quality between the sources and relay can generally be asymmetric due to the nonidentical antenna configuration and relay location. In such a general setup, an accurate upper-bound on the average sum rate (ASR) is derived when beamforming is employed at the sources. We show that the proposed bound is much closer to the exact ASR than the conventional bound under various system configurations. It is also observed that relay location is more important than relay power allocation when the numbers of source antennas are unequal.

This paper considers a two-way relaying (TWR) half-duplex network in which two users communicate each other with the help of a non-regenerative relay when the direct link between the two users is nonvanishing. For the network, we adopt three protocols each with two, three, or four phases either by using analog network coding (ANC) or amplify-and-forward. The performance of the protocols is analyzed by deriving tight bounds on the average sum rate (ASR) and the outage probability in a unified form. Both results from analysis and simulation show that the three-phase ANC for TWR is favored in the outage performance by trading the time resource with the diversity gain while the two-phase ANC is favored in the ASR performance.

This paper provides a low-complexity scheme for peak-to-average power ratio (PAPR) reduction without side information for frequency switched transmit diversity orthogonal frequency division multiplexing (FSTD-OFDM). The proposed scheme generates multiple signal candidates (SCs) by dividing parallel data symbols into subparts and mapping the subparts onto the antennas under a criterion reducing the correlation between the SCs to select one SC with minimum PAPR. The proposed scheme is shown to provide reasonably good PAPR performance at a lower complexity than the conventional schemes. In addition, the proposed scheme can detect the transmitted SC via energy detection without side information.

To reduce the influence of interference on the OFDM-based cognitive radio overlaid with narrowband primary users, we consider a scheme called the variable subband nulling (VSN), in which a VSN mode is selected adaptively according to the result of spectrum sensing for the frames following the sensing period. For reliable detection of the VSN mode embedded in the preamble, we consider two types of metrics. The performances of the metrics are analyzed in Gaussian channels with/without narrowband interference (NBI), and are confirmed by simulation results. In fading channels with/without NBI, the detection performance is examined via simulation results. The analysis and simulation results have confirmed that, if the VSN mode is selected appropriately at the transmitter, the proposed metrics provide us with a reliable detection performance even when the NBI is strong.

This paper introduces a reconfigurable mixed frame structure and a resource allocation algorithm for OFDMA systems supporting both the band-AMC and diversity modes in the frame. To reduce the total feedback without significant performance loss, we assign a user to the diversity subchannel when the band-AMC mode has no gain over the diversity mode based on the frequency selectivity of the user. After user selection, we apply joint power and rate allocation to exploit the asymmetry in required transmit power of the band-AMC mode and the diversity mode. The results reveal that the mixed frame with simple user classification provides a performance comparable to the frame with band-AMC mode only at a much reduced feedback. In particular, it is observed that the mixed frame with frequency division is preferable to that with time division by increasing the throughput of the users at the cell boundary in a large cell.