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Digital Wireless Communications Technology


Source Encoding  |  Channel Encoding  |  Modulation  |  Physical Channel  |  Channel Models
Digital Filters  |  Demodulation  |  Synchronization/Carrier Recovery  |  Detection  |  Data Processing


The following paragraphs summarize the different embedded software technologies essential to the operation of Wide Area Network (WAN) wireless infrastructure.
 

    Source Encoding
Source encoding deals with the encoding analog source signals such as speech and image signals.

Waveform coding: The waveform of the source signal is approximated by mimicking the amplitudes versus time waveform.
Pulse Code Modulation     (PCM)
Differential PCM                (DPCM)
Adaptive DPCM                 (ADPCM)
Delta Modulation                (DM)
Sub-band coding
Linear Predictive Coding (LPC): The human vocal tract is modeled and the parameters of the model are estimated based on the individual speech signal.
Residual Excited Linear Predictive coding                         (RELP)
Code Excited Linear Predictive coding                              (CELP)
Vector Sum Excited Linear Predictive coding                    (VSELP)
Regular Pulse Excitation-Long Term Prediction coding    (RPE-LTP)
Algebraic Codebook Excited Linear Predictive coding       (ACELP)

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    Channel Encoding
Channel encoding deals with error control during the transmission through the communication channel.

Error detection Codes
Parity check codes
Cyclic Redundancy Check Code   (CRC)
Error correction code include Block coding
Block codes: Information symbols are grouped together in blocks for encoding
Fire codes
Repetition code
Linear block code
Single error correcting Hamming code
Cyclic codes: Encoding and decoding can be implemented using shift registers
    and additional small logic.
Bose-Chaudhuri-Hocquenghem (BCH) codes
Golay Codes: only multiple error correcting code.
Reed Solomon Codes: largest possible code minimum distance and error
    correcting capability for any linear code.
Convolutional codes
        Trellis codes
        Turbo codes

Forward Error Correction
Interleaving coding is an effective method to combat error bursts due to fading.

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    Modulation
Modulation is the process in which the carrier signal is modulated according to the information bits. Modulation schemes are as follows:
Amplitude Shift Keying
Frequency Shift keying
Binary Phase Shift Keying
Quadrature Phase Shift Keying
Offset QPSK
Differential PSK
Gaussian Minimum Shift Keying
Quadrature Amplitude Modulation
M-level QAM
Orthogonal Frequency Division Modulation    
ASK
FSK
BPSK
QPSK
OQPSK
DPSK
GMSK
QAM
MQAM
OFDM

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    Physical Channel
Physical Channel: The method of creating physical channels involves allocating the finite resources.

Duplexing methods involves the allocation of the directions of transmission:
Frequency Division Duplexing    
Time Division Duplexing
(FDD)
(TDD)

Multiple access refers to the method of creating multiple channels for each transmission direction
Frequency Division Multiple Access    
Time Division Multiple Access
Code Division Multiple Access
        Direct Sequence
        Frequency Hopping
        Carrier Sense multiple access
                Pseudo noise codes
                Walsh codes
                Gold codes
(FDMA)
(TDMA)
(CDMA)
(DS-CDMA)
(FH-CDMA)
(CS-CDMA)
(PN)

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    Channel Models
Channel Models: Modeling of transmission impairments such as transmission loss and noise.
Additive White Gaussian Noise Channel     (AWGN)
Raleigh fading Channel
Rician fading Channel
Rice fading channel
Multipath Channel
Narrow band interference

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    Digital Filters
Digital Filters: Filters to remove the out of band components
Infinite Impulse Response Filter    
Finite Impulse Response Filter
Hilbert Transform
Fast Fourier Transform
Inverse Fast Fourier Transform
Matched Filters
(IIR)
(FIR)

(FFT)
(IFFT)
(MF)

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    Demodulation
Demodulation: Inverse process of the modulation
Coherent: Carrier reference is required.
Non-coherent

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    Synchronization / Carrier Recovery
Synchronization / Carrier Recovery: In order to demodulate the information bits the locally generated signal should be synchronized with the incoming signal.
Costas Loop
Phase Locked Loops
Delay Locked Loops
Frequency Locked Loops    

(PLL)
(DLL)
(FLL)

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    Detection
Detection: Finding the information bits
Equalizers
        Constant Modulus algorithm (CMA) equalizer
        Viterbi equalizer

I-Q splitter
Viterbi decoding (Convolutional decoder)
Deinterleaver
Squaring envelope detection
Quadrature envelope detection
Peak signal envelope detection
Linear signal averaging
Peak signal averaging
Exponential averaging

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    Data Processing
Data Processing: Processing functions involved in wireless communication
Bit to Symbol converter
Symbol to Bit converter
Frame synchronizer
Bit synchronizer
Bit Error Rate (BER)
Digital correlator
Numerically controlled oscillators (NCOs)
Puncturing
Depuncturing

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