Systems and methods for reducing peak to average power ratio
Various embodiments of wireless communication systems and methods in which the system applies a clipping and filtering procedures iteratively in order to reduce the peak-to-average power ratio of a transmission. In various embodiments, the clipping level changes in each iteration. In various embodiments, the clipping mechanism is a polar clipping mechanism. In various embodiments, out-of-band signal filtering is executed by a filter. In various embodiments, there is a pre-clipping process, which may be executed by a decimation mechanism, or alternatively by a zero-padding mechanism. In various embodiments, the clipping mechanism and filter are embedded in one or more processors, any one of which may be a DSP processor. In various embodiments, clipping levels are determined by a look-up table.
1 . A method for reducing iteratively a peak-to-average power ratio of wireless transmissions, comprising:
applying, by a wireless communication system, on a sequence of modulated data, a peak-to-average power ratio reduction scheme comprising (i) a clipping procedure followed by (ii) out-of-band signal filtering, wherein said clipping procedure is set to a first clipping level, resulting in a first-level clipped and filtered sequence of modulated data;
changing, by said wireless communication system, said setting from said first clipping level to a second clipping level; and
applying again, by said wireless communication system, said peak-to-average power ratio reduction scheme, on said first-level clipped and filtered sequence of modulated data, resulting in an enhanced clipped and filtered sequence of modulated data, better optimized for transmission by said wireless communication system.
2 . The method of claim 1 , wherein said changing and applying again is repeated iteratively until reaching a first criterion, and wherein each said iteration of changing and applying again is associated with a unique clipping level.
3 . The method of claim 2 , wherein said first criterion is a predetermined and fixed number of iterations.
4 . The method of claim 2 , wherein said first criterion is crossing below a first threshold of out-of-band signal power.
5 . The method of claim 2 , wherein the first clipping level, the second clipping level, and each of the other unique clipping levels, are determined based on a look-up table and as a function of iteration number.
6 . The method of claim 2 , wherein the second clipping level is higher than the first clipping level by a fixed amount of decibels, and each of said unique clipping levels is higher than unique clipping level of previous iteration by said fixed amount of decibels as well.
7 . The method of claim 1 , wherein said second clipping level is predetermined and fixed.
8 . The method of claim 1 , wherein said second clipping level is higher than said first clipping level by a predetermined amount of decibels, thereby making the second clipping level more relaxed than said first clipping level, thereby reducing distortions.
9 . The method of claim 8 , wherein said predetermined amount of decibels is between 0.3 decibel and 1 decibel.
10 . The method of claim 9 , wherein said predetermined amount of decibels is approximately 0.5 decibels.
11 . The method of claim 1 , wherein said clipping procedure comprises clipping said sequences of modulated data.
12 . The method of claim 11 , wherein said clipping is a polar clipping.
13 . The method of claim 1 , further comprising: decimating an initial input sequence of modulated data thereby producing said sequence of modulated data which is a decimated version of said initial input sequence of modulated data, thereby matching a rate of said initial input sequence of modulated data to a desired rate of signal at clipping.
14 . The method of claim 13 , wherein said decimating is operative to keep a sampling rate over signal bandwidth ratio within a predetermined range.
15 . The method of claim 14 , wherein said predetermined range is between 3 and 5.
16 . The method of claim 13 , further comprising: interpolating said enhanced clipped and filtered sequence of modulated data, thereby returning to said rate of initial input sequence of modulated data.
17 . The method of claim 1 , further comprising: zero-padding an initial input sequence of modulated data thereby producing said sequence of modulated data which is a zero-padded version of said initial input sequence of modulated data, thereby matching a rate of said initial input sequence of modulated data to a desired rate of signal at clipping.
18 . The method of claim 17 , wherein said zero-padding is operative to keep a sampling rate over signal bandwidth ratio within a predetermined range.
19 . The method of claim 18 , wherein said predetermined range is between 3 and 5.
20 . The method of claim 1 , further comprising: transmitting, by said wireless communication system, said enhanced clipped and filtered sequence of modulated data.
21 . The method of claim 1 , wherein said sequence of modulated data conforms to a wireless transmission standard selected from a group consisting of: LTE, WiMAX, and WiFi.
22 . The method of claim 21 , wherein said modulation is selected from a group consisting of: BPSK, QPSK, 16-QAM, 64-QAM, and 256-QAM.
23 . A wireless communication system operative to reduce iteratively a peak-to-average power ratio of wireless transmissions, comprising:
a clipping mechanism operative to receive sequences of modulated data, clip each said sequence of modulated data using a settable clipping level, and output clipped sequences of modulated data associated with said sequences of modulated data respectively; and
a filter operative to receive said clipped sequences of modulated data, filter out-of-band signals produced by said clipping mechanism out of said clipped sequences of modulated data, and output clipped-and-filtered sequences of modulated data associated with said clipped sequences of modulated data respectively,
wherein said wireless communication system is operative to:
use said clipping mechanism and said filter iteratively, such that at least some of said clipped-and-filtered sequences of modulated data are fed back into said clipping mechanism, thereby constituting at least some of said sequences of modulated data; and
set-up, for each said iteration of clipping and filtering, a clipping level that is unique and different than other clipping levels associated with other iterations.
24 . The system of claim 23 , wherein said wireless communication system is further operative to use a last of said clipped-and-filtered sequences of modulated data as a sequence for wireless transmission by said wireless communication system.
25 . The system of claim 24 , further comprising an interpolation mechanism operative to interpolate said last of said clipped-and-filtered sequences of modulated data, thereby producing said sequence for wireless transmission by said wireless communication system.
26 . The system of claim 23 , wherein said wireless communication system is further operative to feed a first of said sequences of modulated data as an initial input to said clipping mechanism, thereby triggering said iterative clipping and filtering operation.
27 . The system of claim 26 , further comprising a decimation mechanism operative to produce said first of said sequences of modulated data as an initial input to said clipping mechanism.
28 . The system of claim 26 , further comprising a zero-padding mechanism operative to produce said first of said sequences of modulated data as an initial input to said clipping mechanism.
29 . The system of claim 23 , wherein said clipping mechanism is a first processor operative to perform said clipping.
30 . The system of claim 29 , wherein said filter is a second processor operative to filter out-of-band signals.
31 . The system of claim 30 , wherein said first processor and said second processor are same one processor.
32 . The system of claim 30 , wherein said first processor and said second processor are digital signal processors.
33 . The system of claim 23 , wherein said clipping mechanism is a polar clipping mechanism.
34 . The system of claim 23 , wherein each of said clipping levels, excluding a first clipping level, is higher thus more relaxed than previous clipping levels, thereby reducing distortions.