  We Consider a multihop relay network in which two terminals are communicating
with each other via a number of cluster of relays. Performance of such networks
depends on the routing protocols employed. In this paper, we find the
expressions for the average symbol error probability (ASEP) performance of
amplify-and-forward (AF) multihop transmission for the simplest routing
protocol in which the relay transmits using the channel having the best symbol
to noise ratio (SNR). The ASEP performance of a better protocol proposed in [1]
known as the adhoc protocol is also analyzed. The derived expressions for the
performance are a convenient tool to analyze the performance of AF multihop
transmission over relay clusters. Monte-Carlo simulations verify the
correctness of the proposed formulation and are in agreement with analytical
results. Furthermore, we propose new generalized protocols termed as last-n-hop
selection protocol, the dual path protocol, the forward- backward last-n-hop
selection protocol, and the forward-backward dual path protocol, to get
improved ASEP performances. The ASEP performance of these proposed schemes is
analysed by computer simulations. It is shown that close to optimal performance
can be achieved by using the last-n-hop selection protocol and its
forward-backward variant. The complexity of the protocols is also studied.
