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In order to combine the advantages of Amplify-Forward (AF) and Decode-Forward (DF) in relay networks, several strategies have been developed making use of reliability information after decoding at the relay. The use of soft-output channel decoders enables forwarding reliability information for the decoded bits. This soft information can be forwarded in different ways, e.g. by transmission of the Log Likelihood Ratios (LLRs) normalized to the power constraint. In this paper transmitting expectation values after decoding, the so-called Decode-Estimate-Forward (DEF) scheme, will be shown to be the best choice in terms of the mean squared uncorrelated error at the receiver. Additionally, it will be shown that LLR combining is superior to maximum ratio combining at the receiver as the overall disturbance of the received signal is not Gaussian in the case of DEF. Furthermore, in the uncoded case LLR combing also improves the performance in terms of effective signal-to-noise ratio and bit error rate.

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Abstract-In order to approach the theoretical limit of the decode-and-forward strategy for the half-duplex relay channel, distributed LDPC coding schemes have been proposed. In these schemes, the code applied at the source should be decodable at the relay to yield correct parity bits. With the help of the parity bits the destination should also be able to estimate the transmitted information correctly. For successful decoding the distributed coding scheme has to be designed jointly, requiring a high design complexity. As an alternative a distributed LDPC scheme based on puncturing is investigated, which requires only the design of one mother code. In this paper we compare three different approaches for designing distributed LDPC codes with respect to their performance and their design complexity.

Filtered OFDM (F-OFDM) can accommodate diverse service requirements by introducing additional filtering to OFDM and flexibly adapting the filter according to the service requirement. However, when block filtering is flexibly adapted per-subband, the regular resource grid could be violated. In this letter, we propose a solution to maintain the regular resource grid for F-OFDM. The proposed solution is two-fold: 1) it allocates guard bands inside the filter bandwidth which is kept independent of guard band; 2) it introduces timing advance according to the filter used. It is shown in practically relevant scenarios that the proposed solution, despite its simplicity, performs better than another more complex approach.

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This paper proposes a simple, but efficient solution to avoid a potential problem for filtered OFDM (F-OFDM) that may violate regular resource grid structure. F-OFDM is an extension of OFDM by additional per-subband filtering and a well-localized filter can be utilized to significantly lower the outof-band radiation that can mitigate interference in asynchronous access. Even with the filtering, additional guard bands that carry no data may be needed between the subbands for different users to keep the interference level sufficiently low. The required guard bandwidth may vary since various aspects should be taken into account such as interference power, modulation format or quality of service requirement. If the subbands are simply shifted to add the guard bands, the regular resource grid will be destroyed. One option to keep the regular resource grid while supporting flexible guard bands is to define several filters, each of which is optimized for each possible guard bandwidth. But this is rather complex. We propose a much simpler solution allocating the guard bands inside the filter bandwidth, which is kept independent of guard bandwidths. We show through detailed analytical and numerical analysis that the proposed solution performs even better than the more complex one in practically relevant interference scenarios.