**11.2. Spectral efficiency**

20 Wireless Sensor Networks / Book 1

208 Wireless Sensor Networks – Technology and Protocols Cross-Layer Design for Smart Routing in

From the perspective of resource allocation, the effect of energy harvesting can also be observed by analyzing the network lifetime. The network is able to operate at peak performance as long as sufficient transmission resources are available; this occurs until nodes are unable to maintain a high level of performance because remaining energy capacities are insufficient. Since energy harvesting enables us to prolong the network, it also increases the period of time that the network operates at high levels of throughput performance. We will analyze the impact of the replenishment rate *rh* on the network lifetime for smart routing.

We conduct a performance evaluation of our policy based on the following metrics:

• Application criticality and performance improvement of smart routing vs. minimum

• Blocking probability and its dependency on the number of operating channels in the

• Energy harvesting effects on energy capacity and network lifetime for various rates of

Table 6 illustrates the ability of the smart routing protocol to meet performance requirements of a number of applications. The Ultrawideband (UWB) cluster, which executes a video monitoring application, achieves total network throughput that varies between 84.4 Mbps and 3.4 Gbps. Meanwhile, the Zigbee cluster achieves a maximum real-time throughput of 794.9 kbps in performing temperature monitoring; recall that Zigbee transmissions are only capable of achieving single throughputs of 250 kbps. The WiMax mesh network, in providing long-haul transmission to the centralized controlling station, achieves total network throughput of between 39.6 and 485.7 Mbps. This result illustrates the suitability of UWB for next-generation wireless sensor networks (WSNs) as UWB expands the range of applications

Network Maximum Total Minimum Total Mean Total Standard Variance Throughput Throughput Throughput Deviation UWB Cluster 3.4 Gbps 84.4 Mbps 1.8 Gbps 112.2 Mbps 1.3 x 10<sup>16</sup> ZigBee Cluster 794.9 kbps 240.1 kbps 770 kbps 2.2 kbps 5.0 x 10<sup>6</sup> WiMax Mesh 485.7 Mbps 39.6 Mbps 331.5 Mbps 10 Mbps 1.6 x 10<sup>13</sup>

• if *rh* = 0, the network lifetime remains status quo;

• Network lifetime based on finite energy capacity;

that can be used for state-of-the-art resource management.

**11. Results**

• Throughput performance;

• Spectral efficiency;

energy routing;

network; and,

energy replenishment.

**11.1. Total throughput**

**Table 6.** Throughput Statistics

• if *rh* ≥ *rc*, the network lifetime is theoretically infinite.

• if 0 < *rh* < *rc*, the network lifetime is prolonged but finite; and,

Spectral efficiency provides an accurate metric to compare our three communication technologies in terms of the attainable transmission rate per Hz. This is presented in Figure 10 in units of bits/s/Hz. Zigbee provides an effective spectral efficiency of 250 kbps/2.5 MHz = 0.1 bits/s/Hz, Ultrawideband (UWB) attains an effective spectral efficiency of 480 Mbps/500 MHz = 0.96 bits/s/Hz, and WiMax provides improved spectral efficiency of roughly 75 Mbps/20 MHz = 3.75 bits/s/Hz over full channel bandwidths.

**Figure 10.** Spectral Efficiency (bits/s/Hz) over One Week Network Lifetime
