Arne Simonsson

Intercell Interference Coordination in OFDMA Networks and in the 3GPP Long Term Evolution System

Intercell interference coordination (ICIC) in orthogonal frequency division multiple access (OFDMA) networks in general and in the 3GPP Long Term Evolution system in particular has received much attention both from the academia and the standardization communities. Understanding the trade-offs associated with ICIC mechanisms is important, because it helps identify the architecture and protocol support that allows practical systems to realize potential performance gains. In this paper we review some of the recent advances in ICIC research and discuss the assumptions, advantages and limitations of some of the proposed mechanisms. We then proceed to describe the architecture and protocol support for ICIC in the 3GPP LTE system. We make the point that the 3GPP standard is formed in a flexible way such that network operators can employ the most suitable ICIC mechanism tailored to their actual deployment scenario, traffic situation and preferred performance target.

Frequency Reuse and Intercell Interference Co-Ordination In E-UTRA

Intercell interference co-ordination is considered within 3GPP for evolved UTRA (E-UTRA). The objective is to improve coverage and increase cell-edge bitrate. A number of static and dynamic schemes have been suggested. In this study some basic schemes have been evaluated by means of simulations. Also, the impact of link performance and carried services has been investigated. Of the static schemes the simple 1-reuse performs best for wideband services. The bandwidth reduction (in Hz) with other schemes cannot be regained by the link improvement (in bps/Hz) achieved by the interference reduction. The link performance has a significant impact on the co-ordination gain. Static schemes improve the cell-edge bitrate with a single receiver antenna but not with the two receiving antennas expected in E-UTRA. Interference co-ordination will be more efficient for narrowband services since the frequency bandwidth allocated to each cell is then better utilized. For wideband packet data services a dynamic scheme is required to improve compared to a simple 1-reuse.

Uplink Power Control in LTE - Overview and Performance, Subtitle: Principles and Benefits of Utilizing rather than Compensating for SINR Variations

Uplink power control is a key radio resource management function. It is typically used to maximize the power of the desired received signals while limiting the generated interference. This paper presents the 3GPP long term evolution (LTE) power control mechanism, and compares its performance to two reference mechanisms. The LTE power control mechanism constitutes of a closed loop component operating around an open loop point of operation. Specifically, the open loop component has a parameterized fractional path loss compensation factor, enabling a trade-off between cell edge bitrate and cell capacity. The closed-loop component can be limited to compensate for long-term variations, enabling fast channel quality variations to be utilized by scheduling and link adaptation. Simulation results indicate that the LTE power control mechanism is advantageous compared to reference mechanisms using full path loss compensation and SINR balancing. The fractional pathless compensation can improve the cell-edge bitrate and/or the capacity with up to 20% while at the same time battery life time is improved. The fast SINR balancing closed loop mechanism performs poorly at high load since it does not utilize the link adaptation and the full link performance capability in LTE.

Downtilted Base Station Antennas - A Simulation Model Proposal and Impact on HSPA and LTE Performance

This paper proposes a low-complexity model for vertical antenna radiation patterns, e.g. for inclusion in system- level simulations. They can be seen as extensions to the horizontal radiation pattern model used in 3GPP simulation scenarios. The model is verified against and compared to predicted and measured data from real networks. The impact on system-level performance is also investigated. It is seen that using the proposed model, simulated geometry distributions and soft handover statistics closely matching those of real networks may be achieved. The analysis also concludes that many real networks have better cell isolation than what is modeled by the 3GPP antenna model. As a consequence, the horizontal radiation pattern model significantly under-estimates the system level performance in such networks. Furthermore, the proposed model is used to assess the LTE and HSPA system-level performance for realistic scenarios.

15 GHz propagation properties assessed with 5G radio access prototype

This paper presents coverage and penetration loss measurements in an urban environment at 15 GHz to provide insight into the design and deployment of future 5G systems in higher frequency bands. The measurements are performed using a 5G radio access prototype including two transmission points (TPs) and a mobile terminal over a 200 MHz bandwidth. The TPs and the mobile terminal each consists of multiple antennas, enabling spatial multiplexing of multiple data streams. Coverage measurements are performed for both outdoor and outdoor-to-indoor scenarios. Penetration losses are measured for human body, normal and coated windows, a metallic white board, and a concrete pillar. Outdoor microcellular coverage in line-of-sight (LOS) and lightly shadowed areas is shown to be possible with similar antenna directivities as in the existing cellular networks. Transitions into non-line-of-sight (NLOS) bring additional losses in the order of 20 dB, thereby making the NLOS coverage challenging. Outdoor-to-indoor coverage seems to be limited to areas that are in almost LOS with the outdoor TP. Moreover, the penetration loss of indoor blocking objects seems to further restrict the indoor coverage. Potentials of beamforming as a means to improve the coverage are also evaluated via simulations.

LTE HetNet Trial - Range Expansion Including Micro/Pico Indoor Coverage Survey

Adding low power nodes is one option to meet the increased mobile broadband traffic demands. In the resulting heterogeneous network (HetNet) with different node power levels, range expansion is a key feature to improve uplink as well as to increase the coverage of micro/pico nodes. In this paper measurement results from a trial with Release 8 terminals and system verify that range expansion can improve uplink bit rate at a limited cost in downlink bit rate. Also, the macro versus micro/pico indoor coverage is assessed by scanning three office buildings. Coverage using a 2x1 W pico node is assessed to 75 percent of the coverage with a 2x5 W micro node. Range expansion can increase the indoor coverage with 1.5 to 4 percentages per dB.

Uplink Control Channel in E-UTRA, Radio Link and Radio Network Evaluation

Evolved UTRA (E-UTRA) is specified by the Third generation partnership project, 3GPP. E-UTRA is designed to efficiently and flexibly utilize different spectrum bands supporting high physical bit rate and short radio link delay. A reliable control channel is a key component for short delay and high bit rate on higher layers. For user peak bit rate, a low HARQ NACK error ratio is crucial. HARQ ACK/NACK for downlink is sent on the Physical Uplink Control Channel (PUCCH). In this paper the PUCCH performance is evaluated by means of simulations. Results on both link and network level in a multi-cell environment show that the PUCCH is robust and designed for 1-reuse frequency plans. Good performance is shown for different channel types and for high speed mobiles. For up to 12 scheduled users per sub-frame the NACK error rate is maintained well below le-4.

LTE Downlink Inter-Cell Interference Assessment in an Existing GSM Metropolitan Deployment

In a loaded 1-reuse cellular network as e.g. 3GPP Long Term Evolution (LTE) the inter-cell interference limits the user bitrate for link adaptive packet data access. The cell isolation together with the link performance defines the spectrum efficiency and the achievable gain of higher order modulation or other link improving features. In this paper the cell isolation is measured as geometry factor in a dense city network. The measurements are performed on commercial GSM live traffic capturing the real spatial distribution including indoor usage. The cell plan of the studied metropolitan network is found to be very good and well optimised with the potential to support high user bitrates and high capacity for future LTE high speed radio accesses. The measured geometry factor distribution is superior to those that have been used for capacity evaluations in 3GPP indicating good performance of a possible LTE in existing deployments. A very good match between the live traffic measurements and simulations is found when introducing a tilted 3D antenna model into the cellular radio network simulation environment. Further, the tilted 3D antenna model results in a more realistic amount of interfering cells experienced at simulation estimations of spectrum efficiency.

LTE frequency selective scheduling performance and improvements assessed by measurements

In this paper the potential of downlink frequency selective scheduling (FSS) is addressed based on measurements in an experimental 3GPP Long Term Evolution (LTE) system setup. We find that scheduling on the best sub-band has the potential to improve channel conditions by up to 2 Channel Quality Indicator (CQI) units, which represents around 4 dB channel gain improvement. The time-frequency fading characteristics as a function of mobile speed is described and verified in measurements where instances of correlated time-frequency fading are observed. In stationary or semi-stationary scenarios CQI reporting delays are not limiting. However, at a mobile speed of 10 km/h the gain is lost when the reporting delay reaches 20 ms at the studied 2 GHz band. A simple prediction algorithm that utilizes how the best sub-band moves in frequency domain can improve the gain at 10 km/h around one CQI unit (2 dB) for the studied measurements indicating improvement potential for FSS at higher mobile speed.

LTE Downlink 2X2 MIMO with Realistic CSI: Overview and Performance Evaluation

For downlink multiple input multiple output (MIMO) schemes, there is a tradeoff between downlink MIMO performance and uplink reporting cost. The mobile speed has an impact on this tradeoff since the reporting delays the measurements. This paper presents the major downlink MIMO modes in 3GPP Long Term Evolution (LTE) and their related channel state information (CSI) modes. The impact of realistic CSI is investigated through advanced system simulations, showing that the total performance degradation of realistic CSI reporting is at a surprisingly low 20% compared to full, recent channel knowledge. With realistic CSI reporting, a selected set of promising 2x2 MIMO applications are evaluated at different mobile speeds. The open-loop spatial multiplexing mode offers unexpectedly high cell throughput despite its limited feedback requirement. It performs well for a wide range of speeds, as it provides good robustness to delayed channel knowledge. Bitrates can only be further improved by closed-loop spatial multiplexing in stationary scenarios, where CSI delay does not hamper the precoding gain. These results confirm that there are MIMO modes suitable for both high and low speeds.