Chun Nie, Thanasis Korakis, and Shivendra Panwar Department of Electrical and Computer Engineering, Polytechnic University, Brooklyn A Multi-hop Polling Service with Bandwidth Request Aggregation in IEEE j Networks IEEE VTC 2008

OutlineOutline Introduction System model The Multi-hop Polling Service (mPS) Mechanism Performance evaluation Conclusions

IntroductionIntroduction WiMAX has emerged as an advanced broadband wireless access technology and has attracted a lot of attention. Recently the j Relay Task group was formed to standardize a WiMAX multi-hop relay (MMR) system. In an MMR system, MSs are allowed to route through intermediate RSs to reach the BS, which differs from the single-hop WiMAX topology.

IntroductionIntroduction IEEE j has classified MMR systems into a transparent mode and a non-transparent mode. BS RS MS BS RS MS User Data Preamble DL/UL MAP User Data Preamble DL/UL MAP Transparent RS  A transparent RS does not transmit preamble, FCH, DL/UL MAP, and DCD/UCD  Centralized scheduling at MR-BS  Capacity enhancement only Non-transparent RS  A non-transparent RS transmits preamble, FCH, DL-/UL-MAP, and DCD/UCD  Centralized scheduling or distributed scheduling  Capacity enhancement and coverage extension

IntroductionIntroduction Conventional scheduling service in WiMAX Scheduling services in the IEEE e standard 1) UGS: UGS enables the BS to allocate fixed-size bandwidth periodically to the MS. 2) rtPS: rtPS is designed for RT applications. It enables the BS to poll the MS at fixed intervals for bandwidth requests. 3) ertPS: ertPS is designed for voice application. During voice silence, ertPS decreases the grant size to save bandwidth. 4) nrtPS and BE: nrtPS and BE are two scheduling services for delay-insensitive applications by contention-based bandwidth requests. Motivation  These scheduling services are basically designed for a single-hop WiMAX system without considering the requirements of a multi-hop system.

IntroductionIntroduction Goals: To propose a framework for a multi-hop polling service (mPS) to facilitate efficient UL bandwidth allocation in a centralized non-transparent MMR WiMAX. To design a polling service in a multi-hop topology catering to bursty applications. To achieve high bandwidth efficiency without compromising delay performance

System model An RT Bursty ON/OFF Traffic model Multi-hop Scenarios in IEEE j Networks

System model System model - An RT Bursty ON/OFF Traffic model An RT Bursty ON/OFF Traffic model The traffic pattern of applications such as VoIP and gaming, are characterized by bursty ON/OFF flows with varying rates and packet sizes. During each ON period: The variable-sized packets arrive in bursts with variable packet interarrival time During each OFF period: No packet is generated and the MS is idle  These applications also have latency constraints on packet delivery.

System model - Multi-hop Scenarios in IEEE j Networks One BS, one non-transparent RS, and M MSs BS RS MS

One BS, one non-transparent RS, and M MSs MS BS RS Data and Signaling traffic System model - Multi-hop Scenarios in IEEE j Networks

The Multi-hop Polling Service (mPS) Mechanism - Overview MS 1 BS RS ON Period OFF Period RS  MS BS  RS  The key idea is how to properly configure polling parameters to achieve the desired delay performance. ON Period OFF Period

The Multi-hop Polling Service (mPS) Mechanism MS 1 BS RS The basic idea of mPS: 1) MSs send their BWReq to their superordinate RS at their respective polling intervals. 2) RS collects all BWReqs from MSs and generates an Aggregated BWReq to the BS. MS 2 BWReq Aggregated BWReq

The Multi-hop Polling Service (mPS) Mechanism MS 1 BS RS ON Period T i, min : Minimum polling interval used by the ith MS (1 ≤ i ≤ M) N i : Number of initial polls with T i, min during idle period of the ith MS T i, max : Maximum polling interval used by the ith MS (1 ≤ i ≤ M) OFF Period RS  MS

The Multi-hop Polling Service (mPS) Mechanism MS 1 BS RS ON Period T 0, min : Minimum polling interval used by the RS N 0 : Number of initial polls with T 0,min during idle period of RS T 0, max : Maximum polling interval used by the RS OFF Period BS  RS

The Multi-hop Polling Service (mPS) Mechanism mechanism: An example of mPS mechanism: MS 1 BS RS MS 2 ON Period OFF Period RS MS 1 BWReq T 1, min =3 …

The Multi-hop Polling Service (mPS) Mechanism mechanism: An example of mPS mechanism: MS 1 BS RS MS 2 ON Period OFF Period RS MS 1 T 1, min = 3, T 1, max = 9 T 2 = min{2 2-1 ×3, 9} = 6 T 3 = min{2 3-1 ×3, 9} = 9 T 4 = min{2 4-1 ×3, 9} = 9 …… T1T1 T2T2 T3T3 T4T4

The Multi-hop Polling Service (mPS) Mechanism During ON periods: Polling intervals are fixed and short. During OFF periods: Polling intervals are lengthened exponentially. mPS can incorporate the use of piggybacking and bandwidth stealing defined in the standards.

Performance evaluation Performance evaluation One BS, one RS, and multiple MSs

Performance evaluation Performance evaluation

ConclusionsConclusions They have developed a multi-hop polling service for the IEEE j MMR networks. The mPS consumes considerably less bandwidth while still satisfying the delay constraints of most RT applications. Their mPS mechanism enhances bandwidth efficiency significantly, especially when combined with BWReq aggregation.

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