Erika P. L. Almeida

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.

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.

LTE UL Power Control for the Improvement of LTE/Wi-Fi Coexistence

Spectrum sharing is a powerful alternative to deal with the exponential increase on the wireless communication capacity demand. In this context, the coexistence of two of the most prominent wireless technologies today, Long Term Evolution (LTE) and Wi-Fi, is an important research topic. In the most common Wi-Fi network operation, the Distributed Coordination Function (DCF), communication nodes access the channel only if the interference level is below a certain threshold. Then, Wi-Fi operation is severely affected when in coexistence with LTE. This paper proposes the use of LTE uplink (UL) power control to improve LTE/Wi-Fi coexistence. With the introduction of an additional factor to the conventional LTE UL power control, a controlled decrease of LTE UL transmit powers is carried out according to interference measurements, giving opportunity to Wi-Fi transmissions. The proposed LTE UL power control with interference aware power operating point is a flexible tool to deal with the trade-off between LTE and Wi-Fi performances in coexistence, since it is able to set different LTE/Wi-Fi coexistence configurations with the choice of a single parameter. Simulation results show that the proposed approach can provide similar or better performance for both LTE and Wi-Fi networks than a previously proposed interference avoidance mechanism.

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.

Adaptive Transmit Power for Wi-Fi Dense Deployments

The increasing commercial success of Wi-Fi and the wireless communication industry forecast of exponential traffic growth for the next years indicate Wi-Fi dense deployments as scenarios more and more common in the future. Wi-Fi was not designed to operate in such scenarios. Because of its contention based channel access and backoff procedure, Wi-Fi presents low channel access efficiency and sensible performance degradation in terms of user throughput for dense deployments. This paper discusses the challenges of Wi-Fi operation in dense deployment scenarios and the benefits of a proposed adaptive transmit power mechanism. Wi-Fi performance is assessed by standard compliant simulations.

On the protection criteria for the operation of white space systems on TV bands

The use of the white spaces of the UHF broadcasting band (470-790 MHz) by unlicensed users is a huge opportunity for new telecommunication systems and services. A fundamental issue on this new scenario of spectrum usage is the power emission limit of secondary users, since it is mandatory that they do not cause harmful interference to licensed ones. This paper identifies and discusses a common set of parameters and criteria to protect the primary digital terrestrial television (DTT) service taking into account the DTT planning and limitations of DTT receivers. The white space system operation is assisted by a geolocation database, and the protection criteria are used to calculate the maximum permitted transmit power of white space devices. Some numerical results are provided for reference scenarios.

Maximum permitted transmit power of white space devices operating on TV spectrum

In order to have the White Spaces of the UHF broadcast band (470–790 MHz) in use by unlicensed users, new implementation challenges and special efforts still need to be done. Regulators can significantly impact the feasibility of implementation through requirements on sensing thresholds or by defining emission limits of unlicensed users. This paper addresses the emission limits of unlicensed users according to ECC approach, where the maximum output power is calculated for each location and for each device type/class. The problem of coexistence between white space devices and DTT broadcast service for the operation modes considered in CEPT is discussed and evaluated through simulations. With the obtained results, we discuss the relevancy of parameters stored in the geo-location database.

Distributed Wi-Fi Interference Coordination for Dense Deployments

Unlicensed spectrum is increasingly being used by mobile operators to meet the mobile traffic demand, and Wi-Fi is foreseen as one of the technologies for implementing mobile traffic offloading. However, Wi-Fi efficiency does not scale well as node density increases, and IEEE 802.11ax Task Group (TGax) was created in 2014 for developing Wi-Fi technology enhancements in dense deployments. This paper investigates Wi-Fi performance in the presence of Overlapping Basic Subscriber Set (OBSS) Wi-Fi networks in indoor dense deployments. We observe that Wi-Fi could benefit from scheduled operation with proper OBSS interference coordination. We propose a novel distributed interference coordination scheme for Wi-Fi scheduled mode operation, and evaluate it through system-level simulations. Results indicate that the proposed scheme provides significant improvements over Enhanced Distributed Channel Access (EDCA) for downlink (DL) traffic.