LTE-A HetNet Architecture Evolution: Challenges and Solutions

1. LTE-A無線電接取網路協定架構與核心網路 I

2. Evolution for 3GPP

3. Famous Topics of LTE-A • HetNet • eICIC • CoMP • MTC • Cognitive Radio • D2D • LTE-U • LAA • NB-IoT

4. LTE-A architecture in R8

5. LTE-A HetNet • Supporting high data rates has been the most essential requirement for the next generation cellular system. • 1G bps for static; 100M bps for mobility (definition of 4G by IMT-Advanced) • How to significantly enhance the data rate? • Enhancing multiple access, technology • Shortening the distance between the transmitter and the receiver • Extending the bandwidth by allowing more concurrent transmissions. • Reduce the cell size • The cost of re-deployment is too high • Deploying cells with smaller coverage overlaying conventional Macrocells • Femtocells (indoor) • Picocells (outdoor) • Relay nodes (RNs)

6. LTE-A HetNet • Multi-tier network

7. HetNet architecture • Femtocell • enhance the indoor signal strength • backhaul: users’ digital subscription line (DSL), • delivery delay is around the level of milliseconds. • a real-time communication between a femto-BS and a macro-BS is unavailable.

8. Femtocell

9. HetNet architecture • Picocell • share the traffic load of the macrocell on a hop spot area. • identical to a macro-BS, except a smaller transmission. • direct interface (known as X2) between a pico-BS and a macro-BS • a real-time communication between pico-BS and a macro-BS is possible.

10. Relay Station

11. HetNet architecture • RNs • deployed at the coverage edge of a macrocell to enhance the signal strength of a macro-BS at the coverage edge. • Type I RN has a cell identity, • Type II RN does not • a RN is more than just a signal repeater in Layer 1, but may also be capable of scheduling and resource allocation.

12. HetNet Challenges • Haphazard deployment • femto-BSs are deployed by users in a fully dynamic fashion • Restricted/closed access • femto-BSs are paid by the customers, • only users defined by the owners are allowed to access femto-BSs. • No coordination between macro-BS and femto-BS • Backward compatibility:

13. HetNet Technical Issues • Interference management • Access control • Security/QoS • Time Synchronization

14. Interference Management • Severe cross-tier and intra-tierinterference occurs • An effective interference mitigation scheme • Centralized (global) radio resource allocation schemes • High computational complexity • No scalability • Distributed radio resource allocation schemes with information exchange • A large amount of information exchanges among users/cells • Interfaces for information exchange may not be available

15. Interference Management • Inter-cell/intra-tier interference

16. Interference Management • Intra-tier and cross-tier interference

17. Interference Management • Orthogonal /separate channel assignment

18. Interference Management • Co/common channel assignment

19. Location Locking • Emergency Call Location: • Spectrum Use • People may bring the femto-BS to a new location without the operator's awareness and permission to enjoy the free transmission with high quality everywhere. • incur heavy cross-tier and intra-tier interference • Commercial • Operators may decide they can justify charging an additional fee to process a femtocell relocation

20. Location Locking

21. Interference Management

22. Target of Orthogonality • Location/Spatiality • two nodes physically locating closely to each other do not suggest severe interference to/from each other even if a small transmission power is adopted in both nodes • Time-Frequency • Resource blocks (RB) • Antenna Orthogonality • Multiple Input Multiple Output • (MIMO) form different transmissions spatial paths.

23. Methods of Information Acquisition • Exchanging at the BS side • By leveraging wireless/wired interfaces, small cell BSs and macro-BS could directly exchange information • no direct interface between a macro-BS and a femto-BS • heavy communication overheads • Measuring at the UE side • performing periodical channel measurement in UEs and reporting the measurement results to its serving BS • consume power in UEs

24. Methods of Information Acquisition • Measuring at the BS side • BS has the capability of measuring interference • if the received interference power on a RB exceeds a certain threshold, femto-BS identifies that this RB is occupied and retrieves activity

25. Interference Management

26. Interference ManagementTheoretical Analysis – Stochastic Geometry • Consider a network snapshot with a receiver at the origin • All other simultaneous transmissions have randomly located transmitters • Assume all nodes have same transmit power • Nodes are randomly distributed according to a point process • Fading power is • Aggregate interference

27. Interference ManagementTheoretical Analysis – Stochastic Geometry • Reliability:outage probability relative to a SIR threshold • Shot noise interference: • Assume exponential with unit mean • Signal is Rayleigh faded with unit average power • Assume Poisson point process (PPP) • The probability that there are nodes in is given by the Poisson distribution and thus equal to • Outage probability for fetmo-UE receiver (FUE): where

28. Access Control • Closed Access Mode • Only emergency calls if not in closed subscriber group (CSG) • Open Access Mode • All UEs are treated equally in the cell • Hybrid Access Mode • UEs not part of CSG may camp and acquire some level of service.

29. Access Control • Closed Access • Nonsubscribers have strong interference behind the femtocell. • High probability of outage. • Open Access • High frequency of handover. • Not enough cell IDs for femtocells in a macrocell.

30. Security/QoS • 3GPP was not able to complete the security aspect. • Device Authentication • Encryption/Ciphering • QoS control • QoS for delay sensitive traffic, voice • Operator’s backhaul system • Third party entity (DSL, Cable Network)

31. Synchronization • Distributed interference management methods • based on an ideal assumption of perfect timing synchronization between femtocells and Macrocells/picocells, and among all femtocells.

32. Synchronization • Synchronization and timing are very critical • What makes it difficult to achieve in Femtocells • Timing and synchronization depends on reliable receipt and delivery of RF signals. • There can be areas where there are no macro cells nearby. • Macro cell with very bad radio condition. • Number of Femtocells and location of each femtocell is unpredictable.

33. Synchronization • IEEE1588 : A Precision Time Protocol • deliver timing information from a synchronization serverto all femtocell BSs through the wired backhaul, • each femtocell BS can measure the timing difference between the femtocell BS itself and the synchronization server. • Air interface Based : GPS • GPS makes use of multiple continuously moving satellite for synchronization

34. Synchronization • TV Receiver • Femto-BSs equipped with TV receiver are proposed to achieve synchronization by receiving broadcasted TV signals • penetration loss of building walls • User Equipment (UE): • UEs are leveraged to assist the serving BS to synchronize with neighboring synchronized BSs

35. Synchronization • Solution: inter femto-BS communications • Gossip algorithm • fast averaging problem with continuous changes of connections among nodes and the taken values • Voter algorithm • Femto-BS updates its timing to that of only one randomly selected femto-BS. • Asynchronous radio resource management ?

36. Mobility Management • Random deployment • Load balancing

37. M2M Communications in 3GPP • Infrastructure mode

38. M2M Communications in 3GPP • Machine-to-Machine (M2M) involves communication without (or only limited) human intervention • Traditional Human-to-Human (H2H) communications • Also named Machine Type Communication (MTC) in 3GPP

39. Scenarios • Communication scenario with MTC Devices communicating with MTC Server. • MTC Server is located in the operator domain • MTC Server is located outside the operator domain • MTC Devices communicating directly with each other without intermediate MTC Server

40. Methods • Direct transmission between MTCD and eNB • Multi-hop transmission with the aid of an MTC gateway • Each MTCD is controlled by its donor MTCG, which is managed by the eNB. • Peer-to-peer transmission between MTCD • An MTCD may communicate locally with other entities, which provide the MTCD with raw data for processing and communicating to the MTC server and/or other MTCDs

41. Features • Low Mobility • MTC Devices that do not move, move infrequently, or move only within a certain region • Time Controlled • Send or receive data only at certain pre-defined periods • Time Tolerant • Data transfer can be delayed • Packet Switched (PS) only • Network operator shall provide PS service with or without an MSISDN • Online small Data Transmissions • MTC Devices frequently send or receive small amounts of data.

42. Features • MTC Monitoring • Not intend to prevent theft or vandalism but provide functionality to detect the events • Offline Indication • For detecting the condition when it is no longer possible to establish signalling between the MTC Device and the network • Jamming Indication • Require timely notification when an MTC Devices is being jammed due to an intentional broadband interferer • Priority Alarm Message (PAM) • For the need of immediate attention, e.g. theft or vandalism

43. Features • Extra Low Power Consumption • Improving the ability of the system to efficiently service MTC applications • Secure Connection • Convey communication when some of the devices are connected via a roaming operator • Location Specific Trigger • Intending to trigger MTC device in a particular area, e.g. wake up the device • Group based MTC Features • MTC device may be associated with one group

44. MTC subscription control • A MTC device can support different MTC features • are subscribed and controlled by the MTC subscription in the HSS • The MTC features are activated at the time of the MTC device’s subscription to the network and whenever it is supported by the network • MTC subscribers have the flexibility to activate unsubscribed MTC features or deactivate subscribed MTC features

45. MTC subscription control • pressure-sensing MTC devices on a train bridge • each time a train runs over the bridge the MTC pressure devices do their measurements and provide the result to the corresponding MTC application server • alert when the bridge needs to be repaired • Features • low mobility to prevent unnecessary tracking area updates • small data transmission • PS only • mobile originated only

46. MTC subscription control • MTC features may be incompatible among each other

47. MTC Congestion and Overload control • Congestion that may occur due to simultaneous signaling messages from MTC devices • malfunction in the MTC server or application • massive attempts from a potential number of MTC devices to attach to the network all at once

48. MTC Congestion and Overload control • takes soft measures to minimize the frequency of attempts of MTC devices • Reducing signaling due to TAUs from MTC devices with low mobility feature by increasing the TAU period timer

49. MTC Congestion and Overload control • MTC devices are grouped based on different metrics/features • Forbidden/grant times are allocated for each MTC device based on its subscription in HSS

50. MTC Congestion and Overload control • reject connection/attach requests, from MTC devices by specific network nodes • ensure a rejected MTC device does not immediately reinitiate the same request • indicates to the concerned MTC devices a back off time and ensures an even distribution of future incoming attach request