In centralized radio access network (C-RAN) architecture, the baseband unit (BBU) is connected to the remote radio unit (RRU) via a fronthaul (FH) interface. For massive MIMO systems in the 5G era, the traditional FH interface (e.g. CPRI) becomes a network bottleneck since the required FH capacity increases proportional to the number of antennas. New functional split between RRU and BBU is thereby considered where RRU carries out more processing than RF-related operation to make the FH traffic only scale based on the number of MIMO layers. This paper provides one alternative of such functional split in the uplink direction implementing interference rejection combining (IRC). The proposed approach reformulates IRC into a zero-forcing (ZF) process and decomposes the latter into two parts. The first part performs maximum ratio combining (MRC) which is much simpler than the full IRC and is therefore implemented in RRU. The second part handles the remaining calculations (such as matrix inversion) with high complexity and is implemented in BBU. The results show that the proposed functional split can deliver performances with both intra- and inter-cell interferences effectively mitigated, while guaranteeing low-complexity RRU implementation and moderate FH-traffic demands, which is proportional to the number of MIMO layers plus interferers.

Crosstalk cancellation is a crucial issue for traditional digital subscriber line systems. For LTE-over-copper systems, however, the need for crosstalk cancellation varies depending on the analog fronthauling architecture and its parameters. A crosstalk handler that is decoupled as much as possible from the rest of the system architecture is thus preferred. Therefore, we propose a time-domain precoding scheme specifically in downstream direction to separate the precoding unit from the LTE signal flow, and perform crosstalk cancellation in an on-demand manner. Estimation of all direct and crosstalk paths is assisted by LTE cell-specific reference signals. The time-domain precoder transforms the interference channel into a crosstalk-free channel with identical direct paths, which allows for low-complexity inter-symbol interference mitigation. We evaluate the concept in terms of signal-to-noise ratio provided for LTE signals using measured wireline channel data.

Vectoring enables cooperative crosstalk mitigation in wideband wireline systems. A sudden termination change within a vectored group alters the entire perceived channel matrix and thus disturbs the vectoring operation, since the precoder, which is tuned to the channel before the change, is no longer up to date. We analyze the resulting residual crosstalk and its impact on performance degradation during showtime for both linear and non-linear precoding systems. To cover, a new channel matrix must be estimated to update the precoder accordingly. We use a model-based approach to track a vector instead of estimating the full matrix. Based on this vector, simplified precoder updating methods for both the precoding systems are presented accounting for a sudden line deactivation or reactivation in a vectored group. As an alternative to the state-of-the-art methods, the proposed procedures significantly reduce the complexity of both channel estimation and precoder updating and minimize the disturbed period for active users.

Radviz is a radial visualization technique which maps data from multiple dimensional space onto a planar picture. The dimensions placed on the circumference of a circle, called Dimension Anchors (DAs), can be reordered to reveal different patterns in the dataset. Extending the number of dimensions can enhance the flexibility in the placement of the DAs to explore more meaningful visualizations. In this paper, we describe a method which rationally extends a dimension to multiple new dimensions in Radviz. This method first calculates the probability distribution histogram of a dimension. The mean shift algorithm is applied to get centers of probability density to segment the histogram, and then the dimension can be extended according to the number of segments of the histogram. We also suggest using the Dunn's index to find the optimal placement of DAs, so the better effect of visual clustering could be achieved after the dimension expansion in Radviz. Finally, we demonstrate the usability of our approach on visually analysing the iris data and two other datasets.

Next-generation wireline systems may exploit fre- quencies up to several hundred MHz on short lines. Strong crosstalk coupling, comparable to the direct paths, is one of the main channel characteristics at high frequencies. Instead of fully cancelling all crosstalk, we utilize strong crosstalk paths to boost data-rate for active users. Two linear precoding schemes, based on maximum ratio-combining (MRC) and convex optimization, respectively, are proposed and applied to a common network topology. The precoding schemes exploit constructive crosstalk signals on unused lines or in unused parts of the spectrum on neighboring lines to boost data-rate while still complying with the regulated spectral power limits per line. More than 500 Mbps throughput gain per active user can be achieved compared to state-of-the-art linear precoding.

To increase indoor coverage for mobile services, we propose a residential small cell infrastructure making use of the existing copper plant. The system is cabinet-based, collocated with VDSL2 and uses small pieces of spectrum next to VDSL2. Inspired by the Ericsson Radio Dot System, it challenges the femtocell paradigm offering full macro functionality in the small cells. An interesting service potential is offered albeit the added mobile traffic capacity is moderate as it is limited by the copper fronthaul.

Vectoring is a vital component of wideband wireline communication systems. A disorderly leaving event (DLE) disturbs the vectoring operation since the precoder, which was designed for the channel before the change, is no longer up to date. Measurements indicate that the impact of a DLE can be serious for frequencies beyond 30 MHz, which corresponds to the band used by emerging wideband communication systems over short multi-pair copper cables such as G.fast. As an alternative to the state-of-the-art update procedure, this paper presents an approach to mitigating the DLE problem. By interpreting DLE with the FEXT-reflected-NEXT (FRN) model, we propose a scheme that enables the showtime lines to return to disturbance-free transmission once the loss of signal on a certain line is detected while updating the precoder as a background process. Furthermore, the estimation complexity for a K-user vectoring group is reduced from O(K2) to O(K).

The densification of mobile networks in order to meet increased capacity demands is ongoing, needed and costly. A few papers have been published based on the insight that the fixed broadband networks offer a multitude of sites, for instance our homes, for potential small cell deployment providing backhaul capacity and power without site costs. However, in order to reach economical large-scale benefits, we explore the case when radio systems are deployed in coexistence with DSL. In this paper, we establish the feasibility of such a concept under constraints invoked by state-of-the-art and emerging systems (3GPP, VDSL2 and G.fast) and make statements about the required architecture. We also point out that the enthusiasm of previously published results should be lowered a notch.