WO2005086431A1

WO2005086431A1 - Ip phone with dual mode bluetooth stack

Info

Publication number: WO2005086431A1
Application number: PCT/EP2004/003038
Authority: WO
Inventors: Raymond Gass
Original assignee: Alcatel
Priority date: 2004-02-27
Filing date: 2004-02-27
Publication date: 2005-09-15

Abstract

It is an object of the present invention to provide a method, a telecommunications terminal and a wireless handset for setting up a radio link allowing to proceed a wideband communication session. This is achieved by applying a method for setting up a radio link between a telecommunications terminal and a wireless handset while two synchronous connections oriented channels will be assigned to said radio link. These two SCO channels will be used for the transmission of a bi-directional (duplex) communication session. In an embodiment according to the invention, the two SCO channels will be concatenated in time when used for the bi-directional (duplex) communication session. Advantageously, a sampling can be applied to said communication session providing an audio wide-band quality. This can be obtained by choosing a sampling to 16 bits at 16 kHz bandwidth.

Description

IP phone with dual mode Bluetooth stack

Technical Field

The present invention relates to a method for setting up a radio link between a telecommunications terminal and a wireless handset. Furthermore, it is related to a telecommunications terminal as well as a wireless handset comprising each a radio interface for the set up of a radio link with respectively the wireless handset and the telecommunications terminal.

Background of the invention

Telecommunication systems such as the Public Switched Telephone Network (PSTN) and Private Branch eXchanges (PBXs) are generally well known. The PSTN is now considered to be a digital system that is capable of carrying data at a theoretical speed of 64 kilobits per second (kbps). Despite many enhancements to the ca pacity, efficiency and performance that has undergone PSTN over the years, the voice quality is still limited to something less than "true voice" quality for several reasons.

One of the reasons the PSTN limits voice quality is to increase the call capacity of the network by reducing the data rate of each call. The PSTN confines each voice digital data stream to 64 kbit/s. This is achieved by sampling the voice signals at a rate of 8 kHz, and filtering out any frequencies less than 200 Hz and greater than 3.4 kHz. Amplitude compression is also used according to some so called μ-Law in the US or A-Law encoding in Europe resulting in an 8-bit, 8- Hz stream (sampling rate) of data. This amplitude compression is part of a Pulse Code Modulation (PCM) encoding techniques according to the ITU-T Recommendation G.71 1 . Reversing this process at the receive end reproduces the caller's voice but without the original quality. This compression and expansion (companding) process of the G.71 1 algorithm adds distortion to the signal and gives a p hone conversation its distinctive "low fidelity" quality. It is directly related to the used narrow bandwidth of about 3.5 kHz.

In lieu of PCM codecs, digital voice/speech codecs may be utilized by a telecommunication system to transmit audio signals in a different manne r than the conventional PCM encoding techniques. Assuming that a suitable transmit bandwidth is available, such audio codecs can provide enhanced fidelity voice trans- missions by incorporating audio characteristics such as tone, pitch, resonance, and the like, into the transmitted signal. For example, by leveraging th e 64 kbps capability of current telephone networks, wideband voice codecs are a I ready designed to provide high fidelity telephone calls in lieu of conventional audio calls that are governed by the PCM encoding protocols. Such high fidelity calls are transmitted using a bandwidth that exceeds 3.5 kHz, e.g. 7 kHz with a codec sampling to 16 bits at 1 6 kHz or more, like defined already under ITU-T Recommendation G.722.2.

Since nowadays a majority of communications sessions are performed at least partly via a radio link, the question can be risen if a wideband comm unications session could be transmitted also through a radio link. One technology which came up to be quite popular for a short-range radio link is called Bluetooth. Latter is intended to replace the cable connecting portable and/or fixed electronic devices. It operates in the unlicensed ISM band at 2.4 GHz. A frequency hope transceiver is applied to combat interference and fading. A shaped, binary FM modulation is applied to minimize transceiver complexity. The symbo l rate is 1 Ms/s. A slotted channel is applied with a nominal slot length of 625 μis. For full duplex (bi-directional) transmission, a time division duplex scheme is used. On each channel, information is exchanged through packets. Each packet is trans- mitted on α different hope frequency. A packet normally covers a single slot, but can be extended to cover up to five slots. The Bluetooth protocol uses a combination of circuit and packet switching. Slots can be reserved for synchronous packets. Bluetooth can support an asynchronous data channel, up to -three si- multaneous synchronous voice channels, or a channel which simultaneously supports asynchronous data and synchronous voice. Each voice channel su pports a 64 kb/s synchronous (voice) channel in each direction. The Bluetooth system provides a point-to-point connection (only two Bluetooth units involved), or a point- to-multipoint connection. In the point-to-multipoint connection, the channel is shared among several Bluetooth units. Two or more units sharing the same channel form a piconet. One Bluetooth unit acts as the master of the piconet (the one initiating a communication), whereas the other unit(s) acts as slave(s). Up to seven slaves can be active in the piconet.

The core of the Bluetooth application is to make interface of a digital a pparatus wireless. There are several wireless applications based on the Bluetooth technology. Presently, applications using the Bluetooth technology are cellular phone application, wireless headset and others. The cellular phone application can be performed using an audio channel, which is the biggest advantage of the Blue- tooth technology. In addition, the wireless headset is the first application in the early stage of the implementation of Bluetooth technology. An user is able to speak on the phone using the wireless headset when the cellular phone is in a bag or in a pocket, and the wireless headset can be used as a hands free device while the user drives a car. On the Bluetooth air-interface, either a 64 kb/s log PCM format (A-law or μ-law) is used, or a 64 kb/s CVSD (continuous variable slope delta modulation) is used for the audio channel. The latter format applies an adaptive delta modulation algorithm with syllabic companding. When using a log PCM codec then the applied compression method follows ITU-T Recommendations G.71 1 i.e. sampling to 8 bit at 8 kHz. If a CVSD codec is used, then the input to such encoder is 64 ksamples/s linear PCM. Such system is also clocked at 64 kHz.

In US 2002-01 83050 is described a method for direct voice telephone call using a Bluetooth terminal that embodies direct voice telephone call between Bluetooth terminals through a Bluetooth protocol stack. The method comprises a step of trying to set a call, a step of connecting an asynchronous connection-less (ACL), a step of connecting a synchronous connection-oriented (SCO) when the ACL is connected and a step of making a voice telephone call when the SCO is con- nected. The use of such method does not allow the set up of wideband communication sessions but only narrowband ones.

Summary of the invention

In view of the above, it is an object of the present invention to provide a method, a telecommunications terminal and a wireless handset for setting up a radio link allowing to proceed a wideband communication session.

This object is achieved in accordance with the invention by applying a method for setting up a radio link between a telecommunications terminal and a wireless handset while two synchronous connections oriented channels will be assigned to said radio link. These two SCO channels will be used for the transmission of a bi-directional (duplex) communication session. In an embodiment according to the invention, the two SCO channels will be concatenated in time when used for the bi-directional (duplex) communication session. Advantageously, a sampling can be applied to said communication session providing an audio wide-band quality. This can be obtained by choosing a sampling to 1 6 bits at 16 kHz bandwidth. But an alternative sampling could be also applied.

Advantageously, the telecommunications terminal as well as the wireless handset may comprise each a radio interface being possibly a Bluetooth interface. In that case, the synchronous connection oriented channels are the voices channels supporting a 64 kb/s synchronous (voice) channels in each direction. According to an embodiment of the invention, a third synchronous connection oriented chan- nel can be assigned to said radio link. Such third synchronous connection oriented channel can be used for the transmission of control command like in-band audio signaling. Such in-band signaling can be for example some ringing tone transmitted from the telecommunications terminal to the wireless handset where it shall be activated, lead activation, etc. This third synchronous connection ori- ented channel can be also used for the transmission of this bi-directional communication session using a narrow bandwidth. In that case, a sampling will be applied by the respective codec (coder/decoder) of the telecommunications terminal and the wireless handset using a bandwidth of e.g. 3.5 kHz i.e. applying a sampling to 8 bits at 8 kHz. In such a way, an alternative is let available for the set up of the same bi-directional communication session using narrow bandwidth. This is of great advantage when the wireless hand set to be paired (Bluetooth requirement before setting up a radio link) with a telecommunications terminal does not provide a codec able to support wide-band sampling.

In a further embodiment according to the invention, the codec tasks is performed by some computer program comprising specific codes devoted to that tasks. Latter will be performed when running by some Digital Signal Processor (DSP) like. This processor like is usually a specialized microprocessor dedicated to perform fast calculation when processing audio or video signals. The telecommunications terminal as well as the wireless handset comprise each such kind of processor on which the codes devoted to the code tasks will run.

Description of the drawings

An exemplary embodiment of the invention will now be explained further with the reference to the attached drawings in which:

Fig. 1 is a diagram of a profile stack between a telecommunications terminal and a wireless handset according to the in- vention;

Fig. 2a is a diagram showing a process of setting a communication session established by the telecommunications terminal according to the invention;

Fig. 2b is a diagram showing a process of setting a communication session established by the handset according to the invention; Fig. 3α is α diagram showing a process of releasing a communication session by the telecommunications terminal according to the invention;

Fig. 3b is a diagram showing a process of releasing a communication session by the handset according to the invention;

Fig. 4a and 4b are diagrams showing examples of signaling according to the invention.

Detailed description of preferred embodiments

According to an embodiment of the invention, a new profile can be designed to carry wide-band telephony. If using Bluetooth technology, it will be based on the synchronous connection oriented (64 kbits/s time slot) called also the SCO channels. This wide-band audio profile will be depended upon both the serial port profile and the generic access profile.

On figure 1 is shown the profile stack between a telecommunications terminal (phone side) and a wireless handset according to the invention. The baseband is the OSI (Open Systems Interconnection) layer 1 and the LMP and L2P are the OSI layer 2 in the Bluetooth protocol. RFCOM is the Bluetooth adaptation of GSM TS 07.10. SDP is the Bluetooth Service Discovery Protocol. All these Bluetooth protocols are defined in the Bluetooth core specifications. The new characteristic of such audio profile is defined at first at the handset control as shown on figure 1 . It is that part which is responsible for handset specific control signaling. In particular, the set up of SCO channels (for the synchronous option), remote control of "beeper" function (to help user finding his/her handset). On top of the handset control is shown on figure 1 the application of a wide-band audio control. It is this audio part of the handset which will provide a bi-directional communication session of wide-band quality. This is provided by wide-band audio codec in the telecommunications terminal as well as in the handset applying a sampling to a communication session between both with a sampling to 16 bits at 16 kHz with G.722.2 A or μ law. The handset side will usually perform coding/decoding and D/A (digital/analog) A/D conversions to be transmitted using two synchronous connection oriented channels. This is obtained by concatenating in time these two SCO channels. Echo canceling will be implemented in the telecommunications terminals side. The audio connection (bi-directional communication session) between the telecommunications terminal and the wireless handset is a point-to-point connection with usually one audio connection at a time. The user interface could be quite simple governed by the requirement to detect when the user presses a button (on-hook, off-hook), beeper on/off to locate the handset, or possibly also remote audio volume control.

The radio link between the telecommunications terminal (telephone set) and the wireless handset will use a secure connection, with authentication and encryption. The secure connection may be based on the GAP authentication procedure as defined in the generic access profile of the Bluetooth specification. This procedure includes entering a PIN code and the creation of link keys. The PIN code procedure will be used during the GAP authentication procedure initiated foilowing power-on and on-demand by the system. In that way, although Bluetooth devices have the same equivalent hardware, a Bluetooth device may be a master device or a slave device depending on whether or not it opens a communication initially. The Bluetooth device that initiates the communication becomes a master to manage the communication in the so called piconet.

RFCOMM is used for the serial port emulation, to transport the user data, including AT commands from the handset to the telephone set.

When setting up a radio link between such telecommunications terminal and such wireless handset according to the invention, two synchronous connection oriented channels will be used to transport timeslots. These SCO channels will be concatenated in time such that each carry a sample of the voice signal usually at 1 6 kHz. This will provide the audio wide-band quality.

A third SCO channel may be used to carry narrowband voice (8 kHz sampling) for the purpose of compatibility with existing narrowband equipment that could be used simultaneously. On figure 2α is shown α diagram of a connection establishment initiated by the telecommunications terminal. Upon reception of one of the relevant events (e.g. incoming call) the telecommunications terminal will initiate the following steps:

• ringing locally inside the telephone set (this might be inhibited by configura- tion),

• establish the connection with the handset,

• and, once the connection is established, send the RING code to alert the user(useful when the user is not located near the telephone set)

• establish the 3 SCO links or channels • a second mode of operation (alternative) is based on inband audio signaling: the SCO channel is established first, and used to carry ringing tone instead of RING code in ACL.

When the user recognizes the arrival of the call, he/she can accept the audio connection by performing appropriate action (e.g. pressing a button on the handset or on the telephone set, or by the use of the normal on-hook/off-hook procedure). The two user initiated actions are illustrated on figure 2a. For compatibility reasons with other profiles, the ACCEPT code should be set to AT+CKPD=200.

On figure 2b is shown a diagram of a connection establishment performed by the wireless handset. The connection establishment is initiated by the handset following an appropriate user action (e.g. pressing the on/off hook button). Further signaling exchange could take place if the handset is equipped with dialpad as an option (as an example, this option is true when the handset is a poor old GSM set). The figure below illustrates the link set up for the SCO based application, with no dialing options from the handset (dialing might be replaced by voice recognition in that direction, or dialing might be performed directly on the telephone set dialpad or alphanumeric keys. When dialing is offered (keypad on the handset, or GSM set), then it should be based on the CTP(Cordless telephony Profile as defined by the Bluetooth standard).

On figure 3a and figure 3b are shown a connection released respectively by the telecommunications terminal and the wireless handset. An external event (call released by the other party), or a user initiated action (on hook) will release the SCO link and the communication session as shown on the figures 3a and 3b. In both cases, the SCO links (channels) and the communication session (connection) are released under control of the telecommunications terminal. It is usually not left under control of the wireless handset.

On figure 4a and 4b are shown diagrams of two examples of an in-band audio signaling. In figure 4a is shown the case where the user would like to activate some kind of alarm to be able to find his/her wireless handset. A search capabil- ity is offered, that will initiate beep generation in the wireless handset, in case that wireless handset has enough power and can be reached by radio link. On figure 4b is shown how such search process can be stopped by the user. The search stop is initiated by the user from the wireless handset.

The telecommunications terminal can control the volume of the loudspeaker of the wireless handset during an audio communication session. It is preferable but not absolutely required to avoid to offer similar access to the volume of the microphone. Indeed, it may introduce instability in the loop when setting gain at the microphone. The gain setting i.e. the change of volume of the loudspeaker is of particular use for impaired people. To avoid unnecessary user action, the value of the volume might be stored and reused for each further communication session. On the other hand, when the level exceeds those defined by standards related to acoustic shocks prevention, then the level should be tuned back to nominal one for the next communication session. In such a way, an unwanted acous- tical damages shall be avoided.

A realization of an embodiment according to the invention is based on the use of the requirements for the link manager as defined by the Bluetooth standard for the serial port profile together with the addition of the support for the 3 SCOs links (channels) at both ends i.e. telecommunications terminals and wireless handset.

The codec tasks like the applied sampling on the two SCO channels as well as the third one when used and/or the task to concatenate the two SCO in time is preferably but not exclusively performed by some codes of some computer program. These codes will perform the codec tasks when running by some specific processor usually a digital signal processor like. Both, the telecommunications terminal as well as the wireless handset comprise each usually a digital signal processor like (DSP). This computer program is possibly stored on some independent computer storage medium or directly on the DSP.

Claims

Clαi ms

1 . A method for setting up α radio link between a telecommunications terminal and a wireless handset by assigning two synchronous connection oriented channels to said radio link for the transmission of a bi-directional communi- cation session.

2. The method according to claim 1 characterised by concatenating in time these two synchronous connection oriented channels.

3. The method according to claim 1 characterised by applying a sampling to said communication session providing audio wide-band quality possibly of 16kHz bandwidth.

4. The method according to claim 1 characterised by using bluetooth interfaces for performing said radio link.

5. The method according to claim 1 characterised by assigning a third synchronous connection oriented channel to said radio link.

6. The method according to claim 5 characterised by using said third synchronous connection oriented channel for the transmission of control command like in-band audio signalling.

7. The method according to claim 5 or 6 characterised by using said third synchronous connection oriented channel for the transmission of said bidirectional communication session over a narrow band possibly of 8kHz bandwidth.

8. A telecommunications terminal comprising a radio interface for the set up of a radio link with at least a wireless handset, while two synchronous connection oriented channels being assigned to said radio link for a bi-directional communication session, these two synchronous connection oriented channels being concatenated in time.

9. The telecommunications terminal according to claim 8 characterized in that it comprises a codec applying a sampling to said audio communication session providing audio wide-band quality possibly with a sampling to 16 bits at 16 kHz.

10. The telecommunications terminal according to claim 8 characterized in that a third synchronous connection oriented channel being assigned to said radio link possibly for the transmission of said bi-directional communication session over a narrow band possibly with a sampling to 8 bits at 8kHz.

1 1 .The telecommunications terminal according to claim 9 characterized in that it has some computer storage medium for a computer program comprising codes devoted to perform the codec tasks when run on said telecommunica- tions terminal by some digital signal processor like.

12.A wireless handset comprising a radio interface for the set up of a radio link with at least a telecommunications terminal while two synchronous connection oriented channels being assigned to said radio link for a bi-directional com- munication session, these two synchronous connection oriented channels being concatenated in time.

13. The wireless handset according to claim 12 characterized in that it comprises a codec applying a sampling to said audio communication session providing audio wide-band quality possibly with a sampling to 16 bits at 16 kHz.

14. The wireless handset according to claim 1 3 characterized in that it has some computer storage medium for a computer program comprising codes devoted to perform the codec tasks when run on said wireless handset by some digital signal processor like.