Robert Müllner

Contrasting Open-Loop and Closed-Loop Power Control Performance in UTRAN LTE Uplink by UE Trace Analysis

Uplink power control in UTRAN Long Term Evolution consists of an open-loop scheme handled by the User Equipment and closed-loop power corrections determined and signaled by the network. In this study the difference in performance between pure open-loop and combined open and closed-loop power control has been analyzed and the different behavior of fractional vs. full path-loss compensation has been evaluated. A comprehensive system level simulation model has been used with a facility to trace a particular test user during its motion from eNodeB towards the cell border and back to its initial position. This study demonstrates the effect of distance path-loss of a test user on several physical layer performance metrics including throughput, resource allocation as well as modulation and coding scheme utilization. Simulation results in a fully loaded network show high throughput for open-loop fractional power control for the user located in the vicinity of the serving eNodeB, however, steep performance degradation has been observed when the user is moving towards the cell edge. The user throughput at the cell border can be increased by the closed-loop component. The benefit of closed-loop power control is the higher homogeneity in terms of throughput across the entire network area and the ability to automatically stabilize the network performance under different conditions like cell load and traffic distribution.

Load adaptive power control in LTE Uplink

In LTE Uplink, the slow varying pathgain and shadowing are compensated by the standardized open loop power control (OLPC) which is based on a power density offset and a compensating factor for the pathloss experienced by the users. The optimization of those parameters reveals a dependency on the allocated bandwidth. A Load Adaptive Power Control (LAPC) algorithm is proposed to handle the bandwidth variations and ensure optimal system performance. In this contribution it is shown that using closed loop power control commands to adapt the transmission power density to the used bandwidth, it is possible to achieve coverage gains up to 60% while maintaining a cell throughput comparable to the reference case.

Enhancing uplink performance in UTRAN LTE networks by load adaptive power control

Uplink power control in 3GPP UTRAN long term evolution (LTE) networks consists of a closed-loop scheme around an open-loop point of operation. The uplink performance of the network is decisively influenced by power control. This paper provides insight into the uplink power control procedure and its interworking with adaptive transmission bandwidth (ATB) as well as adaptive modulation and coding (AMC). A detailed performance evaluation is presented based on system level simulations. In the first step, the performance of pure open-loop power control (OLPC) was analysed and the impact of parameter settings on resource allocation, utilisation of specific modulation and coding schemes (MCS), re-transmission rate, and resulting throughput was determined. A two-dimensional parameter optimisation for full path-loss (PL) compensation and fractional power control (FPC) was performed to conclude the best strategy for the trade-off between network capacity and coverage. In the second step, the impact of traffic load on the interaction between the different LTE radio resource management algorithms was analysed. A novel strategy is presented which introduces traffic load dependent decisions for the closed-loop power control (CLPC) component to optimise the uplink throughput. This solution provides an automatic configuration for LTE networks without further intervention by the operator. Copyright

Performance analysis of Closed and Open loop MIMO in LTE

This paper provides a detailed performance comparison between closed loop (CL) and open loop (OL) MIMO schemes for the upcoming OFDM based mobile broadband radio access technology 3GPP UTRA LTE. Based on system level simulation results, key performance indicators like cell throughput, user throughput and MIMO utilization have been evaluated for different system load conditions assuming 2×2 MIMO in a regular hexagonal cell deployment and in a real network scenario. A realistic dynamic MIMO switch between diversity and spatial multiplexing has been assumed, which is based on configurable CQI as well as rank filtering and decision thresholds. 3GPP compliant measurement granularity as well as appropriate measurement errors have been applied to both CQI and closed loop PMI reports. Besides dynamic MIMO switching, both MIMO 2×2 diversity and MIMO 2×2 spatial multiplexing scenarios have been investigated for the downlink direction highlighting the differences of the various MIMO transmission modes and their impacts on spectral efficiency and radio performance. It has been shown that ideal closed loop MIMO provides a 2 dB theoretical performance gain over open loop MIMO. Assuming practical limitations such as available granularity, delay and realistic PMI measurement errors, however, this gain significantly decreases below roughly 1 dB. Nevertheless MIMO proves to be an appropriate method to boost user throughput especially at low to medium system load up to a factor of 2. Moreover the dynamic MIMO switch proves to be very robust against variations of parameter settings.

Uplink Power Control Performance in UTRAN LTE Networks

Uplink power control in 3GPP UTRAN Long Term Evolution (LTE) networks consists of a closed-loop scheme around an open-loop point of operation. The uplink performance of the network is decisively influenced by power control. This paper provides insight into the power control procedure and its interworking with Adaptive Transmission Bandwidth (ATB) as well as Adaptive Modulation and Coding (AMC) presenting a detailed performance evaluation by system level simulations for a fully loaded network. The analysis starts for pure open-loop power control as reference, for which the impact of parameter settings on resource allocation, utilization of specific modulation and coding schemes, retransmission rate, and resulting throughput has been determined. A two-dimensional parameter optimization for full path-loss compensation and fractional power control has been performed to conclude the best strategy for the trade-off between network capacity and coverage. Finally on top of this optimized open-loop power control parameter set the closed-loop component has been enabled and proposals for optimum power control threshold settings are provided. The beneficial effects of closed-loop power control are presented highlighting its ability to adjust the transmission power according to the desired quality and level requirements.

Paving the path for high data rates by GERAN evolution EDGE2 with dual-carrier

The introduction of the upcoming GERAN evolution feature package in current GSM/EDGE deployments offers operators significant boost in network capacity and mobile data users UMTS/HSPA like high speed packet data services along with competitive latency. Intelligent radio resource management supports novel dual-carrier capable mobile stations by dynamic configuration of GPRS/EDGE packet data channels (PDCHs) on multiple non-BCCH carriers. In addition the currently standardized EDGE2 level B (EDGE2-B) concept provides enhanced PDCH data rates up to 118.4 kbps per timeslot. In this paper system level simulation results for the end-to-end performance of GERAN over TCP/IP are presented assuming conventional 4 timeslots up to future potential 14 timeslots capable EDGE and EDGE2-B mobiles showing up to 800 / 1600 kbps peak data rates. FTP-application throughput has been investigated with respect to both download file size and important TCP settings such as e.g. receiver window size. The GERAN dual-carrier performance has been evaluated for EDGE and EDGE2-B both under ideal radio conditions and in regular hexagonal cellular deployments depending on system load, exemplifying FTP 500 kbyte download with 8 timeslots capable mobiles. At medium system load EDGE2-B compared to EDGE reveals about 100% capacity gain and more than 60% gain in mean user throughput.

Exploiting AMR-WB Audio Bandwidth Extension for Quality and Capacity Increase

Audio bandwidth extension in AMR-WB to twice of that used in AMR-NB provides essential subjective speech quality improvements, while the link level performance in GERAN networks for codec modes of comparable source bit rate is similar. This study analyzes the effect of improved audio perception as well as the impact of channel errors and call drops on the network performance. Profound system level simulations for relaxed 4times3 and 3times3 frequency re-use as well as tight 1times1 reuse have been performed In 4times3 and 3times3 re-use networks, whose capacity is limited by hard-blocking, the audio advantage provided by AMR-WB is entirely transformed into quality improvements. These amount almost one third on the speech quality indicator (SQI) scale ranging from zero to one. The capacity of 1times1 re-use networks is primarily limited through soft-blocking criteria. Four different quality criteria have been applied: SQI, frame erasure rate (FER), bad quality probability (BQP), and call drop rate (CDR). If only the subjective speech quality criteria were taken into account an increase in network capacity from 21% Erlang fractional load (EFL) for AMR-NB to 32% for AMR-WB is feasible. Since this quality indicator is rather related to general speech quality impression than to intelligibility, additional FER based quality criteria and CDR have been applied. Requiring additionally BQP lower than 5% and CDR lower than 2% limits the capacity of AMR-WB tight re-use networks to 21% EFL. Exactly the same capacity is achieved by AMR-NB, for which subjective speech quality is the more restrictive criterion. Exchanging the BQP criterion by the more restrictive criterion of mean FER per call lower than 2% for 95% of the subscribers leads to capacity advantages for AMR-NB due to lack of sufficiently robust AMR-WB codec modes and the higher latency in codec mode adaptation using tandem free operation. Results indicate that tight re-use networks should not exploit first glance quality advantage of AMR-WB. Instead for the definition of admission control thresholds FER and BQP criteria shall be taken into consideration in addition to subjective speech quality impression.

Geran Evolution: Voice Capacity Boosted by Downlink Dual Antenna Interference Cancellation

Dual antenna interference cancellation (DAIC) recently introduced by 3 GPP standardization as a natural evolution step of its predecessor single antenna interference cancellation (SAIC) to further improve the spectral efficiency in GERAN networks is based on the enhancement of the SAIC inherent downlink advanced receiver performance (DARP) feature by receive diversity. In this study focus has been set on a proper and efficient modelling of DAIC in terms of link-to-system level simulator interface (LSLI). A novel memory saving approach for the design of LSLI suggests a lower and upper bound for the dominant interference ratio (DIR) metric to be used in system level simulations. Using the new approach system level simulations have been performed showing roughly three to four-fold capacity gain w.r.t. todays conventional AMR networks and a gain of factor two compared to deployments with 100% SAIC penetration.

Enhancing Packet Data Performance by dynamic Half-Rate Allocation of Speech Services

As customer demand for wireless data services increases the bandwidth requirements for new applications are rapidly growing Half-rate speech codecs have been introduced in GERAN networks to save operators spectrum shared by circuit switched voice and packet switched data services. The released physical resources by allocating voice calls on half-rate channels can be efficiently utilized to significantly increase the data rate of packet switched services. Since by nature the speech quality on half-rate channels is inferior to that on full-rate channels a dynamic half-rate assignment strategy has been introduced triggering half-rate allocation by taking into account both the radio conditions of the voice call and the cell traffic load. Provided that the radio conditions are sufficient voice calls are temporarily allocated on half-rate channels during periods of high traffic load to ensure high quality of service level for packet data applications. In this study the trade-off between speech quality and data capacity has been analyzed by means of system level simulations. Exploiting half-rate allocation at the expense of certain speech quality degradation results in a substantial reduction of the number of blocked data calls as well as in a significant increase in the packet data throughput. Yet almost the same performance for packet data services is achieved by pure and dynamic half-rate allocation, the latter strategy provides significant speech quality gain for 50% of the subscribers.

Contrasting single-point and multi-point half-rate allocation strategies for AMR-WB in high-capacity cellular networks

In mobile networks a most economic utilization of the channels on the air interface by means of intelligent radio resource management is desired since these resources are the most valuable ones. Half-rate speech codecs introduced in GERAN networks for capacity increase involve quality degradation compared to full-rate codecs especially in error-prone radio channel conditions. To provide best possible speech quality the available resources in the network should be utilized as extensive as possible. In addition flexible mechanisms are required to provide additional capacity whenever needed for obtaining the optimum trade-off between quality expectations and capacity requirements. In this study two different load dependent half-rate allocation algorithms for speech services have been proposed. The performance differences have been evaluated thoroughly by system level simulations and compared in terms of system performance. Applied quality criteria are frame erasure rate, bad speech quality probability, codec mode distribution, speech quality indicator and call drop rate. The results show significant differences in channel utilization, speech quality and achieved network capacity.