Synchronous multiple access procedure for use with an ultra wideband system
Original Publication Date: 2001-Oct-01
Included in the Prior Art Database: 2003-Jul-23
Channelising can be done by applying a relatively large time offset (many nanoseconds) to each impulse and using “pseudo-random noise” codes (PN codes) for distinguishing between channels. The system could then have virtually an unlimited number of channels.
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Synchronous multiple access pro-cedure for use with an ultra wide-band system
Idee: Karl-Heinz Moehrmann, München
Channelising can be done by applying a relativelylarge time offset (many nanoseconds) to each impulseand using “pseudo-random noise” codes (PN codes)for distinguishing between channels. The systemcould then have virtually an unlimited number ofchannels.
This virtually unlimited number of channels may,however, not be of high practical importance sincethe reach of an ultra wideband (UWB) system isseverely limited by the necessary limitation of trans-mit power, in order not to unduly interfere with otherradio systems. This will very probably be a stringentregulatory requirement. Such a limitation in reachand, therefore, of the area of the radio cell means, onthe other hand, that the number of users that is to beinterconnected within the cell is also limited.
Since UWB can only become a success if it can com-pete in cost with other existing radio systems likeWireless local are networks (WLAN), an UWB sys-tem should be as simple as possible.
Basically, a baseband UWB system according to theknown state-of-the-art can only be realised in anasynchronous manner, i.e. the phases of the transmitframes in the two directions are not correlated. Thereason is that in WLANs it is normally not feasible touse directional antennas because the location of theterminals is not known beforehand and may fre-quently, or even dynamically, change. Use of omnidi-rectional antennas causes, however, that (within cer-tain limits) any station can hear any other station.Any transmission from a terminal transceiver (TT)will interfere with transmissions from other TTs inany receiver in an undefined manner because of thelimited propagation speed of the electromagneticwave (30 cm/ns, which means that a difference indistance of 30 m leads to a delay difference of 100ns!). Only the use of user specific codes (de facto avariant of Code Division Multiple Access [CDMA])according to the known state-of-the-art would allowseparation of the signals if omnidirectional antennaswere used.
It might, on the other hand, be interesting to imple-ment a synchronised system . Obviously this is notpossible with Time Division Multiplexing (TDM), asdescribed above. It could be done, however, if it werepossible to somehow separate the upstream anddownstream channels in a point-to-multipoint systemwhere a base station (BS) is used to which all termi-nal transceivers TT of the users are connected byUWB, and where all communication is running over
Siemens Technik Report Jahrgang 4 Nr.13 Oktober 2001
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the base station, even also that between topologicallyneighboured terminal transceivers. Then only the BScould hear the transmissions from the TTs, but notthe TTs themselves.
For separation of upstream and downstream signals,code division®..