Centralized radio access networks (RANs) based on radio-over-fiber (RoF) techniques can simplify the remote access units (RAUs) and maximize the resource sharing among services and operators, thus improving the system efficiency and reducing the operational cost. A scheme of resource sharing is proposed for centralized RANs based on millimeter-wave (MMW) RoF system. Both RoF infrastructure resources and microwavephotonics resources are shared by multiple operators in the heterogeneous system. High-throughput services carried on both V-band (60GHz) and W-band (100GHz) are delivered to RAUs through flexible configuration at the central office (CO). This proposed multi-service centralized RAN with shared infrastructure is successfully demonstrated via both simulations and experiments.

A theoretical and experimental investigation of the nonlinear behaviors of intra- and inter-band cross-modulation (XM) in a multiband radio-over-fiber (RoF) system is presented for the first time. A closed-form theoretical analysis is proposed to characterize and validate the data XM induced by the nonlinearity of optical Mach-Zehnder modulator (MZM). Nonlinear behaviors of the intra-band XM between the in-phase and quadrature (I/Q) components of a single-band vector signal, as well as the inter-band XM between multiband combinations of scalar and vector signals are investigated, and consistent agreement has been verified between the theory and experiments. It was confirmed that scalar signals only suffer from inter-band XM; whereas vector signals suffer from both intra- and inter-band XMs. Intra-band XM induces constellation compression to vector signals; while inter-band XM induces eye diagram degradation to scalar signals, as well as nonlinear constellation scaling to vector signals. Moreover, QPSK shows superior tolerance to MZM nonlinearity than higher order QAM formats due to it intrinsic resistance to intra-band XM.

Small cells have become an integral component in meeting the increased demand for cellular network capacity. Cloud radio access networks (C-RAN) have been proposed as an effective means to harness the capacity benefits of small cells at reduced capital and operational expenses. With the baseband units (BBUs) separated from the radio access units (RAUs) and moved to the cloud for centralized processing, the backhaul between BBUs and RAUs forms a key component of any C-RAN. In this work, we argue that a one-one mapping of BBUs to RAUs is highly sub-optimal, thereby calling for a functional decoupling of the BBU pool from the RAUs. Further, the backhaul architecture must be made re-configurable to allow the mapping between BBUs and RAUs to be flexible and changed dynamically so as to not just optimize RAN performance but also energy consumption in the BBU pool. Towards this end, we design and implement the first OFDMA-based C-RAN test-bed with a reconfigurable backhaul that allows 4 BBUs to connect flexibly with 4 RAUs using radio-over-fiber technology. We demonstrate the feasibility of our system over a 10 km separation between the BBU pool and RAUs. Further, real world experiments with commercial off-the-shelf WiMAX clients reveal the performance benefits of our reconfigurable backhaul in catering effectively to heterogeneous user (static and mobile clients) and traffic profiles, while also delivering energy benefits in the BBU pool.

Carrier Ethernet is becoming the dominating backhaul network due to its flexibility, scalability, interoperability and low-cost. Carrier Ethernet networks (CENs) are inherently high bandwidth-delay product (BDP) networks, hence Traditional TCP, and similar variants, make undesirable choices of transport protocol mainly because of the aggressive multiplicative-decrease algorithm. The Ethernet-Services Transport Protocol (ESTP) has proven relieve the effects of the decrease algorithm by dynamically adjusting the transmission rate according to the level of congestion estimated in the network. It should be emphasized that most protocols detect congestion, but do not estimate the level of congestion. Also ESTP incorporates QoS information to further improve performance. In this work, a steady-state throughput analytical model of ESTP is derived, an experimental testbed is built and simulation results are obtained. All validation methods show good agreement.