WiZi-Cloud is a dual-radio solution for scalibility and energy
efficiency of mobile phones' Internet access. It consists of a set
protocols, and hardware/software components integrating WiFi and ZigBee
radios on mobile phones and access points. WiZi-Cloud aims at providing:
high energy efficiency,
real time intra-device/inter-AP handover,
that is transparent to the applications.
WiZi-Cloud is motivated by the ever increasing density of WiFi Access
Points and large unlicensed RF bandwidth over which they operate. At the
same time cellular networks are limited by deployment challenges and limited
RF spectrum. However, maintaining connectivity through WiFi results in
depleting the mobile phones battery in a very short time. The WiZi-Cloud
dual radio solution overcomes this problem.
WiZi-Cloud is one of the projects carried out on the Open Infrastructure research framework, developed
at CCIS, NEU. For details of the framework and other ongoing projects, please visit
Energy Issue in Mobile Phones
We profiled the energy consumed by different components of the Android G1 phone.
When the G1 is in idle mode, the OS consumes very limited energy. Even though the radios
are mostly idle in this case, the energy consumed by the radio interfaces, including GSM,
WiFi and Bluetooth, predominates the total energy consumption.
In our measurement, the WiFi energy consumption in PSM mode is 29.4mW. Compared with
the measurement data from related research work done 2-3 years ago, the WiFi PSM mode
on G1 shows much higher energy efficiency than before. However, WiFi is still the major
energy drainer. When the WiFi radio interface is actively transmitting or receiving,
its energy consumption can reach 1600mW.
We have prototyped the WiZi-Cloud system with commodity hardware such as Android phones
and OpenWrt capable access points (e.g., the popular Linksys WRT54G). Our extensive set of
experiments demonstrate that for maintaining connectivity, WiZi
achieves more than a factor 8 improvement in energy consumption
in comparison with energy-optimized WiFi, and a factor of 5 in
comparison with GSM. For mobile applications with limited bandwidth requirement but
high delay sensitivity, WiZi can extend the battery lifetime by a factor 2 to 3.
WiZi also provides a better coverage than WiFi and a low delay. This results in a
good Mean Opinion Score (MOS) 4.26 for a VoIP US cross-country communication.
See Design and Prototype for more information about WiZi-Cloud system. See
our Infocom 2010 paper for experimental rsults.
Tao Jin, Guevara Noubir, Bo Sheng, "WiZi-Cloud: Integrating ZigBee into Mobile Phones for Energy Efficient Internet Access in WLANs",
in ACM Mobicom 2010 (demo paper), Chicago, USA, September, 2010. [PDF]
Tao Jin, Guevara Noubir, Bo Sheng, "WiZi-Cloud: Application-transparent Dual ZigBee-WiFi Radios for Low Power Internet Access",
in IEEE Infocom, Shanghai, China, April, 2011. [PDF]
In order to conserver the battery energy on mobile phones, the proposed WiZi-Cloud system
extends mobile phones and access points with an ultra low power, low data rate ZigBee
interface. The phone can switch between the WiFi and ZigBee interfaces while communicating
with WiZi-enabled AP. The core idea is to keep the WiFi interface off under light traffic.
When WiFi is off, the ZigBee interface is reponsible for maintaining the mobile phone's
connection with the WiZi-enabled AP, at a little energy cost. The WiFi interface is waken
up under high throughput because it is more energy efficient to transfer large amounts of
When a WiZi-enabled mobile phone is in the presence of a WiZi-enabled wireless AP, the
phone first establishes a WiFi connection with this AP as usual. Our WiZi software stack
monitors the traffic occuring on WiFi. If the traffic load is below a given threshold, the
phone will switch to the ZigBee interface, and notifies such interface change to the AP.
In the WiZi system, such interface switching is transparent to the upper layer applications.
The established TCP/UDP connections are not be interrupted. When the traffic load
increases above a given threshold, the mobile phone will switch back to the WiFi mode.
Meanwhile, the AP also monitors the traffic going through this WiZi client, and
an interface switching can also be triggered by sending a wake-up-WiFi signal from the
AP to the mobile phone. Besides, the WiZi-Cloud protocol supports tracking the mobile
device as it moves to another WiZi-enabled AP, so that we can tunnel the ongoing traffic
to the new AP without breaking established connections.
We designed our WiZi-Cloud system with an emphasis on the following features:
Energy-Efficiency: WiZi-Cloud system is extremely
efficient for maintaining connectivity and low rate applications such
as VoIP and streaming music in terms of energy consumption.
Leverage of existing HW/SW: WiZi-Cloud system runs on
off-the-shelf mobile phones and wireless routers without hardware modifications.
Flexibility: In the WiZi-Cloud design, a mobile phone
is able to determine the network interface to use according to a user-specified
policy. The WiZi-Cloud provides the mechanism to switch between WiFi and ZigBee
Seamless: WiZi-Cloud system and its protocols (e.g.,
handover from an AP to another) are completely transparent to the applications running
on the mobile phones and peer entities in the Internet.
WiZi-Cloud system infrastructure includes both hardware and software components.
We designed and prototyped the custom external ZigBee interface, called WiZi-Kit, for
mobile phones and wireless APs. See here for more
information about the hardware prototype.
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. IP Packet Multiplexer determines how to propagate the ingress and egress IP packets through OS given currently active interface.
NIB (NIC Information Base) maintains the accounting data for each interface. At AP side, NIB also records the mode in which each LAN client is functioning.
WiZi Bridge: Due to the different maximum packet length in IP protocol and ZigBee prototol, WiZi Bridge fragments the egress IP packets into multiple
ZigBee packets, and reassemble the received ZigBee packets into single IP packet.
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.
WiZi-Cloud software stack consists of four major components: WiZi-Cloud Service Module, WiZi Bridge, UART I/O, and ZigBee logic.
The WiZi-Cloud prototype implements both the mobile client side and the AP side.
We custom-designed a ZigBee module, called WiZi-Kit, to interface the ZigBee chipset to the client and AP devices.
We have developed WiZi software stack to make the dual WiFi-ZigBee radio transparent to the applications.
We also developed WiZi Buddy, an Android application to manage the WiZi interface.
WiZi-enabled wireless APs
LinkSys WRT54GL with
WiZi-Kit serial version
Planex MZK-W04NU with
WiZi-Kit USB version
Wireless AP with
WiZi-Kit Ethernet Adapter version
WiZi AP is prototyped on two brands of APs, LinkSys WRT54GL and Planex MZK-W04NU. Both APs are reflashed with
cutsom-built OpenWrt firmware enabled with WiZi software stack.
We use the onboard serial ports on LinkSys WRT54GL for the ZigBee device and AP to communicate. The Planex MZK-W04NU has a
USB interface ready, which makes the integration work more convenient. Also, we integrate the ethernet to serial module to
our PCB design to make the WiZi-Kit work with any wireless AP's.
WiZi-enabled mobile clients
WiZi-Kit HTC ExtUSB version
Android G1 attached with WiZi-Kit
Netbook attached with WiZi-Kit USB version
The WiZi-Kit client module has a HTC ExtUSB interface and communicates with
android G1 through serial ports. The serial function on the G1 USB has been enabled with rooted Android OS kernel.
The module can be powered with a button battery. The WiZi-Kit can also be used as a USB dongle for netbook.
ZigBee chipset: the ZigBee chipset used in our prototype is TI CC2530 System-on-Chip. CC2530 has a high-performance and low-power 8051 microcontroller, and a rich set of peripheral interfaces such as DMA and UART.
WiZi Software Stack: current prototype is implemented as a user space service program.
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
iptables rules to have AP properly route the packets for WiFi and ZigBee clients.
WiZi Buddy: is an Android application for WiZi interface management.
In this video, we will show you that Android G1 plays stream radio and makes VoIP calls with WiZi interface, and netbook makes Skype video call with WiZi inteface.