Product Specs

Page 13 of 18

Figure 6.

The Bluetooth low energy channels differ from classic channels because of the relaxed

modulation index. This means that the radio energy for each channel is spread wider;

therefore, to prevent interference between adjacent Bluetooth low-energy channels,

they are separated by 2MHz, instead of the classic 1MHz. In the Link Layer, these

channels are divided into two types: advertising channels and data channels. These

channel types are aligned with the advertising packets and data packets, as described

earlier. When a packet is transmitted, if the packet is sent on an advertising channel, it

is an advertising packet. If the packet is sent on a data channel, it is a data packet.

There are 3 advertising channels and 37 data channels, as shown in Figure 6 (the

advertising channels are rendered in light blue shading). The 3 advertising channels are

not all placed in the same part of the ISM band because that would mean that any deep

fade in a single part of the band would stop all advertising. Instead, the advertising

channels are placed a minimum of 24MHz apart from one another.

The advertising channels are placed strategically away from significant interferers such

as a Wi-Fi access point. These public access points typically use one of three 802.11

channels, either channel 1, channel 6, or channel 11. These channels have center

frequencies of 2412MHz, 2437MHz, and 2462MHz and a width of approximately

20MHz. This means that channel 1 extends from 2402MHz to 2422MHz, channel 6

extends from 2427MHz to 2447MHz, and channel 11 extends from 2452MHz to

2472MHz. The advertising channels are placed at 2402MHz, 2426MHz, and

2480MHz. This means that the first advertising channel is below Wi-Fi channel 1, the

second advertising channel is between Wi-Fi channel 1 and channel 6, and the third

advertising channel is above Wi-Fi channel 11. This is illustrated in Figure 6, in which 3

Wi-Fi channels have blocked the use of data channels 0 to 8, 11 to 20, and 34 to 32.

The 3 advertising channels, 37, 38, and 39, are all interference free. Bluetooth LE

Radio traffic hops around these channels in a pseudo random manner so that the data

with get through even though it’s in an areas shared by a number of Wi-Fi networks, or

microwave ovens. One of the differences between Bluetooth LE and classic Bluetooth

is the number and use of these channels.