METHOD AND ARRANGEMENT FOR NARROWBAND COMPATIBLE WIDEBAND COMMUNICATION IN A DECT SYSTEM

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the field of communications and more specifically the invention relates to a method and an arrangement for narrowband compatible wideband communication in a DECT system.

DESCRIPTION OF RELATED ART AND BACKGROUND OF THE INVENTION

Communication in the DECT system is using TDMA (Time Division Multiplex Access), wherein each portable part typically has a pair of time slots assigned to it. There are twelve time slots available in each direction, numbered from 0 to 11 in the downlink direction and from 12 to 23 in the uplink direction.

A DECT cell 31 configured for normal telephone calls is outlined in Fig. 1. During an active telephone call a time slot pair will be filled with speech data at 32 kbps. For example, a telephone call answered in a portable part 32 uses slot 0 and slot 12 for reception and transmission of speech information, a telephone call answered in a second portable part 33 uses slot 2 and slot 14 for reception and transmission of speech information, and a telephone call answered in a third portable part 33 uses slot 10 and slot 34 for reception and transmission of speech information.

The transmitted speech is encoded/compressed to a 32 kbps bit rate and the frequency content is between 300 Hz and 3.4 kHz. Such communication will in the present text be referred to as narrowband speech or voice communication.

A standard telephone system is typically only able to transmit speech up to the same frequency. However, newer technologies exist that make telephone calls using higher bandwidth (for example 50 Hz — 7 kHz) possible. One such technology is telephony over internet or Voice over IP (VoIP).

Since the carrier of the call in home environments probably will be a DECT system, there is a need to extend the DECT standard so that wideband speech or voice communication can be handled.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and an arrangement, respectively, for wideband voice communication in a DECT system, which is backwards compatible with the today's standard portable parts that are capable of handling narrowband voice communication only.

This object is according to the present invention attained by methods and arrangements as claimed in the appended patent claims .

According to an aspect of the invention a method is provided for narrowband compatible wideband voice communication in a DECT system, in which a wideband voice signal is split up into a first and a second component, wherein the first component is a narrowband voice signal having a spectral content of about 300 Hz to about 3.4 kHz and the second component is a wideband residue signal. The narrowband voice signal is encoded by using a G.726 standard encoder creating an encoded narrowband voice signal interpretable by a narrowband capable portable part, whereas the wideband residue signal is encoded by using another encoder. The encoded narrowband voice signal and optionally the encoded wideband residue signal are then transmitted.

If the receiver of the transmission is a portable part capable of handling wideband voice communication, both the encoded narrowband voice signal and the encoded wideband residue signal are transmitted. In the portable part, the encoded narrowband voice signal and the encoded wideband residue signal are received, decoded, and joined together to thereby provide for wideband voice communication.

On the other hand, if the receiver of the transmission a portable part capable of handling narrowband voice communication only, preferably the encoded narrowband voice signal only is transmitted. In the portable part, the encoded narrowband voice signal is received and decoded in the portable part to thereby enable voice communication also for such a portable part — even if it is narrowband.

According to further aspects of the invention an arrangement for performing the above method as well as a DECT system comprising such an arrangement are provided.

The demands of the audio link quality of an inventive DECT system is not higher than those of a standard DECT system since according to the invention, if a piece of the wideband residue signal as received in a wideband capable portable part comprises a bit error while a corresponding piece of the narrowband voice signal is bit error free, the piece of the wideband residue signal is simply skipped and the piece of the encoded narrowband voice signal only is decoded in the portable part to thereby provide for a temporary bit-error free narrowband voice communication.

Further characteristics of the invention and advantages thereof, will be evident from the following detailed description of preferred embodiments of the present invention given hereinafter

and from the accompanying Figs. 2-4, which are given by way of illustration only, and shall thus not limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates, in a schematic layout view, a DECT cell configured for normal telephone calls.

Figs. 2a-b illustrate each, in a schematic block scheme, parts of a DECT transmitter arrangement for wideband voice communication according to a respective embodiment of the invention.

Fig. 3 illustrates, in a schematic block scheme, parts of a DECT receiver arrangement for wideband voice communication according to an embodiment of the invention.

Fig. 4 illustrates schematically a DECT system having inventive DECT transmitter and receiver arrangements implemented.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention proposes a technique for narrowband compatible wideband communication in a DECT system so that new portable parts capable of wideband voice communication may utilize the high bandwidth of the system, while the today's portable parts capable of narrowband voice communication only may still be used in the system.

In the present text narrowband communication or narrowband voice communication refers to speech encoded to a 32 kbps bit rate and having a frequency content between about 300 Hz and about 3.4 kHz. Wideband communication or wideband voice communication refers to speech encoded to a bit rate higher than 32 kbps bit rate and having a frequency content larger than about 300 Hz to

about 3.4 kHz, e.g. speech encoded to a bit rate of 64 kbps bit rate and having a frequency content up to about 7 kHz . Narrowband compatible communication refers to any communication that may be used together with narrowband communication in a system. A narrowband capable part is assumed to be capable to handle narrowband voice communication only, and thus not wideband voice communication. A wideband capable part is assumed to be capable to handle wideband voice communication.

Fig. 2a illustrates, in a schematic block scheme, parts of a DECT transmitter arrangement for wideband voice communication according to an embodiment of the invention.

The arrangement is provided for dividing a wideband voice signal 200 into a first 200a and a second 200b component. The wideband voice signal comprises energy in the frequency range below about 300 Hz, e.g. in the frequency range of about 50 Hz to about 7 kHz.

The first component 200a is received by a band pass filter 201 having a pass band of about 300 Hz to about 3.4 kHz, which forms a narrowband voice signal 202. The second component 200b is received by a band stop filter 203 having a stop band of about 300 Hz to about 3.4 kHz, which forms a wideband residue signal 204.

The narrowband voice signal 202 is next received by a G.726 standard encoder 205, which is provided for encoding the narrowband voice signal 202, thus creating an encoded narrowband voice signal 206 interpretable by a narrowband capable portable part of today since the existing DECT systems use the G.726 standard encoding technique.

The wideband residue signal 204 is received by another encoder 207, which is provided for encoding the wideband residue signal 204, thus creating an encoded wideband residue signal 208. The other encoder 207 is advantageously a suitable ADPCM encoder.

A transmitter is provided for transmitting both the encoded narrowband voice signal 206 and the encoded wideband residue signal 208 or the encoded narrowband voice signal 206 only depending on the capability of the intended receiver.

On one hand, if the intended receiver is a wideband capable portable part both the encoded narrowband voice signal 206 and the encoded wideband residue signal 208 are transmitted, and both the encoded narrowband voice signal 206 and the encoded wideband residue signal 208 are received, decoded, and joined together in the portable part to thereby provide for wideband voice communication.

On the other hand, if the intended receiver is a portable part capable of handing narrowband voice communication only, the encoded narrowband voice signal 206 only is transmitted, and the encoded narrowband voice signal 206 is received and decoded in the portable part to thereby provide for ordinary narrowband voice communication.

The above arrangement is preferably implemented in both fixed parts and in portable parts of a DECT system.

Typically, an increased amount of information to transmit involves a higher error probability. When the speech information is sent in two pieces, e.g. packets, slots or data streams, as in the wideband voice communication of the inventive arrangement described above, the error probability is thus higher than when narrowband voice communication is performed. However, in the

present invention a bit error in a piece of the wideband residue signal can be accepted if no bit error occurs in the corresponding piece of the narrowband voice signal. The piece of the wideband residue signal containing a bit error can simply be skipped since the corresponding piece of the narrowband voice signal provides an acceptable speech quality for a short while. Therefore a wideband capable portable part can manage with a similar audio link quality as an ordinary narrowband portable part without loosing too much in speech quality.

With reference next to Fig. 3, which illustrates, in a schematic block scheme, parts of a DECT transmitter arrangement for wideband voice communication, a further embodiment of the invention will be described.

Here, the wideband voice signal, denoted by 200', lacks energy below about 300 Hz, e.g. it comprises energy in the frequency range of about 300 Hz to about 7 kHz.

The arrangement is provided for dividing the wideband voice signal 200' into a first 200a' and a second 200b' component.

The first component 200a' is received by a low pass filter 201' having a cut-off frequency of about 3.4 kHz, which forms a narrowband voice signal 202'. The second component 200b' is received by a high pass filter 203' having a cut-off frequency of about 3.4 kHz, which forms a wideband residue signal 204'.

The narrowband voice signal 202' is then received by the G.726 standard encoder 205, which is provided for encoding the narrowband voice signal 202', thus creating an encoded narrowband voice signal 206' interpretable by a narrowband capable portable part. The wideband residue signal 204' is received by the other encoder 207, which is provided for

encoding the wideband residue signal 204', thus creating an encoded wideband residue signal 208'.

Finally, a transmitter is provided for transmitting both the encoded narrowband voice signal 206' and the encoded wideband residue signal 208' or the encoded narrowband voice signal 206' only depending on the capability of the intended receiver.

Regarding other features and details the embodiment of Fig. 2b may be similar to the embodiment of Fig. 2a.

Fig. 3 illustrates, in a schematic block scheme, parts of a DECT receiver arrangement for wideband voice communication. The arrangement includes a G.726 standard decoder 301 and another decoder 302. The G.726 standard decoder 301 is provided for decoding a narrowband voice signal, i.e. signal 206 (Fig. 2a) or

206' (Fig. 2b), and the other decoder 302 is provided for decoding the wideband residue signal, i.e. signal 208 (Fig. 2a) or 208' (Fig. 2b) to obtain the respective decoded signals, i.e. signals 202 and 204 (Fig. 2a) or signals 202' and 204' (Fig.

2b) . The decoded signals are joined together in an adder 303 to form the original wideband voice signal, i.e. signal 200 (Fig. 2a) or 200' (Fig. 2b) .

Finally, Fig. 4 illustrates schematically a DECT system 40 having inventive DECT transmitter and receiver arrangements implemented. The narrowband capable portable part 32 is connected via a wideband capable fixed part 41 and a telephone line 42. Another portable part 34 is wideband capable and is connected to the same fixed part 41.

Assume now a scenario with an ongoing telephone conference between the two portable parts 32 and 35, and an external party connected to the fixed part 41 via the telephone line 42. The

telephone line 42 is assumed to be a wideband capable connection, and the party connected thereto is assumed to have transmitter and receiver arrangements capable of handling narrowband compatible wideband voice communication of the present invention. Further, half duplex, i.e. one only of the parties may talk at the same time, is assumed. The fixed part 41 will have to adapt the coding so that all parties can understand the voice signal. According to the present invention such adaptations are easily made.

A narrowband voice signal in the narrowband capable portable part 32 is G.726 coded and is sent to the fixed party for distribution to the party connected to the telephone line 42 and to the wideband capable portable part 35. The fixed party 41 may simply forward the signal since it is interpretable by the party connected to the telephone line 42 and by the wideband capable portable part 35.

A wideband voice signal in the wideband capable portable part 35 is split up into a narrowband voice signal and a wideband residue signal, and the narrowband voice signal is G.726 coded, whereas the wideband residue signal is coded in other manner. The two coded signals are sent to the fixed part 41 for further distribution. Both signals are forwarded to the party connected to the telephone line 42, whereas the G.726 coded narrowband voice signal only is forwarded to the narrowband capable portable part 32.

Similarly, a wideband voice signal at the party connected to the telephone line 42 is split up into a narrowband voice signal and a wideband residue signal, and the narrowband voice signal is G.726 coded, whereas the wideband residue signal is coded in other manner. The two coded signals are sent to the fixed part 41 for further distribution. Both signals are forwarded to the

wideband capable portable part 35, whereas the G.726 coded narrowband voice signal only is forwarded to the narrowband capable portable part 32.

In such manner a telephone conference may be set up with both wideband capable and narrowband capable parts, wherein some of the communication will be wideband and some narrowband. In the example given above, the communication between the party connected to the telephone line 42 and the wideband capable portable part 35 will be wideband, whereas all other communication will be narrowband. The present invention puts very low demands on the fixed part 41 in terms of transcoding, i.e. on conversion from one speech codec to another. Only communication to the narrowband capable portable part 32 has to be transcoded, and the transcoding consists simply in a trivial select operation to select the G.726 coded signal only.

If the narrowband and wideband coding techniques were entirely different, i.e. if a conventional wideband speech codec would have been used, a complex transcoding would have been needed for communication both to and from the narrowband capable portable part 32.