Method for reducing power consumption of bluetooth device

In November 2004, the Bluetooth SIG revised the 2.0+ Enhanced Data Rate (EDR) specification, combining a revolutionary technology to create a more efficient wireless link and data packet transmission mechanism. Although Bluetooth is already a low-power technology, in order to further extend battery life, the Bluetooth Special Interest Group (Bluetooth SIG) continues to integrate many new methods to reduce the power consumption of the new version of the Bluetooth specification. Bluetooth Specification

The

most important method that the Bluetooth SIG has used to reduce the power consumption of Bluetooth devices is the development of EDR Bluetooth. The power consumed by Bluetooth radio components depends on the length of time they are in operation. The v2.0+EDR Bluetooth specification allows data transmission speeds to reach 3 times that of traditional Bluetooth (3Mbps vs. 1Mbps), which means that the operating time of the radio waves is reduced to one-third, and therefore the power consumption is also reduced to one-third.

The increased data transmission rate is due to a fundamental change in the way data packets are transmitted.

Standard transmission rate (1Mbps - such as Bluetooth versions before v1.2) The packet contains four parts:
1. Access Code - The receiving device uses this access code to identify the incoming transmission operation
2. Packet header - describes the type and length of the packet
3. Packet content (Payload) - The actual data content transmitted
4. Inter-packet Guard Band (Inter-packet Guard Band) - transfers the radio waves to the next frequency band

All three transmission parts use Gaussian Frequency Shift Keying (GFSK) to process the RF signal: the carrier frequency is shifted in the range of plus or minus 160 kHz to represent zero or one, and each symbol encodes one bit. The symbol transmission rate is 1 Msps (Mega Symbol Per Second). The resources required for the three parts of the access code, header, and guard band protection band allow the maximum payload data rate to reach 723 kbps.

Bluetooth EDR packets still use GFSK modulation for the access code and header, but use one of two different modulation schemes for the payload data: one is mandatory, which provides 2x the data rate and can tolerate higher noise; the other is a selective modulation scheme that provides 3x the data rate.

2x data rate uses π/4 Differential Quadrature Phase Shift or π/4-DQPSK. This modulation scheme changes the phase of the carrier instead of the frequency. "Quadrature" means that each symbol has four possible phases, allowing two data bits to be encoded in each symbol. The symbol rate remains the same; therefore, the data rate is doubled.

3x data rate uses 8-DPSK (8-Phase Differential Phase Shift Keying), which is similar to π/4-DQPSK, but can shift to any of the 8 possible phases. The reduced phase difference between adjacent positions, combined with the use of ±π phase jumps, means that 8-DPSK is more susceptible to interference, but can encode 3 bits of data per symbol.

After the successful entry of the EDR specification into the actual product stage, the qualified products were launched in 2005, and the SIG continued to study various new methods to reduce power consumption.

CSR BlueCore further reduces power consumption with low power mode and internal clock

The hardware clock built into CSR's BlueCore chips can isolate the digital components from the radio; turn off the radio; and switch the chip to shallow or deep sleep mode. This provides low-power performance that even exceeds the official Bluetooth SIG standard.

Low-power modes and internal clocking

The hardware clock in the BlueCore chip can isolate the digital components from the radio; turn off the radio; and switch the chip to shallow or deep sleep mode.

Figure 1 Power consumption in light sleep mode

In the shallow sleep mode, the clock speed is reduced from 16MHz to 0.125MHz, and the current is reduced from 10mA to 2mA (as shown in Figure 1).

Figure 2 Clock structure of deep sleep mode

In deep sleep mode, the main crystal plus all other clock components are turned off, leaving only 1kHz for the oscillator (Oscillator) to use (as shown in Figure 2).

When switching to deep sleep mode, BlueCore requires 20milliseconds (ms) of idle time without operation. In terms of wake-up, the crystal takes 5ms to restart and the component requires about 20ms of idle time (prediction). BlueCore can wake up the component before the next scheduled operation through a scheduled alarm, or by an interrupt from a PIO, UART, or USB port transmitter to leave deep sleep mode.

Chip Architecture

Figure 3 BlueCore3-ROM CSP chip package

The BlueCore chip architecture itself plays a key role in ensuring power efficiency and reducing power consumption. Figure 3 shows a typical configuration of a BlueCore chip, which is a BlueCore3-ROM CSP chip-level package design.

CSR's move from 0.18 micron to 0.13 micron process for its fifth generation BlueCore5 device has had a significant impact on power consumption. As silicon device size has become smaller, communication between different components in the chip has become more efficient, and the same functions can now be performed with only a small amount of power.

DSP: Reduced Power and Improved Performance

CSR chose to use a DSP architecture in a single chip format to bring a breakthrough solution to the stereo and mono headphone market. In the case of stereo headphones, consumers want their headphones to have a battery life comparable to that of their music player. Today's iPods offer a very long battery life (10 to 15 hours), far exceeding the average mobile phone, and stereo headphones must achieve similar battery life without excessively draining the battery of the music player or mobile phone.
The DSP used in the BlueCore multimedia products helps CSR achieve 10 to 16 hours of battery life in wireless earbuds (BlueCore3-MM and BlueCore5-MM, respectively), far exceeding the best products from other manufacturers, which have a maximum battery life of only 5 hours.

Why does the integration of DSP architecture lead to a significant increase in battery life? The power consumption of DSP architecture is much lower than that of other devices developed by other manufacturers using ARM processors, and the DSP supports a variety of music formats such as MP3, WMA, and AAC in native mode. Native support eliminates the need to use inefficient and power-intensive codecs such as SBC wireless technology to transmit music files.

To ensure interoperability, all products using the Bluetooth AV profile must be able to interoperate with the Bluetooth SIG's mandatory compression encoding/decoding mechanism: Sub-Band Coding (SBC) technology. Although this standard is quite practical, it is inconsistent with the current popular music storage format for consumers. Therefore, if the earbuds only support SBC, the music playback device or mobile phone must perform transcoding operations, decompressing and then recompressing before transmission. Not only does this affect the quality of the music, the transcoding itself is processor-intensive, using up to 80% of the processor bandwidth on some typical processor cores used in today's mobile phones. This processor-intensive operation requires a lot of power, which puts more pressure on battery life.

In addition, SBC is not as efficient at shrinking files as formats such as MP3, so it requires more cycles to stream. This affects the reliability of the connection and consumes more battery power.

To address the inefficiencies and power consumption associated with transcoding, CSR has developed a dedicated Bluetooth stereo headset reference design using its DSP-based BlueCore multimedia components, combining SBC and MP3 format encoding software. By supporting MP3 encoding, there is no need for transcoding, and the power consumption of transmitting MP3 files is lower than before. In a typical headset reference design - BlueTunes 1 using Bluecore3-MM - the power consumption is less than 95mW (25mA and 3.7V - equivalent to the power consumption of a top-of-the-line mono headset in 2004) when receiving streaming SBC music over a standard non-EDR channel. This design significantly reduces the power consumption of transmitting MP3 files while still supporting EDR. The

following table compares the power consumption of CSR products using DSP with other similar products:

Operation Mode Other Manufacturers' Components CSR BlueCore3-MM
Talk (SCO, HV3, master) ~112mW ~45mW
Streaming Music (SBC) ~180mW ~95mW
Standby (call scanning) ~3.3mW ~1mW

Figure 4 Comparison of BlueCore3-MM and components from major competitors

Casual Scanning

When not connected to another device, the Bluetooth radio operates in a "call scan" or standby mode, where the radio waves scan the RF range of other connectable devices every 1.28 seconds. When the radio waves scan other devices, an identifier is sent to the local device so that a connection can be established when necessary. CSR has been using new technologies to reduce the activities required to perform in call scan mode, thereby further reducing power consumption. One approach is to scan the RF range at a frequency that is synchronized with the GSM signal (beacon) interval. The available power is used to scan the RF range. This approach has been further developed into a "conditional scan" mechanism that allows the device to scan the RF range. If there is no RF wave activity, a full call scan is not required, and the device can wait until the next scan cycle to see if there are other devices nearby.

For handheld device manufacturers, power consumption is always a major consideration. While facing the problem of power consumption, the industry must also respond to consumers' increasing demands for product performance, functions, interoperability, and connectivity. As the most suitable wireless transmission technology for battery-powered devices, Bluetooth should be able to provide powerful functions with the lowest power consumption requirements. Therefore, the Bluetooth SIG and various industry players are committed to improving the performance of Bluetooth devices using new specifications or new series. By using a DSP architecture to improve multimedia performance, it can not only further reduce power consumption, but also provide support and performance for different applications, which can be used as a reference for manufacturers developing Bluetooth products when designing.