Frank Frederiksen’s research while affiliated with Nokia Bell Labs and other places

The further densification of small cells impose high and undesirable levels of inter-cell interference. Multiple Input Multiple Output (MIMO) systems along with advanced receiver techniques provide us with extra degrees of freedom to combat such a problem. With such tools, rank adaptation algorithms allow us to use our antenna resources to either exploit multiple spatial streams in low interference scenarios, or suppress interference in high interference scenarios. In this paper, we propose and evaluate an interference-aware distributed rank adaptation algorithm. The concept behind our approach is to discourage the choice of transmitting with multiple spatial streams in highly interfered scenarios, and to exploit and encourage the usage of multiple spatial transmission streams in low interference scenarios. We show that our proposed algorithm can be adjusted to preserve and guarantee a good outage performance, while providing the benefit of higher average throughputs, in both low and highly interfered scenarios, when compared to fixed rank configurations, and distributed selfish schemes.

Time division duplex (TDD) systems offer a substantial amount of freedom to deal with downlink (DL) and uplink (UL) traffic asymmetries. Most TDD-based systems define either multiple static configurations or adaptive approaches to deal with such asymmetries. Our envisioned 5G concept embraces the flexibility brought along by TDD, and allows us to switch the link direction on a slot by slot basis. In this paper we study the interaction of Transmission Control Protocol (TCP) traffic, with a fully flexible UL/DL TDD allocation scheme. We show that flexibility is not only beneficial for exploiting the different instantaneous UL and DL traffic variations, but also performs well with TCP traffic, where the protocol behaviour plays an important role in throughput performance. The advantages of full flexibility compared to fixed static allocations for TCP traffic are reported for both small and large payloads, and for multi-cell scenarios where both DL and UL traffic are present.

5th Generation (5G) small cells are expected to satisfy the increasing demand for wireless data traffic. In the presence of large scale dense and randomly deployed cells, autonomous and distributed configuration mechanisms are highly desirable. However, small cells typically serve a small number of users, such that sudden traffic imbalances between downlink (DL) and uplink (UL) are expected in the new 5G system. We exploit the flexibility of time-division duplex (TDD) to deal with such imbalances by adapting swiftly to instantaneously varying traffic needs. In this paper we propose a distributed algorithm to deal with these varying traffic requirements. We also exploit the availability of interference rejection capable receivers. Simulation results show that in the presence of the aforementioned features, we can approximately double the session throughput and halve the packet delay in a large number of cases. andcopy; 2014 IEEE.

A new 5th generation (5G) radio access technology is expected to cope with an estimated factor of ∼x1000 growth in mobile data traffic in the upcoming years. Such system will be optimized for a massive uncoordinated deployment of small cells, where autonomous operation of the individual nodes may bring unpredictable and fast varying link quality. In this paper, Hybrid Automatic Repeat Request (HARQ) is studied as a solution to cope with such unpredictability. An operational mode of HARQ for our 5G system definition is proposed, and its performance is evaluated for two different scheduling options. Simulation results confirm the capability of HARQ of improving the final throughput and solving outage problems, with limited impact on the end delay.

A method for forming a bit sequence having a number of M bits from a bit sequence having a number of N bits, wherein M/2<N<M, involves extending said bit sequence by M-N bit positions, segmenting said extended bit sequence into at least two blocks with different numbers of bit positions such that the number of bit positions in the first block is less than the number of bit positions in the last block, and filling empty bit positions with bits having a pre-determined value.

Different technical solutions and innovations are enabling the move from macro-only scenarios towards heterogeneous networks with a mixture of different base station types. In this article we focus on multi-layer LTE-Advanced networks, and especially address aspects related to interference management. The network controlled time-domain enhanced inter-cell interference coordination (eICIC) concept is outlined by explaining the benefits and characteristics of this solution. The benefits of using advanced terminal device receiver architectures with interference suppression capabilities are motivated. Extensive system level performance results are presented with bursty traffic to demonstrate the eICIC concepts ability to dynamically adapt according to the traffic conditions.

Different technical solutions are enabling the move from macro-only scenarios towards heterogeneous networks with a mixture of different base station types. In this paper we focus on multi-layer LTE-Advanced networks, and especially address aspects related to co-channel interference management. The network controlled time-domain enhanced inter-cell interference coordination (eICIC) concept is outlined by explaining the benefits and characteristics of this solution. Extensive system level performance results are presented with bursty and non-bursty traffic to demonstrate the eICIC concepts ability to dynamically adapt according to the traffic conditions.

Co-channel deployment of Closed Subscriber Group (CSG) home-cells or Home E-UTRAN NodeBs (HeNBs) will create coverage holes for macro connected user that is not part of the CSG. In this paper, we address the problem of detecting the macro-cell coverage hole and protecting the macro-users that are located inside such a coverage hole. To reduce the impact of HeNB interference on the macro-cell performance, the HeNBs can be partially muted on some subframes, leading to Time Domain (TDM) muting. With TDM muting, macro-users in the coverage hole can be protected by scheduling them only on the muted subframes that are free of HeNB interference. Different methods for coverage hole detection are considered, and their performance is evaluated under the downlink transmission of a Long Term Evolution (LTE) network. These methods are based on user measurements. Recommendations on the coverage hole detection will be provided based on the obtained results.

This paper is focused on interference mitigation for LTE-Advanced multi-layer networks with macro and HeNBs. The autonomous HeNB power setting in the downlink is studied for different HeNB access methods. Our studies show that using the so-called escape carrier configuration and autonomous HeNB power setting is a promising strategy for enabling gradual introduction of user-deployed HeNBs in existing macro-layer networks.

Carrier aggregation is one of the key features for LTE-Advanced. By means of CA, users gain access to a total bandwidth of up to 100 MHz in order to meet the IMT-Advanced requirements. The system bandwidth may be contiguous, or composed of several non-contiguous bandwidth chunks that are aggregated. This article presents a summary of the supported CA scenarios as well as an overview of the CA functionality for LTE-Advanced with special emphasis on the basic concept, control mechanisms, and performance aspects. The discussion includes definitions of the new terms primary cell (PCell) and secondary cell (SCell), mechanisms for activation and deactivation of CCs, and the new cross-CC scheduling functionality for improved control channel optimizations. We also demonstrate how CA can be used as an enabler for simple yet effective frequency domain interference management schemes. In particular, interference management is anticipated to provide significant gains in heterogeneous networks, envisioning intrinsically uncoordinated deployments of home base stations.