A communication system can be seen as a facility that enables communication sessions between two or more entities such as communication devices, network entities and other nodes. A communication device can be understood as a device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit data via the communication system and can thus be used for accessing various applications. A communication device may also enable an unmanned entity such as an application to exploit the communication capabilities of the device.
A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standard or specification may define if a communication device is provided with a circuit switched carrier service or a packet switched carrier service or both. Communication protocols and/or parameters which shall be used for the connection are also typically defined. For example, the manner how a communication device can access a communication system and how various aspects of the communication there between shall be implemented is typically based on predefined communication protocols.
Various communication systems providing wireless communication are known. These systems are often referred to as mobile systems; although in certain systems the mobility may be restricted to substantially small areas. A mobile communication device that is configured for duplex communication is typically provided with a transceiver for enabling wireless communication with a base station or a receiver of the wireless system. An example of the wireless systems is the public land mobile network (PLMN). Another example is a wireless system that is based, at least partially, on use of communication satellites. Wireless communications may also be provided by means of other types of systems, such as by means of wireless local area networks (WLAN) or short range radio or other wireless links.
An example of the short range or local systems are wireless personal area networks (WPANs) where the connections involve little or no infrastructure but are rather based on groups of communicating devices or stations. Thus, in a simple form a wireless communication system comprises at least two stations that are suitably configured for enabling wireless communication there between.
Local communication system such as short range communication systems may also be configured to provide high data rates. High data rates may be enabled by means of mechanism such as ultra-wide band (UWB) signalling. For various reasons, for example due to emission limits imposed by regulatory bodies, coverage radius for those systems may be limited, typically to a few meters, for example ten metres.
The local system may be connected to other networks, for example a data network and/or a telecommunication network, via an appropriate gateway arrangement.
A number of new applications may be made possible in local wireless systems, for example those employing the UWB, if the coverage radius thereof is extended. Different physical layer (PHY) modes have different operating ranges and bit rates. Extended coverage may be possible within emission masks for example by using lower bit-rate, more error-protected physical layer (PHY) modes. Such range extension, however, may impose new constraints on the system design.
One example of a wireless personal network is described in the ECMA international, Standard ECMA-368, High Rate Ultra Wideband PHY and MAC Standard, 1st Edition, December 2005. This standard specifies an ultra wide band UWB physical layer PHY for wireless PANs, utililising the 3100-10600 MHz frequency band. This is also approved as ISO/IEC 26907.
However, the PAN channel is inherently dynamic. The dynamics are caused by moving devices, the moving human body as well as obstacles crossing the line of sight. Typically requirements in terms of data rate and real time performance are constantly increasing. However, the dynamic channel disrupts the signal. To improve the performance of a dynamic channel, the modulation and coding scheme as well as the transmit power could be changed in dependence on the channel state information. To achieve this would require that the current channel state be obtained. Further, the optimum data rate and transmit power needs to be derived and this information has to be fed back to the transmitter.
In the ECMA-368 document, the possibility to feedback the optimal data rate in a beacon by a link feedback information element is disclosed. However, there is a problem in that the beacons are only sent every 65.536 ms, which is too seldom for accurate adaptation. Thus, optimum performance can not be achieved with the current proposals.
Furthermore in the arrangement discussed in ECMA-368, the signal is either not adapted to the channel characteristics or it is adapted using a link feedback information element (IE), which is transmitted in the beacon. The link feedback information element contains a link field for each link with length of three bytes. Two bytes are used for the device address, whereas one byte is used for the data rate and transmit power level change. Four bits are reserved for each part.
There is no disclosure in the ECMA-368 document on how to obtain the optimum data rate or transmit power level.
One or more embodiments of the invention aim to address or mitigate one or several of the above problems.