Designing MAC protocols for ad hoc wireless network -Yanlin Peng 11/18/2018 ©CSL

Introduction In ad hoc networks all wireless devices within a range discover each other and communicate in peer-to-peer fashion without involving central access points Multi-hop connectivity is one of the most prominent features The current version of IEEE 802.11 MAC protocol does not function well in multi-hop ad hoc networks Performance suffers as the number of devices grows, and a large ad-hoc network quickly becomes difficult to manage 11/18/2018 ©CSL

Goals Classify MAC layer protocols for ad hoc networks Provide design guidelines for ad hoc network MAC layer protocols 11/18/2018 ©CSL

Protocol list 11/18/2018 ©CSL

Key features Channel separation and access Topology Power Transmission initiation Traffic load and scalability Range 11/18/2018 ©CSL

Channel Separation and Access How to use the available medium efficiently Physical layers Radio frequency(RF) signal Still the main method for data transmission Ultra wide band radio(UWB) Promising? Acoustic communication Single channel or multiple channel? 11/18/2018 ©CSL

Single Channel All the nodes share the medium for all their control and data transmissions Collisions are an inherent attribute and back-off mechanism is required Hidden node problem Important protocol: BTMA, MACA,FAMA CSMA, MACA, MACAW, FAMA, RIMA-SP, DPC/ALP, MACA-BI, MARCH All of these protocols except CSMA based on RTS/CTS handshake and carrier sensing to avoid hidden node problem. 11/18/2018 ©CSL

Single Channel FAMA Noise c FAMA-NPS FAMA-NCS B C FAMA-NPS FAMA-NCS FAMA Sense carrier before sending an RTS Dominative CTS 11/18/2018 ©CSL

Single Channel MARCH Reduce control signaling proposes a single RTS on the first hop of the path, while only CTS is required for every subsequent hop 11/18/2018 ©CSL

Multiple Channel Generalized separation BTMA,DBTMA,PAMA,DCAPC,GRID-B TDMA (Time Division Multiple Access) FPRP,CATA,SRMA/PA, Markowski, ADAPT, D-PRMA FDMA (Frequency Division Multiple Access) MCSMA 11/18/2018 ©CSL

Multiple Channel CDMA(Code Division Multiple Access) Use orthogonal codes to spread signals One code is one channel MC MAC Use one code for control and N codes for data Dynamically allocates multiple codes for high rate packets IEEE 802.11 FHSS and DSSS Did not use orthogonal codes 11/18/2018 ©CSL

Multiple Channel SDMA(Space Division Multiple Access) Use directional antennas to access the full spectrum Lal Receiver init an omni-directional RTR Neighbors reply by using a directional RTS (DRTS) Receiver replies to the accepted senders with a Directional CTS (DCTS) to complete the handshake 11/18/2018 ©CSL

Multiple Channel Hybrid MMAC PRMA, HIPERLAN, HRMA Bluetooth using smart antennas to establish a multi-hop link between the source and the destination through the RTS/CTS handshake Hybrid PRMA, HIPERLAN, HRMA Use both TDMA and FDMA Bluetooth CDMA and TDMA 11/18/2018 ©CSL

Summary RTS/CTS handshake is the basic solution for hidden node problem. Carrier sensing is the basic solution for collision avoidance. Multiple-channel protocols allow for more users than single-channel protocol. However, multiple-channel need more complex management. 11/18/2018 ©CSL

Topology Features Single-hop flat topology Multi-hop flat topology Changing frequently Single-hop flat topology Multi-hop flat topology Clustered topology Centralized topology 11/18/2018 ©CSL

Single-hop flat topology CSMA, MSC, FAMA, MACA-BI, RIMA-SP, IEEE 802.11 Limited capability and performance in dense or highly loaded network High power consumption and lack of flexibility More suitable for wired networks or smaller scale and lower throughput wireless networks 11/18/2018 ©CSL

Multi-hop flat topology PAMAS MCSMA Frequency channel reuse GRID-B pre-defined geographic area DCA-PC, DCA/APL, Lal, MMAC Establish multi-hop links using directional antennas MARCH Hearing control signaling from the previous hop 11/18/2018 ©CSL

Clustered topology Emulate infrastructure wireless networks by electing a clustered head working as a base station Cluster head burdens more than nodes VBS Simple mechanism for choosing a cluster head randomly periodically send “hello” messages join the cluster of the lowest IP address Nodes with lower IP address suffer from more resource use 11/18/2018 ©CSL

Clustered topology WCA elects cluster heads based on a weight function weight parameters the distance from neighbors the time as a cluster head (battery power available) Mobility Connectivity supports mobile nodes by allowing handovers for nodes moving from one cluster to another 11/18/2018 ©CSL

Clustered topology Jin, GPC Bluetooth HIPERLAN electing a cluster head according to battery power only simpler but less generalized approach than WCA Bluetooth In the form of piconets of one master and up to seven slavers The only protocol statically assigning a master HIPERLAN forwarders and p-supporters share the duties of a cluster head 11/18/2018 ©CSL

Centralized topology BTMA, MACAW, PRMA Ad hoc networks generally do not adopt a centralized topology However, these protocols provide valuable concepts, such as a busy tone channel and time slot reservation that are extendable to ad hoc networks 11/18/2018 ©CSL

Summary a multi-hop flat topology or a clustered topology are more suitable to ensure scalability in ad hoc networks In homogeneous networks, a multiple-hop flat topology is more appropriate In heterogeneous networks, a clustered topology allows the high-power nodes to become cluster heads and handle most of the overhead control messaging For example, a heterogeneous network consisting of WLAN and GSM or 3G 11/18/2018 ©CSL

Power Transmit power control Sleep mode Control the transmit power so that it is just enough to reach the intended receiver. GPC, DCA-PC, DPC/ALP, Lal, MMAC Sleep mode Sleep while idle to reduce power consumption due to overhearing irrelevant transmission PAMAS, HIPERLAN, Blutooth Potential drawback: powering up consume more power 11/18/2018 ©CSL

Power Battery level awareness Reduced control overhead Adjusting node behavior according battery power levels Useful in power-heterogeneous network DPC/ALP, Jin, GPC, WCA Reduced control overhead Reduced overhead of control messages MARCH Savings for particular settings Unaware of any power issues 11/18/2018 ©CSL

Summary The different power-saving mechanisms in this section actually conserves power depending on the application type. A multi-purpose protocol should include as many of these mechanisms as possible to ensure its power efficiency in different application scenarios. 11/18/2018 ©CSL

Transmission initiation Sender-initiated protocols and receiver-initiated protocols Dependent on the potential application areas of that protocol Sender initiated Receiver initiated MACA-BI, RIMA-SP, RICH-DP, Lal 11/18/2018 ©CSL

Summary A sender-initiated protocol is more suitable for generalized networks For some specialized networks, such as sensor networks, receiver-initiated protocols can yields better network performance 11/18/2018 ©CSL

Traffic load and scalability Highly loaded networks RICH-DP, Lal (receiver-initiated) Lal, MMAC (space multiple access) PS-DCC (changing sending probability) GRID-B and ADAPT (Multiple access of channel or slot) TDMA protocols 11/18/2018 ©CSL

Traffic load and scalability Dense networks Promote perform by power control GPC, DCA-PC, Lal, MMAC, GRID-B, MCSMA 11/18/2018 ©CSL

Traffic load and scalability Voice and real-time traffic Priority and reservation PRMA Allows voice nodes to reserve slots for subsequent frames SRMA/PA Allows voice nodes to preempt data nodes VBS ensure a certain bandwidth allocation, which makes them suitable for supporting real-time traffic Markowski Hard real-time nodes preempt soft real-time nodes that also preempt non-real-time nodes PRMA Can work well within a clustered topology of ad hoc network. 11/18/2018 ©CSL

Summary Multiple-channel protocols and power-efficient protocols exhibit better performance for high-load and high-density networks. TDMA and reservation-based protocols perform best for networks dominated by voice and real-time traffic. 11/18/2018 ©CSL

Range In wireless network, a more appropriate measure of offered traffic is bit-meters/second. That is also called spatial capacity. S = B/A S: spatial capacity A: transmission coverage area B: aggregate throughput of all coexisting transmissions in A I.e., a network able to transmit a bit 100 meters, may not be able to transmit the sane bit 200 meters. 11/18/2018 ©CSL

Range 11/18/2018 ©CSL

Summary There are tradeoffs between increasing the range and achieving a high spatial capacity 11/18/2018 ©CSL

Guide Support multiple channels in order to separate control from data and reduce the probability of collisions Adopt a multi-hop topology to ensure scalability The protocol should also support a flat mode and a clustered mode depending on application requirements 11/18/2018 ©CSL

Guide Be power-aware, control transmission, power, and support sleep mode sender-initiated the optimal range for a generalized protocol should be in the short to medium range, because in a long-range network control becomes more difficult and collisions more frequent 11/18/2018 ©CSL

My observations Quality of service This article referred to differentiated service when talking about voice and real-time traffic, but did not emphasize quality of service Qualify of service consists of many aspects, such as throughput, latency boundary Differentiated service is more and more important and cannot be neglected. For example, in DSRC, differentiated service is indispensable, since packets for security apparently have the highest priority 11/18/2018 ©CSL

My observations (cont.) Ad hoc networks with speedy nodes, such as DSRC Multiple channels and limited directions Helps from other sensors, such as speedometer Power is relatively plenty with the support of car inverters Absolute priority needed (for safety messages) Relatively steady topology considering relative speed Predicable moving Heterogeneous wireless networks are possible, such as 802.11, GSM, CDMA, GPS Predicable moving (if cars accelerate or change directions, other sensors can tell this to wireless LAN) 11/18/2018 ©CSL

Vehicle-to-vehicle Safety Messaging in DSRC DSRC is 75 MHz of spectrum at 5.9 GHz allocated by the FCC (Federal Communication Commission) DSRC will support safety-critical communications as well as other Intelligent Transportation System applications based on 802.11a technology DSRC will have six service channels and one control channel This paper design a protocol to send safety messages from vehicle to vehicle in the control channel 11/18/2018 ©CSL

Vehicle-to-vehicle Safety Messaging in DSRC Features Most safety messages produced by a vehicle are useful to many vehicles Safety messages was updated periodically QoS consideration reception probability and channel busy time Protocol based on the repetition ideas implemented in two layers, the MAC layer and MAC extension layer 11/18/2018 ©CSL

Vehicle-to-vehicle Safety Messaging in DSRC MAC extension layer lies between the Logical Link Control layer (IEEE 802.2) and the MAC layer. Schedule safety messages Six protocols based on the same MAC extension layer. Asynchronous and synchronous 11/18/2018 ©CSL

My observation Multiple channels and Medium range Multi-hop or clustered topology Power is not the primarily concerned feature Sender initialized Low latency needed Broadcast is appropriate for safety messages No feedback or detection mechanisms for receipt The collision probability will increase when the highway is jammed 11/18/2018 ©CSL