Petteri Kela

Dynamic packet scheduling performance in UTRA Long Term Evolution downlink

In this paper we evaluate the performance of dynamic Packet Scheduling (PS) of 3GPP UTRAN Long Term Evolution (LTE) Downlink. Packet scheduling is of utmost importance in 3G LTE, because all traffic types with different Quality of Service requirements are competing of the resources. We present a decoupled time and frequency domain packet scheduling framework for LTE downlink. Simulation results with three basic packet scheduler combinations with different amount of fairness are presented in four different 3GPP macro simulation cases to show the both extremes in tradeoff between fairness and spectral efficiency. In addition, the effect of multiuser diversity on packet scheduling performance is studied. It is shown that by dividing the packet scheduler into a time domain and a frequency domain and utilizing different algorithms in both domains, the throughput fairness between users can be effectively controlled.

Channel Quality Indication Reporting Schemes for UTRAN Long Term Evolution Downlink

In this paper we evaluate the performance of channel quality indicator (CQI) reporting schemes in 3GPP UTRAN long term evolution (LTE) downlink (DL). In LTE, time and frequency dependent CQI is needed for DL packet scheduling (PS) and fast link adaptation (LA). Studies have indicated that frequency domain PS (FD-PS) and LA are essential techniques in improving the LTE performance, giving e.g. both cell throughput and coverage gain of around 40 % over a distributed multiplexing scheme. However, there is a tradeoff with signaling overhead related to the CQI feedback and overall LA and PS performance, which is rather overlooked in the literature. We analyze four different CQI reporting schemes with respect to system spectral efficiency and conclude that the best-M average and threshold based CQI reporting schemes seem to be the most promising in terms of the compromise between system performance and signaling overhead.

Voice-Over-IP Performance in UTRA Long Term Evolution Downlink

In this paper, we study voice-over-IP (VoIP) performance in UTRA long term evolution (LTE) downlink (DL). We have utilized fully dynamic system simulations to study the VoIP adaptive multi-rate (AMR) 12.2 codec capacity in four different 3GPP simulation cases. The effects of link adaptation (LA), packet bundling, control channel capacity and number of HARQ processes on VoIP capacity have also been considered. The results present the absolute VoIP capacity numbers of LTE DL. We also show that LA together with packet bundling provides clear gain on the VoIP capacity, because more VoIP packets can be scheduled in each TTI. Also, the control channel limitations can be effectively compensated by packet bundling.

A Novel Radio Frame Structure for 5G Dense Outdoor Radio Access Networks

This paper proposes a novel frame structure for the radio access interface of the next generation of mobile networks. The proposed frame structure has been designed to support multiuser spatial multiplexing, short latencies on the radio access interface, as well as mobility and small packet transmissions. The focus is on ultra dense small cell networks deployed in outdoor environments. This paper also highlights the various prospects and constraints of the proposed dense outdoor system in comparison with alternative system designs. Numerical results are included and a comparison to the Long Term Evolution (LTE) system is provided. Results show that the proposed radio frame structure leads to an improvement of the area spectral efficiency by a factor of ≈ 2.4 as well as a reduction of the average air interface latency by a factor of 5, thus remaining shorter than 1 millisecond.

Borderless Mobility in 5G Outdoor Ultra-Dense Networks

This paper considers borderless 5G ultra-dense networks (UDNs). In particular, a novel scheduling algorithm is proposed that achieves a more uniform distribution of user-throughput than that of the state-of-the-art maximum-throughput (MT) schedulers. The proposed scheduling algorithm also takes the coherence time of the channel into account as well as the impact to the acquired channel state information. A novel radio frame structure that is appropriate for achieving a 1-ms round trip time latency is also proposed. Such a low latency allows one to employ multiuser as well as cooperative multiple input multiple output schemes for mobile users. An evaluation of matched-filter and zero-forcing precoding for mobile users in UDNs is included. The performance of the proposed 5G UDN concept is assessed using a system-level simulator. Extensive numerical results show that the proposed borderless scheduling concept achieves ~77% higher median user-throughput than that of the MT scheduler at the cost of ~17% lower area-throughput. Such results are obtained for a high density of mobile users at velocities of ~50 km/h.

Performance of VoIP with Mobility in UTRA Long Term Evolution

In this paper, we study VoIP capacity in UTRA Long Term Evolution downlink under different mobility conditions. Since LTE is designed to be a wide area system supporting very high mobility, VoIP capacity for different mobility conditions is an important measure for the LTE system. We show how the mobility dynamics affect the VoIP capacity, using a dynamic system simulator to model the effects of both Robust Header Compression (ROHC) and handovers. The results indicate that the effect of non-ideal ROHC to VoIP system capacity is minimal, especially when compared to the mobility effects to system capacity.

Supporting mobility in 5G: A comparison between massive MIMO and continuous ultra dense networks

This paper proposes an approach for providing 5G services to mobile users that is based on continuous ultra dense networks (C-UDNs). The proposed approach outperforms the widely accepted solution based on macro cells and massive MIMO systems (M-MIMO). In particular, we show that the performance of M-MIMO systems deployed on macro cells is significantly limited by channel aging. The proposed mobility solution based on uplink beacons overcomes the handover problem often linked to UDNs. Dense networks make it possible for users to transmit at a power lower than that of macro cells, thus making C-UDN more robust to pilot contamination and allowing for lower Channel State Information (CSI) latencies due to shorter reuse distance of UL pilots. Extensive numerical results from detailed systemlevel simulations are provided in order to compare and highlight the benefits of the proposed C-UDN mobility solution to that of a macro M-MIMO deployment.

Location Based Beamforming in 5G Ultra-Dense Networks

In this paper we consider transmit (Tx) and receive (Rx) beamforming schemes based on the location of the device. In particular, we propose a design methodology for the Tx/Rx beamforming weight-vectors that is based on the departure and arrival angles of the line-of sight (LoS) path between accessnodes (ANds) and user-nodes (UNds). A network-centric extended Kalman filter (EKF) is also proposed for estimating and tracking the directional parameters needed for designing the Tx and Rx beamforming weights. The proposed approach is particularly useful in 5G ultra-dense networks (UDNs) since the high-probability of LoS condition makes it possible to design geometric beams at both Tx and Rx in order to increase the signal-to-interferenceplus- noise ratio (SINR). Moreover, relying on the location of the UNd relative to the ANds makes it possible to replace fullband uplink (UL) reference signals, commonly employed for acquiring the channel-state- information-at-transmitter (CSIT) in time- division-duplex (TDD) systems, by narrowband UL pilots. Also, employing the EKF for tracking the double-directional parameters of the LoS-path allows one to reduce the rate at which UL reference signals are transmitted. Consequently, savings in terms of time frequency resources are achieved compared to beamforming schemes based on full-band CSI. Extensive numerical results are included using a realistic ray-tracing based system-level simulator in ultra-dense 5G network context. Results show that position based beamforming schemes outperform those based on full-band CSI in terms of mean user-throughput even for highly mobile users.

High-Efficiency Device Positioning and Location-Aware Communications in Dense 5G Networks

In this article, the prospects and enabling technologies for high-efficiency device positioning and location-aware communications in emerging 5G networks are reviewed. We will first describe some key technical enablers and demonstrate by means of realistic ray-tracing and map based evaluations that positioning accuracies below one meter can be achieved by properly fusing direction and delay related measurements on the network side, even when tracking moving devices. We will then discuss the possibilities and opportunities that such high-efficiency positioning capabilities can offer, not only for location-based services in general, but also for the radio access network itself. In particular, we will demonstrate that geometric location-based beamforming schemes become technically feasible, which can offer substantially reduced reference symbol overhead compared to classic full channel state information (CSI)-based beamforming. At the same time, substantial power savings can be realized in future wideband 5G networks where acquiring full CSI calls for wideband reference signals while location estimation and tracking can, in turn, be accomplished with narrowband pilots.

Connectionless access for massive machine type communications in ultra-dense networks

This paper proposes an approach for receiving small uplink data transmissions from a massive amount of machine type communication (MTC) devices in ultra-dense networks (UDNs). In particular, we propose using a beamforming based solution for distributing (broadcasting) uplink grants for small data transmissions. Receive beamforming is also employed in order to receive the subsequent uplink small data transmissions. The proposed approach is particularly useful in reaching high transmission success probability of MTC uplink traffic with low consumption of physical resources. Extensive numerical results are provided based on detailed system level simulations in an ultra-dense 5G context. Results show that low collision and decoding failure probabilities can be achieved by employing beamforming and orthogonal codes for connectionless uplink grant distribution. Additionally, it is shown that uplink transmissions can be received efficiently by utilizing receive filters designed to maximize the received power towards the directions where grants were broadcasted. The performance of the proposed scheme is analyzed with a typical uniformly distributed massive MTC (mMTC) traffic as well as with a peak access profile as an extreme case.