The present invention relates generally to wireless communication, and more particularly relates to spectral keying in ultra wideband communications.
Ultra wideband (UWB) communications are a form of radio communication in which a signal is spread over a large portion of the radio spectrum, and in which the signal power at any particular frequency is therefore relatively small. The bandwidth of such systems is typically greater than 500 MHz, and in some UWB systems the bandwidth may be, for example, between 2 GHz and 100 GHz. Early UWB systems imparted information to their signals through the use of pulse position modulation. Such pulse position modulation is sometimes referred to in the context of UWB systems as time modulation.
By slightly changing the pulse position, that is, the time at which a pulse occurs, information can be encoded into, and subsequently derived from, a UWB signal. For example, a slightly early pulse may be interpreted as a “zero”, while a slightly delayed pulse may be interpreted as a “one”. Unfortunately, this only provides one bit of information per transmitted pulse.
What is needed are methods and apparatus for increasing the information content of ultra wideband signalling schemes.
Briefly, the amount of information encoded by spectral keying into a UWB symbol having a plurality of modulation symbol times, is increased by operating two or more frequency band carriers simultaneously during at least one of a plurality of modulation symbol times. In one aspect of the present invention, once a frequency resource, such as a carrier, has been used during a given modulation symbol time, those frequency resources are not used again within that UWB symbol.
Generally, the present invention relates to methods and apparatus for increasing the information content of ultra wideband signalling schemes. More particularly, the present invention relates to spectral keying in an ultra wideband communication system wherein more than one carrier can be turned on at any given time.
Reference herein to “one embodiment”, “an embodiment”, or similar formulations, means that a particular feature, structure, operation, or characteristic described in connection with the embodiment, is included in at least one embodiment of the present invention. Thus, the appearances of such phrases or formulations herein are not necessarily all referring to the same embodiment Furthermore, various particular features, structures, operations, or characteristics may be combined in any suitable manner in one or more embodiments.
Embodiments of the present invention provide advantages with respect to previous spectral keying schemes by allowing more than one carrier to be turned on at any given time. Such previous spectral keying schemes use permutations of available carriers to represent UWB symbols. Embodiments of the present invention take advantage of combinations of carrier frequencies, in addition to permutations, thereby allowing more information bits to be packed within the same bandwidth, UWB symbols can be represented by the same number of “on” carriers, except that embodiments of the present invention allow multiple carriers to be “on” at the same time.
Referring to
In order to calculate the number of bits packed into one UWB symbol as illustrated in
Referring to
It is noted that although the enhanced spectral keying of the present invention contemplates a modulation symbol time within the UWB symbol time in which no frequency carrier is turned on, no modulation information is lost as a result because there are still three “on” carriers in each UWB symbol. It is noted that carriers f1, f2, and f3, may transmit at frequency bands that are contiguous with each other, or they may be separated from each other by any arbitrary amount. It is further noted that the choice of three carriers and three time slots is for illustrative purposes and is not intended as a limitation on the number of carriers or time slots.
To calculate the number of information bits in one UWB symbol formed in accordance with the enhanced spectral keying of the present invention and wherein for illustrative purposes there are three frequency carriers and three modulation symbol times, the combinations with only one frequency carrier turned on at a time are determined, the combinations with a maximum of two frequency carriers turned on at a time are determined, and the combinations with a maximum of three frequency carriers turned on at a time are determined. The number of combinations are added to produce a “total”, and a value for log2(total) is determined.
The combinations described above are enumerated below. The combinations with only one frequency carrier turned on at a time are: {1,2,3}, {1,3,2,}, {2,1,3}, {2,3,1}, {3,1,2}, and {3,2,1} for a total of six. The combinations with a maximum of two frequency carriers turned on at a time are:
{(1,2),3,0}, {(1,2),0,3}, {3,(1,2),0}, {0,(1,2),3}, {3,0,(1,2)}, {0,3,(1,2)}
{(1,3),2,0}, {(1,3),0,2}, {2,(1,3),0}, {0,(1,3),2}, {2,0,(1,3)}, {0,2,(1,3)}
{(2,3),1,0}, {(2,3),0,1}, {1,(2,3),0}, {0,(2,3),1}, {1,0,(2,3)}, and {0,1,(2,3)}
for a total of eighteen. The combinations with a maximum of three frequency carriers turned on at a time are: {(1,2,3),0,0}, {0,(1,2,3),0}, and {0,0,(1,2,3)} for a total of three. Adding 6, 18, and 3 gives the total number of combinations as 27. So the total number of additional information bits is log2(27)=4.75, as compared to 2.58 with the previous spectral keying scheme.
It will be appreciated by those of ordinary skill in this field, and having the benefit of this disclosure, that the amount of data encoded in a UWB symbol in accordance with the present invention significantly increases as the number of frequency carriers is increased.
In one embodiment of the present invention, as shown in
In accordance with the present invention, a symbol, may have one or more modulation symbol times in which no frequency carrier is turned on. Similarly, in accordance with the present invention, a symbol may have at least one modulation symbol time in which at least two frequency carriers are turned on. In typical embodiments, the transmitted symbols occupy a frequency bandwidth greater than 500 MHz. In some embodiments of the present invention the transmitted symbols occupy a frequency bandwidth greater than 2 GHz. Typical embodiments include waiting for a period of time, referred to as a guard time, after the transmission of one symbol until the beginning of the transmission of a next symbol.
One embodiment of present invention is a method of generating information symbols including: (a) turning on, for an ith predetermined length of time, during an ith time period, xi frequency carriers, where 0≦xi≦n, and 1≦i≦n; (b) determining whether n−Σxi=0; and (c) if the determination of (b) is negative, repeating (a) through (b); wherein xi represents an integer number of frequency carriers. In such an embodiment, each ith time period may also be referred to as a modulation symbol time, and the information symbol is made up of n modulation symbol times. In this embodiment of the present invention, the number of frequency carriers and the number of modulation symbol times are the same. In alternative embodiments, the number of frequency carriers may be represented by an integer n, and the number of modulation symbol time periods may be represented by an integer m, wherein n and m are different. In such an embodiment, rather than determining whether n−Σxi=0, one would determine whether the number of modulation symbol time periods has reached the total number m of time periods per USB symbol.
In typical embodiments of the present invention, the frequency carriers are turned on at the beginning of a modulation symbol time and turned off at the end of that modulation symbol time. However, in alternative embodiments of the present invention, identical temporal alignment of frequency carrier operation and modulation symbol time boundaries may not be required, but rather some accommodation is provided for recognizing a symbol wherein there is some misalignment between the time of frequency carrier operation and the modulation symbol time boundaries.
Various embodiments of the present invention include methods and apparatus for providing more information in a UWB symbol, than is possible with pulse position modulation UWB, and further provides more information in a UWB symbol than is possible with previously proposed spectral keying schemes. By taking advantage of combinations of frequency carriers, the number of UWB information bits that can be transmitted within a given time can be increased without requiring additional frequency resources.
An advantage of some embodiments of the present invention, is that higher data rates can be achieved in a communication system in accordance with the present invention.
An advantage of some embodiments of the present invention, is that these scale exponentially as the number of available carriers increases.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the subjoined Claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/IB05/50371 | 1/27/2005 | WO | 00 | 9/20/2008 |
Number | Date | Country | |
---|---|---|---|
60540378 | Jan 2004 | US |