The Bluetooth Transmission For 7.1 Channel Audio System Vinit Tarey 1, Kaushal Bhatt 2 1 Mahakal institute of technology and science,datana Ujjain MadhyaPradesh India 2 Mahakal institute of technology and science,datana Ujjain MadhyaPradesh India 1 vinit.tarey@gmail.com 2 kaushalbhatt15@gmail.com Abstract According to advancement of the technology stereo audio transmission can be achieved on Bluetooth. Some protocols have been designed like A2DP and Bluetooth audio codec technology. Audio transmission can be possible from one point to multi point and hardware for sender and receiver is also on a single chip design. It can be possible that we can transmit a very high quality 3d sound using 7.1 audio channel technology and this technology can be also work with the wireless Bluetooth technology So that we can transmit a very good quality audio sound wirelessly within a range.in this paper we have shown that how the Bluetooth transmission can be achieved on an advance 7.1 channel audio technology, and audio signal can be synchronized during the Bluetooth transmission over all seven speaker. Here we also showed that how the piconet will help us to provide connectivity within this 7.1 audio channel. Keywords Point To Multipoint Transmission, Bluetooth, 7.1 channel, Stereo, Blue-core, DTS-HD. I. INTRODUCTION The Bluetooth wireless technology was prompted in 1998 by the Bluetooth Special Interest Group (SIG),[1] which the promoter members includes Ericsson, Lenovo, Intel, Nokia, Toshiba. Bluetooth operates at 2.4 GHz in the globally available ISM band.edr of Bluetooth specification provides facility to transmit the audio at two channels ( left channel and right channel) this is also called stereo audio.transmission of audio signals using Bluetooth is much cheaper than IEEE 802.11b. The 7.1 Channel audio system usually have 8 speaker which provides very high class crystal clear sound output,basically this system contains one center channel speaker, front left and front right speaker, surround left and surround right speaker,surround back left and surround back right speaker and one subwoofer[4]. This whole assembly will create a very high class realistic sound, but presently this system uses cables for audio signal transmission. Bluetooth technology provide us the freedom that we can place our audio devices without need of cables, generally There are two ways can be applied to replace the audio lines through the Bluetooth technology. First way is to transmit audio through one sender to at two channel left channel and right channel, the audio signals are coded and synchronously transmit these signals to the right channel and left channel speakers after the receiving of the audio track code by left channel and right channel the speakers will decode and plays them individually. This mode saves lots of resources and reduces the cost of the system. Main disadvantage is that it has compatibility issue. Another way is to transmit the audio is one sender and one receiver mode for every speaker. The right and left channel codec are separated using hardware at transmission side and this mode work on point to point transmission mode, this mode is simple but synchronization concept is needed to achieve synchronize play. Here we adopt the second way for transmitting audio from one point to multipoint stereo transmission. We also show that how the Bluetooth piconet is uses to address and transmission of audio signal to all speakers of 7.1 channel audio system. II. TECHNOLOGY FOUNDATION The protocol that has been used for wireless connectivity between audio input and output in 7.1 audio channel audio system the Advanced Audio Distribution Profile (A2DP) and Enhanced data rate (EDR). A2DP defines the protocols and procedures that realize distribution of audio content of high-quality in mono or stereo on ACL channels[5]. The term advanced audio, therefore, should be distinguished from Bluetooth audio, which indicates distribution of narrow band voice on SCO channels as defined in the baseband specification. 166
This profile relies on GAVDP. It includes mandatory support for low complexity sub band codec (SBC) and supports optionally MPEG-1, MPEG-2, AAC and ATRAC. The audio data is compressed in a proper format for efficient use of the limited bandwidth. Surround sound distribution is not included in the scope of this profile. Fig 1 shows the Baseband, LMP, L2CAP and SDP are Bluetooth protocols defined in the Bluetooth Core specifications. AVDTP consists of a signalling entity for negotiation of streaming parameters and a transport entity that handles streaming itself (refer to "Profile Stack: Profile Model"). A/V streams are transported in pseudo-isochronous L2CAP channels. A/V signaling is also transported via L2CAP channels. Signaling provides stream discovery, configuration, establishment, and transfer control as shown in Fig 3. Fig 3 (AVDTPS Control Layers) [5] Fig 1 (Protocol Stack Model) [1] The Application layer is the entity in which the device defines application services and transport service parameters. It also adapts the audio streaming data into the defined packet format, or vice versa. A2DP defines the protocols and procedures that realize distribution of audio content of high-quality in mono or stereo on ACL channels of which maximum transfer rate is 723.2 kbps. The Bluetooth transmission also uses AVDTP protocol uses point-to-point signalling over a connection-oriented L2CAP channel as shown Fig 2 SBC is an audio coding system specially designed for Bluetooth audio/video applications to obtain high quality audio at medium bit rates, and having a low computational complexity [5]. Fig 4 shows the specific Information elements for SBC used in the signaling procedures. The sampling frequencies 44.1 khz and 48 khz are mandatory to support. For the decoder in the SNK device and the encoder in the SRC device should support at least one of the sampling frequencies of 44.1 khz and 48 khz. The channel mode for the decoder in the SNK device shall support MONO, DUAL CHANNEL, STEREO and JOINT STEREO modes. Fig 2 (A/V Architecture Block Diagram) [1] The L2CAP channel is set up in advance, between two devices participating in A/V stream data distribution. L2CAP channels are best suited for the support of A/V stream data distribution links. This is because L2CAP channels can be flexibly configured to enable bandwidth to be shared between A/V content streams. 167 Fig 4 (Allocation of the Audio Signal) The 7.1 channel audio system is defined by DTS-codec master audio which supports variable bit rate audio sequence lossless bit for bit encoding at a frequency of 96 khz[3]. DTS-HD Master Audio is bit for bit identical to the studio master it can also be used as an archival or mezzanine format, with significant file size savings over PCM and the ability to store metadata. DTS-HD Master Audio is an industry standard and the only one-stream surround audio solution for high quality audio transmission.
The piconet is the network method that is been used to create a virtual network to connect embedded devices[6], Piconet is a low-rate, low-range, ad-hoc radio network. Piconet provides a broad range of embedded computing objects with the ability to exploit an awareness of, and connectivity to, their environment. In the piconet each node is been considered individual and each node is been defined in attribute store of piconet. Piconet attribute store is a simple hierarchy directory structure of (name, value) pairs. III. SYSTEM MODEL AND IMPLEMENTED DESIGN Fig 5 shows the system model that is used to connect the 7.1 channel audio system for wireless audio transmission. The sender and the receiver can be connected using the piconet network where the center speaker having a master node and the left channel speaker have slave node L and right channel speaker have slave node R, here is the main factor works for the surround speakers the signals that have been transmitted through the Bluetooth master node (from the center speaker ) on to the left channel and right channel can be subdivided into further surround left(slave node SL) and surround right(slave node SR) speaker and also then in surround back left(slave node SBL) and surround right speakers(slave node SBR). This division can be possible on audio signals using the sampling of the sound signal and transmission of those various frequency signals at different speaker to get a proper sound output. The main factors that are been used for Bluetooth audio transmission is as follows: Compatibility It should support the Bluetooth core specification v2.0 or greater for high speed transmission and for proper sound output. The sender and receiver should support the A2DP, L2CAP Specification and so that the master can easily detect address of slave nodes and provide a faster connectivity between transmitter and receiver. Crystal Clear Sound Both the transmitter and receiver should have built in codec and Sampling strategy and signal processor that can process these signals to achieve the crystal clear sound. Automatic Connectivity The receiver can automatically connect with the transmitter when it comes in valid area or in range of transmitter than it will validate the address and connect to it speedily. Quick response In the piconet the master can easily and quickly identify the slave and locate the protocol A2DP and L2CAP and establish the Bluetooth connection to transmit the audio signal at both the channel. Connection Strategy:- The figure 6 shows the way of transmitting audio from one point to various points[2] for our 7.1 channel audio system. The error generated during the audio transmission is that Audio is transmitted mainly over two channel (left and right channel) and synchronization between this two audio channels stream without any relationship.in figure 5 we shows 7.1 channel audio system by forming the piconet network. The piconet network consist 1 master and 7 slaves network. This will help us to connect all 7 speakers with one center speaker. The center speaker is treated as a master node and subwoofer is slave node. Here we also divide left channel into further surrounded left channel and right channel into further surrounded right channel by using sampling technique. The frequency band of 220 kbps-320 kbps is used by left and right slave and 128kbps-220kbps frequency is used by surrounded left and surrounded right. 96kbps-128kbps frequency is used by surrounded left back and surrounded right back. The synchronization can be achieved over the left and right channel using the following strategy. For the Transmitter and for the receiver. Fig 5 168
(3) Time Mark The transmitter will make or create time mark with each audio packet this will record difference absolute time and synchronization time. The receiver will decode and play the audio packet at each speaker according to time mark. (4) Packet number The transmitter transmit audio packet for each channel and co channel with a packet number automatic increased along with transmitting order, and stores it in a field at the header of packet. After receiving an audio packet, the receiver confirms the packet s position in the audio stream according to the packet number in order to judge whether there any lost of audio packet because of network congestion or wireless disturbance. Besides the system has a synchronizing cycle. The packet number is set with zero after every synchronous cycle. Fig 6 (Prototype of 7.1 Channel Bluetooth Audio System) [6] IV. Synchronization (1) Absolute time Absolute time is adopted to synchronize the two channel audio streams without relationship. Absolute time is adopted to synchronize the two audio channel streams without relationship. Absolute time is set with zero at the time when the connection between transmitter left channel L and receiver left channel(l,sl,sbl), and the connection between transmitter right channel and receiver right channel(r,sr,sbr) are established, and it synchronously increases with the clock. The absolute time is the base for synchronous time and time stamp. (2) Synchronization time The first field at transmitter end it contains audio packet stores the synchronous time. When receiver starts collection of the first audio packet,the synchronous time is set with the current value of the absolute or estimated time noted from the receiver side, and it will set to zero for the next audio packet. (5) Buffer The receiver has a defined buffer which the receiver audio packet can be synchronized in it. This can avoid the network distortion and delay caused by the change of wireless environment. The data flow chart for Transmitter:- Fig 7 shows data flow diagram of transmitter Integer i storing the packet number is initialized with zero at first. Then the Transmitter check whether it receives a packet or not. The data flow is ended without receiving any packet. Otherwise Transmitter splits audio channel into sub channel. if value I is equal to synchronous cycle. the Synchronous time is set with the zero. the Time stamp is set with packet no. If i is not equal to the Synchronous cycle, the Time stamp is set with Packet no., the Synchronous time is set with zero, and i is automatically incremented. 169
Fig 7 The Data Flow Chart For Receiver:- Fig.8 shows the data flow chart of the receiver. Integer num and Time are set with zero. The num is used to synchronize with the Packet no., and it is automatically incremented. The Time stores the Time stamp for every audio packet. The receiver checks whether it receives an audio packet. The data flow is ended without receiving an audio packet. Otherwise, the Time is set with the Time stamp. There is not any lost audio packet if the num equals to the Packet no., and the receiver plays the audio packet according the their arrival. Fig 8 V. REALIZATION The system mainly includes the transmitter and receiver. The transmitter transfers the audio into radio frequency signals and transmits them. The receiver receives signals, decodes and plays them. BlueCore2-Flash is a single chip radio and baseband IC for Bluetooth 2.4GHz systems[7].it is implemented in 0.18mm CMOS technology.bluecore2-flash has the same pin out and electrical characteristics as available in BlueCore2-ROM to enable development of custom code before committing to ROM. The integrated mono audio CODEC allows for more compact designs and low power consumption for battery powered applications. 170
It provides a fully compliant Bluetooth system to v1.2 of the specification for data and voice communications. Moreover, it also has an on-chip DSP and stereo CODEC which support the standard sample rates of 8kHz, 11.025kHz, 16kHz,22.05kHz,32kHz, 44.1kHz,48kHz, and 16-bit resolution. It works on low power 1.8V, and is comes in BlueCore2-Flash 10 x 10mm LFBGA Package. Since the audio input for BlueCore03 Multimedia chip is a couple of differential signal, the pseudo differential input technology which a 2.2K resistance is added between two differential signals is applied to realize sender. The stereo audio single-ended input signal is transferred into a couple of differential signal through the resistance, and is inputted to the BlueCore03-Multimedia chip. The audio player input is single-ended input signals in general, while BlueCore03- multimedia external chip outputs the differential signals. So the receiver needs an audio amplifier to ensure the high quality while transfer the differential signals to singleended input signals. A 3V.35um CMOS Bluetooth receiver IC is used to develop the receiver. Because of its low power-consumption and small volume, it is quite suitable for the receiver. VI. CONCLUSION Today is the world of wireless. Bluetooth Technology are pioneer wireless technology, there are lots of hidden area of Bluetooth technology to be unfolded in future. Considering this we research and give idea to implement 7.1 channel audio system by using Bluetooth technology. References:- [1] Bluetooth SIG. Bluetooth Core Specification Addendum [2] Point-to-Multipoint Stereo Audio Transmitting System Based On Bluetooth International Conference on Communications and Mobile Computing,2010 [3] DTS Codec Overview [4] THX home-entertainment [5] Bluetooth SIG. Advanced Audio Distribution Profile Specification Version [6] Piconet Embedded Mobile Networking [7] BLUE CORE -2 DATA SHEET 171