LTE femtocell system through amplify-and-forward over cable links

The conventional femtocell architecture with Home Node B´s (HNBs) backhauled through xDSL connections can be modeled as a multi-user two-hop decode-and-forward (DF) relay network. The coding/decoding policy is separately optimized over both the air and the cable links. Even if this strategy is well know to be the optimal one in the single-user case, in a multi-user environment the maximum benefits arise from users´ cooperation. Here we propose to trade the DF scheme for the benefits of centralized multi-cell processing through the adoption of amplify-and-forward (AF) devices in place of the HNBs, resorting to the Wireless over Cable (WoC) architecture for femtocells. WoC is based on the relay of wireless signals over the cable infrastructure through a bidirectional (analog) amplify-and-forward device that translates the bandwidth of the radio signals to comply with the specifications of the wired links (and vice-versa). The resulting multi-user two-hop AF relay network benefits from the co-location of baseband processing and radio resource management that are carried out simultaneously for multiple femtocells in a centralized fashion. This paper compares the two femtocell architectures for LTE protocol when copper twisted pairs are the available wired links. System-specific power constraints over the air and cable interfaces are explicitly enforced through static and optimized power allocation strategies. The centralized processing of WoC architecture is shown to be a promising solution for throughput enhancement in realistic dense-urban femtocell scenarios.