Hubert Winkler

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.

Performance analysis of a GERAN switched beam system by simulations and measurements

Switched beam (SB) technology is an appropriate method for boosting GSM/EDGE radio access network (GERAN) capacity especially in hot spots or cell deployments, where the installation of additional sites and new antennas is not possible. A SB solution with four 30 degree sub-sectors is presented and the potential capacity gain in uplink and downlink is evaluated by simulations and drive tests. A performance comparison with the upcoming single antenna interference cancellation (SAIC) feature is given for the downlink. Finally, it is shown that SB and SAIC provide an additive quality and capacity gain.

Smart interference reduction dynamic MAIO allocation strategy for GERAN networks

A novel smart interference reduction dynamic MAIO allocation (SIR-DMA) strategy for boosting voice capacity in synchronized GERAN networks with limited bandwidth is proposed. Global interference reduction is achieved by introducing into a standard DMA algorithm the new concept of concentric MAIO, associating an inner/outer MAIO with a mobile exposed to a low/high inter-site interference. Utilizing the inner/outer MAIO classification SIR-DMA tries to allocate calls in mutually interfering cells on orthogonal timeslots (TS) the degree of orthogonalization, however, depending on the combination of the associated MAIO types, thus minimizing the inter-site interference. Finally SIR-DMA selects the best TS/MAIO combination by taking additionally into account the intra-site interference. The initial evaluation shows a capacity gain of about 20% compared to conventional DMA. The interaction of SIR-DMA with the upcoming SAIC capable MS as well as state-of-the-art switched beam technology has been studied, achieving capacity figures close to the hard blocking limit of a real one by one reuse.

Advanced quality of service strategies for GERAN mobile radio networks

Customer demand for wireless data services is rapidly increasing. The introduction of GPRS, EDGE and UMTS providing high bit rate radio bearer, however, is not the complete response for satisfying the demands of these new high quality services. An advanced quality of service QoS management is necessary to handle the characteristic requirements of both different service types and user expectations. A new QoS strategy is proposed and analyzed comprising 3GPP QoS parameters along with operators specific weighting factors to define the appropriate QoS priority of each service type and user profile. Admission control as well as a deterministic up-and downgrading strategy are applied to ensure a minimum grade of service for low-priority applications. Furthermore, delay time sensitive services and premium users are granted a full bandwidth. Simulation results are provided to qualify the behavior of the proposed QoS strategy under different packet data load conditions. Especially in highly loaded and even overloaded GERAN networks the introduction of QoS provides significant benefits for the end user and offers powerful means to increase the service revenues according to the charging policy adopted by the network operator. The introduction of an appropriate QoS strategy is the prerequisite for an overlay deployment strategy of GSM/EDGE and UMTS.

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

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.

AMR-wideband: enjoying superior voice quality at full coverage and competitive capacity in GERAN networks

The introduction of AMR-WB in 2G and 3G mobile networks represents a quantum leap in speech quality. The perceived voice quality is even superior to that offered in todays wire-line networks. A detailed study on the performance of the different AMR-WB codec types supporting GMSK as well as 8-PSK modulation has been performed based on system level simulations. The investigation is focused on speech quality, coverage and capacity that can be achieved in GERAN networks applying different frequency re-use patterns starting from a relaxed 4/spl times/3 down to a tight 1/spl times/1. The results show that neither additional sites nor a re-planning of the network is necessary for the introduction of AMR-WB. The dynamics of real codec mode adaptation traced along with the experienced radio link quality on an individual link reveal that an excellent speech quality can be achieved. The support of AMR-WB by both GERAN and UMTS offers high network homogeneity and a perfect symbiosis between 2G and 3G technologies providing an outstanding voice quality throughout the complete area of the multi-RAT network.

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.