In this letter, we address the problem of fulfilling quality-of-service (QoS) requirements in a multiple-input multiple-output (MIMO) relay system, where a set of target signal-to-noise ratios (SNRs) should be attained on different substreams. By solving a two-step optimization problem, we obtain a power-efficient relaying scheme that can make the SNR requirements asymptotically fulfilled. A simple relay selection method is also proposed such that the relay-power consumption can be largely reduced when there is a large number of relays.

This paper introduces a novel sequence called the "β-complementary sequence" to encode orthogonal frequency-division multiplexing (OFDM) signals, with which one can substantially increase the code rate while maintaining a tight peak-to-mean envelope power ratio (PMEPR) of at most 2. Moreover, encoding schemes based on-complementary sequences provide very good tradeoff performance between PMEPR and code rate. This observation follows from an intrinsic property of the-complementary sequences considered. Furthermore, the distribution of code rate versus is determined, and numerical results based on these properties are presented. Finally, comparisons with the well-known Golay complementary sequences and the generalized Golayβ-complementary sequences (called "GN-complementary sequences" in this paper) are made. On presente dans cet article une nouvelle sequence denommee "sequence β-complementaire" pourle codage des signaux OFDM, qui permet d'accroıtre de maniere substantielle le taux de code tout en jouissant dune valeur PMEPR (rapport puissance de crete-puissance moyenne denveloppe) resserree dau plus2. En plus, les mecanismes de codage bases sur les sequences-complementaires permettent de realiser un bon compromis entre les performances PMEPR et le taux de code. Cette observation se base sur une propriete intrinseque des sequencesβ-complementaires examinees. En plus de cela, on determine la distribution du taux de code par rapportβet on presente les resultats numeriques bases sur ces proprietes. Finalement, on compare le nouveau modele aux sequences complementaires Golay bien connues et a la sequence complementaire Golay generalisee (d'enommee "sequence complementaire GN" dans cet article).

In this letter, we propose two power allocation schemes based on the statistical channel state information (CSI) and instantaneous s→r CSI at transmitters, respectively, for a 2-N-2 cooperative multicast system with nonregenerative network coding. Then the isolated precoder and the distributed precoder are, respectively, applied to the schemes to further improve the system performance by achieving the full diversity gain. Finally, we demonstrate that joint instantaneous CSI-based power allocation and distributed precoder design achieve the best performance.