Esa Tuomaala

Enabling LTE/WiFi coexistence by LTE blank subframe allocation

The recent development of regulatory policies that permit the use of TV bands spectrum on a secondary basis has motivated discussion about coexistence of primary (e.g. TV broadcasts) and secondary users (e.g. WiFi users in TV spectrum). However, much less attention has been given to coexistence of different secondary wireless technologies in the TV white spaces. Lack of coordination between secondary networks may create severe interference situations, resulting in less efficient usage of the spectrum. In this paper, we consider two of the most prominent wireless technologies available today, namely Long Term Evolution (LTE), and WiFi, and address some problems that arise from their coexistence in the same band. We perform exhaustive system simulations and observe that WiFi is hampered much more significantly than LTE in coexistence scenarios. A simple coexistence scheme that reuses the concept of almost blank subframes in LTE is proposed, and it is observed that it can improve the WiFi throughput per user up to 50 times in the studied scenarios.

Principle and Performance of Semi-Persistent Scheduling for VoIP in LTE System

This paper presents an effective scheduling scheme called semi-persistent scheduling for VoIP service in LTE system. The main challenges of effectively supporting VoIP service in LTE system are 1) the tight delay requirement combined with the frequent arrival of small packets of VoIP traffic and 2) the scarcity of radio resources along with control channel restriction in LTE system. Simulation results show that semi-persistent scheduling can support high system capacity while at the same time guaranteeing the QoS requirements such as packet delay and packet loss rate of VoIP. Furthermore, semi- persistent scheduling requires less control signaling overhead which is very important for efficient resources utilization in a practical system.

Performance Evaluation of LTE and Wi-Fi Coexistence in Unlicensed Bands

The deployment of modern mobile systems has faced severe challenges due to the current spectrum scarcity. The situation has been further worsened by the development of different wireless technologies and standards that can be used in the same frequency band. Furthermore, the usage of smaller cells (e.g. pico, femto and wireless LAN), coexistence among heterogeneous networks (including amongst different wireless technologies such as LTE and Wi-Fi deployed in the same frequency band) has been a big field of research in the academy and industry. In this paper, we provide a performance evaluation of coexistence between LTE and Wi-Fi systems and show some of the challenges faced by the different technologies. We focus on a simulator-based system- level analysis in order to assess the network performance in an office scenario. Simulation results show that LTE system performance is slightly affected by coexistence whereas Wi-Fi is significantly impacted by LTE transmissions. In coexistence, the Wi-Fi channel is most often blocked by LTE interference, making the Wi-Fi nodes to stay on the LISTEN mode more than 96% of the time. This reflects directly on the Wi-Fi user throughput, that decreases from 70% to ≈100% depending on the scenario. Finally, some of the main issues that limit the LTE/Wi-Fi coexistence and some pointers on the mutual interference management of both the systems are provided.

Enabling the coexistence of LTE and Wi-Fi in unlicensed bands

The expansion of wireless broadband access network deployments is resulting in increased scarcity of available radio spectrum. It is very likely that in the near future, cellular technologies and wireless local area networks will need to coexist in the same unlicensed bands. However, the two most prominent technologies, LTE and Wi-Fi, were designed to work in different bands and not to coexist in a shared band. In this article, we discuss the issues that arise from the concurrent operation of LTE and Wi-Fi in the same unlicensed bands from the point of view of radio resource management. We show that Wi-Fi is severely impacted by LTE transmissions; hence, the coexistence of LTE and Wi-Fi needs to be carefully investigated. We discuss some possible coexistence mechanisms and future research directions that may lead to successful joint deployment of LTE and Wi-Fi in the same unlicensed band.

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.

Performance of dual antenna diversity reception in WCDMA terminals

In this paper the performance of a dual antenna reception in WCDMA downlink is studied on the link and network levels for circuit switched service of 64 kbps. An effect of penetration diversity terminals and channel parameters to potential diversity gain are investigated from a point of view of two receivers; dual antenna RAKE and a space-time chip equalizer. Results indicate that the penetration of diversity terminals should be large before the performance gain in link level can be turned into significant increase in system capacity.

Uplink capacity of VoIP on LTE system

In this paper, performance of VoIP service on LTE UL system is studied and analyzed via semi-static system level simulations. Simulations show that different scheduling schemes have a big influence on the UL VoIP capacity - semi-persistent method is quite promising due to its ability to decrease DL signaling overhead and a good performance that is comparable to more advanced methods. The impacts of different VoIP packet sizes, different usage scenarios and different scheduling mechanism are analyzed as well. Those are concluded from the simulation results.

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.

Performance Evaluation of IEEE 802.11n WLAN in Dense Deployment Scenarios

The default medium access mechanism for Wi-Fi, Distributed Coordination Function (DCF), is a simple contention based protocol aimed at providing a fair distribution of resources among Wi-Fi nodes. However, DCF suffers from significant performance degradation in the presence of dense deployments. Hence, improving the performance of the Wi-Fi MAC layer is essential for efficient spectrum sharing among overlapping Basic Subscriber Set (OBSS) for next generation wireless networks. In this context, in this paper, we compare DCF with an existing Wi-Fi mechanisms, Power-Save Multi-Poll (PSMP) and Hybrid Coordination Function (HCF) Controlled Channel Access (HCCA), and show that, although standard scheduled access techniques enhance WiFi throughput, they also suffer a decrease on performance in dense deployments. As a starting point, we propose that scheduled access including contention-free channel access mechanisms should be considered in addition to DCF for dense deployments.

Evaluation of the recent advances of the evolved 3G (E-UTRA) for the VoIP and best effort traffic scenarios

The evolved UMTS terrestrial radio access (E-UTRA) is a new technology being standardized by the 3GPP . E-UTRA targets for a long term evolution of 3G UMTS. This paper addresses the fundamentals of the E-UTRA technology and describes especially its gain mechanisms. As the standardization work is progressing rapidly, this paper does not focus on comparing the specific proposed schemes, but instead aims at outlining the system performance more in general. As E-UTRA operates in the packet-switched domain, all traffic is handled by packet protocols. The cellular analysis is shown with the results for a voice over internet protocol (VoIP) study case and for a best effort (BE) data study case, as these are common examples of a real-time and a non-real-time traffic, respectively. The performance is given in the number of satisfied voice users per cell and in the cumulative probability distributions of user throughput, which is scalable to the spectral efficiency.