CHAPTER 7 SIMULATION OBSERVATIONS

Transcription

1 CHAPTER 7

2 CHAPTER 7 SIMULATION OBSERVATIONS Over a randomly distributed wireless network system with the specification is modeled with the suggested algorithms for communication from a selected source to destination. The architecture is designed to have the suggested algorithm running per node and the observations were made for various quality metrics to evaluate the robustness of the network. Quality metrics such as throughput, average packet delivery ratio, communication delay, BER, at the variation of data rate, offered bandwidth, interference level etc. were evaluated. The developed method is evaluated over two advanced routing schemes in wireless network namely DSR and AODV routing scheme to observe its feasibility. For the simulation of the developed algorithm a distributed network is created with following specifications,

3 Table 7.1: Network specification used for the network modeling

4 Figure 7.1: distributed and random values for parameters and specifications

5 The energy consumption model, which is obtained from the measurements of DS High Rate network interface card (NIC) operating at 2 Mbps. Power consumption in three modes of operation i.e. transmission(tx), Reception (Rx), Idle and sleeping. The values used are given as; Table 7.2: power consumption values used for simulation Figure 7.2: simulated values for used power consumption The link parameters used for the created network is presented in table below. Path loss Model BS antenna gain plus Cable Loss Carrier Frequency Rx antenna Tx antenna User antenna gain Maximun user EIRP Maximum B S EIRP CL Power Control Transmission Rates (kbit/s) TTI Scheduling Period Target L= Log1(R) 14 dbi 2 GHz 1 1 dbi 21dBm 24 dbm 1 db step size 8,16,32,64,128,256,384 1 ms Every 1 TTI 5.23 db (- % 7 load factor) Table 7.3: link parameter for simulation

6 Figure 7.3: link parameters for the created networks

7 System developed three important performance metrics are evaluated: - Packet Delivery Report: This is the data packets delivered to destinations with those generated by the sources. - Goodput: This is the amount of data that the sender is estimated divided by the time the highest ACK was received. If all packets are accepted in certain simulation time, the amount of data is separated from the whole simulation time. - MT Load Routing: This is the number of routing packets transmitted data packet sent to the destination. Also forwarded each packet is calculated as a transmission. This metric is also much related to the number of route changes that occur in the simulation. All the 82.11b wireless interfaces were modeled to have a bit rate of 1 Mbps. Here, a zero pause time i.e. continuous mobility is considered. The number of source destination pairs is 15 and the sources are designed with 512-byte packets. Each data point is an average of at least 3 runs with identical traffic scenarios but randomly generated mobility scenarios. Each of the 15 source destination pairs sends at a rate of 3 packets/s, a relatively low packet rate in order to avoid network congestion. All nodes have the same transmit power, in each experiment the transmit power is varied from 1 dbm to 24.5 dbm. The performance is evaluated for the variation of quality parameters at different data rate and the observation made is as outlined below,

8 packet delivery ratio(%) 1 9 DSR-ref DSR-ma AODV-ma ADOV-ref transmit power(dbm) Figure 7.4 : packet delivery ratio over varaible transmitted power at CST = -84dB Transmit power Packet delivery ratio DSR-ref DSR-ma AODV-ma AODV-ref Table 7.4: Packet delivery ratio for the developed routing methods at CST = -84dB

9 packet delivery ratio(%) 1 9 DSR-ref DSR-ma AODV-ma ADOV-ref transmit power(dbm) Figure 7.5: Packet delivery ratio over variable transmitted power, at CST=-81dBm Transmit Power Packet Delivery Ratio DSR-REF DSR-MA AODV-MA AODV-REF Table 7.5: Packet delivery ratio wrt. Transmitted power at CST=-81dBm Figure 7.4, illustrate that for CST= -84 dbm, the packet delivery ratios for reference and proposed are very similar with transmit power Pt higher than 16 dbm. When the transmit power is lower than 16 dbm, the proposed method outperforms the conventional method in terms of packet delivery ratio. However at any transmit power, the conventional

10 method demonstrates significantly lower routing load than the proposed method. This is due to the conventional method aggressive use of route caching. The conventional method is likely to find a route in the cache and avoid using route discovery every time a link is broken. In previous approaches, it was found that 55 percent of the route replies were from the route caches and even though 41 percent of the route replies were based on cached data contained broken routes, the the conventional method route maintenance was able to deliver good performance. However for Pt < 16 dbm, caching degrades the performance of the conventional method. In this case, low transmit powers yield frequent link failures. As a result, the conventional method caches will not be up to date, and stale routes are chosen from the cache. However, such a big degradation in the proposed method is not observed, largely because of the use of sequence numbers maintained at each node to determine the freshness of the routing information. The proposed method also features timer-based states in each node. A routing entry is deleted if it not used during a specified amount of time. On the other hand, conventional method keeps the routing entries in the cache until a link on the route is found to be broken.

11 normalized routing load DSR-ref DSR-ma AODV-ma ADOV-ref transmit power(dbm) Figure 7.6: Normalized routing load over variable transmitted power, at CST=-84dBm Transmit Power(dbm) Normalized Routing Load DSR-REF DSR-MA AODV-MA AODV-REF Table 7.6: Normalized routing load over variable transmitted power, at CST=-84dBm For both proposed and the conventional method, the gap between the results shrinks as the transmit power increases. However, this gap is

12 much wider for Conventional Method at low transmit power. Thus, our most important observation is that the performance of conventional method can depend strongly on the physical layer model [146][147]. For example, in Figure 7.5 for Pt = 1 dbm that the choice of layer model affects conventional method packet delivery ratio by 5 percent. On the other hand, the performance of proposed method appears to be relatively insensitive to the choice of physical layer model [146][147]. Increasing the CST value increases the packet delivery ratio because the number of instantaneous transmissions increases, but there is no SINR tracking to record the cumulative effect of interference which would actually degrade the performance. When using a specific rate for the unicast data packets, the choice of rate used for the broadcast data packets and the MAC control packets can dramatically affect the results.

13 normalized routing load DSR-ref DSR-ma AODV-ma ADOV-ref packet rate (pkts/s) Figure 7.7: Normalized routing load over variable packet rate at CST=- 81dBm Packet Rate(pkts/s) Normalized Routing Load DSR-REF DSR-MA AODV-MA AODV-REF Table 7.7: Normalized routing load over variable packet rate at CST=- 81dBm

14 packet delivery ratio(%) DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.8: packet delivery ration at 11Mbps with broadcast packets at 1Mbps. Packet Rate(pkts/s) Packet delivery ratio(%) DSR-REF DSR-MA AODV-MA AODV-REF Table7.8: packet delivery ration at 11Mbps with broadcast packets at 1Mbps.

15 packet delivery ratio(%) 4 35 DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.9: packet delivery ration at 11Mbps with broadcast packets at 1Mbps. Packet Packet Delivery Ratio (%) Rate(Pkts/sec) DSR-REF DSR-MA AODV-MA AODV-REF Table 7.9: packet delivery ratio at 4-1 packet/sec variation

16 normalized routing load The route discovery in proposed and conventional routing is made by the use of request packets. These route request packets are sent as broadcast data packets. Therefore the number of nodes participating in the route discovery and the distance between the nodes in the chosen path is affected by the physical rate chosen for transmitting broadcast data packets. A lower rate results in a higher range and therefore longer hops. However, in a single rate environment, the routing should be done with the rate that's used for transmitting the actual unicast data packets. For example, if the rate chosen for data packets is 11Mbps but the route is constructed with 1Mbps packets, the routing protocol may find a route that has hops that can't support an 11Mbps data rate. This may result in frequent link breakages and an unstable network behavior DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.1: Normalized routing load over variable packet rate at 11Mbps with broadcast and control packets at 1Mbps.

17 normalized routing load PACKET PACKET DELIVERY RATIO(%) RATE(ptks/sec) DSR-REF DSR-MA AODV-MA AODV-REF Table 7.1: Normalized routing load over packet rate. The impact of signal sense on the aggregate throughput is observed. It is seen that, the smaller the carrier sense range, the better the spatial reuse; but the interference at a receiver can also increase. With the increase of the carrier sensing range, as carrier sensing range is smaller, more spatial reuse is possible DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.11: Normalized routing load over variable packet rate at 11Mbps with broadcast data and control packets at 1Mbps.

18 PACKET PACKET DELIVERY RATIO(%) RATE(ptks/sec) DSR-REF DSR-MA AODV-MA AODV-REF Table 7.11: Normalized routing load over variable packet rate b supports two types of access modes: the physical carrier sensing mechanism and the RTS/CTS based mechanism. Since transmitting RTS and CTS frames increases the overhead, there is a trade-off between such overhead and the overhead from collisions between packets in the physical carrier sensing mode. Especially in high-rate situations this can degrade the network performance because the physical headers including the PLCP preambles of data, ACK, RTS and CTS frames are transmitted at 1Mbps regardless of the data rate.

19 packet delivery ratio(%) DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.12: packet delivery ratio for variable packet rate at 11Mbps with 512-byte packets RTS/CTS ON PACKET PACKET DELIVERY RATIO(%) RATE(ptks/sec) DSR-REF DSR-MA AODV-MA AODV-REF Table 7.12: packet delivery ratio for variable packet rate

20 packet delivery ratio(%) DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.13: packet delivery ratio wrt. packet rate for 11Mbps with 512- byte packets RTS/CTS ON PACKET PACKET DELIVERY RATIO(%) RATE(ptks/sec) DSR-REF DSR-MA AODV-MA AODV-REF Table 7.13: packet delivery ratio wrt. packet rate

21 normalized routing load The effect of loading the network were observed with two different power levels, Pt=16 dbm and Pt=24.5 dbm. The packet rate of each source is slowly increased from 1 to 1, changing the total offered load to the network from 24 kb/s to 6kb/s in case of 512-byte packets and from 7 kb/s to 176 kb/s for 15-byte packets. The result obtained shows the packet delivery ratio and the normalized routing load for both proposed and reference method at 1Mbps with 512-byte packets and RTS/CTS option turned on DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.14: normalized routing load over variable packet rate at 11Mbps with 512-byte packets RTS/CTS ON

22 PACKET PACKET DELIVERY RATIO(%) RATE(ptks/sec) DSR-REF DSR-MA AODV-MA AODV-REF Table 7.14: packet delivery ratio over variable packet rate The reference s packet delivery ratio is almost the same as proposed at Pt=24.5 dbm, whereas the proposed method is 2% better than reference at Pt=16 dbm at every packet rate. This is due to the fact that in a situation induced by lower transmit power, conventional method fails to find reliable routes during route maintenance because of its aggressive caching strategy.

23 normalized routing load DSR-ref DSR-ma AODV-ma ADOV-ref packet rate(pkts/s) Figure 7.15: normalized routing load at variable data rate of 11Mbps with 512-byte packets RTS/CTS ON PACKET RATE(pkts/sec) PACKET DELIVERY RATIO(%) DSR-REF DSR-MA AODV-MA AODV-REF Table 7.15: % of offered packet delivery ratio at packet rate of 4-1 pkts/sec When focused on the impact of the physical layer model [146][147] on the packet delivery ratio, it is observed that both methods are relatively

24 insensitive to the choice of physical layer model [146][147]. This is because the offered load is high for 1Mbps and packet losses are high due to congestion, regardless of the physical layer model. In above Figure it is observed that the results of the same simulations with RTS/CTS option turned off. Here the qualitative behavior is exactly the same. However, the packet delivery ratios are 1% better than the previous simulations. It is seen that when the packet length is increased, the relative overhead of RTS/CTS handshake decreases therefore the difference in performance between RTS/CTS and basic scheme is much less than the 512-byte case. 1 AODV Mean=.24 std= goodput(mbps) Figure 7.16: observed goodput for mean route of AODV =.24 and standard deviation of.148

25 25 AODV mean=.166 std= normalized routing load Figure 7.17: Normalized routing load for mean route of AODV =.166 and standard deviation of DSR mean=.26 std= goodput(mbps) Figure 7.18: observed goodput for mean route of DSR =.26 and standard deviation of.149

26 25 DSR mean=.44 std= normalized routting load Figure 7.19: normalized routing load for mean route of DSR =.44 and standard deviation of.48 1 AODV mean=.154 std= goodput(mbps) Figure 7.2: observed goodput for mean route of AODV =.154 and standard deviation of.161

27 2 AODV mean=.913 std= normalized routing load Figure 7.21: normalized rotuing load for mean route of AODV =.913 and standard deviation of DSR mean=.184 std= goodput(mbps) Figure 7.22: observed goodput for mean route of DSR =.184 and standard deviation of.141

28 2 DSR mean=.264 std= normalized routing load Figure 7.23: normalized rotuing load for mean route of DSR =.264 and standard deviation of DSR mean=.264 std= normalized routing load Figure 7.24: normalized routing load for mean route of DSR =.264 and standard deviation of 1.191

29 1 AODV mean=.183 std= goodput(mbps) Figure 7.25: observed goodput for mean route of AODV =.183 and standard deviation of AODV mean=.183 std= goodput(mbps) Figure 7.26: observed goodput for mean route of AODV =.183 and standard deviation of.188

30 2 AODV mean=.654 std= normalized routing load Figure 7.27: normalized routing load for mean route of AODV =.654 and standard deviation of DSR mean=.194 std= goodput(mbps) Figure 7.28: observed goodput for mean route of DSR =.194 and standard deviation of.183

31 2 DSR mean=.159 std= normalized routing load Figure 7.29: normalized routing load for mean route ofdsr =.159 and standard deviation of.128 For a 512-byte data packets at 1 Mbps data rate and the transmit power was 1 dbm. In observation Figures obtained, it is observed that three peaks in the good put plot are present. The first peak around.5mbps belongs to the connections with one hop. With one hop communications there can't be any collisions once the route is found since there's just one FTP pair in the network. Therefore there is not much difference between the good put of two method at one hop. When compared, the 1 hop good put distribution of the results of the experiments with RTS/CTS ON with its RTS/CTS OFF complement, it is observed that they are almost the same. The only difference is that throughput with RTS/CTS OFF is a little higher than with RTS/CTS ON because of the overhead of the

32 RTS/CTS. The reason of this similarity is the fact that during route discovery, the route request packets are broadcasted and therefore not preceded with an RTS/CTS exchange. Because of this, the route discovery in two different scenarios is identical. This can be seen in above Figures. It is observe that, despite the fact that the results of stationery scenarios with just one FTP connection, there is still a big difference between the two results. This is due to the sender's inability to accurately determine the cause of a packet loss. The sender assumes that all packet losses are caused by congestion. Thus, when a link on a route breaks, the sender reacts as if congestion was the cause, reducing its congestion window and, in the instance of a timeout, backing-off its retransmission timeout (RTO). Therefore, link breakages degrade the performance, and these breakages occur more often in conventional routing scheme. From all these observations made it is observed that the routing scheme of for a wireless network with distributed architecture is outperforming the performances as compared to the conventional method.