Markku Kuusela

LTE Capacity Compared to the Shannon Bound

In this paper we propose a modification to Shannon capacity bound in order to facilitate accurate benchmarking of UTRAN long term evolution (LTE). The method is generally applicable to wireless communication systems, while we have used LTE air-interface technology as a case study. We introduce an adjusted Shannon capacity formula, where we take into account the system bandwidth efficiency and the SNR efficiency of LTE. Separating these issues, allows for simplified parameter extraction. We show that the bandwidth efficiency can be calculated based on system parameters, while the SNR efficiency is extracted from detailed link level studies including advanced features of MIMO and frequency domain packet scheduling (FDPS). We then use the adjusted Shannon capacity formula combined with G-factor distributions for macro and micro cell scenarios to predict LTE cell spectral efficiency (SE). Such LTE SE predictions are compared to LTE cell SE results generated by system level simulations. The results show an excellent match of less that 5-10% deviation.

Efficient Semi-Persistent Scheduling for VoIP on EUTRA Downlink

Evolved UTRA (EUTRA) is currently under standardization within 3GPP as a long-term evolution (LTE) of universal terrestrial radio access (UTRA) air interface. Due to the potentially large number of VoIP users served in this system, related control signaling overhead for VoIP transmissions with traditional full dynamic scheduling scheme could become a bottleneck and limit the system capacity to a greater extent. In this paper, we present a semi-persistent packet scheduling scheme for VoIP to explore the capacity within the limitation of control channel resources. System level simulation results show that semi-persistent scheduling scheme can reduce control channel usage without using packet bundling technique. With 6 control channels, around 310 users per sector can be supported in 5 MHz bandwidth with both discontinuous reception (DRX) enabled and without packet bundling.

Performance of linear multi-user MIMO precoding in LTE system

For scenarios with a large number of users to be served in one cell, high capacity gains can be achieved by transmitting independent data streams to different users sharing the same time-frequency resources. This technique is known as Multi-User MIMO (MU-MIMO). In this paper we investigate the performance of MU-MIMO operation in 3GPP LTE for different frequency granularities of the precoder at the OFDM transmitter. We also investigate the impact of channel correlation on the performance of the receiver when it is unaware of the interfererpsilas precoding vector. The performance is evaluated by means of semistatic system simulations.

VOIP over HSPA with 3GPP Release 7

This paper presents air interface capacity simulations for VoIP (voice-over-IP) over 3GPP Release 7 high speed packet access (HSPA) networks. The results show that 3GPP HSPA is able to provide VoIP spectral efficiency which is higher than the spectral efficiency for circuit switched voice calls with the same end-to-end quality. The high VoIP efficiency can be attributed to the packet optimization features in 3GPP Release 5, 6 and 7 specifications, to the advanced mobile receiver algorithms and to the VoIP optimized radio network algorithms. The studies also show that HSPA mobility solutions fulfil VoIP requirements with synchronous handover even if HSDPA does not use soft handover

Industrial embrace of smart antennas and MIMO

In this article we provide a practical standardization related viewpoint on beamforming and MIMO technologies. In particular, we address the status in different industry-driven standardization for a (3GPP and IEEE 802) and discuss the rationale for possible adoption or use of such technologies in current or future wireless systems. We draw attention to some practical system-level and implementation aspects that need to be resolved before a successful application of beamforming or MIMO in real systems

A Performance Summary of the Evolved 3G (E-UTRA) for Voice Over Internet and Best Effort Traffic

Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRA) is a new technology that targets the long-term evolution (LTE) of third generation. The E-UTRA technology has recently been standardized by the Third-Generation Partnership Project (3GPP) as a set of (series_36) specifications. The standardization process is almost complete; this paper does not focus on comparing specific proposed schemes but instead aims to outline the system performance more in general. E-UTRA operates in the packet-switched domain; hence, all traffic is handled by the packet protocols. The analysis is shown for Voice over Internet Protocol (VoIP) and Best Effort (BE) data, as these are common examples of real-time and non-real-time traffic, respectively. The performance is given in the VoIP study as the number of satisfied voice users per cell and in the BE study as the cumulative probability distribution of user (or cell) throughput, which was scaled to the spectral efficiency values, given both at the mean and at the cell edge. The VoIP capacity extends beyond 350 users in downlink and 230 users in uplink, which is a considerable increase compared with the high-speed packet-access (HSPA) reference. The BE spectral efficiency meets the 3GPP targets and yields impressive gains of order 2.5-3 times the well-performing HSPA reference. This clearly exceeds the mean of 1.5 b/s/Hz/cell in downlink and 0.8 b/s/Hz/cell in uplink for a baseline antenna configuration with penetration loss of 20 dB. In some scenarios, these mean gains exceed four times the reference.

Enhancing Performance of VoIP over HSDPA

This paper presents a study of packet scheduling enhancements for VoIP service over high-speed downlink packet access (HSDPA) in WCDMA. Taking VoIP traffic characteristics into account in Node B packet scheduling algorithm is a key element in achieving good performance and high VoIP capacity. The novelty of this study consists of dynamic transmission resource allocation method for VoIP service. Dynamic resource allocation takes the estimated channel conditions and the transmission requirements of a user into account to increase the efficiency of resource utilization. Simulation results produced with a dynamic system simulator indicate 20 % VoIP capacity gain achieved with the proposed enhancement when compared to the conventional even share resource allocation.

Effects of Non-Ideal Channel Feedback on Dual-Stream MIMO-OFDMA System Performance

In this paper we analyze the downlink OFDMA system-level performances of a 2times2 dual-stream MIMO multiuser transmission scheme under the assumptions of partial and noisy channel quality indicator (CQI) feedback available from the terminals. The effects on the CQI feedback of the terminal measurement and estimation errors, quantization errors, uplink reporting format and delays are included. Two reduced CQI reporting schemes are evaluated in macro and microcell scenarios when operating in combination with a MIMO outer loop link adaptation (OLLA) and a MIMO aware frequency domain packet scheduling (FDPS) algorithm. We show that, by using OLLA and with a proper choice of the CQI reporting scheme for dual-stream MIMO, the required CQI feedback overhead can be reduced by 90% while limiting the cell throughput losses to less than 10%.

Downlink VoIP Support for Evolved UTRA

This paper presents the design of VoIP optimized packet scheduler and performance simulations for supporting voice services over downlink evolved UTRA. An efficient packet scheduler taking into account the traffic characteristics and adopting optimal resource allocation is proposed. Results are given for different control channel number settings and packet bundling options. Simulation results show that downlink EUTRA VoIP capacity is mainly limited by control channel number with full dynamic scheduling and packet bundling can help to increase capacity within the control channel limitation. In summary, with packet bundling technique, around 378 and 488 users per sector can be supported in 5 MHz bandwidth with 6 and 8 control channels respectively.

System performance of Single-User MIMO in LTE downlink

Orthogonal Frequency-Division Multiplexing is a multi-carrier modulation scheme, where information symbols are transmitted in parallel over the channel by using a set of subcarriers. One of the main advantages is increased robustness against frequency selective fading and narrowband interference. In this paper we study the performance of two dual-codeword Single-User Multiple-Input Multiple-Output (SU-MIMO) schemes, i.e. per antenna rate control (PARC) and Precoded MIMO (PREC), in an OFDM deployment. For PARC we consider 2times2 and 4times4 antenna configurations and for Precoded MIMO 4times4 antenna configuration only. Our study is performed with a downlink Long Term Evolution (LTE) system simulator. The results indicate that in terms of average sector throughput the four-stream schemes outperform the dual-stream scheme by approximately 75-90%. Moreover, the four-stream schemes have significant coverage gain compared to the dual-stream scheme. When comparing the four-stream schemes against each other, the relative gain of the precoded scheme in average sector throughput is about 5-6%. From coverage perspective, PREC is about 13-20% better than PARC.