Link Regime and Power Savings of Decode-Forward Relaying in Fading Channels

Abstract

In this paper, we re-examine the relay channel under the decode-forward (DF) strategy. Contrary to the established belief that block Markov coding is always the rate-optimal DF strategy, under certain channel conditions (a link regime), independent signaling between the source and relay achieves the same transmission rate without requiring coherent channel phase information. Furthermore, this independent signaling regime allows the relay to conserve power. As such, we design a composite DF relaying strategy that achieves the same rate as block Markov DF but with less required relay power. The finding is attractive from the link adaptation perspective to adapt relay coding and relay power according to the link state. We examine this link adaptation in fading under both perfect channel state information (CSI) and practical CSI in which nodes have perfect receive and long-term transmit CSI, and derive the corresponding relay power savings in both cases. We also derive the outage probability of the composite relaying scheme, which adapts the signaling to the link regime. Through simulation, we expose a tradeoff for relay placement showing that the relay conserves the most power when closer to the destination but achieves the most rate gain when closer to the source.

Dual-Band Fading Multiple Access Relay Channels

“…This models practical scenarios where CSI feedback to a transmitter is unavailable, while a receiver can reliably estimate the CSI. Also, this is less restrictive than [31] where full or partial CSI is also available at a transmitter.…”

“…The DR-MARC is a building block for future dual-band multiuser networks. Since, its performance will be significantly affected by the mm-wave links due to their large bandwidths [11], [18], [21], it is useful to understand how allocating the mm-wave band resources optimizes the performance, similar to other multiuser networks [8], [21], [31]. Hence, to quantify the impact of the mm-wave spectrum on the performance of the DR-MARC, we study the power allocation strategy for the mm-wave direct and relay links (subject to a power budget) that maximizes the achievable sum-rate.…”

“…Therefore, we focus primarily on R-MARCs with far underlying c-MARC where the mm-wave links play a key role, and for such R-MARCs, we find sufficient channel conditions under which its capacity is characterized by an achievable scheme.The DR-MARC is a building block for future dual-band multiuser networks. Since, its performance will be significantly affected by the mm-wave links due to their large bandwidths [11], [18], [21], it is useful to understand how allocating the mm-wave band resources optimizes the performance, similar to other multiuser networks [8], [21], [31]. Hence, to quantify the impact of the mm-wave spectrum on the performance of the DR-MARC, we study the power allocation strategy for the mm-wave direct and relay links (subject to a power budget) that maximizes the achievable sum-rate.The contributions of this paper is summarized as follows.• We decompose the capacity of the DR-MARC into the capacity of the underlying R-MARC and two direct links.…”