Simulation Study of a Cellular Aided Mobile Ad-Hoc Network

This report studies the performance of a Cellular Aided Mobile Ad-hoc (CAMA) network by simulation in ns-2. The simulation results are extensions to the previous published results in the paper on CAMA ([1]). The link adaptation, the impact of position error, carrier sense threshold, duration time and mobility, the transmission of CBR, TCP, video and VoIP, and the cellular overhead are studied. The delivery ratio, throughput, network delay, data rate and hop count are presented and analyzed. Gang Ding, Xiaoxin Wu, Bharat Bhargava, and Shan Lei Nov. 6th, 2003 1 Simulator: ns-2 and extension 1.1 Mobile wireless network simulation in ns-2 The mobile wireless part of os-2 is ported from eMU's Monarch group. MobileNode is the basic Node object with added functionalities like movement, ability to transmit and receive on a channel that allows it [0 be used to create mobile, wireless simulation environments. The network stack for a mobilenode consists of a link layer(LL), an ARP module connected to LL, an interface priority queue(lFq), a mac layer(MAC), a network interface(netlF), all connected to the channel. These network components are created and plumbed together in OTcl. Each component is briefly described here. Link Layer The LL used by mobilenode is similar to the LL for wired network simulation in os-2. The only difference is that the link layer for mobilenode has an ARP module connected to it which resolves all IP to hardware (Mac) address conversions. Nonnally for all outgoing packets, the packets are handed down to the LL by the Routing Agent. The LL hands down packets to the interface queue. For all incoming packets, the mac layer hands up packets to the LL. ARP The Address Resolution Protocol module receives queries from Link layer. If ARP has the hardware address for destination, it writes it into the mac header of the packet. Otherwise it broadcasts an ARP query, and caches the packet temporarily. For each unknown destination hardware address, there is a buffer for a single packet. Incase additional packets to the same destination is sent to ARP, the earlier buffered packet is dropped. Once the hardware address of a packet's next hop is known, the packet is inserted into the interface queue. Interface Queue The queue is implemented as a priority queue which gives priority to routing protocol packets, inserting them at the head of the queue. It supports running a filter over all packets in the queue and removes those with a specified destination address. Mac Layer The IEEE 802.11 distributed coordination function (DCI') Mac protocol has been implemented. It uses a RTS/CTSIDATNACK pattern for all unicast packets and simply sends our DATA for all broadcast packets. Network Interfaces The network interface layer serves as a hardware interface which is used by mobilenode to access the channel. The wireless shared media interface subjects to collisions and the radio propagation model receives packets transmitted by other node interfaces to the channel. The interface stamps each transmitted packet with the meta-data related to the transmitting interface like the transmission power, wavelength etc. This meta-data in packet header is used by the propagation model in receiving network interface to determine if the packet has minimum power to be received andlor captured and/or detected (carrier sense) by the receiving node. The model approximates the DSSS radio interface (Lucent WaveLan direct-sequence spread-spectrum).