# 25 Years of Bluetooth Technology
## 2 Bluetooth Technologies
### Bluetooth BR/EDR  
The Bluetooth system operates in the 2.4 GHz Industrial, Science and Medical (ISM) band. The frequency band is in the 2400.0-2483.5 MHz range, with Radio Frequency (RF) channels being spaced at 1 MHz. Two data transmission modes are defined: Basic Rate (BR) that uses a shaped, binary Frequency Modulation (FM) to minimize transceiver complexity, and Enhanced Data Rate (EDR) that uses Phase Shift Keying (PSK) modulation and has two further variants: \(\pi\)/4-Differential Quadrature Phase Shift Keying (DQPSK) and Differential Phase Shift Keying (DPSK). Basic Rate (BR) mode is a mandatory part of the Bluetooth specification. The modulation that BR uses is Gaussian Frequency Shift Keying (GFSK). In Enhanced Data Rate (EDR) mode, the scheme used for modulation is altered inside the packet. The packet header and the access code are sent using the Basic Rate of 1 Mbit/s GFSK modulation scheme, while subsequent synchronization sequence, payload, and trailer sequence are transmitted with the EDR PSK modulation scheme [6].  
A combination of devices connected via Bluetooth in an ad-hoc mode is called a piconet. In a piconet, one Bluetooth device acts as a master and the other devices act as slaves. The device that starts communication is the master node and the other devices are slaves. A piconet consists of a minimum of two connected devices, and can extend up to eight connected devices (one master and seven slaves). Every Bluetooth device can act as a master or a slave device. When there is a single slave device, a piconet is a simple point-to-point link. A point-to-multipoint arrangement can have a maximum of seven active slaves under the control of a single master. Figure 4 shows the two different configurations of a Bluetooth piconet. Slaves always exchange data through the master node. Communication across piconets creates a scatternet. Scatternets exist when a Bluetooth device is a slave in one piconet and simultaneously a master or a slave in another piconet.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Bluetooth** & **v1.1** & **v2.0 + EDR** & **v2.1 + EDR** & **v3.0 + HS** & **v4.0 + LE** & **v4.1** & **v4.2** & **v5.0** \\ \hline _Year_ & 2002 & 2004 & 2007 & 2009 & 2010 & 2013 & 2014 & 2016 \\ _Basic Rate_ & YES & YES & YES & YES & YES & YES & YES & YES \\ _Enhanced Data Rate_ (_EDR_) & NO & YES & YES & YES & YES & YES & YES & YES \\ _High Speed (HS_)_ & NO & NO & NO & YES & YES & YES & YES & YES \\ _Low Power (LE)_ & NO & NO & NO & NO & YES & YES & YES & YES \\ \hline \hline \end{tabular}
\end{table}
Table 1: Bluetooth characteristics [5].  
Figure 4: Bluetooth piconet configurations [1; 7].  
All devices share the Bluetooth master's clock. The basic clock has a clock cycle time of 312.5 microseconds (\(\upmu\)s). The time base of packet exchange is the basic clock. A slot of 625 microseconds consists of two clock cycles; a slot pair of 1250 \(\upmu\)s consists of two slots. The master sends in even slots and receives in odd slots; for the case of slaves, transmission occurs in odd slots and reception occurs in even slots. Upon powering up, a Bluetooth device can operate in slave mode when the master device is already operating. The slave waits for inquiries from the masters and provides replies. The master and slave devices can change roles, which would be necessary when a Bluetooth device participates in more than one piconet.