DISTRIBUTED AND ADAPTIVE MEDIUM ACCESS CONTROL FOR INTERNET-OF-THINGS-ENABLED MOBILE NETWORKS
ABSTRACT
In this paper, we propose a distributed and adaptivehybrid medium access control (DAH-MAC) scheme for a singlehopInternet of Things (IoT)-enabled mobile ad hoc networksupporting voice and data services. A hybrid superframe structureis designed to accommodate packet transmissions from avarying number of mobile nodes generating either delay-sensitivevoice traffic or best-effort data traffic. Within each superframe,voice nodes with packets to transmit access the channel in acontention-free period (CFP) using distributed time division multipleaccess, while data nodes contend for channel access ina contention period (CP) using truncated carrier sense multipleaccess with collision avoidance. In the CFP, by adaptivelyallocating time slots according to instantaneous voice trafficload, the MAC exploits voice traffic multiplexing to increasethe voice capacity. In the CP, a throughput optimization frameworkis proposed for the DAH-MAC, which maximizes theaggregate data throughput by adjusting the optimal contentionwindow size according to voice and data traffic load variations.Numerical results show that the proposed MAC scheme outperformsexisting quality-of-service-aware MAC schemes for voiceand data traffic in the presence of heterogeneous traffic loaddynamics.Index
EXISTING SYSTEM:
In literature, contention-based MAC schemes with servicedifferentiation are commonly used for supporting heterogeneoustraffic. The enhanced distributed channelaccess standardized in IEEE 802.11, is one typical example,in which delay-sensitive realtime traffic is granted smallerarbitration interframe space (AIFS) and contention windowsize to access the channel with a higher probability than nonrealtimetraffic. It is demonstrated in that thecontention window size differentiation a realtime andnonrealtime traffic is superior over the AIFS differentiationin achieving a smaller access delay for the realtime servicein a traffic saturation condition. To grant voice traffic deterministicchannel access priority for further improving thedelay performance, busy-tone based contention protocols areproposed, in which each voice node broadcasts abusy-tone signal, instead of decrementing a backoff counter,after an idle AIFS duration to prevent the contention interventionfrom data nodes. Even if the contention separation isachieved between voice traffic and data traffic in busy-tonebased protocols, contention collisions still exist and accumulatea voice (data) nodes themselves after the voice(data) traffic load becomes relatively high, making the delay(throughput) performance degraded to an unacceptable level.By avoiding contention collisions, distributed TDMAschemes allocate time slots to each node in a distributedway for exclusive use. They are more effective thancontention-based MAC schemes in guaranteeing the delay ofrealtime traffic especially in a relative high traffic load condition,where channel time is accumulated and wasted forpacket collisions resolution in contention-based schemes. Tomaximize resource utilization, the distributed TDMA time slotallocation should be adaptive to the instantaneous voice trafficload, a TDMA-based distributed packet reservationmultiple access (D-PRMA) protocol is proposed, in whichvoice nodes are granted a higher probability than data nodes tocontend for the channel based on slotted-Aloha
PROPOSED SYSTEM:
we propose a distributed and adaptive hybridMAC scheme (DAH-MAC), in which distributed TDMAis employed for voice packet transmissions to guaranteea voice packet loss rate bound and truncated CSMA/CA(T-CSMA/CA) is used for data nodes to access the channel.Most of the existing contention-based MAC schemes evaluatethe average access delay for voice traffic in a saturationcondition or with a constant arrival rate, which is not thecase in reality. We use a more accurate on/off model forvoice traffic generation, and exploit voice traffic multiplexingto improve the voice capacit. Since voice service is realtime,a packet not transmitted after a delay bound should bedropped at the source, and the voice packet delay has to beevaluated in a stochastic manner for calculating the packetloss probability. In this way, the delay requirement for voicetraffic can be satisfied probabilistically by guaranteeing thevoice packet loss rate below a given bound. The contributionsof this paper are threefold.The contributionsof this paper are threefold.1) To guarantee the voice packet loss rate bound, wepresent a distributed and traffic-adaptive TDMA timeslot allocation scheme to allocate one time slot for eachactive voice node according to its transmission bufferstate. Also, we establish an analytical model so that theMAC scheme can determine the voice capacity regionby adjusting an MAC parameter, i.e., the maximum timefraction allocation requirement for voice traffic in eachsuperframe, which facilitates voice session admissioncontrol for QoS guarantee. By exploiting the voice trafficmultiplexing, the resource utilization for voice trafficis improved significantly.2) The T-CSMA/CA based contention scheme is employedfor data traffic access. We establish an analytical modelof data saturation throughput for the DAH-MAC. Thesaturation throughput is a function of the number ofvoice and data nodes as well as the packet transmissionprobability of each data node.3) For the saturation throughput of the DAH-MAC, wederive an approximate closed-form expression of theoptimal data packet transmission probability as a functionof the heterogeneous network traffic load. Further,we obtain a closed-form expression of the optimal contentionwindow size, which establishes a mathematicalrelationship between the MAC layer parameter and theheterogeneous network traffic load. Based on the analysis,the maximum best-effort data saturation throughputcan be achieved by adjusting the contention window sizeaccording to variations of the number of voice and datanodes.
CONCLUSION
In this paper, we propose a distributed and traffic-adaptivehybrid MAC scheme for a single-hop IoT-enabled MANET. Ahybrid MAC superframe structure is devised, in which voicenodes are allocated a time slot in a distributed way by adaptingto their instantaneous transmission buffer states and datanodes contend to access the channel in a CP of each superframeaccording to the T-CSMA/CA. The proposed hybridMAC exploits the voice traffic multiplexing to improve theresource utilization while guaranteeing a voice packet lossrate bound, and reduces the congestion level for data nodesby the contention separation between voice and data traffic.A data throughput analytical and optimization framework isdeveloped for the hybrid MAC, in which a closed-form mathematicalrelationship is established between the MAC layerparameter (i.e., the optimal contention window size) and thenumber of voice and data nodes in the network. With thisframework, the maximum aggregate data throughput can beachieved and be adaptive to variations of the heterogeneousnetwork traffic load. Based on a comparison with two wellknownMAC protocols, simulation results demonstrate theeffectiveness of our proposed MAC in supporting voice anddata services in the presence of heterogeneous traffic loaddynamics.
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