Wireless Communication

for Wearable DevicesHoward M. Harte – November 8, 2014

hharte@cyngn.com

Wireless Technologies for Wearables

Several technologies are being used today in wearables, with Bluetooth being the most prevalent.

Bluetooth Low Energy (BLE)

Low power, low data rate, <100 meter range.

Wireless LAN (WiFi)

Medium power, high data rate,100 meter range.

Near Field Communications (NFC)

Low power, low data rate, short range (20 cm.)

Mobile network (GSM)

GPS for positioning.

Anatomy of a Smart Watch

Bluetooth SMART (BT 4.1, Bluetooth Low

Energy, BLE)

Good for medium range communication at low data rate.

Very low stand-by current, maximum current consumption < 15mA.

Data Rate <1Mbit/S.

Radio operates in 2.4GHz frequency band

Uses Frequency Hopping Spread Spectrum (FHSS.)

Bluetooth and WiFi can interfere with each other since they both use the 2.4GHz

band.

iOS and Android provide API support for BLE.

Android 5.0 introduced Bluetooth SMART Peripheral Role.

BLE devices can Advertise their presence to nearby devices.

Wireless LAN (WiFi) Medium to long-range, high data rate, medium power consumption.

Peer-to-Peer communication alleviates the need for a infrastructure network

Two devices can communicate directly with each other using WiFi-Direct (P2P.)

One device in “Group Owner” role. This role is similar to a WiFi Access Point. Usually this will be the device with more battery capacity due to the increased current consumption in the Group Owner role.

Wearable in the “Group Client” role. This role is similar to a WiFi Station, and can take advantage of standard WiFi power-saving modes.

Radio operates in 2.4GHz or 5GHz frequency bands.

Average standby current consumption ~1mA.

Peak current can be much higher (>100mA) when transmitting.

High data rate, >100Mbit/S for the latest 802.11ac devices.

Even legacy 802.11g and 802.11n devices are >10Mbit/S.

WiFi-Direct APIs are available in Android and Windows 8. Apple AirDrop is notWiFi-Direct.

Near-Field Communication (NFC)

Short Range, low data rate, low power consumption.

Point-to-Point Communication between card and reader.

Radio operates at 13.56MHz.

Power consumption similar to Bluetooth SMART.

Higher when illuminating a passive tag.

Low data rate of 424Kbit/S maximum.

Maximum distance of about 20cm.

Two modes of operation:

Passive communication (target device is not powered.)

Active communication (both initiator and target are powered.)

Impact on Wearables Wearables today typically use Bluetooth LE. This is a compromise:

Low power, but at the expense of data throughput.

Limited range, and needs to be tethered to a host device such as a phone.

Transferring large amounts of data (Photos, Music) between wearable and host takes time:

Creates a poor user experience

Increases power consumption because the wearable’s CPU (and maybe even display) will be on longer.

Some wearables (such as Google Glass) use WiFi:

Higher data throughput, but at the expense of battery life.

Using WiFi, a wearable can connect directly to the Internet via a WiFi Access Point (AP.)

Still others (Apple iWatch) combine BLE, WiFi, and NFC.

NFC for Mobile Payments.

Some wearables use GSM for connectivity when out of WiFi range.

This trend is expected to increase going forward.

Example Wearable Software Stack

(courtesy of Samsung)

Applications for Wearable Devices

Generally, App Developers don’t need to worry about how the

communications between smartphone and smartwatch are handled.

For example, Android Wear and Samsung Gear provide transport-independent APIs

to transfer data between the device and phone.

Sending a message to an Android Wear device:

Node node; // the connected device to send the message toGoogleApiClient mGoogleApiClient;public static final START_ACTIVITY_PATH = "/start/MainActivity";...

SendMessageResult result = Wearable.MessageApi.sendMessage(mGoogleApiClient, node, START_ACTIVITY_PATH, null).await();

if (!result.getStatus().isSuccess()) {Log.e(TAG, "ERROR: failed to send Message: " + result.getStatus());

}

Implications for Developers

Having an understanding of the underlying wireless technology can help

developers write better Apps that are:

More efficient

More responsive.

Conserving of battery on both Wearable and phone.

Creating Your Own Wearable / IOT

Device Development Kits are available for Bluetooth SMART and WiFi:

Broadcom WICED SMART

$20 Development Kit for Bluetooth SMART (BLE.)

Apps (with source code) for iOS and Android.

Broadcom WICED WiFi

Trend is towards moving more networking

functionality into the WiFi module.

Eases implementation.

Reduces Power.

Legacy Laptop/PC WiFi typically perform L2

and WiFi link management in the host.

Current smartphones and wearables move

L1/L2 functionality into the WiFi Module.

WICED moves all networking functionality into

the WiFi Module and presents a Sockets-based

interface to the host CPU.

Development kit and module for WiFi-based

designs.

(Courtesy of Universal Scientific Industrial)

References

http://developer.samsung.com/technical-doc/view.do?v=T000000160

https://developer.android.com/training/building-connectivity.html

http://www.broadcom.com/products/wiced/sense/

http://www.broadcom.com/products/wiced/wifi/

http://www.usish.com/english/products_wiced.php

Thank You