Wireless Technologies Addressing the Too Much Data Paradox May 25, 2011 Reinaldo A. Valenzuela Director, Wireless Communications Research Department Bell Labs, Alcatel-Lucent
Reality The Ubiquitous Goal for Wireless Data requires Profitable Net Growth Crushing Wireless Networks! Degrading Performance! Exploding Network Cost/Sub! Relevant Content on Great Devices with High Quality/Consistent Service At Compelling and Competitive Rates
Mobile Voice ARPU, Cost/Sub, Cost/MB. & Traffic Retail Voice ARPU 50 Network Cash Cost Network Cash Cost + Handset Subsidy + SG&A 900 45 40 Network Cash Cost/min Voice Traffic 850 ($/sub/mo 35 30 25 20 15 3.6 cents/min 19% CAGR 2.7 cents/min Profit -10% CAGR 2% CAGR 1.4 cents/min 800 750 700 650 (min/sub/mo) 10 2005 2006 2007 2008 2009 est 2010 est 2011 est 2012 est 2013 est 2014 est 600
Mobile Data ARPU, Cost/Sub, Cost/MB. & Traffic DATA ARPU 70 Network Cash Cost 1600 60 Network Cash Cost + Handset Subsidy + SG&A Network Cash Cost/MB 1400 ($/data plan sub/mo 50 40 30 20 10 Data Traffic 20 cents/mb Loss Profit 52% CAGR 10 cents/mb 3.8-14% CAGR cents/mb 1200 1000 800 600 400 200 (MB/data plan sub/mo) 0 2005 2006 2007 2008 2009 est 2010 est 2011 est 2012 est 2013 est 2014 est 0
Future Air Interface Technologies Network MIMO Coherent Multi Point coordination (CoMP) Small Cells Green Touch Large Scale Antenna System Wide Band systems
Network MIMO concept Today s network: Each user is connected to a single base Data rates limited by interference Each user is connected to several bases All signals are potentially useful no interference! Overcomes inter-cell interference by coordinating Tx/Rx at several bases Great increase in user rates and system capacity. Fast backhaul needed
Network MIMO Performance Analysis Duality with base station antenna cluster selection Assume that a collection of base station antenna clusters (possibly overlapping) is given. Antenna cluster = subset of base station antennas. UL: Each user must be received at one of these clusters. DL: Each user must receive from one of these clusters.
Network model 127-cell network (center cell plus 6 rings of neighbors), with wraparound to avoid edge effects. 3 sectors/cell in clover leaf arrangement. 3GPP/3GPP2 sector antenna beam pattern (parabolic). 3-dB beam width of 70 deg. Front-to-back ratio of 20 db.
Channel model All links are frequency-nonselective and time-invariant during each transmission. Complex path gain characterizing each link is derived from: Distance-based power loss (exponent of 3.8). Lognormal shadow fading of std. dev. 8 db (50% correlation across base stations). Rayleigh multipath fading (IID across links). Reference SNR at cell edge captures net effect of Tx power, noise bandwidth, Tx/Rx antenna gains, Rx noise figure, etc.
Network MIMO cases Assume equal rate requirement with 10% user outage. No coordination ( Best sector ): Each user receives from (UL) or is received at (DL) a single optimally chosen sector. Full coordination ( All 127 bases ): Each user receives from (UL) or is received at (DL) all sectors of all 127 bases. Limited coordination (see next slide for cluster details): Best 3-sector cluster : Each user is assigned to a single optimally chosen 3-sector cluster. Best n-base cluster (n = 1,3,7,19,61): Each user is assigned to a single optimally chosen n-base cluster.
Coordination clusters 1-base cluster (1 per base) 3-sector cluster (2 per base) 3-base cluster (2 per base) 7-base cluster (1 per base) 19-base cluster (1 per base) 61-base cluster (1 per base)
1 user/sector, 1 antenna/sector, 1 antenna/user 7 All 127 bases Uplink 7 All 127 bases Downlink 6 Best 61-base Best 19-base 6 Best 61-base Best 19-base Spec. eff. (bits/sym/sector) 5 4 3 2 1 Best 7-base Best 3-base Best 3-sector Best 1-base Best sector Spec. eff. (bits/sym/sector) 5 4 3 2 1 Best 7-base Best 3-base Best 3-sector Best 1-base Best sector 0 6 12 18 24 30 Ref. SNR at cell edge (db) 0 6 12 18 24 30 Ref. SNR at cell edge (db)
2 users/sector, 2 antennas/sector, 1 antenna/user 13 All 127 bases Uplink 13 All 127 bases Downlink Spec. eff. (bits/sym/sector) 11 9 7 5 3 Best 61-base Best 19-base Best 7-base Best 3-base Best 3-sector Best 1-base Best sector Spec. eff. (bits/sym/sector) 11 9 7 5 3 Best 61-base Best 19-base Best 7-base Best 3-base Best 3-sector Best 1-base Best sector 1 6 12 18 24 30 Ref. SNR at cell edge (db) 1 6 12 18 24 30 Ref. SNR at cell edge (db)
4 users/sector, 4 antennas/sector, 1 antenna/user Spec. eff. (bits/sym/sector) 30 25 20 15 10 5 All 127 bases Best 61-base Best 19-base Best 7-base Best 3-base Best 3-sector Best 1-base Best sector Uplink Spec. eff. (bits/sym/sector) 30 25 20 15 10 5 All 127 bases Best 61-base Best 19-base Best 7-base Best 3-base Best 3-sector Best 1-base Best sector Downlink 0 6 12 18 24 30 Ref. SNR at cell edge (db) 0 6 12 18 24 30 Ref. SNR at cell edge (db)
Summary Extended UL-DL duality results to cover systems with several clusters of base station antennas. Clusters can be overlapping. Each user is served by one of these clusters. Summary of extended duality result: Achievable SINR vectors on UL and DL are identical. Any feasible SINR vector can be achieved on both UL and DL with the same cluster assignments, the same unit-norm BF vectors, and the same sum Tx power.
Relays: One per sector We assume that the relays are placed in the middles of ideal lines between the source and the center of such a cluster. The users are associated with a sector according to it begin the sector offering closest propagation distance to the base. The sector antenna response is given by
Relays: One per sector The system is modeled as a synchronous cellular network consisting of 19 base stations with 3, 120-degree, sectors per base serving one user per sector at any one time and frequency resource. The radius of the hexagons composing the entire network equals 1000 m. Basic structure --that we will refer to as coordination cluster --
System Model We assume that: the standard deviation of the shadowing components, are: 8dB for the links Source/Destination and Relays/Destination 6db for the link Source/Relay. path-loss, is simulated according to the COST 231 model for a small to medium-sized city, where f c =2 GHz, the bandwith 10 MHz. antenna height: 25 m for the Source, 15 m for the Relays, 2 m for the Destinations
One relay per sector results Bits/sec/Hz IC+Relays IC-No Relays No IC, No Relays Average Throughput 2.2 2.12 1.75 10% Outage 1.46.63.25 I Conclusion: Relays provide moderate gains in average rate but very significant improvement in the edge rate.
Small cells: Interference and noise limited regimes Noise limited Interference limited Many cells in buildings: Net MIMO Many cells are idle: Power savings Macro - Pico coordination Open Closed user groups Interference management Configuration and administration Back haul Base station in the cloud per linear dimension
Overview Performance of small cells examined in three settings Residential femto cells Indoor commercial space (mall) picocell deployment Outdoor picocell network
Coverage in suburban home Great coverage: SNR > 37 db over 99% of locations at P T =22 dbm 1 0.9 0.8 Prob(Recieved Power > abscissa) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0-70 -60-50 -40-30 -20-10 0 10 Received Power (dbm) Indoor Path Loss Simulations Impact of Macro-femto and femto-femto (DL and UL) interference in suburban single-family homes and urban multi-apartment dwellings Use state of the art Ray tracing model (WiSE)
Interference in urban multi-apartment dwelling 1 0.9 Home Femto Only Strongest Signal Femto 0.8 0.7 Prob(SIR < abscissa) 0.6 0.5 0.4 0.3 0.2 0.1 0-20 -15-10 -5 0 5 10 15 20 SINR (db) Interference statistics obtained from middle apt. area in center building. SIR is below 5 db in 70% of locations SIR is below -4 db in 22% of the locations SIR is poorer for associate home (CSG) vs. associate strongest (OSG), 5 db at 10%.
Overview of Femto Interference Study conclusions Statistical Coverage and interference study included femto-femto and macro-femto/femto-macro interference. State-of-the art ray tracing model (WiSE) used in indoor propagation prediction, standard models used for macrocell interference Excellent indoor femto coverage in both suburban and urban dwellings, with 99% of locations having SNR > 37 db. Mild impact of DL Macro interference on femtos: Co-channel interference suffered by the femto from macro downlink and uplink transmissions was mostly benign (SINR>10 db in 95% of the cases), improving further with a dedicated carrier. Femto-femto interference dominant (especially urban areas), where re-use of 1 led to SINR < 0 db in 45% of locations (Closed Subscriber Group). Using Best Server brings 3-5dB improvement in SINR. Interference mitigation Closed Subscriber Group rates may be improved through adaptive frequency plan
Introduction of co-channel femtos in urban area Femtos decrease macro capacity by adding co-channel interference, increase overall capacity by allowing more users in. Femto density (femtos/macro area) Reduction in macro capacity 500 10% 5 1000 20% 10 10,000 82% 100 Increase in overall capacity (closed loop subscriber, one UE/femto limit) Allowing femtos to be public (serving more than one user) would increase capacity much further
Commercial indoor picocell performance (mall)
Propagation indoors suffers exponential loss attributed to absorption 240 220 200 180 Path loss (db) 160 140 120 100 80 60 40 10 0 10 1 10 2 10 3 Distance from transmitter (m)
Increased picocell density increases interference 1 10 picocells in a suburban mall 1 6 picocells in a suburban mall 0.9 0.9 0.8 0.8 Prob (SINR < abscissa) 0.7 0.6 0.5 0.4 0.3 Prob (SINR < abscissa) 0.7 0.6 0.5 0.4 0.3 0.2 0.2 0.1 0.1 0-20 -10 0 10 20 30 40 50 SINR (db) 0-10 0 10 20 30 40 50 60 SINR (db)
Per user rates increase little with increased picocell density (in this case) 1 User rate with full band re-use 30 active users 0.9 0.8 Prob (User rate < abscissa) 0.7 0.6 0.5 0.4 0.3 0.2 10 picobs 6 picobs 0.1 0 0 10 20 30 40 50 60 70 80 90 User rate (Mbps)
Outdoor spectral efficiency gain through picocells Use of smaller cells offers a promise increased system capacity through greater spatial re-use A high level study was conducted comparing spectral efficiency of a fully loaded traditional macro cellular system with a densely placed, below clutter pico cell deployment. For 1/r 4 pathloss dependence, a range reduction by a factor of 10 implies an improvement in link budget by 40 db. This allows for a reduction in transmit power, base antenna gain, and base height to picocellular levels (1W, 10 dbi vertical gain only, lamppost placement). Results: A reduction in cell radius by a factor of 10 (from 1km to 100m), allows an increase in spectral re-use by factor of 30 (100 picocells/macro area, but without the benefit of macro 3-sector reuse). This includes indoor coverage (10 db building penetration loss) Without indoor coverage, cell density may be reduced to 36 picos/macro, offering 12-fold system capacity All Rights gain. Reserved Alcatel-Lucent 2006
Simulation details General parameters: 10 MHz BW, 2 GHz center frequency, 10 db receiver noise figure Macro cell parameters: 10W, 17 dbi 3-sector, above roof-top, 1km cell radius, COST-231 Hata with 10 db building penetration loss Pico cell parameters: 1W, 10 dbi (vertical gain only), COST-231 Hata with 10 db building penetration loss and 20 db BS height loss (Xia, Maciel, Bertoni) All cells are placed hexagonally, users are dropped one at a time, with all interfering cells operating at full power. All rates are computed as Shannon rates, with best effort as a policy.
Other considerations for outdoors Improvement in spectral efficiency clearly depends of the ratio of radii of currently deployed macrocells to minimum feasible cell size. If in an urban area the cell radius is 200m, to get a similar 30-fold improvement would imply picocell radii of 20m, arguably too small. How densely can picocells be placed? Beyond improvements in spectral efficiency, reduction in Tx power, antenna size and antenna height may bring cost savings that would need to be balanced against the need to provide denser backhaul connectivity and site acquisition. Do economics of site acquisition/backhaul change when on lamppost, with high-speed wired connection available everywhere? What are implications of RF planning for picocells? Coverage/interference is expected to be highly anisotropic (low pathloss down the street, high perpendicular to the street) Picocells may be highly advantageous for hot spot coverage.
Overall conclusions for small cells Dense deployment of residential femtocells offers large increases in network capacity. Each femto needs to operate at low SINR due to femto-femto interference Indoor commercial space picocell deployment promises to deliver 12 Mbps median user rates Dense deployment of lamppost picocells offers an increase in capacity that scales with the coverage area (over an order of magnitude when reducing cell radius from 1km to 100m) Reduction in useful budget (lower transmitted power, lower antenna gain, lower antenna height is compensated by the reduction in cell size) Cell splitting is the mechanism responsible for increase in capacity
Conclusions Wireless technologies will be key in dealing with data explosion in a in a cost effective manner New technologies delivering higher capacity at lower cost New services maximizing value of lower bit rates Reducing power consumption