LTE in unlicensed spectrum: are we there yet?
03 Oct 2016-pp 135-148
TL;DR: In this article, the authors explore the potential and impact of unlicensed LTE on WiFi in unlicensed spectrum and propose Ultron, a solution that integrates WiFi's carrier sensing and notification mechanisms into LTE, without any modifications to the LTE PHY standard.
Abstract: In this work, we explore the potential and impact of unlicensed LTE on WiFi in unlicensed spectrum. Our experiments demonstrate that the large asymmetry in the channel access methodologies employed by WiFi and LTE (carrier sensing/notification in WiFi, energy sensing alone in LTE-U), can result LTE-U completely blocking WiFi transmissions, and causing significant degradation to either technologies from collisions. We address this critical sensing asymmetry with Ultron, a LTE-WiFi co-existence solution that integrates WiFi's carrier sensing and notification mechanisms into LTE, without any modifications to the LTE PHY standard. Ultron operates at the LTE base station and consists of two key components: (a) WiFi embedding that embeds appropriate data into the LTE-subframes through an intelligent reverse-engineering of the LTE PHY, so as to realize a WiFi PLCP preamble-header transmission over the air directly using the LTE PHY; and (b) scalable WiFi sensing that employs a single WiFi interface and maximizes its carrier sensing benefits to all the unlicensed channels operating at the LTE node. Our evaluations demonstrate that Ultron can increase the WiFi and LTE throughput by 5x and 6x respectively, resulting from a sharp reduction in LTE-WiFi interference.
Citations
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TL;DR: The comprehensive evaluation reveals that WEBee can achieve a more than 99% reliable parallel CTC between WiFi and ZigBee with 126 Kbps in noisy environments, a throughput about 16,000x faster than current state-of-the-art CTCs.
Abstract: Recent advances in Cross-Technology Communication (CTC) have improved efficient coexistence and cooperation among heterogeneous wireless devices (e.g., WiFi, ZigBee, and Bluetooth) operating in the same ISM band. However, until now the effectiveness of existing CTCs, which rely on packet-level modulation, is limited due to their low throughput (e.g., tens of bps). Our work, named WEBee, opens a promising direction for high-throughput CTC via physical-level emulation. WEBee uses a high-speed wireless radio (e.g., WiFi OFDM) to emulate the desired signals of a low-speed radio (e.g., ZigBee). Our unique emulation technique manipulates only the payload of WiFi packets, requiring neither hardware nor firmware changes in commodity technologies -- a feature allowing zero-cost fast deployment on existing WiFi infrastructure. We designed and implemented WEBee with commodity devices (Atheros AR2425 WiFi card and MicaZ CC2420) and the USRP-N210 platform (for PHY layer evaluation). Our comprehensive evaluation reveals that WEBee can achieve a more than 99% reliable parallel CTC between WiFi and ZigBee with 126 Kbps in noisy environments, a throughput about 16,000x faster than current state-of-the-art CTCs.
138 citations
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TL;DR: This paper provides a comprehensive overview of the various coexistence scenarios in the 5 GHz bands, and discusses coexistence issues between a number of important wireless technologies—viz.
Abstract: As the 2.4 GHz spectrum band has become significantly congested, there is growing interest from the Wi-Fi proponents, cellular operators, and other stakeholders to use the spectrum in the 5 GHz bands. The 5 GHz bands have emerged as the most coveted bands for launching new wireless applications and services, because of their relatively favorable propagation characteristics and the relative abundance of spectrum therein. To meet the exploding demand for more unlicensed spectrum, regulators across the world such as the United States Federal Communications Commission and the European Electronic Communications Committee have recently started considerations for opening up additional spectrum in the 5 GHz bands for use by unlicensed devices. Moreover, to boost cellular network capacity, wireless service providers are considering the deployment of unlicensed long term evaluation (LTE) in the 5 GHz bands. This and other emerging wireless technologies and applications have resulted in likely deployment scenarios where multiple licensed and unlicensed networks operate in overlapping spectrum. This paper provides a comprehensive overview of the various coexistence scenarios in the 5 GHz bands. In this paper, we discuss coexistence issues between a number of important wireless technologies—viz., LTE and Wi-Fi, radar and Wi-Fi, dedicated short range communication (DSRC) and Wi-Fi, and coexistence among various 802.11 protocols operating in the 5 GHz bands. Additionally, we identify and provide brief discussions on an impending coexistence issue—one between Cellular V2X and DSRC/Wi-Fi. We summarize relevant standardization initiatives, explain existing coexistence solutions, and discuss open research problems.
66 citations
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TL;DR: This work proposes a new direction by emulating legitimate ZigBee frames using a Bluetooth radio, achieving dual-standard compliance and transparency by selecting only the payload of Bluetooth frames, requiring neither hardware nor firmware changes at the Bluetooth senders and ZigBee receivers.
Abstract: Cross-Technology Communication is a promising solution proposed recently to the coexistence problem of heterogeneous wireless technologies in the ISM bands. The existing works use only the coarse-grained packet-level information for cross-technology modulation, suffering from a low throughput (e.g., 10bps). Our approach, called BlueBee, proposes a new direction by emulating legitimate ZigBee frames using a Bluetooth radio. Uniquely, BlueBee achieves dual-standard compliance and transparency by selecting only the payload of Bluetooth frames, requiring neither hardware nor firmware changes at the Bluetooth senders and ZigBee receivers. Our implementation on both USRP and commodity devices shows that BlueBee can achieve a more than 99% accuracy and a throughput 10,000x faster than the state-of-the-art CTC reported so far.
57 citations
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TL;DR: This work tackles the unlicensed resource allocation problem by modeling it as a student-project allocation matching game and investigates the carrier aggregation of licensed and unlicensed spectrum by deploying micro-cell base stations to provide cellular users a more reliable and efficient transmission.
Abstract: LTE, as the advanced mobile telecommunication technology, is serving heavy mobile broadband traffic nowadays. Motivated by the potential boost in performance of LTE utilizing the unlicensed spectrum, significant efforts have been devoted into the commonly referred LTE-Unlicensed technique. In this work, we investigate the carrier aggregation of licensed and unlicensed spectrum by deploying micro-cell base stations, which have access to the unlicensed spectrum, to provide cellular users a more reliable and efficient transmission. We tackle the unlicensed resource allocation problem by modeling it as a student-project allocation matching game. In addition, a postmatching procedure of resource re- allocation is introduced to guarantee unlicensed users' quality of service (QoS), as well as the system-wide stability. The simulation evaluation shows the effectiveness and efficiency of our proposed matching-based approach.
46 citations
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TL;DR: ECC is presented that uniquely enables explicit channel coordination among heterogeneities via cross-technology communication (CTC) introduced in the latest studies, while maintaining full compatibility to commodity devices.
Abstract: Under significant coexistence in the ISM band, the impact of cross-technology interference (CTI) has become a major threat to low-power IoT. This paper presents ECC that uniquely enables explicit channel coordination among heterogeneities via cross-technology communication (CTC) introduced in the latest studies, while maintaining full compatibility to commodity devices. Unlike any implicit coordination designs adopting statistical models to probabilistically predict white spaces, ECC generates the white space using WiFi CTS, which is then explicitly notified to ZigBee through CTC for immediate use. Technical highlight of ECC lies in ensuring ZigBee communication under CTI, without disrupting WiFi operation. This is effectively achieved by the dynamic adjustment of CTS duration with respect to traffic amount and spectrum availability, which essentially enables ECC to be generally applied to various scenarios without prior knowledge. Lastly, ECC significantly reduces delay and energy in low duty cycled ZigBee, by waking them up upon channel availability (via CTC). We evaluate ECC on commercial platforms: Atheros AR2425 WiFi card and TelosB motes. Experiment results show that ECC achieves 1.8x ZigBee packet reception ratio, and cuts down delay and energy by 98.6% and 51% under the low duty cycle.
40 citations
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References
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TL;DR: In this paper, a brief review of continuous and non-continuous CA techniques is given, followed by two data aggregation schemes in physical and medium access control layers, and possible technical solutions for the asymmetric CA problem, control signaling design, handover control and guard band setting are reviewed.
Abstract: In order to achieve up to 1 Gb/s peak data rate in future IMT-Advanced mobile systems, carrier aggregation technology is introduced by the 3GPP to support very-high-data-rate transmissions over wide frequency bandwidths (e.g., up to 100 MHz) in its new LTE-Advanced standards. This article first gives a brief review of continuous and non-continuous CA techniques, followed by two data aggregation schemes in physical and medium access control layers. Some technical challenges for implementing CA technique in LTE-Advanced systems, with the requirements of backward compatibility to LTE systems, are highlighted and discussed. Possible technical solutions for the asymmetric CA problem, control signaling design, handover control, and guard band setting are reviewed. Simulation results show Doppler frequency shift has only limited impact on data transmission performance over wide frequency bands in a high-speed mobile environment when the component carriers are time synchronized. The frequency aliasing will generate much more interference between adjacent component carriers and therefore greatly degrades the bit error rate performance of downlink data transmissions.
438 citations
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TL;DR: This work first examines the interference patterns between ZigBee and WiFi networks at the bit-level granularity, then designs BuzzBuzz to mitigate WiFi interference through header and payload redundancy, which improves the ZigBee network delivery rate and reduces ZigBee retransmissions.
Abstract: Frequency overlap across wireless networks with different radio technologies can cause severe interference and reduce communication reliability. The circumstances are particularly unfavorable for ZigBee networks that share the 2.4 GHz ISM band with WiFi senders capable of 10 to 100 times higher transmission power. Our work first examines the interference patterns between ZigBee and WiFi networks at the bit-level granularity. Under certain conditions, ZigBee activities can trigger a nearby WiFi transmitter to back off, in which case the header is often the only part of the Zig-Bee packet being corrupted. We call this the symmetric interference regions, in comparison to the asymmetric regions where the ZigBee signal is too weak to be detected by WiFi senders, but WiFi activity can uniformly corrupt any bit in a ZigBee packet. With these observations, we design BuzzBuzz to mitigate WiFi interference through header and payload redundancy. Multi-Headers provides header redundancy giving ZigBee nodes multiple opportunities to detect incoming packets. Then, TinyRS, a full-featured Reed Solomon library for resource-constrained devices, helps decoding polluted packet payload. On a medium-sized testbed, BuzzBuzz improves the ZigBee network delivery rate by 70%. Furthermore, BuzzBuzz reduces ZigBee retransmissions by a factor of three, which increases the WiFi throughput by 10%.
382 citations
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28 Nov 1994
TL;DR: It is shown that the associated iterative decoder can be formulated in a simpler fashion by passing information from one decoder to the next using log-likelihood ratios as opposed to channel values that need to be normalized for stable decoding.
Abstract: A coding scheme (turbo codes) was proposed, that achieves almost reliable data communication at signal-to-noise ratios very close to the Shannon-limit. We show that the associated iterative decoder can be formulated in a simpler fashion by passing information from one decoder to the next using log-likelihood ratios as opposed to channel values that need to be normalized. Also no heuristically determined correction parameters are necessary for stable decoding. In addition, we can reduce the average number of iterations needed for the same BER performance by determining when further iterations achieve no more benefit. Furthermore, it seems that the trellis-termination problem appears non-trivial and we give a pragmatic suboptimal solution. We investigate different block sizes and also a hybrid scheme that performs extremely well with less computations. A drawback of the codes has been discovered: the BER curves show a flattening at higher signal-to-noise ratios, this is due to the small minimum distance of the whole code. By analyzing the interleaver used in the encoder we can calculate approximations to the BER at high SNRs. Finally, by careful interleaver manipulation the minimum distance of the code can be increased and the error-coefficient for the remaining small distance events can be further reduced. Furthermore, we have investigated the influence of the interleaver length on the SNR needed to achieve a certain BER. Simulations confirm both the analytical approximation to the BER as well as the method for interleaver design which yields a marked improvement at higher SNR.
335 citations
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TL;DR: This paper considers two of the most prominent wireless technologies available today, namely Long Term Evolution (LTE), and WiFi, and addresses some problems that arise from their coexistence in the same band, and proposes a simple coexistence scheme that reuses the concept of almost blank subframes in LTE.
Abstract: 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.
310 citations
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TL;DR: This work presents OpenAirInterface (OAI) as a suitably flexible platform for experimentation modes from real-world experimentation to controlled and scalable evaluations while at the same time retaining backward compatibility with current generation systems.
Abstract: Driven by the need to cope with exponentially growing mobile data traffic and to support new traffic types from massive numbers of machine-type devices, academia and industry are thinking beyond the current generation of mobile cellular networks to chalk a path towards fifth generation (5G) mobile networks. Several new approaches and technologies are being considered as potential elements making up such a future mobile network, including cloud RANs, application of SDN principles, exploiting new and unused portions of spectrum, use of massive MIMO and full-duplex communications. Research on these technologies requires realistic and flexible experimentation platforms that offer a wide range of experimentation modes from real-world experimentation to controlled and scalable evaluations while at the same time retaining backward compatibility with current generation systems. Towards this end, we present OpenAirInterface (OAI) as a suitably flexible platform. In addition, we discuss the use of OAI in the context of several widely mentioned 5G research directions.
302 citations
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