Kurt Kremnitzer

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

Breaking through AMR voice capacity limits due to dropped calls by control channel improvements in GERAN networks

During the last couple of years a series of voice quality and capacity enhancement features have been implemented in narrow-band deployments of GERAN (GSM/EDGE radio access networks) mobile radio networks. Recent field findings revealed call drop rate (CDR) to be the major limiting factor already in medium loaded AMR (adaptive multi rate) networks planned in tight frequency reuse due to excessive failures on the associated control channels (ACCH). The reason for this phenomenon observed at 20% to 30% EFL (Erlang fractional load) is the significant link level performance imbalance of up to 6 dB (in terms of C/I) between AMR 4.75/5.90 kbps voice codecs and signaling ACCH. In this study a novel strategy based on temporary ACCH overpower has been proposed as a practical and fully backwards compatible option to reduce the C/I gap and to improve the probability of successful decoding of the FACCH/SACCH frames. A full description of the CDR contributors (radio link timeout and handover failures) has been provided along with detailed system level simulation results. The initial evaluation of the novel approach is very promising, showing a significant soft capacity gain by substantially reducing CDR allowing a system load well above 30% EFL in homogeneous hexagonal networks. The suggested approach could be efficiently combined with current 3GPP standardization initiatives for control channel improvements in GERAN

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.

Privileged Treatment of UMTS Subscribers in GSM Networks

Different user segments have various requirements and expectations towards the performance of mobile networks. Subscribers having experienced the high quality of UMTS networks desire to maintain high speech quality and excellent data throughput also in areas of missing UMTS but existing GSM coverage. In GSM networks a privileged treatment of UMTS subscribers by means of proper resource allocation provides a substantial quality improvement with respect to standard GSM subscribers. This strategy allows network operators to reduce the performance gap between both network areas experienced by UMTS subscribers. A detailed study on the performance of circuit switched speech and packet data services has been performed based on system level simulations. The results show significant speech quality advantages for users with dual-RAT terminals compared to standard GSM users as well as notably higher data throughput rates.

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.

Smart Quality Enhancement in High Capacity Geran Networks

Smart quality enhancement (SQE) aims at improving traditional quality based power control algorithms by automatically adjusting the transmit power control decision thresholds to the prevailing traffic load conditions. During low traffic periods a high C/I threshold is required to protect calls against quality degradation caused by occasionally emerging interferers. At busy hour traffic level lower C/I decision thresholds are used to reduce the interference level for the most affected calls in the network. Applying this strategy the call is always best served. The benefit from SQE has been investigated by means of system level simulations. The simulation results show an optimum speech quality achieved by SQE over the whole range of feasible traffic load in the network. The percentage of satisfied users at low traffic load that would have been obtained with an optimum static decision threshold configured for busy hour traffic has been increased by SQE from about 93% to above 99%. Correspondingly the percentage of satisfied users at busy hour traffic load that would have been obtained with an optimum static decision threshold configured for low traffic has been improved from 90% up to 93%. Assuming an acceptable outage of 10% the quality improvement of about 3% can be traded-off against a capacity gain of about 10% to 15%. SQE is especially beneficial in network deployments providing mixed indoor and outdoor coverage

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.

Full-rate speech quality on half-rate performance comparison of GMSK and 8-PSK modulated AMR-NB codec modes in GERAN mobile radio networks

Growing traffic load in todays wireless networks brings up new challenges with respect to capacity. Simultaneously the demands for high quality voice services are rising. AMR half-rate in 8-PSK modulation combines both aspects and provides doubling the GERAN capacity just at a slight degradation of the perceived speech quality. A detailed performance study of 8-PSK modulated AMR half-rate codec modes is presented based on network planning studies and profound system level simulations. In addition a performance comparison to GMSK modulated AMR half-rate and full-rate codec modes has been provided. This analysis is focused on speech quality, coverage and capacity by AMR-NB in GERAN networks applying different frequency re-use patterns ranging from relaxed 4times3 to tight 1times1. The trade-off between quality and capacity has been demonstrated as well as the gain provided by 8-PSK modulated AMR half-rate. Network configurations offering full-rate quality by the allocation of half-rate channels have been identified. The capacity gain can be used to serve additional subscribers and/or to increase the quality and capacity of GPRS/EDGE data services