Wireless Networks Lecture 44 4G Issues Dr. Ghalib A. Shah
Outline • 4G Overview • Heterogeneous Wireless networks • Evolution • Issues in 4G • Mobility Management • Handoffs • Types, VHO process, VHO Issues • Standards • QoS Considerations
Last Lecture • Reference Model • Burst profiles • Convergence sublayers • MAC PDU format • MAC PDU Transmission • Fragmentation / Packing • Request/Grant Scheme • Classes of Uplink service • Power management/Handoff
4G Overview • 4G mobile communication systems tend to mean different things to different people: • for some it is merely a higher-capacity new radio interface, • while for others it is an inter-working of cellular and wireless LAN technologies that employs a variant of the Mobile IPv6 mobility management protocol for inter-system handoff. • There is no doubt that 4G systems will provide higher data rates. Traffic demand estimates suggest that, to accommodate the foreseen amount of traffic in the 2010 – 2020 timeframe in an economically viable way, 4G mobile systems must achieve a manifold capacity increase compared to their predecessors. • researchers and vendors are expressing a growing interest in 4G wireless networks that support global roaming across multiple wireless and mobile networks • a system that enables an “Always Best Connected” – or “ABC”
There are many wireless network technologies Cellular networks, Wireless LANs, Wireless PANs, mobile Wimax, etc. • 4G networks will play a key role for integrating various network architectures and technologies and achieving a seamless wireless access infrastructure • 4G provides high-speed, large volume, good quality, and global coverage to roam between different types of technologies
It is widely accepted that the individual (wireless and/or wireline) access networks will interface to core and/or backbone network elements over the IP protocol • these wireless access networks are expected to have the following in common: • A dynamic address assignment mechanism (e.g., DHCP, SLP, IPv6) that is capable of associating a short-lived or long-lived IP address to the respective wireless interface at the mobile terminal (e.g., Mobile IP COA association) • A transparent IP forwarding service that is accessible over the logical termination of the IP layer at the mobile terminal and one or more gateways
Heterogeneous Wireless Networks • A mixture of co-existing radio access technologies. • Different access technologies (radio interfaces) and overlapping coverage. • Different network architectures and protocols for transport, routing and mobility management. • Different service demands from mobile users (low-data rate, high-data rate, voice, multimedia, etc) • Different operators in the market.
Issues in 4G • Need to resolve issues as • Access • Handoff • Location coordination • Resource coordination to add new users • Support for multicasting • Support for quality of service • Wireless security and authentication • Network failure and backup • Pricing and billing.
Mobility Management • Mobility Management • Location Management: enables system to track location of mobile terminal (MT) • Location updates and paging • Handoff Management: the process by which an MT keeps its connection when it moves from one point of attachment (base station or access point) to another
Handoff Management • Low signalling and processing overhead. • Minimum packet loss and delay (seamless HO). • Guaranteeing QoS during the process and transfer of context. • Use of any “triggers” or metrics available to decide when and where. • Efficient use of network and MT resources. • Enhanced scalability, reliability and robustness. • Allow inter-technology handoff (VHO).
Handoff Types • Homogeneous (Horizontal) Handovers • Within Single Network (Localized Mobility) • Limited opportunities • Mainly use received signal strength (RSS) to decide handoff • Heterogeneous (Vertical) Handovers • Across Different Networks (Global Mobility) • More Opportunistic • Handoff metric: RSS, offered bandwidth, price, power consumption, speed, …….
Vertical handoff process • Step 1: “System Discovery” • Step 2: “Handoff Decision” • Step 3: “Handoff Execution”
Step 1: “System Discovery” • MT must know which • wireless networks are reachable. • Periodic beacons from AP. • Signal measurements. • Handoff metrics (network information) gathering: Bandwidth, cost, delay, SNR, power, etc. • Periodic network scanning. • All interfaces always on.
Step 2: “Handoff Decision” • MT then evaluates the • Some example policies: • “Always use the cheapest network”. • “Always use the interface with lower power consumption”. • “Always use the WLAN”. • “Always use the network with more bandwidth”. • Decision may be based on utility / cost functions.
Step 3: “Handoff Execution” • If MT decides to perform a VHO, it executes the VHO procedure required to be associated with the new wireless network.
VHO Issues • When to switch? • VHO policies • WLAN to Cellular ≠ Cellular to WLAN • Seamless handoff • Packet loss and VHO latency. • Load balancing between networks. • QoS guarantees • Security and Authentication. • Billing • Implementation.
Standardization Efforts • IETF • Mobility for IPv4 (MIPv4) • Mobility for IPv6 (MIPv6) • Mobility for IP: Performance, Signalling and Handoff Optimization (MIPSHOP) • IEEE 802.21 Media Independent Handover Group is working toward the seamless handoffs between IEEE 802.XX family and 3G Cellular • 3GPP and 3GPP2 are working in inter-working with WLAN as an extension of their radio access networks. • Loosely Coupled Architecture • Tightly Coupled Architecture
Tightly coupling • Provides common charging and billing service • Provides mobility support using traditional 3G technology • Reuses 3G service (e.g., SMS, MMS, etc.) • Causes large traffic load in 3G core network • Loosely coupling • Provides simple integration approach • Needs minimal requirement on the access network • Provides independent network management
QoS • Supporting QoS in 4G networks will be a major challenge due to varying bit rates, channel characteristics, bandwidth allocation, fault-tolerance levels, and handoff support among heterogeneous wireless networks. • QoS support can occur at the • Packet, • Transaction • Circuit • User
Packet-level QoS • applies to jitter, throughput, and error rate. • Network resources such as buffer space and access protocol are likely influences. • Transaction-level QoS • describes both the time it takes to complete a transaction and the packet loss rate. • Certain transactions may be time sensitive, while others cannot tolerate any packet loss.
Circuit-level QoS • includes call blocking for new as well as existing calls. • It depends primarily on a network’s ability to establish and maintain the end-to-end circuit. • User-level QoS • depends on user mobility and application type. • The new location may not support the minimum QoS needed, even with adaptive applications.
End-to-End QoS • Developers need to do much more work to address end-to-end QoS. • They may need to modify many existing QoS schemes, including admission control, dynamic resource reservation, and QoS renegotiation to support 4G users’ diverse QoS requirements. • A wireless network could make its current QoS information available to all other wireless networks in either a distributed or centralized fashion so they can effectively use the available network resources. • Additionally, deploying a global QoS scheme may support the diverse requirements of users with different mobility patterns.
QoS Parameters • 802.11e • Nominal MSDU size • Min/mean/max data rate • Mean/max service interval • Traffic type (isochronous, asynchronous) • Burst size • UMTS (Release 5) • Traffic class(conversational, streaming, interactive, or background) • Guaranteed, maximum bit rate • Maximum SDU size • SDU/bit error ratio • Transfer delay • 802.16-2004 • Traffic priority • Maximum sustained traffic rate • Maximum traffic burst • Minimum reserved traffic rate • Scheduling type (best-effort, non-real time polling, real-time polling, unsolicited grant) • Tolerated jitter, maximum latency