Rafael C. D. Paiva

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.

Random Access Capacity Evaluation with Synchronized MTC Users over Wireless Networks

Increased attention has been drawn to machine type communication (MTC) lately, which represents important extension for user functionality in todays technologies, as well as an important potential for marketing expansion. GERAN studies over MTC has mainly focused on applications requiring low throughput and wide coverage such as smart meter, which could cause some impacts over normal data users if operating in a synchronous manner. This paper proposes a new methodology for studying the impact on signaling channels when mixture of synchronous and asynchronous traffic is present in the network. This is based on statistical analysis, considering signaling accessing attempts as driven by a Poisson process. In this approach successive random access attempts by the mobile stations are considered as well as the response on the network side. First implementation is held for GSM/GPRS network, although generalization of the method for other technologies is possible. The simulated results show potential problems to be solved when a large number of synchronized users is present. Additionally, an analysis on the effects of the different levels of synchronization and the addition of extra signaling channels is included. Results also point out possible development paths that could be taken when designing new features to make networks more robust to synchronized traffic.

A physical layer framework for interference analysis of LTE and Wi-Fi operating in the same band

The recent digital transition of TV broadcasting has created new opportunities for wireless usage for voice, video and data services in these newly released bands (known as TV white spaces). Some possible wireless technologies that can be deployed in this new spectrum are LTE and Wi-Fi. In this paper, we conduct an in-depth analysis of the physical layer performance of LTE and Wi-Fi in the presence of cross-technology interference. We propose a physical layer simulation framework in order to co-simulate the link level performance of LTE and Wi-Fi and show the impact of different interference patterns on the error rate. Our results show that the Wi-Fi performance is slightly exacerbated in the presence of LTE interference (compared to similar Wi-Fi interference). We also show that LTE pilot boosting has negligible impact on Wi-Fi performance. Finally, we also show the impact of Wi-Fi interference on the LTE performance.

Overload Control Method for Synchronized MTC Traffic in GERAN

Increasing attention has been drawn in Machine Type Communications (MTC), also known as Machine to Machine (M2M) Communications, since it enables implementation of new services, and expansion of revenue sources for mobile equipment manufacturers and mobile network operators. This potential is high, but some issues have to be solved to enable the wide application of MTC services, especially those which could request connections in a synchronized manner. In GSM networks, synchronized channel requests can result in signaling channel overload, which would delay the access procedure for all users trying to access the network. This paper presents a solution for this problem, in which devices connecting in a periodical manner request a future network access already during a previous connection. Simulation results have shown that by using this technique, overload on the access channels is reduced, improving the access delay of normal users and enabling more MTC devices to be included in the network.

GSM Evolution Importance in Re-Farming 900 MHz Band

Re-farming of 900 MHz band into HSPA has been started and is likely to happen later with LTE. Typically operators have less than 10 MHz block of 900 MHz spectrum and therefore co-existence of two systems in that band is causing challenges. One of the major issues is the high GSM voice traffic that will remain in the GSM network. How to cope the same traffic with significantly less bandwidth for GSM? Orthogonal Sub-Channel (OSC) is a new method to increase voice capacity in the GSM system. OSC intends not only increase the GSM voice capacity but enables very efficient usage of hardware and spectrum resources. In this paper a detailed analysis on OSC performance is made based on system level simulations. Aim is to provide results that show how OSC can be used for refarming of the 900 MHz band into HSPA or LTE. Simulations are carried in the GSM network evaluating capacity for different bandwidths and site configurations. Released frequency spectrum can be used for HSPA or LTE to provide good coverage for rural area mobile broadband. Results show that OSC is an efficient method to release resources for the new systems.

GSM voice evolution using orthogonal subchannels

The explosive growth of mobile communications, and the overly crowded and expensive spectrum have pushed both system engineers and operators to make their systems as spectrally efficient as possible in order to accommodate the increasing traffic demand. This article is a tutorial introduction to the orthogonal subchannel (OSC) technique. OSC was adopted to improve the capacity of the GSM/EDGE radio access network GERAN, and it is a new concept in which two users can simultaneously share the same GSM radio resource (time slot and frequency) in both the downlink and in uplink directions. Potentially, OSC could not only provide increased network capacity, but also reduce network-associated costs through more efficient usage of hardware and spectrum resources. In addition, this article presents some challenges related to this method, as well as solutions and their respective impact. The results provided herein may contribute to guidelines for network dimensioning and optimization, as well as list potential enhancements to the OSC radio resource management mechanisms needed to further exploit the benefits of OSC. Currently, in real OSC network deployments a capacity gain of 50 percent has been achieved at the cell level. As an indication of the importance of OSC, GSMA awarded it (called Quad Rate) the Best Technology Breakthrough award at Mobile World Congress 2012 [1].

Improving the Speech Quality with OSC: Double Full-Rate Performance Assessment

Speech quality is an important measurement for performance evaluation in a wireless mobile communication system since voice is still the most used service on it. The speech quality evaluation in GSM system employing narrowband and wideband AMR codecs with Orthogonal Sub Channel (OSC) technique is addressed in this paper. OSC is a feature proposed in 3GPP GERAN to double circuit switched capacity in GSM networks. It has introduced two new channel modes, namely Double Full-rate (DFR), and Double Half-rate (DHR), which have doubled capacity when compared to legacy AMR channel modes.Many of the efforts in standardization are concentrated on studying hardware improvements lead by AMR DHR usage over AMR HR channel mode. Although AMR DFR has not brought hardware efficiency improvements over legacy channel modes, in this paper it is shown that speech quality is improved over AMR HR with the same blocking capacity; therefore it is a good solution for some interference limited networks. Furthermore, we also investigate the speech quality of wideband AMR DFR codecs which provides a substantial improvement when compared with narrowband AMR.

Audio beacon providing location-aware content for low-end mobile devices

Location Based Services can generate variety of new commercial applications and create new streams of revenue. However, there is currently no simple indoor positioning method for low-end devices which have no Wi-Fi or GPS capability. This paper presents a novel and simple audio-based localization system to provide location-aware content for low-end mobile devices, i.e., a location solution that uses acoustic waves to determine the position of the users and/or the content associated to it. In this solution, Audio Beacons send tones which are read by mobile devices for localization. These tones are generated in a barely audible frequency range, that can be hardly perceived by humans. The tones of the Audio Beacons are associated with an identification code that is linked to a location specific content. The solution requires no special hardware at the mobile device side, and a simple localization infrastructure, which can be deployed with low cost loudspeakers. Real experiments demonstrate the effectiveness of the proposed system, and show that the codes can be identified with distances as large as 20 m from the Audio Beacon.