1. Group 2: Qiuxi Zhu, Buchao Yu, Guoxi Wang
WiZi-Cloud: Application-transparent Dual ZigBee-WiFi Radios for Low Power Internet Access
Group 2: Qiuxi Zhu, Buchao Yu, Guoxi Wang

2. WiZi-Cloud Background System Overview System Design
System Infrastructure
Protocol Design
Performance Evaluation
Conclusion

3. Background
Smart phones are necessitate reliable and ubiquitous Internet Access(Cellular/Wi-Fi)
Cellular network require high cost to achieve scaling
Wi-Fi help scale access but suffers from high energy consumption

4. Android Power Consumption Breakdown
(a) Radios Idle, Screen Off
(b) Radios busy, Screen On

5. WiZi-Cloud Solution

6. Brief Introduction of Zigbee
Global operation in the 2.4GHz frequency band according to IEEE
Low power consumption, with battery life ranging from months to years.
Low data rate (<=250Kbps)
50m typical range

7. System Overview
WiZi-Cloud is a dual-radio solution for scalability and energy efficiency of mobile phones' Internet access.
WiZi-Cloud Solution
HW/SW Components
Protocols

8. System Goals Ubiquitous Connectivity High Energy Efficiency
Transparent Intra-device / Inter-AP Handover

9. System Design (Hardware)
WiZi-kit: a custom-designed ZigBee module; interface the ZigBee chipset to the client and AP devices
TI CC2530: ZigBee chipset; has a high-performance and low-power 8051 microcontroller, and a rich set of peripheral interfaces
WiZi-Kit: used to interface the ZigBee chipset to the client and AP devices

10. Hardware (cont.) Wizi-enabled mobile clients: Android phone/ laptops
Wizi-enabled wireless APs: OpenWrt compatible routers

11. Software
WiZi-Cloud software stack:

12. Software (cont.)
WiZi-Cloud Service Module: serves as an interface manager, which monitors the status of ZigBee and WiFi interfaces, and decides when to carry out the interface switching
WiZi Bridge:Due to the different maximum packet length in IP protocol and ZigBee prototol, WiZi Bridge fragments the IP packets into multiple ZigBee packets, and reassemble the received ZigBee packets into single IP packet.

13. Software (cont.)
UART I/O: is reponsible for reliable communication on UART link between the host device (mobile phone or AP) and WiZi-Kit.
ZigBee Modem: provides basic read/write operations on the ZigBee link and is responsible for reliable UART communication.
UART: Universal Asynchronous Receiver/Transmitter

14. Software (cont.) Service Module Variants:
At client end: WiZi stack creates a virtual network interface, which is the only NIC visible to the upper layer applications. The software stack handles the underlying physical interfaces switching.
At AP end: WiZi stack is implemented as a netfilter framework extension, which dynamically modifies iptable rules to have AP properly route the packets for WiFi and ZigBee clients.

15. Protocol Design
The WiZi-Cloud system relies on several mechanisms:
Registration of the mobile device
First associates with one AP, obtain an IP address through DHCP, keep the original IP unchanged
Maintaining reachability
The mobile devices need to be covered by a WiZi-Cloud access point, and inform the system on how they can be reached

16. Protocol Design (cont.)
Paging
The registration-AP needs to inform the mobile device to wake up and start receiving data packets
Handover
Minimize energy consumption, and connectivity disruption

17. Performance Evaluation
Evaluate the overall system performance on the Android G1 integrated with the WiZi-Cloud system from three perspectives:
energy consumption
throughput
user experience

18. Energy Consumption
Categorize the mobile applications into three classes:

19. Energy Consumption (cont.)
Experiments on some applications :
Test a VoIP application called sipdroid with two popular codecs, GSM 13Kbps and Speex 11Kbps

20. Energy Consumption (cont.)
Test the total energy consumption by sipdroid and iheartradio, an Internet Radio application, in active mode
`sipdroid` is making a voice call.
`iheartradio` is streaming music.

21. Throughput UDP Throughput
As the payload increases, the throughput quickly increases due to the better utilization of the ZigBee channel. When the payload exceeds 500 bytes, the curve becomes flat

22. Throughput (cont.) TCP Throughput
The maximum TCP packet size (MSS) is a trade off between better channel utilization and the risk of wasting bandwidth. The optimal TCP MSS is 450 Byte, achieving 60.2Kbps throughput

23. Coverage Performance
Compare the coverage of ZigBee and WiFi, and use packet loss rate to represent the coverage performance

24. Coverage Performance (cont.)
ZigBee has a better coverage than WiFi
ZigBee has a higher SNR than WiFi
ZigBee performance degrades significantly because the RSSI level drops below the RF sensitivity threshold of the CC2530

25. Thank you!