ECE 4371, Fall, 2013 Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 24 Nov. 17 th, 2014

Outline Device-to-Device Communications –Overview –Key Technologies –Variety of Applications Femtocells –Overview –Standardization & Models –Key Challenges

Standardization Facilitates Technology Evolution Each new evolution builds on the established market of the previous Backwards-compatible evolution But larger technology steps require revolutions: From TDMA: to CDMA: to OFDMA:

Future Wireless Challenges Mobile Internet and Smart Phones 1.Bandwidth and data traffic boost (Cisco)  Data traffic increases 2 times/per year, 1000 times by 2020  Wireless network cannot support that! 2.Information aggregate to hotspot and local area  70% in office and hotspot, over 90% in future  Hotspot QoS cannot be guaranteed! Bandwidth demand over 1200MHz ， ITU assignment less than 600MHz

Possible Solutions Number of UE Cell Capacity Add fixed AP Sum rates P. Gupta and P. Kumar, “The capacity of wireless networks,” IEEE Transactions on Information Theory, vol. 46, no. 2, pp , Mar Ad-hoc optimal rate By “Shannon Theory” ， network capacity relies on bandwidth and APs Current ： Add fixed APs By “Shannon Theory” ， network capacity relies on bandwidth and APs Current ： Add fixed APs Combine Cellular and Ad- hoc

Definition and Benefits Definition of Device-to-Device (D2D) Communications –D2D communications commonly refer to the technologies that enable devices to communicate directly without an infrastructure of access points or base stations. eNB ① Increase network capacity ② Extend coverage ③ Offload data ④ Improve energy efficiency ⑤ Create new applications ① Increase network capacity ② Extend coverage ③ Offload data ④ Improve energy efficiency ⑤ Create new applications

Deployment Roadmap Cellular unaware D2D Cellular network is not aware of D2D 2 RATs, e.g. 3G + Wifi No cooperation between cellular and D2D Cellular aware D2D Cellular network is aware of D2D 2 RATs, e.g. LTE + Wifi Kind of cooperation between cellular and D2D Cellular controlled D2D Cellular network fully controls D2D A single RAT, e.g. LTE-A D2D is a part of cellular communication RAT1 RAT2 UE1 UE2 flow1 flow2 Scenario A RAT1 RAT2 UE1 UE2 flow1 flow2 Scenario B RAT1 UE1 UE2 flow1 flow2 Scenario C D2D Benefits Scenario A Scenario B Scenario C Traffic offload Unified & Simplified comm. User experience improvement Cellular capacity enhancement RATs converging

Scenario A: Cellular Unaware App 3G Wifi Example structure: App New App Typical applications – Data synchronization, Social networking, Mobile advertising, Automation control, etc. BS social network Data synchronization Mobile advertising Key technology – D2D opportunity identification & neighbor discovery – Flow distribution among different RATs Benefits/Gains – Offload cellular traffic – Unified & Simplified communications Node functionality – User device: application distribute flows among different RATs – No impact on RAN & CN nodes

Scenario B: Cellular aware App LTE Wifi Example structure: App Core Network New coordination function/services Key technology –D2D opportunity identification –D2D coordination Benefits/Gains –Better user experience, e.g. QoS, mobility, etc. –Core network traffic offload –Unified & Simplified communications Node functionality – User device: new D2D coordination function – RAN node: No impact – CN node: new D2D coordination function Typical applications – Cellular P2P: A, B, C receive data from CN, and share the non-achieved data among themselves NB ABC Core Network CN node

Scenario C: Cellular controlled App Cellular Example structure: App Core Network New Cellular D2D interface New D2D control function/services Typical applications –Cooperative transmission: Mobiles interact to jointly transmit and/or receive information in cellular environments. Node functionality – User device: New D2D control & interface – RAN nodes: New D2D control function – CN nodes: New D2D control function Benefits/Gains – Cellular capacity improvement – Better QoS, security & mobility support – Core network traffic offload – Unified & Simplified communications Key technology – D2D control – D2D air interface design – Cooperative transmission eNB

Key Technologies Access Methods Mode Selection Neighbor Discovery Spectrum Sharing Interference Analysis Power Control MIMO Beamforming Signal and Interference Model Radio Resource Management Operation Protocol

Access Methods The D2D networks can be configured in three ways to allow or restrict their usage by certain users: –Self-organized: u D2D users themselves realizes the communications in a self- organizing way by finding the empty spectrum hole. –Network Assisted : u The D2D users operates in a self-organized way, and exchanges with cellular system limited controlling information for resource management. u cellular network can obtain the status of D2D communications for better control purposes. –Network Controlled: u the base station and the core network control the communication signaling setup and the there after resource allocation for both cellular and D2D users.

Mode Selection Mode selection criteria –Cellular Mode: The mobile works in a traditional cellular way relaying data by a BS. – D2D Mode: The mobiles exchanges information directly. –Mode Adaptation: The mobiles can select the right mode for communication according to the predefined criterions. Typically, all the UEs are implemented with two modes, i.e. cellular mode, and D2D mode, and can adaptively utilize the proper way for transmission.

Device Discovery and Synchronization (1) For D2D communications, network time synchronization is necessary –between cellular networks and D2D users –among D2D users themselves –to minimize multi-access interference, as well as for the proper performance of handoffs. The fundamental problem of device discovery is that –the two peer devices have to meet in space, time, and frequency. Without any coordination –this can be made possible via some randomized procedure and one of the peers assuming the responsibility of sending the beacon. The approaches in IEEE can be readily adopted to enable the synchronization among mobiles.

Device Discovery and Synchronization (2) Traditional peer discovery: –In both the ad hoc and the cellular cases, the discovery is made possible by one party transmitting a known synchronization or reference signal sequence (the beacon). In the case of network assisted D2D, the network can mediate in the discovery process by –recognizing D2D candidates –coordinating the time and frequency allocations for sending/scanning for beacons –making the pairing process more energy efficient and less time consuming

Device Discovery and Synchronization (3) Typical procedure –Use direct signal to discover peer –Set transmission power so that UEs in coverage can hear the broadcast. –Whoever receives the broadcast confirm that with the eNodeB From the aspect that there is response from discovering UE or not, two discovery approaches could be classified: –Beacon-based discovery –Request-based discovery According to whether there is network participation for identification detection, discovery procedure could be categorized into: –Network-assistance detection –Non-Network-assistance detection

Spectrum Sharing Spectrum sharing as an overlay: –The D2D users occupies the vacant cellular spectrum for communication. –completely eliminates cross-layer interference is to divide the licensed spectrum into two parts (orthogonal channel assignment). –a fraction of the subchannels would be used by the cellular users while another fraction would be used by the D2D networks. –Although optimal from a cross-layer interference standpoint, this approach is inefficient in terms of spectrum reuse. Spectrum sharing as an underlay: –allows multiple D2D users to work as an underlay with cellular users, and thus to improve the spectrum efficiency. –co-channel assignment of the cellular and D2D users seems more efficient and profitable for operators, although far more intricate from the technical point of view.

Interference Analysis Considering that these networks define two separate layers, interference can be classified as follows: –Cross-layer: This refers to situations in which the aggressor (e.g., a D2D user) and the victim (e.g., a cellular user) of interference belong to different network layers. –Co-layer: In this case the aggressor (e.g., a D2D user) and the victim (e.g., a neighboring D2D user) belong to the same network layer. Combating the interference –Transmitter: Frequency, time, space, power etc, allocation –Receiver: Signal processing for interference cancelation

Power Control Power control can be performed by two approaches: –Self-organized power control: u the D2D users make power changes in a self-organized way according to a predefined SINR threshold in order to meet the QoS, and meanwhile not affect the cellular users. –Network managed power control: u Both cellular and D2D users adaptively adjust the transmit power according to the SINR report. u Typically, the D2D users can control the transmit power at first, and then the cellular users make change afterward. u This iterative process terminates until all the users meet their SINR requirements. The first method is not going to change the behaviors of cellular users, such that D2D users are invisibly treated. The second method allows all the users to adjust the transmit power, but requires a certain amount of signaling overhead

MIMO and Virtual MIMO By performing transmit or receive beamforming,the use of multiple antennas at the eNB and the UE can –reduce the co-channel interference to other users –improve spectrum efficiency The methods can be summarized as follows: –eNB beamforming: This sort of multi-user MIMO like approach can be performed at the cellular downlink to reduce the interference to D2D users, such that D2D communications can be allowed. –D2D beamforming: This avoids the D2D transmission to disturb the cellular and other D2D users. –Virtual D2D beamforming: This borrows the ideas of cooperative mobiles, such that multiple D2D users collaboratively form the beamforming matrices to improve the system performance.

Radio Resource Management (1) With regards to the underlay approach, to mitigate cross- and co-layer interference, there would be a central entity in charge of intelligently telling each cell which subchannels to use. This entity would need to collect information from the D2D users, and use it to find an optimal or a good solution within a short period of time. The presence of large number of D2D users, and the allowance of multiple D2D users coexistence with cellular user makes the optimization problem too complex. Latency issues arise when trying to facilitate the D2D communication with the central subchannels broker throughout the backhaul. A distributed approach to mitigate cross- and co-layer interference, where the D2D users can manage their own subchannels, is thus more suitable in this case (i.e., self-organization).

Radio Resource Management (2) In a non-cooperative solution, i.e. self-organized approach –each D2D user would plan its subchannels so as to maximize the throughput and QoS for its users. –this would be done independent of the effects its allocation that might cause to co-channel D2D and cellular users. In a cooperative approach, i.e. network assisted approach –the D2D users can gather partial information about subcarrier usage situation. –may perform its allocation taking into account the effect it would cause to its co-channel neighbors. –the average cellular and D2D users' throughput and QoS, as well as their global performance can be locally optimized.

Outline Device-to-Device Communications –Overview –Key Technologies –Variety of Applications Femtocells –Overview –History –Standardization & Models –Key Challenges

Application Scenarios There are two important services of ProSe. –The first one is proximity discovery with which users can discovery each other in proximity. –The second is direct communication with which users can communicate with each other in proximity. There is no causality between proximity discovery and direct communication. –Proximity discovery can be stand alone services to users and doesn’t always trigger direct communication. –Users may initiate direct communication directly without proximity discovery. –However, users can use direct communication easily when they know the proximity information.

Application Scenarios D2D scenarios include proximity discovery and direct communication.

Application Scenarios (1) Social Networking –Without specific target users: ProSe applications discovery all the users in proximity and network helps to choose those of users’ interest. –With specific target users: ProSe applications only discover the specific users, usually the friends of users and show the proximity information on the right of the target user.

Application Scenarios (2) Local Advertisement –The shops will automatically distribute the advertisement to the passagers nearby. –Applications in users’ terminal discover the advertisers automatically and receive the information from them, including introduction, menus, coupons, etc.

Application Scenarios (3) Location Enhancement –The D2D terminals receive the real-time parking space information that helps finding one’s parking space easily. –It can provide more information than a GPS based application by D2D.

Application Scenarios (4) Distance Based Applications –Members of a team or group can obtain the sphere of activities for each other by D2D distance monitoring when touring, keeping a safe movement range to prevent occurring accident.

Application Scenarios (5) Enhance Network Capability (Offloading) –D2D applications can provide coverage enhancement without increasing infrastructure cost, capacity enhancement by multiplexing D2D and cellular spectrum and user experience enhancement of link robustness and throughput. e.g. Concert Networks Stadium Networks

Application Scenarios (5) Disaster and Public Safety –In case of disastrous simulation, where the fixed infrastructures, such as BSs, are in failure, mobiles not in the coverage can possibly reach the BS with the aid of mobiles in the coverage area. –This is similar to multi-hop relaying networks. D2D MMES-GW Emergency Communications ① Mobile Adhoc networks ② Active BS is the final destination

Outline Device-to-Device Communications –Overview –Key Technologies –Variety of Applications Femtocells –Overview –History –Standardization & Models –Key Challenges

Overview of Femtocells Femtocells are low-power wireless access points that operate in licensed spectrum to connect standard mobile devices to a mobile operator’s network using residential DSL or cable broadband connections.

Overview of Femtocells Why femtocells is needed? –Exponentially increasing wireless data traffic.

Overview of Femtocells Why femtocells is needed? –Data offload is real and measurable.

Overview of Femtocells The key attributes of femtocells: –Mature mobile technology –Operating in licensed spectrum –Generating coverage and capacity –Using internet-grade backhaul –At competitive prices –Fully managed by licensed operators Question –What is the difference from WIFI: some control –What is different from microcell: backhaul

A Brief History of Femtocells Early Origins –1980s: u “Small cells” u Cellular repeaters or “boosters” –1990s: u A precursor to cellular picocells u An indoor femtocell-like solution (Southwest Bell and Panasonic) The birth of modern femtocells –March, 1999 u Alcatel announced that they would bring to market a GSM home base station. –2002 u Motorola engineers in Swindon claimed to have built the first complete 3G home base station

A Brief History of Femtocells Development of modern femtocells –2003 u Chipset design company – picoChip – was demonstrating lower-cost 3G chipsets. –Mid-2004 u Ubiquisys and 3Way networks were formed in the UK to develop their own 3G cellular home base stations. –2007 u Products were demonstrated at the 3GSM conference. u The Femto Forum ( was set up. –August, 2008 u Commercial service was launched first by Sprint in the USA with their Airave CDMA offering.

A Brief History of Femtocells Femtocell ecosystem

A Brief History of Femtocells Femtocell products

A Brief History of Femtocells Femtocell service deployments and commitments

Outline Device-to-Device Communications –Overview –Key Technologies –Variety of Applications Femtocells –Overview –Standardization & Models –Key Challenges

Femtocell Standardization Mission: –The mission is to advance the development and adoption of small cells for the provision of high-quality 2G/3G/4G coverage and services within residential, enterprise, public and rural access markets. 3G and 4G

Femtocell Standardization 3GPP standards for UMTS femtocells –Interface between the femtocell (Home Node B - HNB) and the femto network gateway (HNB Gateway, HNB-GW) –Security protocols to authenticate femtocell (HNBs) and secure communications across the un-trusted Internet –Management protocols for “touch free” Operations, Administration, and Management (OA&M) of femtocells (HNB devices)

Femtocell Standardization 3GPP2 standards for CDMA femtocells –SIP/IMS-based 1x circuit services architecture –Packet data architecture –Security framework –Enhancements to mobile devices to make them more femto-aware –Foundations of femtozone services (Local IP Access and Remote IP Access) –Femtocell management architecture

Femtocell Standardization The need for LTE femtocells –There is a limit to how many outdoor cell sites can be built; –The spectrum available to any particular operator is limited; –Cell site backhaul is expensive. LTE is the first cellular technology which will be able to take full advantage of femtocell. –The large quantity of dynamically allocated time and frequency slots.

Femtocell Standardization LTE architecture with deployed HeNB GW

Femtocell Models Traditional hexagonal grid model –Dozens of systems parameters can be modeled; –Other-cell interference can be modeled simply; –The results is sufficiently accurate to enable the evaluation of new proposed techniques. Multi-tiered cellular model –Macrocells –Picocells –Femtocells –Possibly further radiating elements

Femtocell Models Link level modeling –Channel status depend on a large number of factors u The propagation environment u Range & distance u Carrier frequency u Antenna placement u Antenna type

Femtocell Models Femtocell access control model –Closed subscriber group (CSG) u Only pre-registered mobile users can use a certain femtocell. –Open subscriber group (OSG) u Any mobile can use any femtocell or at least one that is “open”.

Femtocell Models Femtocell network model –Keep the grid model for macro base stations, drop femtocells “on top” of it, either randomly or in a deterministic fashion; –Focus on a single femtocell dropped in the cellular network; –Drop both the macrocells and femtocells randomly; –Keep all the channel gains and possibly even the various per-user capacities general, without specifying the precise spatial model for the various base stations.

Femtocell Models System level model

Outline Device-to-Device Communications –Overview –Key Technologies –Variety of Applications Femtocells –Overview –Standardization & Models –Key Challenges

Overview of Key Challenges –Interference scenario relationships

Overview of Key Challenges –Interference scenario relationships

Overview of Key Challenges –Interference level u With open-access and strongest cell selection, heterogeneous, multi-tiered deployments do not worsen the over all interference conditions or even change the SINR statistics. –Interference of femtocell networks in practice u Unregistered mobiles cause significant interference to the femtocell; u The signaling for coordinating cross-tier interference may be logistically difficult.

Overview of Key Challenges –Interference coordination u 3G CDMA femtos l power control strategies l Reserving a “femto-free” band u 4G LTE femtos l Backhaul-based coordination l Dynamic orthogonalization l Subband scheduling l Adaptive fractional frequency reuse

Overview of Key Challenges –Spectrum: Femtocells can use any and all of these standardized bands u Opening up spectrum bands u Re-using existing bands u Spectrum and economic efficiencies u Innovation and competition

Overview of Key Challenges –Cell association and biasing u assign each user to the strongest base station signal it receives

Overview of Key Challenges –Cell association and biasing u Biasing: users are actively pushed onto small cells.

Overview of Key Challenges –Cell association and biasing u How to inform a biased user its channel assignment? u How much biasing is “optimal”? l The throughput/QoS metric of interest l How users and the various base stations are distributed in space l Traffic patterns in space-time l The amount of adaptively and side information the mobiles and small cell base stations are able to exploit

Overview of Key Challenges –Mobility and soft handover u Femto-to-macro handover (outbound mobility) u Macro-to-femto handover (inbound mobility) u Possibly femto-to-femto handover –The most difficult aspect of femtocell mobility u Femtocells are not typically directly connected into the core network u Femtocells are typically unable to share a RNC with a macrocell or other femtocells.

Overview of Key Challenges –Self-organizing networks (SON) u Femtocells must support an essentially plug-and-play operation –Considerable research attention u Automatic channel selection u Power adjustment u Frequency assignment for autonomous interference coordination u Coverage optimization u The autonomous shutting down and waking up of base stations for power savings

Overview of Key Challenges Economic and Regulatory Issues –Operator Business Case u The cost of femtocells must be outweighed by the savings from offloading traffic from the macrocell networks; u Femtocells can be used to delay costly initial capital costs on macrocell network for operators deploying new 4G technology. –Subscriber and ISP incentives u Subscribers and enterprises become responsible for installing the femtocells while private ISPs provide the backhaul.

Overview of Key Challenges Economic and Regulatory Issues –Femto vs. WiFi and Whitespace u WiFi: best-effort service; u Femto: managed service. –Regulatory benefits u Improved access u Spectrum efficiency u Innovation and opportunity

Overview of Key Challenges Economic and Regulatory Issues –Regulatory aspects: u What is the impact of femtocells on spectrum licensing? u What about public health concerns? u What power levels do femtocells transmit? u How do operators stop users transmitting with femtocells on unauthorised frequencies or locations? u Could femtocells be “hacked”? u Do femtocells comply with existing standards? u How about the need to register base station locations? u What other regulatory issues should be considered?

Conclusion Demand for cellular data services skyrockets Setbacks –plug-and-play deployment –Highly democratic cost –Possible chaos to the network Forecast –Dense femtocell deployment –Economic and capacity benefit

Outline Device-to-Device Communications –Overview –Key Technologies –Variety of Applications Femtocells –Overview –Standardization & Models –Key Challenges Thanks!