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Symbol Shaping for Barker Spread Wi-Fi Communications

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Symbol Shaping for Barker Spread Wi-Fi CommunicationsOutlineSlide 3IEEE 802.11 Spectral MaskSlide 5Slide 6Slide 7Motivation for ProjectMATLAB Simulation Methodology for each Pulse ShapeSlide 10Experimentation Methodology for each Pulse ShapeSlide 12Slide 13Slide 14Slide 15Slide 16Performance ResultsLine Coding and Pulse ShapingPlots of 3 bit buffer system.ConclusionsThank you! Questions? Tanim Taher ([email protected])1Symbol Shaping for Barker Spread Wi-Fi Communications Tanim M. TaherMatthew J. MisuracDonald R. Ucci Joseph L. LoCiceroPresented byTanim M. Taher2Outline•Background•Motivation•Simulation and Experimental Methodology•Pulse Shapes Used and Results•Performance Results•Line Coding•Conclusions3Spectral Mask Background•The Industrial, Scientific and Medical (ISM) bands are overcrowded.•The Federal Communications Commission (FCC) limits the output power to 1 watt.•FCC regulates out-of-band Power in Wi-Fi systems using a rigid Spectral Mask.•Most modulation schemes require high order filters to achieve spectral mask.4IEEE 802.11 Spectral Mask5Why Pulse Shaping?•Filters add to hardware cost, and introduce Inter-Symbol-Interference (ISI) that lowers the Bit Error Rate (BER) vs Signal to Noise Ratio (SNR) performance.•Shaping the transmitted symbols as opposed to filtering prevents ISI, while lowering out-of-band interference power.6The Barker spread 1 Mbps 802.11 signal•Access Points and laptops use a spreading code called the 11-chip Barker to expand the bandwidth of 1 Mbps data signals. •The spread spectrum system more robust to noise, multi-path fading, and narrowband interference.•This 1 Mbps communication system is used for transmitting all the Packet headers and Physical Layer Convergence Protocols. •At higher noise levels, this system is used for transferring all data.7More about the Barker Sequence•The Barker chip sequence used in the 802.11 standard is: B = [+1,−1,+1,+1,−1,+1,+1,+1,−1,−1,−1]where rectangular pulses are used to represent each chip (polarities varied according to B) in the sequence.•The Barker sequence (B) has very good auto-correlation properties and this is what minimizes multipath effects.8Motivation for Project•The problem is that the Barker spread data waveform does not adhere to the spectral mask.•The rectangular Barker waveform was modified by pulse shaping to achieve better spectral performance in relation to the spectral mask. •The resulting modulation system was studied by simulation and experimentation. The PSD and BER performance were examined.Simulated PSD of rectangular unfiltered rectangular pulse Barker waveform.9MATLAB Simulation Methodology for each Pulse Shape1) Design Pulse Shape adhering to Barker Sequence. 2) Examine its Auto-correlation properties.Generate random bit sequence and spread each bit by pulse shape to obtain data waveform.Add Additive White Gaussian Noise (AWGN).Obtain the PSD of data waveform using the Welch method.Use Correlator to obtain timing information from the “received signal”Use Correlator to decode the received bits.Examine Bit Error Rate 100101101110101001011010101010Experimental Emulation•Comblock Devices were used to transmit and receive the waveforms experimentally. MATLAB software was used to do the coding and decoding in a workstation.The Comblock receiver. The Comblock transmitter11Experimentation Methodology for each Pulse ShapeDesign Pulse Shape adhering to Barker Sequence in Matlab. Generate random bit sequence and spread each bit by pulse shape to obtain data waveform.Transmit over the Air.Upload the data waveform to the Comblock transmitter.Use Correlator to obtain timing informationUse Correlator to decode the received bits.Examine Bit Error RateComblock receiver captures the received data waveform for computer download.100101101110101001011010101012Logarithmic Symbol Shape:-4 -2 0 2 4x 10-7-1.5-1-0.500.511.5Time (s)p(t) in VoltsThe logarithmically shaped waveform•Practical devices to inexpensively generate these symbols can be manufactured using discrete-time analog memory devices (like Pulse Amplitude Modulation, PAM, chips))log()(010tatkktpL13Sinc Symbol Shape: mocbbtAtp )(sinc)( 14Sinusoidal Symbol Shape:15More of the Sinusoidal Symbol Shape:Experimental PSDSimulated PSD16More Sinusoidal Material:Time Auto-correlationOscilloscope plot of Experimental Data Waveform17Performance Results•Bit Error Rate (BER) dropped as the filter order dropped.Table. 1. Simulated BER measurements.Pulse Shape UsedFilter OrderBit Error Rate at SNR levels:–11.5 dB –11 dB –10 dBRectangular 53.70E-03 2.74E-03 9.00E-04Logarithmic 32.48E-03 1.40E-03 5.60E-04Sinusoidal 22.62E-03 1.36E-03 3.80E-04Sinc-function 22.80E-03 1.98E-03 3.80E-04Table 2. Experimental BER measurements at receiver-to-transmitter distance of 1 meter.Pulse Shape UsedExperimental BERRectangular9.99E-03Logarithmic6.22E-03Sinusoidal3.71E-03Sinc-function5.84E-0318Line Coding and Pulse Shaping•A modified Barker spread system was examined that buffered 2 bits.•A line coding involving a total of 8 pulse shapes was developed and tested.•The idea was to eliminate discontinuities that arises when a bit transition occurs from 1 to 0 or vice versa.•The system buffers 3 bits in order to eliminate discontinuities and by selecting the appropriate pulse shape (from pool of 8) to transmit.19Plots of 3 bit buffer system.+1 to +1 bit transition-1 to +1 to -1 bit transition+1 = bit 1-1 = bit 0•However, the results showed no significant spectral improvement.•The unbuffered sinusoidal system gives best BER performance.20Conclusions•Pulse Shaping was thoroughly applied to 802.11 Barker Spread Signal.•Complete simulation and experimental studies were performed to examine performance. Analytical study was performed for Sinusoidal pulse shape.•The spectral performance was improved and BER reduced.•Future Work will look at 802.11 CCK signals.21Thank you!Questions?Tanim Taher


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