Architecture and Prototyping of an 802.11- based Self-Organizing Hierarchical Ad-Hoc Wireless Network (SOHAN) PIMRC 2004, Barcelona Sept 5-8, 2004 S. Ganu, L. Raju, B. Anepu, S. Zhao, I. Seskar and D. Raychaudhuri Rutgers, The State University of New Jersey Research supported by NSF NRT Grant #ANI0335244 and by a grant from Cisco University Programs 1
Introduction 2
Introduction: Next Generation Wireless Network MSC Custom Mobile Infrastructure (e.g. GSM, 3G) BTS Public Switched Network (PSTN) BSC GGSN, etc. WLAN Access Point Internet (IP-based) Generic mobile infrastructure BTS Infostation cache Increasing role for ad-hoc networks High-speed data & VOIP WLAN Hot-Spot CDMA, GSM or 3G radio access network High-speed data & VOIP Voice (legacy) Ad-hoc network extension Relay node Broadband Media cluster (e.g. UWB or MIMO) VOIP (multi-mode) Today Future Low-tier clusters (e.g. low power 802.11 sensor) 3
Introduction: Flat vs. Hierarchical Ad-Hoc Nets Hierarchical structure is essential, and helps to achieve: Scalability, i.e. improved max throughput and delay/qos Effective integration with 3G/4G, WLAN and Internet Improved coverage & power consumption at subscriber radios Wired Internet Infrastructure Wired Internet Infrastructure Ad-hoc associations Potential bottleneck Gateway node BTS Multi-tiered Interfaces to wired network Wide Area Cell Microcell AP BTS Forwarding Node Extended Coverage End-user radios (with routing capability) Ad-hoc associations 3G cell Forwarding node Flat mesh network with ad-hoc routing Power & computing limitations at low-tier nodes Throughput per node scales ~ 1/sqrt(n) End-user radios (no routing capability) Throughput per node can scale ~1 with right ratio of FN s, AP s Hierarchical architecture with radio forwarding nodes and AP s/bs s 4
Introduction: Hierarchical Ad-Hoc Net Capacity 320 kbps 77 kbps Pkt delivery fraction Throughput (bps) 4 pkts/s 16 pkts/s 3 2 1 x 10 5 Hier Flat 0 0 10 20 30 Packet rate (pkts/s) 1 0.5 Hier Flat 0 0 10 20 30 Packet rate (pkts/s) Routing overhead Avg delay (simulated s) 4 3 2 1 Hier Flat 0 0 10 20 30 Packet rate (pkts/s) 0.4 0.3 0.2 0.1 Hier Flat 0 0 10 20 30 Packet rate (pkts/s) Reference: S. Zhao, I. Seskar and D. Raychaudhuri, "Performance and Scalability of Self-Organizing Hierarchical Ad Hoc Wireless Networks", Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC 2004), March 21-24, 2004, Atlanta 5
Introduction: 3-tier ad-hoc hierarchy Self-organizing hierarchical ad-hoc wireless network (SOHAN) under consideration at WINLAB Tier 1: low-tier mobile nodes, e.g. low-power PDA s, sensors, etc. (MN) Tier 2: forwarding nodes (FN) with multiple radio interfaces (UWB, WLAN, cellular ) Tier 3: wired base stations and access points (BS or AP) Research on new protocols for: ad-hoc discovery, MAC and routing Internet Internet BTS WLAN micro-cell AP Forwarding node FN Access Point Wide-Area Cell low-tier (e.g. sensor) user nodes (MN) personal-area pico-cell 6
Introduction: Application to WLAN Mesh Hierarchical ad-hoc concept can be applied to extend coverage and QoS of 802.11 WLAN s Useful for WLAN s with coverage problems, home networks with QoS and/or coverage needs, outdoor community networks, etc. Some nodes (either network elements or terminals without power constraints) serve as FN s Requires extended discovery protocols (via beacons) and multi-hop routing Optional upgrade of 802.11 MAC for efficient multihop operation Wired Wired Network Infrastructure AP1 802.11 Access to AP AP2 Ad-hoc radio link (w/multi-hop routing Ad-hoc Infrastructure links Self-organizing Ad-hoc WLAN Mobile Node (MN) (end-user) Ad-hoc access To FN Forwarding Node (FN) Forwarding Node (FN) Supported by a grant from Cisco University Programs 7
Hierarchical Ad-Hoc Network Protocols 8
SOHAN Protocols: Components Bootstrapping Mechanism Involves the configuration of the different devices in terms of channel assignments and initial transmit power level settings for now, manual configurations using scripts Discovery Mechanism Filters links made available to the routing protocol based on desired objective function reduces routing overhead Allows each node to apply a different objective depending on the role it plays Supports multi-channel operation of network Routing Mechanism Uses the logical topology information presented by the discovery mechanism in order to create and maintain local neighbor Used to route data from the MN s into the infrastructure network through FN s and AP s 9
SOHAN Protocols: Conceptual Overview AP service advertisement (into wired net) AP1 BTS A Wired Radio Access Network Infrastructure AP2 BTS service advertisement (into wired net) BTS radio beacon Access Point: Seek (AP*, BTS*) Associate (AP2, BTS A) handoff update (AP2) handoff update (BTS A)..forward data & handoff AP3 AP beacon (ID, frequency, power,,bit-rate, service capabilities...) ad-hoc wireless network infrastructure FN beacon FN1 FN2 FN3 med-tier radio (e.g. 802.11x) FN4 Forwarding Node: seek (FN*, AP*) associate (FN3, AP3) routing update (FN3) routing update (AP3) forward data End-user: seek (FN*, AP*) associate (FN1, AP2) routing update (FN1) routing update (AP2) send data laptop may receive BTS beacon for wide-area service sensor node low-tier radio (e.g. 802.15.x) Protocols needed: Ad-hoc discovery (enhanced beacons, etc.) Ad-hoc MAC Ad-hoc network routing (extended metrics including energy) handoff, QoS control, multicast (..features) 10
SOHAN Protocols: Discovery Concepts Creates efficient ad-hoc network topology just above MAC layer in order to reduce burden on routing protocol ##!" #$ % AP coverage area Forwarding Node (FN) Access Point (AP) Low-tier access links (AP/FN Beacons, MN Associations, Data) Low-tier (e.g. sensor) Mobile Node (MN) FN coverage area Ad-hoc infrastructure links between FNs and APs (AP/FN Beacons, FN Associations, Routing Exchanges, Data) "# $ %! 11
SOHAN Protocols: Topology Discovery Delay Constrained Energy Minimization: 12
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