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LA-MAC: A Load Adaptive MAC Protocol for MANETs

This paper introduces LA-MAC, a hybrid MAC protocol combining CSMA and TDMA for Mobile Ad hoc Networks. It discusses implementation, performance evaluation, and outcomes of LA-MAC on MANET testbed.

jeannebriggs
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LA-MAC: A Load Adaptive MAC Protocol for MANETs

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  1. LA-MAC: A Load Adaptive MAC Protocol for MANETs IEEE Global Telecommunications Conference(GLOBECOM )2009. Presented by Qiang YE Smart Grid Subgroup Meeting

  2. Outline • Introduction • LA-MAC Overview • CSMA Mode • TDMA Mode • Hybrid Mode • LA-MAC Implementation • Performance Evaluation • Conclusion LA-MAC: A Load Adaptive MAC Protocol for MANETs

  3. Introduction • CSMA and TDMA are two mainstream MAC protocols currently used in Mobile Ad hoc Networks. • CSMA: a contention-based MAC protocol firstly appeared in IEEE 802.11 Wireless LAN DCF functionality to coordinate the channel access among users • Advantages: • Indepentdent of network topology and sychrony information • Good performance under low contention • Disadvantages: • Degraded performance under high contention LA-MAC: A Load Adaptive MAC Protocol for MANETs

  4. TDMA： A slot-based MAC protocol • Advantages: • Collision free • Good performance under high contention level • Disadvantages: • Global synchrony information • Inefficiency under low contention level LA-MAC: A Load Adaptive MAC Protocol for MANETs

  5. According to the pros and cons of both algorithms, A hybird MAC is motivated to perform better tradeoff between these two. See Fig.1 LA-MAC: A Load Adaptive MAC Protocol for MANETs

  6. The key contributions of this paper: • Strengthen the advantages of both CSMA and TDMA • Make a good cross-layer implementation on the real MANET testbed. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  7. Outline • Introduction • LA-MAC Overview • CSMA Mode • TDMA Mode • Hybrid Mode • LA-MAC Implementation • Performance Evaluation • Conclusion LA-MAC: A Load Adaptive MAC Protocol for MANETs

  8. LA-MAC Overview • CSMA Mode: LA-MAC simply employs a random backoff mechanism similar to IEEE 802.11 MAC protocol. Before transmitting, it waits for a random back-off, then senses the channel, if idle, it tranmits immediately, otherwise wait and back-off again. when the receiver receives the data, it sends ACK to indicate whether it receives successfully or not LA-MAC: A Load Adaptive MAC Protocol for MANETs

  9. TDMA Mode each node collects its one-hop neighbor information utilizing a periodic Ping-like broadcast mechanism. Then each node exchanges its one-hop neighbor list with its one-hop neighbors to get the two hop neighborhood information. Then, Dynamic Time Slot Assignment (DTSA) can be executed. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  10. Hybrid Mode • a node can be in two states: Low Contention (LC) and High Contention (HC) • In LC, all nodes can transmit in CSMA mode. • A node can stay in HC state for a predefined period THC HC LC if it does not receive notification among this period. LC HC if the node misses NthACKs • In HC, the two hop neighbors of the slot owner is not allowed to transmit. Only the owner and its one hop neighbor can compete for the slot access.(more like TDMA) LA-MAC: A Load Adaptive MAC Protocol for MANETs

  11. Outline • Introduction • LA-MAC Overview • CSMA Mode • TDMA Mode • Hybrid Mode • LA-MAC Implementation • Performance Evaluation • Conclusion LA-MAC: A Load Adaptive MAC Protocol for MANETs

  12. LA-MAC Implementation • It presents the implementation of LA-MAC on Universal Software Radio Peripheral (USRP) software defined nodes.See figure 2. • MANET nodes built on USRP and GNU Radio, GNU Radio runs on the host and USRP is connected to the host via a USB connection. • While USRP functions as the RF frontend and the baseband processing unit, the PHY and DATA LINK layers are implemented in GNU Radio. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  13. Fig.2 The system architecture of a MANET testbed node. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  14. Carrier sensing • GNU Radio offers a basic Python-based implementation of CSMA to which we refer as GR-CSMA. It has some problems of carrier sensing . • Inband signaling provides a potential solution to this problem (but the USB delay still unavoidable). See Fig. 3 • LA-MAC can also offload the carrier sensing function to the FPGA chipset on the USRP node to solve this problem. (a random back-off is introduced to avoid collisions among simultaneous transmissions) LA-MAC: A Load Adaptive MAC Protocol for MANETs

  15. Collision Avoidance Collisions are mainly due to hidden terminal problem. RTS/CTS is not used on the host due to the timing issue, so the hybrid mode mentioned before can deal with this problem. • Clock synchronization LA-MAC requires a node to maintain clock synchronization with other nodes in its contention area. The timestamp field in the meta-data is used for synchronization. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  16. Outline • Introduction • LA-MAC Overview • CSMA Mode • TDMA Mode • Hybrid Mode • LA-MAC Implementation • Performance Evaluation • Conclusion LA-MAC: A Load Adaptive MAC Protocol for MANETs

  17. Performance Evaluation • The paper presents the experimental studies to compare the performance of LA-MAC protocol against GR-CSMA and TDMA. • Two scenarios are considered in the paper: • One hop scenario: 16 nodes are distributed within a one-hop distance of one another. • Two hop scenario (With hidden terminals) see fig.4 Fig.4 Topology of Two hop scenario LA-MAC: A Load Adaptive MAC Protocol for MANETs

  18. In the simulation, both the transmission latency(RTT time) and the maximum achievable data throughput(MADT) are analyzed between above three MACs: • Transmission latency: • LA-MAC is forced to be in CSMA mode(LA-CSMA). The RTT time in LA-CSMA is lower than GR-CSMA due to the following reasons: • FPGA carrier sensing • Random back-off mechanism • MADT: • In the one-hop scenario, Fig.5. shows the throughput versus the contention level of the network. LA-CSMA(independent of contention level) out performs GR-CSMA due to the above to reasons to avoid collisions LA-MAC: A Load Adaptive MAC Protocol for MANETs

  19. In the two- hop scenario, see Fig.6, LA-MAC achieves a reasonable trade-off between TDMA and CSMA Fig.5 The throughput comparison of the one-hop experiment. Fig.6 The throughput comparison in the two-hop experiment. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  20. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  21. Outline • Introduction • LA-MAC Overview • CSMA Mode • TDMA Mode • Hybrid Mode • LA-MAC Implementation • Performance Evaluation • Conclusion LA-MAC: A Load Adaptive MAC Protocol for MANETs

  22. Conclusion • In this paper, we present Load-Adaptive MAC (LA-MAC) protocol for MANETs capable of switching modes of operation. • While LA-MAC operates in CSMA mode for light traffic loads, it switches to TDMA mode of operation for heavy traffic loads and increased contention conditions. • We implement and host LA-MAC in a MANET testbed formed by a collection of USRP nodes. Our implementation approach uses GNU Radio and inband signaling technology. • Our experimental results show that LA-MAC achieves a better performance measured in terms of throughput than CSMA and TDMA over either one-hop or two-hop MANET topologies. LA-MAC: A Load Adaptive MAC Protocol for MANETs

  23. LA-MAC: A Load Adaptive MAC Protocol for MANETs

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