Presented at: Wireless @ Virginia Tech 2012 Symposium & Summer School on Wireless Communications

1. Wireless Antenna Distribution and LTE HetNets Kenneth R. Baker, PhD University of Colorado at Boulder Interdisciplinary Telecommunications Program Presented at: Wireless @ Virginia Tech 2012 Symposium & Summer School on Wireless Communications May 31, 2012 CU-Boulder

2. Thesis • Indoor Distribution as path for LTE HetNets • An introduction to Indoor and Outdoor Distributed Antenna Systems. • State of the art today • Describe how these systems form a migration path to hierarchical cell structures planned for 4G/LTE cellular networks. • A review of LTE HCS related standards

3. DAS Systems • A Distributed Antenna System (DAS)is a network of spatially separated antenna nodes connected to a common source via a transport medium that provides wireless service within a geographic area or structure (the DAS Forum) • Provide better coverage in environments like: • Outdoor: Highways, Downtowns, Subways, Tunnels, University Campuses • Indoor: Corporate Offices, Stadiums, Shopping Complexes, Airports, Convention Centers, Hospitals, Hotels etc. • 60% of voice traffic and 90% of data traffic from indoors. (ABI Research) • DAS systems with overall market value of $5.5 billion comprises 96% of indoor systems (ABI Research) • DAS Concept was introduced by Salehetal in 1987 as a solution for better indoor coverage using leaky coax cable to simulcast the RF signal. (A.A.M. Saleh, A.J. Rustako, and R.S. Roman, “Distributed antennas for indoor radio communications,” IEEE Trans. Commn., vol. 35, pp. 1245–1251, Dec. 1987)

4. Why DAS is needed? • Indoor: • Poor coverage in basements, higher floors (above 25 floors), elevators, inner rooms (due to wall attenuations). • Large reflections from walls, roofs, tinted glass windows. • Outdoor: • Other buildings block the coverage in dense areas like downtowns. • To provide coverage to long Highways/tunnels.

5. DAS Components • Donor Unit • BSS, External Antennas • Interconnection Network • Active & Passive Head Ends and Distribution Units • Coax/Fiber/Repeaters • Star or Cascade Connections • Remote Unit • RAUs & multi/wide band antennas Image source: http://www.accu-tech.com/das/

6. Example Airport DAS

7. Example: Outdoor DAS Outdoor DAS serving a University Campus • Neutral Host System • Two Cellular Operators share the transport infrastructure • They also share antennas

9. Interconnection Media • Coax • Cables: 50 ohm (RG174, RG58, LMR240, Standard Heliax etc) • Connectors: SMA, BNC, TNC, N, 7/16 etc. • Other Components: Couplers, Splitters, Bi-Directional Amplifiers • Optic Fiber • Cables: Single Mode, Multimode, Step Index, Graded Index • Connectors: FC,SC, ST, LC or MTRJ • Other Components: Splicers, Splitters, Attenuators, WDM multiplexers, Laser Diodes • Over the Air (RF) • Repeaters or Bi-Directional Amplifiers (BDA), • Antennas: Isotropic, Dipole, Yagi, Panel, Leaky Coax • Hybrid Fiber Cable (HFC): CATV Networks

10. Benefits of DAS(Chow, et al. 1994) d RADIO RADIO Single Antenna System DAS • Consider single slope propagation model: • PT = Transmitted Power • PR = Received Power • C = Path loss at reference distance • γ = Path loss exponent • d = radius of the macro-cell • A = area of the macro-cell = πd2

11. Benefits of DAS (contd.) • Improvement in Coverage: • Area of coverage of single antenna is given by: • Assuming transmitted power is equally divided between N antennas of the DAS, area covered by each individual antenna is given by: = = …. = • Therefore, total area: • Thus, coverage is increased by a factor of:

12. Benefits of DAS (contd.) Reduction in Transmit Power (Forward Link): • For single antenna system: • Assuming transmitted power is equally divided between N antennas of the DAS: • Therefore, total area: • Thus, transmitted power is reduced by a factor of: • On Reverse Link, assuming that path loss is reciprocal, mobiles have to transmit only 1/N of the base station to communicate to a single DAS antenna. Thus power is reduced by a factor of:

13. Q. What’s the vision? A. Small Cells • Heterogeneous Networks • a.k.a. Multi-Tier Networks • Better Coverage, More Capacity • Incorporated in 3GPP LTE Standards • Includes New Network Elements • Includes Interference and Mobility Management Techniques

14. Indoor Distribution Today • Outdoor DAS • Indoor DAS • Neutral Host vs. Single Carrier • Passive vs. Active • The first steps to HetNets … • WIFI Off-load in Stadiums • Femtocells (Home Node-B’s)

15. Indoor Distribution Today • Outdoor DAS • Indoor DAS • Neutral Host vs. Single Carrier • Passive vs. Active • The first steps to HetNets … • WIFI Off-load in Stadiums • Femtocells (Home Node-B’s)

16. Sports Stadium as a Specific Example

17. Traffic Statistics from a Sports Stadium Stadium Traffic Facts (with 60-90K Fans) SMS: 200-600K Data Calls: 300K-1M • Example Traffic profiling look at data services usage during a game Voice calls: 30-60K Data Volume: 4-9 GB Data services used during events Numbers are cumulative over the duration of a game • Data services on Smartphones are driving the traffic today • Background traffic from applications like Twitter, Email, etc. is a significant contributor

18. Stadium Traffic Will Continue to Increase It is expected that mobile video will account for the majority of data growth

19. Stadium Antennas

20. Bowl Design and Some Statistics

21. Super Bowl Data Usage (One of three operators)

22. Offload will get easier: “Hot Spot 2.0” • Three components: • 1. IEEE 802.11u • Pre-association • published on February 25, 2011 • 2. Wi-Fi Protected Access 2 (WPA2)-Enterprise • 3. Extensible Authentication Protocol (EAP) • EAP-SIM (GSM) • EAP-AKA (UMTS) • Mobility Services Advertisement Protocol (MSAP) • transported via IEEE 802.11u Generic Advertisement Service (GAS) • See also: IEEE 802.21 • enables seamless handover between networks

23. Indoor Distribution Today • Outdoor DAS • Indoor DAS • Neutral Host vs. Single Carrier • Passive vs. Active • The first steps to HetNets … • WIFI Off-load in Stadiums • Femtocells (Home Node-B’s)

24. Femtocell Overview • Femtocell • Ethernet Backhaul • In-home base station • Enterprise Base Station • Minimal Customer Requirements: • Any wireless handset or data device • A broadband connection and router 3 Satellites GPS Core Network ISP xDSL/Cable Modem Femtocell

25. Example: Dual-Mode EvDOproduct Bottom Line: It’s a Plug and Play Cellular Base Station

26. Femtocell Interference • Femtocells as two tier network • Open: Any cell phone can attach • Closed: Only specified cell phones can attach Downlink Femtocell Interference

27. Femtocell Summary • 3G Femtocells Today: • Can hand out to the macro layer • Cannot hand-in from the macro layer • 4G (LTE) Femtocells: • Will enable both hand-in and hand-out between the femto layer and the macro • Femto to Femto handover should also be possible.

28. Looking ahead to LTE • Carrier Aggregation • Higher Order Modulation • 4G • MIMO Fig. after Nokia Siemens IEEE 802.16

29. Why LTE?

30. LTE, LTE-A, and 4G

31. LTE Network • MME: Mobility Management Entity • Manages mobility, UE Identity and Security Parameters • S-GW: Serving Gateway • Evolved Packet Core Interface to E-UTRAN • P-GW: Packet Gateway • Evolved Packet Core Interface to Packet Data Network • eNB: Evolved Node B • Performs all Radio Interface Related Functions • Interfaces • X2: between eNBs • S1: between eNB and MME/S-GW

32. Network Elements *S1-C: Stream Control Transmission Protocol / IP (SCTP/IP) stack *S1_U: GSRP Tunneling Protocol/UDP5/IP stack

33. Pico-Cells … Heterogeneous Networks • Increasing data rate requirements • Need better SNR • Increasing capacity requirements • Need more cells • Ergo: Put cells where the users are • Trend is to complement macro network with picocells • Possible with LTE Rel.8 • Enhancements with Rel. 11 • Picocells • S1 interface for backhaul, not ethernet • Picocells exist today in 3G networks

34. Relay Nodes • Donor eNB uses LTE as backhaul • Either in-band or out-of-band Backhaul Link (Un) Relay Cell (Uu) Relay Node Access Link (Uu) (Donor) eNB Macro UE Relay UE Donor Cell

35. Example Application: Public Safety See: Order and Fourth Further Notice of Proposed Rule Making, FCC11-6, “In the Matter of Service Rules for the 698-746, 747-762 and 777-792 MHz Bands; Implementing a Nationwide, Broadband, Interoperable Public Safety Network in the 700 MHz Band; Amendment of Part 90 of the Commission’s Rules,” January 25, 2011

36. Outage Probability as a Function of No. of Relays Ref. Tin-Ei Wang, unpublished work

37. LTE Heterogeneous Networks • Network Elements • Relays • Pico Cells • Femtocells (Home Node B) • Need tight coordination for Handover and Interference management • Negative Impact at small cell edges • Small cells need handover management

38. LTE Heterogeneous Networks • LTE Network Solutions: • Soft Cell • Enhanced Inter Cell Interference Coordination (eICIC) • CoMP • Self-Organizing Networks (SON) • Dynamic Load Balancing • Carrier Aggregation

39. Enhanced Local Access: Soft Cell • In LTE Advanced: • Pico does not create a new cell but is an extension of an overlaid macrocell • Macro – basic coverage (system info, data, control • Pico – enhanced capacity and data rates • Consider this a macro assisted pico layer

40. Inter-cell Interference Coordination (ICIC) • Release 8 (LTE) • Interference mitigation by coordinating DL control and data channels • lowering the power of a part of the sub-channels in the frequency domain • Release 10 (LTE-A) • coordinate blanking of sub-frames in the time domain in the macro cell • Only legacy broadcast signals and channels are transmitted to support legacy Rel 8 UEs

41. ICIC Rel. 8 SINR Distribution Example -5 dB 20 dB Original reuse ICIC Example

42. CoMP • Coordinated Multipoint Transmission • Increases Data Rate • coordinating and combining signals from multiple antennas

43. Rel. 10/11 CoMP • Downlink • joint processing (JP) • coordinated scheduling (CS) • coordinated beamforming (CB) • Uplink • joint reception (JR) • Coordinated scheduling (CS)

44. Self-Optimizing Networks (SON) • “Self-Optimizing and Self-Configuring” • Needed to manage tiers • Identified Use Cases: • Energy Savings • Interference Reduction • Automated Configuration of Physical Cell Identity • Mobility robustness optimization • Mobility Load balancing optimization • RACH Optimization • Automatic Neighbor Relation Function • Inter-cell Interference Coordination • 3GPP TR 36.902 V9.3.1 (2011-03) • Note: HCS is not mentioned specifically in 36.902

45. Dynamic Load Balancing • Between tiers • Listed as a function of the X2 interface: • “This function allows exchanging overload and traffic load information between eNBs, such that the eNBs can control the traffic load appropriately. This information may be spontaneously sent to selected neighboureNBs, or reported as configured by a neighbour eNB.” • 3GPP TS 36.420 V10.2.0 (2011-09)

46. Carrier Aggregation • Between bands • Between tiers

47. DAS or Femto? 1. ABIresearch 2. IBW Solution and Capacity Offload in 3G and LTE (IBW symposium) • Summary of solution comparison

48. One Slide About Backhaul • The backhaul network needs to be able to support the wireless throughput. • Backhaul is one of the major expenses for wireless network operators Max. 802.11b

49. Motivations for HetNets • Better performance: • 1. Better coverage • Chow, et. al, 1994 • 2. Better SNR • Madhusudhanan, et. al, 2011 Madhusudhanan, P.; Restrepo, J.G.; Youjian Liu; Brown, T.X.; Baker, K.R.; , "Multi-Tier Network Performance Analysis Using a Shotgun Cellular System," Global Telecommunications Conference (GLOBECOM 2011), 2011 IEEE , vol., no., pp.1-6, 5-9 Dec. 2011.

50. Simulation study of the entire system is computationally infeasible. Ideal hexagonal grid model is not a good model anymore. Certain entities of the network are essentially random in nature. e.g. the location of the femtocell BSs. Challenges in Studying a Multi-tier Network