Low Complexity Amplify and Forward Relaying without Channel Amplitude Estimation

Abstract

We propose a low-complexity amplify and forward relaying scheme that avoids channel amplitude estimations by combining the signals associated with the individual relays into an equal gain combiner (EGC). An approximate performance analysis of such scheme is conducted using the well-known moments-based approach. Additionally, motivated by the so-called EGC's combining loss, we propose an algorithmic method that sorts out the weakest relayed branches (in a long-term sense), aiming at activating only the relays that substantially contribute to the overall system performance.

On the diversity order of non-orthogonal amplify-and-forward over block-fading channels

“…In order to overcome this limitation, a BFNAF scheme which is based on a constant amplification factor is integrated. The integration of a fixed-gain relay [12]- [14] in the BFNAF protocol, recovers the previously observed loss of diversity gain and efficiently uses all the available diversity degrees of the system. The theoretical analysis of this new protocol is supported by capacity bounds which simplify the diversity analysis.…”

“…This basic observation is in line with the diversity analysis presented above and proves that a CA amplification factor efficiently uses all the diversity degrees of the considered channel. Furthermore, in this figure we plot the simplification steps (approximations) of the presented analysis (equations (11), (14)). As can be seen the proposed approximations follow the same diversity order as the BFNAF scheme, i.e.…”

“…The choice of this gain ensures a constant transmitted power at the relay and therefore the magnitude of the amplification factor decreases with the instantaneous strength of the source-relay channel. However, the CI factor requires a continuous estimate of the channel fading amplitude of the → link at the relay node which is a critical issue if such channel estimation is not available or if simply the complexity of the relay needs to be kept low [14]. On the other hand, a CA factor does not require an estimate of the instantaneous fading and multiplies the received signal with a fixed gain regardless of the fading amplitude of the → link.…”

“…Eq. (14) shows that the outage probability of the BFNAF CA corresponds to a (weighted) sum of two outage probabilities with an associated diversity order equal to three; the relation between the two components depends on the parameter 0 . In particular, the case ≤ 1 is characterized by the sum of two independent exponential random variables ( + ) with the term ≜ 1+ , ( [27] proves that the term corresponds to one diversity branch), and thus provides three independent diversity branches.…”