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Femtocell Introduction

Femtocell Introduction. Femtocell Introduction Femtocell Networks: A Survey Current Business status. Outline. Femtocell Introduction Femtocell Networks Femtocell Networks: A Survey Introduction Technical Aspects of Femtocell Business Aspects of Femtocell Technical Challenges

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Femtocell Introduction

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  1. FemtocellIntroduction Femtocell Introduction FemtocellNetworks: A Survey Current Business status

  2. Outline • Femtocell Introduction • Femtocell Networks • Femtocell Networks: A Survey • Introduction • Technical Aspects of Femtocell • Business Aspects of Femtocell • Technical Challenges • Research Directions • Conclusion • Current Business status

  3. FemtocellNetworks (1/2) • The surest way to increase the system capacityof a wireless link is by getting the transmitterand receiver closer to each other • Higher-quality links andmore spatial reuse • The recent concept offemtocells • Also called home base-stations

  4. FemtocellNetworks(2/2) • A small cellular base station (for home or small business use) • Connects to the service provider’s network via broadband (DSL, cable) • Improvements to both coverage and capacity, especially indoors; reduces operator’s capital expenditure • Features: • Standard mobile technology(GSM, CDMA, WCDMA…) • Licensed spectrum • Better indoor coverage • Internet-based transmission • Low cost

  5. Femtocell Networks: A Survey Vikram Chandrasekhar and Jeffrey G. Andrews, The University of Texas at Austin Alan Gatherer, Texas Instruments IEEE Communication Magazine, September 2008

  6. Introduction(1/4) • The demand for higher data rates in wireless networkshas triggered the design of cellular standards • WiMAX、3GPP’sHSPA、LTE、3GPP2’s EVDO and UMB • In parallel, Wi-Fi mesh networks are also beingdeveloped to provide nomadic high-rate data services[1] • Not be able to support the same level of mobility and coverage as the cellular standard [1] Tropos Networks, “Picocell Mesh: Bringing Low-Cost Coverage, Capacity and Symmetry to Mobile WiMAX,” White Paper

  7. Introduction (2/4) • Martin Cooper of Arraycomm: “The wireless capacity has doubled every 30 months over the last 104 years.” • 25× improvement from wider spectrum • 5× improvement by dividing the spectrum into smaller slices • 5× improvement by designing better modulation schemes • 1600× gain through reduced cell sizes and transmit distance • The enormous gains arise from higher area spectral efficiency[2] [2] M.-S Alouini and A. J. Goldsmith, “Area Spectral Efficiency of Cellular Mobile Radio Systems,” IEEE Trans. Vehic. Tech., vol. 48, no. 4, July 1999, pp. 1047–66.

  8. Introduction (3/4) • The main problem in this continued microi-zationof cellular networks is that the networkinfrastructure for doing so is expensive • Studies on wireless usage show that more than 50 percent of all voice calls and more than 70 percent of data traffic originate indoors[5] • For indoor devices, attenuation losses will make high signal quality and hence high data rates very difficult to achieve [5] Presentations by ABI Research, Picochip, Airvana, IP.access, Gartner, Telefonica Espana, 2nd Int’l. Conf. Home Access Points and Femtocells; http://www.avrenevents.com/dallasfemto2007/purchase_presentations.htm

  9. Introduction (4/4) • The development of femtocellis introduced • Short range, low cost, low power base station • Installed by the consumer for better indoor voice and data reception • Promise fixed mobile convergence with existing handsets • Key advantage: very little upfront cost to the service provider

  10. Introduction－key arguments (1/2) • Better coverage and capacity • Due toshort transmit-receive distance • Lower transmit power • Prolong handsetbattery life • Achieve a higherSINR • Due to interference reduction • More users can be packedinto a given area in the same region of spectrum (spectral efficiency increase[2]) • Improved macrocell reliability • Because the traffic originating indoors can be absorbed into the femtocell networks over the IP backbone [2] M.-S Alouini and A. J. Goldsmith, “Area Spectral Efficiency of Cellular Mobile Radio Systems,” IEEE Trans. Vehic. Tech., vol. 48, no. 4, July 1999, pp. 1047–66.

  11. Introduction－key arguments (2/2) • Cost benefits • Femtocell reduces the operating and capital expenditure costs for operators • Reduced subscriber turnover • The enhanced home coverage provided by femtocellswill reduce motivation for home users toswitch carriers

  12. Technical Aspects of Femtocell • Benefits in network-wide spatial reuse can be obtained by exploiting diversity, and employing interference cancellation, interference suppression, and interference avoidancetechniques • The capacity benefits of femtocells are attributed to: • Reduced distancebetween femtocell and user(high signal strength) • Lowered transmit power(mitigate interference) • Devote a larger portion of resources to each subscriber

  13. Business Aspects of Femtocell(1/4) • Femtocellsoffer savings in site lease, backhaul, and electricity costs for the operator • To compete with ubiquitous Wi-Fi • The features femtocells have to provide are more sophisticated • The nascent femto vendors are facing cost targets set by the mature high-volume Wi-Fi market • Consequently, cost issues are in most cases the central factor driving the selection of solutions to each technical challenge

  14. Business Aspects of Femtocell(2/4) • Predictive return on investment from femtocelldeployments[5] (partial) [5] Presentations by ABI Research, Picochip, Airvana, IP.access, Gartner, Telefonica Espana, 2nd Int’l. Conf. Home Access Points and Femtocells; http://www.avrenevents.com/dallasfemto2007/purchase_presentations.htm

  15. Business Aspects of Femtocell(3/4) • Current standardization and deployments • Requirements standardization across customers is important to accomplish a low-cost femtocell solution • A collaborative organization called the Femto-Forum was formed in 2007 • Objective: develop open standards for product interoperability

  16. Business Aspects of Femtocell(4/4) • The current state of femtocell • deployments

  17. Technical Challenges • Broadband femtocells • Resource allocation,timing/synchronization, and backhaul • Voice femtocells • Interference managementin femtocells, allowing access to femtocells,handoffs, mobility, and providing Emergency-911 services • Network infrastructure • Securely bridgingthe femtocell with the operator networkover IP

  18. Technical Challenges－Broadband Femtocells(1/4) • Two main problems operators face: mitigate RF interference, efficiently allocating spectrum • The RF interference will arise from: • Macrocell-to-femtocellinterference (near-far effect) • Femtocell-to-femtocell interference • Femtocell-to-macrocellinterference (near-far effect)

  19. Technical Challenges－Broadband Femtocells(2/4) • Challenge 1: How Will a Femtocell Adaptto Its Surrounding Environment and AllocateSpectrum in the Presence of Intra-andCross-Tier Interference? • Since femtocells will be placedby end consumers, the ad hoc locations of femtocellswill render centralized frequency planningdifficult • Decentralized spectrum allocationbetween macrocell and femtocell users is anopen research problem • Should macrocell and femtocell users be orthogonal through bandwidth splitting? As 3GPP LTE and WiMax • Alternatively, with shared bandwidth • Which of these two schemes is “better” in various configurations?

  20. Technical Challenges－Broadband Femtocells(3/4) • Challenge 2: How Will FemtocellsProvideTiming and Synchronization? • Synchronization • Align received signals to minimize multi-access interference • Macrocell users can handoff to a femtocell or vice versa • Timing • Immune to packet jitter • Network solutions such as the IEEE-1588Precision Timing Protocol over IP and self-adaptive timing recovery protocols(e.g. G.8261) are promising • Equip femtocell with GPS(synchronized with the macrocell) • High-precision oven-controlled crystal oscillators may be used

  21. Technical Challenges－Broadband Femtocells(4/4) • Challenge 3: How Will Backhaul Provide Acceptable QoS? • IP backhaul needs QoS for delay-sensitive traffic and sufficient capacity • Lack of net neutrality poses a serious concern • Another issue: when users employed Wi-Fi, femtocells experienced difficulty transferring data and even low-bandwidth services like voice[5] [5] Presentations by ABI Research, Picochip, Airvana, IP.access, Gartner, Telefonica Espana, 2nd Int’l. Conf. Home Access Points and Femtocells; http://www.avrenevents.com/dallasfemto2007/purchase_presentations.htm

  22. Technical Challenges－Voice Femtocells(1/6) • Two choices: • Allocate different frequency bands to macrocell and femtocell users • Eliminate cross-tier interference • Serve both macrocell and femtocell users in the same region of bandwidth (preferable) • Maximize area spectral efficiency

  23. Technical Challenges－Voice Femtocells(2/6) • Challenge 4: How Will Femtocells Handle Cross-Tier Interference? • CDMA networks (without femtocells) employ fast power control to compensate for path loss, shadowing, and fading, and to provide uniform coverage • When femtocells are added, power control creates dead zones, leading to non-uniform coverage

  24. Technical Challenges－Voice Femtocells(3/6) • Challenge 5: Should Femtocells Provide Open or Closed Access? • Closed access femtocell: a fixed set of subscribed home users • Open access femtocell: provide service to macrocell users if they pass nearby • Radio interference is managed by allowing strong macrocell interferers to communicate with nearby femtocells • Higher numbers of users communicating with each femtocell • Raises privacy concerns • Needs to avoid “starving” the paying home user • Operators are looking at hybrid models

  25. Technical Challenges－Voice Femtocells(4/6) • Challenge 6: How Will Handoff Be Performed in Open Access? • Current 2G, 3G handoff protocol does not scale to the large numbers of femtocells that neighbor the macrocell • This motivates 4G handover procedures to consider femtocells • In open access, channel fluctuations may cause a passing macrocell user to perform multiple handovers • Developing low-complexity algorithms to predict the dwell time before handing off is an open research area

  26. Technical Challenges－Voice Femtocells(5/6) • Challenge 7: Can Subscribers Carry Their Femtocells for Use Outside the Home Area? • Femtocell networks will operate in licensed spectrum • Femtocell mobility can cause problems when a subscriber with operator A carries their femtocell to another location where the only service provider is rival operator B • Should the femtocell be allowed to transmit on operator B’s spectrum? • GPS inside femtocells for location tracking and locking • Inter-operator agreements

  27. Technical Challenges－Voice Femtocells(6/6) • Challenge 8: How Will Femtocells Provide Location Tracking for Emergency-911, and Should They Service Nearby Macrocell Users with Poor Coverage? • Governmentmandated Emergency-911 services require operatorsto provision femtocells for transmittinglocation information during emergency calls • GPS inside femtocells • Gathering information from the macrocell • Whether afemtocell should service macrocell users withpoor outdoor coverage for making emergencycalls if they are located within its radio range

  28. Technical Challenges－Network Infrastructure • The operator willneed to provide a secure and scalable interfaceover the Internet at a reasonable cost • IMS/SIP and UMA-based interfaces appear to be the architectures of choice

  29. Research Directions－Interference Management (1/3) • Successive interference cancellation appears promising initially, but cancellation errors quickly degrade its usefulness [12] • Interference avoidance approach is more likely to work well in geography-dependent femtocell networks • The low cost requirement is likely to influence the design of low-complexity receivers and transmission schemes • Example: In CDMA femtocell networks with universal frequency reuse, interference avoidance through time hopping and directional antennas provides a 7× improvement in system capacity [9] [9] V. Chandrasekhar and J. Andrews, “Uplink Capacity and Interference Avoidance in Two-Tier Femtocell Networks,” to appear, IEEE Trans. Wireless Commun., http://arxiv.org/abs/cs.NI/0702132 [12] S. Weber et al., “Transmission Capacity of Ad Hoc Networks with Successive Interference Cancellation,” IEEE Trans. Info. Theory, vol. 53, no. 8, Aug. 2007, pp. 2799–2814.

  30. Research Directions－Interference Management (2/3) • Frequency and time hopping • Frequency hopping－GSM, OFDMA • Time hopping－CDMA • Directional antennas • Femtocellscan offerinterference avoidanceby restricting radio interference within anantenna sector • Reasonable unit costand easy end-user deployment are the key challenges • Adaptive power control • Commercial femtocells such as Sprint’sAiravefemtocell tackle cross-tier interferenceusing an “automatic adaptation” protocol thatadjusts the femtocell transmit power

  31. Research Directions－Interference Management (3/3) • Reductions in the outageprobability for a femtocell user

  32. Research Directions－MIMO Femtocells • Multiple antennas at the transmitter and/or the receiver (multiple input multiple output, MIMO) exploit the spatial diversity of the wireless channel • MIMO spatial link adaptation will enable a femtocell to switch between providing high data rates and robust transmission • Link adaptive mode switching for femtocells between diversity and spatial multiplexing [15] • Analyzing the effect of channel state information errors induced by co-channel interference on MIMO femtocell performance • The complexity limitations of MIMO femtocell receivers • Channel models for MIMO femtocells [15] A. Forenzaet al, “Adaptive MIMO Transmission for Exploiting the Capacity of Spatially Correlated Channels,” IEEE Trans. Vehic. Tech., vol. 56, no. 2, Mar. 2007, pp. 619–30.

  33. Conclusions • Femtocells have the potential to provide high quality network access to indoor users at low cost, while simultaneously reducing the burden on the whole system • From a technical standpoint • Provide a low-cost solution while mitigating RF interference • Provide QoS over the IP backhaul • Maintain scalability. • From a business perspective • Generate long-term revenue growth • Overcome initial end-user subsidies

  34. Current Business status

  35. Current Business status • NCC已於2010年7月修改相關規定，預計逐漸開放對Femtocell之管制，11月份宣布開放電信公司申請微型蜂巢式基地台（Femtocell）設立，目前仍持續規畫管理機制 • 國內三大電信業者階有引進Femtocell的計畫，預計2011年即有相關服務在台灣問世 • 基地台電磁波疑慮，Femtocell被視為解決方法 • Backhaul線路多是由中華電信所掌握，須進行管控 • Femtocell單價仍過高

  36. Comment • Femtocell服務在國內仍在實驗階段，並且業者預估推出初期會以免費提供的方式來促使其普及化，商業模式未確立 • FMC趨勢 • Picocell基地台的更微小版

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