Bluetooth 2 with Enhanced Data Rate, EDR

Bluetooth Enhanced Data Rate, EDR was the first major upgrade to the Bluetooth standard since its initial offering, and the new version 2 gave much higher data rates & other improvements.

Bluetooth Tutorial / Summary Includes:
Bluetooth technology basics How Bluetooth works Bluetooth Classic: how it works Bluetooth Low Energy: how it works File transfer Bluetooth profiles Pairing & networking Security Bluetooth 2 EDR How to connect Bluetooth devices

Bluetooth EDR or Bluetooth 2 was the first major upgrade to the Bluetooth standard after the release of the original version 1 which had some minor revisions.

With Bluetooth 2 one of the major new features was the Enhanced Data Rate capability that enabled the data rate to be increased from the 732 kbps up to 2.1 Mbps.

Specification of a product using Bluetooth 2 EDR

Also there was an increase to the nominal range that enabled the the expected distance to increase from about 10 metres up to 30 metres, although this would depend on a number of external variables as well.

The new Bluetooth 2 standard was ratified in November 2004 to provide the improved data rate and other performance improvements.

Of all the features included in Bluetooth 2, it was the enhanced data rate, EDR, capability that gave rise to the most comment, and further established Bluetooth as a universal standard for shorter range wireless communications.

Key Bluetooth 2 features

Bluetooth 2 introduced a number of significant upgrades, making the standard far more attractive to the rapidly growing need for low power, relatively short range wireless connectivity.

The Bluetooth SIG had taken on board the need for the improvements and introduced them in the second standard release for Bluetooth.

Thee were a number of improvements that were made in the second release of Bluetooth which included:

Increase of data throughput: `The release of Bluetooth 2 increased the data throughput rate up to 2.1 Mbps. This was the headline improvement and it was also dubbed EDR for Enhanced Data Rate.
Connection range increased: The range over which Bluetooth 2 could connect was increased up to 30 metres of 100 feet. This gave significant advantages, particularly where interference was high or nearby objects increased attenuation. The new release 2 gave a more reliable and stable connections.
Lower power consumption: The standard was updated so that the power consumption of the Bluetooth radios could be reduced. As most Bluetooth devices were battery powered, this was a key advantage. As the logic devices only needed to remain active for a portion of their operating time, major current savings were made by reducing the time devices were on and switching them off when they were not required.
Improved security with new pairing system: A scheme called Secure Simple Pairing was introduced and this gave much easier, yet secure pairing. If users found pairing difficult, then they would be less likely to use Bluetooth.

The main drawback for Bluetooth 2 was that the SBC codec was retained as the only standard codec. This meant that the sound quality was noted for being mediocre. The sound quality was poor and it was subject to delays.

With all the updates introduced with Bluetooth 2, it was fully backward compatible with Bluetooth 1.

How it worked

One of the main reasons why Bluetooth 2 was able to support a much higher data throughput was that it utilised a different modulation scheme for the payload data. However this was implemented in a manner in which compatibility with previous revisions of the Bluetooth standard was still retained.

Bluetooth data was transmitted as packets that were made up from a standard format. This consisted of four elements:

Access Code: This was used by the receiving device to recognise the incoming transmission.
Header: This described the packet type and its length.
Payload data: This was the actual data that was required to be carried over the Bluetooth link.
Inter-Packet Guard Band: This was required between transmissions to ensure that transmissions from two sources do not collide, and to enable the receiver to re-tune.

In previous versions of the Bluetooth standard, all three elements of the transmission, i.e. Access Code, Header and Payload were transmitted using Gaussian Frequency Shift Keying, GFSK where the carrier is shifted by +/- 160 kHz indicating a one or a zero, and in this way one bit is encoded per symbol.

The Bluetooth 2.0 specification uses a variety of forms of modulation. GFSK is still used for transmitting the Access Code and Header and in this way compatibility is maintained.

However other forms of modulation can be used for the Payload. There are two additional forms of modulation that have been introduced. One of these is mandatory, while the other is optional.

A further small change is the addition of a small guard band between the Header and the payload. In addition to this a short synchronisation word is inserted at the beginning of the payload.

Mandatory modulation format

The first of the new modulation formats which must be included on any Bluetooth 2 device gives a twofold improvement in the data rate and thereby allows a maximum speed of 2 Mbps. This is achieved by using π/4 differential quaternary phase shift keying, π/4 DQPSK.

This form of modulation is significantly different to the GFSK that was used on previous Bluetooth standards in that the new standard uses a form of phase modulation, whereas the previous ones used were based on frequency modulation.

Using quaternary phase shift modulation means that there are four possible phase positions for each symbol.

Accordingly this means that two bits can be encoded per symbol, and this provides the two fold data increase over the frequency shift keying used for the previous versions of Bluetooth.

Higher speed modulation

To enable the full threefold increase in data rate to be achieved a further form of modulation is used.

Eight phase differential phase shift keying, 8DPSK enables eight positions to be defined with 45 degrees between each of them. By using this form of modulation eight positions are possible and three bits can be encoded per symbol. This enables the raw data rate of 3 Mbps to be achieved. It is worth noting that wit the error correct, headers, etc the actual maximum throughput is 2.1 Mbps.

As the separation between the different phase positions is much smaller than it was with the QPSK used to provide the two fold increase in speed, the noise immunity has been reduced in favour of the increased speed. Accordingly this optional form of modulation is only used when a link is sufficiently robust.

Packet formats

The Bluetooth 2 specification defines ten new packet formats for use with the higher data rate modulation schemes, five each for each of the enhanced data rate schemes.

Three of these are for the 1, 3 and 5 slot asynchronous packets used for transferring data. The remaining two are used for 3 and 5 slot extended Synchronous Connection Orientated (eSCO) packets. These use bandwidth that is normally reserved for voice communications.

The new format for these packets does not incorporate FEC. If this is required then the system switches back automatically to the standard rate packets. However many of the links are over a very short range where the signal level is high and the link quality good.

It is necessary for the packet type to be identified so that the receiver can decode them correctly, knowing also the type of modulation being used. An identifier is therefore included in the header which is sent using GFSK.

This packet header used for the previous version of Bluetooth only used 4 bits. This gave sufficient capability for the original system. However there was insufficient space for the additional information that needed to be sent for Bluetooth 2.

It was not possible to change the header format because backward compatibility would not be possible. Instead different link modes are defined. When two Bluetooth 2 / EDR devices communicate the messages are used in a slightly different way, indicating the Bluetooth 2 / EDR modes. In this way compatibility is retained while still being able to carry the required information.

Bluetooth 2 / EDR is a significant improvement to Bluetooth and will enable it to retain its position in the market place. Its introduction, as the Bluetooth has become more widely accepted and used will enable it to build on its position within the market place.