Changsoon Choi

How backhaul networks influence the feasibility of coordinated multipoint in cellular networks [Accepted From Open Call]

Interference is one of the most challenging problems in current cellular mobile access networks. Coordinated nultipoint transmission/ reception, and in particular joint processing, has proven to be a beneficial solution for interference management. Most research so far has investigated the requirements and gains on the wireless side but only superficially showed the impact on and requirements for the backhaul network. We take a different approach by looking at different backhaul topologies and technologies, and analyzing how they can support CoMP cooperation schemes. We study, for different traffic scenarios and backhaul connectivity levels, which base station clusters are actually feasible compared to the ones desirable from the radio access network perspective. We found out that a significant mismatch exists between the desired wireless clusters, as defined by the RAN, and feasible ones, as allowed by the given backhaul characteristics. Based on these findings, we explain how RAN clustering and backhaul clustering have to cooperate to come to feasible solutions. As one possible solution, we present a backhaul network preclustering scheme, which is able to predict which BSs are actually eligible for cooperation during the runtime of the network. The gains of this approach are quantifiable in terms of reduced signaling and user data exchange, and reduced MIMO signal processing.

Coordinated multipoint multiuser-MIMO transmissions over backhaul-constrained mobile access networks

We investigate coordinated multipoint (CoMP) multiuser multiple-input-and-multiple-output (multiuser-MIMO) downlink transmissions over mobile access networks yielding different backhaul constraints. The larger number of base stations (BSs) participating in CoMP, the higher user throughput can be expected if there is no constraint in mobile backhaul networks. Limited capacity and latency in mobile backhaul networks impose constraints on the number of BSs that can actually participate in CoMP. We propose a CoMP system architecture with multiple clustering steps that that takes into account these backhaul constraints and enables to avoid selecting BSs which do not have enough backhaul network capability. The system-level simulation shows how much performance gain user can expect by improving backhaul network capability.

Backhaul network pre-clustering in cooperative cellular mobile access networks

Coordinated Multi-Point (CoMP) transmission/ reception is a promising solution for interference management in wireless cellular systems. Its successful deployment, however, strongly depends on the capability of the mobile backhaul network architecture to support the capacity, latency, and synchronization requirements of cooperation. In this paper, we deal with the “feasibility” aspects related to CoMP transmission/reception. We analyze how different backhaul topologies and technologies can support Base Station (BS) cooperation. We study, for different traffic scenarios and backhaul connectivity levels, which BS clusters are actually feasible compared to the ones desirable from the Radio Access Network (RAN) perspective. We found out that a significant mismatch exists between the desired wireless cluster, as defined by the RAN, and the feasible one, as allowed by the backhaul characteristics. Based on these findings, we explore different approaches to this problem, highlighting how the adoption of layer-2 switching techniques and multicast capabilities can already improve the cooperation feasibility. Finally, we propose an algorithm that includes the backhaul network feasibility information in the wireless cluster formation process. As a result, our system avoids unnecessary signaling and user data exchange among BSs which would have not been eligible for taking part in the desired cooperative cluster.

Power-efficient mobile backhaul design for CoMP support in future wireless access systems

Base Stations (BSs) cooperation techniques, also referred to as Coordinated Multi-Point (CoMP) in the 3GPP terminology, promise significant performance gains in future 4G and beyond systems. The counterpart to such gains is represented by the challenging requirements that CoMP puts on the backhaul network, which may prevent the inclusion of certain BSs selected for the cooperative cluster. The consequences of such a failure can be relevant for the overall power consumption. Those BSs which are not eligible for cooperation would be unnecessarily included in the channel estimation process, which consumes power both at the BS side (sending of reference pilots) and on the backhaul network side (exchange of Channel State Information (CSI) between BSs). To limit the detrimental effects of such CoMP cluster “unfeasibility”, we discuss the benefits of a cross-layer approach which relates wireless CoMP requests to the backhaul network status. We show how the preemptive exclusion of the non-eligible BSs results in a considerable saving of the overall power consumption. We further complement our system by proposing optical bypass techniques aimed at improving the CoMP support from the backhaul perspective. This results, on one side, in the enhancement of the overall CoMP feasibility performance, and, on the other side, in the reduction of the consumed power thanks to the offload of IP processing to the switching layer1.

Fast track article: CoMP clustering and backhaul limitations in cooperative cellular mobile access networks

Coordinated Multi-Point (CoMP) transmission and reception is a promising solution for managing interference and increasing performance in future wireless cellular systems. Due to its strict requirements in terms of capacity, latency, and synchronization among cooperating Base Stations (BSs), its successful deployment depends on the capability of the mobile backhaul network infrastructure. We deal with the feasibility of CoMP transmission/reception, in particular of Joint Transmission (JT). For this, we first evaluate which cluster sizes are reasonable from the wireless point-of-view to achieve the desired performance gains. Thereafter, we analyze how different backhaul topologies (e.g., mesh and tree structures) and backhaul network technologies (e.g., layer-2 switching and single-copy multicast capabilities) can support these desired clusters. We study for different traffic scenarios and backhaul connectivity levels, which part of the desired BS clusters are actually feasible according to the backhaul characteristics. We found out that a significant mismatch exists between the desired and feasible clusters. Neglecting this mismatch causes overheads in real JT implementations, which complicates or even prevents their deployment. Based on our findings, we propose a clustering system architecture that not only includes wireless information, as done in the state of the art, but also combines wireless and backhaul network feasibility information in a smart way. This avoids unnecessary signaling and User Equipment (UE) data exchange among BSs which are not eligible to take part in the cooperative cluster. Evaluations show that our scheme reduces the signaling and UE data exchange overhead by up to 85% compared to conventional clustering approaches, which do not take into account the backhaul networks status.

Mobile WDM Backhaul Access Networks with Physical Inter-Base-Station Links for Coordinated Multipoint Transmission/Reception Systems

This paper describes the design of mobile wavelength-division multiplexing (WDM) backhaul access networks supporting physical inter-base- station (inter-BS) links for LTE-Advanced and beyond systems, especially coordinated multipoint (CoMP) transmission/reception. The proposed inter-BS links are fully compatible to conventional WDM-passive optical network technologies and capable of establishing a dedicated high capacity and low latency optical link between adjacent base stations. The primary application is a CoMP system that requires data and/or information exchange among multiple base stations for cooperatively serving mobile users. Simulation results verify that the proposed inter-BS links enable more base stations to join CoMP by reducing link latency.

Improving CoMP cluster feasibility by dynamic serving base station reassignment

Coordinated Multi-Point (CoMP) transmission/reception, and especially Joint Processing (JP), is a promising solution for managing interference in cellular mobile access networks. Its successful deployment, however, strongly depends on the capability of the backhaul infrastructure as strict capacity and latency requirements have to be fulfilled.

Millimeter-wave beamforming circuits in SiGe BiCMOS

Integrated millimeter-wave 2 bit and 3 bit phase shifters and 4 channel beamforming network are presented in this paper. The 2 bit phase shifter exhibits 4° RMS phase error and a RMS gain error < 1 dB. In the 55–67 GHz range, the 3 bit phase shifter shows RMS phase error < 7° and a RMS gain error < 1 dB. The 4 channel beamforming network consists of four 2 bit RF phase shifter and a fully differential passive power distribution network. Between the 4 channels, the beamforming network exhibits less than 4° and 0.6 dB RMS phase and amplitude mismatch, respectively. The beamforming chip and the phase shifters are fabricated in SiGe BiCMOS technology. The 2 bit and 3 bit phase shifters draws 7 mA and 10 mA respectively from a 3.3 V supply. The circuits are well suited for highly integrated beamforming millimeter-wave transceivers.

Cloud base stations and fixed mobile convergence for the next mobile network

In order to provide the best customer service, mobile operators continuously evolve their network with the next big challenge being a massive increase in transmission speed. In this paper, we combine the concepts of cloud base stations and fixed mobile convergence to deal with this challenge. We examine how the remote radio heads of such a distributed base station architecture can be interconnected over existing in-service fiber-to-the-home networks and present two architectures for this.

60GHz OFDM hardware demonstrators in SiGe BiCMOS: State-of-the-art and future development

We present 60 GHz OFDM hardware demonstrators developed so far and outline design considerations for future developments. OFDM schemes have been developed to combat multi-path interferences in indoor wireless environments and further optimized for multi-gigabit data transmission in 60 GHz-band. RF and IF analogues front-ends (AFEs) have been developed with high-speed SiGe BiCMOS technologies. Future developments on AFE are mainly devoted to one-chip integration of RF and IF components based on a sliding IF architecture. We have already achieved wireless transmission of about 1 Gbps in an OFDM demonstrator, which will be continuously upgraded and optimized for higher data transmission with better link adaptability.