End-to-end outage minimization in OFDM based linear relay networks

Abstract

Multi-hop relaying is an economically efficient architecture for coverage extension and throughput enhancement in future wireless networks. OFDM, on the other hand, is a spectrally efficient physical layer modulation technique for broadband transmission. As a natural consequence of combining OFDM with multi-hop relaying, the allocation of per-hop subcarrier power and perhop transmission time is crucial in optimizing the network performance. This paper is concerned with the end-to-end information outage in an OFDM based linear relay network. Our goal is to find an optimal power and time adaptation policy to minimize the outage probability under a long-term total power constraint. We solve the problem in two steps. First, for any given channel realization, we derive the minimum short-term power required to meet a target transmission rate. We show that it can be obtained through two nested bisection loops. To reduce computational complexity and signalling overhead, we also propose a sub-optimal algorithm. In the second step, we determine a power threshold to control the transmission on-off so that the long-term total power constraint is satisfied. Numerical examples are provided to illustrate the performance of the proposed power and time adaptation schemes with respect to other resource adaptation schemes. Index TermsOFDM, relay networks, outage probability, resource allocation, end-to-end rate.

Optimal power allocation for a full-duplex multicarrier decode-forward relay system with or without direct link

“…where M n ( p n ) is shown in (18) . Since M n ( p n ) is decreasing with p n , a two-layer bisection search algorithm can be formulated (using an idea similar to that of Algorithm 1 ) to solve (50) .…”

“…Many papers on multicarrier (i.e., OFDM based) relay networks such as [9,10] and [11][12][13][14][15][16][17][18][19][20][21][22] assume that the relays operate in halfduplex mode rather than full-duplex mode. And most of these works address non-regenerative (e.g., amplify-forward) half-duplex relays because the problems of regenerative (e.g., decode-forward) half-duplex relays are generally easy to solve and hence of no further intellectual challenge.…”

Resource allocation in decode-and-forward relaying systems based on OFDM

“…As we know, the instantaneous transmission rate of the relay i over hop k on subcarrier n in mk time frame is [12],…”

“…J(T, p * , m, /L, fJ, "\ ) 122 + fJ( PTotal -L L L P; k,n ) + "\(1 -L mk), (12) k=l where /L k,i (i E I, k = {I, 2}),"\, fJ :;0. 0, are the Lagrange multipliers and the domain V is the set of all non-negative P;kn (\Ii E I,n E N,k = { 1,2}) .…”

“…Without considering subcarrier reuse in multihop system along with a source destination path, increasing number of relays does not always result in total transmission power reduction particularly in high transmission rates [11], [12]. Moreover, when the relay operates in time division mode, power allocation provides a significant gain [13].…”